Geology of the country around Penrith Memoir for 1:50 000 geological sheet 24

By R. S. Arthurton and A. J .Wadge

Bibliographical reference: Arthurton, R. S. and Wadge, A. J. 1981 Geology of the country around Penrith Mem. Geol. Surv. G.B., Sheet 24, 177 pp.

• Contributors
• Palaeontology: J. Pattison, M. Mitchell, A. W. A. Rushton and T. R. Lister
• Petrography: R. K. Harrison
• Geophysics F. Collar
• Hydrogeology J. L. Farr
• Authors
• R. S. Arthurton, BSc and A. J. Wadge, MA Institute of Geological Sciences, Ring Road Halton, Leeds LS15 8TQ
• Contributors
• J. Pattison, MSc, M. Mitchell, MA and T. R. Lister, PhD Institute of Geological Sciences, Leeds
• W. A. Rushton, BA, PhD, R. K. Harrison, MSc, J. L. Farr, MSc and F. Collar, MSc Institute of Geological Sciences, London

Geological Survey of Great Britain England and Wales. Institute of Geological Sciences. Natural Environment Research Council

London Her Majesty's Stationery Office 1981. © Crown copyright 1981. ISBN 0 11 884142 4* Printed in England for Her Majesty's Stationery Office by Ebenezer Baylis and Son Limited, The Trinity Press, Worcester, and London. Dd 596482 K16.

(Front cover)

(Rear cover)

Other publications of the Institute dealing with this and adjoining districts

Books

• British Regional Geology
• Northern England, 4th edition
• Classical areas of British Geology
• Geology of the Cross Fell area
• 1: 50 000 (and one-inch to one mile) Sheet Memoirs
• Geology of the country around Carlisle
• Geology of the country around Brampton
• Geology of the country around Cockermouth
• Geology of the country around Brough-under-Stainmore
• Economic Memoir
• Geology of the Northern Pennine Orefield; Vol. 1, Tyne to Stainmore
• Special Report on Mineral Resources
• Gypsum and Anhydrite, Vol. 3

Maps

• 1:625 000
• Sheet 1 Geological
• Sheet 1 Quaternary
• Sheet 1 Aeromagnetic
• 1:250 000
• Lake District
• 1:50 000 (and one inch to one mile)
• Sheet 17 (Carlisle)
• Sheet 18 (Brampton)
• Sheet 19 (Hexham)
• Sheet 23 (Cockermouth)
• Sheet 25 (Alston)
• Sheet 31 (Brough)
• 1:25 000
• Cross Fell Inlier

Six-inch maps

The following is a list of the six-inch geological maps included wholly or in part in the area of 1:50 000 Geological Sheet 24, with the date of survey for each map. The surveying officers are R. S. Arthurton and A. J. Wadge. All of the maps are available for public reference in manuscript form at the libraries of the Institute of Geological Sciences in London and Leeds, and, with the exception of those marked with an asterisk, can be obtained as dyeline copies from the Leeds Office.. All of the maps lie within the 100-km National Grid square NY.

Preface

The district covered by the Penrith (24) Sheet of the 1:50 000 geological map of England and Wales was originally surveyed on the six-inch scale by W. T. Aveline, J. R. Dakyns, R. Russell, D. Burns, E. J. Hebert and C. T. Clough and was published on the one-inch scale as Old Series Sheet 102 NW (Solid and Drift) in 1893.

A systematic resurvey of the entire district on the six-inch scale was carried out in 1962–68 by Messrs R. S. Arthurton and A. J. Wadge under the supervision of Mr B. J. Taylor and Mr W. B. Evans as District Geologists. A list of six-inch maps with the names of the surveyors is given on p. viii. The 1:50 000 map of the district was published in 1974, in two editions, Solid and Drift. Part of the area is covered by the 1:25 000 map of the Cross Fell inlier (published 1972).

The present memoir has been written mainly by Messrs R. S. Arthurton and A. J. Wadge. A large number of fossils was collected during the recent survey, mainly by Messrs J. Pattison and M. J. Reynolds, and their identification has been shared between the Palaeontological Unit and outside specialists. We are grateful for the assistance of Dr C. Skevington, Dr P. T. Warren and Dr R. B. Rickards in the identification of Ordovician and Silurian graptolites, and to Professor W. G. Chaloner for naming the Permian plants. The Ordovician Shelly faunas were identified by Dr A. W. A. Rushton, and the microfossils by Dr T. R. Lister; the Dinantian faunas by Messrs Pattison, M. Mitchell and M. J. Reynolds; the Namurian faunas by Mr J. Pattison and Dr W. H. C. Ramsbottom and the palynomorphs by Dr B. Owens; and the Westphalian faunas by Dr M. A. Calver.

Petrographical descriptions were written by Mr R. K. Harrison, who has also contributed a detailed study of Lower Palaeozoic extrusive and intrusive igneous rocks.

The photographs, a list of which is given in Appendix 2, were taken by Messrs P. Joyce and P. Baker.

The memoir was prepared under the supervision of Mr W. B. Evans.

We gratefully acknowledge the information and assistance generously provided by the County Surveyor, Cumberland County Council concerning boreholes sunk in connexion with the construction of the M6 motorway, and by officials of the Cumberland River Authority and Eden Water Board concerning boreholes within the district, and the helpful cooperation of local landowners and mine and quarry operators, in particular British Gypsum Ltd, Harrisons Limeworks Ltd and Blencow Lime Ltd.

G. M. Brown Director, Institute of Geological Sciences, Exhibition Road, London SW7 2DE 19 May 1981

Notes

In this memoir, the word 'district' means the area included in the 1:50 000 Geological Sheet 24 (Penrith).

Numbers in square brackets are National Grid references within 100-km square NY.

Numbers preceded by the letter E refer to the Sliced Rock Collection of the Institute of Geological Sciences.

Numbers preceded by the letter L refer to the Geological Survey Photograph Collection of the Institute.

Geology of the country around Penrith—summary

The Penrith district is one of great scenic contrasts. It includes the northern part of the Vale of Eden and is bordered in the east by the Pennine escarpment and a tract of high moorland culminating in Cross Fell, the highest of the Pennine summits.

This memoir is the first comprehensive account of the geology of a district that has long attracted the attention of students and researchers. Much attention is given to the widespread outcrops of Carboniferous strata and also to the structurally complex Lower Palaeozoic rocks which make up the northern part of the Cross Fell inlier. The Permo-Triassic red beds which crop out in the Vale of Eden are described with particular emphasis on the part of the sequence containing seams of anhydrite.

Igneous intrusions of various ages include the Whin Sill and the Cleveland–Armathwaite Dyke. Glaciation during the Devensian period of the Quaternary and its widespread and locally complex deposits are described. The structural history is considered with particular reference to events recorded in the rocks of the Pennine Fault Zone.

There are sections dealing with geophysical research, with hydrogeology and mineral products.

(Geological sequence)

Chapter 1 Introduction

Geography

This Memoir describes the geology of the district covered by the Penrith (24) Sheet of the 1:50 000 Geological New Series maps of England and Wales. The district formerly lay within the three counties of Cumberland, Westmorland and Northumberland but, since the re-organisation of local government boundaries, the main part is now in Cumbria while part of the extreme north-east is in Northumberland. The district lies to the north-east of the Lake District and immediately south of the Carlisle Plain, and straddles the northern part of the Vale of Eden, a fertile tract underlain by Permo-Triassic sediments and drained to the Solway Firth by the River Eden (Figure 1). In the east it includes part of the northern Pennines (Figure 2), uplands of Carboniferous strata with a prominent western scarp which dominates the Vale. The Cross Fell inlier of Lower Palaeozoic rocks extends into the district from the south, at the foot of this scarp.

The Pennine escarpment is particularly pronounced to the south of the Hartside Pass, 580 m above OD, which carries the only road across the scarp between the Tyne Gap and Stainmore; the scarp reaches a maximum of 893 m on Cross Fell, the highest peak of the Pennines. Northwards from Hartside the feature is broken by a broad embayment around the valley of Raven Beck and by the valley of Croglin Water. The area to the cast of the watershed lies within the catchment of the River South Tyne.

The western part of the district is a predominantly fertile tract underlain mostly by Carboniferous rocks and separated from the Vale by a line of heathland hills formed of Permian sandstone, in the past quarried in large quantities as an excellent building stone. Like the Vale, most of this area drains to the Solway, the rivers Petteril and Ive being the most important.

Pcnrith is the principal settlement and serves as a market centre for all except the northern fringe of the district. The town has excellent communications to the north and south, lying on the Preston–Carlisle sections of both the M6 motorway and the electrified railway between Glasgow and London. It has trunk road communication eastwards to Teesside, while the A66 road leading to the industrial areas of west Cumbria has been improved. Another railway, connecting Leeds with Carlisle, runs in the Eden valley.

The district lies entirely outside areas designated as National Parks but, in the south-east, is slightly encroached upon by the Moor House Nature Reserve of the Nature Conservancy. The Pennine Way, a bridleway stretching along the length of the Pennines, enters the district for a short distance over the summit of Cross Fell. The district includes parts of two important communication routes used during the Roman occupation of Britain, one linking the fort of Brovacum (Brougham), just south of Penrith, to the town of Luguvallium (Carlisle) near the western end of Hadrian's Wall; the other, known as the Maiden Way, runs northwards from Bravoniacum (Kirkby Thore, in the adjoining Appleby district) to more easterly parts of the wall, crossing the Pennine scarp over Melmerby Fell.

Both the western part of the district and the Vale sustain arable and livestock farming, and there are several small forestry projects. The Pennines provide rough grazing for sheep and some of the more extensive peat-covered tracts are used as grouse-moor.

The district supports a number of extractive industries. Anhydrite is mined near Lazonby in the Vale of Eden, and limestone is quarried for aggregate and agricultural purposes around Greystoke in the south-west. During the eighteenth and nineteenth centuries lime burning was carried out at several places on the escarpment, the kilns being fired by coal mined locally from a number of no longer economic seams. During the same period lead and zinc ores were mined within the district, mostly on the uplands to the east and south-cast of Hartside, peripheral to the Alston Moor orefield. More recently baryte and some ironstone have been extracted near Hartside. The district has considerable reserves of sand and gravel both in and adjacent to the Vale of Eden and these deposits are being exploited.

The water supply potential of the district is substantial, mainly due to the excellent aquifer properties of some of the Permo-Triassic sandstones of the Vale of Eden. Groundwater from the latter is being pumped to meet local demand.

Outline of geological history

The known Lower Palaeozoic history begins in early Ordovician times when the district lay within a rapidly subsiding trough and a great thickness of greywacke sandstones and siltstones accumulated (Murton Formation). They were followed in Llanvirn times by mudstones, interbedded in their lower part with submarine andesitic and spilitic tuffs and rare lavas, and containing scattered graptolite faunas (Kirkland Formation). The rocks of these two formations, which together comprise the Skiddaw Group, were folded, uplifted and deeply eroded, and on their eroded surface were laid down the subaerial lavas and tuffs of the Borrowdalc Volcanic Group. After a further period of folding and erosion, this volcanic landmass was gradually submerged by a shallow shelf sea in which the upper Ordovician mudstones and limestones of the Coniston Limestone Group were laid down. They contain prolific Shelly faunas, but the succeeding Silurian rocks mark a return to deeper water in which mainly barren mudstones, with thin graptolitic bands (Browgill Beds), were deposited. These are the youngest Lower Palaeozoic beds preserved in the district. The Wenlock mudstones and Ludlow greywackes of the Lake District are not exposed but are presumed to have covered the whole area, before the onset of the end-Silurian Caledonian orogeny when all the Lower Palaeozoic rocks were strongly folded and cleaved.

The Weardale Granite and the batholiths beneath the Lake District were emplaced towards the end of this orogeny. These intrusions formed rigid, low-density cores beneath the Alston Block and the Lake District, making these positive areas throughout much of their subsequent history, and have almost continuously influenced sedimentation, structure and topography down to the present day. The Pennine Fault system also dates from this time. It marks the western edge of the Alston Block and has moved intermittently during the Caledonian (late Silurian), Armorican (late Carboniferous) and Alpine (Tertiary) orogenies.

The Devonian period was a time of uplift and deep erosion, producing isolated fans of coarse detritus of Old Red Sandstone facies (Polygenetic and Mell Fell conglomerates). In early Lower Carboniferous times, the relief was gradually reduced and the hollows were filled with fluviatile sandstones and conglomerates of westerly derivation (Basement Beds) forming part of a fluvio-deltaic complex built out into a sea lying to the south.

Throughout the deposition of the remaining Lower Carboniferous rocks, subsidence and sedimentation were evenly balanced and marine and deltaic conditions alternated. In the lower part of the sequence (Orton Group and lower Alston Group) the environment was dominantly marine and the main deposits were shallow-water limestones. The higher beds (upper Alston Group) display a rhythmic alternation of limestones, shales and sandstones of 'Yoredale' facies. In the succeeding Upper Carboniferous (Millstone Grit or Namurian Series and Coal Measures or Westphalian Series), deltaic deposits predominate, consisting mainly of sandstones and shales.

The deposition of the Coal Measures strata was followed by a period of tectonic activity related to the Armorican orogeny; faulting and folding took place along the Pennine Fault system, and the quartz-dolerite Whin Sill was intruded into the sedimentary rocks of the Alston Block in the late Westphalian or early Stephanian.

At a late stage in these movements, subsidence of the Vale of Eden area formed an intermontane basin in which desert sands (Penrith Sandstone) of Lower Permian age accumulated. Mainly arid conditions persisted through the Upper Permian, when the basin became a playa, flooded from time to time by the nearby Zechstein Sea leading to dolomitic limestone deposition and to the establishment of coastal sabkhas in which deposits of gypsum-anhydrite accumulated in a mainly continental mudstone and siltstone sequence (Eden Shales). Throughout the Permian the western edge of the Alston Block formed an escarpment, which was gradually buried by the desert sediments, and was probably finally covered by the fluviatile sandstones of the succeeding Triassic St Bees Sandstone.

There is a long gap between the deposition of the St Bees Sandstone and of the superficial deposits of Pleistocene times. During this interval, the Cleveland–Armathwaite dolerite dyke of Palaeocene age was intruded into Permo-Triassic and older sediments, and, late in the period, the marginal effects of the Alpine orogeny caused further down-west movement on the Pennine line, and formed a fault-scarp, the degraded edge of which is the present Pennine escarpment.

During the Pleistocene, all but the highest ground of the district was invaded by ice from the Lake District, and some parts also seem to have received ice from Scottish sources. A number of valley glaciers became established on the escarpment. Those parts of the Pennines beyond the limits of the ice-sheet were subjected to extreme frost conditions, leading to solifluction and the accumulation of substantial head deposits. As the ice-sheet wasted, glacial meltwater cut a network of channels on the lower ground, and laid down scattered deposits of sand, gravel, silt and clay. The glacial deposits provide positive evidence for only one period of glaciation, believed to be of late Devensian age, though presumably earlier glacial episodes occurred.

Chapter 2 Ordovician and Silurian

The main outcrop of Lower Palaeozoic rocks in the district forms the northern part of the Cross Fell inlier. The Ordovician rocks correlate broadly with the Lake District succession and are subdivided in the same way into the Skiddaw, Borrowdale and Coniston Limestone groups.The classification of the Lower Ordovician sequence in the Lake District and the Cross Fell inlier has recently been revised (Wadge, 1978). Under the new scheme the Kirkland Formation is placed within the Eycott Group of Llanvirn age, the Murton Formation being retained within the Skiddaw Group now restricted to the Arenig. However, for the purposes of describing the published geological map, the former group classification is retained in this account. Outcrops of Silurian rocks are restricted to a small fault-block at the northern end of the inlier, but can be correlated on the basis of their fossils with the Llandovery sequence in the Lake District. The Cross Fell inlier was first described by Buckland (1817) who distinguished broadly between 'slates' (Skiddaw Group) in the east and 'greenstones' (Borrowdale Volcanic Group) farther west. Subsequently, several publications have dealt with the inlier as a whole (Goodchild, 1889, Nicholson and Marr, 1891, Shotton, 1935, Burgess and Wadge, 1974), and many more with particular aspects of the Lower Palaeozoic geology; the latter are quoted below where appropriate.

Ordovician rocks are also encountered in the south-west of the district where volcanic rocks forming the eastern part of the Greystoke inlier are poorly exposed. The rocks of the western part of this inlier and their correlatives on Eycott Hill lie within the Cockermouth district (Eastwood and others, 1968).

Ordovician: Skiddaw Group

The rocks of the Skiddaw Group crop out on the western edge of the Alston Block in the Cross Fell inlier, and also form much of the sub-Carboniferous basement, beneath the remainder of the block. It seems likely that they extend at depth beneath much of the Vale of Eden. The thickness of the group is unknown since neither its base nor its top is seen, but several thousand metres of rocks are present. The group has been divided on lithological grounds into a lower Murton Formation and an upper Kirkland Formation as described below (Figure 3).

Classification

The Skiddaw Group outcrops in the northern part of the Cross Fell inlier, together with some of the included volcanic beds, were first accurately delimited by J. R. Dakyns during the primary survey of Sheet 102 NW, published in 1893. The earliest stratigraphical subdivision of the rocks was made by Nicholson and Marr (1891), who recognised a lower unnamed division cropping out north of Cuns Fell, a middle division of graptolitic shales exposed in Eller Gill (the Ellergill beds), and an upper division of interbedded shales and tuffs cropping out north-east of Milburn. The term 'Milburn Rocks' had already been used for these latter by Goodchild (1889) who recorded Didymograptus murchisoni from them. Together with the Ellergill beds, they were assigned by Nicholson and Marr to the Llanvirn Series although the age of the lowest unnamed subdivision remained unknown. Shotton (1935) discovered further graptolite localities and extended the faunal lists for both the Milburn and Ellergill beds; he rejected Goodchild's record of D. murchisoni and confirmed that both subdivisions lay within the D. bifidus Zone of the lower Llanvirn.

This classification of the Skiddaw Group has been modified as a result of the resurvey. The rocks at the northern end of the inlier are assigned to the Murton Formation and are confirmed as being among the oldest known Skiddaw rocks, having yielded microfossils of probable Arenig age. The remaining rocks of the Skiddaw outcrop are termed the Kirkland Formation. They have yielded both graptolites and acritarchs which establish that the beds at Eller Gill are younger than those of 'Milburn' type, and not older as previously thought. Recent work in the eastern Lake District has shown that, there, the correlatives of the Milburn Rocks—tuffs interbedded with mudstones yielding graptolites of D. bifidus Zone age—are much older than rocks of the Borrowdale Volcanic Group. They are separated from the Borrowdales by upper Llanvirn mudstones with D. murchisoni faunas (Wadge and others, 1969), as well as by a major unconformity (Wadge, 1972). The Milburn Rocks have been regarded in the past either as the off-shore equivalents of the Borrowdales, laid down at the climax of volcanism farther west (Goodchild, 1889, p. 262), or as transitional beds deposited at its onset (Green, 1919, p.156). Neither view can now be sustained in the light of these age relationships and it is concluded that the Milburn Rocks mark a period of Llanvirn volcanism lying well within the Skiddaw Group rather than at its top.

Although upper and lower D. bifidus Zone faunas can be distinguished in the Milburn and Ellergill sections, these subdivisions cannot be mapped separately. Accordingly all the mudstones and interbedded volcanic rocks are grouped within the Kirkland Formation.

Conditions of deposition

At the beginning of the Ordovician, a wide proto-Atlantic (Iapetus) ocean existed between Europe and North America. It became progressively narrower throughout the Ordovician and Silurian and eventually closed in late-Silurian times. Several attempts, summarised by Moseley (1977), have been made to reconstruct the closure in plate tectonic terms. It is generally recognised that northern England lay at that time close to the edge of the European plate, beneath which oceanic crust was subducted to the south. The subduction zone was inclined southwards beneath an island arc which lay across the Lake District (Fitton and Hughes, 1970) and the northern Pennines. The precise surface position of the subduction zone is still controversial, but it certainly lay to the north of the Lake District and was probably situated beneath the Solway. Sedimentary structures in the Skiddaw Group greywackes of the Lake District show that these Arenig sediments were derived mainly from the south ((Jackson, 1961). It seems likely therefore that they were laid down on the trench slope.

The rocks of the Murton Formation at the northern end of the Cross Fell inlier are greywackes correlating directly with the Lake District sediments. They are mainly of siltstone grade but are interbedded with greywacke-sandstones and greywacke-mudstones. The sediments are poorly sorted, with angular to subangular clasts of quartz and feldspar, with many lithic fragments, set in a chlorite-illite matrix. They were rapidly deposited as turbidites in deep water. The supply of sediment was considerable, and came from a wide variety of lithologies represented in the lithic fragments. Towards the end of Arenig times, sediment of finer grade predominated to give the mudstones and siltstones of the upper part of the Murton Formation exposed in the southern part of the inlier (Burgess and Wadge, 1974).

By the beginning of the Llanvirn, the trench seems to have migrated farther north and a volcanic island arc was established across the Cross Fell area and the northern Lake District. The products of Llanvirn volcanism in both districts are more tholeiitic than those of the Borrowdale Volcanic Group, believed to have been erupted during Llandeilo–Caradoc times. This relationship is analogous to the volcanics in modern island arcs where the earlier eruptions tend to lie closer to the subduction zone and be more tholeiitic than later, more talc-alkaline rocks (Fitton and Hughes, 1970). A further analogy is provided by the spilite lavas in the Kirkland Formation of Cross Fell which are common in modern island arcs.

The sediments laid down in the seas near the volcanic islands are represented by the interbedded pyroclastics and graptolitic mudstones of the Kirkland Formation, but their subaerial equivalents are more difficult to identify. However, if a lower Llanvirn age is accepted for the Eycott Volcanic Group in the Lake District (Downie and Soper, 1972) and for its correlatives near Melmerby (p. 11), then the basic andesites and tuffs of these sequences are probably the sub-aerial lavas erupted on the islands of the volcanic arc.

There is little doubt that submarine conditions persisted in the Cross Fell area throughout the deposition of the Kirkland Formation. Both lavas and tuffs are interbedded with graptolitic mudstones; indeed most of the sediment, as during the Arenig, was largely orthoclastic in origin although intermixed with pyroclastic debris. The tuffs generally consist of reworked detritus, commonly showing graded bedding, and there is a marked absence of those features usually taken to indicate subaerial ash-flow tuffs, such as the widespread welding of glass shards.

The youngest exposed beds of the Skiddaw Group were laid down during the late Llanvirn and are known only in the eastern Lake District (Wadge and others, 1972). Prior to the deposition of the calc-alkaline Borrowdale Volcanic Group in Llandeilo–Caradoc times, the sediments which had accumulated in Arenig–Llanvirn times were lithified and folded and had accreted on to the European continental plate.

Biostratigraphy

The biostratigraphy of the Skiddaw Group is based upon graptolites. The current zonation for the Lake District outcrops (Eastwood and others, 1968 p. 26,) is, with minor modifications, the work of Elles (1898, 1933). During the resurvey of the Cross Fell inlier, microfossils were obtained for the first time from both graptolitic and non-graptolitic Skiddaw Group rocks (Wadge and others, 1967), the latter having proved particularly useful for dating purposes (Figure 4).

Macrofossils

The graptolites collected from the Cross Fell inlier (Figure 5) are all of Llanvirn age. They are mainly restricted to the D. bifidus Zone, there being no D. murchisoni Zone faunas comparable with those encountered in the Tarn Moor tunnel in eastern Lakeland (Wadge and others, 1972). The D. bifidus Zone has been subdivided following Ekstrom (1937), who recognised two subzones within the Zone in Scania, Sweden. Skevington (1970, p. 404) has distinguished the upper sub-zone within the Skiddaw Group of the eastern Lake District. It is characterised by abundant Nicholsonograptus fasciculatus and Cryptograptus tricornis schaeferi, and as these forms dominate the faunas from the Eller Gill section, this locality is also assigned to the upper subzone. All the other Skiddaw Group graptolite faunas within the district lie in the lower subzone.

Trilobites are rare in the Skiddaw Group. Skevington has identified Pricyclopyge binodosa from Milburn Beck [NY 6867 2992], and the Sedgwick Museum collection in Cambridge contains Platycalymene tasgarensis from Eller Gill [NY 6768 3117] (Whittard, 1960, p.154) and ?Stapeleyella sp.from Milburn Beck [NY 6865 2992]. All these forms are consistent with the D. bifidus Zone age indicated by the graptolites.

Microfossils

From a total of 77 samples collected, 46 have yielded acritarchs or chitinozoa, producing the fullest collections to date from the group. These were identified by Dr T. R. Lister, The identifications as listed were made by Dr T. R. Lister in 1967–69; since that time the nomenclature of some taxa has been emended. It has not been possible to carry out a full revision but the following passage clarifies the usage of the genus Archaeohystrichosphaeridium.

The genus Archaeohystrichosphaeridium Timofeev 1959 was invalid at publication under article 37 of the International Code of Botanical Nomenclature as no type species was designated, but despite this the name has persisted in the literature. Furthermore the concept of this genus has always been difficult to interpret since the author included in it many dissimilar forms, some of which are clearly attributable to pre-existing genera. In an attempt to clarify this situation, Loeblich and Tappan, 1976 (p. 303), designated a type species, deliberately rendering the genus a junior subjective synonym of Cymatiogalea Deunff 1961. Consequently Archaeohystrichosphaeridium is now unequivocally invalid. Despite this, many species originally described under this generic name have not yet been re-allocated and remain a considerable taxonomic problem. For simplicity the name is retained here as 'Archaeohystrichosphaeridium''.

Assemblage 1

This is the oldest assemblage (Figure 6). Amongst the acanthomorph acritarchs 'Archaeohystrichosphaeridium'is abundant, with many different species present, and both Priscogalea and Vulcanisphaera are common; Baltisphaeridium, however, is comparatively rare. The polygonomorph acritarchs such as Veryhachium are not numerous, but both the diacromorph acritarchs, especially Acanthodiacrodium, and the herkomorph acritarchs particularly Cymatiogalea, are common. The associated chitinozoa are marked by numerous Lagenochitina and a distinctive Conochitina symmetrica–?C. reflexa–Cyathochitina regnelli association.

Dr Lister writes that the assemblage contains 'many species similar to those known from the Tremadocian of Leningrad (Timofeev, 1959) and North Africa (Deunff, 1961) but very few Llanvirn species. Published data from the Arenig is scanty, but most of the forms described from the Lonan Flags of the Manx Slates (Downie and Ford, 1966) are present. An early Arenig age for the Lonan Flags was suggested by comparison with assemblages from the Glauconite Sand of Estonia (Eisenack, 1958). The chitinozoa compare fairly closely with those from the Llanvirn of the Sahara (Benoit and Taugourdeau, 1961) and also with those recorded from Zones 1 and 2 of the Algerian Ordovician (Taugourdeau and Jekhowsky, 1960).' He concludes that the assemblage is best dated as Arenig and is probably upper Arenig.

Assemblage 2

These palynomorphs were partially described by Lister and others (1969) and details are given fully in (Figure 6). Species of 'Archaeohystrichosphaeridium'remain an important element but simple-spined forms, such as Baltisphaeridium aff. breviciliatum, B. hirsutoides var. hamatum and B. cf. multipilosum, are more common than in Assemblage 1. A. cf. phaseolus and B. striatulum appear to be restricted to this assemblage. Amongst the other acanthomorph acritarchs Priscogalea spp. Are much rarer, and Vulcanisphaera is not recorded. Species of Veryhachium are more numerous, especially V. trisulcum and V. lairdi. In a limited chitinozoan association, Conochitina chydea makes its first appearance locally.

Dr Lister remarks that A. cf. arenigum, A. cf. dentatum, A. cf. imperfectum and B. cf. cristatum were recorded from the Lonan Flags of probable lower Arenig age. A. dentatum is recorded from the Glauconite Beds, and A. pungens and A. sukatschevi from the Tremadoc of the Leningrad area (Timofeev, 1959). Three other species, Priscogalea furcata, P. simplex and Acanthodiacrodium lineata are known from the Tremadoc sequence in the Sahara (Deunff, 1961) and Baltisphaeridium striatulum is recorded from the Arenig Klabava Shales of Bohemia (Vavrdova, 1966). Set against this, B. aff. breviciliatum, Veryhachium lairdi, V. sartbernardense and V. valiente are all common in the Llanvirn–Llandcilo sequence of Sart-Bernard in Belgium (Martin, 1966). A late Arenig age appears most likely for the assemblage although an early Llanvirn age cannot be excluded.'

Assemblage 3

The assemblage contains a particularly large number of species; some are common to the other assemblages but many appear characteristic of this particular association (Figure 7). The acanthomorph acritarchs are dominated by many species of Baltisphaeridium, whilst comparatively few Archaeohystrichosphaeridium' , Priscogalea and Vulcanisphaera are present. The wide variety of diacromorphs consists mainly of species of Acanthodiacrodium. Both polygonomorph and sphaeromorph acritarchs are more abundant than hitherto. Chitinozoa are relatively plentiful and include as distinctive species Conochitina cf. lepida, C. parviventer, Siphonochitina formosa, S. tenuicollis, S. clavata and Sphaerochitina vulgaris.

Dr Lister writes that this assemblage contains many species described from the Tremadoc successions of both Leningrad (Timofeev, 1959) and the Sahara (Deunff, 1961), as well as undoubted Llanvirn forms. The presence of both older and younger elements distinguishes it from the other assemblages and suggests an age early in the Llanvirn. This view is supported by the chitinozoa which are almost identical with those described from the basal Hope Shales of Shropshire (,Jenkins, 1967) which are known to be of D. bifidus Zone age. It seems likely that those samples which contain a higher proportion of younger forms, such as those from Milburn Beck, come from higher in the succession, and that, with further collecting, a gradation into Assemblage 4 could be established.

Assemblage 4

This is a smaller group of microfossils and lacks the older elements of the previous assemblage (Figure 7). The acanthomorph acritarchs are represented almost entirely by simple-spined forms, especially Baltisphaeridium; species of Archaeohystrichosphaeridium'are rare and Cymatiogalaea, Priscogalea and Vulcanisphaera are not recorded. Veryhachium spp.and small sphaeromorph acritarchs such as Leiosphaeridia are common in most samples but diacromorph acritarchs arc restricted to rare occurrences of Acanthodiacrodium. The main chitinozoa are Conochitina chydaea, Rhabdochitina turgida, R. usitata and Eremochitina baculata var. brevis. Dr Lister points out that the acritarch assemblage is closely similar to that from the Assize de Huy (D. bifidus Zone) sequence in Belgium (Martin, 1966), whilst the chitinozoans, although restricted, compare closely with upper Llanvirn forms recorded from the Weston and Bctton beds of the Shelve inlier in Shropshire (Jenkins, 1967). He concludes that a Llanvirn age is indicated for the assemblage.

The localities which yielded the assemblages are shown on (Figure 4) together with the sections which produced graptolites. It is clear that, where the rocks yield both graptolites and microfossils, the same indications of age are given by both. For example, the Eller Gill section yields upper D. bifidus Zone graptolites and Assemblage 4 microfossils, whilst at Wythwaite, lower D. bifidus Zone graptolites are associated with Assemblage 3 microfloras. The microfossils suggest further that the rocks of Moray Hill, and perhaps also of Murton Beck, are younger than those around Wythwaite Hole; this cannot be deduced from the graptolites alone. The microfossils have proved of greatest value however in giving ages for non-graptolitic sequences, such as those at the northern end of the inlier, and thereby confirming the succession deduced from the lithostratigraphy.

Murton Formation

Rocks of the Murton Formation crop out at the northern end of the Cross Fell inlier between Meikle Awfell and Thack Moor. The principal exposures are in the streams but, as these tend to follow the regional strike, continuous sections through the sequence are lacking. On the interfluves, the terrain is generally smooth and rounded and good exposures are rare. The rocks are best seen where steep-sided glacial channels are cut deeply into the bedrock. They form large crags on the fellside only where they have been baked by adjacent minor intrusions.

The succession is lithologically distinct from that exposed in the southern part of the inlier (Burgess and Wadge, 1974). It consists mainly of greywacke-siltstones, interbedded with massive beds of fine-grained greywacke–sandstone which vary in thickness from about 5 to 50 cm and occasionally exceed 5 m. Finer bands of greywacke–mudstone commonly overlie the coarsest beds. The rocks are usually medium grey, brown or pale green in colour, and are composed largely of poorly sorted, angular to subangular clasts set in a matrix of illite, chlorite and leucoxene with subordinate micas, iron oxide and quartz silt. The clasts are generally quartz and feldspar with many lithic fragments; the quartz grains commonly show pressure-solution contacts and contain a substantial proportion of igneous quartz, whilst the feldspars show widespread alteration to kaolin. The lithic fragments include chert, quartzite, mudstone, siltstone, sandstone, rhyolite and basic lava, and the coarser greywackes may also contain mudstone phenoclasts. The commonest heavy minerals are blue-green tourmaline, pink garnet, zircon and apatite.

These rocks most closely resemble the Loweswater Flags of the western Lake District (Dixon, 1925) and the Slates and Sandstones subdivision of the Cockermouth district (Eastwood and others, 1968, p. 31). All three sequences show many of the sedimentary features characteristic of greywacke turbidites (Jackson, 1961). The total thickness of the Murton Formation is unknown as the base is not exposed, but in the southerly-dipping succession west of Cuns Fell are at least 1000 m of beds showing little variation in lithology.

Details

The rocks at the northern end of the Cross Fell inlier strike generally east-north-east and two major folds with this same trend can be distinguished (Figure 31), a syncline just north of Cuns Fell and an anticline farther south on Thack Moor. The wavelength of these structures seems to be at least 2 km. Minor folding is seen at some localities (p.100). The dominant surface in all exposures is the bedding. Cleavage is seen only in a few places and is very weak, being restricted to bands of mudstone and siltstone, as on the south bank of Dale Beck [NY 6365 3592].

Sedimentary structures characteristic of turbidites are widespread in the greywacke-siltstones, but are most notable in the coarser greywacke-sandstones, individual beds of which commonly have sharp bases. These bases are downcut locally into underlying finer sediments which, in at least two localities, are marked by flute-casts [NY 6363 3591], [NY 6433 3627]. They indicate derivation of sediment from a southerly direction as is recorded from the Skiddaw Group in the western Lake District (Jackson, 1961; Jeans, 1973). It is usual for graded bedding to occur in the lower part of each bed of sandstone; good examples can be seen on the northern slopes of Catterpallot Hill where massive feldspathic greywackes dipping southwards are interbedded with grey siltstones [NY 6367 3660]. In some parts of the succession, however, graded bedding is rare, particularly where the massive sandstones are thin and interbedded with finely banded siltstones; such beds dip south-westwards in the stream 400 m N of Gale Hall [NY 6308 3687]. The thicker greywacke–sandstones commonly show convoluted bedding towards the top of each bed. The bedding in the coarse sediment is generally crude. Minor slumping is well seen in the north bank of Dale Beck [NY 6433 3627]. The uppermost part of the turbidite unit is usually finer-grained and in some cases is cross-bedded. Sandstones interbedded with thin siltstones show good cross-bedding on the south bank of Dale Beck [NY 6432 3628]. Some of these sedimentary structures have been used (Figure 31) to indicate the direction of younging in steeply-dipping sequences. For example, near-vertical beds cropping out in Dale Beck [NY 6365 3593] are shown to young northwards by the eroded bases, graded bedding and flute casts in the sandstones.

Rocks are baked close to the larger minor intrusions, especially the dolerites, at the northern end of the inlier. The mudstones lose carbon and become paler in colour, locally resembling the 'Blake Fell Mudstones' lithology recorded near intrusions in the Lake District (Eastwood and others, 1968, p.21). More intense heat alteration gives rise to spots of chlorite which transgress the bedding. These are seen in rocks in contact with the dolerite sill on Cuns Fell (E36014). Less intense heat alteration up to 50 m from this intrusion is marked by fine sericite shreds (E31016). About 700 m E of Gale Hall, siltstone in contact with a feldspar-porphyry [NY 6360 3681] has been hornfelsed (E35989), but generally the alteration is less intense. In the extreme northern and north-eastern parts of the inlier, weakly spotted mudstones and siltstones (E31028), (E35919) crop out well away from the nearest intrusion [NY 6424 3747], [NY 6303 3671]. They may lie within the metamorphic aureole of the Weardale Granite to the east, although the presence of buried minor intrusions close by cannot be discounted.

Close to the sub-Carboniferous unconformity the rocks of the Murton Formation are purple and the bedding is poorly defined. Finely divided hematite occurs throughout the rocks and much secondary carbonate is also present. The alteration is most intense in the rocks exposed in streams flowing from Melmerby High Scar [NY 6434 3750] where the weathered zone beneath the unconformity is about 30 m deep, but the rocks in Hungrigg Sike [NY 6353 3708] and Dale Beck [NY 6488 3612] are also affected. Outcrops on the south side of Dale Beck [NY 6433 3587] to the west of the Gate Castle Fault seem to be similarly altered, although they lie well away from the nearest Carboniferous beds. The discolouration possibly shows that the sub-Carboniferous unconformity lay a short distance above the present land-surface.

The formation is well exposed in Melmerby Beck where an unusual 4-m bed of coarse conglomerate is interbedded with greywacke-siltstones [NY 6303 3693]. Rounded clasts of sandstone and siltstone are set in a grey mudstone matrix and probably represent a local slump-breccia of partially lithified sediment. The tributaries of Melmerby Beck also give good sections. Pale green and brown siltstones are interbedded with rare bands of greywacke in Dry Sike [NY 6375 3729] whilst higher upstream a sequence of finer-grained greywacke-siltstones and mudstones has been tightly folded in a closely-defined belt between more massive beds. Farther south, the section in Hungrigg Sike is virtually continuous; greywacke-siltstones dipping at 45° to 70° to the south-south-east contain a band sufficiently flaggy to have been worked for walling-stone [NY 6411 3710].

Massive greywacke-sandstones are more common farther south in the deeply channelled ground north of Catterpallot Hill [NY 6367 3659], but they are best seen in the banks of Dale Beck [NY 6432 3627]. The slopes of Baron Side and Thack Moor are largely underlain by siltstones; the relationship between these rocks and the Kirkland Formation beds in the stream to the south is not known but is likely to be faulted.

Kirkland Formation

The rocks of this formation not only form part of the basement beneath the western edge of the Alston Block but also appear to extend eastwards beneath the Carboniferous beds of Cross Fell to reappear in the Teesdale inlier (Burgess and Holliday, 1979). The principal outcrops in the Cross Fell inlier lie to the south of Thack Moor and east of the Fellside Fault. Further outcrops, assigned to the formation on lithological grounds, crop out west of the Fellside Fault, in a small inlier near Ousby Townhead.

The base of the sequence is not exposed but at least 1000 m of beds are present around Wythwaite Top. The succession comprises mainly grey, silty mudstones with subordinate bands of brown-weathering, pyritic mudstones and dark blue-grey, calcareous mudstones. These sediments are interbedded with many thick bands of tuff and a few thin lavas. The tuffs are usually massively bedded and form many small crags on the high ground around Grumply Hill and Burney Hill. They are mainly intermediate to basic in composition, although locally they also contain rhyolitic material. They are normally fine- to medium-grained but locally become coarse by sharp passage either across a bedding-plane or, more rarely, within a unit showing graded bedding. Most of the tuffs are heterolithic and many contain a high proportion of crystals or pumice fragments. Lapilli-tuffs are most common in the section at Wythwaite Hole (Figure 8). Many of the tuffs show graded bedding and almost all contain pyroclastic debris which has been subaqueously re-worked. In some, the proportion of orthoclastic debris is high enough to warrant the term volcanic sandstone. Jasperoid silica is common, especially on Burney Hill. No systematic thickening of the tuffs that could indicate a direction of derivation has been detected.

Lavas are seen only in the section at Wythwaite Hole where thin, albitised basalts or spilites are interbedded with spilitic tuffs and graptolitic mudstones. The term 'spilite', though unsatisfactory in rigorous nomenclature (Johannsen, 1937, p. 299) is used here in the sense of basalt variably enriched in soda.

Details

The northernmost section of the formation lies in Ashlock Sike south of Thack Moor, where grey, brown-weathering mudstones with thin ironstone bands are strongly folded [NY 6470 3492] to [NY 6455 3487]. The beds strike generally north-north-east and contain two bands of graptolitic mudstones yielding restricted assemblages, but sufficient to identify the D. bifidus Zone with reasonable certainty. On the northern slopes of Ardale Beck the formation is devoid of volcanic beds, but on the southern bank, bands of greyish green, re-worked heterolithic tuffs are interbedded with grey silty mudstones, generally dipping steeply to the east. The tuffs contain pyroclasts of feldspar, microlitic lava and chert set in a chloritic matrix and have been affected by secondary hematite and silica. At the eastern end of the section [NY 6506 3425] a coarse-grained tuff, 14 to 18 m thick, is unusual in containing rounded, re-worked pebbles of pyroclastic debris.

A short distance to the south-west, in an inlier west of the Fellside Fault, broken grey shales crop out in Acorn Sike [NY 6451 3410]. They are correlated with the Kirkland Formation on lithological grounds only; slight thermal spotting is probably caused by the nearby minor intrusion. To the south of Ardale Beck and around Kirkland Beck, the low drift-covered ground is underlain mostly by mudstones, but the volcanic rocks around Wythwaite Top produce higher, craggy topography. In the crags at Wythwaite Hole [NY 6611 3278] to [NY 6618 3269] (Figure 8) the section is:

The flow-brecciation of the spilite and its gradation into the overlying lapilli-tuff show it to be a lava rather than a sill. Professor Skevington comments that the presence of A. cucullus in the overlying mudstones is a firm indication that the sequence lies in the D. bifidus Zone of the lower Llanvirn. The band of graptolitic mudstone is transgressed in the section by the succeeding tuff (f) and thins out entirely 200 m to the north-east. Higher up the hill, the overlying tuffs are less well exposed but have similar textures and compositions.

Tuffs are much less common in the scattered sections along Crowdundle Beck and in the comparatively low-lying ground to the south, where they stand out locally as ridges in the sides of the deep glacial channels, such as Mudgill Sike, east of Red Carle. Heterolithic tuffs predominate, but differ from those farther north in containing many large fragments of Kirkland-type mudstone [NY 6782 3180], [NY 6671 3127], and fewer pyroclasts derive from magma. This may indicate a local pattern of eruption different from that around Wythwaite Hole, with less magma and perhaps more volatiles released to disrupt the partly lithified mudstones. The local conditions of deposition must have varied greatly during the volcanicity and appear to have affected the contemporary graptolites. For example, graptolites are found in 3 m of interbedded tuffs and silty mudstones in Mudgill Sike [NY 6765 3009]. The assemblage (Figure 5) is dominated numerically by Phyllograptus angustifolius, which occurs profusely on certain bedding planes in the coarse tuff bands; all other elements in the fauna are restricted to the mudstones. It appears that this species flourished in the special conditions marked by the tuffs. The fauna is sufficiently varied to indicate to Prof. Skevington that the section lies in the D. bifidus Zone.

The fullest graptolite faunas in the district have been collected from grey, silty, micaceous mudstones in the south-west bank of Eller Gill [NY 6757 3120]; [NY 6768 3117]. The beds are strongly folded and cannot be related directly to other sections, but are believed to lie near the top of the Kirkland Formation. Prof. Skevington writes: 'The abundance of Nicholsonograptus fasciculatus suggests reference to the highest part of the D. bifidus Zone. This assignment is further supported by the occasional presence of D. pakrianus, which is an essential D. murchisoni Zone species, but whose range is known to include the higher part of the D. bifidus Zone.'

Farther south, several hundred metres of interbedded mudstones and tuffs crop out on Burney Hill. The smooth slopes of the hill are mainly underlain by mudstones which are not well-exposed, but the more massive pyroclastics tend to form small crags. The tuffs are largely heterolithic (E36153), (E36155), (E36156), (E36159), (E36160), (E36161), (E36162), (E36163), (E36165), (E36166), (E36167) with poor to moderate sorting, and are generally fine- to medium-grained, although one of the few coarse bands forms a line of low crags on the southern flank of the hill [NY 685 298]. Finally the stream in the south-east corner of the district (Milburn Beck) exposes several small sections in mudstones yielding graptolites (Figure 5). All lie within the D. bifidus Zone. A.J.W.

The Wythwaite spilite consists of non-porphyritic, fluxioned felts of albite-oligoclase needles ranging from 0.2 x 0.02 to 0.7 x 0.06 mm. Microphenocrysts of albite-oligoclase up to 0.9 x 0.2 mm are sparsely scattered in some samples. The mesostasis is mainly chlorite, leucoxene, quartz or micropegmatitic quartz-feldspar growths ((Plate 2).1). Some chlorite particles suggest pseudomorphs after primary ferromagnesian minerals (including clinopyroxene). The flow-brecciation in sections (E36477)-(E36478), (E36480)-(E36481) shows as angular segregations of felted feldspar laths of different size in juxtaposition. Also, small cloudy spherulitic radiating feldspar microliter occur, with green chloritised glass containing scattered feldspar microphenocrysts, fractured and re-cemented devitrified lava, chloritised pumice and quartz-chlorite-pumice and quartz-chlorite aggregates, all cemented by chloritic and microlitic glass. The occurrence of silica is particularly evident in a variety of forms and of several generations (jasper, chalcedony, quartz) associated with chlorite in the mesostasis, in microamygdales (with calcite and chlorite), and in secondary vcinlets.

A complete chemical analysis ((Table 1), col. 1) of one sample from the base of the Wythwaite Hole section shows a high SiO₂ content for spilitic rocks (due partly to free quartz) and conspicuous soda. The soda is less than in a spilite analysed from the Builth Volcanic Series (Nicholls, 1958, p.144), though above average for spilites generally (Hyndman, 1972, p.99). Potash is insignificant in the present sample and is probably accounted for by mica, or by a little orthoclase in the groundmass. Too close a petrographical comparison cannot, however, be made between the present highly altered lava and other spilites, or indeed with the 'basaltic andesites' of the adjacent Cockermouth district (Eastwood and others, 1968), though in terms of petrogenesis, a close relationship may well have existed. Hyndman (ibid., p. 100) notes that spilites are also commonly low in MgO and CaO, and the present sample is well below the average spilite values for these oxides.

Several spilitic tuffs, some containing spilitic lapilli, crop out nearby e.g. [NY 6645 3268] and this close association has been taken as evidence that both lava and tuffs were derived from a common spilitic magma. Indeed, it has been suggested (Hudson, 1937, p.398) that the same spilitic magma produced intrusive equivalents in the soda-rich dolerites of Cuns Fell, Catterpallot Hill and Baron Side. However, many (e.g. Cann, 1969), find that the idea of a specifically spilitic magma is implausible as such melts have not been recognised in present-day volcanicity. The alternative is that the lavas, tuffs and dolerites were all enriched in soda by secondary processes occurring after burial beneath later sediments. Both the hydrolysis of basalt (Valiance in Amstutz, 1974) and its low grade metamorphism (Battey, in ibid.) have been invoked.

The overlying lapilli-tuff in the section (bed c) contains chloritic lapilli and a range of pyroclasts ((Plate 2).2) including pumice, coarsely porphyritic lava, devitrified glassy lava, microlitic spilitic or keratophyric lava, altered feldspar crystals and shards, the coarsest being rounded and up to 1 cm across, admixed with orthoelastic chert, quartz, sericite and apatite. The finer particles are partly orientated and cemented in a finely microlitic and chloritic base. A full chemical analysis is given in (Table 1), col. 2. It is not possible to apportion the oxides to their respective constituents because of their complexity but the relatively high soda content, high silica and conspicuous potash are noteworthy. Of the minor constituents, Ba and Sr are conspicuous. The succeeding crystallithic tuff (bed d) contains closely packed fragments of lava and pumice with crystals and shards, and grades up into a banded tuffaceous siltstone (bed e) consisting of similar pyroclastic detritus re-worked with orthoclastic quartz silt.

Amongst the overlying tuffs, higher up the hill, is a silicified vitroclastic tuff (E36490) [NY 6632 3284] forming a fine-grained (0.1 mm) grey rock with subconchoidal fracture and resembling halleflinta; it is composed of bedded shards, crystal fragments, glassy streaks, minor apatite and leucoxene crystals. Coarser tuffs (E36491), (E36492) [NY 6633 3283]; [NY 6645 3268] include saussuritised oligoclase crystals, carbonated pumice with chlorite-filled vesicles, chloritised lava, carbonated spilite, possible andesite, and conspicuously (in E 36492) pink jasper grains up to 0.5 mm across. The microcrystalline matrix is mainly silica and chlorite, with patches of later albite. The matrix appears to have been both silicified and albitised in one specimen (E36149) [NY 6641 3270]. A vitroclastic tuff (E36493) [NY 6677 3210]-a hard, pale green-grey, fine-grained (0.1 mm) rock-contains abundant close-packed, well-sorted glass shards preserved in cryptocrystalline silica, with coarser feldspar crystals and lava streaks ((Plate 2).3). Two samples (E36133)-(E36134) from a little to the west of Wythwaite Top [NY 6579 3254], [NY 6583 3251] are of interest in showing a range of lithic pyroclasts and conspicuous crystals (0.1 mm) of albite-oligoclase, scattered in a very fine-grained allotriomorphic mosaic of albite and quartz, with crystals of apatite, pyrite and leucoxene.

Variations in grain-size, texture and composition of the tuffs are best seen to the south-east, on crags around Grumply Hill [NY 6710 3210], [NY 6695 3181], where they are mainly medium- to fine-grained, dense, hard, pale grey to purplish rocks, composed of closely-packed, moderately or poorly sorted, angular pyroclasts ranging up to 5 mm across. They include a range of lithologies, though intermediate to basic pumice and spilitic, microlitic lava are common throughout, with saussuritised, marginally resorbed albite-oligoclase crystals. Vesicles in the pumice (ranging from spheroidal to ellipsoidal) are variably filled with green, radially-fibrous chlorite and fine albite aggregates. Cherty silica which may be either of igneous or sedimentary origin also occurs, but undoubted orthoclasts are generally sparse. The matrix consists of finely comminuted pyroclastic dust, pale brown, altered palagonitic glass shards, feldspar particles, quartz, secondary albite aggregates, chlorite, leucoxene, calcite, apatite crystals and secondary hematite. The pyroclasts are thus evidence of accumulated volcanic materials of principally intermediate to basic composition, with little orthodetrital sediment. Two further samples (E36494), (E36495) [NY 6805 3185] are fine-grained (less than 2 mm), well-sorted, closely packed aggregates of carbonated lava particles and plagioclase crystals, in a matrix of chlorite, leucoxene, shards, silica and apatite, but these are highly altered rocks, lying close to the sub-Carboniferous unconformity.

The tuffs on the south side of Burney Hill contain a variety of pyroclasts including saussuritised sodic plagioclase crystals, pumice (vesicles ranging from spheroidal to attenuated and filled with albite and quartz), feldspar-microlitic lava resembling andesite or spilitic basalt, brown palagonite and rhyolitic aggregates. Orthoclasts are generally sparse, but include (E35167) illitic slate, and sandy quartz with illite (E36163). The first sample also shows brecciation and recementation, with much secondary silica. The matrix is largely pyroclastic dust, with common late-stage albite associated with quartz, chlorite, dolomite, ubiquitous apatite, in one sample (E36156) accessory diopside, and a trace of zircon. Secondary products include hematite, leucoxene, pyrite and silica. X-ray powder photographs (NEX957, NEX965, NEX966, NEX967) of tuff matrices showed major feldspar, quartz, illite, kaolinite, chlorite, and in one sample (E36162) dolomite. Hudson (1937, p. 374) noted more andesitic pyroclasts in the tuffs around Burney Hill, indicating 'an approach to an andesite vent farther south', but this has not been confirmed in the present studies, and the overall fineness of granularity with a lack of lapilli or coarser (agglomeratic) material, suggests that the vents were more distant. Secondary silicification is widespread, giving quartz-veining on some crags [NY 6861 3015]. RKH

Ordovician: Borrowdale Volcanic Group

Volcanic rocks, here assigned to the Borrowdale Volcanic Group, crop out only in three small fault-bounded blocks, one in the Greystoke inlier and the others in the Cross Fell inlier, east of Melmerby and north of Milburn Beck. By comparison with the two main volcanic sequences in the Lake District, the andesites, rhyolites and tuffs of Greystoke and Melmerby correlate with the northern Lakeland outcrops whilst the welded ash-flow tuffs of Milburn Beck are more closely related to those farther south.

When the geological map of the district was compiled, it was usual to include both Lake District successions within the Borrowdale Volcanic Group, and it is on that basis that the above outcrops were assigned to it. Recent work suggests however that the two Lake District sequences do not correlate (Downie and Soper, 1972). To accord with the most recent classification of the Lake District rocks (Wadge, 1978), the Greystoke and Melmerby outcrops should now be grouped with the Eycott Group and the Milburn Beck section with the Borrowdale Volcanic Group proper. However, as the previous classification was used on the published geological map, it is retained here.

The deposition of the submarine tuffs of the Kirkland Formation close to a volcanic island arc in Llanvirn times has been discussed above. It now seems likely that the Greystoke and Melmerby lavas and tuffs were laid down at about the same time on the volcanic islands of this arc, which lay above a southerly-dipping subduction zone. Present-day island arcs are characterised by early tholeiitic volcanicity developed close to the oceanic trench and a later calc-alkaline phase farther from it. This sequence of volcanicity compares closely with that associated with the Ordovician island arc. The Llanvirn succession of the northern Lake District, including the Greystoke and Melmerby rocks, is more tholeiitic in composition (Fitton and Hughes, 1970) than the Llandeilo- Caradoc sequence farther south.

Details

Greystoke Park

Most of this inlier lies within the Cockermouth district to the west arid has been described by Hollingworth (in Eastwood and others, 1968, p. 73). Within the present district, exposures of Borrowdale rocks are restricted to a few glacially-rounded hummocks penetrating the thick drift. The dip is generally north-north-easterly at 50° to 60°, becoming easterly in the southern part of the inlier. This conforms broadly to the structure recorded farther west, as does the following general sequence which is only slightly modified from that given by Hollingworth (op. cit.):

The lowest bed in this sequence is poorly exposed [NY 4097 3178] and its stratigraphical relations with the rest of the succession are obscure. It resembles the lowest tuff recorded on Eycott Hill (bed 'a' of Eastwood and others, p.72) and thus may lie close to the base of the local Borrowdale sequence. A specimen (E37859) contains a fragment of highly folded mudstone with an axial plane cleavage ((Plate 2).4). Both the folding and cleavage predate the incorporation of the fragment into the tuff. The age of the deformation cannot be proved, but it seems likely that the mudstone was derived from the underlying Skiddaw Group and that therefore these sediments were folded and cleaved prior to the deposition of the tuff. Other clasts include fluxioned andesite and Eycott-type porphyritic andesite, rhyolite (albite phenocrysts set in a cryptocrystalline silica base), and dolerite; all can be closely matched with local lithologies. The matrix includes fine particles from the clasts together with feldspar crystals, devitrified glass and chlorite.

Beds a to c in the succession are not exposed but the augiteandesite bed d crops out in the south of the inlier [NY 408 318]. The relatively high proportion of pyroxenes in this rock (E37856), (E37857), (E37858) indicates a basaltic affinity although its microscopic appearance confirms it as a basic andesite. It contains fluxioned, variably albitised, basic plagioclase laths (0.2 x 0.02 mm; near Ab₂₆ An₇₄ where unaltered) enclosing subhedral to euhedral, pale green augite plates (0.1 mm) which in turn poikilitically enclose feldspars. Accessory orthopyroxene is completely chloritised. Brown devitrified mesostasis contains specks of ores whilst coarser magnetite is myrmekitically intergrown with quartz and calcite. Small amygdales are filled with carbonate.

Bed e is not exposed within the district but several outcrops of the overlying Eycott-type basic andesites penetrate the drift cover [NY 4044 3288]. The lavas are prominently feldsparphyric, with euhedral feldspar phenocrysts up to 4 mm across, mainly altered to carbonate or secondary mica; the phenocrysts occur individually and in paragonitised glomeroporphyritic clusters (E37852)-(E37853). Phenocrysts of orthopyroxene, up to 2 mm long, have generally been replaced either by chlorite or by aphrosiderite, according to an X-ray diffraction photograph (NEX 1150) taken by Mr K. S. Siddiqui. The groundmass is a lattice-work of labradorite laths (0.2 x 0.02 mm) and tablets (0.5 mm) with a mesostasis of dark brown devitrified glass, chlorite, leucoxene and opaque ore. Primary clinopyroxene is altered to chlorite. Not all these andesites are markedly porphyritic however; one specimen (E37854) has only microphenocrysts (0.5 mm) of altered feldspar, in a fluxioned fclsitic groundmass charged with opaque leucoxene and chlorite. The andesites are also commonly silicified, chloritised and carbonated, with many amygdales lined with chlorite and infilled with quartz and carbonate (E37855).

The highest lavas in the succession (bed g) cropping out in a prominent roche moutonée about 600 m SW of Park House [NY 405 330], are green-grey, aphanitic, amygdaloidal andesites (E37849), (E37850), (E37851). Both the feldspar microphenocrysts and the fluxioned plagioclase needles (0.06 x 0.008 mm) are generally albitised and are set in a groundmass of devitrified glass, iron oxide, chlorite, leucoxene, carbonate and quartz.

Melmerby

In the inlier east of Melmerby, rocks of the group are moderately well exposed, around Deep Slack [NY 623 380] in the north, and in Melmerby Beck [NY 685 373] to the south, but are poorly seen in the intervening ground so that the local sequences cannot be correlated nor can their structural relations be established. The most common lithology is basic andesite and both feldsparphyric and aphanitic types are present. The feldsparphyric type compares closely with the porphyritic rocks of Eycott Hill in the Cockermouth district; similarly the aphanitic andesites can be grouped with the 'nonporphyritic and sparsely microporphyritic andesites' in the Eycott succession (Phemister in Eastwood and others, 1968, pp. 52–60). The Melmerby rocks are more altered however, than those at Eycott. They consist of labradorite phenocrysts (An„), sparse augite, and hypersthene altered to an Fe-rich Mg-chlorite, in a groundmass of labradorite (An„), augite, iron ore, and chlorite pseudomorphs after hypersthene. The classification of these lavas is difficult since the feldspar species is diagnostic of basalt, but the texture is more characteristic of andesite. Chemically and mineralogically, the porphyritic types are grouped with the labradoritedacites or bandaites, but on texture and on the low proportion of ferromagnesian minerals they are classed as andesites. The criterion of quartz content used by Phemister to substantiate their classification as andesites is less strong here as this mineral seems to be either of late-stage crystallisation or secondary.

Exposures of pyroclastic rocks are restricted to fine-grained tuffs; these are crudely stratified and poorly sorted but none are so coarse as to indicate likely local sources of vulcanicity. The Melmerby outcrop is regarded therefore as the easterly extension of the thick Lake District sequence which is thought to be derived from eruptive centres north or north-west of Cockermouth (ibid., pp. 50–51).

In the southern part of the Melmerby inlier at least 55 m of green, porphyritic basic andesites of Eycott type dip eastwards at about 10° to 15° in the eastern bank of Melmerby Beck [NY 625 373]. Dips are steeper and very variable near the faults. The lavas consist typically of euhedral (up to 1 cm long) phenocrysts and glomeroporphyritic clusters of labradorite (near Ab„ An„) set in a dark grey ground-mass (E31018). Fine oscillatory zones in the phenocrysts are common and are marked in places by rows of chloritic and other inclusions ((Plate 2).5). The phenocrysts also show sets of fine-fractures produced by stress during crystallisation (E31018). It is usual for the primary ferromagnesian minerals such as orthopyroxene to have been chloritised ((Plate 2).6). The groundmass is a hyaloophitic mesh of partly-fluxioned feldspar laths and prisms, averaging 0.1 x 0.01 mm and generally albitised. A turbid intersertal mesostasis consists of chlorite with devitrified glass, carbonate and quartz. More altered specimens show albitisation of the phenocrysts as well as the groundmass (E35917), (E35932) with much secondary mica, carbonate and chlorite. Amygdales are present throughout the lavas but are particularly common in the lower beds. They are generally lined with dolomite or quartz and filled with chlorite or chalcedony. Cracks are lined with granular leucoxene indicating a redistribution of titanium. Several flows are probably present but are difficult to distinguish in the field. The cooled crust of a flow is probably represented near the middle of the Melmerby Beck sequence [NY 6251 3742] by a brecciated, microporphyritic andesite (E35927) in which albitised phenocrysts (1 x 2 mm) and amygdales are set in a fluctioned microlitic groundmass, with needles averaging 0.08 x 0.008 mm.

Near the base of the Melmerby Beck sequence are a few bands of non-porphyritic, aphanitic, highly altered andesite [NY 6246 3729], [NY 6245 3736]. They consist of fluxioned, albitised laths (0.3 x 0.06 mm) partly replaced by quartz or carbonate, altered ferromagnesians and disseminated magnetite and leucoxene. They resemble the groundmass of the Eycott-type lavas described above. With the introduction of substantial felsic minerals (quartz, feldspar with carbonate, and leucoxene), however, rhyolitic textures with complex interlayering are developed (E35930). Laminae of alternating 'basic' and 'acid' composition may attain 3 mm thickness (E35933) and indicate hybridisation through the introduction of basic–intermediate and acid residua and perhaps the cooling of immiscible fractions.

Pyroclastic rocks are restricted in the Melmerby Beck area to the disturbed rocks adjoining the Deep Slack Fault, where crystallithic tuffs crop out on the west bank of the stream [NY 6254 3718], so their relationship with the Eycott-type lavas is not known. They contain albite-oligoclase crystals, mainly euhedral or subhedral to broken, and up to 4 mm across. Together with other pyroclasts, including pumice lapilli (up to 5 mm across), glass, rhyolitic particles and fluxioned microlitic andesite, they show crude stratification. They are set in a matrix of shards and other pyroclastic dust cemented by chlorite, quartz, carbonates and clay material. X-ray powder photographs (NEX961, NEX962) by Mr K. S. Siddiqui show that the clays contain chlorite, illite, kaolinite, feldspars and quartz. The feldspars therefore not only form whole or broken crystals but also much of the comminuted dust in the tuffs; as there is no evidence of re-working, the comminution must have taken place before the dust was incorporated into the tuffs.

Farther north in the Melmerby inlier, the Eycott porphyritic lavas are probably faulted out as they fail abruptly northwards along the strike. Beyond the fault, exposures are poor and bedding is obscure. Strongly altered, dark green and brown amygdaloidal and vesicular lavas are sporadically exposed in the banks of Melmerby Beck [NY 6235 3749]. Flow brecciation is common (E35937) with angular clasts of microlitic to cryptocrystalline lava up to 5 mm across.

At the northern end of the inlier, dark green, massive, vesicular basic andesites are well exposed in the sides of two quarries in dolerite intrusions [NY 6228 3814] and [NY 6236 3802]. Although considerably altered, they texturally resemble the aphanitic andesites, described above as interbedded with the porphyritic Eycott-type lavas in Melmerby Beck. In the northern quarry, the andesites dip north-north-westerly at 45° to 70° and overlie thin bands of pumiceous tuff in the south wall of the digging [NY 6228 3813]. The southern quarry is in similar massive andesites with obscure bedding. As the complex faulting visible in the quarries is probably general throughout this tract, there is uncertainty as to the position within the sequence of scattered exposures of the pyroclastic rocks hereabouts. These are highly variable in texture and include crystallithic, pumiceous and heterolithic tuffs. Crystal-lithic tuffs crop out in the east bank of Deep Slack [NY 6241 3796] and closely resemble the tuffs from Melmerby Beck described above. Pumiceous tuffs exposed in the northern quarry at Deep Slack [NY 6228 3813] and in Shieldgreen Wood, 400 m to the south [NY 6237 3781], consist of lapilli of olive-green pumice, set in a matrix of pyroclastic dust and quartz (E35957), (E36377), (E36378). Vesicles in the tuff are filled with chlorite indicating a basic or basic-andesite parentage. Heterolithic tuffs are known only from one locality in Deep Slack [NY 6238 3803]. They contain both pyroclasts, as angular hematitised rhyolite particles formed of interlocking quartz aggregates charged with leucoxene, pumice and yellow chlorite, and orthoclasts of altered slate and silty quartz grains (E35959). It is not known whether the orthoclasts are fragments of country rock caught up in a volcanic explosion or are sedimentary debris.

East of Milburn

The Knock Pike Tuff Formation (Burgess and Holliday, 1979) is entirely drift-covered within the district. A short distance south of the southern margin of the Penrith area, however, a thick sequence of welded ash-flow tuffs dips southwards at 50° to 80° in Milburn Beck. The underlying coarse acidic pyroclastics are also drift-covered north of the stream but crop out on Knock Pike. RKH, AJW

Ordovician: Coniston Limestone Group

Fossiliferous mudstones of Caradoc and Ashgill age crop out in a small inlier lying between the Else Gill and Deep Slack faults, about 1 km NE of Melmerby. They are faulted against Silurian beds to the north and rocks of the Borrowdale Volcanic Group to the south (Figure 9). The Upper Ordovician stratigraphy of the Cross Fell inlier has been summarised by Burgess and Wadge (1974) and details of the principal sections are given in the memoir on the Brough district (Burgess and Holliday, 1979).

Mudstones of similar age to the Melmerby rocks crop out more extensively in the southern part of the Cross Fell inlier where they have been divided into the Dufton Shales and the overlying Swindale Shales, by means of their rich and varied shelly faunas. The fossils indicate that the main part of the Melmerby outcrop consists of Dufton Shales, although the small exposures of calcareous mudstones and thin limestones, lying respectively at the NE- and SW-corners of the inlier correlate with the Swindale Shales. Elsewhere in the Cross Fell district the Swindale Shales rest unconformably upon the Dufton Shales (Burgess and Wadge, 1974) but at Melmerby the junctions between the formations appear to be faulted.

The Melmerby faunas were first identified by Nicholson and Marr (1891, p. 509), whilst Reed (1910) described material collected during the widening of the Melmerby–Alston road. Bancroft (1933, 1945) and Lamont (1948) applied faunal zones established in Shropshire to the Cross Fell sections, including Melmerby, and these were further refined by the detailed work of Dean (1959). During the resurvey, all Dean's localities in the Dufton Shales (A–J on (Figure 9)) were recollected, but his faunal lists were not significantly enlarged. This outcrop of Dufton Shales yields only Longvillian Stage faunas from the middle of the Caradoc Series.

The Swindale Shales have not previously been recognised at Melmerby, although Bancroft collected from 'a quarry south-east of the road junction and west of the occurrence of red fossils' (Lamont, 1948, p. 8) which was probably locality L (Figure 9). The faunas in both outcrops of the Swindale Shales indicate the Staurocephalus clavifrons Zone of the Rawtheyan Stage, in the upper part of the Ashgill Series (Ingham and Wright, 1970, p.238).

At least 150 m of Dufton Shales are probably present, including about 100 m of beds referred to the lower part of the Longvillian Stage, whilst the Swindale Shales are about 30 to 40 m thick. These thicknesses are difficult to estimate accurately, however, as the faulting in these incompetent beds is likely to he more complex than that deduced from the limited exposures. The mudstones in particular have been subjected to brittle fracturing along small closely-spaced faults. There is no sign of fold closures. The bedding generally strikes WSW–ENE, with steep south-south-easterly dips in the Dufton Shales and north-north-westerly dips in the Swindale Shales. A near-vertical cleavage striking with the bedding is seen in the mudstones but is weak or absent in the more massive limestones.

Details

The fossil locality letters(A–J) used by Dean (1959, p.210) are retained in (Figure 9) and new localities are marked by subsequent letters (K–Q). The following faunas, collected from grey-green, silty, ashy mudstones cropping out on the east side of the Alston road, are supplementary to his faunal lists:

Locality C [NY 6232 3841]

Cremnorthis parva

Locality E [NY 6231 3838]

bryozoa, Rhactorthis melmerbiensis, Broeggerolithus nicholsoni, (s.l.), B. nicholsoni cf. globiceps

Locality F [NY 6231 3837]

bryozoa, Dalmanella cf. horderleyensis, Howellites?, Sericoidea?, Skenidioides?, Sowerbyella?, Broeggerolithus nicholsoni cf. nicholsoni, B. nicholsoni cf. longiceps, primitioid and tetradelloid ostracods.

These faunas fully support Dean's view that the beds at these localities are Lower Longvillian in age. A similar age was indicated by Dean for the dark grey, purple-stained, slightly silty mudstones exposed farther east, which yielded the following during the present survey:

Locality J [NY 6231 3832]

Dalmanella sp., Leptestiina cf. oepiki?, orthoid, plectambonitoid, Broeggerolithus cf. nicholsoni, Brongniartella?, calymenid

New localities in the inlier were obtained by trenching. Of these, two yielded lower Longvillian faunas as follows:

Locality N [NY 6231 3831]

Dalmanella sp., Howellites cf. intermedius, Sericoidea sp., Broeggerolithus ef. nicholsoni, Brongniartella sp., Kloucekia sp., crinoid fragment.

Locality O [NY 6234 3827]

bryozoa, Dalmanella horderleyensis, Rhactorthis melmerbiensis?, Howellites cf. intermedius, Leptestiina oepiki, linguloid, Sowerbyella sericea s.l., Broeggerolithus nicholsoni nicholsoni, Brongniartella ascripta, calymenid, Kloucekia apiculata, tetradelloid ostracod.

D. horderleyensis and H. cf. intermedius are particularly common at the latter locality. The dark grey, purple-stained mudstones of these localities, together with similar beds at locality J, form a belt of Lower Longvillian beds at the south-east margin of this inlier.

Younger beds yielding Upper Longvillian faunas were collected as follows:

Locality M [NY 6228 3831]

Dalmanella sp., Dolerorthis duftonensis, Kjaerina sp., Paracraniops sp., cheiruroid?, Estoniops cf. alifrons, Kloucekia?, Otarion sp.

The brown, crumbly decalcified limestone at this locality resembles that at Upper Longvillian locality H, and the faunas are also comparable.

Locality P [NY 6236 3855]

Dalmanella sp., Sericoidea sp., Cerninella (Harperopsis) cf. scripta, Ulrichia cf. bicornis

This fauna, although Caradocian in age, is too restricted to indicate a particular stage. The small trench at this locality penetrated weathered fragments of grey and brown mudstones, resembling the nearby beds at Dean's locality A, with which they are therefore tentatively correlated.

Rocks of Ashgillian age crop out at the south-west and north-east corners of the inlier, in two small diggings probably formerly worked for limestone. The southern end of the south-western digging yielded:

Locality K [NY 6226 3831]

Aegiriomena sp., Chonetoidea sp., clitambonitoid?, dalmanellid, Philhedrella sp., Plectorthis?, Ptychopleurella?, rhynchonelloid, gastropods, Diacalymene cf. drummuckensis, Diacanthaspis?, illaenid, Oedicybele sp., Proceratocephala?, proetoid, Staurocephalus clavifrons, primitioid and tetradelloid ostracods, machaeridian fragments including Lepidocoleus sp., cystoid plates and columnals.

A small trench across the eastern wall of this overgrown digging gave the following section:

Locality L [NY 6227 3831]

Trenching in the other overgrown digging, farther to the northeast, exposed grey, muddy, fine-grained limestone with brown rottenstones, yielding:

Locality Q [NY 6237 3860]

Christiania portlocki, Rhactorthis sp., Philhedrella plectambonitoids, Plectorthis?, Ptychopleurella sp., Ceraurinella intermedia, Diacanthaspis cf. decacantha, Encrinuroides sexcostatus, illaenid, lichoid, Lonchodomas sp., Otarion sp.[' sp. ind. 2' of Whittington, 1966, p.80, pl. 26, figs. 4, 6–15], Panderia cf. lewisii, Prionochielus obtusus, Phillipsinella parabola, proetoid, Pseudosphaerexochus sp., remopleuridid, Staurocephalus clavifrons, Tretaspis cf. granulata, T. kiaeri, Trinodus tardus, otarionoid (gen. nov.), primitoid ostracods, Ulrichia?, Lepidocoleus, cystoid and crinoid fragments. AWAR, AJW

Silurian: Browgill Beds

Silurian rocks are restricted to a small fault-block, lying between the Else Gill and Deep Slack faults, about 1 km NE of Melmerby. They are medium grey, pale green or pink, graptolitic, silty mudstones cut by a weak, near-vertical, ENE-trending cleavage and best exposed in the eastern side of the A686 Melmerby–Alston road (Figure 9). They correlate lithologically with the Browgill Beds, the upper subdivision of the Stockdale Shales in the Lake District sequence (Aveline and Hughes, 1872; Marr and Nicholson, 1888).

Their biostratigraphical correlation is based on the contained graptolite faunas, which indicate the upper part of the Monograptus turriculatus Zone of the Llandovery Series. A summary of Silurian biostratigraphy in the Cross Fell area (Burgess and others, 1970) shows that, hereabouts, this horizon lies in the lower part of the Browgill Beds.

The variable dips within the fault block probably indicate a complex and heavily faulted structure, although the details cannot be demonstrated as only the road-side outcrops have yielded graptolites. Localities MI and M2 were destroyed during recent road-widening which exposed localities M3 and M4. The following faunas were collected:

Locality M1 [NY 6232 3861]

Monoclimacis? galaensis, Monograptus marri, M. planus?, M. aff. pseudobecki, M. ex gr. runcinatus, ?Petalograptus sp., Pristiograptus regularis.

Locality M2 [NY 6234 3863]

Monoclimacis? galaensis, Monograptus halli?, M. marri, M. ex gr. runcinatus, M. turriculatus, Pristiograptus regularis.

Locality M3 [NY 6233 3862]

Locality M4 [NY 6235 3864]

Dr Warren comments that the M1 fauna is probably from the upper M. turriculatus Zone on the presence of M? galaensis and M. marri and that the M2 fauna probably lie about the middle of the Zone. Similarly, the M3 and M4 faunas are from the upper part of the Zone, above the Rastrites maximus Subzone.

The clay bands exposed in the M3 section are too weathered for petrographical determination, but closely resemble tuffaceous beds in the Browgill Shales in Swindale Beck (Burgess and Holliday, 1978); the latter contain feldspar crystals, glass shards and volcanic debris in a mainly kaolinite matrix.

No younger Silurian rocks crop out within the district. The beds in Limekiln Beck [NY 6242 3983] formerly considered to be Coniston Grits of Ludlow age (Shotton, 1935, p. 646), are now referred to the Carboniferous Basement Beds (p. 28). AJW

References

AMSTUTZ, G. C. 1974. Spilites and spilitic rocks (Ed.). International Union of Geological Sciences. Series A, No. 4.

AVELINE, W. T. and HUGHES, T. McK. 1872. The geology of the country around Kendal, Sedbergh, Bowness and Tebay. Mem. Geol. Surv. G.B.

BANCROFT, B. B. 1933. Correlation tables of the Stages Costonian-Onnian in England and Wales. (Privately printed.)

BANCROFT, B. B. 1945. The brachiopod zonal indices of the Stages Costonian to Onnian in Britain. J. Paleont., Vol. 19, pp. 181–252.

BENOIT, A and TAUGOURDEAU, P. 1961. Sur quelques chitinizoaires de l'Ordovicien du Sahara. Rev. Inst. Franc Petrole, Vol. 16, pp. 1403–1421.

BUCKLAND, W. 1817. Description of an insulated group of rocks of slate and greenstone in Cumberland and Westmorland, on the east side of Appleby between Melmerby and Murton. Trans. Geol. Soc. London, Vol. 4., pp. 105–116.

BURGESS, I. C. and HOLLIDAY, D. W. 1979. Geology of the country around Brough-under-Stainmore. Mem. Geol. Surv. G.B.

BURGESS, I. C.  RICKARDS, R. B. and STRACHAN, I. 1970. The Silurian strata of the Cross Fell area. Bull. Geol. Surv. G. B., No. 32, pp. 167–182.

BURGESS, I. C.  and WADGE, A. J. 1974. The geology of the Cross Fell area. vii + 91 pp. (London: HMSO.)

CANN, J. R. 1969. Spilites from the Carlsberg Ridge, Indian Ocean. J. Petrol., Vol. 10, pp. 1–19.

DEAN, W. T. 1959. The stratigraphy of the Caradoc Series in the Cross Fell Inlier. Proc. Yorkshire Geol. Soc., Vol. 32, pp. 185–227.

DEUNFF, J. 1961. Un microplankton à hystrichosphères dans le Trémadoc du Sahara. Rev. micropallontol., Vol. 4, pp. 37–52.

DIXON, E. E. L. 1925. In Summ. Prog. Geol. Surv. G.B. for 1924, pp. 70–71.

DOWNIE, C. and FORD, T. D. 1966. Microfossils from the Manx Slates Series. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 307–322.

DOWNIE, C. and SOPER, N. J. 1972. Age of the Eycott Volcanic Group and its conformable relationship to the Skiddaw Slates in the English Lake District. Geol. Mag., Vol.109, pp.259–268.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the country around Cockermouth and Caldbeck. Mem. geol. Surv. G.B.

EISENACK, A. 1958. Mikrofossilien aus dem Ordovizium des Baltikums. Markasitschicht, Dictyonema - Schiefer, Glaukonitsand, Glaukonitkalk. Senckenberg. Leth., Vol. 39, pp. 389–405.

EKSTROM, G. 1937. Upper Didymograptus Shale in Scania. Sver. Geol. Unders., Ser. C, No. 403, pp. 3–53.

ELLES, G. L. 1898. The graptolite fauna of the Skiddaw Slates. Q. J. Geol. Soc. London, Vol. 54, pp. 463–539.

ELLES, G. L. 1933. The Lower Ordovician graptolite faunas with special reference to the Skiddaw Slates. Summ. Prog. geol. Surv. G.B. for 1932, pp. 94–111.

FITTON, J. G. and HUGHES, D. J. 1970. Volcanism and plate tectonics in the British Ordovician. Earth Planet. Sci. Lett., Vol. 8, pp. 223–238.

GOODCHILD, J. G. 1889. An outline of the geological history of the Eden valley. Proc. Geol. Assoc., Vol. 11, pp. 258–284.

GREEN, J. F. N. 1919. The vulcanicity of the Lake District. Proc. Geol. Assoc., Vol. 11, pp. 258–284.

GUNN, P. J. 1973. Location of the proto-Atlantic suture in the British Isles. Nature, London, Vol. 242, p. 111.

HUDSON, S. N. 1937. The volcanic rocks and minor intrusions of the Cross Fell Inlier, Cumberland and Westmorland. Q. J. Geol. Soc. London, Vol. 93, pp. 369–405.

HYNDMAN, D. W. 1972. Petrology of igneous and metamorphic rocks. (New York: McGraw Hill.) vii + 533 pp.

INGHAM, J. K. and WRIGHT, A. D. 1970. A revised classification of the Ashgill Series. Lethaia, Vol. 3, pp. 233–242.

JACKSON, D. E. 1961. Stratigraphy of the Skiddaw Group between Buttermere and Mungrisdale, Cumberland. Geol. Mag., Vol. 98, pp. 515–528.

JEANS, P. F. 1973. Plate tectonic reconstruction of Southern Caledonides of Great Britain. Nature, London, Vol. 245, pp. 120–122.

JENKINS, W. A. M. 1967. Ordovician chitinozoa from Shropshire. Palaeontology, Vol. 10, pp. 436–488.

JOHANNSEN, A. 1937. A descriptive petrography of the igneous rocks. 3, The Intermediate Rocks. (Chicago.)

LAMONT, A. 1948. B. B. Bancroft's geological work. 2. Upper Ordovician of the Cross Fell Inlier. Quarry Mgrs. J., Vol. 31, pp. 416–418,466–469.

LISTER, T. R., BURGESS, I. C. and WADGE, A. J. 1969. Microfossils from the cleaved Skiddaw Slates of Murton Pike and Brownber (Cross Fell Inlier). Geol. Mag., Vol. 106, pp. 97–99.

LOEBLICH, A. R. and TAPPAN, H. 1976. Some new and revised organic-walled phytoplankton microfossil genera. J. Paleont., Vol. 50, pp. 301–308.

MARK, J. E. and NICHOLSON, H. A. 1888. The Stockdale Shales. Q. J. Geol. Soc. London, Vol. 44, pp. 654–730.

MARTIN, F. 1966. Les acritarches de Sart-Bernard (Ordovicien Belge). Bull. Soc. beige geol., Vol. 74, pp. 1–22.

MOSELEY, F. 1977. Caledonian plate tectonics and the place of the English Lake District. Bull. Geol. Soc. Am., Vol. 88, pp. 764–768.

NICHOLLS, G. D. 1958. Autometasomatism in the Lower Spilites of the Builth Volcanic Series. Q. J. Geol. Soc. London, Vol. 114, pp 137–162.

NICHOLSON, H. A. and MAAR, J. E. 1891. The Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 47, pp. 500–512.

REED, F. R. C. 1907. A new species of Lichas. Geol. Mag., Vol. 4, pp. 396–400.

REED, F. R. C.  1910. New fossils from the Dufton Shales. Geol. Mag., Vol. 7, pp. 211–220,295–299.

SHOTTON, F. W. 1935. The stratigraphy and tectonics of the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 91, pp. 639–701.

SIMPSON, A. 1967. The stratigraphy and tectonics of the Skiddaw Slates, and the relationship of the overlying Borrowdale Volcanic Series in part of the Lake District. Geol. J., Vol. 5, pp. 391–418.

SIMPSON, A.  1968. The Caledonian history of the north-eastern Irish Sea region and its relation to surrounding areas. Scott. J. Geol., Vol. 4, pp. 135–163.

SKEVINGTON, D. 1970. A Lower Llanvirn graptolite fauna from the Skiddaw Slates, Westmorland. Proc. Yorkshire Geol. Soc., Vol. 37, pp. 395–444.

TAUGOURDEAU, P. and JEHOWSKY, B. DE. 1960. Répartition and description des Chitinozoaires Siluro-devoniens de quelques sondages de la C.R.E.P.S., de la C.F.P.A. et de la S. N. REPAL au Sahara. Rev. Inst. Franc. Petrole, Vol. 15, pp. 1199–1260.

TIMOFEEV, B. V. 1959. The ancient Baltic flora and its stratigraphic significance. Mem., VNIGRI, Leningrad, No. 129. 136 pp.

VAVRDOVA, M. 1966. Palaeozoic microplankton from Central Bohemia. Geol. Ustay. CSAV, Prague.

WADGE, A. J. 1972. Sections through the Skiddaw-Borrowdale unconformity in eastern Lakeland. Proc. Yorkshire Geol. Soc., Vol. 39, pp. 179–198.

WADGE, A. J.  1978. Classification and stratigraphical relationships of the Lower Ordovician rocks. In The Geology of the Lake District (Ed. F. Moseley). Occas. Publ. Yorkshire Geol. Soc., No. 3.

WADGE, A. J. NUTT, M. J. C., LISTER, T. R. and SKEVINGTON, D. 1969. A probable Didymograptus murchisoni Zone fauna from the Lake District. Geol. Mag., Vol. 106, pp. 595–598.

WADGE, A. J. and SKEVINGTON, D. 1972. Geology of the Tarn Moor Tunnel in the Lake District. Bull. Geol. Surv. G.B., No. 41, pp. 55–73.

WADGE, A. J., OWENS, B. and DOWNIE, C. 1967. Microfossils from the Skiddaw Group. Geol. Mag., Vol. 106, pp. 506–507.

WHITTARD, W. F. 1960. Ordovician trilobites of the Shelve Inlier. Palaeontogr. Soc. [Monogr.], Part iv, pp. 117–162.

WHITTINGTON, H. B. 1966. The Ordovician trilobites of the Bala area, Merioneth. Palaeontogr. Soc. [Monogr.], Part iii, pp. 63–92.

Chapter 3 Devonian

Several local pockets of coarse elastic sediment rest unconformably upon the Caledonian land-surface of the Cross Fell inlier and the eastern Lake District and underlie the oldest rocks of proved Carboniferous age (Capewell, 1955, 1956). They were termed 'polygenetic conglomerates' by Marr (1900) and are generally considered to be Devonian in age although conclusive evidence is lacking. The term Poly-genetic Conglomerate was formalised by Shotton (1935) and is now restricted to the three outcrops in the Cross Fell inlier, lying to the east of Gamblesby, Melmerby and Ousby respectively. The equivalent deposit in the Lake District is the Mell Fell Conglomerate which in the present district is seen only in the south-west near Greystoke.

The Polygenetic Conglomerate is very variable in thickness. Near Melmerby, for example, about 35 m of beds pinch out entirely along crop within 250 m. The stratigraphical relationships of the deposit are best seen along the fell-track east of Melmerby (Figure 10) where the base rests with marked unconformity upon Skiddaw Group rocks [NY 6280 3705], and the top of the deposit is weathered [NY 6287 3704] beneath the unconformable Basement Beds. The Conglomerate is crudely stratified and dips are generally to the east, exceeding those in the Basement Beds by up to 40°. Whether the steeper dips are tectonic in origin, implying pre-Basement Bed earth movements, or depositional, is still in doubt.

The deposit seems to represent the proximal parts of coalescent alluvial fans of coarse detritus, laid down as fanglomerates in arid conditions and derived from higher ground close to the west. It is possible that the source region was an east-facing scarp, defined near Melmerby by the Deep Slack and Fellside faults (Wadge, 1978, fig. 57a). This view is supported by the provenance of the clasts near Melmerby, which include not only local pebbles of sediments and microgranitic intrusions from the underlying Skiddaw Group but also many volcanic clasts apparently from the Borrowdale outcrops across the faults to the north-west. In all outcrops of the Conglomerate, the clasts range in shape from subangular to well-rounded and are set in a purple-red, sandy matrix. They are up to lm across and are commonly coated with a thin polished hematite layer.

Details

About 1 km E of Melmerby, 35 m of the Conglomerate crop out in the sides of Melmerby Beck but the rocks are best seen in the fell-track [NY 6280 3705] to [NY 6287 3704] where the sequence is 25 m thick. The hematite coating on some of the clasts in this section is striated, the grooves occurring on all types of pebbles irrespective of lithology. The scratches were interpreted by Marr (1899) as tectonic slickensides, but the deposit shows no other tectonic features and the orientation of the striations is random. It seems likely therefore that the clasts were striated prior to deposition, perhaps by violent attrition during rapid transport. The upper surface of the fan is weathered in this section and the crude stratification of the deposit is destroyed for about 1 m below the sub-Basement Bed unconformity (Figure 10). The Conglomerate thins rapidly to the south-east [NY 6303 3696] where the Basement Beds rest directly upon Skiddaw rocks.

North-east of Gamblesby, the Conglomerate is exposed in Grey Mare's Tail [NY 6234 4002] to [NY 6243 4002], Limekiln Beck [NY 6251 3982] to [NY 6258 3981] and in an isolated outcrop [NY 6251 3942] to the south. About 70 m of Conglomerate are seen in the first stream section and 60 m in the second, but the base of the formation is not exposed and it may be much thicker. Dips are steep in both sections and westerly dips in Limekiln Beck may mark local overturning against the Pennine Fault. Well-rounded to subangular clasts, up to 0.5 m across, consist largely of Skiddaw greywackes and Borrowdale andesites but the microgranite boulders characteristic of the Melmerby outcrops are rare. The clasts are commonly coated in hematite varnish and set in a weakly-cemented matrix of hematitic sand, cut in places by thin hematite veinlets.

Two small outcrops of Conglomerate lie in the south bank of Acorn Sike [NY 6455 3408], about 1 km E of Ousby Townhead. Unlike other exposures, these lie west of the main belt of faulting along the Pennine Line. Field relations, though inconclusive, suggest that the deposit rests unconformably on Skiddaw Group rocks, which are poorly exposed close by. Bedding is obscure, but appears to be inclined to the north-east. Some 6 m of deeply-weathered coarse conglomerates are visible, with well-rounded boulders up to 1 m in diameter. These latter are generally coated with hematite, and include purple andesites, grey mudstones and greywackes, and feldspar-porphyries, the latter being closely similar to a minor intrusion exposed nearby [NY 6449 3413]. There are also a few boulders of weathered biotite-granite. According to Mr R. K. Harrison, 'this rock (E36178) is medium grained (2 mm) with microphenocrysts of red feldspars and abundant biotite. Orthoclase is predominant and poikilitically encloses euhedral quartz crystals with biotite flakes. Biotite (Z = deep red-brown; X = pale brown to colourless) is the principal accessory, is partly altered to chlorite and ferric oxide, and contains sparse inclusions of apatite and zircon. The groundmass is largely micaceous, and the rock shows some resemblance to the finest facies of the Shap–Skiddaw–Eskdale suite.' A local source is not exposed but may lie beneath Carboniferous and later rocks.

At least 12 m of coarse grey conglomerate are exposed in Greystoke Park and are correlated with the main outcrop of the Mell Fell Conglomerate lying to the south of the district. The deposit is poorly exposed in the upper part of Summerground Gill [NY 4169 3154] and dips to the east-north-east. It is apparently conformably over- lain by sandstones and shales passing up into the Seventh Limestone. The clasts, generally well-rounded and up to 0.3 m across, are contained within a sandy matrix. They consist largely of andesite, and vein-quartz, siltstone and mudstone pebbles are also common. A J W

References

CAPEWELL, J. G. 1955. The post-Silurian pre-marine Carboniferous sedimentary rocks of the eastern side of the English Lake District. Q. J. Geol. Soc. London, Vol. 111, pp. 23–46.

CAPEWELL, J. G. 1956. The Carboniferous Basement Series of the Cross Fell area, Cumberland and Westmorland. Proc. Geol. Assoc., Vol. 66, pp. 213–230.

MARR, J. E. 1899. On a conglomerate near Melmerby (Cumberland). Q. J. Geol. Soc. London, Vol. 55, pp. 11–15.

MARR, J. E. 1900. Notes on the geology of the English Lake District. Proc. Geol. Assoc., Vol. 16, pp. 449–483.

SHOTTON, F. W. 1935. The stratigraphy and tectonics of the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 91, pp. 639–704.

WADGE, A. J. 1978. Devonian. In The Geology of the Lake District (Ed. F. Moseley). Occas. Publ. Yorkshire Geol. Soc., No. 3.

Chapter 4 Lower Carboniferous

The Lower Carboniferous rocks of the district crop out on the Pennines in the east, and around Greystoke in the west. The sequence of named limestones in each area is shown in (Figure 11). Some of the names in the Greystoke succession were first used in the West Cumberland iron orefield and subsequently extended eastwards via the Cockermouth district (Eastwood and others, 1968), but most of the member nomenclature, both at Greystoke and on the Pennines, originated with the lead miners of Alston Moor, and was first systematised by Forster (1809). In a later account (1821), he included all the Lower Carboniferous rocks of Alston Moor within the 'Lead Measures', the basal subdivision of his Carboniferous sequence. In 1836, Phillips extended his own classification of the Askrigg Block succession northwards into the Cross Fell area and defined a 'Lower Scar Limestone Series' lying between 'Old Red Sandstone' basement conglomerates and the top of the Lower Little Limestone. His overlying Yoredale Series extended up to the top of the Great Limestone. Although his scheme is now obsolete, the term 'Yoredale' has survived to describe a distinctive sedimentary facies.

The primary map of the Penrith district was not accompanied by a sheet-memoir. On the map, published in 1893, all the Lower Carboniferous rocks were included within the Carboniferous Limestone Series, synonymous with Forster's 'Lead Measures'. Two subdivisions, 'Quartz Conglomerates and Red Sandstones' and 'Flags and Sandstones' were recognised below the Melmerby Scar Limestone. This latter extended upwards to include what are now termed the Robinson and Smiddy limestones, but this usage has not been accepted by subsequent researchers.

The division of the Carboniferous Limestone Series of Northumberland into Upper, Middle and Lower Limestone groups (Fowler, 1926, p.18) was extended into Cumberland by Trotter and Hollingworth (1932, p.16), and used with the addition of an underlying Basement Group throughout the North Pennines by Dunham (1948, p.13). A similar classification was subsequently applied by Johnson (1963, p.11) in the Moor House Nature Reserve, where the base of the Lower Limestone Group was taken below the Melmerby Scar Limestone, and the Middle Limestone Group was taken to extend from the Lower Smiddy Limestone to the base of the Great Limestone. This application of the Northumberland 'Group' classification to the Alston Block was founded on correlations which have recently proved doubtful (Johnson, 1963, p.14; Frost, 1969, p. 279). During the resurvey of the Penrith (24) district, therefore, the Lower Carboniferous rocks have been reclassified on the basis of local lithostratigraphy into Basement Beds, Orton Group and Alston Group (Figure 11).

The Basement Beds extend upwards from the sub-Carboniferous unconformity in a sequence consisting mainly of fluviatile conglomerates and greywackes, and their junction with the overlying Orton Group is taken at the base of the lowest limestone. This junction is one of local convenience and is unlikely to be the time-equivalent of the base of the Orton Group as first defined in Ravenstonedale (Burgess, 1970, p. 31). No faunas representative of the lower part of the Orton Group of Ravenstonedale have been found in the Penrith district (p.25) nor has any representative of the Ravenstonedale Group (lying between the Basement Beds and Orton Group at Ravenstonedale) been recognised. It is uncertain whether these strata are absent or are the lateral equivalents of part of the local Basement Beds.

The base of the Alston Group within the present district is taken at a depositional break close below the Melmerby Scar Limestone as exposed on Wildboar Scar (p. 34). Near Greystoke this horizon is at the base of the Sixth Limestone. The Group continues up to the base of the Great Limestone and is conveniently subdivided into informal upper and lower sub-groups at the base of the Smiddy Limestone on the Pennines and the base of the Rough Limestone in the west.

The Pennine and Greystoke sections are thin, block sequences, compared with the successions in the Northumbrian Trough to the north and in the Stainmore Trough to the south. It is not clear if the Lower Carboniferous rocks continue as thin sequences beneath the Vale of Eden where they are unproven beneath Permo-Triassic cover. The Vale, however, has been a depositional basin between the Lake District and Alston blocks for so much of geological time since the late Silurian, that it seems reasonable to suppose that it was also a basin during Lower Carboniferous times. This view is supported by the observed westward thickening of the Basement Beds near Melmerby (p. 27) and by the gravity data (p. 141) which suggests that a thick Lower Carboniferous succession underlies the Vale.

Conditions of deposition

Pre-Carboniferous earth movements gave rise to a land surface of considerable relief and the earliest Carboniferous sediments filled the depressions in this topography. The Basement Beds were laid down as largely fluviatile sediments derived mainly from the Lake District. They appear to be thickest in a narrow sedimentary basin located along, and perhaps controlled by, the Pennine Fault system. They thin rapidly eastwards from the Pennine escarpment and are presumed to thin gradually westwards towards their source, though a much thicker sequence, as yet unproved, may be present under the Vale of Eden. Capewell (1956, p. 225) suggested that the passage from coarse, purple-red elastics in the north-west part of the Pennine outcrop to finer, grey sediments in the south-east represents a lateral transition from fluviatile to marine sedimentation. This view is supported by the absence of fluviatile cycles in the Basement Beds south of the Crowdundle Fault. The line of the fault may have been the local contemporary shoreline. A rapid increase in the feldspar content of the highest Basement Bed greywackes probably indicates the unroofing of a Caledonian granite in the western source area.

By the end of Basement Bed deposition, little physical relief remained and local topographical highs had largely ceased to be sources of sediment. Thereafter, most of the elastic sediment was brought in from far to the north-east and sedimentation was largely controlled by the differential subsidence of basins and blocks. The blocks were marked by thin successions, and were areas relatively slow to subside, since they were generally underlain by Caledonian plutonic granites. The intervening basins subsided more rapidly and accumulated great thicknesses of sediment, particularly where their boundaries were Caledonian faults which remained active during Carboniferous sedimentation.

The lowest beds of the Orton Group were laid down at the beginning of a long period of largely calcareous, marine deposition, which was more continuous in the western part of the district than on the Pennines. In the east, there were occasional influxes of terrigenous material and deltaic conditions were locally established at least once during Orton Group deposition. Furthermore, there was a brief period of local emergence at the top of the Orton Group around Cross Fell which is marked by a dolomitic horizon; this is absent in the west. Although elastic sediments are confined to thin shaly or sandy partings in the west, the Orton Group there is about twice the thickness of its eastern counterpart which suggests that sedimentation was controlled more by relative subsidence than by the supply of sediment.

Throughout the deposition of the Orton and Alston groups, sedimentation kept pace with sinking and the depositional surface remained close to sea level. Indeed, the Melmerby Scar Limestone in the lower Alston Group contains seatearths in places, marking intervals of emergence. These pass laterally into dark grey, shallow-water limestones common not only in the lower part of the Melmerby Scar Limestone but also occurring in the Sixth, Fifth and White limestones. They are usually overlain, with crude cyclicity, by pale grey pseudobreccias and then thin calcareous mudstones. The incoming of deltaic sedimentation is marked by coarsening-upwards cycles towards the top of the lower Alston Group. These seem to have extended into the district from farther to the north-east, where intermittent deltaic sedimentation characterised the whole Group (Frost, 1969, p.282). The cyclic sedimentation resulted from the establishment of a series of deltas and their periodic flooding by the carbonate-rich waters of a warm, shallow sea. A J W

Stratigraphical palaeontology

The zonation of the Lower Carboniferous rocks is shown in (Figure 11) and incorporates some of the regional stages proposed for the correlation of the British Dinantian by George and others (1976). The faunas collected during the resurvey are listed on data cards stored in the Institute's archives, and those from the most important localities are given in the text. The Lower Carboniferous stratigraphical palaeontology of the south-eastern part of the district, lying within the Moor House Nature Reserve, has been summarised by Johnson (1963), who gave detailed faunal lists for each cyclothem. The present collections were limited to those needed to support the mapping and were not sufficiently extensive to yield full faunal lists. Consequently, some of the stratigraphically significant records of Johnson, such as Linoprotonia corrugatohemispherica, Davidsonina septosa, Orionastraea sp.and the zonally diagnostic goniatites, have not been repeated.

Orton Group

In the Ravenstonedale area to the south, the Orton Group yields faunas of the Chadian, Arundian and Holkerian stages, but from the few localities within the present district, only Holkerian faunas have been obtained. Particularly diagnostic is the occurrence of Davidsonina carbonaria in the section in Ardale Beck (p. 30), but in addition, several of the limestones near the top of the Group yield assemblages which include numerous bryozoa, Linoprotonia sp., Pleuropugnoides pleurodon, Productus garwoodi and Punctospirifer scabricosta. These faunas are typical of the 'Bryozoa Band' of Ravenstonedale (Garwood, 1913, p. 473) which is of late Holkerian age (see Ramsbottom and Mitchell, 1969, p. 97).

Alston Group

The Group includes both the Asbian and Brigantian stages and is divided informally into lower and upper divisions which are of Asbian and Brigantian ages respectively (Figure 11), although the early Asbian of Ravenstonedale is absent in the present district.

The Asbian faunas are typical of the shelf limestone assemblages so common at this time throughout Britain. Corals are the most diagnostic fossils and include Axophyllum vaughani, Dibunophyllum bourtonense, Lithostrotion junceum, L. martini, L. pauciradiale, L. portlocki and Palaeosmilia murchisoni. The brachiopod assemblages include Delepinea comoides, Gigantoproductus maximus and the Linoprotonia sp. hemisphaerica group. Other fossils which have been recognised include the algal species Koninckopora inflata and foraminifera which are abundant. Gastropods are common in a pocket of the Melmerby Scar Limestone at Sailrigg [NY 6271 4016].

The collections from the western and eastern parts of the district are generally similar and it has not been possible to distinguish any sequence of faunas within the Stage. Johnson (1963, p. 28) noted the occurrence of Davidsonina septosa, 9 to 10 m below the top of the Melmerby Scar Limestone but this species has not been found during the present survey.

Lonsdaleia is not normally typical of the Asbian Stage but the following occurrences in the present district have been recorded. Melmerby Scar is the type-locality for Lonsdaleia duplicata melmerbiensis (Smith, 1916, p. 242) and the subspecies has also been recorded from disused quarries about 2 km E of Gamblesby [NY 628 398] and from Melmerby Low Scar [NY 6293 3854]. The latter locality also yielded a single specimen of L. floriformis, and at Sailrigg [NY 6268 4019], L. duplicata has been noted. The distribution of the species of Lonsdaleia was summarised by S. Smith (1916, p.262).

The coral and brachiopod faunas of the limestones in the upper Alston Group are characteristic of the Brigantian Stage (George and others, 1976). Further subdivision of the faunas, however, has proved difficult and controversial. The conflicting views were summarised by Johnson (1963, p. 16) who recognised the Lonsdaleia floriformis and Orionastraea garwoodi subzones and an 'upper part of the Dibunophyllum Zone' within the upper Alston Group sequence. His O. garwoodi Subzone, which lies between the top of the Jew Limestone and the base of the Five Yard Limestone, has only been recognised within restricted areas of the Alston and Askrigg blocks. Therefore, the Brigantian Stage is left undivided except by the goniatites discussed below.

The Brigantian faunas are more varied than those of the Asbian Stage and include the corals Aulophyllum fungites, Caninia juddi, Dibunophyllum bipartitum subspp., Diphyphyllum lateseptatum, Koninckophyllum interruptum, Lonsdaleia floriformis subspp. and Nemistium edmondsi. The brachiopods Eomarginifera tissingtonensis cambriensis, Productus productus hispidus, Pugilis pugilis and Tornquistia polita are present; foraminifera are again abundant including Howchinia sp.and Saccamminopsis sp.Most of the fossils are markedly facies-dependent and the faunal variations with lithology are discussed by Johnson (1963, p.61).

The base of the Brigantian Stage has been taken within the Pennine sections of the present district-at the base of the Smiddy Limestone which correlates with the combined Peghorn and Smiddy limestones of the Brough district (Burgess and Holliday, 1979). In the western sections near Greystoke, the base of the Stage has been taken at the base of the Rough Limestone, mainly on the presence of the Girvanella Nodular Bed' low in the Limestone on Berrier Hill [NY 4018 3020]. This bed is traditionally the base of the D₂ Zone (Garwood, 1913, p. 482), although it is now known to lie just above the Stage base (Burgess and Mitchell, 1976).

There are differences in the faunas collected from the eastern and western outcrops of the upper Alston Group, although some variations may arise from the better exposures in the Pennine sections. The shale faunas in particular are poorly known in the west through lack of exposure. Clisiophylloid and caninoid corals, especially species of Caninia, Dibunophyllum and Koninckophyllum, are common in the eastern sections notably in the Scar and Four Fathom limestones. D. lateseptatum occurs in the Jew, Tyne Bottom and Five Yard limestones. The Jew Limestone in the western area has two distinct coral bands: one near the base with Lonsdaleia floriformis crassiconus and Nemistium edmondsi: the other, higher in the limestone, with Lithostrotion pauciradiale and solitary corals. N. edmondsi is generally restricted to the Jew Limestone, although it also rarely occurs in the Lower Little and Tyne Bottom limestones. The type horizon of this important coral is the Potholes Bed of West Cumberland (S. Smith, 1928, p. 117) which correlates with the Jew Limestone. Lithostrotion junceum is common in most of the Alston Group limestones, and is particularly abundant in the Scar Limestone but it has not been recorded from beds higher than the Five Yard Limestone during the present survey. Zaphrentoid faunas are common in the marine shales of the upper part of the group but are known only in the Pennine sections. Cyathaxonia cornu was collected from the Scar Limestone in a gully at the head of Ardale Beck [NY 6659 3545], and this genus was also noted in the Scar Limestone by Turner (1927, p. 350).

The most prolific brachiopods in the limestones are the small productoids Alitaria panderi and Avonia sp., transverse gigantoproductoids and smooth spiriferoids. In the marine shales the productoids Buxtonia sp.and Productus sp., chonetoids and orthotetoids are more common. Johnson (1963, p. 64) remarked on the presence of Gigantoproductus giganteus in the Middle Limestone Group (upper Alston Group) and that G. maximus was restricted to the Lower Limestone Group (lower Alston Group) in the Moor House Reserve. The same change among the gigantoproductoids, from the dominance by the evenly costate forms of the G. maximus group to the strongly corrugated G. giganteus group was noted, at about the lower to upper Alston Group boundary, during the present work.

Mollusca form a relatively insignificant part of the limestone fauna but bellerophontoids are common at some horizons. The marine shale faunas include many mollusca amongst which the most abundant are Euphemites sp., pectinoids (especially the finely ribbed Aviculopecten knockonniensis and related forms), Edmondia sp.and nuculoids. The richest shale faunas are those from above the Five Yard Limestone. Cephalopods other than orthocone nautiloids are rare. JP, MM

Goniatite divisions of the upper Alston Group

The few records of goniatites from the rocks of the upper Alston Group (Johnston, 1963, p.17) and their correlatives on the Askrigg Block (Ramsbottom, fig. 25, in Rayner and Hemingway, 1974), allow a broad correlation with the goniatite divisions of the Craven Basin, but the exact placing of boundaries is not possible. Broadly, however, the lower part of the upper Alston Group lies within the P₁ Zone and the P₂ Zone base is taken at, or close to, the bottom of the Scar Limestone (Rayner, 1953, p. 288). WHCR

Basement Beds

Although the Basement Beds are probably present everywhere within the district at the base of the Carboniferous sequence, their outcrop is restricted to the Pennine escarpment and to the heavily faulted ground immediately to the west. Their thickness varies from 200 to 300 m and the lower beds are especially variable because they fill irregularities in the underlying surface. The buried landscape is best seen on the western slopes of Kirkland Fell (see p. 29). Some of the changes in thickness along the edge of the Alston block are shown in (Figure 12). The increase in thickness of these beds westwards near Melmerby may indicate that there is a much thicker succession, as yet unproved, beneath the younger rocks of the Vale of Eden. To the east of the escarpment drilling shows the Basement Beds to be thin or absent at Rook-hope (Dunham and others, 1965), Allenheads (Burgess, 1971) and Cow Green (Johnson, 1963).

No single section provides a complete sequence through the Basement Beds. North of Melmerby Low Scar sections are fragmentary and heavily faulted, but farther south a broad threefold lithological subdivision is apparent, a basal unit of purple-grey, coarse-bedded conglomerates passing gradually upwards through purple-red, medium-grained pebbly sandstones into fine-grained massive greywackes at the top. Although the broad distribution of these lithologies is indicated in (Figure 12), the subdivisions have been regarded as too imprecise to depict on the published maps. In the extreme south-east of the district the purple colours are gradually replaced by greys.

Fining-upward cycles are locally present in both the lower subdivisions, individual cycles being only a few metres thick. Within each cycle there is an upward passage from conglomerate, through coarse sandstone, into siltstone or silty mudstone. The coarse beds commonly overlie erosion surfaces and are cross-bedded, whilst the finer beds tend to be ripple-marked and to suggest a fluviatile origin for the deposit; the bulk of the Basement Beds are accordingly regarded as a fluvial fan, in this area largely derived from the west-south-west (Figure 13). The south-eastwards passage into grey beds is believed to mark an approach to marine conditions (Capewell, 1956, p. 225).

The disconformity between the Basement Beds and the Polygenetic Conglomerate is visible only near Melmerby (see p. 22). Elsewhere numerous exposures show the Basement Beds resting with marked angular unconformity directly upon rocks of the Skiddaw Group.

Details

The northernmost outcrops of the Basement Beds are too disturbed to yield useful sections. Dips are high as far south as Grey Mare's Tail and Limekiln Beck, although most of the sequence is present. In the lower part of Grey Mare's Tail [NY 6243 4002] to [NY 6260 4010], about 76 m of purple, coarse-grained, well-bedded conglomerate are partly exposed, dipping eastwards at 75° to 80°. The commonest clasts are white quartz; pebbles of volcanic rocks, mudstones and sandstones are also present especially towards the base. Some clasts are coated with a thick hematite pellicle and these are probably derived from the underlying Polygenetic Conglomerate. Fining-upwards cycles are generally rare, although a few exposures show bands of coarse conglomerate with erosion at the base, grading upwards through pebbly sandstone into finer silty sandstone. Directional sedimentary structures are absent, except for a few thin bands showing planar cross-bedding. The junction with the overlying sandstones is poorly exposed [NY 6247 4003], but above a 10-m gap in the section are 10.7 m of purple-red to red-brown, fine- to medium-grained sandstones which dip eastwards at 35° to 40° and pass upwards by intercalation into 16.7 m of grey-green, medium-grained sandstones. These are in turn overlain by 27.5 m of massive fine-grained, greywacke-sandstones [NY 6255 4007] to [NY 6259 4009], that form a prominent feature on the hillside and produce waterfalls in the stream.

The section in Limekiln Beck, just to the south, is less complete. Only 33.5 m of purple-red, massive, well-bedded conglomerate are exposed, dipping eastwards at 50° to 60°, whilst about 40 m of conglomerates appear to be faulted out at the base. The conglomerates are overlain by purple-red sandstones [NY 6269 3979], but less than 5 m of these are exposed.

Farther downstream [NY 6239 3983] to [NY 6242 3983], beds dipping to the south-west at 50° to 65°, and faulted against the St Bees Sandstone, were first regarded as Silurian by the primary surveyors, and were later assigned to the Coniston Grits (Shotton, 1935). They consist of grey, massively bedded, feldspathic greywackes, about 6 m thick, overlain by 3.6 m of yellow-brown siltstone interbedded with thin bands of micaceous sandstone. Although well-jointed, the rocks are not cleaved, and seem to be barren. They appear more likely to correlate with the greywackes in the upper part of the Basement Beds than with the Coniston Grits, which are not otherwise known to crop out in the Cross Fell inlier. Similar rocks are exposed in a small stream about 550 m to the south-south-west [NY 6257 3934] to [NY 6259 3933] and in the side of the nearby A686 road [NY 6259 3926], dipping generally eastwards, but inclined steeply to the south-west near the Else Gill Fault [NY 6254 2915].

Below Melmerby Low Scar, the northerly component of the local dip causes successively lower horizons in the Basement Beds to emerge southwards from the Deep Slack Fault. Thus in the north, the section in White Beck shows only the upper part of the sequence, with about 23 m of green and grey, fine-grained, massively-bedded greywackes and feldspathic sandstones continuously exposed in a fine series of waterfalls [NY 6256 3899] to [NY 6264 3900]. Farther south however, the underlying red sandstones and quartz-conglomerates crop out on the lower slopes. The sandstones are best seen, dipping east-north-eastwards at 16° to 50°, in a 16-m section exposed in a gully below the Low Scar [NY 6256 3825] to [NY 6266 3828], whilst the conglomerates form nearby crags [NY 6214 3803] and are also well-exposed, dipping eastwards at 65° to 85°, in a belt adjacent to the Deep Slack Fault. Higher up these slopes, the massive greywackes near the top of Basement Beds form a continuous feature, and the thin bands of flaggy, cross-bedded sandstone were formerly dug for walling-stone in many small quarries.

On the slopes south of Melmerby Low Scar, the Basement Beds are apparently at least 300 m thick, but there are no good sections.

The base of the sequence is seen in the Melmerby fell-track [NY 6287 3704], where 6.1 m of purple-red, blocky, micaceous siltstone with scattered pebbles rest upon the weathered surface of the Polygenetic Conglomerate. The siltstones are succeeded by at least 20 m of purple, well-bedded quartz-conglomerates, containing many hematite-coated clasts, probably derived from the underlying Polygenetic Conglomerate, and interbedded with thin bands of purple-red sandstone and siltstone. Although these basal siltstones are absent a short distance to the south-east, in the northern bank of Melmerby Beck [NY 6304 3695], where conglomerates rest unconformably upon older rocks, they are again present farther east in Rake Beck [NY 6330 3706], where they form a 2.7-m bed containing thin bands of coarse, purple-red sandstone with rounded dark grey mudstone pebbles, probably derived from the underlying Skiddaw Group. The locally-derived pebbles in these basal beds suggest an initial reworking of local detritus prior to the influx of largely quartz sediment from further afield. In Rake Beck and its tributary Swire Sike, some of the conglomeratic lower part of the Basement Beds is reasonably well exposed [NY 6330 3706] to [NY 6348 3742], with the overlying sandstones cropping out higher up the beck [NY 6348 3742] to [NY 6348 3751] (Appendix 1, p.160).

South of the Low Scar, the Basement Beds thin rapidly eastwards, particularly the lower conglomeratic beds, and the topographic rise of the sub-Carboniferous unconformity in this direction against the regional tectonic dip suggests the burial of a considerable pre-Carboniferous topography. The unconformity is well-exposed in Hungrigg Sike [NY 6360 3713], where massive purple-red quartz-conglomerates rest unconformably upon Skiddaw Group siltstones, and can be followed south-eastwards for about 700 m. To the east of the Gate Castle Fault, the unconformity lies at the foot of a prominent feature, and passes from the headwaters of Swire Sike eastwards across the top of Meikle Awfell. Massive quartz-conglomerates lying close above the unconformity crop out in several of the northern tributaries of Dry Sike [NY 6390 3754] and [NY 6405 3753]. The unconformity continues to rise southwards towards Cuns Fell, but to the south of this hill it falls rapidly to a much lower level on the south side of Dale Beck. This variation seems to be due to the burial of a pre-Carboniferous hill near Cuns Fell, rather than to a local upfold.

East of Cuns Fell, the higher part of the Basement Beds sequence crops out in the headwaters of Dale Beck [NY 6495 3656] to [NY 6531 3692], although most of the lower conglomerates are cut out by the Lad Slack Fault (Appendix 1, p.152).

The conglomerates in the lower part of this section are very variable laterally, as can be seen near a prominent waterfall in the stream [NY 6504 3665], where coarse quartz-conglomerates channel into underlying beds of pebbly sandstone, and pass laterally, within a few metres, into fine-grained sandstones. Higher upstream, within the sandstone division, several fining-upwards cycles can be distinguished, each 1 to 2 m thick, grading upwards from coarse-grained pebbly sandstone overlying an erosion surface through fine-grained sandstone, into micaceous siltstone or silty mudstone at the top: in one of these cycles, the siltstone contains carbonaceous plant debris [NY 6508 3667]. Some of the sandstones exhibit large-scale planar cross-bedding and some trough cross-bedding is also present. One horizon of symmetrical ripple-marks and a thin band of highly calcareous siltstone (possibly a 'calcrete' horizon), have also been noted.

On the northern slopes below Windy Gap, purple, massive conglomerates low in the sequence, form crags 10 to 12 m high. Local channelling of finer beds by coarse conglomerate bands is well-exposed here [NY 6477 3573]. Vein-quartz is the most abundant of the clasts in these, but fragments of mudstone and andesite, both generally purple-stained, are also common. On the Windy Gap col, about 45 m of similar conglomerates have easterly dips of up to 65° close to faults, but dips flatten in the overlying sandstones which are poorly exposed to the east on Muska Hill. On the hill-top, the lowest of the greywacke beds has been extensively worked for walling-stone.

Farther south, in Ardale, only the lower part of the Basement Beds is exposed [NY 6524 3439] to [NY 6558 3454], and the section, some 60 m thick, reproduces most of the features seen in Rake Beck (see above). Conglomerates predominate towards the base of the section, and fining-upwards cycles, including thin sandstone and siltstone bands, are common higher upstream [NY 6548 3451] to [NY 6558 3454], the lowest siltstone in the section yielding abundant plant fragments. Within individual cycles, each generally about I to 3 m thick, the conglomerate and sandstone beds are commonly cross-bedded, and many show erosion at the base. To the south of Ardale, the basal conglomerates can be seen resting unconformably upon Ordovician rocks on Cocklock Scar [NY 6544 3388], but the junction is difficult to trace farther west. To the east, the section in Kirkdale is generally poor, although 18 m of the conglomerates can be seen [NY 6606 3363], and the upward passage of conglomerates into sandstones is exposed higher upstream [NY 6637 3370].

South-eastwards from Cocklock Scar, the basal unconformity rises to the foot of Kirkdale. Below Kirkland Fell, where the trend of the junction is parallel to the regional strike, the Basement Beds thin abruptly, particularly where they rest upon the massive volcanic rocks around Wythwaite Top (spot height 1324 ft.) This local thinning of the Basement Beds, to less than 120 m, is accounted for wholly within the conglomerates, which are only 15 to 20 m thick compared with 80 m in Kirkdale.

South-east of Grumply Hill, the Basement Beds thicken again, as the pre-Carboniferous topography falls. In addition, the colour of the conglomerate division changes southwards, between Crowdundle Beck, where at least 50 m of purple conglomerates are poorly exposed [NY 6826 3210] to [NY 6835 3230], and Eller Gill, where similar beds are wholly grey [NY 6896 3124]. This colour change, which is regional (Capewell, 1956, p. 225) may take place across the Crowdundle Fault.

Within the much-faulted tract of Carboniferous rocks lying immediately west of the Lower Palaeozoic outcrops, the Basement Beds are exposed in several short sections. These are too discontinuous to allow detailed comparison with the escarpment sections, but the lithologies and sequences seem to be broadly similar. Within the sub-Permian oxidation zone, the primary colours are masked by strong purple and yellow staining.

At the northern end of this tract, just east of Gale Hall, dark purple-red, coarse-grained, pebby sandstones [NY 6313 3649] dip gently southwards beneath thick boulder clay. Farther south in Ardale Beck, about 6 m of purple-red conglomerates dip southwestwards below a poorly exposed sequence, 17 m thick, consisting largely of coarse pebbly sandstones [NY 6418 3431] to [NY 6407 3416]. In the southern tributary of Acorn Sike, similar beds crop out dipping in the same direction. The mapping indicates that they rest in places on Lower Palaeozoics, and elsewhere on Polygenetic Conglomerate, although the junction is nowhere exposed.

In the stream 0.5 km N of Bank Hall, poorly exposed purple-red sandstones with thin siltstone bands, are believed to be part of the Basement Beds, and they seem to pass eastwards below the higher beds of Bank Rigg (sec p. 34). Although directly overlain by Penrith Sandstone in the stream [NY 6431 3361], the sandstones show only a few metres of purple and yellow staining beneath the unconformity.

A short distance to the south-east, in Kirkland Beck, about 15 m of purple-red, coarse-grained, cross-bedded, pebbly sandstones, cropping out in a short fault-bounded section [NY 6532 3279] to [NY 6542 3285], probably lie low in the Basement Beds. A similar correlation is suggested for comparable sandstones in a small faulted block in the northern bank of Crowdundle Beck [NY 6636 3132] to [NY 6639 3133]. Finally, near the southern margin of the district, a few metres of heavily oxidised, purple-red, pebbly sandstone, poorly exposed in Stank Beck, north-west of Howgill Castle [NY 6696 2959] to [NY 6703 2968], probably also correlate with the lower part of the Basement Beds.

Orton Group

The Orton Group is poorly exposed in the district, for its shelf-like outcrop is largely obscured by head and scree. Its principal outcrop is on the Pennine escarpment (Figure 15)." data-name="images/P991297.jpg">(Figure 14) with smaller crops in faulted ground near Kirkland and Milburn, as well as in the south-west of the district near Greystoke. On the Pennines the Group consists of about 30 m of interbedded dark grey limestones, mudstones, and sandstones. The sandy parts of the sequence contain many annelid casts and some rootlets. The limestones are commonly finely-banded, and in places alternate with sandy layers and calcareous mudstones containing plant debris. The lithologies indicate shallow-water deposition with a rapid transition from the fluviatile non-marine conditions of the Basement Beds to the largely marine environment of the overlying limestones.

The beds contain a fauna characteristic of the Holkerian Stage with brachiopods, bryozoa and a few corals. The rocks of the Group are, however, generally less fossiliferous than the succeeding beds except for thin limestone bands in its upper part which are packed with bryozoa and brachiopods, giving a distinctive lithology useful for local correlation. Such beds are seen in most sections in the south-eastern part of the district, but are best exposed in the southern bank [NY 7018 3006] of Knock Ore Gill, where Johnson (1963, p. 26) recorded more than 2 m of this lithology. Garwood (1913, p. 473) gave the general name 'Bryozoa Band' to a sequence 9 to 12 m thick at about this horizon in the Ravenstonedale–Shap area. His description refers to one or more layers crowded with fossils, but lacks lithostratigraphical details.

In the south-east the uppermost bed of the Group is generally a dolomitic nodular limestone about 1.6 m thick. It extends south-eastwards to the Brough district (Burgess and Holliday, 1979) through intervening sections in Knock Ore Gill and Swindale Beck. This widespread dolomitic horizon probably represents a local disconformity, with a break in sedimentation and possibly a limited amount of erosion. There is an abrupt transition from Holkerian to Asbian faunas at this level, but no evidence of angular unconformity. The best section is at the southern end of Wildboar Scar (p. 32), where Holkerian fossils have been collected from within 0.91 m of the base of the dolomitic bed, whilst Asbian forms occur in the basal bed of the Melmerby Scar Limestone lying only 0.76 m above its top.

The nodular dolomitic bed has not been recorded north of Kirkdale though Turner (1927, p. 344) claims to have detected an erosional break marked by nodules of limestone in shale 'by the Alston road near Melmerby'. If this locality is Sailrigg Quarry however, then the section is now known to be wholly in beds younger than the Orton Group. Northwest of the High Scar, the basal part of the Melmerby Scar Limestone closely resembles the Orton Group and may indicate that sedimentation was continuous in this area.

Details

In the north-eastern part of the district, the outcrops of the Orton Group are involved in the complex structures along the Pennine Fault, and no exposures can be assigned with certainty to the Group. The most northerly unequivocal exposures lie to the northeast of Gamblesby, at the head of Grey Mare's Tail [NY 6260 4010], where 3.64 m of beds near the base of the group are exposed (Figure 15)." data-name="images/P991297.jpg">(Figure 14). They comprise interbedded sandstones and dark grey limestones with an 0.3-in limestone at the top yielding foraminifera, Buxtonia sp., Linoprotonia sp. hemisphaerica group, Pleuropugnoides cf. pleurodon, Punctospirifer sp., smooth spiriferoids and ostracods.

Close to the south-west in Limekiln Beck [NY 6273 3977], about 6 m of dark grey, thinly bedded, sandy, bioclastic limestone, interbedded with thin bands of grey fine-grained sandstone, and pale grey calcite-mudstone dip steeply eastwards. The limestones yield Fenestella sp., stick bryozoa, Dielasma sp., Pleuropugnoides pleurodon, productoids, Punctospirifer scabricosta, rhynchonelloids, smooth spiriferoids, Spirifer cf. duplicicosta, Spirifer sp. bisulcatus group, Aviculopecten sp., Leiopteria cf. lunulata, and ostracods.

The Group is unexposed for about 5 km to the south-east, where the following section is visible in Ardale Beck [NY 6612 3494] to [NY 6616 3496].

The section begins about 2.5 m above the top of the Basement Beds and ends some 15 m below the base of the Melmerby Scar Limestone. The lower part of this latter interval is exposed in Ranscleugh Beck about 100 m to the south [NY 6613 3484] to [NY 6610 3485], where the section reads:

The base of this section lies near the top of that in Ardale Beck and together they provide the best sequence in the district through the Orton Group. A similar, though less well exposed, section is seen in Kirkdale [NY 6677 3402] to [NY 6669 3398], where the Orton Group is about 26 m thick (Figure 15)." data-name="images/P991297.jpg">(Figure 14)

The uppermost bed in this section is the most northerly exposure of the dolomitic bed which generally underlies the base of the Alston Group to the south and east. It is better exposed on the steep slopes below the southern end of Wildboar Scar [NY 6820 3238] to [NY 6821 3236], where the section is:

The dolomitic bed yielded no useful fossils but the following fauna was collected from the underlying limestones: Koninckopora inflata, Fenestella sp., Stenopora?, Serpula sp., Dielasma sp., Linoprotonia sp., Pleuropugnoides pleurodon, Productus cf. garwoodi, Punctospirifer scabrico sta, smooth spiriferoids, Leiopteria sp., and ostracods.

The occurrence of Productus garwoodi and the general absence of Asbian forms, suggest that the assemblage is Holkerian in age.

In the south-western part of the district, the Seventh Limestone is not seen anywhere in full sequence, although a total thickness of 60 m is recorded at Berrier (Eastwood and others, 1968, p. 176), a short distance to the west. The lowest 13 m of the limestone, however, probably underlie the slope south-west of Summerground Crag, 2 km WNW of Greystoke, where they are faulted against younger beds. At the base of this slope, just above Summerground Gill [NY 4169 3153], 4.7 m of grey sandstone and mudstone rest unconformably upon the weathered surface of the Mell Fell Conglomerate. Similar arenaceous beds underline the Seventh Limestone at Berrier.

Alston Group

The base of the Group is taken at the bottom of a thin bed of grey mudstone which lies just below the Melmerby Scar Limestone on Wildboar Scar, about 2 km SW of Cross Fell. The mudstone rests on the dolomitic limestone at the top of the Orton Group. This Group extends upwards as far as the base of the Namurian which lies at the bottom of the Great Limestone. For convenience, the Group has been split into lower and upper parts at the base of the Smiddy or Rough Limestone and this division corresponds closely with the change from Asbian to Brigantian faunas (Figure 11). The overall thickness of the Group is about 350 m on the Pennines and approximately 400 m near Greystoke.

The succession consists of marine limestones rhythmically alternating with elastic sediments of deltaic facies. In the lower part of the Group the carbonates predominate but higher up, terrigenous sediment is commoner and limestones comprise less than a third of the sequence. They are generally biomicrites and vary from pale to dark grey in colour with increasing organic carbon content. In places, they are highly fossiliferous with concentrations of brachiopods or corals, and may also contain much bioclastic debris of broken shells, crinoid ossicles, foraminifera and bryozoa, denoting accumulation in the high-energy environment of a shallow sea.

Each limestone is generally overlain by mudstones, which are calcareous and fossiliferous near the base and become ferruginous and less fossiliferous upwards. These are succeeded by siltstones and micaceous flaggy sandstones, and then by more massive, cross-bedded sandstones. In turn, these beds are usually overlain by a seatearth and perhaps a thin coal. The repetition of this sequence of lithologies was accurately recorded in the earliest lead-mining records (Forster, 1809). The rhythmic units are generally termed 'cyclothems'. Major cyclothems have been differentiated (Johnson, 1959) from minor ones by their greater thickness and lateral persistence. They seem to have been produced by widespread eustatic or tectonic mechanisms, whilst the minor cyclothems are perhaps due to more local variations in sediment supply and the position of distributaries. Within the district, the Group consists of at least 22 cyclothems; 11 of them are major cyclothems and the remainder are only of local significance.

Details

The most important sections are drawn in (Figure 15), (Figure 16), (Figure 17), (Figure 18), (Figure 19), (Figure 20) and given in Appendix 1.

Lower Alston Group

Pennines

The Melmerby Scar Limestone is about 38 to 40 m thick around Cross Fell. It forms two prominent scars around Melmerby High Scar but south of Ardale, it is split into three features. Farther north, the Limestone is more than 50 m thick. Although the upper, pale grey, pseudobrecciated limestones maintain their thickness here, the lower beds thicken as some limestone beds pass laterally into calcareous mudstones and thin sandstones. Near Melmerby and Gamblesby, the limestone appears to thicken westwards, matching the similar thickening in the Basement Beds hereabouts.

The northernmost section of the Melmerby Scar Limestone in the district is in Sailrigg Quarry [NY 6268 4014]. All the beds in this section are assigned to the limestone and all the faunas are Asbian in age. The section reads:

The upper part of the Melmerby Scar Limestone is exposed close above the quarry, where about 9 to 12 m of pale grey, massive, pseudobrecciated limestone form small scars. In the lowest of these, a 0.61-m band, lying about 7.62 m below the top of the limestone, has yielded: Koninckopora inflata, foraminifera, Axophyllum vaughani, Dibunophyllum bourtonense, Lithostrotion junceum, L. cf. martini, Palaeosmilia murchisoni, Fenestella sp., Athyris sp., Dielasma ?, Echinoconchus sp., Gigantoproductus sp., Linoprotonia sp., iviegachonetes sp., a bellerophontoid, Naticopsis cf. brevispira, Soleniscus?, Straparella fallax, S. sp., Straparollus (Euomphalus) sp., turreted gastropods, Conocardium cf. alaeforme, C. cf, rostratum, pectinoids and ostracods.

Farther south, a section at the head of Limekiln Beck [NY 628 398] shows:

The 3.35 m of limestone with the coral band is exposed in the quarry just east of the Alston road [NY 6281 3979], where it contains extensive colonies of Lithostrotion, and has been interpreted as a small reef (Short, 1954, p.36). This view is open to doubt, for the unusual north-westerly dips here displayed may well be tectonic, and the lithologies and faunas specific to reefs are lacking.

The upper part of the Melmerby Scar Limestone crops out along Melmerby Low Scar and the lower part forms the grassy bank below. The latter beds are exposed in disused quarries [NY 6293 3854] as follows:

As in the Sailrigg section, the lower part of the limestone here contains an unusually high proportion of mudstone. More than 21 m of pale grey pseudobreccia constituting the upper beds of the limestone hereabouts are exposed on the Low Scar and the crags above [NY 6306 3830] to [NY 6318 3813]. They yield: foraminifera, Axophyllum vaughani, Caninia?, Chaetetella depressa, Chaetetes radians, Diphyphyllum sp., Lithostrotion junceum, L. martini, L. pauciradiale, Lonsdaleia duplicata melmerbiensis, Palaeosmilia murchisoni, Syringopora cf. geniculata, Delepinea comoides, Gigantoproductus maximus, Linoprotonia sp., Straparella fallax and ostracods.

The limestone crops out in two scars across Melmerby High Scar.The High Scar rather than the Low Scar is more probably the type-area of the Limestone although the first published reference (Forster, 1809) does not specify which of the two Scars is involved. In the lower scar, at least 10 m of grey, fine-grained, well-bedded limestones with thin pseudobreeciated bands are exposed, and probably another 8 m of beds are present below, in the unexposed lower part of the feature. In the upper scar, at least 10 m of pale grey, pseudobrecciated limestone are separated from the lower scar by a 2- to 5-m gap. The rarely-exposed beds between the two scars are seen in Ardale [NY 6590 3508] to consist of 3.7 m of pale grey, brown-weathering, rubbly, pseudobrecciated limestone with thin partings of calcareous siltstone.

The fullest sections of the limestone hereabouts (Figure 15) are in a southern tributary (Ranscleugh Beck of the 6-inch map) of Ardale Beck [NY 6615 3483] to [NY 6619 3481], farther south in Kirkdale [NY 6677 3402] to [NY 6685 3407], and on Wildboar Scar [NY 6817 3244] to [NY 6820 3238] where the succession reads:

In the tract of faulted ground west of the Cross Fell inlier, the Limestone crops out on Bank Rigg, about 800 m NE of Kirkland, where it is some 30 m thick, patchily dolomitised and pink-stained. A section in disused quarries here [NY 6519 3309] shows:

Small outcrops, presumably of Melmerby Scar Limestone, are present in faulted ground farther north, near Fellside [NY 6320 3546] and Ashlock Sike [NY 6411 3487], where the pale grey, pseudobrecciated limestones have been intensely dolomitised and stained pink, probably during oxidation beneath the nearby sub-Permian unconformity. Farther south, the limestone is at least 30 m thick near Windy Hall [NY 660 304], and close by in Thrushgill Quarries [NY 663 301], about 15 m of pale grey, pseudobrecciated limestone lying in the upper part of the formation were formerly worked for lime. In Stank Beck, about 1 km E of Milburn, a faulted section [NY 6640 2920] to [NY 6645 2925] through the limestone shows two 12-m posts of limestone separated by a 4.5-m gap which includes 1.22 m of dark grey calcareous mudstone. The upper post yields Axophyllum vaughani, Caninia?, clisiophylloids, Dibunophyllum sp., Diphyphyllum sp., Lithostrotion martini?, Lithostrotion?, and abundant Palaeosmilia murchisoni. In addition, Aulophyllum fungites and Lithostrotion junceum have been recorded from this locality (Turner, 1927, p. 367).

The Robinson Limestone is rarely exposed but its feature is consistently present throughout the Pennine part of the district. Above Blea Scar (Figure 15) the following section has been estimated from the features:

The upper bed here, the lowest dark-coloured limestone in the Alston Group, is probably the Birkdale Limestone of the Brough district (Burgess and Holliday, 1979).

The Robinson Limestone is 4.5 m thick above Melmerby High Scar and 5.49 m thick in Ardale [NY 6621 3479]. Farther south, in Kirkdale, a thin sandstone directly overlies the limestone and thickens south-eastwards to 1.5 m on Wildboar Scar [NY 6820 3238]. Here the limestone is 6.10 m thick.

West of the Cross Fell inlier, the limestone is also about 6 m thick around Thrushgill Quarries [NY 6644 3000]. The upper 3 m are seen here to be grey to pale grey, partly pseudobrecciated limestones. Grey, dolomitic limestones dug in the north bank of Stank Beck [NY 6634 2929] probably belong to this horizon.

Greystoke

The Sixth Limestone is not well-exposed in the district. It underlies the slopes south-west of Summerground Crags [NY 418 317], marked by the 1185ft spot height in Greystoke Park, where about 33 m of beds are present (Figure 16). A pronounced 5-m slack, about 8 m below the top, probably marks an argillaceous parting. A white, medium-grained sandstone, 1.52 m thick at the head of Summerground Gill [NY 4162 3202] seems to lie at this horizon.

The upper part of the Fifth Limestonewas proved in the Flusco Limeworks Borehole (Appendix 1). North-west of Park House, the limestone forms a double feature with dark limestones underlying pale grey, pseudobrecciated limestones. About 1.22 m of yellow and greenish grey mudstones are seen in the intervening gap [NY 4063 3363] but the parting thins southwards.

Southwards on Summerground Crags, the uppermost 37.2 m of the limestone are well-exposed in a fine series of scars, giving the following section:

The sandstone (e) of this section is impersistent. Bed (h), containing abundant corals, can be traced as a local marker across Greystoke Park. A further 18 m of the Fifth Limestone appears to underlie the section above, giving a total thickness of about 55 m.

West of Summerground Gill, isolated exposures of pale grey, fine-grained, hematitic limestones [NY 4150 3152] and [NY 4152 3150] dipping steeply to the east against the Summerground and Greystoke faults, yielded: foraminifera, Axophyllum vaughani, Clisiophyllum sp., Lithostrotion cf. martini, L. pauciradiale, Palaeosmilia murchisoni, Syringopora sp., chonetoids, Gigantoproductus sp.and smooth spiriferoids. This Asbian fauna suggests that the Fifth Limestone underlies much of this ground. It is probably also present under the drift-covered, but deeply pot-holed, ground to the north, between the Summerground Fault and the volcanic rocks of the Greystoke inlier.

The upper part of the White Limestone forms scars near Caldew Wood [NY 4432 3197] to [NY 4431 3183], north of Greystoke, where the section reads:

To the south, the Limestone was proved to be 22.8 m thick in the Flusco Borehole (Appendix 1) and farther west, in Greystoke Park, a fine section is exposed on Summerground Crags [NY 4206 3176] to [NY 4231 3191]:

AJW

Upper Alston Group

Pennines

The north-east of the district lacks good sections of the Smiddy Limestone. The overlying elastics are more commonly exposed, particularly in Croglin Water and Loo Gill (Appendix 1), and a 7 to 10-m sandstone is developed at this horizon to form prominent crags between Weather Lair [NY 628 413] and Long Crags [NY 630 402]. In Twotop Beck [NY 6269 4119], 3.2 m of the Limestone yielded ?algal pellets, Axophyllum vaughani and Lithostrotion cf. martini, and in Limekiln Beck [NY 6296 3985], 'Girvanella' nodules were recorded from the Limestone by Short (1954, p. 41). RSA

On the slopes of Cross Fell, the best section is exposed in Ardale (Figure 17) [NY 6632 3517] to [NY 6636 3518] as follows:

The 0.61-m limestone near the top of the section is present elsewhere on the Alston block (Dunham, 1948, p. 17). Encrusting algae of 'Girvanella' type are present in this section at two horizons in the upper part of the Smiddy Limestone and the upper band is also seen on High Cap [NY 6622 3443] where it occurs 2.1 m below the top of the Limestone.

Southwards, the Limestone is 11.9 m thick in Kirkdale and the overlying sandstones and shales thicken to about 20 m across Wild-boar Scar. An 0.3-m coal, lying above these beds and about 3 m below the Lower Little Limestone, was encountered in the Low Middle Tongue Level [NY 6904 3210] of Silverband Mine (Johnson, 1963, p.44).

To the west of the Cross Fell inlier, the Limestone has been tentatively identified near Howgill Castle [NY 6639 2919] where 2.5 m of pink-stained, dolomitised limestone have yielded Saccamminopsis sp., Caninia?, and Lonsdaleia floriformis floriformis. AJW

The Lower Little Limestone and overlying beds are exposed in sections in Croglin Water [NY 5843 4747] and in Loo Gill [NY 6132 4345] given in Appendix 1. In addition, the upper 2 m of the Limestone, containing numerous corals, is well exposed in Loo Gill [NY 6204 4305] and [NY 6263 4282] and yielded: encrusting filamentous algae, Ammodiscus sp., archaediscoids, Earlandia sp., endothyroids, Glomospira sp., tetrataxioids, textularioids, Lithostrotion martini, L. pauciradiale, L. portlocki, Palaeosmilia regia, Syringopora cf. ramulosa, S. cf. reticulata, Avonia sp., Echinoconchus sp., Gigantoproductus cf. edelburgensis, G. sp. giganteus group, Productus sp., Rugosochonetes sp., smooth spiriferoids, Naticopsis sp. RSA

The impersistent coal at the top of the cyclothem reaches 0.15 m in thickness in Raven Beck [NY 6180 4413]. Farther south, in a southern tributary of Ardale Beck [NY 6644 3522] the section is:

The gigantoproductoid shells are more common in the upper part of the Limestone; algal remains are scattered throughout, in contrast to the single thin algal band recorded 2.44 m from the base of the Lower Little in upper Teesdale (Johnson, 1963, p. 36). The beds above the Limestone seem very variable, since a short distance to the north, on Brown Hill, a bed of fine-grained, siliceous sandstone rests directly upon it.

In the faulted ground west of the Cross Fell inlier there are no sections through the Limestone but the features east of Windy Hall [NY 670 303] suggest that it is about 4.5 thick hereabouts. AJW

The beds of the Jew Limestone cyclothem are seen in Croglin Water and Loo Gill (Appendix 1) and a thin coal near the top of the sequence has been extensively worked along its crop. Two seams are present within these beds in places, as at Green Rigg, Renwick [NY 6051 4416]. To the south, in Twotop Beck, a sequence like that in Loo Gill is seen [NY 6308 4107] to [NY 6332 4103]. RSA

Across the largely peat-covered Gamblesby Allotments at least 6 m of blue-grey limestone are indicated by the Limestone feature, with a prominent sandstone cropping out above, although west of Little Knapside Hill two sandstones can be traced including an impersistent bed lying directly upon the Limestone. These continue across Melmerby Fell but are reduced to less than 2 m of micaceous sandstone just north of Ardale. In Ardale Beck [NY 6648 3522] the section reads:

The 2.29-m limestone lying near the top of this section probably correlates with the similar bed recorded at this level in Raven Beck, and also elsewhere on the Alston Block (Dunham, 1948, p. 17). The sandy basal 0.6 m of the Jew Limestone grade into the underlying sandstone.

The section in Stank Beck, just north of Howgill Castle [NY 6645 2926] to [NY 6650 2934] shows about 9 m of grey, massively bedded limestone tentatively identified as the Jew. The uppermost 1.8 m contain Dibunophyllum sp., Latiproductus sp. latissimus group and Rugosochonetes sp., and a coral band lying about 2 m from the base of the section yields Cyathaxonia?, Lithostrotion pauciradiale, Lonsdaleia floriformis, L. floriformis crassiconus, Syringopora sp.and Latiproductus sp. latissimus group. A similar band was recorded (Johnson, 1963, p. 37) near the base of the Jew Limestone on the Moor House Reserve.

In disused quarries [NY 6701 2898], about 400 m ESE of Howgill Castle, the section reads:

Saccamminopsis sp.is abundant in most specimens from the lower limestone in this section. The beds have previously been assigned to an horizon high in the Asbian (Turner, 1927, p.366), but the presence of Dibunophyllum bipartitum konincki, generally a Brigantian form, and the abundance of Saccamminopsis which often proliferates at this horizon, make a correlation with the Jew Limestone more likely. AJW

The Tyne Bottom Limestone and the overlying Alternating Beds sequence which includes the variable succession up to the base of the Scar Limestone are exposed in Croglin Water [NY 5922 4781] to [NY 5986 4800] (Appendix 1).

Within the tightly-folded beds near the Pennine Fault, the Tyne Bottom Limestone, tentatively identified in Glints Beck [NY 5915 4639], crops out at several localities in Raven Beck [NY 6132 4363] to [NY 6153 4378] and in Loo Gill [NY 6151 4350], but is best seen east of Selah [NY 6288 4267] where about 10 m of blue-grey, fine-grained crinoidal limestone yielded: Archaediscoids, endothyroids, tetrataxioids, textularioids, Diphyphyllum lateseptatum, Fasciculophyllum sp., stick bryozoa, Alitaria panderi, Avonia?, costate spiriferoids, Dielasma sp., Echinoconchus sp., Gigantoproductus sp., Latiproductus latissimus, Martinia sp., orthotetoids, Plicochonetes cf. crassistrius, Rugosochonetes sp. Conocardium cf. inflatum, Schizodus sp., trilobite fragments, ostracods and echinoid spines.

Within the Alternating Beds the Single Post Limestone is locally the most prominent bed, cropping out in Raven Beck [NY 6165 4391] as 3.1 m of pale grey, coarsely crystalline, massive limestone with Eomarginifera? and Spirifer sp., whilst in Loo Gill [NY 6309 4264] a similar bed is exposed 2.4 m thick, which yielded ca]cispheres, endothyroids, textularioids, Avonia sp., Gigantoproductus sp. giganteus group, and Rugosochonetes sp.

East of the main watershed, sections through these beds are rare, although more than 21 m of sandstone at the top of the Alternating Beds are seen, above the Whin Sill, in the southern bank of Gilderdale Burn [NY 6912 4701].

South of the Hartside road, in Twotop Beck [NY 6354 4097], the following section is seen:

The lateral variability of the Alternating Beds is well seen in several short sections to the east, in Aglionby Beck. The details of the fullest section, in the east bank of the stream [NY 6607 4007] to [NY 6611 4014], are as follows:

Average thicknesses have been quoted for many of these beds which vary within the exposed section. The limestones are difficult to identify.

To the east, amongst the many short sections of the Alternating Beds in Smittergill Burn, the Cockleshell Limestone is more typical in containing Gigantoproductids [NY 6780 3952]:

The Alternating Beds occupy the lower course of Black Burn, giving scattered sections, particularly of the Single Post Limestone in the river bed south of Hartside House [NY 6896 4217], and of the Maize Beck Limestone in the Burn to the east [NY 6930 4236]; a composite section from these localities reads:

The Single Post Limestone is estimated here to lie about 15 m below the base of the Scar Limestone. The Tyne Bottom Limestone, although not seen at the surface hereabouts, was said to be 6.7 m thick in the West Flats of Rotherhope Fell Mine [NY 6939 4090]. RSA

The Limestone can be readily traced above Melmerby High Scar and across Brown Hill as a feature 7 to 8 m high, southwards to Ardale [NY 6647 3539] where 7.62 m of dark grey, well-bedded limestone yield: algae, foraminifera including Saccamminopsis sp.and textularioids, Caninia cf. juddi, Diphyphyllum lateseptatum, Lithostrotion junceum, Syringopora sp., a zaphrentoid, bryozoa including Penniretepora sp., Alitaria panderi, Antiquatonia sp., Dielasma sp., Latiproductus sp. latissimus group, Martinia sp., Schellwienella sp., Naticopsis sp., Aviculopecten cf. knockonniensis, a non-mucronate trilobite pygidium and ostracods.

The section through the overlying measures is given in Appendix 1. A thin coal lying at the top of the highest sandstone in the Alternating Beds (the Copper Hazle of Alston Moor), about 4 m below the Scar Limestone, has been worked at crop from Brown Hill southwards to Middle Tongue. In Crowdundle Beck [NY 6923 3300] to [NY 6895 3281], the succession above the Tyne Bottom Limestone is well exposed (Appendix 1) apart from the horizon of the Single Post which in this section is occupied by the Whin Sill.

On High Slack, north-east of Milburn, a 3-m, pale grey, fine-grained, dolomitised limestone [NY 6648 3094], yielding Lithostrotion junceum and Lonsdaleia sp., is rather doubtfully correlated with the Single Post Limestone largely because the thicker limestone overlying it to the north-west is thought to be the Scar Limestone (p.43). About 6 m of grey, purple-stained, flaggy sandstone with purple siltstone bands, lying below the latter in the southern bank of Crowdundle Beck [NY 6614 3134], may represent the upper part of the Copper Hazle.

Farther south, in Ardale Beck, the following section is poorly exposed, both in the stream-bed and in Star Hows Quarry [NY 6428 3445] to [NY 6424 3438]:

A previous description of this section, lithologically similar to the above, (Shotton, 1935, p.664) recorded Spirifer bisulcatus from bed (f) and Chaetetes septosa and 'Echinoconchus expansus'from bed (d). Although little of detailed stratigraphical consequence can be gleaned from the faunas, lithologically the sequence resembles the Alternating Beds. Thus, the coal in bed (m) may well correlate with that below the Scar Limestone, which is the only worked coal on the adjacent Pennine escarpment. The absence, however, of a thick sandstone corresponding to the Copper Hazle, and the unusual proximity of two thin limestones, beds (j) and (1), to the base of the Scar Limestone may indicate faulting in this part of the section. The lowest limestone, bed (d), correlates reasonably with the Single Post Limestone. AJW

In disused quarries north-east of Croglin [NY 5834 4815] the Scar Limestoneis 14.6 m thick, with the lower 9.8 m of massive grey limestone, separated from rather darker beds with thin mudstone partings above, by 0.6 m of calcareous mudstone. Lithostrotion junceum is abundant in the middle of the section, Saccamminopsisfusulinaformis is plentiful near the top, and Lithostrotion maccoyanum, Spirifer duplicicosta and S. triangularis are also present. The overlying beds are seen nearby, in the beck north-north-east of Croglin [NY 5816 4842] where 5.2 m of grey sandstone resting upon 6.1 m of dark grey mudstone and siltstone separate the Scar from the overlying limestone (Figure 18).

Complete sections through the Scar Limestone are rare in this area, however, because the Whin Sill generally lies close to this horizon, as in the quarry 400 m ENE of Fieldhead [NY 5855 4792] or in the banks of Croglin Water [NY 5995 4806]. The large quarries in the Scar (Glints Quarries of the 6-inch map), extending about 1 km S of Croglin Water to a point east of Davygill, show the limestoneto be intruded at several levels by dolerite, particularly along the mudstone partings in its upper part.

Farther south, the limestone has been locally worked on Green Rigg [NY 6136 4439] where the section is:

East of the main watershed, good sections are few, despite extensive outcrops. More than 9 m of the grey, wavy-bedded limestone, containing abundant Lithostrotion junceum 4.0 m from the base of the section, crop out in Gilderdale Burn [NY 6788 4584] whilst the overlying beds are exposed to the north in Woldgill Burn [NY 6794 4626] as follows:

The maximum thickness of the Scar hereabouts is 12.8 m cropping out in the south-east bank further down Gilderdale Burn [NY 6947 4737].

To the west of the main watershed a representative section is seen in the quarries on the Alston road about 1.5 km W of Hartside Cross [NY 6301 4194] as follows:

In the eastern face of these workings, 11.6 m of limestone contain a thin band at the top of the section, rich in microfossils including Calcispheres, Ammodiscus sp., archaediscoids, endothyroids, Glomospirella sp., Howchinia sp., tetrataxioids and textularioids.

Farther south at the head of Twotop Beck [NY 6359 4112], the Scar, partly replaced by limonite, is overlain by 4.6 m of silty mudstone, and similar sections are seen in numerous potholes south and east of Fiend's Fell. The Limestone is 10.7 m thick where the western tributary of Rowgill Burn emerges from a cave (Hutton Hole of the 6-inch map) [NY 6607 4153]. Similar thicknesses are recorded further downstream, at the prominent waterfall known as Carlayne Leap [NY 6783 4153], where Lithostrotion junceum is again abundant in the middle part, and in a tributary to the east [NY 6875 4217]. In the eastern bank of Black Burn, the extensive outcrop is mineralised with quartz, pyrite and marcasite adjacent to the many NE-trending faults. RSA

The absence of the Scar Limestone on Melmerby Fell appears to be due not only to local faulting, but also to ingestion by the Whin Sill. Farther east, where the Sill lies lower in the sequence, the presence of the limestone is indicated by a prominent feature with numerous pot-holes on it, although the limestone itself is only rarely exposed beneath the peat e.g. [NY 6600 3798]. The outcrop on Ousby Fell east of Black Burn, is very wide, apparently indicating about 25 m of limestone, but cambering of the feature has probably occurred here, as the nearby section in Black Burn shows less than half this thickness.

To the south, the fine section at the head of Ardale (Appendix 1) includes 14.63 m of Scar Limestone. The band of Lithostrotion colonies recorded here is also present in other Alston Block sections (Johnson, 1963, p.40), but in Crowdundle Beck (Appendix 1) the colonies are scattered more widely, throughout the lower part of the limestone. West of the Cross Fell inlier, the Scar is probably present in Ardale Beck [NY 6423 3437] as 8.8 m of grey, brown-weathering limestone. Its identification in scattered outcrops across High Slack to the south is even more tentative. AJW

The beds of the Five Yard Limestone cyclothem are well exposed in a northern tributary of Croglin Water (Lunchy Beck of the 6-inch map) as follows [NY 6036 4822]:

whilst in Croglin Water itself [NY 6067 4814], a thin coal crops out immediately below the Three Yard Limestone. The strong feature formed by the thick sandstone bed of this sequence, the High Brig Hazle of Alston Moor, can be traced throughout this area.

East of the main watershed, the Five Yard is seen only in Woldgill Burn [NY 6794 4626], where 1.8 m of limestone crops out, but west of the divide, sections are more common. In the headwaters of Raven Beck [NY 6290 4478] and [NY 6238 4479] the Five Yard consists of 2.4 to 2.7 m of dark blue-grey, flat-bedded limestone, but is thicker to the south in Loo Gill [NY 6390 4273] where the section reads:

Still farther east, the limestone is 4.6 m thick in the northern bank of Black Burn [NY 6940 3953] whilst the overlying beds crop out in the nearby southern tributary (Swarth Beck) and include very fossiliferous calcareous mudstone just above the limestone as follows [NY 6874 3934]:

RSA

The Five Yard Limestone, like the Scar, is absent on Melmerby Fell, due possibly to ingestion by the Whin Sill. The overlying High Brig Hazle, however, forms an extensive sandstone plateau on Stony Rigg, where it reaches a maximum thickness of 17 m, and gives the strong sandstone scarp on Brown Hill to the south. The sections in Ardale and Crowdundle Beck (Appendix 1) show 4.88 and 3.66 m of limestone respectively; the latter section includes a coral-brachiopod band not recorded elsewhere. AJW

The Three Yard Limestone crops out in Croglin Water [NY 6067 4814] as 5.5 m of blue-grey, thickly bedded limestone. Within the overlying sequence, a thick sandstone, known on Alston Moor as the Nattrass Gill Hazle, forms a prominent feature on both sides of the valley, whilst two coals, one within the sandstone and the other overlying it, have been extensively worked hereabouts. The lower seam, locally called the Croglin Coal (Trotter and Hollingworth, 1932, p. 56), was mined in 1830 and 1854 from three adits on the northern side of the valley [NY 5945 4845] to [NY 5960 4847] and has also been exploited in scattered workings farther east. The higher seam lying about 5.5 m above, has been worked in adits and shafts on both sides of the valley.

On the escarpment to the south, the higher seam was formerly worked at Burned Edge Mine, where it is 0.38 m thick in a mine-road [NY 5968 4686], resting upon a siltstone-seatearth and with a sandstone roof. The numerous shafts and adits on Renwick Fell also penetrate this seam and similar workings are common farther east on Haresceugh Fell directly above the Nattrass Gill Hazle [NY 6314 4455]. Nearby, about 5.5 m of blue-grey crinoidal limestone is exposed where the Three Yard Limestone is locally folded [NY 6319 4323]. A similar thickness is seen just north of Loo Gill [NY 6395 4288], where grey, medium-grained, crinoidal, brown-weathering limestone, containing bryozoa at the top and brachiopods near the base, yielded: Howchinia sp., Dibunophyllum bipartitum craigianum, Koninckophyllum cf. echinatum, Rotiphyllum sp., thick and slender ramose bryozoa, productoids, smooth spiriferoids, Spirifer sp.and fish.

In Loo Gill, a short distance to the east, the Nattrass Gill Hazle, at least 12.2 m thick, is overlain by a seatearth, but no coal is present. Coal reappears to the south and east, however, where it has been worked in many shafts and adits both east and west of Hartside Cross.

Farther to the north-east, the Croglin Coal is 0.46 m thick in Knar Burn [NY 6510 4832] where the upper seam is represented nearby by 0.23 m of coaly mudstone below the Four Fathom Limestone. Still further east, an increase in the thickness of the latter coal to 0.46 m on Whitley Common [NY 6915 4790] encouraged local working of the seam.

In Gilderdale, to the south, the Three Yard Limestone crops out in Woldgill Burn [NY 6646 4582] to [NY 6652 4586] as follows:

whilst higher in the stream [NY 6622 4583], at least 9.1 m of the overlying medium- to coarse-grained, cross-bedded sandstone are exposed. The upper part of this sandstone is seen in a northern tributary [NY 6676 4625], where it forms a seatearth below a thin coal. This seam thickens eastwards to 0.61 m in disused workings on Park Fell, just beyond the margin of the district. To the south, the section in Black Burn [NY 6910 3977] is:

The Nattrass Gill Hazle is at least 7 m thick here but the overlying coal is only 0.08 m. RSA

Around Cross Fell the Limestone is rarely exposed. It has an unusually wide outcrop at the head of Black Burn but there is no section. At the head of Ardale [NY 6673 3552], about 1.83 m of limonitic ironstone replacing the Limestone was proved in trials for iron ore (Dunham, 1948, p. 126), but natural sections hereabouts are found only in Crowdundle Beck (Appendix 1). AJW

The Four Fathom Limestone produces a strong feature on the fells east of Croglin but the overlying sandstone, the Quarry Hazle, is not generally prominent. The section in a tributary of Croglin Water [NY 6047 4855] is:

Southwards on Renwick Fell, the best section of the Limestone occurs in the headwaters of Raven Beck [NY 6236 4527]:

In a similar section in Loo Gill [NY 6415 4278] to the south, the Limestone has thinned to 9.1 m.

To the north-east the Four Fathom is again thicker, being represented by 12.8 m of cherty limestone exposed in Knar Burn [NY 6505 4821], and 15.2 m of limestone recorded in a tributary of the same stream [NY 648 489] just north of the sheet boundary. Scattered outcrops of the Four Fathom occur on Green Fell and around Black Burn but there is no section. Near the Ardale Head Vein, the feature of the bed disappears where the Limestone is replaced by limonite (Dunham, 1948, p. 126), formerly worked in a small adit [NY 6704 3568]. To the south, the sole section is in Crowdundle Beck (Appendix 1).

The complete Iron Post Limestone cyclothem is seen in the following section in Croglin Water [NY 6343 4638]:

In the headwaters of Raven Beck, farther south, about 0.2 m of carbonaceous siltstone, underlain by a micaceous sandstone–seatearth, occur at the top of the sequence [NY 6362 4454], whilst both here and on Haresceugh Fell [NY 6361 4342] to the south, the Iron Post Limestone has thickened to 0.6 m.

In Loo Gill, however, the thickness of the cyclothem is only 3.4 m, including 0.3 m of limestone, contrasting with a thicker section farther east, in a tributary of Rowgill Burn [NY 6681 4181], which reads:

In Gilderdale, the limestone is also 0.3 m thick, exposed on the north bank of Gilderdale Burn [NY 6657 4427]. Around Cross Fell the only section is in Crowdundle Beck (Appendix 1). RSA

Greystoke

The lower part of the Rough Limestoneis seen on the scars near Caldew Wood [NY 4435 3194] and [NY 4405 3241] as follows:

The full thickness of the Rough was proved to be 14.73 m (Figure 19) in the Flusco Borehole (Appendix 1). To the north-west, the Limestone is about 13.7 m thick near Park House, forming two distinct features. Pavements develop on the lower one, especially southwards towards Summerground Crags [NY 4198 3238] where the section reads:

Just to the south-east, the pavement is formed by an 0.46-m band of pale grey, pseudobrecciated limestone [NY 4242 3183] and [NY 4287 3177] with abundant corals yielding: Koninckopora sp., foraminifera, Caninia sp. subibicina group, Dibunophyllum sp.,,Diphyphyllum lateseptatum, Lithostrotion junceum, L. martini, L. pauciradiale, Dielasma sp.and Gigantoproductus sp.

Beds higher in the Limestone are exposed in several localities hereabouts [NY 4295 3183] and [NY 4277 3183], the best section being in a disused quarry [NY 4315 3179] where 3.66 m of limestone are seen. Collecting from these localities yielded: algal nodules, foraminifera, Lithostrotion junceum, Alitaria panderi, Avonia ?, Eomarginifera sp., Gigantoproductus sp., Megachonetes siblyi, Schizophoria sp., smooth spiriferoids, Spirzfer bisulcatus?, Eoptychia sp., Naticopsis sp., Edmondia? and ostracods.

Algal nodules are common in many of the sections, but no marked concentrations of 'Girvanella' nodules constituting a specific band have been recorded. The overlying elastics are generally more than 20 m thick and consist mainly of sandstone, but some sections also include seatearths and in Greystoke Park [NY 4241 3227] the sequence has been tested for coal, though coal debris is lacking from the tip.

To the south, the Rough Limestone was formerly worked just west of Barffs Wood [NY 4297 2953], where about 4.3 m of medium to dark grey, well-bedded limestone include a thin coral band containing Chaetetella depressa and Clisiophyllum sp., lying 1.52 m above the base of the section. Farther west, on the southern slopes of Berrier Hill, several scattered outcrops have been correlated with the Rough Limestone. In a small digging [NY 4018 3020], 'Girvanella' nodules were collected from about 1 m of medium to dark grey, bioclastic limestone, and are common in the walling-stone nearby. The best exposures however lie about 1 km S of Berrier Hill, where the double feature indicates a thickness of more than 12 m.

The Lower Little Limestonecrops out near Millrigg [NY 4511 2983] where 4.57 m of grey, fine-grained limestone in the lower part of the member yields: archaediscoids, textularioids, Caninia sp., Lithostrotion junceum, cf. L. pauciradiale, smooth spiriferoids, trilobite glabella, and ostracods.

The corals occur in a thin band 0.46 m from the top of this section. The Lower Little was 6.6 m thick in the Flusco Borehole (Appendix 1). Outcrops of brown, dolomitic limestone at Gill [NY 4462 2943] and [NY 4440 2956] may correlate with the dolomitic beds at the base of the Lower Little in this borehole but there are no fossils in the outcrops to confirm this. Beds at this horizon are also exposed in a disused quarry west of Barffs Wood [NY 4254 2954] as follows:

The upper beds of the Jew Limestone crop out north of Caldew Wood [NY 4376 3313] as follows:

A full section of the Jew cyclothem is exposed in Blencow Lime Works quarries [NY 4614 2997], west of Tymparon Hall:

The Jew is known to the local quarrymen as the Flusco Limestone. The base of this section is a bedding-plane forming the quarry floor which lies less than 1 m above the bottom of the Limestone. The thin fossiliferous beds, lying 1.22 and 2.74 m respectively below the Limestone top, are locally persistent. Exploratory drilling ahead of the present quarry face has shown that the non-calcareous part of the sequence is laterally variable, particularly in the local development of thin lenticular sandstones.

Close to the southern margin of the district, extensive quarries have been dug for 800 m down the dip of the Jew Limestone from Flusco Lime Works towards Newbiggin. In the eastern part of the workings [NY 467 292], the section reads:

As in the Blencow Quarry section above, two thin fossiliferous bands occur in the upper part of the Jew, and fossils are also common towards the base. A maximum Limestone thickness of 10.8 m is recorded by boreholes proving quarry reserves in this area. AJW

To the north-west, the best section in the Jew in the Lamonby area lies near the western margin of the district [NY 4005 3590], where a quarry shows:

Samples from throughout this section yielded the following conodonts: Cavusgnathus convexus, Hibbardella (Hibbardella) milleri, and Hindeodella sp.In addition, Hollingworth (in Eastwood and others, 1968, p. 178) recorded large reefs of Lonsdaleia floriformis in the quarry floor.

Near Lamonby Townhead, a disused quarry [NY 4093 3458] gave the following section:

Tracing the Jew southwards across Greystoke Park and around Summerground Gill is difficult as the features are poor. Across the faulted ground south and east of Berrier Hill, however, the Limestone forms a sharp rise, 7 to 9 m high, topped by an extensive pavement, and yielded [NY 4151 3023] abundant Saccamminopsis sp., as well as textularioids, Lithostrotion pauciradiale, Gigantoproductus sp., Martinia sp., Rugosochonetes sp., Murchisonia? and ostracods.

The Tyne Bottom Limestone and the overlying Alternating Beds sequence are readily identifiable around Ellonby and Johnby.

The Single Post Limestone has been dug in Ellonby village [NY 4253 3525] and 2.7 m of grey, dolomitic limestone from this horizon form a small feature east of Johnby. A short section near the base of the Tyne Bottom here reads:

Although both limestones are seen only in scattered outcrops in the River Petteril and to the south, the intervening sandstone is prominent. More than 6 m of grey, purple-stained, fine-grained, massive sandstone, overlain by flaggy beds, were formerly quarried [NY 4562 3138] as a major source of building-stone for the Greystoke area. Similar beds crop out beneath the railway bridge near Tymparon Hall [NY 4656 3035], and in the railway cutting to the west [NY 4611 3042], where they overlie flaggy beds resting directly upon the dolomitic upper part of the Tyne Bottom Limestone, here containing Saccamminopsis sp., Lithostrotion?, Fenestella?, smooth spiriferoids and gastropods.

In the Blencow Limeworks quarry, west of Tymparon Hall, more than 10.7 m of the Tyne Bottom Limestone, known to local quarrymen as the Blencow Limestone, have been worked. Only at the western end of the working is the face accessible [NY 4595 3010] and here the beds contain Fenestella sp., Alitaria panderi, Antiquatonia cf. hindi, cf. Avonia youngiana, Brachythyris sp., Eomarginifera sp., Gigantoproductus sp., orthotetoids, Rugosochonetes sp., smooth spiriferoids and Spirifer bisulcatus. The brachiopods are especially common in a band 0.6 to 0.9 m from the top of the section.

A recent extension of quarrying westwards from Blencow Lime-works, in ground adjacent to the railway [NY 456 297], has exposed the upper part of the Tyne Bottom Limestone in a 7.6-m face as follows:

A short distance to the north-west, 4 m of pink-stained, heavily dolomitised, barren limestone seen in the railway cutting [NY 4541 3002] apparently overlies the above section and is therefore probably the Single Post Limestone.

The latter again failed to yield macrofossils in a quarry-section at Lamonby [NY 4082 3542], but the 3.4 m of pale grey, rubbly limestone did contain the following conodonts: Apatognathus libratus, A. cf. petilus, A. scalenus, Gnathodus girtyi simplex, Hindeodella sp., Neoprioniodus scitulus and Prioniodina subaequalis.

Both the Tyne Bottom and Single Post limestones form prominent features in Greystoke Park, west of Johnby, whilst farther west, in Summerground Gill, the former is overlain [NY 4201 3109] by more than 6 m of red-brown, fine-grained, massive sandstone. Farther upstream, the Single Post Limestone is heavily dolomitised and again barren of fossils, in disturbed ground just south of the Greystoke Fault. Amongst the overlying beds close to the fault, a thin, brecciated, dolomitic limestone [NY 4173 3138] containing only foraminifera and a zaphrentoid, may be the Cockleshell Limestone.

On Berrier Hill, the outcrop of the Tyne Bottom Limestone is restricted by faulting to a small crag [NY 4077 3029], but the overlying beds are better seen, including an 0.3-m coal, formerly worked in bell-pits on the west side of the Hill [NY 4026 3113]. The pale grey Single Post Limestone forms a strong scarp hereabouts, 6 to 7 m high and generally dolomitic in its upper 1.5 m. The sparse fauna collected here [NY 4031 3095] contained orthotetoids, rhynchonelloids, Schizophoria sp., smooth spiriferoids, Edmondia sulcata and ostracods.

Quarries in the Scar Limestone north-west of Ellonby give the most complete local section [NY 4210 3554] which reads (Figure 20):

About 100 m NE of the Hall at Ellonby [NY 4270 3528], the section reads:

East of Johnby, the Scar Limestone has been worked extensively along its outcrop. In the most complete section [NY 4424 3332], 1.5 m of grey, flaggy limestone rest upon 4.6 m of massive, crinoidal beds containing Saccamminopsis sp.and other foraminifera, Axophyllum sp., Diphyphyllum sp., Lithostrotion junceum, zaphrentoid, smooth spiriferoids and Liroceras sp.South-east of Great Blencow, in a small quarry near Spire House [NY 4614 3137], 3 m of grey, fine-grained, massive limestone, lying near the base of the Scar contain Lithostrotion junceum, Fenestella sp., stick bryozoa, Alitaria panderi, Avonia sp. [juv.], Dielasma ?, rhynchonelloids and smooth spiriferoids, whilst the overlying sandstones have been worked locally for walling-stone close to the Penrith–Greystoke road [NY 4705 3079].

Farther west, the upper part of the Scar Limestone and the overlying beds crop out in a western tributary of Summerground Gill [NY 4153 3140] to [NY 4151 3139] as follows:

On the summit of Berrier Hill [NY 4036 3109] the Scar, represented by 9.1 m of grey, bioclastic, wavy bedded limestone, yields only a restricted fauna: cf. Caninia juddi, clisiophylloid [juv.], Lithostrotion junceum, rhynchonelloids and gastropods.

The Five Yard Limestone cannot be definitely identified around Greystoke. It is probably present, however, in a quarry south of Skelton [NY 4395 3517] where 1.2 m of grey, sandy, crinoidal, dolomitic limestone have yielded Avonia?, Linoprotonia sp., Schellwienella sp., smooth spiriferoids, Aviculopecten?, Pernopecten?, Wilkingia elliptica and orthocone nautiloids. The thicker elastic part of this cyclothem, laterally equivalent to the High Brig Hazle of the Pennines, is present throughout the area.

The Three Yard Limestone, seen but rarely in this area, crops out in a quarry [NY 4044 3539] south-west of Skelton Church, where 2.4 m of limestone yielded smooth spiriferoids, a fish tooth, Cavusgnathus naviculus, Gnathodus sp.and Magnilaterella complectens. The overlying beds include a thick sandstone, which is exposed in Skelton village and was proved to be at least 6.6 m thick in a nearby well [NY 4375 3543]. It is also seen north of Ellonby [NY 4260 3580], just west of Starthill [NY 4037 3640] where the features indicate a full thick ness of about 12 m, and in Lamb Beck [NY 4258 3458] where 5.9 m of pale grey, fine-grained, massively cross-bedded sandstone forms a waterfall.

Farther downstream, just west of Auldby [NY 4402 3432], more than 9 m of grey, bioclastic, crinoidal, thinly bedded limestone with scattered white chert nodules, overlain by 4.5 m of coarse-grained, cross-bedded sandstones which pass up into flaggy beds above, yielded Chaetetella depressa, Fenestella sp., Protoretepora?, Alitaria panderi, Avonia sp., chonetoids, Echinoconchus?, Pugnax sp.and Pustula?. Although the fauna is not stratigraphically diagnostic, this seems to be the Three Yard Limestone.

A similar section is exposed east of Johnby [NY 4452 3340], where 2.1 m of grey, crystalline, thinly bedded, crinoidal limestone are overlain by coarse-grained, gritty, cross-bedded sandstone. From a small quarry nearby [NY 4439 3363], the limestone yielded the following conodonts: Apatognathus geminus, Gnathodus bilineatus, G. girtyi, Hindeodella sp., Neoprioniodus singularis, Paragnathodus cornmutatus, P. mononodosus and Prioniodina subaequalis.

To the south-west, on Berrier Hill [NY 4107 3093], where the Limestone is characterised by spots of red chert, macrofossils are rare, being restricted to Rugosochonetes sp.and some smooth spiriferoids, but analysis for conodonts again produced a full fauna: Apatognathus cuspidatus, A. petilus, A. cf. scalenus, Gnathodus bilineatus, G. girtyi girtyi, G. girtyi simplex, Hibbardella (Hibbardella) milleri, Hindeodella sp., Ligonodina levis, L. tenuis, Magnilateralla cf. clarkei, M. complectens, Neoprioniodus scitulus, Ozarkodina sp., Spathognathodus scitulus, S. scitulus subsp.nov. A.

The upper part of the Four Fathom Limestone has been quarried east of Lamonby [NY 4129 3600] and [NY 4140 3593], where 2.4 m of grey, fine-grained, wavy-bedded limestone yielded the following fauna: Zaphrentites sp., Fenestella sp., trepostome bryozoa, Alitaria panderi, Avonia youngiana, Buxtonia sp., Dielasma sp., Echinoconchus sp., Eomarginifera sp., Lingula sp., Linoprotonia sp., Orbiculoidea sp., Productus sp., Pugilis pugilis, rhynchonelloids, Schizophoria sp., Spirifer sp., Naticopsis globosa, Edmondia?, Cypricardella sp., pectinoids?, Weberides sp.and fish spines. Nearby [NY 4120 3630], more than 6.0 in of purple-stained, fine-grained, massive sandstone have been quarried in the otherwise unexposed sequence above the Limestone. North-east of Berrier Hill, the Four Fathom is about 9 m thick, estimated from the features. The overlying beds are seen in a pothole [NY 4095 3122]:

North-western part of the district

At least three limestones have been encountered near Forest House, but correlation with other areas is made difficult by thick drift. In a small quarry adjacent to the cross-roads [NY 4093 4641], the primary surveyors recorded 'coarse grit overlying limestone, bearing Encrinites, and dipping south-east at 32 degrees'. Tip now fills much of the excavation, and the locality has yielded only orthotetoids from the red-stained sandstones still exposed. Limestone also crops out farther along the strike of these beds about 400 m to the west [NY 4059 4618], where it was formerly dug for lime-burning.

Two limestones higher in the sequence were encountered, southwest of Forest House, with a similar dip and strike. Recent excavations by the roadside [NY 4093 4632] penetrated a platy limestone, now inaccessible, whilst a thick bed, correlated with the Great Limestone by the primary surveyors, crops out in a flooded quarry to the south-east. About 1.2 m of grey limestone seen at the southwest end of this quarry [NY 4098 4626] yielded only smooth spiriferoids, whilst the macrofauna of the overlying 3 m of grey, red-stained, silty mudstone seen in the southern face of the working [NY 4102 4625] and [NY 4104 4627] was restricted to Rugosochonetes?, indeterminate bivalves and orthocone nautiloids. A sample from the limestone, however, yielded the following prolific conodont fauna: Apatognathus cuspidatus, A. geminus, A libratus, A. petilus, A. scalenus, Gnathodus bilineatus, G. girtyi girtyi, G. girtyi simplex, G. girtyi cf. soniae, Hibbardella (Hibbardella) milleri, Hindeodella subtilis, Hindeodus cf. alatoides, Kladognathus cf. macrodentatus, Ligonodina levis, L. tennis, Lonchodina furnishi, Magnilaterella cf. clarkei, M. complectens, M. cf. robusta, Neoprioniodus singularis, N. scitulus, Ozarkodina delicatula, O. aff. delicatula, Paragnathodus commutatus, P. mononodosus, Prioniodina cf. laevipostica and Spathognathodus scitulus.

Mr Reynolds comments that this fauna indicates a middle Brigantian age, suggesting that the three limestones described here lie somewhere in the sequence including the Jew and Scar limestones.

The horizon of a dolomitised limestone exposed in workings about 1 km to the west [NY 4006 4626] and [NY 4011 4616], just beyond the sheet margin, is not known. RSA

References

BOTT, M. H. P. 1964. Formation of sedimentary basins by ductile flow of isostatic origin in the upper mantle. Nature, London, Vol. 201, pp 1082–1084.

BOTT, M. H. P.  and JOHNSON, G. A. L. 1967. The controlling mechanism of Carboniferous cyclic sedimentation. Q. J. Geol. Soc. London, Vol. 122, pp. 421–442.

BURGESS, I. C. 1970. In Annu. Rep. Inst. Geol. Sci. for 1969, p. 31.

BURGESS, I. C. 1971. In Annu. Rep. Inst. Geol. Sci. for 1970, p. 33.

BURGESS, I. C. and HOLLIDAY, D. W. 1979. Geology of the country around Brough-under-Stainmore. Mem. Geol. Surv. G.B.

BURGESS, I. C. and MITCHELL, M. 1976. Visean lower Yoredale limestones on the Alston and Askrigg blocks and the base of the D, Zone in northern England. Proc. Yorkshire Geol. Soc., Vol. 40, pp. 613–630.

CAPEWELL, J. G. 1956. The Carboniferous Basement Series of the Cross Fell Area, Cumberland and Westmorland. Proc. Geol. Assoc., Vol. 66, pp. 213–230.

DAY, J. B. W. 1970. Geology of the country around Bewcastle. Mem. Geol. Surv. G.B.

DUFF, P. McL. D. and WALTON, E. K. 1962. Statistical basis for cyclothems: a quantitative study of the sedimentary succession in the east Pennine coalfield. Sedimentology, Vol. 1, pp. 235–255.

DUNHAM, K. C. 1948. Geology of the Northern Pennine Orefield: Vol. 1, Tyne to Stainmore. Mem. Geol. Surv. G.B.

DUNHAM, K. C.  1950. Lower Carboniferous sedimentation in the northern Pennines (England). Rept. 18th Sess. Int. Geol. Congr., G.B. 1948, Part 4, pp. 46–63.

DUNHAM, K. C. DUNHAM, A. C., HODGE, B. L. and JOHNSON, G. A. L. 1965. Granite beneath Visean sediments with mineralization at Rookhope, northern Pennines. Q. J. Geol. Soc. London, Vol. 121, pp. 383–417.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the Country around Cockermouth and Caldbeck. Mem. Geol. Surv. G.B.

FORSTER, W. 1809. A treatise on a section of the strata from Newcastle-upon-Tyne to the Mountain of Cross Fell in Cumberland. (1st Edition, Alston; 2nd Edition (1821), Alston.)

FOWLER, A. 1926. The geology of Berwick-on-Tweed, Norham and Scremerston. Mem. Geol. Surv. G.B.

FROST, D. V. 1969. The Lower Limestone Group (Visean) of the Otterburn district, Northumberland. Proc. Yorkshire Geol. Soc., Vol. 37, pp. 277–309.

GARWOOD, E. J. 1913. The Lower Carboniferous succession in the north-west of England. Q. J. Geol. Soc. London, Vol. 68, pp. 449–586.

GEORGE, T. N. 1958. Lower Carboniferous palaeogeography of the British Isles. Proc. Yorkshire Geol. Soc., Vol. 31, pp. 227–318.

GEORGE, T. N. JOHNSON, G. A. L., MITCHELL, M., PRENTICE, J. E., RAMSBOTTOM, W. H. C., SEVASTOPULO, G. D. and WILSON, R. B. 1976. A correlation of Dinantian rocks of the British Isles. Spec. Rep. Geol. Soc. London, No. 7, 87pp.

HARTLEY, J. J. 1945. Notes on the 'Yoredale rocks' of Tyrone. Irish Nat. J., Vol. 8, pp. 255–260.

JOHNSON, G. A. L. 1957. The goniatite Girtyoceras cf. weetsense Moore from the shales above the Jew Limestone, Northumberland. Geol. Mag., Vol. 94, pp. 229–234.

JOHNSON, G. A. L.  1959. The Carboniferous stratigraphy of the Roman Wall District in Western Northumberland. Proc. Yorkshire Geol. Soc., Vol. 32, pp. 83–130.

JOHNSON, G. A. L. 1963. The Geology of Moor House. Monogr. Nat. Conserv.

KELLAWAY, G. A. 1967. The Geological Survey Ashton Park Borehole and its bearing on the geology of the Bristol district. Bull. Geol. Surv. G.B., No. 27,49–154.

MITCHELL, M. 1972. The base of the Visean in south-west and north-west England. Proc. Yorkshire Geol. Soc., Vol. 39, pp. 151–160.

PHILLIPS, J. 1836. Illustrations of the geology of Yorkshire, Part II, The Mountain Limestone district.

RAMSBOTTOM, W. H. C. 1973. Transgressions and Regressions in the Dinantian: A new synthesis of British Dinantian Stratigraphy. Proc. Yorkshire Geol. Soc., Vol. 39, pp. 567–607.

RAMSBOTTOM, W. H. C. and MITCHELL, M. 1969. In Annu. Rep. Inst. Geol. Sci. for 1968, p. 97.

RAYNER, D. H. 1953. The Lower Carboniferous rocks of the north of England: a review. Proc. Yorkshire Geol. Soc., Vol. 28, pp. 231–315.

RAYNER, D. H. and HEMINGWAY, J. E. 1974. The geology and mineral resources of Yorkshire. (Leeds: Yorkshire Geological Society.) 405 pp.

SHORT, K. C. 1954. The Geology of the Pennine Escarpment from Croglin Water to Ardale. PhD thesis, University of Nottingham.

SHOTTON, F. W. 1935. The stratigraphy and tectonics of the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 91, pp. 639–704.

SMITH, E. G., RHYS, G. H. and EDEN, R. A. 1967. Geology of the country around Chesterfield, Matlock and Mansfield. Mem. geol. Surv. G.B.

SMITH, S. 1916. The genus Lonsdaleia and Dibunophyllum rugosum. Q. J. Geol. Soc. London, Vol. 71, pp. 218–272.

SMITH, S.  1928. The Carboniferous coral Nemistium edmondsi, gen. et sp. n. Annu. Mag. Nat. Hist., Ser. 10, Vol. 1, pp. 112–120.

STEVENSON, I. P. and GAUNT, G. D. 1971. Geology of the country around Chapel en le Frith. Mem. Geol. Surv. G.B.

TROTTER, F. M. and HOLLINGWORTH, S. E. 1932. The geology of the Brampton District. Mem. Geol. Surv. G.B.

TURNER, J. S. 1927. The Lower Carboniferous succession in the Westmorland Pennines and the relation of the Pennine and Dent Faults. Proc. Geol. Assoc., Vol. 38, pp. 339–374.

WALLACE, W. 1861. The Laws which regulate the Deposition of Lead Ore in Veins; illustrated by an examination of the geological structure of the mining districts of Alston Moor. (London.)

WELLS, A. J. 1960. Cyclic sedimentation: a review. Geol. Mag., Vol. 97, pp. 389–403.

Chapter 5 Upper Carboniferous

Classification and nomenclature

The names given to the Upper Carboniferous limestones, sandstones and coals in the northern Pennines have been little modified since they were introduced by Forster (1809). In contrast, the classification of these rocks has always been complicated by the lithological differences between them and their time-equivalents in the central Pennines, where the subdivision into 'Millstone Grit' below and 'Coal Measures' above was first established. The differences relate particularly to the 'Millstone Grit' which, together with parts of the underlying limestone sequence in the Lower Carboniferous, is progressively replaced northwards by the distinctive cyclic lithofacies named the Yoredale Series by Phillips (1836) .

Much has been done to resolve the problem. Detailed work on the goniatite faunas in the central Pennines has established the biostratigraphical divisions which form the basis of the modern classification. Thus the Upper Carboniferous or Silesian is now defined as those Carboniferous rocks lying above the base of the Cravenoceras leion Subzone and is subdivided into the Namurian (Millstone Grit) and the Westphalian (Coal Measures) at the base of the Gastrioceras subcrenatum Marine Band.

This classification can be broadly applied to the present district, though its application lacks precision because goniatite faunas are largely absent. Johnson and others (1962) have shown that the base of the C. leion Subzone lies close below the Great Limestone. Their suggestion that the base of the limestone is thus the most suitable horizon at which to take the base of the Namurian in the northern Pennines has found general acceptance and is followed here. The position of the G. subcrenatum Marine Band is less secure for it appears to fall within an unfossiliferous part of the sequence, and may indeed be cut out by unconformity. The base of the Westphalian has consequently been taken at an arbitrary position near the top of these barren measures. The classification adopted and the member nomenclature are shown in (Figure 21) and (Figure 23).

Distribution

Within the district there are three main outcrops of Upper Carboniferous rocks (Figure 22) and (Figure 24). Exposure is good in two of these, namely on the high ground to the north of Hartside Cross and in the area around Cross Fell, which together form the well-documented western part of the Alston Block where some 265 m of the Namurian succession are preserved. Exposure is poor in the third area which covers much of the lye and Petterill valleys in the western part of the district, and which contains both Namurian and Westphalian strata, totalling some 700 m in thickness.

Two further outcrops, both probably of Namurian age, lie in the faulted ground immediately west of the Pennine Fault, at Scarrowmanwick near Croglin, and near Ousby.

Upper Carboniferous rocks probably underlie the Permian and Triassic sediments preserved in the Vale of Eden syncline, but they are unproved in detail. They were penetrated by a borehole (p. 67) sunk long ago at Honeypot, 4 km E of Penrith (Sedgwick, 1836), but the detailed succession is unrecorded.

Lithology

The Upper Carboniferous succession consists of sedimentary cyclothems ranging in thickness from 5 to 45 m. A complete cyclothem begins with a marine limestone, which is succeeded upwards in turn by mudstone, siltstone and sandstone, and finally by a seatearth and coal. Few of the cyclothems are complete, however, whilst the relative thickness of their component members varies throughout the sequence. The lowest part of the succession contains thick limestones—the Great and Little limestones—and in this respect the cyclothems are akin to those of the Alston Group. Calcareous horizons are progressively thinner and rarer in the upper part of the Namurian and absent in the Westphalian. Seatearths, in contrast, become more common upwards. Sandstones are present throughout the Upper Carboniferous succession, but are more abundant in the Namurian.

The Upper Carboniferous sequence of the eastern outcrops is predominantly grey, and includes thin coals, pyritic and carbonaceous shales, and clay-ironstones. In the west, however, the rocks are largely devoid of carbonaceous material and much of the succession is red, with subordinate patches of purple, yellow or green. The limestones are generally dolomitic. Hematite is common both as nodules replacing sphaerosiderite or pyrite, and as a cement, particularly in the sandstones. The red strata are cut by veins of fibrous gypsum up to 5 cm thick.

There is little doubt that most of these characteristics are due to secondary reddening beneath the sub-Permian unconformity. For example, the reddening which occurs in local patches concentrated along joints or faults, or lying oblique to the bedding, is certainly secondary. The depth and intensity of such reddening is variable; it seems to be deepest and most intense close to the present Penrith Sandstone outcrop, and to become shallower and less intense in the south-western part of the district, towards the probable margin of the Penrith Sandstone basin.

Correlation

Goniatites are rare in the Namurian strata, but both the eastern and western outcrops have yielded marine shelly faunas. These provide only a general guide to correlation with other areas, but they suffice to show that the Pendleian (E₁) and Arnsbergian (E₂) stages are present.

Local correlation within outcrops is based largely upon the tracing of persistent members, especially limestones, within particular cyclothems. This is difficult or impracticable in the western outcrops where sections are few. Detailed correlation between the separate outcrops is also largely uncertain, particularly across the 14 km gap between the eastern and western areas where it is dependable only up to the Little Limestone.

The proposed correlations of the major sections are shown in (Figure 21) and (Figure 23). They show that the Millstone Grit is thicker in the north-east than on Cross Fell, and is even thicker in the Barrock Park Borehole. In general, the thicker sequences contain a greater proportion of sandstone.

The C. subcrenatum Marine Band at the base of the Westphalian has not been proved. Its position may lie within the 50 to 100 m of unfossiliferous strata which separate proven Namurian and Westphalian rocks, or it may be jcut out by unconformity, as was claimed (Eastwood and others, 1968) in the adjoining Cockermouth district. The base of the Westphalian in each section has consequently been taken at an arbitrary position in the unfossiliferous measures, generally above thick sandstones and below abundant seatearths.

The Westphalian succession has yielded a fauna of non-. marine bivalves, mostly variants of Anthraconaia pulchella, which in the Lancashire Coalfield occurs in a thin band near the base of the Lower similis-pulchra Zone. There is, however, some doubt about the age significance of this fauna in the Penrith district. The other faunal bands associated with A. pulchella in Lancashire have not been recorded so far north, suggesting that this particular fauna may be unduly controlled by an unusual Westphalian facies. With reservations, therefore, the fauna is assigned to the same horizon as in Lancashire (Calver, 1970). If this is correct the Namurian and Westphalian rocks are separated by an unconformity.

Eastern area

Namurian (Millstone Grit)

In the following section the localities referred to in the text are shown in (Figure 22) and the positions in the sequence of the named lithostratigraphic units are indicated in (Figure 23).

The Great Limestone ranges from 9 to 19 m, being thickest in the extreme south-east. Along most of its outcrop its base lies at the foot of a prominent scarp and is marked by many springs, whilst its top is generally marked by a line of large swallow-holes. Along the scarp the limestone has commonly foundered over the underlying strata, so that it seems to be abnormally thick, and appears to lie too close to the Four Fathom Limestone.

There are few complete sections through the Great Limestone. The best are in disused quarries and stream-sections near Meathaw Hill on the Penrith–Alston road, and in Crowdundle Beck, east of Blencarn. In these the base of the limestone rests sharply on a soft, fine-grained sandstone or on a thin intervening coal. The limestone is blue-grey, nodular, and partly bioclastic, and comprises wavy-bedded posts, each 0.2 to 0.4 m thick, separated by thin partings of dark grey mudstone and quartz-siltstone carrying calcareous shell and crinoid fragments. Recorded fossils include the corals Dibunophyllum bipartitum bipartitum, Koninckophyllum magmficum and Lonsdaleia floriformis laticlavia. In many sections the upper part of the limestone grades upwards into calcareous mudstones. This makes it difficult to be certain that precisely the same horizon has always been taken as the top of the unit. Thus, in the north some sections show limestone posts—the Tumbler Beds of Alston Moor (Dunham, 1948) in the mudstones up to 6 m above the top of the main limestone and the apparent south-easterly thickening may be partly because the equivalents of these beds have here been included within the Great Limestone.

A sequence of some 30 m of mudstones, siltstones, and impersistent sandstones separates the top of the Great Limestone from the base of the Little Limestone, and is best exposed in tributaries of Croglin Water in the north, and in Crowdundle Beck to the south. Some of the mudstones have yielded an abundant fauna including the brachiopods Pleuropugnoides greenleightonensis and Antiquatonia cf. sulcata. Much of the lower part of this interval is in places occupied by the Low Coal Sill, a sandstone which is locally capped by a thin coal. The thin limestone or shelly sandstone at this horizon in some sections is probably equivalent to the Snope Burn Band of the Brampton district (Trotter and Hollingworth, 1932). Elsewhere, however, the Low Coal Sill is very thin or absent. Two further thin sandstones, the High Coal Sill and the White Hazle, both impersistent, occur in the upper part of these strata, the former being unusually thick and coarse-grained on Scarrowmanwick Fell. Thin coals cap either or both of these sandstones, and in places another is present about a metre above the White Hazle and immediately below the Little Limestone. They have been referred to collectively as the Little Limestone Coals, and have been worked locally in the north.

The Little Limestone is present in all known sections. It is only 0.6 to 1.2 m thick in the Cross Fell outlier, but thickens northwards to around 4.5 m in Croglin Water. It consists of posts of blue-grey crinoidal limestone, each typically 0.3 to 0.6 m thick, with partings of dark grey mudstone and quartzsiltstone. The lowest post commonly contains abundant quartz-sand and, more rarely, fragments of coal. Its fauna includes foraminifera, Buxtonia sp.and Rugosochonetes sp.

The first persistent identifiable horizon above the Little Limestone is the Crag Coal. In the Cross Fell outlier, the intervening strata are about 40 m thick and predominantly argillaceous; in the north they thicken to 50 m and contain more sandstones. The lowest of these sandstones, called the Pattinson Sill, is thin and impersistent at Cross Fell and Greencastle (Figure 23), but is up to 18 m thick in the north, though because it is only weakly cemented it seldom produces a topographic feature. The shales above it have yielded several bands of marine fossils including the brachiopod Antiquatonia cf. sulcata. Thin lenticular and commonly siliceous sandstones lie within these shales and give rise to prominent though discontinuous features. At the top of the sequence is the Firestone Sill, a sandstone ranging up to 6 m thick in Croglin Water and at Cross Fell, though thin at Greencastle (Sheet 25; see (Figure 23)) and absent in Coal Cleugh. In the Cross Fell outlier it is generally siliceous and produces a prominent feature; in the north it is locally coarse-grained and contains a scatter of quartz pebbles.

The Crag Coal is recorded in all sections other than those on The Screes at Cross Fell, where exposure is poor. It is only 5 cm thick in Dunfell Hush in the Alston district, but farther north it is locally divided into two or three seams with a combined thickness of 23 to 53 cm. It has been worked from bell-pits near Hartside Height, and has been tried elsewhere.

The overlying Crag Limestone is exposed only in Dunfell Hush and in White Sike, Croglin Water. At both localities it consists of grey-brown argillaceous limestone forming a single post about 0.3 m thick. It contains indeterminate marine fossils at White Sike.

The sequence between the Crag Limestone and the Lower Felltop Limestone thickens northwards from about 50 m near Cross Fell to some 60 m in Croglin Water. As in the underlying strata the thickening is accompanied by an increase in the proportion of sandstone. In the Cross Fell outlier this sequence comprises mudstones and siltstones, with thin lenticular sandstones up to 3 m thick, and these beds which contain marine shells including Tornquistia cf. polita, are regarded as including the equivalents of both the Knucton and the Rookhope shell beds of Alston Moor (Dunham, 1948). To the north, the Low Slate Sill, which consists of thickly cross-bedded sandstone with a shelly top, is up to 12 m thick in Croglin Water, where it forms a prominent feature and where, because of erosion at the base, it has apparently cut out most of the strata equivalent to the Knucton Shell Beds. The High Slate Sill is a more extensive sandstone with its top at about 45 m above the Crag Coal. It is thickest (14 m) in the north, in Knar Burn, where it is thickly bedded, locally coarse-grained, and has an erosive base. In Croglin Water and in parts of Gilderdale its upper part is richly shelly and in places passes into limestone. This horizon is probably equivalent to part of the Rookhope Shell Beds, and in the adjacent Brampton district it appears to be the bed referred to as the Lower Oakwood Limestone (Trotter and Hollingworth, 1932). About 15 m of mostly argillaceous strata separate the High Slate Sill from the Lower Felltop Limestone, with a thickly bedded sandstone up to 4 m thick lying close beneath the limestone in most sections.

The Lower Felltop Limestone is present in all sections, thickening from about 0.5 m at The Screes, to about 1.5 m in Croglin Water. Where fresh it comprises one or two posts of dark blue-grey limestone with scattered brachiopods, trilobites and crinoid fragments. The base of the limestone has been taken tentatively as the junction between the Pendleian (E₁) and Arnsbergian (E₂) stages.

The overlying strata are poorly exposed, except for scattered sandstone crags. Only on The Screes and in White Sike are there good sections. The succession appears to be a little thicker in the south.

For some 20 m above the Lower Felltop Limestone the strata are mostly argillaceous and yield marine shells near their base. The mudstones contain thin lenses of shelly sandstone which are regarded as the likely equivalents of the Coalcleugh Transgression Beds of Alston Moor (Dunham, 1948), while in Croglin Water and on Grey Nag one or two thicker, locally siliceous, sandstones occur. At Lawyer's Cross and at Greencastle (Figure 23) these strata are capped by a thin grey muddy limestone with scattered crinoid frag ments, while at Daffenside Beacon at the southern end of Black Fell, a coal, probably the Coalcleugh Coal, lies at either the same horizon or a slightly lower one.

Above these mudstones and between 25 to 30 m above the Lower Felltop Limestone lies the Dun Fell Sandstone, a thickly bedded or massive siliceous medium-grained sandstone (Johnson, 1963). On Cross Fell this sandstone is 18 m thick and forms the principal feature around the summit plateau. It thins northwards, but even so produces fine features such as Daffenside Beacon, Watch Hill, and the summit of Grey Nag. On Cross Fell some 15 m of strata are preserved above the Dun Fell Sandstone on the summit plateau; they are poorly exposed, but appear to be argillaceous in their lower part and include the Upper Felltop Limestone, with a thinly bedded sandstone—the Cross Fell

Sandstone of the primary survey above. In the north-eastern crop the Upper Felltop Limestone comprises a single post of blue-grey muddy limestone 0.5 to 0.9 m thick. It closely overlies the Dun Fell Sandstone, although a thin coal intervenes in Croglin Water. About 16 m of mostly argillaceous strata separate the Upper Felltop Limestone from an overlying massive coarse-grained and pebbly sandstone about 11 m thick referred to in the Brampton district (Trotter and Hollingworth, 1932) as the Wolf Crag Grit, and possibly the equivalent of the Cross Fell Sandstone. At least 50 m of strata including sandstones, shales and a thin coal, here termed the Farlam Currick Coal, are poorly exposed above the Wolf Crag Grit on the watershed between Broad Mea and Tom Smith's Stone.

Details

Croglin Water

There are many small sections of the strata from the Great Limestone to the Little Limestone both in Croglin Water [NY 6156 4760] to [NY 6412 4599], and in several of its tributaries. Although there is no continuous section, the Great Limestone appears to be about 12 m thick. The best individual exposure is in a river cliff [NY 6322 4661] where 8.5 m of blue-grey wavy bedded limestone rest on sandstone. The top of the limestone is visible in Kiln Beck [NY 6300 4707], a northern tributary, where 2.1 m of thickly-bedded limestone with argillaceous partings are overlain by 2.8 m of dark grey mudstone. Caudagalli are abundant on the upper surfaces of the individual limestone beds.

The beds beneath the Lower Coal Sill crop out in Weasel Beck [NY 6309 4704], another northern tributary, where the sequence is:

The thin fossiliferous limestone noted is one of the Tumbler Beds (p. 54).

The Low Coal Sill is generally thin or absent in Croglin Water. In a particularly good section in Lunchy Beck [NY 6054 4866], a northern tributary just within the Brampton district (Appendix 1: p.157), it is only 0.15 m thick; whilst in Kiln Beck [NY 6194 4770] it comprises 1.2 m of calcareous sandstone.

In most sections this horizon is overlain by a thin limestone, probably the equivalent of the Snope Burn Band (Trotter and Hollingworth, 1932). In Stockdale Beck [NY 6194 4770], near Lawyer's Cross, 0.6 m of limestone directly overlie the Low Coal Sill, whilst in Croglin Water [NY 6257 4707] a 0.75-m limestone rests on mudstone. This mudstone yielded Buxtonia sp., Echinochonchus?, Pleuropugnoides sp., Productus sp.and Rugosochonetes sp., while the limestone contained ammodiscoids, archaediscoids, endothyroids, textularioids, indet. solitary clisiophylloid, indet. zaphrentoid, Syringopora cf. ramulosa, bryozoa fragments, Lingula sp., trilobite pygidium, and echinoid spines.

The High Coal Sill is more than 4 m thick in Croglin Water [NY 6346 4637] to [NY 6400 4615], and thickens on Scarrowmanwick Fell [NY 6030 4715] to at least 12 m of coarse-grained sandstone in massive or thick, cross-bedded units. This abnormal thickness appears to infill an individual distributary channel. The sandstone is only 2.4 m thick in Lunchy Beck [NY 6056 4874] and is absent in Kiln Beck.

The Little Limestone Coals are extremely variable in their development. In Lunchy Beck 0.3 m of coal overlies the High Coal Sill, and in Kiln Beck [NY 6304 4713] three coals are exposed in the following section: limestone (Little Limestone); on coal, 0.15 m; siltstone and sandstone with roots, 1.70 m: coal, 0.49 m sandstone, thickly bedded, medium-grained with siltstone partings (White Hazle), 1.20 m; mudstone, partly silty, 2.75 m; coal, 0.33 m; siltstone, passing rapidly downwards into mudstone, 6.0 m. The aggregate thickness of 0.97 m of coal in these three leaves is the maximum recorded for these coals in the district. They have been worked from bell-pits or levels on Scarrowmanwick Fell [NY 6047 4686] to [NY 6146 4715], and on the northern side of Croglin Water [NY 625 472] near the outflow of Kiln Beck.

Strata between the Little and Lower Felltop limestones are well exposed in the Croglin Water catchment, where they are about 110 m thick. The most complete sections are in the tributary streams of Lunchy Beck, Stockdale Beck and Coom Gill (Figure 22), as given in Appendix 1.

The thickest record of the Little Limestone is 4.57 m, from a southern tributary [NY 6207 4718] of Croglin Water, north-west of Watch Hill, while the limestone is at least 3.66 m and 4.42 m thick respectively in Stockdale Beck [NY 6210 4789] and Kiln Beck [NY 6305 4714]. At the latter locality the limestone forms flat-bedded posts 0.3 to 0.6 m thick with argillaceous partings. The basal post is sandy and contains fragments of coal. The limestone yielded the following fauna: archaediscoids, endothyroids, Glomospira sp., tetrataxioids, texularioids, Dibunophyllum?, Avonia cf. youngiana, Buxtonia sp., gigantoproductoids, orthotetoid, rhynchonelloid, Rugosochonetes sp. celticus group, smooth spiriferoids, Spirifer cf. bisulcatus, indet. bivalves. Crinoid fragments occur in some posts, and Caudagalli are abundant.

The Pattinson Sill is thick in all sections. In Lunchy Beck, [NY 6056 4878], just within the Brampton district, about 15 m of mainly soft, thickly and thinly bedded sandstone are separated from the underlying Little Limestone by 5.5 m of argillaceous strata, and farther east, in Kiln Beck [NY 6305 4714], the Pattinson Sill comprises two sandstones, 11.2 and 4.3 m thick, separated by 3 m of siltstone, the lower bed being separated from the Little Limestone by only 2 m of argillaceous strata. At this locality, the sandstones are mostly thickly cross-bedded, medium-grained, and generally poorly cemented, the lower leaf showing a distinctive spheroidal weathering pattern. In Stockdale Beck [NY 6220 4783], the Pattinson Sill is a single sandstone 18.3 m thick, and separated from the Little Limestone by about 3 m of argillaceous strata. It is thickly bedded and rather poorly cemented, and bears traces of Caudagalli at its top. A thin shaly sandstone is developed immediately above the Pattinson Sill in Croglin Water [NY 6420 4582], south-west of Tom Smith's Stone.

The succeeding strata up to the Crag Coal are predominantly argillaceous and rich in marine shells, although several sandstones up to 6 m thick occur in some sections. One of the best exposures is in Stockdale Beck [NY 6243 4828], where three such sandstones occur (Appendix 1; p. 160). The lowest is correlated with the White Sill of the Brampton district (Trotter and Hollingworth, 1932), whilst the uppermost (5.5 m thick), which is carbonaceous at its top and immediately underlies the Crag Coal, is equivalent to the Firestone Sill of Alston Moor (Dunham, 1948). In Coom Gill [NY 6312 4622] about 2 km to the south-cast (Appendix 1; p. 148), a thin sandstone 4.5 m below the Crag Coal yielded Antiquatonia cf. sulcata, Buxtonia?, Pleuropugnoides sp., Productus sp., Rugosochonetes sp., Schellwienella sp., smooth spiriferoids, ?Spirifer trigonalis, Aviculopecten sp.About 1 km to the west-north-west, in another southern tributary [NY 6197 4679], the lower part of the Firestone Sill is coarse-grained and pebbly. The section is: coal debris (Crag Coal); on sandstone, soft, with roots, 2.5 m; sandstone (Firestone Sill), massive, coarse-grained with quartz-pebbles, siliceous, 3.6 m; mudstone and siltstone, 15.0 m.

The Crag Coal ranges in thickness from 15 cm in a gully [NY 6097 4702] on Scarrowmanwick Fell to almost 40 cm in a northern tributary [NY 6427 4631], west-south-west of Tom Smith's Stone, where it forms three seams in the following section: mudstone and siltstone, pale grey, with rootlets, 0.9 m; coal, 0.045 m; siltstone, pale grey, with roots, 0.38 m; coal, 0.15 m; dirt, 0.075 m; coal, 0.19 m; sandstone and siltstone with roots, 0.6 m; sandstone, siliceous (Firestone Sill).

The only exposure of the Crag Limestone is in White Sike [NY 6243 4828], west of Lawyer's Cross, where the sequence is: sandstone (Low Slate Sill); on mudstone with marine fossils at base, 11.6 m; unexposed, 1.50 m; limestone, grey-brown, argillaceous (Crag Limestone), 0.30 m; siltstone, carbonaceous, with coaly layers, 0.38 m; coal, bright (Crag Coal), 0.23 m.

In the succeeding strata up to the Lower Felltop Limestone, both the Low and High Slate sills are prominent, the former giving rise to a particularly good topographic feature throughout the area. Both sandstones are well exposed in Coom Gill [NY 6312 4620], east-north-east of Watch Hill (Appendix 1; p. 148) where the Low Slate Sill consists of 12 m of fine- to medium-grained sandstone in thick and massive cross-bedded units, separated from the High Slate Sill (at least 4.5 m thick) by about 14 m of predominantly argillaceous strata with thin richly-shelly sandstone bands that have yielded Productus sp., Spirifer bisulcatus, Mourlonia sp., Retispira sp.and Schizodus?. In White Sike [NY 6246 4840] the Low Slate Sill is cut out by faulting. This also cuts out the base of the High Slate Sill, though at least 6 m of thickly bedded sandstone are present, overlain by 3 m of very sandy, partly decalcified limestone containing marine shells and crinoid fragments (see Appendix 1: p. 161). The High Slate Sill is shelly and calcareous in its upper part in Kiln Beck [NY 6331 4730] about 1.5 km to the south-east, where the sequence is: sandstone, calcareous (partly decalcified), richly fossiliferous, 3.0 m; on sandstone, thickly bedded but flaggy at base, 2.5 m; siltstone and silty mudstone with bands of sandstone, 2.75 m; sandstone, thickly cross-bedded, flaggy at base, 4.0 m; mudstone and siltstone, 9.0 m. Strata above the High Slate Sill are well exposed only in White Sike [NY 6246 4840, (Appendix 1; p.161), in which 4 m of rather poorly cemented sandstone in thick cross-bedded units immediately underlie the Lower Felltop Limestone.

The outcrop of the Lower Felltop Limestone can be traced on a hillside [NY 6201 4850] west of Lawyer's Cross, where its top is marked by a line of small swallow-holes. In White Sike the limestone yielded: ammodiscoids, archaediscoids, Earlandia sp., endothyroids, textularioids, Fenestella sp., stick bryozoa, Echinoconchus?, Gigantoproductus sp., Latiproductus latissimus, orthotetoid, rhynchonelloid, Rugosochonetes sp., smooth spiriferoids, indet. turreted gastropod, trilobite fragment and ostracods. A ferruginous decalcified band 2.74 m above the limestone yielded a profuse fauna including: Chaetetella depressa, stick bryozoa, Alitaria panderi, Buxtonia sp., Eomarginifera sp., Pleuropugnoides sp., Rugosochonetes sp., smooth spiriferoids, Knightella ?, pleurotomarian with spiral ornament, indet. turreted gastropod, Nuculopsis gibbosa and Catastroboceras sp.

The strata above the Lower Felltop Limestone are up to about 75 m thick and crop out extensively on the higher ground. The most complete section is in White Sike [NY 6245 4838] to [NY 6263 4868] (Appendix 1; p.161). Two sandstones equivalent to those close above the Lower Felltop Limestone in White Sike cap Thack Moor [NY 612 463], nearly 3 km to the south-west. The upper sandstone crops out [NY 6270 4837] at Lawyer's Cross, and is overlain by a thin muddy crinoidal limestone, fragments of which are common in the soil, and which yielded the following fauna: archaediscoids, endothyroids, tetrataxioids, textularioids, Alitaria panderi, Avonia . sp.[juv.], Rugosochonetes sp., smooth spiriferoid and indet. gastropod. In White Sike the limestone is altered to 1.2 m of ferruginous famp.

The Dun Fell Sandstone forms prominent scarps where it crops out on hill-spurs and on watersheds, for example in an outlier at Watch Hill [NY 624 460], where the feature suggests that the sandstone is about 9 m thick. In White Sike [NY 6255 4859] the uppermost part of the sandstone yielded: Alitaria panderi, indet. chonetoid, Dielasma sp., Eomarginifera sp., Productus sp., Punctospirifer sp., smooth spiriferoids, gastropods including bellerophontoids, Aviculopecten sp., Edmondia sp., Leiopteria sp., Myalina verneuili, Sanguinolites sp.and Schizodus axiniformis.

The Upper Felltop Limestone is poorly exposed [NY 6485 4466] in the head-waters of Croglin Water, north-north-east of Black Fell, where it is largely famp. It is overlain by 4.5 m of mudstone with an abundant marine fauna including: Fenestella sp., Thamniscus sp., stick bryozoa, Serpula sp., Echinoconchus sp., orthotetoids, Plicochonetes sp., Punctospirifer sp., Pustula?, smooth spiriferoids, Spirifer sp., pleurotomarian fragment, ?Edmondia sulcata, Streblochondria jacksoni, 'Coelonautilus'sp., Weberides sp.and ostracods.

A limestone, believed to be the Upper Felltop is exposed on the hillside [NY 6143 4884] about 2 km WNW of Lawyer's Cross, just within the Brampton district, where it consists of 0.6 m of dark blue-grey limestone overlain by mudstone. The Wolf Crag Grit forms a strong feature on the watershed at Farlam Currick [NY 6362 4779] and consists of massive coarse-grained and pebbly sandstone. About 450 m N of Farlam Currick, abundant coal debris (Farlam Currick Coal) rests on rooty sandstone in a small scar [NY 6355 4824] on the watershed, at a horizon about 15 m above the top of the Wolf Crag Grit. In a crag about 140 m to the south-east another coarse-grained cross-bedded sandstone, ganisteroid at the top, lies 7 to 15 m above the coal.

A partly reddened succession of coarse-grained, pebbly and plant-rich sandstones, siltstones, mudstones with marine shells and thin coals is exposed in the bed and banks of Croglin Water [NY 5809 4731] to [NY 5838 4745], near Scarrowmanwick. The fauna includes: costate spiriferoids, Orbiculoidea sp., Productus sp., indet. gastropods and Catastroboceras sp.Although none of these forms is diagnostic, these strata are believed to be Namurian in age.

Raven Beck–Loo Gill

The Great Limestone forms a prominent feature along much of the escarpment between Croglin Water and Hartside Height. It is nowhere completely exposed, but its thickness is estimated between 10.6 and 12.2 m. The best sections are in a tributary [NY 6337 4488] of Raven Beck where at least 9.25 m of limestone overlie sandstone of the Tuft.

Exposures of the overlying strata are also generally poor. Although the High Coal Sill seems to be thin and impersistent, the features show that the Low Coal Sill occurs throughout much of the area. It has been dug in a disused quarry [NY 6451 4243], north of Hartside Cross, where 6.7 m of sandstone are exposed, mostly thinly bedded except at the base. In a tributary [NY 6356 4470] of Raven Beck it is overlain by a thin coal. At least one of the Little Limestone Coals has been extensively worked by adits and shafts on Renwick Fell, between the south-western slopes of Thack Moor [NY 6076 4600] and Great Stockdale Beck [NY 6237 4510], (Figure 22), where the crops are repeated by strike-faulting. The precise horizon of the worked coal is uncertain, although a poor section in an adit [NY 6187 4495] suggests that it lies directly beneath the White Hazle. Another thin coal immediately underlies the Little Limestone in Great Stockdale Beck [NY 6232 4543]. A coal at about this same horizon has been worked extensively in faulted ground around the headwaters of Loo Gill [NY 6430 4348] to [NY 6490 4279].

The Little Limestone is at least 2.13 m thick in Great Stockdale Beck [NY 6231 4545] where it consists of thickly flat-bedded limestone. The hillside immediately west of this locality is one of only two places along the northern outcrop where the overlying Pattinson Sill forms a prominent feature, the height of which suggests a thickness of 6 to 9 m of sandstone; the other place [NY 6485 4227] in this area lies north-north-east of Hartside Cross.

Traces of coal, presumably the Crag Coal, have been detected on the hillside [NY 6264 4570] south of Watch Hill, and trial shafts and adits [NY 6436 4433] immediately west of the principal scarp of Black Fell proved coal, though apparently not of workable thickness.

The Low Slate Sill forms a prominent feature along the escarpment from Scarrowmanwick Fell as far as the col between Watch Hill and Black Fell, and also at the northern end of Black Fell, but the feature dies out southwards.

Both the High Slate Sill and the sandstone directly beneath the Lower Felltop Limestone produce prominent features around the summit of Thack Moor, eastwards to Watch Hill, and also on Black Fell where they form much of the steep west-facing scarp. The Lower Felltop Limestone has not been seen in this area, although a limestone at about this horizon was recorded on the southern end of Black Fell during the primary survey.

Knar Burn, Thornhope Burn, Gilderdale and Rowgill

The Great Limestone is exposed in Thornhope Burn [NY 6774 4850] where its crop is repeated by faulting, and also in heavily faulted ground at the head of Knar Burn [NY 6505 4783], where it yielded the following fauna: Dibunophyllum bipartitum bipartitum, Koninckophyllum magnificum, Lonsdaleia floriformis laticlavia, indet. bryozoa, Avonia cf. youngiana, Buxtonia sp., Dielasma sp., Latiproductus latissimus and smooth spiriferoids. It is sporadically exposed throughout its outcrop in the Gilderdale Burn catchment and near the Penrith–Alston road, forming a strong scarp [NY 689 433] about 1 km ESE of Scarberry Hill, where its thickness is estimated to be at least 12 m, though locally as on the south-east side of Horse Edge, its outcrop has no topographic expression. On the north-west side of Horse Edge [NY 685 451] and in a faulted outlier [NY 664 453] north of Gilderdale Burn, the limestone has foundered over underlying strata so that it appears to be unusually thick, and to crop out abnormally close to the Four Fathom Limestone. The best exposures are in a disused quarry [NY 6898 4346] 500 m NE of Hartside House, where 12 m of limestone in massive and thick, wavy bedded posts rest on the Tuft. The lowest 8 m of limestone yielded: Dibunophyllum bipartitum bipartitum, Fasciculophyllum sp., Alitaria panderi, Avonia youngiana, sp., Pugnax pugnus, smooth spiriferoids, Spirifer sp., Naticopsis globosa and trilobite fragments. The upper 4 m yielded: calcispheres, ammodiscoids, endothyroids, tetrataxioids, Palaeosmilia?, indet. cryptostome bryozoa, costate spiriferoids and a chonetoid. Other good exposures occur in a disused quarry at Meathaw Hill [NY 6791 4249], where 10.6 m of limestone overlie the Tuft; and in the headwaters of Rowgill Burn [NY 6585 4225] where 11.6 m of limestone occur between the Tuft and the overlying mudstone. The uppermost parts of the Great Limestone, here containing dark grey mudstone and siltstone partings, are well exposed in the headwaters of Gilderdale Burn [NY 6610 4413] and in inliers [NY 6620 4395] in the core of a north-east facing monocline.

The Low Coal Sill is persistent throughout the area, and around the head of Gilderdale Burn locally exceeds 12 m in thickness. The sequence in a tributary stream [NY 6621 4392] is:

The Low Coal Sill is also exposed in swallow-holes along the southern flanks of Grey Nag, and on Whitley Common [NY 6789 4721] where the section is:

The Snope Burn Band is exposed [NY 6764 4835] in a tributary of Thornhope Burn (Figure 22), where 0.6 m of limestone overlie 1.8 m of dark grey mudstone. A similar thickness of limestone is also exposed [NY 6493 4765] in a tributary of Knar Burn.

Around the head of Knar Burn the High Coal Sill comprises 3 to 6 m of sandstone. The section in Wolf Cleugh [NY 6549 4759] is:

A coal seam 0.36 m thick at about this horizon is exposed [NY 6571 4845] north-west of Grey Nag, and also [NY 6505 4751] in a southern tributary of Knar Burn. The Little Limestone coals have been worked on the south-eastern flank of Great Heaplaw [NY 6897 4867] within about 3 m of the base of the Little Limestone. Their outcrops have been traced locally in the headwaters of Gilderdale Burn [NY 6617 4422] where coal fragments are particularly common in the head. Along the Penrith–Alston road, coal has been worked along much of the outcrops mostly from adits. The worked horizon again appears to be close under the Little Limestone, and in a section [NY 6579 4230] 1.2 km E of Hartside Cross the coals lie in a 1.2-m interval between the Little Limestone and an underlying sandstone.

Much of the sequence from the Little Limestone to the Lower Felltop Limestone is well exposed, particularly in the headwaters of Gilderdale and Woldgill burns. The Little Limestone comprises at least 3 m of thickly flat-bedded blue-grey limestone in a tributary of Rowgill Burn [NY 6579 4230]. Over much of the area the feature of the thick Pattinson Sill is inconspicuous apparently due to poor cementation. In a tributary [NY 6505 4738] about 1.5 km W of Grey Nag, the Pattinson Sill comprises at least 9 m of poorly cemented sandstone, mostly in thick, cross-bedded posts. Marine shells occur at its top. Between the Pattinson Sill and the Crag Coal, sandstones are generally thin and impersistent throughout the area. Around Grey Nag, the features suggest that three or four such beds are present, but around Benty Hill and Scarberry Hill only one feature-forming sandstone occurs, lying about 9 m beneath the Crag Coal.

The Crag Coal is exposed in the following section in Coal Cleugh [NY 6544 4317] north-east of Hartside Height, where the Firestone Sill is absent:

There are several other good exposures of the coal in adjacent tributaries e.g. [NY 6558 4367] and [NY 6553 4420] where it ranges from 0.23 to 0.53 m thick, and forms one or two seams. It is also exposed [NY 6597 4545] in a tributary of Woldgill Burn where 0.28 m of coal rest on rooty siltstone. The coal has been worked extensively from shafts and bell-pits in the headwaters [NY 652 431] of Gilderdale Burn.

Strata up to about 20 m above the Crag Coal are well exposed in Coal Cleugh [NY 6534 4315], where the section is:

This is the only locality where the Crag Coal is known to have a sandstone roof, although in a section [NY 6557 4366] 0.5 km to the north, the base of a 4.5 m sandstone lies only 2.5 m above the seam.

The Low Slate Sill thickens southwards towards Hartside Height where it is thickly bedded and siliceous, giving a good feature, while eastwards on Benty Hill and Scarberry Hill it appears to be thin. In Daffenside Cleugh [NY 6545 4420], south-east of Black Fell (Appendix 1: p. 151), the Low Slate Sill is in two bands, the upper 3.7 m and the lower 2.7 m thick, separated by 4 m of mudstone and siltstone.

The High Slate Sill is prominent throughout the area and forms marked features on Grey Nag and Benty Hill. It is thickest in a tributary [NY 6489 4777] of Knar Burn, about 1.5 km W of Grey Nag, where about 14 m of cross-bedded sandstone, including a siltstone layer, occur about 14 m below the Lower Felltop Limestone. In a tributary [NY 6560 4554] of Woldgill Burn, the High Slate Sill consists of 9 m of massive, coarse-grained, feldspathic sandstone while in Daffenside Cleugh [NY 6545 4420], 10 m of cross-bedded sandstone are overlain by 1.2 m of very sandy limestone rich in marine fossils including Buxtonia sp., Eomarginifera sp., Ovatia?, indet. gastropods, Leiopteria?, Schizodus sp.and Sulcatopinna?.

In the last mentioned section, the succeeding strata up to the Lower Felltop Limestone are well exposed. They are 12 m thick, including 4.5 m of thickly bedded sandstone lying immediately beneath the limestone. A thickly bedded siliceous sandstone, also underlying the Lower Felltop Limestone, crops out near the summit of Grey Nag and Benty Hill, while in a tributary [NY 6560 4554] of Woldgill Burn 3 m of fine-grained sandstone with marine fossils occur 12 m above the High Slate Sill. In a tributary [NY 6474 4762] of Knar Burn about 1.5 km W of Grey Nag the sequence beneath the Lower Felltop Limestone is: limestone (Lower Felltop), on mudstone, coaly with rootlets, 0.6 m; gap 1.5 m; sandstone 2.4 m.

The Lower Felltop Limestone crops out on a shelf [NY 6650 4797] north-north-east of the summit of Grey Nag, where debris of grey crinoidal limestone is present in the soil. It is also exposed [NY 6516 4412] at the head of Daffenside Cleugh where its outcrop is marked by small swallow-holes. It consists of 0.9 m of limestone, blue-grey when fresh but largely famped, resting directly on a sandstone, and overlain by 5 m of silty mudstone which passes upwards into siltstone. A bed of blue-grey limestone 0.45 m thick, believed to be the Lower Felltop Limestone, crops out [NY 6472 4761] in a tributary of Knar Burn north-north-west of Tom Smith's Stone. It yielded the coral Aulophyllum fungites.

Two thick and siliceous sandstones are preserved on Grey Nag above the limestone; the lower, about 6 m thick, is equivalent to the Coalcleugh Transgression Beds of Alston Moor (Dunham, 1948) whilst the upper, 7 to 8 m thick with a rooty top, correlates with the Dun Fell Sandstone. The lower sandstone is also present on the summit of Benty Hill and, though much thinner, in a gully [NY 6489 4391] some 2 km to the west-north-west, where it is overlain by an unusually thick Coalcleugh Coal as follows: coal, 0.45 m; on mudstone with rootlets, 0.15 m; siltstone, carbonaceous, 0.16 m; fireclay, 0.07 m; sandstone, fine-grained, very siliceous, 0.9 m; mudstone, 4.5 m. The Dun Fell Sandstone is prominent at Daffenside Beacon [NY 648 437], where it gives a 12 to 14 m feature, with its top lying about 30 m above the Coalcleugh Coal.

A higher limestone exposed in a tributary of Knar Burn [NY 6461 4729] is probably the Upper Felltop Limestone from its relation to the Wolf Crag Grit cropping out nearby. It consists of a 0.45-m post of blue-grey limestone yielding costate spiriferoids, indet. chonetoids, orthotetoids, productoids, Rhipidomella michelini and a ?rhynchonelloid.

The Wolf Crag Grit, a cross-bedded, coarse-grained and partly pebbly, feldspathic sandstone, is exposed in an adjacent tributary [NY 6455 4743], on the Dod e.g. [NY 6543 4511], and as debris on a shelf [NY 651 463] near Woldgill Tarn. The youngest Namurian strata in the area are preserved both at Tom Smith's Stone [NY 652 465], where they include a medium- to coarse-grained siliceous sandstone about 70 m above the Lower Felltop Limestone, and also in a tributary [NY 6449 4751] of Knar Burn where traces of coal, thought to be at the same horizon as that present near Farlam Currick (Figure 23), occur as a solifluxion streak. RSA

Cross Fell

The Great Limestone is best exposed in Crowdundle Beck, just within the Alston district (see Appendix 1; p.150), where it consists of 18 m of blue-grey limestone lying directly on the Tuft. Johnson (1963, p. 50) records three persistent biostromes in the Great Limestone at this locality. The lowest is the Chaetetes Band, normally characterised by abundant compound corals, but a detailed search during the resurvey yielded only a limited brachiopod fauna from a 15-cm band 0.9 m above the base of the limestone. The Brunton Bang, containing calcareous algae, notably Calcifolium bruntonense, lies about 5.2 in above the limestone base in this area. Finally, the Frosterley Band, with brachiopods and simple corals occurs here as two separate posts of dark grey limestone, 0.3 and 0.6 m thick, lying 11.3 and 12.2 m respectively above the limestone base. Northwards from Crowdundle Beck, the Great Limestone forms a good feature, partly mantled by head, across the western slopes of Cross Fell to Green Fell, where the limestone crops out in a prominent scar [NY 6674 3610] in which the Frosterly Band is exposed. Eastwards from Green Fell, the scarp continues through Raehow End [NY 679 366], where the estimated thickness of the limestone is some 15 m. Close to the south [NY 680 362] the outcrop is much disturbed by foundering over the underlying strata. The scarp is inconspicuous in the headwaters of Ardale Beck [NY 669 358], where the limestone has been partly replaced by a limonite 'flat' adjacent to the Ardale Head Vein (p.131).

Exposures above the Great Limestone are largely confined to limited sections in scattered swallow-holes along its top, except at Green Fell and Raehow End where two sandstones, regarded as the High and Low Coal sills, form good features. The lower sandstone is massive with a rooty top, and is extensively exposed on cambered pavements. To the south of the district good sections through these beds in Middle Tongue Beck, Silverband Mine, and Dun Fell Hush have been recorded by Dunham (1948) and Johnson (1963).

The Little Limestone has an extensive outcrop [NY 677 359] on Skirwith Fell, south of Raehow End, where it is poorly exposed in many swallow-holes. A section [NY 6963 3353] in a northern tributary of Crowdundle Beck (within the Alston district, Sheet 25) comprises at least 0.76 m of dark grey crinoidal limestone. On the southern bank of the stream at this locality 1.8 m of thinly bedded sandstone with fucoid markings lie about 1.5 m above the limestone while, about 1 km S of Raehow End, a thickly bedded siliceous sandstone with a pitted top forms a prominent rock-pavement about 6 m above the Little Limestone. These sandstones are probably impersistent equivalents of the lower part of the Pattinson Sill. Exposures higher in the succession are rare, although the sequence seems almost entirely argillaceous up to the Firestone Sill, a siliceous, thickly bedded sandstone traceable around most of the Cross Fell outlier. In the lower part of this sequence about 9 m of shales are exposed in a gully [NY 6966 3359] near the Little Limestone outcrop in Crowdundle Beck. Immediately below the Firestone Sill some 9 m of mudstone crop out about 1 km NW of Cross Fell [NY 6869 3513]. The Firestone Sill at this latter locality is 3 to 6 m thick and is a cross-bedded sandstone, forming an extensive rock-pavement. It is 4.5 m thick in Crowdundle Beck [NY 699 337]. Neither the Crag Coal nor the Crag Limestone is exposed in that part of the Cross Fell outlier lying within the district, but both are recorded (Johnson, 1963) closely above the Firestone Sill at Dun Fell Hush in the Alston district to the east, and the Crag Limestone also outcrops in Middle Tongue Beck in this same general area.

All but the lowest part of the 45 m of strata between the Crag Coal and the Lower Felltop Limestone was completely exposed on the Screes [NY 690 349] north of Cross Fell summit during the resurvey, by 'hushing'—that is, by the repeated flushing of gullies by dammed water. The sequence proved is given in Appendix 1 (p. 150) from which it can be seen that the sandstones are generally very thin and difficult to correlate with those farther north. Marine shells are common at intervals throughout the sequence, suggesting a broad correlation with the Knucton and Rookhope Shell beds, and the following fauna was obtained: ?bryozoa; worm tubes; Avonia?, Buxtonia?, Eomarginifera lobata; Productus sp., rhynchonelloid frag., Rugosochonetes sp., celticus group, Rugosochonetes sp.[wide], Schellwienella sp., smooth spiriferoids, Spirifer sp., Tornquistia cf. polita, pleurotomarians with spiral ornament, Straparollus (Euomphalus) sp., coiled quadrate nautiloid fragments, orthocone nautiloids and Weberides?

Most of the overlying strata between the base of the Lower Fell-top Limestone and the top of the Dun Fell Sandstone was also exposed here by hushing. The sequence is summarised in Appendix 1 (p. 150) and the section yielded; carbonaceous plant remains; chonetoids, orthotetoids including Schellwienella sp., Productus sp., rhynchonelloids, Spirifer bisulcatus, Posidonia corrugata, Posidoniella cf. variabilis, ostracods, and an echinoid plate.

The Dun Fell Sandstone is at its thickest—about 18 m here on Cross Fell, where it is a thickly bedded and massive, mostly medium-grained sandstone, which is siliceous and rooty at its top. On the summit it is capped by about a further 15 m of strata. Of these, the uppermost 9 m or so consist of thinly-bedded, medium-grained sandstone, termed the Cross Fell Sandstone on the Old Series One Inch Geological Map. There is no clean section in this sandstone, but its debris is visible in a cluster of shallow pits and heaps [NY 6874 3455] immediately north of the summit cairn. Johnson (1963) interpreted these pits as swallow-holes into the Upper Felltop Limestone, but excavations suggest they are old diggings for flags. By comparison with sections farther north and east the Dun Fell Sandstone is thought to lie close below the Upper Felltop Limestone.AJW, RSA

Ousby

The heavily faulted and badly exposed tract of Carboniferous rocks close to the east of Ousby is difficult to place within the established sequence though palynology has shown that Namurian rocks are present.

In the fault-block which includes Fellside, solid rocks are seen only in a short stream-section [NY 6341 3512] to [NY 6342 3513] south of Fellside, where 3 m of purple fine-grained sandstone overlie 2 m of grey, silty mudstone containing plant debris and ?Lingula, and in scattered exposures of purple-grey silty mudstone and fine-grained sandstone cropping out in Ashlock Sike [NY 6371 3479] to [NY 6378 3476]. Spoil debris from a small digging for coal [NY 6390 3511] near Fellside and a shallow pit nearbyi [NY 6366 3510] were both tested for spores. Dr B. Owens reports that the organic residue recovered from the former sample (SAL 553) is dominated by fragmentary wood. The principal element amongst the miospores is Lycospora pusilla which accounts for more than 70 per cent of the total population. Of the other spores in the assemblage only two are of stratigraphic significance. Crassispora kosankei is present in very small numbers, which may indicate a Namurian A age since this species does not become plentiful until the base of R₁. The presence of Microreticulatisporites punctatus is of interest as this species is a common component of Namurian A (E_1–E₂) assemblages in the Midland Valley of Scotland and the Stainmore Outlier. On the basis of the limited evidence from this restricted microflora, a Namurian A (E₁–E₂) age is suggested.

The second sample (SAL 554) from debris from the shallow pit nearbyThe following note, recorded on an old field-map by J. G. Goodchild in the IGS archives, refers to this locality: 'shaft for coal said to have been down to two thick seams too much crushed to work'.  [NY 6366 3510] also yields an organic residue consisting mainly of fragmentary wood. The miospore population is again dominated by representatives of Lycospora pusilla. Only two of the remaining components in the assemblage are noteworthy. Microreticulatisporites punctatus which is present in the previous sample and M. microreticulatus which, although recorded in both E₁ and E₂ deposits in the Midland Valley of Scotland, is found to be restricted to E₂ deposits in the Stainmore Outlier (Owens and Burgess, 1965). A Namurian A (possibly E₂) age is suggested for this sample. In the absence of other evidence, all the beds in this fault-block are tentatively assigned to the E₂ Stage.

Within another fault-block lying east of Ousby church, two thick sandstones, with a locally-worked coal lying immediately above the lower, have been proved in the banks of Ashlock Sike [NY 6376 3450] to [NY 6361 3449]. The coal may be one of the Little Limestone Coals (p. 54), though there is no proof of this.

The adjacent fault-block to the east is almost entirely drift-covered. Miospores have been obtained from spoil dug from a group of bell-pits [NY 6415 3439]. Dr Owens reports that the organic residue recovered from this sample (SAL 550) contains large amounts of fragmentary wood, and the dominant miospore type in the population is Lycospora pusilla. Of the accessory spores the following association of species is considered significant: Verrucosisporites cerosus, Acanthotriletes castanea, A. falcatus, Tripartites ianthina, T. vetustus, Crassispora maculosa, Grandispora spinosa, Schulzospora ocellata and S. elongata. Whilst many of the elements in this association are characteristic of both Upper Visean and Namurian A assemblages, the presence of Tripartites ianthina and T. vetustus, which are not known from rocks younger than E₁ in the Stainmore Outlier, appears to be more significant. An E₁ age is therefore suggested for this assemblage. Accordingly, this coal and the associated strata must be separated by faulting from the exposures of the Alston Group limestones in Ardale Beck (p. 41). There are limited exposures upstream as far as a disused quarry [NY 6430 3447] (Star Hows of the 6-inch map) where a further fault brings in the following sequence cropping out in the eastern part of the digging.

Mudstone, dark grey with red staining, silty, with several bands of ironstone nodules 1.8 to 2.0 m from the base; Fenestella sp., Buxtonia sp., chonetoid [juv], Eomarginifera sp., Orbiculoidea sp., rhynchonelloid, Naticopsis sp.[juv.], turreted gastropods, nuculoid, orthocone nautiloid,

A previous section from this locality (Shotton, 1935, p.665) includes an additional 3 m of thin limestones and shales at the base of the above record, but exposures have deteriorated. Dr W. H. C. Ramsbottom comments as follows on the goniatites: 'These specimens of Cravenoceras, although preserved uncrushed, and showing good sutures and ornamentation suggesting the C. malhamense/cowlingense group, cannot be determined with certainty because the inner whorls are not preserved, and these have been shown (Ramsbottom in Burgess and Ramsbottom, 1970) to be essential for correct determination in Cravenoceras.'Nevertheless the section is undoubtedly of E₁ age and may reasonably be correlated with the only other section yielding Cravenoceras in the area, namely the mudstones below the Firestone Sill on Little Dun Fell (Johnson, 1963, p. 53). AJW

Western area

Namurian (Millstone Grit) and Westphalian (Coal Measures)

The localities referred to in the text are shown in (Figure 24). The principal sections are presented graphically in (Figure 21).

The outcrops of the Upper Carboniferous rocks of the western area are largely covered by thick drift. The succession, therefore, is established mainly from boreholes, which show that the Namurian sequence is much thicker here than in the east, and that a substantial thickness of Westphalian strata is also present. Wherever they are seen at outcrop, or have been proved in the shallower borings, these Upper Carboniferous strata are predominantly red.

The thickest proving is in the IGS Barrock Park Borehole (Appendix 1, p. 145; (Figure 21)), near Southwaite, where 45 m of Westphalian rocks rest with faulted contact on 396 m of Namurian, the latter resting in turn on Alston Group strata. The youngest diagnostic Namurian fauna in this borehole is of E₂b age, while the oldest Westphalian fauna is taken as belonging to the Lower similis-pulchra Zone (see p. 54). In the High Head No. 2 Borehole, near Ivegill (Appendix 1, p. 153; (Figure 21)), 292 m of strata were proved above the base of the Great Limestone; this sequence is probably of Namurian age, although no diagnostic fossils were recovered, and correlation with the Barrock Park Borehole, 5.5 km distant, is speculative. The IGS Low Hesket and Petteril Bank boreholes (Appendix 1, p. 157; (Figure 21)) proved shorter sequences, each with Westphalian strata probably of Lower A. similis–A. pulchra Zone age resting on Namurian. In the Low Hesket Borehole the Namurian sequence includes strata of E₂b age but correlation with Barrock Park is imprecise; at Petteril Bank the Namurian fauna is not diagnostic of any Stage but the strata assigned to the Namurian may include some of the youngest in the district. The 91-m sequence of Westphalian strata at Petteril Bank is the thickest proved although as much as 300 m may be preserved elsewhere along the outcrop.

The lower part of the Namurian succession is known only in the Barrock Park and High Head No. 2 boreholes. At Barrock Park, the Great Limestone is 12.2 m thick, and consists of grey, nodular limestone with partings of dark grey mudstone; it is closely overlain by the Tumbler Beds—interbedded grey nodular limestone and dark grey mudstone. At High Head No. 2, where the Namurian sequence is entirely red, the Great Limestone is 16 m thick, but the Tumbler Beds are not present as a separate unit. The strata between the Great and Little limestones at Barrock Park are very similar to their counterparts in the east, consisting of fossiliferous mudstones, and sandstones, and six thin coals with a collective thickness of about one metre; these coals are absent at High Head where a thick sandstone immediately overlies the Great Limestone.

The Little Limestone at Barrock Park consists of 4.3 m of bioclastic, richly crinoidal limestone; it is the same thickness at High Head. Correlation of higher beds proved in the Barrock Park Borehole with those both at High Hcad and in the eastern outcrops is speculative (Figure 21), although it is probable that a limestone 67 m above the Little at Barrock Park is the equivalent of the Crag Limestone. About 14 m of fossiliferous mudstone overlie this limestone and, above these, all the strata are red.

The boundary between the Pendleian (E₁) and Arnsbergian (E₂) stages in the Barrock Park Borehole has been taken at a 20-cm thick sandy, dolomitised limestone lying 158 m above the Little Limestone, and tentatively correlated with the Lower Felltop Limestone; strata including shelly sandstones from about this horizon are well exposed in Raughton Gill, 2 km to the west-south-west. The succeeding 35 m of strata in the borehole are largely arenaceous but include a further two dolomitic limestones. The lower of these is some 2 m thick, nodular in the upper part, and massive and sandy below; it may be equivalent to a fossiliferous calcareous horizon recorded at a depth of 145.11 m in the High Head No. 2 Borehole. The upper is 40 cm thick, in one post, and is here correlated with the Upper Felltop Limestone; it is probably also equivalent to a 0.6-m dolomitised limestone exposed in Raughton Gill, 1.8 km to the west, and also to the dolomitised limestone encountered in the IGS Unthank Borehole (p. 67), near Skelton, where associated strata have yielded a fauna of E_2b age.

The youngest calcareous horizon in the sequence at Bar-rock Park lies 245 m above the Little Limestone, and is here termed the Barrock Top Limestone. This is a nodular dolomitic limestone, and the fauna from the overlying mudstones includes Tylonautilus nodiferus, which signifies an E_2b age. A fossiliferous, calcareous band 192 m above the Little Limestone in High Head No.2 Borehole may be equivalent to the Barrock Top Limestone, as may the calcareous strata with faunas of E₂b age recorded in the IGS Temsend and Woodclose boreholes (pp. 65 and 67), near the western boundary of the district. Thick sandstones are present in this part of the Namurian succession and one of these, 15 m thick, is exposed 15 m above the Upper Felltop Limestone in Raughton Gill; these sandstones, which include some coarse-grained, pebbly beds, from a broad 'hog-back' feature on the watershed between the rivers lye and Petteril from Colt Close to Hill Houses, and are particularly thick in the High Head boreholes (p. 65).

Some 90 m of largely arenaceous strata, presumed to belong to the Namurian, separate the Barrock Top Limestone from a faulted contact with Westphalian strata at Barrock Park, while in the nearby Low Hesket Borehole some 50 m of presumed Namurian beds separate a calcareous horizon with a fauna of Po₎ age (regarded as lying above the Barrock Top Limestone, but faulted out at Barrock Park) from Westphalian strata.

The Petteril Bank Borehole encountered 114 m of presumed Namurian strata under the Westphalian, and some of these may be younger than any proved at either Low Hesket or Barrock Park. Fossiliferous strata equivalent to those in the lowest part of the sequence in this borehole are exposed in Far Pasture Wood (p. 66), 1.7 km to the south-west, while thick sandstones equivalent to those immediately underlying the Westphalian are seen in a tributary gully to the River Petteril, near Elephant (p. 67). Thick sandstones which may also lie in this part of the succession were proved in the IGS Low Braithwaite Borehole (p. 65), and are exposed in the banks of the River lye between Ivegill and Low Braithwaite.

Probably only the lower part of the preserved succession of Westphalian strata has been proved in the borings. The Low Hesket and Barrock Park boreholes encountered largely equivalent sequences of Westphalian consisting of predominantly red strata with many seatearths. A thin band of mudstone which yielded Anthraconaia aff. pulchella and Anthracosia sp.is present 40 m above the base of the sequence at Low Hesket, and four bands in a broadly equivalent part of the succession at Barrock Park yielded Anthraconaia pulchella, A. sp., Naiadites productus, Anthracosia sp.and Carbonita sp.In addition, mudstones some 30 m lower in the sequence at Barrock Park yielded Anthracosia sp.

The correlation of these sequences with that of the Petteril Bank Borehole is uncertain, but it is possible that the fossiliferous mudstones low in that sequence which yielded A. aff. pulchella and Naiadites sp.are equivalent to the younger of the two occurrences at Barrock Park; these mudstones are separated from another band that yielded Anthracosia planitumida by an 8-m thick sandstone that may correlate with a thicker, and partly coarse-grained and conglomeratic sandstone at the top of the Low Hesket sequence. The succeeding strata at Petteril Bank are predominantly argillaceous and include many seatearths; rooty siltstones equivalent to part of this sequence are exposed in the banks of the River Petteril nearby.

Details

For descriptive purposes the outcrop is divided into five areas as shown on (Figure 24).

Ivegill

The best sections in this area come from three boreholes near High Head Farm, and from the IGS boreholes at Low Braithwaite and near Temsend. Exposed sections are few and mostly restricted to the harder sandstone bands.

The fullest sequence was proved in the High Head No. 2 Borehole [NY 4115 4434] (Appendix 1, p. 153). Although few identifiable fossils were recovered, the borehole is believed to have been in Namurian strata from rock-head at 22.96 m to its base at 316 m. The Great Limestone and the Little Limestone are readily recognisable, but higher in the sequence there is an absence of identifiable marker bands. A thin limestone is recorded at about 260 m, and fossils from a closely underlying mudstone include Koninckopecten sp., Palaeoneilo sp.and Phestia attenuata. Other calcareous bands occur at about 156 and 81 m; the latter yields Schellwienella sp.and is tentatively correlated with the Barrock Top Limestone (see (Figure 21)). Apart from these beds, the sequence is made up throughout of alternations of shales and sandstones, the latter becoming thicker upwards and dominating between 53 and 139 m. High Head No. 1 Borehole [NY 4117 4410] appears to have been drilled in this same arenaceous part of the succession. Its log (p. 153) records red sandstones and shales from rock-head to the base of the hole at 155.8 rn. These two holes probably begin at about the same horizon, and a thin calcareous bed at 54.9 m in the No. 1 Borehole may equate with the similar bed at 81 m in No. 2 Borehole. High Head No. 3 Borehole [NY 4062 4359] is much shallower and also penetrates the arenaceous part of the sequence.

The IGS Low Braithwaite Borehole [NY 4259 4209] (Appendix 1, p. 157) proved 40.89 m of siltstones and sandstones, barren other than for traces of plant debris. This succession cannot be matched with that of High Head No. 2, and it may lie near the top of the Millstone Grit. The IGS Temsend Borehole [NY 4055 4184] (Appendix 1, p.161) proved 14.33 m of alternating sandstones and siltstones with intercalations of sandy mudstone, with marine fossils in the lower part, in turn lying above 0.51 m of hard, dolomitic and fossiliferous limestone. The borehole ended in 2.44 m of alternating bioturbate siltstones and sandstones, with many poorly preserved marine shells. The fauna from these beds is not diagnostic of any specific horizon. The limestone is fine-grained, bioturbate, with shell fragments, and contains nodules of fine-textured carbonate packed with shells. It closely resembles the Barrock Top Limestone in the Barrock Park Borehole (Figure 21).

Exposed sections in this part of the succession are rare. In a gutter [NY 4072 4501] close to the north-west of Beacon Hill Farm, a dolomitic and hematitic limestone with crinoid debris crops out, which may equate with the calcareous horizon at 81 m in High Head No. 2.

Strata from the same general part of the sequence are exposed in a disused quarry [NY 4058 4564] some 700 m NNW of Beacon Hill Farm where buff and purple-red, fine-grained, siliceous sandstone has been dug, and in gutters and glacial drainage channels [NY 406 452] nearby. There is an old trial shaft close by [NY 4058 4497], presumably dug for iron-ore.

In the River Ive, barren sandstones, siltstones and mudstones probably lying higher in the sequence are sporadically exposed. One outcrop [NY 4080 4365] is near High Head Castle Farm, and others [NY 4191 4295]–[NY 4230 4269] lie between Ivegill and Low Braithwaite. The western part of this latter section shows some 18 m of massive, cross-bedded sandstone with mudstone pellets; this sandstone is probably equivalent to the thick sandstone in the Low Braithwaite Borehole (p. 157). Ina nearby quarry [NY 4207 4290] the section is as follows: sandstone, fine-to-coarse-grained, massive and thickly cross-bedded, 3.66 m; sandstone, coarse-grained, largely replaced by hematite, 0.91 m; sandstone, fine- to medium-grained, soft, 1.83 m. In the northern bank of the river [NY 4231 4276] purple-grey sandstone is overlain unconformably by Penrith Sandstone, and there are similar sections [NY 4202 4331] in Barrowgill Beck close to the north-east of Ivegill, where red, medium and coarse-grained siliceous sandstones, dipping at 10° to 40° to the north-west, appear to be faulted against purple siltstones of the Coal Measures. Further exposures of barren red siltstones and thinly bedded sandstones lie in the bank of Braithwaite Beck [NY 4251 4132]–[NY 4254 4145] near Braithwaite Shields, where they are contorted and cut by minor faults.

Southwaite

The thickest proven sequence of Namurian strata is in the IGS Barrock Park Borehole [NY 4613 4660], about 200 m NE of Barrockgill (Appendix 1, p. 145). Marine shelly faunas are abundant below 180 m, and Tylonautilus nodiferus, indicative of the E_2b Subzone, was recovered at 185.3 m. The strata are predominantly red from the top of the sequence down to about 355 m, although the sandstones are partially red down to 387.1 m. Below this the strata are grey and include the Little Limestone Coals, present in six thin seams totalling about 1 m in combined thickness. The sequence contains eight calcareous members as described below:

Depth in Barrock Park Borehole:

The Namurian strata above 180 m are barren except for a sparse marine shelly fauna around 168 m.

A thickness of 45.2 m of Coal Measures were proved in this borehole, including five bands rich in bivalves. The four upper bands lying between 50.5 and 57.0 m yielded Anthraconaia pulchella, A. sp.and Anthracosia sp., and the lower band at 85 m contained Anthracosia sp.

The local top of the Namurian sequence was penetrated in the IGS Low Hesket Borehole [NY 4602 4752] (Appendix 1, p. 157), about 1 km N of Barrockgill. Red mudstones containing marine fossils of E_2b age—including costate productids indet., Latiproductus latissimus, orthotetoid (fragment), Rugosochonetes sp., Spirifer sp., Euphemites urii, Nuculopsis gibbosa, Palaeoneilo mansoni, Posidonia corrugata and Streblochondria cf. elliptica—are overlain by red Coal Measures containing many seatearths and, between 98.8 and 100.9 m, a faunal band containing Anthraconaia aff. pachella and Anthracosia sp.This band is believed to be broadly equivalent to the four highest bands in the Barrock Park Borehole. The position of the Namurian–Westphalian boundary has been arbitrarily taken at the base of a sandstone at 184.2 m.

To the west of these boreholes there are sections of Upper Carboniferous strata in the River Petteril and its tributaries. Red, fine-grained, micaceous sandstones and purple-grey siltstones and mudstones which crop out in the hillside and river banks e.g., [NY 4513 4782] about 400 m N of Barrockside, are barren but probably belong to the Millstone Grit. Some 2 km to the south-south-west red Millstone Grit beds are well exposed along much of Raughton Gill [NY 4392 4575]–[NY 4462 4628]. From Raughtongill Bridge [NY 4418 4609] upstream for about 350 m, the stream coincides with the outcrop of a thin-bedded sandstone, 1.8 m thick with abundant marine shells including Buxtonia sp., Eomarginifera sp.lobata group and Schellwienella sp.

These strata are believed to correlate with those occurring at about 274 m in the Barrock Park Borehole. Hematitised sandstone has been worked from an adit in the northern stream bank [NY 4412 4604]. Further downstream [NY 4447 4628] younger strata dipping eastwards at 15° to 20° are exposed in the following sequence, which is believed to correlate with that encountered between 170 and 236 m in the Barrock Park Borehole:

Millstone Grit strata in the following sequence were proved in shallow boreholes [NY 4429 4449] and [NY 4432 4451] sunk 550 m W of High House. The rocks lie in the upper part of the Millstone Grit sequence: mudstone, purple-red with fossils towards base, passing upwards into siltstone with sandstone laminae, 12.2 m; limestone, argillaceous, dolomitic, 1.0 m; sandstone, pale greenish grey, fairly massive, micaceous, 1.5 m.

The red mudstones and sandstones exposed in the stream bed [NY 4477 4449]–[NY 4480 4456] at High House are similarly regarded as lying within the uppermost part of the Namurian sequence, while sandstones exposed 64 m downstream are arbitrarily assigned to the Coal Measures. Some 12 m of barren, pale purple-grey, fine-and medium-grained sandstone and silty sandstone in the River Petteril at Southwaite Hall [NY 4512 4527] are also believed to lie low in the Coal Measures.

Calthwaite

The fullest section of Upper Carboniferous strata in this area was proved in the IGS Petteril Bank Borehole [NY 4665 4271] (Appendix 1, p. 159), just east of the River Petteril near Troughfoot. Here a predominantly argillaceous sequence of red Coal Measures including five mussel bands and many seatearths overlies a more arenaceous, red Millstone Grit succession with a marine shelly fauna. Of the mussel bands, the highest one at 58.2 m contains Anthracosia planitumida and the lower between 72.7 and 86.8 m contains Anthraconaia aff. puichella. The marine fauna includes Lingula mytilloides and Productus carbonarius, but gives no specific indication of age within the Namurian.

To the west, beds believed to be equivalent to those proved in the Petteril Bank Borehole are exposed in the River Petteril and its tributaries. Coal Measures correlated with the highest part of the borehole sequence are exposed at intervals along the northern bank of the River Petteril [NY 4628 4288]–[NY 4692 4248], between 1 km NNW and 540 m NNE of Low Wooloaks. In meander scars [NY 4650 4259] and [NY 4664 4265] 680 m N of Low Wooloaks, purple-grey sandstones, siltstones and mudstones are exposed in sections up to 3 m high; rootlet-beds are common but no fauna has been recorded. About 3 m of purple-red, fine- to medium-grained sandstone lying above these strata, and just above the sequence proved in the borehole, are exposed in a small disused quarry [NY 4685 4256], 230 m farther to the east-south-east. In a gully [NY 4563 4292], 500 m NE of Elephant, there are outcrops of purple-grey sandstone and siltstone believed to lie low in the Coal Measures sequence.

Farther west in this gully, massive red sandstones with subordinate siltstones are well exposed dipping north-east at 10° to 15° [NY 4538 4267] to [NY 4552 4277], and these probably correlate with the uppermost part of the Millstone Grit in the Petteril Bank Borehole. Southwards from this gully, red mudstones, siltstones and sandstones slightly lower in the sequence are exposed in a drain [NY 4558 4156] to [NY 4577 4168] in Far Pasture Wood, 680 m NNE of Hill Houses. At the extreme western end of this section, a typical, though not diagnostic, E₂ shelly fauna, including Productus carbonarius, Donaldina sp., Edmondia sp.and Nuculopsis gibbosa, has been recovered from strata believed to correlate with the marine horizon at 204.8 m in the borehole.

Red strata from this same general part of the sequence were proved in shallow boreholes [NY 4499 4336] - [NY 4592 4179] in the vicinity of Petteril Hill and Elephant. For example, 13 m of barren red mudstones and sandstones are recorded from a borehole [NY 4587 4195] 730 m SE of Elephant, and in another borehole [NY 4585 4190], 45 m to the south-south-west, a similar sequence was proved, with Lingula at 6.9 m.

To the west and north-west of Far Pasture Wood, a thick sequence of massive sandstones, underlying the marine horizon at that locality, form a prominent, broad 'hog-back' feature between Hill Houses and Colt Close. Exposures of these sandstones are numerous between Sceugh Head [NY 4409 4326] and Hay Close [NY 4483 4108], particularly in glacial drainage channels cut into the feature. Some of the sandstones are coarse-grained and pebbly, for example, at Sceugh [NY 4405 4315]. Although faunal evidence is lacking, these strata are believed to correlate with the arenaceous sequence occurring between 53.3 and 139.0 m in the High Head No. 2 Borehole (p.153).

Skelton

The Upper Carboniferous strata are very poorly exposed in this area, and knowledge of the sequence comes from a few stream sections and shallow boreholes. Faulted strata, consisting of alternations of barren red sandstones, siltstones and mudstones and believed to lie near the base of the Coal Measures, were proved in a group of shallow boreholes 320 m ESE of Brackenburgh Cottages. The sequence of one of these boreholes [NY 4798 3893] is typical:

Some 4 km to the south, the following section of barren strata, believed to lie at a similar horizon, is exposed in Henley Sike [NY 4810 3510], 350 m NE of Thornbarrow:

Millstone Grit sections were proved in three IGS boreholes (Appendix 1, pp. 160–162) farther west, at Woodclose [NY 4099 3794], 550 m WNW of Hollyhill; at Skelton Wood End [NY 4157 3867] about 900 m NE of the Woodclose Borehole; and at Unthank [NY 4376 3711], about 1.6 km N of Skelton. The Woodclose Borehole proved a calcareous band between 62.18 and 63.40 m which consisted of buff limestone nodules in a matrix of dull-red calcareous silty mudstone. The overlying mudstone yielded an abundant shelly fauna of E₂b age including: Glabrocingulum sp., Lingula mytilloides, Pleuropugnoides sp., Edmondia sp., Palaeoneilo sp., Posidonia corrugata and Posidoniella sp., and the bed probably correlates with the Barrock Top Limestone. Strata also of E_2b age were proved in the Unthank Borehole; mudstones near the base yielded an abundant shelly fauna including: chonetoids, orthotetoids, Pleuropugnoides sp., productoids, gastropods, Edmondia sp., Phestia attenuata, Streblochondria sp., nautiloids and crinoids. At the base of the borehole, two posts of massive red to buff dolomitic limestone were proved. These contained sparse and poorly preserved bioclastic debris set in a fine-textured matrix, and are believed to correlate with the Upper Felltop Limestone.

Only a sparse and indeterminate fauna was present in the strata proved in the Skelton Wood End Borehole, which are consequently believed to lie high in the Namurian sequence, probably above the Barrock Top Limestone. RSA

Penrith

The Namurian rocks underlying the area north-west of Penrith are almost entirely masked by drift. Outcrops are restricted to the Petteril valley and adjacent high ground, north of Newton Reigny.

The 12.2 m of reddish grey limestone proved in a borehole [NY 4932 3103] at Newton Rigg is tentatively assigned on thickness to the Great Limestone. The overlying beds including the Little Limestone do not crop out hereabouts, but higher in the sequence the Crag Limestone is exposed north-west of Newton Reigny, where 1.2 m of purple-stained, fine-grained limestone dip north-eastwards in the bed of the River Petteril [NY 4693 3275]. Farther downstream, the same bed is seen as brown, dolomitic, crinoidal limestone [NY 4760 3213] 200 m W of Catterlen Hall. The overlying sequence includes four beds of purple-grey sandstone cropping out around High Dyke; the uppermost bed is at least 12 m thick and forms a prominent ridge immediately south-east of Honey House.

The dips in these few exposures are sufficient to suggest that the Coal Measures come on to the east beneath the Penrith Sandstone of Penrith Beacon. This supports the old record of 'coal measures' in a borehole at Honeypot [NY 577 400], about 4 km E of Penrith (Sedgwick, 1836, p. 387). About 108 m of 'coal measures' were proved below 27 m of Penrith Sandstone, although it is not known whether these beds were indeed of Westphalian age. AJW

References

BURGESS, I. C. and RAMSBOTTOM, W. H. C. 1970. A new goniatite horizon in the Hearne Beck Limestone (Namurian E₂) near Lovely Seat, upper Wensleydale. J. Earth Sci., Vol. 8, pp. 143–148.

CALVER, M. A. 1970. In Annu. Rep. Inst. Geol. Sci for 1969, p. 90.

DUNHAM, K. C. 1948. Geology of the Northern Pennine Orefield: Vol. 1, Tyne to Stainmore. Mem. Geol. Surv. G.B.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the country around Cockermouth and Caldbeck. Mem. Geol. Surv. G.B.

FORSTER, W. 1809. A treatise on a section of the strata from Newcastle-upon-Tyne to the mountain of Cross Fell in Cumberland. (1st edition, Alston; 2nd edition (1821) Alston.)

JOHNSON, G. A. L. 1958. Biostromes in the Namurian Great Limestone of northern England. Palaeontology, V ol. 1, pp. 147–157.

JOHNSON, G. A. L. 1963. The Geology of Moor House. Monogr. Nat. Conserv.

JOHNSON, G. A. L. HODGE, B. L. and FAIRBAIRN, R. A. 1962. The base of the Namurian and of the Millstone Grit in north-eastern England. Proc. Yorkshire Geol. Soc., Vol. 33, pp. 341–362.

OWENS, B. and BURGESS, I. C. 1965. The stratigraphy and palynology of the Upper Carboniferous outlier of Stainmore, Westmorland. Bull. Geol. Surv. G.B., No.23, pp. 17–44.

PHILLIPS, J. 1836. Illustrations of the geology of Yorkshire. Part II, The Mountain Limestone district.

SEDGWICK, A. 1836. On the new Red Sandstone Series in the basin of the Eden, and the north-western coasts of Cumberland and Lancashire. Trans. Geol. Soc. London, Ser. 2, Vol. 4, pp. 383–408.

SHOTTON, F. W. 1935. The stratigraphy and tectonics of the Cross Fell Inlier. Q. J. geol. Soc. London, Vol. 91, pp. 639–704.

TROTTER, F. M. and HOLLINGWORTH, S. E. 1932. The geology of the Brampton District. Mem. Geol. Surv. G.B.

Chapter 6 Permian

Introduction and classification

Permian rocks crop out under a partial cover of drift beneath a quarter of the district, principally in a belt six to ten kilometres wide astride the River Eden and parallel to the Pennine Fault. Everywhere they rest unconformably on Carboniferous beds. The generalised section of the strata and the broad classification adopted for them within the district are set out below.

Marine deposits are few and contain only an impoverished fauna, while spores are absent from the red beds that constitute a large proportion of the deposits. In these circumstances correlation with the fully marine succession of south-eastern Europe is necessarily tentative.

The term Penrith Sandstone was introduced by Murchison and Harkness (1864). The Penrith Sandstone is unfossiliferous, and comprises the strata extending from the unconformable junction generally with Upper Carboniferous strata below to the Upper Permian sequence above. In lithology and mode of occurrence the formation closely resembles the Lower Permian sands of much of north-western Europe and it seems likely that it accumulated largely during Lower Permian times. It is, however, unfossiliferous apart from vertebrate footprints.

Early attempts at classification of the Upper Permian rocks (Goodchild, 1893; Dakyns and others, 1897) were based largely on the exposures in Hilton Beck in the Brough district, and on numerous limited sections associated with gypsum workings. Sherlock and Hollingworth (1938) and Hollingworth (1942) subsequently used borehole records to establish the succession of gypsum/anhydrite deposits in the Vale of Eden, but miscorrelated that succession with the Hilton Beck sequence in which no gypsum/anhydrite is exposed, in particular by placing the 'Magnesian Limestone' (Belah Dolomite) of Hilton Beck immediately below the B-Bed (see (Figure 30)). Meyer's (1965) revision of the correlation between these different successions has since been substantiated by the Hilton Beck Borehole (Burgess, 1968, p. 89) and is used here.

In the Carlisle Basin the term St Bees Shales, first introduced in West Cumberland (Smith, 1924), was applied to the red argillaceous strata underlying the St Bees Sandstone (Murchison and Harkness, 1864), and later extended to analogous strata in the Vale of Eden (Sherlock and Hollingworth, 1938; Hollingworth, 1942; Meyer, 1965). The last two authors retained the long-used term Hilton Plant Beds to denote a mainly grey plant-rich division of strata separating the red St Bees Shales from the Penrith Sandstone in the southern part of the Vale, but their usage of this term was inconsistent, and only Meyer (1965) specified the base of the St Bees Shales in terms of a specific section, namely Hilton Beck.

In the Vale of Eden the base of the St Bees Shales of West Cumberland is difficult to recognise precisely, because of the marked lithological differences in the local succession compared with that of the type area (Smith, 1924; Eastwood and others, 1931; Arthurton and Hemingway, 1972). In view of this difficulty, the term St Bees Shales is not used in this account. Instead, all the strata between the top of the Penrith Sandstone and the base of the St Bees Sandstone in the Vale of Eden are referred to as the Eden Shales. The formation is mainly composed of red-brown mudstones and siltstones with thin beds of sandstone particularly in the upper part; several gypsum/anhydrite beds are present, mainly low in the sequence, and there is at least one thin dolomite. It is defined in terms of its position in the Hilton Beck Borehole in the Brough district (Burgess, 1968), and both its base and its top are likely to be diachronous.

The Upper Permian age of the Eden Shales is indicated both by the floras in their lower part (Stoneley, 1958; Clarke, 1965), and by the fauna of the Belah Dolomite at outcrops in the Brough and Kirkby Stephen districts (Pattison, 1970). Their exact position within the Zechstein sequence of northwestern Europe remains, however, in doubt. Similarly the precise position of the boundary between the Permian and Trias has not yet been established in this region, but, for convenience, it is taken at the base of the St Bees Sandstone.

Penrith Sandstone

The Penrith Sandstone crops out on both limbs of the Vale of Eden Syncline (p. 102), the main outcrop lying on the western limb between Holmwrangle and Penrith, while there are small outcrops on the eastern limb, close to the Pennine Fault, near Gamblesby and Kirkland. The Holmwrangle–Penrith outcrop extends to the extreme northwestern part of the district near High Wreay, where it forms part of the southern margin of the Carlisle Basin. Farther south, near Ivegill, there are two further small areas of outcrop. These and other important localities referred to in the text are shown in (Figure 25).

The Penrith Sandstone forms some of the highest ground in the Vale. In all but the northern part of the main outcrop it gives rise to a prominent drift-free escarpment particularly well seen on Lazonby Fell (p. 72). Much of the main outcrop, however, lies to the west and north of this escarpment, and is relatively low-lying and masked by drift. Knowledge of the formation stems largely from natural sections. Along the main outcrop the best of these are in the Eden valley, and lie within about 100 m of the top of the formation as do the many quarry-sections which abound on the high ground just to the east of the escarpment. No stratigraphic markers have been recognised within the unit. (brockram) containing angular fragments of Carboniferous sandstone and limestone. The mudstones and siltstones are mostly laminated, their sedimentary features including load-casts, sand-filled desiccation cracks, and mudstone pellets.

No flora or fauna appears ever to have been recorded from the Penrith Sandstone, although specimens of vertebrate footprints (curated at Carlisle City Museum) have been found in quarries on Lazonby Fell, and in a digging at Slate-quarry Wood (Smith, 1884).

The formation attains a probable thickness of at least 300 m in the southern part of the main outcrop (Figure 26). The commonest lithology is a reddish brown medium- to coarse-grained sandstone containing abundant well-rounded grains. This has long been considered to be a wind-blown deposit, a conclusion supported by recent electron microscope studies (Waugh, 1965). Large-scale cross-stratification, interpreted as dune-bedding (Plate 5), is ubiquitous and is particularly well exposed in quarry sections, as on Lazonby Fell. The individual foreset units range in thickness from less than 2 cm to more than 2 m, and their component grains are commonly graded upwards from coarse to medium or even fine (Plate 6). Measured foreset dips in the upper, and best exposed, part of the formation, lie consistently close to a WNW direction (Figure 27) (Shotton, 1956). The foresets are affected by slumping in a few places.

In the northern part of the main outcrop, between Blackmoss Pool and Holmwrangle (Figure 25), and in the east near Gamblesby and Kirkland, the formation is much thinner, in places probably amounting to only 50 m or so, and includes a different and distinctive facies (see (Figure 26)). The section proved in the Blackmosspool Borehole (p. 73), for example, comprises dune-bedded aeolian sand intercalated with water-laid strata, including flat-bedded and fine-grained red sandstone, purple-red siltstone and mudstone, together with beds of coarse breccio-conglomerate

Two important changes have affected the dune sands, and probably occurred penecontemporaneously with deposition. The earlier is the formation of a porous pellicle of hematite and illite around each sand grain, a process responsible for the characteristic reddish brown colour of the rock (Waugh, 1965). Along much of the main outcrop, this process was followed, or perhaps accompanied, by the formation of secondary silica as crystalline overgrowths around each quartz-grain. In places these overgrowths fill as much as 70 per cent of the original pore-space (Waugh, 1970). The extent of silicification is reflected in the local morphology: where the silica cement is sparse the outcrop of the formation has low-relief and consequently is commonly drift-covered; where it is abundant the relief is strong with prominent scarps and dip-slopes, and the sandstone has been intensively quarried for building stone, as for example on the eastern side of Lazonby Fell. Local variations in silicification are common. Thus, restricted pockets of relatively silicified rock are present within the poorly coherent lower part of the formation while, in some of the quarries on Lazonby Fell, incoherent sand and siliceous sandstone are juxtaposed in adjacent dunes. Waugh (1970) has shown that those dune sands that are associated with the waterlain facies, for example those near Holmwrangle, are generally poorly silicified. Other cementing minerals such as calcite, gypsum and anhydrite are present locally in boreholes or underground workings but have been dissolved at outcrop.

Silicification in the dune sands was a penecontemporaneous process, resulting (Waugh, 1970) from the production of silica dust by abrasion of sand grains in the desert environment, its solution in alkaline groundwaters, and its subsequent concentration by capillary evaporation.

Conditions of deposition

The Penrith Sandstone was deposited in a structurally controlled elongate basin that is broadly coincident with the present Vale of Eden, and is well depicted by the residual gravity anomaly contours (Figure 45). The eastern and southern margins of this basin cannot have lain far beyond the present outcrop of the formation (see p. 73, and Burgess, 1965): to the west, however, the Penrith Sandstone probably extended well beyond its present limit, even though much of the Lake District was an area of positive relief at about this time. The northward extent of deposition is unknown. The formation is thin at Cocklakes (p. 72), and is absent through overlap by the Eden Shales to the south-west at the D2 Borehole (p. 72), and to the north-east near Castle Carrock (Trotter and Hollingworth, 1932). It seems probable that the northward closing of the gravity contours (Figure 45) reflects the northward closure of the Vale of Eden Basin, and that a saddle marked by thin sedimentation, separates this basin from the Carlisle Basin to the north.

The Penrith Sandstone is a continental deposit formed in desert conditions. In the central part of the Vale of Eden Basin wind-blown sand accumulated as dunes, probably of barchan type (Shotton, 1956), up to a thickness of at least 300 m. The environment seems to have been that of a desert sand-sea, perhaps 40 km across, that separated the high ground of the Lake District from that of the Alston Block, and extended along the length of the basin, both southwards into the Appleby and Brough districts and northwards into the Carlisle Basin. Analysis of the directions of dip of the foresets in the cross-bedded units (Figure 27) shows that the direction from which the wind blew was remarkably constant, the prevailing direction (relative to modern azimuths) being from the east-south-east. This is believed to reflect the influence of the east-south-easterly trade winds, for, in the Permian, Britain may have been appropriately orientated in the latitudes affected by these winds.

The source of the accumulating sand is not known but may have lain far to the east-south-east, as the absence of grasses probably made winds far more effective agents of transport in Permian times than they are today.

Although deposition in the central part of the basin seems to have been exclusively aeolian, some water-laid deposits accumulated contemporaneously around at least parts of the basin margin. The angularity of many of the included rock-fragments and, particularly in the east, their composition suggest that the periods of aqueous transport were short-lived and that the fragments were derived from nearby sources; the existence of sand-filled desiccation cracks and mudstone pellets points to the common, if not dominant, occurrence of subaerial conditions. It is likely that torrents from bordering high ground disgorged detritus as local piedmont fans that terminated where the streams disappeared as a result of high evaporation and percolation.

Details

Ivegill

An outlier of Penrith Sandstone, heavily masked by drift, lies on the eastern side of the valley of the River Ive near Ivegill and Low Braithwaite; the maximum preserved thickness being probably less than 100 m. The best sections are in riverside cliffs [NY 4232 4277] to [NY 4301 4197] at Low Braithwaite, where red-brown sandstone in massive cross-bedded units is exposed in sections up to 9 m high (Plate 6). The foresets are typically 2 to 5 cm thick, and are composed almost entirely of well-rounded grains poorly cemented by silica; some foreset units grade upwards from coarse to medium or fine. At the northern end of the section, the Penrith Sandstone crops out in the eastern bank of the river some 3 m above purple-grey sandstone of presumed Carboniferous age; the junction is concealed, but is believed to be an unconformity.

There is a similar section in a stream [NY 4296 4334], 400 m ENE of Ivegill. On excavation, this showed 0.6 m of Penrith Sandstone, comprising soft red-brown cross-bedded sandstone with well-rounded grains, resting unconformably on 0.3 m of soft purple and grey mottled siltstone of presumed Carboniferous age. The Penrith Sandstone is exposed for some 90 m upstream from this locality, and also in a stream [NY 4165 4392], 700 m to the north-west.

In a field [NY 4412 4178] near Bents Cottages, 1.6 km ESE of Low Braithwaite, siliceous pale red-brown sandstone with wind-rounded grains forms a drift-free scar. A fault intervenes between this locality and an exposure of Carboniferous sandstone some 50 m to the east.

Farther down the River lye there is another separate outcrop of Penrith Sandstone at High Head Castle [NY 4031 4334], just within the Cockermouth district (Eastwood and others, 1968). This outcrop may extend east-south-eastwards to within 1.3 km of Ivegill. RSA

High Wreay to Penrith

Although exposures of Penrith Sandstone in this part of the main outcrop are abundant, none is sufficiently extensive for its thickness to be assessed accurately. The formation appears to be thickest in the south, probably exceeding 300 m at and to the south of Lazonby Fell. Farther north estimates are less certain, but it is probable that there is attenuation towards the northern boundary of the district, for in the Cocklakes Quarry Borehole [NY 4563 5094] (Figure 25), just within the Brampton district, only 78 m of Penrith Sandstone separate the Eden Shales from Carboniferous strata, while in the D2 Borehole [NY 3878 4805], just within the Cockermouth district (Eastwood and others, 1968), the Eden Shales rest directly on Carboniferous strata.

In the extreme north-west near High Wreay, two boreholes proved thin water-laid sediments lying at the base of the formation. One [NY 4303 4780] proved the following sequence:

The other [NY 4309 4786] penetrated 14 m of white and brown, fine-to coarse-grained sandstone, with red-brown sandy marl in the basal metre or so. More significantly, the Cocklakes Quarry Borehole [NY 4563 5094], proved some 25 m of water-laid deposits separating aeolian sandstone above from the Carboniferous basement. Layers of breccio-conglomerate are abundant, and the included rock-fragments are mostly of purple-grey Carboniferous sandstone. The full log of this borehole appears in Appendix 1 (p. 148).

Elsewhere natural sections and boreholes are, with rare exceptions, in the aeolian facies. In the north-west, where the formation at the surface is estimated to be 30 to 90 m thick, one of the best sections is in Gill Beck [NY 4309 4786] to [NY 4364 4809], 500 m S of High Wreay. Cliffs up to 9 m high in the stream gorge show moderately to rather poorly silicified red-brown sandstone, cross-bedded in massive units, and with well-rounded sand grains. Near faults and shatter-belts at the western end of the section, the sandstone is bleached and more silicified. Farther south, similar sandstone probably lying within 30 m of the base of the formation, is exposed in a disused quarry [NY 4705 4257] near Troughfoot, and along the River Petteril [NY 4821 3992] to [NY 4855 3954] near Plumptonfoot.

Most of the sections are, however, in the upper part of the formation, in cliffs and railway-cuttings near the River Eden between Armathwaite and Lazonby, in cliffs bordering the River Eamont, east of Penrith, and in the quarries which abound just to the east of the escarpment which extends from Blaze Fell southwards to near Penrith.

A typical section, 100 to 160 m below the top of the formation, is that at Cat Clint [NY 5064 4446], 1.6 km S of Armathwaite, where 15 m of red-brown sandstone with abundant well-rounded grains are exposed; the sandstone is moderately silicified and cross-bedded in massive units. Similar sandstones, lying within 75 to 120 m of the top of the formation, are exposed in a 30 m cliff [NY 5185 4425] on the northern side of the River Eden, 2.2 km SSE of Armathwaite. A nearby section in aeolian sandstone 30 to 90 m below the top of the formation, in a forestry track [NY 5100 4511] to [NY 5151 4442] in Coombs Wood, shows wide variations in the degree of silicification: at the eastern end, and high in the formation, the sandstone is strongly silicified and gives rise to a line of crags; farther west and lower in the sequence it is generally poorly silicified and friable, but locally contains steeply inclined sandstone 'veins' in which the sandstone is bleached and preferentially silicified. These latter weather out as ribs on exposed surfaces and generally coincide with very minor faults. Southwards from this locality there are sections within the uppermost 45 m of the formation in the cliffs on both sides of the river. Here [NY 5195 4401] to [NY 5226 4312], the sandstone is generally strongly silicified and weathered surfaces again carry highly inclined silicified 'veins', and one of the cross-bedded units [NY 5200 4390] is slumped throughout its full thickness of 3 m.

At Nunnery Walks [NY 5356 4222] to [NY 5386 4265], some 2 km WNW of Kirkoswald, red-brown, cross-bedded and sparsely-jointed sandstone in the uppermost 100 m of the formation forms the walls of a gorge some 25 m deep; the foresets dip generally to the northwest with an observed maximum value of 25°, and slump-bedding is present locally. The sand grains range in grade from fine to coarse, the coarser material being highly rounded. As in the sections described above, the sandstone in places includes highly inclined silicified 'veins'.

The aeolian cross-bedding is particularly well displayed in many quarries on the higher ground and there are also good sections in the railway-cuttings between Baronwood and Lazonby, particularly one cutting [NY 5449 4049] which exposes a massive trough-shaped unit. There is a wide range in the thickness of individual foreset-units: in one of the few remaining working quarries [NY 5205 3435], near Bowscar, foresets 2 to 5 cm thick have been won for tiling- and paving-stone, the rock splitting on fine-grained partings; on Lazonby Fell, by contrast, some massive foresets have yielded blocks as much as 2 m thick which have been split for use as pillars and lintels. The foresets of sandstone exposed both in these quarries and in natural sections near the River Eden dip within an arc from north, through west to south-south-west.

The lowest part of the formation was recorded by the primary surveyors in a railway-cutting [NY 4808 3904] near Brackenburgh. The sandstone is no longer exposed, but loose debris in the cut appears to be from the aeolian facies. More recently, the basal sandstone was proved under thick drift in shallow boreholes [NY 490 329] and [NY 490 334] near Catterlen; it is deep red-brown, fine- to coarse-grained with scattered well-rounded grains, and very friable. Two-of these boreholes [NY 4908 3294] and [NY 4911 3295] appear to have penetrated the base of the formation and entered 'weathered siltstone', presumed to be of Carboniferous age. The base of the Penrith Sandstone also appears to have been penetrated near Honeypot [NY 557 301], in the extreme south of the district where, according to Sedgwick (1836), only 27.5 m of 'red sandstone' were passed through before entering 'coal measures'.

The distribution of silicification along this outcrop of the Penrith Sandstone is highly variable. It is most intensive in the upper part of the formation, particularly southwards from Armathwaite, and it is this strongly silicified rock that is responsible for the existence of the prominent scarp features some 50 m high on Blaze Fell, Lazonby Fell, and the heathland hills extending southwards to Penrith. On Lazonby Fell [NY 517 384] this highly silicified rock is partially exposed as a rock-pavement over much of the fell-top, and is particularly well seen in Scratchmillscar [NY 515 380] at the southern end of the fell. The rock has been extensively quarried, not only on Lazonby Fell, but also on Blaze Fell and on the hills to the south. Sections in the quarries show that the silicification is far from uniform, for example in a quarry [NY 5632 3833] near the top of the formation near Eden Lacy, a similar cross-bedded unit consists partly of very hard silicified brown sandstone and partly of soft red sand (Plate 5). On a larger scale, a large pit [NY 5217 3469] near Bowscar, in a part of the formation generally well silicified, has yielded a large quantity of poorly silicified sandstone which was used as sand fill in the construction of the M6 motorway. Farther south the tendency for the upper part of the formation to be the most silicified continues. Silicification is widespread near Udford e.g. [NY 5743 3039] and extends eastwards to where the highest part of the formation is exposed [NY 5868 3071] in the western bank of the River Eden, 850 m SE of Udford House.

The aeolian sandstone forming the lower and middle parts of the formation is generally rather poorly cemented, as around Honeypot e.g. [NY 5743 3039]. Locally, however, it is strongly silicified. For example siliceous sandstone probably lying about 150 m below the top of the formation in a part of the sequence not normally heavily silicified is exposed in a small disused quarry [NY 4835 5166] on a hilltop 400 m NW of Thiefside Cottages; and siliceous Penrith Sandstone is exposed [NY 4963 3386] in the northern bank of the River Petteril at the base of the formation.

Another type is present both in the highly inclined 'veins' referred to above (p. 72), and associated with faults or shatter-zones, as for example in sandstone in the eastern bank [NY 5230 4322] of the River Eden, near Baronwood, and further south at Lacy's Caves [NY 5639 3830] near Eden Lacy. RSA, AJW.

Barrock Fell to Holmwrangle

In the north-east of the main outcrop, around High Stand Plantation and Holmwrangle, a water-laid facies is intercalated with the aeolian sandstones. The best section is that proved in the IGS Blackmosspool Borehole [NY 4824 4815], on the western side of High Stand Plantation. The borehole proved, beneath drift, 37.3 m of Penrith Sandstone which included several layers of breccia, containing fragments of Carboniferous sandstone and silty mudstone. Some massive units of cross-bedded sandstone with wind-rounded grains and graded foresets also occurred. Sedimentary features in the water-laid strata included load-casts, sand-filled desiccation cracks, and mudstone pellets. The cross-bedded sandstone layers ranged from uncemented to moderately silicified, the friable sands being deep red in colour. The full log of this borehole is given in the Appendix 1 on p. 148.

Farther east the water-laid facics is well exposed in the cliffs and banks of the River Eden around Holmwrangle, where interbedded breccias, mudstones and sandstones are common from between 100 and 140 m below the top of the formation, the underlying strata being unexposed. A section showing up to 7.3 m of strata of these lithologies lies on the western bank of the river [NY 5166 4923] to [NY 5149 4840], north-east of Low House, and continues northwards into the Brampton district; part of this section has been previously figured and described (Trotter and Hollingworth, 1932). The sandstones are red-brown, fine- to medium-grained with scattered well-rounded grains, and are generally flat-bedded. They are inter-layered with purplish red mudstone up to 15 cm thick, and with breccio-conglomerate composed of fragments of Carboniferous limestones, siltstones, and sandstones. Silica cementation is generally poor. Similar water-laid deposits are exposed in a stream bed [NY 5166 4833] at Holmwrangle, and in the northern bank of Broad Beck, 360 m E of Holmwrangle. Sandstones of aeolian facies, generally moderately silicified, overlie the water-laid strata near Holmwrangle, and are best seen in the railway cutting [NY 5085 4845], west of Low House, and in the gorge of Broad Beck [NY 5255 4850], 1 km E of Holmwrangle.

Southwards from Holmwrangle, there are no further sections in the water-laid facies, although a little red mudstone debris is present in the eastern bank of the River Eden [NY 5150 4695] north-east of Armathwaite, and in the railway-cutting [NY 5014 4591] immediately west of that village. The mudstone at both localities probably lies about 150 to 165 m below the top of the formation.

Westwards from the Blackmosspool Borehole, debris of red mudstone has been ploughed in fields [NY 4717 4756] just north-east of the summit of Barrock Fell, and must lie at least 60 m below the top of the formation. In the Low Hesket Borehole [NY 4667 4739], where the lowest 71 m of Penrith Sandstone have been proved, water-laid strata are very sparse; a 1-cm band of red mudstone is recorded at the extreme top, and a 0.5-cm breccia lies 27.4 m above the base. The estimated minimum thickness of the formation hereabouts is 150 m. RSA

Gamblesby and Kirkland

Along the foot of the Pennine escarpment, on the eastern limb of the Vale of Eden Syncline, the Penrith Sandstone is exposed only in a few small outcrops east and south-east of Gamblesby and in another small area around Kirkland. In both areas it rests unconformably on Carboniferous rocks, though locally the contact with Carboniferous or Lower Palaeozoic strata is faulted.

Although the basal contact is not exposed it seems clear that the Penrith Sandstone unconformably overlies reddened Carboniferous rocks in the beck [NY 6245 3896] east-south-east of Gamblesby. Southwards the outcrop is interrupted by faulting near Melmerby, but the formation reappears east of Ousby and is continuous southwards almost to Milburn. At several localities the field relations suggest that the Penrith Sandstone is banked against a Permian land surface of some considerable relief rising to the east. One such instance is in a section [NY 6333 3509] near Fellside. Another is in the small outlier [NY 6429 3360] between Ousby and Kirkland, where aeolian sands resting unconformably on the Basement Beds appear to fill a hollow in the Permian land surface. A little farther south [NY 6562 3253] a sharply rising slope of Carboniferous strata lies immediately east of the Penrith Sandstone outcrop and may be another remnant of this land surface. A small outlier of millet-seed sandstone [NY 6515 3262] seems to lie in a small depression on it. Similarly near Wythwaite Farm, 1 km SE of Kirkland, the Penrith Sandstone appears to be banked against a slope of red dolomitic limestone [NY 6605 3167], while north-east of Windy Hall near Milburn, the old land surface [NY 6589 3045] is cut across the Melmerby Scar Limestone.

Most of the outcrops between Milburn and Ousby are small and are of red-brown aeolian sandstone. The best exposures are near Windy Hall [NY 6589 3045]; in Littledale Beck [NY 6592 3151] to [NY 6605 3167], a tributary of Crowdundle Beck; at Hanging Walls of Mark Anthony [NY 652 322]; in the beck [NY 6359 3410] to [NY 6557 3243] near Ranbeck Farm; in Ardale Beck [NY 6359 3410]; and near Holly House Farm [NY 6338 3438]. Near Fellside [NY 6327 3505], thin partings of pale grey fine-grained sandstone, apparently water-laid, occur within the aeolian facies.

Locally bands of dreikanters occur in the aeolian sandstone. In Crowdundle Beck [NY 6600 3134] to [NY 6586 3138] the pebbles are of Carboniferous sandstones and limestones, whilst those seen [NY 6551 3216] near kanbeck Farm also include Lower Palaeozoic siltstones, greywackes and volcanic rocks. All the pebbles are likely to be of local origin. Near the base of the formation pebbles are so numerous near Gamblesby [NY 6235 3888] that they produce a hard breccio-conglomerate with a calcareous cement. They include angular limestone and sandstone fragments, presumably derived from nearby Carboniferous outcrops, set in a matrix of well-rounded sand.

It is difficult to estimate thickness variations along the outcrop, partly because the structural component of dips is hard to isolate—there are dune-bedding dips of up to 20° to the west or south-west near Gamblesby and Kirkland—and partly because sections are poor and discontinuous. Having regard to all this it seems likely that near Gamblesby the Penrith Sandstone has a minimum thickness of about 45 m. East of Ousby it is possible that as much as 90 m are preserved, and around Kirkland, too, thicknesses of this order may obtain. Farther south towards Milburn there is a substantial thinning, probably again to barely 45 m. AJW

Eden Shales

The Eden Shales are preserved in the eastern part of the Vale where, like the Penrith Sandstone, they crop out on both limbs of the Vale of Eden Syncline (p. 102). The most extensive outcrop is on the western limb between Ainstable and Culgaith, and there are limited outcrops on the eastern limb adjacent to the Pennine Fault at Croglin, Gamblesby and Lounthwaite. Two further outcrops are depicted on the geological map on the basis of data from boreholes just within the Brampton district, and these lie in the north-west near High Wreay and in High Stand Plantation. The outcrops and principal localities referred to in the text are shown in (Figure 28).

Generally the Eden Shales form relatively low-lying, drift-covered ground and their outcrop appears to have broadly determined the course of the River Eden in the southern part of the district. Around Ainstable and Culgaith, however, their higher beds form a scarp up to 50 m high which is capped by the overlying St Bees Sandstone.

The Eden Shales are poorly exposed, and, where sections do exist, they are mostly of limited stratigraphic extent. However, the general stratigraphy both in this district and in the neighbouring Brampton and Appleby districts is known from boreholes sunk in connection with the mining of gypsum and anhydrite. The logs and sites of these commercial boreholes are confidential, but generalised local successions have been compiled and are available by the courtesy of British Gypsum Ltd. In addition to this information, largely complete sequences were proved in the Langwathby and Lounthwaite boreholes sunk by the Institute in connection with the present resurvey, while farther to the south-east in the Brough district, a complete sequence—proposed as the type section of the Eden Shales (Arthurton, 1971)—was proved in the Hilton Beck Borehole, also sunk by the Institute (Burgess, 1968, p. 89).

The boreholes have demonstrated that the principal deposits of gypsum/anhydrite within the Eden Shales are sufficiently consistent in their thickness and distribution to constitute effective stratigraphic markers (Figure 29). The evaporites were designated A to D in upward sequence by Sherlock and Hollingworth (1938). The lowest evaporite the A-Bed—is thickest in the Kirkby Thore area but extends only into the southern part of the Penrith district. As a strati-graphic marker it is the least satisfactory of these evaporites both because of its great range in thickness (0 to more than 30 m) and its impersistence. The B-Bed is widespread both in the Vale and at Cocklakes, in the Brampton district, and constitutes the most reliable marker, while C-Bed is only a little less extensive in its distribution. D-Bed is present only in the southern part of the Vale, and has not been recorded with certainty northwards from Long Meg. In addition to these evaporites, a thin dolomite, here termed the Belah Dolomite, which closely underlies, and has a distribution similar to, D-Bed,. forms another useful marker.

The succession can be usefully subdivided at the base of B-Bed and at the top of D-Bed, and these three parts are described below in upward sequence.

Strata below B-Bed

The Eden Shales below B-Bed are poorly exposed but have been proved in boreholes in the Ainstable–Culgaith and Lounthwaite areas, where they overlie Penrith Sandstone in all known sections. Their proved thickness ranges from 12 m at High Stand Plantation in the north to 57 m in the Lounthwaite Borehole. Locally, around Culgaith, there are abrupt variations in this thickness. These variations within the district and in the neighbouring Cocklakes and Kirkby Thore areas, are shown in (Figure 29).

The principal lithologies are purple-red, red-brown, pale green and grey laminated mudstone and siltstone and there are several sharp-based sandstone layers up to 5 cm thick. Common sedimentary features of the red strata are cross-lamination, load-casts, desiccation cracks and mudstone pellets. In the grey strata there are 'cut-and-fill' structures, and traces of algal-mats. In most sections, mudstones and siltstones of the Eden Shales rest sharply on the Penrith Sandstone, which is generally strongly silicified. At Culgaith, however, intercalations of millet-seed sandstone are recorded in the basal part of the Eden Shales, while in the northern outcrops the basal part of the formation consists of red mudstone and siltstone interlayered with red fine-grained sandstone, the latter becoming dominant in some sections. The presence of sandstone in this part of the succession has also been recorded in boreholes at Long Meg and in surface exposures near Culgaith (p. 78).

At its thickest, to the south of Long Meg, this part of the succession includes gypsum and fine-textured (aphanitic) anhydrite occurring as nodules, laminae and layers. Where these are particularly abundant, as in the Langwathby Borehole, they have been classified as the A-Bed, which is thicker farther south in the Kirkby Thore area. Displacive veins of fibrous gypsum are also common, and gypsum pseudomorphs after euhedral halite are sporadically present in the grey strata.

Carbonaceous plant fragments are common in the grey strata, but are only rarely preserved in the red, and even then are in a state of partial oxidation. The red strata are otherwise barren apart from rare Estheria.

Strata between the base of B-Bed and the top of D-Bed

These strata are also poorly exposed, and knowledge of them comes largely from boreholes and, in the case of B-Bed, from mine-workings. Their thickness ranges from 40 to 60 m, and their terrigenous components are mostly similar in lithology, colour, sedimentary facies and fossil content to those of the sub-B-Bed strata. The mudstones and siltstones are mostly laminated, although a structureless red siltstone is recorded towards the base of the division in the Langwathby Borehole (p. 79). Fine-grained sandstone mostly occurs in sharp-based thin layers, and additionally, near the top, as a bed several metres thick with a sharp erosional base. Coarse grains of wind-rounded millet-seed sand are present in some of these sandstone layers, and also in the structureless siltstone referred to above.

Gypsum/anhydrite is abundant in this part of the succession. Gypsum is present in both porphyroblastic and alabastrine forms as a replacement of anhydrite; as poikilitic crystals forming a cement to siltstone or sandstone; and, in its fibrous form, as displacive veins. The various types of gypsum and their distribution are described in greater detail on p. 79. Anhydrite occurs both as nodules and laminae, and in beds up to several metres thick. The B-Bed and C-Bed are the two main beds, and lie at the base of the division separated from one another by 2 to 5 m of mudstone and siltstone. They are present in practically all the known sections, although at Cocklakes, just within the Brampton district, C-Bed is not recorded. The B-Bed is 4.9 to 6.6 m thick, and its fabric varies from being almost wholly nodular to being poorly layered or varved. It ranges from pale grey to dark brownish grey or black and, in the Langwathby Borehole partings of grey, plant-bearing silty mudstone are recorded from within it. The C-Bed is 1.2 to 3.1 m thick and includes nodular and layered fabrics; its colour ranges from pale to mid-grey or grey-brown. Grey, plant-bearing mudstone is interbedded with the anhydrite near its base. Both B- and C-Beds are mostly fine-textured (aphanitic), but lath-anhydrite forms nodules in the red silty mudstone immediately above C-Bed.

A few impersistent beds of aphanitic anhydrite up to about 1.5 m thick occur in the sediments separating C-Bed and D-Bed. One such bed, the Langwathby Bed of the Langwathby Borehole, consists of laminated anhydrite, muddy or silty in parts, and largely replaced by porphyroblastic gypsum ((Plate 7).1). The anhydrite exhibits 'cut-and-fill' structures and traces of probable algal-mats. Grey, plant-bearing mudstone is associated with the anhydrite.

The D-Bed is the youngest anhydrite bed, and has been recorded with certainty only as far north as Long Meg (see p. 78). Where proved it is 1.2 to 3.7 m thick. In the Langwathby Borehole, it comprises aphanitic anhydrite partially replaced by alabastrine gypsum ((Plate 7).2) and, in contrast to the underlying evaporites, ranges in colour from grey to red and pale green. Also in this same section, D-Bed includes thin red silty mudstone layers, one of which rests on an irregular penecontemporaneous erosion surface.

A bed of dolomitic limestone and dolomitic mudstone, 1.0 to 5.5 m thick, closely underlies the D-Bed and is correlated with the Belah Dolomite; the limestone is finely laminated with slight crenulation, and some of the laminae are separated by dark brown partings, perhaps decomposed plant fragments. The bed has not been recorded farther north than Long Meg, and within the district is at its thickest at Culgaith. No macrofauna has been recorded from the Belah Dolomite within the district but it has yielded a marine shelly fauna in the Brough and Kirkby Stephen districts to the south-east (Pattison, 1970).

The strata for about 3 m below the base of the limestone are typically grey, and in the Langwathby Borehole include a thin sandstone with pyritic concretions. Grey strata immediately above the limestone in this section include siltstones, with small concretions and joint-coatings of glauconite.

Strata above D-Bed

In contrast to the lower parts of the Eden Shales succession, the strata above D-Bed are partly exposed in a number of good sections in the southern part of the district. There are also good sections northwards from Lazonby which appear to lie in this part of the sequence, for they are at least 50 m above B-Bed.

This division is 45 to 60 m thick, and although mudstone is common, siltstone and sandstone are generally more abundant than in the underlying strata. The colour is strikingly different from the beds below. It ranges from dull red-brown in the sandstones to deep red-brown in the mudstones; purple-red and grey strata are not recorded, nor have plant debris been found. The strata are generally well-laminated, and sedimentary features include cross-lamination, load-casts, and desiccation-cracks. Structureless layers are common especially in the lower beds, and these comprise ill-sorted silty mudstone with, in some instances, scattered coarse grains of wind-rounded sand. Towards the top, beds of well-sorted, red fine-grained sandstone appear, and in many sections the base of the overlying St Bees Sandstone is poorly defined. Nodules of dolomite and anhydrite, and displacive veins of fibrous gypsum are recorded in the lower part of the division in several boreholes.

Conditions of deposition

The Eden Shales appear to have been laid down over the greater part of the Vale of Eden Basin. Their base is clearly diachronous, for there is evidence of their local overlap of the Penrith Sandstone at the D2 Borehole (p. 78), at Castle Carrock in the Brampton district, and at the southern end of the Vale (Burgess, 1965).

Deposition appears to have commenced in a localised tract that included the Lounthwaite and Kirkby Thore areas, and within this tract the sequence below B-Bed is the thickest proved. Isopachytes of this part of the sequence suggest either that this lowest part of the Eden Shales passes laterally into the Penrith Sandstone or that it was laid down in a hollow that developed on the surface of the sand sea after the deposition of the Penrith Sandstone (Arthurton and others, 1978), and was maintained while some 40 m of sediments accumulated. The latter view is preferred because the abrupt upward change to water-laid sediments, the general absence of aeolian sand grains, and the abundance of plant material in this lowest part of the Eden Shales all suggest that desert conditions had ended, and aeolian transport had largely ceased before deposition of the Eden Shales began. It is conceivable that the hollow was produced by selective deflation of unsilicified parts of the sand sea.

The laminated mudstones and siltstones which make up most of the Eden Shales up to the top of D-Bed are well sorted and seem to have accumulated during the progressive development of an alluvial plain that was initiated in the Lounthwaite–Kirkby Thore area, and gradually spread to fill the basin. The common presence of cross-lamination and cut-and-fill structures points to a shallow water environment, while features such as mudstone pellets and sand-filled desiccation cracks show that the sediment surface was periodically emergent. The occurrence of carbonaceous plant fragments indicates that vegetation was well established in the vicinity of the basin at least up to the time that D-Bed was formed, and the preservation of this organic material shows that it was deposited in reducing environments and was subsequently preserved from recurrent oxidising conditions.

The evaporites in the sequence are of varied types (Arthurton, 1971) and formed apparently as a result of marine influx into, or near to, the basin. Some have lithological analogues in the broad coastal flats (Sabkhas) of hot arid regions, such as the Trucial coast of the Persian Gulf. For example, the nodular anhydrite immediately overlying C-Bed at Langwathby (p. 79) and Lounthwaite (p. 80) is interpreted as the product of displacive, interstitial growth in emergent conditions. However, another lithology, the varved anhydrite, appears to have formed in subaqueous conditions, perhaps in an extensive though shallow lagoon.

The Belah Dolomite alone shows evidence of deposition in salinities which approached those of a normal marine environment, but in contrast to the earlier marine transgressions into the basin which entered from the north-west, this influx probably entered by way of Stainmore, directly from the North Sea basin to the east (Burgess, 1965). The fauna of the Belah Dolomite has an affinity with that of the Upper Magnesian Limestone (EZ 3) of north-eastern England (Smith in Meyer, 1965; Pattison, 1970), and it may be significant that this incursion transgressed the farthest westwards of all those of the Upper Permian in that area (Smith, 1970). In the present district conditions were not conducive to colonisation by a marine shelly fauna. The finely laminated dolomite at Lounthwaite and Langwathby (p. 80) appears to have formed in conditions of low energy in a shallow marine gulf that extended northwards from the Brough and Kirkby Stephen districts at least as far as Long Meg.

An important change seems to have occurred soon after the deposition of D-Bed, at least in those parts of the basin where D-Bed has been recognised. Conditions favouring substantial accumulations of evaporites no longer existed, and an oxidising environment seems to have predominated; at least if reducing conditions did exist any related sediments have been subsequently oxidised. The layers of structureless red silty mudstone, commonly including well-rounded sand grains, contrast with the almost exclusively laminated sequence below, and are interpreted as the products of accretion of aeolian detritus on an emergent surface (Burgess and Holliday, 1974; Arthurton and others, 1978).

Nearly all the sections in the uppermost part of the Eden Shales show intercalation of thick-bedded red sandstones in mudstones and siltstones, and it seems likely that much of the Eden Shales above D-Bed in the south of the district passes laterally northwards into the St Bees Sandstone (Figure 29).

Details

High Wreay and High Stand Plantation

The Eden Shales probably crop out beneath thick drift over an area of about 1.5 km² in the extreme north-western part of the district. Their total thickness is estimated as being 45 to 60 m, for the area lies about midway between the D2 Borehole [NY 3878 4805] in the Cockermouth district (Eastwood and others, 1968), where the formation totals 38 m, and Cocklakes (Figure 28) in the Brampton district where it totals 73 m (Meyer, 1965).

Provings are limited to a group of shallow boreholes which straddles the northern boundary of the district near High Wreay. None of the stratigraphical markers referred to above are recorded, and, at the base of the sequence flat-bedded, fine-grained sandstone is present. A borehole [NY 4296 4896], just within the Brampton district, proved the following sequence:

Another borehole [NY 4295 4879] proved 7.6 m of purple-red and red-brown mudstone and siltstone with a few layers of fine-grained sandstone while farther south, other boreholes [NY 4295 4861] to [NY 4297 4870] proved fine- and medium-grained flat-bedded red sandstone with mudstone pellets, apparently closely overlying the Penrith Sandstone. Similar sandy strata at the base of the formation are recorded in the Cocklakes Quarry Borehole [NY 4563 5093], the log of which is given in Appendix 1.

The B-Bed has been worked extensively for gypsum at Cocklakes, where its general thickness is in the range 5.8 to 7.3 m (Sherlock and Hollingworth, 1938), but C-Bed is not recorded. Red shales 45 to 55 m thick separate the top of B-Bed from the St Bees Sandstone (Hollingworth, 1942; Meyer, 1965).

Some 4 km to the south-east, at High Stand Plantation, a group of boreholes proved a very thin C-Bed separated from B-Bed by 1.6 m of shale; B-Bed is separated from the Penrith Sandstone by 9 to 12 m of shale with bands of sandstone. RSA

Ainstable to Culgaith

A group of boreholes around Ainstable has proved almost the entire sequence of the Eden Shales. Both B-Bed and C-Bed are present, and some 20 m above C-Bed there is a thin bed of gypsum/anhydrite which may possibly be D-Bed. At least 60 m of shales separate the St Bees Sandstone from the top of C-Bed, while B-Bed is separated from the Penrith Sandstone by about 15 m of shales. Near Ainstable, fine-grained red sandstone free from wind-rounded grains has been proved in auger-holes [NY 529 469] and [NY 5301 4660] at the extreme base of the formation.

The generalised succession for the Long Meg area (Figure 28) was given by Meyer (1965), and was based on a large number of commercial boreholes. It is as follows:

More recent borings in the Long Meg area show that the shales beneath B-Bed locally exceed 30 m in thickness.

Near Culgaith (Figure 29), boreholes have proved the entire sequence of Eden Shales. The B-Bed, C-Bed and D-Bed are all present, and the Belah Dolomite immediately underlies D-Bed and is up to 5.5 m thick. The thickness of strata separating the Penrith Sandstone from B-Bed increases markedly to the south-east from about 15 to 30 m: where the sequence is thickest A-Bed is present at its base. About 30 m of strata separate C-Bed from D-Bed, and about 60 m of shales separate D-Bed from the St Bees Sandstone.

Natural sections are mostly poor, although there are several good ones in the upper part of the formation. They are described below in stratigraphical order, starting with the strata below B-Bed.

In a gully [NY 5213 4410] near Beck, about 1.2 m of purple-red mudstone and siltstone, probably lying below B-Bed, are exposed in faulted contact with Penrith Sandstone. A poor section in similar strata, probably within 6 m of the base of the formation, is exposed [NY 5591 4140] on the southern side of Raven Beck. Farther south there are scattered exposures, probably lying below B-Bed, in Glassonby Beck, 2 km SE of Kirkoswald; they show purple-red and pale green micaceous mudstones, commonly steeply inclined suggesting the proximity of a fault, and one of the best sections [NY 5680 3951] exposes 1.8 m of these strata in the southern bank of the stream. Purple-red mudstones probably from about the same part of the succession are exposed below thick drift in the eastern bank [NY 5618 3675] of the River Eden, 800 m NW of Little Salkeld.

Near the southern boundary of the district, sections in a meander scar [NY 5995 2951] on the western bank of the River Eden, show up to m of mudstone lying below B-Bed. The mudstone is mottled red-brown and medium to pale grey, and includes layers of sand and many veins of fibrous gypsum. Some 400 m to the south, 1.5 m of red-brown silty mudstone with bands of sandstone from about the same part of the sequence are exposed in a landslip scar [NY 6002 2930] on the river bank. On the eastern bank of the river, mudstone slightly higher in the sequence, but still below B-Bed, was formerly worked at Culgaith Tileworks [NY 604 292]. In the southern part of the workings [NY 6039 2916] about 7.6 m of pale grey and red-brown mudstone are exposed, and include a layer of gypsum 0.9 m thick and many veins of fibrous gypsum. Hollingworth (1942) recorded grey clays with gypsum and interbedded 'millet-seed' sand and sandstone 'representing intercalations of Penrith Sandstone', from these same workings, but these exposures have since been covered.

The B-Bed is 4 m thick and composed entirely of gypsum where it is exposed in the walls of a disused adit [NY 5655 3805] near Long Meg Mine, about 1.5 km N of Little Salkeld. Eastward under increasing cover anhydrite is preserved within the gypsum and eventually becomes dominant (Sherlock and Hollingworth, 1938). Gypsum was formerly worked on both sides of a valley extending south-eastwards from Lacy's Caves e.g. [NY 5637 3792], about 1 km NW of Long Meg, and there are two other disused adits entering B-Bed in this vicinity [NY 5655 3805] and [NY 5655 3820]. The present mine-mouth [NY 5635 3770] enters just above B-Bed.

The Eden Shales between C-Bed and D-Bed are exposed only in Raven Beck, 1.2 km ENE of Kirkoswald, where a section in the southern bank of the stream [NY 5653 4153] exposes 3.7 m of red-brown micaceous silty mudstone.

Gypsum, possibly D-Bed, was formerly worked by opencast [NY 5291 4373] in the floor of a glacial drainage channel near Ruckcroft (Harkness, 1862). Red-brown mudstones thought to lie just above the horizon of D-Bed are exposed in a landslip scar [NY 5268 4430] west of Ruckcroft, and similar strata, but with thin sandy bands, from about the same part of the sequence, are poorly exposed in a gully [NY 5483 4245], north-north-west of Kirkoswald. Southwards from this village, 1.2 m of purple-red mudstone with sandy bands, lying at about the horizon of D-Bed, are exposed in a stream [NY 5661 3802], and farther up-stream [NY 5674 3794] red-brown mudstone with layers rich in coarse, wind-rounded sand grains crops out. The outcrop of D-Bed probably lies between these two localities.

Some 3.7 m of red-brown silty mudstone, probably lying just above D-Bed, are exposed in the eastern bank of the River Eden [NY 5866 3126], about 200 m N of the confluence with the River Eamont, while weathered red mudstones with thin layers of fine-grained sandstone, also probably lying just above D-Bed are poorly exposed on the steep bank immediately south of Culgaith, and also on the side of the adjacent road [NY 6041 2936] to [NY 6057 2945]. Near the southern portal of Culgaith Tunnel [NY 6066 2942], about 1 m of red-brown hard dolomitic siltstone is exposed. The siltstone includes coarse wind-rounded sand grains, and probably correlates with a similar bed lying some 6 to 9 m above the 'Magnesian Limestone' (Belah Dolomite) in Hilton Beck (Hollingworth, 1942).

In the north, Eden Shales lying high above D-Bed are exposed in a gully [NY 5349 4843] on the escarpment at Lawson Hill: the section comprises 6.1 m of red-brown siltstone and mudstone within 20 m of the top of the formation, and at the head of this gully the base of the St Bees Sandstone is marked by a line of spring-seepage. Similar strata, again lying just below the St Bees Sandstone, are poorly exposed some 2.5 km to the south, in a pit [NY 5378 4606] near Ain-stable, and in a nearby gully [NY 5377 4585]. Farther south, strata within 40 m of the base of the St Bees Sandstone are well seen in two gullies on the northern side of a glacial drainage channel near Ruckcroft; one section [NY 5284 4387] consists of 21.3 in of red-brown mudstone and micaceous siltstone which include a few bands of fine-grained sandstone and layers of grey dolomitic nodules; sedimentary features include mudstone pellets and sand-filled desiccation cracks in mudstone. In a neighbouring gully [NY 5324 4365] 9.1 m of similar strata are exposed. Some 2 km to the east, in a gully [NY 5470 4391] carrying a tributary of Croglin Water near Springfield, about 9 m of red-brown mudstone arid siltstone at the extreme top of the Eden Shales are succeeded by thick-bedded red sandstones with subordinate interbedded mudstones, best included within the St Bees Sandstone. In meander scars of Croglin Water nearby e.g. [NY 5463 4383] and [NY 5437 4354], red-brown mudstone arid siltstone within 30 m of the top of the formation are seen.

Further exposures in the topmost 40 m or so of the Eden Shales lie in Raven Beck and in a tributary about 2 km NE of Kirkoswald. A discontinuous section of about 30 m of red-brown mudstone and siltstone with thin bands of sandstone occurs in the tributary [NY 5726 4203] to [NY 5767 4233], and at the northern end of this section the base of the St Bees Sandstone is again seen. In Raven Beck, there are sporadic exposures of similar strata in the northern bank [NY 5745 4189] to [NY 5788 4175]. Near its base this section includes a few yellow dolomitic layers up to 2 cm thick, and the St Bees Sandstone comes on at its eastern end. Southwards from here, this part of the sequence is exposed in a stream [NY 5690 3783] near Long Meg where, in 13.7 m of strata consisting mainly of red-brown mudstones and siltstone, the proportion of sandstone increases towards the top; and in a gully [NY 5654 3718] about 800 m N of Little Salkeld, where red-brown silty mudstones with sandy bands are seen. Some 400 m to the south-east, it is better exposed in the southern bank of a stream [NY 5685 3694] and [NY 5702 3577], south-east of Little Salkeld, and at the latter locality the section is:

A similar sequence is exposed in a neighbouring stream-section [NY 5705 3590] to [NY 5718 3594].

Near the southern boundary of the district, are some 12 m of red-brown silty mudstone, extending upwards from about 15 m above D-Bed, near the northern portal of Culgaith Tunnel [NY 6012 2982]. The mudstones contain hard sandy and calcareous layers with cross-lamination, rain-pits, and layers of mudstone pellets. Red-brown mudstones and siltstones with calcareous layers, probably from the same part of the sequence, are poorly exposed in the eastern side of the cutting [NY 5962 3007] to [NY 5953 3013] and [NY 5925 3039].

Langwathby Borehole

An almost complete sequence of the Eden Shales was proved in the Langwathby Borehole [NY 5823 3335], sunk for the Institute some 1.2 km ESE of Langwathby. The log of this borehole is given in Appendix 1 (p. 154), and the petrography and sedimentology of the evaporites have been described previously (Arthurton, 1971). The Eden Shales were proved to a thickness of 114.5 rounder the St Bees Sandstone, but the top of the Penrith Sandstone was not reached. All of the stratigraphical markers referred to in the general section of this chapter were recognised.

Below B-Bed the Eden Shales comprised 21.6 m of red, and subordinate grey, mudstones and siltstones—mostly laminated—with, towards the base especially, layers of fine-grained dull red sandstone, with sharp and commonly erosional bases. Sedimentary structures in the red strata include load-casts, desiccation cracks in mudstone, and mudstone-pellet conglomerates; and in the grey, cut-and-fill and traces of algal-mats. Anhydrite is present as nodules throughout much of the sequence, and in some instances these nodules assume an enterolithic form. Between 181.4 and 183.5 m in the borehole, the nodules are abundant, and are regarded as the local equivalent of A-Bed. Gypsum is common, being present both as porphyroblasts replacing anhydrite and, in its fibrous form, in displacive veins. The red strata are barren but for rare ?Estheria, and partly oxidised plant-fragments, while the grey beds contain plant fragments which range in abundance from sporadic to profuse.

The B-Bed is 4.88 m thick and is immediately underlain by, and in its lower part includes, partings of grey plant-bearing mudstone.

It consists almost entirely of aphanitic anhydrite ranging in colour from pale grey to black. The principal accessory minerals are gypsum, which occurs as scattered porphyroblasts, and magnesite, as small nodules. While algal-mat fabrics are present near the base, most of the anhydrite occurs in layered fabrics of two distinct types =diffusely layered', and 'varved'.

The strata separating B-Bed and C-Bed are 3.7 m thick and comprise dark grey plant-bearing, and purple-red laminated mudstone and siltstone with displacive veins of fibrous gypsum. The C-Bed is 1.5 in thick, and like B-Bed is immediately underlain by grey, plant-bearing mudstones. It consists almost entirely of aphanitic anhydrite, the principal accessory minerals again being gypsum in replacive porphyroblasts and magnesite in small nodules. Its colour ranges from pale to mid-grey and brownish grey, and while its lower part is layered, the uppermost 0.46 m comprise ill-defined nodules. The bed is immediately overlain by red silty mudstone containing abundant nodules of lath-anhydrite partly replaced by gypsum in porphyroblasts.

The strata between C-Bed and D-Bed are red and grey in approximately equal proportions. They are mainly mudstones and siltstones and include two thin layers of gypsum and anhydrite, 0.45 and 1.07 m thick, lying respectively 14.8 and 17.7 m above the top of C-Bed. The upper of these layers, termed the Langwathby Bed, consists of laminated aphanitic anhydrite ((Plate 7).1), partly muddy or silty, and largely replaced by porphyroblastic gypsum. The anhydrite includes 'cut-and-fill' structures and probable algal-mats, and is associated with grey, plant-bearing mudstone. The Belah Dolomite is represented by about 0.6 m of buff dolomitic limestone and siltstone which is very finely laminated and includes dark brown partings, apparently due to planty debris. This is underlain by some 4.5 m of fine-grained sandstone with a sharp erosive base; the lower part of this sandstone is dull red, while the upper part is grey and includes scattered coarse well-rounded sand grains and small pyritic concretions. Some 1.5 m of grey-brown siltstone and mudstone, partly dolomitic and anhydritic, and including plant fragments, separates the Belah Dolomite from D-Bed, and in the lower part of this layer green concretions and joint-coatings of glauconite occur.

The D-Bed is 2.59 m thick and comprises aphanitic anhydrite partly replaced by alabastrine gypsum ((Plate 7).2). In contrast to the predominantly grey colours of the underlying evaporites, the D-Bed colour ranges from grey to red and pale green; also, it includes thin layers and partings of red silty mudstone, one of these resting on an irregular erosion surface.

Between D-Bed and the base of St Bees Sandstone, were 45.7 m of mostly red-brown mudstones and siltstones, partly micaceous. Much of the sequence is well laminated but, in its lower part, layers of structureless silty mudstone are present and these commonly include scattered coarse well-rounded sand grains; sedimentary features include ripple-marks and mudstone pellets. Gypsum or anhydrite is present in all but the uppermost part; gypsum mostly in its fibrous form as displacive veins, but also as small nodules and detrital fragments, and as a cement; anhydrite as laminae and small nodules.

Croglin and Gamblesby

Two small outcrops of the Eden Shales are present immediately to the west of the Pennine Fault near Croglin, but none of the strati-graphic markers referred to above has been recognised. The best section is in a stream [NY 5758 4765] to [NY 5785 4816], some 800 m NNE of Croglin, where about 30 m of red-brown mudstone and siltstone with thin layers of fine-grained sandstone crop out; at the southern end of this section the base of the St Bees Sandstone is seen. Some 2 km to the south-east, a passage from the Eden Shales to the St Bees Sandstone is revealed in a steep bank [NY 5896 4623] to [NY 5904 4623] at the southern end of a large glacial drainage channel. The section is poorly exposed but appears to comprise some 10 m of interlayered red-brown siltstone and mudstone, and dull red fine-grained sandstone.

There are two further small outcrops of the Eden Shales immediately west of the Pennine Fault near Gamblesby. Weathered red mudstone and siltstone lie in the northern bank of a stream and have been proved by augering [NY 6232 4136], 2 km NE of Gamblesby. They probably lie near the top of the formation, and a small spring which issues near this locality is taken as marking the base of the St Bees Sandstone, unexposed here but visible in the stream-bed about 55 m to the west. In another stream [NY 6159 3872], 800 m SE of Gamblesby, 9 m of red-brown mudstone interlayered with sandstone and siltstone are overlain by thick-bedded red sandstone of the St Bees Sandstone.

Lounthwaite

The largest outcrop of the Eden Shales on the eastern limb of the Vale of Eden Syncline is near Lounthwaite, in the south-eastern corner of the district. Much of the succession in this crop was proved in the IGS Lounthwaite Borehole [NY 6535 3092]. The Eden Shales were entered beneath the drift 7.3 m above a dolomitic limestone correlated with the Belah Dolomite, and were proved to a thickness of 108.8 m before the Penrith Sandstone was penetrated. All of the stratigraphic markers referred to above were recognised, with the exception of D-Bed.

Between the Penrith Sandstone and the base of B-Bed lie 57.1 m of Eden Shales, which comprise mostly purple-red, red-brown, and grey laminated mudstones and siltstones with sporadic layers of pale grey fine-grained sandstone. Their base lies sharply on the Penrith Sandstone, although scattered, coarse, well-rounded sand grains are present in the lowest few centimetres. Gypsum is present through much of the sequence, either as nodules and laminae or in its fibrous form as displacive veins. Within the lowermost 4 m is a layer of white, coarse-textured gypsum 1.6 m thick. Rarely, gypsum is present in grey mudstone as pseudomorphs after euhedral halite. Between 46.2 and 18.9 m below the base of B-Bed, the laminae and layers of grey mudstone yielded an abundance of carbonaceous plant-fragments. The flora, identified by Prof. W. G. Chaloner, includes: Ullmannia bronni, U. cf. frumentaria, Lepidopteris martinsi, cf. Pseudovoltzia liebeana, Strobilites bronni, cf. Samaropsis triangularis.

The B-Bed is 6.5 m thick, and is both underlain and capped by grey mudstone; it also includes a parting of grey gypsiferous mudstone towards its base. It comprises medium or dark grey-brown translucent gypsum (about 80 per cent of the whole) with subordinate pale grey and white aphanitic anhydrite occurring principally in three layers in its central and highest parts. Accessory minerals include pyrite and ?halite. Although the primary sedimentary fabric is not well preserved, the lowermost 2.5 m appear to be layered or laminated. By contrast the higher part of B-Bed, except perhaps the uppermost 0.5 m, is nodular—ovate nodules up to about 2 cm diameter forming a mosaic fabric. Gypsum is present in two main varieties: the dominant one is a fine-textured alabaster formed by progressive replacement of anhydrite along sub-horizontal stringers or leaves; the other comprises porphyroblasts, which have replaced anhydrite prior to the formation of alabastrine gypsum.

The B-Bed and C-Bed are separated by 2.3 m of purple-red silty mudstone permeated throughout by gypsum, and displaced by veins of fibrous gypsum. The C-Bed is 2.7 m thick and, like its correlative in the Langwathby Borehole, rests on grey mudstone and is capped by red silty mudstone. Its consists largely of brownish grey, fine-textured alabastrine gypsum, although grey aphanitic anhydrite is preserved in its middle part. Layered fabrics predominate and pale, grey brown ?magnesite is present interstitially within its lower half. Other accessory minerals include halite. The red silty mudstone immediately overlying the C-Bed contains abundant nodules of porphyroblastic gypsum, apparently after anhydrite.

The D-Bed was not recorded in this borehole, but a layer of dolomitic limestone, taken to be the Belah Dolomite serves as a strati-graphic marker. The strata between the top of C-Bed and this limestone are mostly purple-red and grey mudstones and siltstones either laminated or, more rarely, structureless. A few layers of purple-red or grey fine-grained sandstone are present and contain coarse well-rounded sand grains and similar grains are common in the structureless mudstones and siltstones in the upper part of the sequence. Gypsum is common, either in its fibrous form as displacive veins or in nodules, and a layer of gypsum 1.3 m thick, associated with grey plant-bearing mudstone, occurs 9.5 m above the top of C-Bed. Yellow-brown medium-grained silty sandstone 2.1 m thick and containing abundant coarse, well-rounded sand grains immediately underlies the Belah Dolomite.

The Dolomite comprises 1.3 m of thinly laminated buff dolomitic limestone; the laminae are slightly irregular and crenulated, and dark brown partings, apparently due to decomposed plant debris, are present in places. Some 7.3 m of strata were proved between the Belah Dolomite and the base of the drift and, although D-Bed was not encountered, the broken nature of the cores for about 2 m above the Dolomite suggests that a layer of gypsum and anhydrite was originally present, but has since been dissolved by groundwater, with consequent collapse-brecciation of the overlying strata. Red-brown silty mudstone, partly laminated but largely structureless, forms the bulk of the sediments above the Dolomite. Scattered coarse well-rounded sand grains are common, especially in the structureless layers and in places are so abundant as to form discrete layers or laminae.

The strata exposed in natural sections nearby are limited to those parts of the sequence lying below B-Bed and to those above the Belah Dolomite. Some 2 km N of Milburn pale and mid-grey plant-bearing mudstone with laminae and nodules of ironstone are exposed [NY 6561 3133] in the southern bank of Crowdundle Beck; the mudstone yielded the following flora: Lepidopteris martinsi, Pseudovoltzia liebeana, Strobilites bronni, Ullmannia bronni, U. frumentaria.

This mudstone is here regarded as lying between A-Bed and B-Bed, and possibly lies in normal sequence with the Penrith Sandstone exposed a few hundred metres upstream.

Farther downstream in Crowdundle Beck are sporadic exposures of Eden Shales, which probably lie above the Belah Dolomite. In the southern bank of the stream [NY 6465 3061] these include 7.6 m of red-brown mudstone with scattered coarse aeolian sand grains throughout, and a single prominent dolomitic bed, 1.0 to 1.5 m thick, which may be the broad correlative of the similar bed exposed near Culgaith Tunnel (p. 79). RSA, AJW

References

ARTHURTON, R. S. 1971. The Permian evaporites of the Langwathby Borehole, Cumberland. Rep. Inst. Geol. Sci., No. 71/17. 18 pp.

ARTHURTON, R. S., BURGESS, I.C., and HOLLIDAY, D. W. 1978. Permian and Triassic. In The Geology of the Lake District. F. MOSELEY (Editor). Occas. Publ. Yorkshire Geol. Soc., No. 3.

ARTHURTON, R. S. and HEMINGWAY, J. E. 1972. The St Bees Evaporites-a carbonate-evaporite formation of Upper Permian age in West Cumberland, England. Proc. Yorkshire Geol. Soc., Vol. 38, pp. 565–592.

BURGESS, I. C. 1965. The Permo-Triassic rocks around Kirkby Stephen, Westmorland. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 91–101.

BURGESS, I. C. 1968. In Annu. Rep. Inst. Geol. Sci. for 1967, p. 89.

BURGESS, I. C.  and HOLLIDAY, D. W. 1974. The Permo-Triassic rocks of the Hilton Borehole, Westmorland. Bull. Geol. Surv. G.B., No. 46, pp. 1–34.

CLARKE, R. F. A. 1965. British saccate and monosulcate miospores. Palaeontology, Vol. 8, pp. 322–354.

DAKYNS, J. R., TIDDEMAN, R. H. and GOODCHILD, J. G. 1897. The geology of the country between Appleby, Ullswater and Haweswater. Mem. Geol. Surv. G.B.

EASTWOOD, T., DIXON, E. E. L., HOLLINGWORTH, S. E. and SMITH, B. 1931. The geology of the Whitehaven and Workington district. Mem. Geol. Surv. G.B.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. The geology of the Cockermouth district. Mem. Geol. Surv. G.B.

GOODCHILD, J. G. 1893. Observations on the New Red Series of Cumberland and Westmorland with especial reference to classification. Trans. Cumberland, Westmorland Assoc., Vol. 17, pp. 1–24.

HARKNESS, R. 1862. On the sandstones and their associated deposits in the Vale of Eden, the Cumberland Plain and the south-east of Dumfries-shire. Q. J. Geol. Soc. London, Vol. 18, pp. 205–218.

HOLLINGWORTH, S. E. 1942. The correlation of gypsum-anhydrite deposits and the associated strata in the north of England. Proc. Geol. Assoc., Vol. 53, pp. 141–151.

MEYER, H. O. A. 1965. Revision of the stratigraphy of the Permian evaporites and associated strata in north-western England. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 71–89.

MURCHISON, R. I. and HARKNESS, R. 1864. On the Permian rocks of the north-west of England and their extension into Scotland. Q. J. Geol. Soc. London, Vol. 20, pp. 144–165.

PATTISON, J. 1970. A review of the marine fossils from the Upper Permian rocks of Northern Ireland and north-west England. Bull. Geol. Surv. G.B., No. 32, pp. 126–163.

SEDGWICK, A. 1832. On the New Red Sandstone Series in the basin of the Eden and the north-western coasts of Cumberland and Lancashire. Trans. Geol. Soc. London, Ser. 2, Vol. 4, pp. 383–407.

SHERLOCK, R. L. and HOLLINGWORTH, S. E. 1938. Gypsum and anhydrite and celestine and strontianite. Mem. Geol. Surv. Spec. Rep. Miner. Resour. G.B., Vol. 3, Third edition. 98 pp.

SIIOTTON, F. W. 1956. Some aspects of the New Red Desert. Liverpool Manchester Geol. J., Vol. 1, pp. 450–465.

SMITH, B. 1924. On the West Cumberland Brockram and its associated rocks. Geol. Mag., Vol. 61, pp. 289–308.

SMITH, D. B. 1970. The palaeogeography of the British Zechstein. Pp. 20–23 in Third Symposium on Salt. RAU, J. L. and DELLWIG, L. F. (Editors). (Cleveland: Northern Ohio Geological Society.)

SMITH, G. V. 1884. On further discoveries of the footprints of vertebrate animals in the Lower New Red Sandstone of Penrith. Q. J. Geol. Soc. London, Vol. 40, pp. 479–481.

STONELEY, H. M. M. 1958. The Upper Permian flora of England. Bull. Br. Mus. (Nat. Hist.) Geol., Vol. 3, pp. 293–337

TROTTER, F. M. and HOLLINGWORTH, S. E. 1932. The geology of the Brampton district. Mem. Geol. Surv. G.B.

WADGE, A. J. 1968. In Annu. Rep. Inst. Geol. Sci. for 1967, p. 85.

WAUGH, B. 1965. A preliminary electron microscope study of the development of authigcnic silica in the Penrith Sandstone. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 59–69.

WAUGH, B.  1970. Petrology, provenance and silica diagenesis of the Penrith Sandstone (Lower Permian) of north-west England. J. Sediment. Petrol., Vol. 40, pp. 1226–1240.

Chapter 7 Trias

St Bees Sandstone

Unfossiliferous red sandstones overlie the Eden Shales and comprise the youngest solid strata preserved within the district. Further north, in the Carlisle and Brampton districts, these red sandstones are overlain in turn by the unfossiliferous Stanwix Shales and by the shales and limestones of the Lower Lias—the first control of stratal age above the Belah Dolomite in the Eden Shales (p. 75). Both the red sandstones and the Stanwix Shales are likely to be largely, if not wholly, Triassic in age and, for convenience, the base of the Triassic System is here taken at the base of the sandstones, even though that boundary is probably diachronous (p. 68).

In many sections, the base of the St Bees Sandstone is difficult to place with certainty, as the junction with the Eden Shales is gradational. In these sections, where a few metres of interbedded shales and sandstones form a transitional sequence, the base of the formation is arbitrarily taken at the base of the lowest, thickly bedded sandstone.

In the Carlisle and Brampton districts the red sandstones have been divided into two formations (Holmes, 1881, 1899; Dixon and others, 1926; Trotter and Hollingworth, 1932), the lower of which, the St Bees Sandstone, is duller in colour and more strongly cemented than the upper, the Kirklinton Sandstone. Both formations were recognised in the Penrith district by Goodchild (1893), but in the present survey this has been considered impractical and the whole of the sandstones are classed as one formation only and referred to as the St Bees Sandstone.

The outcrop of the St Bees Sandstone is some five kilometres wide and occupies the axial part of the Vale of Eden Syncline between the River Eden and the Pennines. It is extensively concealed by boulder clay but gives a light, well-drained soil where free from drift.

The lowermost 100 m or so are well exposed, the best natural sections being in the banks of Croglin Water and Raven Beck in the north, and Aigill Sike and Crowdundle Beck in the south. There are also good sections in several disused building-stone quarries, as near Briggle. These strata were also proved in the Langwathby Borehole where they are dull red and made up of flat and commonly cross-bedded units that range in thickness from a few centimetres to at least three metres. The component grains are generally well cemented and are almost exclusively of subangular quartz sand of fine and medium grade, although scattered coarse 'millet-seed' grains have been reported. Mica is generally sparse but locally abundant. Partings or thin beds of deep red mudstone and micaceous siltstone, some with sand-filled desiccation cracks, are especially common towards the base of the formation which in some sections is transitional from the Eden Shales. Pellets of mudstone are quite common within the sandstone units.

The sandstone higher in the formation is broadly similar, but is mostly a brighter red, and includes cream-coloured bands and patches some of which are richly micaceous. It is less well cemented and consequently rather poorly exposed, some of the best sections being in the banks of Briggle Beck near Croglin, and around Ousby (Plate 8).

The variation in cementation between the upper and lower parts of the formation is clearly expressed in the topography of the outcrop. In the west the basal part forms the cap to a scarp which is particularly strong to the north of Ainstable and at Culgaith; and the overlying 100 m of strata form an upland tract 1 to 2 km wide, as for example around King Harry and Maughanby. Farther eastwards the softer, higher strata form relatively low-lying country, as for example at Melmerby Mire.

The rather poor exposure of the upper part of the formation and the absence of reliable stratigraphical markers make estimates of the thickness of preserved strata somewhat speculative. From the available structural evidence, however, it seems that the thickest sequences lie in the vicinity of Renwick and near Ousby, where they are of the order of 500 to 600 m.

Conditions of sedimentation

The sedimentology of the St Bees Sandstone has not been studied in detail within the district, but the following are general inferences concerning the sedimentary environment of the formation, which appears to have completely covered the Eden Shales, and probably overlapped them on to Carboniferous and Lower Palaeozoic strata.

The sands were deposited in non-marine, shallow water under oxidising conditions, although the desiccation features in the mudstones imply that the surface of the sediment was subject to periodic and perhaps prolonged emergence. In these respects the supposed environment is similar to that envisaged for the upper part of the Eden Shales, but the thick, cross-bedded sandstone units point to deposition as a tract of river alluvium rather than on the broad expanse of a playa. The rivers are likely to have been shallow, braided and seasonal in their activity, migrating to and fro across the basin while depositing sand on their beds and silt and mud on flood plains.

Details

Along the northern part of its outcrop, the basal St Bees Sandstone caps a west-facing scarp, particularly prominent around Lawson Hill [NY 535 486] to [NY 536 479] near Ainstable, and forms a strip of relatively high ground including King Harry [NY 543 476] and Broomrigg Plantation. These strata are well exposed about 1 km S of the Plantation in a gorge [NY 5462 4478] 25 m deep near Dale Mill; a section in a disused quarry at the northern end shows some 12 m of dull red sandstone in thickly cross-bedded units, some separated by partings of mudstone up to a few centimetres thick. Thicker beds of mudstone and siltstone are intercalated with thickly bedded sandstone at the extreme base of the formation in a stream section [NY 5476 4388] about 1 km farther south, and give rise to many springs issuing from the St Bees Sandstone around Dale e.g. [NY 5488 4443].

The basal beds are also exposed some 4 km to the north-east, on the eastern side of the Vale of Eden Syncline, where stream sections and disused quarries around Croglin e.g. [NY 5679 4809] and [NY 5757 4747] show thickly cross-bedded sandstones with partings and thicker beds of mudstone and siltstone.

The section in Raven Beck is one of the best in the lower part of the formation. The base is seen [NY 5773 4178] and [NY 5785 4164] in both banks of the river some 500 m W of Parkhead, and upstream from here to Low Mill [NY 589 422] there are many natural and quarry exposures of cross-bedded sandstone; argillaceous partings appear towards the base. About 2 km to the south, similar strata have been worked for building stone in Ridding Quarry [NY 5907 3999], the present section showing posts of medium-grained sandstone up to 2.5 m thick interbedded with pale grey flaggy sandstone and micaceous siltstone. The base of the formation is exposed in a stream [NY 6159 3872] some 3 km to the east-south-east, near Gamblesby and on the eastern limb of the syncline.

Massive, red sandstone within 100 m of the base was formerly worked [NY 5780 3552] for walling stone just west of Hunsonby, and flaggy, ripple-marked sandstone, also low in the formation has been extensively quarried some 1.5 km upstream [NY 5938 3625].

Between Langwathby and Culgaith the base of the formation is marked by a scarp, partly masked by drift in the north, but prominent in the south. On the adjoining Langwathby Moor the outcrop falls north-eastwards away from the scarp towards Briggle Beck. The Langwathby Borehole [NY 5823 3335], sited on the Moor, penetrated the lowermost 74 m of the St Bees Sandstone (see Appendix 1, p. 154), which comprised red-brown, fine- and medium-grained, slightly micaceous sandstone in beds ranging in thickness from a few centimetres to about 3 m; partings or beds of deep red mudstone and micaceous siltstone, associated with sand-filled desiccation cracks, ripple-marks, and cross lamination were common in the lowest 36 m, along with bands of mudstone pellets within the sandstone units. Pale grey patches and bands were sporadically present in the upper part of the core.

Eastwards from here are many good natural and quarry sections in the lower part of the formation. Some 12 m of fine-grained massive sandstone are exposed in quarries [NY 5858 3414] in the banks of Hole Sike, south of Briggle, while 3 km to the south-east, quarries [NY 6072 3192] on the steep banks of Aigill Sike are in massive and flaggy sandstone. Similar sections are also present in quarries [NY 6073 3266] along Briggle Beck, about 1 km W of Skirwith. Farther to the south-east these strata are well exposed in Crowdundle Beck and Milburn Beck, to the east of Scartop; for example quarry-sections [NY 6303 2958] show up to 30 m of red, medium-grained sandstone, mostly massive but with some flaggy partings. In another quarry [NY 6592 2860], some 3 km to the east, and lying just within the Appleby district, the sandstone includes scattered 'millet-seed' grains.

The higher part of the formation generally forms relatively low-lying ground, and is less well exposed. To the north of Croglin Water, these softer strata form a clearly defined trough which straddles the Vale of Eden Syncline, but within this trough there are scattered knolls of well-cemented rock, as for example [NY 557 489], 500 m SSE of Cairnhead Farm. These strata are mostly poorly exposed in Croglin Water, which has a broad alluvial tract where it traverses their outcrop. In the west, however, 500 m W of Caber, the river flows in a gorge cut some 25 m deep and sections in the northwestern bank [NY 5601 4638] show up to 10 m of sandstone in thickly cross-bedded units, the sandstone being red with cream bands and patches. Similar strata are exposed in the banks of Briggle Beck, a glacial drainage channel some 1.5 km to the south and south-east, the best sections—up to 5 m—being in quarries [NY 5633 4512], near Lowhall Building, and [NY 5805 4501], south of Middle Moor.

These higher beds are fairly well exposed around Renwick, the best sections being in the banks of Raven Beck [NY 589 422] to [NY 596 428]; [NY 6012 4309] to [NY 6118 4340], and in the banks of a glacial drainage channel [NY 5928 4360] and [NY 5944 4297]. To the south-west of Renwick the strata dip steadily to the north or north-east so that 400 to 500 m of the higher beds may be present near the village.

Southwards from Raven Beck, the higher beds are commonly, though not extensively exposed between Cannerheugh and Hazelrigg Beck. For example, sections in disused quarries [NY 6124 4169] near Cannerheugh, and [NY 6101 4084] near Unthank, show up to 6 m of fine-grained sandstone in thickly cross-bedded units, mostly red but with cream bands, and in Woolhead Quarries [NY 5959 3990], 1.2 km WNW of Gamblesby, well-cemented sandstone, massive and red but for a cream-coloured ripple-marked partings of fine-grained sandstone, stands in a face some 10 m high.

Farther south, towards Melmerby, these strata have a low-lying outcrop, as for example at Melmerby Mire [NY 597 384]. The sandstone is mostly poorly cemented, but locally knolls of well-cemented rock are present, such as Tortree Hill [NY 6147 3786] near Melmerby.

There are fine sections of red medium- and fine-grained sandstone with cream-coloured micaceous partings in Melmerby Beck [NY 6231 3754] to [NY 6156 3733] between Melmerby and the Pennine Fault; in Dennison's Sike [NY 6170 3692] to [NY 6216 3646], south-east of the village; and particularly in the banks of Sunnygill Beck [NY 619 357] to [NY 608 367], to the south-west of the village. All these sections are in the higher part of the formation.

Outcrops farther south around Ousby may be of some of the youngest strata preserved in the district; for the steady northeasterly dips which are seen intermittently between the western scarp and Ousby suggest that some 600 m of St Bees Sandstone may be present. There is, however, little to distinguish these strata from lower beds, for red and cream-coloured sandstone in thickly cross-bedded units, and pale yellow flaggy sandstone are the typical lithologies. Good sections can be seen in small disused quarries in Hole Sike [NY 6199 3452] and [NY 6198 3420], where lenticular beds of silty, finely laminated sandstone and red silty mudstone are interbedded with thick units of cross-bedded red sandstone (Plate 8). RSA, AJW

References

DIXON, E. E. L., MADEN, J., TROTTER, F. M., HOLLINGWORTH, S. E. and TONKS, L. H. 1926. The geology of the Carlisle, Longtown and Silloth district. Mem. Geol. Surv. G.B.

GOODCHILD, J. G. 1893. Observations on the New Red Series of Cumberland and Westmorland, with especial reference to classification. Trans. Cumberland Westmorland Assoc., Vol. 17, pp. 1–24.

HOLMES, T. V. 1881. The Permian, Triassic and Liassic rocks of the Carlisle Basin. Q. J. Geol. Soc. London, Vol. 37, pp. 29–38.

HOLMES, T. V. 1899. The geology of the country around Carlisle. Mem. Geol. Surv. G.B.

TROTTER, F. M. and HOLLINGWORTH, S. E. 1932. The geology of the Brampton district. Mem. Geol. Surv. G.B.

Chapter 8 Intrusive igneous rocks

Three groups of intrusions can be distinguished by their ages. The oldest consists of dykes, bosses and sills restricted to the Lower Palaeozoic outcrops and dating from Ordovician, Silurian and early Devonian times. The quartzdolerite Whin Sill, intruding the Carboniferous rocks of the Alston block, is late-Carboniferous or early-Permian in age, whilst the Armathwaite dyke, traversing the northern part of the district, was emplaced in Tertiary times.

Lower Palaeozoic intrusions

Dykes are intruded into the Lower Palaeozoic rocks of both the Greystoke and Cross Fell inliers. They are described separately as they belong to different suites of minor intrusions, each apparently related to a different major intrusion.

Greystoke

Five dolerite dykes cut andesites of the Borrowdale Volcanic Group in the eastern part of the inlier [NY 405 330]. They are near-vertical, 1 to 3 m wide and their ESE-trend is roughly parallel to the regional strike. Similar dykes are probably numerous beneath the extensive drift cover hereabouts, and certainly they occur in large numbers farther west in the Cockermouth district, where they were regarded as a dyke swarm related to the Carrock Fell complex (Eastwood and others, 1968, p.131). They consist of grey, medium-grained, albitised dolerite. In thin sections (E378478), (E378479) corroded albitised plagioclase laths are subophitically associated with pale green augite; much of the interstitial matrix is chloritised, with acicular albite aggregates set in quartz, carbonate and leucoxene dust. There is scattered accessory magnetite and much granular epidote, probably deuteric in origin, whilst small sub-vesicular areas are filled with radially fibrous chlorite and quartz.

Cross Fell

The inlier contains 141 minor intrusions and these are particularly numerous in the northern part (Figure 31). The few dykes in the southern part are described in detail in the Brough memoir (Burgess and Holliday, 1979) but the overall relationships between the suites of dykes throughout the inlier are summarised here.

The intrusions are mostly steeply-inclined dykes intruded along joints or cleavages; they remain essentially discordant even where they locally invade the bedding, as this occurs only where dips are steep. Their general trend is Caledonoid (east-north-east) although there are many exceptions. Where the dykes are most numerous, the total crustal extension normal to their trend is estimated at 5 to 10 per cent. In composition, they fall into three principal groups: dolerites, lamprophyres and microgranites. Field evidence shows that the basic rocks crystallised first and were followed later by the intermediate, and then the acid intrusions.

In the earliest detailed accounts of the intrusions (Harker, 1891, 1892), the lamprophyres and microgranites were related to the Shap Granite and their emplacement was accordingly assigned to early Devonian times, whilst the dolerites were considered to be Ordovician in age. A similar intrusive sequence was proposed by Shotton (1935). Hudson (1937) went further in suggesting that the dolerites were the intrusive equivalents of the spilites in the lower Ordovician Kirkland Formation, and that the lamprophyres and microgranites could be subdivided into a southern Devonian suite of Shap granite affinity and a northern suite of Ordovician age. The acid intrusives of the latter were thought to be probably of Borrowdale age and connected with a Lake District intrusion, whilst the lamprophyres were considered to date from post-Borrowdale and pre-Silurian times.

But these relationships were suggested before the discovery of the Weardale Granite. This early Devonian intrusion was proved beneath Lower Carboniferous cover in the Rookhope Borehole in upper Weardale (Dunham and others, 1965). Regional gravity values indicate that the Weardale granite underlies much of the Alston block and that it approaches most closely to the present district at Tynehead, where a negative gravity anomaly probably marks a hidden granite cupola. As this lies less than 12 km E of the northern end of the Cross Fell inlier, it is the closest major intrusion to which the minor dykes can be related.

The close association of the lamprophyres and micro-granites suggests that they shared a common petrogenesis. It seems likely that they resulted from the progressive differentiation of a calc-alkaline basaltic magma rather than the melting of crustal rocks, but the evidence is not decisive. The field relations clearly show a basic-to-acidic intrusive sequence but the mixture of types and the subtle gradations of composition point to evolutionary changes in the parent magma. The differences in primary mineral phases between the lamprophyres and microgranites are relatively minor. Modal analyses, cast with quartz, feldspar and micas as end-members (Figure 32), show that the lamprophyres contain more mica (above 27 per cent by volume) and less quartz (below 10 per cent), whilst the microgranites are generally enriched in silica, particularly in the groundmass. Fractional crystallisation of a basaltic magma might, with progressive enrichment especially in Fe and Al, have yielded biotite rather than amphibole, and the residual fractions, depleted of Fe but with surplus Al after the formation of feldspar would then, in the presence of sufficient silica, yield muscovite. In reality, this simple fractional crystallisation would be complicated by the streaming of volatiles and the freeing of elements by alteration of pyroxene and olivine. Chemical analyses (Table 5) of selected lamprophyres and micro-granites are plotted on a variation diagram (Figure 33) based on the Larsen Index (Larsen, 1938). These show variation trends linking the microgranites with the Weardale Granite, but failing to relate the lamprophyres to the Carrock Fell gabbro, due to the different petrogenesis envisaged at Carrock (Eastwood and others, 1968, p.109), where the close association of gabbro and granophyre is ascribed to the melting of sialic rocks during the ascent of hot basic magma through the crust.

Recent geochemical research on the mica-lamprophyres (Kay and Gast, 1973; Lees, 1974; Bachinski and Scott, 1979) has suggested that minettes, like kimberlites and carbonatites, are derived directly from the mantle. Very special conditions are however invoked by Bachinski and Scott for the generation of minette magma, including less than 1 per cent partial melting of peridotite together with enrichment in rare earth elements (REE) to five times that of chondrites, and simultaneous metasomatism by aqueous fluids rich in K, Ti, Fe and other elements. While rare earth elemental data are not available for the Cross Fell lamprophyres, there are significant differences with the minettes from New Brunswick studied by Bachinski and Scott (op. cit.). The present lamprophyres are spatially (and apparently, temporally) closely associated in a restricted area with acid porphyries and microgranites, and to a lesser extent with dolerites. The lamprophyres grade mineralogically and chemically into acid porphyries through enrichment of quartz and feldspar at the expense of mica. The New Brunswick minettes are not associated with granitic intrusions. These minettes are enriched in both compatible and incompatible trace elements, whereas the Cross Fell lamprophyres are not abnormally enriched in the compatible elements Co (10 to 20 ppm) and Cr (75 to 290 ppm); of the incompatible elements Zr (66 to 140) is not abnormally high. Fluorine, however, is high (850 to 3100 ppm) suggesting that volatiles may have been important in the crystallisation of these rocks. The conspicuous accessory dark apatite in the present lamprophyres (and to a lesser extent in some of the microgranites) suggests that the rare earth elements may be enriched. Pseudo-morphs after primary ferromagnesians, including olivine, suggest some connection with basic or ultrabasic rocks, perhaps through contamination.

The petrogenesis of the Cross Fell minor intrusions is, however, obscured through their extensive alteration, presumably by deuteric rather than meteoric action. Even so, at the present state of knowledge and particularly in view of the close association between lamprophyres and acid minor intrusions, a co-magmatic origin seems plausible with derivation from basaltic magma through fractional crystallisation. Microxenoliths of lamprophyres in microgranites clearly indicate that order of crystallisation.

Dolerites

There are three principal outcrops of dolerite, marked by extensive crags on Cuns Fell, Catterpallot Hill and Baron Side (Figure 31). These masses are sill-like in form, at least 50 m thick and dip approximately north-westwards with the bedding, although their margins are locally discordant. The baked zone of silicified hornfels, 5 to 10 m thick, surrounding them is best seen beneath the Cuns Fell intrusion [NY 6483 3662]. In addition to the main outcrops, there are ten dolerite dykes in the area and two boss-like intrusions on the Sharp Shears ridge. The lithologies of all the dolerites is sufficiently similar to suggest a common source. If, as suggested by Hudson (1937), these soda-rich dolerites are the intrusive equivalents of the spilites of the Kirkland Formation (p. 12), they are lower Llanvirn in age.

Where fresh, the dolerites are mainly dark green-grey or blue-grey but through alteration, brown, purple, dark green and mottled varieties are common. They are medium-grained and generally non-porphyritic but, in places, have feldspar microphenocrysts up to 3 mm long. Subophitic to poikilitic textures are common and some specimens show small amygdales. Late-stage alteration has converted much of the dolerite, especially in the smaller intrusions, into epidiorite in which the original pyroxene is replaced by actinolite or chlorite and the feldspars are albitised and paragonitised.

The freshest dolerite forms the summit crags and southwest ridge of Cuns Fell [NY 6478 3678], [NY 6457 3629]. Even here, the feldspars are always albitised, but some specimens show glomeroporphyritic groups of unaltered augite (E36021); in others, augite microphenocrysts are schillerised and poikilitically include albitised plagioclase, whilst clinopyroxene is partly altered to actinolite (E36018). Farther to the southwest near Dale Beck [NY 6444 3621], the Cuns Fell intrusion is more highly altered to mottled grey-green epidiorite (E36015) with pale grey, prismatic pseudomorphs of chlorite and dolomite after feldspar and perhaps orthopyroxene, set in a chlorite-dolomite groundmass. The alteration seems to increase towards the Gate Castle Fault.

The masses of dolerite on the southern side of Catterpallot Hill, on Baron Side and Sharp Shears, seem to be entirely altered to epidiorite (E36009), (E36010), (E36011) consisting of sparse albite microphenocrysts set in a groundmass of albitised plagioclase laths, in a subophitic texture with chlorite or actinolite pseudomorphs after pyroxene. Near the western margin of the Catterpallot intrusion, the dolerite is cut by pink micro-granite veins [NY 6381 3622] which have metasomatically added silica, micropegmatite and possibly carbonate (E35963). The effects are similar however to the autopneumatolytic alteration found in some of the epidiorite dykes on the north side of Catterpallot Hill [NY 6376 3662], [NY 6362 3652] and in Rake Beck [NY 6326 3703]. In both cases, micrographic growths of quartz and alkali feldspar (E35899) indicate late-stage alteration by an acid residue.

Lamprophyres

Lamprophyres are classified according to their mafic minerals and feldspars (Rosenbusch, 1887). All the local examples are mica–lamprophyres with biotite as their principal mafic mineral. They are further subdivided into minettes and kersantites with, respectively, orthoclase and plagioclase as the main feldspar.

Thirty-five lamprophyres have been recognised in the Cross Fell inlier (Table 2). In 14 cases, the feldspars cannot be characterised properly and these rocks remain as micalamprophyres. Eleven kersantites and six minettes have been identified. In addition, four hybrid types have quartz and feldspar phenocrysts and therefore grade into the micro-granites. The five lamprophyres occurring within the Brough district are described in the Brough memoir (Burgess and Holliday, 1979). There is no overall pattern to the distribution of the lamprophyres or to their trends (Table 2). It has been claimed (Piper and others, 1978) that the kersantites have an approximate E–W strike and that the minettes -trend roughly NE–SW, but this conclusion is not sustained by the present work.

The rocks are generally grey, purple or brown with prominent biotite phenocrysts. They form narrow, near-vertical dykes generally less than 100 m long. The intrusions are discordant but are usually aligned roughly parallel to the bedding; they may also locally be parallel to cleavage, jointing or faulting. There is so little evidence of baking at the dyke margins that a low magma temperature during intrusion is envisaged. Most dykes show chilled margins, where the rock is aphanatic. Fluxion textures are common, even within the chilled margins. Polymineralic segregations characterise some dykes and may be xenoliths, the most common fragments of this kind consisting of carbonated lamprophyre. Concentrations of quartz in the groundmass are widespread and may have resulted from the breakdown of alkali polysilicates and metasilicates of Fe and Mg into orthosilicates during consolidation of the rock (Smith, 1946). Alternatively, they may be due to secondary silicification. Less common features include pseudomorphs after clinopyroxene and rare pseudomorphs possibly after hornblende. It seems likely that hornblende was produced by reaction between the primary pyroxene and the fluid magma at a late intrusive stage, and followed by alteration to micas. The main accessory mineral is apatite as in most lamprophyres (Johannsen, 1937), with minor sphene and opaque ores. Zircon is rare but does occur, surrounded by pleochroic haloes, in primary biotites even where these have been chloritised.

An increase in the proportion of quartz and feldspar, and a corresponding diminution in the amount of biotite, leads gradually from lamprophyre via hybrid rocks to the acid porphyries. The best example of such a hybrid, from Melmerby Beck [NY 6314 3688], is described in detail below.

All the lamprophyres show some degree of chemical alteration which varies greatly even within the same intrusion. This has been ascribed to supergene weathering (Hudson, 1937, p. 393) but if this were the principal mode of alteration, a more uniform effect would be expected. It seems more likely that much of the alteration is deuteric in origin. There is no consistent pattern of alteration and either the biotites or the feldspars may have suffered the initial attack. Biotite shows variable alteration, commonly to chlorite or sericite, progressing from crystal exteriors along the cleavages to complete replacement. Leucoxcne dust is common and though it tends to be concentrated at biotite-chlorite interfaces suggesting a replacive 'front', much probably stems as well from Ti eliminated from the biotite. Feldspars are usually altered to paragonite or sericite. Both biotite and feldspar are also extensively replaced by calcium carbonate, quartz and iron sulphide. All stages of alteration of the main minerals are present and this is thought to be due to the final cessation of autopneumatolysis with the solidification of the magma. The occurrence of quartz and carbonates, not only in interstices in the rock but in subvesicles and veinlets and replacing biotite and feldspar, shows that these minerals were mobile for a considerable period during the freezing of the magma.

The age relations of the lamprophyres are still uncertain. On field evidence there is no reason to regard the lamprophyres as more than one suite of intrusions, all emplaced at about the same time and closely related to the acid porphyries. Taking this view, the lamprophyres are all post-Llandovery in age, since a minette dyke intrudes the upper Llandovery Browgill Beds in Swindale Beck (Burgess and Holliday, 1979). Furthermore, they must predate the last compressive phase of the end-Silurian earth movements because several dykes, including the minette in Dry Sike [NY 6414 3736] north of Cuns Fell, show an ENE-trending foliation which is presumably the end-Silurian cleavage. The lamprophyres were therefore all intruded towards the end of the Silurian.

A different view has recently been proposed on the basis of palaeomagnetic data (Piper and others, 1978). They conclude that the kersantites were emplaced in Caradocian times and that the minettes are related to the post-orogenic intrusions of northern England, such as the Shap and Skiddaw granites, and date from early Devonian times. The last conclusion is in conflict with the fact that some of the mincttes are cleaved.

Details

Characteristic of the kersantites are phenocrysts of red-brown biotite and reddish feldspar. Biotite and its alteration products form about 30 per cent by volume of the rock. Scattered phenocrysts are set in a lattice-like groundmass of biotite and plagioclase laths. The micas are locally fluxioned (E35990), (E36049) indicating some fluid shear during crystallisation. Feldspar forms microphenocrysts (rarely above 3 mm length), mainly of oligoclase zoned out to andesine but also so altered to sericite and carbonate that K-feldspars cannot be ruled out. Though groundmass feldspars are commonly in random orientation with respect to the micas, in one specimen (E35984) they have an ophitic to poikilitic relation, the micas having apparently crystallised first. The predominant groundmass feldspar is oligoclase to albite though again usually sericitised. Much of the interstitial material is chlorite, carbonate, illitc and quartz. Eight- and six-sided pseudomorphs of chlorite may represent ferromagnesian minerals. Apatite in euhedra (rarely zoned) is a common accessory and forms inclusions in biotite, and there are specks of leucoxene, iron oxide and pyrite. Subvesicular clots, rounded grains or irregular patches occur, and average about 1.5 m across. They include dolomite, chlorite and quartz of deuteric origin.

Typical of the minettes are two dykes cropping out east of Gale Hall (E35944), (E35945). Bronzy micas and red feldspar microphenocrysts, up to 2 mm length, are scattered in a holocrystalline (0.2 mm) groundmass of partly fluxioned biotite flakes, interstitial laths of orthoclase and subordinate oligoclase, very minor quartz, chlorite, grey apatite, carbonate and subvesicular patches containing pyrite, quartz and carbonate ((Plate 9).4). Biotite is fresh, uniaxial with E = pale yellow, 0 = dark red brown, and shows strong colourzonation. Inclusions are common with small crystals of apatite, minute isotropic crystals and specks of iron oxide.

The hybrid rock cropping out in Melmerby Beck [NY 6314 3688] shows gradation from altered kersantite to feldspar-porphyry. The 3.7-m wide dyke was sampled at 0.6-m intervals (E36050), (E36051), (E36052), (E36384), (E36385), (E36386), (E36387), (E36388), (E36389), (E36390), (E36391). A chemical analysis of a hybrid lamprophyre-feldspar-porphyry (E36387) is given in (Table 5). The marginal facies are lamprophyric for about 1.3 m from each dyke wall. Feldspars increase and biotites decrease into a central zone of feldspar-porphyry about 1.1 m wide. The changes are gradual and the dyke is not a multiple intrusion with distinct contacts between facies. The outer lamprophyre (E36384), (E36391) is microporphyritic, with 1.5 mm phenocrysts in a groundmass averaging about 0.1 mm. The biotite phenocrysts are euhedra partly altered to chlorite, or replaced by carbonate (with distortion of the cleavages), iron oxide and rutile. Feldspar phenocrysts occur as individual euhedra or as glomeroporphyritic clusters, and are mostly altered to clay minerals and replaced by quartz, carbonate, chlorite or micropegmatite. Quartz forms rounded, embayed grains less than 0.5 mm across, with reaction rims against the groundmass.

The central part of the dyke (E36051), (E36387), (E36388) is coarser in grain with the groundmass about 1 mm and phenocrysts of plagioclase up to 2.8 mm long ((Plate 9).5). The latter are sericitised and weakly fluxioned. Mica phenocrysts form sparse plates and euhedra, completely chloritised and carbonated, and charged with inclusions of zircon, rutile, leucoxene and unidentified needles of possible TiO₂ polymorphs. Sparse round grains of quartz are marginally corroded and commonly set in radiating growths of potassic feldspar. The groundmass is mainly a mesh of albite-oligoclase laths; the remainder consists largely of fibrous K-feldspar, micrographic growths, secondary chlorite, carbonate, siderite and zoned apatite. In addition, some specimens (E35924), (E36051), (E36388) show segregations of chloritised mica associated with oligoclase laths, which are probably microxenoliths of chloritised, carbonated lamprophyre. It seems likely that the mica segregations were incorporated from partially consolidated lamprophyre magma as consolidation began close to the dyke walls. One further feature, of minute isotropic crystals which may be a feldspathoid (E36387), suggests that the porphyry was a residual differentiate undersaturated in silica; the sparse quartz grains were not magmatic, therefore, hut were introduced later with the carbonate. The other hybrid rocks (Table 2) are similar but lack lamprophyric microxenoliths.

Microgranites

There are 91 microgranite or acid porphyrite minor intrusions in the Cross Fell inlier. Eighty-seven lie within the present district and four within the Brough area (Burgess and Holliday, 1979). They are characterised as micro-granites as they are medium-grained with varying proportions of quartz, alkali feldspars and mica. They have been previously described by Harker (1891), Shotton (1935) and Hudson (1937). They occur as dykes generally 5 to 10 m across and ranging from a few centimetres up to 60 m thick. Trends vary but are most commonly aligned in an east-north-east direction. The dykes tend to be less continuous along strike than the more basic intrusions. It is likely that the microgranites and lamprophyres are acidic and basic differentiates of the same magma (Hudson, 1937). Certainly the field evidence is consistent with a single phase of intrusion towards the end of Silurian times.

When the microgranites are subdivided according to their phenocrysts, as shown below, they form a definite pattern. The quartz-phyric rocks are concentrated around Dale Beck and the Sharp Shears ridge west of Windy Gap. In contrast, the quartz-poor rocks lie mainly to the north-west or southeast of this area. As quartz is commonly the last mineral formed in acid vein deposition, it is possible that the Dale Beck-Sharp Shears dykes were the final differentiate, formed at the end of the intrusive phase.

Microporphyritic textures predominate, with phenocrysts on average about 2 mm across and generally reddened. Feldspar is the commonest phenocryst, particularly sodic plagioclase, and quartz is rarely the sole phenocryst. Ground-mass textures vary from equigranular mosaics about 0.2 mm across to very fine aggregates of 0.05 mm grain size. The groundmass consists of sodic plagioclase, subordinate orthoclase (generally in radiating clusters around quartz phenocrysts) micas and micropegmatite, the last being especially characteristic of thin, rapidly-cooled dykes and offshoots. Quartz is present in the groundmass only in rocks with quartz phenocrysts. The rare fluxion textures are due to volatile action during emplacement. Primary accessory minerals include ubiquitous apatite and zircon, and other accessories are anatase, leucoxene, rutile, hematite and pyrite. Microgranites transitional to the lamprophyres show enrichment in chloritised biotite and occasionally xenoliths of lamprophyric material. As with the lamprophyres, autopneumatolysis seems to have altered many of the micro-granites, feldspars being changed to paragonite and primary micas to chlorite, leucoxene and carbonate. In addition, late-stage veining by quartz, carbonates and pyrite is common.

Details

In some samples (E35991), (E36019), (E36005), (E36013) the quartz phenocrysts are euhedral to rounded, up to 3 mm across and have resorbed margins, marked by rims of potash-feldspar, micas, granular quartz, or undifferentiated groundmass (E36046) showing rapid cooling after the phenocrysts had formed. They are commonly accompanied by red feldspar phenocrysts or glomeroporphyritic aggregates of orthoclase and albite. Muscovite phenocrysts take the form of conspicuous plates. The groundmass is a mosaic of feldspar laths, and radiating aggregates with interstitial quartz and primary mica (E36047), (E36048) plus secondary alteration products. A transition to the lamprophyres is indicated where primary micas are common (E35936), (E35991). Most are chloritised with zircon inclusions enclosed in pleochroic haloes inherited from the primary biotite.

The feldspar phenocrysts are mainly euhedral, up to 1 cm across, and show varying degrees of paragonitisation. The most common and least altered phenocrysts are albite (Ab₉₀ An₁₀) (E35946), (E35948), (E35970); in places these contain smaller plagioclase plates and muscovite (E35971). Finely dispersed ferric oxide gives the red colour to many of the phenocrysts, as in other Caledonian intrusions such as the Shap Granite. Glomeroporphyritic albite clusters (E35996) are rarer than individual phenocrysts. Zoning of the phenocrysts has not been seen directly but may be represented by zoned alteration products (E35946), (E35985). No orthoclase phenocrysts have been detected but these may be amongst the most heavily altered crystals. Muscovite phenocrysts, where present, are generally replaced along cleavages by hematite, leucoxene, chlorite or carbonate, and carry inclusions of sphene, apatite, anatase and rutile (E35967), (E36138).

The groundmass is usually a mosaic of paragonitised feldspar laths, chloritised primary mica, interstitial quartz and micro-pegmatite. Albite predominates and orthoclase is subordinate. In addition to the late-stage interstitial quartz, there are third-stage veinlets of quartz associated with calcite and pyrite (E35985), (E36004). RKH, AJW

Whin Sill and dykes

The western edge of the quartz-dolerite sill which underlies much of north-east England crops out along the Pennine escarpment, together with several ENE-trending dykes similar in composition to the sill. North of Renwick, the sill forms several discrete lenses of dolerite but throughout the rest of the Pennine part of the district it appears to be a continuous intrusive sheet. Its emplacement appears to have been bounded by the Pennine Fault system since the sill is absent from the Carboniferous or earlier rocks of the Vale of Eden. The name 'Whin Sill' means hard bed in the dialect of local miners and quarrymen, and this sill is the original example of a concordant intrusive sheet. Early workers regarded it as a lava flow. It was first recognised as an intrusion by Sedgwick (1827), and further work by Topley and Lebour (1877) established its intrusive character beyond doubt.

The sill maintains its stratigraphical horizon for considerable distances. On the western slopes of Cross Fell, it lies between the Single Post and Scar limestones for at least 6 km along crop. Whcn changes in horizon occur they are generally gradual, as on Kirkland Fell [NY 681 330] or Melmerby Fell [NY 654 378], and abrupt changes of the kind seen in upper Teesdale (Burgess and Holliday, 1979, fig. 4b) are lacking. The summary by Dunham (1948, fig. 7) of the changes in horizon and thickness of the sill is broadly confirmed by the details of sections given below. Overall, it becomes thinner and lies at progressively higher stratigraphical horizons in all directions away from upper Teesdale. To the north-west, it gradually rises in horizon across the present district reaching its highest level within the Lower Coal Measures at Midgeholme in the Brampton district (Trotter and Hollingworth, 1932).

The petrography of the quartz-dolerite sill has been extensively investigated in the past (Teall, 1884a, b; Holmes and Harwood, 1928; Trotter and Hollingworth, 1932; Dunham, 1948) and both the mineralogy and the chemistry of the intrusion have been summarised by Dunham (1970). The rock consists of plagioclase (48%), clinopyroxene (29%), Fe-Ti oxides (7%), with quartz and alkali feldspar occurring interstitially, and small amounts of orthopyroxene, olivine pseudomorphs, chlorite, amphibole, carbonates, sulphides and apatite. It is weakly porphyritic with plagioclase, augite and hypersthene phenocrysts comprising 5% by volume of the rock. The quartz-dolerite generally has a speckled grey appearance and an average grain-size of 2 mm, but it is darker and finer-grained towards the sill margins and a very fine-grained black tachylite is present in chilled margins. The upper parts of the sill, in places, contain lenticular bands of pegmatitic dolerite with augite blades (4 cm), and plagioclase laths (2 cm) zoned from labradorite to oligoclase. Pink patches are common in some parts of the sill and consist of micro-granophyric intergrowths of quartz and K-feldspar. Both pegmatitic and granophyric varieties are best seen within the district in Gilderdale Burn [NY 688 468].

It has been estimated (Dunham and Kaye, 1965) that the sill was emplaced at 1100°C and took up to 60 years to solidify. The country rocks adjacent to the intrusion have been thermally metamorphosed and the effects visible in hand specimen are generally present up to 20 m from the dolerite. Shales are commonly converted to unbedded porcellanous whetstones, and limestones are recrystallised to marble or calcsilicate rocks. The method of emplacement of the sill is not fully understood. In some areas the sill appears to have wholly replaced parts of the sedimentary succession rather than just pushed the beds apart. For example, on Melmerby Fell the Scar Limestone is absent for about 2 km along crop and appears to have been assimilated by the sill. It has been argued that considerable assimilation of country rocks in Teesdale has taken place (Clough, 1880). On the other hand, no large xenoliths have been seen within the sill, and chemical changes in the dolerite of the kind supporting assimilation are lacking (Smythe, 1930). An alternative to assimilation, invoking intrusion along horizontal tension fractures has been proposed by Smythe (1930).

The Whin Sill intrudes rocks of Westphalian A (communis Zone) age at Midgeholme, and associated dykes cut beds of Westphalian B (lower similis-pulchra Zone) age in the Durham Coalfield (Smith and Francis, 1967). On the other hand, pebbles probably from the sill are found in lower Permian brockrams near Appleby in the Vale of Eden (Holmes and Harwood, 1928; Dunham, 1932). The intrusion was emplaced therefore in late-Carboniferous or early-Permian times. It has yielded a K-Ar radiometric age of 295 ± 6 Ma (Fitch and Miller, 1967). It is argued elsewhere (p. 105) that the Whin Sill was intruded in tensional conditions, following a Hercynian compressional phase giving the gentle doming of the Alston Block and reverse faulting along the Pennine Fault system. It has recently been suggested (Francis, 1978) that this magmatism is typically mid-plate and continental in character, probably derived by partial melting at depths of 15 to 35 km and is part of a broad belt of similar and contemporaneous intrusions extending into south-east Scotland and southern Sweden.

Details

The escarpment

The Whin Sill occurs as thin, lenticular sills near Croglin, lying just above or within the Scar Limestone. Its total thickness, though not seen in full section hereabouts, is probably less than 4 m; the best sections are in disused quarries 400 m NE of Fieldhead [NY 5832 4818] and [NY 5865 4792] and about 1 km to the south-east [NY 5929 4671] where the section is:

Farther east in Croglin Water [NY 5996 4804] the sill is thicker and again lies in two leaves just below the Scar, as follows:

At Whity Knots, north of Renwick, the intrusion lies at the same horizon. From here, the outcrop of the sill is continuous to the south-east and probably also to the east. In Raven Beck it is close above the Single Post Limestone and thickens eastwards from 9 m, including a 0.6-m sandstone parting, at [NY 6168 4399] to nearly 17 m further upstream [NY 6256 4473]. Lying at the same stratigraphical horizon in Loo Gill [NY 6342 4258] it is split into two leaves, 4.6 m and 2.4 m thick, by 3 m of sandstone. In a nearby tributary [NY 6346 4233] and [NY 6349 4229], impersistent beds of dolerite up to 4.5 m thick locally transgress the Copper Hazle sandstone. For about 7 km southwards there are no good sections through the sill, but its course can be traced from its feature and from the distribution of dolerite boulders in the head. Across Melmerby Fell the beds beneath the sill are the Copper Hazle sandstones, whilst the overlying beds are the shales below the High Brig Hazle. There is no sign of the Scar or Five Yard limestones which appear to have been incorporated within the dolerite. The missing beds reappear abruptly to the south of Meg's Cairn [NY 657 373]. Across the head of Ardale [NY 665 354] the sill is 16 to 18 m thick in fine crags characterised by prominent near-vertical joints (Plate 4). These are thought by Spears (1961) to be due to the relaxation of stresses after uplift rather than contraction on cooling. The intrusion lies within the Copper Hazle sandstones about 15 m below the Scar, but it gradually transgresses the bedding to the south-east across Kirkland Fell to lie more than 30 m beneath the Scar in Crowdundle Beck [NY 690 328] where it is 23 m thick. Across Middle Tongue the sill changes horizon several times, ascending about 10 m on the south side of Crowdundle Beck to the horizon of the Cockleshell Limestone, before descending near Middle Tongue Beck to lie just above the Tyne Bottom Limestone.

Gilderdale and Black Burn

About 24 m of dolerite crop out in Gilderdale Burn [NY 6886 4680] but the base of the sill is not exposed and its full thickness may be much greater. It lies just above the Single Post Limestone. A lenticular band of coarse-grained, pegmatitic dolerite in the upper part of the sill has augite, as blades up to 4 cm long and as radiating sheaves. A pink interstitial mesostasis is seen in thin section to be a microgranophyric intergrowth of quartz and alkali-feldspar (E14197)-(E14198). Chemical analysis (Tomkieff, 1929) shows the rock to have a higher silica content (54%) than the average (51%) for the Whin.

About 6 km to the south, the sill was proved to be 55 m thick in a shaft at Rotherhope Mine [NY 697 422] just within the Alston district, where it lies immediately below the Tyne Bottom Limestone. To the south-west the sill is exposed in several tributaries of Black Burn. For example, north of Rigg End, about 20 m of dolerite, intruded just above the Tyne Bottom Limestone, are seen in the stream [NY 6858 3893] to [NY 6861 3911], and includes a well-developed, tachylitic, chilled, upper margin to the sill [NY 6858 3895]. Near Smittergill Head [NY 6694 3845] to [NY 6719 3880] and [NY 6737 3800] to [NY 6743 3860], a similar thickness of dolerite lies between the Tyne Bottom and Single Post limestones. In the western tributaries of Black Burn the horizon of the sill is higher in the sequence. In Rowgill Burn [NY 6603 4152] it lies 1.5 m below the Scar Limestone with an irregular upper contact exposed in the stream, whilst several sections in Aglionby Beck [NY 6524 3897] to [NY 6585 3972] show it intruded just above the Single Post. Its full thickness hereabouts is unknown but it is at least 3 m.

Whin dykes

An ENE-trending dyke of tholeiite (E19557), closely resembling the Whin Sill dolerite in composition, crops out over about 1 km in Loo Gill. A width of 6 m has been proved (Dunham, 1948, p. 59) in a cross-cut level from Hartside baryte mine [NY 6421 4288]. Much of the surface outcrop of the dyke has been subsequently faulted, shattering the dyke-rock. The intrusion is 4.5 m wide within the Scar Limestone outcrop [NY 6358 4263] but only 3 m wide a little to the west [NY 6349 4259] where it dips northwards at 75°. Upstream the Low Brig Hazle sandstones are intruded by stringers of fine-grained tholeiite and in beds between the Great and Little limestones, the dyke is a deeply weathered and broken, pale green rock veined with baryte.

Farther south, three olivine-dolerite dykes are intruded into rocks of the Borrowdale Volcanic Group east of Melmerby.The southernmost dyke is poorly exposed [NY 6255 3757] but closely resembles the two northern intrusions which have been quarried for roadstone. The petrography and chemistry of these two dykes have been described and a K-Ar age of 296± 8 Ma has been obtained (Wadge and others, 1972). They are thus contemporaneous with the Whin Sill and probably derived from the same magma. It is suggested that the dykes may represent part of the western margin of the Whin Sill, particularly as Carboniferous and Borrowdale rocks were probably juxtaposed along the Deep Slack Fault (ibid., fig. 4) at the time of intrusion. RSA, AJW

The Cleveland–Armathwaite Dyke

A WNW-trending basic dyke, shown on the map as dolerite though more specifically classed as tholeiite, crops out almost continuously in the northern part of the district between High Wreay and Renwick, and also as small separate outcrops in the Pennines, between Renwick and Hart-side. West of the Pennines, the dyke is well exposed in a number of quarries, as well as in its classic section in the River Eden at Armathwaite (Plate 1), and its outcrop is marked by a chain of elongate hills. Here it is 20 to 35 m wide, and crops out apparently as a number of separate, though locally overlapping components. In the quarries [NY 461 476] at the western end of Barrock Fell, Trotter and Hollingworth (1932, p.120) have described inclined lenticular sills, which seem to connect two such components. In the Pennines, where the dyke is known only at two localities in the valley of Loo Gill, the maximum observed width is about 2 m.

The dyke rock is dark bluish grey in hand-specimen, and finely crystalline but for phenocrysts of clear feldspar. Accounts of its petrography have been given by Teall (1884a), Holmes and Harwood (1929), Trotter and Hollingworth (1932) and Dunham (1948). Trotter and Hollingworth describe the rock in the Barrock Fell quarries [NY 461 476] as an augite-andesite or tholeiite, with porphyritic labradorite feldspar, augite, and a rhombic pyroxene (E14025). One of the Pennine outcrops [NY 6382 4278], discovered during this resurvey in a tributary of Loo Gill, 1.3 km NW of Hartside Cross consists, according to Mr R. K. Harrison, of tholeiite (E31954). Labradorite phenocrysts, up to 8 mm across, are reversely zoned and set in a groundmass of labradorite laths and titanaugite with a partly glassy mesostasis. Extracted glass heated in Ar for 1 hour at 1000°C gave, according to Mr B. R. Young, an X-ray diffraction pattern (X 3391A) of high-temperature feldspar. There is a little accessory ilmenite and pyrite. Alteration effects in the host rock within a few metres of the intrusion have been observed at a number of localities. These include bleaching of the red St Bees Sandstone, and yellowing of sandy mudstones in the Eden Shales, associated with the growth of hematite in the form of specularite, as in a borehole [NY 4295 4896] near High Wreay.

The Cleveland–Armathwaite Dyke has long been recognised as one of several basic dykes in the north of England thought to be related to the Tertiary 'Mull swarm' of western Scotland (Holmes and Harwood, 1929, p. 3). The dyke cuts Liassic sediments in Cleveland, but no more precise strati-graphical evidence of age is available. However, a minimum of 58.4 ± 1.1Ma has been determined for the dyke by the K-Ar method (Evans and others, 1973). The intrusion was sampled at several localities including Whinfell Quarry [NY 564 439] 3 km NNE of Kirkoswald and the age indicates that it was emplaced during Palaeocene times.

Geochemical studies of the dyke by Hornung and others (1966) suggest that the source of the magma was at one end of the dyke, presumably the north-western end. They relate the chemical variations across the width of the dyke, as recorded for example in Whinfell Quarry, to different rates of magma flow consequent upon the temperature gradient across the dyke. A magnetic study of the dyke was carried out by Bruckshaw (1950, p. 26), with a view to delineating its outcrop in unexposed ground, and parts of the outcrop shown on the map are based on his findings.

Details

The dyke is well exposed, though not to its full thickness, in a quarry [NY 4428 4812] at Petteril Crooks Mill; the rock is cut by prominent joints inclined SSW at about 85°. Farther to the east-south-cast there are several good exposures on and near Barrock Fell; the best are in two disused quarries at its western end. The dyke is offset by some 45 m between the two quarries, and a section [NY 4603 4761] along the line of offset shows the dyke rock and bleached Penrith Sandstone in interleaved units 0.2 to 0.6 m thick, slickensided and inclined to the north-west at 40° to 60°. The dyke is 27 m wide at the eastern end [NY 4614 4760] of the more easterly quarry.

The dyke has been worked from four small quarries [NY 4946 4571] to [NY 4988 4549] south-west of Armathwaite, but exposures in these are poor. However, it is well-exposed a little farther east, both in the railway-cutting [NY 4998 4548] where it is at least 18 m wide, and in the bed of the River Eden (Plate 1), at the former site of a weir [NY 5032 4539] to [NY 5040 4537]. At the latter locality, the dyke is about 27 m wide, and, on the eastern side of the river, its contacts with Penrith Sandstone are well seen; eastwards from here it forms a sharp ridge on the hillside.

There are several quarries in the dyke north of Longdales, and in one of these [NY 5139 4510] it appears to be about 35 m wide. Farther east-south-east it is poorly exposed for about 4.5 km, although in a disused small quarry [NY 5266 4468] near Ruckcroft, indurated grey mudstone (Eden Shales) is exposed adjacent to it. The full width of the dyke, about 18 m, is well exposed in a quarry [NY 5650 4391] on Whin Fell; and in another quarry [NY 5802 4340], 1.7 km W of Renwick, it is about 23 m wide. At each of these localities, the dyke rock is deeply weathered, and a zone of bleaching affects the St Bees Sandstone up to about 1 m from the dyke contacts. Immediately south-east of Renwick, the dyke is exposed in a stream bank [NY 5953 4324] where it is about 28 m wide, while, about 1 km farther east, at least 18 m are present in Raven Beck [NY 6025 4321] to [NY 6032 4319].

To the east of the Pennine Fault, the dyke has been recorded at two localities, one in the bed of Loo Gill [NY 6156 4331], about 0.5 km N of Fellgate, and the other a little over 2 km farther east in the banks of Grainings Beck [NY 6382 4278], where 0.6 m of tholeiite are exposed. RSA

References

BACHINSKI, S. W. and SCOTT, R. B. 1979. Rare earth and other trace element contents and the origin of minettes (micalamprophyres). Geochim. Cosmochim. Acta, Vol. 43, pp. 93–100.

BRUCKSHAW, J. McG. 1950. The delineation of a dyke by the magnetic method. Rep. 18th Sess. Int. Geol. Congr., 1948, Part 5, pp. 26–31.

BURGESS, I. C. and HOLLIDAY, D. W. 1979. The geology of the country around Brough-under-Stainmore. Mem. Geol. Surv. G.B.

CLOUGH, C. T. 1880. The Whin Sill of Teesdale as an assimilator of the surrounding beds. Geol. Mag., Vol. 17, pp. 466–471.

DUNHAM, A. C. 1965. The nature and origin of the groundmass textures in felsites and granophyres from Rhum, Inverness-shire. Geol. Mag., Vol. 102, pp. 8–23.

DUNHAM, A. C. 1970. Whin sills and dykes. In Geology of Durham County. HICKLING, G. (Editor). Trans. Nat. Hist. Soc. Northumberland. Vol. 41, pp. 92–100.

DUNHAM, A. C. and KAYE, M. J. L. 1965. The petrology of the Little Whin Sill. Proc. Yorkshire Geol. Soc., Vol. 35, pp. 229–276.

DUNHAM, K. C. 1932. Quartz-dolerite pebbles (Whin Sill type) in the Upper Brockram. Geol. Mag., Vol. 69, pp. 425–427.

DUNHAM, K. C. 1948. Geology of the Northern Pennine Orefield: Vol. 1, Tyne to Stainmore. Mem. Geol. Surv. G.B.

DUNHAM, K. C.  DUNHAM, A. C., HODGE, B. L. and JOHNSON, G. A. L. 1965. Granite beneath Visean sediments with mineralisation at Rookhope, northern Pennines. Q. J. Geol. Soc. London, Vol. 121, pp. 383–417.

EASTWOOD, T. E., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the country around Cockermouth and Caldbeck. Mem. Geol. Surv. G.B.

EVANS, A. L., FITCII, F. J. and MILLER, J. A. 1973. Potassium-argon age determinations on some British Tertiary igneous rocks. J. Geol. Soc. London, Vol. 129, pp. 419–443.

FITCH, F. J. and MILLER, J. A. 1967. The age of the Whin Sill. Geol. J., Vol. 5, pp. 233–250.

FRANCIS, E. H. 1978. Igneous activity in a fractured craton: Carboniferous volcanism in northern Britain. In Crustal evolution in north-west Britain. BOWES, D. R. and LEAKE, B. E. (Editors). Spec. Iss. Geol. J., No. 10.

HARKER, A. 1891. Petrological notes on rocks from the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 47, pp. 512–525.

HARKER, A. 1892. The lamprophyres of the north of England. Geol. Mag., Vol. 29, p. 199.

HOLMES, A. and HARWOOD, H. F. 1928. The age and composition of the Whin Sill and the related dykes of the north of England. Mineral. Mag., Vol. 21, pp. 493–542.

HOLMES, A. and HARWOOD, H. F. 1929. The tholeiite dykes of the north of England. Mineral. Mag., Vol. 22, pp. 1–52.

HORNUNG, G., AL-ANI, A. and STEWART, R. M. 1966. The composition and emplacement of the Cleveland Dyke. Trans. Leeds Geol. Assoc., Vol. 7, pp. 232–249.

HUDSON, S. N. 1937. The volcanic rocks and minor intrusions of the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 93, pp. 368–401.

JOHANNSEN, A. 1937. A descriptive petrography of the igneous rocks. Vol. III. The intermediate rocks. University of Chicago Press. 360 pp.

JOHNSON, G. A. L. 1963. The geology of Moor House. Monogr. Nat. Conserv., No. 2.182 pp.

KAY, R. W. and GAST, P. W. 1973. The rare-earth content and origin of alkali-rich basalts. J. Geol., Vol. 81, pp. 653–682.

LARSEN, E. S. 1938. Some new variation diagrams for groups of igneous rocks. J. Geol., Vol. 46, pp. 505–520.

LEES, G. J. 1974. Petrochemistry of the mica-lamprophyres (minettes) of Jersey. Proc. Ussher Soc., Vol. 3, pp. 149–155.

PIPER, J. D. A., MCCOOK, A. S., WATKINS, K. P., BROWN, G. C. and MORRIS, W. A. M. 1978. Palaeomagnetism and chronology of Caledonian igneous episodes in the Cross Fell Inlier and northern Lake District. Geol. J., Vol. 13, pp. 73–92.

ROSENBUSCH, H. 1887. Mikroskopische Physiographie, 2nd ed. Heidelberg.

SEDGWICK, A. 1827. On the association of trap rocks with the Mountain Limestone Formation of High Teesdale. Trans. Cambridge Philos. Soc., Vol. 2, pp. 139–195.

SHOTTON, F. W. 1935. Stratigraphy and tectonics of the Cross Fell Inlier, Q. J. Geol. Soc. London, Vol. 91, pp. 639–701.

SMITH, D. B. and FRANCIS, E. A. 1967. Geology of the country between Durham and West Hartlepool. Mem. Geol. Surv. G.B.

SMITH, H. G. 1946. The lamprophyre problem. Geol. Mag., Vol. 83, pp. 165–171.

SMYTHE, J A. 1930. A chemical study of the Whin Sill. Trans. Nat. Hist. Soc. Northumberland, Vol. 7, pp. 16–150.

SPEARS, D. A. 1961. Joints in the Whin Sill and associated sediments in Upper Teesdale, Northern Pennines.

Proc. Yorkshire Geol. Soc., Vol. 33, pp. 21–29.

TEALL, J. J. H. 1884a. Petrological notes on some north of England dykes. Q. J. Geol. Soc. London, Vol. 40, pp. 209–247.

TEALL, J. J. H.  1884b. On the chemical and microscopical characters of the Whin Sill. Q. J. Geol. Soc. London, Vol. 40, pp. 640–657.

TOMKEIFF, S. I. 1929. A contribution to the petrology of the Whin Sill. Mineral. Mag., Vol. 22, pp. 100–120.

TOPLEY, W. and LEBOUR, G. A. 1877. On the intrusive character of the Whin Sill of Northumberland. Q. J. Geol. Soc. London, Vol. 33, pp. 406–422.

TROTTER, F. M. and HOLLINGWORTH, S. E. 1932. The geology of the Brampton district. Mem. Geol. Surv. G.B.

WADGE, A. J., HARRISON, R. K. and SNELLING, N. J. 1972. Olivine-dolerite intrusions near Melmerby, Cumberland and their age determination by the K-Ar method. Proc. Yorkshire Geol. Soc., Vol. 39, pp. 59–70.

Chapter 9 Structure

The structural history of the district falls naturally into two parts, divided by the Caledonian orogeny. During Lower Palaeozoic times, a wide proto-Atlantic ocean (Wilson, 1966) lying between Europe and North America gradually closed. In northern England oceanic crust from the north was being consumed by a southerly-dipping subduction zone (Fitton and Hughes, 1970) beneath the leading edge of the European plate. The zone was marked by an oceanic trench characterised by greywacke sediments and bounded to the south by a volcanic island arc where thick volcanic sequences accumulated. Polyphase deformation of the sediments contrasts with the gentle folding and faulting of the volcanic rocks. Volcanism died out in Ashgillian times and the thick Silurian succession of greywackes and shales was deposited in a narrow geosynclinal trough which was all that remained of the proto-Atlantic ocean. Towards the end of Silurian times, renewed subduction and continental collision produced further polyphase deformation and low green-schist metamorphism accompanying cleavage formation in these sediments. The emplacement of the Lake District and Weardale granites brought the Caledonian orogeny to a close.

Thereafter, the district was underlain by continental crust to the present-day (Bamford and others, 1976) and its history is one of shelf-sea marine, deltaic or continental sedimentation, gentle crustal warping and the relative movements of blocks and basins. The Alston Block in the east and the Lake District Block to the west are defined by the underlying plutons and have tended to remain as areas of uplift or relatively thin sedimentation since the end of Silurian times, whilst the intervening Vale of Eden has been a depositional basin of relatively thick sedimentation for much of this period.

Lower Palaeozoic structures

The different Lower Palaeozoic rock groups show contrasting styles and intensities of structure (Shotton, 1935; Moseley, 1972), and although this is partly due to their varying competence in resisting stress, it more fully reflects their different structural histories. These are discussed in strati-graphical order.

Skiddaw Group

The beds of the Skiddaw Group have been affected by several phases of folding, although within the present district, the deformation is not as intense as that affecting either the Murton Formation in the southern part of the Cross Fell inlier (Burgess and Wadge, 1974, p. 73) or the Skiddaw Group in the Lake District (Simpson, 1967; Helm, 1970; Webb, 1972).

Where fully developed, each phase of folding is characterised by a cleavage (S₁, S₂, etc.) and a set of minor folds (F₁, F₂, etc.) which, when formed, all had the same local orientation and style as the contemporary major structures. These fold characteristics can be used to correlate minor structures from outcrop to outcrop, and where later structures re-fold earlier ones, the sequence of fold phases can be deduced. The nature of the major structures can be determined from the style and orientation of the minor folds. Unfortunately, within both the Murton and Kirkland formations in the district, there are few minor folds, and cleavages are weak or absent so that the successive phases of folding cannot be distinguished with confidence. The proposed structural sequence is therefore tentative and is based mainly on analogies with the southern part of the Cross Fell inlier (Burgess and Wadge, 1974) and, to a lesser degree, with the Lake District (Simpson, 1967; Helm, 1970; Roberts, 1971; Jeans, 1971; Webb, 1972).

The following structures are present in the Murton Formation in the southern part of the Cross Fell inlier:

1. F₁ folds are tight, nearly isoclinal in style and commonly asymmetrical. A strong, vertical axial plane cleavage (S₁) trends at about 100°. The F₁ folds show a variable plunge in the S₁ plane which has been interpreted (Webb, 1972) as evidence of even earlier folding, possibly with a north-south trend but lacking an associated cleavage.
2. F₂ folds are open and generally asymmetrical, with an axial planar fracture cleavage (S₂). Both S₂ and the F₂ axial planes commonly lie at a shallow angle and trend north-westwards.
3. F₃ folds are very open and trend approximately east-west. The axial plane cleavage (S₃) is vertical.
4. In addition, the rocks are traversed by linear zones, 1 to 5 m wide, of intense folding which post-date all the previous structures. The zones dip steeply eastwards and consist of folds which are tight but have no axial plane cleavage. The folds generally trend at 340° to 350° but their plunges appear to be random.

The successive deformations cannot be dated directly in the Cross Fell inlier but comparison with the Lake District suggests that F₁ and F₂ probably predate the end-Silurian orogeny and may be ascribed to either pre-Coniston Limestone or pre-Borrowdale earth movements. The F₃ folds seem to correlate with end-Silurian structures in style and intensity, whilst the linear zones of folding commonly lie close to reverse faults of post-Carboniferous age and may result from the same stresses.

In the Murton Formation at the northern end of the inlier, dips are generally steep but fold closures, even of minor structures, are uncommon. The principal structures are large-scale, close folds with half wavelengths of about 1 km and an east-north-easterly trend (Figure 31). On style and orientation these folds correlate equally well with the F_l or F₃ structure farther south but as they are re-folded by structures which seem to correlate with F₂, they are tentatively assigned to F₁. Over most of the inlier, this folding is not accompanied by cleavage, although at a few localities, a weak fracture cleavage lies axial planar to minor folds on the limbs of the major structures, as on the northern side of Thack Moor [NY 6405 3549].

The geometry of the major F₁ folds is generally indicated by the style and orientation of the F₁ minor structures. For example, near the axial region of the syncline on Catterpallot Hill [NY 638 363] minor folds are relatively numerous (Figure 31) and suggest that the syncline plunges generally eastwards and that its axial plane is inclined at 60⁰ to 75° to the north-west. The fold closures on the summit of the hill [NY 6384 3633], [NY 6380 3630] show a consistent sense of vergence or direction of overturning to the south-east indicating that they are all on the southern limb of the syncline, whose axis therefore lies just to the north of the summit. A similar sense of vergence consistently to the south-cast is found in scattered minor F₁ fold-closures on the northern slopes of Thack Moor [NY 6421 3570], and indicates that the major F₁ anticlinal axis lies to the south (Figure 31).

Folding predating the F₁ deformation may be present but the evidence is limited. A feeble bedding schistosity with muscovite, biotite and chlorite in parallel orientation on the bedding planes, is developed in places, as for example in Dry Sike (6387 3732], but is not widespread. Elsewhere, narrow belts of complex, apparently disorientated minor folds, which lack any cleavages, lie along the general Caledonoid strike. Two such belts, each about 50 m wide, cross Dry Sike [NY 6402 3728], [NY 6403 3739]. They are difficult to interpret as each is unrelated to post-Silurian faulting and lies within a sequence of beds dipping uniformly to the south-east at 45° to 65°. The sense of vergence of the minor folds is not consistent and their plunges are very variable. These characteristics could mark the hinge-zones of major isoclinal folds of IT, of earlier age but confirmatory evidence is lacking.

Farther south, within the Kirkland Formation outcrops, the F, folding is more open in style, particularly where massive volcanic beds are involved. This is best seen in the east–west trending folds on Wythwaite Top, east of Kirkland [NY 665 324] and in Mudgill Sike, north-west of Burney Hill [NY 6737 3054]. The folding is correlated with the close folds in the Murton Formation on their common orientation, despite the difference in fold styles. Indeed, when the F₁ folds are found in the Kirkland Formation mudstones rather than tuffs, they are smaller, tighter and more comparable with the style of the structures in the Murton Formation. They are typically developed in the mudstones in Eller Gill [NY 6763 3118] (Moseley, 1972, fig. 3), where they are characterised by a feeble axial plane cleavage and a south-westerly plunge, and also in the south bank of Ardale Beck [NY 6469 3434], where a weak fracture cleavage is present in mudstone bands, but not in the more massive tuffs, around the hinges of the small F₁ folds.

Folds which correlate with the F₂ structures in the southern part of the Cross Fell inlier are best developed within the Kirkland Formation outcrops, where they are characteristically open folds trending to the north or north-west; both axial planes and the associated weak fracture cleavage are usually flat-lying. They are well developed in the cliffs on the south bank of Eller Gill [NY 6757 3121] and the weak fracture cleavage traverses, and is clearly later than, the F₁ structures. Similar flat-lying folds are seen in Milburn Beck [NY 6787 2925]. Farther north, F₂ folds seem to be less common; no flat-lying structures are recorded in the Murton Formation outcrops, although F₂ may be represented here by upright, gentle folds, trending north-north-westerly. These are developed on the limbs of the F₁ folds on the northern slopes of Thack Moor [NY 6403 3566] and in Dale Beck [NY 6364 3592] where they are accompanied by a rare axial planar fracture cleavage.

Borrowdale Volcanic Group

In the small inlier east of Melmerby, the detailed structure of the Borrowdale rocks within the bounding faults is uncertain. Porphyritic andesites of Eycott type dip north-eastwards in Melmerby Beck [NY 6253 3730] but farther north they fail abruptly along strike and are probably faulted out. The bedding in these massive volcanic rocks is generally difficult to determine and cleavage is rarely developed, but where seen, both bedding and cleavage generally trend east-northeast and are steeply inclined. No fold closures are seen in this tract.

The structure of the Greystoke inlier in the south-west of the district is simpler; the volcanic beds dip steadily to the north-north-east at 50° to 70° and are so massive that no cleavage is developed. The Greystoke and Eycott inliers have been interpreted as lying close to the hinge of an eastward-plunging Caledonian anticlinorium and linking the northern and southern outcrops of the Borrowdale Volcanic Group in the Lake District (Eastwood and others, 1968, p.10). However, this broad structure is now in doubt. The pronounced magnetic anomaly along the outcrop of the volcanic rocks (p. 137) across the northern Lake District extends through the Greystoke inlier in an east-south-easterly direction almost as far as Penrith. In addition, there is stratigraphical evidence that the two volcanic sequences are not correlatives (p. 15). It seems probable therefore that the rocks of the Greystoke inlier extend along the recorded strike beneath the younger beds of the Vale of Eden, instead of swinging round to join the southern outcrop of the Borrowdale Volcanic Group. Taking this view, much of the evidence for a major Caledonian anticline through the Skiddaw area disappears.

Upper Ordovician and Silurian rocks

In the small fault-bounded outcrops cast of Melmerby, the beds generally strike east-north-eastwards and a near-vertical cleavage has a similar trend. Dips are steep to the south-south-east in the Dufton Shales (Figure 9), steep to the north-north-west in the Swindale Shales, and variable in the Silurian Browgill Beds. No folding has been seen. Although the overall orientation of these beds derives mainly from the end-Silurian earth-movements, they seem to have responded to later stresses by brittle fracture, so that there are many small faults and slips along planes of weakness present in most outcrops. It is likely that these rocks are affected by much more faulting than has been mapped.

Post-Lower Palaeozoic structures

The emplacement of the Weardale and Lake District granites towards the end of the Caledonian orogeny defined thereafter the Alston and Lake District blocks and the intervening basin of the Vale of Eden. The structures of the Alston Block and the Vale of Eden are described below; the complex structural history of the Pennine Fault system, bounding the Alston Block on its west side, is considered separately.

Alston Block

Overall, the area is a gentle asymmetrical dome (Dunham, 1948, p. 64). Its top lies several kilometres south-east of Cross Fell and it is truncated on the west by the Pennine faults. On that part of the block within the district, the general dip is north-eastwards at 1° to 4° (Figure 34). Towards the Pennine faults however, dips steepen, so that along the Pennine escarpment the beds are generally inclined at about 5° to 10°, and close to the faults, the rocks are near-vertical or even overturned. This pattern of narrow zones of steep dips close to faults is repeated, on a much smaller scale, near many of the faults on the block, and indicates that the thin Carboniferous cover was deformed plastically before breaking, under the stress of vertical movements on fractures in the Lower Palaeozoic basement.

Two principal sets of faults can be distinguished which have the same orientations as the joints of the area; indeed, these directions are common to joints in most of the Carboniferous rocks of northern England (Moseley and Ahmed, 1967).

1 NNW-striking faults

These fractures commonly have substantial throws, generally down to the west, and are not usually mineralised. They are aligned parallel to the Pennine faults and in some instances further resemble the latter by being closely associated with east-facing monoclines. It seems that these unusual structures were formed by a down-east flexuring followed by down-west normal faulting of greater throw so that the combined throw is down to the west.

The most important fault of this type is the Michaelly Sike Fault which throws down to the west about 200 m near Broad Mea [NY 64 48] and about 40 m on Benty Hill [NY 67 43]. Along much of its crop there is little associated folding, but on The Dod, the beds are disturbed in a belt 600 m wide near the fracture. Dips of 20° to the north-east are seen in the Four Fathom Limestone immediately east of the fault [NY 6612 4559], whilst to the west, a broken anticline trends parallel to the fault, with dips up to 40° on its limbs [NY 6555 4552] to [NY 6581 4566]. Although the overall throw is to the west, an initial down-cast monocline is indicated by the local flexures. Similarly, the Great Heaplaw Fault throws down to the west about 75 to 90 m in Gilderdale Burn [NY 6861 4663] to [NY 6870 4657] but is associated with a shallow monocline facing to the east. The Rowgill Fault is also characterised by faulted monoclinal flexuring, which is best seen in a stream [NY 6565 4159] to [NY 6681 4144] east-south-east of Hartside Cross.

The Great Stockdale Beck Fault is unusual amongst faults with this trend in being a simple fracture throwing down to the east, in the Croglin Water valley. Farther south, however, it passes into two subparallel faults with opposite throws, separated by a narrow horst; the structures are both exposed in stream sections [NY 6236 4521] to [NY 6230 4547] and [NY 6237 4531] to [NY 6243 4544].

2 NE-striking faults

The throws on these fractures are usually small and are not consistent, either down to the north-west or to the south-east. The faults tend to be mineralised and are rarely associated with local folding. The presence of a Whin dyke along one of these fractures west of Hartside Height [NY 633 426] suggests that their initial development preceded the intrusion of the Whin Sill.

There are, in addition, two east-trending fractures which do not fit into either of the above categories. Firstly, the Great Sulphur Vein (Figure 34) of Alston Moor is a faulted monocline with northerly dips of 15° to 25°, the flexure being bounded by two parallel faults and invaded by large amounts of quartz. Both fold and faults throw down northwards, the northerly fracture generally having the greater throw. Near Smittergill Head, the structure is about 50 m wide with a total throw of about 80 m (Thompson, 1933), but farther west both width and throw decline. The line of the structure on Melmerby Fell is partly based upon the results of a magnetic survey (p. 138) which suggest that here the Vein hades to the south as a reversed fault. The second fault with an easterly trend is the Crowdundle Fault which also throws down to the north. It extends eastwards into the mineralised Dun Fell Vein of the Alston district (Dunham, 1948, p. 128) which has a maximum throw of 50 m. Within the Carboniferous beds the structure consists of two sub-parallel faults, the Rowpotts and Henrake veins, but it appears to be a simpler, unmineralised fracture within the Lower Palaeozoic rocks.

Vale of Eden

The rocks of the Vale are folded into a broad asymmetrical syncline whose axis lies close to, and subparallel with, the Pennine faults (Figure 34). Both Carboniferous and Permian beds are folded although dips are steeper in the older rocks. On the gentle western limb of the syncline, the regional inclination of the Carboniferous sequence is 6° to 10° to the north-east. The dip of the Permo-Triassic rocks on this limb is 2° to 3°. The eastern limb of the syncline is more steeply inclined, with a general dip of 15° to 20° in the Carboniferous rocks and 10° to 12° in the Permo-Triassic strata. Projection of the observed dips and thicknesses shows that a minimum of 1.5 km of Carboniferous rocks are present beneath the Permo-Triassic strata near the axis of the syncline, including more than 400 m of Coal Measures.

The syncline extends as far north as the prominent line of faulting and local folding, including the Maryport and Stublick faults, which bounds the Carlisle Basin on its south side. This line lies mainly to the north of the district and is seen only in the north-west near Warren Plantation where Carboniferous rocks are anomalously inclined at 32° to the south-east, and around Foulbridge where the Eden Shales dip northwards into the Carlisle Basin.

The Permo-Triassic rocks of the Vale appear to be cut by fewer faults than the older rocks, but this impression is probably misleading. Faults in the Penrith and St Bees sandstones are difficult to trace on the ground, but where exposure is continuous, as in Long Meg mine [NY 57 37], fault densities compare with those of the Carboniferous outcrops. Indeed, the comparison of fault trends and densities in the Carboniferous and Permo-Triassic outcrops is sufficiently close to suggest that many of the fractures in the younger rocks were inherited from pre-existing faults in the older strata, as elsewhere in northern England (Moseley and Ahmed, 1967).

The pattern of faulting over most of the Vale closely resembles that of the Alston Block, with two dominant sets of faults, trending approximately north-north-west and northeast respectively. Within the Pennine Fault system however, the rocks on the eastern synclinal limb between Melmerby and Milburn are heavily faulted in a more complex pattern and these structures are described separately.

1 NNW-striking faults

These include many NW-trending, as well as NNW-trending fractures, but both are grouped together here as their directions of strike are either not consistent, or are not sufficiently well known to allow further subdivision. They generally throw down to the west, often by a substantial amount.

The Milburn Fault, in the south-east of the district, has a throw in the Permo-Triassic rocks of 110 m down to the west where it crosses Crowdundle Beck near the Lounthwaite Borehole [NY 655 310], and this increases to more than 200 m near Milburn village. The throw in the Carboniferous rocks is unknown, but may be much greater as many faults nearby have pre-Permian throws. The Lounthwaite Fault is one of the largest fractures in the Vale. Where it crosses Crowdundle Beck, a belt of St Bees Sandstone about 100 m wide dips steeply to the south-west at up to 80° [NY 646 306]. Near Blencam, the fault throws down about 300 m to the west, and northwards the throw increases to about 600 m near Ousby. The fault seems to intersect the axis of the Vale of Eden syncline east of Ousby (Figure 34), although the change in trend of the axis hereabouts is unusual and may be due to undetected faulting striking north-westwards from the Lounthwaite Fault. Certainly the eastern limb of the fold is absent in Hole Sike and its tributaries, as the dips in the Trias are consistently to the north-east close to the Fault near Row [NY 630 348].

Farther west, the Long Meg–Culgaith Fault, has an unusual down-easterly throw. Near Culgaith, the fault steps back the Eden Shales scarp [NY 610 297] with a throw of about 25 m, which increases northwards to about 50 m near the Langwathby Borehole [NY 58 33]. Farther north however, the throw declines and the fault ends in Long Meg anhydrite mine. The faults are generally encountered in the evaporite workings as folds or monoclinal rolls, rather than as the clean fractures present in the overlying and underlying sandstones.

The faults within the Penrith Sandstone outcrop are mainly deduced from breaks and off-sets in the silicified sandstone scarp. Thus, the Abbott Moss Fault is marked by sharp breaks of slope on the north-east side of Blaze Fell and Lazonby Fell but the amount of its throw is not known. Similarly, the Scratchmillscar Fault separates the north-trending Lazonby Fell scarp from the NNW-trending Bowscar scarp. Its down-westerly throw can only be estimated accurately farther north near Barrockside, where Penrith Sandstone is faulted against Namurian siltstones in the north bank of the River Petteril [NY 4495 4784]; the fault throws the Permian rocks about 50 m but about 100 m of pre-Permian throw is also present.

The prominent NW-striking scarp of Penrith Beacon is bounded on its north-eastern side by the Maidenhill Fault, throwing the Penrith Sandstone 10 to 15 m down to the south-west. To the north however, the throw is much greater in the Carboniferous rocks and is estimated at about 350 m near High Head. The fault bounds the Ivegill Permian out lier on its north-eastern side, and although its post-Permian throw is not known, it is likely to be substantial. A fault of similar trend, the High Braithwaite Fault, throws Penrith Sandstone against Namurian sandstones in the River Ive [NY 4031 4334] and is extrapolated south-eastwards beneath the drift cover.

The Penrith Fault throws down to the east; north-west of the town, it must throw approximately 300 to 400 m to separate the Namurian sandstones of Newton Reigny [NY 483 322] from the Coal Measure outcrops near Thornbarrow [NY 4810 3510], but south-eastwards its course and throw are conjectural beneath continuous drift. The Johnby Fault, on the other hand, has a direct topographical effect as its course is marked by the valley between Greystoke and Johnby. Its maximum down-west throw of 150 m is reached near Johnby; it declines to 100 m farther north near Ellonby and also in the south near Gill. The Summerground Fault also varies rapidly in throw, from only a few metres near its northern end and on Greystoke Moor in the south, to more than 80 m just south of its junction with the Greystoke Fault. Here, the beds on the downthrow side are upturned westwards at 35° to give a shallow syncline in the southern part of Greystoke Park.

2 NE-striking faults

The group of structures in the north-west, near High Burnthwaite, Warren Plantation and High Stand Plantation, are probably the most important with this trend in the district since they divide the Vale of Eden and Carlisle Permian basins. It seems likely that there was a substantial pre-Permian throw along this structural line, as it formed a topographical saddle between the basins during the accumulation of the Penrith Sandstone (p. 71), but direct evidence is available only from the Warren Plantation Fault. This has a throw of several hundred metres in the Carboniferous rocks but only a few metres in the Permian.

Most of the faults in the drift-covered western part of the district are conjectural along much of their strike. For example, the Hollyhill Fault separates the Alston Group outcrops near Ellonby from high Namurian strata in the Woodclose Borehole, with an estimated throw of 450 m, but its detailed course is not known. Similarly, the Newton Reigny Fault is needed to divide the Great Limestone proved at Newton Rigg from the higher Namurian grits cropping out along strike near Newton Reigny, but it is entirely concealed by drift.

Three NE-trending faults displace the Eden Shales scarp between Armathwaite and Kirkoswald. The Beck Fault is exposed west of Ruckcroft [NY 5214 4410], where the throw of about 60 m down to the south-east brings Penrith Sandstone against an horizon just below B-bed in the Eden Shales. The Nunnery Fault is not exposed but has a down-north throw to displace the Eden Shales crop near Staffield. A throw of 75 m down to the north-west on the Kirkoswald Fault can be demonstrated in Raven Beck [NY 5594 4147] where the upper part of the Penrith Sandstone is thrown against beds high in the Eden Shales.

The Pennine Fault system

North of Gamblesby, the term Pennine Fault is used unambiguously for the single fracture separating the Alston Block from the Vale of Eden syncline. Farther south however, many faults are present and a local name is assigned to each fracture; the entire zone of faulting is here termed the Pennine Fault system.

The Cross Fell inlier has been taken as 'the highly disturbed country . . . between the gently dipping Carboniferous sediments which constitute the Alston Block . . . and the down-faulted Permo-Triassic rocks of the Vale of Eden' (Shotton, 1935, p. 640), but this description is misleading in the sense that the inlier contains two parallel outcrops of highly faulted older rocks rather than one. These two belts of country are respectively the upturned edge of the Vale of Eden in the south-west, and the exposed margin of the Lower Palaeozoic basement of the Alston Block in the north-east. They are divided by the Deep Slack–Fellside–Knock Pike faults, which continue south-eastwards into the Swindale Beck Fault of the Brough district (Burgess and Wadge, 1974). On the margin of the Vale of Eden, Triassic, Permian, Carboniferous and various Lower Palaeozoic rocks are exposed; in contrast, the basement rocks of the Alston Block are restricted to the Skiddaw Group. The development of the Pennine Fault system is described below and summarised graphically (Figure 35).

The system was initiated in end-Silurian times, shortly after the intrusion of the Weardale Granite, with an overall throw of several hundred metres down to the west, preserving upper Ordovician and Silurian rocks on the down-throw side. Many of the faults in the system probably date from that time, but later movements along pre-existing fractures make this difficult to prove. Where there has been no subsequent movement however, as on several faults in the Kirkland Formation east of Kirkland, their Caledonian age is clear. There is no evidence of other than normal faulting at this time.

In the late Devonian, sufficient topographical contrast remained across the Pennine Fault system to produce the local fans of the Polygenetic Conglomerate, but by the Lower Carboniferous, the system was marked by a topographical low in which the coarse elastics of the Basement Beds accumulated. If there was contemporaneous movement along the system during this deposition, then much thicker Basement Beds may have accumulated in the Vale of Eden. They do thicken westwards near Melmerby, but evidence in the other exposed sections is inconclusive. Throughout Carboniferous times, the Alston Block was uplifted in comparison to the Northumberland and Stainmore troughs to the north and south respectively. There is no conclusive evidence of a persistent contrast in contemporary subsidence across the Pennine faults, but the history of the Vale of Eden as a depositional basin since end-Silurian times is so consistent as to suggest that it was also a basin in Carboniferous times, and bounded perhaps by growth-faulting along the Pennine Faults. This view is supported by the gravity data (p. 140) and by the westward thickening of the Basement Beds near Melmerby (p.27). From present outcrops, however, the sections are inconclusive; the Namurian sequence is thicker in the Vale than on the Alston Block but the Dinantian successions are comparable. The rocks immediately west of the Pennine faults, where the thickest sequences would be expected, are not exposed.

The Armorican earth movements at the end of the Carboniferous produced an east–west compression. The brittle basement rocks broke as reverse faults along the Pennine Fault system and were pushed eastwards against the edge of the Alston Block, as on the Lad Slack and Windy Gap faults. The more plastic cover of Carboniferous sediments responded initially by tight folding along axes parallel to the underlying faults, and then by the development of an eastward-facing monocline with near-vertical or overturned beds on the steep limb (Figure 35). Where the compression was greatest, the reverse faults penetrate the Carboniferous cover. It is characteristic of this type of structure that although deformation is intense locally, it dies out rapidly away from the fault-plane. Belts of upturned Carboniferous strata are best seen on the east sides of the Deep Slack and Lad Slack faults, whilst a low-angle reverse fault (p. 62) wholly within the Carboniferous cover is exposed in Ardale Beck [NY 6430 3447]. The amount of easterly down-throw on most of the reverse faults is difficult to estimate, but a displacement of 200 to 300 m has been suggested for the Deep Slack Fault (Wadge and others, 1972) and throws of similar magnitude are likely on the other major structures. Different structural levels on the reverse faults are exposed by the present level of erosion. The Deep Slack and Lad Slack faults show comparatively deep structural horizons, where most of the displacement has occurred along a single well-defined fracture, but in the northern part of the district the Pennine Fault is accompanied by folding taking up much of the total throw.

As a result of the compression, the Vale of Eden syncline was initiated and the major sets of joints and faults in the adjacent areas were developed; the gentle doming of the Carboniferous rocks of the Alston Block probably also dates from this time. The intrusion of the Whin Sill and its associated dykes under conditions of tension closely followed this compressive phase. The Sill is not recordcd in the Carboniferous sequence on the eastern limb of the Vale of Eden syncline, but Whin intrusions do occur in Ordovician rocks on the west side of the Deep Slack Fault. It has therefore been argued (Wadge and others, 1972) that the western limit of the Sill may have been impermeable basement rocks on the upthrow side of one of the reverse faults. The Sill is at its lowest stratigraphical level towards the centre of the doming of the Alston Block and it rises gradually through the sequence towards its flanks, so its emplacement must post-date the gentle upward flexuring.

The last phase of the Armorican earth movements was a period of local tension with down-west faulting along the Pennine Fault system, with displacements of either the reverse faults, such as the Deep Slack Fault, or re-activated Caledonian faults, such as the Fellside Fault. Throws of several hundred metres are envisaged for these movements but the combined effect of the Armorican faulting remained an overall throw down to the east. This result is unexpected because the granite-based Alston Block has generally been an area of uplift, but this is the sense of the Armorican structures and the stratigraphy gives supporting evidence as follows.

Prior to the deposition of the Penrith Sandstone, the surface rocks were deeply reddened, and remnants of this oxidised zone indicate which rocks formed the pre-Permian topography. For example, the reddened Lower Palaeozoic and Carboniferous rocks of Roman Fell, in the southern part of the Cross Fell inlier (Burgess and Wadge, 1974, p. 80) show this to have been an upstanding area.

On the other hand, the complete absence of reddened rocks along the western edge of the Alston Block suggests that they lay well below the contemporary level of oxidation and that the surface rocks were either Millstone Grit or Coal Measures. In contrast, the eastern limb of the Vale of Eden syncline was deeply eroded at this time, exposing beds low in the Carboniferous sequence, and even Lower Palaeozoic rocks such as the Knock Pike Tuffs, reddened beneath the sub-Permian unconformity to the east of Milburn. Locally derived clasts of Lower Palaeozoic, as well as the more common Carboniferous rocks are present in the Penrith Sandstone near Ranbeck [NY 6551 3216] showing that contemporary erosion had reached the basement rocks nearby.

The topographical hollow in which the Penrith Sandstone began to accumulate seems to have corresponded approximately with the Vale of Eden syncline. Certainly there is no evidence of thick sandstone sequences immediately along the Penrith Fault system, indicating contemporary down-west movements controlling sedimentation. The Penrith Sandstone succession is generally thinner here than farther west, and although coarse elastic debris from the older rocks is commonly incorporated, this is derived from outcrops on the eastern limb of the syncline rather than the Alston Block.

The latest movements affecting the system were renewed down-west faulting along many of the earlier fractures, with the uplift and eastward tilting of the Alston Block and further flexuring of the Vale of Eden syncline. A minimum displacement of about 600 m is estimated along the Pennine Fault system near Cross Fell and farther north the throw is probably similar. The movements were initiated during the Alpine orogeny. They affect the Triassic St Bees Sandstone, and the Pennine Fault appears to have had a considerable Tertiary throw near Renwick before the intrusion of the late-Palaeocene Armathwaitc dyke. It seems likely that much of this early movement occurred in the early Palaeocene (about 65 Ma) at a time of widespread tension, marked elsewhere by the climax of magmatic activity in the British Tertiary Igneous Province and by rifting in the North Atlantic (Evans and others, 1973).

The faulting has continued subsequently down to the present day. Near the southern end of the Pennine escarpment, an earthquake of unusual intensity for this country with a focus of 15 km, occurred in August 1970 (Browning and Jacob, 1970). The depth of the focus suggests that the fault system continues as a dislocation deep within the crust. The fracture at these depths is likely to lie closer to the vertical than the near-surface faults, which are generally inclined at about 70° in the few places where they are visible. Movements along the crustal fracture have probably had strong lateral components, as well as the vertical displacements described above, but these are generally difficult to determine and no definite lateral movements have been recorded.

Details

In the north the Pennine Fault is generally a single fracture but has a composite throw. It is bounded on the north-eastern side by a belt of lower Alston Group rocks, generally inclined steeply to the north-east and locally overturned to the south-west. Tight folds, with axial trends parallel to the fault, are also common in this belt produced by the Armorican earth movements (Figure 34). The fault also moved substantially in Tertiary times as in many places it cuts Triassic rocks. For example the Eden Shales are faulted against broken, red-stained Alston Group sandstones [NY 5786 4821] in a stream 1 km NNE of Croglin, and in Croglin Water [NY 5839 4745]. Steeply-dipping and contorted Namurian rocks are thrown down against the sandstone beneath the Lower Little Limestone, dipping north-eastwards at 50°. A shallow anticline whose axis lies parallel to the fault, crosses the crop of the Jew Limestone in this stream [NY 5848 4748]. Farther south near Davygill, the fault separates Eden Shales from beds including the Jew Limestone which are folded into two tight anticlines and synclines close to, and parallel with the fracture [NY 591 462].

About 1 km NE of Renwick, St Bees Sandstone is faulted [NY 6026 4399] against a 200-m-wide zone of overturned lower Alston Group beds dipping south-westwards at 50° to 70°, and striking parallel to the fault. Beyond this zone the rocks are folded in a series of parallel flexures whose tightness declines gradually away from the structure. The total width of the folded belt is up to 900 m hereabouts. Farther south the structures are similar. A belt of steeply-dipping or overturned beds up to 300 m wide continues from Raven Beck southwards to the lower slopes of Melmerby Low Scar. In Raven Beck [NY 6114 4350], the Lower Little Limestone is overturned to dip at 60° to the south-west and is faulted against St Bees Sandstone inclined at about 35° in a similar direction. Two anticlines and synclines trending parallel to the Pennine Fault are well seen upstream in Raven Beck but appear to die out south of the good section in Loo Gill.

The Melmerby Scar Limestone and Basement Beds are overturned in scattered outcrops between Loo Gill and Hazel Rigg. The next continuous section through the structure is in Grey Mare's Tail. The fault crosses the stream 800 m E of Hazel Rigg [NY 6234 4002] and throws St Bees Sandstone against near-vertical Polygenetic Conglomerate and Basement Beds. Dips of 80° to the north-east or overturning to the south-west persist up to 200 m from the fault, but farther upstream the dip gradually slackens to less than 40° in the Orton Group beds at the top of the stream section, and less than 10° in the overlying Melmerby Scar Limestone of Sailrigg Quarry, below Long Crags. The section in Limekiln Beck, about 300 m farther south, shows a similar structure but intersected by minor faulting. RSA

The belt of steep dips continues southwards in the Basement Beds outcrop across the lower slopes of Melmerby Low Scar but here the Pennine Fault divides. The Deep Slack Fault to the east is a reverse fault throwing Ordovician volcanic rocks against Basement Beds tilted up at 60° to 80°. It has been suggested (Wadge and others, 1972, fig. 4) that a Hercynian throw of several hundred metres down to the east on this structure was subsequently modified by down-west movements of 200 to 300 m. At its southern end, the fault-plane dips at about 70° to the west in the banks of Melmerby Beck [NY 6254 3717], and a similar inclination is seen on the Else Gill Fault farther down the stream [NY 6231 3754]. This fracture has a strong down-west Tertiary throw and may also have had a late-Armorican displacement although the evidence is not conclusive. The Penrith Sandstone rests unconformably on Alston Group rocks on the down-throw side of the fault and may also have unconformably overlain the Ordovician volcanic rocks on the up-throw side; no Permian rocks are now preserved here but patchy red-staining of the volcanic rocks may have resulted from oxidation a short distance beneath the sub-Permian unconformity. If this view is correct, a substantial pre-Permian throw down-west is indicated on the fault.

Farther east, the Gate Castle Fault is a normal fault throwing down to the west about 70 m on Melmerby Low Scar and about 100 m to the west of Cuns Fell. It has marked topographical effects in repeating the Melmerby Scar Limestone crags on the High and Low Scars and in throwing the sub-Carboniferous unconformity from its outcrop in Rake Beck [NY 6330 3705] up on to the northern slopes of Meikle Awfell. Basement Beds conglomerates are thrown against Skiddaw Group mudstones in both Dry Sike [NY 6362 3725] and Hunrigg Sike [NY 6368 3710]. The Lad Slack Fault is an Armorican reverse fault bounded to the east by a narrow zone of steeply-dipping Basement Beds. These are best seen on the Lad Slack gully [NY 6519 3450] marking the course of the fault north of Ardale, and on the col east of Cuns Fell [NY 6485 3695], where dips in the conglomerates are near-vertical against the fracture, but slacken rapidly eastwards to about 10° on Melmerby High Scar. On Muska Hill [NY 652 355], a down-east displacement of about 80 m on the fault throws the Smiddy Limestone against a shallow syncline of Basement Beds. This plunges gently eastwards and is bounded on the west by the Windy Gap Fault, a similar reverse fault throwing dolerite intruded into the Skiddaw Group against Basement Beds conglomerates inclined up to 50° against the fracture. The amount of throw is unknown.

The Fellside Fault, the southerly continuation of the Else Gill and Deep Slack faults east of Melmerby, throws St Bees Sandstone against Skiddaw Group rocks but in the west bank of Melmerby Beck [NY 6251 3713], a small fault-bounded area of Lower Carboniferous rocks, about 50 m long, is caught up in the fault plane. The course of the fracture is well-marked just north of Gale Hall [NY 6296 3662] where it terminates the ridge-like outcrop of a Lower Palaeozoic dyke. A calcite-veined breccia of Alston Group dolomitic limestone, sandstone and shale fragments marks where the fault crosses Dale Beck [NY 6350 3597] whilst further south, a spring issues from the fracture to the east of Fellside [NY 6371 3537]. Nearby, the fault separates outcrops of Skiddaw mudstones from coal-bearing Namurian sequences [NY 6391 3511], but is unlikely to be a single break here as a small lenticular outcrop of Melmerby Scar Limestone lies within the fault zone. Similarly, at least two parallel dislocations must be present where the fault crosses Crowdundle Beck, as outcrops of both Basement Beds and Alston Group rocks are thrown against beds of the Kirkland Formation. Across Red Carle, the line of the fault is obscured by drift but it passes into the Knock Pike Fault, whose position in Milburn Beck is marked by Skiddaw mudstones thrown against tuffs of the Borrowdale Volcanic Group. AJW

References

BAMFORD, D., FABER, S., JACOB, B., KAMINSKI, W., NUNN, K., PRODEHL, C., FUCHS, K ., KING, R. and WILMORE, P. 1976. A lithosphere seismic profile in Britain, preliminary results. Geophys. J. R. Astron. Soc., Vol.44, pp.145–160.

BROWNING, G. R. J. and JACOB, A. W. B. 1970. Preliminary study of the North of England earthquake of August 9th, 1970. Nature, London, Vol. 228, pp. 835–837.

BURGESS, I. C. and WADGE, A. J. 1974. The geology of the Cross Fell area. Explanation of 1:25,000 Geological Special Sheet. (London: HMSO.) 91 pp.

DUNHAM, K. C. 1948. Geology of the northern Pennine Orefield: Vol. 1, Tyne to Stainmore. Mem. Geol. Surv. G.B.

EASTWOOD, T., HOLLINGWORTH, S. E., ROSE, W. C. C. and TROTTER, F. M. 1968. Geology of the country around Cockermouth and Caldbeck. Mem. Geol. Surv. G.B.

EVANS, A. L., FITCH, F. J. and MILLER, J. A. 1973. Potassium-argon age determinations on some British Tertiary rocks. J. Geol. Soc. London, Vol. 129, pp. 419–443.

FITTON, J. G. and HUGHES, D. J. 1970. Volcanism and plate tectonics in the British Ordovician. Earth Planet. Sci. Lett., Vol. 8, pp, 223–228.

HELM, D. G. 1970. Stratigraphy and structure of the Black Combe Inlier, English Lake District. Proc. Yorkshire Geol. Soc., Vol. 38, pp. 105–148.

JEANS, P. J. F. 1971. The relationship between the Skiddaw Slates and the Borrowdale Volcanics. Nat. Phys. Sci., Vol. 234, p. 59.

MOSELEY, F. 1972. A tectonic history of north-west England. J. Geol. Soc. London, Vol. 128, pp. 561–598.

MOSELEY, F.  and AHMED, S. M. 1967. Carboniferous joints in the north of England and their relation to the earlier and later structures. Proc. Yorkshire Geol. Soc., Vol. 36, pp. 61–90.

ROBERTS, D. E. 1971. Structures in the Skiddaw Slates in the Caldew valley, Cumberland. Geol. J., Vol. 7, pp. 225–238.

SHOTTON, F. W. 1935. The stratigraphy and tectonics of the Cross Fell Inlier. Q. J. Geol. Soc. London, Vol. 91, pp. 639–700.

SIMPSON, A. 1967. The stratigraphy and tectonics of the Skiddaw Slates and the relationship of the overlying Volcanic Series in part of the Lake District. Geol. J., Vol. 5, pp. 391–418.

THOMPSON, L. M. 1933. The Great Sulphur Vein of Alston Moor. Proc. Univ. Durham Philos. Soc., Vol. 9, p.91.

WADGE, A. J., HARRISON, R. K. and SNELLING, N. J. 1972. Olivine-dolerite intrusions near Melmerby, Cumberland and their age determination by the K-Ar method. Proc. Yorkshire Geol. Soc., Vol.39, pp. 59–70.

WEBB, B. C. 1972. North–south trending pre-cleavage folds in the Skiddaw Slate Group of the English Lake District. Nat. Phys. Sci., Vol. 235, pp. 138–140.

WILSON, J. T. 1966. Did the Atlantic close and then re-open? Nature, London, Vol. 211, pp. 676–681.

Chapter 10 Drift deposits (Recent and Pleistocene)

Introduction

To the west of the Pennines the characteristic drift deposits of the district are of glacial origin. They comprise a complex of boulder clay and stratified deposits, the youngest of the latter being associated with a widespread system of drainage channels. On the Pennines, by contrast, glacial deposits are relatively sparse, and the characteristic drifts are solifluxion deposits (head) and peat.

The earliest published accounts of the drift deposits of the Vale of Eden were those of Goodchild (1875, 1887), who interpreted the sequence as the product of three separate glaciations, the first and third emanating from the Lake District, with a second from a Scottish source. In contrast, Trotter (1929) and Hollingworth (1931) interpreted the sequences in the Vale and in the Carlisle Plain as the products of two Scottish glaciations, and an intermediate one emanating from the Lake District. They claimed that the last—the Scottish Readvance—was effective only as far south as the northern end of the Vale. The principal criteria employed by these authors for their recognition of separate glaciations were the different provenances and distribution of the erratics within the boulder clays, and the presence of stratified deposits, including gravel, silt, and stoneless clay separating layers of boulder clay.

Boreholes sunk in connection with the construction of the M6 motorway through the western part of the Vale have shown that the relationship between the boulder clays and the stratified deposits is more complex than was previously realised, and that some of the stratified deposits formed under glacial rather than interglacial or interstadial conditions. Moreover, whilst the occurrence of contrasting suites of erratics indicates provenance from different sources, it need not necessarily imply that the ice-streams were active in distinct and separate glacial episodes. Only the presence of a proven interglacial or interstadial deposit, such as a peat, separating units of boulder clay can be regarded as unambiguous evidence of the occurrence of more than one glaciation, but no such peats have been recorded in the district.

It is, however, possible to assign the bulk of the deposits to the glaciation that affected much of Northern England during the latter part of the Devensian (final) stage of the Pleistocene (Mitchell and others, 1973). At the southern end of the Vale of Eden, organic deposits underlying boulder clay in Scandal Beck in the Kirkby Stephen district have yielded a radiocarbon date of 34 350 years BC (Shotton and others, 1970) and these predate the bulk of the deposits in the present district. An upward limit to the age of this latest regional ice-advance is set by a date of 12 380 years BC obtained from organic deposits in a kettlehole at Blelham Bog, near Ambleside (Pennington and Bonny, 1970). No division of the drift deposits between Recent and Pleistocene is indicated on the map, but it is probable that the alluvium and alluvial fan deposits, most of the river terrace deposits, and nearly all the peat, are Recent, formed within the Flandrian stage (post 8300 years BC).

Boulder clay

Boulder clay is by far the most extensive of the drift deposits of the district, as in the remainder of the lowlands of Cumbria. It comprises ill-sorted rock-fragments ranging from boulders to sand-sized particles set in a matrix that ranges from a stiff clayey silt, as over most of the western part of the district, to a friable clayey sand, as for example in samples closely overlying poorly cemented Penrith Sandstone. Its typical colour is red-brown, though locally it is grey or grey-brown.

The deposit is thickest in the west where it forms an extensive sheet averaging about 20 m thick and masks all but the most prominent rock-head features. Its surface is moulded into drumlins (Figure 36), ranging from short whale-backed forms up to 40 m high to low ridges up to 2 km long. In the extreme north-west, the terrain is more irregular, hummocky but of low-relief.

Between the escarpment of the Penrith Sandstone and the foot of the Pennines, boulder clay forms a patchy veneer rarely exceeding 10 m thick. It is generally absent over the extensive tracts in this area that have been channelled by glacial drainage streams, for example near the Pennine escarpment between Croglin and Renwick and on the western flank of Lazonby Fell, but is preserved in the Eden gorge south of Armathwaite.

On the Pennines, boulder clay occurs in a few isolated patches extending up to a height of about 470 m OD. It mostly forms smooth veneers, such as that in the embaymcnt of the escarpment around Raven Beck, but in the upper reaches of Croglin Water there is a group of whale-backed drumlins. No true boulder clay is present above 470 m OD, but erratic pebbles are common in the head deposits of the Pennine summits and ridges to the north of Hartside Cross. On the southern part of the Pennine escarpment, the valleys of Dale Beck, Ardale and Kirkdale are partially blocked by moraines.

The suites of rocks included in the boulder clay vary from one area to another. In the west Borrowdale Volcanic rocks are abundant together with Carboniferous red sandstones and limestones, but boulders of Scottish granite are rare. In the Eden valley blocks of Penrith Sandstone are abundant, Borrowdale Volcanics and Scottish granites are common, and boulders of dolerite from the Armathwaite Dyke are present in the north. Towards the Pennine escarpment, Carboniferous sandstones and quartz-dolerite become progressively abundant, and, south of Gamblesby, Lower Palaeozoic rocks are common. On the Pennines, Borrowdale rocks and St Bees Sandstone are both common, occurring in the boulder clay and also as erratics on the ridges and summits north of Hartside, where Scottish granites are also recorded (Trotter, 1929).

In some sections, notably those in the valleys of the rivers Petteril and Eamont, boulder clay is interlayered with, and in some cases underlain by, stratified deposits. For example, in the Barrock Park Borehole, 38 m of gravel, sand, and laminated silt and clay underlie the boulder clay and rest on rock-head, and many similar, though thinner, deposits are recorded from boreholes near High Wreay, Calthwaite, Catterlen and Skirsgill (Figure 37), (Figure 38), (Figure 39), (Figure 40). The relationship of these stratified deposits to the boulder clay is commonly so complex that the two are considered together in the following account.

Details

Southwaite to Skelton

Boulder clay is the dominant glacial deposit and forms an almost continuous sheet of irregular thickness averaging about 20 m. Among the best natural sections are those [NY 4043 3961] to [NY 4107 3887] in the banks of a gully at Hole House, some 5 km NW of Skelton. The lithology, which is typical of the area, is a stiff red sandy and silty clay, with abundant rock fragments including Carboniferous limestones and sandstones and Borrowdale volcanic rocks. Similar sections, exposing up to 10 m of boulder clay, are seen in the banks of gullies around Ivegill [NY 4155 4348] to [NY 4163 4388]; [NY 4156 4332] to [NY 4180 4325; and 4172 4296] to [NY 4174 4245]. Boulders and blocks of Borrowdale volcanic rocks are common at the surface while in the extreme north boulders of Scottish granites are also present.

Drumlins are characteristic landforms over most of this area and their distribution and crest-orientations are shown in (Figure 36). A whale-backed type is common in the triangle of ground between Hutton End, Brackenburgh and Hutton-in-the-Forest, the hill [NY 454 372] known as Hutton Bank being typical. It is 800 m long, 350 m broad, and about 20 m high. Some of these whale-backed drumlins have a symmetrical long profile, but many are steeper at their southern ends, a good example being one [NY 474 363] some 300 m NE of Whitrigg. To the north and west of this whale-back field, the drumlins are less pronounced, but more elongate. The swell [NY 4346 3771] to [NY 4436 3607] extending north-north-westwards from Riggdyke, about 1 km N of Skelton, is typical. It is some 2 km long, 100 m wide and has a height of only 5 m. The Unthank Borehole [NY 4376 3711] sunk on its crest proved 17.2 m of boulder clay resting on solid. The Woodclose Borehole [NY 4098 3794] sunk on another elongate drumlin, with a height of only 2 to 3 m, proved 30.6 m of boulder clay on solid.

Some drumlins, both of the whale-backed and elongate varieties, have a core of solid rock at their southern ends. Hutton Bank, is one such example, with Carboniferous sandstone exposed in a quarry [NY 4556 3702]. Others include Kirk Rigg [NY 4444 3540], near Skelton—where a faulted outcrop of Carboniferous sandstone forms a crag from which extends an elongate drumlin—and a hill [NY 483 415], north-west of Thiefside Cottages, where a prominent feature of Penrith Sandstone forms a similar crag.

Drumlins are absent from the extreme north-western part of this area. Around East View, for example [NY 41 47], there is a featureless and gently sloping surface of boulder clay, into which the drumlin terrain merges from the south and east. Northwards this featureless tract passes abruptly into irregular boulder clay terrain comprising smooth hummocks without a preferred orientation, as for example to the north-west of Bankdale Park [NY 414 585].

Although much of the lower ground flanking the River Petteril consists of subdued drumlins, boreholes and natural sections show that the drift deposits are here more complex than those underlying the more pronounced drumlin terrain to the west. In most sections, boulder clay constitutes the upper part of the sequence, but a complex of deposits including silt, sand, gravel, and boulder clay is present below. The sequence proved in the Barrock Park Borehole [NY 4613 4660] is probably typical of the drift deposits of the Petteril valley northwards from Southwaite. Here, some 38 m of sand, gravel, silt and clay, rested on rock-head, and were overlain by 9 m of boulder clay, capped by 3 m of sand and sandy boulder clay. A similar sequence is imperfectly exposed at several localities in the steep banks of the River Petteril and its tributary streams between Southwaite and High Wreay, the stratified deposits apparently filling a rock-head hollow broadly coincident with the present Petteril valley. Comparable deposits (Figure 37) were proved farther north along the Petteril valley, in a group of motorway boreholes [NY 436 512] to [NY 431 498] some 2 km N of High Wreay, just beyond the district boundary. A layer of organic sand was recorded in one of these holes, but no overlying boulder clay was penetrated.

Sections of stiff red boulder clay are seen in the River Petteril to the south of Southwaite and were proved in several motorway boreholes a little to the west between Southwaite and Catterlen. One such borehole [NY 4774 3936] 1 km SE of Calthwaite proved boulder clay 21.4 m thick, but others in a tract of ground [NY 4608 4162] to [NY 4744 4010] to the north of Calthwaite proved sand, silt and clay irregularly interlayered with boulder clay (Figure 38). Away from the Petteril valley stratified deposits have been proved only in the Low Braithwaite Borehole [NY 4259 4209] about 1 km SE of Ivegill, where 30 m of laminated clay and silty clay, resting on solid underlie 12.8 m of stiff red boulder clay. Like those of the Petteril valley north of Southwaite, these stratified deposits occupy a hollow in rock-head. Penrith Sandstone underlying boulder clay is exposed e.g. [NY 4275 4230] immediately to the north-east, in the bed and banks of the River Ive, while, to the south, Carboniferous sandstone underlies boulder clay in the banks [NY 4254 4145] of a stream at Braithwaite Shields. RSA

Greystoke to Penrith

Stiff red or brown boulder clay forms a sheet of irregular thickness averaging about 15 m over most of this area. Except in the east, no stratified intercalations have been recorded. Among the best sections are those [NY 4645 2946] in quarries near Blencow, where the lithology is grey and red stiff sandy clay, with pebbles and boulders making up some 40 per cent of the total. The erratics are largely of Lake District rocks, the largest being from the Borrowdale Volcanic Group: rare pebbles of granite from the Southern Uplands are also present. Boulders and blocks of Borrowdale rocks are common at the surface, one of the largest (2.4 x 9.1 x 4.3 m) lying [NY 4777 3118] 300 m S of Newton Reigny. Many large blocks of Borrowdale rocks and of Carboniferous limestones occur in the boulder clay dug from a cutting [NY 5073 2926] south-west of Penrith railway station and just within the Appleby district. In the extreme south-west around Berrier Hill [NY 4097 2993] boulders of Eycott lava are also present.

Drumlins are widespread (Figure 36) except in parts of Greystoke Park and to the south of Blencow Station. They are mostly whale-backed and among the best examples are two south of Greystoke [NY 444 299] and [NY 440 304]. The latter is 600 m long, 400 m broad, and has a height of 36 m; its long-profile is apparently symmetrical. Other whale-backed drumlins are asymmetrical, with steeper southern ends and more elongate tails to the north, for example [NY 456 342] at Fowrass and [NY 481 336] north of Catterlen. Another [NY 430 310] west of Greystoke Castle is some 40 m high, abutting at right angles against a major scarp of limestone. On the northern side of Greystoke Park, conversely, some drumlins are steeper at their northern ends, and merge imperceptibly with the solid surface to the south; that at Old Wythes Wood [NY 419 340] is typical. Southwest of Greystoke, on Greystoke Moor [NY 425 300], drumlins form elongate ridges.

A drumlin [NY 416 325] in Greystoke Park, some 3 km W of Greystoke, forms an elongate tail northwards from the crest of a major limestone scarp-feature. No other crag-and-tail features are recorded, although the flank of a drumlin [NY 451 330], north-west of Little Blencow, abuts against a solid feature to the west.

Drumlins are also present in the eastern part of the area, and boreholes sited on and amongst them, notably at Catterlen (Figure 39) and south of Penrith Railway Station (Figure 40), have proved stratified deposits at depth, in a complex association with boulder clay. The stratified deposits appear to be confined largely, though not entirely, to a rock-head hollow extending between Lowhouse and the south-western part of Penrith. Temporary sections south of Penrith Railway Station in the cutting which now carries the M6 motorway under the railway, exposed an irregular and lenticular bed of grey-brown laminated clay and silt up to 4 m thick, strongly distorted and sandwiched between stiff, grey and reddish grey boulder clay; the upper surface of the clay and silt layer lying about 10 m below the surface of the drumlin. AJW

Armathwaite, Croglin and Kirkoswald

Although a sheet of boulder clay covers much of this area, drumlins have been recognised only in the extreme west, where they have broad, whale-backed forms. In the west, boulder clay 16 m thick was proved in the Nord Vue Borehole [NY 4940 4424] but eastwards towards the Pennine escarpment the deposit is mostly much thinner and boulder clay is present [NY 5079 4494] in the floor of the gorge of the River Eden, at Coombs Wood, about 1 km S of Armathwaite. Extensive tracts in this area have been scoured free from boulder clay by glacial drainage streams, as for example [NY 503 400] on the western flanks of Lazonby Fell and from much of a belt 1 to 2 km wide adjoining the Pennine escarpment.

The matrix of the boulder clay within this area consists generally of a stiff red, silty and sandy clay, but where the deposit rests on poorly cemented Penrith or St Bees sandstones, the basal two metres or so are commonly very sandy as in the railway cutting [NY 5049 4671], 500 m N of Armathwaite.

The suites of rock fragments included in the deposit vary in their composition across the area. Over the Penrith Sandstone outcrop, boulders from that formation are dominant, while erratic boulders include Borrowdale volcanics, Scottish granites and dolerite carried northwards from the outcrop of the Armathwaite Dyke. Boulders of Carboniferous sandstone and pebbles of hematite and vein-quartz are present on the western flank of Lazonby Fell e.g. [NY 508 401]. Over the St Bees Sandstone outcrop, boulders of Penrith Sandstone become rare towards the east; Borrowdale volcanics and Scottish granites are common; and, in a belt of country 1 to 2 km wide along the eastern margin of the crop near Huddlesceugh Hall e.g. [NY 602 418] Carboniferous grey sandstones are abundant, associated with quartz-dolerite from the Whin Sill. One boulder of Shap Granite was recorded, on the St Bees Sandstone crop [NY 5580 4647] 500 m N of Wallmoorsike. RSA

Lazonby–Culgaith

Boulder clay forms a thin and discontinuous sheet in this area. To the west of the Penrith escarpment its thickness may locally exceed 15 m for an old borehole [NY 5183 2989] in the southern part of Penrith records 13.41 m of drift. Farther east, in a borehole [NY 5591 3179] south-west of Edenhall, 8.2 m of boulder clay were proved. The deposit is up to 8 m thick in boreholes around Glassonby, although averaging only 3 m; whilst boreholes southwards towards Huns onby, record a maximum thickness of 11 m. In the Langwathby Borehole [NY 5823 3335] only 3.81 m were recorded, while in boreholes near Culgaith, the thickness was generally about 4 or 5 m, though exceptionally 8.5 m.

The higher hills of the Penrith escarpment, such as Wan Fell and Penrith Beacon, immediately north-east of Penrith, are largely free from drift although erratics are common. East of the Eden, most of the St Bees Sandstone outcrop flanking the Pennine escarpment between Gamblesby and Ousby is free from thick boulder clay, although a veneer of sandy drift with many erratics, particularly of Skiddaw Group mudstones, is widespread.

The boulder clay generally has a stiff red-brown sandy clay matrix, though where it rests on poorly cemented sandstones its basal 2 to 3 m are very sandy. In the more westerly parts of this area, it contains a high proportion of erratic pebbles and boulders of Lake District provenance. Farther east, erratics from the Cross Fell inlier and the Pennine escarpment become progressively dominant, and in the extreme east, between Gale Hall and Kirkland, these erratics lie in a stiff, brown and grey, clay matrix. Although the boulder clay mostly forms smooth, featureless landforms, drumlins occur locally in the south (Figure 36), and also east of Blencarn [NY 648 312] and [NY 653 313].

In several sections in the southern part of this area stratified deposits are recorded in or under the boulder clay. For example, in the northern banks of the River Eamont floor-plain, near Carleton and Frenchfield, up to 6 m of sand and gravel underlie boulder clay [NY 5281 2948] to [NY 5337 2963]; [NY 5354 2956], while farther east [NY 5420 2953]

3 m of coarse gravel rest on Penrith Sandstone and are overlain by 6 m of red and grey gravelly boulder clay. Still farther east, in a narrow tract [NY 5625 2928] to [NY 5758 3040] bordering the flood-plain south of the Eamont, boulder clay rests on gravel which thins southwards. Lenses of sand and gravel within boulder clay, crop out in the sides of drumlins [NY 5468 3430]; [NY 5480 3411] to [NY 5486 3378] between Burrelgreen and Edenhall Grange. AJW

Pennines, north of Hartside

Boulder clay is present only as isolated patches, mostly on the lower slopes of the Pennine escarpment, and along parts of the valley of Croglin Water. Although the lower slopes of the escarpment between Croglin and Renwick have been severely scoured by glacial drainage streams, patches of stiff red sandy boulder clay are preserved, as for example [NY 5906 4621] 800 m E of Davygill, where some 1.5 m of boulder clay including millet-seed sand lie at a height of about 320 m OD. Farther to the south-east, where the escarpment is deeply embayed around the headwaters of Raven Beck, boulder clay forms a more extensive veneer up to a height of about 380 m OD and is present still higher up the hillside at about 466 m OD in swallow-holes [NY 6249 4541] to [NY 6512 4524] some 700 m S of Watch Hill.

In the valley of Croglin Water [NY 6040 4827], about 1 km E of The Combs, boulder clay extends up to about 350 m OD, while eastwards along the valley, there is a more extensive deposit at least 6 m thick which attains 472 m OD to the north-east of Watch Hill. The best section [NY 6225 4715] is in the southern banks of Croglin Water, where 6 m of red boulder clay with rock fragments including Borrowdale volcanic rocks and St Bees Sandstone, are overlain by 6 m of head.

Another patch of boulder clay forms a veneer up to 457 m OD on the hillside 1 km E of Broad Mea. In a gully section [NY 6484 4832] to [NY 6505 4850] some 3 m of stiff red and grey boulder clay contain fragments of St Bees Sandstone and pebbles of Borrowdale volcanics. A similar veneer lies at up to about 335 m OD on the southeastern flank of Gilderdale Burn e.g. [NY 6933 4702]. Four whale-backed drumlins, each about 100 m long, 35 m wide, and 6 m high, lie en échelon [NY 6316 4676] to [NY 6337 4649] some 800 m NE of Watch Hill; all are aligned approximately NNW–SSE, parallel to the valley.

Stratified deposits are associated with boulder clay in some rock-head hollows. One example [NY 5892 4760] on the southern bank of Croglin Water exposes gravelly boulder clay with pockets of fine-grained sand, and another [NY 6157 4326], some 2 km E of Renwick, exposes layers of silt and gravel within boulder clay.

Erratic pebbles, particularly of Borrowdale volcanic rocks, are common in head deposits in many parts of this area, but are unrecorded south of Hartside Cross. They are especially abundant on the watersheds between Hartside Height and Farlam Currick and between Tom Smith's Stone and Grey Nag.

On the lower part of the Pennine escarpment near Croglin, two masses of Carboniferous limestone, each covering an area about 80 x 50 m [NY 5737 4854] and [NY 5745 4862], appear to rest on St Bees Sandstone just to the west of the Pennine Fault. They are separated from extensive outcrops of limestone to the north-east of the fault by a deep glacial drainage channel, and thus may be regarded as glacial erratics rather than landslipped masses. RSA

Pennines, south of Hartside

Boulder clay is confined to the lower slopes of the Pennine escarpment. It commonly forms smooth sheets which thin out upslope as near Melmerby High Scar and between Grumply Hill and Burney Hill. The boulder clay is stiff and brown, and contains cobbles and boulders of local provenance of which Carboniferous sandstones, Skiddaw Group mudstones and tuffs, and Whin Sill quartzdolerites are dominant, boulders of Carboniferous limestones being rare.

Irregular landforms of morainic drift are also present. An example on the southern side of Dale Beck includes pockets of sand [NY 6422 3619] and has partly blocked the valley [NY 643 362] and diverted the stream northwards. Another coarse deposit including large blocks of quartz-dolerite and Carboniferous sandstone, is banked against a steep south-facing hillside [NY 640 362]. Farther upstream, about 10 m of coarse gravel and clay form indefinite terraces along the valley. Other deposits of coarse morainic drift, up to 15 m thick and including large boulders of local Carboniferous rocks, fill much of Ardale [NY 6561 3460] and the lower part of Kirkdale [NY 663 337]. AJW

Glacial drainage channels

Glacial drainage channels, now mostly either dry or carrying misfit streams, are common landforms within the district. Most are free from boulder clay and many are cut into or through the boulder clay sheet: they are thus contemporary with, or later than, its deposition. In contrast, they predate the accumulation of the more extensive spreads of sand and gravel which in places plug the channels.

Individual channels range from about 100 m to several kilometres long, and from 15 to 400 m wide. A few are deeper than 30 m, while others are only 2 to 3 m deep. In cross-section they are typically U-shaped, with sharp lips, steep walls, and flat floors. Many, however, have been modified in cross-section by the subsequent deposition of sands and gravels within the channel; by solifluction, which has degraded the channel-walls and led to the accumulation of substantial head deposits; and by gullying and landslipping caused by present-day stream erosion. Channels may terminate upslope by merging with the country level, or abruptly in bowl-shaped hollows. Downslope they generally pass into the present river systems, though some grade to country level and have no downslope continuations. In long profile most have a consistent direction of fall, but some, particularly subsidiary and isolated channels, are humped, falling in both directions from a central col.

The distribution of the channels is shown in (Figure 41). Many of those on the lower ground of the Vale are sub-parallel, NNE-falling, west-bank tributaries of the main present-day streams. A humped channel system connects the valleys of the lye and Petteril east of Low Braithwaite and another, running from Brockleymoor to Baronwood, links the Petteril and Eden valleys. Farther east, between the Eden and the Pennines, anastomosing channel systems are common, uniting downslope into a few major trunk channels feeding into the Eden. The component channels of this latter system merge at grade, although a few tributaries have a hanging relationship to the main channels. In the south-east in particular the channels follow two preferential alignments—NW and SSW—individual courses being commonly made up of straight lengths flowing in one or other of these directions irrespective of the general slope of the ground. The total fall to the Eden through this system is of the order of 300 m. The channels die out upslope along a line that rises steadily southwards from about 365 m near Croglin to almost 600 m on Kirkland Fell. The highest channels tend to be short, isolated, and commonly humped. Some are semi-arcuate in plan, with no downslope continuation, while others cut through the present watershed.

Glacial and glacial-lake sands and gravels

Dominantly stratified, well-sorted sands and gravels that post-date the boulder clay, and predate the alluvium and river terrace deposits occur principally in or near the valleys of the rivers Eden and Eamont, on the south-eastern flank of Croglin Water, and near the Pennine escarpment between Renwick and Camblesby. The deposits occur as eskers—elongate mounds up to 15 m high, typically with sharp crests and with flanks inclined at or near the angle of rest, i.e. 30° to 35" and kames, laterally extensive spreads accounting for most of the glacial sand and gravel of the district.

Eskers occur individually or in series or parallel groups. Individual mounds extend up to 1.5 km in length, as at Newton Reigny (see below), while the longest series in the district extends for 10 km from Pearsgill to Holmwrangle (Plate 10). Parallel grouping is exemplified near the Luham (p. 118). The eskers are related to certain glacial drainage channels in their distribution, shown in (Figure 41). For example, those in the west between Morton and Hay Close, and at Newton Reigny, continue the lines of humped channels. Some eskers flank channels, examples occurring low on the Pennine slopes, while a few lie on the floors of channels, as at Pearsgill and Slatequarry Wood.

The karnes are largely confined to the floors and flanks of the major valleys. The deposits in places attain a thickness of 40 m and consist mostly of cross-bedded sands with sporadic pebbles and thin layers of silt and stoneless clay; gravel is common towards the top of many sections. The faces in a working sand-pit at Baronwood (p. 117, Plate 11) are typical. In some instances, for example near Glassonby (p. 118), stoneless clay and silt are common towards the base of the section. The upper surfaces of the kame deposits range from flat to irregular or hummocky, and many terraces are pitted by ketticholes. The principal terraces within the district are listed below, with their estimated heights OD in metres:

The margins of the kame deposits, particularly the terraced forms, are commonly steeply inclined (up to about 30°) and lobate.

In several places hummocky kames and eskers are closely associated, as between Kirkoswald and Glassonby (p. 118) and near The Luham (p. 118). A section across the contact between an esker and a kame in a gravel pit near Abbott Moss (Plate 12) showed that the cross-bedded sands and pebbly sands of the kame were faulted and distorted upwards against a sub-vertical contact with the gravel of the esker. The kame deposits appeared to have collapsed against those of the esker, thus post-dating them. This age sequence is supported by the relationship between the kame-deposits and the glacial drainage channels, themselves closely linked to the eskers, for there are several instances of kame deposits partially plugging channels, one of the best being seen at Baronwood (p. 117) .

In several parts of the Vale, the heights of cols in humped channels correspond with the levels of neighbouring kame terraces. For example, the col of a major channel at Hazelgill 2 km W of Croglin corresponds to the 175-m level of the terrace to the south at Bank Wood (p. 119). The implication of this correspondence is that the pre-existing channels provided spill-ways from their cols for the waters of glacial lakes in which the kame deposits accumulated.

Glacial-lake stoneless clay and silt

Stoneless clay and silt has been proved by augering to cover much of the floor of the Eden valley northwards from Lazonby, particularly between Kirkoswald and Staffield; also, but to a lesser extent, the Petteril valley north of Southwaite, and the hollow between Pearsgill and Abbot Moss. Sections are few and suggest that these deposits rest largely upon boulder clay or solid rock, although near Lockhills (p. 117) they overlie gravel. Silts and clay are intercalated with, and apparently extend under, many of the kame sands and gravel, and give rise to springs or seepages, as at Kirkoswald Castle [NY 5587 4072].

The best sections are near Glassonby (p. 118) where laminated clay and silt some 6 m thick form a layer within sand and gravel.

Details

Southwaite, Calthwaite and Newton Reigny

Glacial sand and gravel is generally sparse in this area, the principal deposits being esker gravels, and the poorly terraced sand and gravel in the Petteril valley at Southwaite and Brockleymoor.

A small esker some 8 m high is present 200 m E of Monk Castle; it flanks a channelled tract which straddles the watershed of Broad Field some 1.5 km to the south. In a section [NY 4301 4607] just below the crest of the esker, 1 m of soft red stony clay overlies 0.3 m of fine-grained sand with layers of clay, while gravel containing much purple Carboniferous sandstone breaks out from the slope below.

Farther south there are two eskers in series with a group of channels which straddles the watershed near Sceugh Head. The northern esker [NY 4501 4402] to [NY 4514 4450], 500 m S of High House, is associated with a more irregular deposit of sand and gravel, and it is aligned SSW–NNE. Plough-turnings from a low mound of gravel [NY 4471 4386] nearby, revealed a high proportion of pellets of purple-grey Carboniferous siltstone, apparently scoured from the walls and floor of the channels to the south-west. The southern esker [NY 4505 3868] to [NY 4430 4134] is beaded, and extends for 2.8 km between Hutton End and Hay Close: a small pit [NY 4432 4107] proved about 6 m of gravel, in which Lake District rock-types abound. The deposit has been worked more extensively 100 m W of Morton.

A smaller esker [NY 4632 3548] to [NY 4647 3514], of NNW–SSE alignment, flanks a glacial drainage channel some 400 m SE of Hutton-in-the-Forest. In a small pit at its northern end, 4 m of coarse gravel are exposed. Between this locality and Greystoke, some 5 km to the south-west, there are several small deposits of sand or gravel; the most important forms a low N–S ridge [NY 442 313], 300 m E of Poplin and comprises 10 m of coarse gravel at its southern end.

A N–S esker extends for about 3 km through Newton Reigny. At its southern end, near Old Riggs, two isolated, low, subparallel ridges of gravel trend diagonally across the flanks of a drumlin. The eastern ridge [NY 4851 2988] to [NY 4846 4017] is about 3 m high; the western ridge [NY 4832 2990] to [NY 4830 3021] is 2.4 m high. Farther north, the esker is continuous as far as Newton Reigny, ranging in height from 5.8 m at Long Barrows to only 3 or 4 m at Newton Reigny; the crest of this section of the esker lies at about 171 m OD at the southern end, rises northwards to the 606 ft spot height (185 m OD), then descends to 168 m at its northern end. North of the River Petteril, the esker continues as a sinuous ridge 3 to 5 m high, its crest rising from 168 m OD to 190 m OD at Honey House [NY 4776 3273], where the esker passes into a glacial drainage channel; sand and gravel are exposed in a small pit [NY 4779 3246].

Deposits are patchily distributed on the low ground of the Petteril valley between Southwaite and Barrock Side [NY 453 452] to [NY 452 479]. They rest on boulder clay and comprise gravel, sand, silt and stone-less clay, forming a poor terrace feature at about 90 m OD flanking the deeply incised modified channel now occupied by the River Petteril. A section [NY 4523 4747] in the eastern wall of this channel is typical; it shows a complex of clay, silt, and coarse gravel about 3 m thick at the top of the bank, overlying boulder clay.

Similar, though poorly exposed deposits are present some 8 km to the south-south-east [NY 4898 3794] to [NY 4961 3471] on the low ground flanking the River Petteril between Brockleymoor and Holme Head. The part of this deposit which lies west of the river and southwest of Brockleymoor forms a gently sloping broad fan apparently debouched from two glacial drainage channels to the west; motorway boreholes sited on the western part of this fan proved up to 3 m of sand and gravel on boulder clay. East of Plumpton Hall, the deposit consists of gravel which forms a moundy terrain and which appears to have debouched from glacial drainage channels to the south-south-east. Part of this deposit e.g. [NY 495 362] forms a poorly defined terrace at about 132 m OD, a level close to that of the kame deposits at Pearsgill, some 4 km to the north. A 10 m mound of gravel [NY 4863 3750] 500 m WNW of Brockleymoor similarly rises to about 132 m OD. The northern limit of this group of deposits coincides with the southern end of a complex series of glacial drainage channels which straddles a low watershed between Castlesteads and Pearsgill.

The floor of the major channel now occupied by the River Petteril, is lined along much of its length by deposits of gravel which form terraced features up to 5 m above normal river level. These deposits are particularly well seen northwards from High Wooloaks, and the terraced gravel [NY 4537 4502] 500 m SE of Southwaite is typical. RSA, AJW

Pearsgill–Baronwood–Armathwaite–Holmwrangle

Between Pearsgill and Abbott Moss a channelled tract is lined by a moundy complex of sand and gravel which attains a level of about 135 m OD. A beaded esker that formerly extended along much of the eastern side of the tract, has been mostly removed by quarrying, but it is preserved to the east of Pearsgill (Plate 10), where it forms a sinuous sharp-crested ridge up to 10 m high [NY 4973 3990] to [NY 5017 4080]. A temporary section c. [NY 505 420] in the gravel workings 800 m SW of Abbott Moss exposed a core of coarse gravel under the esker ridge, flanked by cross-bedded sands with subordinate fine gravel in thin layers; the sands adjacent to the coarse gravel were distorted and faulted. Elsewhere in the flanking deposits layers of silt up to 1 m thick were exposed. In many sections, the uppermost metre or so consisted of soliflucted material including soils. Much of the central, low-lying part of the tract is lined by evenly laminated deposits ranging from clay to fine sand; for example, pits [NY 5043 4206] and [NY 5032 4176] dug about 1 km SW of Abbott Moss proved about 6 m and 2 m respectively of laminated silt, the laminae typically about 6 mm thick; and an excavation [NY 4993 4099] for a pylon, 750 m NE of Pearsgill, yielded laminated clay.

The floor deposits in this tract are flanked to the north-west [NY 5002 4221] to [NY 5085 4273] by deposits of mostly fine-grained sands, which are banked against a steep slope of boulder clay; these sands form a poor terrace at about 155 m OD.

The tract is terminated to the north by a rib of Penrith Sandstone, free from boulder clay, which forms a col [NY 514 429] between the flanking higher ground of Blaze Fell and Baronwood Park. Some of the glacial drainage channels straddling the col have been partly plugged with sand and gravel to form a flat surface at about 131 m OD.

From the eastern side of the col, sand and gravel extend over a wide area towards the River Eden, giving rise to mainly hummocky ground the highest parts of which are terraced at 130 m OD (Plate 11). The thickness of the deposit, which has been worked commercially, increases generally towards the lobate eastern margin, to a maximum of about 40 m. A temporary section [NY 5210 4297], 700 m E of Baronwood, exposed 3 m of gravel overlying 10 m of sand, both flat- and cross-bedded, mostly fine-grained and well-sorted, and including layers of stoneless clay and silt up to 20 cm thick. In other temporary sections in this vicinity, sand was similarly the dominant component, and gravel was confined to the highest parts of the deposit, whether terraced or hummocky. The western part of the deposit includes a sinuous beaded esker [NY 5170 4310] to [NY 5183 4347] which is breached by a railway cutting [NY 5180 4340] 600 m NE of Baronwood, to expose about 10 m of coarse gravel resting directly on Penrith Sandstone.

Separated from the main deposit are two mounds of sand and gravel, similarly terraced at about 130 m OD; one of these [NY 527 432] lies on the eastern side of the River Eden, 1.5 km E of Baronwood; the other [NY 516 436] 600 m NNE of Baronwood. There are two further mounds of sand and gravel about 1 km N of Baronwood. The larger [NY 5170 4387] is terraced at about 100 m OD, and extends to the west-north-west as a poorly defined esker. These mounds are flanked by laminated muds, silts, and sands, including some pebbly muds, about 1 m of which are exposed under 1 m of head in a woodland gully [NY 5156 4377].

Northwards from Baronwood to beyond the northern boundary of the district at Holmwrangle, the floor of the valley flanking the river terrace deposits and alluvium of the River Eden is lined continuously with glacial sand and gravel as featureless spreads, and as eskers and kames. An esker extends along the valley, almost continuously except where it has been removed by river erosion. It is prominent at Armathwaite [NY 5056 4556] to [NY 5116 4628], and further north [NY 5140 4733] to [NY 5194 4867] between Carrholme and Holm-wrangle. Moundy deposits of sand extend eastwards from the esker and attain levels of 100 m OD. Stoneless clay and silt, with subordinate stony clay overlie poorly terraced deposits of gravel some 4 m thick along the western flank of the River Eden, east of Lockhills [NY 5116 4748], and northwards from Low House [NY 5145 4846] to [NY 5147 4867].

A hummocky deposit of gravel with subordinate sand is present on the floor of a valley between Low Plains and Inglewood House [NY 493 416] to [NY 479 428], now draining the Pearsgill–Abbott Moss hollow to the River Petteril, and north-west of Low Plains small deposits of sand and gravel form a narrow, dissected terrace at about 128 m OD e.g. [NY 4925 4195]. RSA

East Brownrigg

Sand is predominant in a deposit around East Brownrigg. The sandpit just east of East Brownrigg [NY 5294 3740] shows up to 5 m of red-brown cross-laminated sand with thin layers of silt and laminated clay, overlain at the top by about 1 m of sandy gravel. Farther south, in a pit from which sand was commercially exploited, up to 10 m of pebbly sand, incorporating layers of laminated clay towards the base were temporarily exposed. Bedding foresets observed in these pits are generally inclined to the east and north. The deposit attains a maximum thickness of 15 to 20 m in a steep-sided mound west of Coldkeld [NY 531 374]. To the north-east the deposit forms poorly terraced low ridges and is pitted with kettleholes [NY 5354 3773]. AJW

Kirkoswald–Staffield–Nunnery

Steep-sided mounds of sand capped by gravel are present around Staffield. The eastern part of the deposit [NY 5465 4302] has terraced summits at about 143 m OD [NY 5465 4302] and [NY 5434 4316], while further west at Nunnery [NY 5373 4304] a mound has a terrace top at about 130 m OD, concordant with the principal terrace of the Baronwood deposit (see above), some 2 km to the west.

High Bankhill–Kirkoswald

A deposit of sand and gravel extends north-eastwards from Kirkoswald to High Bankhill. It forms a smooth and gently inclined slope, falling south-westwards from about 155 m to about 130 m OD and attains a thickness of some 25 m in the south-west. About 1 km N of Kirkoswald, the deposit adjoins a NW–SE esker [NY 5560 4240] to [NY 5572 4223], 200 m long with a crest at about 160 m OD and abrupt terminations. RSA

Little Salkeld–Glassonbybeck–Kirkoswald

One of the largest deposits of glacial sand and gravel in the district is that on the eastern side of the River Eden between Kirkoswald and Glassonby. It covers about 4 km² and its thickness commonly exceeds 30 m. Although much of the deposit has an irregular surface, large areas are terraced at about 130 m OD.

In the southernmost part of this tract, sand and gravel forms a narrow terrace at about 122 m OD on the steepish west-facing escarpment of the Eden Shales between Little Salkeld and west of Glassonby. The variable lithologies and complex interbedding of these sediments, recorded by Goodchild (1875, p.88) in the Throstle Hall railway-cutting, have been confirmed by recent gypsum/anhydrite boreholes which proved up to 16.2 m of gravel with sand and boulders, and with impersistent clay layers. The eastern bank of the River Eden gives a section [NY 5618 3674] to [NY 5614 3695] 7 to 15 m high of laterally variable coarse gravels with subordinate sands and lenses of clay, resting on Eden Shales. A short esker-like ridge up to 15 m high and consisting of coarse gravel is located [NY 5636 3632] to [NY 5637 3658] just north of Little Salkeld.

Farther north, the deposit is continuous from Lacy's Caves to Raven Beck at Kirkoswald, and is extensively terraced at about 130 m OD. Sections are few but suggest that gravel is present at surface over most of the tract with sand apparently predominating at depth, particularly in the thicker sequences. For example, a section [NY 5653 4150] in the southern bank of Raven Beck, exposes 10 m of sand with subordinate gravel resting on Eden Shales; in a section [NY 5620 4036] north of Mains, at least 20 m of sand are capped by gravel apparently less than 4 m thick. Farther south, however, near Glassonby, up to 19.5 m of gravel are recorded in boreholes. Layers of grey, laminated clay and silt within the gravel are exposed [NY 5649 3947] and [NY 5720 3978] in sections low in the deposit northwest of Glassonby, while, in a nearby landslip scar [NY 5731 3993] the section is:

The 130-m terrace is interrupted by a lower hummocky surface of gravel [NY 572 400], west of Old Parks: also by a sinuous beaded esker [NY 5725 4018] to [NY 5612 4140] which extends along the floor of an elongated hollow from near Old Parks to Raven Beck. A shorter esker is present [NY 5739 3941] to [NY 5754 3954] west of Glassonbybeck. AJW, RSA

Nunwick Hall–Great Salkeld–Lazonby

A moundy deposit in which sand is dominant extends from the Luham deposit (see below) past Nunwick Hall and Great Salkeld to Lazonby. Most of the mounds rise to between 107 and 116 m OD, although, just east of Scale Hill, one attains 130 m OD. To the west and north-west of Eden Lacy, sand was being worked from two small pits at the time of survey; the faces of the southern pit [NY 5531 3852] showed up to 10 m of brown, fine- to coarse-grained, cross-bedded sand, with thin layers of pebbles at intervals throughout, but more concentrated in the uppermost 1.2 m of the deposit. The foresets were inclined towards the north and east. In the northern pit [NY 5531 3908] up to 12.2 m of brown, coarse, unbedded sand with a few pebbles, rested on brown boulder clay.

Honeypot–The Luham–Salkeld Dykes

There is a broad spread of gravel west of Honeypot. The deposit is thickest in the south where a 12-m bank bordering the Eamont flood-plain consists almost entirely of gravel resting directly on solid [NY 5577 2936]. Farther north up to 11 m of coarse gravel and sand cap cliffs of Penrith Sandstone in the river bank [NY 5575 2982] to [NY 5570 3004], and form a terrace at about 116 m OD. The surface becomes hummocky to the west and rises to above 122 m OD, but sections [NY 5499 2995] to [NY 5519 2984] in the north bank of the Eamont show that the sand and gravel is here only 1.5 to 3 m thick, resting on sandy boulder clay.

Another spread of sand and gravel west of Whinsfield extends into a channel running northwards through a col in Slatequarry Wood and thence to the Eden. Two eskers [NY 5513 3128] to [NY 5517 3142]; [NY 5517 3154] to [NY 5527 3169], 6 m and 10 m high respectively, rise above the flat and run parallel to the channel. For about 1 km to the north the channel is free from sand and gravel, but east of Slatequarry Wood [NY 554 322] an esker of well-sorted gravel, 6 to 10 m high, is banked against its eastern wall, and extends northwards as a series of gravel mounds. A pit [NY 5531 3288] in one of these mounds shows 7.6 m of coarse gravel and cobbles, largely of Lake District provenance, with subordinate sand.

To the north and east low irregular mounds of variable composition form a broad spread that ends in a steep face overlooking the Eden flood-plain. A section [NY 5601 3374] north-east of The Luham exposes 12.2 m of coarse well-sorted gravel but, farther north where the deposit forms a terrace, there are some impersistent intercalations of laminated clay and silt that give rise to springs. One of these can be seen in a gully [NY 5528 3451], where 1.5 m of red sandy laminated clay underlie 6.1 m of coarse gravel. Three eskers of well-sorted gravel rise above the general level of the deposit. The southernmost [NY 5545 3315] to [NY 5558 3395] is 3 to 5 m high: a parallel esker [NY 5556 3341] to [NY 5573 3392] is 6 to 8 m high, whilst the third [NY 5538 3394] to [NY 5542 3424] is about 5 m high.

Several small eskers with crests at about 137 m OD branch off from the main channel west of The Luham and continue northwards to Salkeld Dykes. One forms a gravel ridge 6 to 12 m high [NY 5529 3305] to [NY 5514 3326] on the western slope of the channel and passes into low gravel ridges and scattered patches of sand and gravel resting on drumlins a little farther north [NY 5517 3345]. The line of a 5- to 7-m ridge of well-sorted gravel [NY 5476 3415] to [NY 5479 3450] just east of Chambers Common is linked to that of a similar ridge [NY 5470 3539] to [NY 5482 3565] near Burrellgreen by a shallow glacial drainage channel. A gravel ridge up to 10 m high extends northwards from Beckbank for over 700 m and passes into more irregular mounds of sand and gravel north of Salkeld Dykes, though the northernmost part of this spread locally retains an esker form [NY 5471 3700] to [NY 5444 3724].

Dolphenby–Edenhall–Langwathby–Little Salkeld

Three separate areas of sand and gravel extend from near the outflow of the River Eamont, north-westwards to Langwathby and Little Salkeld. The deposits are between 105 and 115 m OD and were probably continuous prior to erosion by the River Eden. Sand and gravel in a low mound flanks the floodplain of the River Eden about Dolphenby [NY 576 313] and extends up the Eamont valley to Udford. To the north-west, the village of Edenhall is situated on low mounds of sand and gravel; sections in the river bank [NY 5710 3215] to [NY 5704 3269] consist of at least 12 m of gravel and sand in varying proportions, although, in the northern part of the bank, the more superficial sands are appreciably clayey.

The largest deposit in this tract forms a rough terrace-feature for about 4 km along the east bank of the Eden. From about 115 m OD in the south, the terrace falls to about 105 m N of Langwathby. These deposits are well exposed in the eastern bank [NY 5867 3127] of the Eden just north of the outflow of the Eamont where 12.2 m of gravel and cobbles with subordinate sand lie directly upon Eden Shales. A further 3 to 4 m of poorly exposed deposits above this section appear to consist of sand and gravel, but with a substantial proportion of clay. Similar clayey sand and gravel, resembling soft sandy boulder clay was exposed in foundation trenches [NY 567 340] into the terrace at Langwathby. At least 15 m of sand and gravel are well exposed in the steep river bank [NY 568 336] immediately south of Langwathby.

Northwards from Briggle Beck to Little Salkeld, this deposit lacks any terrace form. It is best seen in the stream [NY 5648 3599] south of Salkeld Hall, where 12 to 15 m of sand with subordinate gravel rest on boulder clay. Elsewhere, the presence of local clay layers within the sand is indicated by spring-lines [NY 5668 3530] and [NY 5637 3569], south-east and north-west of Little Salkeld railway station.

Carleton

Gravel, including cobbles and boulders and brown silty sand, was proved to a thickness of at least 12.2 m [NY 5244 2931] in shallow boreholes on the floor of a glacial drainage channel south-west of Carleton. Temporary sections exposed during motorway construction included well-sorted coarse gravel forming terraces about 30 m wide, flanking the channel.

North-west of Carleton, at least 1.5 m of coarse, well-sorted gravel, resting on boulder clay, lines a small hollow [NY 535 299] between drumlin slopes. The deposit, revealed during road works, appears to extend eastwards beneath the enclosed area of low ground north of Frenchfield. AJW

Westgarth Hill–Bank Wood–Caber

Glacial sand and gravel extends for some 2 km northwards from Westgarth Hill to Bank Wood. Over its southern part, where the deposit rests variously on boulder clay and St Bees Sandstone, the upper surface is gently undulating—generally between 160 and 175 m OD—and consists largely of gravel. Farther north, for example north-west of Crindledyke, the eastern fringe of the deposit forms a conspicuous terrace at 175 m OD, and this continues as far as Bank Wood. The terrace surface is of gravel and pitted by a kettle-hole [NY 5508 4460], while the western slopes of the deposit which are steep and lobate, and some 30 m high, consist largely of sand. The western margin of the central part of this deposit, 1 to 2 km S of Bank Wood, is marked by a beaded esker [NY 5495 4408] to [NY 5492 4345], the crest of which reaches about 170 m OD; a pit [NY 5491 4347] exposed about 6 m of sand and gravel, including a layer of silt up to 0.3 m.

Between Bank Wood and Caber, sand and gravel flank the flood-plain deposits on the southern side of Croglin Water, and extend eastwards, partly as masses detached by stream erosion, to coincide with the northern ends of major glacial drainage channels near Lowhall Building. Immediately north-east of Croglin Low Hall, a terraced surface of gravel lies a few metres above river terrace deposits, while both northwards and southwards from Croglin High Hall mounds of sand and gravel rise to about 175 m OD. At, and to the north of, Croglin High Hall there are concordant terraces at about 162 m [NY 5615 4600], while some 100 m farther east, mounds have concordant tabular summits at about 172 m OD [NY 5630 4625].

Gravel with a terraced surface at 175 m OD, probably continuous with that around Croglin High Hall prior to fluviatile erosion, forms an elongate shelf [NY 562 466] on the northern side of Croglin Water, 500 m WNW of Caber. The terrace extends to the east for about 1 km, as a thin strip flanking the stream bank, its upper surface rising to about 180 m OD at the eastern end; north-westwards, a lobe of this deposit coincides with the southern end of a major glacial drainage channel, the floor of which falls northwards from a col [NY 558 469] at about 174 m OD. A small deposit of gravel, apparently predating the Westgarth Hill–Caber deposits, lies at and to the south of Caberslack. It consists largely of an esker [NY 5650 4538] to [NY 5694 4592] and partly occupies the floor of a glacial drainage channel. A separate esker bead is present at the northern end of this channel, immediately north of Caberslack.

Croglin

A deposit of sand and gravel [NY 588 472], adjacent to the Pennine escarpment on the southern side of Croglin Water, flanks the western (downslope) side of a major glacial drainage channel 0.5 km E of Scarrowmanwick. The deposit, probably more than 30 m thick at its northern end, gives a general surface which falls north-westwards from 335 to 275 m OD. Less extensive deposits of gravel, rise to similar levels on the northern side of Croglin Water, to the north and north-east of Fieldhead [NY 5818 4805]. Gravel, partly terraced at about 230 m OD and pitted by a kettleholc, forms the lower ground [NY 582 475] flanking Croglin Water south of Fieldhead. To the west, this deposit converges on the eastern end of a deeply incised glacial drainage channel, with a floor falling north-westwards from a col [NY 5748 4742] at about 210 m OD.

Hazel Rigg–Busk–Renwick

A complex group of deposits, mostly moundy gravel, occupies much of the ground flanking the Pennine escarpment between Gamblesby and Renwick. The highest deposit is an elongate mound [NY 632 423], 1.5 km WNW of Hartside Cross, and rises to about 410 m OD. Downslope from here irregular tracts of sand and gravel flank Loo Gill for some 1.5 km SE of its confluence with Raven Beck. The deposit is some 30 m thick in the steep southern bank of Loo Gill [NY 6220 4290] near Selah, and here coarse gravel at the base has been cemented with tufa.

On the lower ground to the south-west, between Hazel Rigg and Busk, a series of eskers and esker-beads are aligned generally north-north-west and associated with patchy broader spreads of gravel and subordinate sand. Near the southern end of the series, an esker 350 m S of Cannerheugh is 400 m long and about 10 m high; a pit [NY 6148 4133] at its southern end exposed coarse gravel with boulders up to 1 m across. The largest member of the series is a sinuous esker at Busk [NY 6107 4251] to [NY 6112 4180], 800 m long and up to 15 m high. Farther north, a moundy deposit of sand and gravel rising to 255 m OD extends from Haresceugh to the southern banks of Raven Beck.

Two deposits of sand and gravel occupy much of the lower ground, west of the Hazel Rigg–Busk esker series. The more southerly flanks Hazelrigg Beck, and lines the low ground for about 1 km both east and west of Unthank [NY 610 405]; it includes mounds of gravel up to 10 m high [NY 6025 4013] and [NY 6129 4032], but mostly has a gently undulating surface. However, a small part [NY 5998 4040] of the deposit, 1 km W of Unthank, forms a terrace at about 170 m OD; sections hereabouts expose about 3 m of gravel capping sand.

The northern deposit is mostly of gravel and occupies the low ground around Renwick, and the valley of Raven Beck. The deposit is terraced along Raven Beck, the level falling south-westwards from about 210 m OD [NY 6022 4274] near Raven Bridge Farm to about 185 m OD [NY 5935 4250] north of Low Huddlcsceugh. Around Renwick, the surface of the deposit is generally 200 to 215 m OD, with a clearly defined terrace at 215 m OD between 300 m and 2 km NW of Renwick; to the north-west this terraced deposit converges on a glacial drainage channel falling north-westwards from a col [NY 5812 4515] about 1 km NW of Lincowell, similarly at about 215 m OD.

Broadmeadows

A hummocky deposit of sand and gravel resting on boulder clay south of Broadmeadows, includes sinuous ridges up to 8 m high. Gravel is exposed at the surface of these ridges, and a section [NY 5985 3728] through the northernmost ridge exposes cobbles in the core. RSA

Interpretation of glacial deposits and channels

Boulder clay

The material here termed 'boulder clay' is assumed to be the accumulated residue of melting, detritus-charged ice. In a few localities it is clear that the boulder clay is a lodgement till formed at the base of an ice-sheet. Thus at Stoneybeck, 3 km N of Pcnrith, borehole sections show the basal boulder clay to be almost indistinguishable from the underlying Penrith Sandstone. The relationship between boulder clay and rock-head features at Hutton Bank (p. 111) similarly imply accumulation in situ. In contrast the morainic mounds along the foot of the Pennine escarpment (p. 114), and the hummocky boulder clay terrain in the extreme north-western part of the district (p. 111) are apparently due, at least in part, to collapse, following the melting of underlying ice, and thus represent englacial or supraglacial debris.

The presence of stratified deposits intercalated with boulder clay in broad rock-head hollows, as at Skirsgill (Figure 40) and along the Petteril valley (Figure 37), (Figure 38), (Figure 39), implies the periodic existence of local bodies of water, but the relationship between such water-bodies and the ice is by no means clear, nor indeed is it certain that ice was present. However, the complex association between boulder clay and the stratified deposits suggests that the latter were formed either subglacially or englacially. The contortions and faulting recorded in stratified deposits in sections like those at Skirsgill may be the result either of their collapse following the melting of underlying ice, or more likely of ice overriding the deposit, with consequent shearing.

In previous accounts the broad history of glaciation has been interpreted on the basis of the distribution of boulder clay, and the provenance of the included rock-fragments. Goodchild (1875), Trotter (1929), and Hollingworth (1931) all stressed the importance of these criteria, and the results of the present survey support their findings in that several contrasting glacial events are recognised in an area comprising the Vale of Eden, the Pennine escarpment, and the Pennines north of Hartside (see below). However, the sequence of earlier events is somewhat confused by the possibility of multiple derivation of the indicator rock fragments. For example, the rare pebbles of Scottish granites which are now associated with those of Borrowdale volcanics and St Bees Sandstone on the Pennines north of Hartside Cross (p. 114) may have been transported either directly from their Scottish source, or indirectly, removed from an earlier deposit of Scottish boulder clay in the Vale by ice moving north-eastwards from the Lake District.

The suggested sequence of active glacial events is as follows:

1. ice moved south-south-eastwards, up the Vale; its deposits included boulders of Scottish granites.
2. ice moved north-eastwards, from the Lake District across the Vale, on to the Pennines, at least to the north of Hartside Cross where Borrowdale volcanics were deposited. Some of the earlier deposits in the Vale, which included Scottish granites, were redistributed on the Pennines.
3. ice moved north-north-westwards, down the Vale, producing drumlins elongated from south-south-cast (stoss ends) to north-north-west (tail or ice ends); this movement may have been impeded in the extreme north-western part of the district, where the terrain is irregular (Figure 36). Probably contemporaneously, ice moved north-westwards from the Pennine escarpment, depositing boulders and smaller fragments of Carboniferous sandstone, Whin Sill quartz-dolerite, and Lower Palaeozoic rocks over the extreme eastern part of the Vale.

Glacial drainage channels

The glacial drainage channels are interpreted as the result of erosion of the subglacial surface by rapid stream-flow during a period between the deposition of the boulder clay, and that of the main mass of the glacial sand and gravel. Though some of the channels occupy pre-existing valleys and could perhaps have been formed as a result of unimpeded flow along the line of greatest slope, the great majority—including those parallel and oblique to the slope contours—have clearly been formed as a result of laterally confined flow along alignments imposed by the ice-sheet.

The regimented alignments of channels in several areas, notably around Ousby, are interpreted as the results of sub-glacial stream erosion along cavities in the ice-sheet perhaps corresponding to major crevasse-joints. The dendritic distribution and the graded nature of the major systems of linked channels, such as that extending north-westwards from Milburn (Figure 41), implies that the systems functioned in their entirety as subglacial drains, water entering at their branch-tips and flowing to their trunks; in the instance cited above, water would have entered the system largely on the lower part of the Pennine escarpment and flowed to a trunk channel near Little Salkeld, a fall of some 300 m. If the upper surface of the ice-sheet is assumed to have been horizontal, then the thickness of ice covering this trunk would be of the same order. From the distribution of the channels (Figure 41), it appears that a relatively large amount of water was available at the subglacial surface on and immediately west of the Pennine escarpment, on the escarpment of Penrith Sandstone at and southwards from Blaze Fell, and in the west between Ivegill and Skelton. Elsewhere, for example around High Hesket, the amount of water reaching the subglacial surface was insignificant. The apparent absence of channels on the Pennines within the district eastwards from the escarpment implies either that this area was free from ice, or more likely, if ice was present, that little water reached the subglacial surface.

While most of the channels could have been eroded as a result of water carried by gravity flow, those with humped longitudinal floor profiles, such as the system linking the Ive with the Petteril valley, are interpreted as having been formed by confined water-flow under hydrostatic pressure, water being forced up-grade over a rise of several metres. Such an interpretation would require that the water flow was confined not only laterally, but also vertically on the side of the hump nearest to the water source.

From the distribution of the dendritic systems of linked channels throughout the district, the overall flow-regime of the water responsible for the formation of the channels is interpreted as having been from south to north, and sub-glacial rather than 'ice-marginal', as supposed by Trotter (1929) and Hollingworth (1931). While the trunks of the dendritic systems either enter or coincide with present topographic hollows, e.g. the valley of the River lye, the several instances of major channels of humped longitudinal profile which straddle present watersheds show that subglacial water under hydrostatic pressure had an important influence on the overall flow-regime. For example, much of the sub-glacial drainage from the upper Petteril catchment seems to have, at some time, followed a course to the north-north-east, away from the River Petteril, via humped channels near Pearsgill and Baronwood, to the valley of the River Eden; farther east, at least some subglacial drainage from the vicinity of Kirkoswald seems to have followed a course, generally northwards from the River Eden, to beyond the district boundary near Cairnhead Farm, via humped channels at Scales and Hazelgill.

Glacial sand and gravel, and glacial-lake stoneless clay and silt

Evidence cited above implies that the eskers predate the kame sands and gravels, but that the latter are genetically related to the glacial-lake stoneless clays and silts. Similarly, a close relationship has been demonstrated between the distribution of the glacial drainage channels and the eskers, implying that these two groups of features originated under similar conditions.

The association of eskers and glacial drainage channels implies that the esker gravels represent the bed-load of high energy streams similar to those responsible for the erosion of the channels. However, from the present evidence, the original position of formation of any of the eskers relative to the subglacial surface is not clear, for the sharp-crested and steep-sided form which characterises eskers appears to be the result of collapse of a wall-like deposit, following the melting of laterally confining ice. The distance through which collapse has occurred is unclear. Some eskers, for example that between Honey House and Newton Reigny, seem to have been built-up as crevasse-stream bed-loads more or less from the subglacial surface; others, for example those at Slatequarry Wood, and between Pearsgill and Abbott Moss, are interpreted as having collapsed into underlying glacial drainage channels.

The general distribution of eskers in the district (Figure 41) supports the interpretation of regional drainage based on the evidence of glacial drainage channels. Moreover, if the glacial drainage channels and the eskers are broadly contemporaneous then the eskers should mark the positions of englacial streams in those areas where channels were not eroded, as along the Eden valley between Baronwood and Holmwrangle.

The original position of formation of many of the kame deposits, like those of the eskers, is also unclear. Their typical hummocky and irregular landforms imply an origin in collapse, but collapse over a considerable area due to the melting of underlying ice. Conversely, the terraced landforms of some kame deposits, such as those at Baronwood or Bank Wood, imply little or no collapse since deposition, which must have occurred on an ice-free surface, an implication supported by the evidence of undisturbed sediments at Baronwood (Plate 11). However, the steep bounding slopes which characterise these deposits are apparently the result of collapse due, as with the eskers, to the melting of laterally confining ice.

The general upward sequence of deposits, which ranges from clay and silt, through cross-bedded sand, to gravel, and which characterises those kame deposits for which sections are available, is interpreted as indicating a progression from lacustrine-floor, to delta front, and finally delta-top, braided stream, conditions.

The levels of these partially ice-confined lakes up to which the terraced kame deposits were accumulated appear to have been constant during the deposition of any individual kame, and, in some instances, controlled by lake water overflowing through pre-existing glacial drainage channels, grading away from the lakes. The best example of this feature within the district is the control exerted by the level of the col on the channel-floor at Hazelgill over the level of the extensive terrace in the valley of Croglin Water to the south. In all instances for which there is similar evidence, the lakes appear to have overflowed along channels to the north. The 130 m-level of the lake in which the Baronwood and Kirkoswald–Glassonby kames and the extensive stoneless clay and silt between Staffield and Kirkoswald were deposited appears to have been determined by a sill beyond the northern boundary of the district.

In the several instances where eskers are present within hummocky kames, as at Abbott Moss, the kame sand and gravel are interpreted as having been deposited on or against an irregular layer of ice, which included wall-like bodies of uncollapsed esker-gravel. Subsequent melting of the ice supporting the kame and laterally confining the esker-gravel, led to the kame deposits being collapsed at first on top of, then against the sides of the bodies of esker-gravel, with consequent disruption of the bedding (Plate 12).

Head

Poorly consolidated and ill-sorted deposits of clay, silt, sand and larger clasts are present on the Pennines, particularly in the valleys to the east of the escarpment, where their thickness commonly exceeds 10 m. The deposits are interpreted as being due to processes of solifluction and have accordingly been classed as 'head', but it is not beyond doubt that some of them are poorly consolidated boulder clay. Only the thickest deposits are shown on the published map.

The head of the Pennine valleys, for example [NY 6833 4142] flanking Black Burn, is mostly poorly consolidated, comprising angular to subrounded rock debris almost exclusively of local derivation set in a subordinate brown or grey, sandy silty clay matrix. Sandstone boulders and blocks are by far the most abundant rock-debris, although limestone blocks are locally common over outcrops of Carboniferous limestone e.g. [NY 6733 4613] and boulders of quartz-dolerite lie downslope from the outcrop of the Whin Sill. The deposits generally rest directly on solid, although locally in Croglin Water e.g. [NY 623 472] they overlie boulder clay. They may completely mask the solid geology and are commonly distributed asymmetrically, relative to present-day stream-courses, so that solid rock is exposed on one side of a valley, and head, forming banks several metres high, on the other, as, for example, in Gilderdale Burn [NY 6793 4583]. In places, for example on the flanks of Black Burn [NY 683 407] the deposits are extensively landslipped.

Of the head deposits not shown on the geological map, the most important are the deposits typically a metre or two thick, of stiff, pale grey silty clay with scattered angular rock debris—mostly sandstone—which are widely distributed, particularly to the east of the escarpment; and deposits of angular blocks of sandstone, common as aprons or tongues downslope from prominent sandstone scarps.

Alluvium, river terrace deposits and peat

Alluvium

An almost continuous tract of alluvium, in places about 1 km wide, lines the Eden valley upstream of the Armathwaite gorge, and a similar tract is present in the Eamont valley upstream of the gorge at Udford. The deposit consists largely of brown sandy and silty loam with lenses of gravel increasing with depth, though organic silt and peat may be present in abandoned channels. In the Petteril valley, the river is for the most part incised, and extensive spreads of alluvium are confined to its more open course in the south, notably at Brockleymoor and Holme Head. Still farther south, between Catterlen and Penrith, a broad low-lying tract adjoining the Petteril is prone to flooding and carries a deposit of alluvium.

River terrace deposits

River terrace deposits, post-dating the glacial sand and gravel, and consisting mainly of gravel, are present in places along most of the larger streams and rivers. They are best seen in the Eden valley, both in the Armathwaite gorge and near Lazonby. Downstream of Armathwaite a broad terrace is present about 5 to 6 m above normal river level, while upstream, e.g. [NY 507 458], the apparently corresponding terrace lies some 9 m above the river. Similar examples of terraces converging downstream with the present river profile are seen farther up the gorge at Baronwood. Here a terrace falls downstream from about 12 to 4 m above river level over a distance of 1.3 km [NY 506 444] to [NY 519 441]. Some of the streams flowing off the Pennines are flanked by terraces which are largely erosional into St Bees Sandstone and carry only very thin deposits of gravel. Good examples are those in Raven Beck [NY 603 432] to [NY 611 434], 1 km E of Renwick.

Generally within the district, the terraces are considered to have formed in response to local conditions within individual valleys rather than to fluctuations in base level on a regional scale. Indeed it is likely that the profiles of the main streams and rivers changed markedly after the wasting of the Devensian ice, as the extensive kame deposits which are thought to have plugged the valleys along much of their lengths were eroded.

Peat

A blanket of peat up to about 3 m thick is widespread on the gentler slopes and shelves of the Pennines, and peat or organic sediments are present in hollows with restricted drainage on high and low ground alike. On the low ground the peat forms raised bogs, and examples of these are common on the floors of glacial drainage channels, such as those [NY 520 412] in Baronwood Park, and in kettle-holes within glacial sand and gravel, such as near Broadmeadows [NY 598 372] and at Abbott Moss [NY 510 426]. The distribution of pollen in the deposits at Abbott Moss was studied by Walker (1966) who demonstrated a long vegetational history, and his findings have been correlated by Pennington (1970) with similar deposits at sites elsewhere in north-western England. One such site, Blelham Bog, near Ambleside, has yielded radiocarbon dates ranging back to 12 380 years BC (Pennington and Bonny, 1970). The age range of the deposits of most of these sites, including Abbott Moss, straddles the Devensian–Flandrian boundary, taken by Pennington at 8300 years BC, the end of a cold period in which glaciers became re-established in Lake District corries, and marked in the sediments by an abundance of Artemesia pollen.

The blanket peat of the Pennines is generally confined to ground above 400 m and rests on a surface of grey, stony clay. Tree stumps and roots are seen at its base in many sections below about 600 m, notably in Gilderdale Forest, e.g. [NY 685 456]. A similar forest layer has been described by Johnson (1963) from the Moor House Nature Reserve, adjoining the Penrith district to the south-east, and pollen analysis of this layer gave an early Boreal age (corresponding to about 7000 years BC). The basal peat gave ages ranging from early Boreal to early Atlantic (corresponding to about 5000 years BC). The blanket peat is presently under erosion in many places, notably on high level shelves and watersheds where a network of gullies has dissected the blanket into isolated 'haggs'.

Landslips

The most important landslip failures in the district have occurred in Carboniferous rocks on the Pennines, notably in the Croglin Water valley and to a lesser extent on the Pennine escarpment. One of the largest is a rotational slip affecting Dinantian strata on the steep northern slopes of Croglin Water at The Combs [NY 587 477], and, farther up the valley on Scarrowmanwick Fell, rotational failure has taken place in strata near the base of the Namurian sequence [NY 609 473]. The largest landslips on the Pennine escarpment have involved the collapse of Melmerby Scar Limestone and strata of the Orton Group over the Basement Beds, and are seen [NY 644 380] and [NY 628 390] to the east and north-east of Melmerby, and similar but smaller slips affecting these strata are present on the escarpment to the south-cast, for example on Wildboar Scar.

Some of the thicker limestones, in particular the Scar and Great limestones are cambered over older strata in places on Pennine dip slopes, as a result of the squeezing out of incompetent strata underlying them. Examples of cambering of the Great Limestone are seen [NY 685 451] below Horse Edge in Gilderdale, and [NY 680 363] at Raehow End, some 2 km NNW of Cross Fell. At Rigg End [NY 692 378] on Ousby Fell the Scar Limestone is similarly affected giving the impression from its outcrop of an abnormally large thickness.

Failures in solid rocks in the Vale are few and these are confined to the outcrop of the Eden Shales. For example, the red mudstones of this formation have slipped on the steep northern banks of Raven Beck [NY 563 417], and farther south they have failed from time to time in the railway cutting [NY 563 368] south of Throstle Hall, Little Salkeld.

The boulder clay is prone to landslipping where it is thick and cut by deep gullies, as in the western part of the district, for example around Skelton Wood End and in the valley of the River lye. More superficial failure is seen affecting a thin sheet of boulder clay on Eden Shales, on the northern side of the Raven Beck valley [NY 570 420] near Kirkoswald.

Catastrophic failures of blanket peat, of a type known as hog-bursts, have occurred at two localities in the Pennines during the period 1947–1968. In one of these [NY 6448 4358] on Haresceugh Fell, peat was removed over an area of about 12 000 m², and redeposited downslope over a distance of 500 m.

References

GOODCHILD, J. G. 1875. The glacial phenomena of the Eden valley and the western part of the Yorkshire Dale district. Q. J. Geol. Soc. London, Vol.31, pp.55–99.

GOODCHILD, J. G. 1887. Ice work in Edenside and some of the adjoining parts of North Western England. Trans. Cumberland Westmorland Assoc., No.11, pp.111–167.

HOLLINGWORTH, S. E. 1931. The glaciation of western Edenside and adjoining areas and the drumlins of Edenside and the Solway Basin. Q. J. Geol. Soc. London, Vol. 87, pp.281–359.

JOHNSON, G. A. L. 1963. The geology of Moor House. Monogr. Nat. Conserv.

MITCHELL, G. F., PENNY, L. F., SHOTTON, F. W. and WEST, R. G. 1973. A correlation of Quaternary deposits in the British Isles. Spec. Rep. Geol. Soc. London, No. 4,99 pp.

PENNINGTON, W. 1970. Pp. 41–79 in Studies in the vegetational history of the British Isles—essays in honour of Harry Godwin. (Cambridge University Press.)

PENNINGTON, W.  and BONNY, A. P. 1970. Absolute pollen diagram from the British Late-Glacial. Nature, London, Vol.226, pp. 871–873.

SHOTTON, F. W., BLUNDELL, D. J. and WILLIAMS, R. E. G. 1970. Birmingham University Radiocarbon Dates IV. Radiocarbon, Vol. 12, pp. 385–399.

TROTTER, F. M. 1929. The glaciation of eastern Edenside, the Alston Block and the Carlisle Plain. Q. J. Geol. Soc. London, Vol. 85, pp. 549–612.

WALKER, D. 1966. The Late Quaternary history of the Cumberland Lowland. Philos. Trans. R. Soc. London, Ser. B, Vol. 251, No. 770.

Chapter 11 Economic geology

Gypsum and anhydrite

There are several beds of anhydrite, the anhydrous form of calcium sulphate, within the Eden Shales. The most extensive workable deposit is the B-Bed (p. 74), and this is mined on the pillar-and-stall system by British Gypsum Limited at Long Meg Mine [NY 563 377] near Little Salkeld where it is about 5 m thick. The output is dispatched by rail to be used principally for the manufacture of sulphuric acid.

Near outcrop, and under shallow cover (less than about 70 m), the calcium sulphate is hydrated to gypsum, and has long been worked both underground and in open-cut for use in the manufacture of plaster and plaster products. The principal workings lie just outside the present district, the most extensive being those in the B-Bed at Cocklakes in the Brampton district, where production has now ceased, and those in the A- and B-Beds around Kirkby Thore in the Appleby district.

Within the present district gypsum has been worked only near outcrop at Long Meg, where it was quarried from 1879–95 and then mined until 1914. There have also been attempts to work what is presumed to be the D-Bed near Ruckcroft [NY 5290 4373] (p. 79). Details of the older workings for gypsum in this, and adjoining, districts are given by Sherlock and Hollingworth (1938).

The reserves of anhydrite in B-Bed are large, as the deposit is probably of workable thickness and quality over most of the ground between its main outcrop and the Pennine Fault. The reserves of gypsum, on the other hand, are much smaller, for the A-Bed, from which most of the gypsum is mined around Kirkby Thore, has not been proved in the Penrith district to be thicker than about two metres; and the B-Bed lies at shallow depth only in restricted areas, the largest being to the south-west of Ruckcroft, between Kirkoswald and Glassonby, and between Langwathby and Culgaith. The B-Bed was largely gypsum in the Lounthwaite Borehole [NY 6535 3092], near Milburn, and it is possible that there are further reserves in this area.

Limestone

Quarrying of the more accessible outcrops of the thicker Carboniferous limestones has gone on for more than 200 years. The stone has mostly been burnt for agricultural lime, though latterly it has also been used as aggregate. Limestone quarrying is now confined to the south-western part of the district around Greystoke. The largest workings are at Blencow Quarry [NY 464 302] where the Blencowe Lime Co. Ltd. extracts about 300,000 tonnesInformation kindly supplied by the Blencowe Lime Co. Ltd.,Penrith. annually from the Tyne Bottom and Jew limestones. About 25 per cent of the quarried rock is burnt to produce lime for steel-making, sewage treatment and agriculture; the balance is used to produce concrete bricks, ready-mixed concrete and roadstone for the Cumbrian and Scottish markets. A representative analysis of the limestone is:

Close to the south of Blencow Quarries, the Jew limestone is worked by Harrison's Limeworks Ltd., in Flusco Quarry [NY 460 292]. About 50 000 tonnesInformation kindly supplied by Harrison's Limeworks Ltd., Flusco, Penrith. are extracted annually; some is burnt and supplied for steel-making in West Cumbria and Scotland whilst the remainder is finely ground for use in making asphalt and as an additive to cattle-feed.

Both the Jew and Tyne Bottom limestones are relatively thin and future quarrying developments in this area are more likely to be based on the thicker limestones lower in the sequence. For example, the quarry at Park House [NY 409 332], 3 km NW of Greystoke, was opened in the White Limestone to produce aggregate for the construction of the M6 motorway, and extensive drift-free outcrops of limestone are available nearby.

On the Pennine escarpment, local quarries formerly worked most of the thicker limestones in the sequence. The Clints Quarries [NY 594 465] near Croglin and the Grenfell Quarries [NY 632 418] near Hartside Cross are amongst the largest and are both in the Scar Limestone. Farther south, where the main limestones crop out high on the flanks of Cross Fell, easily accessible quarries were developed on the lower slopes, as at Thrushgill Quarries [NY 663 301] north-east of Milburn, or adjoining main roads, as in Limekiln Beck [NY 628 398]. Reserves of limestone within the district are large, both on the Pennines and in the south-west, although the latter area is potentially the more valuable because access is good and quarrying is relatively easy.

Coal

No coal seams of economic value are known in the district, although in the past several thin seams in the Dinantian and Namurian sequences of the Pennines have been worked. In the western part of the district, the Coal Measures are mainly red and devoid of coal, as are the older Carboniferous strata, except for those at considerable depth as encountered in the High Head No. 2 (p. 153) and Barrock Park boreholes (p. 145).

The most important of the previously worked coals are the Four Fathom Limestone and Little Limestone coals, much of the production from which was used to fire local limekilns. In Croglin Water, the Four Fathom Limestone Coal was worked by adits at Guide Mine [NY 5945 4845] to [NY 5960 4847]; it occurs here in two leaves, the lower known locally as the Croglin Coal. Farther south it was mined from an adit at Burned Edge Mine [NY 5968 4686], where it was 38 cm thick, and from adits such as Horse Level [NY 6148 4479], and bell-pits, on Renwick Fell, and on Haresceugh Fell [NY 6318 4469] to [NY 6325 4343]. It has also been worked locally on Gamblesby Fell e.g. [NY 6565 4190], and on Whitley Common e.g. [NY 6915 4800]. One of the Little Limestone coals, probably a seam overlying the High Coal Sill, was worked until 1911 at Thackamoor Mine [NY 6076 4601] to [NY 6106 4581] on Renwick Fell, and also by bell-pit and adit farther southeast [NY 6213 4527]; another of the leaves lying close beneath the Little Limestone has been worked by adit at Gillhead Mine [NY 6430 4348] to [NY 6477 4266] in the headwaters of Loo Gill, and also by adits [NY 6548 4233] to [NY 6745 4231] close to the Penrith–Alston road east of Hartside Cross, and [NY 6850 4406] to [NY 6856 4374] east of Scarberry Hill. Less extensive workings are located near Scarrowmanwick e.g. [NY 5910 4766] in a seam lying between the Jew and the Tyne Bottom limestones; east of Hartside Height in the Crag Coal [NY 6557 4369] to [NY 6525 4256]; and in Ardale, in a seam lying close beneath the Scar Limestone [NY 6667 3511] to [NY 6688 3453].

Building stone

The most important source of building stone in the district was the Penrith Sandstone, particularly the upper part of that formation where the sand grains are well cemented with silica. The quarries which abound on the rough hcathland between Blaze Fell and Penrith Beacon yielded freestone, tiling, paving and rough walling-stone; stone from massive foreset beds was used for pillars, lintels and gate-posts, some of which were transported to distant parts of the Vale. A great deal of this stone was also used in the construction of the railway between Carlisle and Appleby. Lazonby Fell was particularly intensively quarried and the products from there and neighbouring areas are still known locally as Lazonby Stone. The stone is still worked on a small scale on Lazonby Fell and Bowscar. Its principal use is as a facing or decorative stone on modern buildings; it is widely used in this way on the bridges and embankments of the M6 motorway in Cumbria.

In former times the St Bees Sandstone, particularly its lower part, was quarried in many places (Plate 8). Most of the stone was used locally for walling, and, although it is generally less durable than the silicified Penrith Sandstone, it has also been used a great deal as freestone.

In the west, Carboniferous sandstone is the traditional building stone, the most important sources being quarries [NY 412 362], near Lamonby and near Greystoke [NY 456 314]. In the south-west, limestone has been used extensively as a rough walling-stone.

Roadstone

Surfacing stone is no longer produced within the district, although quarries in the Armathwaite Dyke once satisfied local demand. The principal workings were at the Cobble Quarries [NY 4607 4762], north of Low Hesket, Coombs Quarry [NY 5141 4511] near Armathwaite and at Blundcrfield Quarry [NY 5652 4391], north-east of Kirkoswald; smaller quarries [NY 4972 4555] near Armathwaite were served by the railway.

There are no workings in the Whin Sill, which elsewhere in northern England is quarried on a large-scale, but two dolerite dykes were formerly dug near Melmerby [NY 623 381].

Limestone currently being produced in the south-western part of the district is not used for road-metal, although it is used as a base layer in the construction of new or realigned roads, and also for coated macadam.

Sand and gravel

There are extensive deposits of sand and gravel within the district, particularly within the glacial deposits along the Eden valley. The glacial sands and gravels include both eskers and kames (Plate 11), the latter being by far the more important in terms of bulk. The deposits have long been worked on a small scale in many places. Since 1963, however, workings have greatly increased in scale, notably at Low Plains Quarry [NY 502 410] to [NY 520 431] near Baronwood, sited on an esker and associated kames. Other sand is produced from kames south of Lazonby [NY 5531 3908] and [NY 5530 3852] and near East Brownrigg [NY 5294 3740]. Gravel has been worked from eskers [NY 448 397] near Morton, [NY 549 435] near Springfield, and [NY 6149 4133] near Cannerhcugh.

The Penrith Sandstone has also been exploited as a source of sand in those parts of its outcrop where it is poorly cemented. It was formerly dug on a small scale [NY 550 314] near Barbary Plains, and more recently in an extensive pit [NY 521 347] near Bowscar for use as road-base in the construction of the Penrith bypass section of the M6 motorway. The uses of this sand are, however, limited on account of the high rounding of the component grains.

There are large reserves of sand and gravel within the district. The largest untried deposits lie on both sides of the valley of the River Eden as far south as the River Eamont, especially between Kirkoswald and Glassonby, and along Croglin Water between Staffield and Croglin.

Base metal ores

The high ground in the eastern part of the district forms the western part of the northern Pennine orefield. The minerals in the orefield are broadly zoned with an inner zone characterised by fluorite and sulphides and an outer zone marked by baryte and relatively minor sulphides. The mineralisation occurs generally as veins, following joints or faults, or as flats extending laterally away from the veins. During the resurvey, the extent of known mineralisation was inferred largely from abandoned shafts, adits and opencuts, together with their dumps. Mineralisation has been recognised in natural sections only in a few instances, though at several localities the course of a vein has been traced by the presence of mineralised float in the local head deposits.

Galena has been the main ore, with sphalerite present in subordinate amounts; baryte, fluorite, calcite and quartz were the common gangue minerals. The mineralisation is known to post-date the intrusion of the Whin Sill (295 Ma), and two attempts have been made to obtain radiometric ages for its emplacement. A study of lead isotopes in galenas (Moorbath, 1962) suggested a major mineralisation episode at about 280 ± 20 Ma, whilst K/Ar determinations on the clay minerals associated with the veins (Dunham and others, 1968) indicated initial mineralisation at 284 ± 40 Ma, followed by at least two further episodes. It seems clear therefore that much of the mineralisation dates from the Permian.

The source of the mineralisation is not definitely known. The Weardale granite underlying the orefield is Devonian in age and cannot be the direct source. Fluid inclusion studies show that the minerals in the baryte zone were deposited from saline brines cooling within the temperature range 130° to 50°C (Sawkins, 1966), although within the fluorite zone the brines were hotter; a range 211° to 119°C has recently been determined (Smith, 1975) for inclusions in fluorite from Weardale. It was concluded from determinations of the sulphur isotope ratios in the orefield (Solomon and others, 1971) that the warm brines were not of magmatic origin. The minerals of the outer baryte zone were thought to be deposited from sulphate-rich connate brines derived from the Lower Carboniferous succession whilst the minerals of the fluorite zone were probably derived from chloride brines, also of connate origin, which had penetrated deeply within the Weardale Granite. The latter suggestion is supported by the generally high rare earth values, especially yttrium, within the fluorites of the orefield. Such values are characteristic of fluorites associated, directly or indirectly, with igneous sources.

It seems likely that the brines emplacing the minerals were derived, at least in part, from the surrounding Lower Carboniferous basins. In early Permian times, the Hercynian earth movements may have stimulated the migration of formation waters from the basins, capped by impermeable Upper Carboniferous sequences, into the regions of lower fluid pressure above the adjacent blocks. The fluid inclusion temperatures suggest burial of the source rocks under about 3 to 6 km of cover (Sawkins, 1966), and such depths of burial would have been attained within the Carboniferous sequences in the basins. The brines emplacing some of the mineralisation of the present district may thus have been derived from the Northumbrian trough to the north and perhaps from a Lower Carboniferous basin, as yet unproved, beneath the Vale of Eden.

A comprehensive account of the mineralisation in the ore-field and the history of its commercial exploitation is given elsewhere (Dunham, 1948). The information relating to the present district is summarised in the detailed section below, together with new data obtained during the present survey.

Details

The most northerly mineralisation on the escarpment is in the headwaters of Raven Beck. Two minor north-westerly trending veins of baryte in the Whin Sill and adjacent strata are exposed in the banks of Raven Beck [NY 6239 4467] and [NY 6224 4450]. Traces of baryte are present to the north-west, both in the Scar Limestone [NY 6209 4454] and, associated with hematite, in the Great Limestone [NY 6186 4483], while to the north-east baryte is present in the Scar Limestone [NY 6271 4473] where a few trial shafts have been sunk.

Some 2 km to the south-east, on Haresceugh Fell and in the headwaters of Loo Gill, baryte mineralisation extends along several fractures trending between north-east and east-north-east; workings in the most northerly of these, the Rowton Beck Vein, proved nearly 4 m of baryte in veins in the Nattrass Gill Hazle, and a vein up to 2.4 m wide is exposed in the Four Fathom Limestone [NY 6337 4330]. A little to the east baryte has been worked from the Daffenside Vein over a length of about 100 m on a fault throwing one of the Coal Sills against the Great Limestone; nearly 2 m of baryte are exposed in this vein [NY 6403 4333]. About 250 m to the south-east, the Loo Gill No. 2 Vein, comprises baryte up to 1.2 m wide and has been worked over a length of about 300 m from a level driven from Harrison Adit in Loo Gill. The vein consists of about 1 m of baryte where it cuts the top of the High Brig Hazle at outcrop [NY 6391 4284], where further limited working has been carried out. The Loo Gill No. 1 Vein carries baryte along a complex fault zone along Loo Gill; the strata involved range from the Nattrass Gill Hazle to the Low Coal Sill. The vein has been worked to the north-east from two adits [NY 6446 4299] and [NY 6447 4302] in or just below the Low Coal Sill. About 200 m to the south-east of the gill, surface trials along a parallel fracture have yielded further traces of baryte, for example in the Low Coal Sill [NY 6438 4268].

Weak mineralisation has been explored in the valley of Gilderdale Burn, in veins referred to collectively as the Gilderdale Veins (Dunham, 1948, p.143). A level has been driven in the Copper Hazle north-westwards from the banks of the Burn, some 1.4 km ESE of Black Hill and limonitic debris is present in the dump [NY 6911 4712]. Trials in strata ranging from the Copper Hazle to the Five Yard Limestone on the northern side of the Burn 800 m to the south-west have proved limonite and traces of malachite in the vicinity of a small fault. Some 3 km farther upstream, faulted strata including the Great Limestone and the Low Coal Sill have been explored by shaft and level, e.g. [NY 6644 4422], but there is little mineralisation to be seen in the workings. Evidence of baryte is seen 76 m N of Tom Smith's Stone, where much baryte float is present in the head deposits that cap strata about 50 m above the Wolf Crag Grit [NY 6518 4676].

The Great Limestone is replaced by iron ore and veined with baryte below Horse Edge, about 1 km SE of Gilderdale Burn, along a mineralised belt known as the Horse Edge Vein. A series of trenches of the south-east side of Horse Edge e.g. [NY 6846 4464] have proved limonite over a length of 300 m in a zone 10 to 19.5 m wide assocciated with a fault trending at 050° that throws down about 3 m to the south-east, although the principal mapped fault, trends at 040° and throws down about 5 m to the north-west.

The Great Limestone and associated strata are weakly mineralised by baryte and possibly also galena 750 m to 1 km E of Scarberry Hill, and have been explored by a level and numerous shafts e.g. [NY 6876 4385]. Some 2 km to the south-west, near Meathaw Hill, surface exposures show partial replacement of the Great Limestone by limonite e.g. [NY 6772 4231].

The most important mineralisation within this area is on Rotherhope Fell (Figure 34), between Black Burn and Smittergill Head, where a series of NE-trending fractures carry quartz, lead, iron ores and fluorite. The northernmost veins of this group are the Birchy Bank Veins. The mineralisation is mostly of quartz with marcasite and pyrite, and affects strata ranging from the Copper Hazle to the Three Yard Limestone. Some of the dumps from abandoned shafts on or near the outcrops of these veins include galena and fluorite e.g. [NY 6856 4116]. A little to the south-east lies the Smittergill Hill Vein, which intersects Black Burn some 100 m N of the outflow of Srnittergill Burn. It has been intensively worked in strata ranging from the Copper Hazle to the Five Yard Limestone, largely from shafts, the dumps of which include quartz, fluorite and galena e.g. [NY 6876 4074]. The Smittergill Hill Sun Vein consists mainly of quartz mineralisation along a fault that throws down to the south-east; its position along the line of Smittergill Burn has been deduced from geophysical evidence (Hallimond and Eyles, 1949). The vein has been tried by opencut immediately north-cast of Black Burn e.g. [NY 6865 4033], and is exposed in Smittergill Burn both on the southeastern side of a small inlier of Whin Sill [NY 6834 4005], where it carries tabular epimorphs after pyrite and marcasite, and in the stream some 500 m to the south-west, where it comprises quartz up to 4 m wide with inclusions of altered sedimentary rock. The vein probably extends farther to the south-west to merge with the Great Sulphur Vein.

A group of veins consisting mostly of quartz, but with subordinate iron sulphides, intercepts Black Burn between 300 and 950 m SE of the outflow of Smittergill Burn; of these the Weatheral Mea Vein and the Greencastle Vein have been tried, the former by shafts and the latter by an opencut and a level entering just above the Scar Limestone. The Greencastle Vein is exposed in Black Burn [NY 6894 3962] where it is nearly 3 m wide and consists of quartz with pyrite and marcasite. A parallel vein, lying some 130 m to the south-east, is also exposed in Black Burn [NY 6910 3959] and is some 2 m wide consisting of quartz with pyrite.

The most important mineralisation within the area is along the Great Sulphur Vein, more properly described as a lode, which coincides with a fault, or faulted monocline, throwing down to the north (Thompson, 1933]. The lode is probably continuous westwards with the Knapside Vein and has been worked or tried over a length of 465 m by opencut, shafts and levels in strata ranging from probably the Jew Limestone to the Three Yard Limestone and including the Whin Sill. Galena was obtained, accompanied by sphaleritc, iron sulphides, quartz, purple fluorite and carbonates. Sandstones of the Copper Hazle, which are exposed in tributaries of Smittergill Burn to the north of the lode, carry prominent thin quartz veins trending north-eastwards up to about 100 m from the lode. Large blocks of vein quartz from the Great Sulphur Vein are present at a number of localities [NY 6774 3903] to [NY 6807 3911] on the hillside to the south of Smittergill Burn, and the lode is exposed in a stream section 1.2 km E of Smittergill Head, where it includes a mass of quartz-dolerite about 1 m across [NY 6863 3915]. On the hillside father east there are several small exposures of vein-quartz with inclusions of sandstone [NY 6877 3914] to [NY 6908 3914], while in the stream-section of Black Burn [NY 6977 3892], the lode is well exposed and comprises much disturbed and heavily quartz-veined sandstone and siltstone in a belt 33 m wide.

The Knapside Vein to the east of the escarpment has been explored in 'hushes' and tried by levels [NY 6546 3875] and [NY 6577 3892]; a northeasterly extension continues beyond the presumed junction with the Great Sulphur Vein and is exposed [NY 6615 3921] as quartz-veined sandstone 1.3 km W of Smittergill Head. The Aglionby Vein lies parallel to, and 350 m NW of the Knapside Vein, and is exposed in the headwaters of Aglionby Beck [NY 6529 3904], where an attempt has been made to work a low-grade iron-ore, present as a replacement of the adjoining Whin Sill. Quartz and limonite are present in the vein, and traces of galena are seen in sandstone just to the north.

A group of ENE-trending faults, 200 m S of Hartside Cross, carry baryte mineralisation in the Gamblesby Fell Veins, one of which has been worked in an opencut [NY 6472 4159]. Iron ore is present at three localities to the south-west. In faulted ground just to the south of Twotop Hill, the Scar Limestone has been replaced by iron ore, which has been worked along a NE-trending vein and in a small flat e.g. [NY 6362 4110]. A WNW-trending fault some 500 m to the west also carries iron ore; much limonitic debris is present on the dump of a trial working [NY 6293 4112]. A NE-trending fault just to the south of Long Crags is similarly mineralised, and from the distribution of abandoned adits and shafts it appears that several flats are present in the Melmerby Scar, Robinson and Smiddy limestones. RSA

The Melmerby Scar Limestone is mineralised along the Gate Castle Fault, which lies just to the east of Melmerby Low Scar. It has been replaced by iron ore e.g. [NY 6354 3802], and traces of azurite and malachite are present e.g. [NY 6321 3917].

Galena is said to have been obtained from the Knapside Vein (Dunham, 1948, p. 126), the western part of which intercepts the escarpment just to the north of Melmerby High Scar. The vein follows the High Scar Fault, affecting strata from the Basement Beds at least up to the .Jew Limestone, and has been worked from three levels driven partly through landslip. Siliceous limonite and quartz with a little galena have been recorded on the dumps. A parallel vein some 100 m to the south-east is feebly mineralised with limonite, with traces of malachite in places.

Strata from the Three Yard Limestone to the Little Limestone are mineralised along a group of ENE fractures, of which the principal is the Ardale Head Vein. This has been proved by trials over 1.2 km, and dumps include iron and lead ores. A flat of iron ore in the Great Limestone adjacent to the vein at its western end e.g. [NY 6701 3570] has been proved by boring and opencut. The scarp of the Great Limestone breaks down for some 250 m to the north of the Ardale Head Vein, and it is possible that this is due to widespread replacement of the limestone by ironstone. Another ENE vein affects strata from the Four Fathom Limestone to the Low Coal Sill, some 500 m SE of the Ardale Head Vein; dumps from shafts and opencuts include iron ore and baryte.

Southwards from the Great Sulphur Vein the Black Burn catchment is sparsely mineralised within the district, although on Skirwith Fell there are several exploratory hushes, such as that [NY 6901 3600] across the crop of the Three Yard Limestone, in which traces of azurite are seen. Levels within, and at the top of, the Great Limestone e.g. [NY 6812 3594], some 900 m to the west, appear to have tried a vein parallel to, and some 250 m to the south-east of, the Ardale Head Vein, but there is no record of mineralisation. Some 600 m to the south-south-east, the dump from a level [NY 6831 3536] into strata just above the Pattinson Sill includes baryte.

The ground immediately to the north of the Cross Fell Scrces has been tried from an adit [NY 6902 3537] at the top of the Great Limestone; no workable deposits were found, although the dump contains galena and fluorite as well as quartz.

Finally, in the south-cast of the district, slight baryte mineralisation is present on the Crowdundle Fault, where it is exposed [NY 6907 3125] in Eller Gill; a little to the east, in the Alston District, important lead ore and baryte mineralisation is present in the Dun Fell and related veins. AJW

Iron ore

There are several replacement deposits of iron ore in the Pennines area, although none is likely to be of economic interest. One of the largest is at Horse Edge [NY 6846 4464] where umber and limonite flats have replaced the Great Limestone adjoining the Horse Edge Vein. Analyses of ore from trials and disused workings show Fe₂O₃ in the range 28.73 to 66.22% and 16.74 to 52.60% SiO₂. An estimate of the tonnage of ore at outcrop is given as 70 000 tons (Dunham, 1941, 1948).

Farther south in faulted ground at Twotop Hill [NY 6362 4110], the Scar Limestone has been replaced by iron ore, which has been worked opencast; and in Aglionby Beck [NY 6529 3904] the quartz-dolcrite Whin Sill has been partially altered to limonite in the vicinity of the Aglionby Vein. An analysis of the Aglionby Beck deposit, which has also been worked by open-cut, shows 38.20% SiO₂, 20.95% Al₂O₃, and 18.93% Fe₂O₃. Farther east, iron sulphides including pyrrhotite, pyrite and marcasite were encountered in workings in the Great Sulphur Vein at Smittergill Head [NY 6730 3895], mostly as tabular masses within quartz (Dunham, 1948).

At Ardale Head, iron ore has been proved in strata ranging from the Three Yard Limestone to the Little Limestone, adjoining the Ardale Head Vein. The principal deposit, which has been worked opencast, occurs as a flat replacing the Great Limestone [NY 6701 3570]. Analysis of this orebody gave 65.7% Fe₂O₃ and 13.1% SiO₂, while analyses of ore from the vein averaged 48% Fe and 7 to 9% Mn.

In the mainly red Carboniferous strata cropping out in the western part of the district, hematite is a widespread minor component. In some of these strata, particularly the sandstones, it is present as a cement or replacement, and layers of iron ore up to about lm thick have been recorded. One such layer, exposed in Raughton Gill [NY 4412 4604] is said to have been worked for ore; and similar material was probably encountered in a shaft [NY 4058 4497], now abandoned, near Beacon Hill Farm. Exploration near Ivegill around 1920 led to the sinking of the High Head boreholes e.g. [NY 4115 4434], but no significant deposits were found.

A band of hematite about 0.4 m thick crops out in a tributary of Crowdundle Beck [NY 6598 3043] 1 km N of Milburn. The ore lies along the bedding of the Melmerby Scar Limestone a short distance below the sub-Permian unconformity.

Fluorite

Fluorite is present in association with galena and quartz in a group of veins on Rotherhope Fell [NY 69 41], in the extreme east of the district. The mineral was extracted as gangue during lead mining operations at Rotherhope Fell Mine, and 894 tons were produced between 1906 and 1914. A great deal was dumped in the mill-tailings, which have recently been reworked for fluorite. Analysis of these tailings gave CaF₂ as high as 50.57% (Dunham, 1948, 1952). The underground reserves of fluorite in the veins already worked for lead ore are unknown, and the tract between Rotherhope Fell and Smittergill Head, where fluorite is present in the Great Sulphur Vein, is largely unproved. Analyses of coarse tailings at the Smittergill Head Mine [NY 6730 3895] gave 52.7% CaF₂, and of the fine tailings 39.4% CaF₂ (Dunham, 1948).

The fluorite zone of the northern Pennine orefield lies to the east of most of the present district, and it is unlikely that commercial quantities of fluorite remain undiscovered in the old mines along the Pennine escarpment.

Baryte

Baryte was worked between about 1940 and 1960 at the Hartside Mines in a group of north-easterly trending veins on Haresccugh Fell and in the headwaters of Loo Gill. Production from these workings was about 2500 tons per year in the mid-1940's. Analysis of the baryte by B. Laporte and Co., gave 95.5% BaSO₄, 1.2% SrSO₄ and 0.1% CaSO₄ (Dunham, 1948). Baryte mineralisation may extend some way to the north-east from the worked ground in Hartside Mines. No other commercial prospects are known within the district. RSA, AJW

Water supply

The catchments of the River Eden and River Petterill cover most of the district and lie within Hydrometric Area 23, administered by the North West Water Authority (NWWA). A small area in the north-east draining to the River South Tyne lies within Hydrometric Area 76, which is controlled by the Northumbrian Water Authority. The public demand for water within the district is low, as there is no urban or industrial development outside Penrith and there is negligible irrigation of arable land.

The climate of the district is characterised by relatively low precipitation over the Vale of Eden with an extremely steep precipitation gradient along the Pennine escarpment. The Vale is protected from easterly winds by the northern Pennines and from westerly ones by the Lake District mountains, with the result that mean annual rainfall over most of the area is only 900 to 1000 mm, rising rapidly to 2400 mm (standard period 1916–50) on the summit of Cross Fell. Seasonal variations are small, with 54 per cent of annual precipitation falling in the months of October to March; the driest period is from April to June. Potential annual evapotranspiration varies inversely with precipitation, ranging from 425 mm over most of the area to 350 mm on the Pennine hills (Cumberland River Authority Section 14 Survey). Data which may relate potential to actual evaporation is sparse but it is estimated by the NWWA that annual cumulative soil deficits are small and hence potential and actual rates of evaporation will equate closely. The 'effective precipitation' (i.e. actual precipitation minus actual evapo-transpiration) may be divided into run-off and infiltration components but these are difficult to quantify because of the short past period of river flow observation and the inadequacy of aquifer information (changes in storage, groundwater gradients). Hence no local reliable values of infiltration to groundwater have yet been established.

Within the district river flow is recorded only at Udford on the River Eamont [NY 575 305]. However, gauging stations are situated on the River Eden just south of the area at Temple Sowerby [NY 604 283] and to the north at Warwick Bridge [NY 471 567]. The mean annual flow (1966–74) at each of these stations is calculated as 12.85, 13.45 and 32.15 m³/sec respectively. Earlier records at these stations are subject to revision due to weed growth at the gauges. The River Petteril is gauged at Harraby Green [NY 412 547] near Carlisle, where the mean annual flow (1966–74) is 1.63 m³/sec. Over the whole area a total of 9.8 m³/sec is extracted from surface sources, divided almost equally between water supply (public and private) and industrial usage, with only minor quantities for agricultural purposes. On the eastern side of the Vale of Eden some of the numerous springs which emerge along the Pennine escarpment are used to supply small service reservoirs situated on the lower slopes of the hills.

The potential of each formation as an aquifer is discussed below. Within the drift deposits the boulder clay is unlikely to yield any useful water supplies and forms a relatively impermeable cover over wide areas, and peat—although restricting rapid surface run-off—is not a significant source of water. Glacial sands and gravels may yield supplies of varying chemical quality to shallow wells but the risk of pollution is high and supplies could fail during periods of drought.

The St Bees Sandstone is the second most important potential aquifer of the area and at its maximum is 500 to 600 m thick. No wells are recorded in the St Bees Sandstone but moderate yields of fairly hard water may be possible especially from the upper beds which are less well-cemented and contain fewer argillaceous partings than the lower ones. A large portion of its outcrop is covered by boulder clay which will inhibit direct infiltration but infiltration will occur where the sandstone crops out, especially between Ousby and Melmerby. Average intrinsic permeabilities as determined in the laboratory from outcrop samples range from kv = intrinsic permeability in a vertical direction; kh = intrinsic permeability in a horizontal direction.kv = 590, kh = 230 millidarcys (0.38, 0.18 m/day) near Croglin [NY 5753 4744] to kv = 1725, kh = 1700 millidarcys (1.1, 1.0 m/day) at Melmerby [NY 6194 3791].

The Eden Shales form an almost impervious layer 45 to 180 m thick and are unlikely to yield useful quantities of water. In suitable geological situations these strata form a confining aquiclude to the Penrith Sandstone beneath.

The Penrith Sandstone is the principal aquifer of the district and directly underlies approximately 25 per cent of the area, predominantly on the western limb of the Eden Syncline. A large proportion of the outcrop is covered by boulder clay through which recharge will be restricted. Exposed portions form the higher ground north of Penrith and the watershed between the rivers Petteril and Eden. Hydraulic gradients indicate local groundwater flow in an eastward direction. Significant anisotropy of intergranular permeability is created by the cross stratification and graded bedding, together with extremely irregular secondary silicification. In the Blackmoss Pool [NY 4824 4816] and Nord Vue [NY 4941 4425] boreholes near Armathwaite, sections of virtually uncemented Penrith Sandstone have intrinsic permeabilities of 170 00 to 23 000 millidarcys (10.9–14.8 m/day) while, in the more cemented strata in the Edenhall [NY 5637 3314] and Lounthwaite [NY 6535 3092] boreholes, intrinsic permeabilities may be 1 to 2 orders of magnitude smaller. The overall ratio of intergranular horizontal permeability (kh) to vertical permeability (kv) is approximately three which, to produce a value for bulk aquifer permeability, is probably exaggerated 20 to 30 times by the presence of sub-horizontal fissures. Extensive fissuring through which most of the groundwater flow occurs has been determined by conventional borehole logging and observed by the use of down-hole television techniques (see (Plate 13)) during investigations at the Edenhall boreholes (Tate and others, 1970). In an investigation of the Penrith Sandstone at Cliburn, 8 km SE of Penrith, it was established that groundwater movement takes place primarily along subhorizontal fissures, especially common close to the water table and contributing over 90 per cent of the total aquifer transmissivity which at this site ranges from 1900 to 3300 m²/day. However, the matrix properties of the sandstone control the release of groundwater from storage to this fissure system and silicified, fine pore-size zones inhibit free drainage to the fissures and may be capable of exerting considerable capillary suction (Lovelock and others, 1975).

There is major abstraction from three 300 mm diameter boreholes in the Penrith Sandstone at Edenhall [NY 563 331] which are licensed at 1.5 m³/sec and which during a pumping test yielded 1.6 m²/sec from two holes for 10 m drawdown. Water is also drawn from two 380 mm diameter boreholes at Nord Vue [NY 494 442] where the licensed abstraction is 0.4 m³/sec with test pumping indicating a yield of 1.2 m³/sec for a drawdown of 10.6 m. The analyses of groundwater shown in (Table 6) are representative for this aquifer. Total licensed abstraction from the Penrith Sandstone of the area is 5.37 x 10⁶ m³ annum.

The permeability of the Carboniferous rocks is generally considerably less than that of the Permian sandstones and yields are much less. Occasionally reasonable yields may be produced from groundwater in fissures in the more massive rocks but the quality of the water may be variable and is frequently poor. Total licensed abstraction from Carboniferous strata of the western portion of the district totals 1.89 x 10⁵ m³/annum.

Each of the relatively thin Lower Carboniferous limestones and sandstones of the Pennine escarpment forms a distinct hydraulic unit and gives rise to numerous springs, but the prospects for useful groundwater supplies are limited. JLF

References

ANON. 1966. Cumbrian Rivers Hydrological Survey. Hydrometric Areas 75, 76 and part 74. (Ministry of Housing and Local Government.)

ANON. 1970. Water Resources Act 1963, Section 14, First Survey. (Cumberland River Authority.)

DUNHAM, K. C. 1941. Iron ore deposits of the Northern Pennines. Wartime Pamphlet Geol. Surv. G.B., No. 14.

DUNHAM, K. C.  1948. Geology of the Northern Pennine Orefield: Vol. 1, Tyne to Stainmore. Mem. Geol. Surv. G.B.

DUNHAM, K. C.  1952. Fluorspar. Spec. Rep. Miner. Resour., Mem. Geol. Surv. G.B., Vol. 4.

DUNHAM, K. C.,  FITCH, F. J., INESON, P. R., MILLER, J. A. and MITCHELL, J. G. 1968. The geochronological significance of A³⁹/A⁴⁰ age determinations on White Whin from the northern Pennine orefield. Proc. R. Soc., Ser. A, Vol. 307, pp. 251–266.

HALLIMOND, A. F. and EYLES, V. 1949. A magnetic survey in Cumberland; the results of an investigation of faults in the Whin Sill at Smittergill Burn, Alston. Mining Mag., Vol. 80, pp. 329–333.

HERBERT, R. 1975. Groundwater Conditions in the Penrith Sandstone at Cliburn, Westmorland—Discussion. J. Inst. W. Eng. Sci., Vol. 29, No. 7.

LOVELOCK, P. E. R. 1972. Aquifer Properties of the Permo-Triassic Sandstones of the United Kingdom. Unpublished Ph.D. Thesis, University College, London.

LOVELOCK, P. E. R., PRICE, M. and TATE, T. K. 1975. Groundwater conditions in the Penrith Sandstone at Cliburn, Westmorland. J. Inst. W. Eng. Sci., Vol. 29, No. 4.

MOORBATH, S. 1962. Lead isotope abundance studies on mineral occurrences in the British Isles and their geological significance. Philos. Trans. R. Soc., Ser. A. Vol. 254, pp. 295–360.

SAWKINS, F. J. 1966. Ore genesis in the North Pennine Orefield in the light of fluid inclusion studies. Econ. Geol., Vol. 61, pp. 385–401.

SMITH, F. W. 1975. Factors governing the development of fluorspar orebodies in the north Pennine orefield (abstract). Trans. Inst. Min. Metall., Sect. B: Appl. Earth Sci., Vol. 84, p. 71.

SOLOMON, M., RAFTER, T. A. and DUNHAM, K. C. 1971. Sulphur and oxygen isotope studies in the northern Pennines in relation to ore genesis. Trans. Inst. Min. Metall., Sect. B, Appl. Earth Sci., Vol. 80, pp. 259–275.

TATE, T. K., ROBERTSON, A. R. and GRAY, D. A. 1970. The hydrogeological investigation of fissure flow by borehole logging techniques. Q. J. Eng. Geol., Vol. 2, pp. 195–216.

THOMPSON, L. M. 1933. The Great Sulphur Vein of Alston Moor K. C. DUNHAM, (Editor). Proc. Univ. Durham Philos. Soc., Vol. 9, pp. 91–98.

Chapter 12 Geophysical investigations

Magnetic surveys

The aeromagnetic data (Figure 43)." data-name="images/P991325.jpg">(Figure 42) were obtained in 1959 from north–south flight lines spaced 2 kin apart at a mean height of about 300 m (1000 ft) above the ground. Total magnetic field was measured and expressed as departures from a linear regional field which increases by 2.178 gamma/km northwards and 0.259 gamma/km westwards from a datum value 47033 gamma (1 gamma = 1 nanotesla) at the origin of the British National Grid (Inst. Geol. Sci., 1972).

The three major groups of magnetic anomalies in the district are attributed to igneous rocks. These are the Armathwaite Dyke, the Whin Sill and the Eycott Volcanic Group. The Vale of Eden basin has very little magnetic expression and the trend of the Pennine Fault system is only vaguely apparent through the presence of anomalies on its eastern side.

The Tertiary Armathwaite Dyke causes a strong WNW–ESE linear dipolar anomaly traceable from Dumfriesshire to Yorkshire. Across the Vale of Eden, the anomaly coincides with the mapped outcrop of the dyke; the anomaly also extends 2.5 km E of the Pennine Fault on to Haresceugh Fell although for much of this distance the dyke fails to reach the surface. It is presumably present however at a shallow depth. Immediately beyond here the anomaly cannot be traced, suggesting that the dyke is absent, but the anomaly resumes in the Smittergill valley, 5 km to the east-south-east, where its trend is aligned with the next dyke outcrops in Cross Gill, in the Alston district.

The anomaly has a reversed polarity, caused by the natural remanent magnetism (NRM) of the dyke and baked contact rock (Giddings and others, 1974). Although the direction of total remanence is rather scattered (Bruckshaw and Robertson, 1949), the direction of primary remanence obtained by subjecting the samples to magnetic cleaning in an alternating field is more uniform and indicates an averaged palaeomagnetic pole position at 75°N, 120°W with a Fisher Index α₉₅ of 5.5° (Giddings and others, 1974). This index is a radius of 95 per cent confidence. The authors show that this pole position is similar to the averaged position obtained from nine British Tertiary dykes.

On the Pennines, the aeromagnetic map comprises a number of small, indistinct anomalies which are due both to the Whin Sill and to magnetic horizons within the shallow Lower Palaeozoic basement. Greer and others (1959) have measured the natural remanence of the Whin Sill and, taking into account its variable dip, calculate the direction of magnetisation as D = 187.8°, I = 4.9° and the palaeomagnetic pole as 168.9°E, 37.3°N. This value supports earlier conclusions (Hallimond and Eyles, 1949) and is consistent with a Lower Permian pole. The values represent total remanence although from a few alternating field demagnetisation tests, a reasonable stability of remanence is claimed (Greer and others, 1959).

The outcrop of the Eycott Volcanic Group in the northern Lake District is marked by a large linear dipolar anomaly which with decreasing amplitude and some displacements, extends laterally as far east as Penrith. It is likely that the anomaly is caused by particular lavas which contain a relatively high proportion of magnetite. The general profile shape of this anomaly is produced by magnetic lavas dipping steeply southwards. This is in contrast to the few surface dips recorded in the volcanic rocks which are inclined steeply to the north or north-east. As the anomaly records the overall attitude of the magnetic rocks through several hundred metres vertically however, it is possible that the volcanic rocks are overturned southwards just beneath their outcrop.

Within the present district, the magnetic anomaly comprises two dipolar components (Figure 43), which are interpreted as being due to sub-crops of lavas in the Eycott Volcanic Group beneath the Lower Carboniferous cover. Residual anomalies have been obtained along profiles A and B (Figure 43) by subtracting a regional field which increases uniformly northwards at 2.75 gamma/km. For each profile two models have been obtained, one representing induced magnetism only, and the other, remanent plus induced magnetism. The NRM parameters D = 10°, I = 45° adopted for the dip-corrected Eycott sequence on Binsey (Briden and Morris, 1973) have been used here, and a mean intensity of remanence M_R =100 gamma and a Koenigsberger ratio Q=1 have been estimated from Morris (1973) . These values give an intensity of induced magnetisation of 100 gamma.

In each case, the lavas have been considered as long thick sheets and directions of remanence have been determined for successive adjustments of dip. The northern sub-crop (Figure 43) strikes at about 115° through Greystoke Park just north of the Greystoke Fault and seems to terminate eastwards against the Johnby Fault. The southern sub-crop strikes at 65° through Greystoke, Spire House and Newton Rigg, to end near Penrith. The broadening of the anomaly associated with this sub-crop between profiles A and B suggests an eastward deepening of the Lower Palaeozoic floor perhaps by as much as 500 m. As only about 250 m deepening is expected from the north-easterly dip of the Carboniferous rocks, the remainder is unaccounted for but may be due to a rapid thickening of the Mell Fell conglomerate beneath the Carboniferous sequence. The trends of both sub-crops are roughly parallel to the strike of the volcanic rocks of the northern Lake District and the WNW strike of the northern sub-crop is consistent with that of the volcanic rocks in the Greystoke inlier. It is difficult, however, to match the orientation of the southern sub-crop with the north-westerly strikes of the rocks in the Eycott inlier. It seems likely therefore that the orientation of the rocks in this inlier is not typical of the volcanic belt overall, which has a general trend just south of east at least as far eastwards as Penrith. The closure of the anomaly to the east of the town shows that the magnetic rocks are absent here, although they reappear in a fault-hounded crop to the east of Melmerby where they are marked by a distinct anomaly.

In addition to the regional magnetic survey, more detailed magnetic work was carried out in the Pennines to trace faults displacing the Whin Sill near Smittergill Head [NY 674 390], specifically because these fractures are in some cases mineralised. Hallimond and Eyles (1949) measured the vertical magnetic field along a number of ground traverses over the Smittergill Head Sun Vein and were able to delineate the fault plane, recognising and allowing for the palaeomagnetic properties of the Sill to interpret the anomaly curves. Similar traverses (McQuillin and Rutter, 1966) were made across the Great Sulphur Vein and the Smittergill Head Sun Vein on Melmerby Fell measuring total magnetic field, electromagnetic and self potential properties. The amplitudes of the magnetic anomalies varied greatly from traverse to traverse, the maximum being about 1000 gamma with a wavelength of approximately 100 m. Extensions of the two faults were traced across Melmerby Fell and were incorporated in the published geological map.

Gravity survey

Regional gravity data have been obtained in the Penrith district by IGS, Bott (1974) and Bott and Masson Smith (1957). These data, reduced at variable densities and adjusted for compatibility with the Geodetic Reference System 1967 and the National Gravity Reference Net 1973 (Masson Smith and others, 1974), have been incorporated in the 1:250 000 Bouguer anomaly map for north-west England (Institute of Geological Sciences, 1976). That part of the map which includes the Vale of Eden and surrounding areas is reproduced (Figure 45)." data-name="images/P991327.jpg">(Figure 44), together with an inset indicating the density of data. An elongated north-west to south-east trending negative anomaly is associated with the Vale of Eden sedimentary basin. It has an apparent central value of approximately −9 mGal but part of this is attributable to the Weardale Granite (Bott, 1967) to the east, which is marked by a strong negative anomaly with a central value of −28 mGal near Rookhope (Figure 45)." data-name="images/P991327.jpg">(Figure 44). To the south-west, a negative anomaly with a minimum of −5 mGal, marks the outcrop of the Shap Granite; the source of the positive anomaly north of the granite is unknown.

To aid interpretation, the Vale of Eden anomaly has been isolated from other superimposed anomalies, firstly by the removal of large-scale regional trends, and then by the separation of local anomalies. The regional effects have been determined by manual smoothing of Bouguer anomaly profiles on a 20-km grid covering northern England and southern Scotland. The smoothed gravity values for the area of northern England enclosed by National Grid lines 310 to 420E and 490 to 570 N have been represented by the fourth order polynomial:

g =A₀ + A₁x + A₂y + A₃x² + A₄xy + … A₁₄y⁴

where x and y are grid references expressed in units of 100 km and the coefficients A_o , A₁, A₂ … A₁₄ are

−48.7777, 41.9422, 3.7320, −6.6190, −2.8362, 3.9978, −2.6405, −0.7675, 0.7637, −0.1991, 0.1850, 0.4046, −0.0164, −0.0470, −0.0719

Models have been devised for the large anomalies surrounding the Vale of Eden using a computer iterative technique, and then the effect of each model on the anomaly values within the Vale has been assessed. Small errors in this procedure are unavoidable particularly during the manual separation of the anomalies. To model the Weardale Granite, an arbitrary line [NY 378 516] to [NY 360 548] was selected to separate its anomaly from that of the Vale of Eden, marginal anomaly values being slightly adjusted. The model, initially based upon interpretations by Bott (1967), incorporates a density contrast of −0.15 g/cm³ against the Lower Palaeozoic basement, a base depth of 8.9 km below ground level and a minimum roof depth of 400 m, the latter being compatible with the Rookhope Borehole section (Dunham and others, 1961).

The Shap Granite model has been similarly developed, its areal limits being confined within the steepest anomaly gradients. To obtain an adequate match with the residual anomaly, the base depth had to be limited to a maximum of 4 km beneath ground level for a single density contrast of 0.12 g/cm³ (cf. Bott, 1974). An arbitrary model has been assigned to the positive anomaly north of the Shap Granite, invoking a density contrast of +0.15 g/cm³ and a maximum base depth of 2.5 km below ground level. These values are compatible with a basic igneous body within the Lower Palaeozoic basement and although there is no corresponding aeromagnetic anomaly here, such a body is the likeliest source of this anomaly.

The vertical gravity field of each of the above models has been evaluated at the intersections of a widely surrounding 1-km grid, which was expanded until the calculated gravity field had declined to less than 0.5 mGal. These gravity fields have then been subtracted from the residual anomaly map to isolate the Vale of Eden negative anomaly (Figure 45), leaving an amplitude of −15 mGal in its centre and making the steep gravity gradient on its eastern side more continuous laterally, the contours extending approximately parallel to the Pennine Fault system. The negative anomaly between Penrith and Appleby [NY 368 520] for which Bott (1974) invoked a granite ridge, has been accounted for by the lateral effects of the Shap and Weardale granites.

The source of the Vale of Eden anomaly has been assumed to be mass deficiency in the Lower Carboniferous, Upper Carboniferous and Permo-Triassic strata, which have lower densities than the Lower Palaeozoic rocks. In the following quantitative interpretations, density contrasts of −0.05, −0.15 and −0.3 g/cm³ respectively have been assigned to these rocks (Table 7) relative to a background density of 2.75 g/cm³. No allowance has been made for changes of density with depth of burial. The thicknesses of the Lower Carboniferous, Upper Carboniferous and Permo-Triassic rocks within the basin have been estimated by combining the gravity data with information from boreholcs and surface sections.

A generalised 3-dimensional geological model of the basin has been devised using horizontal polygonal laminae with appropriate density contrasts (Figure 46). Towards the southern end of the Vale, a dextral displacement of the basin axis, perhaps by as much as 2.5 km, is indicated to the east of Appleby. The basin shallows to the south, the Penrith Sandstone thinning to 150 m or less beyond Warcop. South of Dufton, the Lower Carboniferous sequence thickens toward the Stainmore trough, although farther south at Ravenstonedale the model cannot accommodate the proven thickness of these rocks, over 1500 m, the residual Bouguer anomaly being 3 or 4 mGal too positive here.

For much of its length the Pennine Fault is paralleled by a belt of steep residual anomaly gradient which north of Melmerby markedly decreases. This change suggests faulting extending 4 to 5 km westward into the Vale, probably as a continuation of the down-north faulting to the east of

Gamblesby. About the eastern end of this faulting, the gravity data indicate that the sediments are deeper on the northern side, deflecting the margin of the basin dextrally by about 1 km. The reverse situation applies toward its western end where the structural belt coincides with the Glassonbybeck Fault.

The maximum apparent dip of the basin floor adjacent to the Pennine Fault occurs south of Melmerby, and is approximately 45°, a figure generally consistent with the interpretation given by Bott (1974). The maximum thickness of Permo-Triassic rocks probably occurs in the area of greatest anomaly east of Culgaith and could be as much as 800 m, although the actual thickness could be less than this figure if a comparatively large thickness of Upper Carboniferous rocks is preserved beneath.

Near the Greystoke Park and Eycott Hill inliers, the anomaly is diminished and a ridge of Lower Palaeozoic rocks seems to project eastward for several kilometres be- neath the Dinantian cover. This ridge broadly coincides with the sub-crops of the magnetic lavas discussed above and it is possible here to compare the amounts of Dinantian cover indicated by both the magnetic and gravity methods. On profile A, the magnetic interpretation gives thicknesses of 500 and 250 m (Figure 43) agreeing well with 400 and 250 m deduced by the gravity data. On profile B however, the magnetic data suggests 1150 m of cover, although this figure could be exaggerated by the simple model used, whilst the gravity data gives about 450 m. The latter figure seems more realistic.

The gradual closure of the residual anomaly northwards from Lazonby indicates progressive shallowing of the basin. By Holmwrangle the basin closes completely and immediately to the north the Permo-Triassic rocks may be less than 100 m thick. Similarly the Upper Carboniferous rocks are also likely to be thin in this locality and denser Dinantian rocks are expected to lie close to the surface. Near Low Hesket, however, the average thickness of the Upper Carboniferous rocks indicated by the gravity interpretation is approximately 150 m less than the thickness recorded by the Barrock Park Borehole. Disregarding the effects of local faulting, a discrepancy of up to 2 mGal is implied in the residual gravity anomaly here.

Seismic survey

A limited number of seismic refraction lines with reversals, have been shot by the Cambridge University Geophysics Department. One of these lines extended over 5.7 km from Langwathby [NY 569 331] to south of Culgaith [NY 603 285]. The geophones were arranged in linear spaced groups. The first arrival data have been broadly grouped into three branches on a time-distance graph. They are complicated near Langwathby by a shallow layer at 37 m with a high apparent velocity of 5.9 m/ms, which is probably a gypsum-anhydrite bed in the Eden Shales.

The data have been interpreted by the present author assuming horizontal plane layering as the line is close to the strike of the beds, although southward dips of 2° could be incorporated. Velocity data based upon single sample measurements (Hart, 1970 and (Table 7)) and density data (Bott, 1974) suggest a velocity inversion from the Eden Shales to the Penrith Sandstone where the latter is unsilicified.

The simplest interpretation of the data gives a 3-layer model. The upper layer with an apparent velocity of 2.3 m/m/ and an apparent thickness of 87 m, probably represents the Eden Shales although this is inconsistent with data from (Table 7). The middle layer has an apparent velocity of 3.4 m/ms and an apparent thickness of 838 m; this is not easy to identify and undoubtedly the problems of velocity inversion and second arrival head waves may combine to corn-plicate the interpretation. The lowest layer has a high apparent velocity of 5.7 m/ms which suggests a limestone or evaporite bed, either near the base of the Penrith Sandstone or in the Upper Carboniferous succession. F C

References

BOTT, M. H. P. 1967. Geophysical investigations of the northern Pennine basement rocks. Proc. Yorkshire Geol. Soc., Vol. 36, pp. 139–168.

BOTT, M. H. P.  1974. The geological interpretation of a gravity survey of the English Lake District and the Vale of Eden. J. Geol. Soc. London, Vol. 130, pp. 309–331.

BOTT, M. H. P.  and MASSON SMITH, D. 1957. The geological interpretation of a gravity survey of the Alston block and the Durham coalfield. Q. J. Geol. Soc. London, Vol. 113, pp. 93–117.

BRIDEN, J. C. and MORRIS, W. A. 1973. Palaeomagnetic studies in the British Caledonides—III, igneous rocks of the Lake District, England. Geophys. J. R. Astronom. Soc., Vol.34, pp. 27–46.

BRUCKSHAW, J. MCG. and ROBERTSON, E. I. 1949. The magnetic properties of the tholeiite dykes of north England. Mon. Not. R. Astronom. Soc., Geophys. Suppl., Vol. 5, pp. 308–320.

CREER, K. M., IRVING, E. and NAIRN, A. E. M. 1959. Palaeomagnetism of the Great Whin Sill. Geophys. J., Vol.2, pp. 306–323.

DUNHAM, K. C., BOTT, M. H. P., JOHNSON, G. A. L. and HODGE, B. L. 1961. Granite beneath the northern Pennines. Nature, London, Vol. 190, pp.899–900.

GIDDINGS, J. W., TARLING, D. H. and THOMAS, D. H. 1974. The palaeomagnetism of the Cleveland–Armathwaite dyke, northern England. Trans. Nat. Hist. Soc. Northumberland, Vol. 41, pp.220–226.

HALLIMOND, A. F. and BYTES, V. A. 1949. Magnetic survey in Cumberland. Mining Mag., Vol. 80, pp. 329–333. HART, C. G. 1970. University of Cambridge. Department of Geodesy and Geophysics. Unpublished report.

INSTITUTE OF GEOLOGICAL SCIENCES. 1972. Acromagnetic map of Great Britain, 1:625 000, Sheet 1. (Southampton: Ordance Survey.)

INSTITUTE OF GEOLOGICAL SCIENCES. 1976. 1:250,000 Series Bouguer Gravity Anomaly Map (Provisional edition), Sheet 54N 04W, Lake District.

MASSON SMITH, D., HOWELL, P. M. and ABERNETHY-CLARK, A. B. D. E. 1974. The National Gravity Reference Net 1973 (NGRN 73). Prof. Pap. Ord. Surv., New Ser. No. 26.

MCQUILLIN, R. and RUTTER, H. 1966. Institute of Geological Sciences, Geophysics Department. Report No. GD/16/54. Unpublished.

MORRIS, W. A. 1973. Palaeomagnetic studies in the British Caledonides. Unpublished Ph.D. Thesis, The Open University, Milton Keynes.

Appendix 1 Boreholes and sections

1 Ardale Beck Section

National Grid ref. [NY 6648 3540] to [NY 6669 3551]. Measured by A. J. Wadge.

2 Barrock Park Borehole

National Grid ref. [NY 4613 4660]. Drilled for IGS by Foraky Ltd, Nottingham. Cores examined by R. S. Arthurton and C. G. Bradley

3 Blackmosspool Borehole

National Grid ref. [NY 4824 4816]. Drilled for IGS by Foraky Ltd., Nottingham. Cores examined by R. S. Arthurton.

4 Cocklakes Quarry Borehole

National Grid ref. [NY 4563 5093]. Drilled for Carlisle Plaster and Cement Co Ltd. by J. S. Davidson and Son, St Bees. Cores examined by S. E. Hollingworth.

5 Coom Gill Section

National Grid ref. [NY 6312 4622] to [NY 6321 4635]. Measured by R. S. Arthurton.

6 Croglin Water Section

National Grid ref. [NY 5986 4800] to [NY 5844 4748]. Measured by R. S. Arthurton.

7 Cross Fell Screes Section

National Grid ref. [NY 6935 3485] to [NY 6885 3506]. Measured by R. S. Arthurton and A. J. Wadge.

8 Crowdundle Beck Section

National Grid ref. [NY 6969 3353] to [NY 6895 3281]. Measured by A. J. Wadge.

9 Daffenside Cleugh Section

National Grid ref. [NY 6514 4411] to [NY 6545 4420]. Measured by R. S. Arthurton.

10 Dale Beck Section

National Grid ref. [NY 6495 3656] to [NY 6531 3692]. Measured by A. J. Wadge.

11 Flusco Limeworks Borehole

National Grid ref. [NY 4587 2905]. Drilled for Harrisons Limeworks by J. S. Davidson & Son, St Bees. Examined by A. Templeman and S. E. Hollingworth.