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Geology of the Moreton-in-Marsh district — a brief explanation of the geological map sheet 217 Moreton-in-Marsh

A J M Barron, M G Sumbler and A N Morigi abridged from the sheet description by A A Jackson

Bibliographic reference: Barron, A J M, Sumbler, M A, and Morigi, A N. 2002. Geology of the Moreton-in-Marsh district — a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 sheet 217 Moreton-in-Marsh (England and Wales).

Keyworth, Nottingham: British Geological Survey. © NERC copyright 2002

The grid, where it is used on figures, is the National Grid taken from Ordnance Survey mapping. © Crown copyright reserved Ordnance Survey licence number GD272191/2002.

(Front cover) The face of Cleeve Cloud [SO 984 256], overlooking Cheltenham, exposes the Birdlip Limestone Formation of the Inferior Oolite Group. It was formerly a building stone quarry, and the slopes below are covered in degraded limestone spoil heaps. The escarpment here is crowned by an Iron-Age hill fort (Aerofilms 599571).

(Rear cover)

(Geological succession) Geological succession in the Moreton-in-Marsh district.

Geology of the Moreton-in-Marsh district (summary from rear cover)

(Rear cover)

This sheet explanation describes the geological 1:50 000 sheet 217 Moreton-in-Marsh. The district includes the northernmost part of the Cotswolds, a designated Area of Outstanding Natural Beauty, which derives much of its distinctive character from the use of the local limestone in the buildings and in the dry-stone walls that border most fields and lanes in the upland areas. Thus the influence of the underlying geology is very apparent and this, coupled with the abundance of fossils and availability of rock exposures led to the district receiving attentions from geological scholars from the very early days of the science. However, a full, systematic and detailed survey of the district was completed only in 1998. The results of this survey, along with information from older, published sources and BGS archives is summarised here. Rocks at outcrop include Lower and Middle Jurassic overlain in places by Pleistocene glacial deposits. A section on the applied aspects of the geology is included, giving information of importance to those concerned with planning and commercial activities, such as civil engineering and mineral extraction.

Notes

Throughout the sheet explanation, the word 'district' refers to the area covered by the geological 1:50 000 series sheet 217 Moreton-in-Marsh. National grid references are given in square brackets. Numbers associated with the plates refer to the BGS photographic archive.

Acknowledgements

This sheet explanation has been abridged from the sheet description written by A J M Barron, M G Sumbler and A N Morigi. D C Entwisle and A Forster provided details for the account on engineering geology; M A Lewis on Hydrogeology and T C Pharaoh contributed to the basement geology and structure. This text relies heavily on information from other BGS publications, particularly the technical reports, listed in Information sources.

Chapter 1 Introduction

This sheet explanationdescribes the geological 1:50 000 series sheet 217 Moreton-in-Marsh, which lies largely within Gloucestershire. The northernmost part of the Cotswold Hills lies in the centre of the district; their prominent escarpment, the Cotswold Edge, overlooks the vales of Evesham and Gloucester in the west. Moreton-in-Marsh, Stow-on-the-Wold and other picturesque Cotswold towns and villages lie within the district. Many buildings are constructed of local Cotswold limestone that provides stone both for walls and roofs, and weathers to a characteristic yellow-brown colour. The Cotswold countryside is also renowned for the dry-stone walls that border many of the fields and lanes.

The vales and plateaux are predominantly arable farmland, with some areas of forestry. The steep slopes below the escarpment are generally grassland and woodlands. There are a number of limestone quarries producing building stone, roofing 'slates' and aggregate, and a clay pit producing bricks.

This region holds particular significance for geologists as it was here that the canal engineer William Smith deduced the constancy of the order of strata and their included fossils. In 1799, he compiled a geological map of the Bath district and a 'Table of the Order of Strata and their embedded Organic remains....' which extended from the Coal Measures up to the Chalk. This was published in 1813 and in the following years was revised and refined, and geology was established as a science. The area attracted the attention of a number of other early geologists, and in 1856 the Geological Survey published a map of the north Cotswolds [Old Series] sheet 44 at a scale of 1:63 360 together with an accompanying memoir.

The detailed survey of the Moreton-in-Marsh district began in 1966, with mapping at 1:10 560 scale of the Bredon Hill area accompanied by the drilling of two stratigraphical boreholes there. The area south from Bredon Hill to Cheltenham was mapped in 1980–82 at 1:10 000 scale as part of the survey of the adjoining Tewkesbury district. The completion of the remainder of the Moreton-in-Marsh district between 1994 and 1998 followed a full survey of the Cirencester district to the south between 1984 and 1994. Together, these projects led to the revision of the nomenclature of the Inferior Oolite Group (Barron et al., 1997). In 1997, the Gloucestershire RIGS group (Regionally Important Geological and Geomorphological Sites, now Gloucestershire Geoconservation) undertook conservation work in several quarries on Cleeve Hill, including the famous Rolling Bank Quarry (Angseesing et al., 2002).

Geological summary (from rear cover)

(Rear cover)

The oldest rocks at depth beneath the district (see inset map of Palaeozoic strata beneath the Permo-Triassic on sheet 217) are thought to be part of a Late Precambrian volcanic arc complex, deformed during the Cadomian orogeny. They now form the floor of the Midland Platform, which acted as a stable crustal area throughout the early Palaeozoic. Cambrian, Ordovician and Silurian rocks consist largely of siltstone and mudstone deposited in shallow marine conditions, but include about 700 m of Silurian basaltic lavas. Lower Devonian rocks are red-brown mudstone and sandstone of the continental Old Red Sandstone facies that was deposited across England and Wales in Early Devonian times. Deposition was interrupted by the Acadian orogeny, and Upper Devonian sandstone and conglomerate rest unconformably on the Lower Devonian.

Carboniferous rocks underlie the eastern part of the district and rest with marked unconformity on the older strata. These are Westphalian Upper Coal Measures, comprising mudstone, siltstone and sandstone with thin coal seams, and form a north-westward extension of the Oxfordshire Coalfield Syncline. The strata were subjected to folding, faulting and erosion during the Variscan orogeny at the end of the Carboniferous; folded Palaeozoic strata form the Variscan basement.

A major north-south-trending structure crosses the district, well illustrated on the inset aeromagnetic anomaly map on Sheet 217. This is the Worcester Basin created by crustal extension in Permian and early Triassic times. Structurally it is a fault-bounded graben and contains a thick sequence of Mesozoic sedimentary rocks. To the east of the basin, the London Platform acted as a stable 'high' throughout much of this era, and the sequence thins markedly eastwards. There were two phases of rapid subsidence (Chadwick and Evans, 1995), one in Late Permian and the other in early Triassic times; each was followed by a period of slower subsidence. The Permo-Triassic succession is dominated by continental sandstone (Bridgnorth Sandstone Formation and Sherwood Sandstone Group) and mudstone (Mercia Mudstone Group). A marine transgression led to the deposition of the late Triassic Penarth Group. In the succeeding Lower Jurassic strata there is a progressive eastward overlap of successive units in the lower part of the Lias Group, and sedimentation seems to have kept pace with subsidence in this marine environment. This phase of basin infill terminated with deposition of the shallow-water Marlstone Rock Formation.

Some subsidence continued in the Worcester Basin, and the top formations of the Lias Group, the Whitby Mudstone and Bridport Sand together with the Mid Jurassic Inferior Oolite Group, are thicker here than to the east. The presence of many breaks in the Inferior Oolite succession, marked by hardground beds or erosion of strata towards the margin of the London Platform–the Vale of Moreton Axis, has been taken to indicate that this subsidence was episodic. Alternatively, these phenomena may relate to periods of lowered sea level while slow subsidence continued. The highest formation of the Inferior Oolite Group, the Salperton Limestone, was deposited across the region without any apparent influence from the Vale of Moreton Axis. In the Great Oolite, too, the effect of the axis appears to have been minimal, but is reflected in the distribution of the sedimentary rocks. Limestones were deposited in very shallow water in the east of the district, while mud accumulated in deeper water to the west and eventually spread across the entire district. Sandy beds at the top reflect the proximity of the London Platform, and there is local downcutting at the base of the Taynton Limestone in the neighbourhood of the axis. In latest Jurassic times, uplift led to much of England and Wales forming an extensive landmass. This tectonic activity may have produced most of the faulting seen at surface in the district.

The drainage pattern of the district may have been instigated by uplift during the Alpine orogeny in the early Palaeogene. The early to mid-Pleistocene, Thames–Evenlode system had a far larger catchment before the development of the Severn and the Cotswold escarpment truncated its upper reaches. Later, the advance of the Anglian ice sheet deposited till as far south as Broadwell, and outwash material accumulated in the Evenlode valley in two phases, the first rich in Triassic clasts, the second containing chalk and flint. Head and fluvial sediments accumulated in the valleys. The gravelly river terraces were later dissected, and lower terraces and modern alluvium were deposited. This process continues to the present day.

Chapter 2 Geological description

Lias Group

The oldest strata that crop out within the district are Early Jurassic in age. The Lias Group underlies all of the low ground, as well as the lower slopes of the Cotswold escarpment. The sequence is over 500 m thick in the west, in the deepest part of the Worcester Basin, and thins to less than 200 m in the south-east where the lower formations are gradually overlapped and condensed on to the London Platform. It is subdivided into five formations.

Blue Lias Formation

This is the lowest formation of the group and crops out in the north-west of the district around Sedgeberrow. It is dominated by grey, more or less calcareous marine mudstone, but is characterised by the presence of thin beds of grey argillaceous limestone (cementstone) in repetitive cycles of sedimentation.

Charmouth Mudstone Formation

This was formerly known as the Lower Lias Clay. It floors the vales in the west and east of the district, and produces a brownish grey clay soil. The formation is dominated by grey mudstone, and the uppermost beds are somewhat siltier. Nodules and thin beds of argillaceous limestone are developed at some levels and some of these have been mapped at the surface locally. They are believed to include the 70, 85 and 100 geophysical marker 'members' (Figure 1) that were first described in the Chipping Norton district to the east. Fossils include Gryphaea and other bivalves, and ammonites.

Dyrham Formation

The Dyrham Formation (formerly the Middle Lias silts and clays) crops out on the lower slopes of the escarpments capped by the Inferior Oolite Group. It comprises grey mudstone and silty mudstone, with interbeds of highly micaceous, weakly cemented siltstone or very fine-grained sandstone. Brown micaceous sandstones are widespread close to the top of the formation. One bed, the 'Subnodosus Sandstone' crops out on Dumbleton Hill [SP 01 35], about 3 m below the Marlstone Rock; it is 1.5 m thick, and fine grained.

The Dyrham Formation is generally very poorly exposed, but it is seen at Aston Magna Brickworks [SP 199 354], where there are lenses containing ammonites, bivalves, gastropods, belemnites, echinoids, serpulids, brachiopods and fish debris.

Marlstone Rock Formation

The Marlstone Rock Formation forms a ledge along the Cotswolds escarpment and around the outlying hills. It is a brown to grey variably ferruginous sandstone containing limonitic ooids. Sporadic shells, mostly brachiopods occur, and the rock is locally rich in crinoid or serpulid debris. The formation includes at least three non-sequences and evidence of deposition in very shallow water. It is not well exposed, and in many places the outcrop is obscured by landslipping or cambering.

Whitby Mudstone Formation

The Whitby Mudstone Formation (formerly the Upper Lias) comprises dark grey, very finely silty and micaceous mudstone with fossils preserved in aragonite and sporadic beds of argillaceous limestone nodules. Pale limestone and sideritic ironstone beds, commonly conglomeratic, occur at the base of the formation in the east of the district. These beds generally contain abundant ammonites, and rest, with an erosive base, on the underlying Marlstone Rock.

Bridport Sand Formation

The Bridport Sand Formation (formerly known as the Cotteswold Sand) is best developed in the western and central parts of the district; eastwards, it passes into the Whitby Mudstone and both are overstepped by the Inferior Oolite. Widespread cambering and landslipping make it difficult to map the Bridport Sand Formation, and although it is thought to be present in the west, it is not shown extensively on sheet 217, but is included with the Whitby Mudstone. The formation consists of fine- to medium-grained sandstone, sand and silt.

In Eyford Park [SP 1449 2437], 3 m of micaceous sandstone of the Bridport Sand are overlain by a thin mudstone containing dark granules; this bed is similar to the Cephalopod Bed, which is the youngest unit of the Lias in the Cotswolds. Elsewhere in the district, the formation may be represented by traces of yellow sand at the base of the Birdlip Limestone.

Inferior Oolite Group

The Inferior Oolite Group of Mid Jurassic age is made up predominantly of shallow marine, ooidal and shell detrital limestone, with subordinate thin mudstone, calcareous mudstone and sandstone beds. Its outcrop forms a broad dissected plateau, bounded by escarpments, through the centre of the district, overlain in parts by the Great Oolite Group.The group is divided, in ascending order, into the Birdlip Limestone, Aston Limestone and Salperton Limestone formations, which correspond with the Lower, Middle and Upper Inferior Oolite of previous workers. The standard zonation of the Inferior Oolite, based on ammonites, is shown in (Figure 2).

Within the district, the Inferior Oolite Group is up to about 110 m thick, the thickest at outcrop in Great Britain, but eastwards it thins dramatically to 10 m or less in the vicinity of Stow-on-the-Wold (Figure 3). Sedimentation appears largely to have kept pace with subsidence for there is no indication of deeper water facies within the Worcester Basin. However, interruptions to sedimentation are marked by bored and oyster-encrusted hardground surfaces. The most important of these non-sequences occur at the two levels which separate the three formations of the Inferior Oolite Group. The strata above these non-sequences variously overlap or overstep the strata beneath. For example, the Aston Limestone Formation is overstepped by the Salperton Limestone Formation across the Vale of Moreton Axis.

Birdlip Limestone Formation

The Birdlip Limestone Formation (formerly Lower Inferior Oolite) comprises mainly ooidal, shell-fragmental, sandy and marly limestone, with subordinate sandstone, marl (calcareous siltstone) and mudstone. It is the thickest formation of the Inferior Oolite Group, reaching a maximum at Cleeve Hill. It is divided into five members (Figure 2) and these have been shown on the map where possible.

The Leckhampton Member (Scissum Beds of previous accounts) rests on the Bridport Sand Formation in the west of the district, overstepping onto the Whitby Mudstone Formation in the east. In places in the east, it is cut out entirely by the Salperton Limestone. It comprises grey limestone with thin beds of calcareous mudstone. The limestone is rubbly, ferruginous, sandy to argillaceous, shelly, peloidal and ooidal, and weathers to a yellow or orange-brown colour. Much of the non-carbonate material is probably derived from the underlying strata. It becomes sandier eastwards passing into the Northampton Sand Formation near Chipping Norton. This member is generally poorly exposed in the district, although its full thickness (locally 1.5 m) is visible in Eyford Park, and it is exposed at Cleeve Cloud [SO 9841 2549] (Plate 1). Fossils include brachiopods and large myacean bivalves; belemnites and ammonites are less common.

The Crickley Member is present only in the western half of the district (Figure 3). It consists of pale grey to yellow-brown, peloidal, ooidal and shell-fragmental grainstone (Lower Limestone of previous accounts) grading upwards into rubbly, poorly sorted, shelly, shell-detrital, pisoidal grainstone and packstone (Pea Grit of previous accounts). The full thickness, 6.9 m thick, is exposed at Cleeve Cloud (Plate 1). At outcrop, the pisoids may be found loose in the soil, together with fossils that include brachiopods, bivalves, gastropods, echinoids and corals.

The Cleeve Cloud Member (formerly Lower Freestone) is dominated by well-bedded, well-sorted medium- to coarse-grained ooidal grainstone. As a building stone of some importance, it is still well exposed in the district. In the west, the lowest third includes yellowish sandy ooidal limestone with burrows, the 'Yellow Stone' that weathers to brownish yellow hues. Farther east, this facies forms an increasing proportion of the member (Figure 3), and it becomes more ferruginous and markedly orange-yellow. At Cleeve Cloud, about 16 to 20 m of off-white to pale grey, markedly cross-bedded oolite is exposed (Front cover). An oyster-encrusted hardground occurs at the top of the member at Cleeve Hill and is seen elsewhere in the district.

The Scottsquar Member (equivalent to the Oolite Marl and Upper Freestone of previous authors) is dominated by pale grey and brown, medium- to coarse-grained peloidal and ooidal packstone and grainstone (Upper Freestone) in which beds of lower energy, white to mid-grey micrite and shell-detrital, peloidal, silty marl (Oolite Marl) occur. The Oolite Marl facies tends to predominate in the lower part of the member, and the Upper Freestone facies in the upper part, but the two facies interdigitate in a complex manner, and there is some local erosion. The full thickness of the Scottsquar Member is seen in several major quarries. In Cotswold Hill Quarry [SP 081 292], local penecontemporaneous erosion is evident from hardground formation, and at the nearby Jackdaw [SP 077 310] and Guiting [SP 080 305] quarries channelling has been observed. This facies has long been known for the richness and excellent preservation of its fauna that is dominated by brachiopods, including the distinctive terebratulid Plectothyris fimbria. Corals, serpulids and bryozoa also occur.

The Harford Member is laterally very variable although overall there is an ascending sequence of sandstone, mudstone and limestone. Where possible, these divisions have been differentiated on sheet 217, mainly in the north between Taddington [SP 087 311] and Blockley [SP 165 350]. The member contains a sparse fauna of bivalves and gastropods. The lithologies suggest deposition in a shallow-water, land-marginal environment. Sand and sandstone (up to 6 m thick) at the base is grey to orange-brown and fine to medium grained; it weathers to a light stoneless loamy soil. The overlying mudstone (up to 8 m) is grey to brown, silty, variably sandy or shell detrital. Limestone beds are shown on sheet 217 only around Taddington and Northwick Hill [SP 15 36], and are exposed at Jackdaw and Cotswold Hill quarries. The limestone is up to 2.5 m thick, pale grey and brown sandy, shell detrital, peloidal, and ooidal. In general, the Harford Member rests conformably on the Scottsquar Member (Plate 2), but a local non-sequence occurs at the base near Lower Swell [SP 163 251], and south-west of Blockley [SP 16 34] area the older Scottsquar Member is absent due to channelling at the base of the Harford Member or to a local lateral passage between the two. The type section of the member is at Harford railway cutting [SP 1363 2184].

Aston Limestone Formation

The Aston Limestone Formation (formerly the Middle Inferior Oolite or 'Ragstones') consists of limestone that is grey and brown, rubbly, ooidal, sandy, with a shell detritus, and contains sandy and marly beds in places. It is present in the western part of the district (Figure 3) thinning eastwards where it is ultimately cut out as a result of erosion beneath the Salperton Limestone Formation. Where complete, the formation is divisible into four members, in ascending order, the Lower Trigonia Grit, Gryphite Grit, Notgrove and Rolling Bank members (Figure 2), and where possible these have been shown on sheet 217.

The Lower Trigonia Grit Member comprises wackestone, packstone and grainstone that is grey, very shelly, moderately sandy, peloidal and ooidal. Many of the abundant peloids are ferruginous, producing a distinctive orange-brown speckled 'ironshot' appearance. It thins and becomes more marly and conglomeratic north-eastwards. It rests sharply and non-sequentially on the Birdlip Limestone Formation, and commonly contains pebbles of derived material at the base. The presence of a non-sequence within the member in places, as well as its northwards facies change and attenuation, indicate that it is becoming increasingly condensed, probably as a result of shoaling. The fauna includes ammonites, bivalves,brachiopods and colonial serpulids. Corals are common at the base on Cleeve Hill.

The Lower Trigonia Grit Member is fully exposed in the Harford and Aston Farm [SP 145 213] railway cuttings (0.7 to 0.3 m thick) and in Jackdaw Quarry (0.8 to 1.0 m).

The Gryphite Grit Member (formerly the Gryphite Grit and Buckmani Grit) comprises grainstones, packstones and wackestones, with thin calcareous mudstone and sandstone beds. The limestone is grey and brown, hard, rubbly, shelly, sandy and peloidal. The member generally rests non-sequentially on top of the Lower Trigonia Grit (where present) and is difficult to distinguish from it as both weather to grey-brown shelly rubble in a sandy clay soil. The fauna includes abundant Gryphaea and belemnites in the upper part, and the serpulid Sarcinella and the brachiopod Lobothyris buckmani in the lower part.

Over 4 m of the Gryphite Grit is exposed in Pot Quarry on Cleeve Hill [SO 9869 2667] (Angseesing et al., 2002), where it is notably rich in the oyster Gryphaea.

The Notgrove Member (formerly Notgrove Freestone) comprises ooidal grainstone that is pale brownish grey, well-bedded and commonly cross-bedded, medium to coarse grained and moderately peloidal. Where it immediately underlies the Salperton Limestone Formation (Figure 3), the top of the member is typically a well-developed, planed and oyster-encrusted hardground with abundant borings. The most conspicuous are narrow, near-vertical annelid borings that may penetrate as much as 0.3 m below the hardground surface. Burrows occur beneath the Rolling Bank Member in the upper part of the member, suggesting that possibly soft-sediment erosion may have occurred. At outcrop, the Notgrove Member produces a distinctive blocky brash of pale grey oolite with pieces of the heavily bored and oyster-encrusted hardground from its top.

The member is well exposed at its type section, Notgrove Railway Cutting, where the uppermost 1.8 m are visible (Plate 3). The fauna is generally very sparse, but shell debris occur in the lowest beds.

The Rolling Bank Member (formerly Witchellia Grit, Bourguetia Beds and Phillipsiana Beds) is named after the quarry on Cleeve Hill [SO 9872 2668] where it was once fully exposed (Angseesing et al., 2002; Cox and Sumbler, 2002). The member is present only in the western part of the district, on Cleeve Hill plateau and near Taddington [SP 081 324]. It consists of limestone that is variously shelly, sandy, ironshot, peloidal and ooidal, packstone and wackestone. Following conservation work by RIGS almost 5 m of the upper beds of the member are currently visible in the Rolling Bank Quarry (Plate 4). In addition, the lowest beds are exposed in the nearby Pot Quarry. Fauna of this member includes bivalves, brachiopods and ammonites.

Salperton Limestone Formation

The Salperton Limestone Formation (formerly Upper Inferior Oolite) comprises ooidal, peloidal, shelly and shell-fragmental limestones. In the west of the district, the formation rests unconformably on the Rolling Bank Member, but it progressively oversteps lower parts of the Inferior Oolite towards the east to rest on the uppermost beds of the Lias Group (Figure 3). The upper surface of the underlying limestone strata is generally a hardground, with borings and encrusting epifauna. The type section of the Salperton Limestone Formation is at Notgrove Railway Cutting [SP 0845 2090] to [SP 0862 2098], near the village of Salperton. It is divided into two members, the Upper Trigonia Grit Member overlain by the Clypeus Grit Member.

The Upper Trigonia Grit Member consists of grainstone and packstone that is very hard, grey and brown, shelly, moderately peloidal and ooidal. The limestone occurs as rubbly, medium to thick beds, at outcrop weathering to orange-brown, uneven slabs. The fauna is dominated by bivalves, including large myaceans and trigoniids commonly preserved as empty moulds; these are conspicuous on weathered slabs and other fossils include brachiopods. An extensive fauna of ammonites is known from the member, and indicates the Upper Bajocian Garantiana Zone (Parsons, 1980).

It is fully exposed at its type section, Notgrove Railway Cutting (Plate 3), where it is 1.0 to 1.2 m thick, and in Harford railway cutting it is 0.1 to 1.0 m thick.

The Clypeus Grit Member is the youngest and most laterally extensive unit of the Inferior Oolite Group in the Cotswolds, and forms broad plateau outcrops throughout the district. It comprises pale grey to yellowish or pinkish brown, fine- to coarse-grained, shell-detrital, ooidal and peloidal packstone and grainstone with subordinate wackestone. Characteristically, it contains sporadic, orange-skinned pisoids and aggregate grains, the latter suggesting reworking of partially cemented sediment. At outcrop, the Clypeus Grit weathers to rubble, producing a stony soil that commonly contains loose fossils. The abundant fauna includes ammonites, bivalves, brachiopods and the large echinoid Clypeus ploti. Below the Chipping Norton Limestone in the east, the top of the Clypeus Grit is sharp and locally marked by a planed and oyster-encrusted surface.

The full thickness of the Clypeus Grit is visible at its type section, Notgrove Railway Cutting, where it is between 10.5 and 12.0 m thick (Cox and Sumbler, 2002). The basal part of the member is exposed at Rolling Bank Quarry and Broadway Quarry.

Great Oolite Group and Ancholme Group

The outcrop of the Great Oolite Group occupies substantial areas on the plateau of the north Cotswold Hills. It was deposited in shallow water with some episodes of emergence. However, the succession is largely complete (Figure 4), and there is little evidence of the eastward overstep seen in the Inferior Oolite Group. Nonetheless, the Vale of Moreton Axis persisted as a zone of reduced deposition at the margin of the London Platform, and the Great Oolite Group is thinner here (45 to 55 m) than in the Cirencester district (60 to 90 m) to the south.

The Ancholme Group is represented by the Kellaways Formation, which is present as a small faulted outlier near Condicote.

Chipping Norton Limestone Formation

The Chipping Norton Limestone is the most widespread unit of the Great Oolite Group in the Moreton-in-Marsh district. The thickness of the formation is highly variable. It is thickest in the east, thins westwards (Figure 5) and dies out along a north-west to south-east line passing close to the village of Hawling [SP 065 230], a trend that is markedly transverse to the Vale of Moreton Axis. The formation is dominated by ooidal limestone, composed of pale brown to buff or grey, variably shell-fragmental, ooidal grainstone that is generally fine to medium grained and slightly sandy, but coarser limestones occur in places. Typically, the formation is cross-bedded with platy weathering. Thinly bedded, fine-grained limestone also occurs, and this has been worked for tilestones near Upper Swell. Other lithologies include calcareous mudstone, some oyster-rich or coral-bearing, and calcilutites. The basal beds of the formation tend to be particularly sandy and argillaceous with burrows and fragments of black lignite. Generally the contact with the underlying Salperton Limestone is sharp and in places is marked by a hardground.

Some ammonites and reptile remains have been recorded from New Park Quarry [SP 175 282] and Hornsleasow Quarry [SP 131 322]. Both sites have yielded vertebrate remains that include crocodiles, dinosaurs, mammal-like reptiles and 'eupanothere' mammals.

Fuller's Earth Formation

The Fuller's Earth Formation shows an eastward facies passage into the Chipping Norton Limestone (Figure 5), and locally, where the formation is absent the Taynton Limestone rests directly on Chipping Norton Limestone.

The lower part of the formation is dominated by grey mudstone, and the upper part consists of sandy limestone and sandstone, known as the Eyford Member. The mudstone weathers to a very heavy grey-brown clay soil. The best exposures occur at Huntsman's Quarry [SP 125 255] area, where there is interbedded laminated siltstone, fine-grained sandstone and limestone containing abundant small oysters and other bivalves.

The Eyford Member comprises grey sandy limestone or calcareous sandstone in beds typically 0.3 m thick, interbedded with soft, brown, fissile, poorly cemented bituminous sand and sporadic, very thin clay seams. The limestones include both massive bioturbated types, and well-laminated fissile types that were used as tilestones. The oyster Praeexogyra acuminata occurs in abundance in some of the limestones. The type section of the Eyford Member is Huntsman's Quarry, near Eyford Hill where it is up to about 7 m thick; it is also exposed at Hampen Cutting (Cox and Sumbler, 2002). In the past, these strata were worked as a source of tilestones for roofing, particularly in the Eyford and Sevenhampton Common areas, and were known as Cotswold Slates.

The rich fauna includes bivalves and ammonites. A vertebrate fauna includes crocodiles, dinosaurs and pterosaurs (Benton and Spencer, 1995). Fish, plants and insects have also been recorded (Savage, 1961).

Taynton Limestone Formation

The Taynton Limestone is confined to the central part of the district, where it generally overlies the Eyford Member. To the south-west (Figure 5) around Sevenhampton Common [SP 01 22] it passes laterally into the Hampen Formation. It is dominated by white to pale buff, medium- to coarse-grained, generally well-sorted, cross-bedded ooidal and shell fragmental grainstone. The limestones are cross-bedded with foresets indicating currents from the north-east. Thin calcareous mudstone and shelly beds occur in places. Fossils from the Taynton Limestone include bivalves and brachiopods.

The Taynton Limestone was used in many walls and vernacular buildings, so that there are many disused pits, and it is still worked at Brockhill and Grange Hill quarries [SP 135 238]; [SP 113 244].

Hampen Formation

Formerly known as the 'Marly Beds' and the 'Hampen Marly Beds', the Hampen Formation is actually dominated by limestone, which makes up 55 per cent of the thickness. Marl (calcareous mudstone) tends to predominate near the top and becomes increasingly dominant eastwards.

The dominant lithology is grey to brown, fine- to medium-grained ooid grainstone, variably sandy and shell-detrital, with mud flakes, whole shells and scattered coarse-grained white ooids. It has an oily or bituminous smell when freshly broken. The limestones are typically flaggy due to pervasive small-scale cross-bedding, and fissile ripple-bedded tilestones are common, with burrows and trails on bedding surfaces. Lenses of coarser grained limestone similar to the Taynton Limestone occur locally. The thicker limestone beds of the formation have been widely used in walls, and the fissile beds have been used for tiling. The calcareous mudstone beds are pale grey, shelly, ooidal, sandy, bituminous and shaly, and grade into argillaceous limestone. The type section for the formation is Hampen Cutting [SP 060 204] (Cox and Sumbler, 2002).

The fauna of the Hampen Formation are dominated by bivalves, including the oyster Praeexogyra hebridica, which may be cemented into lumachelles. Brachiopods (notably Kallirhynchia), gastropods, echinoids and corals also occur.

White Limestone Formation

The White Limestone Formation occurs as a number of faulted outliers between Hampen and Condicote; the lowest part is exposed in Hampen Cutting. The formation consists of limestone that is largely off-white to pale grey or pinkish brown in colour; it is a poorly sorted, peloidal, fine- to medium-grained wackestone with subordinate peloidal packstone and ooidal grainstone. Bedding varies from platy to massive. Thin beds of calcareous mudstone and clay also occur. Gastropods are abundant at certain levels, and brachiopods, corals, bivalves and echinoids also occur; ammonites are rare.

Forest Marble Formation

The Forest Marble Formation forms several small faulted outcrops in the centre of the district. It consists largely of mudstone, which forms a brown clay or loamy clay soil. Brash of flaggy, oyster-rich, shell-fragmental ooidal limestone and fissile sandy limestone occurs in places.

Cornbrash Formation

The Cornbrash is the uppermost formation of the Great Oolite Group, and is preserved adjacent to the faults on either side of the Kinetonhill graben [SP 137 281]; [SP 138 263]. The limestone is typically very compact due to recrystallisation, and generally lacks bedding structures. It produces a brash of orange-brown, rubbly to platy, finely shell-fragmental, slightly sandy packstone.

Kellaways Formation

The Kellaways Clay Member of the Kellaways Formation is the basal unit of the Ancholme Group. It consists of dark blue-grey and purplish grey clay with pyritic patches. It is estimated that about 3 m of Kellaways Clay is present in a faulted outlier in the Kinetonhill graben [SP 137 282], but it is possible that the Kellaways Sand or even the succeeding Oxford Clay Formation, which crop out elsewhere in the region, may also be present here.

Quaternary

Northern Drift Formation

The preglacial Northern Drift Formation is now generally believed to represent a suite of ancient river terrace sediments laid down during early and mid Pleistocene times, by an ancestral Thames–Evenlode river with headwaters in the English Midlands and Welsh Borders (Whiteman and Rose, 1992). Most of the pebbles can be matched with material in the conglomerates of the Triassic Kidderminster Formation (Bunter Pebble Beds) and Devonian Old Red Sandstone, which crop out in these areas.

The Northern Drift Formation deposits in this district are assigned to the Combe Member, which caps hilltops and spurs on the margins of the Evenlode valley south-east of Moreton-in-Marsh (at up to about 150 m OD) and at Pebbly Hill near Bledington (about 137 m OD). The outcrops are characterised by a loamy soil with abundant quartz and quartzite pebbles, with some larger cobbles and boulders.

Baginton Formation

In the north-east of the district, a deposit of cross-bedded sand with quartz and quartzite pebbles up to 9 m thick has been recorded beneath the Paxford Gravel. This is the Stretton Sand, which is inferred to lie in a channel from Ditchford Hill to Stretton Hill [SP 219 382] to [SP 219 372]. It has not been mapped as it is not possible to separate it from the Paxford Gravel. From its elevation, it is younger than the Combe Member, and has yielded a fauna that suggests correlation with the Baginton Formation of the Coventry area (Sumbler, 2001).

Wolston Formation

Formerly referred to as the 'Moreton Drift', an assemblage of glacial and associated deposits that occurs in the Vale of Moreton is now assigned to the Wolston Formation, which is probably Anglian in age; (Figure 6); (Bowen, 1999). The formation lies at the head of a northward-trending preglacial valley, probably the Proto-Soar/Bytham River. The internal stratigraphy of the deposits suggests that ice advanced from the north or north-east down the Bytham valley, and that ice-ponded waters escaped into the Evenlode valley through a col at Adlestrop. Members of the Wolston Formation, in ascending order, are Paxford Gravel Member, Moreton Member, Oadby Member, Wolford Heath Member (Sumbler, 2001).

The Paxford Gravel Member encompasses all the sand and gravel (other than the Stretton Sand) that occur at the base of the drift succession, and outcrops in the north-east. It is typically a poorly sorted limestone-rich gravel, with subangular to subrounded pebbles composed mainly of local Inferior Oolite lithologies. Sporadic Lias fossils occur, and other lithologies including sparse flint and chalk. It also includes lenses of clay and silt, suggesting that it interfingers with the overlying Moreton Member. In places, glaciofluvial outwash gravels (Oadby Member) with flints and chalk interdigitate with limestone-rich gravel and so the Paxford Gravel as mapped includes materials from substantially different phases of the glaciation.

The Moreton Member is a heterogeneous assemblage of silt, sand and clay that floors the Vale of Moreton north of Lower Oddington [SP 230 260]; this is believed to be the southern limit of glaciation in the region. Up to 21 m have been proved in boreholes. The member is composed of soft silty clay, silt and silty sand, generally reddish or ochreous brown and grey in colour, with a few scattered flints and chalk and commonly with a poorly laminated structure. Locally, the deposits include brown, plastic, laminated clays. Stonier, reddish brown diamicton (till) occurs and has been distinguished on sheet 217. Typically these tills dominate the lower part in the south, and interdigitate with other Moreton Member lithologies. A few lensoid bodies of sand and gravel occur e.g. [SP 190 314]. The association of sand and laminated clay and silt with Trias-rich till suggests accumulation in proglacial lakes, water ponded up in front of glacier ice. The maximum height of the water-laid deposits (137 to 140 m OD) may relate to a col, which probably lay between Lower Oddington and Adlestrop. The lake drained south over the Adlestrop col down the Evenlode and into the Thames.

The Oadby Member occurs as outliers north of Moreton-in-Marsh. It generally overlies the Moreton Member, but cuts down onto Paxford Gravel or bedrock in places. It is generally a few metres in thickness with a probable maximum of 15 m at Wolford Wood [SP 236 332]. Tills (Oadby Till) make up the bulk of the deposit, comprising grey to brownish diamictons with erratics of flint and chalk, and subordinate limestone, quartz, quartzite, sandstone and Charmouth Mudstone fossils. Glaciofluvial sand and gravel bodies within the Oadby Member have been separated on the map locally.

The Wolford Heath Member consists of poorly sorted gravels, containing flint, quartz/quartzite and other pebbles and cobbles (up to 20 cm across), set in a clayey sand matrix. The gravels are commonly highly ferruginous, and locally iron pan is developed. The member forms a dissected sheet-like body that is best preserved around Moreton-in-Marsh, where it is up to about 4 m thick. The deposit is interpreted as a valley sandur of outwash gravels, derived from the Oadby Member ice, and represented farther downstream by the Daylesford Member.

Upper Thames Valley Formation

This term is used to encompass all of the river terrace deposits (excluding the Northern Drift Formation) of the upper River Thames and its tributaries such as the Evenlode and Windrush (Figure 6).

The Freeland Member (formerly regarded as the youngest unit of the Northern Drift Formation) comprises pinkish brown sand with abundant quartz and quartzite pebbles; flints occur rarely. It outcrops downstream from Evenlode village [SP 222 291], and probably represents outwash from the Moreton Member, deposited when ponded waters drained southwards through the Adlestrop col; it has been equated with the Anglian glaciation (Bridgland, 1994).

The Daylesford Member encompasses the terraced sand and gravel deposits along the upper Evenlode. The soil on the terrace is a reddish brown loam with abundant quartz and quartzite pebbles and up to 30 per cent flint. Local limestone pebbles and ironstone are also generally present. The deposit was formerly worked and up to 4.6 m were exposed.

In the vicinity of Bourton-on-the-Water, two gravel terraces (Sherborne and Rissington members) have been recognised along the rivers Windrush, Dikler and Eye. Correlation with the Thames succession downstream is uncertain. The deposits of the Sherborne Member form a degraded terrace generally about 5 to 6 m above the present-day floodplain. They are over 6 m thick, locally extending below the floodplain, and are composed mainly of locally derived limestone gravel, with pebbles up to 8 cm. The member probably originated as head, derived from the scarp to the west, which has undergone further reworking. The gravel was formerly worked in a number of pits in which woolly mammoth (Mammuthus primigenius) and woolly rhinoceros (Coelodonta antiquitatis) remains have been found (O'Neil and Shotton, 1974); they are probably 'Wolstonian' to earliest Devensian in age.

The Rissington Member forms a well-developed terrace up to 2 m above the floodplain. The gravel is generally finer grained than that of the Sherborne Member; pebbles are up to 4 cm across. The member was formerly worked in the southern part of Bourton-on-the-Water. The distribution of the now flooded pits shows that the deposits extend beneath the alluvium; records indicate that they may be up to 5 m in thickness.

Undifferentiated river terrace deposits occur near Sydenham Farm [SP 221 271], where three poorly defined gravel terraces are evidently associated with the Caudwell Brook. They comprise limestone-dominated gravel and sand with quartz and quartzite pebbles.

Avon Valley Formation equivalent

Terrace deposits of the River Avon/Carrant Brook

Along Carrant Brook in the north-west of the district, sand and gravel deposits form a more or less continuous slope on the north side of the valley extending over a vertical height of 15 to 20 m, and comprising the Beckford Terrace of Briggs et al. (1975). On the map they have been subdivided and correlated with the Avon terraces on the basis of the stepped profile at the base of the deposit. The highest (oldest) deposits are provisionally assigned to the Fourth Terrace (Cropthorne Member of the Avon). They comprise up to 4.5 m of sandy, limestone-dominated gravel, with medium- to coarse-grained sand beds. The lower and greater part of the outcrop is assigned to the Second Terrace (Wasperton Member). North of Carrant Brook the deposits have been extensively worked for aggregate around Beckford. Exposures show sandy well-rounded limestone gravel, somewhat finer grained than the Fourth Terrace deposits, with some interbedded sand. South of Carrant Brook, the deposits are assigned to both Second and First Terrace (Bretford Member) and consist of sandy clay with sparse gravelly material.

Terrace deposits of Knee Brook

In the north-east of the district, fairly extensive but poorly developed terraces are developed about 1.5 m above the floodplain. The deposits consist mainly of sand with pebbles of limestone and some flint, quartz and quartzite, and clay, and are up to about 2 m thick. The material has largely been reworked from local head gravel. They are classified as First Terrace, but this designation is purely local and no long-distance correlation is implied, although it seems probable that they represent the Bretford and/or Wasperton members of the Avon Valley Formation.

Alluvium

Alluvial floodplains are present along the courses of the rivers and streams. In the vales, the alluvium is generally brown, silty clay, derived largely from weathered Lias Group. It is overlain by a dark brown, humic, loamy clay soil. This loam and clay is about 1 m in thickness, and may overlie limestone gravel or sand. In the upper Evenlode valley, the alluvium overlies glacial and glaciofluvial deposits, which is reflected in its composition. The alluvial deposits are still accumulating with thin layers of mud being left on the fields after floods.

Along the higher reaches of the Coln, Windrush, Eye and Dikler and their tributaries, the floodplain is generally less than 100 m wide and the alluvium infills a channel incised into bedrock. Typically, the alluvium is a brown peaty loam or brownish grey clay, commonly with disseminated tufa as silt or pellets, and no more than 1.5 m thick; the underlying gravel (about 1 m thick) consists of locally derived limestone.

Tufa

Tufa is a calcareous deposit, precipitated around springs from water that has percolated through limestone and is saturated with calcium carbonate. Most of the deposits are too small to be shown on sheet 217, but one is depicted near Winchcombe [SP 023 371].

Cheltenham Sand and Gravel

Substantial deposits of head gravel between Gotherington and Cheltenham are separated as Cheltenham Sand and Gravel. This forms a gently sloping dissected apron at the foot of the Cotswold scarp. Thickness is up to 15 m, but varies widely over short distances. It was laid down partly in deep channels running from the foot of the scarp, probably scoured by meltwater. The deposit consists of yellowish brown, medium-grained quartz sand with beds of poorly sorted predominantly limestone gravel at the base and also in those parts close to the scarp. The age of the Cheltenham Sand and Gravel is uncertain; it is probably largely of Devensian age (Figure 6).

Head

Head and dry valley deposits consist of accumulations of solifluction debris of periglacial origin and more recent hillwash (colluvium). They occur in most of the valleys and on some slopes in the district, but only the thicker, laterally more extensive deposits are shown on sheet 217. The lithology varies according to the materials from which the deposits were derived.

Because of the permeability of the bedrock dry valleys in the Cotswolds normally contain streams only when the water table is particularly high (see p.25). Examples include the upper reaches of the Dikler and the Eye, and tributary valleys of the rivers Windrush and Coln. Typically, a flat, floodplain-like tract of brown loamy clay overlying limestone gravel (up to 2 m thick) and evidently an ancient alluvium, floors such dry valleys. This is partially or wholly covered by gravelly solifluction material, and thus all of the deposits of the dry valleys are indicated as head on sheet 217.

Head gravel deposits are most extensive on the low-lying ground in the north-west of the district, where they form gently sloping, fan-like tracts that extend for several kilometres from the foot of the escarpment. They are coarse-grained, unstratified, angular or subangular limestone gravels of local origin, with some bodies of sand and clay, overlain by a brown loam and pass downhill into finer grained, stratified gravel and sand. Geophysical investigations between Broadway and Winchcombe indicate channels several metres deep in the underlying mudstone, radiating from the base of the escarpment. Their formation by solifluction during repeated cold climate episodes has led to interdigitation with river terrace deposits.

In general, head gravel deposits are not widespread in the eastern part of the district, and some have probably been incorporated into fluvial deposits.

Landslip

Landslips have occurred widely throughout the district wherever mudstone or, in some places, sandstone crop out on a slope. The largest landslips have been recorded along the main Cotswold escarpment and around Bredon Hill, where they principally affect the Whitby Mudstone Formation. Less extensive slipping occurs along the slopes of the vales of Moreton and Bourton between Chipping Campden and Bourton-on-the-Hill, around Stow-on-the-Wold and Icomb Hill. The upper limit of the slip is marked by large, arcuate scars, generally in the basal beds of the Inferior Oolite. Below the scar, rotated masses of limestone-capped mudstone form terrace-like features with their tops sloping slightly in towards the hillside. Farther downslope, the uneven ground reflects the complex rotational and translational processes within the landslips. Below the slip, mudflows may cover the lower slopes. In addition, less extensive landslips may affect the outcrops of the Dyrham Formation. The most intensive period of landslipping probably occurred during periglacial phases of the Pleistocene, but signs of recent activity were observed in many places.

Landslips also affect the Fuller's Earth outcrop around Hawling and Brockhampton commonly overriding the Salperton Limestone outcrop.

Structure

At surface, the predominant fault trend in the district is east-south-east; throw is generally in the order of a few metres, but some faults with larger displacements, between 20 and 40 m, may be traced for several kilometres, and some graben structures occur.

A set of north-north-east-trending faults occurs in the eastern part of the district, from near Chipping Campden to Bourton-on-the-Water. Geophysical surveys suggest that these are the surface expression of the eastern margin of the Worcester Basin (see p.2). These faults thus mark the Vale of Moreton Axis that is recognised by a marked thinning in the Jurassic rocks.

At outcrop the strata dip predominantly to the south or south-east at an angle of about 0.5°. Where the dip is higher this is generally due to cambering or valley bulging.

Cambering and valley bulging

Valley bulging and cambering are caused by the deformation and consequent movement of clay where it is subject to the load of overlying strata. These structures originated during a period of intense cold that prevailed during the Pleistocene glaciations. Generally, they are not active at the present time except along escarpments, but their effects must be considered as potential engineering hazards. The approximate extent of known cambering is shown in an inset map on sheet 217.

In this district, valley bulging occurs mainly within the Charmouth Mudstone and Whitby Mudstone formations. In the Vale of Gloucester, the inferred eastward dip of the Charmouth Mudstone strata in the Cheltenham–Oxenton area may be, in part, a result of valley bulging, and in the Vale of Moreton it may account for the relatively narrow outcrop of the Dyrham and Whitby Mudstone formations and the anomalous dips on the mapped outcrops of the 85 and 100 markers east of Icomb. Along the valleys of the Dikler, Windrush and Eye the outcrops of the Whitby Mudstone Formation are inferred to be substantially deformed by valley bulging where they occur at elevations up to 25 m higher than might be expected. In places the adjoining strata have been disrupted and steep dips are observed.

In the north Cotswolds, cambering affects the resistant limestone or sandstone strata (cap-rock) overlying mudstone formations, and is associated with valley bulging near escarpment edges and on plateaux. It also affects thin limestone beds within mudstone sequences. Where mudstone beds have bulged, the overlying cap-rock strata may be disrupted, laterally extended and lowered as a camber, comprising blocks separated by 'dip and fault structures' in the cap-rock. The faults show displacements of 1 to 3 m, and are closely spaced (up to 15 m). Cambering of thick cap-rock sequences (20 to 90 m) on escarpments may result in outward movement causing parallel vertical linear voids or gulls to open (p.21).

The Birdlip Limestone outcrops of Bredon Hill, the flanks of Cleeve Hill and Stanley Hill are extensively cambered. Surface gulls are found on many of the slopes, forming linear hollows up to 8 m deep, 60 m wide and 500 m long, including a gull known locally as Happy Valley [SO 991 239]. It has been estimated that up to 53 m of strata is missing beneath the tips of the cambers on Bredon Hill, and downslope extension of over 200 m has occurred on the south side of the hill. Along the main escarpment, where a much greater thickness of Inferior Oolite Group strata is present, intense gull formation has taken place. In places including around Broadway Tower (Plate 5) up to five surface gulls may lie side-by-side, parallel to the escarpment edge. These are up to 1.2 km long, 30 m across and 5 m deep with subsurface structures up to 80 m deep. Near Broadway Tower, it was reported that a line of hollows 200 m long had opened [SP 115 359] and an underlying gull cave had been explored for some distance. Overlooking the Vale of Moreton, cambering and intense gull formation was observed in the Inferior Oolite from Chipping Campden to Longborough.

Chapter 3 Applied geology

Geotechnical properties of formations

A broad classification of the engineering behaviour of the principal (solid) geological formations that crop out in the district is shown in (Figure 7). The natural superficial deposits comprise combinations of normally consolidated and over-consolidated clay, silt, sand and gravel. The varied nature of the geological materials and the effects of periglacial processes influence ground conditions in ways pertinent to land use and construction.

Pleistocene periglacial activity has caused the bedrock to be disrupted to a depth of several metres. Limestones are generally broken-up in the near-surface zone, and bedding and joint planes are dilated. Mudstones are also disrupted, and show an increase in moisture content, and reduction in strength to firm or soft clay. Thus, strength measurements should be obtained by in situ methods (Higginbottom and Fookes, 1971). It is likely that material of contrasting properties is present within the superficial deposits and it is important that a site investigation appropriate to the individual development is carried out to determine the precise nature of the materials present.

In general, the limestones of the district offer good foundation conditions, but some may contain cavities and voids. These may take the form of widened joints, a few centimetres across, or more significantly they may be found in the form of gulls. These are linear, tensional features that occur in cambered strata, and present significant problems for land use and construction on upper valley slopes and plateaux. Gulls may be open or more or less filled by material from above with a bearing capacity and compressibility very different from that of the surrounding limestone. In some instances open gulls may be bridged, and possibly concealed, by naturally cemented limestone, although in this district it is thought that most gulls show a hollow at the surface (Plate 5). In addition, the possibility of man-made voids should be considered. Backfilled quarries may no longer be apparent at the surface.

The mudstone in the district may offer reasonable foundation conditions if suitable designs are adopted. They are generally of high plasticity but may range from intermediate to very high plasticity. In the weathered zone, strength is likely to be lower and plasticity higher. High plasticity clays are particularly prone to shrink-swell problems (Building Research Establishment, 1980a, b; 1985, 1993). Low (remoulded) strength values may be encountered in landslipped mudstone and clay. The disposal of surface water away from areas of actual or potential landslipping is particularly important. Valley bulged mudstone formations are also likely to have suffered a loss of strength.

Geotechnical data for similar geological formations in other districts (Forster et al., 1995) indicate that conditions for sulphate attack on concrete foundations excavated within limestone units below the water table are likely to fall into Class 1 as defined in Building Research Establishment Digest 363 (1991). Similarly, most mudstone units in the area are likely to fall into Class 1 or 2, except for the Charmouth Mudstone Formation, which is likely to be Class 3. However, unless there is a high level of dissolved sulphate in groundwater that is flowing and in contact with the concrete structure, there is unlikely to be a significant problem of sulphate attack. Geotechnical data for alluvium in other areas indicate that conditions for sulphate attack on concrete foundations below the water table are likely to fall into Class 1 (Building Research Establishment Digest 363, 1991).

The sandstone units of the district should offer reasonable foundation conditions where they are sufficiently dense and are protected from erosion. Shallow foundations in sandstone may be affected by frost heave.

Alluvium and till are the natural superficial deposits that are most significant in the context of construction. Alluvium is generally a soft to firm, compressible material, and does not usually offer good foundation conditions. Where peaty or organic layers or lenses are present, it may suffer from differential consolidation. Alluvium may also have a desiccated crust with a higher strength than the underlying material. Till is a heterogeneous deposit that ranges from over-consolidated, stiff to very stiff, plastic clay to very dense sand and gravel. The variability in thickness and composition of alluvium and till necessitates investigation and determination of geotechnical properties for individual sites.

Slope stability

All geological formations may exhibit some form of slope instability under some circumstances, but within the Moreton-in-Marsh district, the Dyrham, Whitby Mudstone and Fuller's Earth formations are most commonly affected. These formations include highly plastic clays, and underlie strata that act as aquifers. The clay at the interface reduces in strength as pore water pressure increases, ultimately failing and leading to relatively deep-seated rotational or translational slides. Surface water increases the moisture content in the near-surface zone, including landslipped material, leading eventually to the development of mudflows. The progression from the terraced slopes of multiple rotational failure, downhill through the hummocky ground of mud and debris-slides, to spreading, lobate mudflows, is commonly seen on slopes in the district.

The most intensive period of landslipping probably occurred during periglacial phases of the Pleistocene, but some of the landslips within the district are still intermittently active, as demonstrated by fresh cracks in the ground, tilted trees and buildings or roads showing structural damage or even partial burial. In Cleeve Hill village, there are recent instances of building collapse and road damage requiring frequent repairs. The surface expression of inactive landslips may be obscured within very few years (Hutchinson, 1967), but the material will remain weak and contain shear surfaces that may be reactivated if the pore water pressure rises or the slope is undercut. Before construction work takes place on slopes in susceptible clay formations, investigations should be made for evidence of past movement, such as relict shear surfaces.

Artificial ground

Not all artificial ground (worked wround and infilled ground, made ground and disturbed ground) is shown on the 1:50 000 series sheet 217. Made ground comprises fill on the existing ground surface, and is mainly engineered, such as road and rail embankments. Worked ground and infilled ground are excavations that may be partially or wholly backfilled, including road and railway cuttings. However, the majority are quarries or gravel pits. The most extensive backfilled quarries are Slade Quarry [SP 071 215], which has been entirely filled with refuse, and the limestone quarry at Saintbury Hill [SP 126 385] now partly backfilled with construction waste. The main areas of disturbed ground are associated with shallow tilestone workings in the Eyford Member near Naunton, and the Chipping Norton Limestone near Snowshill.

Hydrogeology and water resources

In the Moreton-in-Marsh district, the aquifer formed by the Inferior Oolite together with the Bridport Sand and the Chipping Norton Limestone is the principal source of groundwater; it thins from 110 m in the west to less than 15 m in the east. These strata crop out and are thus unconfined with an extensive recharge area over much of the district; locally they are confined by younger beds. The aquifer is highly permeable; transmissivities are highest in the west.

The mean annual rainfall in the district ranges from 650 mm on the low ground to more than 850 mm on the high ground. Recharge of the limestone aquifer has been estimated at 370 mm/a (Morgan-Jones and Eggboro, 1981) and over much of the high escarpment is in excess of 450 mm/a. The water resources of the district are administered by the Midlands and Thames regions of the Environment Agency.

Groundwater abstraction, protection and chemistry

The limestones of the Inferior Oolite and Great Oolite groups constitute major aquifers as defined by the Environment Agency (National Rivers Authority, 1995a, b, c; Environment Agency, 1996; Allen et al., 1997), and there are several minor aquifers (Jones et al., 2000), or variably permeable solid formations and superficial deposits. The regional groundwater flow in the aquifers is down-dip towards the south-east. The mudstones and other lithologies are classified as non-aquifers or are negligibly permeable. Groundwater in the district is naturally of high quality, but it is highly vulnerable to contamination from both diffuse and point-source pollutants. The soils on the aquifer outcrops have little ability to attenuate pollutants, and liquid discharges may move rapidly through them to underlying strata or shallow groundwater.

Licensed groundwater abstractions within the district total 7 661 000 m3/a; the great majority (96%) is taken from the Inferior Oolite aquifer. Most is used for public supply by Thames Water Utilities and Severn-Trent Water. Major pumping stations are sited at springs issuing from the base of the Inferior Oolite at a number of locations.

The Charmouth Mudstone and Whitby Mudstone formations are generally poor aquifers due to their low permeabilities. However, the Cheltenham Spa saline mineral waters, which show large variations in chemistry, derive from over 50 wells and springs in the Charmouth Mudstone, although the true chalybeate (iron-rich) springs of Cheltenham originate from the superficial deposits (see below). A number of springs and seepages occur at the base of the more permeable Dyrham Formation.

The Great Oolite aquifer comprises up to 25 m of limestone above the Fuller's Earth. However, yields from wells are generally low, and it becomes a more important aquifer farther south.

Many permeable superficial deposits yield water to springs, wells and boreholes, although some sources are now polluted by surface contamination.

Many springs along the escarpments issue from within landslips, but the water has actually percolated down from the interface of permeable strata on impermeable mudstone through displaced limestone strata or fissures and shears. The largest spring of this type is at Stanway [SP 0748 3237], which yielded 19.4 l/s in a dry summer.

The major ions in waters from these unconfined aquifers are calcium and bicarbonate, with tufa deposits common at springs. Iron and fluoride concentrations are low, but water from some springs and wells exceeds the European Community maximum admissible concentration for nitrate, due to inputs of agricultural fertiliser and contamination from septic tank discharges (Morgan-Jones and Eggboro, 1981).

In the limestone aquifers changes in hydrostatic head may be transmitted rapidly over long distances. This may affect borehole water levels and spring flows at several kilometres distant. These substantial and rapid changes can result in rivers having very high peak flows in winter that fall rapidly in summer, as groundwater levels decline. In dry years this can cause intermittent flow in the rivers and streams traversing the plateau where they cross the aquifer outcrops, for instance in the Dikler north-east of Condicote and the Windrush around Naunton. Additionally, some abstractions may be unable to operate throughout the year.

Mineral and energy resources

Up-to-date information on quarry operators is available from BGS in the form of the Directory of Mines and Quarries (latest edition 2002).

Building stone

The use of local limestones for building purposes has given the towns and villages of the district their typical Cotswold character. Pale grey to yellow-brown limestones from the Great Oolite and Inferior Oolite have been quarried in the district since Roman times. From the medieval churches and manors to modern housing projects, the limestones have been in continuous demand for building purposes (Clifton-Taylor, 1972). The dry-stone field walls that are so characteristic of the Cotswolds were generally constructed from the most convenient stone that came to hand and almost every field had its quarry.

For building construction, the masons preferred certain limestone beds. The Birdlip Limestone Formation was quarried for building stone at many localities, notably Jackdaw Quarry, Syreford, Temple Guiting, Bourton-on-the-Hill, Saintbury Hill and Westington Hill and in galleries at Whittington, Syreford and Westington Hill. It is still quarried on a large scale at ARC Guiting and Cotswold Hill quarries at Ford, and at Stanley and Broadway quarries near Chipping Campden. The characteristic honey-coloured oolite is much in evidence in many of the buildings of Broadway, Chipping Campden, Winchcombe, Bourton-on-the-Water, and Cheltenham. Exceptional examples in the district of buildings constructed from this stone include Stanway House [SP 061 323], Sudeley Castle [SP 031 276] and Batsford Park [SP 185 336], as well as many parish churches, for example, St James's, Chipping Campden.

Roofing tilestone

The use of local tilestones for roofing contributes much to the character of local buildings. The fissile, sandy limestone of the Eyford Member was the premier source of 'Cotswold slate', and was extensively quarried north and east of Naunton [SP 13 25] and [SP 13 23] and north of Whittington [SP 01 22]. The Chipping Norton Limestone is also fissile, and widespread shallow workings in this formation are found between Snowshill [SP 09 33] and Hinchwick [SP 14 30]. Currently, tilestones are quarried from the Eyford Member at Brockhill Quarry [SP 133 238].

Bulk minerals

Most of the limestones have the potential for use as crushed aggregate in construction, and nearly all have been used at some time for this purpose. Currently crushed aggregate is produced at ARC Guiting and Cotswold Hill quarries at Ford (Birdlip Limestone Formation), and Huntsman's Quarry (Eyford Member) at Eyford Hill.

The sand and gravel resources of the district lie within Quaternary deposits, including Cheltenham Sand and Gravel, head gravel, alluvium, river terrace deposits, and glaciofluvial deposits of the Wolston Formation. Extensive spreads of Cheltenham Sand and Gravel occur around and to the north of Cheltenham. This was formerly used as a source of sand, but it is now sterilised by development. Head gravel deposits occur widely in the north-west and have been worked near Beckford [SO 955 355]; [SO 966 358], together with underlying river terrace deposits. These deposits may constitute a potential sand and gravel resource but are likely to vary in composition and especially thickness, and may include clayey lenses.

River terrace deposits have been worked along the north side of Carrant Brook, in the north-west, and around Bourton-on-the-Water, but this has now ceased.

Potential resources of glaciofluvial gravel remain at Ditchford and Todenham, and gravel was worked around Moreton-in-Marsh, but the deposits, though very extensive, are too thin and clayey to have much resource potential.

The Charmouth Mudstone Formation was formerly worked for brickclay at Battledown [SO 962 218] and Harp Hill [SO 967 224] in Cheltenham, and at Aston Magna [SP 199 354], where the Dyrham Formation was also utilised. The only current works is Northcot Bricks Ltd at Blockley [SP 180 370].

Coal

The eastern part of the district includes the westernmost part of the Oxfordshire Coalfield (Dunham and Poole, 1974). As proved in the Cirencester district, the coal seams are thin and not of workable quality, and there is little likelihood that they will be worked in the foreseeable future.

Hydrocarbons

Commercial exploration surveys, including seismic profiling and the drilling of the Guiting Power and Ash Farm boreholes, were carried out during the 1970s and 1980s in this and adjoining districts. Despite minor gas shows at some levels, the lack of suitable source rocks for much of the district indicates low prospectivity.

Information sources

BGS publishes an extensive range of geoscience maps, memoirs, regional geology guides, offshore regional reports, technical reports and other publications for the United Kingdom and adjacent continental shelf; these are listed in BGS Catalogue of geological maps and books, available on request. A data catalogue is also available at the BGS web site (addresses on the back cover).

Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. Geological advice for this area should be sought from the Regional Geologist, Integrated Geological Surveys (South), BGS, Keyworth.

Other geological information held by the British Geological Survey includes borehole records, fossils, rock samples, thin sections, hydrological data and photographs. Searches of indexes to some of the collections can be made on the Geoscience Data Index system available in BGS libraries and on the web site. Some of the geological information specific to the Moreton-in-Marsh district is listed below.

Maps

Books and reports

Documentary collections

Borehole records BGS holds the records of approximately 315 boreholes and wells for the district (March 2001). For further information and conditions of access contact the Chief Curator, BGS Keyworth.

Hydrogeology Data on water boreholes, wells and springs are held in the BGS (Hydrogeology Group) databases at BGS Wallingford.

Material collections

Copies of 79 photographs Geological Survey photographs taken in the district are deposited for reference in the library at BGS, Keyworth, Nottingham. Black and white prints and colour prints for the more recent photographs can be supplied at a fixed tariff. In addition, the British Association for the Advancement of Science collection of geological photographs is held at BGS Keyworth.

The registered Petrological collection for the Moreton-in-Marsh district comprises 132 hand specimens and thin sections. Further information including methods of accessing the database, charges and conditions are available on request from the Curator, Petrography and Mineralogy Collections, BGS Keyworth.

Macrofossils from some 188 localities are held in the BGS Biostratigraphy collections. Enquiries should be directed to the Curator, Biostratigraphy Collections, BGS Keyworth.

Mineral industry operators (2002) thirteen active quarries in the district are listed in the BGS Directory of Mines and Quarries (2002 edition).

Eleven Sites of Special Scientific Interest (SSSI) lie wholly or partly within the district. For further information contact English Nature, Northminster House, Peterborough PE1 1UA.

References

A complete bibliography for this district together with a full geological account is given in the sheet description(Barron et al., 2002). Most of the references listed here are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies can be purchased from the Library, subject to the current copyright legislation.

Allen, D J, Brewerton, L J, Coleby, L M, Gibbs, B R, Lewis, M A, MacDonald, A M, Wagstaff, S J, and Williams, A T. 1997.The physical properties of major aquifers in England and Wales. British Geological Survey Technical Report, WD/97/34. Environment Agency R and D, Publication No. 8.

Angseesing, J, Barron, A J M and Campbell, M. 2002. Geology on Cleeve Hill: enlarged sections in the Aston Limestone Formation (Middle Inferior Oolite).Proceedings of the Cotteswold Naturalists' Field Club, Vol. 42, 128–145.

Barron, A J M, Sumbler, M G, and Morigi, A N. 1997. A revised lithostratigraphy for the Inferior Oolite Group (Middle Jurassic) of the Cotswolds, England.Proceedings of the Geologistsꞌ Association, Vol. 108, 269–285.

Barron, A J M, Sumbler, M G, and Morigi, A N. 2002. Geology of the Moreton-in-Marsh district. Sheet Description of the British Geological Survey, Sheet 217 (England and Wales).

Benton, M J, and Spencer, P S. 1995. Fossil reptiles of Great Britain.Geological Conservation Review Series. No. 10. (London: Chapman and Hall.)

Bowen, D Q (editor). 1999. A revised correlation of Quaternary deposits in the British Isles. Geological Society of London Special Report, No. 23.

Bridgland, D R. 1994. The Quaternary of the Thames.Geological Conservation Review Series. (London: Joint Nature Conservation Committee and Chapman and Hall.)

Briggs, D J, Coope, G R, and Gilbertson, D D. 1975. Late Pleistocene terrace deposits at Beckford, Worcestershire, England. Geological Journal, Vol. 10, 1–16.

Building Research Establishment. 1980a. Low rise buildings on shrinkable clay soil. Part 2. Digest. No. 241. (Watford: Building Research Establishment.)

Building Research Establishment. 1980b. Low rise buildings on shrinkable clay soil. Part 3.Digest. No. 242. (Watford: Building Research Establishment.)

Building Research Establishment. 1985. The influence of trees on house foundations in clay soils.Digest. No. 298. (Watford: Building Research Establishment.)

Building Research Establishment. 1991. Sulphate and acid resistance of concrete in the ground.Digest. No. 363. (Watford: Building Research Establishment.)

Building Research Establishment. 1993. Low rise buildings on shrinkable clay soil. Part 1.Digest. No. 240. (Watford: Building Research Establishment.)

Chadwick, R A, and Evans, D J. 1995. The timing and direction of Permo-Triassic extension in southern Britain. 161–192 in Permian and Triassic rifting in northwest Europe. Boldy, S A R (editor). Special Publication of the Geological Society of London, 91.

Clifton-Taylor, A. 1972. The pattern of English building. (London: Faber and Faber.)

Corfield, S M, Gawthorpe, R, Gage, M, Fraser, A J, and Besly, B M. 1996. Inversion tectonics of the Variscan foreland of the British Isles. Journal of the Geological Society of London, Vol. 153, 17–32.

Cox, B M, and Sumbler, M G. 2002. British Middle Jurassic Stratigraphy.Geological Conservation Review Series. No. 21. (London: Joint Nature conservation Committee/Chapman and Hall.)

Dunham, K C, and Poole, E G. 1974. The Oxfordshire Coalfield. Journal of the Geological Society of London, Vol. 130, 387–391.

Environment Agency. 1996. Groundwater vulnerability of the Northern Cotswolds. Groundwater vulnerability map Sheet 30. 1:100 000. (Solihull: Environment Agency.)

Forster, A, Culshaw, M G, and Bell, F G. 1995. Regional distribution of sulphate in rocks and soils of Britain. 95–104 in Engineering geology of construction. Eddleston, M, Walthall, S, Cripps, J C, and Culshaw, M G (editors). Geological Society Engineering Geology Special Publication, No. 10.

Higginbottom, I E, and Fookes, P G. 1971. Engineering aspects of periglacial features in Britain. Quarterly Journal of Engineering Geology, Vol. 3, 85–171.

Hutchinson, J N. 1967. The free degradation of London Clay cliffs. Proceedings of the Geotechnical Conference, Oslo, 1, 113–118.

Jones, H K, Morris, B L, Cheney, C S, Brewerton, L J, Merrin, P D, Lewis, M A, MacDonald, A M, Coleby, L M, Talbot, J C, McKenzie, A A, Bird, M J, Cunningham, J, and Robinson, V K. 2000.The physical properties of minor aquifers in England and Wales. British Geological Survey Technical Report, WD/00/4. Environment Agency R&D Publication, No. 68.

Morgan-Jones, M, and Eggboro, M D. 1981. The hydrogeochemistry of the Jurassic limestones in Gloucestershire, England. Quarterly Journal of Engineering Geology, Vol. 14, 25–39.

National Rivers Authority. 1995a. Groundwater vulnerability of Worcestershire. Groundwater vulnerability map Sheet 29. 1:100 000. (Solihull: National Rivers Authority.)

National Rivers Authority. 1995b. Groundwater vulnerability of the Southern Cotswolds. Groundwater vulnerability map Sheet 37. 1:100 000. (Solihull: National Rivers Authority.)

National Rivers Authority. 1995c. Groundwater vulnerability of the Upper Thames and Berkshire Downs. Groundwater vulnerability map sheet 38. 1:100 000. (Solihull: National Rivers Authority.)

OꞌNeil, H E, and Shotton, F W. 1974. Mammoth remains from gravel pits in the north Cotswolds. Proceedings of the Cotteswold Naturalistsꞌ Field Club, Vol. 36, 196–197.

Parsons, C F. 1980. Aalenian and Bajocian Correlation chart. 3–21 in A correlation of Jurassic rocks in the British Isles. Part 2: Middle and Upper Jurassic. Cope, J C W (editor). Geological Society of London Special report, No. 15.

Savage, R J G. 1961. The Witts collection of Stonesfield Slate fossils. Proceedings of the Cotteswold Naturalistsꞌ Field Club, Vol. 33, 177–182.

Sumbler, M G. 2001. The Moreton Drift: a further clue to glacial chronology in central England. Proceedings of the Geologistsꞌ Association, Vol. 112, 13–27.

Whiteman, C A, and Rose, J. 1992. Thames river sediments of the British early and middle Pleistocene. Quaternary Science Reviews, Vol. 11, 363–375.

Index to the 1:50 000 series maps of the British Geological Survey.

The map below shows the sheet boundaries and numbers of the 1:50 000 series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately.

(Index map)

Almost all BGS maps are available flat or folded and cased. The area described in this sheet explanation is indicated by a solid block. British geological maps can be obtained from sales desks in the Surveyꞌs principal offices, through the BGS London Information Office at the Natural History Museum Earth Galleries, and from BGS-approved stockists and agents. Northern Ireland maps can be obtained from the Geological Survey of Northern Ireland.

Figures and plates

Figures

(Figure 1) Lithostratigraphical classification of the Lias Group.

(Figure 2) Lithostratigraphical classification of the Inferior Oolite Group.

(Figure 3) Schematic cross-section of the Inferior Oolite Group.

(Figure 4) Lithostratigraphical classification of the Great Oolite Group.

(Figure 5) Generalised cross-section through the Great Oolite Group.

(Figure 6) Chronology of the Quaternary deposits of the district.

(Figure 7) Engineering characteristics of the main bedrock units.

Plates

(Plate 1) Base of the Birdlip Limestone Formation exposed at Cleeve Cloud (1981). The Leckhampton Member (0.6 m seen) is overlain by the lower part of the Crickley Member (total 6.9 m) (GS1049).

(Plate 2) Broadway Quarry [SP 117 366]: eastern face showing the Gryphite Grit Member (about 6 m), the Harford Member (7.7 m) and the Scottsquar Member (about 2 m seen). The conspicuous dark beds are mudstone at the top of the Harford Member (GS1045).

(Plate 3) Notgrove Railway Cutting [SP 0845 2090]. Upper Trigonia Grit (about 1 m) resting on Notgrove Member (1.8 m). Staff is 1 m long. (GS1046).

(Plate 4) Rolling Bank Quarry. Section exposed following 1998 restoration and installation of information board; rubbly Clypeus Grit (about 39 m) resting on Upper Trigonia Grit (2.58 m), resting on Rolling Bank Member (4.96 m). (GS1048).

(Plate 5) Surface gull seen from the top of Broadway Tower (GS1047).

(Front cover) The face of Cleeve Cloud [SO 984 256], overlooking Cheltenham, exposes the Birdlip Limestone Formation of the Inferior Oolite Group. It was formerly a building stone quarry, and the slopes below are covered in degraded limestone spoil heaps. The escarpment here is crowned by an Iron-Age hill fort (Aerofilms 599571).

(Rear cover)

(Geological succession) Geological succession in the Moreton-in-Marsh district.

(Index map) Index to the 1:50 000 series maps of the British Geological Survey. The map below shows the sheet boundaries and numbers of the 1:50 000 series geological maps. The maps are numbered in three sequences, covering England and Wales, Northern Ireland, and Scotland. The west and east halves of most Scottish 1:50 000 maps are published separately. Almost all BGS maps are available flat or folded and cased. The area described in this sheet explanation is indicated by a solid block. British geological maps can be obtained from sales desks in the Surveyꞌs principal offices, through the BGS London Information Office at the Natural History Museum Earth Galleries, and from BGS-approved stockists and agents. Northern Ireland maps can be obtained from the Geological Survey of Northern Ireland.

Figures

(Figure 7) Engineering characteristics of the main bedrock units.

Lithology Engineering Charecteristics Lithostratigraphical unit
Limestone Generally weak to moderately strong, more rarely strong to very strong; may contain cavities in the form of widened joint or gulls in cambered strata. Possibility of adits and old mines in the Cleeve Cloud Member Cornbrash Formation

White limestone Formation

Hampden Formation

Taynton Limestone Formation

Chipping Norton Limestone Formation

Salperton Limestone Formation

Aston Limestone Formation

Birdlip Limestone Formation

(Scottsquar, Cleeve Cloud, Crickley, and Leckhampton members)

Marlstone Rock Formation
Mudstone Overconsolidated, fissured, generally stiff (weathered clay) to weak (fresh mudstone). Generally high plasticity, ranging from intermediate to very high. Weathered zone, strength is likely to be lower and plasticisity higher, shrink swell problems. Loss of strength in valley-bulged mudstone. Sulphate attack Class 1 or 2 for most mudstone units, Class 3 for the Charmouth Mudstone Formation† Kellaways Clay Member

Forest Marble Formation

Fullerꞌs Earth Formation

Birdlip Limestone Formation (Hartford Member (part))

Whitby Mudstone Formation

Dyrham Formation

Charmouth Mudstone Formation
Sandstone Reasonable foundation conditions where sufficiently dense and protected from erosion. Shallow foundations in sandstone may be affected by frost heave Eyford Member
Sand Generally dense to very dense Birdlip Limestone Formation (Hartford Member, part)

Bridport Sand Formation
† Building Research Establishment Digest 363 (1991).

(Geological succession) Geological succession in the Moreton-in-Marsh district.

Quaternary Holocene Thickness
Alluvium up to 3
Tufa clay and silt, calcareous silt up to 2
Pleistocene
Head variably stony clay up to 3
Head gravel limestone gravel, sand and clay up to 5
Cheltenham sand and gravel sand and limestone gravel up to 15
River Terrace Deposits sand, gravel, and loam up to 6
Wolston Formation silt, clay, stony clay, sand and gravel up to 30
Baginton Formation sand up to 10
Northern Drift Formation sand, gravel and pebbly clay up to 5
Kellaways Formation
Kellaways Clay Member mudstone, dark grey up to 3
GREAT OOLITE GROUP
Cornbrash Formation limestone, shelly-detrital, rubbly 3
Forest Marble Formation mudstone with beds of shell-detrital, ooidal limestone 6
White Limestone Formation limestone, peloidal 10 to 15
Hampen Formation limestone sandy, with beds of mudstone 2 to 9
Taynton Limestone Formation limestone, shell-detrital, ooidal 0 to 7
Fullerꞌs Earth Formation
Eyford Member limestone, sandy and sandstone 0 to 9
Fuller's Earth, undifferentiated mudstone, grey, with minor beads of limestone 0 to 10
Chipping Norton Limestone Formation limestone, sandy, ooidal shell-detrital 0 to 16
INFERIOR OOLITE GROUP
Salperton Limestone Formation 5 to 18
Clypeus Grit Member limestone, peloidal, ooidal, shell-detrital 5 to 16
Upper Trigonia Grit Member limestone, shelly, ooidal 0 to 3
Aston Limestone Formation 0 to 22
Rolling Bank Member shelly, sandy, limestone 0 to 8.5
Notgrove Member ooidal and peloidal limestone 0 to 13
Gryphlite Grit Member limestone, sandy, shelly 0 to 7
Lower Trigonia Member limestone, shelly and shell-detrital ooidal 0 to 2
Birdlip Limestone Formation 0 to 74
Harford Member sand, sandstone, mudstone and limestone 0 to 14
Scottsquar Member limestone, peloidal, ooidal and lime mudstone 0 to 10
Cleeve Cloud Member limestone, ooidal, sandy and shell detriral in lower part 0 to 51
Crickley Member limestone, shell detrital, pisoidal, peloidal and ooidal 0 to 10
Leckhampton Member limestone, shell-detrital, sandy 0 to 6
Lower Jurassic LIAS GROUP
Bridport Sand Formation sandstone fine-grained and sandy mudstone 0 to 17
Whitby Mudstone Formation mudstone grey 25 to 110
Marlstone Rock Formation limestone, grey 0 to 6
Dyrham Formation limestone, ferruginous, sandy ooidal 15 to 61
Charmouth Mudstone Formation mudstone, grey with nodules and rare thin beds of limestone 130 to 290
Blue Lias Formation mudstone, grey, with thin beds of argillaceous mudstone 10 to 75