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The geology of the neighbourhood of Edinburgh

By G. H. Mitchell, D.Sc., F.R.S. and W. Mykura, B.Sc. with Contributions by W. Tulloch, B.Sc., J. Knox, B.Sc., and J. R. Earp, Ph.D. Palaeontology by R. B. Wilson, B.Sc. and J. D. D. Smith, B.Sc.

Bibliographic reference: Mitchell, G.H. and Mykura, W. 1962. The geology of the neighbourhood of Edinburgh. Edinburgh: Her Majesty's Stationery Office

Department of Scientific and Industrial Research

Memoirs of the Geological Survey Scotland The geology of the neighbourhood of Edinburgh

By G. H. Mitchell, D.Sc., F.R.S. and W. Mykura, B.Sc. with Contributions By W. Tulloch, B.Sc., J. Knox, B.Sc., and J. R. Earp, Ph.D. Palaeontology by R. B. Wilson, B.Sc. and J. D. D. Smith, B.Sc.

Third Edition. Edinburgh: Her Majesty's Stationery Office 1962. Price £1 15s. 0d. net

Published by Her Majesty's Stationery Office © Crown copyright 1962. First published 1861; Second edition 1910; Third edition 1962

To be purchased from 13A Castle Street, Edinburgh 2 York House, Kingsway, London W.C.2 423 Oxford Street, London W.1 109 St. Mary Street, Cardiff 39 King Street, Manchester 2 50 Fairfax Street, Bristol 1 35 Smallbrook, Ringway, Birmingham 5 80 Chichester Street, Belfast 1 or through any bookseller

Front cover

Rear cover

Preface

Preface to First Edition notice

The first published sheet of the Geological Survey in Scotland, that which contains the metropolis of the kingdom, is illustrated in the present Memoir through the joint labours of MM. Howell and Geikie.

The origin and prosecution of the Surveys of Edinburghshire and Haddingtonshire, as ably devised and carried out under the local direction of Professor Ramsay, is clearly explained in the Preface to this Memoir.

It would be unbecoming on my part to select for special approbation any one portion of the Survey of the British Isles; but I may truly say, that of the many maps we have published (and the rapid sale of them attests their value), there is, perhaps, no one which conveys a greater amount of useful knowledge than the sheet representing the country in and around Edinburgh, the authors of which are entitled to great credit for the manner in which they have completed their task.

Roderick I. Murchison, Director-General.

In the year 1855 the Ordnance Survey had made so much progress in surveying part of the Eastern Counties of Scotland, that many of the Maps on a scale of six inches to a mile were engraved. On consultation with the late Director-General, Sir Henry De la Beche, the time seemed to have arrived for extending the Geological Survey of Great Britain into Scotland. We also considered it desirable to commence the work in such a way that it would bring the survey as quickly as possible into the great Coal-fields of Scotland, but the Ordnance Survey of the Western Counties being then scarcely commenced, we deemed it best to begin the Survey amongst the Old Red Sandstone and Carboniferous rocks of Berwickshire and Haddingtonshire, unusually perfect sections of these strata being exposed on the sea cliffs between North Berwick and the base of the Old Red Sandstone west of St. Abb's Head. In doing so it was felt that a key might be obtained to the right understanding of these strata in inland areas, where the rocks are often much concealed by deep superficial accumulations of drift. Accordingly, I personally commenced the mapping of that district, extending my work southward to the Lammermuir Hills, and westward beyond Belhaven, and by degrees, as the Survey progressed, it was extended by Mr. Howell and Mr. Geikie into the rest of Haddingtonshire, Edinburghshire and Fifeshire. During the progress of the work I superintended and examined the whole, and occasionally assisted when doubtful questions arose, and I believe that the mapping of the outline of the different formations of the beds of coal, the limestones, igneous rocks, faults, etc., is as accurate as the data and the present state of geological science will permit.

In the Edinburgh sheet the whole of the district east of the fault that bounds the Pentland Hills was surveyed by Mr. Howell, taking it in connexion with his work in Haddingtonshire; and the Pentland Hills and all to the west of them were mapped by Mr. Geikie. In the following Memoir each has described the area mapped by himself.

In surveying the united area of East and Mid Lothian it so happened that the sheet of map comprising most part of Edinburghshire was completed and published first. Since then, Sheet No. 33 (Haddingtonshire) has also been published, and the Memoir descriptive of the district is in progress. Fife and Kinross and part of Berwickshire are also far advanced.

It will be observed that this Memoir refers directly to the one-inch maps of the Geological Survey, but six-inch maps of those parts of the Carboniferous strata that contain beds of workable coal, and sections on the same scale, to be accompanied by printed descriptions, are very far advanced.

Andrew C. Ramsay, Local Director of the Geological Survey of Great Britain. Geological Survey Office, June 1861.

Preface to Second Edition

The present volume forms the second edition of the Memoir on "The Geology of the Neighbourhood of Edinburgh", which was written by H. H. Howell and (Sir). A. Geikie, and published in 1861, when Sir R. I. Murchison was Director General and (Sir) A. C. Ramsay, Local Director. That Memoir described the geology of the districts included in the one-inch map 32 — the first published sheet of the Geological Survey in Scotland — together with a strip of ground, about two miles broad, along the eastern margin of Sheet 31. The present edition deals with the same districts, except a small part of the county of Fife to the east of Inverkeithing, which was described by Sir A. Geikie in the Memoir on "The Geology of Central and Western Fife and Kinross" (1900).

The development of the oil-shale fields in the Lothians, after the ground had been originally mapped by the Geological Survey, necessitated the revision of the shale-bearing areas, which was carried out by Mr. H. M. Cadell between 1884 and 1887. This additional information was embodied in a second edition of Sheet 32, published in 1892.

The results of the revision of the Carboniferous districts, which was begun in 1902 and continued at intervals till 1906, by Messrs. Peach, Clough, Hinxman, Grant Wilson, Gibson, Crampton, Maufe, Bailey, Anderson, and Grabham, are incorporated in this volume. These officers have furnished descriptions of their respective areas. Dr. Peach re-examined a tract embracing the city of Edinburgh and Leith, southwards to Liberton and Colinton, thence along the north-west slope of the Pentland chain to the Cairn Hills. Mr. Clough revised the Coal Measures of the Mid-Lothian basin south of Smeaton and Sheriffhall, together with an area between Crossgatehall and Gorebridge, composed partly of Millstone Grit and partly of the Carboniferous Limestone Series. The eastern part of this basin, from Prestongrange to Crossgatehall was re-examined by Mr. Anderson, and from Cousland to Temple by Dr. Crampton; the southern part from Borthwick by Mount Lothian to Carlops and Penicuik, by Mr. Hinxman; the western portion from Penicuik to Gilmerton, by the late Mr. Grant Wilson; and the north-western area from Gilmerton to Portobello and Musselburgh, by Messrs. Gibson and Bailey.

West of Edinburgh and the Pentland Hills, the Carboniferous districts were thus apportioned: to Dr. Crampton was assigned a triangular area stretching from Newhaven and Cramond in the north to the village of Currie in the south; to Mr. Grant Wilson, the fertile tract comprising the oil-shale fields extending westwards to Blackness, Dechmont, and Leven; to Mr. Bailey, the ground surrounding Blackburn and Bathgate; to Mr. Maufe, the central portion of the volcanic area of the Bathgate Hills; to Mr. Grabham, the part between Carribber and Linlithgow; and to Mr. Clough, the region between Linlithgow and the Forth. North of the Firth of Forth, Mr. Maufe revised that part of the county of Fife lying between Crombie Point and Inverkeithing.

In 1906 an economic Memoir dealing exclusively with the Oil-shales of the Lothians was published by the Geological Survey, in which the geology of the various shale-fields was described in detail. Only a few typical sections illustrating the structure of the shale region are here reproduced from that Memoir.

The descriptions of the Carboniferous districts have been almost wholly rewritten owing to the acquisition of fuller information, but in some cases the accounts by H. H. Howell and Sir A. Geikie have been retained.

The Lower Old Red Sandstone volcanic rocks of the Braid Hills were revised by Dr. Peach, and of the Pentland Hills by Mr. Cunningham Craig when attached to the staff of the Geological Survey, and afterwards in part by Dr. Peach, but the account of the stratigraphy of that formation has been furnished by Dr. Peach.

The description of the isolated areas of Silurian rocks in Sheet 32 by Dr. Peach and Dr. Horne has been reproduced from the Memoir on "The Silurian Rocks of Scotland", published in 1899.

No systematic re-examination of the glacial deposits was carried out during the revision of the Carboniferous districts, but a brief outline is given of the history of that period based partly on the work of the Geological Survey and partly on the researches of other observers.

Dr. Flett has contributed the chapters on the Petrography of the Volcanic Rocks of the Pentland Hills and of the Carboniferous Volcanic Rocks of the Edinburgh and Linlithgow district. The rock analyses have been made by Dr. Pollard and Mr. Radley.

The lists of fossils in the palaeontological part of the Appendix have been compiled by Mr. D. Tait. These lists are based on determinations made by R. Etheridge, junr., Dr. Peach, Dr. Crampton, and Dr. Lee, with the assistance of Messrs. H. B. Brady, T. Rupert Jones, J. W. Kirkby, Dr. Traquair, Dr. Kidston, Dr. Wheelton Hind, and Dr. Foord. Dr. Lee has furnished notes on the Distribution of Life in the Lower Carboniferous Rocks of Sheet 32.

The bibliographical part of the Appendix, containing a list of works referring to the geology of the districts included in this Memoir, was prepared by Mr. D. Tait.

Special thanks are due to those associated with the mining industry of Mid and West Lothian for information supplied when the revision was in progress, and to Mr. Reid of Messrs. Leslie and Reid, C.E., for notes regarding the water supply of Edinburgh and the surrounding district.

The photographs reproduced in Plates I. to IV., VI. and VIII., were taken by Mr. R. Lunn, and the micro-photographs in Plates IX. to XII. by Mr. T. C. Hall. The photograph of the east and west dyke in Inchcolm (Plate V.) has been kindly supplied by Mr. A. G. Stenhouse.

The Memoir has been edited by Dr. Horne.

J. J. H. Teall, Director. Geological Survey Office, 28 Jermyn Street, London. 17th November 1910.

Preface to Third Edition

The area covered by Sheet 32 of the one-inch geological map of Scotland was originally surveyed by A. Geikie and H. H. Howell and the map published in 1859. A second edition dated 1892 included revision by A. Geikie, H. H. Howell, B. N. Peach, J. S. Grant Wilson and H. M. Cade11. Later B. N. Peach, C. T. Clough, L. W. Hinxman, J. S. Grant Wilson, W. Gibson, E. H. Cunningham-Craig, C. B. Crampton, H. B. Muff, [Sir] E. B. Bailey, E. M. Anderson and G. W. Grabham combined to revise the area and the Third Edition was published in 1910. New Drift and Solid Editions, incorporating minor alterations, appeared in 1928 and 1930 respectively.

The present map is the work very largely of Messrs. W. Tulloch, H. S. Walton, W. Mykura and H. E. Wilson who resurveyed some three-quarters of the ground between the years 1947–1956. It also includes work, mainly on the margins of the area, undertaken by J. B. Simpson, Dr. J. E. Richey, J. K. Allan, Dr. T. Robertson and Professor W. Q. Kennedy between 1937 and 1941 and a considerable area of the West Lothian Oil-Shale field revised by Professor J. G. C. Anderson in 1941–42. E. M. Anderson and Dr. A. G. MacGregor were responsible for new editions of the six-inch sheets of Edinburgh City issued in 1938–1954. The portion of the area within Fife was surveyed by C. H. Dinham and D. Haldane between 1923–29. With the reconstitution of county six-inch sheets to form National Grid maps in the eastern and northern parts of the forthcoming one-inch map the opportunity has been taken to effect certain minor amendments, mainly as a result of the re-examination of parts of the ground by Dr. J. R. Earp, Mr. J. Knox and Dr. G. H. Mitchell.

The first edition of the memoir on "The Geology of the Neighbourhood of Edinburgh", published in 1861, was the work of H. H. Howell and A. Geikie. The second edition, under the authorship of B. N. Peach, C. T. Clough, L. W. Hinxman, J. S. Grant Wilson, C. B. Crampton, H. B. Maufe and [Sir] E. B. Bailey, with petrological chapters by J. S. Flett, appeared in 1910.

Mention must also be made of the work of Mr. R. G. Carruthers in compiling the Third Edition of the memoir "The Oil-Shales of the Lothians" which, published in 1927, contained a detailed description of these peculiar strata as developed within the present area, an account which was later supplemented by three Wartime Pamphlets bearing the same title under the authorship of Dr. J. E. Richey, Professor W. Q. Kennedy and Professor J. G. C. Anderson.

The present edition has been compiled by Dr. G. H. Mitchell from the notes and contributions of the surveyors and in this great assistance has been rendered by Mr. R. W. Elliot and Mr. G. A. Goodlet. It includes new information which has been acquired during the last 50 years and in addition references to original papers which comprise a more detailed account of certain features than is possible in this account. The identification of the Lower Palaeozoic fossils has been carried out by Mr. J. D. D. Smith except for the graptolites which were identified by Professor O. M. B. Bulman, F.R.S. Dr. E. I. White, F.R.S. has identified Palaeozoic fishes ; Dr. Ethel Currie goniatites, Dr. R. Crookall fossil plants, Mr. R. B. Wilson and Mr. M. A. Calver respectively Lower and Upper Carboniferous invertebrate fossils. Mr. R. B. Wilson under Dr. F. W. Anderson, the Chief Palaeontologist, has furnished the palaeontological chapter, following the work of G. W. Lee, John Pringle, David Tait and Mr. W. Manson, augmented by collections made recently by Messrs. W. E. Graham, P. J. Brand and D. K. Graham. Messrs. W. Mykura and J. D. D. Smith have written the Silurian chapter and the former of these two the Lower and Upper Old Red Sandstone, Pre-Glacial and Glacial accounts. Petrographical information has been collected over the years by Dr. J. Phemister and Dr. A. G. MacGregor.

Thanks are recorded to many officials of the National Coal Board and of private mineral and oil-shale companies as well as to mining engineers, boring contractors, quarry owners and water engineers, for much assistance given and information provided.

C. J. Stubblefield, Director. Geological Survey Office, Exhibition Road, South Kensington, London, S.W.7. 26th April, 1962.

Six-inch maps

An index map showing the National Grid six-inch geological maps which cover the area is given in (Figure 1). Except in the case of those marked with an asterisk these maps are published. They are issued in three forms (1) Uncoloured; (2) Solid edition, coloured to show solid geology; and (3) Drift edition, coloured to show superficial deposits. All maps are available for public reference in the library of the Geological Survey and Museum, South Kensington, London, S.W.7, or at the Geological Survey Office, 19 Grange Terrace, Edinburgh, 9. Published maps may be purchased through Ordnance Survey Agents.

Note: At the time of going to press the eastern portion of the area is still shown on revised Six-inch County geological sheets issued between 1948 and 1960. Re-issues of this information on the six-inch National Grid sheets shown below are in an advanced state of. preparation.

Chapter 1 Introduction

The area represented on Sheet 32 of the one-inch geological map of Scotland comprises the greater parts of the counties of Midlothian and West Lothian with portions of East Lothian, Peebles, Lanark and Fife. Most of the ground lies south of the Firth of Forth and contains the rich coalfield of Midlothian and almost the whole of the oil-shale fields of the Lothians. The extent of the area, the general distribution of the rocks and the principal rivers and towns are shown on (Figure 2).

This account is designed as a short explanation of the one-inch map. It gives a brief summary of the geology of the area and directs attention to the chief exposures and sections. Unless otherwise stated the latter are everywhere given in descending order. By means of references at the end of each chapter the reader is referred to many detailed papers descriptive of particular aspects of the geology. There already exist a number of admirable accounts of the area, but unfortunately several of them are out of print. Many contain extensive bibliographies, particularly of earlier literature which it is not practicable to repeat in the present account and they should be studied by anyone who wishes to delve deeper. Copies are available in many libraries and in particular can be consulted in the libraries of the Geological Survey and Museum in South Kensington, London, S.W.7 and at 19 Grange Terrace, Edinburgh, 9. The most important of these works are those of Flett and others (1927), Howell and Geikie (1861) and Peach and others (1910), while among early workers Maclaren (1839) and Geikie (1897) should also be mentioned.

The Midlothian Coalfield, which occupies the eastern part of the present area and includes the principal outcrops of the Upper Carboniferous strata, has been described in a recent memoir by Tulloch and Walton (1958). Since this volume deals in detail with the Lower Limestone Group, Limestone Coal Group and succeeding strata up to and including the Coal Measures, a summary treatment of these beds in the present volume was felt to be justified. The opportunity has been taken, however, to treat in somewhat greater detail the glacial phenomena of the whole area.

A detailed account, with route maps, of many geological excursions in the Edinburgh area is contained in "Edinburgh Geology — An Excursion Guide" recently published by the Edinburgh Geological Society and Messrs. Oliver and Boyd Ltd., Edinburgh.

Geological sequence

The geological formations occurring within the area are summarised below.

A generalized section of the sedimentary and volcanic rocks is given in (Figure 3). The interpretation adopted here and on the one-inch and six-inch maps is the one at present generally accepted, but the available evidence is insufficient to enable a detailed succession within the Lower Oil-Shale Group to be given with confidence. In particular, recent palaeontological examination of the fossiliferous strata within the group suggests the possibility that part of the Wardie Shales of the Edinburgh City area may in fact be the equivalent of part of the Queensferry Beds of West Lothian (p. 105). Such a correlation would imply an appreciable reduction in the estimated thickness of the Lower Oil-Shale Group. The Upper and Lower Oil-Shale groups, together with the Cementstone Group, are sometimes collectively referred to as the Calciferous Sandstone Measures.

Geological history

The oldest rocks in the district are believed to be of Ordovician age. They crop out about two miles south-south-east of Penicuik and again near Middleton Moor in the extreme south-east and consist of greywackes, pebbly grits and shales.

Silurian grits, greywackes and fossiliferous mudstones appear in three inliers within the Pentland Hills (Figure 2); their age is probably topmost Llandovery and Wenlock.

The North Esk Inlier, which forms the largest area of Silurian rocks, has a prolific shelly fauna in the middle part of the succession and contains red sandstones and conglomerate bands in the upper part. The source of the sediments seems to have been to the east or north-east.

Before the deposition of the Old Red Sandstone the earlier rocks were disturbed by severe earth-movements and subjected to considerable erosion. As a consequence the Lower Old Red Sandstone in the Pentland Hills rests with strong unconformity on nearly vertical Silurian beds striking north-east to north-north-east.

The Lower Old Red Sandstone consists of coarse conglomerates and sandstones succeeded by volcanic rocks. The sediments are exposed only in the Pentland Hills where they attain a thickness of about 2000 ft and contain rounded pebbles of greywackes, cherts and jasperized lavas probably derived from the Lower Palaeozoic rocks now exposed in the Southern Uplands. They would seem to have originated as fluviatile outwash-fan deposits accumulating on the margin of the intermontane basin adjoining the south-eastern front of the Caledonian Chain. The volcanic rocks are developed both in the Pentland and Braid hills. They are up to 6000 ft thick near the northern end of the Pentlands and thin out rapidly southwards, the four lowest groups of flows being present only in the north. The Pentland volcanic centre is the most north-easterly of an aligned series of centres which extends along the southern margin of the Midland Valley as far as Ayrshire.

Sub-basic to basic minor intrusions are common in both the Silurian and Lower Old Red Sandstone sediments, but are rare in the lavas, suggesting that the phase of dyke and sill-formation was drawing to a close when the lavas were being poured out. A small boss of quartz-diorite intruded into Lower Old Red Sandstone sediments near the head of the Lyne Water is the sole representative of the Old Red Sandstone granitic intrusions of southern Scotland.

Further earth-movements followed the deposition of the Lower Old Red Sandstone, and the sandstones, conglomerates and cornstones of the Upper Old Red Sandstone rest on an undulating erosion surface exposing all groups of Lower Old Red Sandstone as well as some Silurian beds (George 1960, pp. 58–63). Part of the northern end of the Pentland Hills seems to have formed high ground throughout Upper Old Red Sandstone times, for near Bonally Castle Carboniferous sediments appear to rest directly on Lower Old Red Sandstone lavas. In most other parts of the area there seems to be a normal passage from Upper Old Red Sandstone to Lower Carboniferous sediments, but there is a suggestion at the south end of the Midlothian Coalfield of a progressive overlap of Lower Carboniferous strata on to Lower Old Red Sandstone (Tulloch and Walton 1958, p. 8).

The Carboniferous sedimentary rocks commenced with the Cementstones, but in places there was an outbreak of volcanic activity at the beginning of the period, which gave rise to the lavas and tuffs of Craiglockhart. A more important outburst seems to have occurred a little later when, from vents such as Arthur's Seat, were erupted the lavas and tuffs of Whinny Hill, Duddingston, and Calton Hill, probably also those of Corston Hill and the volcanic rocks found in the D'Arcy (Midlothian) No. 1 Oil-Bore near Cousland. A number of basaltic intrusions are probably of this general age.

Thereafter sedimentation took on more of the rhythmic character prevalent in the Upper Carboniferous, for the Lower Oil-Shale Group includes not only thick sandstones but in addition marine bands, shell-beds with non-marine fossils, and also bituminous beds, which in the Upper Oil-Shale Group become even more common and provide many workable oil-shales. It is remarkable that in both these formations coal seams are rare. That volcanicity had not altogether ceased is clear from the occasional beds of 'ash' which are recorded from place to place in the succession (Figure 20).

Goodlet's (1957) work on the Lower Limestone Group suggests that the present area was situated towards the south-eastern margin of the delta of a large river debouching from the north.

The groups of the Carboniferous so far mentioned form part of the Carboniferous Limestone Series of England and Wales, but close correlation is as yet not possible. The latest published work (Currie 1954) suggests that the beds to the top of the Upper Oil-Shale Group should be assigned to the Cracoean (B) and Lower Bollandian (P₁) stages of the goniatite sequence and she would place the Lower Limestone Group in the Upper Bollandian (P₂).

In the west of the area on the borders of the Bathgate Hills, a further burst of volcanic activity attained considerable importance in Lower Limestone Group times and persisted during the formation of the Limestone Coal Group, only to die away within the period of the Upper Limestone Group.

The earliest representative of the Millstone Grit Series as defined in the Pennine district of England is the Limestone Coal Group. As already mentioned it includes much volcanic material in the west of the area, but of this there is no trace in the Midlothian Coalfield, where the rhythmic sedimentation of the strata is again pronounced although the high proportion of shallow-water beds is a feature and land conditions are suggested by the seatclays and numerous workable coals. The group is believed to form the Pendleian Stage (E_l) of the goniatite classification.

The succeeding Arnsbergian (E₂) beds, here known as the Upper Limestone Group, show a return to a more marine environment as witness the number of thin limestone beds and the amount of marine fossiliferous shale.

The marine tendency continued for a time in the overlying Passage Group, for marine beds are frequent in the lower part of that formation and contain goniatites belonging to the Arnsbergian (E₂) Stage in the case of one band about 27 to 32 ft above the base. These are the highest diagnostic goniatites yet found in the Scottish Carboniferous, except those in Skipsey's Marine Band, for no representatives of faunas of Homoceras (H), Reticuloceras (R) or Gastrioceras (G) age have been discovered.

The increasing proportion of sandstones in the upper part of the Passage Group, some of which have more than a suggestion of unconformity at their bases, coupled with the fact that the lowest recognized non-marine lamellibranch fauna in the Coal Measures belongs to the Zone of Carbonicola communis, suggests the possibility of an important break or breaks in the Passage Group. The lower beds (Arnsbergian) of the latter clearly fall within the Millstone Grit Series, but the upper may well belong to the Lower Coal Measures (Trotter 1952). It is for this reason and for the fact that the group forms only a part of the Millstone Grit Series of England and Wales that the name Passage Group is preferred to the older name of Millstone Grit (MacGregor 1960).

The uppermost beds of the Passage Group pass without any known break in sedimentation into the Lower Coal Measures. The latter, together with the overlying Middle Coal Measures, form a group of coal-bearing strata, comparable with beds of like age in many parts of Great Britain. Both are marked by rhythmic sedimentation showing at one end of the scale frequent emergences of the area above water-level during the formation of coals and seatclays and at the other the occasional presence of marine conditions marked by marine bands.

It is unfortunate that the Gastrioceras subcrenatum Marine Band, widely used in England, Wales and Northern Ireland to define the base of the Lower Coal Measures, has not yet been recognized in Scotland; as a consequence an arbitrary base has to be adopted. Of recent years, however, the discovery that the Queenslie Marine Band (Manson 1957) is the equivalent of the Clay Cross and other correlated marine bands in the English and Welsh coalfields enables the same horizon to be taken throughout Great Britain as the boundary between Lower and Middle Coal Measures.

The conditions of sedimentation seem to have varied but little throughout the Coal Measures. Indeed they probably continued unchanged into Upper Coal Measures times in the present area, for there is much to suggest that the red colour and many of the other characteristics of these uppermost Carboniferous strata are the result of mineral alterations which took place when the rocks formed the earth's crust below a land-surface in late-Carboniferous early-Permian times (Mykura 1960; Tulloch and Walton 1958, p. 7). It is also perhaps to this period that the quartz-dolerite dykes and sills belong.

On a point of classification it should be noted that in Scotland Skipsey's Marine Band is adopted as the boundary between Middle and Upper Coal Measures, a procedure in conflict with established English and Welsh practice in which the Top Marine Band, somewhat above the horizon of Skipsey's Band, serves as the junction. This divergence of practice is rendered necessary by the fact that at only one place in Scotland is a marine band known above Skipsey's and also because the bottom of the reddening marking much of the Upper Coal Measures is a distinctly variable horizon (MacGregor 1960).

Between the Upper Coal Measures and the earliest glacial deposits there are no strata remaining in the Edinburgh district. The Carboniferous rocks are severely folded and faulted but the history of the earth-movements which caused their disturbance can only be suggested by comparison with other areas. From such indirect evidence it would seem likely that the age of the main movements was late-Carboniferous.

The detailed relationships of the various deposits of the Great Ice Age have still to be worked out. There seem, however, to have been several glaciations with intervening warmer periods, at least two of the glaciations being major episodes.

Their legacy is a thick pile of boulder clay, in places filling pre-Glacial valleys, the streams of which have frequently not regained their original courses. With the clays are frontal and lateral morainic clays, sands and gravels and the abandoned channels of glacial drainage. Many of the outwash gravels pass downstream into the terraces of the modem rivers lying at varying heights above their alluvium.

In late-Glacial times the sea appears to have stood at the level of the 100-ft Raised Beach. Subsequently it fell to a level of some 50-ft above Ordnance Datum and continued to fall to a considerable depth below the present sea-level, only to rise again to form the 25-ft Raised Beach before subsiding to its present level.

The influence of the geology on topography and geography generally is dealt with in an admirably illustrated article by Cossar (1911). G.H.M., W.M.

References

COSSAR, J. 1911. Notes on the Geography of the Edinburgh District. Scottish Geographical Mag., 27, 574, 643; 1912. 28, 10.

CURRIE, ETHEL D. 1954. Scottish Carboniferous Goniatites. Trans. Roy. Soc. Edin., 62, 527–602.

FLETT, J. S., BALSILLIE, D., CAMPBELL, R., DAY, T. C., DINHAM, C. H., ECKFORD, R., GORDON, W. T., MACGREGOR, M., MANSON, W., READ, H. H. and TAIT, D. 1927. The Geology of the District around Edinburgh. Proc. Geol. Assoc., 38, 405–517.

GEIKIE, A. 1897. The Ancient Volcanoes of Great Britain, vol. I, London.

GEORGE, T. N. 1960. The Stratigraphical Evolution of the Midland Valley. Trans. Geol. Soc., Glasgow, 24, 32–107.

GOODLET, G. A. 1957. Lithological Variation in the Lower Limestone Group of the Midland Valley of Scotland. Bull. Geol. Surv. Gt. Brit., 12, 52–65.

HOWELL, H. H. and GEIKIE, A. 1861. The Geology of the Neighbourhood of Edinburgh. Mein. Geol. Surv.

MACGREGOR, A. G. 1948. Problems of Carboniferous–Permian Volcanicity in Scotland. Quart. J. Geol. Soc., 104, 133–53.

MACGREGOR, A. G. 1960. Divisions of the Carboniferous on Geological Survey Scottish Maps. Bull. Geol. Surv. Gt. Brit., 16, 127–30.

MACLAREN, C. 1839. A Sketch of the Geology of Fife and the Lothians, including detailed descriptions of Arthur's Seat and the Pentland Hills. 1st edit. Edinburgh.

MANSON, W. 1957. On the Occurrence of a Marine Band in the Anthraconaia modiolaris Zone of the Scottish Coal Measures. Bull. Geol. Surv. Gt. Brit., 12, 66–86.

MYKURA, W. 1960. The replacement of coal by limestone and the reddening of Coal Measures in the Ayrshire Coalfield. Bull. Geol. Surv. Gt. Brit., 16, 69–109.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

TROTTER, F. M. 1952. Sedimentation of the Namurian of North-west England and adjoining areas. Liv. and Manc. Geol. J., 1, 77–112.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 2 Ordovician and Silurian Ordovician

Ordovician

Ordovician strata are confined to two small and poorly exposed areas. The one about half a square mile, triangular in shape and bounded by the Leadburn Fault and a minor fault, lies a little south of Howgate on the line of the Herbershaw Anticline; the other occurs at the extreme south-eastern corner of the area on the upthrow side of the Lammermuir Fault south of Middleton Moor. The country rocks are apparently greywackes, pebbly grits and shales which by reference to adjoining, areas are probably to be assigned to the Caradoc Series. G.H.M.

Silurian

Silurian strata crop out in three small areas in the Pentland Hills, where they form the North Esk, Bavelaw Castle and Loganlee–Craigenterrie inliers. They are everywhere highly inclined and are overlain by beds of Lower or Upper Old Red Sandstone age, which rest with marked angular unconformity on their truncated edges. It has long been thought that the age of Silurian rocks in the Pentland Hills ranges from Wenlock to Downtonian (Peach and Horne 1899, p. 589; p. 19 of this account). In a detailed re-investigation of the Pentland fauna, Lamont (1947, pp. 193–208; 289–303) has claimed that the rocks formerly classed as Wenlock and Ludlow are of Gala–Tarannon, that is Llandovery, age and fall largely within the zone of Monoclimacis [Monograptus] crenulata. Lamont (1952; 1954, p. 271) later stated that this Scottish group of rocks is represented in Shropshire and the English Midlands by a non-sequence or 'pseudo-conformity' between topmost Llandovery and basal Wenlock, and he proposed the term Pentlandian' (1952, p. 27) for a new division of the Silurian System to accommodate these. The beds formerly termed Downtonian are tentatively assigned by Lamont to the Wenlock.

Details

North Esk Inlier

The North Esk inlier (Figure 4) is the largest of the Silurian inliers and covers an area of 2.25 sq. m. It is composed of highly inclined or vertical strata which strike N.30°E. to N.35°E. and, with the possible exception of some minor folds, form an ascending succession from east-south-east to west-north-west (p. 12). The succession in the inlier was first described by Geikie (in Howell and Geikie, 1861, p. 4) who considered that the sequence can be divided into a lower series of Ludlow age and an upper predominantly red series ascribed to the Lower Old Red Sandstone. Henderson and Brown (1867; 1870) produced the first detailed map of the inlier and recognized eight distinct fossiliferous horizons termed 'A' to 'H' (p. 12) in the North Esk and its tributaries. They concluded that the age of the strata ranges from Wenlock to Ludlow and drew the boundary between the two systems at the top of their bed E (1867, p. 29; 1870, p. 269). Peach and Horne (1899, p. 603) considered that the Silurian beds in the inlier range from Wenlock to Downtonian. They did not precisely define the boundary between Wenlock and Ludlow, apparently accepting the dividing line suggested by Henderson and Brown. The base of the Downtonian was drawn at the base of the red conglomerate and sandstone which crops out near the head of the North Esk and on the shore of Baddinsgill Reservoir.

The following table summarizes the succession in the inlier:

Peach and Horne (1899, figs. 120, 121) believed that the beds forming group (1) and groups (6) to (10) of the above sequence are folded into a series of almost isoclinal folds with near vertical axial planes. Current bedding and sole structures are poorly developed in the sandstones and siltstones, but, where present, they indicate that as a general rule the beds become younger to the west-north-west. There are, however, considerable sections in argillaceous parts of the sequence where no good younging criteria are found and the presence of local isoclinal folds can thus not be ruled out. In some of the strata belonging to group (9) exposed in the Lyne Water, bottom structures are mostly obscured or obliterated by shear planes trending parallel to or at low angles to the bedding planes, and in many exposures throughout the inlier thrust planes or west-north-west to north-west trending transcurrent faults, generally with small displacement, are seen to cut the beds, making the accurate determination of the succession difficult. No reliable estimate can thus be made of the thickness of strata forming group (1) and groups (9) to (10) and the thicknesses of other groups as shown on the table must be regarded as approximate.

(1). Reservoir Beds

Good exposures of the Reservoir Beds are seen in the gorge cut by overflow waters from the North Esk Reservoir, 250 yd S.E. of North Esk Cottage and on the east and north shores of the reservoir. Incomplete sections occur along the North Esk above and below the reservoir and in the lower reaches of the Deerhope Burn. The succession consists of mudstone and siltstone with thin ribs of fine-grained grit but contains also some predominantly arenaceous sequences (Figure 4). The fine-grained beds are often laminated, laminae of purple mudstone alternating with pale green siltstone. In the fine-grained sequences the grit beds range in thickness from 0.25 in to 4 in. In the sandy horizons grit beds, normally up to 1 ft 4 in thick, though locally attaining 4 ft, are interbedded with alternating bands of pale siltstone and dark grey to purple mudstone. Graded bedding is nowhere well developed, either within individual grit beds or within larger sedimentary units, and both upper and lower junctions of the grit bands are usually well defined. Small scale cross-bedding is common in both grit and siltstone, and convolute bedding is present in the upper part of some grit bands. Orientation of foreset beds of cross-bedded units suggests current movement during deposition from east to east-north-east.

The beds are very sparsely fossiliferous. Craniops implicata (J. de C. Sowerby), Glassia compressa (J. de C. Sowerby), and very rare Lingula sp.are scattered throughout the sequence; fragments of Dictyocaris sp.are abundant in the siltstones and grits at the south-east corner of the Reservoir. Henderson and Brown (1867, p. 27) have recorded Monograptus priodon (Bronn) and Retiolites geinitzianus Barrande from a rock knob 150 yd E.20°S. of North Esk Cottage. Near the top of the sequence in three localities along the North Esk the following faunal assemblage has been recorded^‡2  Survey during the recent revision of the area are given. References to other fossil records are given in the text. (c=common; r=rare.): Crinoid columnals c; Plumulites sp.r; Atrypa reticularis (Linnaeus) r, Craniops implicata r, Dicoelosia aff. biloba (Linnaeus) r, Eospirifer radiatus (J. de C. Sowerby) r, Fardenia applanata (Salter) c (in one band), Leptaena rhomboidalis (Wilckens) c (in one band), Plectodonta canastonensis (O. T. Jones) c (in one band), Resserella elegantula (Dalman) r, Skenidioides lewisii (Davidson) r, Sphaerirhynchia cf. wilsoni (J. Sowerby) r; Phacops cf. stokesii (Milne Edwards) r, Proetid pygidium; Beyrichia kloedeni McCoy r, Entomis impendens Haswell.

A similar, but less comprehensive fossil assemblage occurs in the mudstones exposed in the Deerhope Burn, 625 yd W. 22° N. of North Esk Cottage. The latter have also yielded Monograptus cf. vomerinus (Nicholson) and Diversograptus?

The zones of shattered but not greatly slickensided rocks exposed on the east and north banks of North Esk Reservoir (Figure 4) may mark the line of a fault trending approximately N.30° W. To the north-east of this line the generalized sequence of strata exposed on the shores of the reservoir and along the Gutterford Burn is as follows:

Sedimentary structures suggest younging to west-north-west throughout the sequence though few are seen in the upper stretches of Gutterford Burn. The strata near the base of the Gutterford Burn Mudstones (ii) contain worm tracks, orthocones, Craniops implicata and Glassia compressa. A high proportion of the graptolites recorded from the Pentland Hills has been obtained from the Gutterford Burn Flagstones (iii) and the lower 60 ft of the succeeding group. They include Dictyonema sp., Koremagraptus sp., Monograptus cf. priodon (Bronn) and Monograptus vomerinus aff. var. gracilis Elles and Wood. In addition Peach and Horne (1899, pp. 593, 595) recorded Cyrtograptus murchisoni?, C. sp., Dictyonema venustum Lapworth and Dictyonema (Chondrites) verisimile (Salter)' from the top of the group. Lamont (1947, pp. 196–198; 1952, p. 29) has stated that Monoclimacis [Monograptus] crenulata (Tornquist), Koremagraptus sp., Acanthograptus sp., Spirograptus aff. falx (Suess) and ? Spirograptus cf. spiralis (Geinitz) have been obtained from the Gutterford Burn Flagstones. Not all the specimens recorded by these authors have been re-examined, but none of the specimens of Monograptus in the possession of the Geological Survey appears to be M. vomerinus var. crenulatus.

A brown-weathering limestone, varying from 8 to 10 in in thickness is interbedded with siltstones and mudstones near the top of the Gutterford Burn Flagstones (iii). It is composed largely of crinoid columnals and contains a number of corals, as well as a varied Shelly fauna. The following forms were collected during the recent revision by the Geological Survey (vc = very common; c =common; r =rare):

The siltstones and mudstones associated with the limestone have yielded crinoid columnals, Orbiculoidea rugata (J. de C. Sowerby) as well as fragments of Dictyocaris and Chondrites.

In addition to the above a list of fauna collected from the limestone has been published by Peach and Horne (1899, p. 595) and further comments on the fauna have been made by Lamont (1947).

The Eurypterid-bearing beds consist of flaggy micaceous grit intercalated with grey siltstone and mudstone. The Eurypterid remains are associated with those of the Phyllocarid Dictyocaris ramsayi Salter, which forms black patches on the bedding planes, and with occasional graptolites. The Dictyocaris was redescribed and figured by Stormer (1935). A list of fauna collected from this horizon was published by Peach and Horne (1899, pp. 593–5) and descriptions of the Chelicerata were published by Laurie (1893, 1899).

A series of siltstones with flaggy grit ribs crops out on the North bank of the North Esk Reservoir, where it is bounded to the east by the purple mudstones (group ii) and to the west by the belt of broken strata. These beds appear to represent part of the Gutterford Burn Flagstones, but none of the fauna which characterizes the latter has so far been found.

The transition from the predominantly arenaceous Gutterford Burn Flagstones to the overlying mainly argillaceous beds is gradual. Where individual beds in the transitional zone can be traced for any distance along the strike there is an increase in the number and thickness of the arenaceous beds in a north-north-easterly direction. Two starfish-bearing horizons have so far been recorded from these beds. The upper horizon is exposed at the classical starfish locality (Peach and Horne, 1899, p. 593), and from this the following species of asteroids have been described by Spencer (1914–1940): Crepidosoma wenlocki Spencer, Furcaster leptosoma (Salter), Lepyriactis nudus Spencer, Protactis wenlockensis (Spencer), Schuchertia wenlocki Spencer, Taeniactis wenlocki Spencer, Urasterella gutterfordensis Spencer.

The starfish are associated with a sparse shelly fauna, which includes Glassia compressa, and from which Peach and Horne (1899, p. 593) have recorded Glassia obovata, Orthis sp., Cheirurus bimucronatus (Murchison), Phacops stokesii (M. Edwards) and Monograptus vomerinus. The lower starfish bed is near the base of the group, the starfish occurring in a 2-mm band of buff siltstone within a sequence of grey mudstone and siltstone. The following fauna has been collected; the starfish being less well preserved than in the classical locality: Serpulites sp. r; Conularia? r; Furcaster leptosoma c; Glassia compressa, Lingula symondsii Davidson.

The Silurian strata exposed near the head of the Monk's Burn consist of thin bands of fine-grained grey sandstone with interbedded grey shales and siltstones, apparently passing west-north-westwards into grey and purplish shales and mudstones. Henderson (1874, p. 374) has recorded fragments of Dictyocaris from these beds.

(2). Deerhope Burn Flagstones

Both in the Deerhope Burn and in the River North Esk the alternating purple and grey silty mudstones which form the top of the Reservoir Beds are overlain by 350–400 ft of fine-grained, flaggy greywacke interbedded with purplish grey and green siltstones and mudstones. These beds become progressively more sandy in a north-westerly direction (upward succession) and grade into the coarse greenish grits of the overlying group. The siltstones exposed in both streams have characteristically corrugated surfaces, which appear to be due to shear and are not original sedimentary structures. A band of siltstone exposed on the left bank of the North Esk, at an acute-angled bend of the stream, 935 yds N.30° W. of North Esk Cottage has yielded an assemblage of corals, and a shelly fauna which is somewhat similar to that from the limestone in the Gutterford Burn Flagstones. The fauna collected by the Geological Survey from this bed is as follows:

Pleurodictyum problematicum c, Streptelasma sp. vc; crinoid columnals vc; Chonetes aff. novascoticus vc, Orthid r, Strophomena walmstedti Lindström r; Goniophora antiquata Hind i, Modiolopsis sp.c, Orthonota? scotica Lamont r; indeterminate gastropods c; Hyolithes sp. c; Phacops aff. stokesii r; Beyrichia kloedeni r; Eurypterid fragments r. Lamont (1954) has recorded nine new species of lamellibranchs, together with Chonetes aff. edmundsi H. S. Williams, C. striatellus, Strophomena walmstedti, Idiorthis sp. nov., Eophacops aff. sufferta Lamont, Petraia cf. subduplicata McCoy, Plumulites sp., Monotrypa? and Myelodactylus? from a three-inch layer of siltstone in this locality.

Lamont (1954, p. 271) tentatively correlated the Deerhope Burn Flagstones with the flagstone group in the Gutterford Burn, and he suggested that the lamellibranch-bearing siltstone occupies the same horizon as the Gutterford Burn limestone. He has presumably assumed that the displacement of the outcrop implied by this correlation is due to dextral displacement along the crush belt passing through the North Esk Reservoir. The correlation of the two flagstone groups cannot, however, be substantiated on lithological grounds. The Gutterford Burn Flagstones are overlain by up to 600 ft of predominantly argillaceous beds with a scarce shelly fauna, whereas the Deerhope Burn Flagstones pass upwards into the Haggis Grit and Conglomerate which is in turn overlain by highly fossiliferous siltstones and mudstones (Beds 'D' to 'H'). It could be argued that the Haggis grits and conglomerates are of purely local character and that the higher Gutterford Burn beds are the equivalents of the fossiliferous beds ('D' to 'H') of the North Esk. This would imply a rapid facies change within a distance of less than one mile, which is not in accordance with the remarkable consistency in both lithology and fauna of beds 'G' to 'H' within the North Esk and Lyne Water basins. It seems more likely that the Gutterford Burn beds are on a lower horizon than the Deerhope Bum Flagstones (possibly 2000 ft lower) and that there is very little if any displacement along the crush belt exposed at the reservoir.

(3) Haggis Grit and Conglomerate

The Deerhope Burn Flagstones grade upwards into a sequence of grits with thin partings of contorted shale or silty shale. In the North Esk valley the grits contain two somewhat ill-defined beds of pebbly grit with a greenish-grey matrix and sub- to well-rounded pebbles ranging up to 1 in in diameter and locally with numerous pellets of purple or pale green 'marl'. The pebbles consist of quartzite, quartz-porphyry and feldspar-quartz-porphyry often with graphic intergrowth of quartz and feldspar in the groundmass, haematite impregnated chert consisting of small radiating spheres of chalcedony, microgranite, altered sub-basic lava with quartz amygdales, and indurated fine-grained sediment. The matrix is composed largely of ungraded angular grains of quartz together with small fragments of fine-grained intermediate to basic igneous rock and an irregular chloritic aggregate in the interstices.

Current bedding and sole structures indicating younging to west-north-west are seen at several horizons in the group.

Exposures of this group in the Deerhope Burn are generally of finer grain and there is only one conglomeratic horizon present. The latter represents the upper conglomerate of the North Esk, but is considerably thinner and contains pebbles not exceeding 0.25 in diameter.

The sandstones and one band of siltstone exposed in the North Esk valley near the top of the group have yielded a scarce shelly fauna which includes Lingula lewisii; Grammysia cf. undata (J. de C. Sowerby), Orthonota sp.and a Modiolopsid. A similar fauna has also been recorded by Peach and Horne (1899, p. 596) from the sandstones exposed in the Deerhope Burn.

(4) Fossiliferous mudstones and siltstones (Beds 'D' to 'H' of Henderson and Brown)

The Haggis Grit and Conglomerate is overlain by approximately 950 ft of greenish-grey to yellowish mudstone and siltstone with occasional bands of soft greenish-brown sandstone. The beds are generally unlaminated with a tendency to spheroidal weathering. Lamination is, however, well developed between 480 ft and 520 ft above the base of the group. The top of the group is poorly exposed in the North Esk and Henshaw Burn, where Peach and Horne (1899, p. 599) have recorded a gradual transition from grey siltstone through soft red shale to the overlying red conglomerate. In the headwaters of the Lynslie Burn, however, the passage from silty mudstone to pebbly grit and conglomerate is abrupt, though there is no sign of angular unconformity.

The group contains a number of horizons with an abundant marine fauna. Appendix II shows the distribution of fossils collected by the Geological Survey during the recent revision. In the appendix the group is for convenience subdivided into the 'zones' D' to 'H' established by Henderson and Brown, which cannot, however, be regarded as more than convenient local units, and are not zones of stratigraphical significance. Full lists of the fauna collected from these 'zones' during the last century are given by Peach and Horne (1899 pp. 596–602). Lamont (1947; 1952, pp. 27–30) has recorded a number of additional forms from several horizons and has studied the ecology of the entire fauna. He concluded (1952, pp. 28–29) that the faunal assemblage from the 'Plectodonta mudstones' (lower 'E' and ?topmost 'D') exposed in the Deerhope Burn was adapted to conditions of slow sedimentation in clear waters, possibly combined with seasonal periods of emergence and erosion, whereas the fauna from the same and higher horizons (e.g. Henshaw silts =bed 'H') in the North Esk was adapted to deeper, quieter waters and a faster rate of sedimentation.

(5) Red Igneous Conglomerate and Sandstone

Red sandstone and conglomerate forms the base of the beds formerly classed as Downtonian. The group consists of red and ochre mottled micaceous sandstone with angular quartz grains interdigitated with pale green and reddish-brown pebbly grit containing pebbles up to 2 in in diameter and with some thick lenses of conglomerate with rounded pebbles ranging up to 1 ft in diameter.

A high percentage of the pebbles is composed of acid igneous rocks, prominent among which is a fine-grained granite with graphic intergrowths of quartz and orthoclase or quartz-albite myrmekite enveloping euhedral feldspars. Other common types are quartz-rich granite with a high proportion of albite but without graphic structures, microgranite, quartz-feldspar-porphyry, felsite, partially silicified rhyolite, trachyte and some altered sub-basic lavas. Less than half the total number of pebbles are formed of sediments. These include indurated, partly silicified mudstone, fused fine-grained quartzose grit with mudstone pebbles, purplish grit with angular grains of acid lava, and reddish-brown and pale green siltstone and mudstone. Quartzite and vein quartz pebbles are rare. The source area of the conglomerate appears thus to have contained an outcrop of graphic granite associated with acid minor intrusions and probably lavas. Neither sediments nor igneous rocks show traces of shearing or schistosity, indicating that the source area was not affected by the post-Arenig (early Caledonian) earth movements.

(6) Lower Red Sandstone

The red and purple sandstone overlying the conglomerate attains a thickness of about 700 ft. It is best exposed on the north shore of Baddinsgill Reservoir, where it contains occasional pebbles of purple mudstone and igneous rock. A layer of quartzite conglomerate, 5 ft thick, resting on 3 ft 4 in of laminated mudstone and siltstone, is intercalated with the upper beds of this group. It crops out in the Henshaw Burn and does not appear to extend south-westward into the basin of the Lyne Water. The pebbles in the conglomerate are well rounded, and though generally small, range up to 4 in in diameter.

(7, 8). Lower Argillaceous Beds and Middle Red Sandstone

The Lower Red Sandstone of the North Esk basin appears to be represented in the Lyne Water basin by two horizons of red sandstone separated by up to 230 ft of fine sediments. Peach and Horne (1899, figure 121) considered that the western outcrop of red sandstone in the Lyne Water is part of the lower sandstone repeated by folding. Evidence from current bedding and sole structures, however, indicates that these beds young consistently to west-north-west, and that the fine-grained sediments form a true intercalation in the sandstone. The sequence of the fine-grained sediments (7) exposed along the Lyne Water is as follows:

The upper part of the sequence is made up of thin layers of alternating sandy and fine-grained sediments which display cross-lamination, convolute bedding and occasional flute casts. Younging is consistently to west-north-west and, assuming there has been no significant rotation during the folding of the beds, the direction of current movement during deposition was from approx. E. 10° S. The beds occurring approximately 90 ft below the base of the second red sandstone have, according to Peach and Horne (1899, p. 602) yielded Glauconome, Spirorbis and a fragment of Ateleaspis tessellata Traquair. The last was probably identified by Traquair. A Eurypterid fragment has been obtained from this horizon during the revision of the ground.

The Middle Red Sandstone attains a thickness of 175 ft in the Lyne Water area. It is fine-grained and contains lenses of pebbly grit with pebbles of vein quartz, acid lavas and chocolate-brown mudstone. Current bedding, suggesting current movement from east-north-east is seen near the base of the group.

(9) Upper Argillaceous Beds

The Middle Red Sandstone of the Lyne Water sequence is succeeded by a series of purple or pale green mudstones interbedded with bluish-grey flaggy sandstones and siltstones. Near the top of the group beds of micaceous greywacke up to 30 ft thick are interbedded with striped siltstone and mudstone. It is not possible to make a reliable estimate of the thickness of the group as the beds are cut by transcurrent faults of small displacement and by at least one thrust. In many exposures small shear planes run parallel to or at low angles to the bedding planes and sedimentary structures which can be used to determine the direction of younging are rare. From strata exposed near the base of the group in the Lynslie Burn, Peach and Horne (1899, p. 603) have recorded a sponge, crinoid stems and minute fragments of Birkenia elegans Traquair, Ateleaspis tessellata and Lasanius problematicus Traquair, (?identifications by R. H. Traquair), and during the revision of the area Glauconome disticha Goldfuss, Eurypterid traces and indeterminate fish fragments were found at this locality.

(10) Upper Red Sandstone

The highest Silurian strata in the Lyne Water basin are composed of reddish-brown poorly bedded sandstone with thin partings of red silty mudstone passing up into reddish conglomerate and grey medium-grained pebbly grit. The sandstone rests on an eroded surface and contains pebbles of reddish-purple mudstone.

Loganlee–Craigenterrie Inlier

The Silurian strata forming the Loganlee–Craigenterrie inlier crop out in a narrow strip extending from the Logan Burn, 200 yd to 300 yd W.S.W. of Loganlee, north-north-westwards along the east and north slopes of Black Hill to the west slope of Bell's Hill, 730 yd S.E. of Craigenterrie (Figure 2). The inlier is bounded on the west by the Black Hill Felsite, whose junction with the Silurian sediments is vertical near the southern end of the outcrop, and on the east by a north-north-east trending fault with a large easterly downthrow.

In the greater part of the inlier the strike of the beds varies from N. to N.22° E. and the dip is near vertical, with a range from 80° to W.N.W. to 50° to E.S.E. Along the north-east slope of Black Hill, close to the junction with the felsite the strike of the Silurian shales is roughly parallel to the margin of the felsite (range W.10° S. to W.40° N.) and the dip with one exception varies from 35° to 60° away from the felsite.

The sediments are best exposed on the south-east slope of Black Hill close to the footpath leading from Loganlee to Bavelaw. They consist of greenish-grey and purple shales with layers of siltstone and occasional thin beds of flaggy sandstone as well as a number of thicker sandstone posts. Small scale ripple marks (Lamont 1954, p. 272) as well as occasional flute casts and mud flow structures are found in and on the soles of some siltstone and sandstone beds. These indicate that the beds young to the west-north-west and that, if there has been no appreciable tectonic rotation, the direction of current movement during deposition varied from north-east to east-south-east.

Several species of graptolites were collected by Henderson in this locality. Lapworth (1874), who considered them to be a Wenlock assemblage, identified a variety of Monograptus colonus Barrande, M. priodon, M. flemingi, Retiolites geintzianus and Dictyonema assimile. Lamont (1947, p. 197), however, has pointed out that these identifications cannot all be substantiated, and that the specimens on which the identification of M. flemingi was based, are lost. Protovirgularia sp., Pterotheca sp.and an indeterminate fragment of graptolite were collected during the recent revision.

Bavelaw Castle Inlier

The Bavelaw Castle inlier forms a triangular area extending eastwards from Bavelaw Castle to the western slope of Black Hill and south to the northern slope of Hare Hill. The strata are fairly uniform and consist of grey to purplish-grey mud-stones or silty mudstones frequently interlaminated with siltstones. Thin ribs of flaggy sandstone up to 3 in thick are found at some horizons, but predominantly arenaceous beds are rare. The strike of the beds varies from N.30° W. in the Bavelaw Castle quarries to N.–S. at the eastern end of the outcrop. The dip is vertical or steeply inclined to west or west-north-west.

The lithology of these beds closely resembles that of the lowest group (Reservoir Beds) in the North Esk Inlier, but the fauna is slightly more varied. The main fossiliferous localities are two quarries respectively 200 and 300 yd S.S.E. of Bavelaw Castle and two gullies on the north slope of Hare Hill, respectively 1020 yd and 1180 yd E.S.E. of Bavelaw Castle. Faunal lists from these localities were published by Peach and Horne (1899 p. 605). These include in addition to the shelly fauna Monograptus sp.and Retiolites geinitzianus from the more easterly of the two gullies. No additional species were collected during the recent revision by the Geological Survey. Lamont (1952, p. 27) has recorded Lingula minima, Buthotrephis, Stylonurus and washed out worm tubes of Monocraterion cf. clintonense from the Green Cleugh area, and an Acidaspid trilobite from Bavelaw. He considers that the fauna from the inlier indicates deposition in clear shallow water with periodic emergence of the land, possibly leading to the formation of tidal flats.

Lamont (1954, p. 272) considers the beds of this inlier to be slightly older than those of the Loganlee–Craigenterrie Inlier, which he takes to be roughly contemporaneous with the Gutterford Flagstones of the North Esk Inlier.

Age of the Pentland Silurian Rocks: stratigraphical conclusions

A summary of the various opinions about the age of the Silurian rocks in the inliers is given in the following table:

In addition O. T. Jones (in Evans and Stubblefield 1929, p. 108) has stated that the brachiopods from the beds assigned by previous workers to the Ludlow, suggest a Wenlock age and that there is nothing sufficiently distinctive in the other elements of the fauna to prove the presence of Ludlovian. Westoll (1951, p. 7) considered that "... it is at least certain that the fish beds of the Lesmahagow, Hagshaw Hills and Pentlands are not of Downtonian age. A late Wenlock or early to middle Ludlow age would seem reasonable".

Lamont's new synchrony is based on a detailed study of the invertebrate fauna from the inlier, with particular reference to the graptolites. He has claimed that the occurrence of Monograptus vomerinus var. crenulatus and Spirograptus aff. falx indicates an upper Gala, that is post-Llandovery and pre-Wenlock age. Prof. O. M. B. Bulman and Dr. Isles Strachan have examined the Geological Survey collection of graptolites from the Pentland Hills, but have not recognized any of the vomerinid Monograptids as M. vomerinus var. crenulatus. Spirograptus falx is attributed by Münch (1952, p. 117) and others to the Gala–Tarannon (Upper Llandovery), but the specimen recorded from the Pentland Hills by Lamont is claimed only to have affinities with S. falx. Prof. Bulman has reported that the graptolites identified by him support either a topmost Llandovery or a basal Wenlock age. Dr. Lamont has collected one graptolite from an exposure in the Henshaw Burn (Bed 'G' or 'H'); this specimen has been identified by Prof. Bulman as Monograptus vomerinus aff. var. gracilis, and is similar to the vomerinid Monograptids from the Gutterford Burn, possibly some 2500 ft lower in the succession. This graptolite precludes a Ludlow age for the beds exposed in the Henshaw Burn and adds weight to Lamont's claim (1955, p. 200) that the higher horizons in the Pentland Hills are not much younger than the Gutterford Burn beds.

Dr. Strachan reports that the Pentland Hills graptolites are most likely to be of pre-Wenlock age. He states that the fauna does not match with that from the basal Wenlock beds exposed on the Solway Firth, but agrees well with the immediate pre-Wenlock fauna of Continental Europe.

The presence of Plectodonta canastonensis (O. T. Jones) supports the suggestion of a pre-Wenlock age for the Plectodonta canastonensis Mudstones, since the eponymous brachiopod has been recorded only from Upper Llandovery rocks (O. T. Jones, 1928, p. 447).

It should be pointed out, however, that many of the non-graptolite invertebrate species used by Lamont as evidence for a Gala–Tarannon age of the beds are new and still undescribed. Descriptions of the Chelicerata (Lamont 1955), some trilobites (Lamont 1948, 1949, pp. 319–321) and some lamellibranchs (Lamont 1954) have now been published, and it is considered by the present writers that there is evidence for the Pentlandian strata, possibly up to Bed 'H', being of Upper Llandovery age.

Recent work by Rolfe (1960, 1961) has suggested that the lower beds exposed in the Hagshaw Hills and Carmichael inliers of Lanarkshire are of highest Valentian (Llandovery) age and can thus be roughly correlated with the lower beds of the Pentland Silurian. W.M., J.D.D.S.

References

EVANS, J. W. and STUBBLEFIELD, C. J. 1929. Handbook of the Geology of Great Britain. London.

HASWELL, G. C. 1865. On the Silurian Formation in the Pentland Hills. Edinburgh.

HENDERSON, J. 1874. On some Silurian Fossils found in the Pentland Hills. Trans. Edin. Geol. Soc., 2, 373–5.

HENDERSON, J. 1880. On some recently discovered Fossiliferous Beds in the Silurian Rocks of the Pentland Hills. Trans. Edin. Geol. Soc., 3, 353–6.

HENDERSON, J. and BROWN, D. J. 1867. On the Silurian Rocks of the Pentland Hills, Part I. Trans. Edin. Geol. Soc., 1, 23–33.

HENDERSON, J. 1870. On the Silurian Rocks of the Pentland Hills, Part II. Trans. Edin. Geol. Soc., 1, 266–72.

HOWELL, H. H. and GEIKIE, A. 1861. The Geology of the Neighbourhood of Edinburgh. Mem. Geol. Surv.

JONES, O. T. 1928. Plectambonites and some Allied Genera. Mem. Geol. Surv. Palaeont., 1, part 5, 367–527.

LAMONT, A. 1947. Gala–Tarannon Beds in the Pentland Hills, near Edinburgh. Geol. Mag., 84, No. 4, 193–208; No. 5, 289–303.

LAMONT, A. 1948. Scottish Dragons. Quarry Managers' J., 31, 10, 531–35.

LAMONT, A. 1949. New Species of Calymenidae from Scotland and Ireland. Geol. Mag., 86, 313–23.

LAMONT, A. 1952. Ecology and Correlation of the Pentlandian — a new Division of the Silurian System in Scotland. Rep. 18th Int. Geol. Congr., London, Part 10, 27–32.

LAMONT, A. 1954. New Lamellibranchs from the Gutterford Burn Flagstones (Gala‑ Tarannon) of the Pentland Hills, near Edinburgh. Proc. Roy. Soc. Edin. B., 65, Part 3, 271–84.

LAMONT, A. 1955. Scottish Silurian Chelicerata. Trans. Edin. Geol. Soc., 16, 200–16.

LAPWORTH, C. 1874. Note on the Graptolites discovered by J. Henderson in the Silurian Slates of Habbies Howe, Pentland Hills. Trans. Edin. Geol. Soc., 2, 375–7.

LAURIE, M. 1893. Some Eurypterid Remains from the Upper Silurian Rocks in the Pentland Hills. Trans. Roy. Soc. Edin., 37, 151–61.

LAURIE, M. 1899. On a Silurian Scorpion and some additional Eurypterid Remains from the Pentland Hills. Trans. Roy. Soc. Edin., 39, 575–90.

MÜNCH, A. 1952. Die Graptolithen aus dem Gotlandium Deutschlands and der Tschechoslowakei. Geologica, 7, 1–157.

PEACH, B. N. and HORNE, J. 1899. The Silurian Rocks of Great Britain, 1, Scotland. Mem. Geol. Surv.

PEACH, B. N. , CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY; E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

ROLFE, W. D. I. 1960. The Silurian Inlier of Carmichael, Lanarkshire. Trans. Roy. Soc. Edin., 64, 245–60.

ROLFE, W. D. I. 1961. The Geology of the Hagshaw Hills Silurian inlier, Lanarkshire. Proc. Geol. Soc. London. No. 1585, 48–52.

SPENCER, W. K. 1914–1940. British Palaeozoic Asterozoa, Parts 1–10, Palaeont. Soc.

STØRMER, L. 1935. Dictyocaris, Salter, a large Crustacean from the Upper Silurian and Downtonian. Norsk Geol. Tidsskr., 15, 267–98.

WESTOLL, T. S. 1951. The Vertebrate-Bearing Strata of Scotland. Rept. 18th Int. Geol. Congr., London, Part 11, 5–21.

Chapter 3 Lower Old Red Sandstone

Rocks of Lower Old Red Sandstone age form the belt of high ground extending south-westwards from the southern suburbs of Edinburgh for twelve miles to the edge of the area shown on the sheet. They form the greater part of the Pentland Hills, the Braid Hills and Blackford Hill, the igneous rocks of which area have recently been the subject of a detailed paper by Mykura (1960).

The Lower Old Red Sandstone rests unconformably on an eroded land-surface of Silurian rocks. The lower part of the succession consists of sediments, the upper of lavas with thin intercalations of tuff and sediment. Basic and sub-basic minor intrusions cut the sediments and underlying Silurian rocks, but are rare in the volcanic group. A small intrusion ranging in composition from diorite to microgranite crops out near the head of the Lyne Water, and a felsite with distinctive petrographical characteristics forms North Black Hill (p. 27).

Sedimentary rocks

In the south-western part of the area the sediments which here form the lowest beds of the Old Red Sandstone consist of about 2000 ft of interbedded conglomerates and pebbly grits. They are not exposed north of the latitude of Harbour Hill and it seems probable that they thin gradually northwards and that the lowest lava groups are contemporaneous with part of the sedimentary succession.

The sediments consist of thick lenses of coarse greenish conglomerates interbedded with greenish or grey, pebbly grits and sandstones. The conglomerates are generally coarsest near the base of the series; they recur throughout the succession. Isolated pebbles are also found in both grits and sandstones. The majority of the pebbles are well rounded and derived from Siluro-Ordovician rocks such as now form the Southern Uplands. They include greywackes, pebbly grits, radiolarian cherts and jasperized basic lavas, of which the first are by far the most abundant. Near the base of the succession local material derived from the underlying Silurian rocks is common and in particular pebbles from the three Silurian conglomerate bands have been noted just above the plane of unconformity. Most common amongst these are well-rounded, often broken quartzites, granites and acid lavas.

Blocks of Silurian limestone in the Lower Old Red Sandstone conglomerate cropping out in the Logan Burn, between 100 and 150 yd upstream from the lowest waterfall at Habbie's Howe have yielded the corals Tetradium, Favosites, Halysites, Plasmopora, Heliolites and other fossils including trilobites, brachiopods and orthocones (Peach and Horne 1899, p. 606). These blocks were first discovered by Henderson (1874), who pointed out that they are less rounded than the other pebbles in the conglomerate and are thus probably of local origin; and suggested (Henderson 1880), that they were derived from bands of limestone similar to that cropping out in the Gutterford Burn (p. 14).

Except in the case of the basal conglomerate of Loganlee (p. 10) pebbles of Lower Old Red volcanic rocks do not normally occur in the lower portion of the sedimentary sequence, but in the topmost sediments pebbles from a number of lava groups are found. There is also an increase in the content of feldspathic material in the highest sediments (Peach and others 1910, p. 22).

The post-Silurian plane of unconformity is nowhere well exposed, but its position is clearly seen near the head of the Lyne Water at the western edge of the North Esk Inlier (Figure 4), on the east bank of the North Esk, 450 yd S.S.E. of the North Esk Reservoir, and on the hillside just north of Fairliehope Burn, half a mile south-west of the reservoir. The best sections of the sedimentary beds are to be found in the River North Esk, between the Pentland Fault at Carlops and the Silurian inlier, in the Monk's Burn, and in the gorge cut by the Logan Water half a mile south-west of Loganlee.

Volcanic rocks

The volcanic rocks of the Pentland Hills consist of ten distinct lava groups with interbedded pyroclastic and some sedimentary beds. They attain a thickness of over 6000 ft in the Caerketton–Allermuir area but thin rapidly to the south. For particulars of their petrography and distribution the reader is referred to the recent detailed description by Mykura (1960) who recognized the following downward succession (Figure 5):

The petrography of the various groups has been described in detail by Flett (in Peach and others 1910, pp. 29–41).

In the Braid Hills and Blackford Hill area there is a sequence of trachytes, andesites and basalts with subsidiary tuff bands (Mykura 1960, p. 142). A rough similarity can be suggested between this sequence and the Pentland Hills succession, but it seems more likely that the two sequences are not related, and that the volcanic rocks of the Braid Hills occupy a higher horizon than the Pentland lavas and are separated from the latter by a fault which may extend along the depression between Fairmilehead and Swanston (Figure 5). Recent temporary exposures of macroporphyritic basalt in the West Mains Road area of Edinburgh at the top of the succession were described by Cockburn (1956).

(Figure 6) shows the extent and approximate thickness of the various volcanic groups and associated sediments within the main Pentland outcrop. It illustrates the thinning of the lavas from north-east to south-west and the pronounced southward overlap of the higher groups. The distribution of the lavas supports the suggestion made by Peach (in Peach and others 1910, p. 27) that the main vent of the Pentland volcanic centre, if such existed, must have lain to the north of the Pentland Hills, possibly in the neighbourhood of Colinton.

The pale red felsite or microgranite which forms North Black Hill was considered by Peach (in Peach and others 1910, p. 26) to be a laccolith intruded along the plane of unconformity between the Silurian and Lower Old Red Sandstone sediments. Additional field evidence has shown that this felsite mass has a more complex history, and Mykura (1960, p. 145) has suggested that it may have originated as an extrusive dome on the early Lower Old Red Sandstone land-surface. It is possible that several other early acid extrusive domes were formed on this land-surface within the area now forming the northern Pentland Hills. The rhyolite of Braid Law and the trachyte of Torduff Hill are examples.

Intrusions

A considerable number of minor intrusions cut the Silurian and Lower Old Red Sandstone sediments in the Pentland Hills. Descriptions of them with maps showing their distribution have been given by Cockburn (1952) and Mykura (1960). As they are less common in the lavas and absent in the Upper Old Red Sandstone it is supposed that they are of Lower Old Red Sandstone age. They vary in composition from fine-grained olivine-dolerites and basalts to acid andesites.

On Harbour Hill there is a small boss-like intrusion of felsite similar to the mass of Black Hill; this perhaps represents a feeder for the upper beds .of the Bell's Hill or higher acid lavas.

A small intrusion of quartz-diorite showing vertical contacts with Lower Old Red Sandstone sediments on one side and overlain elsewhere unconformably by Upper Old Red Sandstone, occurs at the head of the Lyne Water. There is appreciable induration of the Lower Old Red Sandstone conglomerate where it is in contact with the Lyne Water diorite.

Volcanic vents of Lower Old Red Sandstone age have been mapped near Swanston and on the southern flanks of the Braid Hills. Most are infilled with agglomerates consisting mainly of acid and sub-basic lava fragments with a rhyolitic matrix, but some basic andesite and olivine-basalt fragments are found. W.M.

References

COCKBURN, A. M. 1952. Minor Intrusions of the Pentland Hills. Trans. Edin. Geol. Soc., 15, 84–99.

COCKBURN, A. M. 1956. Notes on the Geology of the Eastern Slopes of Blackford Hill, Edin‑ burgh. Trans. Edin. Geol. Sac., 16, 307–12.

HENDERSON, J. 1874. Notice on some Fossils from the Conglomerate at Habbie's Howe, Logan Burn, near Edinburgh. Trans. Edin. Geol. Soc., 2, 389–90.

HENDERSON, J. 1880. On some recently discovered Fossiliferous Beds in the Silurian Rocks of the Pentland Hills. Trans. Edin. Geol. Soc., 3, 353–6.

MYKURA, W. 1960. The Lower Old Red Sandstone igneous rocks of the Pentland Hills. Bull. Geol. Surv. Gt. Brit., 16, 131–55.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

PEACH, B. N. and HORNE, J. 1899. The Silurian Rocks of Great Britain, 1, Scotland. Mem. Geol. Surv.

Chapter 4 Upper Old Red Sandstone

Introduction

The Upper Old Red Sandstone has been mapped around the nose of the northeastward pitching anticlinal structure of the Pentland Hills from the Pentland Fault near Craigmillar by way of the City of Edinburgh and thence southwestwards through Oxgangs and along the north-western flank of the Pentland Hills.

The depositional phase of the Lower Old Red Sandstone period came to an end with the onset of important earth-movements, which were the final phase of the Caledonian orogeny in Scotland. The earth-movements were followed by a long period of erosion which gave rise to an undulating topography. The lavas of the northern Pentland Hills and the folded Ordovician rocks south of the Southern Upland Fault formed prominent features in this landscape, and the sediments deposited on the surface appear first to have filled up the basins and covered the low ground. Final drowning of the upland features was not complete until the close of Cementstone Group times. The first deposit in the Edinburgh district was a pink waterlaid quartzose sandstone with which are interbedded thin conglomerates and bands of marl. The sandstone contains calcareous concretions which have locally coalesced to form concretionary cornstones (Allen 1960). In the south-western Pentland Hills and in the Edinburgh district this basal sandstone is over 1000 ft thick and is conformably overlain by predominantly argillaceous beds with marls and cementstones which are similar to the Ballagan facies of the Cementstone Group. There is, however, a marked interdigitation of the two facies and in places pink sandstones are developed right to the top of the Cementstone Group.

On the original Geological Survey map of one-inch Sheet 32 and in the first edition of the memoir (Howell and Geikie 1861, p. 17), which followed the classification suggested by Maclaren (1839, p. 70), the base of the Carboniferous System was, with local exceptions, drawn at the unconformity separating the Pentland lavas from younger rocks. On later editions of one-inch Sheet 32 the basal red sandstone was assigned to the Upper Old Red Sandstone, the change being made partly on lithological grounds and partly as a result of the finding of Old Red Sandstone fish in what were taken to be the corresponding rocks of Fife (Traquair 1891, p. 386). The discovery of scales identified as Holoptychius nobilissimus (Peach and Horne 1905, p. 546, Traquair 1905) in the red sandstone underlying the teschenite sill of Salisbury Craigs and at Craigmillar provided the first faunal evidence within the area for the Upper Old Red Sandstone age of the sandstones. Since that time evidence from bores and temporary excavations in the Edinburgh district (Tait 1936, p. 307; 1939) has shown that the partially argillaceous strata immediately overlying the red sandstone contain a bed which has yielded Alcicornopteris convoluta Kidston. Tait has suggested that this horizon can be used as a fossil-marker indicating Carboniferous age and that the Old Red Sandstone–Carboniferous boundary can be drawn just below it. Alcicornopteris however in one-inch Sheet 32 has been recognized with the city of Edinburgh at several horizons.

In the course of a re-investigation of the Carboniferous succession within the City of Edinburgh (p. 34) fragmentary fish remains originally thought to be Holoptychius, both from the original collections and from subsequent bores, were re-examined. Dr. E. I. White, F.R.S., who examined the best of these fragments, has reported that they might be Holoptychius, but they might also be Rhizodus. He concludes that they must be pronounced indeterminate and is unable to place any great value on them for precise stratigraphical purposes. The matter is further discussed on p. 34. It is also becoming increasingly obvious that the genus Holoptychius by itself is not a satisfactory index fossil, and the age of the basal red sandstone is thus once again uncertain. On the forthcoming edition of one-inch Sheet 32 the lower boundary of the Carboniferous, as on preceding editions, is drawn at the lowest horizon at which red sandstones give way to argillaceous beds of Ballagan type. It must be emphasized (Macgregor and others 1940, pp. 256–7) that this boundary is a purely lithological one and has no true time significance. It may be possible to draw a more exact boundary when the problem of the Old Red Sandstone–Carboniferous junction has been investigated over a wider area.

Conditions of deposition

Peach (in Peach and others 1910, p. 46) suggested that the sediment of the Upper Old Red Sandstone was derived from the north and deposited in inland seas in an area undergoing gradual subsidence. The absence of marine fauna, together with evidence of dessication, chemical precipitation and contemporaneous erosion suggests that the climate was arid and that the inland seas periodically dried up. Much of the coarser material in the conglomerates appears to have been deposited as screes around the hills which locally rose out of the inland seas and was merged in the deposits coming in from the north. The origin of concretionary cornstones already mentioned (p. 28) was discussed by Maufe (1910) who compared them to the kanker of India and Africa, which forms a short distance below the surface in districts subject to alternating dry and wet seasons. A recent detailed investigation by Burgess (1960) of cornstones in the Upper Old Red Sandstone of Ayrshire appears to confirm Maufe's theory of their origin. Burgess has shown that the profiles of the Ayrshire cornstones are closely comparable with the Pliocene caliche limestones of south-central U.S.A., which have been described as pedocal soils formed under semi-arid conditions. Dessication breccias and 'marl' pellet rocks (including conglomeratic cornstone), whose origin has been discussed by Wills (1948, p. 28), provide further evidence for the periodic dessication of the floors of the inland seas.

Details

City of Edinburgh

The Upper Old Red Sandstone in the Edinburgh District is folded into a northward pitching anticline with a core of Lower Old Red Sandstone lavas and tuffs, which forms the Braid Hills and Blackford Hill. The outcrop is bounded to the east by the Pentland Fault and to the north-west in part by the Colinton Fault.

The Upper Old Red Sandstone consists of reddish to pale brown sandstone which contains occasional bands of red marl and thin cornstones, as well as some pebbly sandstones and conglomerates. The conglomerates are most strongly developed near the base of the succession in the Liberton–Craigmillar area, where they contain sub-angular pebbles of vein quartz, quartzite, radiolarian chert and rarer greywacke; near the base fragments of Lower Old Red Sandstone lava are abundant. Farther west in the Blackford and Morningside areas conglomerates and pebbly sandstones are poorly developed and occur only as isolated bands in the sequence. Intercalations of red and green marl and manly shale, often with calcareous concretions as well as local dessication breccias, occur sporadically throughout the sandstone (Goodchild 1901, pp. 2–3).

The thickness of the Upper Old Red Sandstone can only be roughly estimated, as the bores in the area have only proved small portions of the sequence. A bore for water at Craigmillar is said to have cut Upper Old Red Sandstone to a depth of 1800 ft (Peach and others, 1910, p. 44) but no record of this can now be traced. The estimated thickness of the beds in the Liberton and Craigmillar areas, based on the assumption that there is no major faulting, is about 1800 ft, and that in the area between Blackford and Bruntsfield may be as much as 2100 ft. The Upper Old Red Sandstone was encountered in bores at Grange Loan, Edinburgh (Tait 1920) and near Craiglockhart (Tait 1925).

Bonally, Torphin and Threipmuir

Peach (in Peach and others 1910, p. 45) has suggested that the Upper Old Red Sandstone must thin out between Craiglockhart and Bonally. He did, however, consider that the conglomerates and sandstones, which crop out close to the Lower Old Red Sandstone lavas near Torphin Hill, should be included in the Upper Old Red Sandstone. More recent evidence (pp. 38–41) suggests that the basal beds in this area and possibly those exposed south of Threipmuir Reservoir belong to the basal Carboniferous and that this area was high ground throughout Upper Old Red Sandstone times.

Hare Hill, Cairn Hills and Colzium Hill

The basal red sandstone thickens rapidly south of the latitude of Bavelaw Castle to form the two-mile-wide outcrop which extends from Hare Hill south-westwards to Colzium Hill (Figure 7). The sandstone, which is about 1000 ft thick in the Cairn Hills area, consists very largely of pink, medium-grained, quartzose sandstone. It is frequently current-bedded and patchily calcareous, showing typical 'honeycomb' weathering on exposed surfaces. A thin basal conglomerate is developed at the northern end of the outcrop. It is exposed on the northern slope of Hare Hill and in the headwaters of the Logan Burn, some 900 yd S.E. of the summit of Hare Hill. The contained pebbles are generally sub-angular, up to 4 in in diameter and are made up of Lower Old Red Sandstone basalts, andesites, felsites and grits together with derived pebbles from the conglomerate. Other pebbles include vein quartz, quartzite, jasper and chert; angular fragments of mudstone are common in certain bands which resemble dessication breccias. Conglomerates have not been recorded south of the latitude of West Kip, and near the head of the Lyne Water, where the plane of unconformity is again exposed, pink calcareous medium-grained sandstone rests directly on the older rocks. A band of concretionary eomstone occurring near the base of the formation has been quarried for lime some 750 yd S.W. of Bavelaw Castle, and another fairly persistent comstone band, which also occupies an horizon low in the Upper Old Red Sandstone succession, has been quarried between Baddinsgill Burn and Ravendean Burn, near the southern edge of the sheet.

The junction between red sandstones of Upper Old Red Sandstone facies and the lowest beds of Ballagan type is not exposed in the Cairn Hills area, and a consideration of the structural evidence in the area tends to support the possibility that the junction may be faulted. Up to 700 ft of red sandstone, lithologically very similar to that exposed on the Cairn Hills, overlie the lower beds of Cementstone type (p. 40) and crop out at Baad Park and in the East Burn, just south of Harperrig Reservoir. This is a further example of the interdigitation of beds of Upper Old Red Sandstone and Cementstone facies.

Selms and Kirknewton

A white and red quartzose sandstone crops out in a small inlier north of Selms. This sandstone contains three bands of concretionary cornstone or limestone which were formerly quarried for lime. Peach (in Peach and others 1910, p. 46) assigned this outcrop to the Upper Old Red Sandstone on purely lithological grounds. More recently Anderson (1942, fig. 1) has extended the outcrop of Upper Old Red Sandstone to include about 700 ft of white and yellow sandstone with manly beds, which overlie the dolerite sill of Selms and Kirknewton. Re-examination of the available evidence suggests that these beds may be the lateral equivalents of the sandstones exposed above and below the Dalmahoy Sill (p. 41). The latter have now been tentatively assigned to the Middle Sandstone of the Cementstone Group (p. 38).

D'Arcy, Midlothian

The only record of Upper Old Red Sandstone sediments in the area of one-inch Sheet 32 to the east of the Pentland Fault is from No. 1 Bore, Midlothian, which was put down during 1937 and 1938 on behalf of the Anglo-American Oil Company at D'Arcy, two and a half miles south-east of Dalkeith. The bore reached a depth of 3857 ft, and passed through volcanic rocks believed to be at the horizon of the Arthur's Seat lavas, between 3132 ft and 3382 ft. From there to the base the bore encountered hard calcareous sandstone, which was usually white in colour and contained occasional siltstone partings. A thin bed of black shale recorded at 217 ft below the lavas yielded poorly preserved plant, ostracod and fish remains and lamellibranch fragments determined by R. B. Wilson as Naiadites?. Robertson (in Anderson and Simpson 1938) has suggested that this horizon should be taken as the local base of the Carboniferous System and that the presence of strata of typical Upper Old Red Sandstone facies above this fossiliferous bed of Carboniferous aspect is evidence of the interdigitation of the sandstone and cementstone facies. A similar example of the interdigitation of the two facies has also been recorded near Oldhamstocks in East Lothian (Clough and others 1910, p. 86). W.M.

References

ALLEN, J. R. L. 1960. Comstone. Geol. Mag., 97, 43–8.

ANDERSON, F. W. and SIMPSON, J. B. 1938. Geological Notes on the Borings for Oil now in Progress at Cousland and D'Arcy, Midlothian. Oil Shale and Cannel Coal, 27–31. Institute of Petroleum.

ANDERSON, J. G. C. 1942. The Oil-Shales of the Lothians — Structure — Area II. Pumpherston. Geol. Surv. Wartime Pamphlet, No. 27.

BURGESS, I. C. 1960. Fossil Soils of the Upper Old Red Sandstone of South Ayrshire. Trans. Geol. Soc. Glasgow, 24, 138–53.

CLOUGH, C. T., BARROW, G., CRAMPTON, C. B., MAUFE, H. B., BAILEY, E. B. and

ANDERSON, E. M. 1910. The Geology of East Lothian. Mem. Geol. Surv.

GOODCHILD, J. G. 1901. Some Recent Exposures of Rock near Edinburgh. Trans. Edin. Geol. Soc., 8, 2–9.

HOWELL, H. H. and GEIKIE, A. 1861. The Geology of the Neighbourhood of Edinburgh. Mem. Geol. Surv.

MACGREGOR, M. and others. 1940. Discussion on the boundary between the Old Red Sandstone and the Carboniferous. Advancement of Science, 1, No. 2, 256–8.

MACLAREN, C. 1839. A Sketch of the Geology of Fife and the Lothians, including detailed descriptions of Arthur's Seat and the Pentland Hills. Edinburgh.

MAUFE, H. B. 1910. In Sum. Prog. Geol. Surv. for 1909. 35–6.

PEACH, B. N. and HORNE, J. 1905. The Base-line of the Carboniferous System around Edinburgh. Rep. Brit. Assoc., Cambridge, 1904, 546–7.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

TAIT, D. 1920. On the Section in a Borehole in the Calciferous Sandstone Series, Upper Old Red Sandstones and Lower Old Red Sandstone Lavas in the Grange District, Edinburgh. Trans. Edin. Geol. Soc., 11, 18–22.

TAIT, D. 1925. On a Bore for Brewing-Water near Craiglockhart. Trans. Edin. Geol. Soc., 11, 271–4.

TAIT, D. 1936. A Journal of and Notes on a Boring for Water at Messrs. Bartholomew's Works, Duncan Street, Edinburgh. Trans. Edin. Geol. Soc., 13, 304–7.

TAIT, D. 1939. Recent Bores for Water in Edinburgh and the Correlation of some Bore Sections. Trans. Edin. Geol. Soc., 13, 445–52.

TRAQUAIR, R. H. 1891. List of the Fossil Dipnoi and Ganoidei of Fife and the Lothians. Proc. Roy. Soc. Edin., 17, 385–400.

TRAQUAIR, R. H. 1905. Note on the Fish Remains recently collected by the Geological Survey of Scotland at Salisbury Craigs, Craigmillar, Clubbiedean Reservoir and Torduff Reservoir, in the Edinburgh District. Rep. Brit. Assoc., Cambridge, 1904, 547. WILLS, L. J. 1948. The Palaeogeography of the Midlands. London.

Chapter 5 Cementstone Group

Introduction

Since the discovery of fish remains believed to be diagnostic of Upper Old Red Sandstone age, in the sandstones at Craigmillar and beneath Salisbury Craigs (p. 28) the base line of the Carboniferous System in the Edinburgh district has been drawn at the bottom of a group of grey, green and red mud-stones, shales and cementstone bands, with occasional sandstones and rarely some thin seams of dark carbonaceous shale yielding plants, ostracods and Palaeoniscid fish (Carruthers in Carruthers and others 1927, p. 5). These are the characteristics of the Cementstones developed in the west of Scotland, particularly in Ballagan Burn, Strathblane, from which the term Ballagan-type sediments is derived.

With the adoption of the classification outlined above, the sandstones of Craigmillar, previously assigned to the Lower Carboniferous, were referred to the Old Red Sandstone as also were those beneath Salisbury Craigs. In the latter case the St. Leonard's Fault was postulated to explain the presence of beds belonging to the older formation in the midst of patently Carboniferous strata.

Though it would seem likely that the Craigmillar rocks should be assigned to the Upper Old Red Sandstone as mapped in the Edinburgh area, a view which is supported by the character of the rocks encountered in several deep bores in the Craigmillar area, there are certain difficulties in this procedure in the case of the sandstones beneath Salisbury Craigs. As already mentioned their classification as Upper Old Red Sandstone required a fault (the St. Leonard's Fault) between them and the Cementstone Group to the west. On this interpretation the thickness of the Cementstone Group in the centre of Edinburgh as worked out by E. M. Anderson and recently confirmed by Mr. G. A. Goodlet, totals some 1750 ft of strata, whereas no more than about 800 ft of these beds can be present in Hunter's Bog. Such a rapid thinning of these measures within about half a mile is difficult to explain. Moreover a similar though less spectacular westward thinning of the Salisbury Craigs Sill is required, for no sign of it appears to the west of the supposed St. Leonard's Fault. Furthermore recent temporary exposures in the ground to the north-east of the St. Leonard's Sill have revealed rocks with a Carboniferous aspect; thus it is now necessary to orient the line of the postulated St. Leonard's Fault that it so closely follows the curved strike of the rocks as to throw doubt on its feasibility. The opportunity was therefore taken to re-examine the fragmentary fossils collected from beneath Salisbury Craigs, originally thought to be Holoptychius, but even so considered by some workers to be possibly derived from earlier rocks as pebbles. As already mentioned (p. 29) a re-examination by Dr. E. I. White, F.R.S., was inconclusive.

Two alternatives seem possible. The first is that, as originally believed by Howell and Geikie, there is an unbroken Cementstone succession from the centre of Edinburgh to the base of the Arthur's Seat lavas and that the sandstone below Salisbury Craigs is Carboniferous in age although it resembles some Upper Old Red sandstones. Such an explanation overcomes the difficulty of the rapid change of thickness across the St. Leonard's Fault. In support of the suggestion that the red sandstones under Salisbury Craigs are in fact of Cementstone Group age, despite their Old Red Sandstone aspect, may be quoted the presence of a similar sandstone in a like position near Harperrig Reservoir and again in Ayrshire as noted by Richey (Bailey 1925). A further case of comparable interdigitation is known from East Lothian (p. 32).

The second alternative would postulate a considerable unconformity beneath the Arthur's Seat lavas. Such an explanation does not seem likely to explain the striking change in thickness in the City of Edinburgh. There still remain, however, considerable variations of the Cementstone Group as mapped over the wider area shown on the Edinburgh sheet and it may be that some of these may be due to an unconformity at the base of the Arthur's Seat Volcanic Rocks. In (Figure 20) and on the one-inch and six-inch maps the assumption is made that a large number of outcrops of volcanic rocks, including those of Arthur's Seat, are on approximately the same horizon though it is not possible to prove this. At a considerably lower level (according to the interpretation here adopted) lie the Craiglockhart Volcanic Rocks at or very close to the base of the Cementstone Group. If there is in fact such an unconformity as is suggested above, it may even be that the Craiglockhart lavas are on the same horizon as those of Arthur's Seat and the Cementstone Group, so well developed in the City of Edinburgh, was removed by erosion at Craiglockhart in pre-Lower Oil-Shale Group times.

In the new editions of the maps the first alternative discussed above is adopted for the Salisbury Craigs area and a further modification is proposed with regard to the ground to the east of Duddingston where on the 1930 edition of the one-inch map a tongue of Arthur's Seat Volcanic Rocks is shown extending to the Pentland Fault, though there are no exposures or other evidence to substantiate this outcrop. It is remarkable that the volcanic rocks, where exposed on Whinny Hill and near Duddingston, make bold features, whereas the supposed continuation of the outcrop between the latter place and the Pentland Fault is in country of low relief. The present review of the evidence suggests that a fault extending from Newington through Duddingston Loch and beyond Duddingston House to the Pentland Fault, throwing down to the north and thus setting a limit to the outcrop of the Arthur's Seat volcanics, affords a better explanation of the relationships of the rocks in that area. It also allows ample room for the outcrop of the Cementstone Group. A gravitational survey was carried out across the line of the Pentland Fault, near Portobello by McLintock and Phemister (1929, pp. 10–28) and a magnetic survey in the same area by Hallimond (1931, pp. 30–8). These surveys were to the north of the present postulated fault and the results in both cases were thought to be in accordance with the view that the upper beds of the Arthur's Seat Volcanic Rocks are present at a depth of some 100–200 ft on the west side of the Pentland Fault.

Details

Craiglockhart Volcanic Rocks

The Craiglockhart Volcanic Rocks are only known in the Craiglockhart area where they apparently occur at or very close to the base of the Cementstone Group. Their outcrop forms Wester and Easter Craiglockhart hills, 2.5 m S.W. of Edinburgh

Castle. They dip westwards off the Leith Anticline and are bounded on the west by the Colinton Fault. (Peach and others 1910, p. 74.)

The succession of the strata is as follows in downward order:

(ii) Basalt lava: approx. 100 ft Slaggy base slightly transgressive, veins and cavities infilled with tuff and bedded limestone; columnar centre; slaggy upper surface with infilling of mud. Type locality of Craiglockhart type, macroporphyritic olivine-basalt (Flett in Peach and others 1910, p. 318).

(i) Tuff: approx. 100 ft Well-bedded, largely fine-grained with lithic fragments of basalt, crystals of augite and olivine, together with quartz grains; occasional blocks of basalt and sedimentary rock.

N.B. — A feldspar-phyric lava of Dunsapie type was encountered in temporary exposures below the tuff during the construction of Redford Barracks.

Beds between the Craiglockhart and Arthur's Seat Volcanic Rocks

Sediments generally form the lowest beds of the Cementstone Group and are then in general only with difficulty separated from the underlying Upper Old Red Sandstone (p. 29).

There are three areas where details are available (Figure 8): (i) City of Edinburgh; (ii) Between the Pentland Hills and the West Lothian Oil-Shale Field; (iii) Midlothian Coalfield.

City of Edinburgh

The outcrop in the centre of the City of Edinburgh includes the Old Town between the Castle, Holyrood Palace and Hunter's Bog east of Salisbury Craigs, as well as a small area in the south-west corner of Calton Hill.

By piecing together borehole sections (MacGregor and others 1942) and records of temporary sections, in which work the manuscripts of E. M. Anderson and papers by Tait (1936, 1939a, b) have been invaluable, the following provisional section for the strata developed in the centre of Edinburgh has been put together by Mr. G. A. Goodlet (Figure 8).

This gives a thickness for the Cementstone Group of 2583 ft. A bore through the lavas of Calton Hill (Goodchild 1899) probably encountered some 200 ft of beds of this group below the lavas.

Area between Pentland Hills and West Lothian Oil-Shale Field (Dalmahoy Syncline)

Sediments of Cementstone Group age crop out along the north-west side of the Pentland Hills, where they form a shallow, south-westward pitching syncline. They are bounded to the south-east by Upper Old Red Sandstone and older rocks and to the north by the Colinton Fault and its south-westward continuation, the Murieston Fault. Beds belonging to the Lower Oil-Shale Group crop out discontinuously along the axis of the syncline, in which secondary basin-structures with roughly north-south trending axes, similar to those in the Oil-Shale field to the north, appear to be developed. The Cementstone succession in this area is less well known than that in the central Edinburgh outcrop, and the subdivisions established in the latter cannot be recognized here. Though there is considerable variation in facies within the area, the following tentative downward sequence can be established:

The possible outcrops of the various subdivisions are shown in (Figure 7), though, because of lack of exposures and the absence of fossil marker-horizons, the implied correlations must be regarded as tentative. The map suggests that the lithological units listed above gradually disappear south-east of a line extending from Torphin Hill to Crosswood Reservoir. Thus south of Threipmuir Reservoir all the formations below the Upper Shale appear to be represented by sandstone of 'Upper Old Red Sandstone' facies shown on the map as belonging to that formation, and at Dykehead, 2.5 miles S.W. of Crosswood Reservoir (Sheet 24), the Carboniferous basalts and mugearites rest directly on this basal red sandstone facies. This interpretation is based on the assumption that the Corston Hill, Torweaving Hill and Dykehead lavas represent a single volcanic horizon, the formation of which was possibly contemporaneous with the extrusion of the Arthur's Seat lavas. It might, however, be argued that these three lava outcrops represent three separate volcanic episodes which took place respectively at the end, middle and beginning of Cementstone Group times. The objection to this interpretation is that there is nowhere in the Dalmahoy Syncline or in the area to the south-west any evidence of more than one major volcanic horizon in the Cementstone Group.

Details of the development of the Cementstone Group in various localities on the north-western flank of the Pentland Hills are given below.

Dreghorn to Clubbiedean Reservoir

As suggested on p. 31 strata of Cementstone Group age appear to rest directly on Lower Old Red Sandstone lavas in the area between Dreghorn Castle and Clubbiedean Reservoir. Conglomerate occurs at or near the base of the exposed succession just north and east of Torphin Quarry, where pink calcareous conglomerate with angular pebbles of Lower Old Red Sandstone lavas, quartzite and sandstone, crops out in a small elongate east-north-east trending dome. Bands of conglomerate intercalated with sandstone are also found near Clubbiedean Reservoir and in Kinleith Burn, just south of the outcrop of Lower Old Red Sandstone lavas. It seems probable that these conglomerates were deposited by intermittent floods which entered the area from the north and received a high proportion of detritus from the local hills of Lower Old Red Sandstone lava. The basal conglomerates pass laterally into pink or buff calcareous sandstone with occasional cornstones and silty mudstone partings. This sandstone is less than 150 ft thick at Torduff Reservoir, where it is overlain by purple silty mudstone and marl with thin limestones and bands of white and pale green sandstone belonging to the Lower Shale (ii). The shales and limestones exposed in a small southern tributary of Clubbiedean Burn have yielded Naiadites cf. obesus (R. Etheridge jun.) and Spirorbis as well as several plant genera of undoubted Carboniferous aspect (Salter in Howell and Geikie 1861, p. 144). Plant fragments were also recorded in a disturbed section of siltstones, cementstones and sandstones seen in a temporary exposure north-east of Torduff Reservoir, close to the post-Lower Old Red Sandstone unconformity.

Currie to Balerno

The Cementstones are well exposed in the Water of Leith and its tributaries between Currie and Balerno, but since little is known about the structure of this area it is not possible to construct a reliable sequence or to give definite thicknesses. Conglomerate belonging to the Basal Sandstone (i), exposed north of Torphin (see above), appears to be succeeded by variegated red and yellow marls which are in turn overlain by buff or grey shales, sandstones and siltstones with cementstone bands referred to the Lower Shale (ii) and containing ostracods and Spirorbis. The last-mentioned beds are exposed in the Water of Leith between 500 and 1200 yd E.N.E. of Currie; they appear to be succeeded by the Middle Sandstone (iii) here a thick series of white or buff, medium-grained, locally calcareous sandstones with argillaceous partings and occasional plant remains. The sandstones are well seen in the Water of Leith at Currie, and in the Kinleith Burn between Braeburn and its confluence with the Water of Leith. Several bands of cornstone and calcareous conglomerate with pebbles of green chert, quartzite and Old Red Sandstone lavas, interbedded with sandstones and marls, which are exposed in the Water of Leith near Lennox Tower, 0.5-mile W.S.W. of Currie, probably belong to the upper part of the sandstone sequence.

Red and ochre marls and grey silty shales with thin limestone and cementstone bands belonging to the Upper Shale (iv), which have yielded ostracods and contain at least one Modiolid? bed, are exposed in the tributaries entering the Water of Leith from the south between Balerno and Currie. These appear to overlie the sandstones exposed in the Water of Leith.

Flaggy brown and white sandstones, with pebbly layers and thin bands of conglomerate, crop out in the Bavelaw Burn at Balerno. They appear to rest on grey and greenish shales with siltstones and bands of calcareous sandstone. Though it seems likely that these beds are the equivalents of the Middle Sandstone exposed in the Water of Leith, the presence of a number of east-west and north-east trending faults makes a definite correlation impossible. Buff, flaggy sandstones with calcareous bands containing limestone nodules and occasional beds of purplish-grey siltstone and mudstone crop out in the Bavelaw Burn between Balerno and Harlaw Reservoir. On the 1910 edition of one-inch geological Sheet 32 these beds were included in the Lower Oil-Shale Group, but as during the recent revision the evidence on which this correlation is based was not borne out, it seems more probable that they should be equated with the Middle Sandstone.

Threipmuir Reservoir to Harperrig

The basal beds of the Cementstone Group are exposed in the small streams which enter Threipmuir Reservoir from the south. Here the strata are folded into a steep-limbed east-north-east trending syncline. The Basal Sandstone (i), which contains thin limestones, cornstones and conglomerates, is probably less than 500 ft thick and is overlain by purple and purplish-grey marls with calcareous concretions of the Lower Shale (ii) interbedded with nodular calcareous sandstones and thin argillaceous limestones or cementstones. The latter are exposed in the centre of the syncline. Higher strata are poorly exposed north and west of Threipmuir Reservoir, and the evidence from the sparse exposures suggests that the strata in the ground as far north as Balerno have a consistently gentle dip to the south-west and consist mainly of red marls with calcareous concretions interbedded with sandstones and belong to the Upper Shale (iv).

Within the Upper Sandstone (v), conglomerate, which contains sub-rounded pebbles of Pentland lava as well as vein quartz, quartzite, chert and red jasperized lava has been quarried in two localities near Cockburnhill, some two miles south-west of Balerno. This conglomerate may be a coarse band belonging to the predominantly arenaceous series of beds exposed in the Cock Burn 450–650 yd and 1900–2500 yd S. of its junction with the Water of Leith as well as at the mouth of a small stream entering the Water of Leith 1100 yd W. of Cockburn. The beds exposed at the last three localities contain bands of coarse pebbly sandstone with pebbles of Old Red Sandstone lavas as well as quartz, radiolarian chert and jasper. These are interbedded with calcareous concretionary sandstones closely resembling the cornstones of the Upper Old Red Sandstone and with red and pale green marls containing thin argillaceous limestones.

Harperrig to Torweaving Hill

The Cementstone Group in the Colzium area can be subdivided as follows:

The massive sandstone underlying the Torweaving Hill lavas is indistinguishable from the lower sandstone, which has been included in the Upper Old Red Sandstone Series. The upper sandstone appears to thin gradually to the north-east and thicken to the south-west; while the underlying predominantly argillaceous beds apparently thin out to the south-west. About one mile south of Torweaving Hill, Calciferous Sandstone lavas, apparently on the same horizon as the Torweaving Hill lavas, rest directly on pink sandstone which passes without a break down to the post-Lower Old Red Sandstone unconformity.

Linhouse Water, Gogar Burn and Selms

The Cementstones underlying the Corston Hill lavas are well exposed in the Linhouse Water, where the succession is as follows:

The shales and marls (iv) are also found in the Gogar Burn, about 1.5 miles farther north-east. The pink sandstone with cornstone bands cropping out in the Selms area, which was taken by Peach to be of Upper Old Red Sandstone age (Peach in Peach and others 1910, p. 46) and the white sandstone cropping out south and east of Selms (p. 32) which has been included in the Upper Red Sandstone by Anderson (1942, fig. 1) can probably be correlated with the Middle Sandstone of Currie (p. 39) and Dalmahoy below.

Dalmahoy

The strata underlying the Dalmahoy dolerite sill consist of three posts of sandstone up to 34 ft thick interbedded with softer, fine-grained beds, which are now largely obscured by scree. The highest sandstone contains two highly calcareous bands which in places resemble cornstones and were formerly quarried for lime. Bands of shale and siltstone as well as conglomeratic bands with shale pellets and limestone fragments are found in all three posts. These beds, together with the sandstones overlying the Dalmahoy Sill, which are exposed in the Water of Leith between Balerno and Hannahfield, may possibly be correlated with the Middle Sandstone of Currie (iii).

Representatives of the Lower Shale (ii) crop out in the Green Burn, 0.75-mile W. of Dalmahoy Hill. The Upper Shale (iv) is seen in the Water of Leith between 1150 yd and 1700 yd W. of Balerno and consists of purple and grey marls and shales with cementstone ribs, calcareous concretions and thin posts of buff sandstone. A Modiolid? has been recorded at one locality and Naiadites cf. obesus (R. Etheridge jun.) at a nearby exposure.

Midlothian Coalfield

At the south end of the Midlothian Coalfield between Borthwick and Middleton Moor, as also at Howgate, there are certain badly exposed strata mapped as undifferentiated Calciferous Sandstone Measures and perhaps including beds of this age.

In the D'Arcy (Midlothian No. 1) Bore near Cousland, the following section was logged below volcanic rocks believed to be Arthur's Seat Volcanic Rocks at 3382 ft: sandstone with bands of 'marl' or shale 211 ft; on black shale, fossiliferous 6 in (Anderson and Simpson 1938, p. 31; Tulloch and Walton 1958, p. 10). G.H.M., W.M.

References

ANDERSON, F. W. and SIMPSON, J. B. 1938. Geological Notes on the Borings for Oil now in Progress at Cousland and D'Arcy, Midlothian. Oil Shale and Cannel Coal, 27–31, Inst. Petroleum.

ANDERSON, J. G. C. 1942. The Oil-Shales of the Lothians-Structure-Area II. Pumpherston. Geol. Surv. Wartime Pamphlet, No. 27.

BAILEY, E. B. 1925. in Sum. Prog. Geol. Surv. for 1924; 90–91.

CARRUTHERS, R. G., CALDWELL, W., BAILEY, E. M. and CONACHER, H. R. J. 1927. The Oil-Shales of the Lothians. 3rd edit. Mem. Geol. Surv.

GOODCHILD, J. G. 1899. Notes on a Borehole through the Rocks of the Calton Hill. Trans. Edin. Geol. Soc., 7, 259–64.

HALLIMOND, A. F. 1931. On a Preliminary Magnetic Survey over the Pentland Fault, near Portobello, Midlothian, Scotland. Sum. Prog. Geol. Surv. for 1930, pt. 3, 30–8.

HOWELL, H. H. and GEIKIE, A. 1861. The Geology of the Neighbourhood of Edinburgh. Mem. Geol. Surv.

MACGREGOR, A. G., ALLAN, J. K. and LAWRIE, T. R. M. 1942. Water Supply from Underground Sources of South-East Scotland, Part II, Well-Catalogue for One-inch Sheet 32 (Lothians Portion). Geol. Surv. Wartime Pamphlet No. 28.

McLINTOCK, W. F. P. and PHEMISTER, J. 1929. A Gravitational Survey over the Pentland Fault, near Portobello, Midlothian, Scotland. Sum. Prog. Geol. Surv. for 1928, pt. 2, 10–28.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

TAIT, D. 1936. A Journal of and Notes on a Bore for Water at Messrs. Bartholomew's Works, Duncan Street, Edinburgh. Trans. Edin. Geol. Soc., 13, 304–7.

TAIT, D. 1939a. Recent Bores for Water in Edinburgh and the correlation of some Bore Sections. Trans. Edin. Geol. Soc., 13, 445–52.

TAIT, D. 1939b. The National Bank Excavation, St. Andrew Square, 1936–7. Trans. Edin. Geol. Soc., 13, 457–63.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 6 Lower Oil-Shale Group

The Lower Oil-Shale Group includes strata from the base of the Arthur's Seat Volcanic Rocks to the base of the Burdiehouse Limestone (Figure 9) and, south of the Forth, is developed in six areas: (i) City of Edinburgh: Portobello to Cramond, (ii) Main Outcrop: Queensferry–Cramond–Corstorphine–Ratho–Oakbank–Crosswood Reservoir, (iii) Pumpherston Inlier, (iv) Livingston Station Inlier, (v) Hopetoun and Inchgarvie inliers, (vi) Deep bores in the east of the area. The sediments and lavas of Inchkeith, some of which perhaps belong to the upper part of the Queensferry Beds, are described on p. 74. North of the Forth the Lower Oil-Shale Group is developed in the area between Aberdour and Rosyth Dockyard.

It has already been noted (p. 4) that available information leaves much to be desired in the interpretation of the succession in the Lower Oil-Shale Group which is adopted in this account. In particular attention is drawn to the possibility (p. 105) based on palaeontological evidence that the upper part of the Wardie Shales might be the equivalent of the lower part of the Queensferry Beds. In this case the Hailes Sandstone would occupy a position in the Queensferry Beds.

South of the Forth

For the purposes of this account and bearing in mind the remarks made above, the succession south of the Forth is separated into the following divisions; the stated thicknesses are approximate:

The precise age of the Lower Oil-Shale Group in terms of Carboniferous zonal classification is as yet undetermined, but according to Currie (1954, p. 540) the Pumpherston Shell-Bed in the Queensferry Beds may be of Beyrichoceras Stage age. The petrography of the sandstones of the group has recently been discussed by Greensmith (1961).

Arthur's Seat Volcanic Rocks

In the Edinburgh City area the principal developments of the Arthur's Seat Volcanic Rocks are at Arthur's Seat and Holyrood Park, Calton Hill and Waverley Market. In the main outcrop there are important exposures at Corston Hill, Torweaving Hill, Black Hill and Harperrig, and at Buteland Hill and Cock Burn. Another possible occurrence within the area of the sheet is in a borehole near D'Arcy, Midlothian.

Details

Arthur's Seat and Holyrood Park ((Plate 2), (Figure 10))

Two vents occupied by vent agglomerate and intrusive basalt are centred on Arthur's Seat, Lion's Head the older, and Crow Hill and Nether Hill (Lion's Haunch) the younger; a third minor vent lies to the west above Salisbury Craigs, near Camstone Quarry (Western Vent). A small vent is claimed by Clark (1956) at the Pulpit Rock. An alternating sequence of lava flows and tuff bands derived from these vents forms Whinny Hill, north of the vents, and a smaller area south-east of the vents near Duddingston.

Intrusive basalts are associated with the extrusive rocks and adjacent sediments.

Detailed descriptions of these rocks are given by Maclaren (1839), Judd (1875), Peach and others (1910), Peach (1921), Day (1933), Flett and others (1927), Clark (1952, 1956), Oertel (1952), Rutledge (1952) and Hamilton (1957).

Vents

Lion's Head Vent

Agglomerates filling the Lion's Head Vent consist of alternating coarser and finer layers, stratified with steep inward dip. Included blocks are almost entirely basalt of Craiglockhart and Dunsapie types, i.e. comparable with the lower flows on Whinny Hill. There is an absence of fragments of basalt of Markle type — the rock type of the higher flows of Whinny Hill — fragments of which, abundant in Lion's Haunch Vent, led Peach (in Peach and others 1910, p. 65) to suggest that Lion's Head Vent was only active in the earlier stage of igneous activity in the area.

The vent agglomerates are pierced by an intrusion of basalt of Dalmeny type which forms the top of the hill; feeders of this sill-like mass form ramifying dykes on the west side of the hill above the footpath, but unite upwards. Another basalt dyke traceable for 50 yd on the northern margin of the vent is brecciated as it approaches the vent.

Specimens of petrified plant remains, unfortunately indeterminable, were collected from the matrix of the agglomerate of the Lion's Head Vent by Campbell (1914).

Lion's Haunch Vent

The Lion's Haunch Vent is filled mainly by agglomerates but with lavas at three different levels, as well as sandstones, marls and cementstones.

The finest section is on Queen's Drive where blocks in the red agglomerate, up to 15 ft across, include conspicuous basalt of Markle type, ashy sandstone, shale, limestone or cornstone. The dip is steeply inwards from the margins of the neck. The north-western margin of the vent is drilled in agglomerates and in the intrusion of Lion's Head and is marked by a conspicuous gully (Gutted Haddie) formed by erosion along the contact. At the head of the gully, scree from the older vent is mingled with material erupted from Lion's Haunch vent.

The vent agglomerates are intruded by basalts of Dunsapie type at Crow Hill, Lion's Haunch and Dunsapie (Peach in Peach and others 1910, p. 69).

Western Vent

The vent agglomerate cuts the highest beds of the Cementstone Group (pp. 34, 36) but is indurated by the Salisbury Craigs Sill: it includes fragments of "Old Red Sandstone" and blocks recalling the lower lavas of Whinny Hill, but not Markle type basalt. Thus Peach (in Peach and others 1910, p. 71) inferred that the activity of this vent, like that of Lion's Head, was restricted to the earlier part of the volcanic history of Arthur's Seat.

Lavas and tuffs

Whinny Hill–North of Vents

Flows of olivine-basalt and mugearite were considered by Peach (in Peach and others 1910, p. 59) to number 20, but only 13 by Clark (1956, p. 40; fig. 2). Certain flows are separated by well defined tuff bands. Most flows (except mugearites) are macroporphyritic olivine-basalts of Dunsapie, Craiglockhart or Markle types but Clark maintains the presence of microporphyritic basalts of Dalmeny and Jedburgh types. The dip is east-north-east.

A recent re-examination of the ground suggests the following succession:

Duddingston–South of Vents

Despite its proximity to Whinny Hill the Duddingston sequence shows marked differences. The dip is east-north-east and the general downward succession is:

Intrusions

Closely associated with the extrusive and vent rocks of Arthur's Seat are various basic intrusive masses of which the following are the most important: (1) Heriot Mount and St. Leonard's Craig, (2) Dasses and Girnal Craig, (3) Salisbury Craigs, (4) Duddingston, (5) Lion's Head, (6) Lion's Haunch (Crow Hill), (7) Dunsapie, (8) Samson's Ribs, (9) Whinny Hill. Their characters are summarized below:

Heriot Mount and St. Leonard's Craig

The Heriot Mount and St. Leonard's Craig Sill is a composite intrusion in which the central portion is very rich in analcite, but otherwise resembles a Dunsapie basalt. The outer portion of the sill is almost non-porphyritic. MacGregor (1936) believed that explosion took place in the mass. T. C. Day (1923) described exposures of the sill revealed during building at St. Leonard's Hill.

Dasses and Girnal Craig

Oertel (1952) and Rutledge (1952) have shown the Dasses Sill to be a composite intrusion. At both Dasses and Girnal Craig the rock type closely resembles that of Heriot Mount.

Salisbury Craigs

A great sill of analcite-olivine-dolerite (teschenite) with fine-grained margins forms Salisbury Craigs and is columnar in part (Peach in Peach and others 1910, pp. 72, 276). The age of the intrusion is probably later than the Arthur's Seat volcanicity.

Duddingston

A basalt of Dunsapie type truncates tuffs and calcareous bands overlying the Loch Craig basalt. Oertel (1952, p. 374) claimed that it is an intrusion on the flank of the volcano intruded simultaneously with Samson's Ribs and Crow Hill basalts.

Lion's Head

Dyke-like masses on the west side of Arthur's Seat pass up to a stem which upwards spreads out to form a sill-like cap (Peach in Peach and others 1910, p. 66). Oertel (1952, p. 364) suggests the intrusion represents a lava bulge formed at the surface, or a lava-lake, probably choking the vent. Petrographically the rock is a fine-grained, microporphyritic Dalmeny type olivine-basalt.

Lion's Haunch (Crow Hill)

A sill-like intrusion of Dunsapie type, macroporphyritic olivine-basalt, lying above agglomerate but inclined parallel to the bedding in the latter (Peach in Peach and others 1910, p. 70) and with a tongue-like mass descending from the main body (Peach in Peach and others 1910, pp. 68–9, fig. 5) forms the Lion's Haunch. Oertel (1952, p. 373 and figs. 6–8), by a study of flow planes, interpreted the mass as a lava-lake showing convection-currents.

Dunsapie

At Dunsapie is an intrusion of massive, columnar jointed olivine-basalt; this is the type locality of Dunsapie type olivine-basalt; according to Oertel (1952, p. 375, fig. 7) it forms three domed bulges which are recognized on the evidence of flow lines.

Samson's Ribs

A strikingly columnar olivine-basalt intrusion of Dunsapie type forms Samson's Ribs. It was claimed by Oertel (1952, p. 371, figs. 5, 8) to show vertical flow-planes. The main mass formed a feeding channel believed to pass into the adjacent lava-flows within the vent, which dip to the north-east.

Whinny Hill

A coarsely porphyritic intrusion of olivine-basalt of Craiglockhart type is intruded into the lower part of the Whinny Hill lava sequence. According to Clark (1952, pp. 77–8) the adjacent lavas are of Jedburgh type. A smaller but similar intrusion occurs a little lower in the sequence to the north-west of the main mass.

Petrography

The petrography of the Arthur's Seat Rocks has been studied in great detail by Flett (in Peach and others 1910, pp. 287–323; in Peach 1921, pp. 25–6) and more recently by Clark (1952; 1956). The structural petrography was described by Oertel (1952). Smith (1959) has noted the alteration of olivine in Markle-basalt to haematite, chlorite and quartz. The most important types are olivine-basalts which form several varieties found both as lava flows and intrusions. Definitions of these are given on p. 85.

The mugearite lavas are platy rocks showing fluxion structure and are sometimes vesicular; constituents are oligoclase, orthoclase, olivine and iron-oxide with augite, hornblende and biotite at times in addition. The feldspars are often albitized.

History of volcanicity

It is clear from the relationships of the rocks that a sequence of lava flows and tuffs was erupted from the Lion's Head Vent. This then became choked and eruptions were transferred to the Lion's Haunch Vent. The centre of activity thus moved from the north-west to the south-east of the volcano; certain flows of lava remain within the later crater. The role and precise age of the western crater are unknown.

There is room for differences of interpretation regarding the place of the individual intrusions in the history of the volcano. That the Lion's Head intrusion took place at the time of the closing of this vent after the lowest (pre-Markle type) flows seems assured. The Crow Hill, Dunsapie and Duddingston intrusions are probably later than any of the lava-flows. Opinion differs however as to whether the Dasses, Girnal Craig and St. Leonard's intrusions were very early — even pre-lava flows — (Oertel 1952, p. 363) or much later, during the effusion of the upper lavas (Peach in Peach and others 1910, p. 72). Peach would apparently include the Duddingston mass with this group. The exact age of the Samson's Ribs intrusion is also a subject of discussion, For details of these problems, as also for questions of the sequence of magmas in the history of the volcano and the implications of the structural relationships the works of Peach, Clark, Oertel and Rutledge should be consulted.

The Salisbury Craigs teschenite and the quartz-dolerite dykes which cut it are probably the result of later Carboniferous activity.

Calton Hill

Arthur's Seat Volcanic Rocks form a triangular, faulted area bounded on the south by the Calton Fault, on the north-west by the Leith Links Fault and overlain to the north-east by the Abbeyhill Shales (Plate 2). There are excellent exposures on the paths and slopes leading to the Nelson Monument (Peach in Peach and others 1910, p. 73; Peach 1921, p. 20).

The sequence is generally similar to that of Arthur's Seat but the basal beds consist of tuffs interbedded with sediments of Ballagan type and the basalt of Long Row probably did not extend to Calton Hill. The thickness of the beds is about 800 ft, made up of the following:

Castle Rock

The plug of Dahneny type basalt rising almost vertically through Cementstone Group strata to form Castle Rock may have sealed an orifice through which lavas of Lower Carboniferous age flowed.

Waverley Market

Tuffs found in temporary excavations to the north-west of the conjunction of the Leith Links and Calton faults may possibly belong to the Arthur's Seat Volcanic Rocks (Goodchild 1901, p. 6; 1905, p. 271).

The tuffs found in High Street (Peach 1921, p. 22), formerly considered to be possibly of this age, are now thought to be lower in the sequence in the middle part of the Cementstone Group (p. 36; (Figure 8)).

Silverknowe

Tuffs at one time quarried at Laurieston Cottage near Silverknowe are now assigned tentatively to the Arthur's Seat Volcanic horizon. G.H.M.

Corston Hill

Lavas thought to belong to the Arthur's Seat period of volcanicity crop out at and near Corston Hill (Figure 7) and in a small area some three-quarters of a mile south-west of Oakbank. The lava succession consists of a lower series of flows of sparsely porphyritic basalt intermediate between Jedburgh and Markle types and an upper series of platy-weathering mugearites. The basalt is exposed in the Linhouse Water, half a mile west-north-west of Corston and on the scarp face of Corston Hill. It appears to be composed of a very small number of flows which have a total thickness of about 50 ft in the Linhouse Water, 30 ft near the summit of Corston Hill and then thin out rapidly north-eastwards. The mugearites are made up of several thin flows of platy weathering, locally brecciated, lava, which attain a maximum thickness of about 120 ft and thin out gradually north-eastwards from Corston Hill. They are well exposed in the Linhouse Water between 1.25 and 2.5 miles S.S.W. of Oakbank and on the dip slope of Corston Hill. Thin bands of tuff intercalated with the higher mugearite flows are seen in the Murieston Water between Skivo and Murieston House and in the railway cutting 350 yd W.S.W. of Corston. The petrology of the Corston Hill mugearite has been described by Flett (in Peach and others 1910, pp. 321–2). Isolated exposures of the mugearite and a band of the overlying tuff also occur between the Murieston and Calder Faults at Calder Wood, 0.5-mile S.S.W. of Mid Calder. Volcanic rocks, which may possibly be contemporaneous with the Corston Hill lavas, were recorded in the West Calder Bore (Figure 9).

Torweaving Hill, Black Hill and Harperrig

A faulted outcrop of olivine-basalt lavas, which consist of an upper series of microporphyritic basalts of Jedburgh type and a lower series of macroporphyritic basalts of Markle type, is exposed along the southern limb of the Dalmahoy Syncline. It extends from the southern margin of the area of one-inch Sheet 32 near Crosswood Reservoir by way of Torweaving and Black hills to the vicinity of Harperrig Reservoir and appears to be the south crop of the Corston Hill lavas. The lavas are best exposed at the junction of the East and West burns, where the upper group consists of several thin flows of amygdaloidal, platy jointed and locally brecciated basalt totalling about 80 ft in thickness, and the lower group is made up of thicker basalt flows with abundant feldspar phenocrysts up to 0.25 in diameter, with a total thickness Of about 50 ft. Outcrops of lava, which were correlated with the Torweaving Hill lavas (Peach and others 1910, p. 85) have been recorded at the outlet of Harperrig Reservoir and in the Water of Leith, 1100 yd N.E. of Harperrig. These outcrops are now no longer exposed and must represent a very thin band of lavas, indicating that Torweaving Hill lavas thin rapidly north-eastwards.

Porphyritic olivine-basalt of Dunsapie type, which probably consists of a single lava flow, is exposed on Fauch Hill, 0.75-mile N.W. of Crosswood Reservoir. This flow is separated from the Torweaving Hill lavas by about 500 ft of sediments and appears to be of restricted lateral extent. This horizon may be contemporaneous with one of the tuff bands intercalated with the Lower Oil-Shale sediments in the Corston Hill area (see above).

Peach (in Peach and others 1910, pp. 83–5) correlated the Corston Hill lavas with the Torweaving Hill lavas and overlying lavas and tuffs, including the 'Crosswood Ash' (p. 60). He suggested that the volcanic centre was situated to the north of Corston Hill. He concluded that its activity was prolonged, the lavas of Corston Hill being represented by a series of thin lavas and tuffs intercalated with sediments in the Torweaving area. This conclusion is not borne out either by the petrography or the evidence from bores, and it is considered that only the Torweaving Hill lavas are contemporaneous with those of Corston Hill.

Buteland Hill and Cock Burn

A coarse-grained basalt of Markle type, with tabular feldspar phenocrysts up to 3 mm in size, crops out in an old quarry 550 yd N.E. of Buteland Hill (Flett in Peach and others 1910, p. 321). There is no evidence of the thickness or field relationships of this basalt. Farther east a fine-grained, non-porphyritic basaltic rock crops out in the Cock Burn, some 2.5 miles S.W. of Balerno. The rock is ophitic with a glassy and chloritic mesostasis and might be a basic variety of Jedburgh basalt, but it also bears some resemblance to an intrusive tholeiite. W.M.

D'Arcy, Midlothian

The Arthur's Seat Volcanic Rocks are not known from any other outcrops, but are believed to occur in the deep bore, Midlothian No. 1, situated near D'Arcy to the east of the Midlothian Coalfield. Below about 3130 ft at this hole, specimens of fine-grained, decomposed basalt with apparently a mugearitic groundmass were obtained and at lower horizons porphyritic basalt was recognized (Anderson and Simpson 1938, p. 30). Sediments below the volcanic rocks were encountered at 3382 ft.

Abbeyhill Shales

A sequence of shales, often bituminous, with ironstone nodules and interbedded with thin sandstones as well as thin limestones, is known to overlie the volcanic rocks of Calton Hill on its east side in Regent Terrace, Edinburgh. A bore at Abbeyhill (Henderson 1883) passed through at least 320 ft of these beds, some with fish remains and ostracods. Their probable distribution in the immediate vicinity of Edinburgh is suggested in (Figure 11) where they are shown to crop out in the city and on the east side of Arthur's Seat. By inference it is thought that they are the beds of which poor exposures are seen in the core of the Granton Dome south of Granton. There is a good exposure immediately above the Corston Hill lavas between Corston Hill and Auchinoon Hill. Carruthers (in Carruthers and others 1927, p. 50), discussing the Linhouse Water sections, says that some 50 ft of "shaly blaes with thin ribs of platy entomostracan limestone, and a few ashy bands interstratified near the base" are "taken to represent the Abbeyhill Shales .". He also considers (p. 34) that the "black blaes with several thin beds of platy entomostracan limestone, associated with a good deal of shaly blaes and some thin ash ribs", amounting to some 150 ft of beds, appearing in the Murieston Water at Skivo, "probably represent the Abbeyhill Shales", but they are not separately distinguished on the maps.

Granton Sandstones

In the Edinburgh City area notable occurrences of the Granton Sandstones are known at Blackhall and Granton, in the centre of the city and at Abbeyhill. In the main outcrop information is available near Baberton and in the Linhouse Water.

Details

Blackhall and Granton

The detailed succession proposed by E. M. Anderson (in MS.) includes the Craigleith Sandstone at the base followed upwards by a group of shales, in turn succeeded by the Ravelston Sandstone.

Craigleith Sandstone

A highly siliceous, fine-grained rock much worked for building stone at Craigleith Quarry as well as at Blackhall, Craigcrook and Granton, apparently forms an almost closed outcrop running round the Granton Dome (Figure 12). Between Craigleith and Blackhall quarries the outcrop is shifted by a north-westerly trending fault. A minor anticlinal fold, parallel to the north-easterly fault separating the Granton Land and Sea quarries, results in a tongue of the Craigleith Sandstone extending to Hanging Craig. This bifurcates to the north-east where lower beds, presumably belonging to the Abbeyhill Shales, but including a 20-ft sandstone proved in a neighbouring bore, are brought up in the core of the fold. At Granton Land Quarry the sandstone is overlain by a 2-ft limestone. Across the north-easterly fault already mentioned, in Granton Sea Quarry, a 6-in irony limestone overlies the sandstone, which is here taken to be the same as that exposed in the Land Quarry. The dip, however, is to the east-south-east as opposed to the north-westerly inclination seen in the Land Quarry and it seems likely that E. M. Anderson's suggestion that the axis of the Granton Anticline (Dome) is shifted about a quarter of a mile to the east on the south side of the Granton Fault separating the two quarries is correct. The interpretation here adopted is that another fault separates the Granton Sea Quarry from the exposures of sandstone dipping north-west nearly half a mile to the south-west. The latter are believed to belong to the Craigleith Sandstone and to lie on the western side of the anticline, the relationships being displayed in (Figure 12). Above this sandstone is the Muirhouse 'Shrimp Bed' discovered by D. Tait (1925), containing abundant Tealliocaris sp., as well as gastropods, lamellibranch and nautiloid fragments in a different layer from the arthropods. The maximum thickness of the Craigleith Sandstone appears to approach 350 ft.

Craigleith Sandstone to Ravelston Sandstone

The beds between the Craigleith and Ravelston sandstones are nowhere well exposed, but were estimated by E. M. Anderson to be some 300 ft thick, a figure which would be supported by the Pilton Farm Bore if it could be certain that its correct position is as tentatively shown in (Figure 13). In the lower part of these shales Crampton and Tait (1910) recorded dark shale with ostracods and fish remains as well as very bituminous shale on the south side of the Queensferry Road, some 200 yd N.W. of the railway cutting in which Craigleith Station stands. Mudstones and sandy mudstones (blaes and fakes) were recorded in the railway cutting itself and presumably lie above the bituminous beds. The fossiliferous beds of the Queensferry Road are taken to be on approximately the same horizon as the shelly limestone bared in a sewer section at Craigleith Hospital, the 2-ft limestone in Granton Land Quarry, the 6-in irony limestone in Granton Sea Quarry mentioned above, and also the Muirhouse 'Shrimp-Bed'. According to calculations the upper part of this shale succession was encountered in Duncan's Works Water Bore (Figure 13).

Ravelston Sandstone

The Ravelston Sandstone is best exposed at Ravelston Quarry where the main beds are brown but higher lifts include a black sandstone (Tait 1932). On the one-inch and six-inch maps and on (Figure 12) the probable outcrop of this bed around the Granton Dome is shown, but information is somewhat meagre except along the western outcrop and on the coast. To the west of Granton harbour it is thought that General's Rock is formed of this sandstone as well as the reef of Long Craig across the Granton Fault, and the Birnie Rocks on the other limb of the Granton Anticline or Dome. The thickness of the Ravelston Sandstone is approximately 125 ft at its maximum.

Central Edinburgh

The study of temporary exposures, borehole records and isolated outcrops suggests the presence of the Granton Sandstones in the area between Warriston and Craiglockhart Station to the north-west of the Colinton Fault and forming part of a north-north-westerly trending anticline (Figure 11). The Craigleith Sandstone is thought to occur in the area of Queen Street Gardens half a mile north of the Castle. Flaggy, grey, ripple-marked sandstones which are believed to belong to this horizon were temporarily exposed in the angle between Hanover Street and Rose Street in 1938 (Tait 1942). At its southern end the Ravelston Sandstone is first recognized at Craiglockhart Station. Apart from temporary sections there are important exposures at Dean Bridge where the rock was formerly quarried. Here also are to be found at least 180 ft of bituminous shales (blaes), a thin coal and sandstone and sandy shales (faky blaes) presumably belonging to the strata between the Craigleith and Ravelston sandstones. The remainder of the outcrop of the latter sandstone is plotted with the help of boreholes. The group was cut in the tunnel of the old Edinburgh and Granton Railway which extended from Waverley Station to Scotland Street in strata considerably faulted and folded. The railway cutting at Craiglockhart shows a 25-ft. sandstone evidently forming the top leaf of the Ravelston Sandstone, separated from a lower 20-ft post of sandstone by about 100 ft of black and grey shales (Henderson 1885, p. 72). In the new cutting (1958) nearby Mr. W. E. Graham found Naiadites obesus in the shales below the higher sandstone. This evidence suggests that the Ravelston Sandstone may here be split into two leaves. Below the lower post of sandstone are found some 220 ft of black, bluish and grey shales with sandy beds and then about 130 ft of conglomerates, sandstones and seatclays, below which are about 150 ft of black and bluish shales and thin sandy beds. Under these the cutting traverses thick bedded sandstones about 18 ft thick and then a few feet of thin bedded sandstones nearly vertical where they adjoin the Colinton Fault. On the interpretation here suggested these last named are probably the highest beds of the Craigleith Sandstone.

Abbeyhill

Following on the Abbeyhill Shales to the east of Calton Hill (Figure 11) the Craigleith Sandstone is believed to occupy a belt crossing Royal Terrace Gardens where it was formerly quarried. Little is known of the succeeding shales, but the Ravelston Sandstone is thought to follow in orderly sequence with a north-north-westerly strike between Quarryholes and St. Margaret's Locomotive Works. Across the St. Margaret's Fault the outcrop of the Granton Sandstones presumably extends south-eastwards to the Pentland Fault.

Baberton

The sandstone quarried at one time near Baberton House, north of Currie and also exposed in Murray Burn (Figure 11) would appear to be the Craigleith Sandstone brought in by a northward pitching anticline or dome, faulted on the eastern side. The overlying shales are also exposed in places in Murray Burn and in the Water of Leith. The Ravelston Sandstone, though nowhere well exposed, is presumed to lie above the shales and the undivided Granton Sandstones outcrop is considered to be approximately as shown in (Figure 11).

Linhouse Water

Thick white sandstones exposed in the Linhouse Water and formerly quarried to within a short distance of the Murieston Fault, are regarded as probably the equivalents of the Granton Sandstones (Grant Wilson in Peach and others 1910, p. 87). They are also considered to crop out again in the same burn between the Calder Fault and a smaller fault to the south of it.

Wardie Shales

The probable outcrop of the Wardie Shales is shown on (Figure 11) and a suggested generalized section in (Figure 14). The relations of outcrops to structure may be followed by reference to (Figure 21).

Details

Wardie and Leith

The type area of the Wardie Shales is at Wardie. The lower members are exposed on the shore in and on both sides of Granton Harbour where the rocks are folded into the Wardie Syncline. Unfortunately the higher beds of the Wardie Shales are not exposed. The sequence was studied by E. M. Anderson who recorded (in MS.) the following section, partly derived from notes by R. G. Carruthers:

This gives a thickness of 491 ft for the lower part of the Wardie Shales. Anderson noted that it differs somewhat from the section given by Crampton (in Peach and others 1910, p. 77). He concluded that the uppermost 230 ft of the latter was an attempt to piece together a faulted section, chiefly of shales and sandstones, which includes a thin tuff and oil-shales; three of the latter occur in Granton Harbour and analyses of them were given by Grant Wilson (in Peach and others 1910, p. 351). Anderson did not attempt to give a precise section of these upper beds. Nor is there any detailed information about the highest beds of the Wardie Shales which must crop out to the east under Leith. Some indication of their character may be gained from the Roperie Water Bore in Bath Street, Leith on the north side of Leith Links. This showed a succession of sandy shales, thin sandstones and shales to a depth of 607 ft, where it entered a sandstone taken to be the Ravelston. Two thin coals were encountered, a 6-in seam at 193 ft 6 in and a 4-in seam with 8 in of 'coaly blaes' below at 307 ft, which may represent the Wardie Coal. Between about 440 and 540 ft several 'whin' intercalations were recorded in the shales.

Tunnels driven north-eastwards beneath the sea at Portobello Power Station showed Wardie Shales dipping at up to 65° to the east.

Dean Bridge, Craiglockhart, Slateford and Hailes

A poor coal is reported a little west of Dean Bridge. It is likely to be the Wardie Coal and is probably on the same horizon as the seam proved in Craiglockhart railway cutting to be 2 ft 3 in thick, dipping north-west. This coal was again proved about half a mile to the south-west and some 750 yd E. of Slateford church, dipping steeply to the north-west.

The base of the Wardie Shales appears to be exposed in the new (1958) railway cutting about 140 yd N.W. of Craiglockhart Station where it curves away to the west to join the old Caledonian line near Slateford Junction.

Here Mr. W. E. Graham recently examined in detail a section which is evidently the equivalent of one mentioned by Henderson (1885) in the adjoining cutting. The uppermost beds of the Granton Sandstones are represented by about 25 ft of sandstone surmounted by a 1-in seatclay. Some 1 ft 8 in of argillaceous measures with Spirorbis sp., Naiadites obesus (R. Etheridge, jun.), and ostracods, lie above the seatclay and are succeeded by a 4-in bed of irony limestone carrying N. obesus. Another 3 in of shale and faky blaes with the same fossil lie above the limestone and then follows a marine band 2 ft 8 in thick with Lingula mytilloides J. Sowerby; Naiadites obesus, N. crassus? (Fleming), Sanguinolites clavatus (R. Etheridge jun.), S. striatus Hind, Schizodus pentlandicus (Rhind), and gastropods. The highest beds seen are shales and faky blaes over 25 ft thick.

In another part of the cutting approximately 200 yd N.W. of the Canal Bridge the same worker observed a coal, evidently the Wardie, surmounted by a marine band. The details of the section as recorded by him, in downward succession are: whin 12 ft; red stained sandstone 28 ft; fakes and thin sandstone 22 ft; faky blaes 10 ft; whin 12 ft; black blaes (ostracods and fish-remains) 8 ft; faky blaes and fakes 4 ft; mushed blaes 2 in; faky blaes (Lingula sp.; Bucanopsis sp.; Leiopteria hendersoni R. Etheridge jun., Myalina sublamellosa R. Etheridge jun., Sanguinolites clavatus?; goniatite fragments and ostracods) 1 in; black blaes (ostracods) 6 in; blaes, faky in part 1 ft; hard limestone with ostracods up to 1 ft; coal 2 ft 3 in on seatclay.

By putting together the details of many recorded sections in the outcrop of Wardie Shales extending south-westwards from Craiglockhart, Slateford, Colinton and the middle reaches of the Water of Leith (Figure 14) has been compiled by Mr. G. A. Goodlet. It owes much to the observations of Tait (1916), including the valuable record of the Slaughterhouse Bore at Slateford. An interesting point about the section is the oncoming of oil-shale towards the top and the suggestion of a rhythmic arrangement of the strata.

Mid Calder

Black shales, thought to be on the horizon of the Wardie Shales, were found in trial pits between Hoghill and East Langton in ground bounded by the Calder and Murieston faults (Grant Wilson in Peach and others 1910, p. 87).

Hailes Sandstone

The probable outcrop of the Hailes Sandstone may be followed on (Figure 11); it is not known with certainty in the south-west of the district but sandstone met in bores at Pumpherston may belong to this horizon (Grant Wilson in Peach and others 1910, p. 90). The Hailes Sandstone is a white, greyish or blue and pink stone, at one time in great demand as a building stone and was formerly worked on a large scale at Hailes and Redhall quarries. These quarries are respectively on the western and eastern sides of the Hailes Syncline (Figure 21) which has a north-north-easterly trending axis with dips of from 10–15 degrees eastwards at Hailes and 12–25 degrees westwards at Redhall. The lower beds of the sandstone hereabouts, the 'Blue Hailes', are said to be about 40 ft thick; the higher or 'Pink Hailes' reach some 150 ft in thickness.

Queensferry Beds

The beds between the top of the Hailes Sandstone and the base of the Burdiehouse Limestone, here named the Queensferry Beds (Figure 9), crop out between Hound Point and the Colinton Fault south of Ratho (Figure 11). To the south-west of that fracture they have not been separately distinguished from the remaining members of the Lower Oil-Shale Group. Something is known, however, of their character at depth from bores in the south-west of the area.

The beds above the Hailes Sandstone have been recorded in shallow borings near Hailes Quarry and from here two shell-beds were noted within 50 ft of the top of that sandstone. It is tempting to suggest that they may be represented at Cousland No. 1 Bore by the shell-beds a little above and below 1700 ft but no palaeontological investigation has been possible. Apart from these fossiliferous beds there are no distinctive horizons in the lower part of the sequence which, as seen in (Figure 15), consists largely of sandy shales and sandstones with subsidiary shales and occasional calcareous bands, though the tuffs exposed between faults in Dalmeny Park may belong to this part of the succession. Such a succession does not apply in the south-west, however, where as shown by the West Calder Oil-Bore a thick development of tuff takes its place.

The next horizon which appears to be reasonably persistent is an oil-shale or belt of thin oil-shales which on (Figure 15) is termed the Dalmahoy Oil-Shale, in the belief that it is on the horizon of the outcrops of that area. If the correlation here adopted is correct this seam of oil-shale, which locally is said to reach some 14 ft thick with partings, includes at New Farm near Livingston several beds within a thickness of some 50 ft of strata. These oil-shales are locally known as New Shales. The Crosswood Ash probably lies some 20 ft below the oil-shales.

In No. 1 Bore at Humbie above the oil-shales referred to the Dalmahoy horizon a marine band known as the Humbie Shell-Bed was found and at other places (Figure 15) there is another thin oil-shale about 100 ft higher. In the Queensferry area two beds of cementstone, the lower 3 ft 10 in and the upper 1 ft 2 in thick, separated by some 3 ft of grey shale, are named the Queensferry Cements. They underlie a marine band known as the Pumpherston Shell-Bed which in its turn is succeeded by an important group of oil-shales known as the Pumpherston Oil-Shales, interbedded with which are at least two shell-beds. The Pumpherston Oil-Shales show considerable variation (Figure 15) but a typical section in the type area of Pumpherston is shown in the No. 1 Mine as follows : Jubilee Shale 7 ft; blaes 14 ft; Maybrick Shale 5 ft 3 in; blaes 13 ft 6.5 in; Curly Shale 7 ft 5.5 in; fakes and blaes 22 ft; Plain Shale 7 ft 8 in; fakes and blaes including a 1 ft 5-in oil-shale 10 ft 11 in on Wee or Under Shale 4 ft 3 in.

For further details the following authors should be consulted: Carruthers and others (1927), Richey (1942), Anderson (1942), Kennedy (1943).

The Pumpherston Shales are not known in the west of the area; near Livingston their place is taken by a thick bed of tuff, the Seafield-Deans Ash.

The highest of the Queensferry Beds again contain much arenaceous material particularly in the shore section east of the Forth Bridge where a thick sandstone is present. In the west tuff is predominant, as at Long Livingstone^‡3  No. 23 Bore, but a possible approach to marine conditions is suggested in the east where the Midlothian No. 1 Bore afforded evidence of several fossiliferous horizons, some with marine shells, and a number of limestone bands. A section in these beds is exposed in the middle reaches of the River Almond between Clifton Hall and Almondell (Grant Wilson in Peach and others 1910, p. 87). A marine horizon known as Macconochie's^‡4  Marine Band near Carlops in Midlothian has been tentatively correlated with the Pumpherston Shell-Bed (Tulloch and Walton 1958, p. 13). G.H.M.

North of the Forth

Strata referred to the Lower Oil-Shale Group occupy the coastal area between Aberdour and Rosyth Dockyard, south of the Rosyth Fault.

Details

The lower beds appear in the core of the Inchcolm Anticline, on the island of Inchcolm, where highly baked sandstones, siltstones, and shales are intruded by the well-known teschenite-picrite sill (Campbell and Stenhouse 1908). These are overlain by more than 50 ft of calcareous and tuffaceous beds, followed by basaltic lavas mainly of Dalmeny type and forming the westernmost tidal reefs of Inchcolm and the islands of Meadulse and Craigdimas. Amygdaloidal basalt lavas of Dalmeny type with thin bands of red tuff exposed in the core of an anticline at Charles Hill and Port Haven are probably the upward continuation of the same volcanic group. They are capped at Charles Hill by fine and medium grained tuffs and it is possible that tuffs forming the westernmost tidal reefs of the island of Carcraig are at about the same horizon.

Overlying the volcanic group of Charles Hill there are about 100 ft of mudstones and shales with beds of argillaceous limestone up to 3 ft thick; it is possible that the limestones of Carcraig (Day and Stenhouse 1930, p. 242) are at about the same horizon. The argillaceous group is followed by 500 ft or more of strata in which thickly bedded sandstones predominate; the sandstones of Bell Rock, Aberdour, lie at the base of this group, and the intrusive sills of Braefoot (Campbell, Day and Stenhouse 1932, 1934) lie some 200 to 400 ft above the base.

West of Braefoot the broad syncline of Dalgety Bay is occupied by the upper part of the sandstones, which include a thin bed of impure limestone visible at outcrop on both limbs of the syncline. The sandstones are folded over the Donibristle Anticline, where the sequence is partially obscured by faults and by intrusion in the core of the anticline. On the western limb of the anticline they dip beneath a group of thickly bedded coarse tuffs and agglomerates, the lower part sharply folded and the upper part broken by faults, so that the thickness and spatial relationship of the volcanic mass are obscure. About half a mile inland from the coast the mass appears to terminate abruptly as a broad semi-circle centred on the landmark known as The Steeple; it is possible that a vent occupies the ground hereabouts.

Nothing is now visible of the higher beds between St. Davids and Seafield House, but an excavation on the shore, just east of the house, exposed a marine band, again seen a mile to the north-east in an abandoned railway cutting and named the Fordell Marine Band. The fauna of this marine band and its probable stratigraphical position suggest that it may be at or near to the horizon of the Pumpherston Shell-Bed (Francis 1961).

The stratigraphy of the higher parts of the Lower Oil-Shale Group is much confused by the presence of the great sill of Inverkeithing and North Queensferry. Only disjoined exposures are available and among these the quarries (now covered) at Gartmhor and Welldean alone revealed more than a few feet of strata. In these quarries some 400 ft of well-bedded sandstones were exposed and they are inferred to lie high in the Lower Oil-Shale Group. The higher beds were formerly exposed on the coast now occupied by Rosyth Dockyard west of Gartland Hill, where the structure is gently undulating and relatively unfaulted. They consist mainly of sandstone with subordinate shales and thin limestones and include a Myalina Limestone some 25 ft below the Burdiehouse Limestone. J.R.E.

References

ANDERSON, F. W. and SIMPSON, J. B. 1938. Geological Notes on the Borings for Oil now in Progress at Cousland and D'Arcy, Midlothian. Oil Shale and Cannel Coal, 27–31, Inst. Petroleum.

ANDERSON, J. G. C. 1942. The Oil-Shales of the Lothians-Structure-Area II. Pumpherston. Geol. Surv. Wartime Pamphlet, No. 27.

CAMPBELL, R. 1914. On the Occurrence of Petrified Plant Remains in the Lion's Head Vent, Arthur's Seat. Trans. Edin. Geol. Soc., 10, 248.

CAMPBELL, R. and STENHOUSE, A. G. 1908. The Geology of Inchcolm. Trans. Edin. Geol. Soc., 9, 121–34.

CAMPBELL, R. DAY, T. C. and STENHOUSE, A. G. 1932. The Braefoot Outer Sill, Fife: Part I. Trans. Edin. Geol. Soc., 12, 342–75.

CAMPBELL, R. 1934. The Braefoot Outer Sill, Fife: Part II. Trans. Edin. Geol. Soc., 13, 148–73.

CARRUTHERS, R. G., CALDWELL, W., BAILEY, E. M. and CONACHER, H. R. J. 1927. The Oil-Shales of the Lothians. 3rd edit. Mem. Geol. Surv.

CLARK, R. H. 1952. The Significance of Flow Structure in the microporphyritic Ophitic Basalts of Arthur's Seat. Trans. Edin. Geol. Soc., 15, 69–83.

CLARK, R. H. 1956. A Petrological Study of the Arthur's Seat Volcano. Trans. Roy. Soc. Edin., 63, 37–70.

CRAMPTON, C. B. and TAIT, D. 1910. On certain New Localities for Oil-bearing Shale near Edinburgh. Trans. Edin. Geol. Soc., 9, 102–7.

CURRIE ETHEL D. 1954. Scottish Carboniferous Goniatites. Trans. Roy. Soc. Edin., 62, 527–602.

DAY, T. C. 1923. Note on the Exposure of St. Leonard's Crag at No. 39 St. Leonard's Hill. Trans. Edin. Geol. Soc., 11, 266–7.

DAY, T. C. 1933. Arthur's Seat, a Ruined Volcano. Edinburgh.

DAY, T. C. and STENHOUSE, A. G. 1930. Notes on the Inchcolm Anticline. Trans. Edin. Geol. Soc., 12, 236–51.

FLETT, J. S., BALSILLIE, D., CAMPBELL, R., DAY, T. C., DINHAM. C. H., ECKFORD, R., GORDON, W. T., MACGREGOR, M., MANSON, W., READ, H. H. and TAIT, D. 1927. The Geology of the District around Edinburgh. Proc. Geol. Assoc., 38, 405–55–517.

FRANCIS, E. H. 1961. The Economic Geology of the Fife Coalfields. Area II, 2nd edit. Mem. Geol. Surv.

GOODCHILD, J. G. 1901. Some Recent Exposures of Rock in Edinburgh. Trans. Edin . Geol. Soc., 8, 2–9.

GOODCHILD, J. G. 1905. Further Remarks on Some Recent Exposures of Rock in Edinburgh. Trans. Edin. Geol. Soc., 8, 266–72.

GREENSMITH, J. T. 1961. The Petrology of the Oil-Shale Group Sandstones of West Lothian and Southern Fifeshire. Proc. Geol. Assoc., 72, 49–71.

HAMILTON, J. 1957. Banded Olivines in some Scottish Carboniferous Olivine Basalts. Geol. Mag., 94, 135–9.

HENDERSON, J. 1883. Notice of a Bore Section at Abbey Hill, and its relation to the Rocks of the Calton Hill. Trans. Edin. Geol. Soc., 4, 34–7.

HENDERSON, J. 1885. On Rock Sections exposed in cutting for the Suburban Railway: With Observations on the Geology of the District around Edinburgh. Trans. Edin. Geol. Soc., 5, 71–82.

JUDD, J. W. 1875. On the Structure and Age of Arthur's Seat, Edinburgh. Quart. J. Geol. Soc., 31, 131–48.

KENNEDY, W. Q. 1943. The Oil-Shales of the Lothians-Structure-Area IV. Philpstoun. Geol. Surv. Wartime Pamphlet, No. 27.

MACGREGOR, A. G. 1936. The Composite Sill of St. Leonard's Craig and Heriot Mount, Edinburgh. Trans. Edin. Geol. Soc., 13, 317–31.

MACLAREN, C. 1839. A sketch of the Geology of Fife and the Lothians including detailed descriptions of Arthur's Seat and Pentland Hills. Edinburgh.

OERTEL, G. 1952. A Structural Investigation of the Porphyritic Basalts of Arthur's Seat, Edinburgh. Trans. Edin. Geol. Soc., 14, 360–78.

PEACH, B. N. 1921. Description of Arthur's Seat Volcano. 2nd edit. Mem. Geol. Surv.

PEACH, B. N. CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

RICHEY, J. E. 1942. The Oil-Shales of the Lothians-Structure-Area I. West Calder. Geol Surv. Wartime Pamphlet No. 27.

RUTLEDGE, H. 1952. A Petrological Note on a Composite Sill, The Dasses, Arthur's Seat. Trans. Edin. Geol. Soc., 14, 379–88.

SMITH, W. W. 1959. Pseudomorphs after Olivine in Markle Basalt. Miner. Mag. 32, 324–31.

TAIT, D. 1916. On Bores for Water and Medicinal Wells in the Wardie Shales, near Edinburgh. Trans. Edin. Geol Soc., 10, 316–25.

TAIT, D. 1925. Notice of a Shrimp-bearing Limestone in the Calciferous Sandstone Series at Granton, near Edinburgh. Trans. Edin. Geol. Soc., 11, 131–4.

TAIT, D. 1932. On the Occurrence of Petroliferous Sandstones in the Carboniferous Rocks of Scotland and their Relation to certain Black Sandstones. Trans. Edin. Geol. Soc., 12, 90–104.

TAIT, D. 1942. On the Excavation made for the Foundation of the Head Office of the Edinburgh Savings Bank in South Hanover Street during 1938. Trans. Edin. Geol. Soc., 14, 1–4.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol Surv.

Chapter 7 Upper Oil-Shale Group

THE Upper Oil-Shale Group includes strata from the base of the Burdiehouse Limestone to the base of the Cobbinshaw or Hurlet Limestone in West Lothian or its supposed equivalent the Gilmerton Limestone of Midlothian. This correlation depends on lithological and not palaeontological comparisons.

The outcrop of the group is plotted on (Plate 3) which shows that south of the Forth it consists of three separate areas (i) Cobbinshaw to Queensferry, (ii) Carlops to Portobello, (iii) Borthwick. North of the Forth it occupies the coastal area between Rosyth Dockyard and Limekilns. Details of outcrops of individual beds may be studied on the one-inch and six-inch maps. Included also in this chapter (p. 74) is a note on the Island of Inchkeith where sediments and lavas believed to straddle the horizon of the Burdiehouse Limestone, were described by Davies (1936).

The oil-shales are most distinctive strata in the Upper Oil-Shale Group. These economically valuable beds, varying from an inch or two in thickness to as much as 15 ft and of which some nine or ten have been widely worked, are however, but thin when compared with the mudstones, sandstones, clays and tuffs which make up the bulk of the 1200–2800 ft of strata that comprise the group. The mudstones frequently include numerous ostracods and several beds carry a marine shelly fauna which gives them great value in correlation. The oil-shales themselves pass laterally into ordinary carbonaceous mudstones so that the distinction between the two is often arbitrary. The group as a whole appears to have been formed in a shallow basin surrounded by land to north, west and south with probably an outlet to the sea eastwards towards Dunbar. The petrography of the sandstones has recently been discussed by Greensmith (1961).

With such an old established industry as the mining of oil-shale, in which it is standard practice to resort to intensive drilling to prove the ground, an enormous amount of geological detail has been accumulated. It is quite impracticable to publish this in extenso but already very detailed descriptions of the Oil-Shale fields are available in the works of Carruthers and others (1927), Richey (1942), Anderson (1942) and Kennedy (1943). A general account was given by Peach and others (1910). The south-western corner of the district was described by Macgregor and Anderson (1923). The present account gives no more than a summary of the succession and distribution and for further details the reader is referred to the works mentioned as well as to the six-inches to one mile geological maps of the area (Figure 1).

South of the Forth

An indication of the general variation in lithology and thickness can be gained from (Plate 3); the principal horizons are shown in more detail in (Figure 16). The thickness of the group varies from about 2800 to approximately 1600 to 1800 ft, the maximum being found in the West Calder area and a noticeable thin area occurring near Blackness. Variations in thickness in the Philpstoun area are set out in some detail by Kennedy (1943, p. 16). They show that in a distance of little more than a mile there is a uniform southerly increase in thickness of the Upper Oil-Shale Group whereby the sequence is almost doubled.

Details

Burdiehouse Limestone

The Burdiehouse Limestone, so named from the locality on the south-eastern outskirts of Edinburgh, is an estuarine or fresh-water limestone with abundant remains of plants, fish and ostracods. It is dark grey or cream-coloured and usually banded, though occasionally massive with chert bands. On breaking, i t has a characteristic glassy fracture. The thickness varies from 5 to 48 ft. Because of folding and faulting the outcrop of the Burdiehouse Limestone has a somewhat intricate pattern which can be followed readily on the one-inch map or by reference to Robertson and others (1949, p. 141 and fig. 41); in that memoir modern quarries and mines are described. Details of the countless old workings are to be found in Carruthers and others (1927). The chemical and petrological features of the rock are treated by Muir and others (1956).

Camps Shale

Though the thickness of mudstones between the Burdiehouse Limestone and the Camps Shale may in places be somewhat greater, as a rule only some 5 to 9 ft separate the two horizons. Occasionally as on the Harwood Water east-north-east of West Calder, there is a sandstone bed at this level. The seam is usually represented by a thin oil-shale or bituminous band and it is only in the Mid-Calder, Pumpherston, ingliston and Duddingston areas that it reaches a workable thickness of up to 8 or 9 ft. An interesting occurrence is the marine band 17 in thick found at Rosyth Docks immediately above the 18-in shale which represents the Camps (Carruthers and others 1927, p. 100). Recently J. T. Greensmith (1957) has described a sandstone dyke cutting measures from above the Camps Shale to quartzose sandstones below the Burdiehouse Limestone, on the beach at Banks, two miles west-north-west of the Forth Bridge. He suggested that the dyke was intruded from below during Oil-Shale Group times and invoked seismic activity and thixotropy in explanation. Francis (1960, p. 42), however, maintains that the dyke is an intrusive tuff.

Dunnet Sandstones

Succeeding the Camps Shale it is usual to find thick sandstones known as the Dunnet Sandstones. These are at least 720 ft thick in the Deans and Livingston district but over wide areas north and east of Broxburn they are replaced by a thinner sequence of argillaceous beds including the so-called 'marls' and occasional cement ribs. Interbedded with the greenish-grey or brownish sandstones are conglomerates and beds of red, brown and green 'marl'; the better posts of sandstone have been worked in places, as for example east-north-east of West Calder, close to the point where the railway crosses the Harwood Water. In this case it was the lowest grey beds which proved profitable. In the Rosyth area sandstones on this horizon have been known as Grange Sandstone, a name derived from Bumtisland.

Port Edgar Ash

A valuable stratigraphical horizon in the northern part of the West Lothian Oil-Shale Field from Dalmeny to Philpstoun is provided by the Port Edgar Ash which occurs high up in the Dunnet Sandstones where those beds are present, as at Philpstoun, or where they are thin or absent, as near Society, only a short distance above the Camps Shale. In Port Edgar railway cutting it attains its maximum known thickness of 37 ft. It is remarkable in that it does not contain igneous material but is composed of angular fragments of clay ironstone, cementstone, mudstone, sandstone and occasional chips of bright coal. These characters have led authors to suggest that it is an explosion-breccia.

Barracks Limestone

At the top of the Dunnet Sandstones there is developed in the neighbourhood of Deans, Livingston and Pumpherston a thin limestone which thins out rapidly since it is not found north or east of Philpstoun or Broxburn. The limestone, known as the Barracks Limestone, which is never more than a few feet thick, is hard and dark in character, carries ostracods and has a rough, hackly, fracture.

Barracks Ash

Resting on the Barracks Limestone where that is present, and widespread throughout the field, is a thin band of tuff, soft, greenish and feldspathic in the Mid Calder region, but in the north containing much fine sedimentary material. This bed is known as the Barracks Ash. Often no more than an inch or so thick, it swells to as much as 18 ft in such places as the Pumpherston area where it is separated from the Barracks Limestone, itself 5 ft thick, by about 12 ft of conglomeratic sandstone. Its wide occurrence makes the Barracks Ash a most useful horizon for correlation.

Dunnet Shales

In most parts of the West Lothian Oil-Shale field a belt of argillaceous rocks of variable thickness, of the order of 130 to 200 ft, succeeds the Barracks Ash and contains one or more workable oil-shales known as the Dunnet Shales, locally attaining thicknesses of 10 to 12 ft or even as much as 16 ft. In the Cobbinshaw, West Calder and Broxburn areas as well as at Duddingston, Society and Queensferry, a sandstone is locally developed at the base of this sequence and may attain a thickness of at least 100 ft. When only one workable oil-shale is found it is usually known as the Dunnet Shale and in many areas it lies close above the Barracks Ash. Elsewhere as many as three workable oil-shales are present and it is often not certain which of these represents the single seam of other areas. Where fully developed, as in the Pumpherston area, the names Under or No. 3 Dunnet Shale, New, Gavin or No. 2 Dunnet Shale and Dunnet or No. 1 Dunnet Shale are given in upward succession. These appear to represent respectively the Under Dunnet, Dunnet and Upper Dunnet Shales of West Calder. The Under Dunnet of West Calder lies almost directly on the Barracks Ash. The Under Dunnet of Pumpherston and Deans lies only a foot or two below a marine band, a few inches thick, known as the Dunnet Shell-Bed. In the latter district the Under Dunnet has been known as Pattison's Shale. In places dolerite intrusions such as that of Houston Wood have 'burnt' the shales and rendered them unworkable. This oil-shale is probably represented by the Pentland Shale of Straiton and the Carlops Shale of Carlops (Tulloch and Walton 1958, pp. 12–3). Details of the local development of these important oil-shales are to be found in the works already quoted (p. 65). Here it must suffice to say that at least one of these oil-shales is normally developed over almost the whole field, though not always of workable quality. The important exception is near Blackness where there is apparently a great attenuation of measures between the Burdiehouse Limestone and the Broxburn Shale to no more than about 170 ft and the Dunnet Shales are not recognized. The optimum development of the Dunnet Shales as regards thickness and quality is in the Broxburn–West Calder area.

Dunnet Marls

The highest of the Dunnet Oil-Shales is in many areas overlain by grey limy mudstones with thin brown ribs of sandstone known as the Dunnet Marls. These may be no more than a few feet in thickness but in places, as in the Pumpherston district, they swell out to a thickness of several hundred feet.

Binny Sandstone

An important siliceous sandstone horizon formerly widely worked for freestone under the local names of Binny, Hermand, Humbie or Dalmeny Sandstone separates the Dunnet and Broxburn oil-shales and in places reaches a thickness of over 400 ft. Near Cobbinshaw this horizon is occupied by some 240 ft of grey sandstone and brown or greenish marl. In the West Calder district it includes grey or greenish sandstone with an ochreous limestone 1 ft thick overlain by a thin black bituminous mudstone, both the last containing ostracods: Near Hermand not less than 90 ft of yellow and light grey sandstone were actually worked in the quarry. Near Breich, however, the sandstones, though still some 240 ft thick when the interbedded argillaceous beds are included, have deteriorated in quality, a condition which applies also near Deans. North and east of Broxburn 300 to 360 ft of sandstones occur, an even greater thickness than at Binny itself. At the old Humbie Quarry and other abandoned quarries at Craigend west of Swineburn the sandstone was formerly worked and the horizon is also represented at Ecclesmachan. In the Champfleurie and Philpstoun area the sandstones vary greatly from massive beds over 500 ft thick at Craigton to some 240 ft around Midhope while farther south near Bridgend no more than 27 ft are present, the thinning taking place in two miles. At Dalmeny the sandstone was also quarried. In the Midlothian Coalfield at Straiton the Binny Sandstone was recorded as 65 ft thick.

Champfleurie Shale

Resting on the Binny Sandstone in the Broxburn, Ecclesmachan, Philpstoun and Champfleurie areas is the Champfleurie or Lower Grey Shale. Another name given to this seam is the Wee or Champfleurie Dunnet. It is locally worked, attaining its maximum thickness in the Gateside Anticline from Philpstoun to the south of Gateside where is it from 10 to 15 ft thick, but thinning rapidly to north and south, though a thin representative is recognized as far east as Dalmeny.

An interesting case of lithological variation in the measures between the Burdiehouse Limestone and the Champfleurie Shale is discussed by Kennedy (1943, p. 14). He terms the beds between the Champfleurie and Dunnet shales, the Binny Sandstone Group and those between the Dunnet Shale and the Burdiehouse Limestone the Dunnet Sandstone Group. He shows that south-west of Philpstoun, where the Champfleurie Shale is thick the underlying Binny Sandstone Group is thin, only a few feet of actual sandstone being present. Moreover the Dunnet Shale below the sandstone group is not developed, being represented by dark blaes, yet the still lower Dunnet Sandstone Group is very thick with 220 ft of sandstone apart from the associated argillaceous beds. As these beds are traced eastwards, over a distance of about 1.5 miles, to the south-east of Philpstoun, the Champfleurie Shale thins from 7 ft of oil-shale to 2 ft of shaly blaes; the Binny Sandstone Group increases from 133 ft, of which only 23 ft are fakes (sandy shales) and sandstone, to 360 ft of sandstone. At the same time the Dunnet Shale comes in and attains a thickness of 15 ft 8 in, of which only 1 ft 1 in consists of partings, while the Dunnet Sandstone Group decreases from 316 ft (of which 220 ft are sandstone) to 230 ft, comprising only blaes, manly blaes and marls. The relationship between the Champfleurie and Dunnet shales, in which, where the latter is absent the former is very well developed, is stated to be so constant that it can be taken to be an empirical rule.

Broxburn Shales

A persistent and economically important group of oil-shales, in some places represented by several seams but elsewhere reduced to a single bed, is known as the Broxburn Shales. In the south-west near Cobbinshaw the group includes two thin oil-shale beds 9 in and 13 in thick, but to the north, in the southern part of the West Calder area, a seam less than 3 ft thick and rather inferior, has nevertheless been worked. In the northern part of the West Calder workings an average thickness is 3 ft 7 in with additional top and bottom ribs; hereabouts the bed was known as Thornton's Shale or the Under Shale of Addiewell. At Breich, Cousland and Deans there are often several beds of oil-shale and at the first named place one of these reaches a thickness of 4 ft 4 in. Near Mid Calder the group includes the following succession: WEE SHALE 1.5 ft; strata 13 ft; BIG SHALE 4.5 ft; strata 12 ft; LOWER BIG SHALE 6 ft; strata 10 ft; CURLY SHALE 6 ft; strata 5 ft; on MCLEAN SHALE 4 ft. This gives a ratio of 22 ft of oil-shale to 40 ft of strata. In the Pumpherston district the Broxburn Shales reach their greatest development where 60 ft. of oil-shale, all of high quality, occur in 138 ft of strata and in one small 'pocket' the McLean Seam attained a thickness of 28 ft, but these oil-shales are now worked out. At Broxburn the section, which includes three valuable seams, is as follows, the probable Mid Calder equivalents being given in brackets: Shale (Wee) 1 ft 1 in; strata 12 ft. 3 in; shale 8 in; limestone 6 in; shale (Big) 1 ft. 6 in; strata 3 ft 10 in; GREY SHALE (Lower Big) 5 ft 10 in; strata 5 ft 4 in; CURLY SHALE (Curly) 5 ft 4 in with dirt 1 ft 2 in; strata 4 ft; on BROXBURN SHALE (McLean) 5 ft. The proportion of oil-shale to strata in this case is 18 ft 3 in to 27 ft 1 in.

Near Ecclesmachan there appears to be only one seam; averaging 7 ft 10 in in thickness, and in places this is spoilt by the sill of Binny Craig. Attenuation to thin layers occurs north of Winchburgh towards Duntarvie but the seam improves again towards Tottlywells except where affected by the Dundas Castle sill. The Broxburn Oil-Shale is as much as 16 ft thick in places in the Champfleurie–Philpstoun area where is has a roof of limy blaes carrying ostracods and in some localities there is a 6-in band with Curvirimula scotica (R. Etheridge, jun.) a few feet below it. Despite a general great thinning of the measures in the Blackness area a bore there encountered 10 ft of oil-shale at this horizon; another however proved only blaes. Well to the east, on the margin of the field, the beds of oil-shale at this position have been well nigh exhausted near Dalmeny where a typical section is: shale 2 ft 6 in; blaes 4 in; shale (Six-Foot Seam) 3 ft; blaes 5 ft; shale (Curly) 8 in; shale (plain) 2 ft 3 in; blaes 1 ft 4 in; shale (Curly Shale) 3 ft; blaes, shaly 4 ft; shale (inferior) 2 ft; shale (good) (Broxburn Shale) 6 ft. At Dalmeny a thin basalt lava is present in the upper part of the Broxburn Shale group; this is the type locality for olivine-basalts of Dalmeny type. In Midlothian the Broxburn Shale has been worked at Straiton where it was some 3 ft 6 in thick.

Broxburn Marls

Much of the interval between the Broxburn Shales and the Fells Shale is occupied by a characteristic set of beds known as the Broxburn Marls. These "comprise greenish, marly, or ashy clays, interbedded with carbonaceous shale and ribs of very hard, unfossiliferous cementstone or calcareous bands that vary in thickness from 1 in to over 3 ft" (Carruthers and others 1927, p. 10). In the Cobbinshaw area the beds are some 180 ft thick, greenish and greyish in colour with bands of ostracod limestone and thin sandstones. Some shales occur between them and the Fells Shale. In the West Calder field the blue and greenish-grey blaes and marls with faky sandstone bands which form the Broxburn Marls have swelled to some 250 ft in thickness and include 1-in to 3-ft ribs of cementstone. Towards their top ironstone bands come in and there is a 6 to 8-ft limestone in the middle surmounted by calcareous mudstone; the limestone carries plant and fish remains and ostracods. Similar beds occur near Breich, but in the neighbourhood of Deans there is a great range in thickness, which varies from about 60 to 120 ft and the beds include a conglomeratic sandstone in the middle part and thin limestone bands in the upper part. A dark platy limestone with ostracods is recorded from the middle of the marls near Mid Calder. In the Pumpherston, Broxburn and Winchburgh districts the thickness appears to average 120 to 210 ft with the usual greenish lower part and the thickness increases to 240 to 270 ft at Champfleurie only to diminish considerably to about 90 ft near Philpstoun and as little as 36 to 60 ft west of Midhope. At Blackness this reduction is most marked for in places no more than 5 in of typical Broxburn Marls are found, but this is counterbalanced by an exaggerated development of the cement bands usually found in the marls so that they form thick limestones. The characteristic marl facies apparently does not extend into Midlothian for at Straiton their position is occupied by about 137 ft of sandstone and blaes.

Fells Limestone

The Fells Limestone, which in the Cobbinshaw and West Calder areas lies directly below the Fells Oil-Shale and forms a most useful indicator for the latter, is a band of cream or grey limestone from 3 to 5 ft thick. This limestone, carrying Spirorbis and ostracods is overlain by about 3 ft of blaes with Lingula, ostracods and fish remains. In the Deans district several beds of limestone occur close under the Fells Shale. In bores near Philpstoun no limestone was recorded under the Fells Shale.

Fells Shale

The principal oil producer in the south-west corner of the West Lothian area was the Fells Shale which with a thickness of about 3 ft at Cobbinshaw and 4 ft south of Tarbax ranges from 2.5 ft up to as much as 7 ft near West Calder where it was locally known as the Hartwood Shale or the Thick Shale of Addiewell. Elsewhere throughout West Lothian, though its position in the sequence can be recognized, it is usually either thin or not of economic value, the exception being the small area near Newfarm where the workings practically exhausted the reserves. At Blackness the seam is totally absent and arenaceous sediments take its place. In the Straiton district of Midlothian the thickness of the oil-shale is given as 1 ft 8 in.

Beds between Fells Shale and Houston Coal

The measures separating the Fells Shale and the Houston Coal are almost everywhere sandstones and sandy mudstones with only occasional interbedded mudstones, shale or clayband ironstones. At Straiton in Midlothian a thin coal is found in these measures. Representative average thicknesses are as follows: Cobbinshaw 78 to 126 ft; West Calder 200 ft; Deans 120 to 162 ft; Newfarm 210 ft; Ecclesmachan 240 to 300 ft; Champfleurie 180 ft; Dalmeny 220 ft; Straiton 100 ft. In the extreme north-west near Blackness the Fells Shale is not recognized but the corresponding measures must again be little more than 100 ft thick.

Houston Coal: Though it is an inferior and pyritous seam and workings in it are handicapped by its bad roof and pavement, the Houston Coal is "practically the lowest bed of workable coal in the Scottish Carboniferous System" (Carruthers and others 1927, pp. 10–11), for only a few thin seams have been wrought below this horizon and those in a very small way. Moreover, except for the unimportant Two Foot Coal above the Houston Marls, some 1000 ft of strata separate the Houston from the next workable coal, the Cobbinshaw Seam at the very top of the Upper Oil-Shale Group. In the Cobbinshaw area the Houston Coal measures about 6 ft in thickness, while in the West Calder region a typical section is: coal 9 in; clay 6 in; coal 6 in; sclit (probably coaly clay) 2 in; coal 20 in; sclit 2 in; coal 10 in; sclit 2 in; on coal 12 in. Hereabouts the quality is rather better than usual. A thickness of 6 to 7 ft is recorded from Newfarm; at Broxburn an average section shows: coal 2 ft 3 in; blaes 1 ft 5 in; on coal 1 ft 4 in. Near Winchburgh the old Priestinch pit is the farthest point to the north-east at which the coal has been worked, a record from the neighbouring workings showing a thickness of 3 ft 9 in with three fireclay partings each a few inches thick. At Ecclesmachan the seam is rather thinner: coal 1 ft 3 in; dirt 3 ft 2 in; on coal 1 ft 10 in. A further reduction occurs at Champfleurie where the coal is down to 1 ft 8 in. At Dalmeny railway cutting, with a thickness of some 2 ft, the seam rests on an ostracod limestone and is surmounted by tuff. Finally in Midlothian near Straiton the measures above the Fells Shale include two thin coals, the higher of which is probably the Houston.

Grey Shale and Houston Marls

In the Cobbinshaw district about 18 ft of fireclay and faky sandstone separate the Houston Coal from the overlying Grey Shale but this interval increases to 90 ft at Addiewell, a mile south-west of West Calder. These measures are from 70 to 80 ft thick near West Calder whereas at Deans and Mid Calder the Grey Shale is but a few feet above the coal. The Grey Seam (of Addiewell or West Calder as it is sometimes named) is 20 in thick at Addiewell but is not known south of the Blackbrae Fault at Blackbrae Bridge, half a mile south-west of Burngrange. In West Calder it may reach 1 ft 8 in and contains many ostracods. Very thin at Deans, it is not recognized at Blackness, but at Dalmeny 4.5-ft of shaly blaes, resting on the Houston Coal, represent the Grey Shale; they are overlain by 20 ft of blaes and flaggy ostracod limestone. The Houston Marls occupy most of the interval between the Grey Shale and the succeeding Two Foot Coal; they consist of greenish massive, amorphous mudstones, hard when fresh but crumbling on weathering, with sandstone bands which are often limy. They vary in thickness from about 135 to 200 ft except in the Blackness area where they thin to as little as about 45 ft. The name marl is a misnomer as the rocks are not sufficiently rich in lime to warrant that term (Carruthers in Carruthers and others 1927, p. 11). Petrological notes and chemical analyses were given by Teall and Radley (1925).

Two Foot Coal

The Two Foot Coal is widespread but usually thin and only occasionally reaches 2 ft in thickness, being more generally only a few inches. It is of interest as marking the level of a well-defined volcanic episode marked by a bed of tuff which occurs immediately above it in the north-western part of the main oil-shale field. When decomposed the fine-grained tuffs may easily be mistaken for the Houston Marls.

Mungle Shale

At Addiewell the Mungle Shale was worked with a thickness of 20 to 24 in but it is unworkable at Cobbinshaw, being no more than 8 to 15 in thick. In the northern part of the West Calder area the seam, separated from the Two Foot Coal by 130 ft of measures, is again 20 to 24 in thick and was worked. Near Broxburn it is the same thickness but inferior; the measures between it and the coal have swelled to 168 ft.

Raeburn Shale and Shell-Bed

The shell-bed below the Raeburn Shale is the lowest of three important fossiliferous horizons in the upper part of the Upper Oil-Shale Group. Near Cobbinshaw it is over 13 ft thick, but it is widely developed throughout the West Lothian area as well as at Carlops in Midlothian. It was even found at Blackness, an area noteworthy for the attenuation of the succession. The Raeburn Shale was formerly regarded as the richest seam in the West Calder area where a typical section was: shale 3 ft 1 in; brown blaes 1 ft 3 in; shale 10 in; fireclay 4 in; shale with ribs 9 in on shale, soft, leafy 3 ft 8 in. At Cobbinshaw, however, it was reduced to 1 ft 6 in but again in the Addiewell district, where it was known as the 'Dam Shale' or the 'Upper Shale of Addiewell' a section was: shale, good 1 ft 7 in; shale, soft 2 in; shale, good 10 in; shaly blaes 6 in; blaes and fireclay 9 in on shale 10 in. In the Broxburn ground the Raeburn lies 30 ft above the Mungle Shale and consists of 2 ft 11 in of shaly blaes. At Blackness this bed appears to be represented by 9 ft 6 in of shaly blaes and grey blaes underlain by fossiliferous beds. The Paper Shale of Straiton in Midlothian, a finely laminated bed, may be the equivalent of either the Mungle or Raeburn Shale.

Fraser Shale and Shell-Bed

Some 80 to 100 ft above the Raeburn Shale lies the Fraser Shale and its underlying shell-bed, known in the south-west. Well-developed at Cobbinshaw with an average of 3.5 ft, locally increasing to 6 to 8 ft, it is distinguished from the Raeburn by having no more than 2 to 4 ft of blaes above in contrast to the 20 ft or so of the latter. At Addiewell the seam was recorded as 11 in thick lying 150 ft above the Raeburn with a thin coal between. The characteristic shell-bed was found in a bore at Blackness but the shale itself is altered by the neighbouring sill.

Fraser Shale to Cbbbinshaw Limestone

Beds above the Fraser Shale are known in the south-west of the district where the section extends up to the Cobbinshaw (Hurlet) Limestone. They include in upward succession 30 to 60 ft of clays, sandstones and marls with thin cementstone ribs. These measures are followed by a coal, in one or two leaves, lying about 9 to 15 ft below a marine band which has been correlated with the Basket or Cot Castle Shell-Bed of East Kilbride and Strathaven. There is a higher marine horizon corresponding to the Under Limestone of Strathaven 48 to 108 ft higher. This lies about 90 to 150 ft under the Cobbinshaw Limestone. Twelve to eighteen feet below the Under Limestone is a coal, parroty in character and coaly shale locally carrying Lingula and fish remains. Four or five thin ostracod limestones are also known 18 to 30 ft below the Cobbinshaw Coal. The Cobbinshaw (Hurlet) Coal is separated from the overlying Cobbinshaw Limestone by 2 ft 6 in to 3 ft of dark, fossiliferous mudstone and is about 4 ft thick, pyritous and, though poor in quality, has been worked to a considerable extent.

In the Philpstoun area some 215 ft of mainly sandstone, fakes and blaes with ironstone ribs separate the Fraser Shale from the overlying Riccarton Limestone which is probably not far below the Cobbinshaw Limestone.

On the margins of the Midlothian Coalfield the highest beds of the Upper Oil-Shale Group are difficult to correlate with those of West Lothian. A thin oil-shale may represent the Fraser Shale (Tulloch and Walton 1958, fig. 5, p. 13). Above this the Cephalopod Limestone seems to be on the horizon of the Cot Castle Shell-Bed and the Bone Bed Limestone is likely to be the Under. At the base of the Bone Bed Limestone there are shales with Rhipidomella and it is probably the equivalent of the Lower Crichton Limestone of the eastern side of the Midlothian basin.

Volcanic rocks of Riccarton Hills

As already mentioned a bed of tuff occurs above the Two Foot Coal; it can be traced from Drumcrosshall northwards almost to the Firth of Forth and is also found east of the main outcrop at Little Ochiltree. This bed forms the lowest member of a volcanic sequence which is intercalated in the upper part of the Upper Oil-Shale Group at Riccarton Hills and extends up into the Upper Limestone Group as developed in the Bathgate Hills. This tuff is overlain by shales and sandstones and then in Longmuir Plantation by a further bed of tuff and several flows of olivine-basalt, the lowest of which is a compact flow of Dalmeny type, but others of which show exposures of decomposed and vesicular basalts. These volcanic rocks dip westward beneath shales and sandstones near Broomyknowes but thin out northwards. The sedimentary rocks in turn give place higher in the succession to more olivine-basalts which form the Riccarton Hills. Northwards the lavas also thin out while southwards they coalesce with the Longmuir group of lavas to the exclusion of the intervening sediments. Above the Riccarton Hills volcanic rocks come further sediments including the Tartraven Limestone, which is taken to be the equivalent of the Cobbinshaw or Hurlet Limestone in this ground.

G.H.M.

North of the Forth

In Fife, strata belonging to the Upper Oil-Shale Group occupy the coastal stretch from Rosyth Dockyard westward to Limekilns: their general dip is westerly. The rocks are cut by several faults, the largest of which is the Rosyth Fault, with west to east trend and displacement, of unknown amount, down to the north.

Details

The lowest beds of the group come to the surface immediately south of the Rosyth Fault in the area of Rosyth Dockyard by which they are now almost entirely obscured. The following section of these beds was recorded by R. G. Carruthers in 1913 during constructional work by the Admiralty:

North of the Rosyth Fault and extending westwards from Rosyth Dockyard to Limekiln there is an ascending succession through the upper part of the Upper Oil-Shale Group. The sequence recorded there is as follows:

Inchkeith

Some 330 ft of shales, mudstones, limestone and sandstones, interbedded with about 500 ft of Dalmeny and Hillhouse type lavas, making a total of approximately 830 ft of beds, are exposed on the Island of Inchkeith (Davies 1936). The middle of the sequence is thought to be at about the horizon of the Burdiehouse Limestone (Davies 1936, p. 777; Anderson 1950, p. 24). G.H.M.

References

ANDERSON, F. W. 1950. Some reef-building calcareous algae from the Carboniferous rocks of Northern England and Southern Scotland. Proc. Yorks. Geol. Soc., 28, 5–28.

ANDERSON, J. G. C. 1942. The Oil-Shales of the Lothians — Structure — Area II. Pumpherston. Geol. Surv. Wartime Pamphlet No. 27.

CARRUTHERS, R. G., CALDWELL, W., BAILEY, E. M. and CONACHER, H. R. J. 1927. The Oil-Shales of the Lothians. 2nd edit. Mem. Geol. Surv.

DAMES, L. H. 1936. The Geology of Inchkeith. Trans. Roy. Soc. Edin., 58, 753–86. FRANCIS, E. H. 1960. Intrusive Tuffs related to the Firth of Forth Volcanoes. Trans. Edin. Geol. Soc., 18, 32–50.

GREENSMITH, J. T. 1957. A Sandstone Dyke near Queensferry, West Lothian. Trans. Edin. Geol. Soc., 17, 54–9.

GREENSMITH, J. T. 1961. The Petrology of the Oil-Shale Group Sandstones of West Lothian and Southern Fifeshire. Proc. Geol. Assoc., 72, 49–71.

KENNEDY, W. Q. 1943. The Oil-Shales of the Lothians-Structure-Area IV. Philpstoun. Geol. Surv. Wartime Pamphlet No. 27.

MACGREGOR, M. and ANDERSON, E. M. 1923. The Economic Geology of the Central Coalfield of Scotland, Area VI. Bathgate, Wilsontown and Shotts. Mem. Geol. Surv.

MUIR, A., HARDIE, H. G. M., MITCHELL, R. L. and PHEMISTER, J. 1956. The Limestones of Scotland. Chemical Analyses and Petrography. Mem. Geol. Sun,. Min. Resources, 37.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

RICHEY, J. E. 1942. The Oil-Shales of the Lothians-Structure-Area I. West Calder. Geol. Surv. Wartime Pamphlet No. 27.

ROBERTSON, T., SIMPSON, J. B. and ANDERSON, J. G. C. 1949. The Limestones of Scotland. Mem. Geol. Surv. Min. Resources, 35.

TEALL, J. J. H. and RADLEY, E. G. 1925. Petrological Notes on the Houston Marl, with chemical analyses. Trans. Edin. Geol. Soc., 11, 327–37.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 8 Lower Limestone Group

In the neighbourhood of Edinburgh there are a number of separate outcrops of the beds which form the Lower Limestone Group. There is a general similarity in the succession in most of these areas as is evident from a study of (Figure 17), but in the ground east of Linlithgow a very different sequence is found. Here the generally rhythmic succession of sediments including limestones, calcareous shales, sandstones and argillaceous beds with rare coal seams, gives place to dominantly volcanic beds with only subsidiary sediments.

The Midlothian area, in which the limestones are thickest, has recently been described in some detail by Tulloch and Walton (1958). The base of the group is taken at the bottom of the Gilmerton Limestone which is thought to be the Hurlet of West Lothian and the Charlestown Station Limestone of Fife. The top is considered to be at the top of the Top Hosie Limestone which is equated with the Upper Kinniny of Fife.

As will be seen from (Figure 17) detailed correlation between the different areas is still somewhat doubtful; it may be possible to suggest closer comparison when time is found to study closely the palaeontology of the beds. The chief points of interest, however, are the comparatively thick limestones of Midlothian, many of which are, or have been, worked for lime, and the considerable sandstones also developed in that district.

In the much smaller outcrop of West Lothian near Cobbinshaw it will be noticed that limestones are much thinner. Details are given by Grant Wilson (in Peach and others 1910, p. 105).

The volcanic sequence near Linlithgow (Maufe and Bailey in Peach and others 1910, pp. 145–9, Macgregor in Macgregor and Haldane 1933, pp. 79–97) is the result of a volcanic episode, which commenced after the formation of the Two Foot Coal in the Upper Oil-Shale Group and continued throughout the Lower Limestone Group, the Limestone Coal Group and the Upper Limestone Group until approximately 2000 ft of volcanic rocks, known as the Bathgate Lavas, were deposited. The thickest part of the pile exposed lies about the latitude of the Bathgate Hills rather south of Linlithgow and along the strike both northwards and southwards the lavas and tuffs thin as they are interbedded with the sediments. Correlation is naturally particularly difficult in the dominantly volcanic succession and indeed it is not possible to fix the exact position of the boundary between the Lower Limestone and Limestone Coal groups. The Tartraven Limestone, which is taken to represent the Cobbinshaw (Hurlet) is recognized in places; elsewhere the base of the Lower Limestone Group is conjectural. Thin shales succeed the Tartraven Limestone but in turn are overlain by flows of basalt probably some 400 ft thick, followed by the Petershill Limestone and then by more basalts, one of which bears analcite, which must occupy the horizon of the Top Hosie Limestone and straddle the junction between the Lower Limestone Group and the Limestone Coal Group (Figure 3).

Thin beds of tuff which probably belong to the same outbursts of volcanic activity occur in places near Charlestown north of the Forth but the sequence in Fife is generally a sedimentary one, again with comparatively thin limestones, and a considerable amount of calcareous shale and several thick sandstones (Figure 17). The rocks are, however, not well exposed in the area under consideration except for the coast sections near Kinniny Point and Charlestown. For details of these see Haldane and Allan (1931, pp. 21–5).

There are also good exposures in the measures between the Charlestown Main Limestone and the Upper Kinniny Limestone in Pinkerton Burn and Balbougie Glen north of Inverkeithing.

A detailed description of working limestone quarries is given by Robertson and others (1949) and their chemical and petrographical characters are dealt with by Muir and others (1956). G.H.M., J.R.E.

References

HALDANE, D. and ALLAN, J. K. 1931. The Economic Geology of the Fife Coalfields Area I. Mem. Geol. Surv.

MACGREGOR, M. and HALDANE, D. 1933. The Economic Geology of the Central Coalfield of Scotland. Area III, Bo'ness and Linlithgow. Mem. Geol. Surv.

MUIR, A., HARDIE, H. G. M., MITCHELL, R. L. and PIIBMISTER, J. 1956. The Limestones of Scotland. Chemical Analyses and Petrography. Mem. Geol. Surv. Min. Resources, 37.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Sun,.

ROBERTSON, T., SIMPSON, J. B. and ANDERSON, J. G. C. 1949. The Limestones of Scotland. Mem. Geol. Surv. Min. Resources, 35.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 9 Limestone Coal Group and Upper Limestone Group

THE Limestone Coal Group, of Lower Eumorphoceras (E₁) age, together with the Upper Limestone Group and the lowest beds of the Passage Group (p. 82), both of Upper Eumorphoceras (E₂) age, form the only undoubted representatives in the Edinburgh district of the Millstone Grit Series as known in England and Wales. They both crop out in a belt around the Midlothian basin and the lower of the two groups also appears at Carriden, as well as in scattered outcrops north of the Forth (Figure 2).

Their development in Midlothian has recently been described in detail by Tulloch and Walton (1958). In this coalfield the Limestone Coal Group, which includes the strata from the top of the Top Hosie Limestone to the base of the Index Limestone, is of importance because of the rich coal-seams which it contains. For the purpose of this account the section of Loanhead (Figure 18) may be taken as an example of the sequence of coals, sandstones and mudstones, occurring as they do in a rhythmical manner, which makes up the group. The feature which distinguishes this group from those immediately above and below it is the recurrence of coals of such quality and thickness that they are much mined for fuel. The other noteworthy members of the succession are the Lingula bands and marine bands (Figure 18), of which the most important for correlation purposes are the Johnstone Shell-Bed and the Black Metals Marine Band.

The Limestone Coal Group near Carriden in West Lothian (Figure 18) differs greatly from its character in Midlothian. A great thickness of volcanic rocks comes in and includes the beds here called Muirhouses and North Bank basalt lavas, while just west of the ground shown on the Edinburgh sheet volcanic beds almost completely replace the sedimentary rocks. Detailed correlation between the two areas is uncertain. Though the Johnstone Shell-Bed is recognized in places, the position of the Black Metals is thought to be occupied everywhere at outcrop by volcanic rocks (Macgregor and Haldane 1933, pp. 7, 8). G.H.M.

In Fife the lowest part of the Limestone Coal Group occupies a small synclinal area north of the Rosyth Fault between Hillend and Balbougie. Exposures are few but several thin coals were proved above the Upper Kinniny Limestone in a water borehole at Scots Mill.

The whole of the Limestone Coal Group is at outcrop between Crombie and the north-west corner of the sheet, immediately north of which lies Preston Island. There are records of two coals near the base of the group, probably the Smithy and Dunfermline Splint coals, having been worked near Bullions Farm. Higher measures underlie the mud of Torry Bay; such details as are known were given by Haldane and Allan (1931, pp. 44 and 51). J.R.E.

The Upper Limestone Group includes the strata between the base of the Index Limestone and the top of the Castlecary Limestone (Figure 19). In the area here considered it is only found within the Midlothian Coalfield where thick sandstones, shales, sandy shales and five stratigraphically important limestones occur in rhythmic sequences which includes in addition thin coal seams and marine or Lingula bands (Tulloch and Walton 1958, plate iv). The principal limestones in upward succession are Index, Lyoncross, Orchard Beds, Calmy and Castlecary. Several fossiliferous horizons, of great value in correlation, are described by Wilson (in Tulloch and Walton 1958, pp. 80–2). G.H.M.

References

HALDANE, D. and ALLAN, J. K. 1931. The Economic Geology of the Fife Coalfields. Area I. Mem. Geol. Surv.

MACGREGOR, M. and HALDANE, D. 1933. The Economic Geology of the Central Coalfield of Scotland. Area III. Mem. Geol. Sun,.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 10 Passage Group and Coal Measures

Within the area of the Edinburgh sheet the Passage Group and the Coal Measures occur only in the centre of the Midlothian Coalfield (Figure 2). The former beds, previously known as the Roslin Sandstone Group or Millstone Grit and described in detail by Tulloch and Walton (1958) consist of a succession of sandstones, often gritty in character and not infrequently pebbly, with intervening beds of mottled red, yellow and grey clays and argillaceous sandstones, both of which in places include nodules of sphaerosiderite and occasional marine bands. Their lower boundary is taken at the top of the Castlecary Limestone and their top at the base of the Seven Foot Coal in the north of the coalfield or the base of the Melville Group of coals and fireclays in the south.

The only diagnostic goniatites are in a marine band 27–32 ft above the Castlecaly Limestone and are of Upper Eumorphoceras (E₂) age. Minor unconformities or non-sequences are present throughout the succession. The lowest non-marine lamellibranchs known from the Coal Measures are referred to the Zone of Carbonicola communis. The greater part of the group, therefore, occupies some place in the stratigraphical succession between the Arnsbergian (E₂) Stage and the Carbonicola communis Zone, but it is uncertain whether they should be classed with the Millstone Grit Series of the Pennines or the Lower Coal Measures, a difficulty which led to the adoption for them of the term Passage Group (MacGregor 1960, p. 129). In common with the rest of Scotland no evidence of beds of Homoceras, Reticuloceras or Gastrioceras age is known and at least a non-sequence is suspected within the Passage Group.

As described in detail by Tulloch and Walton (1958, p. 84) Kidston long ago found a palaeobotanical break within these beds and Traquair noted a difference between the estuarine fish faunas found below and above the 'Millstone Grit' and it may be that an appreciable unconformity exists within the Passage Group, the lower beds belonging to the Millstone Grit Series of the Pennines while the upper should be classed with the Coal Measures.

Though the beds differ considerably from place to place, as shown by Tulloch and Walton (1958) the section at Joppa provides probably the most reliable and best documented succession and this is reproduced in (Figure 19).

The Coal Measures as a whole are lithologically similar to the Passage Group save that coal seams, being much more frequent and thicker, provide valuable sources of fuel which have been widely worked. Bands with non-marine lamellibranchs are also common in parts of the succession and afford useful indices for correlation. The uppermost beds, though originally apparently lithologically similar to the lower, have, however, suffered severe secondary reddening and are genefally red in colour; in some cases the coals have been altered to limestones. All these features are dealt with in detail by Tulloch and Walton (1958). As will be seen from (Figure 19) the beds are divided into Lower, Middle and Upper Coal Measures, the appropriate dividing lines being taken at two important marine bands known as the Queenslie and Skipsey's Marine Bands. G.H.M.

References

MACGREGOR, A. G. 1960. Divisions of the Carboniferous on Geological Survey Scottish Maps. Bull. Geol. Surv. Gt. Brit., 16, 127–30.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 11 Carboniferous lavas and tuffs

Lavas

The characteristics of the various types of Carboniferous lavas described in this memoir have been given in detail by MacGregor (1928) and by Macgregor and MacGregor (1948). MacGregor (1948) has also attempted a synthesis of Carboniferous–Permian volcanicity in Scotland.

For convenience the principal types of Carboniferous olivine-basalt are here summarized:

• MACROPORPHYRITIC BASALTS
• Markle type: with phenocrysts of labradorite and olivine.
• Dunsapie type: with phenocrysts of labradorite, olivine and augite.
• Craiglockhart type: with phenocrysts of olivine and augite.
• MICROPORPHYRITIC BASALTS
• Jedburgh type: with phenocrysts of labradorite and olivine.
• Dalmeny type: with phenocrysts of olivine, and sometimes sporadic labradorite and augite.
• Hillhouse type: with phenocrysts of olivine and sometimes of augite.

The main groundmass constituents are labradorite, augite and iron ore in all cases except the Hillhouse type, in which they are augite, iron ore and a little labradorite, with much analcite or glass. Analcite is often present in small amount in other types.

The known outcrops of lavas and tuffs of Carboniferous age and their stratigraphical distribution are shown on (Figure 20).

Notes on their chief characteristics are given below; further details and references may be found on the pages mentioned.

1. Craiglockhart Lavas and Tuffs: Olivine-basalts of Craiglockhart type (large phenocrysts of olivine and augite) and basaltic tuffs (p. 35). Well exposed at Craiglockhart Hill.
2. Canongate Tuffs: Thin bands of supposed tuff found interbedded with sediments in temporary exposures (p. 36).
3. Arthur's Seat Lavas and Tuffs: Olivine-basalts and mugearites with interbedded basic tuffs (p. 45). Well exposed on Whinny Hill, north of Arthur's Seat, Calton Hill, and probably also at Corston Hill and Tor-weaving Hill (pp. 45–52).
4. 4, 5. Granton: Thin beds of probably basaltic tuff in Wardie Shales exposed on shore at Granton harbour at two horizons (p. 57).
5. 4, 5. Granton: Thin beds of probably basaltic tuff in Wardie Shales exposed on shore at Granton harbour at two horizons (p. 57).
6. Dalmeny Park: Several exposures of basaltic tuff between faults in Dalmeny Park (p. 60).
7. Crosswood Ash: Beds of tuff in sediments found near Crosswood Reservoir and in boreholes in that neighbourhood (p. 60).
8. Seafield–Deans Ash: Tuffs locally reach 300 ft or more in thickness in the Seafield and Deans area (p. 62). The lower part of the lavas of Inchkeith may be at about this horizon (p. 74).
9. Port Edgar Ash: Tuffs composed entirely of sedimentary debris. Good exposures occur in Port Edgar railway cutting (p. 67). The upper lavas of Inchkeith probably occur at about this position (p. 74).
10. Barracks Ash: A feldspathic tuff with much sedimentary material particularly in its northern development. Found over a wide area in bore-holes (p. 68).
11. Dalmeny Lava: Thin lava exposed south-east of Dalmeny village (p. 70).
12. Dalmeny Railway Cutting: Tuff and agglomerate, well bedded, exposed in the railway cutting at Dalmeny (p. 71).
13. Bankhead, Little Ochiltree, Tuffs: Green and red tuffs above the Two Foot Coal traceable over a wide area, marking the oncoming of the great volcanic activity responsible for the lavas and tuffs of the Bathgate Hills area (pp. 72–73).
14. Riccarton Hills Lavas: Compact, dark olivine-basalts often decomposed and vesicular with occasional thin beds of tuff. Dalmeny and Hillhouse types of lavas recognized (p. 73).
15. Linlithgow Lavas and Tuffs: A thick group of tuffs and basaltic lavas often individually thin with vesicular tops, in which both Dalmeny and Hillhouse types are found (p. 76).
16. Muirhouses Lavas: Dalmeny type basalts (p. 79).
17. North Bank Lavas: Dalmeny type basalts (p. 79).

Vent agglomerates

Agglomerates filling the orifices of presumed Lower Carboniferous volcanoes include the Arthur's Seat vent-agglomerates and numerous examples in West Lothian. While much of the fragmentary material forming these pyroclastic rocks is basaltic in character many vents include appreciable quantities of sedimentary fragments. Some are traversed by basaltic intrusions while occasional examples such as the Castle Rock, Edinburgh consist entirely of basalt plugs. G.H.M.

References

MACGREGOR, A. G. 1928. The Classification of Scottish Carboniferous Olivinebasalts and Mugearites. Trans. Geol. Soc. Glasgow., 18, 324–60.

MACGREGOR, A. G. 1948. Problems of Carboniferous–Permian volcanicity in Scotland. Quart. J. Geol. Soc., 104, 133–53.

MACGREGOR, M. and MACGREGOR, A. G. 1948. The Midland Valley of Scotland 2nd edit. revised. British Regional Geology. Geol. Surv.

Chapter 12 Structure

In the area of one-inch Sheet 32 it is possible to recognize three main periods of earth-movement as follows

1. Pre-Lower Old Red Sandstone earth-movements: The evidence outside the area of one-inch Sheet 32 shows that in parts of the Midland Valley the pre-Lower Old Red Sandstone movements can be separated into two main orogenic phases, the earlier post-Arenig and pre-Caradoc in age and the younger late Silurian, pre-Lower Old Red Sandstone. In the Southern Uplands and in the area under description, however, only the late Silurian, pre-Lower Old Red Sandstone phase of these main Caledonian movements has been recognized.
2. Post-Lower and Pre- Upper Old Red Sandstone earth-movements, forming the final phase of the Caledonian orogeny.
3. Carboniferous and Post Carboniferous earth-movements, by inference probably mainly Hercynian in age.

Pre-Lower Old Red Sandstone structures

The earth-movements which preceded the deposition of the Lower Old Red Sandstone were responsible for the steep inclination of the Ordovician and Silurian rocks of the district. The Silurian strata of the Pentland inliers strike roughly N. 30° E., with deviation up to 30 degrees, and are generally nearly vertical. Since the evidence points to an almost consistently upward succession to the west-north-west, the isoclinal folds postulated by Peach and Horne (1899, p. 592, fig. 120) cannot be substantiated. Fold structures are rare in the inliers. In the North Esk Inlier minor folds are seen in the gorge 270 yd S. 38° E. of North Esk Cottage, on the west shore of the North Esk Reservoir and in the Lynslie Burn, 400 yd N. 39° E. of its junction with the Lyne Water. The first-named locality shows a complex recumbent fold trending N. 20° E. and closing to east-south-east. Transcurrent faults trending west-north-west, and some thrusts, all of small displacement, occur throughout the inliers, but they are probably all of post-Lower Old Red Sandstone age.

Pre-Upper Old Red Sandstone structures

The pre-Upper Old Red Sandstone earth-movements (Mykura 1960, pp. 152–3) imparted a general south-easterly tilt, locally modified by gentle flextures, to the Lower Old Red Sandstone rocks exposed within the area. During this period a system of large faults was either initiated or reactivated along pre-existing fault-lines. The south-west trending strike faults with downthrow to south-east, which, in the area under description include the Pentland and Loganlee faults, were among the prominent tectonic features of the period. They now separate areas of relatively thick deposits of Lower Old Red Sandstone rocks from areas where the latter have been partially or completely removed during the period of erosion preceding the deposition of the Upper Old Red Sandstone sediments. Thus the marked difference in thickness of the Lower Old Red Sandstone rocks on either side of the Loganlee Fault is very apparent in the North Black Hill–Bavelaw Castle area. The similar effect of the Pentland Fault cannot be seen within the area of one-inch Sheet 32 but is very marked between Tinto Hill and Lanark, within the area of one-inch Sheet 23. West-north-west trending, generally sinistral, transcurrent faults and a number of thrusts, all of small displacement, cut the Lower Old Red Sandstone and older rocks. These are probably due to pressures directed from the east-south-east.

Carboniferous and Post-Carboniferous structures:

Carboniferous rocks form much the greater part of the district at outcrop and considerably more is known of the structures which affect them.

A certain amount of information is available from the study of isopachytes of various formations regarding the movements which were taking place during the deposition of the Carboniferous rocks. Such studies, which are essentially attempts to unravel the history of sedimentation and earth-movements in the Midland Valley, of which the Edinburgh area forms but a small part, include the works of such authors as Anderson (1951), Goodlet (1957, 1959), Kennedy (1958) and George (1960). The divergence in shape of the original basin of deposition and the later structural basin of the Midlothian Coalfield was touched on by Tulloch and Walton (1958, p. 118).

The axes of the principal folds and the lines of the important faults are plotted on (Figure 21). Two maps (Figure 22), (Figure 23) give details of the structure in the Midlothian Coalfield and the West Lothian Oil-Shale Field respectively, the latter prepared by Mr. A. Davies. In the broad sense the structure of the Edinburgh district is dominated by the Pentland anticlinal uplift, a broad elongated dome, trending north-east and plunging to the north-east in the neighbourhood of Edinburgh and to the south-west near West Linton to the south of the present ground. The effect of this post-Carboniferous dome is to bring to outcrop earlier folded and faulted Silurian and Lower Old Red Sandstone rocks which form the Pentland Hills and to separate the Carboniferous rocks of the Midlothian Coalfield from those of the West Lothian Oil-Shale Field. The Midlothian Coalfield is structurally an asymmetrical syncline, also with a north-easterly trend, but the West Lothian Oil-Shale Field comprises a large number of minor domes and basins on the eastern margin of the great basin of the Central Coalfield. To the east the Midlothian and East Lothian coal basins are separated by the D'Arcy–Cousland Anticline.

Prominent among the faults is the Pentland Fault, a reverse fault which may be said in part to replace the south-eastern limb of the Pentland anticlinal fold. It bounds the Midlothian Coalfield on the north-west and trends northeastwards. In the Oil-Shale Field there are several large east-north-easterly trending fractures one of which, the Murieston Fault, takes on a north-northeasterly direction near Edinburgh, where it is known as the Colinton Fault. A number of arcuate fractures, including the Vogrie, Crossgatehall and Sheriff-hall faults, concave to the north, cross the Midlothian Coalfield and several of these provide evidence of lateral shift where they cut fold structures. Details of the extent and throw of these various fractures as well as the folding can be found in Carruthers and others (1927), Richey (1942), Anderson (1942) and Kennedy (1943) for the West Lothian Oil-Shale Field. Tulloch and Walton (1958) have likewise described the structure of the Midlothian Coalfield. In these various publications there are also numerous cross-sections which are additional to those shown on the published one-inch map.

Although horizontally striated fault-planes are not uncommon it is rarely possible to demonstrate lateral movement along fault-planes in a convincing manner. As already mentioned above, the Vogrie, Crossgatehall and Sheriffhall faults afford evidence of such movement by the manner in which the axes of folds are shifted by them (Tulloch and Walton 1958, pp. 123–4). Reference to (Figure 23) shows similar cases in the Oil-Shale Field, particularly with regard to the Winchburgh, Middleton Hall and Uphall faults. Details of the last named as proved underground were described by Kennedy (1944). He shows it to have a low hade to the south and a horizontal component of displacement of 600 ft relatively eastwards on its northern side.

The Lammermuir, Leadburn and Pentland faults and probably also the Loganlee Fault (Figure 21) form part of the suite of north-easterly faults which together form the Southern Upland fault-belt (Anderson 1951, pp. 97–100). These faults have a complex history and in some the direction of throw was reversed during the post-Carboniferous phase of movement (Eyles and others 1949, pp. 16–8; Mykura 1960, pp. 152, 154). In addition strong strike-slip movements have been postulated for both the Pentland Fault (Anderson 1951, pp. 99–100) and for the Southern Upland fault-belt in general (George 1960, p. 89). G.H.M., W.M.

References

ANDERSON, E. M. 1951. The Dynamics of Faulting and Dyke Formation with Applications to Britain. 2nd edit., Edinburgh.

ANDERSON, J. G. C. 1942. The Oil-Shales of the Lothians-Structure-Area II. Pumpherston. Geol. Surv. Wartime Pamphlet No. 27.

CARRUTHERS, R. G., CALDWELL, W., BAILEY, E. M. and CONACHER, H. R. J. 1927. The Oil-Shales of the Lothians. 3rd edit. Mem. Geol. Surv.

EYLES, V. A., SIMPSON, J. B. and MACGREGOR, A. G. 1949. Geology of Central Ayrshire. Mem. Geol. Surv.

GEORGE, T. N. 1960. The Stratigraphical Evolution of the Midland Valley. Trans. Geol. Soc. Glasgow., 24, 32–107.

GOODLET, G. A. 1957. Lithological Variation in the Lower Limestone Group in the Midland Valley of Scotland. Bull. Geol. Surv. Gt. Brit., 12, 52–65.

GOODLET, G. A. 1959. Mid-Carboniferous sedimentation in the Midland Valley of Scotland. Trans. Edin. Geol. Soc., 17, 217–40.

KENNEDY, W. Q. 1943. The Oil-Shales of the Lothians-Structure-Area IV. Philpstoun. Geol. Surv. Wartime Pamphlet No. 27.

KENNEDY, W. Q. 1944. Transcurrent Movement exemplified by a Fault in the West Lothian Oil-Shale Field. Trans. Geol. Soc. Glasgow., 20, 287–90.

KENNEDY, W. Q. 1958. The Tectonic Evolution of the Midland Valley of Scotland. Trans. Geol. Soc. Glasgow, 23, 106–33.

MYKURA, W. 1960. The Lower Old Red Sandstone igneous rocks of the Pentland Hills. Bull. Geol. Surv. Gt. Brit., 16, 131–55.

PEACH, B. N. and HORNE, J. 1899. The Silurian Rocks of Britain, 1, Scotland. Mem. Geol. Surv.

RICHEY, J. E. 1942. The Oil-Shales of the Lothians-Structure-Area I. West Calder. Geol. Surv. Wartime Pamphlet No. 27.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 13 Intrusions

Though differing in age the intrusions mapped in the Edinburgh district fall within the three classes, sills, dykes and plugs. The distinction between the first two is sometimes rendered difficult by the manner in which sill-like bodies suddenly transgress the adjacent strata in a dyke-like manner.

The oldest intrusions are of Lower Old Red Sandstone age; another large group appears to be Lower Carboniferous; yet others cannot be more closely dated than probably Carboniferous, while the youngest are probably late Carboniferous or Permian. Details of the various groups are set out below:

Lower Old Red Sandstone

Minor intrusions cut the Silurian and Lower Old Red Sandstone sediments and lavas in the Pentland Hills. Near Swanston and in the Braid Hills volcanic vents pierce Lower Old Red Sandstone volcanic rocks. As both are believed to be connected with the latter episode they are described after the volcanic rocks of that age on p. 27 (Cockburn 1952; Mykura 1960).

Carboniferous

A large number of sills are intruded in Lower Carboniferous sediments in the Edinburgh area and one or two in the volcanic rocks of Arthur's Seat (pp. 36–8, 47–8). For the most part they occur at definite horizons and their outcrops and stratigraphical positions are plotted on (Figure 24). It is, however, not uncommon for them to change their horizon, in which case the connecting portions are often dyke-like or form irregular masses.

There are many dykes with an east-west trend cutting rocks varying in age from Upper Old Red Sandstone to Coal Measures.

In addition volcanic necks with basaltic agglomerate are often accompanied by basic vent-intrusions.

The age of these various intrusions cannot be precisely determined and apart from the broad generalization that all are Carboniferous or post-Carboniferous, attempts to work out a more detailed history of igneous intrusion are dependent on petrographical affinities rather than structural relationships. Thus a group of intrusions which includes the basaltic necks of Arthur's Seat and Castle Rock, Edinburgh, as well as others such as St. Leonard's Craig, Edinburgh, are so similar to the neighbouring extrusive rocks as to justify the supposition that they were formed during the same burst of activity (pp. 47–8). A number of sills are of teschenite and allied rock-types, some of which contain a layer of picrite or picroteschenite. They belong to a group that cuts sediments which are mainly Lower Carboniferous in age and yet are absent from Coal Measures. Among them may be mentioned the rocks of Salisbury Craigs and the essexite of Lochend. Other important examples are those of Easter Dalmeny (Flett 1930), Blackness (Flett 1931, 1934), Stankards (Flett 1932), Braefoot (Campbell, Day and Stenhouse 1932, 1934), Inchcolm (Campbell and Stenhouse 1908), Fordell and Crombie. It is generally assumed that the sills of this group are of Lower Carboniferous age. A third group, characterized by quartz-dolerite and tholeiite dykes and sills, cuts rocks ranging from Lower Old Red Sandstone to Coal Measures as well as teschenite sills, and is thought to be of the same age as the Permo–Carboniferous earth-movements. Among rocks of this type may be mentioned the quartz-dolerite sills of Hound Point, Craigiehall (West Craigs), Ratho and Inverkeithing, the unusual types of Binny Craig (Lunn 1932) and the tholeiites of Dalmeny (Walker 1923), Dalmahoy and Kaimes (Campbell and Lunn 1927; Day 1925). Detailed accounts of the petrography of many of these rocks will be found in Peach and others (1910, pp. 275–323) where not only the igneous rocks themselves but their marginal phenomena such as chilling and the metamorphism of the adjacent sediments are described. Among the alteration products is the formation of the characteristic 'white trap' found at such localities as the shore at Newhalls, South Queensferry (350 yd E. of the Forth Bridge). This rock is formed by the alteration of the igneous rock to an aggregate of carbonates of lime, magnesia and iron, with kaolin and muscovite, consequent on its reaction with the carbonaceous shales, oil-shale or coals into which it happens to have been intruded (Day 1932).

A more general account of the problem of the Carboniferous igneous rocks is given by Macgregor and MacGregor (1948, pp. 50–76) who include tables of the composition of the main rock types and a bibliography of the principal papers on the subject. A more philosophical approach is provided by MacGregor (1948) who endeavours "to account for the eruptive sequence of Scottish Carboniferous–Permian igneous rocks by means of a synthesis involving the mechanism of eruption as well as the broader aspects of differentiation".

Recent work not covered by the references given above includes an account of exposures of the quartz-dolerite dyke of Broughton in Edinburgh (Tait 1945) and a note on a composite sill at The Dasses, Arthur's Seat by Rutledge (1952) which contains new chemical analyses. The trace elements of the Braefoot Outer Sill were discussed by Higazy (1952). G.H.M.

References

CAMPBELL, R. 1934. The Braefoot Outer Sill, Fife: Part II. Trans. Edin. Geol. Soc., 13, 148–73.

CAMPBELL, R. DAY, J. C. and STENHOUSE, A. G. 1932. The Braefoot Outer Sill, Fife: Part I. Trans. Edin. Geol. Soc., 12, 342–75.

CAMPBELL, R. and LUNN, J. W. 1927. The Tholeiites and Dolerites of the Dalmahoy Syncline. Trans. Roy. Soc. Edin., 55, 489–505.

CAMPBELL, R. and STENHOUSE, A. G. 1908. The Geology of Inchcolm. Trans. Edin. Geol. Soc., 9, 121–34.

COCKBURN, A. M. 1952. Minor Intrusions of the Pentland Hills. Trans. Edin. Geol. Soc., 15, 84–99.

DAY, T. C. 1925. Igneous Intrusive Phenomena of Upper Whitfield, near Macbiehill; and at Ravelrig and Kaimes Hill Quarries, Balerno. Trans. Edin. Geol. Soc., 11, 14–7.

DAY, T. C. 1932. Chemical Analyses of White Trap from Dalmeny, Granton, Weak Law and North Berwick. Trans. Edin. Geol. Soc. 12, 189–94.

FLETT J. S. 1930. The Teschenite of Easter Dalmeny. Sum. Frog. Geol. Surv. for 1929, pt. 3, 59–74.

FLETT J. S. 1931. The Blackness Teschenite. Sum. Prog. Geol. Surv. for 1930, pt. 3, 39–45.

FLETT J. S. 1932. The Stankards Sill. Sum. Prog. Geol. Surv. for 1931, pt. 2, 141–56.

FLETT J. S. 1934. A Thomsonized Inclusion from the Blackness Sill. Sum. Prog. Geol. Sum for 1933, pt. 2, 85–90.

HIGAZY, R. A. 1952. The Distribution and Significance of the Trace Elements in the Braefoot Outer Sill, Fife. Trans. Edin. Geol. Soc., 15, 150–86.

LUNN, J. W. 1932. The Intrusion of Binny Craig, West Lothian. Trans. Ellin. Geol. Soc., 12, 74–9.

MACGREGOR, A. G. 1948. Problems of Carboniferous–Permian Volcanicity in Scotland. Quart. J. Geol. Soc., 104, 133–53.

MACGREGOR, M. and MACGREGOR, A. G. 1948. The Midland Valley of Scotland. 2nd edit. revised, British Regional Geology, Geol. Surv.

MYKURA, W. 1960. The Lower Old Red Sandstone igneous rocks of the Pentland Hills. Bull. Geol. Surv. Gt. Brit., 16, 131–55.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

RUTLEDGE, H. 1952. A Petrological Note on a Composite Sill, The Dasses, Arthur's Seat. Trans. Edin. Geol. Soc., 14, 379–88.

TAIT, D. 1945. Notes on the Geology of the Broughton District of the City of Edinburgh. Trans. Edin. Geol. Soc., 14, 21–7.

WALKER, F. 1923. The Igneous Geology of the Dalmeny District. Trans. Roy. Soc. Edin., 53, 361–75.

Chapter 14 Palaeontology

MR. J. D. D. Smith has dealt with the palaeontology of the Silurian rocks in Chapter 2. The palaeontology of the Upper Limestone Group, Passage (formerly Roslin Sandstone) Group and Coal Measures was dealt with by Wilson and Calver (in Tulloch and Walton 1958). It has not been possible as yet to examine in detail the faunas of the Lower Limestone and Limestone Coal groups, but in the present chapter the palaeontology of the Calciferous Sandstone Measures, which include the Cementstone and Lower and Upper Oil-Shale groups, is considered. The spore flora of some coals in the Limestone Coal Group and Upper Limestone Group have recently been examined by Butterworth and Williams (1958).

Introduction

The fossils present in the Calciferous Sandstone of West and Midlothian have long attracted the attention of palaeontologists. The plant, fish and ostracod remains which were to be found in the quarries in the Burdiehouse Limestone at Straiton, and in ironstone nodules in the shales on the coast at Granton were well known to early collectors, and were described in the works of Kidston, Traquair and Jones. A bibliography of these earlier works is given in the second edition of this memoir (Peach and others 1910). The presence of molluscs was barely acknowledged, although as early as 1838 W. Rhind in a short work called 'The Age of the Earth' drew attention to the presence of lamellibranchs at Woodhall, Water of Leith. Etheridge (1878) described a marine invertebrate fauna found in the Wardie Shales in the Edinburgh area, but the greater part of earlier works dealt with estuarine or freshwater forms and the conception arose, still quoted in general works, that the Calciferous Sandstone in the Lothians area was deposited under non-marine conditions.

Carruthers (1912, pp. 92–4; 1927, pp. 106–8), showed, mainly from borehole evidence, that marine bands are present in the Oil-Shale groups and that they could be traced over the oil-shale field. Anderson and Simpson (1938, pp. 28–30), in a preliminary account of deep boreholes in search of oil, recorded marine bands in the Cousland area in the eastern part of the present ground. The results of Currie's study of the goniatites from the area has already been discussed (p. 6). A generalized description of the Calciferous Sandstone was given by Tulloch and Walton (1958, pp. 11–6) in which they recorded six marine horizons in the Lower and Upper Oil-Shale groups. Recently Love (1960) has described the small spores found in the Pumpherston Shell-Bed, Pumpherston Oil-Shale and Burdiehouse Limestone.

For this account, the fossils collected by the Geological Survey from the Calciferous Sandstone of West Lothian and Midlothian have been examined. Since many of these specimens have come from boreholes and from recently made collections from surface exposures, much previously undescribed material has been studied. The most striking result has been the finding of a number of marine horizons, the fossils of which have not been adequately recorded before and may be of importance in future work in the area.

In terms of the abundance of individuals, ostracods are by far the most common fossils found. They occur in great numbers, sometimes accompanied by Spirorbis, in most of the so-called freshwater limestones and their remains make up a considerable proportion of the shales at some levels. They range all through the succession, as do the plant and fish remains, but as yet, no one has demonstrated that any of these forms can be used stratigraphically within the Calciferous Sandstone.

The vertical distribution of the non-marine lamellibranchs, derived from a study of borehole specimens, is of some interest. These shells, presumably the forerunners of the 'mussels' of the Upper Carboniferous, are represented by three groups. The first contains forms which have been tentatively referred to Carbonicola antiqua Hind; they are of rare occurrence, poorly preserved, and appear to be confined to the Lower Oil-Shale Group. The second group is that of Curvirimula scotica (R. Etheridge jun.), formerly Anthraconauta scotica, and closely related forms; they are found in large numbers in some of the shales of the Upper Oil-Shale Group and the earliest specimens recorded in boreholes occur just above the Pumpherston Shell-Bed, that is near the top of the Lower Oil-Shale Group. The last, and most abundant group comprises shells identified as Naiadites obesus (R. Etheridge jun.) and closely allied forms. They range up from the Cementstone Group to just above the Pumpherston Shell-Bed. At some levels in the Wardie Shales some specimens are closely associated with marine forms but usually they occur in discrete bands with occasional specimens of Spirorbis adhering to them as on Naiadites in the Coal Measures. This change in the genera of 'mussels' just above the Pumpherston Shell-Bed is found in boreholes not only in the West Lothian Oil-Shale Field but also in the Cousland area just above beds taken to be equivalent to the Pumpherston Shell-Bed. It also applies to the majority of field exposures, the exceptions being at localities where the exact horizon is in doubt. This feature of vertical distribution can only be used as a general guide, however, as an insufficient number of boreholes has been examined to provide an adequate check.

For convenience of description, the distribution and faunas of the marine bands will be treated under the separate areas in which they occur. As the upper part of the succession is better known the sequence will be described in downward order.

West Lothian Oil-Shale Field

During the exploration of the West Lothian area for oil-shales, numerous borings were sunk and some of these were examined by Survey officers and the fossils collected. Enough information is available to make the stratigraphical correlation of the Upper Oil-Shale Group succession a relatively straightforward matter, and the positions of the five marine bands are well known (Figure 16). The faunas of the marine bands are given in tabular form below, the numbers referring to the following boreholes and shafts: 1 — Fraser Shaft No. 1; 2 — Fraser Shaft No. 2; 3 — Baads No. 1 Bore; 4 — Baads Mine No. 1 Bore; 5 — Blackness No. 2 Bore; 6 — Baads Mains Farm Bore; 7 — South Cobbinshaw Bore; 8 — Burngrange No. 1 Bore; 9 — Midhope Burn No. 477 Bore; 10 — Newyearfield Bore; 11 — Cobbinshaw Estate Bore; 12 — Stankards Bore.

In addition to the five marine bands in the Upper Oil-Shale Group, a Lingula band was found in Baads Mains Farm Bore about 100 ft above the Raeburn Shell-Bed and probably below the Fraser Shell-Bed. In five of the six occurrences of the Dunnet Shell-Bed in boreholes, the strata immediately above the shell-bed contained Euestheria. This is the only horizon in the Upper Oil-Shale Group at which this genus has been recorded. The highest occurrence of Curvirimula scotica was just below the Raeburn Shell-Bed and the species ranges down to just above the Pumpherston Shell-Bed. With the exception of the Dunnet Shell-Bed, the strata between the Raeburn and Pumpherston shell-beds appear to be of non-marine origin, containing plants, Spirorbis, Naticopsis? scotoburdigalensis (R. Etheridge jun.), Curvirimula sp., ostracods and fish remains.

Relatively little exploration for oil-shales was carried out in the Lower Oil-Shale Group and our knowledge of the measures is meagre. The highest marine band is the Pumpherston Shell-Bed near the top of the group. It was first discovered in a bore near Livingston (Carruthers 1912, p. 35) where the band contained Pectinid, goniatite and orthocone fragments. Naiadites was found immediately above and shrimp-like arthropods below. The marine band on the shore at South Queensferry has been correlated with the Pumpherston Shell-Bed (Carruthers 1912, p. 35) and has yielded a richer fauna than that obtained from boreholes in the western part of the oil-shale field. The fossils collected recently from the marine band by Mr. P. J. Brand include: Lingula sp.; Euphemites sp.; Aviculopecten subconoideus? (R. Etheridge jun.), Edmondia?, Pernopecten sp., Pteronites sp. (juv.), Sanguinolites clavatus, Schizodus cf. trigonalis (de Koninck), Streblochondria sp., Streblopteria?; orthocone nautiloid fragments. Shales 60 ft thick occurring above the marine band contain Naiadites obesus and Euestheria sp.

In a borehole at Humbie another marine band was found about 180 ft below a band taken to be the Pumpherston Shell-Bed. This lower band, for convenience called the Humbie Shell-Bed, contained Actinopteria persulcata, goniatite and orthocone nautiloid fragments and Euestheria sp.occurred immediately above. In the south-west corner of the area, in Harburn No. 2 Bore, a marine band with crinoid columnals, Sedgwickia? and orthocone nautiloid fragments was found some 700 ft below marine beds thought to be equivalent to the Pumpherston Shell-Bed, but the correlation of this geographically isolated borehole is dubious. The general distribution of marine bands in West Lothian is now seen to include a group of four near the top of the Upper Oil-Shale Group; the Dunnet Shell-Bed, indicating an isolated marine incursion between the Raeburn and Pumpherston shell-beds ; and in the Lower Oil-Shale Group, the Pumpherston Shell-Bed (which is reasonably well recorded) and in addition one record of the Humbie Shell-Bed and possibly even a much lower marine band in Harburn No. 2 Bore.

Edinburgh District

In the City of Edinburgh area, marine fossils have been known to occur in the Wardie Shales division of the Lower Oil-Shale Group for many years, but apart from the work of. Etheridge jun. (1878) and various papers by Henderson (p. 59) little attention has been paid to them. Crampton (in Peach and others 1910, p. 79) suggested that all the occurrences of marine fossils at various localities were of one marine band near the base of the Wardie Shales. The measures between the Arthur's Seat Volcanic Beds and the Burdiehouse Limestone consist mainly of shales and sandstones which are poorly exposed and folded. The thickness of the succession and the correlation of parts of it over the area is open to more than one interpretation. Our present knowledge of the rocks and of the structure of the area is insufficient to determine with certainty the precise stratigraphical position of the isolated outcrops containing the marine bands. There is a close similarity in the faunas from the various localities, a fact which was noted by the early workers and which led them to conclude that only one or two bands were involved. From evidence in the Water of Leith in the Colinton-Slateford area it would appear that two or possibly three bands are present and one interpretation of the succession in the whole area points to as many as five bands. Because of this uncertainty the fossils recorded from the various localities are given in tabular form below. Many of the localities from which the fossils were collected are now inaccessible and the forms named are from old collections.

• Localities
• 1. Portobello Power Station tunnel, c. 1200 ft from shaft.
• 2. Shore between Granton and Cramond opposite Muirhouse, associated with 'Shrimp-Bed'.
• 3. Granton shore between breakwater and General's Rock.
• 4. Shore on west side of Granton Harbour, 4 to 6 ft above Wardie Coal.
• 5. Ravelston Quarry, most westerly of old quarries.
• 6. Craigleith Quarry, in ironstone and shale above Craigleith Sandstone.
• 7. Craiglockhart Hill Quarry, on north side of Craiglockhart Road.
• 8. Craiglockhart Railway Cutting, behind signal post on north side of canal tunnel.
• 9. Craiglockhart Railway Cutting, near junction with suburban railway between Craiglockhart Station and Slateford Junction, 140 yd from station, due north of Meggetland.
• 10. Craiglockhart Railway Cutting, 200 yd N.W. of canal bridge.
• 11. Water of Leith, right bank, 1100 yd S.15° W. of Wester Hailes House.
• 12. Water of Leith, left bank, 900 yd S.30° E. of Wester Hailes House and at 970 yd S.23° W. of Redhall Mill.
• 13. Water of Leith, left bank, 90 yd due N. of Redhall Mill.
• 14. Slaughterhouse Bore at 130 ft.
• 15. Slaughterhouse Bore at 180 to 210 ft.
• Fossils
• Encrusting polyzoan?-11 Crinoid columnals-13, 14
• Camarotoechia cf. pleurodon (Phillips)-12
• Lingula cf. mytilloides J. Sowerby-3, 6, 7, 8, 9, 10, 11
• Orbiculoidea cf. nitida (Phillips)-7, 11
• Bucanopsis undatus (R. Etheridge jun.) 6, 11, 12
• Bucanopsis sp.-10, 12
• Donaldina?-8
• Straparolus s.1.-2
• Aviculopecten sp. -6,12
• Leiopteria hendersoni (R. Etheridge jun.)- 1, 7, 10, 11, 12
• Lithophaga lingualis? (Phillips)-1, 2.
• Myalina sublamellosa-7, 10, 11, 12
• Myalina  verneuili? (McCoy)-12
• Naiadites crassus? (Fleming) (thin-shelled) -11
• Polidevcia? attenuata (Fleming) sharmani (R. Etheridge jun.)-11
• Promytdus?-7 , 8, 12
• Pteronites?-13
• Sanguinolites aff. abdenensis-8
• Sanguinolites clavatus-5, 6, 8, 9, 10, 11, 12
• Sanguinolites  cf. clavatus 3, 6, 15
• Sanguinolites  striatus Hind-6, 8, 9, 12
• Schizodus pentlandicus (Rhind)-3, 4, 6, 7, 8, 9, 11, 12
• Goniatite fragments indet.-10, 15
• Coiled nautiloid-2
• Orthocone nautiloid fragments-6, 8, 11, 12, 15

The non-marine lamellibranchs associated with the marine bands are found to be Naiadites obesus at all localities except No. 13 where Curvirimula cf. scotica is present.

Straiton–Carlops area

In the area between Carlops and Straiton, Calciferous Sandstone has been mapped along the south-eastern border of the Pentland Hills. Tulloch and Walton (1958, p. 13. fig. 5) have shown that the succession here is thinner than that of West Lothian and have suggested a correlation with the latter area. The rocks are not well exposed but parts of the succession are to be seen in the River North Esk and some of its tributaries.

The faunas of the marine bands in the Upper Oil-Shale Group from these exposures tend to support the correlation with West Lothian (op. cit.). In particular, the presence of the Pleurotomariid Glabrocingulum beggi in the Pleurotomaria Beds supports the correlation of this marine band with the Raeburn Shell-Bed which is the only band yielding this fossil, or any other Pleurotomariid, in the West Lothian sequence (p. 100).

The most abundant marine fauna collected from this area is from the bed known as Macconochie's Marine Band. It was discovered by the Geological Survey collectors Macconochie and McVey, about fifty years ago, at a small scarp 50 yd from the right bank of the North Esk and 100 yd north of Rogersrig Farm, Carlops. Lee (in Peach and others 1910, p. 370) commented briefly on the rich fauna. The bed was stated to be 18 in thick and the matrix is a silty mudstone weathered to a brown colour. In recent years, attempts have been made to find the exposure, but have been unsuccessful. The fauna collected by Macconochie and McVey is as follows: Lithostrotion? [very poor] ; Crinoid columnals ; echinoid plates; Fenestellid and trepostomatous polyzoan fragments; Camarotoechia cf. pleurodon, Composita?, Productus (Productus) redesdalensis? Muir-Wood, Pugnax?; Bellerophon cf. randerstonensis Weir, Bucanopsis sp., Euphemites sp., Naticopsis sp., Straparolus (Euomphalus) sp.; Actinopteria persulcata, Aviculopecten forbesi (McCoy), Edrnondia senilis?, Leiopteria hendersoni, Limipecten dissimilis (Fleming), Lithophaga lingualis, 'Nucula' luciniformis Phillips, ‘N’. oblonga Hind nonMcCoy, Pernopecten?, Polidevcia? altenuata, Posidonia?, Promytilus?, Schizodus subaequalis? (de Koninck), S. aff. trigonalis (de Koninck), aff. Streblopteria concentricolineata (Hind), Wilkingia elliptica (Phillips); orthocone and coiled nautiloid fragments. Naiadites obesus is also present but not associated with the marine forms above. At a nearby exposure on the right bank of the North Esk below Carlops Bridge, Macconochie also found a shale containing abundant 'shrimp'-like arthropod remains underlying a shale with Naiadites sp.Tulloch and Walton (1958, p. 13, fig. 5) tentatively correlated Macconochie's Marine Band with the Pumpherston Shell-Bed.

Cousland area

To the east of the Midlothian Basin, the anticlinal structures at Cousland and D'Arcy have been drilled for oil and gas by the Anglo-Iranian and Anglo-American oil companies. Anderson and Simpson (1938) gave an account of the succession found in the first two boreholes. Both of these borings were subsequently deepened and several more have been sunk in the area. Unfortunately none of the holes was cored throughout. Cousland No. 1 Bore was cored sufficiently to give a reasonable sequence of fossiliferous bands in the Calciferous Sandstone but no cores were taken from about 1300 ft to 1585 ft and the hole did not reach measures proved in the Midlothian No. 1 Bore, D'Arcy, which was only partly cored.

The Cousland No. 1 Bore, when described by Anderson and Simpson (1938) had penetrated four marine horizons in the Calciferous Sandstone. Tulloch and Walton (1958, p. 13, fig. 5) suggested the correlation of these in descending order, with the Basket (or Cot Castle), Raeburn, Dunnet and Pumpherston shell-beds respectively. The correlation of the band at about 750 ft in the bore with the Dunnet Shell-Bed tends to be supported by the presence of Euestheria sp.in the roof (p. 100). The lowest Curvirimula and highest Naiadites were found just above the marine strata at about 1000 ft, the beds suggested by Tulloch and Walton (1958) as possibly equivalent to the Pumpherston Shell-Bed. In fact, the bed of limestone shown, on a small scale diagram, by Tulloch and Walton as the possible equivalent of the Pumpherston Shell-Bed comprises three separate sets of limestone and shale containing marine fossils, as detailed by Anderson and Simpson (1938, p. 30). The uppermost one at about 1020 ft is separated by shale, with Spirorbis and Naiadites obesus, from the lower ones which occurred at about 1080 ft and from 1110 to 1130 ft. The fossil contents of the three bands are similar and a combined fauna is as follows: Crinoid columnals ; Paraconularia sp.; Camarotoechia sp., Composita?, Lingula sp., Orbiculoidea sp., Productus (Dictyoclostus) sp., Punctospirifer?, Spirifer sp; Bellerophontid indet ; Aviculopecten sp., Edmondia maccoyi? Hind, Leiopteria sp., Myalina?, Naiadites crassus? (thin-shelled), Polidevcia? attenuata, Sanguinolites striatus, Schizodus cf. axiniformis (Portlock non Phillips); Orthocone nautiloid fragments. These beds were the lowest in the bore to yield a rich marine fauna. No cores were taken between 1303 ft and 1585 ft, from which latter depth coring continued to the bottom of the hole at about 2780 ft. In this lowest 1205 ft the fossiliferous bands generally contained plants, Naiadites obesus and ostracods but there was a Lingula band at 2228 ft and a bed with Lingula and Schizodus pentlandicus occurred at 2340 ft.

In five of the other oil exploration boreholes, partly cored, one or two bands with rich marine faunas, similar to those in Cousland No. 1 Bore, were found. If two are present in any one bore, they are within 200 ft, or less, of each other. Some, or even all of these marine phases in the other boreholes may be equivalent to those in Cousland No. 1 Bore from 1080 ft to 1130 ft, but the evidence is not sufficient to suggest correlations as other marine bands may be present in the uncored parts of the sequences penetrated. Naiadites obesus is found in the measures containing the marine bands, suggesting that the bands occur in the Lower Oil-Shale Group.

Correlation of Marine Bands

It now remains to comment on what correlations can be made between the marine bands from the four areas briefly described above. In West Lothian, the presence of five marine bands in the Upper Oil-Shale Group is well established and the equivalents of some of them can be traced into the Midlothian basin in the Straiton–Carlops and Cousland areas. Difficulties arise when the Lower Oil-Shale Group is considered. In West Lothian, below the horizon taken to be equivalent to the base of the Burdiehouse Limestone, the Pumpherston and Humbie shell-beds have been found in boreholes and occur close to each other in the succession. The marine band on the shore at South Queensferry was correlated on stratigraphical grounds with the Pumpherston Shell-Bed by Carruthers (1912, p. 35) who also suggested that the band at Carlops (Macconochie's) was on the same horizon. Tulloch and Walton (1958, p. 13, fig. 5) regarded the marine strata at about 1100 ft in Cousland No. 1 Bore as possibly equivalent to Macconochie's Marine Band which in turn was tentatively correlated with the Pumpherston Shell-Bed. The correlations imply that the relatively poor fauna of thin-shelled lamellibranchs and cephalopods in the oil-shale field area were contemporary with much richer faunas farther east, that is that local environment controlled the composition of the population. This is in general accord with the lithological evidence which shows the oil-shales, which were presumably deposited near land, becoming poorer in quality and development when traced from west to east.

The marine bands which no one has correlated outside the area in which they occur are those found in the Wardie Shales in the Edinburgh district. The interpretations of the succession and structure in the area are uncertain but from stratigraphical considerations, the Wardie Shales are judged to be well below the Pumpherston Shell-Bed, as developed at South Queensferry, separated from it by some hundreds of feet of strata — the Queensferry Beds (p. 43). If this is so, and assuming the correlations mentioned above are correct, then the relatively rich marine development in the Wardie Shales was not recorded in Cousland No. 1 Bore. It may be represented as a much poorer development, by the Lingula bands found in the lower part of the borehole, one of which contained Schizodus pentlandicus, a common Wardie Shale species. If this is the case, it is contrary to the general trend of Lower Carboniferous faunas which become richer towards the Cousland area. On the other hand, a case can also be made for the correlation of the Wardie Shale marine bands with the Pumpherston and Humbie shell-beds and the marine developments at South Queensferry, Carlops and at about 1100 ft in Cousland No. 1 Bore. There is some palaeontological evidence to support this in that the only localities where abundant arthropod remains have been found are in a bore near Livingston associated with the Pumpherston Shell-Bed, at Carlops, associated with Macconochie's Marine Band and at Granton, associated with one of the marine bands in the Wardie Shales. Some of the species present in the Wardie Shales are found in the faunas at South Queensferry, Carlops and in Cousland No. 1 at about 1100 ft, but not enough is known of the vertical distribution of the species to use this as positive evidence. All that can be said is that the composite fauna of the Wardie Shale bands is of the same type as those from the other localities mentioned above. The solution to this problem, and others, awaits definite knowledge of the succession in the different areas, which could only be gained by cored borings. R.B.W.

References

ANDERSON, F. W. and SIMPSON, J. B. 1938. Geological Notes on the Borings for Oil now in Progress at Cousland and D'Arcy, Midlothian. Oil Shale and Cannel Coal, 27–31, Inst. Petroleum.

BUTTERWORTH, MAVIS A. and WILLIAMS, R. W. 1958. The Small Spore Flora of Coals in the Limestone Coal Group and Upper Limestone Group of the Lower Carboniferous of Scotland. Trans. Roy. Soc. Edin., 63, 353–92.

CARRUTHERS, R. G. 1912. The Oil-Shales of the Lothians. 2nd edit. Part I. Mem. Geol. Surv. 1927. The Oil-Shales of the Lothians. 3rd edit. Part I. Mem. Geol. Surv.

ETHERIDGE, R., Jun. 1878. On our Present Knowledge of the Invertebrate Fauna of the Lower Carboniferous or Calciferous Sandstone Series of the Edinburgh Neighbourhood, especially of that Division known as the Wardie Shales; and on the First Appearance of certain species in these Beds. Quart. J. Geol. Soc., 34, 1–26.

LOVE, L. G. 1960. Assemblages of Small Spores from the Lower Oil-Shale Group of Scotland. Proc. Roy. Soc. Edin., B, 67, 99–126.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. H., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 15 Tertiary landscape and pre-glacial topography

Landscape development

The topographic pattern of the Midland Valley in its present form was probably initiated in late-Tertiary times. It was originally suggested (Mackinder 1902, pp. 126–33; Peach and Horne 1910, p. 466; Cadell 1913, p. 240) that the consequent drainage of Scotland had its origin on an extensive plateau which was tilted to the south-east and drained from north-west to south-east, and that the rivers of the Southern Uplands had their sources in the West Highlands. Most of the evidence for this hypothesis naturally lies outside the limits of the ground shown on one-inch Sheet 32. The presence of windgaps in the Pentland Hills near the sources of three south-eastward flowing streams, the Lyne Water, North Esk and Glencorse Burn was, however, taken to indicate that the original sources of these streams lay far to the north-west (Peach and Horne 1910, p. 466).

The study of the drainage systems of the Rivers Tweed (Linton 1933), Earn and Tay (Linton 1940) has led Linton to the conclusion that the original consequent rivers in central and eastern Scotland drained to the east. More recently Linton (1951, pp. 69–73) has developed the hypothesis, originally formulated by Bremner (1942), that the consequent drainage of Britain east of the 'Hebridean Rift' was initiated on the inferred Upper Chalk (Senonian) surface which covered the marine-planed sub-Cenomanian surface and was tilted eastwards during the late-Cretaceous uplift. A contour map (Linton 1951, p. 70) suggests that when uplift and tilting, probably of a pulsatory nature, had reached its maximum the pre-Chalk surface was slightly convex and had an eastward gradient of approximately 20 ft to the mile. The original consequent rivers were taken to include the Forth and the middle Tweed, which flows roughly eastward between Broughton and St. Boswells. Linton (1933, pp. 169–70) suggested that the initial watershed between the primitive Forth and Tweed extended from the latitude of the most northerly Pentland Hills eastwards to intersect the present crest of the Lammermuirs at Lammer Law (Figure 25). The three Pentland streams mentioned above were considered to have risen on this watershed. The Lyne Water, which now rises below the wind gap of the Cauld Stane Slap, still crosses the Southern Upland Fault by the water gap at Romannobridge to join the Tweed. The North Esk, which now rises below the wind gap of the Borestane, was considered to have joined the Lyne Water at Broomlee, 0.75-mile south-east of West Linton, prior to its capture by the Lower Esk. The Glencorse Burn, tributaries of which now rise below the wind gaps north and south of Harbour Hill and in the gap just west of Bell's Hill (a wind gap subsequently modified by glacial melt waters) appears, according to Linton (1933, p. 169) to have flowed to the Eddleston Valley via the wind gap just south of Leadburn, before being captured by the primitive North Esk.

Linton's hypothesis of a superimposed drainage pattern inherited from a tilted Chalk surface has been disputed by George (1955; 1960, pp. 97–105). Following Hollingworth (1938, pp. 75–8) George has recognized a number of residual base levels, probably former wave-cut benches, whose heights are remarkably constant throughout Scotland. In southern Scotland he claims to recognize fossil planes at 2600–2700 ft, 2300 ft, 1900 ft, 1670 ft, 1070 ft and a little below 600 ft. In the area under consideration George (1960, p. 101) recognizes the 1670-ft bench (presumably in the northern summits of the Pentlands, the Moorfoot Hills and the Cloich Hills) and still higher remnants of the 1900-ft bench forming the highest Pentland hills. Hollingworth and George have attributed the formation of these benches to uplift, probably eustatic, which commenced after the final mid-Tertiary orogenic movements. As the latter were responsible for the flexuring and faulting of the Tertiary basalts of Antrim and also affected the remainder of Midland Valley (George 1960, pp. 101–6) the periods of eustatic uplift are said to be confined to the Pliocene Period.

The marine bench levels of George are not readily correlated with the residual peneplains recognized in south-east Scotland by Ogilvie (1930, p. 245; 1951, pp. 14–5). The latter has distinguished a 'summit peneplane' at above 1800 ft, to which he attributes the summit plateau of the western Moorfoot Hills, and as vestigial remnants the Broughton Heights and the southern Pentland Hills. He also mentions a 'higher Lowland peneplane' between 500 ft and 750 ft, rising in places to 1000 ft, which forms a large portion of the southern Midlothian Basin, the broad belt of flattish country flanking the Pentland Hills between Currie and Cobbinshaw Reservoir and the summits of the Torphichen and Riccarton Hills near the western edge of the sheet. Ogilvie has also tentatively recognized a 'lower Lowland peneplane', now much obscured by drift, between 100–500 ft.

Pre-glacial topography

Pre-glacial river development in the Midlothian and West Lothian basins cannot be traced in detail as the area is now largely mantled by drift and the former stream courses are obliterated. Evidence furnished by buried channels within the area under discussion indicates that, at some time before the 'Main Highland Glaciation' (p. 111), sea-level was considerably lower than at present. As deposits of earlier glaciations have not been distinguished in this area it is not possible to say if the river channels are pre-glacial or were excavated during an inter-glacial period.

The approximate courses of some of the channels are indicated in (Figure 25), and the thickness of superficial deposits where proved by boring is shown. It should be noted that bores are not sufficiently closely spaced to permit the accurate delineation of the 'pre-glacial' stream courses or the construction of rockhead contour maps.

River Avon

Cadell (1913, p. 84) has suggested that the River Avon, whose present channel extends from Linlithgow Bridge, one mile west of Linlithgow, north-westward to join the Forth at Inveravon, formerly flowed through the hollow now occupied by Linlithgow Loch and continued north-eastward to join the Forth just east of the basalt promontory at Blackness. Bores between Linlithgow and Blackness have proved that the drift in this 'pre-glacial' channel is more than 90 ft thick.

River Almond

The course of the buried channel of the Almond (Figure 25) first described by Cadell (1903, p. 194) is fairly well known in the sector extending from Mid Calder to Carlowrie, one mile east of Kirkliston. The floor of the channel at Mid Calder is approximately 100 ft above sea level, and at Carlowrie the lowest level in the channel proved by boring is 142 ft below sea level. The thalweg of the 'pre-glacial' Almond is thus fairly steep and estimated by Cadell to average 31 ft per mile. Cadell has suggested that north of Carlowrie the ancient Almond flowed west of the dolerite ridge extending from Craigiehall to Snab Point and reached the present shore-line in the vicinity of Dalmeny House. He estimated that, assuming a gradient similar to that above Carlowrie, the bottom of the old bed near Dalmeny House should be more than 200 ft below high water mark. Above Mid Calder the buried channel can be roughly traced for a further five miles, its course coinciding approximately with that of the present river. The buried channel of the Linhouse Water can also be mapped, partly from limited borehole evidence and partly from natural exposures on the banks of the present stream. A bore sited 3.5 miles south of Mid Calder recorded 119 ft of drift which suggests that the original stream was already in a fair sized valley at the latitude of Harperrig Reservoir.

Water of Leith

The ancient course of the Water of Leith has been definitely recognized only in the lower reaches of the present valley. Tait (1930, p. 292) has recorded two bores in the grounds of St. George's School, Edinburgh which reached a depth of 102 ft (approximately 98 ft O.D.) without encountering rockhead and a further three bores close to Murrayfield Station, one of which reached rockhead at approximately −50 ft O.D. (200 ft below surface). North of Murrayfield the ancient valley appears to lie west of the present post-glacial gorge, probably passing under the Botanic Garden where one bore encountered rockhead at −25 ft O.D. and then crossing the present stream to enter the sea just east of Leith Harbour Docks. The lowest rockhead level recorded in borings south of Leith Harbour Docks is −92 ft O.D. (Figure 25). The seaward extent of the channel is partly proved but not accurately defined by extensive borings carried out between 1923 and 1936 to prove the foundations for extensions to Leith Harbour.

South of Murrayfield the only evidence for a buried channel is found just south and east of Hailes Quarry, where a north-north-east trending channel, containing up to 51 ft of superficial deposits, has been traced for approximately half a mile (Figure 25). Farther upstream, between Colinton and Balerno the Water of Leith is entrenched in solid rock, and though Henderson (1873, pp. 197–9) has found boulder clay overlying river gravel on the sides of the river valley, it seems unlikely that a 'pre-glacial' valley, deeper than the present one, exists in this area. There is room for a narrow buried channel to the northwest of the present stream, but there is no evidence from bores or excavations to indicate the existence of such a channel. The possible 'pre-glacial' course of the Water of Leith is from near Haugh Head via Kirknewton Airfield, Kirknewton and Humbie to the River Almond, though no definite evidence for a buried channel in this area exists.

River Esk

Although little is known of the course of the buried channel of the River Esk between Dalkeith and Musselburgh a number of drift-filled channels have been recognized in the Midlothian basin. Short portions of what is presumably an integrated buried drainage system have been proved by boring and opencast coal operations. These channels have been described by Tulloch and Walton (1958, pp. 127–9); their approximate courses are shown in (Figure 25). Two bores close to the mouth of the River Esk at Inveresk Paper Mill and half a mile west-north-west of Musselburgh Station (Olivebank No. 2 Bore) have proved respectively 93 ft and 107 ft of surface deposits, indicating that the floor of the buried river channel is here at least 100 ft below sea level.

Within the Pentland Hills a short section of the pre-glacial channel of the Logan Burn can be traced south and east of the Habbies Howe Waterfall, two miles south-west of Glencorse Reservoir (Mykura in Mitchell, Walton and Grant 1960, p. 18).

River Forth

The buried channel of the River Forth has been described by Cadell (1913, p. 97) who has suggested that the bed of the 'pre-glacial' channel in the Firth of Forth is at least 500 ft below the present sea-level, and that at the time this river was in existence, the bed of the North Sea must have been entirely above sea-level. Cadell's evidence is based on proved rockhead levels in the Forth and lower Carron Valley between Grangemouth and Bridgeness and in the valley of the River Devon between Tillicoultry and Abbey Craig. The lowest rockhead level was recorded in 1936 when a mine driven at Bridgeness Colliery encountered gravel at approximately 675 ft below Mean Sea Level (Macgregor 1940, p. 253). As the known rockhead depths of over 300 ft below O.D. are confined to the Devon Valley and Grangemouth–Borrowstounness stretch of the River Forth it has been suggested that these two basins were formed by glacial overdeepening of the pre-existing valleys (Dinham and Haldane 1932, p. 205). More recently a seismic refraction survey to prove the level of rockhead has been carried out in the lower reaches of the Firth of Forth on behalf of the National Coal Board (Drysdale 1956, p. 449). The lines of traverse and a number of the rockhead levels obtained by this survey are shown on (Figure 25). The data obtained suggest that, though there are a number of hollows, one of which attains a depth of 425 ft below mean sea level, there is no evidence of a buried channel deeper than 200 ft below sea level.

References

BREMNER, A. 1942. The Origin of the Scottish River System. Scot. Geog. Mag., 58, 15–20; 54–9; 99–103.

CADELL, H. M. 1903. Note on the Buried River Channel of the Almond. Trans. Edin. Geol. Soc., 8, 194–6.

CADELL, H. M. 1913. The Story of the Forth. Glasgow.

DINHAM, C. H. and HALDANE, D. 1932. The Economic Geology of the Stirling and Clackmannan Coalfield. Mem. Geol. Surv.

DRYSDALE, W. S. 1956. Firth of Forth Seismic Refraction Survey. Trans. Inst. Mining Eng., 115, 435–54.

GEORGE, T. N. 1955. Drainage in the Southern Uplands: Clyde, Nith, Annan. Trans. Geol. Soc. Glasgow, 22, 1–34.

GEORGE, T. N. 1960. The Stratigraphical Evolution of the Midland Valley. Trans. Geol. Soc. Glasgow, 24, 32–107.

HENDERSON, J. 1873. On the Evidence of the Existence of an Old River Course previous to the deposition of the Boulder Clay, at the Water of Leith, above Colinton. Trans. Edin. Geol. Soc., 2, 196–201.

HOLLINGWORTH, S. E. 1938. The Recognition and Correlation of High-level Erosion Surfaces in Britain: a Statistical Study. Quart. J. Geol. Soc., 94, 55–84.

LINTON, D. L. 1933. The Origin of the Tweed Drainage System. Scot. Geog. Mag., 49, 162–75.

LINTON, D. L. 1940. Some Aspects of the Evolution of the Rivers Earn and Tay. Scot. Geog. Mag., 56, 1–11, 69–79.

LINTON, D. L. 1951. Problems of Scottish Scenery. Scot. Geog. Mag., 67, 65–85.

MACGREGOR, M. 1940. The buried channel of the Forth. Advancement of Science, 1, No. 2, 253–4.

MACKINDER, H. J. 1902. Britain and the British seas. Oxford.

MYKURA, W. 1960. In MITCHELL, G. H., WALTON, E. K. and GRANT, DOUGLAS (editors): Edinburgh Geology — An Excursion Guide. Edinburgh.

OGILVIE, A. G. 1930. Central Scotland [Great Britain: Essays in Regional Geography]. Cambridge.

OGILVIE, A. G. 1951. South-Eastern Scotland. The region and its parts. In Scientific Survey of South-Eastern Scotland. 11–35. Brit. Assoc. Handbook. Edinburgh.

PEACH, B. N. and HORNE, J. 1910. The Scottish Lakes in Relation to the Geological Features of the Country. Bathymetrical Survey of the Scottish Freshwater Lochs, 1, 439–513. Edinburgh.

TAIT, D. 1930. Excavations in the Vicinity of the Water of Leith, chiefly in Material Filling its Preglacial Valley. Trans. Edin. Geol. Soc., 12, 289–96.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Chapter 16 Glacial and Recent deposits

THE various glacial and inter-glacial stages of the Pleistocene Period, which have been recognized in England and Wales and on the Continent of Europe cannot as yet be distinguished in Scotland. The boulder clay covering much of central Scotland has been taken to be the product of the Newer Drift, comprising the "Main Scottish" or York and the North British glaciations (Wright 1937, pp. 94–6; Charlesworth 1957, p. 993), which have been tentatively correlated with the Early and Main Wiirm stages of the Alps and the Weichsel stage of North Germany (Flint 1957, pp. 404–13). As interglacial deposits in Central Scotland are very rare (Macgregor and MacGregor 1948, pp. 85–6, Flint 1957, p. 405) it has not been possible to recognize deposits which can be definitely ascribed to earlier ice-sheets. It seems probable that the effects of the earlier glaciations in Scotland have been largely obliterated by the last major phase of the glacial period.

The most extensive Pleistocene deposit within the area of one-inch Geological Sheet 32 is the tough argillaceous basal till, which was deposited by ice from the Highlands and covers much of the low ground, usually thinning towards the hills. In the southern Pentland Hills the basal till is overlain by a brown or red sandy morainic drift, which is not recognized elsewhere within the area. During the northward retreat of the Highland Ice deposits of moundy sand and gravel and flat terraces and spreads of sand and gravel, as well as local deposits of lacustrine clays and silts were laid down on the ground below 1100 ft 0.D: The gravels are particularly abundant within the Midlothian Basin, where the retreating ice has also left a large number of meltwater channels. In the Loanhead–Roslin district of Midlothian the fluvio-glacial gravels are overlain by a thin boulder clay which is believed to have been deposited by a lobe of ice originating in the Southern Uplands and moving north-eastwards into the Midlothian Basin.

Details

Basal Boulder Clay

Direction of ice movement

The direction of ice movement in the area north and west of the Pentland Hills, as deduced from striated pavements, crag and tail features, orientation of drumlins and the lithology of till particles and erratic blocks, appears to be essentially from west to east, minor variations being due to deflection by topography (Figure 26). Among the first ice-moulded surfaces to be recognized in Scotland is the Agassiz Rock, on the south side of Blackford Hill, beside the Braid Burn. In 1840 Charles Maclaren showed this to Agassiz, who claimed it as the work of land-ice (Scotsman 2nd January 1841). Later critics maintain that some of the striae are in fact slickensides of tectonic origin. The basal boulder clay shows no evidence of separate phases of ice-movement and except within the Pentland Hills there is no suggestion of more than one direction of ice-flow, as is the case in Ayrshire (Richey, Anderson and MacGregor 1930, p. 318; Eyles, Simpson and MacGregor 1949, p. 124) and Kincardineshire (Bremner 1934, Campbell 1934). Indicator stones in the till suggest that most of the ice originated in the Loch Lomond area of the Highlands. It first travelled south but was subsequently diverted by northward flowing ice from the Southern Uplands, the combined ice-sheet moving eastwards to the North Sea. Southern Upland stones are common in the till near the southern edge of the sheet. The more important indicators used to determine the provenance of the ice include the Dalradian rocks of the south-western Highlands, granites and diorites probably derived from the Garabhal Hill complex, Lower Old Red Sandstone quartzite conglomerates, apparently from the Callander region (Peach and others 1910, pp. 329–30) and essexite from Lennoxtown (Peach 1909). McCall and Goodlet (1952) have used the felsites of North Black Hill (Pentland Hills), Tinto and Cairngryfe to determine the provenance of the two boulder clays and associated fluvio-glacial deposits in the Midlothian Basin (see below).

Lithology

The composition of the boulder clay varies according to the rocks over which the ice has moved. In the western part of the area and in the greater part of the Midlothian Coalfield the basal boulder clay is a stiff grey clay containing mainly small stones with occasional large boulders up to about 6 ft in diameter. Apart from a high proportion of Carboniferous sediments, such as sandstone, limestone, shale and coal, the boulder content includes a varied suite of Carboniferous igneous rocks, both lavas and intrusive rocks and a lower percentage of erratics from the Highlands, which are found throughout the area. In districts where the bedrock contains a high proportion of sandstone, as in the ground to the south-east of the Roman Camp Ridge, the basal boulder clay is very sandy and in places reddish in colour (Tulloch and Walton 1958, p. 129). Within the Pentland Hills the basal boulder clay is a tough, dark grey, brownish weathering clay, which is locally slightly more sandy than that covering the low ground. Near the headwaters of the North Esk and Lyne Water the basal boulder clay is overlain by red or reddish-brown, sandy morainic drift which contains a higher proportion of boulders including many large Highland and Carboniferous igneous erratics. The upper sandy drift locally attains a thickness of 10 ft, the junction between the two drifts is often a sharply defined more or less horizontal surface (Eckford 1952, p. 137), but sections exposed in the headwaters of the Lyne Water, close to the Cauld Stane Slap (Figure 25) show some interdigitation of the two deposits with lenses of sandy drift in the lower boulder clay as well as shear structures and thrust wedges along the junction. There is no record of waterlaid deposits separating the two types of till, though small patches of sand and laminated clay have been found associated with both. A cursory examination of the boulder content of the two tills has suggested that, though both originated in the Highlands, the lower contains a proportion of lower Palaeozoic greywackes and may have been carried by ice approaching the Pentland Hills from a south-westerly direction, while the upper ice could have come directly from the west or west-northwest. No detailed study of the boulder content of these drifts has, however, been carried out, and there is as yet no definite evidence to suggest that the two tills were carried by separate ice-sheets or even by separate phases of advance of one ice-sheet. Eckford (1952, p. 137), who has studied the two drift deposits in the southern Pentland Hills (within the area of one-inch Geological Survey Sheet 24), has suggested that both were transported by the same ice-sheet, the lower till being the lodgment till (ground moraine) and the upper the ablation till (englacial and supra-glacial moraine). Campbell (1951, p. 198) has recorded three distinct superimposed boulder clays in the Henshaw Burn, a tributary of the River North Esk within the Pentland Hills. The boulder content of the lowest of these is said to indicate ice-movement in an east-north-east direction, that of the middle one a local origin within the Pentland Hills, and that of the uppermost to suggest ice-movement in a direction slightly south of east. During revision of this ground by the Geological Survey, however, no evidence of three separate boulder clays was found.

“Middle” Sands and gravels

Deposits of sand and gravel were formed during the retreat of the Highland Ice. They cover extensive areas in the Midlothian Basin and the Tyne Valley south-east of the Roman Camp Ridge but form only isolated patches in the ground to the northwest of the Pentland Hills.

The stratified drift was deposited by glacial meltwaters and extra-glacial streams along the margin of and within the shrinking ice-sheets. It gives rise to a variety of surface forms such as kame terraces, kames, 'knob and kettle' topography and eskers. Many of these surface features have, however, been modified by subsequent erosion and it is now not always possible to recognize the original forms.

Flat terraces or spreads of sand and gravel occur in the Borthwick area where a number of terraced surface levels up to 800 ft O.D. have been mapped. The fluvioglacial deposits in the North Esk Valley between Dalkeith and Penicuik are locally up to 30 ft thick. They are flat-topped but their original surface topography may to some extent have been obliterated by a later ice-sheet (see below).

Moundy sands and gravels are well seen in the Midlothian Basin south of Penicuik and Fullarton where they form elongated kame ridges, often orientated parallel to the former ice-margin, as well as isolated mounds, and groups of mounds with kettleholes. Sinuous ridges, which may be eskers, have been mapped in the Fullarton area, near Straiton and at Sheriffhall, north-west of Dalkeith. Moundy gravel with kettle topography is also developed between Linlithgow and Philpstoun, and thin, fairly even spreads of gravel, which may be part of an outwash fan, occur between Kirkliston and Corstorphine.

The spreads of sand and gravel are composed of well sorted, often current-bedded and ripple-marked material containing occasional layers of silty clay.

Along the flanks of the Moorfoot Hills the gravels contain a high proportion of greywacke pebbles derived from the Southern Uplands, but farther west around Penicuik the pebbles are mainly of igneous rocks similar to those cropping out in the Pentland Hills (Peach and others 1910, p. 331). Pebbles collected from a gravel pit recently opened near Borthwick Castle include, in addition to much Carboniferous material of local origin and Lower Palaeozoic greywackes, a number of felsites which can be attributed in roughly equal proportions to North Black Hill in the Pentland Hills and to the Tinto–Cairngryfe outcrops. McCall and Goodlet (1952, p. 406) investigated the pebble content of gravels in the Penicuik–Roslin area and recorded abundant Carboniferous sediments and Lower Old Red Sandstone lavas of Pentland Hill type, as well as fairly common greywackes and Highland rocks. Felsites were common and these could be almost entirely referred to North Black Hill.

Deposits of lacustrine clays are not often found among the glacio-fluvial sands and gravels of Midlothian, within the area under description, though small thicknesses of plastic clay usually interlaminated with silt, are occasionally found in the southern part of the Midlothian Basin, as in the vicinity of Borthwick (Tulloch and Walton 1958, p. 130). The laminated stoneless clays recorded in an old clay pit 500 yd northwest of Newtongrange and present in a buried channel near Smeaton Farm are overlain by boulder clay and must thus predate the "Middle" Sands and Gravels.

Southern Upland Readvance Boulder Clay and Gravel

A thin layer of stiff red clay with abundant stones rests on the fluvioglacial sands and gravels which overlie the basal boulder clay of the Roslin district. This upper boulder clay was first described by J. G. C. Anderson (1940), who recorded its presence in a number of gravel pits within an area of 2.5 to 3 square miles. From 2 to 10 ft thick it is, in some exposures, underlain by 1 or 2 ft of stoneless laminated clay. The bedding of the underlying gravel in which ice wedges are occasionally developed (Common and Galloway 1958) is not usually disturbed, but in Burghlee Sand Pit, near Loanhead, current-bedded sand with clay bands immediately under the boulder clay, together with some of the boulder clay, has been distorted into minor overfolds with thrusts. The direction of movement of ice depositing the upper clay was, on this evidence, from south to north.

The pebble content of the boulder clay was analysed by Anderson, who recorded a high proportion of Lower Old Red Sandstone igneous rocks, as well as Devonian and Carboniferous sediments, along with a small number of stones of Highland origin. Anderson concluded that the upper boulder clay bears evidence of a re-advance of the Highland ice. This view has been challenged by McCall and Goodlet (1952), who re-examined the pebble content of certain Midlothian glacial deposits, paying special attention to the provenance of the felsites. The Roslin Upper Boulder Clay was shown to contain abundant felsites, almost all of which were referable to Tinto Hill; no Highland rocks were found. Thin gravels overlying the bedded sands near Pentland Mains and in Penicuik Sand Pits were also found to contain a high proportion of Tinto felsites. McCall and Goodlet concluded that the Upper Boulder Clay was derived from the south, probably from the Southern Uplands and reached the Roslin area by way of Tinto, Dolphinton and West Linton.

Pebbles of felsite, apparently derived from the Tinto and Cairngryfe outcrops, as well as some greywacke pebbles from the Southern Uplands have been found in sandy moraine and in gravel within a three- to four-mile wide belt of ground adjoining the north-west slopes of the Pentland Hills. The most northerly record of felsites is from a temporary exposure at Woodhall Road, Colinton. Here a bedded sandy gravel rests on 2 ft 6 in to 5 ft of laminated silty clay, which in turn rests with an irregular junction on coarse sandy drift. Felsites occur both in the gravel and the sandy drift. Other exposures which have yielded felsite pebbles include a small cutting through a drumlin, three-quarters of a mile west-south-west of Dalmahoy House, where coarse sandy drift is locally overlain by bedded gravel; 'a small gravel pit just west of Kaimes Hill; the "Mound" at Mid Calder, 650 yd N.N.E. of Calder House; a number of subsidence-hollows in Harburnhead Moss, one and three quarter miles north-east of Cobbinshaw Station where peat rests on sandy boulder-clay; and a number of natural exposures in sandy drift near the headwaters of the Crosswood Burn. In the Dalmahoy exposure felsite and undoubted Highland pebbles are found together in the same deposit.

It seems most probable that during the maximum extent of the Southern Upland Readvance the ice flowing northward from the Tinto area past Cobbinshaw was deflected north-eastwards by the Highland ice, which was still active in the Forth valley. The line of junction between the two ice sheets has not yet been traced by a systematic study of the distribution of indicator stones, but it seems likely it extended from the vicinity of West Calder by way of Mid Calder and Dalmahoy to the southwestern outskirts of Edinburgh.

The extent of the area in which the Upper Boulder Clay has been recorded is shown on (Plate 4); the probable limits of the Southern Upland Readvance are discussed on pp. 122.

Retreat of the Highland ice

During the decay and ablation of the Highland ice, the ice-sheet retreated in a general northward direction. Charlesworth (1926, pp. 44–5) has suggested that the belt of kame moraines extending along the southern boundary of the Central Valley between St. Abbs Head and the vicinity of New Cumnock marks the southern limit of a phase of readvance of the ice-sheet. He suggests that at this stage the ice-sheet overrode the Pentland Hills and extended to the flanks of the Moorfoot and Lammermuir hills, where the ice margin was maintained at a level of 900–1000 ft, attaining a maximum altitude of 1100 ft. Charlesworth traced out the major stages in the retreat of this sheet throughout the Midland Valley. More detailed accounts of the retreat of ice in East Lothian had already been produced by Kendall and Bailey (1908) and by members of the Geological Survey (Clough and others 1910, pp. 172–81). Sissons has re-examined the evidence left by the retreat of ice in East Lothian (1958A) and in the Eddleston Valley, just south of the area of Sheet 32 (1958B) and has reinterpreted the data in the light of modern research.

Eastern slopes of Pentland Hills

At an early stage of ablation of the ice-sheet the summits of the Pentland Hills were freed of ice and formed nunataks. As the ice-free area increased, the eastern slopes of the Pentland Hills, which during the advance of the ice-sheet had formed an ice-shadow area, became clear of ice. The lowest level of the ice-margin appears to have lain in the vicinity of Silverburn, in the lee of Scald Law and Carnethy .hills. South-west of this area most melt water channels cutting the hill-slopes (1–5, (Plate 4)^‡5 ) fall to the north-east, and to the north the few meltwater channels which have been definitely recognized (Plate 4)(6–7) fall to the south. Higher channels were cut by meltwater crossing the cols in the ridges between adjacent valleys in the southern Pentland Hills (Plate 4)(8–10), and in the main range farther north (Plate 4)(11–14). These col gulleys (Mannerfeldt 1945, fig. 13, p. 224) were not necessarily formed as glacial spillways draining ice-dammed lakes, but may have formed at the point of separation of the shrinking ice masses, meltwater flowing from the thicker ice through the now ice-free pass to the isolated dead ice on the other side. The channel cutting the ridge between Fala Knowe and Woodhouselee Hill (Plate 4)(7) has a pronounced 'up and down' profile and crosses the ridge not at the true col but about 10 ft above and 70 yd to the south-east of this point. This appears to be a case of an entirely sub-glacial channel cut by waters capable of flowing uphill under hydrostatic pressure.

Along the south-eastern slopes of the hills, channels are only found on spurs and positive features; in the depressions between the ridges meltwater deposited gravel in crevasses within, on top of, and along the margin of the ice, and in one case the subglacial continuation of a stream course can be traced as a narrow well-defined esker (Plate 4)(15), which runs along the bottom of a pre-existing valley. To the southeast of the Edinburgh–Biggar road the slope of the hillside becomes much gentler and the ice-meltwaters may during this phase have deposited the large patches of sand and gravel in the vicinity of Silverburn and at a later period those near Easter Howgate. Much of the Silverburn gravel is moundy with summit levels rising to 940 ft, suggesting that the sand and gravel was deposited in crevasses within decaying ice, whose en-glacial water-table remained for some time constant at approximately 940 ft (Sissons 1958B, pp. 168–71). It should be noted, however, that some of this gravel may have been deposited or at least overridden by the 'Southern Upland Readvance' ice-sheet (pp. 113).

Upper North Esk Valley

Charlesworth (1926, pp. 28–9) suggested that after the ice had cleared from the south-eastern slopes of the Pentland Hills an ice-free zone appeared in the vicinity of Penicuik, and the ice which had filled the North Esk Valley eventually split into two separate lobes. The ice retreating north-eastwards towards the Forth was termed the 'Esk Lobe' and that retreating south-westwards the 'Dolphinton Lobe'. The lake said to have been formed in the Esk Valley, first impounded by both ice-lobes, and later by the Esk Lobe only, was termed 'Lake Esk'. Charlesworth traced the major retreat stages of the two ice-lobes by a series of arcuate moraine belts said to cross the Midlothian Basin and by a number of spillways.

The re-mapping of Midlothian by the Geological Survey has not confirmed the distribution of Charlesworth's moraine belts. Extensive deposits of sand and gravel extend along the North Esk Valley from near Carlops to Dalkeith. With local exceptions these are now largely flat-topped, but as they appear to have been over-ridden by the Southern Upland Readvance ice-sheet (p. 113), their original topography imposed by the ablation of the Highland Ice has been obliterated. The shape of the intakes of meltwater channels crossing the high ground to the east of the North Esk Valley suggests that the water cutting these channels drained directly from melting ice rather than from an open lake. It is thus likely that dead ice occupied the North Esk Valley to a late stage in the retreat of the ice sheet and that its margin at any one time was only gently sloping towards the vicinity of Penicuik.

Auchencorth Moss, Cauldhall Moor, Borthwick

The Midlothian Basin is bounded to the south-east by the escarpment of the Moorfoot Hills. This slope and the gently sloping ground immediately to the north-west are relatively free from ice retreat features and deposits. The highest marginal channels and sand and gravel deposits occur about one mile south-east of Rosebery Reservoir, at a level of approximately 1025 ft O.D. These mark the southern limit of the Stranraer–Lammermuir Readvance, as contended by Charlesworth (1926, p. 27) or the line of separation of Highland and Southern Upland Ice, as suggested by Kendall and Bailey (1908, p. 20). To the west and north, in the area between Howgate and Borthwick, the topography is gently undulating, with only a very gentle slope to the north. The lowering of the ice on this ground led first to the emergence of the higher ridges and hills to form nunataks. The first of these to appear above the ice was Kingside Edge, north-east of Leadburn, followed by King's Seat and a small hill at Upper Side. These can be recognized as former nunataks as they have meltwater channels on their southern slopes, in contrast to most other marginal channels in the area, which are cut on north-facing slopes.

Fullarton Sand and Gravel deposits

At this early stage of ice ablation the water liberated from the melting ice sheet and the winter snow laid down the deposits of sand and gravel which extend from Scarce Rig 1.5 miles S.S.W. of Mount Lothian at the south end of the area to Edgelaw Reservoir in the north. The gravel has a typical kettle topography with some well-marked kames with ice contact features, kettle holes and several esker-like ridges, suggesting that it was deposited in and probably on top of stagnant, deeply crevassed ice which was gradually decaying.

Glacial drainage channels of Herbershaw–Rosewell ridge and Cauldhall Moor

South of a line joining Herbershaw and Upper Side there are no major drainage channels, but to the north of this a number of more or less parallel dry channels cut both gravel and solid rock. These channels run from west to east and carried meltwater roughly parallel to the southern margin of the ice-sheet, the waters eventually passing through the Borthwick Gap, to the valley of the Tyne Water. The channels vary greatly in size, the largest being up to 45 ft deep and locally 200 yd wide. Many follow a fairly sinuous course which is to some extent determined by the depressions in the preexisting topography, and occasionally minor sub-parallel channels are developed on both the south and north sides of the main ones.

A number of the channels (Plate 4)(24–28) have their intakes on the ridge of high ground which extends from Kingside Edge (Gray Brae) by way of Herbershaw to Rosewell. The thalwegs of three of these (Plate 4)(24, 25, 27) have "up and down" profiles at the crest of the ridge with distinct uphill portions of varying length. Such humped bedrock profiles have been discussed by Sissons who concluded that the uphill flowing portions were cut by sub-glacial streams flowing uphill under hydrostatic pressure (Sissons 1958c, p. 166). Only the lowest of the parallel sequence of channels cutting the ridge, has an intake which without doubt started as a marginal channel. Other channels (Plate 4)(e.g. 29–32) commence well to the east of the Kingside–Rosewell Ridge and some of these (Plate 4)(e.g. 30–32) start as bowl-shaped depressions in gravel or boulder clay. Such a depression at the head of a dry channel would suggest that it was formed by a supra-glacial stream cascading down a crevasse or moulin and then continuing either under or outside the ice. Many of the channels are cut partly in gravel and often there is no difference in the level of the gravel on either side of them.

The above-mentioned features are not normally associated with true marginal channels, and it seems likely that the streams forming some of these channels may have either started on ice and later become superimposed on the underlying deposits, or flowed in tunnels or crevasses within the decaying ice. The fact that a number of channels have uphill intakes would suggest that, when they were initiated, the ice was still sufficiently uncrevassed to retain sub-glacial water at considerable hydrostatic pressure.

There are other anomalies in the late-glacial drainage system of this area which can best be explained by postulating a sub-marginal drainage pattern in dead ice. These include:

1. The sinuous course of many channels and the existence in one case of an apparently incised meander breached by a later channel (Plate 4)(26a).
2. The diversion of normal west-east channels (Plate 4) (e.g. 29, 32), to a north-northeasterly course along a pre-existing depression (Plate 4)(Channels 29 and 32 at Rosebery Reservoir). This feature could, however, also be explained by the meltwater forming a marginal channel passing into the ice along a crevasse.
3. The discontinuous nature of some small early-formed channels. This is particularly strongly marked in the case of the two channels, 24 and 29, formed on the south slopes of 'nunataks'; these die out after being traceable for a short distance, the meltwater presumably having passed on to the ice.
4. The partial obliteration of one channel (Plate 4)(29a between Outerston and Esperston) by deposits of sand and gravel and the presence of small patches of sand and gravel in others, locally modifying the original channel shape. This feature could be explained by postulating a local readvance of the ice sheet after the channels had been abandoned. The remarkably fresh outline of all channels and associated ice-retreat features, however, rules out the possibility of any widespread ice-readvance or for that matter, a subsequent glaciation. These patches of gravel may have been deposited by either (i) ice carrying gravel bridging a sub-glacial channel and melting after the channel had ceased to function or (ii) water liberated by the late melting of a residual mass of ice depositing sand and gravel in an abandoned channel. Moundy gravel would be formed in the first case and an alluvial spread in the second.

The last channel which carried water draining eastwards to the Borthwick gap appears to have been the Edgelaw Channel (Plate 4)(26), whose lowest intake is at 780 ft O.D. North of this there are three lower parallel west-east channels (Plate 4)(27, 28, 33). These are cut on a steeper slope than the channels farther south and they appear for at least part of their course to have been truly marginal. The lowest levels of two of these channels near Carrington are respectively 570 ft and 470 ft O.D., and as the intake of the lowest channel leading to the Borthwick Gap (Plate 4)(34) is 575 ft O.D. it is concluded that drainage from the former passed either over or under the ice into the basin of the South Esk.

Roslin–Dalkeith Area

When the Borthwick Gap ceased to be utilized by glacial meltwaters the level of the ice margin in Midlothian stood between 600 and 500 ft O.D. There are no marginal drainage features at this level on the west slope of the Roman Camp Ridge, suggesting that in the area between a line joining Rosewell and Carrington in the south and the latitude of Dalkeith in the north, meltwater drained away north-eastwards above or in the ice, eventually crossing the northern end of the ridge by a series of west to east channels (Plate 4)(42–44). Sissons (1958A, fig. 6, p. 76) has shown that at this stage the ice had largely disappeared to the east of the ridge.

With the 'retreat' of the ice below the 500-ft contour the southern margin of the ice became so broken that it ceased to be a positive barrier to glacial meltwater. Its line is now marked by a belt of gently undulating sand and gravel which extends east and west of Rosewell and is cut by a number of small meltwater channels (Plate 4)(45–49) running for at least part of their course directly downhill. This suggests that meltwater flowed north-eastwards over the ice, first spreading over its entire surface and depositing sand and gravel, and later, as it became channelled along depressions, forming several streams which eroded the gravel and residual ice, locally cutting into the underlying boulder clay.

Gravels of the lower North Esk Valley

The Rosewell sands and gravels form part of an extensive belt of sand and gravel ('Middle Gravels') which stretches along the North Esk Valley from Penicuik to beyond Dalkeith and extends westwards as far as Bilston and Straiton, where it is overlain by the Upper Boulder Clay (p. 113). There is a marked contrast between the abundance of fluvioglacial deposits in the valley of the North Esk and their virtual absence in the South Esk Valley between Upper Dalhousie and Eskbank. This can be explained by the supposition that the North Esk gravels were deposited on the ice and along the ice margin both by the extra-glacial North Esk and its tributaries and by the glacial meltwaters flowing through the Pentland Hills via the Logan Burn channel (Plate 4)(60). Little extra-glacial water would at this stage have passed on to the ice in the South Esk valley as the water from the North and South Middleton Burns (Crampton and Hinxman in Peach and others 1910, p. 326) and possibly the headwaters of the South Esk would at this stage still pass through the Borthwick Gap to the Tyne Water.

The sand and gravel extending northwards from Dalkeith as far as Old Craighall is a terrace-spread sloping very gently to the north-east and now dissected by recent drainage. It is directly connected with a well-defined curving gravel ridge which extends from Sheriffhall near Dalkeith for one mile to the north-north-west. This may be an esker which marks the course of a sub-glacial stream flowing from the thicker ice to the north to the ice margin, eventually debouching into the ice-free plain about Dalkeith. The lowest marginal drainage channel in Midlothian, which marks the final stage in the ice retreat from the Esk Valley, is cut along a glacial groove on the north-facing slope half a mile south of Prestonpans and falls from 150 ft O.D. at its intake to approximately 120 ft O.D.

Gilmerton Ridge

The ridge extending north-eastwards from Straiton to New Craighall at one stage appears to have separated stagnant ice in the Esk valley from the ice occupying the Forth Valley and still moving eastwards. A parallel series of meltwater channels (Plate 4)(53–58) with successive intakes falling from 450 ft O.D. to 180 ft O.D. crosses this ridge. Two of these (Plate 4)(53, 58) have cut notches utilizing pre-existing cols and have marked 'up and down' profiles, and three others (Plate 4)(54, 56, 57) start as gentle depressions on its south-east side. This together with the character of one channel (Plate 4)(54) suggests that that ice-sheet still overlapped the ridge when the meltwater channels were formed and that the ground to the south-east was at least partly ice-free.

North-west slopes of Pentland Hills

The range of the Pentland Hills formed a barrier to the Highland Ice advancing from west to east and, during the earlier stages in the ablation of the ice-sheet it appears to have separated the stagnant or 'dead' ice occupying the Midlothian Basin from still slightly 'active' ice forming part of the Forth Glacier. The belt of terminal moraine composed of coarse sandy drift, which crosses the upper valley of the Lyne Water (Plate 4), may mark the limit of a tongue of ice moving eastwards through the Cauld Stane Slap after the ice in the eastern Pentland Hills had largely disappeared. Elsewhere this ice did not cross the divide, but glacial meltwaters have cut gulleys through the lowest points of several cols in the main range (Plate 4)(11–13, 59). The intakes of these col gulleys are between 1320 ft and 1400 ft O.D., and the effect of meltwater erosion on the south-east slope can, in the case of the Upper Esk Valley, be traced to approximately 1100 ft O.D. This suggests that the height difference of the two portions of the ice-sheet near the southern end of the chain was at least 220 ft. The ice-margin subsequently retreated north-westwards down the hill slopes, meltwater escaping first by way of Green Cleugh (60) and the valley of the Logan and Glencorse Burns to the Midlothian Basin (Peach 1908, p. 145). The moundy deposits of sand and gravel, 2.5 miles S.S.W. of Balerno, now deeply dissected by later drainage, reach a level of just over 1130 ft O.D. This coincides approximately with the intake level of the highest of the Bavelaw system of marginal channels (Mykura in Mitchell, Walton and Grant 1960, p. 177), and the level of an ice-marginal bench three-quarters of a mile west-south-west of Hare Hill. The gravel deposit may be the eroded remnant of a kame terrace or, more likely, the remains of a kame-belt deposited within the crevassed and decaying margin of the ice-sheet, whose englacial water-level was controlled by the levels of the successive intakes of the Bavelaw channels.

The Bavelaw Channel was abandoned by glacial meltwater when the ice-margin west of North Black Hill fell below 1000 ft. As the water from this channel appears to have flowed without obstruction into the Midlothian basin at Flotterstone, where the base of the channel was approximately 650 ft, the difference in ice-level on the two sides of the Pentland Hills at that stage was at least 350 ft.

The second spillway through the Pentland Hills passes from the ice-gouged depression now occupied by Threipmuir Reservoir through the wind-gap between North Black Hill and Bell's Hill (Plate 4)(61) to join the earlier channel near the head of Glencorse Reservoir. Threipmuir Reservoir and the area of lake alluvium to its south-west occupy the site of a former ice-dammed lake. The approximate positions of the ice-margin at this stage are marked by meltwater channels, ice-marginal benches and sand and gravel deposits near East Colzium (Plate 4)(62), Harperrig Reservoir (Plate 4)(63) and Listonshiels (Plate 4)(64). A low ridge extending north-east from Listonshiels is traversed by three shallow overflow channels (65–67) with open intakes which appear to have been cut in south-west to north-east sequence by water, ponded by the ice to the north of the ridge, flowing into the Threipmuir Loch.

The meltwater-channels below the 800-ft contour are small and ill-defined. They are confined to two areas:

1. To the west of the Cock Burn, two miles south-west of Balerno (Plate 4)(68), and
2. the south-west side of Bavelaw Burn and the Water of Leith, immediately south and west of Balerno (Plate 4)(69).

In both areas a parallel series of marginal channels stops short at a stream valley, with some of the channels turning downhill into sub-glacial chutes before reaching the stream. It is likely that the ice-margin at this stage was fairly broken up, marginal meltwaters escaping into the ice along crevasses or ice-tunnels. The lines now followed by the Cock Burn and Bavelaw Burn would on this hypothesis mark the courses of two large crevasses which captured all marginal drainage during successive stages of ice-retreat.

The valley of the Water of Leith between Glenpark, one mile west of Balerno, and West Mills near Colinton (Plate 4)(70) follows an ice-gouged depression. This depression appears at this stage to have been utilized by sub-glacial drainage and later acted as a partly marginal and partly extra-glacial drainage channel. The original eastward continuation of this channel appears to have been by way of the alluvial flat at Redford Barracks and the Braid Burn valley (Plate 4)(71) to Craigmillar.

Three small horse-shoe channels which are cut in the gentle slope one and a half miles south-west of Balerno present some unusual features. The channels are up to 15 ft deep and 30 yd wide. The crest of the horseshoe is at the highest point of the slope and the sides are at their widest up to 300 yd apart. As in the case of a horseshoe channel near Temple (Plate 4)(38a) they enclose a central mound of sand, but unlike the latter they have no connection with a near-horizontal channel at their base. These channels were probably formed by water flowing downhill and eroding a channel around a residual mass of ice covered by sand and gravel.

North slopes of Pentland Hills

Ice retreating northwards from the northern slopes of the Pentland Hills left few marks of its retreat. A channel along the hollow containing Clubbiedean and Torduff reservoirs (Plate 4)(72) and a number of small dry channels opening into the shallow depression between Swanston and Fairmilehead (Plate 4)(73) are the only traces left by meltwater. The deposit of sand at Comiston, which is locally overlain by a large transported mass of Lower Old Red Sandstone lava (Campbell and Anderson 1909) has been described as a lake deposit laid down in a sheet of water bounded to the north and west by the ice-margin and to the south and east by the ridge extending from the Braid Hills via Fairmilehead to Dreghorn, the water-level in the lake being controlled by the level of the overflow channel (Plate 4)(74) crossing the ridge of Hunter's Tryst.

Cobbinshaw, Kirknewton, Dalmahoy

It has already been stated (p. 114) that there is evidence that at some stage during the retreat of the Highland ice, ice from the Southern Uplands penetrated into the area west of the Pentland Hills and extended north-eastwards as far as Colinton. Most morphological features in the area concerned, however, indicate that the final retreat of the ice was in a north- to north-westerly direction. This would suggest that during its ablation the Southern Upland ice in this area behaved as a part of the Forth Glacier.

To the north-west of the Edinburgh–Carnwath road the topography is undulating and the over-all slope to the north-west is gentle. It is therefore no longer possible to recognize successive stages of the ice-margin. As in the Howgate–Temple area (p. 116) the hills and ridges were freed of ice first to form nunataks and prominent features like Dalmahoy Hill and Craw Hill have marginal channels both to the north and south. Later the ice tended to become isolated into separate areas of stagnant ice which decayed in situ.

Compared with the ground to the east of the Pentland Hills, meltwater channels are small and poorly developed and gravel deposits occur only as isolated patches. Channels are of three types:

1. Marginal and sub-marginal channels in parallel series. These are developed on fairly steep north-facing slopes as on the north face of Selms Hill (Plate 4)(75), on the slope between the Ratho Hills and the River Almond (Plate 4)(76) and the hill-slope between Kirknewton and the Gogar Burn (Plate 4)(77). Locally these channels are in part interconnected by sub-lateral channels and in places (e.g. (Plate 4) (78) near Oakbank) they turn abruptly downhill to continue as sub-glacial chutes.
2. Integrated drainage systems trending roughly parallel to the contours. These are developed in gently undulating glacially grooved topography near Wester Murieston (Plate 4)(79), just west of Kirknewton, on the flat ground south and west of Dalmahoy Hill (Plate 4)(80), between Currie and Sighthill (Plate 4)(81). In these systems the branch channels join without marked truncation of the higher channels by lower ones, suggesting that they may have functioned simultaneously. Integrated systems of this type were most likely originated on the ice, the streams flowing close to and roughly parallel to the margin, eventually cutting through the ice into the underlying boulder clay.
3. Channels utilizing cols between adjacent hills. The best developed of these is the channel extending for three miles west and east of Ratho (Plate 4)(82), making a deep cut through the ridge formed by the Ratho Sill (p. 96). This channel was excavated to its present depth when the ice-margin to the west of the sill was standing at 300–280 ft 0.D., a north-north-east trending marginal channel having here been diverted through a pre-existing deep col in the hill to form the present gorge.

Dalmahoy Moraine

A belt of moraine up to one mile wide extends for 5.5 miles east-north-eastwards from Hatton House near Kirknewton to Kingsknowe Station on the outskirts of Edinburgh. This belt lies between the 275- and 425-ft contours and has a well-developed drumlin topography. It contains many small patches of sandy drift and gravel elongated parallel to the direction of ice movement, and has a number of depressions threading their way between drumlins, which appear to have been used by glacial meltwaters. The belt has the appearance of a lateral or median moraine, possibly formed along the junction between the Highland and Southern Upland Ice. A puzzling feature, however, is its limited local extent and the absence of a similar deposit which might mark the lateral continuation either to the west or east of it. A similar deposit occurs south of Harburn Station near the west edge of map.

The later stages in the retreat of the ice-sheet in Midlothian and West Lothian were marked by a great reduction in the amount of meltwater which found its expression first in the decline in size and number of meltwater channels and finally in their virtual disappearance. This is probably explained by the supposition that much of the water which cut the large channels in the Midlothian Basin and through the Pentland Hills was formed during the springs and early summers by the melting of a heavy winter snowfall. By the time the ice-sheet had shrunk back into West Lothian and the Edinburgh area the climate may have ameliorated to such an extent that the winter snow was insignificant and the meltwater was formed only by the ablation of the ice sheet.

City of Edinburgh

Within the City of Edinburgh meltwater from the shrinking ice-sheet was not sufficient in quantity to form distinct channels. The lowest channel crossing the high ground south of the city is Craiglockhart Glen (Plate 4)(83), whose intake is at 360 ft O.D. This was possibly formed by meltwater from the ice which deposited the sandy drift of the Dalmahoy moraine. The water forming the Craiglockhart channel appears to have flowed entirely outside the ice-margin, first following a glacial groove eastward for nearly one mile and then flowing northward downhill to form the depression now utilized by the Biggar Road just south of Morningside Station, eventually debouching into the hollow between Morningside and Newington stations.

North of Morningside meltwater channels are absent and only isolated spreads of gravel remain as evidence of the retreat of ice. The depressions in the ice-moulded surface formed lakes, many of which have remained to historic times. The seven most important lochs were: Gogar Loch, Corstorphine Loch, Craigcrook Loch, The Borough Loch, Holyrood Loch, Lochend Loch and Duddingston Loch (A to G (Plate 4)). A map and description of these was published by Cadell (1893) and temporary sections through their deposits have been recorded by Bennie (1891) and Tait (1934A; 1934n, pp. 68–9).

Corstorphine Loch was by far the largest of the Edinburgh lochs and Tait has shown that here, as well as in superficial deposits at Hailes Quarry, there are two sets of lake deposits separated by a varying thickness of rusty gravel. The lacustrine beds below the gravel consist of grey silt or sandy silt with bands of clay, which is locally laminated. They are in places at least 12 ft thick and are present throughout the area. From these beds Bennie and Tait have obtained arctic plants, including willows (Salix polaris Wahlberg, S. herbacea Linnaeus, S. reticulata Linnaeus), the dwarf birch (Betula nana Linnaeus), the white dryas (Dryas octopetala Linnaeus) and Oxyria digyna Hill (Reid 1899, p. 62), as well as such animals as Lepidurus [Apus]glacialis Kroey, Limnea, Planorbis and the bones of a lemming. Patches of peat have in places been recorded at the top of this deposit. The overlying gravel is generally coarse, with boulders, normally up to 1.5 ft in diameter, and sometimes much larger. A considerable proportion of the pebbles were said to be Highland metamorphic rocks and Lower Old Red Sandstone lavas believed to be from the Ochil Hills. The gravel is always present in the eastern portion of the former loch but passes westward into clay with sand and gravelly bands. The higher lake deposit is thin and patchy and often appears to rest in hollows eroded in the gravel.

An antler of the Irish elk Cervus giganteus (Blumenbach) and remains of Bos primigenius Bojanus were found in the excavations, but the exact layers from which these remains were obtained are not recorded. Mitchell and Parkes (1949) have shown that within the British Isles Cervus giganteus is usually found in the deposits of late-glacial Zone II, and have stated (1949, p. 307) that the Corstorphine Loch deposits are apparently late-glacial.

The Corstorphine gravel appears to be contemporaneous with the gravel spreads of Gogar, Stenhouse and Hailes. Charlesworth (1926, p. 40) considers that these were formed as outwash fans at the stage of the Polmont and Bathgate moraine (p. 122).

Linlithgow–Kirkliston area

The area north-west of the River Almond contains few features from which details of the retreat of the Forth Glacier can be deduced. There are a number of meltwater channels (Plate 4)(84–90, 93) on the southern slopes of the sub-parallel ridges which extend eastwards from the Riccarton Hills by way of Binny Craig to the neighbourhood of Winchburgh. These channels fall to the east or southeast and the intakes of most of them (Plate 4)(84, 85, 93) cut through the crest of one of the east–west ridges. One channel (Plate 4)(87) commences as a marginal channel on the north slope of a ridge, before turning south. Others (Plate 4)(86, 88, 93) run roughly parallel to the contour on the southward-facing slope (marginal channels) but their gradient normally steepens near the lower end of their course as they turn to flow directly down the hillside. The distribution and shape of the channels suggests that as the ice retreated, the south-facing slopes became ice-free first, the small east-west depressions remaining blocked with dead ice to a later stage.

Eventually the ice split into two lobes, the smaller occupying the valley of the Upper Almond and the larger filling the Forth Valley. The gravels forming several elongated detached mounds between 500 ft and 600 ft O.D. south-west of Bangour Hospital, which are the eastward extension of the extensive gravel deposits developed around the southern end of the Bathgate Hills (within the area of one-inch Sheet 31) appear to have formed along the northern margin of the Almond lobe.

A more widespread sand and gravel deposit extends eastward from Linlithgow as far as Philpstoun. At Linlithgow and between Champany and Philpstoun the sands and gravels are moundy, with kettle topography, the mounds in the latter area trending roughly west-north-west. The tops of the mounds are generally about 230 ft O.D. The deposit forms part of an extensive belt of hummocky gravel which extends westwards for about 12 miles as far as Falkirk (Haldane in Macgregor and Haldane 1933, p. 102) and includes the Polmont Kame or Esker. Charlesworth (1926, p. 40), following Gregory (1913) considers that the Polmont Kame and the Linlithgow gravels were formed along the southern margin of the Forth Glacier and mark an important stage in its retreat. Outwash material from this ice-margin is said to extend as far east as the Corstorphine gravels.

Retreat of the Southern Upland Readvance Ice

Midlothian Basin

The evidence for the readvance of the Southern Upland ice is to be found largely outside the area of one-inch Sheet 32 (Eckford 1952, pp. 140–1, 147, McCall and Goodlet 1952, p. 403). Within the Midlothian Basin the only deposit which can confidently be ascribed to this period of re-advance is the Upper Boulder Clay of the Roslin–Loanhead district. An estimate of the maximum extent of the ice-tongue is thus largely based on indirect evidence. The glacier must have been confined to the area in which the surface features formed by the northward retreat of the Highland ice have been largely obliterated. Its eastern margin was thus west of the ridge extending from Kingside Edge to Rosewell (Page 116), and the level of the ice appears to have been below the intakes of the dry channels crossing the ridge. The western margin of the glacier cannot be so readily delineated, as the marginal channels on the south-east flank of the Pentland Hills might have been utilized by meltwaters from both the earlier and later ice. An approximate estimate of the upper limit of the latter can, however, be obtained by comparison with the maximum height of its eastern margin. The probable maximum extent of the Southern Upland readvance glacier is shown on (Plate 4).

As the Southern Upland ice was thickest near its source in the south-west and thinned towards the north-east its general direction of retreat must have been to the south-west. It thus 'retreated' uphill in the area between Loanhead and Auchencorth Moss and glacial meltwaters were usually able to escape freely into the North Esk basin. No extensive fluvio-glacial deposits which can be ascribed to the Southern Upland ice have been recognized in this northern area. The only major meltwater channel within the area occurs one mile south-west of Penicuik (Plate 4)(92) and extends from near Lockhart Halls Farm west-north-westwards to the valley of the North Esk. This channel must have formed when the valley of the Black Bum north of Lockhart Halls Farm was blocked by ice, suggesting that near its margin the melting Southern Upland ice may have separated into a number of more or less isolated ice-masses which remained for some time in valleys and depressions.

South-west of the high plateau which forms Auchencorth Moss the ground slopes south-westwards towards the Lyne Water, and the retreating front of Southern Upland Ice at one stage impounded the valley of the Lyne Water to form late glacial Lake Linton (Eckford 1952, p. 145), the site of which is entirely within the area of one-inch Sheet 24. The water from Lake Linton escaped over the watershed near Rutherford and flowed into the North Esk via the valley of the Harlawmuir Burn, which is now deeply incised. Similarly the sand and gravel spreads and underlying deposits in the area north-east of Carlops are deeply incised by the channels now occupied by the North Esk and Carlops Burn, which are continuations of the Windy Gowl complex of meltwater channels (within area of one-inch Sheet 24). It is probable that the latter channel-system was used by meltwaters during the retreat of both the Highland and Southern Upland ice. On the first occasion these waters deposited the sands and gravels now occupying the Upper North Esk valley, and on the second, when drainage was not impeded by ice to the north-east, they cut the present gorges of the North Esk and its tributaries.

North-west slopes of Pentland Hills

It is difficult to define the limits of the Southern Upland ice in the area north-west of the Pentland Hills, as it has left no separate ice retreat features, all ice in the area apparently retreating in a general north-westerly direction. There is no lateral moraine along the north-west slopes of the Pentland Hills which could be used to define the south-eastern margin of the ice. A detailed study of indicator stones in the sandy drift and gravels over a wider area would be necessary for a precise delineation of this ice sheet.

Raised beaches

Deposits belonging to the 100-ft, intermediate and 25-ft raised beaches have been mapped along the coastal belt extending from Bridgeness to Prestonpans.

100-ft Raised Beach

To the east of Edinburgh deposits of sand and gravel attributed to a raised beach have been mapped up to the 100-ft contour line. The feature marking the inner margin of the beach terrace is nowhere definite, and the deposits are not readily distinguishable from the fluvio-glacial deposits which adjoin them along the Esk Valley south of Musselburgh. The two types of deposit merge into each other, and on the 1928 edition of one-inch Geological Sheet 32 sands and gravels rising to over the 150-ft level near Dalkeith were shown as raised beach deposits. On the forthcoming edition of this geological map, however, they are mapped as fluvio-glacial deposits.

Laminated clay, which was proved by borings to be at least 100 ft thick and which has yielded remains of the arctic seal was formerly worked at the Portobello brick works. The greater part of this clay is believed to belong to the deposits of the 100-ft Raised Beach (Peach and others 1910, pp. 335, 349; Tait 1934B, pp. 61–5).

West of Edinburgh the landward limit of the highest raised beach terrace appears also to be close to the 100-ft contour, but the feature is not everywhere seen. Along the valley of the River Almond 100-ft Raised Beach deposits have been mapped along a narrow strip as far inland as Craigiehall. Clough and others (in Peach and others 1910, p. 336), considered that the alluvial flat along the River Almond between Hallyards, half a mile south-east of Kirkliston, and Craigiehall (Plate 4), which lies just below the 100-ft contour, was an estuary in 100-ft Raised Beach times, and was connected by a narrow neck with the outer channel at Cramond. Many bores in this area have proved sand, mud and gravel to depths of up to 43 ft, and it was considered that, apart from a thin covering of river alluvium, these deposits were of marine origin. During the recent re-survey of the area, leaves, twigs and seeds of ash and beech were found at depths of up to 10 ft from the surface, suggesting that the river alluvium is here thicker than was formerly thought. W.M.

In Fife the beach is probably represented by a small but well-defined flat with inner margin at about 100 ft O.D. at 'The Green', Charlestown, and by disconnected features just below that level in the vicinity of Brucehaven. A feature, probably marking its inner margin, is visible for nearly half-a-mile west of Pitreavie, close above the 100-ft contour. An extensive area below this level on both sides of the broad east-to-west valley of Brankholm Burn appears to be mainly underlain by sand and laminated clay which are mapped as High Raised Beach deposits. Farther east a nearly flat expanse of Boulder Clay at about 90 ft O.D., formerly the site of the main runways of Donibristle Airfield, may be a High Raised Beach terrace feature. J.R.E.

Intermediate raised beaches

Impersistent features close to the 75-ft and 50-ft contours marking the margins of intermediate beaches have been recorded at Monktonhall just south of Musselburgh, at Leith and just west of Granton. The features are poorly developed and no deposits which can be ascribed to the intermediate beaches are now exposed on the south side of the Forth. W.M.

In Fife well-defined terrace features cut in Boulder Clay immediately below the 75-ft contour, north of Barnhill Bay, along the north side of Dalgety Bay and near the mouth of Lyne Burn, west of Charlestown, are probably relics of an intermediate Raised Beach. Only at the last mentioned locality have any associated deposits been mapped. Deposits of clay and silt, making broad flats just below 50 ft O.D. north of Inverkeithing are probably, at least in part, the alluvial deposits of Keithing Burn and Brankholm Burn.

25-ft Raised Beach: The 25-ft Raised Beach, which is partly rock cut, forms a good feature along the coast of the area under description. The beach deposit is normally sand and gravel loosely cemented and contains the common shells found on the present shore. In part of Portobello clay pit the upper 10 ft of clay are thought to belong to the 25-ft Beach deposits (Peach and others 1910, pp. 335, 349; Tait 1934n, pp. 61–5).

Between the mouth of the River Almond and Blackness Castle the landward margin of the beach terrace appears locally to reach a height of 35–40 ft O.D. (Peach and others 1910, p. 336). W.M.

The Low Raised Beach is well represented north of the Forth particularly between Crombie and Limekilns and around Dalgety Bay. It is usually backed by a well defined, sometimes cliff-like feature, whose base may vary in level from 30 to 40 ft above O.D.

The variation in height of the Scottish raised beaches and their correlation with the major Scottish glacial retreat stages has been discussed by Donner (1959), who concluded that, whereas the 50-ft and 25-ft raised beaches maintained a constant level of 15–5 m to 18.5 m (50.8 ft to 60.7 ft) and 9 m to 11 m (29.5 ft to 32.8 ft) respectively throughout Scotland, the level of the 100-ft Raised Beach varies in height from 30 m (98.4 ft) to 40 m (131 ft). The distribution of the isobases of the 100-ft Raised Beach suggests, according to Dormer, that the beach reaches its maximum height in the vicinity of Callander and falls in level at an average gradient of 1 in 9000 from this central area. This conclusion implies that within the area of one-inch Sheet 32 there should be a gradual eastward fall in the level of the 100-ft Raised Beach. Although a detailed investigation of the heights of the seaward margins of the raised beach terraces has not been carried out, the data available do not indicate any appreciable variation in the height of the shore line.

Donner (1957, p. 225; 1959, fig. 5) has correlated the 100-ft Raised Beach period with the Perth Readvance Moraine (Simpson 1933), which is said to fall within the late-Glacial Pollen Zone I (>10000 B.C.); the 50-ft Raised Beach period with the Highland Readvance Moraine which is taken to fall within Pollen Zone III (Late Glacial, approx. 9000–8000 B.C.). The 25-ft Raised Beach period is correlated with the Post Glacial Zone VIIa (approx. 5000–3200 B.C.).

River terraces

A number of river terraces are usually found along the main rivers and these are shown on the drift edition of the one-inch map.

Five well defined terraces are developed along the River Esk between Dalkeith and Musselburgh and the lower terraces are cut in raised beach deposits. Some of the higher terraces may therefore be contemporaneous with the raised beaches. The large area of alluvium along the River Almond between Kirkliston and Craigiehall appears to consist of a thin cover of freshwater sand, silt and silty clay apparently resting on the deposits of the 100-ft Raised Beach. In the Almond valley between Clifton Hall and Kirkliston there are two distinct river terraces ranging in height from 100 to 200 ft O.D.

Lake alluvium

A number of areas of alluvium unconnected with rivers or streams are found in and around Edinburgh and West Lothian in the north-western part of the area of one-inch Sheet 32. These mark the sites of late-glacial lakes. Some of the Edinburgh lake deposits are described on p. 121. The West Lothian deposits appear usually to be thin and consist of yellowish weathering blue-grey laminated clay or silt. Bores have penetrated lacustrine deposits just north and west of Winchburgh, one mile east of Ecclesmachan and at West Bangour. Most of the bore records give no detailed picture of the deposit, but a bore, 150 yd N.N.W. of Winchburgh, has recorded 20 ft of running sand overlying 30 ft of clay and gravel. W.M.

References

ANDERSON, J. G. C. 1940. Glacial Drifts near Roslin, Midlothian. Geol. Mag., 77, 470–3.

BENNIE, J. 1891. The Ancient Lakes of Edinburgh. Proc. Roy. Phys. Soc. Edin., 10, 126–53.

BREMNER, A. 1934. Meltwater Drainage Channels and other Glacial Phenomena of the Highland Border Belt from Cortachy to the Bervie Water. Trans. Edin. Geol. Soc., 13, 174–5.

CADELL, H. M. 1893. A Map of the Ancient Lakes of Edinburgh. Trans. Edin. Geol. Soc., 6, 287–96.

CAMPBELL, A. C. and ANDERSON, E. M. 1909. Notes on a Transported Mass of Igneous Rock at Comiston Sand Pit, near Edinburgh. Trans. Edin. Geol. Soc., 9, 219–24.

CAMPBELL, R. 1934. On the Occurrence of Shelly Boulder Clay and Inter-glacial Deposits in Kincardineshire. Trans. Edin. Geol. Soc., 13, 176–83.

CAMPBELL, R. 1951. Geology in Scientific Survey of South-Eastern Scotland, 185–99. Brit. Assoc. Handbook.

CHARLESWORTH, J. K. 1926. The Readvance Marginal Kame-moraine of the South of Scotland and Some Later Stages of Retreat. Trans. Roy. Soc. Edin., 55, 25–50.

CHARLESWORTH, J. K. 1957. The Quaternary Era. London.

CLOUGH, C. T., BARROW, G., CRAMPTON, C. B., MAUFE, H. B., BAILEY, E. B. and ANDERSON, E. M. 1910. The Geology of East Lothian. Mem. Geol. Surv.

COMMON, R. and GALLOWAY, R. W. 1958. Ice Wedges in Midlothian: a Note. Scot. Geog. Journ., 74, 44–6.

DONNER, J. J. 1957. The Geology and Vegetation of Late-glacial Retreat Stages in Scotland. Trans. Roy. Soc. Edin., 63, 221–64.

DONNER, J. J. 1959. The Late- and Post-Glacial Raised Beaches in Scotland. Suomalainen Tiedeakatemia, 53, 1–25.

ECKFORD, R. J. A. 1952. Glacial Phenomena of the West Linton–Dolphinton Region. Trans. Edin. Geol. Soc., 15, 133–49.

EYLES, V. A., SIMPSON, J. B. and MACGREGOR, A. G. 1949. The Geology of Central Ayrshire. Mem. Geol. Surv.

FLINT, R. F. 1957. Glacial and Pleistocene Geology. New York.

GEIKIE, J. 1894. The Great Ice Age. 3rd edit. London.

GREGORY, J. W. 1913. The Polmont Kame and on the Classification of Scottish Kames. Trans. Geol. Soc. Glasgow, 14, 199–203.

KENDALL, P. F. and BAILEY, E. B. 1908. The Glaciation of East Lothian south of the Garleton Hills. Trans. Roy. Soc. Edin., 46, 1–31.

MACGREGOR, M. and HALDANE, D. 1933. The Economic Geology of the Central Coalfield of Scotland. Area III, Bo'ness and Linlithgow. Mem. Geol. Surv. .

MACGREGOR, M. and MACGREGOR, A. G. 1948. The Midland Valley of Scotland. 2nd edit. revised. British Regional Geology, Geol. Surv.

MANNERFELDT, C. M. 1945. Några Glacialmorfologiska Formelement. Geographiska Annaler, 27, 1–239.

MCCALL, J. and GOODLET, G. A. 1952. Indicator Stones from the Drift of South Midlothian and Peebles. Trans. Edin. Geol. Soc., 14, 401–9.

MITCHELL, G. F. and PARKES, H. M. 1949. The Giant Deer in Ireland. Proc. Roy. Irish Acad. (B), 52, 291–314.

MYKURA, W. 1960. In MITCHELL, G. H., WALTON, E. K. and GRANT, DOUGLAS. (editors): Edinburgh Geology-An Excursion Guide, Edinburgh.

PEACH, A. M. 1909. Boulder Distribution from Lennoxtown, Scotland. Geol. Mag., 6, 26–31.

PEACH, B. N. 1908. In Cochrane's Pentland Walks. 1st edit., 145–7.

PEACH, B. N. , CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

REID, C. 1899. The Origin of the British Flora. London.

RICHEY, J. E., ANDERSON, E. M. and MACGREGOR, A. G. 1930. The Geology of North Ayrshire. Mem. Geol. Surv.

SIMPSON, J. B. 1933. The Late-Glacial Readvance Moraines of the Highland Border, West of the River Tay. Trans. Roy. Soc. Edin., 57, 633–46.

SISSONS, J. B. 1958A. The Deglaciation of East Lothian. Int. Brit. Geogr., 25, 59–77.

SISSONS, J. B. 1958n. Supposed Ice Dammed Lakes in Britain, with particular reference to the Eddleston Valley, Southern Scotland. Geographiska Annaler, 40, 159–87.

SISSONS, J. B. 1958c. Sub-glacial Stream Erosion in Southern Northumberland. Scot. Geog. Mag., 74, 163–74.

TAIT, D. 1934A. Excavations in the Old Lake Deposits at Corstorphine during 1930–32. Trans. Edin. Geol. Soc., 13, 110–25.

TAIT, D. 1934B. Braid Burn, Duddingston and Portobello Excavations. Trans. Edin. Geol. Soc., 13, 61–71.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

WRIGHT, W. B. 1937. Quaternary Ice Age. 2nd edit. London.

Chapter 17 Mineral resources and water supply

An account of the nature and distribution of the rocks and minerals that are or have been exploited in the past for economic purposes in the Lothians was given by MacGregor (1945) but this is out of print. It contains a valuable list of references to sources of information. A summary of this and more recent information, as far as they concern the Midlothian Coalfield, was given by Tulloch and Walton (1958). The following notes, relating to the whole area of the one-inch sheet, list the principal known workable materials and afford references to accounts which may be consulted if further study is intended.

Coal

Almost the entire output of coal in the Edinburgh district comes from the Limestone Coal Group and Productive Coal Measures of the Midlothian Coalfield, the only other workings being a few small undertakings in the Oil-Shale Group of West Lothian such as the pits working the Hurlet Coal at Baads Mains and Harwood near West Calder.

In the Midlothian Coalfield the important seams include the North, South, Bryans, Peacock, Blackchapel, Stairhead and Great in the Limestone Coal Group and the Fifteen Foot, Nine Foot, Salters, Cowpits Five Foot, Musselburgh Jewel, Rough and Splint coals of the Productive Coal Measures.

The most recent estimate of reserves in Midlothian was made in 1944 (Scottish Coalfields Committee 1944) and in the Limestone Coal Group, a total of 712 million tons was calculated with a possible additional 85 million tons not counting possible undersea areas. A further 184 million tons were thought to remain in the Productive Coal Measures. Two large new collieries at Bilston Glen, near Loanhead, and Monkton Hall north of Dalkeith, are at present under construction. Recent exploratory boring has included trial-bores sunk from the sea-floor off Musselburgh.

Oil-shale

The oil-shale industry, which is situated very largely in West Lothian in the country between Cobbinshaw, Blackness and Dalmeny, with small outlying centres at Straiton and Carlops in Midlothian, reached its maximum productivity in the early years of the present century with outputs of more than three million tons of oil-shale. It has since declined to 740,943 tons in 1950, produced at half a dozen mines and three opencast sites, of which three of the former and one of the latter are in the south of the West Lothian area near West Calder and the remainder in the north of that field. In the past, nine main oil-shale seams have been worked in the Upper Oil-Shale Group and there are two in the Lower Oil-Shale Group. At the present time (1959) the workings are in the Dunnet and Broxburn shales.

Mineral oil and natural gas

Borings put down for oil and gas along the crest and on the flanks of the D'Arcy–Cousland Anticline to the east of the Midlothian Coalfield were noted by Tulloch and Walton (1958, p. 134). One of them (Midlothian M₃) produces some oil; gas from the Anglo-Iranian Cousland No. 1 Bore is piped to Mussel-burgh to augment the town supply. A small amount of gas is given off by a third bore, Midlothian M₆. A recent account of the explorations for oil in the area by the British Petroleum Company, Limited is given by Falcon and Kent (1960, p. 39). The possibility of using the anticlinal structure as a large underground gas-holder, after the removal of most of the natural gas, has been mentioned by Ricketts and Elgin (1957, p. 1445).

Bedded ironstone

Ironstone present in mudstones as nodules or layers has been worked both in the Lower Limestone Group and the Limestone Coal Group in Midlothian (Tulloch and Walton 1958, p. 135). In particular a blackband ironstone in the former group was at one time worked at Gilmerton while the Loanhead Nos. 1 and 2 ironstones, respectively above the Bryans and the Gillespie coals, were wrought in the Limestone Coal Group. Another band, the Rumbles or No. 3 Ironstone above the Great Seam, was once much worked near Dryden between Burghlee and Roslin.

The area lies outside that of the main bedded ironstone industry of West Lothian in the Bo'ness district.

At the present time no ironstone is worked for its own sake, the only stone raised being produced in very small quantities during the working of coal seams.

Fireclay, shale (blaes) and clay

In the past seatclays have been worked for brickmaking at collieries in Midlothian including Ramsay, Roslin and Prestongrange in the Limestone Coal Group and at Whitehill in the Productive Coal Measures.

Shale has likewise been worked at Prestongrange, Newbattle and Arniston in the Limestone Coal Group and Newcraighall and Woolmet in the Productive Coal Measures. Material from colliery bings has also been utilized. These and other instances are mentioned by Tulloch and Walton (1958, p. 136).

In the neighbourhood of Winchburgh and East Calder the older small brickworks gave place to large works at Winchburgh, Camps and Ecclesmachan where the 'blaes' and boulder clay were excavated and mixed, but these are no longer working. The 'blaes' of Hailes Quarry, Edinburgh afford another example of a similar, now abandoned, brickfield.

Raised beach clays belonging to the 100-ft Beach were also formerly worked for brickmaking and roofing and draining tiles, some as at Blackness well over one hundred years ago. Other similar clays were dug at Portobello and Smeaton, two miles south of Musselburgh.

Finely laminated, stoneless glacial clays were worked in bygone days at Eskbank and Newtongrange.

Shale for honestones

Shale in the Lower Oil-Shale Group, hardened by proximity to a sill of quartz-dolerite, a little north of west of Ratho Hall was at one time quarried and wrought into honestones (Day and Tait 1928).

Limestone

The limestones of Mid and West Lothian are described in detail by Robertson and others (1949, pp. 139–48; 192–6). The majority of the workings are in the Carboniferous but one or two small quarries were formerly worked in the cornstones of the Upper Old Red Sandstone. Chemical analyses and petrographical details of many limestones are given by Muir and others (1956). At present limestone is mined at Guildyhowes near Borthwick and Harburn near West Calder as well as at Cousland and Clippens (Straiton). Quarrying continues at Guildyhowes and Esperston.

Ochre

It is reported that ochre was once worked at Bilston Burn, the parent rocks before the weathering which produced the deposit, being the Gilmerton and North Greens limestones (Hinxman in Peach and others 1910, p. 180).

Sandstone

By far the larger number of quarries providing building stone were in Carboniferous rocks but the industry is now defunct in the Edinburgh district though ample reserves remain. MacGregor (1945, p. 15) gives the following geological distribution of the more important of the old workings: Upper Old Red Sandstone 8; Calciferous Sandstone 30; Lower Limestone Group 10; Limestone Coal Group 28; Upper Limestone Group 13; Passage Group 3; Coal Measures 10. Among the most celebrated of these stones, which collectively provided a very large proportion of the building stone of Edinburgh and the other towns and villages in the neighbourhood, are the Binny, Dalmeny, Hermand, Hailes, Dunnet, Granton and Craigleith sandstones of the Carboniferous and the Craigmillar Sandstone of the Upper Old Red Sandstone. Many of these are described in detail (Peach and others 1910, pp. 356–61; MacGregor 1945, pp. 16–21; Tulloch and Walton 1958, pp. 137–9). Several particularly siliceous sandstones as those of Barnton Park, Craigleith, Ravelston and Binny have been used to manufacture stone wheels for glass-cutting. Other ganister-like sandstones in Midlothian have been tried for refractory purposes but do not appear to have been found satisfactory. Soft sandstones found in the Lower Limestone Group, Limestone Coal Group and Passage Group, also in Midlothian, have been used as moulding and glass sands.

Detailed references to all these occurrences are given by MacGregor (1945).

Igneous rock

The many igneous rocks in the area, particularly the sills in the western part of the ground, afford valuable sources of roadstone and, in the past, provided large numbers of stone setts and walling stones.

At present the great quarries at Torphin in the Lower Old Red Sandstone basalts are outstanding in that group but there are many disused quarries in similar rocks including the great Blackford Hill Quarry, and the Mortonhall Quarry, both in andesite.

The quartz-dolerite and teschenite sills, however, provide the majority of present quarries and include Braehead and Lenny near Cramond Bridge, as well as the Ratho group of workings and Craigton near Winchburgh — all in quartz-dolerite. Examples of quarries recently working teschenite and allied rock are Craigiehill near Dalmeny, and Barnton, while the Kaimes quarries near Kirknewton are worked to exploit the Dalmahoy type of dolerite.

Many rocks worked for roadstone are also used for concrete aggregate.

Sand and gravel

Sand and Gravel has been worked at many places within the Edinburgh region, the majority being confined to the Midlothian Coalfield where about a dozen pits are at present active. A summary of the known sand pits both working and disused was given by Haldane (1948). Tulloch and Walton (1958) have a map showing the principal deposits of sand and gravel in Midlothian and the sites of the recently working pits.

Peat

At the south end of the Midlothian Coalfield there are considerable areas of peat between Penicuik, Carlops, Leadburn and Gladhouse, the largest being Auchencorth Moss, which extends into the area of one-inch Sheet 24. A sample of peat from Side Moss, three miles south-west of Temple, was tested some years ago in connection with the extraction of ester waxes (Cawley and King 1946, p. 21). Other large deposits have been mapped near Cobbinshaw Reservoir, in the Pentland Hills west of West Cairn Hill and also at Kitchen Moss, south of Hare Hill. There are no workings of importance.

The deposits of Cobbinshaw and Auchencorth Mosses have recently been examined in detail by the Moss Survey Group of the Scottish Peat Committee (Scottish Home Department) and the following notes have been supplied by Mr. A. Tomter of that body. At Cobbinshaw over 2000 acres of moss were surveyed and the peat averages 13 ft in thickness with a range from 0 to 29 ft. It is estimated that the deposit contains some 26 million cubic metres of raw peat, composed largely of Sphagnum moss. The Auchencorth Moss covers some 3000 acres of which about 830 acres were surveyed. The latter portion contains about 9 million cubic metres of raw peat and the whole deposit may contain something of the order of 50 million cubic metres. The area not surveyed is mostly composed of very shallow peat, but in the surveyed part up to 31 ft were recorded; again the deposit is mainly formed from the remains of Sphagnum sp.

Shell marl and diatomite

MacGregor (1945) quotes a number of old records of shell marl, in places up to 20 ft thick, found in the now vanished lakes in the neighbourhood of Edinburgh, such as Corstorphine Loch, The Borough Loch (now 'The Meadows') and Holyrood Loch. Diatomite up to 14 in thick was discovered in 1925 at the edge of a peat-covered, marshy flat just south of Dalmahoy Hill, west of Balemo.

Water supply

By far the larger part of the water supplies of the Edinburgh district is derived from surface catchment areas with their attendant reservoirs, but a certain proportion is provided by boreholes and springs.

The more important reservoirs within the area of one-inch Sheet 32 include Glencorse, Loganlee, North Esk and Baddinsgill in the heart of the Pentland Hills, the two first named forming part of the Edinburgh supply, the last named serving West Lothian and North Esk supplying Penicuik paper mills.

On the northern slopes of the Pentland Hills, Clubbiedean, Torduff and Bonally are storage reservoirs for Edinburgh and draw much of their supply from numerous springs. In the same area are the important compensation reservoirs of Crosswood, Harperrig, Threipmuir and Harelaw. Another large reservoir in this district is Cobbinshaw, which is the property of British Railways.

A further source of water for Edinburgh and district is afforded by the supply reservoirs of Gladhouse and Portmore and the compensation reservoirs of Rosebery and Edgelaw on the north-western slopes of the Moorfoot Hills.

These supplies are, however, greatly augmented by the large Talla Reservoir outside the present area, in the Southern Uplands in the upper reaches of the Tweed Valley which, with its attendant auxiliary supplies from neighbouring valleys, is the largest of the Edinburgh reservoirs.

Among important springs is the Crawley Spring near Loganlee which yields some half a million gallons of water daily.

Of supplies obtained from borings, the Upper Old Red Sandstone and the sandstone of the Oil-Shale groups and the Lower Limestone Group furnish many examples. The yields from the Cementstone Group are not high and the water is hard, a characteristic also shown by waters from the Limestone Coal Group as well as those of the Upper Limestone Group, though in this case yields are greater. The Passage Group and the Coal Measures have also furnished valuable supplies and the highest yield in Scotland was probably given by a borehole in the Productive Coal Measures at Inveresk, near Musselburgh, which provided 60,000 gall per hour on test.

Details of water supplies drawn from boreholes are given by MacGregor, Allan and Lawrie (1942) and MacGregor (1945, p. 36) and a summary of many of the more important bores is included in Appendix I (p. 133). G.H.M.

References

CAWLEY, C. M. and KING, J. G. 1946. The Extraction of Ester Waxes from British Lignite and Peat. Fuel Research Board. Technical Paper No. 52.

DAY, T. C. and TArr, D. 1928. An old Hone-Stone Quarry near Ratho. Trans. Edin. Geol. Soc., 12, 122–3.

FALCON, N. L. and KENT, P. E. 1960. Geological Results of the Petroleum Exploration in Britain 1945–57. Mem. Geol. Soc. London, 2.

HALDANE, D. 1948. Sands and Gravels of Scotland. Quarter-Inch Sheet 15; Fife‑The Lothians-Berwickshire. Geol. Surv. Wartime Pamphlet No. 30, pt. 4.

MACGREGOR, A. G. 1945. The Mineral Resources of the Lothians. Geol. Surv,. Wartime Pamphlet No. 45.

MACGREGOR, A. G., ALLAN, J. K. and LAWRIE, T. R. M. 1942. Water Supply from Underground Sources of South-East Scotland (Quarter-Inch Geological Sheet 15): Well Catalogue for One-Inch Sheet 32 (Lothians Portion). Geol. Surv. Wartime Pamphlet No. 28, pt. 2.

MUIR, A., HARDIE, H. G. M., MITCHELL, R. L. and PHEMISTER, J. 1956. The Limestones of Scotland, Chemical Analyses and Petrography. Mem. Geol. Surv., Min. Resources, 37.

PEACH, B. N., CLOUGH, C. T., HINXMAN, L. W., GRANT WILSON, J. S., CRAMPTON, C. B., MAUFE, H. B. and BAILEY, E. B. 1910. The Geology of the Neighbourhood of Edinburgh. 2nd edit. Mem. Geol. Surv.

RICKETTS, T. S. and ELGIN, D. C. 1957. Natural Gas in Scotland. Nature, 180, No. 4600, 1444–5.

ROBERTSON, T., SIMPSON, J. B. and ANDERSON, J. G. C. 1949. The Limestones of Scotland. Mem. Geol. Surv., Min. Resources, 35.

SCOTTISH COALFIELDS COMMITTEE. 1944. Scottish Coalfields, The Report of the Scottish Coalfields Committee. Scottish Home Department.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Appendix 1. Table of principal wells and boreholes for water in sheet 32

(EDINBURGH)

The standing water levels and yields are generally those measured at the time the wells and boreholes were sunk. The levels and yields in many vases may have diminished.

Appendix 2 Table of fossils collected by the Geological Survey from mudstones and siltstones of the North Esk Silurian Inlier–1950–59

(Beds 'D' to 'H' of Henderson and Brown (1867) only)

Appendix 3 Recent borings in the Midlothian Coalfield

Since the publication of the Memoir on the Midlothian Coalfield (Tulloch and Walton 1958) a number of important borings have yielded valuable information. Notes on the geological results are given in this appendix.

Esk Mouth Bore

The Esk Mouth (No. 50/56) Bore, sited on the west bank of the River Esk, 230 yd W. of the Gasworks at Musselburgh, was in progress while the recent Memoir on the Midlothian Coalfield (Tulloch and Walton 1958) was being prepared, and though the higher horizons are mentioned, an account of the strata passed through in the lower part of the boring is not included.

The base of the Productive Coal Measures was cut at 1298 ft 4 in, and the underlying Passage Group was found to be 549 ft 8 in thick. A most unusual feature was the occurrence, 178 ft 7 in from the top of the Passage Group, of a thick coal seam, with the following section: coal 1 ft 9 in; parting 9 in; coal 9 ft 3 in; coal with thin partings 1 ft 10 in; seatclay and shale 2 ft 5 in; on coal 2 ft 8 in.

The Upper Limestone Group was 815 ft 9 in thick, with a 60-ft fault in the lower part. The Castlecary Limestone is thought to be missing in the shore section at Westpans, about 1 mile east of the bore-site (Tulloch and Walton 1958, pp. 76, 80), but it is interesting to record that this limestone was found to be well developed in the boring. The Limestone Coal Group was 704 ft 11 in thick, with a good development of coal seams, and the Top Hosie Limestone, in the Lower Limestone Group was 6 ft 6 in in thickness, the lower 1 ft 2 in being sandy.

Levenhall bores

During 1957 and 1958 a number of bores were put down by the National Coal Board near the shore in the Levenhall area, east of Musselburgh, to prove the lower part of the Productive Coal Measures and the upper part of the Passage Group. Three of these bores, Levenhall Nos. 69, 70 and 71, passed through a thick coal in the upper part of the Passage Group, on the same horizon as the coal proved in Esk Mouth Bore. In Levenhall No. 71 Bore, sited 0.75-mile S. of E. of the mouth of the River Esk the section of this coal was: coal 1 ft 9 in; shale, carbonaceous 2 in; coal 6 ft 8 in; seatclay 1 ft 10 in; coal 2 ft 10 in. About 233 ft below the coal a limestone with the following section was cut: limestone, grey, nodular 6 in; mudstone, calcareous, with small limy nodules 3 in; on limestone, grey with argillaceous streaks 2 ft 6 in. This is thought to be the Castlecary Limestone, and if this is so the Passage Group in this bore is about 192 ft thinner than in the Esk Mouth Bore 0.75-mile to the west.

The thick coal in the upper part of the Passage Group was again found in three bores put down by the National Coal Board in 1958 in the Pinkieburn–Barbachlaw area, S.E. of Musselburgh.

Offshore bores

During 1957 and 1958 three bores were put down by the National Coal Board off the Midlothian coast between Portobello and Musselburgh, to explore the structure and succession in that part of the undersea coalfield. The drilling-rig used was a specially constructed tower from which three bores were sunk off the Fife coast between 1955 and 1957 (Ewing and Francis 1960A, 1960a).

No. 1 Bore

No. 1 Bore, sited about 2.25 miles W. of N. of Musselburgh, reached a depth of 4557 ft 6 in. Coring began at 1003 ft 8 in in strata near the top of the Productive Coal Measures and apart from a number of relatively small faults, a complete succession was proved to the North Coal near the base of the Limestone Coal Group. The bore continued for 79 ft 8 in below this coal, but the Top Hosie Limestone was not found.

Productive Coal Measures

The total thickness of Productive Coal Measures was 1392 ft 8 in. The exact stratigraphical position at which coring began is uncertain; about 70 ft below the top of the cored part two coal-seams were encountered, approximately 13 ft apart; the upper coal was overlain by shale with small Lingula and the lower by shale with small Lingula and Orbiculoidea. These fossil bands may be on the same horizon as the two Lingula bands found about 20 ft below Skipsey's Marine Band in Dalkeith No. 49 Bore (Tulloch and Walton 1958, p. 113). The strata between the lower of the two coals and the Splint Coal were found to include numerous thin coal seams and a number of mussel bands, a development unusual in the Midlothian Coalfield. The Queenslie Marine Band was passed through at 1743 ft, and the base of the Productive Coal Measures at 2396 ft 4 in. This interval is slightly larger than in the Esk Mouth Bore, and 86 ft greater than in Monkton House No. 37 Bore. A good development of coals was found in this part of the succession.

Passage Group

The Passage Group was 619 ft 3 in thick, some 64 ft greater than in the Esk Mouth Bore, and almost the same as in Monkton House No. 37 Bore. The thick coal in the upper part of the group was passed through at 2592 ft 3 in, the section of the coal being: coal in 8 leaves 6 ft 7 in; parting 4 in; coal 2 ft 10 in; parting 3 in; coal 7 ft 7 in; seatclay 1 ft 11 in; on coal, foul 8 in.

Upper Limestone Group

The Upper Limestone Group strata were 762 ft 11 in thick (with a fault of about 40 ft throw in the upper part), as compared with 815 ft 9 in in the Esk Mouth Bore, and 898 ft in the Monkton House Bore; the Castlecary and Calmy limestones, the Orchard Beds and the Index Limestone were all present in the boring.

Limestone Coal Group

The exact thickness of the Limestone Coal Group in the Off-shore Bore is uncertain because the Top Hosie Limestone was not found; a sandstone 78 ft + thick was cut just below the North Coal, the horizon of the Top Hosie Limestone probably lying near the top of this sandstone. The interval between the base of the Index Limestone and the base of the North Coal was 699 ft 4 in, as cOmpared with 686 ft in Esk Mouth Bore. The section of the Great Seam, cut at 3926 ft 7 in, was: coal 2 ft 9 in; seatclay and fakes 3 ft 4 in; on coal 1 ft 7 in. The Stairhead Coal, 20 ft lower in the succession, was in two leaves as follows: coal 2 ft 2 in; parting 5 in; on coal 8 in. The Calpatie Coal at 4095 ft 7 in was 2 ft 7 in thick, and Bryans Coal, at 4253 ft 9 in was 3 ft 5 in thick. The remaining coals were much thinner than those found in the Esk Mouth Bore.

No. 2 Bore

Sited between 1.5 and 1.75 miles N.W. of Musselburgh and 0.75-mile S.W. of No. 1 Bore, the total depth of No. 2 Bore was 527 ft 10 in; coring began at 216 ft, and the dip of the beds was found to be 75–89°. Seatclay, sandy shale and shale were passed through, in addition to two thin coals, and a Lingula band was encountered at a depth of 332 ft 7 in.

No. 3 Bore

The third Off-shore Bore was sited about 0.25-mile E.S.E. of No. 2. Coring began at 600 ft and continued to 857 ft; from this point to a depth of 1292 ft drilling was by rock-bit, and from 1292 ft to the final depth of 2359 ft 2 in by coring. The strata passed through from 600–857 ft belonged to the upper part of the Productive Coal Measures; the Queenslie Marine Band was cut at 1395 ft 3 in. The interval from the Queenslie Marine Band to the base of the Productive Coal Measures was 737 ft 2 in, and the Cowpits Five Foot Coal, Salters Coal and the Nine Foot, Pinkie Four Foot and Seven Foot coals were all well developed.

The thick coal in the upper part of the Passage Group was cut at 2343 ft 11 in; the section was: coal 1 in; parting 7 in; coal 1 ft 11 in; seatclay 5 in; coal 1 in; parting 6 in; coal 6 in; seatclay 4 in; coal 2 ft 9 in; seatclay 4 in; coal 1 ft 1 in; seatclay 5 in; coal 1 ft 6 in; parting 4 in; coal 3 ft 1 in; parting 7 in; coal 2 ft 8 in; parting 4in; coal 1 ft 7 in; seatclay 1 ft; on coal 2 ft 10 in. w.T.

References

EWING, C. J. C. and FRANCIS, E. H. 1960A. Nos. 1 and 2 Off-Shore Borings in the Firth of Forth (1955–1956). Bull. Geol. Surv. Gt. Brit., 16, 1–47.

1960a. No. 3 Off-Shore Boring in the Firth of Forth (1956–1957). Bull. Geol. Surv. Gt. Brit., 16, 48–68.

TULLOCH, W. and WALTON, H. S. 1958. The Geology of the Midlothian Coalfield. Mem. Geol. Surv.

Appendix 4 List of Geological Survey photographs (one-inch Sheet 32) Taken by Messrs. R. Lunn, W. Manson and W. Fisher

Copies of these photographs are deposited for public reference in the library of the Geological Survey, South Kensington, London, S.W.7 and in the library of the Scottish Office, 19 Grange Terrace, Edinburgh, 9. Prints and lantern slides are supplied at a fixed tariff on application to the Director.

Figures and plates

Figures

(Figure 1) Six-inch Geological sheets included in one-inch Geological Sheet 32 (Edinburgh).

(Figure 2) Sketch map showing main physical features and distribution of principal rock-groups in the area.

(Figure 3) Generalized section of the sedimentary and volcanic rocks of the Edinburgh district.

(Figure 4) The North Esk Silurian Inlier.

(Figure 5) Geological sketch map of the northern part of the Pentland Hills.

(Figure 6) Diagram illustrating the extent and approximate variation in thickness of the lava groups of the Pentland Hills.

(Figure 7) Geological sketch map of the Old Red Sandstone and Lower Carboniferous strata on the north-west of the Pentland Hills. (For explanation of (i)-(v) see text.)

(Figure 8) Outcrops of the Cementstone Group and generalized section in Central Edinburgh.

(Figure 9) Outcrops, successions and suggested correlation of the Lower Oil-Shale Group

(Figure 10) Horizontal section across Arthur's Seat.

(Figure 11) Sketch map showing probable distribution of rocks of Lower Oil-Shale Group in the vicinity of Edinburgh.

(Figure 12) Sketch map showing probable arrangement of Granton Sandstones in the Granton Dome.

(Figure 13) Suggested succession and correlation of boreholes in the Granton Sandstones.

(Figure 14) Generalized section of the Wardie Shales.

(Figure 15) Queensferry Beds: typical sections and suggested correlations.

(Figure 16) Upper Oil-Shale Group: generalized section in West Lothian.

(Figure 17) Outcrop of the Lower Limestone Group and representative vertical sections.

(Figure 18) Limestone Coal Group of Carriden and Loanhead.

(Figure 19) Representative sections of the upper beds of the Carboniferous.

(Figure 20) Carboniferous lavas, tuffs and vents of the Edinburgh district.

(Figure 21) Map of principal Folds and Faults.

(Figure 22) Contour Map of the Great Seam and the Nine Foot Coal.

(Figure 23) Contour Map of the Burdiehouse Limestone in West Lothian.

(Figure 24) Outcrops and horizons of Igneous sills intruded in Carboniferous sediments

(Figure 25) Pre-Glacial topographical .features.

(Figure 26) Glacial striae and crag-and-tail features indicating direction of ice-movement.

Plates

(Plate 1) Arthur's Seat and Salisbury Craigs from Calton Hill. The twin vents of the Lion's Head and the Lion's Haunch occupy the centre of the photograph in the distance with the great teschenite sill of Salisbury Craigs running right across the view in the middle distance. At the top of the old quarry at the left hand end the Cementstones overlying the sill are visible. The left third of the picture is occupied by the lavas and tuffs of Whinny Hill, the lowest lava forming the prominent line of cliffs near the base, called The Long Row. (D475)-(D476)

(Plate 2) Sketch map showing the distribution of the volcanic rocks of Arthur's Seat and Calton Hill.

(Plate 3) Outcrop and typical sections of the Upper Oil-Shale Group.

(Plate 4) Map showing Fluvio-glacial deposits, ice-retreat features and raised beaches.

(Front cover)

(Rear cover)