Survey Memoir Research Articles

Seismic Velocities Measured in Rocks of the Troodos Igneous Complex

Summary The Troodos igneous complex of Cyprus is an ophiolite body composed of ultramafics, gabbros, dolerites and pillow lavas. Seismic velocities measured in these rocks were expected to be similar to- those in the layers under the deep ocean. Seismic experiments made in the field in individual rock types revealed only low velocities typical of deep sea layer 2. We suggest that the low velocities are due to high porosity in the shattered rocks. Geophysical field work was carried out during March 1971, in order to measure the seismic velocities at outcrop of the rocks of the Troodos igneous complex. The aim of the experiment was to compare the velocities obtained with those of the oceanic crust already established by marine seismic refraction work. Financial support for the expedition came from I.B.M. (U.K.) Ltd grants to the University of Cambridge. A preliminary account of the results has already appeared (Matthews etal. 1971). The Troodos Massif is believed to be a fragment of Mesozoic oceanic crust which has been thrust up on land during the northerly movement of the African plate towards Europe (Gass & Masson-Smith 1963; Gass 1968). The Massif occupies the central and south-eastern part of the island (Fig. 1); the ultramafics form the domed central circular outcrop around the summit of Mt Olympus at 6403ft, and are pierced by a serpentinite diapir. The rocks belong to an igneous suite characteristic of ophiolite complexes, and comparable petrologically with rocks dredged from the deep ocean floor (Moores & Vine 1971). The plutonic members range from dunites, harzburgites and pyroxenites to olivine gabbros, gabbros and quartz diorite and are ringed by the Sheeted Complex which is a swarm of steeply dipping altered basic dykes, without intervening screens, possibly formed by sea floor spreading. The Pillow Lavas occupy the outer margin of the oval outcrop pattern, and are divided into Upper Pillow Lavas with few dykes and Lower Pillow Lavas with abundant basic dykes, separated by an unconformity recognizable in only a few places. Moores and Vine classify the rocks into 3 units: Pillow Lavas, Sheeted Complex and Plutonic Complex, and these are used for the purposes of the following discussion rather than the more complicated scheme of the Cyprus Geological Survey. They suggest that a correlation may be made with rocks of the oceanic crust and upper mantle. Experimental work was carried out after careful site selection, using the geological maps of the Survey memoirs (see Appendix), and the detailed field knowledge of Drs I. G. Gass and F. J. Vine. With three exceptions all the lines were shot using the

Ordnance Survey Memoir for the Parish of Antrim : a description compiled as part of the field survey for the first edition of the six inch ordnance survey maps, and edited and illustrated by James Boyle of the Ordnance Survey, 1838. With an introduction to the ordnance survey parish memoirs, 1830–40, by Brian Trainor. Pp xlii, 109. Belfast: Northern Ireland

Ordnance Survey Memoir for the Parish of Antrim : a description compiled as part of the field survey for the first edition of the six inch ordnance survey maps, and edited and illustrated by James Boyle of the Ordnance Survey, 1838. With an introduction to the ordnance survey parish memoirs, 1830–40, by Brian Trainor. Pp xlii, 109. Belfast: Northern Ireland Public Record Office. 1969. 25p. - Volume 17 Issue 67

The sedimentation and geotechnical properties of the Cromer Till between Happisburgh and Cromer, Norfolk

Summary The cliff-section between Happisburgh and Weybourne, on the north Norfolk coast, provides one of the most representative exposures of glacial sediments in the British Isles and this sequence is now generally accepted as being the product of the Lowestoft Stage. The Cromer Till, as defined in the Geological Survey Memoir , forms the lowermost part of the glacial sequence and is composed of two tills separated by a layer of laminated silts and clays; these units may be termed as follows:The Lower Cromer Till is a dense, stiff, fissured grey or dark grey sandy boulder clay which lies on the Cromer Forest Bed, the Leda Myalis Beds and the associated deposits. The Laminated Beds rest on the hummocky, locally faulted, surface of the till. At Happisburgh two divisions of laminated sediments have been recognized, the upper unit being finer-grained and having a more evenly-bedded structure. The Upper Cromer Till is a dense, fissured grey-blue sandy boulder clay containing a significant proportion of chalk pebbles. The sequence within the Cromer Till represents the three phases of an ice advance followed by retreat associated with the development of a glacial lake followed by a re-advance. The coarse-grained lower unit of the Laminated Beds at Happisburgh is not present at Cromer and this may reflect the early history of the glacial lake while ice was still present in the vicinity of Cromer. The upper unit of the Happisburgh sequence is coarser than that at Cromer and this condition is reflected by variations in liquid limit measured on scrape samples. A wide range of sedimentary structures, which have been formed by traction and fall-out processes associated with turbulent suspension, occur within the Laminated Beds. The associations of structures present are the product of specific bed forms and can be related to flow régimes. Many beds are the result of rapid deposition from turbidity currents. All the sediments studied have been heavily over-consolidated and are fissured to a greater or lesser degree. Disturbed, block and scrape samples were collected in the field and soil mechanics classification, strength and consolidation tests carried out. Particular attention has been given to different methods of assessment of the effects of pre-consolidation load and the variation in properties of the Laminated Beds with orientation. The influence of the pre-consolidation load has been examined by a field study of fissuring in the Laminated Beds based upon the dissection of excavated blocks, undrained and drained shear-box testing of samples taken from the Lower Cromer Till and consolidation testing of samples from the Laminated Beds to estimate the pre-consolidation load. This study has revealed that the strength of the Lower Cromer Till is significantly greater near Cromer than at Happisburgh. In addition, the pre-consolidation loads at Cromer are equivalent to an ice thickness of some 300 ft above the present level of the top of the Cromer Ridge as compared with a possible ice thickness of about 200 ft at Happisburgh. The fissure measurements tend to confirm the previous studies of pebble and fold-axis orientation in that the direction of ice movement was probably slightly south of east. The geological and geotechnical evidence, therefore, together provide a picture of an ice sheet moving and thinning towards the east and south-east.

Discussion

Dr G. P. B lack referred to the author’s interest in the structure of the ring-complex. There had been an unfortunate tendency for petrologists to class all masses of igneous rock that had even the merest semblance of an arcuate outcrop as ring-dykes without considering the need to apply further criteria. The literature of ring-complexes showed that the rock masses described as ring-dykes fell readily into two contrasted types. Characteristics generally shown by the first type included narrow, annular, or highly arcuate outcrops, contacts everywhere with older rocks, and steeply inclined or vertical junctions whose attitude could be determined with confidence. Such masses seemed invariably to be acidic in composition. The Loch Ba felsite of Mull—the ‘holotype’ of all ring-dykes—belonged to this type, as did many examples described from Nigeria. Members of the second type formed a less well-defined group but all showed a majority of a number of features, including crescentic or irregular outcrops often of considerable breadth, contacts with younger intrusions on one or more margins so that the original form of outcrop could not be determined, and junctions that were so poorly denned or so poorly exposed that their attitude could not be ascertained. The members of this type were generally of basic composition. The best assemblage of examples came from the Ardnamurchan complex where almost all of the thirty-two ‘ring-dykes’ listed in the Geological Survey memoir (Richey & others 1930, pp. 201–2) fell into this type. Even the Great Eucrite, despite its annular outcrop,

VIII.— The Islay — Jura Dyke Swarm

1. Introduction Portions of the Islay—Jura dyke swarm have been dealt with petrographically in the Geological Survey Memoirs covering sheets 19, 27 and 28. In the Knapdale Jura and Kintyre memoir, Flett (1911, p. 117) coined the term “crinanite” for the ophitic analcite-olivine-dolerites so abundantly represented in the area, but it is perhaps unfortunate that the name indicates their occurrence round Crinan — that is in the Mull swarm — whereas the analysed type rock was taken from Jura and is a member of the Islay—Jura swarm. A more general treatment of the swarm was given by Tyrrell (1928, pp. 238-239) who considered that the Islay—Jura swarm was connected with a plutonic focus in Arran in spite of the gradual diminution in the number of dykes in the direction of that island. McCallien (1932, pp. 52-55) suggested that on the other hand the Arran swarm should be divided into (1) the Islay—Jura swarm consisting almost entirely of crinanites and olivine dolerites and (2) the Arran swarm, which is compound and associated with more than one centre. He suggested further that the focus of the Islay—Jura swarm may be N.W. of Islay since the dykes become more numerous in that direction, but that the complex Arran swarms comprising crinanitic and tholeiitic injections of different ages, has two centres, one being North Arran and the other (dominantly tholeiitic) to the south of the island. Richey (1939, p. 425) in his comprehensive survey of the dykes of Scotland, accepts McCallien’s suggestion as to This 250-word extract was created in the absence of an abstract

III.— The Petrology of the Ben Vrackie Epidiorites and their Contact Rocks

I. HISTORY OF PREVIOUS WORK AND GEOLOGICAL SETTING Ben Vrackie (2,757 feet) is a conspicuous hill in the Perthshire Highlands, about two and a half miles east of the Pass of Killiecrankie. The country rocks belong to the Dalradian series, and are in the garnet zone of metamorphism. The stratigraphical succession in the district was elucidated by Bailey (1925, p. 673 and 1930, p. 90). Within the Dalradian series, there occur a number of metamorphosed basic intrusions known as epidiorites and such rocks are well-developed at Ben Vrackie. The epidiorites at this locality and their contact rocks were described by Barrow and others in the Geological Survey memoir on the Blair Atholl, Pitlochry and Aberfeldy district (1905, pp. 77, 79). Wiseman, following his study of the progressive metamorphism of epidiorites, remapped most of the area at Ben Vrackie where such rocks are found. The present map (Fig. 1) incorporates his work, and extends it for short distances to the east and south. The northern part of the map area is largely occupied by epidiorite and Ben Lawers Schists. In the east, the outcrop of the latter formation joins the main belt of Ben Lawers Schists, which runs north-east and south-west, and crosses the Ben Vrackie massif about half a mile south-east of the summit. On the north, west and south, the northern area of Ben Lawers Schists is bounded by an extensive development of the Ben Eagach Schist, with some epidiorite and quartzite. These rocks are involved in folding on This 250-word extract was created in the absence of an abstract In conclusion, the writer wishes to express his thanks to Professor C. E. Tilley, Dr. S. R. Nockolds and Professor K. C. Dunham, under whose guidance the work was carried out. He further wishes to thank Professor T. Neville George and Dr. B. C. King for helpful criticism of the script. The writer is greatly indebted to Dr. J. D. H. Wiseman for access to field maps covering the greater part of Ben Vrackie, and for the loan of rock specimens and thin sections. Finally, he desires to thank Trinity College, Cambridge, for the tenure of the Lees Knowles Exhibition during the first two years of the work.

XXV.— The Liassic Sequence in Morvern

1. General Account The sedimentary succession in Morvern, ranging in age from Carboniferous to Cretaceous, has been described in the Geological Survey Memoir on “The Pre-Tertiary Geology of Mull, Loch Aline and Oban” (Lee and Bailey, 1925). Later contributions to the study of these rocks have been made by Scott (1928), Lee and Pringle (1932), Macgregor and Manson (1934; Carboniferous only) and Richey (1935). The Jurassic is represented by beds of Lower Lias age only, but these are well-developed and on the basis of ammonite remains the Survey has established in them the existence of the following zones: rotiforme, bucklandi, semicostatum, birchi and obtusum. The presence of the birchi zone, somewhat tentatively indicated in the Survey Memoir (p. 79), has been confirmed by the evidence of fossils recently obtained by the present writer. The Lias of Morvern which, like other Mesozoic rocks in the West of Scotland, owes its presence to the protection of Tertiary lavas and to some extent to faulting, is irregular in its distribution and varies considerably in thickness over short distances; it attains locally a maximum thickness of a little over 200 ft. The succession is divided by the Survey on a lithological basis into a lower series of alternating limestones and shales, the Broadford Beds, and an upper series of shales, sandy shales and shaly sandstone known collectively as the Pabba Beds. The most complete section is that seen in the Allt Leacach on the east side of Loch Aline (Figs. 1 and 2). In This 250-word extract was created in the absence of an abstract

South African Plants

The Genera of South African Flowering Plants By Dr. E. Percy Phillips. (Union of South Africa: Department of Agriculture, Division of Botany and Plant Pathology: Botanical Survey Memoir No. 25.) Second edition. Pp. xi + 923. (Pretoria: Government Printer, 1951.) 40s.

The Geology and Mineral Resources of the Fraser's Hill Area, Selangor, Perak, And Pahang, Federation of Malaya, with an Account of the Mineral Resources. By DrF. W. Roe. pp. ix + 138, with coloured map. Geol. Survey (Federation of Malaya) Memoir 5. 1951. Price 6 dollars (Straits).

The Geology and Mineral Resources of the Fraser's Hill Area, Selangor, Perak, And Pahang, Federation of Malaya, with an Account of the Mineral Resources. By DrF. W. Roe. pp. ix + 138, with coloured map. Geol. Survey (Federation of Malaya) Memoir 5. 1951. Price 6 dollars (Straits).

Dr. J. G. C. Anderson

DR. J. G. C. ANDERSON, of the Geological Survey, who is to succeed Prof. A. H. Cox as professor of geology at University College, Cardiff, received his early training under Sir Edward Bailey at Glasgow. After graduating, he carried out postgraduate research, obtaining a Ph.D. in 1935. During his stay at Glasgow he was awarded the Mitchell Trust Bursary in science, and the Mackinnon Scholarship in geology. He was appointed to the Scottish Office of the Geological Survey in 1937, and worked for a time on routine work in the west of Scotland. When the outbreak of war interrupted normal Survey work, Dr. Anderson, in common with other members of the staff, undertook a series of investigations into the mineral resources of Scotland, the results of which were published in emergency wartime pamphlets. Among the materials investigated by Dr. Anderson were sands and gravels, silica rocks, limestone, oil shale and talc ; and he was also the principal author of a Survey memoir on the Scottish granites. Apart from these official activities, Dr. Anderson has published a number of papers dealing especially with the igneous intrusions of the west of Scotland, and with the geology of the Dalradian rocks of the Highland Border region. Latterly he has extended his researches to the crystalline rocks of- the west of Ireland, and has recently published an important paper on. the Moinian rocks of Donegal.

Memoirs of the Geological Survey of Great Britain

THE Lizard district had long been famous as a field of geological research and controversy prior to the publication in 1912 of the Geological Survey Memoir on it, and on many of its petrological, structurah and stratigraphical problems there was scarcely a general consensus of opinion. This second edition, by the late Sir John Flett, one of the original authors, reveals him in the full maturity of his scientific judgment and mental vigour. It has been entirely rewritten after a re-examination of the area that, followed his retirement from the directorship of the Geological Survey in 1935. Many will visualize in these accounts of the cliffs and exposures "alongside the path leading from the hotel to the beach" that powerfully built figure with deliberate step and penetrating all-embracing eye.

VIII.— Note On Spathulopteris decomposita (Kidston)

The purpose of this note is to place on record the finding of a specimen of Spathulopteris decomposita (Kidston) in the Calciferous Sandstone Series of East Fife. It was obtained by the writer from a bed of sandstone in the cliff section midway between Pittenweem and Anstruther. According to J. W. Kirkby’s detailed table of the strata seen along this part of the East Fife coast, published in the Geological Survey Memoir on East Fife (1902, pp. 77 seq. ), the sandstone bed lies more than 2000 ft. below the Hurlet Limestone. The plant was first described by Kidston in 1883 as Sphenopteris decomposita (Kidston), in the Transactions of the Royal Society of Edinburgh, vol. xxx, p. 538 and Plate xxxii, Figs. 1, 4 and 5. In Volume II, Part II (1923) of the same author’s “Fossil Plants of the Carboniferous Rocks of Great Britain” it is described and figured under the name of Spathulopteris decomposita (Kidston), page 178, Plate xliii, Fig. 7, and Plate xliv, Figs. 2-4. In the list of plant-remains published in the East Fife memoir (pp. 358-360) Sphenopteris decomposita is not recorded, nor is it mentioned under its present designation. Spathulopteris decomposita (Kidston) has been found at a few localities, but is described as rare and as characteristic of the Oil Shale Group of the Calciferous Sandstone Series. The localities are: Oil Shale Group at West Hermand, West Calder; Wardie Shales near Edinburgh; at Cot Castle, Strathaven, a few fathoms below the Hurlet Limestone; in the River This 250-word extract was created in the absence of an abstract

The Geological Structure of Wirral

The rocks of the Wirral Peninsula in Cheshire were originally described by John Cunningham in 1839, as three series, two moderately resistant to the east and the west, separated by a central region of soft sandstones and marls, dipping uniformly eastwards. G. H. Morton noted this in 1872, as a good description of the strata, ignoring faults, and pointed out the significance of the faulting. Since that date the faults have been mapped in great detail, and most of the structural features ascribed to them. G. H. Morton was particularly accurate with his mapping of faults both in Liverpool (1899), and in Storeton (G. H. Morton, 1883, and H. C. Beasley, 1914). The folding finds its first mention in the Geological Survey Memoir of 1923, two elongated synclines being mentioned, one from Heswall northwards and the other from Storeton to Prenton. The former is undoubtedly an important synclinal feature, but the latter is made up of two folds, a north to south anticline at Storeton, and an east to west syncline at Prenton. The only other records of folding in Wirral are by F. T. Maidwell in 1920 and by T. A. Jones in 1937, who mention an anticline at Ellesmere Port. This paper is therefore chiefly devoted to a description of the folding in the area.

An account of the struy lead mines, Inverness-shire, and of wulfenite, harmotome, and other minerals which occur there

The Struy lead mines (Six-inch ordnance Survey, Inverness-shire, sheet 17) are situated on the west side of Strath Glass, about two miles south-west of Struy village, and comprise three distinct sets of small long-abandoned workings, two of them being in the nature of trials only. All three workings are shown on the six-inch map, and are on veins traversing the Moine schists. The Geological Survey Memoir of the district says that four veins may be traced on the hill face between the Dùn south of Struy school and Crelevan; if this is correct there are two outcrops I have not seen. The mines are on what was until a few years ago part of Lord Lovat's estate. The date of their discovery is not known, but they were apparently worked about the year 1818 by Thomas Alexander Fraser (afterwards 12th Lord Lovat) at the same time as his graphite mine in Strath Farrar; most of the work seems, however, to have been done by him between 1838 and 1845, when miners were brought from England and housed in cottages specially built for them in Struy village. In 1864 the Loch na Mèine workings were cleared and prospected, but since then no further work has been done.

Geological Survey (Scottish Office) Dr. Murray Macgregor

THE retirement of Dr. Murray Macgregor during the past autumn brings to a close a long and eventful term of office in charge of the Geological Survey in Scotland and north-east England. On joining the staff in 1909, Dr. Macgregor was stationed at Edinburgh, and in 1921 succeeded the late Mr. L. W. Hinxman as district geologist for the Central Coalfield and Northern Highlands; and in 1925 he was appointed assistant director for Scotland. Dr. Macgregor has rendered signal service both in organizing and personally conducting geological investigations for industrial developments in Scotland. He will, however, be remembered especially for the close contact which he maintained with those engaged in the coal-min ing industry. In addition to his many contributions to the economic geology of the coalfields in Survey memoirs he has written a comprehensive account of Scottish Carboniferous stratigraphy, which was published by the Geological Society of Glasgow in 1930. During the past twenty years a large programme of normal survey work was carried out under Dr. Macgregor's guidance. The first revision of the Scottish and Northumberland Coalfields was completed, as well as a second revision of a large part of the Central and Lothians Coalfields and the oil-shale field of the Lothians. Up to the outbreak of war in 1939, striking progress had also been made with the primary survey in several areas in the Highlands and Islands. During the war years the activities of Dr. Macgregor and his staff were concentrated upon economic aspects of geology, related to the War itself and to reconstruction. A number of special investigations were carried out at the request of several ministries and to meet various industrial needs. Among these may be mentioned a detailed examination of Scottish limestones, mainly for agricultural purposes, a search for feldspar, silica-rock, mica and iron ore, surveys of underground water resources and of areas for open-cast coal production, and an investigation of building materials, including slates, brick-clays and granite.

Geological Survey (Scottish Office) Mr. T. H. Whitehead

DR. MURRAY MACGREGOR is succeeded at Edinburgh by Mr. T. H. Whitehead, who joined the Geological Survey in 1914. During the First World War he served in the Suffolk Regiment, reaching the rank of captain, was severely wounded and afterwards was appointed to the Intelligence Staff. Among his important published work is the Geological Survey memoir on the South Staffordshire Coalfield, in which he collaborated with T. Eastwood, now assistant director in England; other memoirs of which he is a principal author are those on Coventry, Birmingham, Stafford, Wolverhampton and Shrewsbury. In 1933 he was transferred to the Manchester branch office, and from 1935 until it was closed in 1938 he was in charge of that at York. During the War he has been the district geologist responsible for urgent revision work on the coal and other resources of the Midlands, and for the six-inch survey, now completed, of all the Jurassic and Cretaceous iron-ores south of the Humber. Whitehead's judicial mind and terse clarity in argument are acknowledged and admired by his colleagues of the Survey and Museum, whom he has served well both as counsellor and advocate, and by his fellow-members of the Council of the Geological Society. These qualities, coupled with his extensive and intimate knowledge of British geology and its economic applications, make him admirably suited for his new post.

The glaciation of the Highland Border district of south-eastern Perthshire

Introduction. The purpose of this paper is a study of the late Glacial stages in the retreat of the last ice to occupy the area along the border of the Highlands from the River Isla in the east to the River Tay in the west. The last ice seems to have been of ice-sheet form emanating from an ice-centre in the south-west and it is the retreat of this ice mass, south-westward along Strathmore, with its consequent division along the Highland Border escarpment, which forms the main subject of this paper. It is hoped later in Part II. of this paper to trace the westward retreat of the Strathmore-Ice from the River Tay to the River Almond, with a description of the moraines and outwash fans of the Sma’ Glen and Upper Glenalmond. II. Previous Literature. Existing literature on this area is scanty being almost entirely confined to the Geological Survey Memoir on Sheet 55 where the Glacial Deposits are dealt with in a short section by Grant Wilson (5, pp. 135-145). P. Macnair in ‶Geology and Scenery of the Highlands,″ vol. ii. (3, p. 102), deals with the general glaciation of the Highlands, drawing attention to kames, and lateral and terminal moraines left by the retreating glaciers. Mention is also here made of the supposed lake terraces of Strathtay described by Grant Wilson (5), doubt being thrown upon their mode of origin as lake-shore deposits and an alternative suggestion advanced that they are not lake but river terraces. Dr

The CNOC Nan Cuilean Area of the Ben Loyal Igneous Complex

I. I ntroduction T he Ben Loyal Igneous Complex forms an impressive group of mountains situated in northern Sutherland about six miles south of Tongue. The rock types include three distinct varieties of syenites, composing respectively the Ben Loyal range, Cnoc nan Cuilean and Ben Stumanadh, together with related syenites, aplites and pegmatites which constitute numbers of dykes, sheets and veins. The only previous work on this area of which an account has been published was carried out by the officers of the Geological Survey during the mapping of sheets 108 and 114 (Scotland). In the Geological Survey memoir on Central Sutherland (1931, pp. 174—9), H. H. Read gives a brief description of the field occurrence and petrology of the syenites; the rocks are described as unfoliated syenites and nordmarkites and their general petrographic characters are noted. The evident similarity of the Ben Loyal rocks to those of the Loch Ailsh intrusion is demonstrated both mineralogically and with the aid of chemical analyses. For more general references see J. Phemister (1936, p. 57) and E. B. Bailey and 0. Holtedahl (1938, p. 35). During the investigation here recorded, a field study was made of the Cnoc nan Cuilean and the Ben Loyal intrusions, and, for purposes of comparison, several traverses were made over the Ben Stumanadh mass. The primary purpose of this paper is to describe and interpret the petrography of the Cnoc nan Cuilean mass. This intrusion presents features not to be seen in the other two masses, namely, the development

XV.— A Note on the Base of the Lias near Broadford, Skye

As further work on the Jurassic rocks of Skye is likely to be delayed it may be useful to record the results of observations made at Lusa Bay, near Broadford, several years ago. The section is well known and has been described or referred to by Macculloch, Murchison, Hugh Miller, Geikie, Judd and H. B. Woodward: a general account by the latter in the Geological Survey memoir (1910) gives adequate references and summarises the succession. The lower part of the Lower Lias (the Broadford Beds) is there divided into four subdivisions; the uppermost yields Arnioceras and Coroniceras, and a great abundance of Gryphaea incurva. There is little doubt that this group belongs to the upper part of the Bucklandi Zone ( s. lat. ). Dr. L. F. Spath has more recently emphasised that the reference of the upper part of these beds to the Semicostatum Zone is inappropriate (1922); correlation with other areas (as with the Loch Sligachan and Heast districts) is certainly facilitated when it is recognised that the beds with Arnioceras are not higher than the Bucklandi Zone. The age of the underlying subdivisions has been in doubt owing to the absence of ammonites. In the memoir referred to the ‘passage beds’ immediately overlying the Trias (about 4 feet thick) were doubtfully referred to the Rhaetic, but the palaeontological evidence is not convincing (Lee and Pringle, 1931, p. 170). The presence of the Angulata Zone below the Bucklandi Zone has been inferred, and Dr. W. J. Arkell has suggested that This 250-word extract was created in the absence of an abstract

The Carboniferous Limestone of the Castleton-Bradwell area, North Derbyshire

I. Introduction The area included in the investigation forms a limestone plateau north of the line Perryfoot-Great Hucklow, generally about 1200–1400 feet above sea-level with broad valleys down to 900 feet and hills up to 1500 feet. The west side is formed by the broad valley running south from Windy Knoll; the northern edge runs along the steep slopes from Treak Cliff, behind Castleton to Bradwell; eastwards the area is confined by the valley running south from Bradwell to Hucklow. On these three sides the limestone is bounded by Edale Shales. On the south the area is bounded naturally by the broad depression in the limestone known as Perrydale. The northern edge of the limestone massif is incised by four narrow gorges: beginning on the west, the Winnats, Cavedale, Pindale, and Bradwell Dale. These display the most important profiles. Between the dales the limestone is exposed on the uplands but good continuous sections are rare, although the large quarries opened between Bradwell and Pindale help considerably in the interpretation of the structure and succession. Mining along the numerous lead veins has also exposed the limestone, but these sections are often disappointing owing to the presence of gangue minerals covering the surface of the veins or joints. The Castleton area has long been famous for its fossils, especially the brachiopod limestones of Treak Cliff and the Winnats, but, although frequently mentioned, the limestone has never been described in detail. The Geological Survey memoir on North Derbyshire (Green 1887) did not describe