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 BOUGHT WITH THE INCOME OF THE 
 
 SAGE ENDOWMENT FUND 
 
 THE GIFT OF 
 
 HENRY W. SAGE 
 
 1891 
 
- ^ Cornell University Library 
 
 QE 264.G97A7 1903 
 
 The geology of North Arran, South Bute, 
 
 3 1924 004 019 380 
 
The original of tiiis book is in 
 tine Cornell University Library. 
 
 There are no known copyright restrictions in 
 the United States on the use of the text. 
 
 http://www.archive.org/details/cu31924004019380 
 
MEMOIRS OF THE GEOLOGICAL SURVEY. 
 
 SCOTLAND. 
 
 THE GEOLOGY 
 
 OF 
 
 NOKTH ARRAN, SOUTH BUTE, 
 
 AND THE 
 
 CUMBRAES, 
 
 WITH PAKTS OF 
 
 AYRSHIRE AND KINTYRE. 
 
 (Sheet 21, Scotland.) 
 the description of north arran, south bute, and the 
 
 CUMBRAES BY W. Gunn, F.G.S. ; PART OF AYRSHIRE by Sir 
 A. Geikie, D.C.L. ,F.R.S.; PART OF KINTYRE by B. N. Pbach,F.R.S.; 
 WITH CHAPTER ON THE PETROGRAPHY OF THE TERTIARY 
 IGNEOUS ROCKS OF ARRAN, SOUTH BUTE, AND THE CUMBRAE 
 ISLANDS BY A. Habker, M.A., F.R.S. 
 
 PUBLISHED BV ORDER OF THE LORDS COMMISSIONERS OF HIS MAJESTY S TREASURY. 
 
 GLASGOW : 
 
 PRINTED FOR HIS MAJESTY'S STATIONERY OFFICE. 
 
 By JAMES HEDDERWICK & SONS, 
 
 At " The Citizen Pebss," St. Vincent Place. 
 
 And to be purchased from 
 JOHN MENZIES & Co. , Rose Street, Edinburgh ; 
 
 B. STANFORD, 12, 13, and 14 Long Acre, London ; 
 
 HODGES, FIGGIS & Co., Ltd., Grafton Street, Dublin ; 
 
 From any Agent for the sale of Ordnance Survey Maps ; or through any 
 
 Bookseller from the Ordnance Survey Office, Southampton. 
 
 1903. 
 Price Four SMllings. 
 
LIST OF PUBLICATIONS OF THE GEOLOGICAL 
 SURVEY OF SCOTLAND. 
 
 -Maps on One-inch Scale. 
 
 1. Wigtownshire, South- Western Districts, is. 
 
 2. Wigtownshire, South-Eastern Districts. 4s. 
 
 3. Wigtownshire, Western Districts. 6«. 
 
 4. Wigtownshire, East Part ; Kirkcudbright, portion of S.W. Division, 6». 
 
 5. Kirltcudbrightshire, Southern Districts. 6s. 
 
 6. Kirkcudbrightshire, E. margin ; Dumfriesshire, S. margin. 4s. ■ 
 
 7. Ayrshire, South- Western Districts. 6s. 
 
 8. Kirkcudbrightshire, Ayrshire, and Wigtownshire. 6s. 
 
 9. Kirkcudbrightshire, N.E.; Dumfriesshire, S.W. 6». 
 
 10. Dumfriesshire. 6s. 
 
 11. Rdxburghshire and Dumfriesshire. 4s, 
 
 12. Argyllshire (Kintyre, S. half of). 4s. 
 
 13. Ayrshire, Turnberry Point, and S. part of Arran. is. 
 
 14. Ayrsliire, Central Districts. 6s. 
 
 15. Dumfriesshire, N.W. ; Ayrshire, S.E. ; and Lanarkshire, S. 6s. 
 
 16. Dumfries, Selkirk, Peebles, Lanark, and Roxburgh shires (parts of). 6«. 
 
 17. Roxburghshire, Selkirkshire, and Dumfriesshire (parts of). 6s. 
 
 18. Roxburghshire, B. part. 4s. 
 
 19. Argyllshire (S. part of Islay). is. 
 
 20. Argyllshire (Kintyre, Gigha L, part of Islay). 4». 
 
 21. Argyllshire ; Arran, Central and N. part ; Bute, S. part ; Cumbraea ; 
 
 Ayrshire (part of N.\V.). 4s. 
 
 22. Ayrshire, Renfrewshire, Lanarkshire (parts of). 6s. 
 
 23. Lanarkshire, Central Districts ; Ayrshire (part of W.)- 6s. 
 
 24. Peeblesshire, Lanarkshire, Edinburghshire, Selkirkshire (parts of). 6s. 
 
 25. Berwickshire ; parts of Roxburgh, Selkirk, and Edinburgh. 6s. ' 
 
 26. Berwickshire and Roxburghshire (parts of). 4s. 
 
 27. Argyllshire ; parts of Islay and Jura, Oronsay. 4s. 
 
 29. Argyllshire, Ayrshire, Buteshire, Dambartonshire, and Renfrewshire (parte 
 
 of). 6s. 
 
 30. Renfrewshii'e ; parts of Dumbarton, Stirling, Lanark, and Ayr. 6s. 
 
 31. Lanarkshire, Stirlingshire, Linlithgowshire, Dumbartonshire, Edinburgh-, 
 
 shire (parts of). 6s. 
 
 32. Edinburghshire, Linlithgowshire, Pifeshire, Peeblesshire (parts of). 6s. 
 
 33. Haddingtonshire and parts of Edinburghshire and Berwickshire. 6s. 
 
 34. Eastern Berwickshire. 4s. 
 
 38. Perthshire, Stirlingshire, Dumbartonshire, Argyllshire (parts of). 6s. 
 
 39. Perthshire, Clackmannanshire, Stirlingshire, and Fife (parts of). 6s. 
 
 40. Fife and Kinross. 6s. 
 
 41. Fife, East part. 6s. 
 
 46. Perthshire, Argyllshire (parts of). 6s. 
 
 47. Perthshire. 6s. 
 
 48. Perthshire, Forfarshire, and Fifeshire (parts of). 6< 
 
 49. Forfarshire and Fifeshire (parts of). 4s 
 55. Perthshire. 6s. 
 
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MEMOIRS OF THE GEOLOGICAL SURVEY. 
 
 SCOTLAND. 
 
 THE GEOLOGY 
 
 OF 
 
 NOETH AERAN, SOUTH BUTE, 
 
 AND THE 
 
 OUMBEAES, 
 
 WITH PARTS OF 
 
 AYESHIRE AND KINTYEE. 
 
 (Sheet 21, Scotland.) 
 the description of north arran, south bute, and the 
 
 OUMBRAES EY W. Gusn, F.G.S. ; PART OF AYRSHIRE by Sir 
 A. Geikie, D.C.L.,F.R.'Sn part OF KINTYRE by B. N. Pbach.F.R.S.; 
 WITH CHAPTER ON THE PETROGRAPHY OF THE TERTIARY 
 IGNEOUS ROCKS OF ARRAN, SOUTH BUTE, AND THE CUMBRAE 
 ISLANDS BY A. Harker, M.A., F.R.S. 
 
 PrBLISHBD BY ORDER OT THE LORDS COMMISSIONERS OF HIS MAJESTY S TREASURY. 
 
 GLASGOW : 
 
 FEINTED FOR HIS MAJESTY'S STATIONERY OFFICE 
 
 By JAMES HEDDERWIOK & SONS, 
 
 At " The Citizen Press," St. Vincent Place. 
 
 And to be purchased from 
 
 JOHN MENZIES & Co., Rose Street, Edinburgh; 
 
 E. STANFORD, 12, 13, and 14 Long Acre, London ; 
 
 HODGES, FIGGIS & Co., Ltd., Graj?ton Street, Dublin ; 
 
 From any Agent for the sale of Ordnance Survey Maps ; or through any 
 
 Bookseller from the Ordnance Survey Office, Southampton. 
 
 1903. 
 Price Four Shillings. 
 
 
PREFACE. 
 
 This memoir describes the geology of the area included in Sheet 21 
 of the one-inch map of Scotland, which embraces the north part of 
 Arran, South Bute, and the Cumbraes, with parts of Ayrshire and 
 Kintyre. The ground in Ayrshire was surveyed by Sir A. Geikie-, 
 who also mapped a narrow belt along the east coast of Arran in 
 1872. Bute and the Cumbraes were surveyed by Mr. Gunn, and the 
 small area in Kintyre by Mr. Symes. The survey of the southern 
 part of Arran was commenced in 1892 by Mr. Gunn, who gradually 
 traced his lines northwards till he completed the mapping of the 
 whole island ; the field-work being carried on under the supervision 
 of Mr. B. N. Peach, F.E.S. 
 
 The geological description of North Arran, South Bute, and the 
 Cumbraes has been written by Mr. Gunn, that of the Ayrshire 
 coast by Sir A. Geikie, and that of Kintyre by Mr. Peach. Chapter 
 XI., on the petrography of the Tertiary Igneous Rocks of Arran, 
 South Bute, and the Cumbraes, has been supplied by Mr. Harker, 
 F.R.S. In Part II. of the Appendix, the notes on the petrography 
 of the Old Eed Sandstone Igneous Rocks have been contributed 
 by Mr. Kynaston, and those on the Carboniferous Igneous Rocks 
 by Mr. Seymour. While the field-work was in progress, petro- 
 graphical notes on various rocks from tliis sheet were also supplied 
 by Mr. Teall, F.R.S. , Dr. Hatch, Professor Watts, Professor Grenviile 
 Cole, and Dr. Flett. 
 
 The lists of Carboniferous fossils have been prepared by Mr. 
 Peach, Dr. Crampton, and Mr. Tait, and the notes on the Mesozoic 
 fossils found in the island of Arran have been supplied by Mr. B, 
 T. Newton, F.R.S. Special thanks are due to Dr. TraqTiair. K.K.S., 
 Mr. Kidston, F.R.S., and Dr. Wheelton Hind for their valuable 
 assistance in the determination of the fishes, the plants, and the 
 lamellibranchs respectively. 
 
 Part III. of the Appendix, which gives a list of publications 
 relating to the geology of the areas included in this sheet, has been 
 prepared by Mr. Gunn with the assistance of Mr. Harker and Mr. 
 Tait. 
 
 The photographs reproduced in Plates I. to X. were taken by 
 Mr. Robert Lunn of the Geological Survey. 
 
iv PREFACE. 
 
 The principal additions to our knowledge of the geology of Arran, 
 made during the progress of the Geological Survey, may here be 
 briefly summarised : — 
 
 1. The discovery of the former extension of Cretaceous, Liassic, 
 and Ehsetic deposits in the island from the presence of fragments 
 enclosed in a volcanic vent. 
 
 2. The determination of the Triassic age of the sandstones, con- 
 glomerates, and marls of the southern part of Arran, and their 
 unconformability to the Carboniferous Rocks. 
 
 3. The discovery of strata of Coal-measure age, though of limited 
 development, in the island. 
 
 4. The identification of black schists, cherts, and grits probably 
 of Arenig age in North Sannox. 
 
 5. The discovery of no less than six difierent sets of volcanic 
 rocks, in addition to that formerly known in the Lower Carboniferous 
 strata. Of these, one is probably of Arenig age ; two belong to 
 the Old Red Sandstone period ; two are of Carboniferous age, and 
 the last, forming a huge volcanic vent, is probably Tertiary. 
 
 J. J. H. TEALL, 
 Director. 
 
 Geological Survey Office, 
 
 28 Jermyn Street, 
 
 London, 28th March 1903. 
 
CONTENTS. 
 
 PAGE. 
 
 Preface, - iii 
 
 CHAPTER I. 
 
 Introductory. Physical Features, &c., - 1 
 
 CHAPTER II. 
 Table of Formations and General Geological Description, 5 
 
 CHAPTER III. 
 
 Metamorphic Rocks, - 12 
 
 CHAPTER IV. 
 
 (a) Black Shales, Cherts, and Grits, with Contemporaneous 
 
 Volcanic Series, probably of Arenig age, - 18 
 
 (6) Intrusive Rocks, 21 
 
 CHAPTER V. 
 (a) Old Red Sandstone — 
 
 2. Upper, . 28 
 
 1. Lower, 23 
 
 (6) Contemporaneous Volcanic Series — 
 
 2. Upper, - 34 
 
 1. Lower, - 26 
 
 (c) Intrusive Rocks of Old Red Period, 27 
 
 CHAPTER VI. 
 Carboniferous Formation — 
 
 {a) Sedimentary, - - 37 
 
 (6) Igneous Rocks, 56 
 
 CHAPTER VII. 
 
 New Red Sandstone or Trias — 
 
 2. Upper, 72 
 
 1. Lower, 68 
 
 CHAPTER VIII. ' 
 
 Patches of Secondary Formations in Volcanic Vents — 
 
 3. Cretaceous, 76 
 
 2. Lias, 75 
 1. Rhsetic, 73 
 
VI CONTENTS. 
 
 CHAPTER IX. PAGE. 
 
 Large Volcanic Vent, probably Tertiary, 79 
 
 CHAPTER X. 
 
 Intrusive Igneous Rocks of Tertiary Age, 84 
 
 CHAPTER XI. 
 
 Petrographical Notes on do., 103 
 
 CHAPTER XII. 
 
 Faults and Earth Movements, 128 
 
 CHAPTER XIII. 
 Glaciation and Glacial Deposits, I33 
 
 CHAPTER XIV. 
 Recent Deposits, I39 
 
 CHAPTER XV. 
 
 Economic Geology, 146 
 
 LIST OF ILLUSTRATIONS 
 
 FIGURES IN TEXT. 
 
 ■ PAGE. 
 
 Fig. 1 . Section along shore opposite Corrie, Arran - 38 
 
 ,, 2. Section across the Little Oumbrae, from west to east 59 
 
 PLATES. 
 
 Plate I. View from top of GoatfeU, looking north. The 
 so-called north top of Goatfell forms the prominent 
 peak to the right, and to the left of this, in the 
 distance, appears the deep rift of Ceum na Caillich. 
 A basic dyke crosses the near ridge on the left. 
 
 Frontispiece 
 
 „ II. Contorted mica schist with quartz-veins in shore 
 cliiFs, opposite Imachar, two miles north of Dougrie, 
 Arran, to face page 14 
 
 „ III. " Pillowy " structure in supposed Arenig lavas, Torr 
 na Lair Brice. North side of North Glen Sannox, 
 Arran, to face page 20 
 
 ,, IV. South of Farchan Mor, Sannox, Arran. Local 
 unconformability in " Upper Old Red Sandstone." 
 The coarse conglomerate, on which rests the 
 "Rocking Stone," overlaps, on the left, soft red 
 shaly sandstone, to face page 30 
 
CONTENTS. vn 
 
 Plate V. Unconformability. North Newton Shore, north-east 
 of Lochranza, Arran. The gently dipping corn- 
 stones and sandstones of Lower Carboniferous age 
 repose unconformably on the Highland Schists, 
 which are highly inclined and dip in a contrary 
 direction. These last appear in the lower left hand 
 corner, to face page 52 
 
 „ VI. " Pillowy " structure in Lower Carboniferous lavas ; 
 about 300 yards north of Corrie Schoolhouse, 
 Arran, and near the large granite boulder called 
 " Clach an Phionn," to face page 58 
 
 „ VII. False-bedding in the lower division of the New Red 
 Sandstone cliff of Maol Donn, about two miles 
 south of Corrie, Arran, to face page 68 
 
 ,, VIII. (1) Jointing in the coarser granite, near top of 
 
 Goatfell, Arran, to face page 101 
 
 (2) Tertiary dolerite dyke traversing '-'New Red 
 Sandstone." The cross-jointing is well shown. 
 East of Brodick Pier, Arran, to face page 101 
 
 „ IX. Moraines in Glen Dubh (Glen Cloy), near Brodick, 
 Arran. They in great part surround an alluvial 
 flat which was once a moraine-dammed lake, 
 
 to face page 136 
 „ X. Landslip of Upper Old Red Sandstone Conglomerate, 
 which goes by the name of " The Fallen Rocks," 
 east coast of Arran, nearly four miles north of 
 Corrie, to face page 144 
 
THE GEOLOGY OF NORTH ARRAN. 
 
 CHAPTER I. 
 
 INTKODUGTION. 
 
 Considerably more than one half (about five eighths) of the area of 
 this sheet is occupied by sea — the Firth of Clyde and its branches — 
 and the land amounts to only about 161 square miles. The 
 land area belongs to three different counties, and consists of no less 
 than nine separate portions — seven of them being islands or parts 
 of islands, and the other two belong to the mainland of Scotland. 
 
 In the north-west corner of the map is a small portion (about 13 
 square miles) of the peninsula of Kintyre in the neighbourhood of 
 Skipness, Argyllshire. On the eastern border is a somewhat larger 
 area, about 16 square miles, which is part of the county of Ayr. 
 It embraces a strip of coast land stretching from Largs to near 
 Ardrossan, together with the Horse Island opposite to its southern 
 end. The six remaining portions belong to the county of Bute. 
 Near the northern edge of the map occur four of these — the southern 
 parts of the islands of Bute and Inchmarnock, the whole of the Little 
 Cumbrae, and nearly all of the Great Cumbrae. The largest land 
 mass is the northern portion of Arran, nearly three quarters of the 
 whole area; and the northern end of Holy Island, which closes in 
 Lamlash Bay, completes the list. 
 
 The extent of coast line in the sheet is about 91 miles. 
 
 Millport in the Great Cumbrae is the most important town, but a 
 portion of Largs comes into the sheet on the Ayrshire side at the 
 north-east corner. Lamlash, Brodick, Corrie, and Lochranza are 
 important villages in the Isle of Arran, and so are Kilchattan 
 in Bute, and West Kilbride in Ayrshire. Inchmarnock, Little 
 Cumbrae, and Holy Island are but sparsely populated, while the 
 Horse Island is an uninhabited rock. 
 
 Physical Features. — Naturally, from the small size of the 
 separate portions of land, there can be no large streams, but some 
 of the ground rises to a great height, especially in the Isle of 
 Arran. 
 
 The Kintyre portion is an undulating table-land rising rapidly 
 from the sea level to a height of 500 or 600 feet, and the highest 
 point is Cruach an t-Samhlaidh, which reaches to 849 feet above the 
 sea. This area is drained by the Claonaig Water and the Skipness 
 Water. 
 
2 The Geology of North Arran. 
 
 Inchmamock is a low, rocky island of less than 200 feet in eleva- 
 tion. 
 
 The western side of Bute is of much the same physical character 
 as Inchmarnock, but rises to 279 feet above the sea. The ground 
 south of Loch Quien is below the 50-feet contour, and is part of a 
 low, narrow valley which runs northward to Eothesay. East of 
 Loch Quien the ground rises into a comparatively featureless area, 
 the highest part of which, near Birgidale Butts, is 400 feet above 
 the sea. To the south of this, and stretching across the island 
 between Kilchattan Bay and Stravanan Bay, is a low, flattish, sandy 
 tract which rises to a little above the 50 feet contour. In great 
 contrast to this rises the ridged and rocky part which composes 
 South Bute, between Kilchattan and the Garroch Head. Its 
 highest points are Suidhe Chatain 517, south of the village, and 
 Torr Mor 485, near Glencallum. 
 
 The Great Cumbrae is generally in character like that portion of 
 Bute to the north of Kilchattan, and rises to about the same height 
 above the sea — 417 feet. Some intrusive igneous masses, however, 
 diversify its surface considerably. 
 
 The Little Cumbrae, on the other hand, rising to 409 feet above 
 the sea, is rocky, like the southern end of Bute, only that instead 
 of marked ridges there is a series of gently sloping terraces. 
 
 On the Ayrshire side is the rocky promontory of Portincross 
 rising to 456 feet above the sea, which is connected with the main 
 mass of land to the eastward by ground less than 100 feet in elevar 
 tion. To the east of the railway the land rises rapidly, as it does 
 along the coast generally, much of the border of the sheet being 
 over 800 feet, and in one place it exceeds 1000 feet. 
 
 The iine peaks of the northern granite mountains, with their 
 deep-cut glens, are the dominant features in the scenery of Arran. 
 These are contained within a nearly circular area about eight miles 
 by seven across. All the principal streams take their rise in this 
 mass, or from a smaller oval area near the centre of the southern 
 edge of the sheet, which is belted by a granitic ring, and in which 
 are the hills of Ard Bheinn 1676, A' Ghruach 1679, and feeinn 
 Bhreac 1649. The streams that flow eastward from this smaller 
 mass of high ground are Benlister Burn and Glencloy Burn, while 
 those which flow to the west are tributaries of the Machrie Water 
 and the Black Water. 
 
 The larger granitic area is nearly divided into two equal parts by 
 the glens of lorsa Water and Easan Biorach, which coalesce at the 
 watershed of Loch na Davie. The lorsa stream, which is about 
 eight miles long, is the largest in the island. Some of its branches 
 drain the western part of the high ground, which is not so high 
 and rugged as the eastern half, nearly all the highest hills being 
 round or flat topped. Beinn Bharrain 2345, and Beinn Bhreac 
 2333 — the highest points of a continuous ridge ; Meall nan Damh 
 1 8 7 , and Meall Mor 1602, isolated conical hills ; and another Beinn 
 Bhreac 1881, west of Loch na Davie, are the most important summits 
 in this part, which is partly drained by Allt Gobhlacb and the 
 stream which flows north down Glen Catacol. 
 
Introduction. 3 
 
 From the masses of Caisteal Abhail 2817,* and Oir Mhor 2618, 
 diverge ridges that embrace the glens of Sannox and North 
 Sannox, which drain eastwards, and that of Rosie, which drains 
 southward into Brodick Bay. One ridge with a gradual descent 
 runs northwards from Caisteal Abhail to Creag Dubh, and bounds 
 the valley of North Sannox on the west. Another, and very 
 rugged, ridge runs eastward to the rift of Ceum na Caillich, and 
 then in a smooth outline continues in a north-east direction past 
 Suidhe Fhearghas, 2156. This ridge separates the two Sannox 
 glens. A high col, the lowest part of which is 2046, joins Caisteal 
 Abhail to Cir Mh(3r. In a south-south-west direction from this 
 peaky mountain we have successively A' Chir (the most difficult 
 to traverse in the whole island), Beinn Tarsuinn 2706, and Beinn 
 Nuis 2597. The height of A' Chir is not given, but is probably about 
 2335, and the pass to the south of it is over 2000 feet, while the 
 pass on the north side is 1933. The highest point of Beinn a' 
 Ohliabhain, which is on the west side of Glen Rosie, is 2217 feet in 
 height. Cir Mh6r is connected with the Goatfell range by the 
 low col of the saddle 1414, which has a precipitous and difficult 
 descent on the Sannox side. Goatfell, 2866, the highest summit in 
 the island, is on a continuous range of high ground, over 2000 feet in 
 elevation, which runs in a curved line from Cioch na h-Oighe, 2168, 
 round the head of the White Water, past Goatfell, some half a mile 
 down its southern spur. For three quarters of this distance the ridge 
 is nearly everywhere over 2500, and only falls slightly below that 
 height at one or two points. From its highest point north of Goat- 
 fell, 2716, a ridge which bounds the White Water on the north runs 
 eastward to Am Binnein, 2172. 
 
 Holy Island, which is on the eastern side of Lamlash, is steep 
 and rugged, and rises to above 1000 feet, but its highest point is 
 outside the limit of this sheet. 
 
 Several freshwater lochs diversify the surface of Arran, and one. 
 Loch Quien, comes into the portion of Bute with which we have to 
 deal. Nearly all the lochs in Arran are in the western part of the 
 island. The largest is Loch Tanna, which is a mile in length, but 
 not particularly interesting, being immediately surrounded by low- 
 lying, peat- covered ground. It is probably shallow, and drift- 
 dammed. The Dubh Loch to the west of it is partly surrounded 
 by rock, and may be a rock basin. Loch Nuis and Loch lorsa are 
 shallow lochs, probably, in drift, as is also Loch na Davie. Two 
 small lochs occur to the south-west of Sail Chalmadale, one of 
 which is not on the ordnance maps. The finest of the lochs is 
 Loch Chorein Lochain at a height of 1080 feet above the sea, 
 picturesquely surrounded by granite crags between Meall nan 
 Damh and Meall Biorach. 
 
 For sea lochs we have only Loch Eanza, and the bays of Brodick 
 and Lamlash in Arran, for the coast is not much indented. 
 Brodick Bay is the most interesting, for into it debouch the Cnocan 
 Bum; the Eosie Bum, into which Glen Shurig Burn drains; the 
 
 The highest point of Caisteal Abhail is not indicated on the one-inch map. It is 
 about 200 yards east of the parish boundary where is the height, 2735. 
 
4 The Geology of North Arran. 
 
 Glencloy Burn, and the Allt Beidh. There are thus the openings 
 of five separate glens diverging from this short sea loch. In Bute 
 the principal indentations of the coast are at Scalpsie Bay and 
 Kiichattan Bay ; and Millport Bay is the only one of importance in 
 the Great Oumbrae. 
 
 In the following pages an outline only can be given of the 
 complicated geology of the northern part of the Isle of Arran, 
 which forms the bulk of the land in the sheet, fuller details being 
 reserved for a complete memoir on the island. In this forth- 
 coming volume it is also proposed to give an historical sketch of 
 the geological discoveries made in the island by the principal 
 observers, with full references to the books and papers in which 
 they are contained. 
 
 A separate short explanation of the rocks in the southern part 
 of Arran to accompany Sheet 13 of the one-inch geological survey, 
 will succeed the present publication. 
 
 Attention is here called to the following points, embracing the 
 principal additions to our knowledge of the geology of Arran made 
 during the progress of the survey : — 
 
 The discovery of the former extension of Cretaceous, Liassic, and 
 Rhsetic formations in the island from the presence of fragments of 
 these rocks enclosed in a Tertiary volcanic vent. 
 
 The definite determination of the Triassic age of the sandstones, 
 conglomerates, and marls of the southern part of Arran, and their 
 unconformability to the Carboniferous rocks. 
 
 The restriction of the Carboniferous formation to an extremely 
 narrow compass in the island — a much broken and faulted strip 
 which does not extend to the west coast — and the discovery in it 
 of strata of Coal-measure age. 
 
 The discovery of beds of probable Arenig age in North Glen 
 Sannox in the form of black schists, cherts, and grits, associated 
 with old lavas and volcanic tufis similar to those occuring near 
 Ballantrae in Ayrshire. 
 
 The discovery of no less than six different sets of volcanic rocks 
 in addition to that formerly known as occurring in the Jower part 
 of the Carboniferous formation. Of these newly discovered volcanic 
 series one is probably of Arenig age, two belong to the Old 
 Eed Sandstone period, two are of Carboniferous age, and the 
 newest, which is a huge volcanic vent, is probably of Tertiary age. 
 
 In addition to these, the age and character of the numerous 
 intrusive rocks both acid and basic have been more definitely fixed, 
 and their distribution more accurately determined. While the 
 majority of the intrusive rocks of the sheet are of Tertiary age, a 
 considerable number belong to the Carboniferous period, and some 
 to that of the Old Red Sandstone, while a few are as old as the 
 Lower Silurian period, or even earlier in date than this. 
 
 When we take into consideration all these important additions 
 to our knowledge of the island, we are more disposed to admit that 
 the geology of Arran is, as it has often been said, an epitome of 
 that of Scotland, 
 
CHAPTER II. 
 
 Table of Formations occurring in the Sheet and general Geological 
 
 Description. 
 
 The following Table gives a complete list of the various formations 
 and subdivisions of formations that are found within the area, 
 together with the varieties of intrusive igneous rock met with. 
 The stratified formations are arranged first, beginning with the 
 mpst recent and proceeding to the oldest. Next follow the con- 
 temporaneous volcanic rocks, and last of all the intrusive igneous 
 rocks. 
 
 In the descriptive parts a somewhat different arrangement is 
 followed, for we begin with the oldest rocks — the metamorphic 
 schists^and end with the newest or most recent strata. In the 
 description, also, of the different volcanic zones, it has been found 
 more convenient to take them along with the aqueous rocks, with 
 which they are associated, than to class them together as contem- 
 poraneous igneous rocks. An endeavour has also been made to 
 describe together the intrusive igneous rocks that are known to 
 belong to one and the same period. 
 
 ns 
 
 >^ 
 
 S c3 
 
 O 1 
 
 CD -t= 
 
 Ph o 
 
 Sub-aerial 
 
 and Fresh 
 
 Water. 
 
 Aqueous. 
 
 Blown sand. 
 Lvium of 
 old lakes 
 
 { 
 
 ) Alluvium of stream terraces and 
 
 (.Peat 
 
 Tj,^, ^. ( Mud and sand of pi-esent beach . 
 *' , J Eaised beaches (25 feet) 
 
 m'"^"- 1 :; tmT^'"'' ■ 
 
 Sands, gravels, and stratified clays. Bskers and 
 
 glacial shell-beds. 
 Erratic blocks. 
 
 Boulder clay or Till. Drumlins. 
 Ice markings on rocks. . . . . 
 
 Limestone with siliceous concretions. 
 
 ^ ■ ) occurring in volcanic vent 
 
 J . \ Dark shale with many fossils, occurring 
 
 I in volcanic vent .... 
 
 r Black shale with ironstone and lime- 
 Ehsetic. < stone, occurring in volcanic vent . }. fg 
 
 ( Pale-coloured mudstones, do. 
 
The Geology of North An-an. 
 
 g 
 
 o 
 O 
 
 TEed marls and shales with white and"] f" 
 j yellowish sandstones. I 
 
 Trias. ■{ Thick red, yellow, and whitish sandstones )■ 
 
 I with masses of conglomerate . I f 
 
 [_i'alse-bedded red sandstones. J 
 
 r Coal-measures with contemporaneous lava 
 ] Carboniferous ( Upper Limestone group. 
 J Limestone < Edge-coal group. 
 ' Series. (^ Lower Limestone group. 
 Calciferous Sandstones with intercalated volcanic 
 
 } 
 
 series 
 
 !' Upper Red Sandstones and conglomerates 
 with volcanic series 
 Lower Red Sandstones, mudstones, and 
 conglomerates with volcanic series 
 Lower J Cherts, grits, and dark schists associated 
 Silurian. \ with a volcanic series (Arenig ?) 
 
 !Mica schist ..... 
 Limestone 
 Slate 
 Gritty schists or schistose grits 
 
 ds 
 
 d2 
 
 di 
 
 b 
 I 
 
 Igneous. 
 
 A. — Interstratified or Gontenvporaneous with the Formations 
 among which they lie. 
 
 In Carboni 
 
 ferous 
 
 System. 
 
 'Basalt (in Coal-measures, Car- 
 boniferous Limestone and 
 Calciferous Sandstone) as in- 
 tercalated sheets of lava 
 Andesite in Calciferous Sandstone 
 Trachyte „ „ 
 
 Volcanic tufis „ „ 
 
 Agglomerate in necks 
 In Old Red f Basalt in upper Old Red Rocks . 
 Sandstone I Basalt in lower „ „ ,, • 
 TEpidiorite or Greenstone lava of 
 In Lower J Arenig (?) age — slightly 
 
 Silurian, j schistose .... 
 
 l^Tuff and agglomerate of do. 
 
 Bd5, Bd2, & Bdi 
 Podi 
 Trdi 
 Tsdi 
 
 Ndi 
 
 Be 
 
 Bel 
 
 Bb? 
 Tsb? 
 
 ^i. — Fragmental Volcanic Bocks subsequent in date to the strata 
 among which they lie. 
 
 m . ■ f Agglomerate and conglomerate in large ^r- 
 
 Tertiary. | ^%ent probably of Tertiary age. ^^ 
 
<i 
 
 •i-H 
 
 a> 
 
 
 General Geological Description. 7 
 
 ■B- — Intrusive or subsequent in date to the rocks amiong 
 which they lie. 
 
 Gabbro - 
 
 Basalt and dolerite in dykes, sills, and bosses f B 
 
 Andesite \ Po 
 
 Diorite and f D 
 
 Hyperite ... . . 1 
 
 Syenite. S 
 
 Pitchstone . F' 
 
 Quartz-diorite ... . . . G" 
 
 Granophyre .... G" 
 
 Granite — fine-grained .... G 
 
 Granite — coarse-grained ..... G 
 
 Late Car- /Basalt and 1 • -, , j -i, -r> 
 
 boniferous. 1 Dolerite | ^ dykes and sills . . B 
 
 Of Earlv f Oli'^ne basalt in dykes and sills B 
 
 p -L ■ ) Andesite in dykes . . . . Po 
 
 ferons Age. | 1°"^^!!'^^ °i" ^ostonite in dykes . . F 
 
 ° [ Trachyte m dykes . . . . Tr 
 
 Probably J Malacolite or Salite-Dolerite in dykes 
 
 OldEedAge. \ and sills B 
 
 Lower Silurian ? — Epidiorite and Hornblende Schist Bg 
 
 Of Uncer- f Serpentine 2 
 
 tain Age. I Hornblende Schist . . . Bg 
 
 General Geological Bescriftion. 
 
 Metamorphic rocks, as mica schists, etc., occupy the whole of the 
 Kintyre area, the island of Inchmarnock, and the western part of 
 Bute. In these areas the strike of the rocks is generally north- 
 east and south-west, with a steep dip to the south-east, and 
 prominent features or ridges often run in the same direction as the 
 strike of the beds. These rocks, which are the oldest in the sheet, 
 also form an incomplete ring round the granite in the northern 
 parts of Arran where they occupy high ground generally, for though 
 the formation is found on the sea coast from Dougrie to Newton 
 the land rises rapidly from the sea level. These rocks often occupy 
 a kind of plateau rising to over 1000 feet in the district reaching 
 from Glenshant Hill to Whitefarland. In the north-east of Arran 
 the formation attains a height of 1453 feet above the sea. Crags 
 and minor features are common in the formation, both on the sea 
 coast and inland, some of which are in a great measure due to 
 joints or faults. 
 
 Separated from the metamorphic rocks by a fault, the 
 Lower Old Red Sandstone forms in the main a curved, highly 
 dipping strip, stretching from Corloch on the east side of 
 Arran to Dougrie on the west coast. The conglomerates of this 
 division form prominent hills in North and South Glen Sannox, but 
 
8 The Geology of North Arran. 
 
 the highest point of this band is AnTunna, 1184 feet, north of the 
 String Eoad. There is also a detached portion of this sub-formation 
 to the east and south of the smaller granite area at the heads of 
 Glen Dubh, Benlister Glen, and Clachan Glen. It rises to 1346 
 feet in Cnoc na Croise. 
 
 The main portion of the Great Cumbrae and a large portion of Bute 
 consist of Upper Old Eed Sandstone rocks, which are comparatively 
 featureless except near the coast. This formation also occupies a 
 portion of the Ayrshire coast. 
 
 In Arran these rocks occupy the shore between the Fallen Kocks 
 (near Corloch) and Oorrie, and they form a narrow band to the east 
 and south of the Lower Old Eed Sandstone and apparently confor- 
 mable to that division. On the north side of North Glen Sannox 
 the conglomerates of this division form a marked set of features with 
 a northerly dip, and here they are unconformable to the lower 
 division. 
 
 Carboniferous rocks (aqueous) form small portions of south 
 Bute, Great and Little Cumbrae, and Ayrshire. They are also 
 found in several places in north Arran, the principal area being 
 between the Cock and the Fallen Eocks, where they occupy a 
 narrow band dipping steeply northward and bounded on the west 
 by a fault. On the south side of a great anticlinal we find these 
 rocks with a southerly dip for a distance of half a mile along the 
 shore at Oorrie, and they form a narrow, interrupted band, stretching 
 thence southward and inland to near the head of Benlister Glen. 
 
 The New Eed Sandstone occupies a small area in the north of 
 Arran near the Cock, and the whole eastern shore southward from 
 Corrie. Inland, we find it as far west as Glen Ormidale and Gleann 
 Dubh, and high up Benlister Glen. There are fine crags formed of 
 this rock in Gleann Dubh. This formation rises to near 1000 feet 
 above the sea close to the Cock of Arran, in Maol Donn to over 1200, 
 and on either side Gleann Dubh to 1250. On the western side of 
 the island it spreads over the vale of Shiskine on either side of the 
 mouth of the Machrie Water. 
 
 The Ehaetic, Lias, and Cretaceous formations are fragments found 
 in a volcanic vent of Tertiary age. 
 
 Of the contemporaneous Igneous Eocks — the lavas and tuffs of 
 probable Arenig age are only found in North Glen Sannox in 
 Arran, where some bands form prominent crags. 
 
 The lavas of Lower Old Eed age are only found on the west side 
 of Arran in a narrow inconspicuous band, and those of Upper Old 
 Eed age occupy a much faulted strip on the east side of the island 
 between the mouth of North Glen Sannox Burn and Corloch. 
 
 The Lower Carboniferous Volcanic Eocks occupy considerable 
 areas in Ayrshire, Little Cumbrae, and South Bute. In the latter 
 locality the lavas form a striking set of ridges, which dip steeply to 
 the south-west ; in the Little Cumbrae they are disposed in a shallow 
 synclinal, and the beds form a series of gently sloping terraces, 
 which feature caused the island to be named in ancient times 
 Cumbrae Beas. These rocks are found in several parts of Arran, 
 where they form few conspicuous features. 
 
General Oeological Bescription. 9 
 
 Intrusive rocks of Carboniferous age are numerous in Great 
 Cumbrae, diversifying its surface and giving rise to crags in the 
 interior. An intrusive mass of this period forms the conspicuous 
 hill of Suidhe Chatain in the southern part of Bute. 
 
 Intrusive rocks of Tertiary age forni all the marked features of the 
 topography of Arran, and they comprise nearly one half the area 
 of the island. The large granitic mass which has been already 
 referred to as forming all the highest ground and the grandest 
 scenery in the island belongs to this period, and in the southern 
 part of the sheet nearly all the prominent hills are formed of 
 intrusive rock, acid or basic, of Tertiary age ; and Holy Island also. 
 Ard Bheinn which overlooks the vale of Shiskine, is one of the 
 most rugged hills of the island of Arran, and it consists of several 
 varieties of intrusive igneous rock which have penetrated a 
 Tertiary volcanic neck. The agglomerate of this vent forms 
 marked crags on the eastern side of the Glenloig valley, the lower 
 part of Glen Craigag. 
 
 The different forms of the hills in the northern part of Arran in 
 the districts of the coarse and fine granites, has often been referred 
 to, and generally ascribed to the different mode of weathering in 
 the two rocks. But it is clear that in many cases the deep nicks 
 crossing the ridges are due to more rapidly weathering basic and 
 other dykes. Oeum na Caillich is a marked example, and A' Chir, 
 the most serrated mountain in the island, is the one most traversed 
 by dykes. Of course there are dykes in both granites, but the 
 difference in weathering between dyke and granite, which gives 
 origin to the nick; is greater in the case of the coarse than of the fine 
 granite. In addition to this, the coarse granite is penetrated in 
 places by veins of finer granite, and there are lines of weakness 
 which occasionally give rise to hollows. It seems also probable that 
 the original upper surface of the coarse granite was in the form of 
 a dome (covered by schists, etc.). If such were the case, the 
 coarser granite, after removal of the sedimentary cover by 
 denudation, must have been exposed a long time to denuding 
 forces before the finer granite appeared at the surface, and thus, 
 whatever tended to produce the peaks and nicks, would have a 
 longer time to operate in the case of the coarse than of the fine 
 granite. It may be remarked, however, that some of the lower 
 hills formed of coarse granite, like Meall nan Damh 1870, and 
 Meall Mor 1602, are not unlike in form to the hills formed of 
 fine granite. 
 
 Our admiration of this grand hill and valley system in 
 Arran is by no means diminished on realising that it is all of 
 recent geological date, and that none of it was in existence before 
 the Tertiary Period. W. G. 
 
 AYRSHIRE DISTRICT. 
 
 The north-eastern part of Sheet 21 of the Geological Map of 
 Scotland, on the scale of one-inch to a mile, includes a part of the 
 coast of Ayrshire which extends from the southern outskirts of the 
 
10 The Geology of North Arran. 
 
 village of Largs almost as far as the seaport of Ardrossan. This 
 strip of country is about ten miles long, and at one point, where 
 the land juts out into the Firth of Clyde, has an extreme breadth 
 of nearly three miles. Stretching along the eastern margin of the 
 broad firth, it includes a band of low ground next the shore, from 
 which the land rises rapidly until it forms the great hilly plateau, 
 which in the interior reaches a height of more than 1500 feet above 
 the sea. 
 
 With this range of feature the tract of country unites consider- 
 able variety and interest of geological structure. The Upper Old 
 Eed Sandstone is well developed along the shore and on the lower 
 slopes, and its component strata can be satisfactorily studied both 
 on the beach and in the numerous ravines which have been eroded 
 by the streams down the inland declivities. The passage of the 
 red sandstone conformably upwards into the base of the Carboni- 
 ferous system can be followod in these bum-sections, where the 
 lowest sub-division of that system, known as the Calciferous Sand- 
 stones, is likewise displayed in the characteristic development which 
 it assumes in the West of Scotland. Immediately above these 
 sandstones comes the thick volcanic series which forms so notable 
 a feature in the scenery and geology of Central Scotland. Only the 
 extreme western edge of the plateau formed by the lavas and tufis 
 comes into the ground here described, but it includes excellent and 
 typical illustrations of the general character and arrangement of 
 these rocks and of their influence in the landscapes of the country. 
 Good natural sections may be found along the craggy slopes of the 
 hills, and also in the numerous gullies of the burns. The hillsides 
 on the east of Noddisdale Glen, the gorge of the Gogo Glen above 
 Largs, and Kelburn Glen near Fairlie, are particularly worthy of 
 attention by those who wish to study the volcanic history of this 
 district. 
 
 But the interest of this history is not confined to the sheets of 
 lava and tuff of which the inland plateau is built up. Owing to 
 the vast denudation which has removed the westward extension of the 
 volcanic sheets, probably once continuous across the Cumbrae islands 
 and the south end of Bute to the north-east of Arran, the under- 
 lying strata through which the erupted materials made their way 
 have been extensively laid bare, and with them have been revealed 
 many of the subterranean connections of the volcanic sheets. Sills 
 and dykes traverse both the Carboniferous and Upper Old Eed 
 Sandstone strata, and may be examined in great numbers along the 
 shore and in the ravines. But still more remarkable is the display 
 of volcanic necks which mark the sites of some of the vents up 
 which the eruptions took place. To the west of the edge of the 
 plateau, between Largs and Ardrossan, at least a dozen of these 
 necks may be counted. They generally form rounded, green hills, 
 which rise conspicuously above the surrounding sandstone slopes. 
 
 Besides these memorials of Carboniferous volcanic action, the 
 district includes some examples of the great series of younger basalt- 
 dykes which plays so important a part in the geology of the West 
 of Scotland, and may be assigned to an older part of Tertiary time. 
 
General Geological Description. 11 
 
 The glacial phenomena of the tract of country here described, 
 though not striking, furnish evidence that the whole of the ground 
 was ground down by ice which moved in a southerly direction from 
 the Highlands. The proofs of this movement are found in ice-worn 
 rock-surfaces and in the contents of the drift-deposits. 
 
 Traces of raised beaches are found at various heights from the 
 100-feet Terrace down to the latest at about 15 feet above the 
 present level of the sea. Of recent deposits the most extensive are 
 the marine alluvia, which are laid bare in wide sandy flats at low 
 water. The streams which descend from the hills have slopes too 
 rapid to permit any marked deposition of sediment. There is con- 
 sequently little fluviatile alluvium. Peat covers the depressions on 
 the surface of the plateau, and in at least one place, Carlung Moss, 
 forms a peat-moss on the lower ground. Some trifling accumula- 
 tions of blown sand only suffice to indicate that the conditions for 
 this variety of geological process are not here favourable. A. G. 
 
CHAPTER III. 
 
 MetamorpMc Bodes. 
 
 All the rocks to be described in this chapter have undergone 
 some amount of deformation. They have been folded and cleaved, 
 and mica or chlorite has been developed along the cleavage planes 
 to a greater or less extent. The original grains or pebbles in the 
 rock, such as quartz and felspar, have also been more or less drawn 
 out or elongated in certain directions along the planes of foliation, 
 so as to produce a schistose structure. Sometimes these planes of 
 schistosity coincide with the original bedding of the rock, but very 
 often they do not, and over considerable areas the true bedding is 
 obscured by the superinduced structures. 
 
 These rocks are the oldest we have to deal with, but their exact 
 age is still undetermined. They make up the whole of the 
 Kintyre area included in this sheet, the island of Inchmarnock, and 
 the part of Bute west of Loch Quien, and they form an incomplete 
 ring round the central granite mass in the north of Arran, which 
 varies much in width, but which at Dougrie and to the east of 
 Lochranza is about two miles across. 
 
 In texture these rocks vary from very coarse, gritty, and pebbly 
 varieties to fine-grained slaty rocks or phyllites. They are in this 
 district a continuation (of course with sea intervals) of the schists 
 on the southern margin of the Highlands which have been described 
 in the Memoir on the Cowal district of Argyllshire, and in the main 
 they have the same north-east and south-west strike as in the Dunoon 
 district, but with some variations due apparently to the intrusion 
 of the granite mass in Arran. Quartz veins, often coinciding with 
 the foliation planes, are characteristic generally of these schists, but 
 the amount of these varies much in different places ; sometimes 
 they are abundant, while in maiiy districts in Arran few are to be 
 observed. This paucity of quartz veins or the reverse, has, however, 
 no relation to proximity to the granite, as the older writers sup- 
 posed, for they were developed in the rock long prior to the 
 intrusion of the granite. There is also great variation in the 
 amount of mica developed in the schists. The term mica-schists, 
 under which they have been referred to, is scarcely applicable to 
 them as a whole, seeing that mica is sparingly developed in them 
 except in the finer-grained varieties that appear along the coasts 
 about Imachar, Pirnmill, and Thundergay, and the more gritty 
 varieties in the neighbourhood of Lochranza. Along this north- 
 western part of Arran, however, the rocks have been more than 
 usually plicated, and contain numerous quartz veins. Along the 
 eastern and south-eastern sides of the granite mass the schists con- 
 
Metamorphic Rocks. 13 
 
 tain little mica, and are little more than schistose grits. Generally 
 the rock is a moderately fine-grained schistose sandstone, including 
 occasional bands of a fine blue slate, and also rocks of a decidedly 
 gritty character, schistose greywacke, and conglomerate with 
 deformed pebbles. 
 
 No order of succession has been made out over a large part of 
 the area. In Arran the rocks are much folded on the south-side of 
 the lorsa valley and along the west coast. To the north-east of the 
 granite mass there is a fairly uniform dip to the south-east and 
 east, and there appears to be a regular upward succession from the 
 ordinary gritty schists east of Lochranza through a thick series of 
 slates (Dunoon ?) into a thick series of alternating coarse grits and 
 fine beds, which apparently includes in its upper part a contem- 
 poraneous volcanic group, presumably of Arenig age. 
 
 Detailed Description. — To the east of Glen Eosie there is a 
 good exposure of schists all over Glenshant Hill. In the Cnocan 
 Burn, below the mill dam, the true dip of the schists is to the S.E. 
 or S.S.E. at a high angle, and the foliation dip is there coincident 
 with that of the bedding. The rocks are mostly gritty and some 
 are pebbly, and this type of schist prevails nearly all over Glen- 
 shant Hill. In Creag Rosie some alternations of thin gritty, and 
 slaty bands show that the beds are vertical with a north-east strike. 
 To the north-west of this the foliation strikes in one place to the 
 N.N.E., while the bedding strikes E.N.E., so that the true dip is at 
 a high angle to the S.S.E. Near the granite these rocks are con- 
 siderably altered, and appear to be more contorted than usual. 
 Much of the same type of schist prevails on the opposite side of 
 Glen Rosie, about the hill called Cul nan Creagan, where thin 
 quartz veins occur occasionally in the rock. In Gleann Easbuig, 
 east side, and 950 yards north from the top of An Tunna, is a very 
 coarse pebbly band of a slightly greenish tinge, which is about 30 
 feet in thickness. The deformed pebbles are of quartz and felspar, 
 and the rock which contains them set in a slightly chloritic 
 matrix, may be traced in a direction slightly north of west for about 
 200 yards, cutting across the foliation of the ordinary schist near. 
 There is much gritty schist on the north-west side of Gleann Easbuig, 
 but no rock so coarse as that described above was noticed there. 
 On the hills called Beinn Ghaorach and Beinn Lochain to the south 
 of the lorsa valley the schists are generally so plicated that it is 
 difficult to make out any prevailing strike. Much of it is fine- 
 grained with quartz veins. On the north side of the lorsa the 
 rock is altered by the granite, and the foliation rendered obscure in 
 many places, the most prominent planes being joints, which seem 
 the result of the granite intrusion. The rocks are well exposed in 
 the lower part of Glen Scaftigill, and in the adjacent burn of 
 AUt na h-Airidhe. In Glen Scaftigill the schist is moderately fine- 
 grained, and bluish or grey in colour, the foliation is generally even 
 and regular with little contortion and few quartz veins. The 
 foliation dip is to the south or S.S.E. at a high angle ; sometimes 
 it is vertical, while the bedding as seen distinctly in one place 
 strikes N.E., and dips steeply S.E. The foliation at this place dips 
 
14 The Oeology of North Arran. 
 
 S.S.E. To the westward, about Cnoc Donn and between this hill 
 and Dougrie Point, there is a strong band of gritty rock which is 
 very slightly schistose, and is apparently overlying a thick band 
 of black, bluish and grey phyllitic schist, which is much contorted. 
 Some very coarse and pebbly bands of the gritty rock are exposed 
 in the old sea cliffs three quarters of a mile north of lorsa Foot, and 
 the contorted slaty rock is exhibited in many places to the S.E. of 
 Balliekine. Alternations of gritty and slaty schists, very much 
 plicated, appear along the shore between Balliekine and Imachar, 
 opposite which latter place the schists are more than usually 
 contorted, with abundant veins of quartz (see Plate II.). On the hills 
 nearly a mile E.N.E. of Imachar alternations of pebbly bands with 
 rocks of a finer grain show that the strike of the foliation is from 10° 
 to 15° farther west of north than that of the bedding. Both are 
 practically vertical. North of Allt Gobhlach, along the shores of 
 Penrioch and Auchmore, the schists are not so much plicated, but 
 numerous faults crossing the alternations of fine and coarse rock are 
 exposed on the shore. At North Thundergay, again, the rocks are as 
 plicated as at Imachar. There are some very coarse bands about 
 Penrioch, but they are usually thin and cannot be traced far. One of 
 them contains pebbles from two to four inches long. There is also, east 
 of North Penrioch, a band of light-coloured, schistose, micaceous 
 limestone some four or five feet thick, which was formerly quarried 
 and burnt for lime. It can be traced for a considerable distance to 
 the northward. Some other very thin calcareous bands are inter- 
 calated in a dark-coloured schist. 
 
 In the lower part of the Pirnmill district the schist forms a 
 remarkable series of ridges and hollows nearly coincident with the 
 strike; higher up the hillsides other marked features are appar- 
 ently due to joints or faults, as their direction makes an angle with 
 the strike. Near the granite the schist is much hardened, and the 
 finer varieties assume a bluish colour. A marked set of joints 
 appears also to have been developed in this altered rock by the 
 action of the granite. These joints are in places much more 
 prominent than the foliation planes, which are nearly obliterated. 
 
 The ring of altered schist near the granite is here and there 
 some two or three hundred yards in width. As the rock is less 
 easily decomposed than the granite itself it occasionally forms a 
 ridge at a higher elevation than the granite immediately adjoining. 
 This is finely shown in Glen Catacol and Glen Easan Biorach, 
 where the streams have cut narrow gorges through the altered schist. 
 
 On the north side of the stream Allt nan Eireannach, nearly half 
 a mile S.S.W. of Catacol Bridge, there occurs a beautifully glossy, 
 gritty mica schist with abundant sericite mica on the foliation 
 planes. Along a great part of this bum runs a thick band of dark 
 slaty schist, which is probably identical with that which appears near 
 the foot of Abhuinn Bheag on the east side of Glen Catacol. And 
 there is strong probability that the same band continues southward 
 from Glen Catacol nearly parallel to the boundary of the granite, 
 but at no great distance, as far as to Allt Gobhlach opposite 
 Pirnmill. 
 
o 
 
 o 
 
 .5Q 
 
 a-2 
 
 o 
 U 
 
Metamorphic Eochs. 15 
 
 North-westerly dips prevail in the schists in the districts between 
 Catacol and Pirnmill, though, of course, there are many minor folds 
 parallel to the general strike. On the eastern side of Catacol Bay 
 there is a marked synclinal fold, which runs nearly parallel to and 
 not far from the coast. The line of it crosses the loch a little north 
 of Lochranza Castle, and it can be observed for some distance east of 
 the loch but gradually disappears, so that from North Newton 
 there seems to be a regular and apparently ascending series in the 
 schists all along the edge of the high ground to the south-east- 
 ward as far as to Corloch, where we come upon the supposed Arenig 
 lavas. On the shore at North Newton, where the rocks have a high 
 dip to the south-south-east, the schists are gritty, somewhat 
 greenish and chloritic, with alternating bands of finer slaty schist, 
 more micaceous or chloritic and with more abundant quartz veins. 
 Some bands outcropping to the east of the hamlet are very strong 
 and coarse. Variable rocks of more or less gritty character 
 prevail over Onoc nan Sgrath and Torr Meadhonach till, near the 
 road leading to the Cock, we come upon the edge of a thick slaty 
 series, in which there are two old slate quarries about a quarter of a 
 mile south of the road. In the larger and more easterly quarry there 
 are rather coarse and thickly laminated bluish slates with some pale 
 coloured or greenish, probably chloritic, bands. The slates are not 
 glossy, and there is not much mica on the foliation planes. Dark 
 bluish, fine slaty schist with quartz veins appears in Creag Ghlas 
 Cuithe at the edge of the high ground, where the dip is almost due 
 south. In Glen Chalmadale the dip is eastward, and between 
 these. two localities the strike describes a curve of a quarter of a 
 Qircle. This slate band is most probably the Dunoon series 
 described in the Memoir of the Gowal district. To the eastwards 
 succeeds a strong, coarse, and thick gritty mass, which is probably 
 • the Kilcreggan series. It is a very massive grey and greenish 
 greywacke, only slightly schistose, the bedding of which is as even 
 and as regular as a sandstone. In one place there is interbedded 
 a few feet of greenish slaty rock, which much resembles the green 
 beds in character. Pebbly bands are common in this rock and show 
 the bedding clearly, which dips from 30° to 50° E.S.E. This rock 
 forms a very fine set of crags, some of which are bounded by straight 
 faces running nearly across the strike. They appear to be due to 
 joints, along which the rock has parted, and masses have fallen 
 away. In the upper part of this series are alternations of slaty and 
 gritty beds which give rise to strike features crossing the line of 
 crags. These pass up into a greenish slaty series which forms the 
 highest ground at the Ordnance Station 1453, and this is the highest 
 point attained by the schists in the island. About half a mile south 
 of this the gritty series below forms crags at Creagan a'Choilich, 
 where a very coarse, pebbly, quartzo-felspathic band may be seen. 
 Eastwards from the Ordnance Station another thick gritty series 
 comes on above the finer band, the upper part of it being marked 
 by a very coarse, quartzose pelDbly band 100 yards in breadth. In 
 various places along the course of this band it may be observed 
 that the true dip as shown by the quartz pebbles is high, some- 
 
16 The Geology of North An an. 
 
 times nearly vertical, while the planes of schistosity or foliation 
 dip about 30° or 40''. At the southern exposure of this band 
 there is a cross fault which shifts it westward 100 feet or more. The 
 crag here is visible at long distances. The pebbly quartzose rock 
 is white in colour, and is penetrated by conspicuous white quartz 
 veins. A portion of the rock might be described as a conglomerate. 
 Another band of dark and bluish slaty schist succeeds to the east- 
 wards, and is some 200 yards across, but is little exposed except on 
 the crags ; and then comes a gritty series, variable in character, 
 half a mile across, which continues till we arrive at the so-called 
 Arenig traps. W. G. 
 
 SKIPNESS DISTRICT. 
 
 In that portion of Kintyre which enters into Sheet 21 the meta- 
 morphic rocks which floor the whole area consist of alternations of 
 quartzose mica schists and phyllites, the former being greatly in 
 excess of the latter. The microscopical examination of specimens 
 [9545, 9546, 9547,] by Dr. Flett shows that the quartzose 
 varieties exhibit every grade of alteration from schistose grits 
 in which pebbles of blue quartz and cleavable felspar occur, 
 which are only granulitized paripherally and set in a 
 schistose matrix composed of a secondary granulitic mosaic of 
 quartz and felspar traversed by wavy films of white mica and 
 more or less chlorite, into schists in which the remains of pebbles 
 are not readily detected, as the whola rock is converted into a 
 granulitic mica-schist in which the pebbles are represented by 
 flattened granulitic aggregates. There is a regular gradation from 
 these quartzose schists into phyllites and mica schists by the 
 increase in the proportion of mica to the other ingredients, evidently 
 owing to original difierences in texture and composition, the finer 
 phyllites and mica schists doubtless representing the more 
 argillaceous bands. When»not stained these rocks are usually 
 greenish-grey in colour, according to the amount of chlorite they 
 contain, but the phyllites are leaden-grey coloured and slightly 
 calcareous. Both sets of rocks are much traversed by quartz veins. 
 
 In a great many cases the original bedding is still readily made 
 out, while the foliation for the most part does not coincide with the ' 
 bedding planes. In some cases at least two sets of foliation planes 
 can be seen to lie oblique both to the bedding planes and to one 
 another. 
 
 The rocks in the area are evidently a continuation to the N.N.B. 
 of the beds which make up the greater part of the eastern side of 
 the peninsula of Kintyre. From their relation to " Green Beds " 
 and to the " Loch Tay " Limestone, to which they behave in Kin- 
 tyre in the same manner as the Ben Ledi grits do in the rest of 
 Argyll and in Perthshire, there can be little doubt that these rocks 
 in the present area represent the upper members of the " Ben Ledi 
 grit " group. 
 
 The schists are much crumpled and wrinkled, and in the N.W. 
 corner of the sheet they can be seen to be folded upon almost 
 
Metamorphic Rocks. 17 
 
 vertical axes, while over all the rest of the area they appear to dip 
 towards the south-east ; but this does not necessarily imply that 
 there is an ascending order of succession in that direction. The 
 apparent dip is due to their heing isoclinally folded, the axial 
 planes of the folds being inclined in that direction. That this is 
 the case throughout the whole eastern side of the peninsula of 
 Kintyre is shown by the behaviour of the overlying " Green Beds " 
 and " Loch Tay " Limestone in the Campbeltown region. By 
 following the outcrops of these beds it can be shown that the 
 apparent axis which runs along the centre of the peninsula, away 
 from which the rocks appear to dip on each side, is in reality an 
 axis from which the axial planes of isochnally folded beds dip 
 away, and that in spite of the apparent easterly dip of the strata in 
 the present area the beds which crop out at Skipness may actually 
 underlie those exposed along the great central axial line. This is 
 rendered highly probable, for in the adjoining region in Sheet 20, 
 just out, of the present map, a fold of the " Green Beds" is found 
 on the shoulders of Bhein Bhreac between the schistose grits which 
 crop out on the shore at Oour and the central axis, the Cour rocks 
 being a continuation of those that occur near Skipness. 
 
 The best exposures of rock are found along the coast, but owing 
 to the coast-line coinciding more or less with the long axes of 
 the folds, the same beds often form the coast-line for long distances. 
 Inland, the principal streams do not as a rule expose rock-sections 
 near their mouths, but flow over glacial deposits, raised beach 
 material, or through their own alluvia. This is propably due to the 
 land having stood at a higher level in pre-glacial times than at 
 present, so that the rocky bottoms of these drift-filled valleys are 
 actually below sea level at or near the coast, phenomena common 
 around our shores. Further up the valleys the streams have cut 
 down through the drift and exposed sections, but the best inland 
 exposures are to be found on the hillsides, which are often rocky. 
 
 B. N. P. 
 
CHAPTER IV. 
 
 Arenig (?) Hocks. 
 
 A strip of rocks that may be separated from the ordinary schists 
 of the island is found in North Glen Sannox, It crosses the valley 
 from south to north at a distance of rather over a mile from the sea. 
 It is upwards of a mile and a half in length, and its width varies 
 from 100 to 400 yards, being narrowest at its northern end. The 
 rocks in this area, so far as can be ascertained, are not separated by 
 any structural line from the ordinary schistose grits on either side 
 of them, and they appear to be essentially a part of the metamor- 
 phic series of the Highlands. They differ much in character, how- 
 ever, from ordinary schists, in that they consist mainly of igneous 
 rocks, both volcanic and intrusive, with which are intercalated 
 bands of black shales or schists, and thin bands of chert. 
 
 The black shales and cherts are associated together, as they are 
 in the Aberfoyle district along the Highland border, and in the 
 band of similar deposits intercalated with volcanic rocks in the 
 Arenig group of Ayrshire. The black shales are partly in the con- 
 dition of phyllites, and are much contorted in places. The cherts 
 are perceptibly granulitized, and in structure similar to those parts 
 of the cherts which have been altered by the granite of the 
 southern uplands. When in this condition, such rocks have 
 generally lost all trace of their organic remains, and no radiolaria 
 have yet been found in these Arran cherts. The most prominent 
 members of this group of rocks are those of igneous origin, and it 
 is now definitely ascertained that there is in Arran a very 'old 
 volcanic series which includes undoubted lavas and volcanic tuffs. 
 The lavas form bands of a dull-green, fine-grained rock, which may 
 be conveniently spoken of as "greenstone." Like their associated 
 sediments they have undergone a considerable amount of deforma- 
 tion, and are now in the condition of epidiorite. The whole of the 
 rocks, both aqueous and igneous, appear to be in the same state of 
 metamorphism as the schists to the east and west of them. They 
 have an apparent dip to the east-south-east at high angles, and 
 sometimes are practically vertical, and it is by no means certain 
 which is the top or bottom of the series. They have also under- 
 gone much plication, which is particularly observable in the inter- 
 calations of black schist, and, as has been before observed, they 
 are flanked on either side by schistose grits of the ordinary 
 southern Highland type. 
 
 The strip of rocks thus defined is truncated at its southern 
 end by the intrusion of Arran granite at the north-east end of 
 the ridge of Suidhe Fhearghas, while its northern boundary is a 
 
Arenig (?) Rooks. 19 
 
 fault which brings down against it a part of the Lower Carboni- 
 ferous series. The schistose grits, which apparently underlie 
 these rocks, are well exposed in the North Sannox Burn at the 
 bridge, while another series of schistose grits, which apparently 
 overhes these volcanic rocks, can only be observed in the 
 main stream and on the south side of the glen, as they are cut 
 out on the north side by the Highland border fault, which 
 brings down the Lower Old Eed Sandstone against the igneous 
 rocks. This fault gradually crosses the line of strike of the 
 igneous group, so that only the lower portion of it is represented 
 at its northern end. 
 
 The general succession of the members of this group of rocks, 
 together with the underlying and overlying sedimentary strata 
 belonging to the Highland schists, is apparently, in descending 
 order, as follows: — 
 
 L Coarse schistose grits or gritty schists, grey in colour, and 
 weathering with a smooth surface. 
 
 2. Thin bands of slaty schist, with traces of dark schist or 
 shale, apparently alternating in places with thin bands of 
 greenstone. 
 
 3. Upper bed of greenstone, generally fine-grained and quite 
 schistose in places, with some lenticular bands of agglomerate. 
 
 4. Bands of Kght-coloured and dark chert, associated with 
 bands of laminated black shale or schist. Lenticular bands of 
 volcanic tuff and of schistose grit also occur on this horizon. 
 
 5. Lower bed of greenstone, often massive. It contains an 
 agglomerate band on the north side of the valley. 
 
 6. Bands of black shale or schist, associated with chert, and 
 with some fine-grained slaty schist. There are traces of agglo- 
 merate also. 
 
 7. Thick mass of strong and coarse schistose grit, sometimes 
 greenish in colour and generally different in character from No. 1. 
 
 The whole succession may be observed in the North Sannox 
 Burn, and on the hillside to the southward. On the north side of 
 the glen the upper grit and greenstone are obscured by glacial 
 drift for some distance till they are cut ofi" by the Highland fault. 
 Nos. 2 to 6 embrace the rocks supposed to be of Arenig age. 
 
 The gritty schists. No. 7, are well exposed in the stream where 
 the road to Lochranza crosses, both above and below the bridge. 
 They are here crossed by some basalt dykes. About 70 yards east 
 of the bridge the coarser rock contains a band of fine-grained 
 schist, and 80 yards further down the stream dark schists are seen 
 to be associated with a brecciated rock like that which occurs in 
 several places. It is composed of fragments of old lava, but is not 
 exactly like a true volcanic agglomerate, and may have been pro- 
 duced by the brecciation of igneous rock in motion before final con- 
 solidation. Above these rocks in the main stream comes the lower 
 mass of lava (No. 5), which occupies the burn for a hundred yards. 
 It is for the most part a massive rock, moderately fine-grained, and 
 of a greenish-grey colour. It exhibits well developed " pillow- 
 structure " identical in character with that of the basic lavas of 
 
20 The Geology of North Arran. 
 
 Arenig • age in the southern uplands, but not on so large a 
 scale (see Plate III.). The chilled and rounded margins of these 
 "pillows," and the numerous amygdales that are found a short 
 distance inward from their surfaces are marked features. The dark 
 schist that apparently overlies the pillowy lavas is much contorted 
 in places, and is accompanied by a breccia or agglomerate similar 
 to that previously described in No. 6, and also by some thin lava- 
 like bands. The cherts that are associated with the black schists 
 are well exposed about 200 yards up AUt Cairn Bhain, a small 
 stream on the north side of the glen. Some of them are dark in 
 colour, but the thickest and purest bands seem generally to be grey 
 or light-coloured. High up on the south side of the valley there is 
 associated with this black schist a strong gritty band, and im- 
 mediately upon this rests the upper greenstone, No. 3. In the 
 main stream this is but occasionally exposed, and the best sections 
 of it are in the hillside to the southward. It much resembles the 
 lower- bed, but the pillowy structure is not so prominent. In its 
 upper part the rock is often so schistose that it might be taken for 
 the so called "green beds" of the southern Highlands. There is a 
 good exposure of this upper lava on and about the two small hills 
 called Cnocan Donna, where the doubtful Arenig rocks attain their 
 highest point above the sea (944 feet). On each of the knolls a 
 band of true agglomerate is interbedded with the greenstone. 
 These bands are lenticular, and are made up of large angular frag- 
 ments of fine-grained lava. Neither of them can be traced for more 
 than 40 or 50 yards along the strike, and the more southerly is not 
 more than 6-feet across at its widest part. The other is larger, and 
 probably as much as 30 feet across in its broadest part. 
 
 The upper schistose grits, but partly exposed in the main stream, 
 are a prominent feature on the hillside to the southward, where 
 they form a strip of ground 200 yards in width. -They can be 
 followed in this direction along the strike to the eastward of 
 Cnocan Donna till they in turn are cut ofi" by the granite. 
 
 The lower greenstone forms prominent crags, one of which, about 
 300 yards south-south-east from the bridge, is a conspicuous 
 object from the road. The same rock forms crags at Corloch, at the 
 northern extremity of the area, and all the crags on the north side 
 of the valley between AUt Cam Bhain and Allt Dornach, the next 
 small stream to the west. 
 
 There can be little doubt that these bands which we have called 
 greenstone are true lavas, and they show many points of 
 resemblance to the lavas of the Arenig volcanic series of Ayr- 
 shire. 
 
 Two specimens from these doubtful Arenig lavas have been sliced 
 and submitted to microscopical examination by Mr. Teall. One of 
 these from Cnocan Donna on the south side of North Glen Sannox, 
 is a fine-grained, greenish-grey massive, rock (8666) composed of 
 minute prisms of nearly colourless hornblende, epidote, leucoxene 
 after iron ores, quartz, and chlorite. 
 
 It is evidently an altered basic igneous rock, a variety of 
 epidiorite. 
 
o 
 
 o 
 
 m 
 
 J 
 
 
 X 
 
 > a 
 
 " CO 
 
 -<^ 
 
 o 
 
 
 Cl, 
 
Arenig (?) Bodes. 21 
 
 Another specimen from Torr na Lair Brice on the north side of 
 the glen (slide 8667) is a scoriaceous rock, the cavities of which have 
 been filled by calcite. The main mass is formed of microlitic 
 felspar, chlorite, leucoxene, and carbonates. It is an altered basic 
 rock, but differs from the first in having recognisable felspar. It 
 is closely allied to, but not identical with, the common forms of 
 pillow lavas. 
 
 These two fine-grained rocks are highly altered greenstones, 
 allied to those found in association with cherts in other areas. 
 
 Some additional specimens have lately been cut, and the slides 
 are described by Dr. Plett. Three of these (9381, 9382, 9383) from 
 Torr na Lair Brice, 550 yards N.E. of North Sannox Bridge, though 
 differing somewhat in individual characters have a general resem- 
 blance to those described by Mr. Teall. A specimen (9384) from a 
 small burn on the south side of the glen opposite AUfc Cam Bhain 
 is rather peculiar, being a grey-green rock with brovra streaks 
 and patches. It is a fine-grained basic igneous rock which has 
 undergone much deformation. There is a band of this rock along 
 the strike, and it may be seen also just south of the main stream. 
 Two specimens of the supposed lavas altered by contact with 
 granite (Nos. 9385 and 9386) are very different from the rest, and 
 one of them (9386) appears to have lost all trace of its igneous 
 origin (can it be altered black shale ?) . The last of these new 
 slides (9387) is taken from a fragmental rock of a tuffaceous 
 character in the upper part of AUt Oarn Bhain. Many of the frag- 
 ments are fine-grained and not certainly igneous, but the band 
 from which the specimen was taken is several feet thick and the 
 coarser parts contain undoubted large fragments of the lavas. This 
 band is associated with the black schists. 
 
 Intrusive Igneous Eocks, Probably of Arenig age. 
 
 At a distance of 600 yards north from the main stream in North 
 Glen Sannox, and near Allt Dornach, is a rock which differs 
 considerably in character from the lavas. It is coarser grained than 
 these, and was probably a hornblende gabbro originally. It was the 
 first of the igneous massesi;o be noticed in this area, and from the way 
 in which it is associated with ordinary schistose rocks of a clastic 
 origin it was regarded as an intrusive rock, which view has 
 subsequently been corroborated by the result of a microscopie 
 examination and also by its similarity to undoubted intrusive 
 rocks associated with the Arenig lavas of Ayrshire. It forms a 
 band some 15 to 20 yards in width, which is about 50 yards east of 
 the small stream mentioned, and on the west side of the bedded 
 lavas, and separated from the latter by a considerable band of black 
 schists with chert. The intrusive band, however, as given above, 
 includes some lenticular and irregular strips of schist. The best 
 section occurs a few yards below the old track or road which was 
 formerly the highway to Lochranza, and the intrusive rock there 
 forms a small crag, bat it cannot be traced far either way. A rock 
 of a somewhat similar character is found on the west side of 
 
22 The Geology of North Arran. 
 
 Allt Oarn Bhain (the next small burn to the east) between 100 
 and 250 yards north from the main stream of the glen. 
 
 Epidiorite or Hornblende Schist. 
 
 To the south of Scalpsie in Bute there is a considerable mass of 
 epidiorite or hornblende schist which appears to form a sill or 
 intrusive sheet in the schist. It is nearly 400 yards in length 
 from north to south, and it occupies the hill called the Dun, on which 
 is an old fort, and the edge of the high ground to the southward as 
 far as the head of Scalpsie Bay. It is bounded by the sand and 
 gravel of the raised beach on the east side, and the schists into which 
 it is probably intruded are only seen to the west of it. On the 
 south side oi the Dun the rock is mainly a fine-grained, dark-green 
 massive rock which may be termed an epidiorite. It is a confused 
 aggregate of chlorite, hornblende, epidote, carbonates, felspar, and 
 leucoxene. This altered basic, igneous rock varies considerably in 
 character, passing southward and northward into a fine-grained 
 hornblende schist with epidote. 
 
 There is strong reason for the view that this mass of epidiorite is 
 closely related to that associated with the supposed Arenig rocks of 
 Arran, and there is every probability that we are in this part of 
 Bute just below the horizon of those contemporaneous volcanic 
 rocks. 
 
 Serpentine. 
 
 On the west side of Scalpsie Bay in Bute serpentine occurs in 
 two places in or near the large fault skirting the west side of the 
 bay. In the first case it is about 76 yards from the head of the 
 bay and just below high-water mark of the ordinary spring tides. 
 It is apparently just at the edge of the fault, is much crushed, but 
 can be traced for a little distance westward. No other rock is 
 seen in contact with it. About 75 yards farther to the south-west, 
 and nearly at the shore line, serpentine again occurs. This locality 
 is 25 yards from the wall which here runs parallel to the shore, 
 and nearly opposite a cross wall. Here again no rock is seen in 
 contact with the serpentine, but a short distance to the south-east 
 white carboniferous sandstone on the other side of the fault appears, 
 dipping south-south-east at 30°. The serpentine is a compact 
 pale-greenish rock, remarkably uniform in character, and the 
 alteration so complete as to make it impossible to say what the 
 original mineral was which makes up its aggregate of irregular 
 scales, but it was probably not olivine. It must, however, have been 
 some basic or ultra-basic rock intrusive in the schists, for similar 
 rocks are thus seen west of Loch Fad, and near Innellan in the sheet 
 to the north (29, one-inch). 
 
CHAPTER V. 
 
 Old Red Sandstone. 
 
 A strip of the Old Red Sandstone occupies the eastern coast of 
 Arran from the Fallen Rocks at Oorloch southwards to near Corrie, 
 and continues inland as far as the Brodick woods, whence it sweeps 
 as a belt across the centre of the island to the western coast 
 near Dougrie. A detached part of the formation is found on the 
 eastern and south sides of the smaller granite area from Glen 
 Dubh by Onoc na Croise and the head of the Olachan Glen round 
 to near Cnocan Biorach. This portion, which is some three miles 
 to the south of the String Road, is invaded by intrusions of granite, 
 granophyre, and diorite, by which all the surrounding strata are 
 highly altered. 
 
 Lower Old Red Sandstone. 
 
 This subdivision of the formation does not appear on the 
 eastern coast, but is well exposed in North and South Glen Sannox, 
 partly in the streams and partly on the hillsides. It consists of 
 course conglomerates, red mudstones, and purplish felspathic sand- 
 stones. The blocks in the conglomerates are well rounded, and 
 many of them are of a pinkish or white quartzite, often associated 
 with pebbles of andesite derived from the denudation of lavas be- 
 longing to a lower part of the formation. The conglomerates are 
 associated with, or alternate with beds of red or purplish fine sand- 
 stone and mudstone, and generally form the lowest and most 
 westerly part of the formation as exposed in these glens. The 
 middle portion is composed largely of mudstones and flaggy sand- 
 stones, and the higher part is mainly felspathic sandstone, 
 somewhat coarser and thicker bedded than that in the middle 
 part. All these beds have a general easterly dip often at high 
 angles. 
 
 A great series of purplish-red and chocolate-coloured sandstones, 
 generally hard and micaceous, and often thin bedded, occupies 
 Glen Shurig and strikes south-west, with a high dip to the south- 
 east, across the String Road. These rocks have been quarried in 
 places for road metal. They form, apparently, the highest portion 
 of the lower division of the formation. As the dip is high, they 
 must be between 2000 and 3000 feet in thickness. Although in 
 places the dip is reversed there are no apparent contortions, so that 
 the strata are probably occasionally inverted as they must 
 be in the Cnocan Burn, and on the west side of Glen 
 Rosie. It was in this group of rocks in Glen Shurig, in a 
 
24 5%e Geology of North Airan. 
 
 burn near the String Road, that Sir A. Geikie and his 
 students found a specimen of Psilophyton in the year 1882. 
 From the same upper part of this subdivision in Glen Shurig 
 about a dozen specimens of plants were obtained by Messrs. 
 Macconochie and Tait, the fossil collectors of the Geological Survey, 
 in 1897. Mr. Kidston, to whom these were submitted for examin- 
 ation, could only identify one of them specifically as Psilophyton 
 frinoe'ps, var. ornatus, Dawson.* He, however, thinks that all the 
 other specimens belong to this species, which is characteristic 
 of the Perthshire and Forfarshire Old Red Sandstone, and is not 
 known in the Caithness Flags. The strata in which these plants' 
 were found are hard, purplish, flaggy, micaceous sandstones, often 
 weathering of a yellow tint, and they must be several hundred feet 
 lower in the formation than those which yielded Psilophyton in 
 1882, but both belong to the same set of beds. The exact 
 locality for the specimens collected by the Geological Survey in 
 1897 is in the main stream of Glen Shurig, about 200 yards above 
 its junction with Allt Mor, which is its principal tributary on the 
 south side. In the south bank of the stream at this point is a 
 good shale band about three inches thick, and it was from this bed 
 that the plants were obtained. Some fragments were also got on 
 a somewhat higher horizon, some 100 yards lower down the burn 
 and nearer Allt Mor, and it was in Allt Mor itself, but some 
 distance up from its foot, that the specimen was obtained in 
 1882. 
 
 The thick masses of mudstone, interstratified with coarse conglom- 
 erates made up mainly of quartzite pebbles, so conspicuous in 
 North and South Glen Sannox, are much attenuated in Glen 
 Shurig, while the upper felspathic sandstones are much thicker. 
 
 In Glen Rosie, near the schists, a type of the formation occurs 
 which is not red but grey in colour, and contains a different set of 
 pebbles, which are mostly of quartz. It may be observed in a 
 vertical position at the bend of the burn half a mile west of the 
 wood. The rocks here have a north-north-east strike, and appear 
 to have been confounded with the schists by some observers. 
 Epidote is pretty common in these rocks, and also in some similar 
 in character and position near the schists in Garbh Allt, north of 
 Monyquil. 
 
 Bast of Dougrie there are fine sections in the Old Red Sandstone 
 on the shore and in the old sea-cliffs, but a portion of the rocks 
 there exposed probably belongs to the upper division of the forma- 
 tion. The Lower Old Red Division, which is characterised by thick 
 bands of coarse quartzite conglomerate, alternating with red and 
 purplish sandstones, must in places on this side of the island have 
 a thickness of several thousand feet, with a high southerly dip 
 ranging from S.S.W. to S.S.E. The coarse conglomerate forms a 
 broken ridge of high ground east of Auchencar, and is apparently 
 unusually thick in the hill of Garbh Thorr, near Monyquil, which 
 is probably bounded on either side by a large fault. Below this 
 mass of conglomerate is found a volcanic zone, composed of lavas 
 
 * These plants were obtained from Locality No. 49, given in Appendix A. 
 
Old Bed Sandstone. 25 
 
 some 50 or 60 feet thick, which is elsewhere described (see page 26). 
 These crop out in Auchencar Burn, to the north of the hill 
 Baniorlach, one and a quarter miles farther east, and to the north- 
 west of Garbh Thorr. Below this zone the rocks consist mainly of 
 sandstone. The sandstones which overlie the conglomerate, 
 mostly thin-bedded or flaggy, are exposed in the Machrie Burn, 
 west of Cnoc na Oeille. 
 
 The boundary between these undoubted Lower Old Red Sand- 
 stones and the beds above which may belong to the upper division 
 of the formation, is somewhat arbitrary and uncertain, as the dip 
 and strike of the two set of rocks are, on this side of the island, 
 everywhere the same, and no fossils can be obtained to assist us in 
 the determination of the exact line. In the old sea-cliff, near the 
 Dougrie schoolhouse, more than half a mile north of Auchagallon, 
 there is a variegated marl bed covered with oval or round white 
 and greenish spots, and there are also narrow bands of the same 
 material along joints, some of which are also lines of movement. 
 This bed, which is 12 to 15 feet in thickness, with some irregular 
 sandstone on one side, contains doubtful traces of plants. This 
 band is included in the lower division, and the rocks above are 
 referred doubtfully to the upper or middle division. Similar 
 greenish marl bands are found along the strike in the Machrie 
 Burn, and in a smaller bum farther east, and some much thinner 
 bands of the same kind also occur in the Machrie Water, so that 
 the line given on the map seems to follow a definite horizon, if it 
 is not an actual boundary between two sub-formations. Below 
 these bands in the Machrie Water the rock is much hardened and 
 jointed, for which alteration there is no visible cause except an 
 intrusive basic dyke. 
 
 In the Clachan Glen, to the south of Beinn Bhreac, the rocks of 
 this sub-formation have been intensely altered by the granophyre, 
 so that now they are totally unlike Old Red Sandstones in char- 
 acter. They are, in fact, more like old silurian greywackes, 
 very hard and tough, and of a bluish-grey colour. They are also 
 apparently contorted in places, and the bedding cannot always 
 be determined. A similar alteration in the rock has taken place 
 on the north side of Gleann Dubh. 
 
 In the upper part of the Merkland Burn, outside the Castle 
 woods at Brodick, there are some rocks of a peculiar type in this 
 division. Near the edge of the wood, but inside, conglomerates 
 with well rounded pebbles of the true Lower Old Red type may be 
 observed in a vertical position and with a northerly strike. 
 Succeeding to these, outside the wood we find sandy red mudstones 
 in the stream for a hundred yards. They have the same vertical 
 strike as the conglomerates, but the last visible strata of this kind 
 have a strike directed somewhat west of north. These rocks are 
 abruptly truncated at a waterfall by a totally different set which 
 come on along a line running about north-north-east. The junction 
 line may be a fault, and the rock which we first come to on the 
 other side has somewhat the appearance of a dyke a few feet in 
 width. North of this we seem to have recognisable purplish mud- 
 
26 ■ The Geology of North Arran. 
 
 stones, altered, however, with another possible green dyke parallel 
 to the stream on the west side. Below the first branch stream on 
 the west side there appear to be fairly recognisable altered mud- 
 stones striking north-east and dipping south-west. All these rocks 
 have a number of yellowish-green veins and patches of epidote. 
 
 Above this, in the main stream, for a long way, is a mass of 
 apparently fine-grained, blue-grey rock with very indistinct traces 
 of bedding, and not at all resembling the ordinary type of Old Eed 
 Sandstone. Similar rocks may be seen in both the branch streams 
 on the west for a distance of about 200 yards up them, where rocks 
 of an undoubted gritty character appear. In the upper branch 
 stream this is a white hard-baked sandstone, almost a quartzite, 
 which has evidently undergone considerable alteration. This has 
 been microcopiscally examined by Mr. Kynaston, and is seen to con- 
 sist principally of numerous small rounded grains of quartz and 
 felspar, some of which is microcline and some plagioclase. The 
 interstitial material often has the appearance of a fine quartzose 
 mosaic, as if it had been recrystallized, but the larger grains show no 
 perceptible alteration. There are some grains of epidote. The 
 highest observed rock in the main stream, 700 yards above the 
 wood, is clearly an altered sedimentary rock, a rather coarse grit 
 with numerous fragments of andesite, more or less rolled, quartz- 
 grains, felspar, epidote, etc. 
 
 The doubtful rocks, some of which have been sliced, will be re- 
 ferred to again (see p. 27) with some remarks on the probable cause of 
 the alteration which is visible in the undoubted grits. 
 
 Contemporaneous Igneous Eocks of Lower Old Eed Sand- 
 stone Age. — In the Lower Old Eed Series of Arran, on the west 
 side of the island, is an interbedded volcanic series. It occurs near 
 Auchencar as a band of lava, and may be traced eastward for about 
 two and a half miles as far as to the north-west side of Garbh Thorr 
 near Moniquil. Everywhere it dips steeply to the south and under- 
 lies the main mass of the conglomerates, while the strata below it 
 consist principally of sandstones. Where this lava crops out at the 
 surface it is largely amygdaloidal and apparently of a basic char- 
 acter, though the lower portion of it is in places more compact, and 
 seems to be more basic than the rest. The best section of it occurs 
 in the Auchencar Burn, about seventy yards east of the moor 
 fence, where a thickness of from fifty to sixty feet is exposed. 
 Here the rock is amygdaloidal above and compact below. As the 
 band is nearly vertical it occupies but a narrow strip of ground, 
 and, besides, it is a good deal concealed by drift. Still, traces ol it 
 may be found in several places to the eastward, and undoubted 
 outcrops of it occur to the north of a conglomerate" hill called 
 Baniorlach, and also to the north-west of Garbh Thorr, where the 
 band appears to be thicker than in the Auchencar Burn. For the 
 appearance of these rocks under the microscope see Appendix. 
 
 In the conglomerates above this volcanic zone, pebbles of an 
 andesitic rock, presumably derived from the lava, are common. It 
 seems probable that the volcanic series was largely denuded before 
 and during the formation of these conglomerates, which contain 
 
Old Bed Sandstone. 27 
 
 these basic igneous pebbles in various parts of the island where no 
 other traces of the former presence of these contemporaneous rocks 
 exist. Some of these pebbles from near Auchencar and from Glen 
 Sannox have been microscopically examined, and descriptions of 
 of them by Mr. Kynaston are in the Appendix. 
 
 Intrusive Igneous Rocks of Lower Old Eed Sandstone Age (?). 
 — In Glen Rosie, about three quarters of a mile west of the hamlet, 
 is an intrusive sill in the Lower Old Red Sandstone. It crops out in 
 the southern bank of the stream, and may be traced up the hillside 
 to the southward and over the moor for nearly a mOe. Two promi- 
 nent knolls formed by it are called Torr Breac and Torr Dubh, and 
 at these places the sill is about 300 feet in width. The rock is 
 very massive, fine-grained, grey in colour or pinkish, and contains 
 in places veins of epidote. It is a peculiar rock, and seems of an 
 intermediate rather than basic composition. It appears always to 
 contain a pale-coloured augite, and is a salite diabase. 
 
 In the Lower Old Red Sandstone on the south side of Glen 
 Sannox is a large dyke which forms a marked ridge trending west- 
 south-west for nearly three quarters of a mile. It crosses the stream, 
 Allt a' Chapuill (which enters the Sannox Burn near the old barytes 
 workings), and runs toward the granite hill of Oioch na h-Oighe, but 
 no trace of it is to be found in the granite. Its average width is 
 about 150 feet. It is a coarse grained, brown-coloured rock, 
 apparently a kind of salite-dolerite. See Appendix for the micro- 
 scopical characters of these intrusive rocks. 
 
 Doubtful Rocks. — In Merkland Burn, Brodick, a mile and 
 upwards from the sea, in the Lower Old Red Sandstone area, are 
 some rather puzzling rocks, which seem at first sight a good deal 
 like altered grits, in which the bedding is often very obscure. 
 Some specimens from this locality, however, are very like felsitic 
 tuffs or agglomerate, and some of the fragments have points of 
 resemblance to the salite-diabase of Glen Rosie. But it must be 
 remembered that in places the undoubted Lower Old Red con- 
 glomerates are largely made up of fragments of old basic lavas. 
 Mr. Kynaston, however, has examined and reported on some micro- 
 scopic slides cut from the rocks as well as some undoubted Old Red 
 rocks from the immediate neighbourhood, and is inclined to the 
 view that they are of pyroclastic origin, of the nature of tufis or 
 agglomerates. One of the specimens sliced ,was the supposed dyke 
 at the edge of the mass, which is a fine-grained dark rock, apparently 
 of a massive character. Under the microscope, however, it appears 
 partly andesitic, and in a more or less fragmentary condition, and 
 partly consists of small fragments of quartz and patches of calcite 
 in a fine matrix. It is difficult to determine the exact nature of 
 this rock, and it seems possible that it is essentially a massive 
 rock which has been broken or crushed along or near a line of 
 fault, which may be of later date than the alteration surrounding 
 the doubtful rock, for there is no trace of such alteration on this 
 side in the Lower Old Eed Mudstones. 
 
 These doubtful rocks cannot be observed in the drift covered and 
 peaty ground east of the main stream, but they would appear to 
 
28 The Geology of North Arran. 
 
 be comprised in an oval area which is about 500 yards in length 
 from north to south. As the rocks of this area differ so much in 
 character from the genuine Lower Old Red Sandstone of the neigh- 
 bourhood, and as they have many points of resemblance to tuffs or 
 agglomerates of pyroclastic origin, it seems more probable that 
 they belong to the latter class. It will be most convenient, then, 
 to consider this small area as the site of a volcanic vent in the 
 Lower Old Eed Sandstone rocksj the age of the vent or the period 
 when there was outpouring of either lavas or tuffs being still to be 
 determined. 
 
 There remains to be considered the undoubted alteration in the 
 surrounding rocks ; at all events on the western border of the area. 
 The large mass of granite suggests itself as the cause of the alter- 
 ation; but the edge of the granite is half a mile distant, and 
 metamorphism in the surrounding rocks cannot be traced so far 
 away from its mass. Often in the case of Old Red Sandstone it 
 only extends some 40 or 50 yards away from the boundary. On 
 the contrary, the evidence, so far as it goes, favours the view that 
 the alteration in the surrounding rocks came from within the 
 doubtful area itself, and it seems extremely probable that the 
 operating causes were gaseous exhalations and emissions of heated 
 aqueous vapour in connection with a solfatara. 
 
 Uppee Old Red Sandstone. 
 
 The rocks of this division of the Old Red Sandstone have been 
 much studied in the island of Arran, where they occupy the shore 
 from the old march of Achag (not Achab) Farm, north of Corrie, to 
 the Fallen Rocks at Oorloch, a distance of three miles. They were 
 supposed to be typical of the whole formation of the island, but, as 
 will be seen from the sequel, they only represent the upper part of 
 the formation, while the Lower Old Red division is only seen in the 
 interior on this side of the island. The equivalents of these beds in 
 Great Oumbrae and in Bute were, while the survey of those islands 
 was in progress, classed with the Lower Carboniferous rocks, with 
 which they are in general perfectly conformable in the matter of 
 dip and strike. In all three localities there are alterations of red 
 sandstones, often false-bedded, with brecciated conglomerates, made 
 up largely of fragments of quartz and schist derived from the 
 denudation of the metamorphic rocks. Mingled with these, which 
 are often more or less angular, are well rounded pebbles or blocks of 
 quartzite derived from the conglomerates of the Lower Old Red 
 division. Bands of shale, when they occur, are thin, but they form 
 but an insignificant portion of the whole. As may be gathered 
 from the name of the division the rocks are generally of a red colour. 
 
 No organic remains have been found in these rocks within the 
 limits of this sheet, except doubtful fragments of plants found on 
 the shore about a quarter of a mile south of Farchan Mor. 
 
 On the north side of North Glen Sannox there are two distinct 
 sets of beds, separated by a contemporaneous volcanic series, which 
 probably belong to the upper division of the Old Red formation. 
 
Old Red Sandstone. 29 
 
 Above the shepherd's house we find, along the hillside, a purplish- 
 red felspathic sandstone which is pebbly in places. The pebbles 
 are generally small, and are of coarse, reddish quartzite and white 
 quartz, which are mingled together. Some thin bands of purplish 
 and red mudstone, like the thick masses which occur lower down in 
 the formation, are occasionally seen. The pebbles which occur in 
 the sandstone are well rounded, especially those of quartzite. The 
 dip of these rocks is clearly to the east-north-east, at angles of from 
 20° to 30°. These beds undoubtedly are the upper portion of the 
 Lower Old Red Sandstone. 
 
 At the top of the slope where these beds are found a Hue of 
 crags may be observed which consist of a very difierent type of 
 rock, a whitish conglomerate nearly in a horizontal position, and 
 with every appearance of being unconformable to the beds first 
 described. The pebbles in this conglomerate are mainly of white 
 quartz not well rounded, though a few of the well-rounded 
 quartzite pebbles common in the lower division also occur. The 
 numerous quartz pebbles give the rock a decidedly grey colour 
 when seen from a distance, though the matrix is often somewhat tinged 
 with red. Further west, beyond the first large fault, there are many 
 rounded quartz pebbles and some of schist in the basement beds. 
 The rocks in these crags must be considered as the lowest portion 
 of the Upper Old Red division. They have a gentle dip to the 
 northward and pass under a succession of massive, whitish, conglo- 
 merates of like character, which alternate with reddish, flaggy 
 sandstones. The whole forms a fine set of parallel escarpments 
 much broken by faults. The dip gradually increases till it reaches 
 25° or 30° in the highest beds of the series, a set of whitish and 
 somewhat flaggy sandstones which are pebbly occasionally and 
 which underlie the contemporaneous igneous rocks. The beds as 
 above described have a probable thickness of about 800. feet below 
 the lavas. The latter are purplish-red rocks, often amygdaloidal and 
 decomposed, which are elsewhere described (see latter part of this 
 chapter). They are much faulted ; their thickness is probably not 
 more than 100 feet at the most, and they appear to thin away rapidly 
 to the southward. Above them comes a series of red, flaggy sand- 
 stones which are surmounted by the ordinary red conglomerates and 
 sandstones partly exposed along the adjacent coast, the highest bed of 
 which has furnished the material for the Fallen Rocks. To the south- 
 east of these rocks it is principally conglomerate we find on the shore 
 for a distance of half a mile, when, after passing a fault ranging 
 north-east, we come upon the flaggy sandstones which overlie the 
 volcanic series. These occupy the shore for some 600 yards farther. 
 They dip N.E. and N.N.B. at comparatively low angles, 15° on 
 average, and at the south end are faulted against a coarse conglo- 
 merate, which occupies the shore for 200 yards, and is then cut ofi" 
 by a fault ranging E.N.E., which brings up much lower beds. From 
 this point, which is 700 yards from North Sannox Burn, the section 
 is very complicated and could not be described accurately without 
 much detail. There are numerous faults and in one place irregular 
 bands of impure cornstone, perhaps on the same horizon as one seen 
 
30 The Geology of North Arran. 
 
 at Farchan Mor. There is no trace of the volcanic series, and 
 nearer to North Sannox there is strong evidence for an unconfor- 
 mability, where in more than one place dull red sandstone abuts in 
 a peculiar way against conglomerate. Perhaps this may be the 
 reason for the absence of the bedded traps. As we approach the 
 bum the dip tends more and more towards the east, and on the 
 south of the stream it becomes south of east, and we have passed 
 over the anticlinal line so called. The sandstones and conglomerates 
 that lie immediately south of the burn dip about E.S.B. at angles 
 of 30° to 40°. They strongly resemble the beds formerly described 
 as lying below the lavas, and it is very probable they are a part of 
 that series. Above them there appears to be an unconformability 
 of the same kind as that occuring north of the burn. The rocks 
 which succeed are a series of flaggy red sandstone with occasional 
 pebbly bands, and these continue to the cross-wall, where comes 
 on the thick conglomerate which extends a long way on the 
 shore and which forms the fine crag called the Blue Rock. 
 At the south end of the shore section, nearly a quarter of a 
 mile from, the South Sannox Burn, is an interesting section. 
 A sharp line on the foreshore running N.N.W., which appears 
 to be a joint and not a fault, divides sandstone from conglomerate 
 for the greater part of its length, but near low-water mark 
 sandstone is found on both sides of this line, iDeyond the point 
 where the conglomerate is seen to overlap beds of sandstone. 
 Near high-water mark, also, conglomerate occurs east of the 
 line, wrapping round beds of sandstone. It is clear in this case 
 there is a local unconformability. Somewhat similar cases 
 occur south of Farchan Mor, one of which is near the Eocking 
 Stone. The coarse conglomerate bed on which stands this stone 
 overlaps beds of soft, shaly, red sandstone which lie below. This 
 section was photographed and is reproduced in Plate IV. A large 
 fault which runs nearly parallel to the coast truncates this 
 conglomerate near high-water mark, perhaps a continuation of the 
 fault which passes on the west of the Blue Rock; and some 
 distance southward there are several smaller faults. Near these 
 some curious hardened markings project from the surface of the 
 sandstone ; some appear vertical like finger ends, and others 
 resemble worm castings which are arranged into various patterns. 
 The rocks to the southward are mostly red sandstones, sometimes 
 false-bedded, which dip S.E. at angles from 20° to 30°. There are 
 some beds of conglomerate, one of which forms the highest part of 
 the formation, about a quarter of a mile north of the Corrie School- 
 house. These higher beds are shown in the section of the 
 Carboniferous rocks. 
 
 To the west of Corrie the ground occupied by the Old Red 
 Sandstone is much faulted, and also obscured by glacial deposits, 
 and the division between the upper and the lower parts of the 
 formation is very uncertain. Most of the writers on Arran describe 
 a narrow band of schist or slate along the eastern border of the 
 granite for a distance of about three miles southward from 
 Glen Sannox, but Old Red Sandstone certainly is the rock which 
 
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Old Red Sandstone. 31 
 
 occupies this position excepting for a length of half a mile to the 
 east of Cioch nah-Oighe, where a band of altered schist occurs next 
 to the granite. It is mainly the lower division of the Old Eed 
 Sandstone that is in contact with the granite along this line, and 
 it is doubtful if the upper division and the granite ever come 
 together. The width, however, occupied by the whole formation 
 as it is exposed at the surface is narrowed to 500 yards at the 
 Locherim Burn, and is not more than 400 yards south of the 
 White Water. 
 
 The lower boundary of the upper division to the south of Corrie 
 is but an arbitrary line, as the dip and" strike of both divisions 
 are the same. It has been drawn, however, through the Brodick 
 woods and up Glen Shurig, so as to include in the upper division 
 rocks which could not be referred to the lower division. South of 
 Gleann Dubh, where nearly all the Old Eed rocks are much 
 altered, the more felspathic rocks of the Lower Old Red become 
 grey in colour, while the more quartzose rocks of the upper division 
 are turned white, and this difference in colour assists one consider- 
 ably in deciding on the boundary between them. Some of the 
 rocks of the Upper Old Red are converted into quartzite. 
 
 In the Glachan Glen, to the south-west of Beinn Bhreac, there 
 is a thick series of white sandstones and conglomerates which 
 apparently occupy the position of the Upper Old Red rocks, though 
 they do not much resemble them in character, and certainly not in 
 colour. The white colour may be due, however, to the same cause 
 which has so highly affected the Lower Old Red Sandstone of this 
 district, viz., the intrusion of the granophyre and other rocks of 
 Beinn Bhreac. 
 
 On the western side of the island the beds above the genuine 
 Lower Old Red Sandstone are very variable. On the shore and in 
 the old sea-cliffs north of Auchagallon they are mainly conglom- 
 erates with some pebbly sandstones. In the Machrie Bum the 
 proportion of conglomerate to sandstone is not so great, and in the 
 Machrie Water there is a great thickness of soft red sandstone with 
 few or no pebbles in what has been taken as the lower part of the 
 upper division. 
 
 GREAT CUMBKAE. 
 
 In the Great Oumbrae, as in Bute, the rocks which are now 
 regarded as of Upper Old Red Age were formerly classed with the 
 Lower Carboniferous. The upper limit of the formation as now 
 defined follows the horizon of a cornstone band which may be 
 traced at intervals from Doughend Hole, near the south-west end 
 of the island, past Upper Kirkton, in a curved line by Terrach Hill to 
 Ballykellet. Superficial accumulations and numerous intrusive rocks 
 make the line somewhat uncertain in various places. On the west 
 coast the dip is to the S.E., but becomes almost due south inland, 
 and is never at a high angle. To the east of Ballykellet a large 
 fault, which runs close to and parallel to the road, throws up lower 
 beds of the Old Red Sandstone against the Carboniferous rocks, 
 which are not found on the eastern side of the island. 
 
32 The Geology af North Arran. 
 
 Prom Doughend Hole the descending section in the Red 
 Sandstone may be followed along the shore and in the old sea-clifFs. 
 The rocks consist of alternations of false-bedded red sandstone 
 and coarse conglomerate. The dip is at first to the south- 
 west at 10° but soon changes, and afterwards continues steady 
 towards S.E. or S.S.E. all along the west coast of the island. 
 Much of the sandstone is coarse and pebbly, and false bedding is 
 very marked in places. At the north side of Bell Bay the true dip 
 is to the south-south-east, while the false-bedding dip is eastward. 
 Many irregularities in the stratification may be observed, certain 
 beds dying out and being replaced by others ; and at one place, on 
 the south side of Pintray Bay, a kind of local unconformability is 
 seen, coarse beds overlapping on to fine. 
 
 Along the east side of the island the direction of the dip is not 
 so constant, though the rocks are similar in character. On the 
 eastern side of Millport Bay the rocks dip westward towards the line 
 of fault, and the amount of dip near Parland Point is considerably 
 greater than on the west coast, being from 20° to 25°. The westerly 
 dip continues till we pass the Lion Rock, when it changes to east- 
 south-east, and north of the Butter Lump to east-north-east, which 
 is the prevalent direction as far as Clashfarland Point. The amount 
 is as high as .30°-40° in places. On either side of Bessy's Port 
 there is no rock on the foreghore for some distance. About 
 Downcraig Perry the dip is to north-east, which changes towards the 
 north end of the island to almost due east. 
 
 Near the Glaid Stone on Minnemoer, the highest part of the island 
 (A 417), there are numerous and rather large quarries in the massive 
 red sandstone, which is not very coarse and occasionally weathers 
 to nearly a white colour externally. The beds here dip almost due 
 south at angles of 15°-20°. 
 
 The numerous intrusive igneous rocks of the island, the majority of 
 which are of Carboniferous age, will be found noticed in Chapter VI. 
 
 It is somewhat difficult to estimate the thickness of this forma- 
 tion as exposed in the island, but it probably amounts to as much 
 as a thousand feet. There is no sign that we anywhere are near 
 the base of the division. 
 
 * BUTE. 
 
 The conglomerates and sandstones in Bute are of the usual 
 character. Inland sections are few and poor, and mostly confined 
 to the burns, except in the small area bordering the road to the 
 west of Cosson and Piper Hall, where the conglomerate is soft 
 and much decomposed generally. The dip everywhere, both 
 here and along the shores, where are the best sections, is 
 generally to west-south-west, inclining to south-west in the 
 peninsula south of Kilchattan, and to nearly due west along the 
 northern edge of the map. The average amount is between 15° 
 and 20°. It is impossible to give the exact thickness of the 
 formation exposed in this island, as there is no long continuous 
 section. The best is that on the shore between Little Kilchattan 
 
Bute — Old Red Sandstone. 33 
 
 and Bruchag Point, which consists of alternations of sandstone 
 and conglomerate amounting to about 1250 feet in thickness. 
 The total thickness is probably more than double this amount, as 
 there is a wide interval occupied by the sands of Kilchattan 
 Bay before the upper beds are reached. The higher beds may be 
 seen along the western coast where the best section, exposing 
 probably 1000 feet of strata, occurs to the north of Lubas 
 Port. Owing to faults small patches of these rocks appear among 
 the Carboniferous traps to the southward, and in Dunagoil Bay the 
 highest beds pass naturally under the Lower Carboniferous 
 rocks. There is a good exposure of these upper beds of the sub- 
 division along the shore to the south-east of Kilchattan, and their 
 passage up into the Lower Carboniferous may be traced. The 
 thick cornstone or dolomitic limestone, which has been largely 
 quarried in former times, is regarded as the upper limit, but 300 
 yards S.E. of White Port a white cornstone three or four feet thick 
 occurs among the red sandstones and several hundred feet below the 
 horizon of the limestone quarried. 
 
 A peculiar tract of columnar sandstone is found on the shore 
 about 400 yards east of the pier, which has been noticed by Mr. 
 D. C. Glen*. The tract is about 20 yards wide on the shore at 
 high-water mark, and it appears to run in a north-east direction 
 parallel to the course of many of the intrusive dykes along this 
 shore, for the columnar structure may be observed in the old sea- 
 cliff 70 yards south-west of the shore-line at this point. The 
 columns are fairly regular five and six sided prisms, some of them 
 as much as seven inches in diameter. The dip of the sandstone 
 and conglomerate is to the south-south-west at 30°, and the 
 columns- are arranged nearly at right angles to the planes of bed- 
 ding, so that they incline steeply to north-north-east. , The pebbly 
 rocks or conglomerates appear to be as much altered as the finer 
 sandstone ; both are much hardened, in fact converted into a kind 
 of quartzite, and they are much lighter in colour than the un- 
 altered rock. It seems probable that this structure is due to a 
 . concealed dyke — one which does not reach the present surface — 
 running in a north-east direction. 
 
 De la Beche(" Geological Manual," 3rd ed.,pp. 471, 472) observes 
 that some sandstones when kept in our furnaces at a heat in- 
 sufficient to fuse them take a columnar form. A Coal-measure 
 sandstone between Halifax and Huddersfield is thrown into kilns 
 and burnt for road-making material, when it frequently becomes 
 columnar. The columns are variable in the number of their sides, 
 are generally curved, and about half-an-inch in diameter. 
 MaccuUoch ("Quart. Journ. of Science," 1829) connected this altered 
 structure in furnaces with the columnar character of sandstone 
 occurring in nature, and he noticed prismatic structure in a hearth- 
 stone taken from a blast furnace. Columnar sandstone occurs in 
 the island of Eum, according to MaccuUoch. 
 
 In connection with this subject, reference may be made to a 
 
 * Trana, Geol, Soc, Glasg., vol. v,, 154, 
 
34 The Geology of North Arran. 
 
 paper by Mr. James Haswell on "Columnar Structure developed in 
 Mica Schist from a VitriEed Fort in the Kyles of Bute." [Trans. 
 Geol. Soc. Edin., vol. i., p. 229.] 
 
 The faults in South Bute that affect both the Old Ked Sandstone 
 and Carboniferous rocks will be noticed in connection with the 
 latter formation. 
 
 CONTEMPOIUI^EODS IgNEOUS RoCKS OF UpPEE OlD ReD 
 
 Sandstone Age. — The Upper Old Red Sandstone of Arran 
 contains an interstratified and contemporaneous set of lavas on the 
 north side of North Glen Sannox. The area in which these 
 volcanic intercalations occur is much faulted, but the position of 
 the interbedded igneous rocks is quite clear. The Old Red Sand- 
 stone of this part of the island consists of three distinct members, 
 the lowest of which is made up of coarse, well-rounded conglomerates, 
 alternating with felspathic sandstones and purplish mudstones. 
 These are the undoubted Lower Old Red rocks. Above this set 
 comes a middle series of light-coloured or reddish conglomerates 
 and sandstones, the pebbles in which are mostly of quartz. This 
 series is apparently unconformable on the lower. Lastly comes an 
 upper series of red sandstones and conglomerates which occupy 
 nearly the whole of the coast-section in which the Old Red Sand- 
 stone appears, and it is this series which has generally been supposed 
 to be typical of the whole of the Old Red Sandstone of the island. 
 The volcanic series is intercalated between the middle and the 
 upper divisions above described, and it crops out in many places 
 high above the hillside between the shepherd's house at North 
 Sannox and Laggantuin, butls very discontinuous from being much 
 faulted. It consists of dull-red or purplish lavas, in places soft, and 
 often much decomposed. The general character of the rock is 
 basic, but a specimen from near the Fallen Rocks which Mr. Teall 
 examined was found to be too much altered for precise determin- 
 ation, though it was probably a basalt originally. No trace of 
 these rocks is found along the coast, nor in any other part of the 
 island of Arran. 
 
 Some additional specimens were afterwards collected, and 
 examined by my colleague Mr. Kynaston. The description of these 
 (slides 9394 and 9395) will be found in an Appendix to this 
 chapter. W. G. 
 
 ayrshike district. 
 
 The strata which are included here as belonging to the Upper 
 Old Red Sandstone, were formerly regarded as the lowest member 
 of the Carboniferous System, and were so treated in the Map and 
 Memoir (Sheet 22) immediately to the east. Subsequent investi- 
 gation, however, has shown that they may more conveniently 
 be classed in the older system, the line of demarcation between 
 the two series being taken at a tolerably persistent zone of corn- 
 stone which, throughout a large part of the south of Scotland, 
 appears to mark the cessation of the peculiar conditions of sedimen- 
 tation in which the strata underlying it were accumulated. 
 
Ayrshire District. 35 
 
 The Upper Old Red Sandstone of this district consists of red 
 and reddish-grey sandstones, red marls, and conglomerates. Its base 
 is nowhere visible, and owing to frequent change of dip its thick- 
 ness here is not easily computed. The inclination of the strata is 
 tolerably continuous towards S.B. from the north of Ardrossan to 
 Ardneil Bay, a distance of three miles, and the angle varies from 10° 
 to 17°. If no serious faulting occurs there may be a depth of more 
 than 2000 feet exposed on the beach without the appearance of 
 either the upper or lower portions of the whole series. 
 
 Probably a line of anticlinal axis, possibly, also, a great line of 
 dislocation comes to the surface about Parland Head. The strata 
 there stand on end, with a nearly north and south strike, but imme- 
 diately to the north they begin to dip towards N. and N.N.B. at high 
 angles (30° to 60°) and continue this inclination at lessening angles 
 for about two miles. Hence the oldest portions of the whole series 
 are probably those exposed on the beach at Farland Head and 
 Portincross. On the east side of Farland Head thin-bedded, ripple- 
 marked sandstones and red marls appear from under the shingle of 
 Ardneil Bay dipping westward at 25°. The strata soon become 
 vertical, and have here undergone so much crushing and movement 
 as to assume a fissile structure which externally resembles that of 
 some of the Highland schists on the opposite side of the Firth. A 
 well-marked dolerite dyke passes in an east and west direction 
 through the strata at the promontory, and a much smaller dyke, 
 running towards N.B., traverses the disturbed zone farther 
 west. Pebbly and flaggy red and reddish-grey sandstones, cut by 
 an occasional small basalt-dyke, succeed each other to beyond the 
 Throughlet, their angle gradually rising northwards to 60°. 
 Between the old and the new harbours of Portincross the conglo- 
 meratic sandstones include rounded and subangular pieces of 
 difierent amygdaloidal and porphyritic igneous rocks, possibly 
 derived from some of the volcanic ranges of the Lower Old Eed 
 Sandstone. At the gap of the Throughlet a large dolerite dyke 
 descends from the interior to the coast, and has hardened and 
 bleached the sandstones on each side of it. 
 
 The shore south of Ardneil Bay affords the most continuous 
 section of the Upper Old Eed Sandstone in this district. Thin- 
 bedded red sandstones with occasional seams of red sandy marl 
 form the lowest visible members of the series, and probably belong 
 to the same series as the similar strata on the west side of the bay. 
 As at Portincross, also, they here pass upward into false-bedded, red 
 pebbly sandstones with bands of conglomerate. One of these bands, 
 conspicuous on the shore west of Overtonshore, is marked by 
 numerous layers and patches of white quartz-pebbles. Their 
 marked false-bedding and abundance of fragments of white-quartz 
 give these rocks some resemblance to the Triassic sandstones of 
 Broadford Bay in Skye. Except for the abundant dykes by which 
 they are intersected, the red and reddish-grey sandstones present 
 little variety along the rest of the coast to Ardrossan. They may 
 be followed from the shore up the courses of the burns. One of 
 the best of these inland sections will be found in the Kirkland Glen, 
 
36 The Oeology of North Arran. 
 
 in which, from Ann's Lodge up to Tailorleap Bridge, a distance of 
 a mile, a gorge has been excavated in the sandstones and in the 
 boulder-clay. 
 
 No organic remains have yet been met with in any of the strata 
 of the Upper Old Red Sandstone of this district. A. G. 
 
CHAPTEE VI. 
 
 Carboniferous Formation. 
 
 AERAN. 
 
 One of the most remarkable results of the geological survey of 
 Arran is the restricted area now assigned to the Carbonifei-ous 
 rocks which were formerly supposed to cover a large part of the 
 island, and it may be as well before entering into details about 
 these strata to remove certain misapprehensions as to their posi- 
 tion, distribution, and thickness. The Carboniferous series, it has 
 long been known, is typically developed and best studied along the 
 eastern coast, where it forms a narrow strip which stretches for 
 about three miles between the Cock and the Fallen Eocks. Its 
 thickness here has been much exaggerated from' no account having 
 been taken of numerous faults by which the strata are repeated. 
 A narrow band of the formation, 200 yards in width, also occurs 
 on the north shore near the mouth of the burn east ot North 
 Newton. This strip lies between two large faults. Along the 
 shore at Oorrie, Carboniferous strata stretch for two-thirds of a mile, 
 with a dip of 20° to 25°, until they are overlapped by the New Eed 
 Sandstone 250 yards south of the Oorrie Hotel. The total thick- 
 ness of the Carboniferous rocks on this shore may be as much 
 as 1200 or 1500 feet, inclusive, as at Laggan, of a volcanic group 
 300 or 400 feet thick. Several thin red limestones occur near the 
 upper part of the series, but the most prominent members are the 
 volcanic group, the thick Oorrie limestone, and the white sandstones 
 immediately above that bed. It is by these well-marked bands 
 that the series can be followed inland and recognised among the 
 numerous faults, some of which bring up the Old Eed Sandstone 
 and confine the Carboniferous rocks to a comparatively narrow 
 belt. One of these north-north-west dislocations, with a throw 
 greater than the total thickness of the series, shifts the base of the 
 volcanic group into the burn north of Maol Donn, and another 
 large fault running along the west side of that hill has moved the 
 main body of the Carboniferous rocks southward again for more 
 than a mile. The strata reappear in the Clachland Burn, whence 
 they can be traced to the south-west through the wood, and behind 
 Brodick Castle, in a steeply dipping band altogether not more than 
 200 to 300 yards in width. Though they disappear under the 
 Brodick alluvium, some of the sandstones and shales are visible in 
 the Eosie Burn about the bridge, and the white thick sandstones 
 are a conspicuous feature about the manse and church. Behind 
 the churchyard the thick Oorrie limestone was formerly 
 
38 
 
 The Geology of North Airan. 
 
 is<e 
 
 CjiJ.- 
 
 •1 
 
 IE 
 
 
 I- 
 
 worked. A little farther west a large fault throws the rocks up to 
 the hillside where the thick white sandstone forms a marked 
 feature, and the limestone immediately below has been worked. 
 The Carboniferous band here is 200 yards wide only, and 
 
 dips steeply to the south-east ; the New 
 Eed rocks, extremely false-bedded as 
 usual, forming the high bank above. 
 The volcanic group crops out here and 
 there at the base, and the whole series 
 can be followed south-west to the Wind- 
 mill Hill, where it becomes entangled 
 among intrusive masses of various kinds, 
 which, along with faults, have displaced 
 the rocks so that they do not occur again 
 till the south side of Glen Dubh is 
 reached. This locality is more than a 
 mile south-east of the Windmill Hill, 
 where they were lost sight of. Prom 
 Glen Dubh the Carboniferous formation 
 may be traced in a broken way south- 
 wards by Benlister Glen to near Cnoc 
 a' Chapuill in Sheet 13, being recognis- 
 able by the presence of the volcanic 
 group, after the Corrie limestone has 
 been overlapped by the New Ked Sand- 
 stone. There is no trace of these rocks 
 on the west coast, the Triassic rocks 
 reposing directly on the Old Red Sand- 
 stone without the interposition of any 
 Carboniferous strata. 
 
 Detailed Description. — It will be 
 advisable to describe the Corrie shore- 
 section in some detail, as it is easy to 
 examine at low water, and is compara- 
 tively little faulted. (See No. 1 section, 
 Corrie shore.) From the schoolhouse 
 northward there is exposed on the shore, 
 for a distance of 350 yards, the lower 
 volcanic series, made up mainly of 
 massive lavas, with a thick band of 
 coarse volcanic agglomerate at the base 
 or northern end. To the north of this 
 for a distance of about 36 yards are 
 various members of the lower Carboni- 
 ferous rocks, including three limestones 
 or cornstones, and below these projects 
 a mass of red conglomerate which is 
 the^highest bed of the Old Eed Sandstone. This is the locality 
 called the March of Achag Farm by the older writers. The 
 red conglomerate itself is 50 feet broad at high-water mark, 
 but considerably less at low water, and the junction between it 
 
 
 z 
 o 
 
 is 
 
 XJ3 
 
Corrie Section. 39 
 
 and the Cai'boniferous beds is peculiar. A joint or crush at the 
 shore line, running N.N.B., appears to die out towards the sea, 
 or is overlapped by sandstone and limestone, which abut against 
 a nearly vertical face of the conglomerate, so that this is clearly 
 an unconformable junction. This mass of calcareous sandstone and 
 pebbly cornstone, several feet thick, may be faulted along a N.N.B. 
 line against a few feet of overlying white sandstone which dips to 
 the south-east at 25° to 30°. Above this lies red shale, and then 
 comes a nodular cornstone, about 15 feet thick, with a red argil- 
 laceous matrix. A gap of a few feet separates this from the uppermost 
 cornstone, which is a whitish, irregular, calcareous sandstone some- 
 what mixed with reddish sandstone, and shaly below. It may be 
 three feet thick. The 15 yards of distance between this and the base 
 of the agglomerate is almost entirely occupied by white sandstone, 
 the beds of which dip S.E. at 25° or more, so that it is probably as 
 much as 20 feet thick. The whole thickness of strata between the 
 volcanic rocks and the conglomerate cannot, however, be more 
 than 45 feet. 
 
 The volcanic agglomerate itself is 45 yards in width on the 
 shore, and must be 50 feet thick or more. It is a very coarse rock, 
 made up of fragments of basic trap, sometimes as much as 6 feet 
 in length. The lower beds of the lavas are massive, bluish, and 
 fine-grained, and some of the upper are purplish in colour, but the 
 whole is similar in composition, being a porphyritic olivine basalt. 
 Near the big boulder called Clach an Fhionn, there are very fine 
 examples of " pillow " structure in the lava. This mass of Carboni- 
 ferous lavas, which are certainly contemporary with the sedimen- 
 tary rocks adjacent, is probably 300 feet in thickness. 
 
 South of the school, for a distance of 75 yards, we find sandstones 
 and shales that overlie the lavas. The dip is in the same direction 
 as before, but only about 20°. Most of the rocks here are of a red 
 colour, and the shales are specially so, and some are tufiaceous. 
 Among these occurs a thin red limestone from one to two feet in 
 thickness. 
 
 We now arrive at a projecting mass of purplish and much- 
 veined trap 10 yards across. This is a lava bed, about 10 feet 
 thick, and the last outflow from the old volcano in this locality. 
 Above this is a gap of 20 yards or so, probably occupied by shales ; 
 to which succeed thick beds of white and pinkish stone, which have 
 been quarried both on the shore and up the hillside to the west- 
 ward, There is probably a thick mass of red shale above this and 
 underlying the Cowrie limestone, but it is poorly exposed on the 
 shore. 
 
 The Corrie limestone, which occupies the old harbour, is pro- 
 bably the equivalent of the Hurlet. It is said to be 20 feet in 
 thickness, and is crowded with innumerable specimens of Produdus 
 giganteus, well exposed on the under surfaces of many of the beds 
 in the old quarry to the westward, which extends for nearly a 
 quarter of a mile up the hillside. The beds of limestone are 
 separated by thin partings of reddish shale, and from the calcareous 
 shale immediately overlying the limestone were obtained by the 
 
40 The Geology of North Air an. 
 
 fossil collector of the survey, Mr. Tait, about 60 species of 
 organic remains, which are enumerated in the Appendix. Two 
 basic dykes cross the limestone in a N.N.W. direction. One of 
 these, just above the old lime-kiln, is 5 feet wide, and the other, 
 nearly 50 yards higher up, is 4 feet in width. Several small faults 
 also cross the quarry. One of these above the kilns coincides with 
 one of the dykes just mentioned, and it throws down east 7 to 8 
 feet. A second fault a little farther up, throws down 2 feet to the 
 west, and a third fault is down east 3 to 4 feet. Near the top of 
 the quarry there is the following section : — 
 
 Thick Sandstone, . . 
 Shale and shaly sandstone. 
 Thick sandstone, . 
 Shale and shaly sandstone (red), 
 Limestone, upper bed thick, . 
 
 6 feet. 
 . 3 „ 
 10 to 12 „ 
 3 to 5 „ 
 16 feet visible. 
 
 There are slight calcareous shale partings where Produeti are 
 very numerous. 
 
 Between the two upper faults the hearing above the limestone 
 is much less, being only 10 to 15 feet, but east of this there is 
 probably 30 feet of sandstone and shale in the artificial clifi" above 
 the limestone. The two shale bands are variable, but the inter- 
 mediate sandstone is not so thick and massive as near the top of 
 the quarry, while 10-12 feet of the upper sandstone appears. 
 
 Headrick (op. cit. p. 344) gives some analyses of limestone at 
 Corrie, from which it appears that the proportion of carbonate of 
 lime varies from 90J to 97 per cent. He also gives the following 
 for South Currie Quarry: — 
 
 Carbonate of Lime, ...... 98^^. 
 
 Clay, 1|. 
 
 This is probably the old quarry at An Sgriob, north of Maol Donn, 
 which is in the same bed as the Corrie Quarry, and which has also 
 yielded a numerous suite of fossils. The beds between the Corrie 
 limestone and the Index limestone are well exposed on the shore 
 for -220 yards south of the old harbour, and consist mainly of 
 alternations of thick white sandstones and flags, with occasional 
 shale bands. The dip continues much the same in amount and 
 direction, 20" to 30° towards the S.E. The sandstones have been 
 much quarried for building material in the wood above the houses, 
 and at the landing place. There is an ironstone band in one place, 
 and fireclays, such as often underlie coal seams, occur, but there 
 are no coals, though we are on the horizon of the coals worked at 
 the north end of the island near the Cock. There are traces of coal 
 plants however. The thickness of this part of the series must be 
 about 250 feet. 
 
 A thin red limestone with Prodmctus latissimus occurs about 25 
 yards south of the Perry rock, and not far to the south of it occur 
 two others, as in the following section in descending order : — 
 
Gorrie Section. 41 
 
 3. Eed limestone in one place, . . 1 foot thick. 
 
 Shale and sandstone, some of the 
 
 sandstone fine and like gannister, . about 20 feet. 
 
 2. Red limestone, ..... 1 foot. 
 
 Shale, red, 7 to 8 feet. 
 
 1. Red limestone, . . . . . . 2 to 3 feet. 
 
 Shale, argillaceous, red and mottled sandstone, 5 feet. 
 
 No. 1 of this section is the Index or Produdus latissimus limestone 
 (Loc. 26). No. 2 is in the locality lists described as a ferruginous 
 band with many gasteropods (Loc. 27), and No. 3 band, which also is 
 a Productus latissimus limestone, is locality 28. The fossils collected 
 from Nos. 1 and 3 are pretty numerous, and will be given in the 
 Appendix. We give here only those from No. 2 band. 
 
 Lingula squamiformis. 
 Peoteus.p. 
 Aclisina elougata. 
 , , striatula. 
 Dentalium ingens. 
 Maorocheilus aoutus. 
 
 Macrocheilus imbricatus. 
 Metoptoma elliptioa. 
 Murohisonia angulata. 
 
 ,, qiiadrioarinata. 
 Strepsodus striatulus. 
 
 There are numerous small faults about this, part of the shore which 
 in the main run parallel to the coast-line, crossing the beds nearly 
 at right angles, and shifting their outcrops again and again for a few 
 feet. A mass of sandstone now projects into the sea, and south of 
 this, in front of the hotel, is a little bay in which occur two or three 
 thin red limestones, from one to two feet thick, which are probably 
 separated by shale, but the section is not clear. To the south of 
 this bay there is a mass of sandstone with irregular shale bands. 
 One of the shale bands, 8-10 feet thick at the shore-line, gradually 
 thins away seaward, till at low-water mark it has almost disappeared. 
 The thick sandstone underlies a mass of red and mottled clays, red 
 and purplish shales, with occasional thin sandstones which occupy 
 the larger bay south of the hotel. The beds in this bay are classed 
 with the Coal Measures as they contain organic remains of 
 Upper Carboniferous facies, but they and the equivalent beds else- 
 where may possibly be Millstone Grit. About 25 yards south of 
 the northern boundary of Oromla gardens, and near high-water 
 mark, there was obtained a specimen of Neuropteris gigantea, and 
 opposite the Oromla House the beds yielded Lepidodendron sp., 
 Garhonicola acuta, C. aquilina, Naiadites modiolaris. 
 
 These Ooal-measure strata also crop out in the lower part of 
 Locherim Bum 200 yards from the sea, where in fine red shale 15 
 yards from the faulted New Red junction there were obtained : — 
 
 Mariopteris muricata. 
 Neuropteris heterophylla. 
 Carbonioola acuta. 
 
 Carbonioola aquilina. 
 Myalina sp. (?Verneuili. ) 
 Naiadites sp. 
 
 Another locality near Oorrie where these beds occur is on the north- 
 west side of the Maol Donn clifi". In red sandy shale above the 
 limestones were found : — 
 
 Artisia(Sternbergia) approximata. 
 Calamitea ramosus. 
 „ sp. 
 
 Neuropteris gigantea. 
 
 sp. 
 Stigraaria sp. 
 
42 The Geology of North Arran. 
 
 There is another fossiliferous band up the Locherim Burn the 
 existence of which was first made known by Prof. W. Ivison 
 Macadam,* but it is in the Upper Limestone Series some 330 yds. 
 from the sea, where the stream forks at a waterfall, and it is separated 
 by a fault from the Coal-measure strata previously mentioned. 
 Alternations of shale and sandstone occur with a thin limestone 
 band. The beds above the limestone yielded the following plants 
 to the Geological Survey Collectors : — 
 
 Aaterocalamites sorobiculatus. 
 Carpolithes sulcata. 
 Lepidodendron veltheimianum. 
 Lepidostrobus sp. 
 
 Rhodea sp. 
 Sigillaria Taylori. 
 Sphenopteridium disseotum. 
 Stigmaria. 
 
 and the limestone and calcareous shale band underlying the plant 
 bed afforded : — 
 
 Orthis resupinata. 
 Orthotetes crenistria. 
 Productus sp. 
 AUorisma sulcata. 
 Edmondia unioniformis. 
 Myalina Verneuili. 
 „ s.p. • 
 
 Nucula gibbosa. 
 -Nuculana attenuata. 
 Protosoliizodus axiniformis. 
 
 ,, obliquus. 
 
 Bellerophon sp. 
 Macrocheilus canaliculatus. 
 
 In the Merkland Burn about three-quarters of a mile north of 
 Brodick Castle there is a pretty continuous outcrop of the 
 Carboniferous rocks, except that the section is obscured where the 
 Corrie limestone should appear. The thick sandstones above it 
 appear, and lower down the burn two of the Upper Limestones. 
 From the lowest of these were collected : — 
 
 Crlnoid ossicles. 
 Athyris ambigua. 
 
 Koysi? 
 Lingula mytiloides. 
 Streptorhynchus crenistria. 
 Productus oostatus. 
 
 ,, longispinus. 
 
 , , semireticulatus. 
 
 Spirifera glabra ? 
 Allorisma sulcata. 
 Edmondia Josepha. 
 Lithodomus lingualis. 
 Nucula sp. 
 Pecten Sowerbyi. 
 Orthoceras sp. 
 
 The limestone a few yards still lower down the stream yielded 
 Productus latissimus. The more shaly beds still further down the 
 stream are similar to the highest beds on the Corrie shore, and from 
 them were obtained the following Coal-measure forms : — 
 
 Anthracomya modiolaris ? 
 Carbonicola acuta. 
 
 ,, ,, var. rhomboidalis. 
 
 Naiadites quadratus. 
 
 Naiadites, periostracum of. 
 Megalichthys Hibberti. 
 Rhizodopsis sauroides. 
 
 The same beds in a parallel burn nearly a quarter of a mile to the 
 south-west of this gave Oa/rbonicola acuta, C. aquilina, Bhizodopsis sp. 
 All these beds have a steep dip to the E.8.E., and the dip increases 
 towards Brodick Castle. The Corrie limestone was at one time quarried 
 at the edge of the wood about half a mile north of the Castle, 
 
 * See his paper entitled " Notice of a New Fossiliferous Bed in the Island of Arran." 
 Trana. Geol. See. Edin., vol. v., p. 316. 
 
Brodick Sections. 43 
 
 and there are traces of small limestone quarries west of the Castle. 
 In the Sawmill stream 300 yds. S.W. of the Castle the beds are 
 practically vertical. Here, a few yards above a foot-bridge, were 
 collected the following : — 
 
 Produetus latissimus. 
 
 „ sp. 
 Edmondia Josepha. 
 Nuoulana attenuata. 
 Parallelodon Geinitzi. 
 Pecten dissimilis. 
 
 „ sp. 
 Bellerophon decussatus. 
 
 Bellerophon Urei, 
 Euomphalus sp. 
 Loxonema rugiferum. 
 
 , , scalaroideum. 
 
 Natioa sp. 
 Pleurotomaria sp. 
 Orfchoceras sp. 
 
 They must belong to the Upper Limestone Series. In the mill- 
 lade Lingula squandformis was found. Shelly ironstone bands 
 associated with shales and sandstones are found in the Eosie Burn 
 on either side the bridge near Brodick Manse, and from one of 
 these, a few yards above the bridge, a " musselband ironstone," 
 there were obtained a Lycopod branch and a species of Garhonicola. 
 Here we have the Coal Measures again. 
 
 The Corrie limestone was formerly quarried north-west of the 
 church, just beyond the boundary wall of the kirkyard ; and on the 
 hillside a quarter of a mils S.E. of the String Eoad and half a mile 
 and upwards west of the wood. The beds are nearly vertical in both 
 localities and they yielded Produetus giganteus. The Carboniferous 
 rocks here have diminished to a band not more than 600 feet in 
 thickness, and yet we have the Coal Measures above and the 
 volcanic series below ; bnt there is no trace in Glen Shurig of the 
 Upper Limestones. We find a portion of the formation entangled 
 in the intrusive masses of Windmill Hill and nearly dividing it 
 into two. In a little gully nearly in the centre of the north side of 
 this hill there is a section in sedimentary beds. The lowest part 
 of the exposure contains a few feet of sandy shale, and above these 
 there are several feet of rather thick yellowish sandstone, which 
 dips south-east about 80°. Higher up dykes of felsite and basalt 
 render the section somewhat confusing, but after passing these we 
 find much red sandstone, thin-bedded and shattered, dipping like 
 the beds below but at a higher angle ; and still higher up some 
 pebbly sandstone which is not red, but is not well exposed. The 
 lower part of the section is certainly part of the Carboniferous, and 
 probably the whole is. Near the highest part of the hill on the 
 crags overlooking Glen Ormidale is a mass of red Carboniferous 
 shale dipping steeply to the N.N.W. It contains some veins of 
 calcite, and is a very conspicuous object when viewed from the high 
 ground to the south, the colour of it being strongly contrasted 
 with the light-coloured, intrusive quartz-felsite. It is certainly a 
 portion of the cement-stone series. 
 
 By the disruptive action of igneous rocks and of faults the 
 Carboniferous rocks are shifted more than a mile to the southward, 
 and next occur on the south side of Gleann Dubh above a wood 
 and north of a fine set of scars called Oreag nam Fitheach. They 
 form a triangular area bounded on the east and west by faults. 
 
44 The Geology of North Arran. 
 
 That on the east side throws down against them the Triassic sand- 
 stones and conglomerates of Creag nam Pitheach ; that on the west 
 brings up the Upper Old Eed Sandstone. The volcanic series of 
 the Carboniferous, dipping southward at angles of 25°-30°, rests on 
 the Upper Old Eed beds at the top of the wood. In the southern 
 angle of the triangle massive white sandstone, which probably 
 overlies the Corrie limestone, is seen, but the limestone itself does 
 not crop out, and no other beds are to be observed. Near the west- 
 end of Oreag nam Pitheach another and still smaller Carboniferous 
 patch occurs which is faulted on either side, but no other rock is 
 visible than the volcanic zone. 
 
 South of this small isolated patch and beyond Brisderg, two 
 other detached areas of Carboniferous rocks occur in" Benlister 
 Glen, on either side of a synclinal, the centre of which is occupied 
 by Trias. It would seem that the unconformability between the 
 two formations is more marked here than in any other part of the 
 island yet described, for in one place beds containing plants and 
 animals of Coal Measure age occur, while elsewhere the New Eed 
 rocks rest directly upon the Corrie limestone or even overlap that 
 bed and repose on the shales below. On the western side of 
 the synclinal the Corrie limestone may be seen at Benlister Burn, 
 nearly half a mile S.S.W. from Brisderg. It appears to be repeated 
 by a fault on the north side of the burn, but must be several feet 
 in thickness, and from it has been collected numerous fossils, for 
 which we refer the reader to the Appendix. Among them are six 
 species of Productus, several of Spirifera and Spiriferina, and other 
 well-known Carboniferous forms. This limestone is overlain by 
 Triassic sandstone and conglomerate, while a few yards away, on 
 the south side of the burn, the conglomerate rests immediately on 
 red shaly clay, and the limestone has disappeared. However, nearlj'' 
 300 yards farther to the south-west the Prod/iictus limestone appears 
 again for a short distance, but in a very attenuated form (only 3 
 feet thick) under the conglomerate, but not immediately, and over- 
 lying a thick series of red shales and clays, with a few thin tuffaceous 
 bands. The dip is high, being 50°-60° towards the south-east, and 
 to the westward comes on the volcanic zone which underlies the 
 red shales. All these rocks are much pierced by acid and basic 
 dykes. 
 
 On the eastern side of the synclinal the limestoue appears in the 
 southern bank of a small burn 400 yards due south of Brisderg. 
 It is of considerable thickness, and is overlain by several feet of 
 white blocky sandstone, on which rests the Triassic conglomerate. 
 To the westward the conglomerate appears to overlap both the sand- 
 stone and limestone, and rests immediately on the red shales 
 below. The greater part of the small valley to the eastward seems 
 to be occupied by these red shales, though not many sections 
 occur in them, owing to a thick deposit of drift, and the Triassic 
 conglomerate appears to form the feature on the west side, which 
 runs southward to a waterfall in the Benlister Burn, where it dips 
 westward. No limestone here appears below the conglomerate, 
 though red shales and sandstone, probably of Carboniferous age, are 
 
Laggan Section. 45 
 
 visible, dipping westward at 35°. However, by following the base 
 of the conglomerate we come, some 200 yards to the southward, upon 
 the limestone again, with the usual Produdus giganteus and Monti- 
 culipora tumida, where a small stream occurs. The rocks liere are 
 much disturbed however. Lower down the main stream below a fall 
 called Eas Geal (white water), at the bend of the stream there occur 
 some shales and sandstones of a red colour, with a bed of shelly 
 ironstone, dipping steeply to the south-east. This locality is 2J 
 miles west of Lamlash Bay, and half a mile S.S.E. from Brisderg. 
 These beds have yielded Ooal-measure forms like those of Corrie, 
 etc. There were collected here — 
 
 Calamites Suokowii. 
 
 „ sp. 
 Carbonicola acuta. 
 
 Edmondia Josepha ? 
 Naiadites crassus ? 
 
 These rocks on the west side appear to be faulted against the con- 
 temporaneous volcanic zone elsewhere described (see latter part of 
 this chapter), and on the east they are thrown against Triassic 
 rocks by a large fault which passes east of Brisderg. Another 
 fault with a throw in the opposite direction passes west of Brisderg, 
 and brings down the Triassic rocks on that side against the Lower 
 Carboniferous zone, which is also bounded on the south side by a 
 fault running eastward, throwing the red shale down against the 
 traps. 
 
 Laggan Section of the Carboniferous Formation. — This 
 stretches along the north-eastern shore of Arran, from the Fallen 
 Rocks near Corloch for a distance of 3^ miles to within 600 yards 
 of the Cock of Arran. The shepherd's house at Laggan is 2 miles 
 from the Fallen Rocks, while Millstone Point is a like distance from 
 the northern end of the strip, the length of which, however, is only 
 3^ miles, as the coast-line is not straight. The width of the strip 
 varies, but in general is not more than a quarter of a mile; it widens 
 to half a mile at Cock Farm, but in two places south of Millstone 
 Point it does not exceed 200 yards. 
 
 The dip is everywhere high, and nearly in the same direction ; 
 lowest at the north end, where it is about 30°, but for the greater 
 part of the distance it is 40° or 50°, and even 60° in places. 
 This high dip suggests an enormous thickness of beds, but it must 
 be remembered that the general dip is in a direction to the east of 
 north, while the trend of the coast is about 40° north of west, and 
 is only 30 and 40 degrees removed from the general strike of the 
 beds. In fact, there are parts of the coast-line where its direction 
 coincides very nearly with the strike for some distance. In addition 
 to this consideration it must be borne in mind that there are 
 several large faults, especially in the lower part of the section, 
 which repeat many hundred feet of the strata. Still, there is no 
 doubt that we have here a much greater development of Carboni- 
 ferous rocks than we have at Corrie; probably the thickness of the 
 whole is twice as great, and if we confine our attention to the 
 sedimentary beds alone the disproportion is still greater. The in- 
 creased thickness is not confined to one part of the section. All , 
 the limestones are thicker than they are at Corrie, and they are 
 
46 The Geology of North Arran. 
 
 more in number — there are coals wMch are absent at Oorrie, and 
 naturally there is a much greater development of sandstone and 
 shale. The following is a comparative estimate of the thicknesses 
 of the various subdivisons in the two sections : — 
 
 COEME. LAGGAN. 
 
 Coal-measures ..... 150 feet. 250 feet. 
 
 Limestone Series 425 „ 750 „ 
 
 Calciferous Sandstone Series above and / 275 „ 575 „ 
 
 below traps .... \ 75 „ 700 „ 
 
 925 „ 2275 „ 
 
 Add thickness of Volcanic Series . 450 „ 375 „ 
 
 1375 „ 2650 „ 
 
 The greatest difference is in the thickness of that part of the 
 Oalciferous sandstone series below the volcanic zone, which is less 
 than 100 feet at Gorrie contrasted with 700 feet in the Laggan 
 section. It has been suggested that the trap at Oorrie is a great 
 dyke which conceals a very large fault, and that this accounts for the 
 differences be tween the two sections ; but the fault at Oorrie, if 
 it existed, would not explain why we have increased thicknesses 
 at Laggan in all the sedimentary beds. Besides, we know that 
 the thinning of the Oarboniferous beds at Oorrie as compared with 
 those at Laggan is continued southward, so that in the neighbour- 
 hood of Brodick Castle and in Glen Shurig the total thickness is 
 about 600 feet. 
 
 Some three hundred yards south of the Fallen Rocks the corn- 
 stone base of the Oarboniferous rocks occurs in two places separated 
 by a small fault. The cornstone is pebbly and adheres to the con- 
 glomerate below in an unconformable manner, like that described 
 in the junction north of Oorrie. This is separated by a considerable 
 north-trending fault with a downthrow eastward from the main 
 mass of the Carboniferous section which commences on the north 
 side of the Fallen Eocks. The beds here have a fairly steady dip of 
 30°-40° to the northward, often inclining east of north sometimes 
 as much as 15° or 20°. There are two cornstones of the usual 
 light-coloured concretionary character, which are sometimes pebbly, 
 and irregular in thickness. They are separated by a few feet of 
 sandstone. There succeed to the northward a series of red clays 
 with some lenticular calcareous bands, and red sandstone with 
 quartz-pebbles. These are bounded on the north by a fault which 
 crosses the foreshore in an easterly direction, and throws down on 
 the north an alternating series of grey shales, thin sandstones, and 
 calcareous bands. Among these Mr. James Thompson* discovered 
 a brecciated or tuffaceous rock from which he obtained remains of 
 plants and fish. At this locality, about 300 yards north of the Fallen 
 Edcks, Mr. Tait, the collector for the survey, obtained the following 
 species : — 
 
 Rhizodus ornatus. 
 Strepsodiis striatulus. 
 Eish-head plate. 
 
 Cordaites sp. 
 Fern rachis. 
 Sphenopteris sp. 
 Palseoniscid scales, (indet.) 
 Rhizodus Hibbei-ti. 
 
 Various bones and plates, (indet. 
 * See his paper in Trans. Geo). Soe. Glasgow, vol. xi., pp. 12-30. 
 
Laggcm Section. 47 
 
 Above these grey beds there come about 150 feet of an alternating 
 set of white sandstones and red clays or shales, the clays containing 
 several small, lenticular cornstone bands, the uppermost of which 
 are fairly good continuous limestones, 1-2 feet thick, of the same 
 character as the basal cornstones. These beds are surmounted by 
 thick-bedded white sandstone, which continues for but a short 
 distance, and then the section is lost for several hundredyards. Some 
 200 yards, however, beyond the most northerly Laggantuin Burn, 
 white sandstones, with a northerly dip of 60° appear in the old sea- 
 clifi", and these strongly resemble the pebbly sandstones of Millstone 
 Point, a long way to the northward. In fact, there is not much doubt 
 this is their position in the series. To the west of these is a large 
 fault with a downthrow east of several hundred feet. On the 
 west side of this the upper beds of the Old Red Sandstone, and all 
 the lowest beds of the Carboniferous, including the cornstones, are 
 exposed in a precipitous hill. The fault runs northward along the 
 east side of of this hill, but on reaching the shore it, or a branch 
 of it, runs along the foreshore in a north-west direction for 250 
 yards and then passes out to sea. On the inner side of this fault, 
 along the foreshore, we again come upon the Millstone Point grits, 
 but we do not find a continuous section up to the base of the 
 volcanic series, for the beds immediately underlying that series are 
 cut out by two parallel faults along the strike. Nearly a mile 
 from the Fallen Rocks there is exposed on the shore a good section 
 of the volcanic series, consisting of alternations of basic lavas with 
 coarse and fine tuffs, the whole amounting in thickness to between 
 350 and 400 feet. These, which are elsewhere described in some 
 detail (see latter part of this chapter), occupy the shore for a distance 
 of over 200 yards, dipping steeply northward at 50° to 60°, but they 
 do not appear in the old sea-cliff to the west, being cut off on that 
 side by a large fault which runs in a northerly direction across the 
 foreshore. This brings up again the beds below the trap, which 
 are seen at intervals on the shore, the highest beds being grey 
 cement-stones like those underlying the trap near Laggan. Above 
 these comes a portion of the volcanic series again, which is bounded 
 on the west by another large fault bringing up against it sandstones 
 and shales of a much lower horizon. 
 
 To the northward come white sandstones, some of which are 
 coarse, alternating with red shale and clay bands, and in one place 
 some cement-stones and grey beds. These continue as far as the 
 bay, south of Millstone Point, where there is a gap in the section. 
 The rocks, however, are almost continuously exposed on the hillside 
 to the south of this bay, and there can be no doubt whatever about 
 the general Order of succession. The dip is almost everywhere to 
 the east of north, and between 50° and 60°. On the north side of 
 the little stream called the Garbh Allt, white pebbly grits are well 
 exposed at Millstone Point. In places the quartz-pebbles in the 
 rock are large, some being as much as four inches in length. We 
 cross a small and unimportant fault, and pass upward into alternations 
 of white sandstone and dark shale with traces of coal. These are 
 succeeded by grey sandstones and blue and grey cement-stones 
 
48 The Geology of North Arran. 
 
 alternating with thin tuff bands, and in the upper part with two thin 
 beds of lava. This is the spot, some 750 yards south-east of Laggan 
 cottage, where Mr. E. A. Wiinsch discovered trees and plant-remains, 
 imbedded in trappean ash*, in the year 1865. It is interesting to 
 note that these plant-remains, which are accompanied in this 
 locality by thin coal-seams, occur on the same geological horizon 
 as the coal which was formerly worked at Ambrisbeg, and at Ascog 
 in the island of Bute, but in no other place within this sheet is a 
 coal known to occur at the base of the volcanic series. 
 
 The following list of fossils was obtained from 750 yards south- 
 east of Laggan cottage : — 
 
 Lepidophloios wiinschianus. 
 
 „ sp. 
 
 Ehaoopteris sp. 
 Sphenopteris (Rhodea) moravica. 
 
 ,, ,, patentissima. 
 
 Sphenopteris sp. 
 Stigmaria. 
 AUorisma sulcata. 
 Edmondia pentonensis. 
 Sedgwickia gigantea. 
 
 These beds, which dip at a somewhat less angle, viz., from 35° to 40° 
 are succeeded by the principal mass of trap, elsewhere described 
 {see latter part of this chapter), and above this there is a thin 
 cement-stone series again, alternating bands of grey beds, shales, 
 comstones, and sandstones with some tuffaceous bands. A thick 
 series of blocky sandstones (white), alternating with thin bands of 
 red shale, forms marked features west of the shepherd's house, and 
 these continue till we reach the Corrie or Hurlet limestone, nearly 
 250 yards north-west of the house. 
 
 From a place 100 yards south-east of the cottage Sphenopteris 
 crassa and another species {Rhodea ?) of Sphenopteris were obtained, 
 and a few yards north of the cottage Sphenopteris (crassa L. and 
 H. ?) and a species of Stigmaria. 
 
 The main or Hurlet limestone is here considerably thicker 
 than elsewhere in the island, and is overlain at some distance by 
 two other dark calcareous bands which are not represented at Corrie, 
 and may be the equivalents of the Hosie limestone. The highest 
 of these three limestones occurs nearly a quarter of a mile north- 
 west of the shepherd's house, at a point where the shore-line bends 
 westwards, and coincides with the strike of the beds. The section 
 of these three limestones is as follows, in descending order : — 
 
 Black, hard calcareous shale and shaly limestone . 10-12 feet. 
 
 White sandstone, some of it coarse and pebbly . . 60 feet about. 
 
 Black, hard calcareous shale with limestone in middle 10-12 feet. 
 
 Coarse sandstone with a little black shale . . 30 feet. 
 
 Thick Corrie limestone with calcareous shale below 35 feet. 
 
 Blocky sandstone 
 
 These beds all dip northward at 40°- All the limestone con- 
 tains many fossils, and lists of the collections made from the three 
 separate beds wiU be found in the Appendix. A fault trending 
 north with a downthrow west crosses these limestones, the lowest 
 of which can be traced as far as the footpath to the westward, but 
 beyond this it is unknown. On the shore where the coast-line 
 again trends N.W. there is a pretty example of a sharp syncline in 
 
 » See his paper in Trans. Geog. Soc. Glasgow, vol. ii., p. 97, and Geol. Mag. iv., 551 . 
 
Cock, of Arran Section. 49 
 
 sandstone with thin, dark shale bands. This extends for about 50 
 yards, and appears to be bounded by a N.B. fault. North of this 
 the dip increases from 30° to 60°. The rocks are mostly sand- 
 stones with some bands of black shale and flags, and in one place 
 there is a thin ironstone. South of the ruins of the old salt 
 pans we come upon the crop of the coal or coals worked on this 
 coast, and which have no representatives at Corrie. The coal was 
 worked here upwards of a century ago, and there have been some- 
 what different accounts given of it. All agree, however, that it 
 was a kind of blind or glance coal, which burned without much 
 smoke or flame — an aribhracite in fact. Headrick, who first 
 described these workings* in detail, states — " there are three or four 
 seams of coal running parallel from north to south ; the principal 
 or main seam being 14 feet in thickness," but this statement is 
 hardly credible, especially when compared with an account of a 
 working which he got from a Mr. Oowie who had wrought the 
 coal. Mr. Cowie's description was as follows : — " The seam of 
 coal at the Cock of Arran, wrought by James Cowie, is first about 
 ten inches, then eight or ten inches of a dauchy till, then twenty 
 
 inches of coal the till between the two seams of coal 
 
 seems to burn lime." The dauch or till was always mixed with the 
 blind coal in burning lime. It seemed to kindle more readily than 
 the coal ; and the only difference was that the dauch always left a 
 large guest (cinder), whereas the coal burnt into a fine white ash of 
 very small quantity. The thicknesses above given are very much 
 less than 14 feet, when added together, and in fact do not amount 
 to 4 feet, which thickness we may confidently give as the utmost it 
 attained. Two outcrops have been traced, but it seemed probable 
 these were two sets of workings in one and the same coal separated 
 by a fault. Near the salt pans Lepidodendron veltheimianum (?) was 
 collected, and 140 yards N.W. of the old ruins there is a hard, 
 brown weathering, argillaceous limestone in the position apparently 
 of the Index or Productus latissimus limestone. This bed appears to 
 be five or six feet in thickness, and has yielded the following forms : — 
 
 Archffiocidaris Urei. 
 Retepora undata. 
 Lingula mytiloides. 
 ' „ squamiformis. 
 
 Streptorhynchus creniatria, 
 Productus latissimus ? 
 Gasteropod, small. 
 
 "The section above this is a good deal obscured, but some 70 yards 
 farther along shore, where the dip is N.W. at 50*^ or 60°, there is 
 obscurely seen a thin band of dark-coloured limestone associated with 
 hematite bands. This yielded the following list : — Gamarophoria sp., 
 Streptorhynchus crenistria, Bellerophon Urei. Some 450 yards, or a 
 quarter of a mile N.W. of the salt pans, in a small bay, are tesselated 
 ferruginous beds with an ironstone band where were collected : — 
 Productus giganteus. Nuoulana attenuata. 
 
 Rhnychonella pleurodon. 
 Edmondia sp. 
 Entolium Sowerbyi. 
 Myalina Verneuili. 
 
 „ sp. 
 Nuoula gibbosa. 
 
 See his " View of the Mineralogy, etc., of the Island of Arran," pp. 212-219 (1807). 
 D 
 
 Peoten knookonnienais. 
 Protoschizodus axiniformis. 
 Sanguinolites tricostatus. 
 Bellerophon hiulcus. 
 
 ,, Urei. 
 
 Orthoceras annulare. 
 
50 
 
 The Geology of North Arran. 
 
 At the same spot in bands overlying the ironstone were col- 
 lected : — 
 
 Allorisma sulcata. 
 Edmondia rudis. 
 Entolium (yoting). 
 Nucula gibbosa. 
 Nuculana attenuata. 
 
 Peoten (Streblopteria) laevigata 
 Bellerophon Urei. 
 Orthooeras sp. 
 Cladodus striatus. 
 
 The beds here dip northward at 20°-25'?. Beyond these we pass 
 over an alternating series of sandstones and clays on to a thick 
 blocky sandstone which forms a kind of headland. The coast now 
 trends more westerly, and we soon come upon a fault running at 
 right angles to the shore which throws down on the east 20 to 30 
 feet. Beyond this we get a portion of the beds repeated, and soon we 
 arrive at a red limestone in which Productus latissimus is abundant. 
 This is more than a quarter of a mile south-east of the junction with 
 the New Red rocks. It is bounded by a fault on the west side, 
 which must be an upcast to the east, and is apparently some 15 
 feet in thickness. It has yielded . — 
 
 Monticulipora tumida. 
 Zaphrentis sp. 
 Archseocidaris Urei. 
 Crinoid stems. 
 Fenestella sp. 
 Athyris ambigua. 
 Chonetes laguesaiana. 
 Ortliis resupinata. 
 StreptorhjTichus crenistria. 
 Productus costatus. 
 
 Productus latissimus. 
 
 ,, longispinus. 
 
 ,, semiretioulatus. 
 
 „ sp. 
 
 Spirifera triradialis. 
 Spiriferina cristata var. octo- 
 
 plicata. 
 Phillipsia Eichwaldi var. muc- 
 
 ronata. 
 
 Nearly 100 yards west from this spot and 375 yards S.E. of the 
 New Bed junction occurs a thin " cephalopod limestone " about 2 
 feet in thickness, which yielded : — 
 
 Athyris sp. 
 Orthis resupinata. 
 Streptorhynchus crenistria. 
 Productus giganteus. 
 
 sp. 
 Spirifera trigonalis var. bisulcata. 
 
 Spirifera lineata. 
 
 Nautilus (Acantho-nautilus) bis- 
 
 pinosus. 
 Nautilus (Pleuro-nautilus) nodi- 
 
 ferus. 
 Nautilus sp. 
 
 A few yards west of this, in bands overlying the cephalopod lime- 
 stone and 365 yards S.E. of the New Bed junction, there were got : — 
 
 Streptorhynchus crenistria. 
 Productus giganteus ? 
 
 , , costatus var. muricatus. 
 Spirifera ? 
 
 Terebratula. 
 Nucula gibbosa. 
 Nuculana attenuata. 
 Orthoceras sp. 
 
 A few yards farther west and 350 yds. S.E. of the New Red rocks, 
 there were collected : — 
 
 Carbonicola sp. 
 Edmondia. 
 Nucula acuta. 
 
 Nuculana attenuata. 
 Sanguinolites olavus ? 
 Solenopsis minor. 
 
 Above these beds comes a brecciated-looking limestone of consider- 
 able thickness, which is repeated by a fault ranging N.N.E. This 
 
Unconformable Junction. 51 
 
 only yielded Lithostrotioh Portlocki. It has been called the Coral 
 limestone. 
 
 Some of the upper limestones crop out on the hillside a quarter 
 of a mile west of Cock Farm, and from one of these were 
 obtained : — 
 
 Alveolites depressa. 
 Crinoid stems. 
 Streptorhynohus orenistria. 
 Produotus latissiraxxs. 
 
 Brachymetopus ouralicus. 
 AUorisma sulcata. 
 Myalina Verneiilll. 
 
 and a thin limestone occurs in the faulted strip of AUt Mor 
 between North Newton and the Cock of Arran, which yielded 
 Crinoid ossicles, Orthis resupinata, and a species of Productus. 
 
 Above the Coral limestone on the shore the beds consist 
 largely of shales and red clays, with some rough and irregular 
 sandstones. The highest marine band noticed was 100 yards S.E. 
 of the New Red junction, and here were obtained : — 
 
 Crinoid ossicles. 
 Lingula mytiloides. 
 Streptorhynchus crenistria. 
 Productus fimbriatus ? 
 ,, mnricatus? 
 
 Productus sp. 
 Spirifera glabra. 
 
 ,, trigonalis. 
 Lamellibranch. 
 Bellerophon Urei. 
 
 Coal-measure plants were obtained from a spot 72 yards south-east 
 of the New Red rocks : — 
 
 Calamites sp. i Lepidostrobus ? 
 
 Cordaites principalis. | 
 
 A longer and more important list was collected from a locality 20 
 yards S.E. of the New Red junction, and these are the following : — 
 
 Calamites ramosus. 
 ,, varians. 
 Cordaites principalis. 
 Mariopteris muricata. 
 
 Neuropteris gigantea. 
 
 „ sp. 
 
 Sphenopbyllum myriophyllum. 
 „ sp. 
 
 North Newton — unconformable section. — This remarkable 
 junction of schists and newer rocks has often been described. It 
 seems to have first been noticed by the celebrated James Hutton 
 in the year 1785, and his description of it appears first in the 
 3rd volume of his " Theory of the Earth," which has remained in 
 MS. till edited by Sir Archibald Geikie in 1899.* It may be worth 
 while to quote a part of this description : — "Lochranza, at the north 
 end of the island, is properly within the alpine schistus ; but, in trac- 
 ing the shore, upon the east side of the loch or bay, we come to the 
 extremity of this schistus district. Here the first thing that occurs 
 is the immediate junction of the inclined strata of schistus and 
 the other strata, which here appear to be a composition of sandstone 
 and limestone ; these strata are equally inclined with the schistus, 
 but in the opposite direction. Those two different kinds of stratified 
 bodies rise to meet each other ; they are somewhat confused at the 
 immediate junction ; but some of the sandstone or calcareous strata 
 
 See " Theory of the Earth, with Proofs and Illustrations," by James Hiitton, vol, 
 jii., p. 235. Edited by Sir A, Geikie, 
 
52 The Geology of Noiih Arran. 
 
 overlap the ends of the alpine schistus." Hutton made a drawing 
 of the junction, which has been lost. Its place is supplied in the 
 volume by a sketch from Sir A. Geikie. These beds of red and 
 yellowish sandstone with lenticular calcareous bands, and distinct 
 beds of white cornstone, we refer to the base of the Carboniferous 
 formation. They stretch along the shore for nearly 400 yards, and 
 project nearly halfway across the raised beach. At the^ south end 
 they dip N.N.W. at 30°, and at the north end W.N.W. at 25°, so 
 that the strike describes a curve of 45°. The schists on which they 
 rest unconformably dip S.S.B. at 40°. {8ee Plate V.) 
 
 Catacol Cairn. — ^The coping of the wall in front of the police 
 station, Lochranza, near the pier, is made of white Carboniferous free- 
 stone collected on the foreshore nearly a quarter of a mile north of 
 Catacol, and the coping of the wall round the most easterly house in 
 Catacol is from the same locality and of the same character. At first 
 it seemed possible the materials might have been derived from 
 ballast blocks or from scattered boulders on the shore, but on 
 examining the ridge below high-water mark (called a "cairn"), 
 whence the stones were obtained, it was found there were still 
 remaining numerous large and not rounded blocks of the white 
 .Carboniferous sandstone, and also many blocks of red fossiliferous 
 limestone belonging to the same formation. The sandstone blocks 
 are much too large to have been used for ballast, and if there is not 
 an outcrop of Carboniferous rock near, the ridge must be regarded 
 as a kind of moraine. But the latter explanation does not appear 
 very probable when we consider that the nearest place where rocks 
 of this kind occur in situ is more than two miles away to the east 
 of North Newton. It seems more likely that the blocks have been 
 cast up by storms from an outcrop not far away, beneath the sea. 
 
 There are many limestone blocks in the old dyke by the road- 
 side between Catacol village and the bridge over Catacol Burn, 
 which must also have been derived from the foreshore. 
 
 Mr. D. Tait, the fossil-collector of the survey, has obtained the 
 follovsdng suite of organic remains from the limestone blocks of 
 the " cairn," and these were examined and named by Mr. B. N. 
 Peach. The fossils apparently may all belong to the Upper 
 Limestone group of the Carboniferous formation, and this lends 
 support to the view that they have come from rocks in situ at a 
 short distance. 
 
 FOSSILS FROM LOOSE LIMESTONE BLOCKS CAST ASHORE AT 
 
 " THE CAIRN " BETWEEN TIDE MARKS NEAR \ MILE 
 
 NORTH OF THE VILLAGE OF CATACOL. 
 
 Coral, rugose (Zaphrentis?). Produotus giganteus. 
 
 Lithosfcrotion Portlooki. „ latissimus (abundant). 
 
 Crinoid stems. „ semiretioulatus. 
 
 Phillipsia Eichwaldi. Spirifera bisulcata. 
 
 Eeteporasp. „ trigonalis. 
 
 Athyris ambigua. Avioulopeoten interstitialis. 
 
 Lingula squamiformis. Nucula gibbosa. 
 
 Orthis resupinata. • Diseoceras (Disoites) oarinifenim, 
 Produotus cora. 
 
•- -n 
 
 0) 
 
 a, 2 
 
 j3 
 
 .B-Ji 
 
 
 
 
 -3 13 
 
 G 
 
 >, Jf 
 
 j^ 
 
 "Z^ "T^ 
 
 rf 
 
 rH ►-^ 
 
 OJ 
 
 CD O 
 
 D, 
 
 -C-G 
 
 D- 
 
 
 rt 
 
 aj ^ 
 
 
 j3 C 
 
 ^_, 
 
 ^ o 
 
 crt 
 
 
 rf 
 
 _>^ 
 
 
 
 
 rt'^ 
 
 <U 
 
 
 -G 
 
 ■< ^ 
 
 H 
 
 
 
 - G 
 
 
 
 ^ 
 
Lower Carboniferous Moclcs. 53 
 
 BUTE AND THE CUMBRAES. 
 
 The Carboniferous rocks of Bute and the Cumbraes belong to 
 the lower part of the Calciferous Sandstone division. 
 
 LITTLE CUMBEAE. 
 
 On the eastern side of the island sandstones which appear to be 
 interbedded with the lower part of the volcanic series crop out. 
 A rough, reddish sandstone is visible at low water on the eastern 
 side of Castle Island dipping westward under the bed of trap that 
 forms the island, and much jointed, roughly-bedded sandstone crops 
 out in several places south of the houses on the main island. It is 
 mostly of a reddish tinge, but the upper beds, which dip westwards 
 at 10° to 12° under the main mass of the lavas, are whitish in 
 colour. 
 
 GREAT CUMBRAE. 
 
 In this larger island the Lower Carboniferous rocks occupy a con- 
 siderable area on the north side of Millport Bay, and the larger 
 islands in the bay are formed of sandstones of the series. The 
 lowest bed, which is a white cornstone, follows a curved line from 
 Doughend Hole round to Ballykellet, nearly parallel to the curve 
 of the bay on its northern side. This has already been described 
 as the upper boundary of the Old Red Sandstone. 
 
 The rocks generally consist of white sandstones and red clays or 
 shales, with occasional bands of conglomerate and some white corn- 
 stones. There are not many exposures in the interior of the island, 
 except to the west of Ballykellet, and the best sections are along 
 the coast from Doughend Hole southward to Portachur Point, and 
 round the northern curve of the bay. The general direction of the 
 dip of the beds is toward the S.S.W., which becomes due south 
 towards the east end. The average amount is about 20'-', but about 
 Foul Port, west of the pier, it is between 30° and 45°, while on the 
 islands of the bay the dip is about 10°. The eastern side of the' 
 bay is occupied by the Upper Old Red Sandstone, brought up against 
 the Carboniferous rocks by the large north and south fault before 
 referred to when treating of the Old Red Sandstone. It may be 
 noticed that the sandstones of the islands, which are the highest 
 beds visible, as well as the rocks on the shore to the northward, 
 and those outcropping near Ballykellet, are all striking directly at 
 this line of fault. 
 
 The sandstone of the islands has been a good deal quarried. It 
 is generally thick-bedded, whitish in colour, and not very coarse, 
 but in some places the bedding is irregular, and the rock is mixed 
 with much quartzose conglomerate. On the shore of the New 
 Town at the eastern end of the outcrop there are alternations of 
 white sandstones and red clays with bands of white cornstone. 
 Some of the sandstone is coarse and pebbly, with false bedding. 
 Westward from this point the sandstone is generally white in 
 
54 The Geology of North Arran. 
 
 colour and rather fine-grained, alternating with bands of red, 
 purplish, and mottled clays, and occasional nodular limestone. On 
 the west side of Foul Port near the West Bay there is a thick 
 mass of red clays, with occasional thin sandstone bands. A great 
 portion of this series does not appear on the east side of the little 
 bay owing to two N.N.W. faults. There are several small faults 
 along the shore to the southward, and in all this part west of the 
 pier there are several bosses of intrusive igneous rock, besides 
 dykes running in various directions. Several of these intrusive 
 igneous rocks have altered the sandstones and clays in their vicinity. 
 The prominent rugged hills about Upper Kirkton and to the east- 
 wiird are all formed of intrusive igneous rocks, which are later in 
 date than the Lower Carboniferous rocks which they penetrate. 
 Some of these, as Sheughends and Playbill, are composed partly of 
 trachyte and partly of olivine dolerite. 
 
 BUTE. 
 
 In the island of Bute the Lower Carboniferous rocks are found at 
 Ambrisbeg, near Loch Quien, on the west side of Scalpsie Bay, and 
 in the Garroch Head district south of Kilchattan. 
 
 Ambrisbe g. — The rocks here appear to form the southern end 
 of a small synclinal, in the centre of which is the lowest bed of trap. 
 Immediately beneath this bed there appears to be a seam of 
 anthracitic coal about 18 inches thick, which was formerly worked, 
 and there still exist remains of the old adits. A small sandstone 
 quarry lies to the south of Ambrisbeg, and limestone, and white 
 and red sandstone were found in a cut close by. 
 
 Scalpsie Bay. — Carboniferous Rocks are seen near the 
 fault which runs along the west side of the bay. Some small 
 sections in white sandstone appear near the northern end of the 
 bay, and near Ardscalpsie Point there is a considerable exposure of 
 Lower Carboniferous sandstones and conglomerates, some of which 
 are reddish, others are white or yellow and calcareous, approaching 
 to cornstone. There are two old limekilns here, and limestone is 
 said to have been formerly burnt. The beds are undulating a good 
 deal, and are penetrated hj intrusive basic masses, both dykes and 
 bosses, the latter being probably of Carboniferous age. 
 
 Kilchatta n. — The Carboniferous district south of Kilchattan 
 is complicated by faults, and much of the ground not occupied 
 by the volcanic rocks is obscured by glacial drift. The limestone, 
 which has been taken as the boundary between the Carboniferous 
 and Old Red formations, also appears to be absent in places, and 
 the volcanic series apparently overlaps or rests unconformably on 
 the Old Red Sandstone. 
 
 The cornstone was at one time extensively quarried to the east 
 and north of the ruins of Kelspoke Castle, but the quarries are now 
 full of water. The rock is a kind of dolomite, containing from 17 
 to 34 per cent, of carbonate of magnesia, and it is remarkable that 
 where the rock is in contact with intrusive igneous material the 
 magnesia almost disappears. For interesting points connected 
 
Lower Carboniferous Rocks. 55 
 
 with this fact we refer to Bryce.* The limestone is from 15 to 20 
 feet thick, and dips to the south-west at 25°. It may be followed 
 south-eastward to its outcrop on the shore near to a mass of volcanic 
 agglomerate, but its thickness appears considerably less than in 
 the quarries. About 200 yards farther south a large fault having 
 a W.N.W. course and downthrow north, brings up the Old Eed 
 Sandstone against the lower beds of lava. At the mouth of a small 
 burn is a fault ranging north-east and throwing down on the south- 
 east side, and a little beyond this, on the foreshore, we find the 
 cornstone much invaded by basic igneous rocks. The white lime- 
 stone crops out on the north side of the small burn, where it is also 
 penetrated by igneous intrusions, and traces of it are found near 
 Kelspoke Oastle, but its repetition here is probably due to a fault 
 ranging N.W., which appears to cut off the old quarry workings. 
 The south-westerly dip at a high angle continues in the traps and 
 other beds all across the peninsula, and yet we find at a distance of 
 a mile and a half across the strike the same cornstone and associated 
 beds at the south side of Dunagoil Bay on the west side of the 
 island. It is manifest there must be some large fault or faults re- 
 peating the beds, but the difficulty is to find their exact position 
 and direction. The base of the trap series is found at Port Dornach, 
 and northward from this we see along the shore for more than a 
 hundred yards beds of white sandstone and conglomerate, with 
 bands of cornstone or limestone, some of which are pebbly or 
 cherty. These beds dip to the S.S.W. at 25°, and are succeeded 
 by the upper beds of the Old Red Sandstone of a red colour, some- 
 what streaked and mottled with white. A fault passes in a north- 
 easterly direction along the edge of the raised beach, and by it the 
 cornstone is shifted eastward, so that it appears again behind 
 the isolated igneous mass, which is probably an old vent. Now 
 we. have the traps again on the north side of Dunagoil Bay, so that 
 it seems clear they must be repeated by a downthrow fault which 
 probably runs in a S.B. direction nearly in a line with the northern 
 edge of the bay, turns S.S.W. by South Garrochty, and then 
 turning S.B., again follows the hollow which strikes the southern 
 shore near Port Uisg, which is south of Port Leithne. In Port 
 Uisg we find again the base of the traps, and see dipping under 
 them, but a good deal invaded by intrusions, a portion of the white 
 Carboniferous sandstone. 
 
 Northward from Dunagoil Bay we find the traps on the shore, 
 but after passing Barr Point we come again to the base of them at 
 the southern end of Lubas Bay. Here, however, there are no 
 traces of the cornstones, and the sandstones, which are generally 
 red, seem to be portions of Old Eed Sandstone dipping in a 
 direction 30° west of south at angles of 20° to 25°. The trap 
 appears to dip at a lower angle than the sandstones, and evidently 
 transgresses the edges of their beds in places. If we look eastward 
 from the trap at Barr Point towards the higher ground, which is 
 upwards of 100 feet above the sea, we observe that the base of the 
 Trap clifi" has only a dip of about 10°-. In front of it is a portion 
 
 * "Geology of Arran and other Clyde Islands," 4th ed., p. 325, 
 
56 The Geology of North Arran. 
 
 of an old beach, and below this is a cliff of red sandstone in which 
 the beds dip about 25°. Now, if we examine the base of the trap on 
 the shore we find clear evidence of an unconformability. The 
 porphyritic trap, which is decomposed at the base, fills up in one 
 place a hollow denuded out of the thin-bedded white and reddish 
 sandstone on which it reposes. 
 
 We suppose that to the northward an east and west fault again 
 repeats the beds of trap, and that the Dunstrone outcrop on the 
 south side of Lubas Port is the same as that at Lubas, only shifted 
 by a north and south fault. In both cases there is no cornstone, 
 and the trap rests on red sandstone and conglomerate. Another 
 north and south fault with a downthrow east separates the Lubas 
 outcrop from that in Suidhe plantation, which is continuous with 
 those on the east side of Glen Galium. The fault at the west end 
 of Suidhe plantation is probably continued down this glen, and 
 must have here a large downthrow on the north-east side, where 
 there is a thick series of trap beds. The base of the traps appears 
 on the west side, and sandstone below is visible at the northern 
 end of the glen and in Glencallum Bay at its southern extremity. 
 
 Igneous Eocks of Carboniferous Age. 
 
 aeran, bute, and cumbeae. 
 
 Contemporaneous Volcanic Roclts. 
 
 There appear to be within the limits of this sheet Carboniferous 
 volcanic series belonging to three different periods. The most 
 recent of these, which is probably of Coal-measure age, is found in 
 Benlister Glen ; another, which is of somewhat older date, and 
 near the horizon of the uppermost limestones, occurs in the 
 streams north of Brodick Castle ; while a third, and by far the most 
 important, is low down in the Calciferous Sandstone. This last 
 occupies a considerable area in South Bute, forms nearly the whole 
 mass of the Little Oumbrae, and in Arran is a conspicuous feature 
 in the sections of the Carboniferous rocks on the north-east shore, 
 at Oorrie, and elsewhere in the island, Everywhere old lava-flows 
 of basic composition make up the bulk of the volcanic material, 
 while the fragmental portions vary from coarse agglomerates to the 
 finest well-bedded tuffs. In a few places in the island of Bute we 
 find the sites of volcanic vents now filled with coarse fragmental 
 material, or with intrusive igneous masses of later date than the 
 surrounding rocks. 
 
 i. Lower Volcanic Zone. 
 
 A r r a n. — On the north-eastern shore, near Millstone Point, the 
 lower volcanic group occurs three times between Corloch and the 
 shepherd's house at Laggan. The most northerly exposure occupies 
 the shore for nearly a quarter of a mile, its southern boundary being 
 nearly half a mile from Laggan. The greater portion of the out- 
 
Lower Volcanic Zone. 67 
 
 crop consists of massive, fine-grained grey trap in which no dip is 
 visible, but the vt^hole series is inclined to the north at an angle 
 between 30° and 40°, so that the total thickness must be over 
 300 feet. There are two fine tuff bands in the lower portion of the 
 mass, and between these the rock is very scoriaceous, while the part 
 below these fragmental bands is soft. Below the main mass are 
 alternations of thin lava beds and fine shaly tufis, in some of 
 which Mr. A. E. Wunsch was the first to discover remains of Carboni- 
 ferous plants (see Trans. Geol. Soc. Glasgow, vol. ii., pp. 97 and 160, 
 " On the occurrence of Fossil Trees imbedded in Trappean Ash in 
 Arran "). 
 
 The ordinary Calciferous Sandstone and shales underlying the 
 traps succeed to the southward, but owing to large faults we find 
 repetitions of the volcanic series to the south of Millstone Point, 
 where the old lavas again occur, but the tufis are much coarser 
 than in the last section and form a large proportion of the whole 
 series, so that here we are probably nearer the site of a volcanic 
 vent. Nearly half a mile south of Millstone Point we find the 
 following section on the foreshore : — 
 
 The upper portion is for the most part a slaggy and amygdaloidal 
 lava with a little tufiaceous material, about 150 feet in thickness. 
 Succeed in descending order well-bedded greenish and red tuffs, 75 
 feet thick. 
 
 Lava. — slaggy above and with pillowy structure below, often an 
 irregular mass in which are several red and dark flinty bands 
 apparently filling up cracks in the lava-fiow — 75 feet. 
 
 Finer tufis with some lava — few feet, perhaps 10. 
 
 Coarse volcanic agglomerate — 75 feet. 
 
 The dip is slightly east of north at a high angle, 50^ to 60°, 
 and the total thickness must be near 400 feet. 
 
 These beds only appear on the foreshore and on the raised beach, 
 being cut ofi" on the west by a large fault running nearly due north 
 with a downthrow east of some 600 feet. Some distance to the 
 north, therefore, we find the volcanic zone again on the foreshore 
 resting on the cement-stone series. It has the same steep northerly 
 dip, but we only see a portion of it, the lower agglomerate band 
 about as thick as before but intercalated with some finer tufi" 
 bands, and surmounting it a portion of the grey trap bed; and then 
 another northerly-running fault with a large downthrow east 
 destroys the continuity of the section. 
 
 Qn the south side of the North Sannox anticline this Lower 
 Carboniferous volcanic band appears on the shore north of Corrie, 
 where it is about 350 yards in breadth. It dips southward like the 
 other Carboniferous rocks at an angle of about 20°, and the thick- 
 ness is altogether about 350 feet probably. The lowest portion is 
 a very coarse agglomerate containing some fragments of basic trap 
 6 feet in length. To the south of this, and overlying it, is a fine- 
 grained bluish basalt, which opposite to and southward of the large 
 granite boulder called Clach an Fhionn exhibits a remarkable pillowy 
 structure, and it seems probable that many of the large rounded 
 blocks on the foreshore and raised beach about here are simply 
 
58 The Geology of North Arran. 
 
 detached pillows {see Plate VI.). The upper part of the mass near 
 the schoolhouse is much reddened and veined with calcite, etc. 
 
 Seventy yards farther south and opposite the Established Church 
 is a later lava-flow, a purplish and miich veined bed, 10-12 feet 
 thick, separated from the older by some 70 feet of shales, sands- 
 stones, and cement-stones. Both beds are exposed in the burn that 
 flows past the church, but the base of the lower volcanic mass is 
 not seen here, for a large fault cuts off the outcrop 600 yards from 
 the sea. This fault shifts the rocks to the southward, and both 
 beds are exposed again in the Locherim Burn, where some inter- 
 calations of tuff occur in the lower and larger bed. Another large 
 fault, which must have a throw of over 1000 feet, shifts the volcanic 
 rocks again to the south, this time a distance of three quarters of a 
 mile to the burn called Uisge nam Fear, which is the first stream 
 north of Maol Donn. In the southern bank of this burn there is a 
 fine section of the lower part of the series, for the most part a soft 
 red or purplish decomposing lava of basic composition, overlying 
 red shales, some of which are tuffaceous. All are much veined with 
 calcspar, and several intrusive dykes of much later age (Tertiary) 
 cut through both igneous and aqueous rocks. The large faults to 
 the southward which cause the outcrops of this bed to be so dis- 
 connected are elsewhere described ; it suffices to say that there are 
 exposures of it in the burns in Brodick wood, north of the Castle; 
 by the side of the road leading to Goatfell ; along the 
 southern side of Glen Shurig; in two places on the south 
 side of Glen Dubh; and around Brisderg; from which last 
 locality a continuous strip runs southward across the head of 
 Benlister Glen to the southern edge of the sheet near the boundary 
 of the two parishes. Throughout nearly the whole of its course 
 southwards from Maol Donn it dips steeply towards B.S.B. orS.B., 
 and the outcrop is generally but a narrow band. Bands of tufi" 
 occur here and there as in Benlister Glen and on the south side 
 of Glen Dubh, and these sometimes merge into red sandstones or 
 shales by a diminution of the amount of the volcanic material. 
 The massive rocks consist of basic lavas generally of a red oi purple 
 colour, due to decomposition and oxidation of the iron ores and 
 ferro-magnesian constituents. Those which have been sliced were 
 originally olivine basalts, but they are now highly altered, and the 
 ferro-magnesian minerals have almost entirely disappeared, and 
 their place is taken by carbonates, chlorite, ferric oxide, and quartz. 
 Owing to the great alterations these rocks have undergone it is some- 
 times difiBcult in hand specimens to distinguish between the 
 massive rocks and the tuffaceous sediments. 
 
 The rock from Benlister Glen, east of Lag na Croise, is a highly 
 altered olivine basalt of a dull, darb purplish colour, which when 
 examined with a lens shows red spots in a greenish matrix. 
 
 The highly altered olivine basalt from 500 yards north-east of 
 Windmill Hill is a fine-grained, dark purplish rock. 
 
 Little Cumbra e. — The Lower Carboniferous Traps form the 
 whole of the Little Cumbrae, except a small portion on the east 
 side. The island is beautifully terraced ; each separate lava-flow 
 

 O -^ 
 
 o u 
 
 [/I — 
 
 £ 5c 
 
 '~ .?, 
 
 3 5 
 
 U - 
 
 '-' b 
 
 3 i; 
 
 - o 
 
 &-^ 
 o o 
 
Lower Volcanic Zone. 
 
 59 
 
 ''^ 
 
 :l^ 
 
 making a distinct feature, often a 
 crag, at the outcrop. The flows 
 are often slaggy or scoriaceous at 
 the top, but there is little real tuff. 
 The beds are disposed in a shallow 
 synclinal the axis of which ranges 
 N.N.W. through the highest part 
 of the island, where is the remains 
 of the old lighthouse. As this 
 axis is nearer to the west than to 
 the east side, and the beds have 
 also a less dip on the west side, 
 the eastern limb of the synclinal 
 gives the more complete section. 
 The westward dip in this part is 
 as much as 10 degrees or even 
 more, and the thickness must be 
 as much as 600 to 800 feet. The 
 base of the main mass, which 
 reposes on white sandstones, has a 
 north and south course near the 
 farmhouse, but older and separate 
 parallel flows form Castle Island 
 and Trail Isle to the eastward. 
 See section across the Little Oum- 
 brae. 
 
 All the specimens sliced are 
 basalts, and the rock is often por- 
 phyritic in character and usually 
 of a purple colour, though some 
 beds are blue in colour and fine in 
 texture. The slaggy or coarsely 
 amygdaloidal varieties often con- 
 tain much calcite in the cavities. 
 In several places the flows exhibit 
 a rather markedly columnar struc- 
 ture, as, for example, in the crags 
 below the lighthouse. 
 
 Along the north-eastern shore 
 in more than one place there 
 occurs a coarse volcanic agglome- 
 rate with fragments reaching one 
 foot in length. There appears 
 nowhere any great thickness of 
 this fragmental rock, and in all 
 probability it is in each case a true 
 volcanic tuff intercalated between 
 sheets of lava. 
 
 South But e. — In South Bute 
 the same volcanic series forms a 
 striking series of ridges ranging 
 
60 The Oeology of North Arran. 
 
 N.W. with their scarped edges facing to the north-east. The dip 
 to the south-west is on the average quite 30°, and the thickness 
 must be great, probably much more than that exposed in the Little 
 Oumbrae, notwithstanding that the beds are several times repeated 
 by faults along the strike, elsewhere described. In neither locality, 
 however, do we reach the upper limit of the series. One of the 
 main lines of fault is along Glen Galium, while another passes by 
 South Garrochty. 
 
 The flows vary in character and thickness. Some near the base 
 of the series are fine-grained, bluish in colour, and weather with a 
 marked columnar structure, but generally the rock is tinged red or 
 purple and shows large porphyritic felspars. Many of the flows 
 are scoriaceous at top as in Little Cumbrae, and most of them are 
 basic in character like the olivine basalt of Dunstrone Fort, or the 
 porphyritic dolerite that caps the ridge north of Tor Mor. Some 
 beds may be more intermediate in character, like the basaltic 
 andesite of Barr Point and the coarsely porphyritic andesite of 
 Dunagoil Port. One bed on the west side of Port Luchdach, half 
 a mile west from Runnan Eun Point, is a brownish trachyte with 
 a green pyroxene, and this bed can be traced nearly to North 
 Garrochty. 
 
 Volcanic agglomerate and tufis are found in several places, but 
 form only a small portion of the series. A strip of coarse 
 agglomerate runs for a long distance by the shore near South 
 Garrochty, and is probably an intercalated mass ; in one place it 
 includes a block of sandstone four feet in length. Bast of Port 
 Leithne are finer tufis, beautifully laminated beds of ash and ashy 
 sandstone, into which a late Carboniferous dolerite sheet is 
 intruded. The tufis dip to the south-west at 30°. 
 
 Ambrisbeg. — On the east side of Loch Quien at Ambrisbegis a 
 small area of this volcanic series. It forms a portion of a larger 
 volcanic district which stretches between Lochs Quien and Pad, in 
 Sheet 29, to the north. The rocks are old lavas, resembling in 
 character those already described, and all apparently basic. 
 
 ii. Second Volcanic Zone. 
 
 There is a volcanic series nearly on the horizon of the Upper 
 Limestones in the wood three quarters of a mile to the north of 
 Brodick Castle. The lava, of which it mainly tionsists, is stained of 
 a red colour, and in character closely resembles that of the lower 
 group. In one place it attains a thickness of 25 to 30 feet. This 
 bed is probably nearly contemporaneous with the lower part of 
 the series at Sliddery Water Head and with some of the inter- 
 stratified volcanic rocks in the higher part of the Carboniferous 
 Limestone in Ayrshire. 
 
 iii. Third Volcanic Zone. 
 
 The best exposures of traps and tuffs of Upper Carboniferous or 
 Coal-measure age occur at Sliddery Water Head in Sheet 13, and for a 
 detailed description of these the reader is referred to the annual 
 
Intrusive Carboniferous Bodes. 61 
 
 summary of the Geological Survey for 1897, pp. 112-123. It now 
 seems probable from the evidence of the fossils that in this locality 
 there is included in the one volcanic series representatives 6f both 
 Coal-measures and of the Upper Limestones, and the volcanic 
 action must have been prolonged during a portion of both 
 geological periods. 
 
 In Sheet 21 there is an outcrop of Carboniferous trap at the 
 fall called Bas Geal in Benlister Glen, 2|- miles west of Lamlash. 
 It occurs in a much faulted area and the age of it is somewhat 
 doubtful, but as it is in conjunction with beds of red shale and 
 and sandstone belonging to the Coal Measures it seems natural to 
 suppose the trap to be of the same period. The volcanic rock 
 appears to be faulted against the shales a little below the bend in 
 the stream ; it is there reddish and much decomposed. Above the 
 fall the rock is fine-grained, grey in colour, and more like an 
 intrusive rock, but it is probably another portion of the contem- 
 poraneous lava. It occupies the bed of the stream for about a 100 
 yards, and in one place is pierced by an intrusive basalt d3'ke. On 
 the west side this mass is probably bounded by a fault which 
 brings up the Lower Carboniferous rocks. 
 
 Intrusive Oarhoniferous Hocks. 
 
 But e. — Volcanic Vents. — No intrusive igneous rocks of Car- 
 boniferous age have been noticed in Arran, but in South Bute 
 these occur near the base of the Trap Series half a mile north of 
 RunnanEun Point; bosses, sills, and irregular masses of fine-grained 
 dark basic rocks, and similar intrusions, are found a quarter of a mile 
 east of the Garroch Head. The large oval mass of altered olivine- 
 basalt which forms Suidhe Hill was probably intruded into an old 
 volcanic vent, some of the fragmental material of the neck being 
 still visible at the south-western end of the mass. This plug is 
 some 600 yards long from north-east to south-west. 
 
 About half a mile north of Runnan Eun Point there is a crag 
 formed of volcanic agglomerate which contains fragments of trap ; 
 also limestone and baked sandstone or quartzite. An intrusive 
 basic sheet appears to occupy part of the site of this vent. 
 
 At Creag a Mhaid, 300'yards farther north, is another mass of 
 coarse agglomerate, apparently of an oval form and about 150 
 yards in length, and here again the neck has been invaded by an 
 intrusive mass. 
 
 On the south side of Dunagoil Bay is an isolated mass which 
 may be the site of a vent, though there is not much fragmental 
 material visible, and the rock is for the most part massive in 
 character. 
 
 Great Oumbra e. — Trachyte. — There are at least four distinct 
 groups of intrusive rocks in Great Oumbrae, and three of these 
 are probably of Carboniferous age. The oldest of these is trachytic 
 in character, and occurs both as sheets and dykes which have a 
 general E.N.E. direction. The rock is usually of a pink colour, 
 but is sometimes grey or purplish. A specimen from the dyke of 
 
62 The Geology of North Arran. 
 
 the Hawk's Nest north of Parland Point was analysed by Mr. Teall, 
 and was found to contain 11 per cent, of alkalies, principally 
 potash, while the percentages of lime and iron were very law. 
 Sometimes these rocks are fine in grain with but a few porphyritic 
 orthoclase crystals visible, though numerous small crystals of 
 this mineral are revealed by the microscope. These red trachyte 
 dykes and sills are almost confined to the Upper Old Eed Sandstone, 
 rarely intruding into the Calciferous Sandstones, and being appar- 
 ently older than the Carboniferous lavas of the Little Oumbrae and 
 South Bute. Several of the sills form marked features in the 
 interior of the island. Some bosses of rock in Millport Harbour, 
 known as The Olach and the Miller's Thumb, which are described 
 as porphyrite or bostonite, are probably of nearly the same age 
 as the trachyte. 
 
 Olivine-hasalt. — The next group has the same general direction 
 but clearly cuts the trachytes, and must therefore be of later date. 
 A fine example occurs on the shore near Craig nan Pitheach be- 
 tween Doughend Hole and Sherifi" Port, where one of these dykes 
 cuts a trachytic sill and both are crossed by a tertiary dyke running 
 north-west. 
 
 The dykes of this set are the most numerous of the whole, and are 
 found on every part of the island. On the north-east shore about 
 •10 of them may be counted in half a mile of coast-line, and some 
 of them are large. They appear to be all porphyritic olivine- 
 basalts of the type of the Lion's Haunch on Arthur's Seat, 
 Edinburgh. Generally they are bluish or grey in colour, and finer 
 at the edges than in the centre, which is often coarsely porphyritic 
 and amygdaloidal. Some of them, however, are much decomposed 
 and stained. Olivine seems always characteristic, but has often 
 been replaced by hematite and calcite. In Bute, a good many 
 dykes occur on the north side of Kilchattan Bay and a few around 
 Stravanan Bay, which have the same general direction as these 
 basalt dykes in Cumbrae, and as their character is similar they 
 probably all belong to the same geological period, which is 
 probably that of the Lower Carboniferous lavas. Most of these 
 dykes in Bute are much stained with hematite. 
 
 Bolerites. — The dykes of the third group are basalts or dolerites, 
 with or without olivine, and they have, on the whole, an east and 
 west direction like that of the Dunoon dyke, which belongs to "this 
 class. They cut the two sets of dykes previously described, and 
 must therefore belong to a far later period of intrusion ; probably 
 they are not older than late Carboniferous time. One of these 
 dykes in Great Cumbrae, about 50 feet in width, is a nodular basalt, 
 and it can be traced westward from Ballykellet to the western shore. 
 It traverses in its course many dykes and sills belonging to the two 
 classes just described. Another dyke of this kind runs all across 
 the island from Fintray Bay, where it is 100 feet wide, past Figga- 
 toch to Downcraig Ferry, where its width is 75 feet. Its course, 
 however, is not continuous ; it is broken up into three detached 
 portions, which remind one strongly of the similar behaviour of the 
 Dunoon dyke and those near Eothesay, which probably belong to 
 
Ayrshire — Calciferous Sandstone Series. 63 
 
 the same period. In Bute, a dyke to the south-east of Lubas and 
 one at Kilchattan probably belong to this set, as does also a 
 dolerite sill that traverses the Carboniferous traps in a north- 
 easterly direction from Garroch Head to near Eunnan Eun Point. 
 
 W. G. 
 
 Calciferous Sandstone Series. 
 
 ayrshire. 
 
 The portion of this lowest subdivision of the Carboniferous system 
 included in the present district follows continuously and conform- 
 ably upon the Upper Old Eed Sandstone, passes under the great 
 overlying volcanic plateau, and attains a thickness of about 1500 
 feet. It consists mainly of yellowish sandstones, often pebbly, and 
 including many zones of fine conglomerate. The cornstone at the 
 top of the Old Eed Sandstone has not been detected here, nor do 
 we encounter more than a mere trace of the cement^stones, marls, 
 and shales, which, farther north, emerge in considerable thickness 
 from under the volcanic series. The Carboniferous strata are not 
 exposed on the shore, but are well displayed in the numerous burns 
 and on the inland slopes, Of these natural sections the best will be 
 found in the channel of the Kippen Burn north of Fairlie, in 
 Fairlie Glen, and in the Glen Burn a mile-and-a-half farther south. 
 
 The Fairlie Glen section may be described as typical for the 
 whole district. The passage from the Upper Old Eed Sandstone 
 into the Carboniferous system is to be seen immediately above the 
 ruins of Fairlie Castle. The red sandstones are there succeeded by 
 intercalations of grey and yellow sandstone and fine conglomerate 
 dipping up-stream. The hard conglomerate bands tend to form 
 waterfalls in the course of the burn, of which a good example 
 occurs at the line of the 250-feet contour. Eed and reddish- 
 grey sandstones still make their appearance, generally more or 
 less pebbly, and often much false-bedded. At last the yellow 
 sandstones prevail, generally full of false-bedding, and more or 
 less conglomeratic. The conglomerates contain abundant white 
 quartz-pebbles. The most important of them, crossed by the 
 Fairlie Burn at the 1000-feet contour, not far below where the 
 stream-section ends, is a well-marked conglomerate, with large 
 pebbles of white quartz. It can be traced as a definite horizon 
 for nearly a mile northward along the hill-slopes. Though thrown 
 backward and forward by occasional faults it maintains its per- 
 sistence until it comes against the large fault above Kelburn. 
 It is probably the same band of conglomerate and pebbly sand- 
 stone which underlies and surrounds the outline of the volcanic 
 plateau forming Kaim Hill, and which has been worked at the 
 Kaimhill Millstone Quarry. 
 
 Above the conglomerate band in the Fairlie Burn a thin zone 
 of reddish tuff marks the first beginnings of the volcanic series. It 
 is immediately followed ,by mottled clays with dark sandy shales, 
 which, however, have been greatly broken up by the invasion of an 
 
64 The Geology of North Arran. 
 
 intrusive sill. These strata, of which only a small thickness is here 
 displayed, present typical features of the Cement-stone group. The 
 shales contain cyprids and plant-remains. They pass' immediately 
 under the lavas of the plateau. 
 
 Volcanic Group. 
 
 This important member of the stratigraphical series of Central 
 Scotland lies between the Carboniferous Limestone, as represented 
 by the well-known and persistent Hurlet seam, and the Upper Old 
 Red Sandstone. In the western counties it does not descend so 
 low as in the east of tjie country, for, as we have seen in the fore- 
 going account of the section in the Pairlie Glen, a great thickness 
 of the Calciferous Sandstones here intervenes between the base of 
 the volcanic rocks and the top of the Old Eed Sandstone. Only a 
 few projecting and outlying parts of the volcanic plateau came into 
 the present district, but they afford illustrations of most of its 
 characteristic features. They show it to be built up of successive 
 sheets of andesite, with occasional partings and bands of tuff. 
 These rocks present the usual petrographical types, which are so 
 well exhibited in the . Little Cumbrae, and the south end of Bute, 
 in the same Map. They vary from compact, finely-crystalline por- 
 phyritic masses, in which the characteristic andesite structure is 
 manifest, up to coarse decomposing amygdaloids, which here- and 
 there furnish good agates and zeolites. The upper and under sur- 
 faces of the flows are frequently slaggy and brecciated. 
 
 The rocks are well exhibited in the courses of the burns, but 
 perhaps the most instructive sections are to be foiind on the steep 
 hill-slopes to the north of Largs, just beyond the northern limit of 
 the present Map. On the face of the great escarpment a succession 
 of sheets of andesite with occasional well-marked intercalations of 
 tuff, can be followed up to the edge of the plateau, which stretches 
 thence eastward into the great volcanic centre of the Misty Law. 
 (Sheet 30.) 
 
 To the west of the escarpment a number of sills and intrusive 
 bosses of a pinkish or yellowish felsitic or orthophyric rock form 
 prominent ridges and detached hills. Some of these traverse the 
 Old Eed Sandstone, as in the case of the masses to the south- 
 west of Hunterston and the sheet which runs along the slope 
 behind Pairlie, as well as another to the south of The Glen. But 
 most of them lie within the Carboniferous area. The chief mass 
 occupies a breadth of about 800 yards immediately to the west of 
 Glentane Hill. A little to the north it divides into two separate 
 sheets, the lower or westmost of which can be followed for a mile- 
 and-three-quarters nearly as far as Fairlie Glen. It, as well as the 
 upper sheet, has been shifted by three faults, and both of them are 
 pierced by volcanic necks. They not improbably belong to an early 
 part of the volcanic history. There occur also numerous dykes of 
 similar material, as well as of varieties of andesite and dolerite. 
 The number of these intrusions must be vastly greater than is 
 expressed on the map, for only a small proportion of them can 
 
Ayrshire — Volcanic Group. 65 
 
 actually be seen. Their multitude may be inferred from the pro- 
 fusion of them in the burns and along the shore. Most of these 
 dykes, no doubt, belong to the Carboniferous volcanic period. But 
 the dolerites and basalts, especially those which trend in a north- 
 westerly direction, are more probably of Tertiary age. 
 
 Reference has above been made to the occurrence of at least a 
 dozen volcanic necks which mark the sites of some of the eruptive 
 vents connected with the plateau. These interesting features are 
 dotted along the slopes between Ardrossan and Largs, and many 
 more occur to the north of the latter village. They are filled with 
 agglomerate or tufi, consisting- of blocks and lapilli of various 
 andesites, and porphyries with pieces of red and white sandstone or 
 other sedimentary material imbedded in a dull green matrix of 
 comminuted andesitic debris. 
 
 Beginning at the south end of the chain, we find the first of the 
 series in the Tarbert Hill, a prominent, rounded, green eminence 
 rising to a height of 445 feet above the sea on the sloping ground 
 immediately to the east of Sea Mill. Like most of them, it is elliptical 
 in form, measuring about 550 yards in length by 360 yards in 
 breadth. In the centre it is composed of a yellowish or dirty green, 
 fine, compact, sandy and granular tuff, with occasional quartz-pebbles, 
 and here and there exhibiting traces of vertical stratification. 
 Eound its outer margin, and thus along what must have been the 
 walls of the volcanic orifice, the material becomes a coarse agglo- 
 merate, mainly composed of rounded blocks and lapilli of various 
 andesites, but enclosing also pieces of red sandstone some of which 
 measure several feet in diameter. 
 
 Half-a-mile farther to the north-east stands the larger neck of 
 the Law Hill, the summit of which is 551 feet above the sea. It 
 has an irregularly oval shape, measuring about 850 yards from east 
 to west, and about 450 from north to south. It is filled with a 
 coarse agglomerate in which, besides red sandstone blocks, pieces 
 of black shale may be observed. The date of this vent must thus be 
 later than the time when the black shales of the Calciferous Sand- 
 stones began to be laid down. Only 160 yards from the eastern 
 edge of this neck lies another, measuring 250 yards in its longest 
 diameter, beyond which stands a third which, rising prominently 
 into Blackshaw Hill (709 feet), measu.res 330 yards in its longer 
 and 250 in its shorter diameter. It is specially remarkable in 
 enclosing a lava-plug in the form of a dull, dark-grey, porphyritic 
 andesite, which is much decomposed. This neck also includes 
 black shale enclosing Spirorhis, together with pieces of a coarsely 
 crystalline "greenstone." 
 
 A quarter of a mile to the north of West Kilbride a conspicuous 
 vent forms Drummilling Hill (848 feet). It measures about 500 
 yards in length by 200 in breadth. Half a mile to the west two 
 small necks occur on the estate of Carlung. The smaller of these 
 appears on the little eminence called the North Mound, and 
 measures only 100 by 65 yards. It is filled with a coarse, dirty- 
 green agglomerate in which, among the volcanic materials, lapilli 
 and larger fragments of the pale felsitic varieties of rocks are 
 
66 The Geology of North Arran. 
 
 abundant. The other and larger neck, forming Crock Hill, is 
 distinguished by possessing a small plug of compact purplish-grey 
 andesite. 
 
 About a quarter of a mile to the south-east of Glentane Hill, and 
 therefore just beyond the limits of the present map, two green 
 eminences rising above the surrounding moorland mark the posi- 
 tions of two vents. One of these, known as Greenside Hill, 
 about 800 feet high and filled with the usual coarse, green agglom- 
 erate, measures 300 by 200 yards. The other, only about 200 
 yards to the east, forms Lairdside Hill (850 feet), and measures 
 about 230 by 180 yards. A mile to the north a smaller neck 
 rises from the moor of Whiteside Hill, about 350 yards to the 
 south of the Kaim Hill, of which the western edge comes into the 
 present map. 
 
 A still more diminutive neck has pierced the edge of the 
 escarpment of the intrusive sheet of Biglees Hill, a mile due east 
 from Hunterston House. It measures no more than 100 yards 
 from east to west by 50 from north to south. It is filled with the 
 ordinary coarse agglomerate. 
 
 Next in order in our northerly course we come upon a small vent 
 rising within tide mark at the promontory of the Black Eock on 
 the south side of Fence Bay. In its coarse agglomerate sandstone 
 fragments are abundant. Still farther north, on the declivity 
 above St. Annan's Chapel, two good examples of vents may be 
 seen. The lower or more westerly of these forms the eminence 
 known as Diamond Hill (450 feet), and measures 400 yards in the 
 longer axis and 325 in the shorter. The volcanic detritus with 
 which it is filled is partly a coarse agglomerate and partly a 
 compact tuff. This neck, as already mentioned, has broken through 
 an intrusive sill, so that it cannot belong to the earliest phase of 
 the volcanic activity. Immediately to the east the second and 
 smaller vent pierces the upper of the two sills. Its line of junction 
 with the contiguous sandstones may be seen in the watercourse, and 
 exhibits there the usual signs of disturbance and disruption in the 
 strata. A. G. 
 
CHAPTER VII. 
 
 New Bed Sandstone or Trias. 
 
 The age of the red rocks which occupy so large a portion of South 
 Arran was for a long time much disputed, and by various authors 
 they had been regarded as of Old Ked Sandstone, Carboniferous, 
 or New Red age ; while one author classed part of them with the 
 Carboniferous and part with the New Red rocks. The question 
 was definitely decided in the year 1894, when it was ascertained 
 that these rocks are unconformable to the Carboniferous forma- 
 tion, though often at junction the two sets of rocks appear perfectly 
 conformable. So long ago as 1874 Messrs. James Thompson and E. A. 
 Wtinsch had discovered derived Carboniferous fossils in these New 
 Red conglomerates at the north end of Arran near the Cock ; but 
 apparently they did not see the importance of their discovery, as 
 they were still disposed to class these rocks with the Carboniferous 
 formation and to consider them as Millstone grit. This discovery 
 of derived fossils in the overlying red rocks was confirmed by the 
 Geological Survey in 1894. Near the Cock these strata rest upon 
 the Lower Coal-measures, as they also do at Corrie and in the 
 woods behind Brodick Castle. But towards the head of Benlister 
 Glen they repose on the Corrie limestone, hundreds of feet lower 
 down in the Carboniferous formation, while on the west coast, to 
 the north of the mouth of the Machrie Water, they lie directly on 
 the Old Red Sandstone, all the rocks of the Carboniferous system 
 having disappeared. 
 
 No fossils, except some derived from the Carboniferous forma- 
 tion, have as yet been found in these newer red rocks, so that there 
 must be a little uncertainty about their exact age. On account of 
 the close resemblance of the lower false-bedded sandstones to those 
 of Ballochmyle in Ayrshire, Sir A. Geikie was disposed to class them 
 with the Permian formation, and in the map of the southern part 
 of Arran all the newer red rocks were doubtfully lettered and 
 coloured as of this age, but the general lithological character of the 
 rocks is much more like the Trias of England, and the finding of a 
 portion of the upper marls immediately connected with beds of 
 of Rhsetic age in a fragment in the Ard Bheinn volcanic agglomerate 
 fixes pretty definitely the Triassic age of the upper division of the 
 formation. 
 
 These unconformable and overlapping red strata may be 
 divided into two great groups, as in the following Table : — 
 
 / Red and mottled shales or marls with thin 
 
 „ „ „ I beds of white, yellow, or grey sandstpne, 
 
 Uppek Trias-Keupbr? ^^^ occasional thin bands of nodular 
 
 Lower Trias. 
 
 limestone. 
 '4. Light coloured and yellowish sandstones, 
 
 sometimes red, with calcite in cavities. 
 3. Reddish sandstones with some conglomerates. 
 2. Conglomerates alternating with sandstones. 
 1. False-bedded red sandstones of Brodick 
 
 and Corrie, 
 
68 The Geology of North Arran. 
 
 The upper group is poorly represented in this sheet, and its 
 thickness cannot be estimated. In the southern part of Arran — 
 Sheet 13 — where it is well developed, its thickness is probably 
 nearly 1000 feet. 
 
 Lower Division. — The lower group may for convenience of 
 description be subdivided into four parts, as shown in the fore- 
 going Table, but the subdivisions cannot be indicated on the map. 
 Probably the total thickness of the Lower Triassic beds in Arran 
 amount to as much as 2000 feet, of which the lowest subdivision — 
 the false-bedded sandstone — occupies one-half. 
 
 1. The lowest subdivision is well exposed along the shore 
 between Corrie and Brodick Castle, and consists of extremely false- 
 bedded, bright red sandstones, traversed in many places by ridges 
 formed of hardened joints and crushes, and in others fall of 
 ramifying hardened veins which cause the rock to weather with a 
 honeycomb structure. Some of the crushes are certainly faults, 
 but the rock is so uniform in texture generally that the amount of 
 throw is not discernible. Numerous basic dykes cross the foreshore, 
 in various directions and discharge the red colour of the rock, 
 making it white or yellow, and hardening it. Some of the ridges 
 are probably in the line of dykes which end at the surface, and 
 some may be due to dykes which have not reached the present 
 surface. The false bedding conveys a very exaggerated idea of the 
 real thickness of the series. Pine sections in the old sea-cliffs, and 
 in caves, show that the true dip towards the S.E. is not more, 
 generally, than 10°-15°, while the false bedding has an inclination 
 of twice as much, and is, besides, very variable in direction. The 
 great cliff on the north side of Maol Donn, which is formed of this 
 sandstone, shows a similar gentle inclination of the beds. (8ee 
 Plate VII.) This great scarp is largely due to an extensive slip, the 
 material from which covers several acres to the northward. 
 There are large quarries in this sandstone at Corrie and in 
 Brodick wood at the back of the school. Prom the Corrie quarries 
 much stone is shipped to Ayrshire and various parts for building 
 purposes. This sandstone forms the ridge on the north side of 
 Glen Cloy, where both the true and the false bedding dip to the 
 southward or S.E. at a high angle, as they do also to the west of 
 the old Brodick pier near the Castle. The boundary between this 
 rock and the underlying Carboniferous series may be observed on the 
 shore about 200 yards south of the Corrie Hotel, and it crosses the 
 Rosie Bum a little below the bridge. 
 
 2. The alternating brecciated conglomerates and sandstones of 
 the south side of Brodick Bay overlie the false-bedded sandstones 
 just described, and the conglomerates of this division are so like 
 in character to the Upper Old Red conglomerates north of Corrie 
 as to be undistinguishable from them except in position ; in fact, 
 several observers have classed them with the older formation. 
 They are largely made up of debris of the metamorphic rocks, such 
 as pieces of vein-quartz and angular fragments of schist, with 
 occasional pebbles of quartzite, like those characteristic of the Lower 
 Old Red conglomerates. 
 
i'late VII 
 
 False-l)eiiding in the lower division of llie New Ked Sandstone Cliff on 
 North face of Maol Donn, aliout 2 miles Sonth of Conie, Arran. 
 
Lower Trias. 69 
 
 _ This subdivision strikes westward up Glen Cloy and forms the 
 ridge between Glen Dubh and Glen Ormidale. 
 
 Near the heads of these glens it, along with the false-bedded 
 sandstone below, has been much altered, being often converted 
 to a white quartzite by contact with the intrusive igneous masses 
 there. On the shore at Springbank the rock is pierced by two 
 masses of agglomerate which appear to be of the nature of volcanic 
 necks, though they contain no igneous material. The larger of 
 these is about 150 feet in diameter and the smaller about 50 feet, 
 though in neither case can the whole circumference of the mass be 
 seen. The smaller is about 100 yards west of the hotel grounds, 
 and the larger is some 150 yards farther west, and the breccia 
 which composes both is entirely made up of fragments of the 
 surrounding strata. 
 
 In this subdivision there is not much false bedding apparent, 
 and the rocks at Springbank dip southward at about 15^. East of 
 the pier numerous faults as well as dykes cross the outcrop, and 
 the red conglomerate is sfien to overlie false-bedded red sandstone 
 of the same type as that on the north side of the bay. One of 
 these faults ranging N. 25° B., which is 50 yards east of the pier, 
 brings up the lower sandstones against the conglomerate. The 
 sandstone occupies the foreshore for 300 yards eastwards when it is 
 cut off by a fault, coincident with a dyke ranging N. 25° W., which 
 throws down the conglomerate again on the east. For about 500 
 yards eastward from this point we see nothing but conglomerate on 
 the foreshore till a north-west running fault, with a downthrow 
 south-west, again brings the lower sandstone into view. This is 
 continued for 300 yards farther in the most easterly part, being 
 overlaid by conglomerate, when a fault ranging N. 25° E. causes the 
 whole of the foreshore to be occupied by conglomerate, but this is 
 only for a distance of 30 to 40 yards, when a powerful fault, N. 30° E., 
 brings up the lower sandstones, which occupy not only the shore 
 for a long distance but the cliffs also, which are much increased in 
 height. Hitherto along this shore the conglomerate series could be 
 seen either on the shore or on the boundary cliffs, but the efiect of 
 this large fault, which must have a downthrow west of several 
 hundred feet, is to raise the conglomerate a long way above the top 
 of the crags at this point, and it does not appear again on the shore 
 till the southerly dip causes it gradually to descend and occupy the 
 shore about Corrygills Point. Along this half mile of shore and in 
 the cliffs bounding the raised beach the false-bedded lower sand- 
 stones are well exposed, with the same curious spires and ridges 
 which we found characterising them on the north side of Brodick 
 Bay. The southerly dip is everywhere nearly the same in amount, 
 ranging between 10° and 20°, but as we proceed the direction 
 gradually changes till, in the alternating conglomerates and sand- 
 stones on either side of Corrygills Point, it is nearly S.S.W. 
 
 This series is well exposed in the middle part of Benlister Burn 
 where the conglomerates form occasional cascades, and it occupies 
 a strip of ground to the northward (east of Brisderg) which is 
 bounded by two large faults. The beds in this strip dip to the 
 
70 The Geology of Nm-th Arrcm. 
 
 south-west, and their termination north is in the fine scar of Oreag 
 nam Fitheach, on the south side of Glen Bubh. 
 
 3. Along the South Corrygills shore the alternating conglo- 
 merates and sandstones pass gradually up into the beds of this 
 subdivision, which consists almost entirely of red sandstones, 
 moderately coarse, with only occasional pebbly bands, and with 
 comparatively little false bedding. The dip inclines more and more 
 to the west and generally increases in amount, so that in places 
 along the shore east of the Olauchland Hills the dip is as high as 
 30° or 40° and the strike is parallel to the shore. Near Olauchland 
 Point the dip is in one place as much as 60°, but this high dip is 
 probably the effect of the intrusion of the great sill of dolerite 
 there. On the south side of the Olauchland Hills the inclination of 
 the beds is much more gentle, generally not more than 10°, and 
 nearly coinciding with the slope of the ground to S.S.B. There are 
 numerous sections in the small streams here, and along the 
 northern shore of Lamlash Bay. 
 
 The beds of this subdivision occupy nearly all the area between 
 Lamlash and Glen Oloy, and there is a fairly continuous exposure 
 of them in the Birch Burn (Lag a' Bheith). They also form a 
 marked feature above the wood to the south-east of Bruce's Oastle 
 in Gleann Dubh, and it is probably the higher beds of this series 
 that appear beneath the thick sills of felsite along the west side 
 and at the north end of Holy Island. 
 
 4. On the south side of Gleann Dubh the beds of the previously 
 described subdivision pass up into white carious sandstones, 
 which form the highest beds of the lower division of the Trias ; but 
 these cannot be everywhere distinguished as a separate subdivision 
 and they might very well have been grouped as a variety of 3, from 
 which they only differ essentially in possessing drusy cavities 
 which once contained calcite. 
 
 The detached outlier of New Eed Sandstone at the Oock of Arran, 
 in the north part of the island, contains false-bedded, bright red 
 sandstone like that of Oorrie, and beds of conglomerate which 
 mainly overlie the sandstone, though there are bands of conglo- 
 merate at the base of the sandstone in the lowest 40 feet of it. 
 The mass of conglomerate is like that on the south side of Brodick 
 Bay, and probably on the same horizon, so that we have in this 
 small area representatives of the lower two subdivisions of the 
 formation, with a total thickness of not less than 1200 feet. The 
 beds generally dip northward and toward the sea, so that several 
 landslips on a large scale have occurred, and the hillsides show 
 gaping fissures. 
 
 On the western side of the island the Trias is found along the 
 coast south of Auchagallon, and takes up the interior eastward to 
 the foot of Ard Bheinn, but the subdivisions described as occurring 
 on the eastern side of the island are not equally conspicuous here. 
 The lower false-bedded red sandstones are well exposed in the 
 Machrie Water; but there appears to be no equivalent of the conglo- 
 merate series, unless these are represented by some pebbly bands 
 in the sandstone three quarters of a mile W.S.W. of Derenenach, 
 
Derived Carboniferous Fossils. 71 
 
 near the main bend in the course of the stream. In this part of the 
 island the Trias rests directly on the Old Eed Sandstone and appears 
 quite conformable to the older rock, so that it is extremely difficult 
 to fix the exact boundary between them. The gently inclined 
 New Eed Sandstone in the Machrie Water when traced up stream 
 gradually increases its S.S.W. dip from 10° to about 30° as far as 
 the outcrop of a conglomerate band, which is doubtfully referred to 
 the Old Red Sandstone. A similar difficulty is found in the section 
 in the Machrie Burn and on the coast opposite Auchagallon. 
 There is no fossil evidence to settle the question by fixing a definite 
 line, but there is no doubt whatever about their being here two 
 distinct formations and that the boundary between them is not far 
 from the line drawn on the map. The soft, thick, and rather 
 false-bedded sandstones near the top of this division, which are 
 carious (having many cavities in places), have been quarried west 
 of Traighliath, where they form a narrow gorge in the Ballymichael 
 Bum, and by the side of the Machrie Water about a mile from its 
 mouth. At the latter locality the cavities are of various shapes 
 and sizes, some of them very irregular, and one was observed more 
 than a foot in length and upwards of an inch in breadth. The 
 natives call these cavities moss-holes. These upper beds are finely 
 exposed along the Tormore shore for about a mile south of Leacan 
 Ruadha. The sandstone varies from a deep or almost brick-red 
 colour to yellow or white, and the changes, some'times rather abrupt, 
 are not easily accounted for. At the north end of the section the 
 beds dip to the north-east at 10°, and this direction continues for 
 some distance, so that as we advance southward lower and lower 
 beds successively rise from the shore and form the clifi". Then the 
 beds for some distance remain horizontal, but before reaching An 
 Cumhann the strata begin to dip gently to the south-east, and we 
 observe the rocks a second time as we proceed southward. The 
 cai'ious and false-bedded sandstones enclose lenticular masses 
 which seem slightly calcareous, and the weathering of some of the 
 rock is very curious and irregular, sometimes not unlike bunches 
 of grapes. Much of the sandstone is quartzose and rather coarse, 
 but the bunches and lenticles are formed of a finer and harder rock, 
 concretionary in structure. The massive red and yellow sandstones 
 in which the large caves are formed is the highest part of this 
 series, and a short distance to the southward we find these beds 
 passing under the marls of the Upper Trias (Keuper ?). 
 
 DERIVED CARBONIFEROUS FOSSILS IN THE NEW EED SANDSTONE. 
 
 In the lowest part of the New Red Sandstone which immediately 
 overlies the Carboniferous formation in the northern part of Arran, 
 there are bands of conglomerate which contain pebbles of Carboni- 
 ferous limestone from which several derived fossils have been 
 obtained by the geological survey. Rather more than a quarter 
 of a mile north-west of this spot, and about 100 yards east of the 
 Cock of Arran, is another locality where derived fossils may be 
 collected. There occurs a very irregular pebbly band, which 
 
72 Th& G-eology of North Arran. 
 
 appears to have accumulated in a hollow of the sandstone during 
 the process of rock formation. It" contains, among others, large 
 blocks of trap and white quartz, etc., and from it the following 
 collection was made: — 
 
 Lithostrotion irregulars. 
 ,, Portlocki. 
 
 Zaphrentis ? 
 Crinoid ossicles. 
 Rhabdomeson rhombiferum. 
 Orthis resupinata. 
 
 Retzia ? 
 
 Spirifera trigonalie. 
 Entolium Sowerbyi. 
 Nuculana attenuata. 
 Protoschizodus axiniformis. 
 Bellerophon deoussatus. 
 
 It was probably in the first-mentioned locality that derived Carboni- 
 ferous fossils were obtained by Messrs. James Thompson and B. A. 
 Wiinsch, as reported in the Trans. Geol. Soc. Glasgow, vol. v., p. 
 313 (1874), and described in vol. xi. of the same Transactions, p. 
 30 (1897). 
 
 Upper-Division of New Bed Sandstone. — The red shales or 
 marls of the upper division of the Trias (of Keuper age ?) are not 
 well exposed in this sheet. They occupy but a small area, but are 
 found in three separate localities, in one of which the rock is part 
 of a fragment in the volcanic vent of Ard Bheinn, and is described 
 in connection with the Rhsetic beds. This section, though small, 
 is interesting, however, as it presents us with what are presumably 
 the very highest beds of the formation, which are nowhere else 
 exposed in the island. In the two other localities only small 
 portions of the lowest beds of this division occur. One of these is 
 at the head of the Birch Burn to the south of Brodick and north of 
 Onoc Dubh. The rocks may be seen in both HDranches of the bum, 
 but the longest branch yields the better section. Overlying the 
 red sandstones rather more than half a mile north of Onoc Dubh, we 
 find beds of red and mottled clays or argillaceous shales with 
 occasional thin bands of nodular limestone. The dip is first to the 
 south at a low angle, but higher up the stream the dip is eastward 
 or undulating, and the strata are traversed by dykes or sills of 
 felsite, pitchstone, and basalt. Traces of the mottled shales or 
 marls, variegated red and green, are found occasionally up to near 
 the head of the stream where it issues from a peat moss. The 
 size of this patch of the upper beds appears to have been limited 
 by a fault on either side which brings up the lower sandstones. 
 
 The third locality where the rocks occur is on the western side 
 of the island at Ballymichael, and they are exposed in three small 
 streams on the east side of the road and south of Ballymichael Glen. 
 The red shales or marls with occasional thin sandstones here seen, 
 dip generally to the S.W. at 10°-20°, but sometimes the dip is 
 easterly at a low angle or even S.B. They pass gradually dovwi 
 into the underlying sandstones. 
 
 These rocks form but a small portion of the division, which will 
 be more fully described in the explanation of the southern part of 
 Arran. 
 
CHAPTER VIII. 
 
 Patches of Secondary Formations in Volcanic Vent. 
 
 The Rhsetic, Liassic, and Cretaceous formations now to be 
 described do not actually occur in situ in the island, but consist of 
 fragments or masses of rock of various sizes which have fallen into 
 a volcanic vent of post-Oretaceous (presumably Tertiary) age. The 
 igneous rocks, both massive and fragmental, with which these 
 fragments are associated are elsewhere described. As will appear 
 from the detailed description of the fragments which contain fossils, 
 they do not occur in close proximity, and sometimes as much as a 
 mile intervenes between one fragment and another. In addition to 
 the fossiliferous masses, there are others of limestone, of sandstone, 
 and of shale, in which no organic remains have been found. It 
 seems probable that these also are of Secondary or Mesozoic age, 
 though it is not possible in each case to determine what formation 
 they belong to. 
 
 In several instances the fragments have been much altered by 
 intrusive igneous rock, and some of them have Tertiary dykes or 
 sills traversing them. Especially is this the case with the largest 
 of the fragments, which contains not only beds of Rhsetic age but 
 grey marls in the upper part of the Trias and a portion of the red 
 marls which lie below. 
 
 RHiETIC EOCKS. 
 
 A short distance north of the farmhouse of Derenenach, two 
 small streams which have cut gorges in the low lying mass of 
 granophyre cross the road. The longer and more northerly of 
 these two burns is called Allt an Dris, and is the only one of the 
 two which is marked on the one-inch map. In the middle part of 
 its course this stream traverses the largest of the identifiable 
 fragments in the volcanic vent, which is of an irregular shape and 
 extends over several acres. It is probably quite a quarter of a mile 
 in length from north to south, and its vsddth is at greatest about 
 150 yards. This patch contains the black shales and thin lime- 
 stones of Ehsetic age, which are exposed for a length of nearly 90 
 yards in Allt an Dris about a quarter of a mile north-east of 
 Derenenach. The greater portion of this fragment, however, 
 consists of grey and red Triassic marls, the red marls forming the 
 bulk of it. One cannot be quite certain about the actual order of 
 succession in this mass, as the rocks are broken, or faulted and 
 disturbed, and we do not see the difierent subdivisions actually in 
 
74 The Geology of North Arran. 
 
 contact, but the following is the probable arrangement in descending 
 order . — 
 
 Black shales and thin grey limestones of Rhaetic age. 
 Greenish-grey or pale-coloured compact marls — Upper 
 
 Keuper. 
 Red marls — Keuper. 
 
 These beds are bounded on thewest by the granophyre before mentioned 
 which occupies a strip of ground nearly a quarter of a mile in width 
 between them and the road. They are best reached by following 
 the burn upwards. On coming to the old sheepfold some of the 
 red marls or mudstones may be noticed in the slope opposite with 
 a high dip to the west, and they are also exposed in a small branch 
 stream which we pass on the left. Soon the stream inclines more 
 to the eastward, and we find in it a considerable section in the red 
 marls, which appear to be nearly flat or have a gentle inclination 
 eastward. The section is somewhat obscured, however, by several 
 sills and dykes of felsite. Above this steep part the stream takes a 
 sharp turn to the left and we lose sight of the rocks. A little 
 higher up on the south side we observe the grey marls in the bank, 
 lying nearly horizontal or with a gentle dip to the south-west, and 
 a few yards farther we come upon the Rhastic black shales on 
 the same side. They do not occur here, however, on the north-east 
 side, but are opposed to the grey marls which on the north-east 
 side are at a higher level than the Rhsetic shales of the south-west 
 side, so that there is manifestly a fault or break of some kind along 
 the burn. Nearer to the sharp bend there occurs in one place a 
 mass of the RhEetic shale containing thin limestone bands on the 
 north-east side, and it was from this locality that all the best 
 specimens were obtained. We do not, however, see the relation of 
 this mass to the grey marls, and the junction is probably not 
 natural. 
 
 The black shales on the south-west side of the stream here 
 have yielded organic remains, but they are ia a crushed and frag- 
 mentary condition. Altogether these Rhsetic shales seem to be 
 more disturbed than either the red or grey marls, and it is 
 impossible to make out any order of succession in them. Often 
 they appear to be nearly vertical, as in the fragment from which 
 the fossUs were obtained. The whole length of the exposure is in a 
 small rocky gorge, and about 40 yards of it is below the sharp bend 
 where the stream turns from a south-east to a due east direction. 
 Above this bend the black shales may be traced for about 50 yards 
 on the south side of the burn, but they do not extend so far on the 
 north side. It seems probable, however, that they may occupy a 
 considerable area to the south-west of the bend in the stream, where 
 there is a smooth grassy slope, and excavations here might reveal 
 other fossiliferous bands. The exposures above the bend in the 
 stream have yielded no fossils. 
 
 The grey marls, as we have stated, appear on both sides of the 
 stream, but the outcrops are not exactly opposite, as they are 
 
Lias. ' 75 
 
 higher up on the north side, and opposed to the Rhaetic beds on the 
 south side. 
 
 These rocks were surveyed in the year 1899, and their peculiar 
 characters, as being unlike anything occuring elsewhere in Arran, 
 were remarked on. Specimens of the dark ferruginous shales were 
 obtained, and were supposed to resemble certain rocks occuring in 
 the Old Red Sandstone near Strathpeffer and elsewhere in the 
 north of Scotland. In May 1900, however, the fossil collector of 
 the Survey, Mr. A. Macconochie, who accompanied me to the 
 locality, was successful in obtaining undoubted organic remains 
 from the beds, and the collections made by him on being examined 
 by Mr. Newton were referred to the Ehsetic beds. 
 
 The following is Mr. Newton's determination of the specimens: — 
 
 FOSSILS FROM THE EH^TICS OF SHISKINB, ARKAN. 
 
 Modiola minima ? Sow. 
 Estheria miniita ? Gold/. 
 Gyrolepis Alberti ? Ag. 
 
 Avicula contorta, Portl. 
 Peoten valoniensig, Defr. 
 Schizodus (Axinus) cloacinus, 
 
 Quenst. 
 Protocardium philipianum ? 
 
 Dunk. (=C. rhsetioum, 
 Merian. ) 
 
 Nearly three-quarters of a mile distant from the Rhsetic beds in 
 Allt an Dris in a north-east direction, and about the same distance 
 south of Glenloig, is a mass of unfossiliferous shale which may 
 belong to this formation. It is about 35 yards in length from 
 N.N.E. to S.S.W., and is nearly vertical or dipping steeply to 
 E.S.B. The rock is much altered and hardened ; is now of a blue 
 colour and a kind of porcellanite, bounded on the east by volcanic 
 agglomerate and on the west by an intrusive mass of quartz- 
 felsite. The volcanic agglomerate has undergone much alteration 
 as well as the shale, and there is not much hope of obtaining fossils 
 from this locality. 
 
 Lias. 
 
 The locality in which the Lias fossils are found is about one mile 
 south-east from that of the Rhsetic patch in Allt an Dris, and nearly 
 half a mile due south from the top of Ard Bheinn. It is 300 yards 
 north of a fork in the Ballymichael Burn, and near the head of the 
 glen in a dry gully on the north-west side of the stream. The 
 patch consists of brownish, crumbling, calcareous shale and impure 
 decomposed limestone, in some parts of which fossils are abundant, 
 but mostly in the form of casts. The exact area occupied by this 
 shale cannot be ascertained, but it is probably 100 yards in length 
 and nearly 50 yards in breadth. Between it and the stream is 
 found a yellowish granophyre, and on the north-east side occurs 
 a fine, dark, basic rock. On the south-west side of it occurs the 
 volcanic agglomerate, the boundary between which and the shale 
 appearing to be vertical, and in one place the two rocks seem some- 
 what mixed. 
 
76 
 
 The Geology of North Arran. 
 
 My colleague Mr. B. N. Peach, to whom I showed this singular 
 fragment of a formation, was the first to obtain fossils from it and 
 to recognise their Liassic facies, and the joint collection then made 
 by him and myself (June, 1900) was despatched to Mr. E. T. 
 Newton, who fully confirmed Mr. Peach's observations. In October 
 of the same year a further search at this locality was made by 
 Mr. Macconochie, which resulted in considerable additions to the 
 original list. The fossils all belong to the Lower Lias (Ammonites 
 angidatus zone), and no traces of any beds that will fill up the gap 
 between these rocks and the Cretaceous formation have been found, 
 so that it is very probable they were related to one another in 
 Arran as they are in Ireland, where the Cretaceous rocks repose 
 unconformably on those of the Lower Lias. Mr. Newton has 
 examined the whole set of fossils from this locality, and has 
 furnished the following list of them : — 
 
 FOSSILS FROM THE LOWER LIAS (AMMONITES ANGOLATUS BEDS), 
 
 ARRAN. 
 
 Ammonites (.rEgoceras) augu- 
 
 latus, Schloth. 
 Amberleya acuminata, Chap. 
 
 and Dew. 
 Cerithium semele ? Martin. 
 
 „ sp. (c/. Falsani, 
 Dumorlier .) 
 Pleurotomaria tectaria, Tate. 
 Area? 
 Astarte sp. 
 
 Avioula lanoeolata, Sow. 
 Cardinia Listeri, Sow. 
 Cardita Heberti, Terg. 
 Goniomya sp. (cf. rhombifera, 
 
 Goldf; and ainemuriensis. 
 
 Gryphsea arouata, Lamarck. 
 Inooeramua (Crenatula). 
 Lima pectinoides ? Sowerhy. 
 
 Lima suooincta, Schloth. 
 
 Modiola sp. 
 
 Myoooncha psilonoti ? Quenst. 
 
 Niioula sp. (2 forma. ) 
 
 Nuoiilana (Leda) Tatei N. (=L. 
 
 Renevieri, Tate.) 
 Nuciilana sp. (cf. Quenstedti, 
 
 Tate.) 
 Ostrea irregularis ? Qiieiist. 
 Pecten subulatua ? Ooldf. 
 Pholadomya ? 
 
 Pro'tooardium tnmcatum ? Sow. 
 Tancredia? Peaohi, n. sp. 
 Unioardium cardioides, Phillips. 
 Ditrupa globiceps, Qxienst. 
 
 „ sp. 
 Serpula sp. 
 
 Peutacrinus basaltiformis. Miller. 
 Wood. 
 
 Cretaceous. 
 
 Rather more than one mile to the east of the road Ballymichael 
 Glen branches into two. A smaU stream comes in from the east, 
 but the main valley continues in a north-east direction. A few 
 yards above this fork there are lying at intervals in the bed of the 
 main sti'eam some blocks of a lighl^coloured limestone containing 
 irregular lumps of chert or flint. They are not numerous, and 
 have been apparently derived from the coarse volcanic agglomerate 
 which forms here the western bank of the stream ; for about 60 
 yards from the branch stream a small trail of these limestone blocks 
 was observed on the slope. There is, however, no mass of the rock 
 anywhere, and no fragment large enough to be indicated on a map 
 of any scale. The limestone of these blocks is in character remark- 
 ably like to that of the chalk of Ireland, which is not a soft friable 
 rock like that of England, but a hard and compact limestone, 
 especially where it has come in contact with igneous rock. The 
 
Cretaceous Boohs. 
 
 77 
 
 siliceous concretions in the limestone are irregular in shape, and 
 occur just like flints in chalk or like chert in cherty limestone. 
 They are almost pure white, certainly lighter in colour than the 
 limestone itself, and they project on a weathered surface. The 
 limestone itself is compact, fine-grained, and of a grey colour. 
 
 This locality is only about 200 yards south of the patch or frag- 
 ment of Lia.'^ already described, and the volcanic agglomerate 
 occupies intervening ground. 
 
 These blocks were noticed by Mr. B. N. Peach in June, 1900, 
 who remarked at the time on their resemblance in character to the 
 Antrim chalk. They were afterwards, in October of the same year, 
 searched by Mr. A. Macconochie, and the organic remains were 
 examined by Mr. E. T. Newton, who has furnished the following 
 list :— 
 
 FOSSILS FROM THE LIMESTONE AND CHERT OF BALLYMICHAEL GLEN, 
 SHISKINE, ARRAN. 
 
 Inoceramus (piece of shell show^ 
 
 ing prisms). 
 Polyzoa (Entalophora ? and 
 
 Escharina ?) 
 Echinoderm fragments. 
 Porosphsera globularis, d'Orb. 
 
 Hexatinellid sponge fragment 
 
 (Plocosoyphia ?). 
 Tetractinellid and other spicules. 
 Globigerinacretacea, d'Orfc. (and 
 
 other species). 
 Textularia, &o. , &c. 
 
 Rather more than a mile N.N.W. of this locality, and 1100 yards 
 N.E. from Derenenach, a mass of cherty limestone of the same 
 character occurs in a cave on Ard Bheinn, and some specimens of 
 the limestone taken from this cave contain Cretaceous foraminifera. 
 This "pigeon cave," as it has been called, can be traversed for many 
 yards sloping downward in a W.S.W. direction. The arched roof 
 of the cave, which slopes downward like the floor, appears to be 
 composed entirely of basic igneous rock — one of the numerou 
 intrusive masses of the vent. On the north side, near the entrance, 
 occurs two to three feet of dark-coloured hardened shale, which dips 
 westward at 20°-25°. Below this the section is somewhat obscure, 
 but appears to be first basic igneous rock, then a light-coloured 
 crystalline limestone — the Cretaceous rock — and afterwards a white 
 baked sandstone or quartzite. These rocks on the north side are 
 cut out on the south side by the arching over of the trap roof. Some 
 of the limestone of this locality is converted to crystalline marble 
 by igneous action, and all traces of organic remains have been 
 destroyed. 
 
 Probably other patches of the limestone occur in the agglomerate 
 of this neighbourhood, as there is a line of swallow-holes about 200 
 yards S.W. of the cave, and there is one about the same distance 
 due south from the cave. 
 
 Three quarters of a mile north-east from the "pigeon cave" of 
 Derenenach is another cave in which limestone occurs, about 500 
 yards south of Glonloig. The locality where this occurs is called 
 Oreag an Pheidh, and there is a steeply sloping hollow about 20 
 yards wide running in an N.N.E. direction and bounded by crags 
 on either side. On the western side of the hollow, and running in 
 
78 The Geology of North Arran. 
 
 the same direction as it, occurs a basalt dyke four feet in width, and 
 there appears to be on the east side another dyke the width of 
 which is not clear. The cave is on the western side of the hollow, 
 and has a slanting 'opening some 12 to 15 feet high. It runs back 
 at right angles to the hollow about 15 yards at the north end. It 
 is at this part of the the cave that the limestone is visible, but it is 
 very irregular in thickness, and only some two to three feet at the 
 most, though, as the rock was once quarried, it may have been much 
 thicker. It occurs in association with sandstone and some shale, 
 and dips to the N.N.W. apparently from 30° to 40°. A patch of 
 limestone may also be seen at the foot of the crag on the eastern 
 side of the hollow. The limestone at this locality is much altered 
 by contact with intrusive igneous rock which overlies it, and 
 which has converted it into crystalline marble. There is no trace 
 of chert in it and no organic remains, so that it is doubtful to 
 what geological period it belongs. The cave has no doubt been 
 enlarged by artificial means, but it is certainly to a great extent 
 natural, and water sinks at the western end at a place now covered 
 by loose stones. Probably this was at one time open. 
 
 An old road leads up to the cave. 
 
 Headrick* notices the occurrence of limestone at this place, but 
 was mistaken as to its mode of occurrence, and in another part of 
 his work he gives the following analysis of the limestone (p. 345): — 
 
 Glenluig Chalky Limestone. 
 
 Carbonate of lime, ...... 98 
 
 Clay, 2 
 
 100 
 
 Othee Masses. 
 
 In addition to the above, there occur in the volcanic vent several 
 large masses of a whitish, fine-grained sandstone, which probably 
 are fragments of some Secondary formation. The largest of these 
 is found in a lino between the top of Ard Bheinn and the, summit 
 of Beinn Bhreac, and about 700 yards distant from the latter. It 
 is some 250 yards in length and 15 to 20 yards in breadth, and 
 forms a rather marked feature running in an B.N.B. direction. It 
 is bounded on one side by agglomerate and on the other by granite, 
 and it appears to dip nearly S.B. at an angle of 50°. 
 
 The next largest mass of the same kind is found about 200 yards 
 south of the "pigeon cave" and is oval in form, and apparently 
 about 70 yards in length. Smaller patches of the same kind may 
 be seen about 100 yards S.W. of the same cave. 
 
 Other masses of sandstone occur about 150 yards north-east of 
 the Ehsetic patch in Allt an Dris, and 200 yards north of the old 
 sheepfold on the same stream. 
 
 * See Bibliographical Appendix, p. 181. 
 
CHAPTBE IX. 
 
 Tertiary Igneous Rocks. 
 
 VOLCANIC VENT. 
 
 Reference has been made to the existence of a complicated area, 
 composed of various igneous rocks, lying on the south side of the 
 road leading from Brodick to Shiskine. It is of an oval form, 
 between three or four miles in length, and embraces the high 
 ground of Cnoc Dubh, A'OhrUach, Beinn Bhreac, and Ard Bheinn, ■ 
 while its northern limit is the Machrie Water. The ring of acid 
 igneous rocks which forms the exterior of this mass is elsewhere 
 described, and we have here to deal with masses of conglomerate 
 and agglomerate of very irregular outline which occupy for the 
 most part the centre of the oval. For some time the age of 
 these fragmental rocks was doubtful, but a more careful examina- 
 tion of some of the material found in them, and the discovery in 
 various parts of the mass of separate portions containing Ehsetic, 
 Liassic, and Cretaceous fossils, established the post-Oretaceous or 
 Tertiary age of the whole, which we must regard as of pyroclastic 
 origin — fragments of various kinds of rock, both aqueous and 
 igneous, that have fallen into the vent of an old volcano or have 
 been forced up from below by explosive action. For the description 
 of the Triassic marls, shales, and limestones of Rhsetic age, the Lias 
 shales, and the Cretaceous limestones, we must refer the reader to the 
 foregoing chapter which treats of these rocks. In this place we can 
 describe only the general character of the volcanic agglomerate and 
 some of the igneous rocks which are intrusive in it. The fragmental 
 material may be traced over an area two and a half miles in length 
 by two and a quarter miles in breadth, and may have once extended 
 farther. Masses of igneous rock, both acid and basic, penetrate 
 the fragmental rock in all directions, isolating portions, and making 
 a kind of patchwork, the separate parts of which have very 
 irregular outlines. In many places the volcanic agglomerate has 
 been intensely altered by the intrusive rocks, shale being changed 
 into a flinty porcellanite rock, limestone into crystalline marble, 
 and the matrix of the agglomerate generally profoundly modified. 
 Probably quite or e half of the area over which the agglomerate can 
 be traced is occupied by these intrusive igneous rocks. 
 
 The general character of the agglomerate is not easy to describe, 
 for it varies much in different places. The matrix of the fragments 
 is very often arenaceous, much like that of an ordinary coarse 
 sandstone, and in this are found pebbles and blocks derived 
 from various sources, igneous rocks of an acid character often 
 predominating. 
 
80 The Geology of North Arran. 
 
 To the west of Ard Bheinn the rock may be called a brecciated 
 conglomerate, which weathers of a brown colour, and when broken 
 is found to have a fine grey matrix. The included fragments are 
 quartz pebbles (generally small), quartzites, acid igneous rocks such 
 as granite and quartz felsite, schists, etc., all being rather angular in 
 outline. 
 
 In Oreag Shocach, to the east of Glenloig, the prominent pebbles 
 and blocks in the rock are grits and sandstones of various kinds, 
 more or less angular, small quartz pebbles, and quartzite pebbles 
 generally well rounded, like those found in the Lower Old Eed Con- 
 glomerates. In ascending the northern end of this cragwe find many 
 pebbles of quartz and quartzite in the coarse agglomerate, as well 
 as several varieties of acid igneous rocks (but few of basic lavas) 
 set in the ordinary grey paste. In the upper part of the crag is 
 a quite different kind of rock, which is distinctly red in colour, 
 with a sandy matrix containing only pebbles of quartz. All over 
 the crag we find the nature of the rock varying. At one extreme 
 is an agglomerate made up almost entirely of coarse angular or 
 sub-angular fragments of sandstones, etc., of various shapes and 
 sizes, with little or no matrix ; while at the other the rock has a 
 fine-grained appearance externally, and on a fractured surface is 
 seen to consist principally of a bluish-grey hard paste imbedding 
 small angular fragments. There is every gradation between these 
 two extreme varieties. In no part is there any satisfactory indica- 
 tion of bedding. The rock weathers of the usual brown or rusty- 
 brown colour where the grey matrix 'exists, but does not appear to 
 be so much altered as in some other places — as in the burn to the 
 west for example. 
 
 In several places besides Oreag Shocach the rock is a coarse 
 conglomerate, very like the characteristic quartzite conglomerate 
 of the Lower Old Red formation, and there is no doubt that this 
 formation has contributed a large part of the material which now 
 fills the volcanic vent, though it has in most cases been broken up 
 and mingled largely with fragments of granite, quartz-felsite, etc. 
 It is only in a few places that the brecciated rock assumes the 
 character of a true volcanic tuff or agglomerate made up of igneous 
 fragments alone, and basic lavas are seldom represented in it. On 
 the east side of the Rhaetic patch in Allt an Dris the rock has 
 generally a fine dark-grey matrix, which in places is calcareous 
 and becomes carious on the brown-coloured weathered surface. It 
 contains pebbles of white quartz (small), and quartzite, 
 always well rounded. Rarely there are pebbles of quartz-felsite, 
 and the schist fragments are always angular. Occasionally there 
 are no prominent fragments, and the rock then has more the 
 character of a fine tuff. A pebble of amygdaloidal andesite was 
 got out of the rocks about 500 yards north-east of Derenenach, 
 and pebbles of similar character are apparently not uncommon 
 between this locality and Creag Mhor, where, near the edge of the 
 granite, the rock has a chloritic and ferniginous matrix, probably 
 from altered basic tuff-material. At the junction with intrusive 
 basic rock 100 yards south-west of the Derenenach cave, a speci- 
 
Volcanic Vent. 81 
 
 men showed a pebble of crushed and schistose grit (schist), besides 
 the usual quartz grains, chips of andesite, etc. The agglomerate 
 is much altered about three quarters of a mile south of Glenloig 
 farm. One of the specimens collected from near the mass of 
 altered shale described in Chapter VIII. has a large piece of micro- 
 granitic quartz porphyry in a fine grey matrix much metamorphosed, 
 with abundant new-formed biotite. To the west of this, and near the 
 edge of the granophyre or granite, there is a vein one and a half 
 inches wide of a fine-grained biotite granite ti-aversing the matrix 
 of metamorphosed tufi", apparently of trachytic composition, with 
 new-formed biotite ; there are also fragments of metamorphosed 
 basic lava with much biotite. 
 
 Some pebbles collected from the agglomerate in Allt Euadh to 
 the east of Derenenach are of felsite, with small isolated spherulites. 
 Others are much decayed, but may have been andesitic in character. 
 A fairly large collection of pebbles was made from the agglomerate 
 in various localities, and they quite bear out the statement that of 
 the igneous fragments those of a decidedly acid character predom- 
 inate, though, basic material may have entered more largely into 
 the formation of the matrix. 
 
 West of Oreag Mhor the agglomerate comes probably directly 
 into contact with the Lower Old Red formation, and there appears 
 to be a break in the igneous ring. 
 
 Between Beinn Bhreac and Cnocan Biorach a portion of the 
 fragmental rock appears to be surrounded by the later intrusive 
 masses, and in two places we find the agglomerate outside the 
 igneous ring, or only partly included in it. One of these is at the 
 head of Benlister Glen, to the north of Cnoc na Oroise. The extent 
 of this cannot be ascertained, as it only occurs as a small section in 
 the burn. A dark-greenish fragmental rock, apparently of a 
 tufiaceous character, and considerably altered, occurs nearly close to 
 the granophyre. The fragments are of quartz and of a felsitic rock, 
 in a greenish matrix containing much hornblende (actinolitic) which 
 has evidently been formed in situ. The other locality is at Onoc 
 an Biorach, on the south side of Ballymichael Glen, where a 
 considerable mass of a dark, fine-grained, almost flinty rock, occurs 
 around the Ordnance Station and to the south-west of it. Some of 
 it is obviously fragmental, and portions which appear massive when 
 examined under the microscope are found to consist of metamor- 
 phosed gritty tuflT with much new biotite. Along the eastern 
 margin of the mass a coarse agglomerate is visible in two places. 
 This area appears to be bounded by granophyre and quartz diorite, 
 except on the south-west side, where it adjoins the rocks of the 
 Upper Old Red formation. 
 
 Some of the larger unfossiliferous masses included in the agglo- 
 merate are described with the secondary fragments. 
 
 The intrusive rocks of the vent have been generally described 
 elsewhere, and some of the more important varieties, as granite, 
 granophyre, quartz-diorite, diorite, hyperite, etc., have been more 
 particularly noticed. There remain to be described here some of 
 the more prominent intrusive masses that, together with the agglo- 
 r 
 
82 The Oeology of North Arran. 
 
 merate, form the intricate patchwork of outcrops around Ard 
 Bheinn. Two of the largest run along the western side of the hill 
 in parallel bands ; the outer a basic rock, and the more easterly a 
 quartz-felsite, which becomes in places coarsely porphyritic. The 
 basic rock, the course of which has been given elsewhere (see Chap. X.), 
 is an ophitic dolerite which, 200 yards S.B. of Oreag Mhor, is 
 replaced by gabbro. 
 
 The quartz-felsite is a light-coloured rock, somewhat coarse 
 textured, and very different in character from most of the acid 
 intrusions that occur between Ard Bheinn top and Glenloig. It 
 covers a considerable area, and has in places a width of outcrop 
 amounting to nearly 400 yards. 
 
 The dark rock at the summit of Ard Bheinn is magnetic and 
 aflfects the compass strongly. It appears to be a felsite with a fine- 
 grained matrix containing whitish felspar crystals. Around the 
 summit are some bands of a white weathering rock of a more acid 
 character apparently. Two hundred yards S.S.'B. of the summit is 
 a grey rock banded with red ; it is a rhyolite with strong flow 
 structure, and may be connected with the mass of quartz-felsite 
 that runs along the wes't side of the hill, but there is some doubt 
 whether it is not a portion of a fragmental rock to which it is 
 adjacent, as there are several fragmental masses in the intrusive 
 rocks of this part of the hill. 
 
 A number of small, basic, intrusive masses occur about the 
 Derenenach cave and around Binneiu nah-Uaimh, and others are 
 found near the Glenloig cave, but most of the intrusive rocks of 
 the north side of the hill are of an acid character. Those which 
 occupy the largest area, and which are most regular in 
 their outline, are either granite or granophyre. The 
 masses with such tortuous outlines consist generally of a fine- 
 grained, grey felsitic rock, sometimes almost of a flinty character, 
 minutely jointed and breaking up into splinters. It forms 
 prominent scars at Oreag Dhubh overlooking Glen Craigag. Some- 
 times the rock is of a darker colour and of a bluish cast. Quartz 
 in small blebs is generally present in both varieties, and most of the 
 rock is nearly white on the weathered surface. In places the 
 jointing in this rock is beautifully close and parallel, and very 
 striking. Good examples occur 300 yards south of the Glenloig 
 cave and nearly a mile S.S.B. of Glenloig, both near the junction 
 of felsite and agglomerate. The latter locality is about a quarter of 
 a mile west of the main stream of Glen Craigag. 
 
 In several places in this burn about three quarters of a mile from 
 Glenloig sections occur in a dark, almost black, fine-grained rock, 
 which appears to alternate with masses of undoubted agglomerate. 
 Some of the fine-grained rock is manifestly banded felsite, but here 
 and elsewhere in this area it is almost impossible without the aid 
 of the microscope to distinguish between the fine-grained massive 
 rocks which are free from quartz and the highly altered matrix of 
 the agglomerate where it is devoid of fragments. A pitchstone 
 dyke pierces the agglomerate in a small stream two thirds of a 
 mile south-east of Glenloig and nearly 300 yards west from the 
 
Volcanic Vent. 83 
 
 main burn. It is dark coloured, two to three feet in width, with a 
 hade to the south-west. It runs in a south-east direction, and 
 perhaps has contributed in the formation of the prominent scar of 
 felsite there. 
 
 Intrusive dykes are seldom met with in Ard Bheinn, but a few 
 occur in Glen Craigag. The deep and narrow gorge in which the 
 stream runs, from 300 to 600 yards above Glenloig house, is 
 occupied by a basic dyke which here pierces the agglomerate. 
 Another gorge nearly one and a half miles from the house, is partly 
 due to a basic dyke which invades the granite. Other dykes, both 
 basic and acid in character, are found in a higher part of the stream 
 penetrating both agglomerate and granite. 
 
 In many, if not most volcanic necks, the material forming them 
 has often a more or less definite arrangement on a large scale, so that 
 its different portions have an inclination, to wards the centre of the 
 vent. There is, however, no approach to such arrangement in the case 
 under consideration. In fact, the evidence we have, so far as it goes, 
 points to an inclination in the reverse direction, i.e., towards the 
 circumference of the mass. This is noticeable in the material near 
 both the caves, and in the edge of the agglomerate west of Beinn 
 Bhreac. 
 
CHAPTER X. 
 
 Tertiary Igneous Rocks — continued. 
 
 GRANITE. 
 
 Of the Tertiary intrusive rocks of Arran granite is by far the 
 most important. It occurs in two detached areas, each of which 
 has an oval form. The larger of these, which is the nucleus of the 
 northern portion of the island, has been a subject of interest to 
 geologists since the time of Hutton towards the close of the 
 eighteenth century. Its form is nearly circular, being eight miles 
 by seven, and its circumference, viewed on the large scale, is very 
 even and regular, with no large projections or detached bosses, and 
 generally its boundary is sharply defined. There are two varieties 
 of the granite ; one coarser-grained and earlier in age forms the 
 exterior of the mass, while a finer-grained and newer variety is in 
 the interior. The coarser kind is composed mainly of quartz and 
 orthoclase felspar., with abundance of black or brown mica in 
 certain places, but generally the mica is not conspicuous. Some 
 plagioclase felspar also occurs in the granite. Here and there in 
 the granite, dykes, sheets, and patches of a finer-grained rock occur, 
 and these are not always later intrusions, but rather of the nature 
 of segregations, for they may be seen sometimes to merge insensibly 
 into the general mass. Patches of this kind are not uncommon 
 near the junction of the granite with the surrounding rocks. 
 
 Many joints traverse the granite, and these in places are hori- 
 zontal, or they dip at a comparatively gentle angle, so that the 
 rock has a remarkably bedded appearance (see Plate VIII., No. 1). 
 The most marked joints in other localities are vertical, or dip at 
 steep angles into the glens, their inclination not seldom coinciding 
 with the slope of the ground, and forming ground which is very 
 difficult to traverse. Occasionally we find more than one set of 
 joints developed in the same rock, e.g., both horizontal and vertical ■ 
 joints, but the latter are generally most conspicuous near and 
 parallel to the numerous intrusive dykes. 
 
 Some of the finest intrusive junctions of the granite with the 
 older schists in North Glen Sannox were described by Hutton* more 
 than a century ago, and these and other junctions at Tor Nead an 
 Eoin, and elsewhere on the eastern side of the mass, have since 
 been often referred to, but others quite as striking occur on the 
 east side of Glen Catacol at Madadh Lounie, and in several places 
 north of Meall nan Damh. The granite maintains generally its 
 ordinary coarse character near its junction with the schists, but 
 there are several places where it is fine-grained at the margin. 
 
 * See his " Theory of the Earth," vol. iii., p. 220, 
 
- Granite. 85 
 
 Fine-G rained Granit e. — Several writers have described 
 the finer-grained granite in the interior without, however, defining 
 its exact boundaries. It is intrusive in the coarser variety which 
 surrounds it, and is evidently of somewhat later date, but both 
 belong to the same geological period and are probably parts of 
 the same igneous magma, for they have generally the same sets of 
 joints, and are alike pierced by similar dykes of pitchstone, felsite, 
 quartz porphyry, and basalt. The finer variety occupies nearly all 
 the west side of Glen lorsa, so that on this side of the island the 
 coarser kind of granite is but a comparatively narrow strip varying 
 from one mile in width to not more than a furlong at lorsa Loch. 
 On the east side of the lorsa most of the granite is of the coarser 
 variety, and the boundary between it and the fine is tortuous, some 
 bays of the fine being almost detatched and surrounded by the 
 coarse. The fine granite occupies about 14 square miles, which is 
 one third of the whole granitic area. 
 
 All the peaky hills are formed of the coarse kind, the fine variety 
 forming rounded or flat-topped hills, generally of lower elevation. 
 (Plate I.). Usually the fine variety breaks up into small slabs, 
 which often so entirely cover the surface of the ground that no 
 solid rock is observable. The debris of this rock is nearly white 
 in colour, while the decomposition of the coarse granite produces 
 a coarse, brown sand. Occasionally, however, the finer granite 
 becomes coarse-grained and massive ; it then breaks up into larger 
 blocks and forms crags. Good junctions of the two rocks are to be 
 seen on the south side of Beinn Bharrain, on Sail Ohalmadale, and 
 in Glen Easan Biorach. South of Beinn Bharrain the junction of 
 the two rocks is generally a vertical line which passes across the 
 jointing, and both kinds of granite may be observed in one and 
 the same slab. In Glen Basan Biorach also, the finest junction at 
 the foot of the stream running north from Creag Dubh is vertical ; 
 but often in this glen the boundary line is not well defined for 
 some yards, owing to admixture of the two kinds. There seems no 
 evidence anywhere that the fine overlies the coarse granite, and 
 the appearances west of Cir Mhdr relied on for the support of this 
 view are certainly deceptive. 
 
 In addition to the main mass of finer granite, numerous small 
 dykes and sheets of it have been intruded into the coarse in vai'ious 
 places, but most of these are not large enough to be separately 
 mapped. One of the largest detached masses occurs on the top of 
 Beinn Nuis, between the Ordnance Station and the remarkable rock 
 called Caisteal an Fhionn. It is apparently of an oval outline, and 
 its greatest length from north to south about 300 yards. Another 
 is found near the head of Glen Sannox on the south side of 
 Caisteal Abhail, where the rock has a markedly jointed structure. 
 In this is a closely laminated band of fine granite, about nine feet 
 in width, which may be traced for a hundred yards or more. This 
 is a peculiar rock, and difiers from the fine granite which surrounds 
 it in having an approach to a linear arrangement of the quartz in 
 the rock, and it weathers into such thin plates or slabs that at first 
 sight it reminds one rather of a schist than of a granite. Its 
 
86 The Oeology of North Arran. 
 
 laminae, however, dip steeply to the west, exactly in the same way 
 as do the joints in the neighbouring fine granite. In some places 
 it has the appearance of an injected vein. 
 
 A specimen from lorsa Water, 650 yards below Loch na Davie, 
 may be taken as a type of the fine granite. It consists essentially 
 of quartz and the two felspars (oligoclase and orthoclase), biotite 
 and hornblende occurring as accessory constituents. 
 
 Drusy cavities containing smoky quartz and orthoclase crystals 
 are common in both granites. 
 
 The alteration of the surrounding rocks by the intrusion of this 
 great mass of granite is much less than might have been expected. 
 Often the metamorphism seems to amount to little more than mere 
 induration, and the adjoining rock is in some cases not more altered 
 apparently than sandstone is near some of the dykes in the island. 
 The fine-grained schistose rocks assume a bluer colour and break 
 vnth a splintery fracture, while the Old Eed Sandstone loses its 
 purple or chocolate colour and becomes grey and very hard. 
 Yet in most cases the bedding still remains distinct, though in 
 some the bedding or foliation is rendered very obscure and a set of 
 joints produced parallel to those in the granite itself. The altera- 
 tion is perhaps greatest in Glen Rosie, where it seems to extend 
 300 yards into the schists from the junction. Between Glen 
 Catacol and Glen Basan Biorach the altered and hardened schist 
 band is 200 yards wide or more, and it forms a marked ridge which 
 is higher than the granite adjacent, and it also gives rise to gorges 
 in the two streams. 
 
 Under favourable circumstances certain minerals appear to have 
 been developed in adjacent rocks by the action of the granite, as 
 andalusite in the schists of North Glen Sannox, and epidote in the 
 altered rocks at the White Water junction, and at Allt a Ghapuill 
 near Gioch nah-Oighe. Biotite has also been developed at the 
 White Water by contact alteration. Perhaps the most marked 
 instances of metamorphism are those which are found in 
 certain' basic dykes which are of earlier date than the granite 
 intrusion. One of these, penetrated by granite or granophyric 
 veins, is visible in the Cnocan Burn below the old mill-dam.* 
 It is an altered dolerite in which the plagioclase felspars and 
 the patches of iron ore have retained their original characters, 
 while the augite has been converted into aggregates of pale- 
 green hornblende, with which some brown mica is associated. 
 On the opposite side of the mass of granite another example of the 
 same Idnd of alteration is found in a dyke nearly half a mile north- 
 west of Lochan a Mhill. This is described by Ramsay (Geology of 
 the Isle of Arran, p. 49), who, however, thought that the dyke was 
 intrusive into the granite. One of the most marked examples of 
 alteration by the granite is found in Glen lorsa, 400 yards W.N.W. 
 of the boathouse, Loch lorsa. A highly altered argillaceous 
 schist seems totally reconstituted, and contains abundant andalusite 
 in relatively large irregular crystals, and much finely-divided 
 
 * This dyke is described by Bryce (" Geology of Arran," ith ed., p. 79), but he does 
 not notice the alteration of it due to the granite. 
 
Granite. 87 
 
 biotite. This locality is nearly a quarter of a mile from the edge of 
 the granite. In Glen Scaftigill, near the granite, a gritty schist is 
 highly metamorphosed. There is new-formed biotite in large 
 flakes,' and there has been a recrystallisation of much of the finer- 
 grained portion of the rock, with doubtful andalusite formed in 
 places. 
 
 This large mass of granite comes into contact only with the 
 schists and the Lower Old Eed Sandstone, and is certainly of later 
 date than the latter formation. That it is also more recent than 
 any of the other formations which are found in the island — Upper 
 Old Eed Sandstone, Carboniferous, and Trias — seems very probable, 
 from the fact that no fragments of granite are found in the rocks 
 of these formations ; and its similarity in character to the granite 
 of the Mourne Mountains in Ireland, which is post-Oretaceous, 
 lends support to the view that the Arran granite is of Tertiary age. 
 This view is confirmed by the alteration observed in the dykes 
 mentioned above, which are probably of Tertiary age. Further 
 evidence on this point will be adduced in a subsequent page. 
 
 Area South of String Eoa d. — The smaller granite area 
 occurs south of the road leading from Brodick to Shiskine and 
 occupies the highest ground in this part of the island, where are 
 found the hills A'Ohruach, Beinn Bhreac, and Ard Bheinn. The 
 granite is here associated \^ith granophyre and quartz-diorite (into 
 which rock it appears to graduate), and with many other intrusive 
 masses, both acid and basic, which have penetrated a large volcanic 
 vent of post-Cretaceous age. This oval district, which is extremely 
 complicated in structure, is 3|- miles in length from south-west to 
 north-east, and 2f miles in breadth, and its area is about 7 square 
 miles. 
 
 Granophyre passing into granite and quartz-diorite occupies the 
 south side of Glean ant-Suidhe (through which the String road 
 passes) and all the highest ground to the south, from Cnoc Dubh 
 by A'Ohruach and Beinn Bhreac round to beyond Ballymichael 
 Glen.* A triangular detached portion runs along the east side of 
 Ard Bheinn and takes up a great part of Glen Craigag. A smaller 
 body of the rock runs westward from Glenloig and includes the 
 granite of CreSg Dubh, described by Bryce (Geology of Arran, 4th 
 ed., p. 19). A detached area of granophyre occurs south-east of 
 this, and another is found close to and due north of Derenenach. 
 The common type of rock in most of the patches referred to, is a 
 yellowish granophyre or granophyric granite, for in several places 
 besides Ploverfield and Creag Diibh the rock may be called a granite, 
 e.g., in Ballymichael Glen; the burn north of Derenenach; the moss, 
 half a mile due east of Ard Bheinn top ; and on the east side of Glen 
 Craigag, about three quarters of a mile E.S.B. ot Glenloig. Granite 
 is also found in veins which penetrate the more basic intrusive 
 rocks within this area. Granite veins in this way may be seen in 
 the diorite mass at the head of Gleann J3ubh, three quarters of a 
 mile W.N.W. of Brisderg ; and in a burn 500 yards B.N.E. of 
 Oreag nam Mult, Gleann ant-Suidhe, granite with traces of 
 
 * The " Ploverfield granite " of Necker and Ramsay is a portion of this mass. 
 
88 The Geology of North Arran. 
 
 granophyric structure is intrusive into a fine-grained basic rock, 
 resembling some of the rocks described as diorite. 
 
 Quartz-diorite is a very prominent rock in Gleann ant-Suidhe 
 and in several of the streams that join it from the south, and it 
 occupies a good deal of the high ground between A'Ohruach and 
 Beinn Bhreac, though here the exposures are not good as the hill- 
 tops are covered v^ith peat. There is a good exposure in Allt nan 
 Oalaman (which is the first stream to the west of Cnoc Dubh), and 
 in the stream at Glenloig. It was probably in one of these streams 
 that it was noticed and described by Zirkel 30 years ago (see his 
 " Geologische Skizzen von der Westkiiste Schottlands," p. 30). The 
 older writers, from Jameson in 1798* to Ramsay in 1841,t have 
 described or included this rock under the head of syenite. It varies 
 much in composition, in colour, and in grain. Sometimes the rock 
 is light-grey, contains little hornblende, is very acid in character, 
 and approaches granite in composition, as in a burn 150 yards 
 north-east of Oreag nam Mult, Gleann ant^Suidhe. The specimen 
 described by Zirkel consisted of white felspar and greenish-black 
 hornblende with some quartz, plagioclase and orthoclase felspars 
 being both present. The rock often contains finer and darker 
 patches which are richer in horneblende and appear to be more basic 
 than the general mass of the rock. In fact, the composition of the 
 mass seems to be constantly varying, and occasionally we 
 find that the most basic portions of it are penetrated by acid strings 
 and veins approaching granite in composition, which are probably 
 derived from the same magma which produced the more basic 
 portions. Some attemps were made to map the quartz-diorite 
 separately from the granite and granophyre, but the attempt was 
 given up because the rocks are so intermingled, and because it was 
 evident that there are transitional forms betweeen the quartz- 
 diorite and the granophyre, and practically the Kicks seem to be 
 but difierent stages in the consolidation of one and the same molten 
 mass. At all events, this is the impression one gets after examining 
 the sections in the bums on the south side of Gleann an't Suidhe. 
 
 At the edge of the mass nearly half a mile south-west of the top 
 of Beinn Bhreac, the granophyric rock is beautifully spherulitic. 
 The same kind of structure occurs in a similar rock 300 yards 
 north-east from the summit of Ard Bheinn. The rock forms here 
 an oval patch about 40 yards long, the relations of which to the 
 surrounding acid and basic rocks is not clear. The colour of it is 
 nearly white on the weathered surface, but when broken it is seen 
 to be a mass of spherules, each averaging half an inch in diameter. 
 
 In some places, as near the head of Ballymichael Glen, and 
 between the heads of Glen Dubh and Glen Ormidale, the fine- 
 grained granophyre of the edge of the mass appears to pass into a 
 felsite-like rock. There is a great mass of this rock at the latter 
 place, and the boundary between it and the granite and the 
 granophyre to the west is not clear. 
 
 * K. Jameson, ' ' An Outline of the Mineralogy of the Shetland Isles and of the Island 
 of Arran, p. 84. 
 t A. C. Ramsay, " The Geology of the Island of Arran from Original Survey." 
 
Granophyre. 89 
 
 In Glenloig Burn, 200 yards west of the house, the rock is a 
 granitite with traces of granophyric structure, and ferro-magnesian 
 minerals are very scarce. 
 
 One of the most instructive sections occurs in Ballymichael 
 Glen, rather more than half a mile above the road, where we come 
 on to the mass of igneous rock. After passing over several yards 
 of yellowish, crushed, felsitic rock, which probably represents a 
 dyke, we approach a massive, dark-grey, basic-looking rock, 
 probably a variety of diorite. Higher up this rock appears more 
 distinctly acid, a quartz-diorite in fact; and just below the next 
 sharp bend in the stream an irregular, yellow granitic band, four 
 to five yards wide, which is intrusive in the diorite, crosses the 
 burn. Some thin and still more acid veins penetrate both rocks 
 alike. At the next bend above is a more basic-looking rock which 
 may be a dyke, into which coarse granite intrudes, as also into 
 granite or granophyre of the finer variety, while a thin acid vein 
 or elvan runs along the burn in the darker and more basic rock. 
 At the next bend to the north the rock is more decidedly an acid 
 variety of quartz-diorite. Just above this is another intrusion of 
 granite, and then the rock in the stream assumes a very massive 
 character, weathering into large rounded masses, with marked 
 joints inclined across the burn northward. This is a dark and 
 coarse quartz-diorite. At the next bend to the north we come 
 upon the main mass of light-yellowish acid granite, much jointed. 
 The junction appears to be an intrusive one, the granite being the 
 more recent rock of the two. 
 
 From the foregoing description it will be gathered that the 
 granitic rocks form an almost complete ring on the outside of the 
 oval complex. Various members of this acid series of rocks come 
 into contact with both members of the Old Red Sandstone and also 
 with the Triassic rocks, and the sedimentary formations are in every 
 case altered, so that the intrusive rocks must be of later date than 
 these formations. The granophyre at the head of Glen Dubh is 
 also clearly intrusive into the mass of diorite there, which is nearly 
 a mile in length, and there seems considerable evidence in favour 
 of the view that this diorite is but a basic form of the quartz-diorite 
 so often occuring to the westward. It is certainly very difiicult to 
 separate the two rocks by any definite boundary line, though an 
 attempt has been made to do so on the map, and the diorite may 
 conveniently be considered as part of the igneous ring. 
 
 The alteration effected by these igneous masses on the adjoining 
 sedimentary strata is very great. Along the north side of the oval 
 the actual junction of the igneous rocks with the Old Eed Sand- 
 stone is not visible, and there is no opportunity of studying the 
 altered rocks, but on the south and east sides the effects are 
 marked. The red sandstones and conglomerates of the Trias and 
 Upper Old Red Sandstone have their colour changed to white and 
 the rocks are converted in quartzites, while the more felspathic 
 sandstones of the Lower Old Red formation are changed from a 
 chocolate to a grey or bluish colour, their bedding sometimes is 
 nearly obliterated, and the rock is very tough and hard. The 
 
90 The Geology of North Ai-t-an. 
 
 chocolate mudstones of the same formation are in like manner 
 altered to flinty rocks resembling porcellanite. 
 
 If we now examine the inside of this igneous ring we find that 
 its various members are intruded into the material, filling up a 
 large volcanic vent which is known to be of post-Cretaceous age 
 from the fossUiferous fragments included in it. There is thus a 
 continuous chain of evidence in favour of the Tertiary age of this 
 granitic tract, and this age must now be accepted. 
 
 Several writers have remarked on the resemblance of the granite of 
 this outlying tract to the fine granite in the interior of the northern 
 mass, and the evidence for their being contemperaneous is very 
 strong. On the specimen before referred to from 650 yards south of 
 Loch na Davie, Mr. Teall remarks that the rock is evidently the 
 granitic phase of the magma which has elsewhere produced 
 granophyre, so that both microscopic and field evidence agree in 
 assigning these rocks to the same age. The coarser granite, as has 
 been already shown, in all probability is only slightly earlier in 
 date than the finer granite, and there is independent evidence for 
 its being of Tertiary age. Hence, we arrive necessarily at the 
 conclusion that all three granites are practically of one geological 
 period. 
 
 If we look at the geological map of this northern portion of 
 Arran we cannot help remarking on the nearly circular outline of 
 each of the two areas in which granite is found, and that in both 
 areas the sedimentary strata have been efiected in the same way, 
 having been upheaved so that their curved outcrops, especially on 
 the eastern and southern sides of the masses, are roughly parallel 
 to the edge of the igneous intrusions. May there not be a still 
 further resemblance ; and as the smaller area is proved to be a 
 volcanic centre, may not the larger granitic area be the stump of 
 an old volcano ? 
 
 Granitic Dyke s. — A dyke of pink-coloured syenite may be 
 seen in a small burn called Allt nan Eireannach, about half a mile 
 due south of Oatacol. The point where the dyke is visible is 150 
 yards above the outlet of the stream, which flows into the Oatacol 
 Burn. The dyke has a course about W.S.W., and is here intrusive 
 in dark phyllicic schists. Its width is at least 6-7 feet, but it may 
 be a little more, as the exact contact with the schists is not exposed. 
 This locality is about a quarter of a mile distant from the edge of 
 the mass of granite, which the dyke does not much resemble in 
 character. 
 
 A granitic or granophyric dyke occurs in Glen Chalmadale to 
 the east of Lochranza, and appears to have an N.N.W. course. 
 It crosses the main stream of the glen at a point nearly due north 
 of the hill called the Clachan and 200 yards S.B. of the foot of a 
 branch burn called Allt na Meanie which comes in from the north. 
 The rock is light-coloured, of rather fine grain, has many small 
 drusy cavities, and altogether much resembles some varieties of the 
 finer granite of the interior or the granophyre of the southern tract. 
 The dyke is from 25 to 30 feet wide, but only the central portion 
 appears to be granitic ; the edges are finer in grain and of a darker 
 
Acid Sills. 91 
 
 colour, and are probably of intermediate or basic composition. Tne 
 dyke appears again in Allt na Meanie, but cannot be traced 
 continuously. Eock, however, of the same character appears at 
 the head of a burn a mile distant to the northwest and a little to 
 the south of the most westerly of the old slate-quarries. This is 
 quite three quarters of a mile distant in a straight line from the 
 edge of the great granite mass. 
 
 The granite dykes which are found within the granite area are 
 much finer in grain than even the fine-grained mass of the interior ; 
 they are, in fact, of the nature of elvans, and seem essentially 
 composed of felspar and quartz. 
 
 FELSITE AND QUARTZ PORPHYEY, EHYOLITE, TRACHYTE, 
 AND PITCHSTONE. 
 
 Sills. — The larger sills and bosses of acid rocks other than 
 granite are all in the southern part of the sheet. The most 
 important of these are found at Dun Dubh near South Corrygills, 
 near Cnoc Dubh north-west of Lamlash, the Windmill Hill on 
 the north side of Glen Ormidale, Holy Island on the east side of 
 Lamlash Bay, Torr Eigh Beag on the west coast, and at Derenen- 
 ach, and around Ard Bheinn. Many of the acid intrusions in the 
 agglomerate on the north side of the latter hill are of a fine-grained, 
 grey quartz-felsite, which is a white weathering rock. The quartz- 
 porphyry of Windmill Hill is in general a rather fine-grained rock 
 of a light-grey colour, and only here and there is it more largely 
 porphyritic. It appears not to be pierced by any dykes of quartz 
 porphyry or felsite, though there are several in the crags south of 
 Glen Ormidale and in the adjacent stream, whose course might be 
 expected to cross it. It is penetrated, however, by several basalt 
 dykes, and crossed by faults that are of earlier date than these 
 dykes. The rock has a yellowish, flesh-coloured, or grey, ground- 
 mass, with white quartz and orthoclase crystals imbedded in it. The 
 rock of Dun Dubh is somewhat similar, and has been described as a 
 rhyolite. It is disposed in fine nearly vertical columns on the 
 Horth side, but these change to horizontal at the west end. 
 
 The felsite sheets, which have seldom free quartz and are not 
 usually porphyritic in character, such as those of Holy Island on 
 the one side of Arran and of Torr Eigh Beag on the other, are 
 probably of later date than the quartz porphyries. In the southern 
 part of Arran we can see the felsite dykes and sheets piercing 
 the porphyritic rocks, and in this area we have evidence that the 
 felsite sills are about the most recent of all the intrusive igneous 
 rocks, for we seldom find them pierced by the ordinary basalt- 
 dykes. None have been met with in the Torr Eigh Beag mass or 
 in the felsite of Holy Island, though dykes are common in the 
 adjacent rocks. A north-west running dyke on the South Corrygills 
 shore does not penetrate the felsite sheet there, though it is traced 
 for long distances on either side of it. The same felsite sheet 
 appears two-thirds of a mile west from this place in a burn between 
 North and South Corrygills, and here again it is clearly later in 
 
92 The Geology of North Arran. 
 
 date than a basalt dyke which crosses the burn at the same spot. 
 The larger felsite sheets in the southern part of Arran are often 
 beautifiiUy columnar, but examples are not common in this area, 
 though one occurs on the north-eastern side of Holy Island. 
 
 The smaller felsite sheets, usually of a yellowish colour, are 
 rather common near the head of the Birk Glen south of Brodick, 
 and one which has been quarried appears by the side of the road to 
 Lamlash, rather more than a mile south of Brodick pier. It is a 
 somewhat fissile rock, fine-grained, of a pale-yellow colour, and 
 minutely spherulitic. It has been described along with other 
 felsites (Geol. Mag., vol. ix., p. 542) by Mr. S. Allport. Two sills of 
 this character are found on the Corrygills shore on either side of 
 Corrygills Point, and these have been described by several of the 
 writers on the geology of Arran. 
 
 Dykes. — The dykes of quartz felsite which occur in Arran 
 are not so numerous as those of basalt, and most of them occur to 
 the south of the main granite area. Those which are found i» the 
 northern part of the island may be counted on one's fingers. 
 Even in the southern part of the sheet where they are abundant 
 in the interior, as in Benlister Glen, Gleann Dubh, Glen Ormidale, 
 and Glen Shurig, they are seldom met with on the coast, where the 
 basic dykes far exceed them in number. The largest dyke on the 
 shore is at An Cumhann on the west coast. This is a coarsely 
 porphyritic rock about 100 feet broad, running in a north-east 
 direction. As a general rule the average width of these acid dykes 
 exceeds that of the basic dykes. One of them is 150 feet wide on 
 Beinn Tarsuinn, and has been traced southward for two miles or 
 more, but in the southern part of its course it is not more than 50 
 feet in breadth. Another appears to extend from the west side of 
 Oaisteal Abhail into the corrie south-west of Gir Mh6r, and a third 
 can be traced at intervals from the burn a quarter of a mile north 
 of the Windmill Hill across Glen Shurig into Glen Rosie. 
 
 Comparatively few of these acid dykes are of the type of the 
 smaller felsite sills, which are often spherulitic and contain little or 
 no free quartz; they are nearly all quartz felsites, and some of 
 them are like the An Cumhann dyke before mentioned, coarsely 
 porphyritic. 
 
 PiTCHSTONE. — Dykes and sills of Pitchstone, for which the Isle of 
 Arran has long been celebrated, are pretty numerous in the island, 
 and a good many of them occur in out of the way places in the 
 interior which are not often visited. This glassy rock, which in 
 some parts is called 'bottle-rook by the natives, is found of various 
 shades of green from a light yello-vcish green through various dark 
 shades of the same colour to a black rock. Yellowish-brown and brown 
 varieties occur, and occasionally the rock is reddish. In composition 
 the rock varies from an almost perfectly clear glass to a coarse 
 pitchstone porphyry, and there are spherulitic and banded varieties 
 which remind us of similar structures in the felsites. 
 
 Both the dykes and sills of this rock are, as a rule, much more 
 irregular or inconstant than those of the basic rocks, or of the 
 felsites or quartz porphyries, and we find sills changing into dykes, 
 
Pitohstones. 93 
 
 and vice versa without any apparent cause. None of the dykes or 
 sills can be traced for very long distances, and any attempt to 
 correlate rocks of this character at widely separated intervals is 
 futile. One of the longest as well as earliest described dykes is 
 that on the Tormore shore, which can be traced for about 500 
 yards. The dyke or sill at the Brodick schoolhouse can be followed 
 for nearly 350 yards into the wood to the west, but its continuation 
 is uncertain. The sill on the Clauchland shore so often described, 
 can be followed southward; with breaks, for about 330 yards, when 
 it disappears on the foreshore. The dyke or sill south of Dun 
 Fionn is traceable for 300 yards, and it may be continuous with the 
 lower Oorrygills sill, when its total length would be about 700 
 yards. 
 
 Altogether there are about 40 different pitchstone outcrops in 
 this sheet, and there are also a good number in sheet 13. 
 
 LIST OF ARRAN PITOHSTONES IN SHEET 21. 
 
 Lamlash. — A black pitchstone dyke is in the burn near 
 Clauchland's Cottage. Its direction appears to coincide with that 
 of the burn at the point. 
 
 Dun Fionn. — A dark pitchstone sill or dyke south of the fort 
 accompanies a spherulitic felstone. 
 
 Dun Fionn, Bast of — A green columnar pitchstone sill near 
 the shore, which has often been described. It is visible near the 
 base of the crags for 150 yards, and dips S.S.W. at 30°, nearly as 
 the sandstone below it, but it clearly cuts the sandstone, though 
 there is little alteration effected by it. Nearly 200 yards south of 
 this it is visible on the foreshore for about 50 feet in length. 
 
 Dun Fionn, West of. — Two dark pitchstones occur beneath 
 the crags of the Clauchland Hills, between Dun Fionn and Dun 
 Dubh. The lower of these, which may be continuous with that 
 south of Dun Fionn, is about 15 feet thick. 
 
 South Coerygills. — On the shore, 650 yards north of Dun Fionn, 
 a pitchstone two to three feet thick accompanies the large felsite 
 sill there on the north side. 
 
 South Coerygills. — About 50 yards above the main road, and 
 200 yards west of the road leading down to the shore, a pitchstone 
 is visible for 25 feet in length. 
 
 North Coerygills. — South side of branch stream close to main 
 road, a pitchstone accompanies a felsite sill. 
 
 North Coerygills.- — Same burn, 500 yards S.W. of road, a dark 
 pitchstone dyke running N.W. 
 
 BiRK Glen. — On old Lamlash road, dark-green pitchstone, often 
 described. Also visible in the burn (AUt Beith). 
 
 Allt Beith. — Dark pitchstone occurs near the head of Allt 
 Beith about one and three quarters miles south of Invercloy. 
 
 Lag a Bheidh. — A dark pitchstone, probably a sill, about a 
 quarter of a mile east of the Brodick and Lamlash road and 650 
 yards E.N.E. of the Birk Glen outcrop. 
 
94 The Geology of North Arran. 
 
 Carn Ban. — On the south-east side of this old cairn three- 
 quarters of a mile south of Invercloy are many small fragments of 
 a dark-grey pitchstone, probably nearly in place. 
 
 Glen CLoy. — South side of road, qiiarter of a mile north of 
 Glenrickard, a black pitchstone, probably a sill ; three to four feet 
 visible. 
 
 Brodick School. — A dark green pitchstone sill with prominent 
 felspar crystals. It is much laminated, and the lamination is 
 parallel to its upper and under surfaces. 
 
 Glen Shtjeig. — A dark porphyritic pitchstone occurs half a mile 
 west of the church in the road leading down to the highest house 
 in the glen. 
 
 Beinn a' Ohliabhain. — A composite dyke with basic sides and 
 porphyritic pitchstone centre occurs 50 yards north of the highest 
 point, 2217, and again 300 yards to the east. 
 
 Beinn Ndis. — A dark pitchstone dyke six feet wide is found 
 about 500 yards south-east of the summit. 
 
 Beinn Taesuinn. — A dark pitchstone is visible 150 yaids 
 south-west of the summit. There are probably other small out- 
 crops on this hill. 
 
 The Saddle. — To the east of Cir.Mhdr and nearly a quarter of a 
 mile south-east of the Saddle is a greenish grey pitchstone, 
 running nearly W.N.W. Some of it is columnar. 
 
 CiR Mh6e. — Green porphyritic pitchstone forms the centre of 
 the composite dyke on Oir Mhdr, running east and west, described 
 by Prof. Judd.* 
 
 Caisteal Abhail. — On the ridge between Cir Mh6r and 
 Caisteal Abhail a dark pitchstone dyke occurs in the cliff a little 
 south-east of the strong spring, and a quarter of a mile south of the 
 point marked 2735 on the one-inch map. 
 
 Caisteal Abhail. — A dark columnar pitchstone occurs west of 
 the highest point, and may be traced a considerable distance in a 
 north-west direction by the loose fragments lying at the surface. 
 
 Another dark-coloured pitchstone dyke may be found under a 
 crag about 100 yards north of the summit. 
 
 Oreag Dhubh. — About a mile north of Caisteal Abhail a pitch- 
 stone dyke about sis feet wide is visible for a short distance under 
 the scars of Creag Dhubh. 
 
 Penrioch. — North-east of Penrioch and nearly half a mile E.S.E. 
 of Auchmore or South Thundergay is a remarkable porphyritic 
 pitchstone, only visible for about six yards. 
 
 Ddbh Loch. — On the slopes of Beinn Bharrain a quarter of a 
 mile N.W. of the Dubh Loch is a yellowish, streaky pitchstone, 
 three to four feet wide, which may be traced to the W.S.W. for 
 nearly 200 yards. 
 
 loRSA Valley. — In a stream about one mile N.B. of the outlet 
 of Loch Tanna there is a pitchstone dyke three to four feet wide 
 with a course due north. 
 
 loRSA Valley. — Near the heads of two small streams three- 
 
 * On composite dykes in Arran. — Quart. Jour. Geol. See, vol. xlix., p. 543. 
 
Pitchstones. 95 
 
 quarters of a mile north of Loch Nuis dykes and sills of various 
 kinds of pitchstone crop out in at least four places. 
 
 loRSA Valley. — About 600 yards S.S.W. of the outlet of Loch 
 lorsa a dark green pitchstone with a width of seven or eight feet 
 is visible for about ten yards. 
 
 Machrie Burn. — A dyke of light-green pitchstone six feet in 
 width crosses this stream in a N.N.W. direction about three 
 quarters of a mile N.N.B. of Onoc na Ceille. The stream here is 
 called Allt Airidh Niall. 
 
 AuchagalLon. — In the stream a quarter of a mile north-east of 
 the village there are two pitchstone dykes near together, and 
 the more northerly of the two is accompanied by felsite. Both 
 range somewhat north of east. 
 
 AXJCHAGALLON. — A small pitchstone dyke occurs in the old 
 sea-cliff to the west of the village on the north side of a sandstone 
 quarry. 
 
 AucHAGALLON, — A brown pitchstone also occurs on the shore 
 about 80 yards south of the ferry. 
 
 Glenloig. — In a small stream on the west side of the main 
 valley, two thirds of a mile south-east of Glenloig Farm, there is a 
 dark pitchstone dyke two-three feet wide. It runs in a north-west 
 direction and hades south-west. 
 
 ToRMORE. — On the Tormore shore, opposite Torr Eigh Beag, 
 there are several dark pitchstone dykes. The largest and longest 
 runs in a N.N.B. direction across the foreshore near An Cumhann, 
 and then follows the shore-line in a more northerly direction a 
 little above high-water mark. It can be traced altogether for 
 about 500 yards. At its northern end another pitchstone dyke 
 crosses the foreshore in an E.N.B. direction, but dies out in the old 
 sea-cliff. 
 
 Two hundred yards south of this point a composite dyke running 
 in a N.W. direction crosses the line of the larger dyke first 
 mentioned. This composite dyke has banded pitchstone on its 
 north-east side. 
 
 There are traces of pitchstone in more than one place to the 
 south of Lecan Euadh. 
 
 From the local distribution of these acid dykes and sills in Arran, 
 as well as from the local occurrence of the other acid dykes and 
 sills of felsite, quartz porphyry, etc., it appears to be pretty certain 
 they are not due to the widespread cause which produced the numerous 
 Tertiary basalt dykes all over the West of Scotland, but are inti- 
 mately connected with volcanic action or vulcanicity in the island 
 itself. The distribution of the numerous basic sheets and bosses in 
 the southern part of the island is a confirmation of this view, 
 and they are probably also the products of local volcanic action 
 which did not reach the surface. Many of the basic dykes, espe- 
 cially those which are so numerous along the south coast, may also 
 have had a local origin. 
 
 One of the surprising things connected with the intrusion of the 
 acid sills is the little alteration they effect on the rocks which they 
 have penetrated. There was much dispute as to the intrusive 
 
96 The Geology of North Arran. 
 
 character of the pitchstone sill east of Dun Fionn on this account, 
 and many other examples might be quoted. 
 
 INTERMEDIATE ROCKS. 
 
 Masses of intrusive rock of an altered basic character are found 
 in connection with the smaller granite area, and seem to be of 
 earlier date than the acid rocks adjacent to them. 
 
 Hyperite. — To the east-south-east of Glenloig, about three 
 quarters of a mile, there is on the east side of a little tarn a 
 projecting mass of rather coarse black rock. It is somewhat balloon- 
 shaped in outline, and about 250 yards in length. The rock is a 
 hyperite composed of labradorite, diallage, and hypersthene, with 
 some insterstitial magnetite and biotite. It is surrounded by a 
 granophyric rock, but no junction is visible. 
 
 About a quarter of a mile N.N.W. of this is Creag nam Mult, 
 a prominent object from the road which runs through Gleann ant- 
 Suidhe. The dark rock here forms a long and narrow outcrop with 
 a steep face to the north, and consists of plagioclase, augite, hyper- 
 sthene, and hornblende, with some interstitial quartz and micro- 
 pegmatite. In the middle of this mass, which is 250 yards in 
 length, is a gully where may be a basalt dyke. The surrounding 
 rock is a granophyre which appears to have penetrated the hyperite 
 in veins. There is a small detached area of a similar rock to that 
 of Creag nan Mult 250 yards to the north-east. 
 
 Augite-Porphyrit e. — About 500 yards east of Glenloig is 
 a small section where two kinds of rock are seen — a coarse ophitic- 
 dolerite, and an augite-porphyrite, which is probably intrusive in 
 the former rock. This section is nearly close to the mass of volcanic 
 agglomerate which is on the south of it. On the other side it is 
 probably bounded by quartz-diorite, but no contact is visible. 
 
 D i o r i t e. — The only mass of diorite of importance in the island 
 is found at the head of Gleann Dubh (Glen Cloy). It is more than 
 a mile in length (from N.E. to S.W.) by half a mile at its widest 
 part, and it has an irregular outline, having penetrated the Old Eed 
 formation on its eastern margin, and being itself intruded into by 
 granophyric and felsitic rocks on its western and northern edge. 
 It is a massive, dark-coloured and generally coarse rock, with few 
 prominent joints, forming crags on steep ground and rough rocky 
 knolls on more gently inclined surfaces. Near its contact with the 
 Old Red Sandstone it is often fine-grained, however. At its S.W. 
 end, between the branches of the burn, a district known as Tir 
 Dubh, the massive rock of the knolls is pierced with many little 
 acid strings and granite veins. A specimen from one of the bosses 
 near the burn is a dark green rock composed of plagioclase and 
 green hornblende in grains and patches, with iron ores and a little 
 biotite. Near its northern edge the rock is coarsely crystalline, 
 with large crystals of diallage. Veins of granophyre and felsite 
 penetrate the diorite in many places, especially near its north- 
 eastern margin, in the crags on the north side of Gleann Dubh, 
 where the rock is often a light-coloured quartz-diorite. At the 
 
Basic Bocks. 97 
 
 head of Glen Ormidale are several long, narrow strips of a fine- 
 grained greenish rock, which is probably derived from the same 
 magma as the larger mass of diorite, and several small dykes of a 
 similar kind of rock occur in the crags between the heads of the 
 two glens. 
 
 BASIC ROCKS. 
 
 Sills. — The largest mass of basic rock is that which forms the 
 Clauchland Hills, and rmis out to sea at Clauchland Point. It is 
 a great intrusive sill, and fine intrusive junctions are visible near 
 Clauchland Point (west of) and at several other places along its 
 southern margin, the adjacent red sandstone being changed to a 
 white, hard, quartzose rock. Reference may here be made to 
 descriptions of this rock by Zirkel (Zeit. d. deutsch. Geol. Ges., 1871, 
 p. 38) and Allport (Quart. Journ. Geol. Soc, 1874, p. 563). It is 
 often a coarse gabbro-like rock with large crystals of augite, olivine, 
 and plagioclase, and without any groundmass. Tliis coarsely crystal- 
 line rock passes into a more compact rock of a basaltic character, 
 which is the type of the rock that prevails over a large part of its 
 extent. Allport describes a specimen from Dun Pionn as containing 
 plagioclase crystals, beautifully striated, augite and olivine in a 
 remarkably fresh condition, magnetite, a few plates of brown mica, 
 a little apatite, and a clear amorphous glass in the interstices of the 
 constituents. This sill crosses the Lamlash road to the south of 
 the Stone Circle, and shortly after narrows considerably, and then 
 separates into two dyke-like portions, with sandstone between. It 
 cannot be found in the most westerly branch of the Birk Glen 
 stream. 
 
 To the southward another considerable sill of coarse-grained 
 dolerite, often much decomposed, is found at Onoc Dubh, spreads over 
 a wide extent southward, crosses Benlister Glen, and in Sheet 13 
 forms the prominent hill called The Eoss. The rock much 
 resembles in character the sill of the Clauchland Hills. The hills 
 called Sheeans to the N.W. of Cnoc Dubh, which form marked 
 features in the view up Glen Cloy from Brodick, are composed of a 
 finer and harder variety of basic rock. In the western Sheean the 
 dark-coloured rock is variegated with numerous white acid strings 
 and irregular veins, which appear to be segregations. Southward 
 from the Sheeans are some smaller basic intrusions of a like 
 character, and other masses are found round Brisderg intrusive in 
 the Carboniferous and Old Red rocks. 
 
 South of the String road at the summit occurs a mass of dark 
 basic rock under the granitic crags. It is exposed in several small 
 gullies, and appears to be an altered, coarse-grained, ophitic dolerite 
 in which -the augite has been replaced by green hornblende. This 
 alteration is probably due to contact with the granite or granophyre, 
 which is a late intrusion. 
 
 In the north-eastern part of the island a considerable mass of 
 basic trap, nearly a quarter of a mile in length, is found to the 
 west of Millstone Point. It is probably intrusive, but its 
 G 
 
98 The Geology of North Arran. 
 
 boundaries are not well defined, and it is by no means clear that it 
 may not be of Carboniferous age. 
 
 A considerable number of separate basic masses are found around 
 Ard Bheinn intrusive in the agglomerate of the volcanic vent. 
 One of the most conspicuous of these forms a craggy ridge called 
 Creagan Liatha na Gluain Monaidh between the two branches of 
 the stream near the head of Ballymichael Glen. At its eastern 
 end this dark basic rock is highly magnetic. The largest mass 
 runs from the west side of Ballymichael Glen in a north-west 
 direction to above Derenenach, and then bends towards the north- 
 east. It is altogether one and a half miles in length and more 
 than 200 yards wide where it is broadest, and the rock of which 
 it is composed is similar to that last mentioned and also highly 
 magnetic in places. At a point 550 yards E.S.B. of Derenenach 
 the rock is a natural magnet, possessing polarity. This basic mass 
 is certainly earlier in date than the granophyre. Another mass of 
 a somewhat different character, but also magnetic, is found round 
 and at the top of Ard Bheinn, but this is rather a felsite. It has 
 a fine-grained dark matrix which encloses felspar crystals, but 
 there are no quartz grains. 
 
 Perhaps the most interesting of all the Tertiary sills is that 
 which traverses the Carboniferous volcanic rocks in the southern 
 part of Bute, and also cuts through a dolerite sUl of late 
 Carboniferous age. This remarkable compound sheet rises from 
 the sea at Eoinn Clumhach on the west side of Glencallum Bay, 
 and after a winding course of nearly two miles enters the sea 
 again on the east side of Uamh Capuill. Thus its general course 
 is from east to west across the successive outcrops of the Carboni- 
 ferous lavas, which dip steeply to the south-west and form marked 
 features striking north-west. The intrusive mass inclines south- 
 ward, and forms prominent crags at its northern side, which are in 
 striking contrast to those formed by the Carboniferous lavas. This 
 sheet rises to over 300 feet above the sea south of Torr Mor, whpre 
 it cuts through the older intrusive sill, falls to about lOO feet near 
 Loch na Leighe, and rises in St. Blane's Hill to 400 feet, which is 
 the highest point it reaches. 
 
 This peculiar sill has a basic centre with fringes or selvages of an 
 acid rock above and below. A specimen from the central portion 
 near Loch na Leighe is an enstatite dolerite, while the lower part 
 is a quartz porphyry having magnificent crystals of quartz and 
 sanidine imbedded in a crypto-crystalline groundjnass. The 
 quartz grains are corroded, and the felspar slightly kaolinized. 
 
 The acid borders accompany the basic sheet throughout its whole 
 extent, as far as can be ascertained, though in some places they 
 must bei thin. Generally the quartz porphyry forms the actual 
 boundary of the intrusive mass, but in one place west of Loch na 
 Leighe, where the lower acid sheet is 1 feet thick, there is from 
 18 inches to two feet of amygdaloidal pyroxene andesite of a 
 basaltic type interposed between it and the Carboniferous Traps. . 
 The rock contains numerous derived quartz grains with pyroxene 
 envelopes. 
 
Basic Rocks. 99 
 
 A little basic rock is also seen below four feet of quartz porphyry 
 near the top of St. Blane's Hill on the north side. The greater 
 part of the basic intrusion seems fairly uniform in character — a true 
 dolerite, occasionally weathering in a nodular or spheroidal form, 
 and sometimes rudely columnar. It is apparently only near its 
 edges that it becomes an intermediate rock. 
 
 The quartz porphyry is pretty uniform in character throughout, 
 and always a coarsely crystalline rock. Ehyolite or eurite seem also 
 to be names for this kind of rock, but the most appropriate is quartz- 
 sanidine-trachyte. A specimen from the upper acid border near 
 Eoinn Clumhach is a good fresh rock with traces of derived basic 
 matter. There is a spherulitic groundmass, and spherulitic aggrega- 
 tions round the porphyritic quartz crystals. In the small 
 outlier of this upper sheet east of Uamh Capuill the rock has a 
 fibrous, delicate, spherulitic ground, which has broken up into 
 granular crystals, as in the spherulitic felsite of Arran. Sometimes 
 the rock contains dark objects which are probably pyroxene, and 
 these may have been derived from a foreign source. 
 
 At the base of the dolerite sheet, north-east of Uamh Capuill, the 
 rock assumes variable characters. The more normal kind is an 
 enstatite-augite-andesite of basaltic type, with a little minute 
 biotite among the chloritic products of decomposition. These are 
 derived quartz grains with augite prisms forming an envelope 
 about them. Another variety is a glassy rhyolitic andesite, 
 including some much corroded crystals. It is probably a rock of 
 mixed origin, its rhyolitic character being due to absorption of 
 highly silicated materials. Minute biotifce and pyroxene prisms 
 occur, with much tufty chlorite. Other specimens contain porphy- 
 ritic orthoclase of sanidine type and also porphyritic quartz, and 
 the rock approaches the rhyolites in composition, but its porphy- 
 ritic crystals may be derived. 
 
 There seems evidence from the foregoing description that both 
 the acid and basic portions of the intrusive mass contain foreign 
 material; or do these last mentioned specimens indicate a passage 
 from the basic into the acid rock ? The association is somewhat 
 like that described by G. S. Corstorphine in the rocks of Benan 
 Head in the southern part of Arran (see his paper — " Ueber die 
 Massengesteine des Sudlichen Theiles der Insel Arran," Tscherm. 
 Min. u. pet. Mitth. xiv., pp. 453-463 and 469). In both localities 
 there is strong evidence for the view that the acid and basic rocks 
 are practically contemporaneous. 
 
 A specimen showing the junction of the acid and basic rocks 
 from the south side of Barr Hill, east of Uamh Capuill, is called 
 granophyre and dolerite [2612], 
 
 Dykes. — Basic dykes are very numerous in the Isle of Arran, 
 but are not uniformly distributed. In some places they are 
 abundant, as along the shore about Brodick from Invercloy east- 
 ward to Corrygills Point, while they are few in number between 
 Oorrie and Sannox ; in the Carboniferous formation on the north- 
 east shore between the Fallen Eocks and the Cock; and again 
 between Lochranza and Catacol. They are much more numerous 
 
100 The Geology of North Arran. 
 
 in the interior than would be inferred from an inspection of the 
 geological map, as their outcrops are often covered by debris 
 and glacial drift, and it is only in clear sections in burns that many 
 of them can be observed, and then only for a distance of a few 
 yards. 
 
 These dykes vary in composition. Some of them are true olivine- 
 basalts, while others, such as those described by Prof. Judd,* are 
 augite-andesites. It was found impossible, however, to divide 
 the dykes of Arran, which may be counted by hundreds, into these 
 two classes, and they must all be coloured alike as basic. The 
 amount of olivine in a dyke varies much, and it seems quite 
 possible to obtain from one and the same dyke rock specimens 
 containing olivine, and others without that mineral. 
 
 As regards the direction of the dykes, there is a general tendency 
 towards a north-westerly course, but there are many exceptions. 
 Along the Brodick shore several of the dykes have a trend nearly 
 north, and several of those found between Sannox and the Fallen 
 Eocks have a similar direction with a tendency towards north- 
 east. They do not often keep one direction for a long distance, 
 for we observe them bending about in a zigzag fashion, separating 
 into two or more portions, enclosing clastic rock and uniting again. 
 Generally their sides are vertical, and sometimes they project above 
 the general surface of the ground; but often thfey decompose more 
 readily than the surrounding rocks, and form hollows along the 
 shore and rifts in the cliffs. Examples of the latter may be observed 
 in the ivy-clad rocks of the Corrygills shore, while marked examples 
 of projecting dykes are found along the northern shore of Lamlash 
 Bay, and in the Lion Rock and the Devil's Dyke of Great Oumbrae, 
 east of Millport Bay. 
 
 The dykes vary much in width. Some are but a few inches 
 broad, while a- great many, perhaps the majority, are less than ten 
 feet wide. The dyke that has a W.N.W. course between Imachar 
 and Balliekine on the west side of Arran is in places 100 feet or 
 more in breadth. At Eudha Ban, North Penrioc, a dyke with a 
 course parallel to the last is about 50 feet wide. On the south 
 side of Brodick Bay the largest is from 30 to 50 feet ; it runs 
 nearly N.W. from the Birch Burn, near the Free Church, to the 
 shore at Invercloy. 
 
 The absolute lengths of the dykes can only be determined in a 
 very few cases where they are seen to die out on the foreshore or 
 in inland cliffs. Probably a good many of the. small dykes, which 
 are only visible in burn sections, have a very short course, at all 
 events above ground. As regards others mapped for some distance, 
 we can but say how far they have been traced. The large Imachar 
 dyke can thus be said to have a course of about one mile, and the 
 North Penrioc dyke can be traced for three quarters of a mile. 
 In the granite area west of Loch na Davie, a north-west running 
 dyke has been followed over Beinn Bhreac for one and a quarter 
 miles, and some W.N.W. dykes near Goatfell can be traced almost 
 as far. One of the longest and most remarkable is that which 
 
 * "On Composite Dykes in Arran." Quart. Journ. Geol. Soc, Vol. 49, pp. 536-565. 
 
I. JcMiiting in lliK coarser f^'ranite, near top of Goalfell, Arran. 
 
 Tertiarv dolerile dvke traversinfr " New Red Sandstone.' 
 jointint; is well shown. East of l->rodick Pier, 
 
 The cross 
 
Basic Dykes. 101 
 
 forms the deep rift of Ceum na Caillich, east of Oaisteal Abhail, 
 crosses in a southerly direction the head of Glen Sannox, makes a 
 gorge on the north side of the Saddle by no means easy to traverse, 
 and runs for some distance down Glen Eosie, being altogether 
 more than two miles in length. Probably it extends much farther 
 in both directions ; a dyke which appears in the bed of the Rosie 
 Burn for some distance about three quarters of a mile above the 
 Garbh Allt being a probable continuation to the south. This 
 dyke is 24 feet wide at Oeum na Caillich, 12 to 15 feet at the rift 
 in the Saddle, and farther south in Glen Eosie about 10 feet. 
 
 Dykes are perhaps nearly as numerous in the granite as in 
 the other rocks of the island. There are a great number about 
 a'Chir andBeinn a'Oliabhain, but many of the dykes in the granite 
 are small and might easily be ovei-looked. Some of them also, in 
 addition to those above described, form deep, narrow rifts in the 
 mountain sides, which require an expert mountain climber to 
 negotiate. 
 
 The alteration effected by these basic dykes on the adjacent rock 
 is best seen where they traverse red sandstones, when we always 
 find that the rock is considerably hardened and the red colour dis- 
 charged, so that the sandstone is white for a variable distance from 
 the edge of the dyke. One of the most remarkable instances of 
 this may be seen about 100 yards east of Brodick pier, where on 
 the eastern side of a dyke running N.N.B. the sandstone is 
 whitened for a distance of 30 to 40 feet from the edge of the 
 dyke (see Plate X-2). 
 
 These numerous basic dykes appear to be nearly all of one age, 
 though some, as we have seen, are older than the granite. Most 
 of them, however, are more recent than the granite; they 
 penetrate the coarse acid and basic sills, are less numerous in the 
 fine grained basic sills, and are almost entirely absent from the 
 felsite sheets. W. G. 
 
 AYESHIRE DISTRICT. 
 
 Brief allusion may here be made to the younger dolerite or 
 basalt dykes which are probably referable to the Tertiary series. 
 Several of these may be observed on the shore. The largest and 
 most continuous has been already noticed running down to the 
 coast at Portincross. It can be traced interruptedly for four miles, 
 but it is lost before it crosses to the eastern margin of the 
 volcanic plateau. As shown on the map, this dyke displays a 
 feature not infrequently to be observed among the Tertiary system 
 of dykes — the occurrence of short parallel dykes at no great distance 
 from the main dyke. It will be noticed that the dyke is lost after 
 it enters the west front of Law Hill above West Kilbride, but 
 that two smaller dykes, a little to the north, continue the general 
 line, while one dyke in the same line is found a short distance 
 farther east on the south side of Blackshaw Hill. These interrup- 
 tions probably point to parallel fissures, the uprising lava some- 
 times forsaking one for another. 
 
102 The Geology of North Arran. 
 
 A second and still broader dolerite dyke runs from the raised 
 beach on the southern side of Largs for more than two miles up 
 the slopes of the volcanic plateau. A. G. 
 
 KINTYEE DISTRICT. 
 
 A few basalt and dolerite dykes with well-defined margins and 
 having a N.W. trend cut the schists at nearly right angles to their 
 strike. These are of the ordinary type of the Tertiary basic dykes 
 of the region. As might be expected, they are best seen on the 
 shore. A small dyke is thus exposed at about half a mile N. 
 of Skipness Point. No fewer than seven of these dykes are found 
 between the mouths of the Skipness and Olaonaig Waters. Most of 
 these are thin and of fine-grained basalt, none exceeding four feet in 
 width, but one which occurs at about 400 yards N.B. of Sgeir na 
 Luinge (Skerry of the Long-boats) is 20 feet across and is com- 
 posed of coarse dolerite. Three more dykes are seen between the 
 Cleonaig Water and the mouth of Allt a Bhuic (Burn of the Bucks), 
 and other two are exposed in the bed of the latter stream a little 
 way above the public road. A group of four dykes, varying 
 from 10 to 20 feet thick, occur within a half mile on each side of 
 Port Alasdair Euadh (Port of Red Alexander), near the point 
 where the coast is cut by the edge of the map. 
 
 Inland, although they probably continue their course, the dykes 
 more readily escape detection, owing to superficial deposits and 
 the coating of turf-peat. In addition to those mentioned as 
 visible in the Allt a Bhuic a dyke is exposed in the Larach M6r 
 Burn (Big Shelling Burn), a tributary of the Skipness Burn, a 
 little below Garveoline, while a small dyke is seen at the head of a 
 stream on the eastern slopes of Cnoc a Moine Raibert, about one 
 mile N. of Skipness. 
 
 Although they cannot be traced inland, groups of similar dykes 
 appear to occur together in such a manner as to suggest that if they 
 could be followed they would be seen to branch and anastomose. 
 
 B. N. P. 
 
CHAPTER XL 
 
 Petrography of the Tertiary Igneous Bocks of Arran, Southern 
 Bute, and the Gumhrae Islands. 
 
 The following notes are based upon specimens collected by Mr 
 Gunn during the progress of the survey, with some collected hj 
 Sir A. Geikie at an earlier time: — 
 
 (i.) VOLCANIC AGGLOMERATE. 
 
 A number of specimens have been examined of the volcanic 
 agglomerate of the large vent, and of the various rocks enclosed as 
 fragments in it [9421-9430, etc.]. In general they show a 
 gritty-looMng matrix, stained of various colours, in which are 
 imbedded pebbles and fragments of quartzite, vein-quartz, and 
 other rocks. The matrix itself consists largely, and often princi- 
 pally, of quartz-grains, angular and subangular ; but there is also 
 finely divided instertitial matter, which is probably to be 
 interpreted as representing basic igneous material, too much 
 altered for identification. Often it is largely chloritic ; in other 
 cases there is a ferruginous or a ferruginous and calcareous cement 
 [9423 and 9421]. In addition to quartz-grains, we find sometimes 
 little crystals and fragments of felspar [9424], grains of partially 
 epidotized augite, and little chips of fine-textured basalt and 
 especially of a pyroxene-andesite. 
 
 Among the larger elements enclosed in the general matrix we 
 may remark especially fragments and rounded pebbles of quartzite 
 and vein-quartz. Numerous other rocks are represented in frag- 
 ments of all sizes. One specimen has cavities which probably 
 represent destroyed limestone pebbles [9423]. A piece of crushed 
 and schistose grit occurs, showing films of sericitic mica, strain- 
 shadows in the quartz, and a characteristic mylonitic structure 
 [9424]. Especially noteworthy are the fragments of igneous rocks, 
 including andesites [9426, 9427], microgranitic quartz-porphyry 
 [9428], and biotite- or biotite-hornblende-granite [9479-9481]. 
 
 The intrusive rocks which break through the agglomerate 
 mass are various. Besides gabbro and granite, they include 
 quartz-porphyries, an ophitic dolerite with pleochroic purplish- 
 brown augite, pitchstone, and other rocks, all of types to be 
 described below. The metamorphism produced in the agglomerate 
 by these intrusions is evident in some of the specimens. One, 
 traversed by a granite vein, is apparently a trachytic or rhyglitic 
 tufi", in which biotite has been developed by metamorphism, while 
 denser patches richer in biotite represent enclosed fragments of' 
 
104 The Geology of North Arran. 
 
 andesite [9429]. Other specimens, representing the gritty tuff 
 which is the most usual matrix of the agglomerate, show in varying 
 degree the same development of new -formed biotite, resulting 
 presumably from the metamorphism of the chloritic matter 
 mentioned above [9430, 9428]. In another specimen, from the 
 edge of the mass, the chief product of metamorphism is a pale- 
 green fibrous hornblende, often with partial radiate arrangement 
 [6387]. 
 
 (ii.) GEANITE AND OTHER PLUTONIC ROCKS. 
 
 The first microscopicaj investigation of the Arran granites was 
 made by Prof. Zirkel,* whose account of the rocks was published in 
 1871. Mr Teallt has added to this some particulars, and, like 
 Delesse, has compared the Arran granites with those of the Mourne 
 Mountains in Ireland, doubtless also of Tertiary age. Several 
 writers have recorded the occurrence of special minerals in the 
 druses of the granites. 
 
 Although the northern a/rea of granite has been separated into 
 coarser and finer varieties, the rocks do not differ in any important 
 particular, excepting texture. They are biotite-granites, with some 
 tendency to granophyric modifications. A specimen of the coarse 
 type from the top of Goatfell [9469] shows crystals of felspar up to 
 |-inch long and quartz-grains and mica-flakes up to |-inch. The 
 rock of the central part of the area is of considerably finer texture ; 
 and the same is true of apophyses, in which also there is sometimes 
 a porphyritic tendency, indicated by the occurrence of a few 
 relatively large crystals of felspar [9476], It can be seen in the 
 hand-sp£!cimens that the quartz tends to form grains, which are 
 sometimes enclosed in the felspar; also that the biotite, which 
 occurs only sparingly, is often in very irregular shapes, having 
 crystallized after part of the felspar. Another feature, very 
 conspicuous in most of the rocks, is the occurrence of numerous 
 little drusy cavities of irregular form, on the walls of which the 
 quartz and felspar assume good crystal-faces. 
 
 Thin slices reveal no other mineral, except an occasional grain 
 of magnetite and some minute crystals of zircon enclosed in the 
 biotite. The felspar is partly striated oligoclase, but chiefly what 
 more resembles orthoclase. Much of the latter, however, has a 
 fibrous appearance, becomingmore evident with incipient alteration, 
 and probably indicating a microperthitic intergrowth. The quartz 
 contains many minute fluid-pores with bubbles, and in some of 
 these cavities Zirkel detected minute cubes of salt. The mineral 
 is generally idiomorphic towards the orthoclase and microperthite, 
 but it also tends to be intergrown in an irregular fashion in those 
 felspars. In the finer-gr'ained type of rock the micrographic inter- 
 growth is sometimes more regular, and one specimen from Glen 
 Catacol, at the foot of AUt-nan-Calman, is a very beautiful 
 granophyre [9471]. It contains much micropegmatite of a very 
 
 * Zeits. deuts, geol. Ges., vol. xxiii, pp. 6-9 ; 1871. 
 • t Brit. Petrography, p. 328 ; 1888. See also Ann. R^. Geol. Sur. for 1896, pp. 75, 76. 
 
Petrography of Tertiary Bocks. 105 
 
 delicate kind, which is often grown round the felspar crystals, and, 
 when it surrounds orthoclase, has its felspathic element in crystalline 
 continuity with the crystal itself. 
 
 The granites of the northern and larger area, coarse and fine 
 together, belong thus to a well characterised type. The British 
 rocks with which they compare most closely are undoubtedly those 
 of the Mourne Mountains. The other British Tertiary granites — 
 such as those of Skye and Mull — are usually hornblendic or 
 augitic, and they run more frequently than these into granophyric 
 varieties. An interesting point in common between the Arran and 
 the Moume rocks is the occurrence of special minerals in the druses. 
 Albite, beryl, topaz, and garnet have been recorded in the druses 
 of the Arran granite, besides stilbite (MaccuUoch). 
 
 A specimen from an isolated area of coarse granite in North Glen 
 Sannox is found to be identical with the rock of the main mass 
 [9475]. Some dykes traversing the mica-schists show a very 
 different micro-structure. Two examples have been examined, one 
 from Glen Ohalmadale and the other from S.W of the Cock slate- 
 quarry [9482, 9483]. They are fine-textured but still drusy rocks of 
 pale colour. Both are found to be typical spherulitic granophyres. 
 Crystals of quartz and felspar of small dimensions are enclosed in 
 the spherulitic groundmass and have often served as nuclei for the 
 spherulites. The inclusions in the quartz are here of glass, not of 
 liquid. 
 
 The granitic rochs of the more southerly area, forming part of the 
 ring surrounding the volcanic vent, have many points in common 
 with the preceding, and especially with the finer-grained variety of 
 the northern area ; but there are also points of difference which are 
 probably significant. There is the same tendency to rude micro- 
 graphic intergrowths and sometimes a frankly granophyric structure, 
 the same abundance of quartz, and sometimes very clear indications 
 of microperthitic intergrowth in the untwinned part of the felspar. 
 There is, however, a somewhat larger proportion of the coloured 
 silicates, and these embrace not only biotite, often as before of 
 allotriomorphic habit, but also green hornblende accompanying it, 
 or even almost excluding it. Granules of sphene come in occa- 
 sionally, and in some slices there are conspicuous little crystals of 
 zircon, in addition to the minute ones enclosed here and there in 
 the mica. This description applies not only to the rocks intrusive 
 in the volcanic agglomerate, but also to granite pebbles contained 
 in the agglomerate itself and therefore derived from an older rock. 
 It is interesting to find that here, as in the Isle of Skye, the frag- 
 ments in the agglomerate preserve evidence of the existence of 
 older plutonic rocks which are not elsewhere exposed, and that 
 these concealed rocks were of closelj" the same type as those 
 subsequently intruded in the immediate neighbourhood. 
 
 The ring of plutonic rocks surrounding the volcanic vent consists 
 in part of granite, but in part of more basic rocks which have been 
 been termed quartz-diorite, diorite, and gabbro. The granite itself 
 shows by its mineralogical constitution a certain range of variety 
 in chemical composition, the most obvious difference being in the 
 
106 Tlie Geology of North Arran. 
 
 amount of the ferro-magnesian minerals. The increasing amount 
 of hornblende observed in a series of specimens, with other 
 differences developed concurrently, corresponds presumably with 
 the transition noted in the field between normal granite and the 
 type styled quartz-diorite. This latter was first described by 
 Zirkel,* whose account is as follows : — " ... A fine-grained 
 aggregate of white felspar and greenish-black hornblende, which, 
 in spite of the smallness of the individual crystals, stand out 
 clearly from one another, and quartz, which is first seen in.the thin 
 slice ; plagioclase preponderates, but, as is common in similar 
 rocks, there is some orthoclase present ; green epidote borders the 
 hornblende in places ; the quartz is very rich in fluid-inclusions ; 
 except magnetite and apatite needles, often of surprising slender- 
 ness with great length (e.g., a needle 0'9 mm. long and only 0"008 
 mm. thick), felsitic matter is not present. Here and there occur 
 roundish dark concretions, in which the constituents are still finer- 
 grained and the hornblende predominates strongly, like the 
 concretions rich in dark mica in the granites. The rock is thus a 
 beautiful quartz-diorite, the only one of its kind known from 
 Arran, and essentially difierent from the augite-bearing diabasic 
 traps." 
 
 Some of our specimens answer very well to this description. 
 One from Glen Dubh, north side, for example, has all the characters 
 of a typical quartz-diorite. It has not the fine texture of Zirkel's 
 specimen. A thin slice [7447] shows that it consists principally 
 of plagioclase felspar and abundant idiomorphic crystals of green 
 to greenish-brown pleochroic hornblende. The plagioclase, as in 
 most quartz-diorites, shows strong zonary banding between 
 crossed nicols, indicating a great difference in composition between 
 diSerent coats of the crystal. It can often be verified that the 
 interior and principal part is of labradorite, while towards the 
 margin this passes successively through andesine and oligoclase to 
 albite. Orthoclase is quite subordinate. Quartz too is not 
 abundant, and always occurs interstitially, either by itself or in 
 micropegmatite. The other minerals are magnetite, in fairly 
 plentiful crystals and grains, and apatite, here building rather stout 
 prisms to as much as 0"01 inch (0"25 mm.) in thickness. 
 
 Examining and comparing other specimens, however, we find 
 unmistakable indications that at least part of these rocks are of 
 abnormal nature, in that they have not originated simply by the 
 consolidation of an ordinary rock-magma. - Almost all the slides 
 show in the interior of many of the hornblende crystals a core of 
 colourless augite, with a highly irregular and intricate boundary 
 between the two minerals which proves that the hornblende has 
 replaced augite by a process which ate its way inwards into the 
 the crystal. Nevertheless it is not a case of the simple conversion 
 of augite crystals into hornblende, which might be a secondary 
 change, for the crystals have always the external forms proper to 
 hornblende. We may infer that the augite was transformed (in 
 great part) to hornblende in a still fluid magma, and the crystals 
 
 * Zeiis. deuts. geol, Ges., vol, xxiii, p. 30 ; 1871. 
 
Petrogra]}hy of Tertiary Bocks. 107 
 
 thus transformed, wholly or in their external parts, continued to 
 grow as hornblende, assuming the proper crystal forms. This 
 suggests that the augite was of foreign derivation, and other 
 peculiarities leave no doubt that this conclusion is the correct one. 
 The proportion of the ferro-magnesian element in the rocks is 
 variable, and this even in one specimen, a mottled or patchy appear- 
 ance being often very evident to the eye. Further, there occur in 
 some parts of the mass numerous ovoid dark patches, an inch or 
 less in diameter, of finer texture than their matrix. These are the 
 "concretions" of Zirkel, but they are to be interpreted as repre- 
 senting the debris of a basic rock almost completely digested by 
 the originally acid magma in which they were enveloped. Thin 
 slices show that these " xenoliths," or enclosed foreign fragments, 
 have been totally reconstituted, not merely by metamorphism but by 
 interchange of material between them and the surrounding magma. 
 The mineralogical composition of the dark patches, and especially 
 the occurrence of a noteworthy amount of quartz and alkali-felspars, 
 denotes a certain degree of acidification ; and this is the case even 
 when the patches appear quite sharply defined to the eye on a 
 hand-specimen [7524]. The richness of the matrix in ferro- 
 magnesian elements results from the correlated process of 
 basification of the magma, which, however, results also in great 
 part from bodily dissolution of the xenoliths, as proved by their 
 rounded form. The mottled rocks without defined inclusions 
 represent a further stage of intermingling between matrix and 
 xenoliths, and the homogeneous-looking rocks, such as the quartz- 
 diorite first noticed, represent complete amalgamation. 
 
 A full petrographical account of these interesting rocks cannot 
 be given in this place. The interpretion set forth is arrived at in 
 the light of very similar phenomena displayed at numerous localities 
 in the Isle of Skye, where they have been studied in detail. One 
 case of the modification of a granophyre by incorporation of a large 
 amount of gabbro dSbris has already been described.* This is 
 near Kilchrist in the parish of Strath, and it presents a special 
 point of resemblance to the Arran occurrence, in that the rocks are 
 intruded in the form of a broken ring at the edge of a large 
 volcanic vent filled with coarse agglomerate. 
 
 Our observations are not sufficient to warrant the assertion that 
 the basic rock represented by the highly altered xenoliths in Arran 
 has been, as in Skye, a gabbro ; but perfectly typical gabhros are 
 found in the neighbourhord, and are in all respects comparable 
 with those which form larger masses in Skye, Mull, etc. Two 
 specimens of rocks intrusive in the agglomerate of the vent illustrate 
 this : they are from 200 yards S.B. of Creag Mhdr Derenenach 
 [9435, 9436]. The rocks are of average texture, and consist 
 essentially of felspar, sub-ophitic light-brown augite, and irregular 
 grains of black iron-ore. The felspar is a labradorite, with 
 extinction-angles up to 34° in symmetrically cut sections. The 
 
 * Harker, " On Certain Granophyres, modified by the Incorporation of Galibro-Frag- 
 ments, in Strath (Skye)." Quurt. Jowm. Geol. Soc., vol. lii, pp. 320-328, pi. xiii, xiv ; 
 1896. 
 
108 "The Geology of North Arran. 
 
 augite lias a strong striation and sckiller-structure parallel to the 
 basal plane. Olivine is apparently not present. A rock from 
 another locality has all the appearance of a gabbro in which the 
 augite has been completely transformed to green hornblende [7536]. 
 
 One of the most interesting of the Arran rocks is that which has 
 been designated hyperite. It is a very fresh rock of dark aspect 
 and of moderately coarse texture, the pyroxene and felspar Jseing 
 clearly distinguishable in a hand-specimen. An example from, three- 
 quarters of a mile B.S.E. of Glenloig Farm [7530] gave the specific 
 gravity 2-97. In a thin slice it is seen that by far the greater part 
 of the pyroxene is of the rhombic kind, though some augite is also 
 present. The rock might therefore be termed norite. The dominant 
 pyroxene is of pale colour, but always decidedly pleochroic, varying 
 from a reddish to a greenish tint. It may therefore be called bronzite. 
 Both this and the augite show schiller structures, parallel to the 
 pinacoidal and basal planes, but not constantly developed. It is 
 especially noticeable that these minerals have the ophitic habit, a 
 circumstance not common in rhombic pyroxenes. The felspars are 
 perfectly fresh, but show, except at the border of each crystal, a 
 dirty appearance due to very minute inclusions. Carlsbad and 
 albite twinning are found, and the extinction-angles in symmetri- 
 cally cut sections rise to 33° or 34°, indicating labradorite but not 
 one of the more basic varieties. Grains of black iron-ore occur, 
 moulded on the felspar, and occasionally little scraps of biotite 
 clinging about the iron-ore. 
 
 Specimens from Creag-nan-Mult show many points of resem- 
 blance with the preceding, but also certain diflferences, and they 
 may be termed" quartz-hyperite [7531, 7532]. Here the accessory 
 iron-ore is idiomorphic, and apatite becomes a noticeable con- 
 stituent. Augite is abundant as well as bronzite, and there is also 
 a considerable amount of strongly-coloured hornblende, varying 
 from brown to green. The browner kind has proper crystal 
 outlines, and is therefore a primary constituent of the rock, but 
 it often contains a core of pyroxene, about which it has grown 
 with the usual crystallographic relation. The greener hornblende, 
 on the other hand, is evidently formed at the expense of pyroxene, 
 usually if not always of augite, and relics of the latter mineral, of 
 highly irregular form and with intricate boundaries, are often pre- 
 served in the interior. Not only the pyroxene, but the felspar 
 also has a well-marked schiller-structure, the arrangement follow- 
 ing the two pinacoid planes and the basal. Knallj'-, and especially 
 characteristic of this rock, there are interstitial patches consisting 
 of delicate micropegmatite. 
 
 It seems possible that the conversion of augite to hornblende in 
 these latter rocks may be an efiect of metamorphism due to the 
 neighbouring granophyre, but this is not a necessary supposition. 
 
 (iii.) SYENITE DYKES. 
 
 A very unusual type of rock forms an E.-W. dyke 150 yards up 
 AUt-nan-Bireannach, on the south side of Glen Catacol. It is a 
 
Petrography of Tertiary Bocks. 109 
 
 hornblende-syenite. It has a medium texture, the greenish horn- 
 blende and pinkish felspar being clearly distinguishable. A specific 
 gravity determination gave the figure 2'76. In a thin slice [9419] 
 the abundant crystals of hornblende are seen to be well shaped, 
 with the usual habit. They are usually y^ to -^-^ inch in diameter, 
 and are of brown colour, a character not usually found in syenites 
 excepting those rich in alkalies. These idiomorphic crystals of 
 hornblende are set in an allotriomorphic aggregate of felspar, 
 twinned and untwinned ; apparently oligoclase and orthoclase, the 
 latter predominating. The only other constituents of the rock are 
 small scattered crystals of magnetite and rather abundant needles 
 of apatite. 
 
 About 600 yards south of the above dyke is another parallel one, 
 which is highly metamorphosed by the granite. This dyke is men- 
 tioned by Ramsay, who, however, mistook its relation to the 
 granite. The specimen [9414], traversed by a |-inch vein of 
 granite, shows a rock of somewhat coarser texture than the preced- 
 ing, the little black crystals contrasting sharply with the white 
 felspar in which they are imbedded. Under the microscope the 
 rock shows, however, a very decided resemblance to the other. 
 The hornblende crystals, here often ^^inch long, show the same 
 well-shaped outlines, but each is wholly converted into an aggregate 
 of biotite-flakes. There are in addition some rather irregular 
 crystals of pale augite, not found in the former dyke, and these 
 show a partial conversion to biotite but never complete replace- 
 ment. The felspathic element of the rock has much the same 
 characters as before, though it has apparently been recrystallised, 
 and the little needles of apatite are also seen. Imbedded in the 
 clear felspar, but clustering thickly in the neighbourhood of the 
 biotite-aggregates, are a vast number of minute rods, apparently of 
 augite, doubtless a new-formed mineral. Those rods which are 
 actually attached to the biotite-pseudomorphs after hornblende 
 have a parallel arrangement. 
 
 Excepting only the original accessory augite, this rock must 
 prior to metamorphism have been practically identical in character 
 with the other, and the two seem therefore to represent a special 
 group of dykes, certainly older than the granite and not known 
 to cut any other rocks than the schists. The type being quite 
 unlike anything known among British Tertiary igneous rocks, it 
 seems not unlikely that these dykes belong to a much older suite 
 of intrusions. 
 
 (iv.) QUAETZ-PORPHYRY SILLS AND DYKES. 
 
 A suite of specimens from the acid sills of the district shows 
 comparatively little variety among the difierent occurrences. The 
 commonest type is a qua/rtz-porphyry rich in porphyritic elements, 
 which are quartz and felspar, the former usually ^ to ^ inch in 
 diameter, and the latter with a length of ^ to J inch. These are 
 often rather closely crowded in the grey groundmass, which is 
 of fine-texture, no other mineral being evident to the eye except 
 
110 The Geology of North Arran. 
 
 in some examples an occasional flake of dark mica (Drnmadoon, 
 etc.). Thin slices show that the felspar is commonly sanidine, 
 though often accompanied by some oligoclase in addition, Both 
 quartz and felspar, but especially the former, contain abundant 
 minute glass-inclusions, and sometimes larger inclusions of the 
 groundmass, besides having ofteij. a rounded or irregular outline 
 indicative of magmatic corrosion. The biotite is often considerably 
 altered, and its presence is sometimes only to be inferred from 
 brown ferruginous patches. In no case is it abundant. Earely a 
 little crystal-grain of augite is seen [6396]. The groundmass is 
 always micro-crystalline, sometimes having the felspar in little 
 crystals upon which the interstitial quartz is moulded, but more 
 usually with a granular structure and with varying degrees of fine- 
 ness of texture. There is in this common type little or no approach 
 to spherulitic or other intergrowths, though exceptionally we may 
 see a tendency to micropegmatite in a narrow fringe on the border 
 of a felspar crystal [6396]. Rocks answering to the above general 
 description constitute the large sills at Drumadoon Point and 
 Corrygills and numerous others. 
 
 A less common type shows a more evidently crystalline, though 
 still fine-textured, appearance in a hand-specimen, and is without 
 conspicuous porphyritic elements. A thin slice of one of these is. 
 seen to have the character of an ordinary microgranite [6384]. 
 This rock is from the west branch of Urie-Loch Burn in Arran. 
 
 There remain the spherulitic varieties. These, as represented in 
 the specimens, are not conspicuously porphyritic, though the 
 microscope shows a few small crystals of quartz, ^^ to -^-^ inch in 
 diameter, and occasionally a small sanidine. The spherulites are 
 very evident to the eye, owing to their assuming a pale tint with 
 weathering. They are usually not more than -^ inch in diameter, 
 but in some specimens as much as -J- inch. Two specimens 
 [6406, 6407], from near Tormore, have very perfect spherulites 
 exhibiting the black cross with polarised light. They tend to grow 
 round such porphyritic elements as are present. In the former 
 of the two rocks the spherulites are isolated and surrounded by a 
 finely crystalline or cryptocrystalline groundmass. In the second 
 rock the spherulites are more closely packed, with a smaller 
 proportion of interstitial groundmass, which is here microcrystalline, 
 probably owing to recrystallisation. There has been some ferro- 
 magnesian mineral, probably augite, now destroyed and represented 
 only by rather abundant chloritic matter, which shows as little 
 dark patches on the hand-specimen. 
 
 It seems probable, from comparison, that a microcrystalline 
 groundmass in these spherulitic rocks is in general the result 
 of secondary changes. The spherulites themselves seem to have 
 been less readily afiected, but in a number of cases these too appear 
 to have been recrystallised. The radiate structure is not quite 
 lost in the process, but the excessively slender fibres have been 
 destroyed, giving place to irregular narrow sectors, each of which 
 polarises uniformly throughout its extent. A good example of 
 this is furnished by a rock from near the head of Sliddery 
 
Petrography of Tertiarg Bocks. Ill 
 
 Water [6372]. Another specimen [6398] from the neighbourhood 
 of Sliddery Water, illustrates a further stage of alteration and a 
 more complete disguise of the original nature of the rock. The 
 little round spots representing the spherulites are still very- 
 apparent on the hand-specimen, and they are seen as relatively 
 clear areas in a thin slice, but all trace of their radiate structure has 
 been destroyed by the recrystallisation as a granular aggregate. 
 
 The type of quartz-porphyry first described seems to be char- 
 acteristic of the larger sills, while the spherulitic type is exemplified 
 by sills of smaller'dimensions. Oorstorphine* has a like observa- 
 tion. 
 
 The acid dykes have not been studied in such detail as the acid 
 sills, but it is clear that they present petrographically a general 
 correspondence with them. The quartz-porphyry rich in phenocrysts, 
 which appears to be the general type among the large sills, is also 
 represented among the dykes. A specimen [2455] from King's 
 Cove is in all respects identical with those described above, having 
 abundant corroded crystals of quartz, -|-inch in diameter, and of 
 sanidine, often more than |^-inch long. Another dyke-rock [6381], 
 from AUt Dhepin, a mile south of Loch na Leirg, is essentially 
 similar, but with smaller porphyritic crystals. 
 
 Besides these rocks, there are other acid dykes belonging to a 
 different set of intrusions. They are closely associated with the 
 pitchstones, and some of them have arisen by the alteration of 
 rocks which were originally pitchstones. These will be noticed 
 below. ' 
 
 (v.) DOLERITE SILLS, INCLUDING TESCHENITE. 
 
 The basic sills of Arran present some variety of petrographical 
 characters, and doubtless of composition. Zirkelt states that the 
 sills, with the dykes which fed them, are mostly free from olivine, 
 and often carry quartz ; contrasting with the later basic dykes, 
 which are usually olivine-bearing and never contain quartz. 
 Allport,+ who, like Zirkel, behoved the sills to be of Carboniferous 
 age, described an olivine-dolerite from Dun Fion, besides other 
 doleritic rocks from Kildonan and Dippin. Corstorphine§ has also 
 given descriptions of some of the basic sill-rocks in the southern 
 portion of the island, incluciing some quartz-bearing examples. 
 
 While quartz in these rocks is certainly often of foreign origin, 
 it is in some cases a normal constituent. A good example of these 
 normal quartz-do lerites comes from the north side of Glen Dubh. 
 It is of quite coarse texture, and, like some other rocks in this 
 collection, might be equally well named gabbro on petrographical 
 grounds. It closely resembles some of the gabbros of Carrock Pell 
 in Cumberland, or the coarsest portion of the Whin Sill of Teesdale. 
 The augite and felspar are very evident, but the quartz is visible 
 
 * Tscherm. Min. Petr. Mitth., vol. xiv, p. 455 ; 1895. 
 t Zeils. deuts. geol. Ges., vol. xxiii, p. 21 ; 1871. 
 J Qumrt. Journ. ffeol. Soc.j vol. xxx, pp. 562-564 ; 1874. 
 § rscherm. Min. Petr. Mitth., vol. xiv, pp. 460-469 ; 1895. 
 
112 The Geology of North Arran. 
 
 only here and there in small spots. The specific gravity of the 
 rock is 2-87. In a thin slice [2458] the felspar is found to be 
 labradorite, with carlsbad and albite twinning and with strong 
 zonary banding in polarised light, this being a constant feature in 
 normal quartz-gabbros and quartz-dolerites. The pale-brown 
 augite shows occasional striation and schiller-structure, parallel 
 sometimes to the orthopinacoid (diallage-structure), sometimes to 
 the basal plane fsalite-structure). Needles of apatite and irregular 
 grains of black iron-ore occur as accessories ; and there is occasion- 
 ally a flake of dark biotite intergrown with a fibrous light-green 
 hornblende, which in places has been formed at the expense of 
 the augite. Quartz is fairly abundant, partly in interstitial grains, 
 but chiefly in interstitial patches of micropegmatite. The felspathic 
 element ofthe latter is probably orthoclase, but is so turbid as to be 
 almost opaque. 
 
 It is probable that some of the coarse doleritic rocks which are 
 free from quartz contain orthoclase. A rock from Cnoc Ballygown 
 is an example [6389]. It shows interstitial patches of a very 
 turbid, apparently untwinned, felspar moulded upon the zoned 
 plagioclase crystals. In this rock the augite is idiomorphic. 
 Apatite needles and crystals of magnetite are found as usual. 
 Another specimen [6390] has little augite, and is much richer in 
 orthoclase, as if graduating into a felspar-porphyry. 
 
 Other coarse dolerites are of types familiar in many districts. 
 Ilmenite, with encrusting patches of leucoxene, is sometimes found 
 instead of magnetite [6375]. In the niore altered rocks the augite 
 is sometimes replaced by a scaly aggregate of green chlorite. In 
 other cases it has been converted into green hornblende, still 
 preserving a partial diallagic structure [7536]. 
 
 Olivine-dolerites are also found among the sills, as recorded by 
 Allport, though, if our collection is representative, they are in a 
 minority. An example comes from near the bend of AUt Oul- 
 na h-Eildor [6374]. It has not the ophitic, but rather the granu- 
 litic type of structure, and consists essentially of little striated 
 " lath-shaped" crystals of labradorite, with a tendency to parallel- 
 ism in places, pale brown augite, and serpentinous pseudomorphs 
 after olivine. There are a few larger and broader crystals of 
 felspar, and some magnetite and apatite are pi'esent. This rock, 
 forming only a thin sill, is of finer texture-than those described 
 above. 
 
 A peculiar rock is that which forms a large sill in the south- 
 eastern corner of Arran, and may be termed teschenite. It has 
 been described (under the name olivine-bearing analcime-diabase) 
 by Oorstorphine,* but is of sufficient interest to be noticed here. 
 It is represented in our collection by five specimens from Dippin 
 and Kildonan. 
 
 In hand-specimens the rocks appear as ordinary coarse-textured 
 diabases, dark in colour, but with some variation in the relative 
 proportion of black augite and white felspar, etc. A specimen 
 [6361] gave the specific gravity 2-89. Thin slices show a 
 
 * Tsdierm. Min. Petr. Mitth., vol. xiv, pp. 463-465 ; 189.'). 
 
Petrography of Tertiary BocTcs. 113 
 
 typical ophitic structure. Olivine is abundant in irregular 
 crystal-grains, sometimes fresh [6361], but usually replaced 
 by green or yellow-brown serpentine. Apatite is always 
 abundant in little prisms about O-Ol-inch long, or varying 
 fi'om 0-005 to 0-02 inch. Black iron-ore is also rather plentiful in 
 grains and imperfect or skeletal crystal shapes ; probably magnetite 
 for the most part, but in some cases with outlines suggestive of 
 ilmenite. The felspar is in crystals which give elongated 
 rectangular sections, with Carlsbad and albite twinning. It is 
 labradorite, but not usually of a very basic variety. The ophitic 
 plates of augite show in thin slices the light purple colour and 
 decided pleochroism often seen in the augite of nepheline-dolerites 
 and other rocks rich in alkali, and probably indicating a certain 
 content of soda and titanic acid in the mineral. Rotating over a 
 Nicol's prism, the colour is often seen to change from a 
 purplish or pale claret tint to pale apple-green or pale 
 brownish-yellow. In natural light the ruddy colour is some- 
 times seen to pass gradually in one crystal into a pale apple- 
 green, which is also pleochroic. Most of the crystals show, though 
 imperfectly, the hour-glass structure which is so generally associated 
 with augite of this kind. Small flakes of brown mica occur rather 
 rarely in the rock. 
 
 In addition to the foregoing minerals there are abundant wedge- 
 like and irregularly-shaped spaces occupying the interstices 
 between the felspar and other crystals, and often enclosing 
 numerous needles of apatite. These spaces consist in general of 
 analcime, clear, colourless, feebly refringent, and isotropic, rarely 
 with obscure traces of cleavage. In other cases we find patches of 
 zeolites partly or wholly taking the place of the analcime, forming 
 a yellowish aggregate* with more or less pronounced radiate-fibrous 
 structure [6361, 6887, etc.] and, if not too fine, showing brilliant 
 interference-colours. Corstorphine identifies natrolite and scolezite : 
 the former might be derived from the analcime, but the latter 
 would have to come from the felspar. In our slices the fibrous 
 zeolites seem clearly to be formed at the expense of the analcime, 
 and are found only in association with other secondary changes in 
 the rock. The analcime itself has all the appearance of an original 
 constituent of the rock. It is most abundant in the freshest speci- 
 mens, and is there perfectly pellucid and unchanged; in other 
 specimens it is seen in process of conversion to what is probably 
 natrolite. Corstorphine recognises that the analcime cannot be 
 derived from the felspar, which is often quite fresh, but he supposes 
 it to represent vanished nepheline. While this is possible, there 
 is nothing whatever to indicate the former presence of nepheline, 
 and the supposition seems to be based merely upon reluctance to 
 admit analcime to the rank of an original product from a rock- 
 magma. Various researches on the monchiquites and allied rocks 
 during late years render it difiicult to maintain this attitude, and 
 
 * Zirkel seems to have observed, but not identified, this aggregate. He also notes 
 quartz-grains (presumably of foreign origin) in a rock frcm Dippin Head. Zdts. deuts. 
 geol. Ges., vol. xxiii, p. 36 ; 1871. 
 H 
 
114 The Geology of North Arran. 
 
 the balance of probability in the case of our rock is decidedly in 
 favour of the view that the analcime is merely the latest product of 
 consolidation of the magma. 
 
 Specimens from another sill, on Auchenhew Hill, may also have 
 contained analcime, interstitial patches of a radiate-fibrous zeolite 
 being seen in the slices [6886, 6887]. This rock has, however, been 
 altered by crushing and perhaps otherwise, and contains a certain 
 amount of quartz. The augite here has a pale-green or greenish- 
 yellow colour, with in places a basal striation and schiller structure. 
 This rock seems to be the " salite-diabase " of Corstorphine. 
 
 (vi.) MODIFIED BASIC SILLS, WITH XENOCRYSTS, AND COMPOSITE 
 
 SILLS. 
 
 It has been remarked above that most of the quartz which is 
 found in some of the dolerite sills is to be regarded as of extraneous 
 origin and foreign to the normal composition of the rocks. This is 
 most evident as regards the quartz which occurs in the form of grains 
 or rounded and corroded crystals. Derived crystals, or "xenocrysts," 
 both of quartz and of felspar (oligoclase and orthoclase), are found in 
 not a few of the basic sills of Arran, and they present the peculiarities 
 which attach to such a mode of occurrence. The qilartz-grains are 
 surrounded by an envelope of granular augite formed by reaction 
 between the quartz and the basic magma in which it became 
 involved. Most usually this is only a thin crust, but sometimes 
 it attains a more considerable thickness, equal perhaps to half the 
 diameter of the quartz-grain which it surrounds. In this case the 
 augite-granules take on a rather elongated form with a radiate 
 arrangement [6376]. The felspar xenocrysts have usually a very 
 turbid appearance in a thin sUce. 
 
 The reactions between the xenocrysts and the enveloping basic 
 magma necessarily occasioned not only a corrosion of the former 
 but a certain modification of the composition of the latter, in the 
 general sense of acidification ; and there is often sufficient evidence 
 that this action has proceeded far. There has resulted a corres- 
 ponding modification in the products of final consolidation of the 
 magma, which appears in the formation of relatively acid felspars, 
 in a diminished proportion of augite as compared with felspar and 
 iron-ore, and in an excess of silica crystallising as interstitial 
 quartz. The micro-structure of the rock is also modified, the 
 texture often becoming rather fine and the ophitic structure being 
 usually lost. These peculiarities are seen in varying degree in a 
 number of the basic or quasi-basic sills, or in portions of them. 
 Rocks originating in this way may be regarded as in a certain sense 
 abnormal, and they often refuse to range themselves uilder recog- 
 nised petrographical types. 
 
 Closely connected with the frequency of xenocrysts in these 
 rocks, and, like that phenomenon, pointing to a peculiarly intimate 
 relationship as regards origin between the acid and basic rocks of 
 the district, is the occurrence of composite sills and dyhes, in which 
 
 • Loc. cit., pp. 467-469. 
 
Petrography of Tertiary Bocks. 115 
 
 acid and basic rocks form parts of a single intrusive body, and 
 seem to have been intruded almost contemporaneously. The 
 existence of such composite intrusions in Arran seems to have 
 been recognised more or less clearly by Boue* and Delesse.t who 
 describe a sill of quartz-porphyry resting upon, and apparently 
 passing into, one of dolerite at Drumadoon Point (named " Eue 
 Varey"). In late years Corstorphine + has described what is 
 probably a composite dyke in Glen Struey. Composite sills and 
 dykes are known among the Tertiary intrusions of other parts of 
 the Western Isles of Scotland, and it will be suflBcient in this place 
 to refer briefly to two examples. 
 
 The first is a composite sUl at Kildonan Castle, which consists 
 of a central acid member with upper and lower members of basic 
 composition. A specimen from the lower part is a grey, fine 
 textured rock, without evident porphyritic crystals, and gives the 
 specific gravity 2-68. In a thin slice [6358] it is found that the 
 felspars, in little, " lath-shaped " sections about ^n ^^'^^ o'" ^^^s in 
 length, constantly gives quite low extinction-angles. Many of the 
 crystals are striated, and the dominant felspar must be near 
 oligoclase in composition, though orthoclase may perhaps be present 
 in addition. The augite preserves its ophitic habit, but is in great 
 part destroyed. In addition there are abundant little crystal-grains 
 of magnetite, and in places a little interstitial quartz. The rock 
 presents the characters of a partially acidified dolerite, the low 
 density being very significant in this respect. 
 
 A specimen of the middle part of the sill, taken in the same quarry, 
 is a compact-looking rock of light-grey colour, showing scattered 
 slender felspars up to :^-inch long, and containing ovoid druses also 
 about ^-inch in length. A specific gravity determination gave 2 '48, 
 to which some small addition must be made to allow for the druses 
 in the interior of the specimen. A slice [6359] shows that the 
 rock consists essentially of a plexus of little felspars giving " lath- 
 shaped " sections ^h^ to j^ inch long, simple or once twinned, 
 and with sensibly straight extinction. These must be orthoclase, 
 and the rock is in composition a trachyte. Besides the scattered 
 felspar phenocrysts there are a few irregular grains of quartz and a 
 rare crystal-grain of augite, now decayed. 
 
 The other composite sill to be mentioned is the large one in the 
 southern part of Bute. This difiers from all other composite sills 
 and dykes recorded in that it has the basic rock forming the 
 interior part and the acid rock the upper and lower borders. The 
 acid rock seems to have little about it that is abnormal. An 
 example of the upper member, taken east of Uamh Capuill, is of 
 the type already described as characteristic of the larger quartz- 
 porphyry sills of the district. It is rich in porphyritic elements, 
 set in a compact-looking light-grey groundmass. The porphyritic 
 minerals are felspar, (chiefly sanidine) in rectangular or rather 
 rounded crystals up to ^-inch long, and crystals or crystal-grains 
 
 * Ilssai geologique mr VEcosse, p. 296, pi. iv, fig. 20 [1820]. 
 
 t Ann. dps mines (5), vol. xiii, pp. 349, 350 ; 1858. 
 
 X Tscherm Min. Petr. Mitth., vol. xiv, pp. 460-466 ; 1895. 
 
116 The Geology of North Arran. 
 
 of quartz about -l-inch in diameter [4640]. A specimen from south 
 of Barr Hill shows a sharp junction between the acid and the 
 basic rock [2612]. The former has to the eye the same appearance 
 as before, but a thin slice shows that the groundmass is- here 
 spherulitic, the spherulites being of the cryptographic type. 
 
 The basic or quasi-basic portion of this large composite sill is 
 variable in character, and a full description of it is outside our 
 present scope. The normal dolerite constituting the central part 
 has not been examined, but some specimens have been sliced from 
 the modified variety which prevails towards the junction with the 
 acid rock. These are from south of Loch-na-Leighe [4637] and 
 from north-east and east of Uamh Capuill [4639, 4642, 4643]. They 
 show the turbid xenocrysts of felspar and corroded quartz-grains 
 with envelopes of granular augite, as already described. They 
 illustrate also the other peculiarities which we have noticed as 
 accompanying the presence of abundant xenocrysts, viz., abnormally 
 acid felspars, some interstitial quartz, an altered micro-structure, 
 and a finer texture. We may add also another peculiarity often 
 observed in similar hybrid or mixed rocks in other districts, viz., 
 the occurrence of microscopic druses lined with crystalline quartz 
 and filled in with calcite. sometimes also enclosing little needles of 
 actinolite [4637]. A very beautiful rock from the scar at the east 
 end of Loch-na-Leighe deserves more particular notice [2610]. It 
 is a dark evidently crystalline rock without conspicuous porphy- 
 ritic elements, though small quartz-grains may sometimes be 
 detected. A slice shows that it is mineralogically a bronzite- 
 dolerite. The rhombic pyroxene forms abundant idiomorphic 
 crystals, y^-jj- to -gig- inch in length, clear and distinctly pleochroic, 
 with change from a pale rose to a pale apple-green : it is therefore 
 a bronzite rather than a enstatite. The felspar is partly in 
 idiomorphic striated crystals, partly in more shapeless crystal-grains 
 with strong zonary banding between crossed nicols. Augite is seen 
 to be quite subordinate in the general mass of the rock, where it 
 forms little sub-ophitic patches. Needles of apatite and grains' of 
 black iron-ore are accessory constituents. A remarkable feature 
 in this rock is the unusual development of the augite-fringes which 
 surround the enclosed quartz-grains. These have a breadth of from 
 twice to four times the diameter of the quartz-grain itself, and show 
 a very marked radiate arrangement. 
 
 The phenomena of composite sills and dykes in Arran, seem, so 
 far as they have been observed, to be very closely comparable with 
 those in the Isle of Skye, which will be fully described in another 
 place. A special interest, however, attaches to Arran in this 
 connection, from the fact that the peculiar conditions which 
 determine the afmost simultaneous intrusion of basic and 
 acid rocks have here been realised at two distinct epochs. Besides 
 the intimate associations of dolerite and quartz-porphyry which 
 have been mentioned, there are similar associations of augite- 
 andesite and pitchstone (including certain felsitic rocks closely 
 related to pitchstone). The best known examples of these are 
 the composite dykes of Cir Mhdr and Tormore, which have been 
 
Petrography of Tertia/ry Bocks. 117 
 
 noticed from an early time,* and have been fully described by 
 Prof. Judd.t 
 
 (vii.) DOLERITE AND BASALT DYKES. 
 
 The few specimens of basic-dykes chosen for examination scarcely 
 include representatives of more than one type. Four are ophitic 
 oUvine-dolerites, from the following localities : — 
 
 Quarry at E. end of Suidhe Plantation, Bute [2592]; " Eough 
 part of dyke," E. of Port Uisg, Bute [4624]; W. of Runnan 
 Eun Point, Bute [4635]; E. of Einn-S,-Chrubain, Corrie 
 Oravie, Arran [6364]. 
 They are dark medium-grained dolerites of thoroughly basic 
 composition. The first specimen gave the specific gravity 2-98. 
 Thin slices show the following minerals : — abundant olivine-grains, 
 almost always converted to serpentine, green, yellow, or yellowish- 
 brovsTi ; labradorite in little striated crystals giving elongated 
 rectangular sections, usually about 0'03 inch long, but varying 
 in difierent rocks from 0'02 to 0-05 inch; irregular grains of black 
 iron-ore, often wrapping round the felspars; and light brown 
 ophitic plates of augite. ' In one rock [6364] the augite is of a 
 stronger brown colour, with a purplish tone and distinct 
 pleochroism. A rock from " smoother part of dyke," E. of Port 
 Uisg, Bute [4623], differs from the above type only in having the 
 augite in granules instead of in spreading ophitic plates. 
 
 Some dolerite-dykes of the same general type as those described, 
 but apparently devoid of olivine, are older than the granite, 
 and have been metamorphosed by it. One such occurs in the 
 Cnocan Burn, below the old mill-dam. A specimen taken in actual 
 contact with the granite shows in a hand-specimen no noticeable 
 peculiarity, but in a thin slice [7442] it is seen that each ophitic 
 plate of augite has been transformed into an aggregate of green 
 hornblende. Occasionally a flake of brown mica is seen, usually 
 clinging about a grain of magnetite. There is no indication that 
 either the felspar or the iron-ore of the original rock has sufiered 
 any change, and the metamorphism is thus not of an extreme kind. 
 Two dykes 60 or 70 yards from the granite in Glen Sannox Burn, 
 one a dolerite, the other probably an augite-andesite, show a lower 
 grade of metamorphism, the augite being replaced partly by little 
 blades of green hornblende but partly by chlorite [9416, 9417]. 
 
 Although the very numerous basic dykes in Arran have attracted 
 attention from an early time, there is very little published informa- 
 tion concerning their petrographical characters. Some observa- 
 tions, however, are of sufficient interest to be briefly noticed. 
 
 Among the most interesting of the basic dykes are those which 
 pass at the margin into tachylyte, presenting thus a blaclc vitreous 
 
 * Jameson, Mineralogy of the Scottish Isles, vol. i, pp. 81, 102-105 ; 1800. Neoker, 
 Edin. PhU. Trans., vol. xiv, pp. 677-698 ; 1840. Ramsay, Geology of the Island of 
 Arran, p. 26 ; 1841. Br^ce, Geology of Clydes&aXe and Arran, pp. 81, 82 ; 1859. Zirkel, 
 Zeits. deuts. geol. Ges., xxiii, p. 41, pi. ii, fig. 6 ; 1871. Allport, Geol. Mag., 1872, pp. 5, 
 541. Bryoe, Geology of Arran a/iid the other Olyde Islands, p. 164 ; 1872. 
 
 t Quart. Journ. Geol. Soc, vol, xlix, pp. 536-565, pi. xix ; 1893. 
 
118 
 
 Tlie Geoloyy of North Arran. 
 
 selvage, which, however, is usually less than an inch in thickness. 
 An instance in the south-eastern part of Lamlash was noticed many- 
 years ago by Delesse,* and the microscopical and other characters 
 of the glassy rock have been described by Professors Judd and 
 Cole.f Delesse's chemical analyses, quoted in columns I, II, show 
 a practical identity in composition between the basalt and its 
 glassy modification. Another basalt-dyke with tachylyte selvage 
 is found in the Castle grounds at Brodick (see column III.). 
 
 In the memoir just referred to (Etudes sur le mgtamorphisme) 
 Delesse makes some interesting remarks upon the metamorphic 
 efi'ects produced by the basic dykes of Arran in their immediate 
 vicinity, more particlarly upon the granite. Bou6+ had already 
 remarked how the dykes have sometimes broken irregularly through 
 the granite and caught up fragments of it ; and he had regarded 
 
 
 I. 
 
 II. 
 
 III. 
 
 SiOj . 
 
 55-20 
 
 56-05 
 
 53-96 
 
 Al.Og 
 
 16-98 
 
 17-13 
 
 
 FesOs 
 
 11-00 
 
 10-30 
 
 
 
 MnO . 
 
 traces 
 
 traces 
 
 
 
 MgO . 
 
 0-52 
 
 1-52 
 
 
 
 OaO . 
 
 6-80 
 
 6-66 
 
 
 
 NajO . 
 
 . \ 5-65 
 . j by diff. 
 
 f 3-29 
 \ 0-98 
 
 
 
 KjO . 
 
 
 
 Ignition 
 
 3-85 
 
 3-50 
 
 
 
 
 100-00 
 
 99-43 
 
 
 Specific gra-v 
 
 ity . 2-649 
 
 2-714 
 
 2-83 
 
 I. Basalt, centre of dyke 8 inches wide, S.B. of Lamlash Is. ; anal. A. 
 
 Delesse, Ann. des. mines (5) vol. xiii, p. 369 ; 1858. 
 
 II. Tachylyte, selvage an inch thick on edge of same dyke ; anal. A. 
 
 Delesse, ibid. The total is given in the original as 99-53. 
 III. Tachylyte, selvage less than J-inch thick oh edge of dyke at 
 Brodick Castle ; Judd and Cole, Quart. Journ. Geol. Soc. , vol. 
 xxxix, p. 462 ; 1883. 
 
 the stilbite crystals found in the druses of the granite in Garbh- 
 choire and Glen Eosa as a result of infiltration from the basalt-dykes. 
 Delesse § found that the basaltic magma had penetrated and injected 
 the fissures and druses of the contiguous granite and even the micro- 
 scopic fissures of its constituent minerals, imparting a greenish 
 colour to the rock. The orthoclase has thus had its specific gravity 
 raised from 2-532 to 2-591, and its content of water is as much as 
 3-10 per cent., comparing with about one per cent, at a distance 
 from the dyke. The dyke itself was found to contain 3-85 of 
 volatile matter (water with a trace of carbon dioxide) and to have 
 a specific gravity 2-829. It is not quite clear from Delesse's 
 account that the injection of the granite with basic material, as 
 
 * Jim. des mines (5) vol. xiii, pp. 368-370 ; 1858. 
 
 t Quart. Journ. Geol. Soc. , vol. xxxix, pp. iii-46i, plates xiii, xiv ; 1883. 
 $ I^ssai giologime mr I'JScosse, pp. 19, 499 ; pi. v., fige. 25, 26 ; 1820. 
 § Loc. «■(., pp. 366-368. 
 
Petrography of Tertia/ry Rocks. 119 
 
 described, is anything more than infiltration of chloritic decompo- 
 sition-products . 
 
 (viii.) AUGITE-ANDESITE DYKES AND SILLS. 
 
 Among the specimens selected for petrographical examination a 
 well-marked type of sub-basic composition is illustrated by five 
 examples from dykes in the Oumbrae Isles and Arran. The 
 localities are : — 
 
 Devil's Dyke, Great Cumbrae [4581, 4582]; W. of Craig nan 
 Fitheach, Great Cumbrae [4585]; Broad Island, Little 
 Cumbrae [4595]; Dyke 'in intrusive sill, roadside, Dippin 
 Quarry [6362]. 
 
 These rocks are nearly black and of fine texture, with small 
 scattered felspar crystals or sometimes more abundant crystals and 
 crystal-groups up to -f-inch long. Nos. 4582 and 6362 both gave 
 the specific gravity 2 '70. 
 
 Thin slices show that these rocks are augUe-andesites with a 
 glassy base. The porphyritic crystals are labradorite. The little 
 felspars of the groundmass, presenting striated " lath-shaped" 
 sections usually about 0'01-inch long, are acid labradorite or 
 andesine-labradorite. Augite, of light-brown colour, occurs in 
 little granules, and there may be a few crystals of an earlier genera- 
 tion with perfect outlines and a length of 0'02 or 0'03 inch. Little 
 granules of magnetite are found, but not abundantly. Occurring 
 interstitially among these elements is a considerable amount of 
 glassy base of a brown colour. Sometimes it is merely a globulitic 
 glass [4581] ; more usually it encloses abundant minute 
 crystallitic elements in the form of felspar fibres and little rods and 
 granules of opaque iron-oxide. Very noticeable is the uneven 
 distribution of the glassy base, which shows a tendency to collect 
 in patches in certain places. 
 
 These dykes clearly belong to the "younger augite-andesites " of 
 Prof. Judd,* a group which that geologist assigns to a late epoch 
 in the history of Tertiary igneous activity in Britain. He has 
 describedt one rock of this group from Cir Mh6r in Arran, and has 
 given a chemical analysis of it, which we quote below ('column 
 "VIZ., p. 124). This rock forms the two marginal members of a 
 triple composite dyke, of which the central member consists of 
 pitchstone ; and in general this group of augite-andesites seems to 
 have a peculiarly intimate relationship with the pitchstone group, 
 which points to community of origin. The glassy base of the 
 andesites has probably a composition similar to that of the pitch- 
 stones, and there are, as Prof. Judd has remarked, many 
 indications of a tendency for this glassy residue to become in part 
 separated from the crystalline portion of the rock. 
 
 A somewhat difierent type is represented by a conspicuously 
 porphyritic andesite from a dyke in Millport Harbour, Great 
 Cumbrae [4575]. This contains closely-set porphyritic elements 
 
 " Quart. Jmrn. Gfeol. Soc, vol. xlvi, pp. 371-381 ; 1890, 
 t Ibid., vol. xlix, pp. 547, 548, pi. xix, flg. 2 ; 1893. 
 
120 The Geology of North Arran. 
 
 |- to ^ inch in length, mostly of felspar, but including also black or 
 dark-green pseudomorphs, which are seen in the slice to be augite 
 crystals replaced by green chlorite. The porphyritic felspars are 
 of medium labradorite. The ground-mass consists of little striated 
 felspars, decayed augite, rather abundant granular magnetite, and 
 a light-brown interstitial mass, which seems to have been a 
 globulitic glass full of felspar fibres and other crystallites, but is 
 now considerably altered. There are little irregularly-shaped 
 amygdules, lined with chlorite and occupied by chalcedonic quartz 
 or hj calcite. This rock is probably to be attached to the augite- 
 andesites rather than to the basalts, and represents one of the 
 varieties richer in crystallised elements, and therefore more basic 
 in composition than the foregoing. 
 
 One specimen only among the collection of sill-forming rocks 
 seems to belong to the andesites. It is a dark close-grained rock 
 from near the head of Allt-na-Slaic in the southern part of Arran ; 
 and, as it is described as intrusive in a felsite, it is presumably to 
 be referred not to the epoch of the basic sills but to a later time, 
 probably that of the andesite dykes. In seems to have had a fair 
 amount of glassy base, but is now too much altered for any close 
 examination [6379]. We may further note an andesite intruded 
 in the form of a thin band in the schists west of Creag Eosie, in 
 Glen Eosa [9405]. 
 
 (ix.) PITCHSTONES AND DEVITKIFIED PITCHSTONES. 
 
 Since Jameson* more than a hundred years ago gave descriptions, 
 in the Wernerian fashion of the time, of several varieties, the 
 pitchstones of Arran have become more widely known than any 
 other group of rocks in the island. This is owing especially to 
 their very beautiful micro-structure, which has been made familiar to 
 all geologists by the descriptions of. Sorby,t Zirkel,t Allport,|| 
 Vogelsang,§ Teall,ir Judd,** Eosenbusch,tt Oorstorphine,!! and 
 others. Since the rocks are so well known, and specimens are to 
 be found in most collections, a brief account will be sufiicient in 
 this place. 
 
 The specimens selected for examination are dark-grey or greenish- 
 grey rocks, sometimes almost black, with the characteristic resinous 
 lustre. They show usually only small crystals visible to the naked 
 eye, rarely more than ^J-inch in length, and often rather sparingly 
 scattered. There are, however, some conspicuously porphyritic 
 pitchstones in the island, as described from Brddick Castle, 
 Invercloy, and Cir Mhdr. Thin slices show under the microscope 
 
 * Outline of tJte Mine}'alogy of the Skedaiid Islands and of the Isla^id of Arraiij pp. 76-82 ; 
 1798. 
 
 t Quart. Journ. Geol. iSoc, vol. xiv^ pp. 476, 477, pi. xviii ; 1858. 
 
 t Sitz. Aiad. Tl'ijs. Wien., vol. xlvii, pp. 260-262., pi. ii, iii ; 1863. Zeits. devis. geol, 
 Ges., vol. xlx, pp. 785-788, pi. xiv ; 1867. Ibid., vol. xxiii, pp. 42-46 ; 1871. 
 
 II Geol. Mag., 1872, pp. 1-10, pi. i, and pp. 536-545. Hid., 1881, p. 438. 
 
 § Die Ktystallilen, pp. 122-126, pi. xiii, xiv ; 1875. 
 
 '^ British Petrography, pp. 344-347, pi. xxxiv ; 1888. 
 ** Quart. Jou/rn. Geol. Soc, vol. xlix, pp. 536-564 ; pi. xix. 
 
 ft Mikroskopische Physiographic der masdgen Gesteine, pp. 699-702, of 3i'd ed. ; 1896 
 U Tscherm. Min. Fetr. Mitlh. (2) vol. xiv, pp. 448-451 ; 1895. [Sheet 13.] 
 
Petrogrwphy of Tertiary Books. 121 
 
 that the general body of the rock consists of a glass more or less 
 crowded with minute crystallites. These are of two orders of 
 magnitude, the larger easily visible, the smaller appearing with a 
 low magnifying power only as a pigment, colouring and rendering 
 turbid the glassy matrix. There are thus four sets of elements in 
 the rocks — the porphyritic crystals, the larger crystallites, the 
 smaller crystallites, and the glassy base, the last enclosing the rest 
 and constituting the principal part of the bulk. 
 
 The porphyritic crystals embrace quartz, felspars, augite,* and 
 magnetite, all with idiomorphic outlines, excepting only when they 
 are aggregated in groups, as is frequently seen. In this case the later 
 crystallised minerals are moulded upon the earlier, and it is seen 
 that magnetite has preceded augite, and both have preceded the 
 quartz and felspars. Apatite is found rather rarely. The quartz is 
 in pyramidal crystals, sometimes rounded at the angles and often 
 having considerable inlets of the groundmass. Both quartz and 
 felspars also contain glass-inclusions, and the glass often encloses 
 minute crystallites.f The felspar is partly striated oligoclase, 
 partly what looks like sanidine ; but the latter, as remarked by 
 Prof. Judd,has sometimes a vague appearance of very fine lamellation 
 which is suggestive of cryptoperthite. The augite is in crystals 
 with the usual octagonal cross-section, and is of a light-green 
 colour. 
 
 The larger crystallites are in the form of minute rods (microlites) 
 or needles, tapering at one end (belonites of Zirkel), and are 
 constantly transparent and of green colour. The belonites are 
 often aggregated into radiate groups, joined at the base, but not so 
 regularly developed as to form perfect stars. Again, they grow 
 attached to, and set perpendicularly upon, the faces of the porphy- 
 ritic crystals, so as to appear in the slice as a thick fringe. These 
 larger crystallites themselves have in turn served as starting-point 
 for the growth of the much smaller crystallites of what we have 
 styled the second order, and in this way have been built up 
 elaborate fern-like and arborescent growths which give a very 
 remarkable appearance to a thin slice of any of the Arran pitch- 
 stones. The mineralogical nature of the green microlites and 
 belonites in these rocks has been the subject of some ^discussion. 
 In the specimens examined by us the mineral, whenever sufficiently 
 characteristic, seems to be hornblende. The extinction-angles 
 observed were in all cases low, and pleochroism is often to be 
 detected. It is possible that augite occurs in some of the Arran 
 rocks not examined, and indeed Rosenbusch has noted in some 
 cases, though rarely, extinction-angles up to 35°. The largest 
 crystallites show in cross-section characteristic crystal outlines, 
 which are those of hornblende. They are, as Mr. Teall+ has 
 remarked, hollow, the glassy core corresponding in shape with 
 the exterior. In size these larger crystallites vary in different 
 
 * Corstorphine records a rhombic pyroxene as occurring, subordinate to augite, in a 
 pitchstone in An Sloe, in the southern part of the island. 
 
 ' -j- jSeeSorby, I.e., pi. xviii, figs. 57-63 ; Teall, British Petrography, p. 19 (in felspar) 
 and Zirkel, I.e., 1867, pi. xiv, figs. 16-22 (in quartz). 
 J L.c, p. 345, pi. xxxiv, fig. 4. 
 
122 The, Geology of North Arran. 
 
 rocks and also within a certain range in a given rock. In different 
 specimens they have a length of '005 to '01 inch or •01 to "02 inch, 
 with a width rarely more than '0002 or -0003 inch. There are 
 often, however, a few rather larger rods, up to '04 or "05 inch in 
 length. As a rule, these largest crystallites do not, like the rest, 
 act as the trunks of arborescent and other complex growths. 
 
 The much more minute crystallitic growths, which represent the 
 latest effort of crystallisation in the pitchstone magma, occur in two 
 ways — disseminated uniformly through the glassy matrix and 
 clustered thickly upon the larger and earlier crystallites to form 
 complex arborescent and other aggregates. In the former case 
 they impart to the general matrix a yellow colour and a somewhat 
 turbid aspect in a thin slice, an appearance resolved by the use of 
 a higher magnification. It is then seen to be due to the presence 
 of an immense number of excessively minute bodies usually in the 
 shape of short rods. With the short rods there may be still smaller 
 bodies in the shape of globulites, and less commonly the globulites 
 occur alone or almost alone [2448, 2451]. The complex growths 
 built up by the aggregation of the minute crystallitic elements 
 about the larger ones assume various forms. A very characterisric 
 one resembles exactly a pine-tree, of which the trunk is made by a 
 belonite and the foliage by a vast number of the smaller bodies. 
 Another beautiful shape is made up by two or three rather small 
 rod-like crystallites of the first order, crossing one another at their 
 middle points, with their four or six extremities bearing complex 
 plumose growths, which unite to form in sfection a feathery circle 
 having the little rods as diameters. These two forms are well 
 illustrated by specimens from Corrygills and Tormore respectively, 
 and have frequently been figured* The mineralogical nature of 
 the more minute crystallites cannot be investigated directly, for, 
 excepting their greenish-yellow colour, they do not exhibit any 
 optical properties. It may be inferred, however, with high 
 probability, that they are of the same nature as the larger 
 crystallites, and therefore of hornblende. Those which take part in 
 the complex growths have the same appearance as the trunks of 
 the same growths. Further, it cannot be doubted that the minute 
 crystallites disseminated through the glass are identical with those 
 in the aggregates; for an invariable feature of these rocks is a ring of 
 clear colourless glass surrounding each complex growth, as if the 
 fine crystallitic matter which would otherwise have been scattered 
 through this space had been abstracted to make up the aggregate 
 in thQ centre. 
 
 The glass itself, apart from the minute crystallitic bodies with 
 which it is charged, is always clear, colourless, and structureless. 
 It does not, as a rule, show any perlitic structure. Indeed the 
 " pitchstones," such as those of Meissen in Saxony, which show best 
 this breaking up by minute curving fissures due to contraction, are 
 mostly lava-flows, while these Arran rocks occur exclusively in the 
 form of dykes and intrusive sills. There are, however, exception^. 
 A specimen [2451] from a dyke at Oaisteal Abhail shows very 
 
 * See, e.g., Cohen'a Sammlung von Mikrophotographieii, pi. iv., fig. lof 3rd ed., 1899. 
 
Petrogra/phy of Tertiary Rooks. 123 
 
 perfect perlitic fissures, which mostly occur immediately sur- 
 rounding phenociysts of quartz and sometimes of felspar. 
 
 Many of the rocks show no evident indication of flowing 
 movement in the magma subsequent to the beginning of 
 crystallisation ; but in others fluxional phenomena are seen, and 
 are of various kinds. Sometimes the porphyritic crystals of 
 felspar are arranged with their long axes parallel to the direction of 
 flow ; less commonly the larger crystallites and crystallitic 
 aggregates exhibit alike orientation [111, 6392]. Again, in some 
 examples from Tormore [5656, 5657] and elsewhere the matrix of 
 the rock is finely banded, the narrow bands following flow-lines, 
 and being visible as an alternation of fine darker and lighter stripes 
 upon a hand-specimen. In the slices this appearance is seen to 
 arise from the unequal distribution of the crystallites through the 
 glassy matrix. Stellate, plumose, and other groupings occur 
 abundantly in certain bands and only sparsely in others. The 
 more minute crystallitic elements are perhaps equally plentiful in 
 the two cases ; bnt in the former they are aggregated, leaving the 
 glassy matrix clear, and in the latter they are dispersed, producing 
 a cloudy yellowish appearance. 
 
 The pitchstones of Arran, with those of the other western islands 
 of Scotland and of the north of Ireland, difier from all other known 
 acid rocks in their richness in crystallites of a ferro-magnesian 
 silicate. Though always present, these are not always equally 
 abundant, and the difierences may be connected with diflereuces 
 of chemical composition. It is also to be remarked that some of 
 the rocks do, and others do not, carry porphyritic quartz. The 
 analyses which we quote of pitchstones and rocks closely connected 
 with fchem from Arran show a certain range of chemical composition, 
 some of the rocks being acid and others sub-acid. Our specimens 
 selected for examination probably belong for the most part to the 
 truly acid type, but one, picked out fr«m the rest on account of its 
 richness in the ferro-magnesian element, is perhaps a sub-acid rock. 
 It is from a sill at Brodick school [7537]. It does not difier 
 notably from the rest in appearance in a hand-specimen, except 
 that it has a more decided black colour ; but its specific gravity is 
 found to be at 2 '45, while a more ordinary variety from Corry gills 
 [110] gives only 2 '34. In a thin slice this Brodick rock shows a 
 plexhs of closely packed fine fibres imbedded in a brown glass. 
 The fibres seem to be, at least in general, of felspar, and the larger 
 ones show a central core of glass. The smaller are arranged in 
 parallel groups attached to the larger and grown nearly at right 
 angles to them, but there is no special orientation of the groups 
 thus built up. The crowding of these crystallitic elements makes 
 it difficult to examine the interstitial glass, but the brown colour 
 is probably proper to the glass itself and not merely due to 
 globulites. 
 
 Doubtless other pitchstones of sub-acid and intermediate composi- 
 tion occur in Arran. Delesse* mentions a thick sill in the red 
 sandstones which gave the specific gravities 2'532 and 2'548 in the 
 
 * Ann, del mines (5) vol. xiii, p. 356 ; 1858. 
 
124 
 
 The Geology of North Arran. 
 
 
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Petrography of Tertiary Bocks. 125 
 
 I. Pitchstone, Arran ; anal. T. Thomson, Outlines of Mineralogy, vol. i, p. 
 
 392; 1836. 
 n. Pitchstone, Arran ; anal. J. H. Player, in Teall's British Petrography, 
 p. 347 ; 1888. 
 
 III. Pitchstone, Tormore, probably the N.-S. dyke; anal. M. M. Tait, in 
 
 Bryoe's Geology of Arran, p. 203. 
 
 IV. Felsite ("olaystone"), Tormore, probably from the southern composite 
 
 dyke ; anal. M. M. Tait, ibid. 
 V. Porphyritio Pitchstone, centre of Cir Mh6r dyke ; anal. E. C. Thomson, 
 
 Quart. Joum. Oeol. Soc, vol. xlix, p. 545 ; 1893. 
 VI. Quartz-Felsite, centre of same dyke ; anal. .1. A. Schofield, ibid. Con- 
 tains a trace of sulphur (in pyrites). 
 VII. Augite-Andesite, outside of same dyke ; anal. J. A. Schofield, ibid. 
 The last item in the column includes 0'45 of sulphur. 
 VIII. ' ' Hornstoue " nodule in pitchstone dyke. King's Cove ; anal. J. A. 
 Phillips, Geol. Mag. 1872, p. 540. The mean of two analy.ses ; of 
 the water 2 '37 was moisture. 
 IX. Red Felsite or ' ' hornstone " forming part of the same dyke ; anal. J. 
 A. Phillips, ibid. The mean of two analyses ; of the water 1 '32 was 
 moisture. 
 X. Spherulitio Felsite, dyke on Corrygills shore ; anal. J. A. Phillips, 
 Md. The mean of two analyses ; of the water 0'65 was moisture. 
 
 centre and at the margin respectively. The corresponding 
 percentages of water were only 1'65 and 1'75, which are remarkably 
 low figures. 
 
 Numerous geologists have noticed the occurrence in Arran of 
 felsitic rocks in close association with pitchstones. In the older 
 literature these rocks figure usually under the names "hornstone" 
 and " claystone." Some which have been analysed (see columns IV, 
 VI, VIII, IX, above) have a chemical composition not essentially 
 difierent from that of the pitchstones, and the intimate association 
 of the two rocks decidedly suggests that they are closely cognate 
 and are in some cases parts of the same rock-body, the one having 
 assumed a finely crystalline and the other a vitreous state. 
 Assuming this, it remains a question to be considered in any given 
 case whether the finely crystalline texture is original or is the result 
 of devitrification of a pitchstone. In an example on Cir Mh6r 
 carefully studied by Prof. Judd, that writer arrived at the former 
 conclusion,* but the other alternative may be entertained in 
 other instances. The remarkable micro-structure of the pitchstones 
 may not improbably become obscured or obliterated by secondary 
 changes when the glassy character is lost, and the absence 
 of perlitic fissures in most of the Arran pitchstones usually 
 precludes a criterion which has often been relied upon in other 
 districts as indicating a formerly vitreous condition in rocks now 
 cryptocrystalline or microcrystalline. 
 
 There are nevertheless specimens in our collection which give 
 many indications of having originally been pitchstones and having 
 lost their glassy texture, though the alteration evinced has been 
 in general of a more radical kind than mere devitrification. 
 
 An interesting specimen comes from a quarter of a mile N.E. of 
 Kilmichael, Glen Cloy [7539]. It is a dull-grey, compact rock, 
 with numerous minute white spots, which look like spherulites. 
 
 * Quart. Joum. Geol. Soc, vol. xlix, p. 551 ; 1893. The expression " primary devitri- 
 fication " in this connection seems to be confusing, since devitrification is predicable only 
 of what was once a glass. 
 
126 l^he Geology of North Arran. 
 
 A thin slice shows in natural light a vast number of little needles 
 answering exactly to those seen in the pitchstones (Zirkel's 
 belonites), but replaced by some chloritic or ferruginous substance. 
 There are also abundant relics of the more minute crystallitic bodies 
 attached like branches and twigs to these trunks, though the 
 delicate arborescent growths which have probably been present 
 have been in great measure destroyed, and clotted patches of the 
 same ferruginous material represent the destroyed crystallites. 
 Polarised light shows that the groundmass is not glassy, but 
 consists of irregularly interlocking and interlacing crystalline 
 areas. An imperfect radiate arrangement is seen in places, but no 
 complete spherulites. The rock has probably been a pitchstone, 
 and has undergone devitrification and other changes. Some little 
 interstitial areas of clear quartz must be regarded as of secondary 
 origin. 
 
 A specimen from a dyke north of Tor Eigh Mdr [6405] is a 
 dull compact rock mottled with pink and white streaks and with 
 little scattered quartz crystals. It has something of a fissile 
 structure, corresponding with very evident fluxion-lines. In the 
 slice we see well developed perlitic fissures traversing the rock 
 everywhere, and, with other circumstances, leaving little doubt that 
 it has been originally a pitchstone. There are still little irregular 
 brown patches which are dark between crossed nicols, and are 
 crowded with what have presumably been crystallites, now replaced 
 by reddish-brown ferruginous matter. The rest of the slice shows 
 double refraction in a blotchy irregular fashion. In natural light 
 there are clearer spots, often coalescing with darker yellowish 
 interspaces. The spots often polarise as individuals. Another 
 rock, comparable with this, comes from Termor e [6404]. This 
 also shows marked flow-structure, with bands of pale green and 
 pale yellow. It has a very compact, almost porcellanous, appearance, 
 and is one of Jameson's hornstones. There are here no perlitic 
 fissures, except occasionally surrounding the little porphyritic 
 crystals. In natural light the appearance is otherwise very similar 
 to that of the preceding rock, the clearer spots and yellow inter- 
 spaces being strongly marked. Between crossed nicols, however, 
 the groundmass breaks up into a much more fine-textured 
 aggregate than before. The blotchy or spotted appearance of these 
 and similar rocks seems to be connected with changes other than 
 mere devitrification. There are, however, rocks which show no 
 such peculiarity, and in which the only noticeable change from the 
 presumed original pitchstone is the resolution of the glass into 
 minutely crystalline elements. 
 
 There are other cases of the association of felsitic rocks with 
 pitchstones in which the two rocks must be considered to represent 
 distinct intrusions. An instructive example is a rock from a dyke 
 in Glen Dubh, 100 yards above its junction with Glen Ormidale. 
 This is a light-grey, compact rock with minute quartz-grains, 
 enclosing rounded patches up to |-inch diameter of a darker grey 
 colour. These patches are seen in the slice [7540] to be of the 
 same general character as the matrix, both having a very finely 
 
Petrogrofhy of Tertiary Bocks. 127 
 
 crystalline texture, though with rather different structures. The 
 grey matrix includes, however, other and smaller dark patches, 
 which have all the appearance of a pitchstone under the microscope, 
 except that the glassy base is devitrified, and only the larger and 
 stouter crystallitic bodies retain their shape and groupings. 
 
 One well-known dyke on Oorrygills shore may be mentioned 
 here as being associated with the pitchstones, though there 
 is nothing to indicate that it has itself been vitreous. 
 Since the rock has been described and figured more 
 than once,* no detailed account is necessary here; the 
 chemical composition is shown above in column X. It is a 
 spherulitic felsite of dull-grey aspect, ■ the little spherulites 
 appearing in our specimen [3323] as dead white spots -ji,;^ to ^ inch 
 in diameter, often with a dark nucleus and a dark border. There 
 is a flow-structure, partly marked by lines of spherulites. The 
 appearance in a thin slice, and especially the blotchy or spotted 
 character already remarked in other rocks, are well shown in Mr. 
 Teall's coloured plate, and the rock seems to have suffered alteration 
 of the kind already pointed out in other cases. The spherulites, 
 which make up most of the bulk, have had their radiating fibres 
 replaced by irregularly interlocking narrow sectors, or in the 
 central portion by a merely granular aggregate. This latter 
 structure is seen also in the interspabes between the spherulites. 
 In our specimen, from the edge of the dyke, the flow-lines are seen 
 to run uninterruptedly through the spherulites. 
 
 * Allport, Geol. 'Mag., 1872, pp. 540, 541 ; Bonney, Oeol. Mag. 1877, p, 506, with fig. ; 
 Teall, British Petrography, plate xxxix, fig. 1 ; 1888. 
 
 A. H. 
 
CHAPTER XIl. 
 
 Faults. 
 
 We can notice here only the most important of the numerous 
 faults, some of which have been treated of in the descriptions of the 
 various formations. 
 
 Great Cum brae Paul t. — This fault runs almost due north 
 from the eastern margin of Millport Bay to the northern end of the 
 island, and has a large downthrow to the west, probably of more 
 than a thousand feet. It affects both the Carboniferous and Old 
 Eed Sandstone formations and is a marked feature in the geology 
 of the island in that its position coincides almost exactly with one 
 of the important roads. This happens because the road has been 
 formed in a kind of depression of the ground, no doubt due to the 
 fault. In the northern part of its course the western or downthrow 
 side forms the higher ground, while in the opposite direction it is 
 the eastern side that is most prominent, and this line of higher 
 ground is prolonged to near Farland Point. To this line of fault 
 we owe the straight eastern boundary of the bay, and it seems 
 clear that its age is subsequent to that of most of the intrusive 
 igneous rocks of the island. 
 
 Highland Border Fault in But e. — This crosses the 
 island of Bute from Rothesay to Ardscalpsie Point in a valley a 
 great part of which is occupied by lochs at a low elevation. It has 
 a large and variable downthrow on the south-east side, and in the 
 part with which we have to deal throws down on the the west side 
 of Scalpsie Bay Lower Carboniferous rocks against the schist, so 
 that the fault is, in part at least, later than Old Red Sandstone 
 times, On the upthrow side of the fault is a remarkable relic of 
 the denudation of the district in a conical hill called the Haystack. 
 This is surrounded by the raised beach due south of Ardscalpsie 
 House, and is about 20 yards in diameter and 25 feet high, 
 composed of coarse conglomerate, mainly of large angular schist 
 and of vein-quartz fragments. There is not much indication of 
 bedding, but on the east side the blocks are arranged as if dipping 
 to N.N.W. This is the basement portion of the Old Red Sandstone, 
 resting unconformablj' on the schists and mainly composed of the 
 debris of those rocks. 
 
 Boundary Fault in Arra n. — There is not clear evidence 
 that the boundary between the schists and the Old Red formation 
 in Arran is everywhere a fault, but the general evenness, and in 
 some cases straightness, of the line of junction is not in favour of 
 its being natural. On the other hand, there is a general absence 
 of signs of great disturbance or crushing along the line of junction 
 
Faults. 129 
 
 except in a few places. It is pretty clear that the line is a faulted 
 one at Dougrie, and in the small burn south of Beinn Lochain 
 there appears to be a fault breccia, Then in the Garbh Allt above 
 Moniquil the rocks of Old Red Sandstone ar£i striking at the line 
 of junction, as they do also to some extent on the south side of 
 Glen Rosie. In the Cnocan Burn the junction is hidden under 
 glacial drift. North of Maol Donn the boundary must turn almost 
 at right angles and run nearly north-west for about three miles, 
 but it has been obscured by the intrusion of granite except for a 
 short distance east of Cioch nah-Oighe. From the north side of 
 Glen Sannox the junction runs almost due north to Oorloch, and 
 here it is undoubtedly a fault, for there occurs on the upthrow side 
 a mass of brecciated rock, triangular in outline, some 150 yards in 
 the side. This rests unconformably, dipping at a gentle angle north- 
 ward, on the highly dipping lavas of supposed Arenig age, and is 
 opposed to the ordinary sandstones and conglomerates of Old Eed 
 age dipping at a steep angle on the eastern side of the fault. At 
 the foot of the crag several other faults occur and the district is 
 very complicated. A large north-west fault throws out the Old 
 Red Sandstone entirely and brings down the Lower Carboniferous 
 beds against the old lavas and schists. Farther north-west, and 
 between two faults with a northerly trend, we find the upper beds 
 of the Old Red formation brought up again, and also the cornstones 
 and lowest beds of the Carboniferous formation in a very striking 
 hill. These two faults, which have each a large downthrow to the 
 east, disappear northwards under the sea, and may be connected 
 with the Ardscalpsie fault in Bute. Westward we appear now to 
 have two large faults running to the north-west, one of which is 
 entirely in the schist and the other, which is nearest to the sea, forms 
 the boundary between the schists and the Carboniferous rocks 
 exposed on the coast. The strike of the latter brings in succession 
 higher and higher beds of the formation against the fault, till at last, 
 west of the Cock, we have not only the Coal-Measures but also the 
 unconformable Triassic sandstones brought down by the fault against 
 the metamorphic rocks. This main fault runs out to sea at the 
 foot of the stream called Allt Mor, east of North Newton, and on 
 the eastern side of the stream is another and nearly parallel fault. 
 Between the two is a narrow strip of the Upper Limestone series 
 of the Carboniferous formation. 
 
 Sannox Fault s. — There are many faults large and small in 
 the Old Red Sandstone of the Sannox district, but only a few of 
 them can be noticed here. Perhaps the most important of these is 
 that which passes west of the crag from which the Fallen Rocks 
 have come. Towards the north it joins the boundary^ fault as 
 already described, and near the Ordnance Station 664 it is joined by 
 a fault which comes southward from the shore and there repeats 
 the cornstone at the base of the Carboniferous formation. It is the 
 largest fault which crosses the Upper Old Red Trap. United, these 
 two faults run southward as one to North Glen Sannox, forming a 
 marked feature for a considerable distance. The fault is probably 
 prolonged to South Sannox, as the mudstones of the Lower Old 
 
130 The Geology of North Arrati. ' 
 
 Eed formation appear everywhere faulted against the felspathic 
 grits which naturally overlie them. West of Parchan Mor, along 
 this line the large dolerite dyke is apparently shifted some 200 
 yards to the north on the downthrow side; the grits and mudstones 
 so far as can be observed have not the same strike, and the mud- 
 stones near the line have a higher dip than is usual. 
 
 Oorrie Fault s. — There are three large and important faults 
 in the Oorrie district which have nearly parallel courses in a 
 N.N.W. direction, and all throw down eastward. The most easterly 
 of these is visible in Oorrie Ohurch Burn, where it throws the 
 Oarboniferous Traps against the Upper Old Eed rocks. It shifts 
 the outcrop of the trap half a mile to the southward and must 
 have a downthrow of several hundred feet, but in a southerly 
 direction it divides into several branches forming a series of step 
 faults. The next large fault shifts the trap about three quarters of 
 a mile farther south, and has a downthrow greater than the total 
 thickness of the Oarboniferous formation — probably as much as 
 1500 feet. The nearly parallel fault west of Maol Donn throws out 
 nearly the whole of the Oarboniferous rocks for a long distance, but 
 it is more nearly in the direction of the strike than the other two. 
 
 Brodick Ohurch Fault. — West of the church at Brodick 
 a large fault with a southerly course shifts all the Oarboniferous 
 Eocks on to the hillside to the southward. It has a large throw 
 down eastward greater than the thickness of the formation, but as 
 this is here much attenuated and probably not greater than 600 
 feet in thickness, the fault is not so great as it at first sight 
 appears. 
 
 Gleann Dubh F a u 1 1 s.— The N.N. W. fault at the east end 
 of Creag nam Fitheach has a large downthrow east, perhaps 1000 
 feet, and brings a high part of the Trias against lower beds. Its 
 course southwards is somewhat uncertain, but northwards it is 
 probably joined by other faults from the west, and increasing in 
 throw becomes connected with the east and west fault north of the 
 glen which throws down the Trias against the Lower Old Eed 
 rocks. The. New Eed Sandstone of Oreag nam Fitheach is striking 
 against the triangular patch of Oarboniferous rocks and must 
 obviously be separated from it by a fault, while that which bounds 
 the Oarboniferous on the west is visible in the stream at the west 
 end of the crag formed by the volcanic zone. The fault with large 
 downthrow east, at the west end of Oreag nam Fitheach, passes 
 southward to Benlister Glen where several faults running north 
 are visible in the stream to the east of the small Coal-Measure 
 area. The main throw down east, however, appears to be in the 
 fault which goes off to the southward. 
 
 Oorriegills Faul t. — Several faults have been noticed in the 
 account of the Oorriegills shore section. The largest of these 
 which throws down the Springbank conglomerates on the west 
 against the lower false-bedded sandstones on the east is visible on 
 the shore and in the cliff. Its south-westerly course inland is 
 inferred from the fact that conglomerate bands which crop out on 
 the north side of the Clauchland Hills appear to be cut off on the 
 
Ages of Faults. 131 
 
 west and do not reach the Birk Glen, and the patch of Keuper- 
 marls cannot have a natural boundary on the east side. It also 
 appears to be faulted on the west side. 
 
 Ard Bheinn Faul t. — The large fault on the west side of 
 Ard Bheinn is a continuation of one in the sheet to the south 
 which has a large downthrow west, bringing Triassic rocks against 
 Old Eed Sandstone. By it the outcrops of various subdivisions 
 are shifted a long way to the northward on the west side, but the 
 actual position of the fault has been subsequently obscured by the 
 intrusive rocks of the volcanic vent. 
 
 Monyquil Fault s. — The great mass of Old Red conglom- 
 erates forming the hill of Garbh Thorr is bounded by faults on 
 either side, and both have large downthrows to the west. The 
 most easterly of these is probably near the Garbh Allt, though 
 nowhere visible. The conglomerates dipping at high angles are 
 striking against the rocks in the stream which apparently belong 
 all to the lower series of beds which underlie the trap. The more 
 westerly large fault shifts the outcrop of the volcanic zone and the 
 conglomerates, and has probably a downthrow south-west of 1500 
 feet. Though its direction is somewhat different it may be con- 
 nected with the Ard Bheinn fault before mentioned. 
 
 Ages of Faults. — Some of the faults which affect the 
 metamorphic rocks may be of very old -date, but their age cannot 
 be proved. Reference has been already made to physical features 
 due to faults in the Pirnmill or Penrioc neighbourhood. There 
 are others south of the lorsa valley about Beinn Lochain. Such 
 features are common in the schists of the Oowal district of 
 Argyllshire. 
 
 From what is known of the Highland boundary fault elsewhere, 
 it is possible, or even probable, that the portion of this in Arran, 
 which is south of the large granite area, may be pre-Oarboniferous 
 or even of earlier date than the Upper Old Red rocks, and some 
 of the faults which -affect the Lower Old Red formation abont 
 Monyquil and in the Sannox glens may be of a like date. 
 
 In the qtiartz porphyry of Windmill Hill there are faults and 
 crushes which are of older date than basalt dykes which pierce it. 
 
 None of the large faults in the Gorrie and Sannox districts, some 
 of which are undoubtedly post-Triassic, are found to affect the 
 granite in any way, and the even outline of the latter is a clear 
 demonstration that the large faults must have been formed previous 
 to, or during, its intrusion, and not subsequently. 
 
 The anticline of North Sannox is much broken by faults, but is 
 manifestly later than the Carboniferous and Triassic periods, for 
 we find rocks of both these dates on either side the anticline 
 dipping in opposite directions. Strange to say, however, the anti- 
 cline does not affect the schists, and their strike has no relation to 
 that of the newer rocks. Hence it appears that the metamorphic 
 rocks had nearly their present strike before Old Red times, and 
 the boundary faults along the north-east shore are contemporaneous 
 with the formation of the anticline. It follows that many, if not 
 most, of the faults are post-Triassic. 
 
132 Hie Geology of North Arran. 
 
 On the southern side of the great granite mass, if we compare 
 the dip and strike of the rocks near Brodick Castle and in Glen 
 Shurig with those in the Shiskine district, we find that the Upper 
 Old Eed, the Carboniferous, and the Lower Triassic beds have all 
 been nearly equally afiected by upheaving or disturbing move- 
 ments, so that these movements must have been very considerable 
 since the Triassic period. And when we notice a general parallelism 
 between the successive outcrops of these beds and the edge of the 
 great granite mass we are driven to the conclusion that the intru- 
 sion of the latter has been the principal factor in causing the present 
 arrangement of the strata in question. 
 
 The effect of the southern granitic mass in truncating all these 
 three formations, and causing the outcrops to be carried a long 
 distance southward, as far as to the Clachan Glen, is remarkable. 
 Of course the result is partly due to faults, as we have shown, but 
 there is a tendency, as in the case of the larger granite mass, for 
 the strike of the rocks to become more or less parallel to the edge 
 of the intrusions, and this, as was before observed, is noticeable in 
 the metamorphic rocks on the western side of the northern granite 
 region. 
 
CHAPTER XIII. 
 
 Glaciation and Glacial Deposits. 
 
 NORTH ARRAN, SOUTH BUTE, AND THE CUMBRAES. 
 
 A great part of the land area in this sheet was at one time 
 covered by an ice-sheet which moved generally from north to south. 
 This is evident not only from the distribution of erratic boulders in 
 various parts of the district, but more particularly from a study of 
 the glacial strise on the solid rocks. The direction of these is almost 
 due south in many examples on either side of the Little Oumbrae* 
 and near Ardscalpsie in Bute. Sometimes there is a deviation 
 towards the east as on the rock called Miller's Thumb in Millport 
 Harbour, where the direction is about 15° east of south, and near 
 Barr Buidhe, South Bute, where it is S.S.B. In other cases it is 
 west of south, as in Bute to the east of Barefield (S.S.W.). It is 
 clear, then, that the ice-sheet from the north moved over the 
 comparatively low ground of Bute and the Cumbraes without let or 
 hindrance, but the high hills of Arran divided the stream of ice 
 as a rock in a running stream divides its current. For along the 
 western side of the high ground south of Catacol we find almost 
 universally the direction of the strise parallel to the edge of the 
 granitic mass. At first the direction is nearly S.W., as near 
 Lochan a'Mhill. Prom Penrioc to Imachar the general trend of 
 the ice-markings gradually changes from S.S.W. to almost due 
 south, and about Balliekine it becomes east of south. Thus 
 we have clear evidence that the ice-sheet ooasted the high ground 
 instead of going over it. The striee on the granite inland to the 
 west of the lorsa valley have the same southerly tendency, but as 
 the direction of these coincides with that of the valleys there it is 
 not clear whether they are due to the great ice-sheet or to local 
 glaciation. Portions of the great sheet may have gone over the 
 watersheds at the heads of Oatacol Burn and Easan Biorach, which 
 are both under 1200 feet in height, and been augmented by local 
 shed from the neighbouring hills. 
 
 The larger granitic mass east of the lorsa caused a much 
 greater deviation in the direction of the ice-sheet, for from Torr 
 Meadhonach, in the north of the island, all along the skirts of the 
 mountains we find the general direction of glaciation to have been 
 between E.S.B. and due B. This continues at least as far as 
 Parchan Mor on the south side of Glen Sannox. It now becomes 
 pretty clear that the high mountains of Arran were not overridden 
 by the general ice-sheet, but they must, both before and at the time 
 of greatest glaciation, have been covered by a local ice-cap which 
 
 * Most of the groovings on the Little Cumbrae are within tide range, and it seems sur- 
 prising at first sight that they are so fresh where exposed to tidal action. It must be 
 borne in mind, however, that they have b^een so exposed for a comparatively short time, 
 for till the last upheaval of the land they were " full fathom five " below water, 
 
134 The Geology of l^orth Arran. 
 
 shed material all round to increase the general mass of ice. The 
 high ground south of Gleann an't Suidhe may have formed a local 
 ice-sheet also. At all events we have evidence that to the south of 
 this the general ice-sheQt moved south-vs^estvp-ard over Arran towards 
 Kintyre. It may be mentioned that glacial striae are particularly 
 numerous and good on the west side of Arran near the road 
 between Whitefarland and Imachar ; a particularly fine example of 
 a grooved and polished surface of schist may be observed by the 
 roadside at the former place. 
 
 To the east-south-east of Auchencar ridges of drift or drumlins 
 which are parallel to the general direction of the glacial striae are 
 very prominent. They trend somewhat to the west of south, and in 
 several cases are evidently examples of the phenomenon called crag 
 and 'tail, for each of them is under the lee of a crag behind which 
 the glacial material has accumulated. 
 
 Erratic Blocks. — At the north end of Great Cumbrae schist 
 boulders which must have travelled from the north are found in 
 several places, and blocks of gritty schist occur on the east side of 
 the island near Bessy's Port. In South Bute schist blocks are fairly 
 numerous. There is one on the foreshore of Kilchattan Bay called 
 the Black Eock. Another west of the old quay measures 8 feet by 
 7 by 5, and there is a pebbly schist boulder 7 feet long to the west of 
 the pier. A large block of quartzose pebbly schist veined with quartz 
 350 yards W.S.W. of Lubas is 8 feet long, and large fragments of 
 a similar rock are near the seashore half a mile west of Quochag. 
 A gneiss boulder also occurs in Quochag plantation, and there is a 
 large boulder of gritty schist south of the west end of Suidhe 
 plantation. A boulder of grey granite 3 feet 6 inches long, but 
 partly buried, is found three quarters of a mile W.N.W. of Quochag. 
 These are all far-travelled blocks, and a few erratics are also found 
 in Arran, but most of the boulders of that island are of local rocks. 
 A well-rounded boulder of coarse granite with large crystals of 
 pink felspar is -on the shore about half a mile west of the Cock of 
 Arran. It is probably an example of the granite of Glen Fyne 
 which has been carried from the north. About three quarters of a 
 mile west of Lochranza pier there is at a height of about 200 feet 
 above the sf^a and reposing on the schists a large boulder of 
 brecciated conglomerate very like the kind so common in the Upper 
 Old Red rocks of Bute. Its dimensions are 12 feet long by 9 feet 
 broad, and it is four feet high. This block of coarse rock is composed 
 mainly of fragments of quartz and schist. It may have travelled 
 across from Bute. Rock of much the same character occurs also in 
 Arran, but it would not be easy to account for its position here 
 unless it came from outside the island. 
 
 The largest of the local erratics are of granite. The heaviest is 
 probably the Clach Mhor, on the highest raised beach south of the 
 the Oorrie Burn and about three quarters of a mile south of the 
 hotel. It is 30 feet square at the base, about 15 feet high, and 
 must weigh about 400 tons. A block stilll longer than this (36 feet) 
 but probably not so heavy, occurs among the moraines north of 
 Ceum na Gaillich. Clach an Fhionn, a split boulder north of Corrie 
 
Glacial Deposits. 135 
 
 by the roadside, measures 17 feet by 10 by 7, and Clach a Ohait, 
 600 yards farther north, is 18 feet long, 6 to 9 feet wide, and about 
 15 feet high. There is a large granite boulder on the Oorrygills 
 shore, and large blocks of granite are numerous on the Olauchland 
 shore on the north side of Lamlash Bay, and a few occur high up 
 on the northern slopes of Holy Island. They are abundant on the 
 Old Red Sandstone slope east of Moniquil, where one was 
 measured 17 feet by 8 feet 6 inches ; and on the hill-slopes north of 
 Dougrie and on the seashore to the west, where several are as much 
 as 10 feet long. The numerous large boulders of granite and schist 
 that encumber the shore for a distance of a mile and a half north- 
 west from the lorsa Water have been derived from the denudation 
 of the boulder-clay during the process of cutting back the cliflF to 
 form the present raised beach, and the Olauchland shore boulders 
 have probably in like manner been derived from the denuded till 
 of the neighbourhood. 
 
 Glacial Deposits. — Till or Boulder-clay. — This well known, 
 irregularly accumulated deposit is often tinged of a red colour 
 and is v£ry unevenly distributed, being mostly confined to the 
 valleys and low-lying ground. Probably the best exposure of it 
 in this area is on the north side of Ballymichael Burn, nearly half a 
 mile above the road, where reddish till or stony clay appears from 
 40 to 50 feet in thickness. Thick masses of grey till may be seen 
 in the banks of the Cnocan Burn, Brodick, about half a mile above 
 the wood, and compact red till appears in the south bank of Glen- 
 cloy Burn near Knowe. The general drift of the granite area is 
 less clayey and more loosely aggregated, sometimes much like 
 morainic material in character, though not in form. Thick 
 masses of loosely-constructed brownish drift, with large blocks in it, 
 are exposed in the banks of Allt Gobhlach, Pirnmill, half a mile 
 from the sea, and fine exposures of this loose granitic drift are found 
 by the stream called Allt ant Siorraim which issues from Loch 
 Tanna. In places on the west side of the stream the drift 
 would appear to be from 50 to 100 feet thick. 
 
 MOEAINES. — Relics of a later and more local glaciation also occur 
 in nearly all the valleys in the shape of moraines. They are 
 especially conspicuous in the valleys at the head of the North 
 Sannox stream on the north side of Oaisteal Abhail, and in the 
 upper part of Glencloy in both its branches. Glen Dubh, and Glen 
 Ormidale. In the three valleys into which North Sannox 
 stream divides the moraines are generally an irregular assemblage 
 of small mounds composed of huge blocks of granite, but in addi- 
 tion to this there is a fine example of a lateral combined with a 
 terminal moraine on the eastern and north-eastern sides of the 
 heaps S.B. of Oreag Dhubh. There is also a linear moraine in the 
 eastern valley — Ooire nan Oeum — in addition to the formless heaps. 
 In South Glen Sannox there is a well-formed lateral moraine, more 
 than half a mile in length, which forms a sloping ledge nearly 
 parallel to the stream on the north side of the valley, under Oeum 
 na Oaillich. In Ooire nan Larach to the north of Am Binnein 
 there is a beautifully-formed lateral moraine strewn with granite 
 
136 The Qeohgy of North Arran. 
 
 blocks, and there is another in Ooire La,n at the head of the White 
 Water. A well-marked linear moraine, which is at a low level to 
 the north of Maol Donn, can be easily discerned from the high 
 road south of Oorrie. It has a north-east trend. Moraines are 
 common in the lorsa valley, and there are fine examples near the 
 head of the Garbh Choire Dubh west of Cir Mhor. In Glen Kosie 
 they are found less than half a mile west of the wood and below 
 the upper limit of the 100 feet beach, and they are prominent 
 again two mUes farther up the valley where it divides into three. 
 The upper part of the Garbh Allt branch glen, for a distance of a 
 mile from" the head of the valley, is almost one sea of moraines. 
 In Gleann Dubh (Glen Cloy) there is a magnificent series arranged 
 for the most part in concentric curves round an alluvial flat at the 
 foot of the crags which must at one time have been a glacial lochan, 
 or a tarn, dammed by moraines (see Plate IX). 
 
 BsKEKS. — In the valley of the Machrie Water, about Monyquil 
 and Glaister, and also up the Machrie Burn, mounds of detritus 
 occur which at a distance might be mistaken for moraines, but 
 which when closely examined are found to consist of washed sand 
 and gravel. They are, threfore, more of the nature of eskers or 
 kames. On the Machrie Burn they are conspicuous to the west of 
 Cnoc na Ceille, where they form an irregular group stretching 
 for a quarter of a mile parallel to the burn on its east side. On 
 the west side, a line of them, almost a continuous ridge, may be 
 traced to the north-westward for nearly half a mile. On the 
 Machrie Water the best examples of them are found between 
 Monyquil and Machrie Bridge on the west side of the river, and 
 mounds of much the same character are found near the road which 
 runs past Derenenach and Ballymichael to Shiskine. Bast of 
 Ballymichael these mounds are very striking, and pits have been 
 opened in them in several places for gravel and sand. Pits have 
 also been made in the long mound between Machrie Bridge and 
 Glaister. One of these mounds of a curved shape, south-west of 
 Monyquil, is known as " The Serpent Mound," and is supposed to 
 be artificial. 
 
 Laminated-Clays and Sands with Glacial Srells. — These 
 are found in Bute at the Kilchattan Tileworks, and they occur 
 also in the Great Cumbrae. The beds at Oumbrae College have 
 been described by the Rev. H. W. Crosskey and D. Robertson in 
 Trans. Geol. Soc. Glasgow, vol. iii, p. 113 (1868). The same 
 observers describe the Kilchattan beds in the 4th vol., p. 128, of the 
 Glasgow Geol. Soc. Trans. (1872) ; and these have also been 
 described by (Sir) A. Geikie in his paper " On the Phenomena of 
 the Glacial Drift of Scotland," Trans. Geol. Soc. Glasgow, vol. i, 
 part 2, p. 132 (1863); and by James Coutts in the Proc. Nat. 
 Hist. Soc. Glasg., vol, ii, p. 33 (1870). 
 
 AYESHIRE DISTRICT. 
 
 In the part of Ayrshire described in this memoir the movement 
 of the ice of the Glacial Period has been persistently from north 
 
Jly* 
 
Olaciation. 137 
 
 to south, the actual direction varying slightly with the form of the 
 ground or from other causes. If we take the observed striae on the 
 rocks at the greatest distance from the heights which would 
 influence the motion of the ice, we find them at the Portin- 
 cross beach as a well ice-worn surface of pebbly red sandstone, 
 running towards S. 25° B. As the ice which engraved them 
 must have come from N.N.W. across the Firth of Clyde we 
 may assume that this was the general trend of ice-movement here. 
 But the steep volcanic escarpment could not fail to afiect the flow 
 of at least the lower portions of the ice-sheet. Consequently on 
 bare surfaces of andesite on the south side of the Gogo Burn above 
 Largs the striae are found to have been turned round and to point 
 to S. 25° W. But a little farther south they run towards 
 S. 20° B. 
 
 That the ice moulded itself upon the surface of the 
 rock over which it moved and that it was pressed up hill is well 
 shown at several places in this district. Thus, in the ravine of the 
 Gogo Burn, 1000 yards due east from Gogo Bridge, a well ice- 
 ground face of andesite, with an inclination of 60°, has been scored 
 from bottom to top by the ice that was driven upward out of 
 the hollow. Again, on the east side of the smaller of the two 
 necks which rise from the slopes to the south of Pairlie, the sur- 
 rounding sandstone has been striated from below upward by a mass 
 of ice that was here moving towards S. 9° E. 
 
 The boulder-clay is abundantly spread over the surface of the slopes 
 between the edge of the volcanic plateau and the sea. It is full of 
 local stones, but contains also many from the Highlands. Sections of 
 the deposit may be seen in almost any of the watercourses. It 
 likewise forms the smooth grassy blufis that rise from the inner 
 edge of the platform of the raised beach. The large number of 
 boulders everywhere strewn along the beach afibrd good material 
 for studying the march of the ice-sheet, and remain as evidence of 
 the contents of the boulder-clay which has been removed from so 
 much of the lower ground. A. G. 
 
 KINTYEE DISTRICT. 
 
 Although the nature of the rocks in the area is not favourable to 
 the preservation of Glacial striae, the track of the ice which 
 enveloped Skipness is indicated by the nature and disposition of 
 the Boulder-clay and the carry of material. These indicate that 
 during the period of maximum glaciation this part of the peninsula 
 shared in the general movement of the great ice-sheet which 
 crossed Kintyre approximately from east to west. As shown in 
 the Eeport of the Committee on the High-level Shell-beds of 
 Kintyre to the British Association in 1896,* striae pointing west- 
 wards are found on the watershed at elevations of over 1200 feet 
 to the north-west of Carradale, just outside the present area, and 
 boulders of Arran granite have been traced in the drift across the 
 peninsula from Carradale to the west coast. 
 
 * Eeport Brit. Assoc, 1896, pp. 386-389. 
 
138 The Geology of North Arran. 
 
 The Boulder-clay found over the Skipness area is red in colour and 
 contains a large amount of red sandy matter and boulders of red 
 sandstone and conglomerate entirely foreign to the area. It every- 
 where lies on the western slopes of the rising grounds, while the 
 eastern slopes are bare. It fills the valleys of the Skipness and the 
 Claonaig waters to great depths, and in the former case to over 
 200 feet in places, and both streams down a great part of their 
 lower courses are cutting their present trenches between the 
 Boulder-clay and their ancient western rocky sides, so that they 
 have rocky banks on the left and high Boulder-clay blufis on their 
 right, and do not appear to have as yet reached the bottom of their 
 old pre-glacial channels. The Skipness Water, however, appears to 
 leave its old valley to cut into its rocky side for half a mile below 
 Coalfin close to Skipness. 
 
 It is singular that the colour of the Boulder-clay in Skipness 
 should be red. It cannot be of local origin, as the rocks of 
 the region could not give rise to a deposit of that colour; nor 
 can it have derived its colour from the rocks now seen on the 
 shores of Loch Fyne, as the Boulder-clay found on the shores 
 further up are described in the Memoir on Cowal as greenish- 
 grey or pale-buff in colour.* Red boulder-clay, however, is 
 common in the south part of Cowal.t It occurs throughout 
 Kintyre south of this region, and is continued across Islay. 
 It is highljr probable that the redness is due to the rocks over 
 which this part of the ice-sheet passed having been stained 
 by an extension of Triassic rocks which may have filled the 
 Clyde Basin and only been removed in late Tertiary times. The 
 discoveries connected with the great Tertiary neck already 
 described, give great support to such a supposition. It may be 
 that even yet outliers of Triassic rocks occur in the Clyde to the 
 east of Skipness, for Triassic rocks pass out to sea at the Cock of 
 Arran,+ and stained carboniferous limestone blocks full of 
 characteristic fossils form a bank at the mouth of Catacol Bay § 
 in such a manner as to suggest that they are not far out of place. 
 
 No moraines have been with certainty detected in this area. 
 
 B. N. P. 
 
 * "Geology of Cowal," Mem. Geol. Soc. Scot., p. 255. 
 
 t Ibid., p. 255. 
 
 J See ante, Chap. vii. 
 
 § See ante, Chap. vi. 
 
CHAPTER XIV. 
 
 Saised Beaches and Recent Deposits. 
 
 Raised Beaches. — The 25 feet raised beach is a marked feature 
 on the long coast-line of this map. Though often very narrow it is 
 very persistent. It may disappear for a time at a rocky promontory 
 but shortly re-appears. Sometimes it is but a shelf cut in the 
 rocky shore with no deposit of gravel on it, and occasionally, as in 
 the case of the Scriden and the Fallen Eocks in Arran, the original 
 shelf has been obliterated by a comparatively recent landslip. The 
 rocky shores of South Bute and of the Little Cumbrae show the 
 least traces of it. The marine shells found in the sand and gravel 
 of this lower raised beech or lying loose on its surface, appear all to 
 be of species now living in adjoining seas, and are a testimony to the 
 recent elevation of the land. A list of some found in a iield about 
 a mile south of Gorrie is given by Ramsay in his " Geology of Arran," 
 p. 19. In the southern part of Great Cumbrae, west of Millport, 
 the shells in places are so numerous as to form a kind of shell marl. 
 A separate beach at the height of the "40 feet" seldom occurs, except 
 at the mouths of the large streams or in sheltered bays. In fact, 
 both the 25 and 40 feet beaches are represented by the continuous 
 marine terrace above described, which is often bounded by high 
 sea-cliffs in which water- worn caves occur at various levels. These 
 latter are conspicuous between Brodick and Gorrie on the eastern 
 side of Arran in the New Red Sandstone; and several are found 
 hollowed out of the schist on the north-west coast. The remark- 
 able group associated with the King's Cove near An Cumhann are 
 just at the south-westerly edge of the map. 
 
 The higher and older marine terraces have evidently suffered 
 much denudation by the action of the sea along the exposed part 
 of the coast, and by streams at their mouths, and in the bays of 
 Brodick and Lamlash, where several burns enter the sea. In these 
 latter situations the marine and freshwater alluvia are mingled so 
 that it is difficult to class them separately. We have evidence, 
 however, of several beaches at different levels rising from 40 or 50 
 feet to over 100 feet above the sea, which are beautifully exhibited 
 near the mouths of the lorsa and Machrie streams in Arran, and 
 in the extensive tract of low lying land, west of Kilchattan, in 
 Bute. At the time of greatest depression, when the highest beaches 
 were formed, Inchmarnock was separated into two islands, and the 
 portion of Bute included in this map was divided into three ; 
 the northern part of Great Cumbrae was in like manner a separate 
 island from the rest. In Arran the sea penetrated far up into 
 many of the valleys ; Glen Rosie and Glen Cloy were sea lochs, each 
 
140 The Geology of North Arran. 
 
 one and a half miles in length ; Lochranza was lengthened by one 
 mile, and Lamlash Bay extended one mile farther to the west.. 
 North Glen Sannox was a long narrow sea loch, and at Oatacol and 
 South Sannox there were broad, short lochs. Perhaps the greatest 
 changes in Arran would be on the western coast, where not only 
 was there a sea loch at the mouth of the lorsa but in the plain of 
 Shiskine the sea penetrated in an irregular way to more than two 
 miles eastward of its present boundary, and the hilly ground of Torr 
 EighBeagandTorr EighMor formed a separate island. Good sections 
 of the gravel and sand of the higher beaches are exposed in the north 
 bank of the Eosie Burn one mile from the sea, the south bank of 
 Sannox Stream opposite Mid-Sannox House, the east side of the 
 lorsa Water above Dougrie Lodge, and in a gravel pit at Loch- 
 ranza above the junction of the two main streams and west of 
 Ballarrie. W. G. 
 
 The coast-line between Ardrossan and Largs affords a typical 
 example of the raised beaches of the Firth of Clyde. These 
 terraces form a platform of level ground along which the coast- 
 road runs, and on which the maritime villages are built. On the 
 seaward side of this platform lies the present sea-beach ; on the 
 inland side the ground rises steeply as a grassy bank, or occa- 
 sionally as a wooded cliff, according to the nature of the material 
 out of which it has been eroded. The smooth slopes usually mark 
 the position of the Boulder-clay, while the more cliffy faces 
 indicate the outcrop of harder rock. 
 
 At least four terraces may here and there be discriminated, but 
 their boundaries are apt to become so faint that they seem to 
 merge into' each other, and they cannot, therefore, be continuously 
 shown on the map. The lowest and youngest of the beaches 
 has a height of about 15 feet along its inner margin. It 
 forms the platform on which the seaward part of Largs stands, 
 where its limits can here and there be readily traced. The gentle 
 bank which marks its landward edge may be seen on the south 
 side of the mouth of the Gogo Burn, on the flat to the south of 
 Broomcraig Park, and to the south of Pairlie. It is on this terrace 
 that most of the coast-road runs between Largs and Pence Bay, 
 and again between Seamill Bridge and Ardrossan. 
 
 The next beach, usually known as the 25-feet terrace, covers a 
 broader, more continuous, and more easily recognised space. Its 
 inner margin runs, on the whole, tolerably parallel with the contour- 
 line of 25 feet above ordnance datum, at a little higher elevation, 
 but occasionally it sinks below that line or rises farther above it. 
 These variations, which recur at frequent intervals, may be due to 
 irregular local differences in the accumulation of littoral detritus. 
 It should be noted that this terrace is fundamentally a platform cut 
 out of the rocks underneath and with a variable thickness of sand 
 and gravel spread over these rocks. At the same time it is unfor- 
 tunately true that no careful levelling has yet been undertaken 
 in the basin of the Pirth of Clyde, or indeed anywhere in Scotland, to 
 ascertain if a recognisable increase or diminution of the height of 
 any of the marine terraces can be detected, such as might indicate 
 
Baised Beaches, 141 
 
 inequality of movement between one part of the country and 
 another. 
 
 The terrace continues as a well-marked platform about 200 yards 
 broad to beyond Seamill Bridge. From its inner border a steep 
 bank rises to more than 100 or even 150 feet above the sea, and 
 shows here and there outcrops of red sandstone on its declivities, 
 as in the "braes" of Boydston, Glenhead, and the Bank. Beyond 
 Seamill Bridge, where the road quits the shore, the 25-feet beach 
 continues towards the north-west with its wooded landward banks, 
 which probably consist mostly of drift. At Portincross, however, 
 it is interrupted by the projecting promontory formed by the broad 
 and long dolerite-dyke already mentioned. Immediately beyond 
 this point the platform reappears in its most characteristic form. 
 It is here in places less than 70-yards broad, and is bounded inland 
 by a range of wooded cliffs which rise to a height of 300 feet. 
 The contrast between the dark rocky wall behind, and the strip of 
 level green fields at its base, with the blue sea in front, forms a 
 singularly striking piece of coast-scenery. After a distance of 
 about a mile the cliffs sink down into sloping ground which makes 
 a curve inland for three-quarters of a mile to Hill House, where it 
 forms a promontory and then turns abruptly southwards away from 
 the coast. By this disposition of the topography bays were formed 
 in the old shore-line ; the marine accumulations were there laid 
 down under more sheltered conditions, and now cover a wider area 
 and attain a greater development than elsewhere along this coast. 
 To the south-west of Hill House the 25-feet beach expands into a 
 fertile platform 1400 yards long, and with an extreme breadth of 
 of 750 yards. Its inner margin follows the line of a low bank to 
 the north of the grounds of Hunter ston House. To the southward 
 a higher platform makes its appearance, which will be further 
 referred to immediately. The 25-feet beach stretches north by 
 Fairlie to Largs, and for many miles beyond, carrying with it the 
 same type of scenery which has now been described. Here and 
 there it seems to merge insensibly into higher and older terraces 
 especially where a stream, descending from the high grounds of the 
 interior, has mingled its alluvium with that of the marine terraces, 
 as in Kelburn Park, where the Kel Burn enters the sea, and at 
 Largs where the Gogo Burn has carried down a large quantity of 
 detritus from the hills above. 
 
 The next beach in succession is that to which the name of 50- 
 feet terrace has generally been given, though its average height is 
 probably rather less than that number of feet. At one time it was 
 no doubt well developed along this part of the Ayrshire coast, but it 
 has been in great part cut away during the prolonged period when 
 the 25-feet beach was in course of formation. The only consider- 
 able portion of it that can be recognised is that which fills up the 
 deep and broad hollow that extends from Poteath, beyond 
 Hunterston, for a mile and a half to the south, with a breadth of 
 more than half a mile. There, can be no doubt that this was once 
 a sheltered sea-bay where marine deposits might accumulate, and 
 where they would be more likely to escape subsequent demolition 
 
142 The Geology of North Arrcm. 
 
 than on the exposed coast-line to the north and south. Unfortu- 
 nately there are hardly any sections to be seen of the deposits of 
 this terrace. They include fine clays, which have been worked at 
 Carlung for the making of tiles. That these clays lay at the surface 
 over considerable spaces may be inferred from the position of 
 Carlung Moss, which is an extensive tract of peat lying immediately 
 on the marine platform and filling a small bay at its northern end. 
 No marine organisms are known to have yet been obtained from 
 these clays. 
 
 The highest beach which is generally recognisable in this part of 
 Scotland is that to which the name of the 100-feet terrace has been 
 assigned. Being older than the others it has been much longer 
 exposed to denudation and has consequently been much more 
 extensively demolished, so that for the most part only fragments of 
 it now survive in such sheltered places as could afibrd it protection. 
 The high gravel platform behind Largs appears to belong to this 
 terrace. 
 
 Marine alluvium of younger date is well displayed along the 
 shore from Largs southward. At low tide the Southannan and 
 Hunterston sands present a plain of wet sand extending for nearly 
 a mile out towards Pairlie Eoads. 
 
 As already stated, the conditions have not been favourable for 
 the formation of blown sand. But a small patch of this deposit may 
 be detected here and there as, for instance, on the promontory close 
 to the volcanic neck at the south end of Pence Bay. A. 6. 
 
 Fragments of the 100-feet raised beach terrace are found near 
 the mouth of Skipness Water above Skipness Castle, and over- 
 looking the eastern angle ot Claonaig Bay, as well as at Escairt, 
 just above Escairt Point. A lower terrace, probably representing 
 the 50-feet beach, is also found at the same localities. Eelics of a 
 still lower terrace, probably the 25-feet beach, are found all along 
 the coast bordered by a steep bluff of cliff often cut in the rock or 
 pierced with caves, forming a feature which easily arrests the eye. 
 
 Present Beach. — As already stated, the coast-line for the most 
 part is rocky and no beach is being formed on these exposed parts, 
 but the material abstracted by the sea is carried forward and heaped 
 up in the sheltered bays. The higher raised beaches also occur 
 in the same places, showing that a similar action took place during 
 their accumulation. In Skipness Bay the marked deflection of the 
 Skipness Water towards the west by the beach shows plainly that 
 the greatest wave-action along this shore is by waves from the east. 
 
 B. N. P. 
 
 Freshwater Alluvia. — As might be expected from the small 
 size of the streams the patches of freshwater alluvium are generally 
 small and unimportant. The largest are found in the plain of 
 Shiskine, on the Machrie Water above the old bridge, in the lorsa 
 valley above lorsa Loch, and at the mouths of the lorsa, Catacol Burn, 
 Easan Biorach, the two Sannox Burns, and those which enter the 
 bays of Brodick and Lamlash. The alluvium at the debouchure of 
 the streams has been to a great extent formed from the denudation 
 and rearrangement of the material forming the raised beaches. In 
 
Freshwater Alluvia. 143 
 
 the Shisldne district the alluvium qf the swift running streams on 
 the east side has been spread out in fan-like or delta forms over 
 the marine material. The alluvial sand and gravel of the Machrio 
 is two miles in length and nearly half a mile broad in places, and 
 has been accumulated by several swift running streams of consider- 
 able size. At first sight it might be supposed that the material 
 has filled up an old loch, but the fact that there is a rise of quite 
 100 feet between the foot and the upper end rather militates 
 against this view. The patch of alluvium in Glen lorsa is nearly 
 as broad as the last and is three miles long, and here there must 
 have been at one time an extensive sheet of freshwater which, 
 including the present Loch lorsa, may have been three and a half 
 miles in length. For a distance of more tlian a mile above the last- 
 named loch the alluvial flat is studded with small lochans, and the 
 rise in level is but 7 or 8 feet. Even at a distance of more than 
 two miles above Loch lorsa the alluvial flat is only 30 feet higher 
 than the loch. A beautiful example of a filled-up lochan, an old 
 moraine-dammed tarn, occurs in Gleann Dubh (Glen Cloy) at the 
 foot of the steep crags. The present extent of the alluvial flat 
 shows this lochan was about 400 yards long and 300 broad. Old 
 lochans or tarns which have been filled up are now generally peat- 
 bogs, like Branzet Moss in Glencallum in Bute, and a bog east of 
 Breckoch in Great Cumbrae. There were several on a small scale 
 in Little Cumbrae. It is evident that several of the streams have 
 changed their courses in the low-lying ground near the sea. In 
 an old" manuscript map of the latter part of the 18th century the 
 Rosie Burn is represented as taking a sweep round to the eastward 
 in what is now the deer-park, and the Cnocan Burn came south- 
 ward towards it. The marked bank in the park south-west of the 
 cottages shows where the old stream ran. At that time there was 
 a project to make an artificial channel connecting the Eosie Burn 
 with the mouth of the Cnocan in order to form a harbour opposite 
 the castle. The lower part of the Cnocan Burn is now an artificial 
 cut. There is still trace of a large bend, an old course of the 
 Rosie, west of Strabane. The mouth of this stream has undergone 
 several changes. At one time it ran along the sands towards the 
 Cnocan, and afterwards changed to a straight course out to sea. 
 Then it turned to the north again and its outlet, when the 
 Ordnance Survey was made, must have been nearly 700 yards 
 north of what it is now. The present run straight out to sea is, 
 however, said to be owing to an artificial cut having been made. 
 It has been in existence many years, but strange to say is not on 
 the revised ordnance map. The greater part of the water of 
 Ballymichael Burn is now carried by an artificial channel into the 
 Machrie Water, to the east of the Stone Circles of Tormore, and 
 this having been made a good many years ago ought to have 
 appeared on the revised ordnance map. 
 
 Peat. — The peat of the old lochans has been already noticed, 
 and only the moor or hill peat will be described here. The higher 
 granite hills are almost bare of vegetation, and the higher ground 
 on which peat accumulates is in the southern part of the map, from 
 
144 The Geology of North Arran. 
 
 Beinn Bhreac to A'Oliniach. There is a good deal of peat, 
 however, on the lower granite area from Glen Oatacol eastward to 
 An Tunna, and it is abundant on the high plateau-like or gently- 
 sloping ground formed of schists, nearly all round the granite 
 district. It is found, in fact, over the rocks of all formations in 
 Arran, from the oldest to the Boulder-clay of the Glacial period. 
 
 Blown Sand. — Low hillocks of blown sand, but of no great 
 extent, may be observed on the raised beaches at the north end of 
 the Great Oumbrae, near Millport east of Breckoch, and coasting 
 Scalpsie Bay and Stravanan Bay in the island of Bute. A more 
 extensive area of blown sand, a typical sea-side links, occurs at 
 Machrie Bay, Arran, to the soiith of the Machrie Water. 
 
 Landslips.— Probably the largest area covered by a landslip in 
 Arran is that which is found in the hollow north of Maol Donn, 
 between it and An Sgriob. Large masses both of Carboniferou.i 
 and Triassic rocks are scattered over an area which is 600 yards in 
 length from S.W. to N.B., and on an average more than 200 yards 
 in breadth. The extent of this slip must be quite 25 acres. Other 
 notable landslips, which have often been described, are those which 
 form the Fallen Rocks and the Scriden. The former make a 
 striking debacle of large blocks, from a height of 500 or 600 feet 
 down to the sea level between North Glen Sannox and Millstone 
 Point. The slipped masses are all of Upper Old Red Conglomerate 
 (see Plate X.). The Scriden covers a larger area at the most 
 northerly part of the island. It is formed of large blocks of 
 Triassic sandstone and conglomerate which fell, it is said, some 
 two hundred years ago. The concussion shook the earth, and the 
 fall was heard in Argyllshire and Bute. In addition to the masses 
 which have actually fallen several parts of the hill above have 
 moved slightly from their position and left deep and narrow rents, 
 one of which is known as the Fairy Dell. W. G. 
 
 - No fresh-water alluvium exists in the Ayrshire district of suffi- 
 cient importance to find a place upon maps on so small a scale as 
 one inch to a mile. The slopes are too steep to permit of the 
 deposit of sediment, and when the bottom of the declivities is 
 reached the water-courses are within a stone-cast of the edge of the 
 Firth. The only tract of fresh-water accumulation that may be 
 referred to here is Garlung Moss already noticed. Considerable 
 tracts of peat and peaty moor occupy the hollows of the volcanic 
 plateau just beyond the present district. A. G. 
 
 Small alluvial plains are found along the course of the Kintyre 
 streams, the broadest and most continuous being found on the 
 Claonaig Water. High terraces showing stages in the lowering of 
 the valleys are well shown along the same stream, especially where 
 it runs through boulder-clay. They also occur in the Skipness 
 Water where the river has cut deep down into the boulder-clay 
 above the rocky gorge of Coalfin close to the village of Skipness. 
 Small patches of alluvium occur along the smaller streams, but they 
 are two small to be shown on the one-inch map. 
 
 Cultivation is mainly confined to areas covered by boulder- 
 clay, the raised beaches, and the alluvial terraces, the best 
 

 H 
 
 c o 
 *^ o 
 
 ^ r- 
 
 
 < 
 
 XJ 
 
 o 
 
 r;; 
 
 o 
 
 C5 
 
 
 CO 
 
 CO 
 
 
 iD 
 
 •T3 
 
 w 
 
 Pi 
 
 : 
 
 n3 
 
 cr? 
 
 
 ^ 
 
 o 
 
 n 
 
 
 o 
 Cu 
 
 a 
 
Freshwater Alluvia. 145 
 
 land being found on the two latter formations, as owing to their 
 arrangement of the materials they afford natural drainage. 
 The areas where the rock is not covered by these deposits are either 
 bare, or, where the rocks readily decompose, are covered by a thick 
 coating of grassy or heathery turf, while peat, thick enough to be 
 worked, occupies hollows both overlying boulder-clay and decom- 
 posing rock debris. B. N. P. 
 
CHAPTBE XV. 
 
 Uconomic Geology. 
 Coal. 
 
 At Ambrisbeg, in Bute, some 200 or 300 tons of coal were said 
 to have been got out many years ago. The seam is in the same 
 position as that once worked at Ascog, and is probably of the same 
 character, a kind of anthracite, locally called " blind coal." In 
 Blain's History of Bute the Ambrisbeg coal is said to have been 
 from a foot to 16 or 20 inches thick, but the field of it being small 
 and the dip great combined with the thickness of the seam to 
 occasion it being neglected. Several attempts have been made at 
 various times to find a thicker seam, but invariably without result. 
 There are traces of the old adits to the south and also to the north- 
 west of Ambrisbeg. 
 
 The coal formerly worked on the shore of the Cock Farm in 
 Arran is referred to by most of the older writers on the island. 
 All agree that the seam or seams belonged to the type of blind 
 or glance coal. It was difficult to work, and principally used for 
 the purpose of making salt from the sea-water. (The old salt 
 pans are close to the old workings.) It was probably also used 
 for burning the limestone near Laggan. Two or three seams are 
 said bo have been worked, the principal seam being three or four 
 feet thick ; but though more than one seam may have been 
 found it seems probable that the workings were almost entirely 
 confined to the thickest seam. They are very old and were dis- 
 continued considerably more than lOO years ago, probably before 
 1773, as under that date in the estate accounts there is a record of 
 boring at Cock for coal. In the same year a boring for coal was 
 made on the north side of Lamlash Bay on the Clauchland shore 
 to a depth of 114 feet 5 inches, which naturally proved unsuc- 
 cessful. 
 
 It is remarkable that no coal is found at Corrie or elsewhere in 
 the island in the strata corresponding to those at the Cock in 
 which coal has been worked; nor has any coal been discovered in 
 the highest Carboniferous beds in Arran which, on the .evidence of 
 their fossU contents, are assigned to the Coal-measures. 
 
 Peat. 
 
 There are extensive tracts covered with thick peat in the island 
 of Arran, mainly on the higher plateau-like ground between 700 
 and 1700 feet above the sea, but occasionally it is found at lower 
 levels, as on the old raised beaches on either side the lower part 
 of the Machrie Water. It was formerly much used for fuel all over 
 
Economic Minerals. 147 
 
 the island, and almost everywhere old peat roads to the hills still 
 exist, though they are not marked on the ordnance maps. On the 
 east side peat for fuel has almost entirely been replaced by coal, 
 but on the west side it is still cut and largely used in the 
 Shiskine district and northwards to Imachar and Lochranza. 
 
 Ironstone. 
 
 To the north of the landing-place at Corrie is a thin band of 
 clay-ironstone which crops out also to the westward on the hillside, 
 where it is from four to six inches in thickness. It appears to be 
 of good quality, and we were informed that some hundreds of tons 
 of it were formerly exported. Probably it was not mined for, but 
 was collected during the working of the white freestone quarries. 
 A similar band occurs in the section on the Cock shore. A number 
 of old bloomeries exist in the island which have been described by 
 Mr. W. Ivison Macadam.* Three of these are on the farm of 
 Glenkiln near Lamlash, and in one case there is evidence that bog- 
 iron ore was used. Two sites occur in Glencloy to the south-west 
 of Glenrickard, and there were two near the road leading from 
 Brodick to Lamlash, in one of which the slag was utilized for 
 road-making. Another was at Coillemore near Lochranza. In all 
 these cases charcoal appears to have been the fuel used for smelt- 
 ing, and the slag remaining is of the dense black type characteristic 
 of the early period when the smelting process was very imperfect, 
 and a large percentage of iron still remains in the slag. 
 
 Barytes. 
 
 A vein of sulphate of barytes which was formerly worked crosses 
 Glen Sannox Burn in a northerly direction about three quarters 
 of a mile from the sea. The workings above ground extend for a 
 distance of about 100 yards, mostly on the north side of the burn, 
 and shafts have been sunk within the opencast workings. One 
 shaft also is found 70 yards south from the burn. At the northern 
 end of the workings the vein is from 12 to 15 feet wide, and 
 purest on the west side. In the river the worked part of the vein 
 is four to five feet wide, and there is about as much more mixed 
 with sandstone on the west side, and also a little on the east side. 
 The general direction of the vein is a few degrees west of north, 
 but it has a rather wavy course. South of the stream, about 125 
 yards, a small cross-cut was made at the surface, apparently as a 
 trial to find the vein. In a burn to the S.S.B., another, or the 
 same, vein occurs having a course towards the north-west. It is 
 two feet or more wide in places and fairly pure, and has a hade to 
 the south-west. The barytes occurs in a massive form, sometimes 
 almost pure white but occasionally with a pinkish or yellowish 
 tinge. Ramsay gives an account of the manufacturing processt 
 carried on at the old mill of which traces still exist. 
 
 * "Notes on the Ancient Iron Industry of Scotland." Proo. Antiq. See. Scotland, 
 1886, pp. 89-1-32. 
 t " Geology of the Island of Arran," p. 24, , 
 
148 The Geology of North Arran. 
 
 Building Stone. 
 
 There are extensive old quarries in the "white Carboniferous 
 freestone of Corrie which was much wrought a century or more 
 ago. It was used in the construction of the Crinan Canal, and 
 is said to have been shipped to the Isle of Man for building 
 purposes. At present the red freestone of the Triassic rocks is the 
 principal building stone in Arran, and there are large quarries in 
 it at Brodick and Corrie. The stone is soft and easily worked, and 
 is said to harden by exposure to the air. Large blocks of it can be 
 obtained, and from Corrie the stone is largely exported to various 
 parts of the Clyde district, and some going much farther away^a 
 mansion in Eum being built of it. Troon harbour is said to 
 have been built out of the material from the northern quarry. 
 In the neighbourhood of Lochranza a tough, gritty schist is used 
 for building purposes. At Millport the white freestone of the 
 islands in the bay is quarried for like purposes, and the Upper Old 
 Ked Sandstone is largely worked south of Figgatoch. 
 
 Slate Quarries. 
 
 Slate has been worked in small quarries on Inchmarnock, both 
 on the eastern and the south-west side of the island, the two 
 extremities of a band that crosses the island in a N.N.E. direction. 
 The slate is of a rough kind, grey in colour, and resembles that 
 formerly worked at the quarries south of the Cock Farm in Arran. 
 In the Brodick estate office there are records of these last workings, 
 from which we learn that between 1773 and 1776 between two 
 hundred and three hundred thousand were sold at prices of £1 
 per thousand and upward. Work was also carried on here between 
 1776 and 1781. Most of the slates from this locality have dis- 
 appeared from the house-roofs of the neighbourhood, but some still 
 remain in Lochranza and North Newton. 
 
 Limestone. 
 
 There are extensive old limestone quarries at An Sgriob, to the 
 north of Maol Donn, and at Corrie. The latter are much the 
 largest ; they extend up the steep hillside for a quarter of a mile, 
 and the limestone has been much wrought in artificial caves, 
 besides having been worked at the outcrop towards the dip till in 
 places there was nearly 30 feet of cover. Much lime was formerly 
 exported, but very little is now burnt in the island, and on the 
 Shiskine side lime is imported from Ireland. The only other large 
 limestone quarries in this sheet are to the south of Kilchattan in 
 the island of Bute. They are old workings, and are now filled with 
 water and used as a reservoir, but a portion of them is newer than 
 any of the Arran workings. According to an analysis of the rock 
 given by Bryce* it is a species of dolomite, one specimen contain- 
 
 * Notes on the altered dolomites of the Island of Bute, PhU. Mag. xxxv, pp. 81-91, and 
 Geology of Arran, etc., 2nd ed., 1869, pp. 56-59 (4th ed., pp. 326-330). 
 
Economic Minerals. 149 
 
 ing 33-72 per cent, of carbonate of magnesia. Another specimen 
 was analysed by Dr. K. D. Thomson with the following result : — 
 
 Silica and Alumina . . 9 '70 
 
 Protoxide of Iron 1'12 
 
 Carbonate of Lime . 67 '42 
 
 Carbonate of Magnesia . . 17 '31 
 Water, Coaly Matter, and Carbonic 
 
 Acid 4-45 
 
 100-00— Spec, gravity, 2-679. 
 
 It is remarkable that where the rock has been converted into 
 crystalline marble by the action of a dyke it loses nearly all its 
 magnesia, the altered rock containing only from one to two and 
 a half per cent, of it. 
 
 Road Metal. 
 
 The numerous igneous intrusions, especially the basic dykes and 
 sills, afford abundance of excellent material for road-making almost 
 everywhere. The acid rocks are not so much used for this purpose. 
 However, a felsite sill is so used near the Brodick and Lamlash 
 road, and a granitic mass near Derenenach on the Shiskine side of 
 Arran. The hard sandstones of the Lower Old Red formation 
 are used for road material in one or two places, as on the String road 
 in Glen Shurig, and the gravel from a raised beach near Ballarrie, 
 Lochranza, is taken for a like purpose. 
 
 Cl&y or Tileworks. 
 
 At Kilchattan in Bute is found a laminated fine clay which has 
 been much worked for tilemaking. At the tile sheds it was about 
 14 feet thick resting on red till, but to the eastward it dies out and 
 gravel is found reposing on the red till. Sometimes there are 
 stones as big as one's fist in the laminated clay. Fine red sand, 
 apparently without lamination, irregular in occurrence, but some- 
 times 10 to 12 feet thick, generally overlies the clay. The clay at 
 the west end of the working has a ridgy upper surface, and also 
 contains shells, and is useless for tilemaking purposes. This clay 
 belongs to the glacial series. 
 
 Population. 
 
 The distribution of the people has little connection with the 
 geological formations, the population being confined in Arran to 
 the neighbourhood of the coast and to the lower parts of some of 
 the glens. The district of Shiskine, on the west side, is the only 
 exception, and here a few scattered farms are found some distance 
 from the sea. In Bute and the Great Cumbrae we find scattered 
 farms in the interior of the islands. The resident population of 
 Arran is small but is much increased in the summer months by 
 an influx of visitors, so that the inhabitants are probably doubled 
 
150 The Geology of North Arran. 
 
 in number. Many of the natives find employment in the summer 
 in catering for the visitors in various ways, but the majority of the 
 people are engaged in agriculture, and the cultivated parts of the 
 island are practically those in which the people reside. The 
 remainder, and by far the larger portion, is devoted to sheep and 
 deer. 
 
 The fishing industry is almost extinct, and chiefly confined to 
 that of herrings on the west coast of Lochranza and Pirnmill. 
 
 Soil and Agriculture. 
 
 The alluvial flats and raised beaches at the mouths of the 
 principal streams afford the best soil, and the narrow terrace or 
 raised beach round the island is in general carefully cultivated. 
 The upper limit of enclosed and cultivated land is between 400 
 and 500 feet above the sea, but the greater portion is below 300. 
 As the ground rises steeply from the sea almost everywhere the 
 arable land is necessarily but a narrow belt along the coast and 
 oven there is not continuous, though apparently more land was 
 formerly cvltivated in the olden times. In the Millstone Point 
 district there were at one time 14 families residing at Cock, Cuithe, 
 Laggan, and Laggantuin, where there are now but a farmer and a 
 shepherd. In North Glen Sannox there was once a large popula- 
 tion where is now but a solitary shepherd's house. Several 
 deserted farmsteads in the'high fields above Corrie, at North High 
 Oorrie, and elsewhere, tell of former cultivation where all is now_ 
 pasture land. 
 
 We also find evidence that it was at one time the general custom 
 in the island to take the cattle to mountain pastures in the summer- 
 time, and remains of the summer shielings or airidhs, as they were 
 called, are common in nearly all the high glens. 
 
 The old runrig system of cultivation, which was general 100 
 years ago, still exists at Balliekine. 
 
 Wood. — There- is much natural wood in Arran, mostly of birch, 
 alder, hazel, rowan, and willow, with some scrubby oak. Belts of 
 these trees are found along the sea coast from Dougrie to Loch- 
 ranza on the west coast, and on the east coast between Sannox 
 and Brodick. There is a good deal of natural wood also in the 
 lower parts of some of the glens, especially in Lag a Bheidh and in 
 Glen Cloy, also in the Shiskine district near the Machrie Water, 
 and in the lower part of Glen Eosie. In Glen Dubh (Glen Cloy) 
 the wood grows up to about 800 feet above the sea, and to nearly 
 the same height in Coire Fhraoich (Glen Rosie), and on the higher 
 ground west of Corrie. Along several of the smaller streams trees 
 flourish up to nearly 1000 feet, especially if the streams run in 
 ravines, but the only locality where there is a small forest at this 
 height is at Doire na Ceardaich, to the east of the summit of the 
 Corrie and Lochranza road. One or two stunted specimens of the 
 rowan tree were observed on the north side of Glen Sannox at a 
 height of about 1500 feet near Suidhe Fhearghas. 
 
 There are many artificial fir plantations in Bute and a few in 
 
Economic Minerals. 151 
 
 Great Cumbrae. In Arran the largest are around Brodick Bay ; 
 and up the Merkland Burn and in Glen Shurig these trees flourish 
 up to nearly 700 feet above the sea. There are plantations also 
 at Whitefarland, Sannox, South Corrygills, etc. Suidhe plantation 
 in Bute rises to above 500 feet. Glen lorsa in Arran is almost 
 treeless, and the granite district generally is comparatively bare 
 of wood. 
 
 Water Supply. 
 
 The rainfall in this west country is heavy, some 40 inches per year 
 and upward ; and the water suppty from springs and streams is 
 almost everywhere abundant. The water from the northern granite 
 area is beautifully fresh and clear, and several of the springs which 
 supply the streams are very powerful. One of these, three quarters 
 of a mile from the shore at Oorrie, rises near the edge of the granite 
 and furnishes the greater part of the water of the Locherim Burn. 
 Another strong spring is found near the head of North Sannox at 
 the foot of Garb Choire, south-east of Greag Dubh. It rises at the 
 edge of a moraine, and strong springs rise in a like position in the 
 Oorrie west of Oir Mhor. One of the most remarkable of the 
 springs is that which rises on the ridge south of Caisteal Abhail 
 at a height of nearly 2400 feet. The hUlside west of Caisteal 
 Abhail is called from it Leac an Tobair, or the Slope of the Well. 
 One famous well at Mid Thundergay on the west side of Arran, 
 Tobar Challumchille, takes its name from St. Columba. Several 
 shallow wells have been sunk for water in the gravel and sand of 
 the raised beach at Tormore. Another at the most southerly 
 house by the roadside is about 14 feet deep. The greater part of 
 it is in rubble and clay (glacial drift), but the lower part is sunk 
 two and a half feet in yellowish sandstone like that seen at the 
 King's Cove. W. G. 
 
APPENDIX. 
 
 PART I.— PAL^ONTOLOGICAL. 
 Note by B. N. Peach, P.RS. 
 
 A. — List of Localities from which Fossils have been obtained. 
 
 B. — General List of Fossils from the Carboniferous Eocks of 
 North Arran. 
 
 C. — Special List of Fossils found in each of the Sub-Divisions 
 of the Carboniferous System. 
 
 D. — Notes on the Mesozoic Fossils found in the Island of 
 Arran. 
 
 PART II.— PBTEOGRAPHICAL. 
 
 Notes on the Petrography of Old Red Sandstone Igneous Rocks, 
 by H. Kynaston, B.A. 
 
 Notes on the Petrography of the Carboniferous Igneous Rocks of 
 Arran, Bute, and the Cumbraes, by H. J. Seymour, B.A. 
 
 PART III —BIBLIOGRAPHICAL. 
 
APPENDIX, 
 
 PART L— PALiEONTOLOGICAL. 
 
 The following lists of fossils are based entirely on collections made 
 by the Geological Survey, chiefly by Messrs. Macconochie and Tait. 
 
 The Carboniferous fossils have been named by Mr. B. N. Peach 
 and Dr. C. B. Crampton, with assistance from the following specialists, 
 viz. : — Dr. Traquair, who has determined the Fishes ; Mr. Kidston, the 
 Plants ; and Dr. Wheelton Hind, the Lamellibranchs. 
 
 The Secondary Fossils found in the masses of strata preserved in 
 the great volcanic vent have been determined by Mr. E. T. Newton, 
 who has supplied special notes and lists. 
 
 The lists of Carboniferous fossils have been drawn up by Dr. 
 Crampton and Mr. Tait, under my supervision. 
 
 BEN. N. PEACH. 
 
 A. LIST OF LOCALITIES FEOM WHICH FOSSILS HAVE 
 BEEN OBTAINED BY THE GEOLOGICAL SURVEY 
 IN NORTH AERAN (Sheet 21). 
 
 Cretaceous, 
 (a) Ballymichael Glen, l^m. E.N.E. of Ballymichael. Blocks in 
 
 Volcanic Agglomerate. 
 (6) Dove Cave on Ard Bheinn, l|m. N.E. of Ballymichael. Masses in 
 
 Volcanic Vent. 
 
 Liassic. 
 
 (c) Ballymichael Glen, on north slope above stream, about 100 yards 
 
 above locality (a) ; l|m. E.N.E. of Ballymichael. Masses in 
 Volcanic Vent. 
 
 Rhaetic. 
 
 (d) Stream gully, ^m. N.E. of Derenenach. Mass in Volcanic Vent. 
 
 Triassic 
 
 1. Cock Shore, derived Carboniferous blocks in Red Conglomerate, 
 
 100 yds. east of the Cock of Arran. 
 
 Carboniferous and Old Red Sandstone. 
 
 2. AUt Mor, between North Newton and Cock of AiTan. 
 
 3. Hill slope, 500 yds. west of Cock Farm, Lochranza. 
 
 4. Cock Shore, north of Cock Farm, 20 yds. south-east of junction 
 
 with Triassic Rocks, and 620 yds. south-east of Cock of 
 Arran. 
 
154 The Qeology of North Arran. 
 
 5. Cock Shore, north of Cock Farm, 72 yds. south-east of junction 
 
 with Triassic Eocks. 
 
 6. Cock Shore, north of Cock Farm, 100 yds. south-east of junction 
 
 with Triassic Hocks. (Highest marine band observed.) 
 
 7. Cock Shore, north of Cock Farm, 220 yds. south-east of junction 
 
 with Triassic Rocks (" Coral Limestone "). 
 
 8. Cock Shore, 350 yds. south-east of junction with Triassic Rocks. 
 
 9. Cock Shore, 365 yds. south-east of junction with Triassic Rocks. 
 
 (Band overlying " Oephalopod Limestone.") 
 
 10. Cock Shore, 375 yds. south-east of junction with Triassic Rocks. 
 
 (" Cephalopod Limestone.") 
 
 11. Cock Shore, 460 yds. south-east of junction with Triassic Rocks. 
 
 {Productus latissimus limestone.) 
 
 12. Cock Shore, ironstone band, 450 yds. north-west of Saltpans. (In 
 
 the small bay here, are tessellated ferruginous beds.) 
 12a.Cock Shore, as above, bands overlying. 
 
 13. Cock Shore, opposite Cock Farm, 225 yds. north-west of Salt Pans. 
 
 (Dark-coloured limestone associated with hsematite beds.) 
 
 14. Cock Shore, 140 yds. north-west of old Salt Pans. 
 
 15. Salt Pans, sandstone at. 
 
 16. Laggan Shore, 170 yds. west of Hurlet Limestone (? Hosie Lime- 
 
 stone). 
 
 17. Laggan Shore. This band overlies the Hurlet Limestone and is 
 
 separated from it by 30 ft. of coarse sandstone, black alum 
 shale and 1| ft. impure limestone. 
 
 18. Laggan Shore. Hurlet Limestone, 220 yds. north-west of Laggan 
 
 Shepherd's cottage. 
 
 19. Laggan Shore, a few yards north of Laggan Cottage. 
 
 20. Laggan Shore, 100 yds. south-east of Laggan Cottage. 
 
 21. Laggan Shore, 750 yds. south-east of Laggan Cottage (" Wiinsch's 
 
 beds"). 
 
 22. Laggantuin Bay, Corloch, 300 yds. north-west of " Fallen Rocks." 
 
 (J. Thompson's fish band.) 
 
 23. South Glen Sannox Burn, at footbridge, about ^ mile from mouth. 
 
 (Lower Old Red Sandstone.) 
 
 24. Sannox Shore, about | mile south of Farchan Mor. (Upper Old 
 
 Red Sandstone.) 
 
 25. Corrie Limepits, Corrie. (Band above Hurlet Limestone.) 
 
 26. Corrie Shore, between Post Office and Ferry, 1st limestone south 
 
 of the sandstone at Ferry. {Productus latissimus limestone.) 
 
 27. Corrie Shore, a few yds. south of P. latissimus limestone. (FeiTu- 
 
 ginous band with many small gasteropods.) 
 
 28. Corrie Shore, between Post Office and Ferry, five or six_ yds. south 
 
 of preceding locality. 
 
 29. Corrie Shore, opposite Post Office, dark shale below the massive 
 
 sandstone opposite the Post Office garden. 
 
 30. Corrie Shore, opposite Oromla House, near low-water mark, 20 yds. 
 
 west of massive grey sandstone which underlies the Triassic 
 Sandstone. 
 
 31. Corrie Shore, near high-water mark, and 25 yds. south of northern 
 
 boundary of Cromla garden. 
 
 32. Locherim Burn, lower part, 200 yds. from sea, and 15 yds. up stream 
 
 from junction with Triassic Sandstone. 
 
 33. Locherim Burn, at waterfall, 330 yds. from sea. (Professor Ivison 
 
 Macadam's locality.) 
 
Appendix. 155 
 
 34. Maol Donn, old quarries at An Sgriob, | mile north of Maol Donn 
 
 cliff. (Shale below Hurlet Limestone.) 
 
 35. Maol Donn, higher on the slope and nearer the cliff than loc. 34. 
 
 (In red sandy shale above the limestone.) 
 
 36. Merkland Burn, | mile north of Brodick Castle. No. 1 loc, lowest 
 
 limestone seen in stream. 
 
 37. Merkland Burn, | mile north of Brodick Castle. No. 2 loc, a few 
 
 yards down stream from No. 1. 
 
 38. Merkland Burn, | mile north of Brodick Castle. No. 3 loc, a few 
 
 yards down stream from No. 2. , 
 
 39. Brodick Castle Policies, streamlet ^ mile north of Brodick Castle. 
 
 40. Brodick Castle, streamlet 300 yds. S.W. of, a few yards above 
 
 bridge. 
 
 41. Brodick Castle Sawmill, in mill lade. 
 
 42. Glen Rosie Burn, a few yards above the bridge near Brodick 
 
 Manse (" Musselband Ironstone "). 
 
 43. Glen Rosie, about 1 mile west of Glen Rosie Cottages, at streamlet 
 
 descending hill slope on the south side of the Glen, not far 
 from junction with schist. (Lower Old Red Sandstone.) 
 
 44. Brodick Church, limestone north-east of. 
 
 45. Glen Shurig, hill slope 5 mile south-east of String road. Old 
 
 quairies about i mile west of wood. 
 
 46. Benlister Burn, in bed of main stream below wateifall, 2^ miles 
 
 west of Lamlash Bay and | mile S.S.E. of Brisderg. 
 
 47. Benlister Glen, shale below Hurlet Limestone, 2| miles west of 
 
 Lamlash Bay, and neai-ly | mile S.S.W. of Brisderg. 
 
 48. Benlister Glen, streamlet entering from S. and 620 yds. south-east 
 
 of preceding locality. Hurlet Limestone. 
 
 49. Glen Shurig, main stream, about 1| miles from mouth and 200 
 
 yards above junction with Allt Mor. (Lower Old Red Sand- 
 stone.) 
 
 [List B. 
 
156 
 
 The Geology of North Arran. 
 
 B. GENEEAL LIST OF THE FOSSILS OBTAINED BY THE 
 GEOLOGICAL SUEVEY FEOM THE CAEBONIFEEOUS 
 EOOKS OF NOETH AERAN (Sheet 21). 
 
 
 Lower. 
 
 1 
 
 t3 
 
 
 
 
 Carbon. 
 
 
 
 
 1 
 
 Limestone 
 
 
 
 
 S i 
 
 Series. 
 
 OQ 
 
 
 
 
 1 
 
 Locality Numbers. 
 
 bpecies. 
 
 
 - 
 
 
 
 
 m 
 
 CQ 
 
 CQ 
 
 a> 
 
 
 
 il 
 
 §3§ 
 
 •3 
 
 O 
 
 (D O 
 
 ^ 
 
 
 
 •^ 
 
 O CD 
 
 O 
 
 
 "i 
 
 
 
 
 ^a 
 
 ^ 
 
 t=s 
 
 o 
 
 
 
 o 
 
 3 
 
 s 
 
 s 
 
 
 
 li'lUCALES AND CyCADOFILICBS. 
 
 
 
 
 
 
 
 Cardiopteris, Schimper 
 
 
 
 
 
 
 
 „ nana, Mchw 
 
 
 X 
 
 
 
 
 16 
 
 Mariopteris, Zeiller 
 
 
 
 
 
 
 
 „ murioata, Schloth. 
 
 
 
 
 
 X 
 
 4,32. 
 
 Neuropteris, Brongniart 
 
 
 
 
 
 
 
 ,, gigantea, Stemh. 
 
 
 
 
 
 X 
 
 4, 31, 35. 
 
 „ heterophylla, Brmigniart 
 
 
 
 
 
 X 
 
 32. 
 
 Rhacopteris, Schimper 
 
 
 
 
 
 
 
 „ sp. 
 
 X 
 
 
 
 
 
 21. 
 
 Sphenopteridium, Schimper 
 
 
 
 
 
 
 „ disseotum, GOpp. 
 
 
 
 
 X 
 
 
 38. 
 
 Sphenopteris, Brongniart 
 
 
 
 
 
 
 
 , , crassa, L. and H. 
 
 X 
 
 
 
 
 
 19 ?, 20. 
 
 , , (Rhodea) moravica, Mtt. 
 
 X 
 
 
 
 
 
 21. 
 
 ,, ,, patentissima, 
 
 
 
 
 
 
 
 Ett. 
 
 X 
 
 
 
 
 
 21. 
 
 „ sp 
 
 X 
 
 
 
 X 
 
 
 20. 21, 22, 33. 
 
 Stems of Ferns indt 
 
 X 
 
 
 
 
 X 
 
 4,22. 
 
 Equisetales. 
 
 
 
 
 
 
 
 Calamariai. 
 
 
 
 
 
 
 
 Asterocalamites, Schimper 
 
 
 
 
 
 
 
 ,, scrobiculatus, Schl. 
 
 
 
 
 X 
 
 
 33. 
 
 Calamites, [Suckow. ) ScUotheim 
 
 
 
 
 
 
 
 Group 1. , Calamitina, Weiss. 
 
 
 
 
 
 
 
 „ varians, jStem6 
 
 
 
 
 
 X 
 
 4. 
 
 GroupII.,Euoalamites, Weist, 
 
 
 
 
 
 
 
 ramosus, Artis = nodosus, 
 
 
 
 
 
 
 
 L.andH. 
 
 
 
 
 
 X 
 
 4,35. 
 
 Group III., Stylocalamites, 
 
 
 
 
 
 
 
 Weiss. 
 
 
 
 
 
 
 
 ,, Suokowi, Brongniart 
 
 
 
 
 
 X 
 
 46. 
 
 ,, sp. ? indt. 
 
 
 
 
 
 X 
 
 4, 5, 32, 35, 46. 
 
 Sphbnophs;l,lales. 
 
 
 
 
 
 
 
 Sphenophylluni, Brongniart 
 
 
 
 
 
 
 
 „ myriophyllum, Orepin 
 
 
 
 
 
 X 
 
 4. 
 
 sp 
 
 
 
 
 
 X 
 
 4. 
 
 Lycopodiales. 
 
 
 
 
 
 
 
 Lepidodendron, Sternberg 
 
 
 
 
 
 
 
 „ veltheiinianum,/S<em6. 
 
 
 X 
 
 X ? 
 
 X 
 
 
 15 ?, 33, 34. 
 
 „ sp 
 
 X 
 
 X 
 
 
 X 
 
 X 
 
 17, 18, 21, 30, 33. 
 
 Lepidophloios, Sternberg 
 
 
 
 
 
 
 
 ,, wiinsohianus, Oarr. ... 
 
 X 
 
 
 
 
 
 21. 
 
 ..• sp 
 
 X 
 
 
 
 
 
 21. 
 
Appendix. 
 
 157 
 
 
 Lower. 
 
 S3 
 
 
 
 a 
 
 Carbon. 
 
 
 
 
 Limestone 
 
 
 
 
 ^ 
 
 Series. 
 
 t 
 
 
 Species. 
 
 a to 
 
 
 1 
 
 Locality Numbers. 
 
 
 
 
 
 OJ a 
 
 
 
 
 cd 
 
 
 
 ^ '7^ 
 
 □9 
 
 m 
 
 01 
 
 flj 
 
 
 
 3 ^ 
 
 ;3 
 
 
 "3 
 o 
 
 o 
 
 -1 
 
 hi n 
 
 Qj to 
 
 ^1 
 
 
 
 
 
 ;3 
 
 ? 
 
 a 
 
 
 
 Lycopodiales — contimied. 
 
 
 
 
 
 
 
 Lepidostrobus, Brongniart 
 
 
 
 
 
 
 
 „ sp 
 
 
 
 
 X 
 
 X 
 
 5,33. 
 
 Sigillaria, Brongniart 
 
 
 
 
 
 
 
 ,, Taylori, Carr 
 
 
 
 
 X 
 
 
 33. 
 
 Stigmaria, Brongniart 
 
 
 
 
 
 
 
 sp 
 
 ■^ 
 
 X 
 
 
 X 
 
 X 
 
 16, 19, 21, 33, 35. 
 
 Gtmnospbrm^. 
 
 
 
 
 
 
 
 Artisia, Presl. 
 
 
 
 
 
 
 
 „ approximata, Brongniart ... 
 
 
 
 
 
 X 
 
 35. 
 
 Carpolithes, Brongniart 
 
 
 
 
 
 
 
 „ sulcata, Lindl 
 
 
 
 
 X 
 
 
 33. 
 
 Cordaites, Unger 
 
 
 
 
 
 
 
 „ principalis, Oerinar 
 
 
 
 
 
 X 
 
 4,5. 
 
 sp 
 
 X 
 
 
 
 
 
 22. 
 
 PORIFEBA. 
 
 
 
 
 
 
 
 Sponge spicules in chert nodules 
 
 
 X 
 
 
 
 
 48. 
 
 ACTINOZOA. 
 
 
 
 
 
 
 
 Alveolites, Lamarck 
 
 
 
 
 
 
 
 ,, depressa? Flem 
 
 
 
 
 X 
 
 
 3. 
 
 Lithostrotion, Lhwyd. 
 
 
 
 
 
 
 
 Portlocki, M. Edw. ... 
 
 
 
 
 X 
 
 
 37. 
 
 Syringopora, Goldfuss 
 
 
 
 
 
 
 
 ,, ramulosa, Gold/. 
 
 
 X 
 
 
 
 
 34. 
 
 sp 
 
 
 X 
 
 
 
 
 18. 
 
 Zaphrentis, Jiafine-ique 
 
 
 
 
 
 
 
 sp 
 
 
 X 
 
 
 X 
 
 
 11, 16?, 18. 
 
 Incertce sedis^ 
 
 
 
 
 
 
 
 Monticulipora, d'Orbigny 
 
 
 
 
 
 
 
 ,, tumida, Phill. 
 
 
 X 
 
 
 X 
 
 
 11, 47, 48. 
 
 sp 
 
 
 X 
 
 
 
 
 25. 
 
 ECHINODEBMATA. 
 
 
 
 
 
 
 
 Archseocidaris, M'Ooy 
 
 
 
 
 
 
 
 ,, Urei, Flem 
 
 
 X 
 
 X 
 
 X 
 
 
 11, 14, 16, 17. 18, 34; 47. 
 
 .. sp 
 
 
 X 
 
 
 
 
 48. 
 
 Asteroid, part of ? 
 
 
 X 
 
 
 
 
 25. 
 
 Crinoid ossicles 
 
 
 X 
 
 
 X 
 
 
 2, 3, 6, 11, 17, 25, 26, 
 
 34, 36, 47. 
 
 Echinoid plates and part of lantern... 
 
 
 X 
 
 
 
 
 16, 47. 
 
 Annelida. 
 
 
 
 
 
 
 
 Spirorbis, Lamarck 
 
 
 
 
 
 
 
 sp 
 
 
 X 
 
 
 
 
 34. 
 
 Worm tubes? 
 
 
 X 
 
 
 
 
 18. 
 
 Artheopoda. 
 
 
 
 
 
 
 
 Ostrokcoda. 
 
 
 
 
 
 
 
 Beyriohia, M'Coy 
 
 
 
 
 
 
 
 sp 
 
 
 x 
 
 
 
 
 25. 
 
158 
 
 The Geology of North Arran. 
 
 
 Lower. 
 
 
 1 
 
 
 
 
 Carbon. 
 
 
 
 § 
 
 Limestone 
 
 
 
 
 1 
 
 Series 
 
 . 
 
 i 
 
 
 Species, 
 
 Is 
 
 
 
 
 Locality Numbers. 
 
 
 K 
 
 
 
 il 
 
 d3 
 
 1 
 
 ^1 
 
 1 
 
 
 
 3 
 
 3 
 
 H 
 
 3 
 
 
 
 Abthropoda — contiimed. 
 
 
 
 
 
 
 
 Trilohita. 
 
 
 
 
 
 
 
 Braeliymetopus, M'Coy 
 
 
 
 
 
 
 
 ,, ouralious, de Vem. 
 
 
 
 
 X 
 
 
 3. 
 
 Phillipsia, Portlock. 
 
 
 
 
 
 
 
 „ Eiohwaldi, Fischer var. 
 
 
 
 
 
 
 
 mucronata, ilf'Cof/ 
 
 
 X 
 
 
 X 
 
 
 11, 25. 
 
 ji sp 
 
 
 X 
 
 
 
 
 47?. 
 
 POLTZOA. 
 
 
 
 
 
 
 , 
 
 Fenestella, Lonsdale 
 
 
 
 
 
 
 
 „ plebeia, M'Coy 
 
 
 X 
 
 
 
 
 25,47. 
 
 ^, .- sp 
 
 
 X 
 
 
 X 
 
 
 11, 25, 26, 34. 
 
 Glauoonome, Goldfuss 
 
 
 
 
 
 
 
 sp ■. 
 
 
 X 
 
 
 
 
 25. 
 
 Polypora, M'Coy 
 
 
 
 
 
 
 
 sp 
 
 
 X 
 
 
 
 
 18. 
 
 Retepora, Lamarck 
 
 
 
 
 
 
 
 „ undata, M'Coy 
 
 
 
 X 
 
 
 
 14. 
 
 Rhabdomeson, Young 
 
 
 
 
 
 
 
 rhombiferum, Philt. 
 
 
 X 
 
 
 X 
 
 
 28, 34. 
 
 sp 
 
 
 X 
 
 
 
 
 17. 
 
 BkaohiopOda. 
 
 
 
 
 
 
 
 Athyris, M'Coy 
 
 
 
 
 
 
 
 „ ambigua, Sow 
 
 
 X 
 
 
 X 
 
 
 11, 16, 26, 36, 47. 
 
 „ lamellosa, L&veilU 
 
 
 X 
 
 
 
 
 18?. 
 
 „ Roysi, LiveilU 
 
 
 
 
 X 
 
 
 36?. 
 
 sp 
 
 
 X 
 
 
 X 
 
 
 10, 18, 25, 47. 
 
 Camarophoria, King 
 
 
 
 
 
 
 
 „ crumeiia, Martin 
 
 
 
 
 X 
 
 
 26. 
 
 sp 
 
 
 
 X 
 
 
 
 13?. 
 
 Chonetes, Fischer 
 
 
 
 
 
 
 
 „ buohiana, de ^o» 
 
 
 X 
 
 
 
 
 16?. 
 
 „ laguessiana, rfe ^on. 
 Disoina, Lamarck 
 
 
 X 
 
 
 X 
 
 
 11,16,18,25,26,34,47. 
 
 „ nitida, Phill. 
 
 
 X 
 
 
 
 
 16, 17. 
 
 Lingula, Brugui^re 
 
 
 
 
 
 
 
 ,, mytiloides, Soio 
 
 
 X 
 
 X 
 
 X 
 
 
 6, 14, 16, 17, 18, 36. 
 
 ,, squamiformis, Phill. 
 
 
 X 
 
 X 
 
 X 
 
 
 14, 16, 17, 27, 29, 41. 
 
 Orthis, Dalman 
 
 
 
 
 
 
 
 ,, resupinata, Martin 
 
 
 X 
 
 
 X 
 
 
 2, 10, U, 18, 33. 
 
 ., sp 
 
 
 X 
 
 
 
 
 48. 
 
 Produotus, Sowerby 
 
 
 
 
 
 
 
 „ aouleatus, Martin 
 
 
 X 
 
 
 
 
 18. 
 
 ,, coatatus, /Soto 
 
 
 
 
 X 
 
 
 11, 36. 
 
 fimbriatus, Sow 
 
 
 X 
 
 
 ? 
 
 
 6 ?, 25, 34, 47. 
 
 ,, giganteus, Martin 
 
 
 X 
 
 X 
 
 X 
 
 
 9 ?, 10, 12, 13, 17, 18, 
 25,34,44,46,47,48. 
 
 „ latissimus, Sow 
 
 
 X 
 
 ; 
 
 X 
 
 
 3, 11, 14, 25, 26, 28, 
 37, 40, 47. 
 
 ,, longispinus, Soto. 
 
 
 X 
 
 
 X 
 
 
 11, 16, 34, 36, 47. 
 
Appendix. 
 
 159 
 
 
 Lower. 
 
 
 
 
 1 
 
 Carbon. 
 
 
 
 
 Limestone 
 
 
 
 
 
 Series 
 
 
 i 
 
 
 Species. 
 
 «S w 
 
 
 
 1 
 
 Locality Numbers. 
 
 
 „ 
 
 
 
 CZ2,g 
 
 
 
 
 rt 
 
 
 
 OCI3 
 
 S3 
 
 31 
 
 o 
 
 S3 
 
 s g 
 
 CO 
 
 o 
 
 o 
 
 
 
 "3 
 o 
 
 ;3 
 
 s 
 
 H 
 
 
 
 Brachiopoda — continued. 
 
 
 
 
 
 
 
 Productus mesolobus, Phill. 
 
 
 
 
 X 
 
 
 26. 
 
 „ muricatus (?), PAiS. 
 
 
 
 
 X 
 
 
 6 ?, 9 ?. 
 
 „ proboscideus, de Vem. ... 
 
 
 X 
 
 
 
 
 34. 
 
 „ piinctatus, Mart. 
 
 
 X 
 
 
 
 
 25, 47. 
 
 ,, pustiilasus, Phill. 
 
 
 X 
 
 
 
 
 34. 
 
 „ scabrieulus, Jlfart. 
 
 
 X 
 
 
 
 
 25, 34. 
 
 „ semiretioulatus, Mart. ... 
 
 
 X 
 
 
 X 
 
 
 11, 18,25,34, 36,47. 
 
 ,, youngiamis, Z)az/. 
 
 
 X 
 
 
 
 
 18, 34. 
 
 sp 
 
 
 X 
 
 
 X 
 
 
 2, 3, 6, 9, 10, 11, 16, 17, 
 18, 25, 33, 36, 40, 47. 
 
 Retzia, King 
 
 
 
 
 
 
 
 „ radialis, Phill. 
 
 
 X 
 
 
 
 
 16. 
 
 „ sp 
 
 
 X 
 
 
 
 
 25, 47. 
 
 Rhynchonella, Fischer 
 
 
 
 
 
 
 
 ,, acuminata, Mart., ... 
 
 
 X 
 
 
 
 
 34. 
 
 ,, pleiirodon, Pftitf. 
 
 
 X 
 
 X 
 
 X 
 
 
 12, 17, 25, 26, 34. 
 
 „ pugnus, Mart. 
 
 
 X 
 
 
 
 
 34. 
 
 sp 
 
 
 X 
 
 
 
 
 17, 47. 
 
 Spirifera, Sowerhy 
 
 
 
 
 
 
 
 „ duplicicosta (?), Phill. 
 
 
 X 
 
 
 
 
 34. 
 
 „ glabra, Mart. 
 
 
 X 
 
 
 X 
 
 
 6, 16, 36 ?, 47. 
 
 ,, grandicostata{?), Jlf'(7oy ... 
 
 
 X 
 
 
 
 
 34. 
 
 ,, lineata, Martin 
 
 
 X 
 
 
 X 
 
 
 10, 18. 25. 
 
 ,, trigonalis. Mart 
 
 
 X 
 
 
 X 
 
 
 6, 16, 17, 18, 25, 34, 47. 
 
 ,, ,, var. bisulcata, Sow. 
 
 
 X 
 
 
 X 
 
 
 10, 16, 17, 25 ?, 48. 
 
 „ triradialis, Phill 
 
 
 
 
 X 
 
 
 11. 
 
 sp 
 
 
 X 
 
 
 
 
 17, 25, 47. 
 
 Spiriferina, d'OrUgny 
 
 
 
 
 
 
 
 ,, cristata, Schloth. 
 
 
 X 
 
 
 
 
 17, 18, 25,34, 47?. 
 
 ,, ,, var. octoplioata, iSoio. 
 
 
 X 
 
 
 X 
 
 
 11, 18, 25, 47. 
 
 ,, laminosa (?), ilf' Coy 
 
 
 X 
 
 
 
 
 34. 
 
 „ sp 
 
 
 V 
 
 
 
 
 17. 
 
 Strepborhynohus, King 
 
 
 
 
 
 
 
 „ (Orthotetes), creni- 
 
 
 
 
 
 
 (3, 6, 9, 10, 11, 13, 14, 
 
 stiia, Phill. 
 
 
 X 
 
 X 
 
 X 
 
 
 \ 16,18,25,26,33,36, 
 I 47. 
 
 Terebratula, Lhivyd. 
 
 
 
 
 
 
 
 ,, (Dielasma), hastata, Soio. 
 
 
 X 
 
 
 
 
 34, 47. 
 
 sp. ... 
 
 
 
 
 X 
 
 
 9. 
 
 LaMELLIBRANCHI AT A . 
 
 
 
 
 
 
 
 Actinopteria, ffall 
 
 
 
 
 
 
 
 ,, (Pteronites), sulcata. 
 
 
 
 
 
 
 
 M'Ooy 
 
 X 
 
 
 
 
 
 16. 
 
 AUorisma, King 
 
 
 
 
 
 
 
 ,, sulcata, i'Vem 
 
 X 
 
 X 
 
 
 X 
 
 
 3, 16, 18, 21, 26, 28, 29, 
 33, 34, 36. 
 
 sp 
 
 
 
 X 
 
 
 
 12a. 
 
 Anthracomya, Salter 
 
 
 
 
 
 
 
 ,, modiolaris, Sov. 
 
 
 
 
 
 X 
 
 38? 
 
160 
 
 The Geology of North Arran. 
 
 
 Lower. 
 
 
 ft 
 
 
 
 
 
 
 a 
 
 
 
 a 
 
 o 
 
 Carbon. 
 
 
 
 
 Limestone 
 
 
 
 
 1 
 
 Series 
 
 . 
 
 ra 
 
 
 Species. 
 
 1- 
 
 
 
 
 c» 
 
 Locality Numbers. 
 
 
 « 
 
 
 
 CC IB 
 
 
 
 
 c3 
 
 
 
 
 4 
 
 CO 
 
 -a 
 
 -1 
 
 M 
 
 5 
 
 
 
 6 
 
 3 
 
 f 
 
 3 
 
 
 
 Lamelliebanchiata — cmitinued. 
 
 
 
 
 
 
 
 Aviculopeoten, M'Goy 
 
 
 
 
 
 
 
 ,, ocelatus, M'Goy 
 
 
 X 
 
 
 
 
 48. 
 
 ,, dissimilis, Phill. 
 
 
 
 
 X 
 
 
 40. 
 
 M\ax,M'Ooy 
 
 
 X 
 
 
 
 
 17 ?, 25, 34. 
 
 Hardingi, M'Coy ... 
 
 
 X 
 
 
 
 
 17?. 
 
 knockonnieusis, 
 
 
 
 
 
 
 
 M'0(yy 
 
 
 X 
 
 X 
 
 
 
 12, 12a, 16?, 18,2.5. 
 
 ,, semiciroularis, M'Coy 
 
 
 X 
 
 
 
 
 25. 
 
 ,, textilis, de Ken. 
 
 
 X 
 
 
 
 
 17. 
 
 sp 
 
 
 >< 
 
 
 
 
 1, 12, 16, 25, 27, 29, 34, 
 40. 
 
 ,, with colour bands ... 
 
 
 V 
 
 
 
 
 17, 18. 
 
 Carbonioola, M'Goy 
 
 
 
 
 
 
 
 , , (Anthracoaia), acuta, Sow. 
 
 
 
 
 
 X 
 
 30,32,38,39,42?, 46. 
 
 „ „ var. rhom- 
 
 
 
 
 
 
 
 boidalis, Hind. 
 
 
 
 
 
 X 
 
 38. 
 
 ,, ,, aquilina, (Soto. 
 
 
 
 
 
 X 
 
 30, 32. 
 
 sp 
 
 
 
 
 X 
 
 
 7, 8, 42. 
 
 Cardiomorpha, de Koninck 
 
 
 
 
 
 
 
 „ parva, Hind 
 
 
 X 
 
 
 
 
 34. 
 
 Ctenodonta, Salter 
 
 
 
 
 
 
 
 „ pentonensis, Hind. 
 
 
 X 
 
 
 
 
 16. 
 
 Cyprioardella, Hodl 
 
 
 
 
 
 
 
 „ rectangularis, M'Coy 
 
 
 X 
 
 
 
 
 34. 
 
 Edmondia, de Koninck 
 
 
 
 
 
 
 
 , , Josepha, de Kon 
 
 
 X 
 
 
 X 
 
 1 
 
 16,17,18,26,36,40,46?. 
 
 ,, pentonensis, Hind. 
 
 X 
 
 X 
 
 
 
 
 17, 18, 21. 
 
 ,, ludia, M'Coy 
 
 
 X 
 
 X 
 
 X 
 
 
 12a, 16, 17, 26, 28. 
 
 „ soalaris, M'Coy 
 
 
 X 
 
 
 
 
 16 ?, 34. 
 
 ,, sulcata, Pfo'M 
 
 
 X 
 
 
 
 
 17, 18, 34. 
 
 ,, unioniformis, PhUl. 
 
 
 X ? 
 
 
 X 
 
 
 33, 34. 
 
 „ sp 
 
 
 X 
 
 X 
 
 X 
 
 
 8, 12, 16, 25, 34. 
 
 Entolium, Meek 
 
 
 
 
 
 
 
 ,, (Pecten) Sowerbyi, M'Coy 
 
 
 X 
 
 X 
 
 X 
 
 
 12, 16, 17, 18, 34, 36. 
 
 „ young of 
 
 
 
 X 
 
 
 
 12a. 
 
 Leiopteria, Hall 
 
 
 
 
 
 
 
 ,, (Avicula), lunulata,PMK. 
 
 
 X 
 
 
 
 
 25, 34. 
 
 ,, ,, recta,, M'Coy... 
 
 
 X 
 
 
 
 
 34. 
 
 ,, ,, squamosa,PAiK. 
 
 
 X 
 
 
 
 
 25, 34. 
 
 sp 
 
 
 X 
 
 
 
 
 25, 28. 
 
 Lithodomus, Cuvier 
 
 
 
 
 
 
 
 ,, lingualis, Phill. 
 
 
 X 
 
 
 X 
 
 
 16, 25, 36. 
 
 Myalina, de Koninck 
 
 
 
 
 
 
 
 ,, Flemingi, M'Coy 
 
 
 X 
 
 
 
 
 17, 25, 34. 
 
 ,, peralata, rfe /Cow 
 
 
 X 
 
 
 
 
 25. 
 
 „ Vemeuili, M'Coy 
 
 
 X 
 
 X 
 
 X 
 
 V ? 
 
 3, 12, 17, 32?, 33, 
 
 ,, sp 
 
 
 X 
 
 X 
 
 X 
 
 
 12,25,287,33,34. 
 
 Naiadites, Dawson 
 
 
 
 
 
 
 
 ,, (Myalina) crasaa, i^fem. ... 
 
 
 
 
 
 X 
 
 46?. 
 
 ,, modiolaris, Sow 
 
 
 
 
 
 X 
 
 30. 
 
 ,, quadrata, Soio 
 
 
 
 
 
 X 
 
 38. 
 
Appendix. 
 
 161 
 
 ypecies. 
 
 Lower. 
 
 -a 
 
 02.2 
 
 S ID 
 Ot/3 
 
 Carbon. 
 
 Limestone 
 
 Series. 
 
 a o 
 
 1^ S 
 
 3 
 
 Locality Numbers. 
 
 Lamellibkanchiata — continued. 
 Naiadites (periostraoiim of) ... 
 
 sp 
 
 Nucula, Lamarck 
 
 ,, gibbosa, Flem. 
 
 „ luciniformis, PM?. . . . 
 
 „ scotica, Hind. 
 
 sp. 
 
 Niiculana, Lin!c. 
 
 ,, acuta, tlow. 
 
 „ attenuata, i'7em 
 
 „ brevirostris, PMK. 
 
 Paralielodon, Morris and Lycett 
 
 „ Geinitzi, cic .2'on. 
 
 Pecten, Linnasus 
 
 ,, (Streblopteria) laevigata ? 
 
 M'Coy 
 
 Pinna, Linnceus 
 
 „ flabelliformis, Mojrtin 
 
 ,, mutioa,, M'Coy 
 
 „ young form 
 
 Protosohizodus, de KonincJc 
 
 ,, axiniformis, Portl.... 
 
 ,, obliquus, M'Coy ... 
 
 sp 
 
 Sanguinolites, M'Coy 
 
 ,, clavatviB, Mh. Jr. 
 
 ,, striatus, Hind. 
 
 , , tricostatus, Portl. 
 
 „ ,, (very short form) 
 
 ,, variabilis, M'Coy 
 
 Sedgwickia, M'Coy 
 
 ,, gigantea, Jf'Ooy 
 
 Solenomya, Lamarck 
 
 ,, primssva, Phill 
 
 Solenopsis, M'Coy 
 
 ,, minor, M'Coy 
 
 Gasteropoda. 
 Aolisina, de Koninck 
 
 ,, elongata, Flem 
 
 ,, (Murchisonia) striatula, 
 
 de Kon 
 
 Acroculia, PMlvps 
 
 „ (Capulus) trilobus, Phill... 
 
 Bellerophon, Montfort 
 
 ,, decussatus, Mem. 
 
 ,, striatus, Flem. 
 
 ,, hiulous, Martin 
 
 ,, Urei, i'Vem 
 
 38. 
 32, 46 ?. 
 
 9, 12, 12a, 26, 33, 34. 
 26, 28. 
 28. 
 11, 36. 
 
 12. 
 
 8, 9, 12, 12a, 18, 26, 28, 
 
 29, 33, 40. 
 16, 18. 
 
 40. 
 
 12a. 
 
 16, 17, 28, 34. 
 34. 
 
 18. 
 
 12, 17, 28, 33, 34, 40 ?. 
 
 25, 33, 34. 
 
 26, 34. 
 
 26. 
 
 12, 16, 17, 34. 
 
 17. 
 
 16, 17, 26, 34. 
 
 17, 21. 
 29. 
 
 8. 
 
 27, 28. 
 
 27. 
 
 17. 
 
 25, 26, 28, 29, 34, 40. 
 25. 
 
 12, 16 ?. 
 
 6, 12, 12a, 13, 16, 25, 
 26, 34, 40. 
 
162 
 
 The Geology of North Arran. 
 
 
 Lower. 
 
 
 
 
 <u 
 
 Carbon. 
 
 
 
 
 Limestone 
 
 
 
 Species. 
 
 1 
 
 Series. 
 
 3 
 
 Locality Numbers. 
 
 <3 m 
 
 
 .^ 
 
 
 
 012 aj 
 
 
 
 
 
 
 
 
 to 
 
 ID 
 
 1" 
 
 <0 
 
 i 
 
 II 
 
 1 
 
 1 
 
 
 
 ■M 
 
 ^B 
 
 ID 
 
 Pl 
 
 o 
 
 
 
 6 
 
 3 
 
 w 
 
 3 
 
 
 
 Gasteropoda — contimied. 
 
 
 
 
 
 
 
 Bellerophon sp. 
 
 
 X 
 
 
 X 
 
 
 33,34,45?. 
 
 Dentalium, Linnceus. 
 
 
 
 
 
 
 
 „ (Entalis) ingens., dc .K'om. 
 
 
 X 
 
 
 X 
 
 
 26, 27, 34. 
 
 „ inornatum, M'Coy 
 
 
 
 
 X 
 
 
 3. 
 
 Euomphalus, Sowerby 
 
 
 
 
 
 
 
 ,, carbonarius, Sow. 
 
 
 X 
 
 
 X 
 
 
 16, 26, 34. 
 
 „ catillus, (Sow 
 
 
 y; 
 
 
 
 
 16. 
 
 ,, nodosus, /Sow 
 
 
 X 
 
 
 
 
 34. 
 
 pentangulatus, (Sow. ,,, 
 
 
 X 
 
 
 
 
 25. 
 
 >) sp.. 
 
 
 X 
 
 
 X 
 
 
 17, 34, 40. 
 
 Loxonema, Phillips 
 
 
 
 
 
 
 
 ,, constriotum, Sow. 
 
 
 X 
 
 
 X 
 
 
 26, 34. 
 
 „ Lefebvrei, L4v 
 
 
 
 
 X 
 
 
 26. 
 
 „ rugiferum, PMll. 
 
 
 
 
 X 
 
 
 40. 
 
 „ soalaroideum, Phill. 
 
 
 
 
 X 
 
 
 40. 
 
 sp 
 
 
 X 
 
 
 
 
 25. 
 
 MaorooheiluB, Phillips 
 
 
 
 
 
 
 
 ,, (Macrochilina) aoutus, 
 
 
 
 
 
 
 
 Sow. 
 
 
 y 
 
 
 X 
 
 
 3, 16, 26, 27, 28. 
 
 „ (Maoroohilina) canali- 
 
 
 
 
 
 
 
 eulatus, M'Coy ... 
 
 
 
 
 X 
 
 
 33. 
 
 „ (Macroohilina) imbri- 
 
 
 
 
 
 
 
 catus, Sow. 
 
 
 
 
 X 
 
 
 26, 27, 28. 
 
 sp 
 
 
 X 
 
 
 
 
 25, 48 ?. 
 
 Metoptoma, Phillips 
 
 
 
 
 
 
 
 „ elliptica, PM/ 
 
 
 
 
 X 
 
 
 27, 28. 
 
 Miorodoraa, Meeh and Worthen 
 
 
 
 
 
 
 
 , , (Trochus) biserrata, Phill. 
 
 
 X 
 
 
 
 
 34. 
 
 ,, „ senilimba, Phill. 
 
 
 
 
 X 
 
 
 40. 
 
 Murchisonia, d'Arch. and de Vem. 
 
 
 
 
 
 
 
 „ angulata, Phill. 
 
 
 X 
 
 
 X 
 
 
 26, 27, 28, 34. 
 
 „ cincta?, Donald 
 
 
 
 
 X 
 
 
 28. 
 
 ,, (Hypergonia) quadri- 
 
 
 
 
 
 
 
 oarinata, M'Coy 
 
 
 
 
 X 
 
 
 27. 
 
 Nariea, Beclvz 
 
 
 
 
 
 
 
 „ variata, Phill. 
 
 
 X 
 
 
 
 
 34. 
 
 Natieopsis, M'Coy 
 
 
 
 
 
 
 
 „ oanalioulata, Jlf' Coy 
 
 
 X 
 
 
 
 
 16. 
 
 „ -plicistiia,, Phill 
 
 
 X 
 
 
 
 
 17.25. 
 
 >. sp. 
 
 
 X 
 
 
 X 
 
 
 25, 40. 
 
 Pleurotomaria, Defrance 
 
 
 
 
 
 
 
 ,, (Ptyohomphalus) 
 
 
 
 
 
 
 
 a,toTaB,Tia,, Phill. ... 
 
 
 
 
 X 
 
 
 26. 
 
 „ momiiteia, Phill. 
 
 
 X 
 
 
 
 
 25. 
 
 „ tvLtaida, Phill. 
 
 
 X 
 
 
 
 
 25. 
 
 >, sp 
 
 
 X 
 
 
 X 
 
 
 25, 40. 
 
 ,, (Baylea) Yvani, Liv. 
 
 
 X 
 
 
 
 
 25. 
 
 Porcellia, LiveilU 
 
 
 
 
 
 
 
 „ Puzosi) L4v. 
 
 
 X 
 
 
 
 
 25. 
 
Aj>pendix. 
 
 163 
 
 
 Lower. 
 
 1 
 
 
 
 
 <D 
 
 Carbon. 
 
 
 
 
 § 
 
 Limestone 
 
 
 
 
 Species. 
 
 
 Series. 
 
 03 
 
 
 
 S i 
 
 
 K 
 
 
 g 
 
 Locality Numbers 
 
 
 
 
 □3 
 
 03 
 
 m 
 
 (U 
 
 
 
 
 
 §3i 
 
 
 0) 
 
 s 
 
 
 
 
 
 11 
 
 o 
 
 
 'c8 
 O 
 
 
 
 
 z 
 
 ^1 
 
 60 
 
 t=l 
 
 O 
 
 
 
 
 6 
 
 3 
 
 ^ 
 
 3 
 
 
 
 
 Pteropoda ? 
 
 
 
 
 
 
 
 
 Conularia, Miller 
 
 
 
 
 
 
 
 
 „ quadrisulcata, Sow. 
 
 
 X 
 
 
 
 
 17. 
 
 
 Cephalopoda. 
 
 
 
 
 
 
 
 
 Aotinoceras, Brown 
 
 
 
 
 
 
 
 
 „ . sp 
 
 
 X 
 
 
 
 
 25. 
 
 
 Cyrtoceras, Goldfuss 
 
 
 
 
 
 
 
 
 sp 
 
 
 X 
 
 
 
 
 25. 
 
 
 Nautilus, Breymus 
 
 
 
 
 
 
 
 
 „ (Aoanthonautilus) bispin- 
 
 
 
 
 
 
 
 
 osus, A. H. Foord 
 
 
 
 
 X 
 
 
 10 
 
 
 ,, (Planetoceras) globatus, 
 
 
 
 
 
 
 
 
 Sow 
 
 
 
 
 X 
 
 
 26. 
 
 
 „ (Ccelonautilus) subsulcatus, 
 
 
 
 
 
 
 
 
 Phill 
 
 
 X 
 
 
 
 
 16, 25. 
 
 
 „ (Stroboceras) (Dixoites) 
 
 
 
 
 
 
 
 
 sulcatus, Sow 
 
 
 X 
 
 
 
 
 17. 
 
 
 (Pleuronautilus) nodiferus, 
 
 
 
 
 
 
 
 
 Armstrong 
 
 
 
 
 X 
 
 
 10. 
 
 
 sp 
 
 
 X 
 
 
 
 
 17, 25. 
 
 
 Orthoceras, Breymus 
 
 
 
 
 
 
 
 
 „ annulare, Mem. 
 
 
 X 
 
 X 
 
 
 
 12, 34. 
 
 
 , , insequiseptum, Phill. 
 
 
 X 
 
 
 
 
 34. 
 
 
 sp. 
 
 
 X 
 
 X 
 
 X 
 
 
 9, 12a, 16, 17, 25, 
 36. 40. 
 
 34, 
 
 Trigonooeras, M'Ooy 
 
 
 
 
 
 
 
 
 ,, meyerianum, de Kon. 
 
 
 X 
 
 
 
 
 25. 
 
 
 Pisces. 
 
 
 
 
 
 
 
 
 Selachii. 
 
 
 
 
 
 
 
 
 Cladodus, Agassiz 
 
 
 
 
 
 
 
 
 „ striatus, Ag. 
 
 
 
 1^ 
 
 
 
 12a. 
 
 
 Coehliodont tooth s. «. 
 
 
 X 
 
 
 
 
 25. 
 
 
 Pceoilodua, Agassiz 
 
 
 
 
 
 
 
 
 „ Jonesi, M'Ooy 
 
 
 X 
 
 
 
 
 25, 48. 
 
 
 Polyrhizodus, M'Coy 
 
 
 
 
 
 
 
 
 „ magnus, M'Coy 
 
 
 X 
 
 
 
 
 25. 
 
 
 Xystrodus, Agassiz 
 
 
 
 
 
 
 
 
 ,, striatus, M'Ooy 
 
 
 X 
 
 
 
 
 25. 
 
 
 Teleostomi- Crossopterygii. 
 
 
 
 
 
 
 
 
 Megalichthys, Agassiz 
 
 
 
 
 
 
 
 
 „ Hibberti, j4(7. 
 
 
 
 
 
 X 
 
 38. 
 
 
 sp 
 
 
 X 
 
 
 
 
 16, 25, 48. 
 
 
 Rhizodopsis, Huxley 
 
 
 
 
 
 
 
 
 „ sauroides, Will. 
 
 
 
 
 
 X 
 
 38. 
 
 
 sp 
 
 
 
 
 
 X 
 
 39. 
 
 
 Rhizodus, Owm 
 
 
 
 
 
 
 
 
 ,, Hibberti (Ag. and Hib.) ... 
 
 X 
 
 
 
 
 
 22. 
 
 
 ornatus, Traq 
 
 X 
 
 
 
 
 
 22. 
 
 
164 
 
 The Oeology of North Arran. 
 
 
 
 
 u 
 
 
 
 
 
 (U 
 
 
 
 
 Lower. 
 
 1 
 
 
 
 1 
 
 Carbon. 
 
 
 
 
 Limestone 
 
 
 
 Species. 
 
 □Q 
 
 <3 00 
 
 Series. 
 
 OS 
 
 1 
 
 Locality Numbers. 
 
 
 „ 
 
 
 
 OQ © 
 
 
 
 
 cd 
 
 
 - 
 
 P 
 
 GO 
 
 II 
 
 o 
 Q 
 
 II 
 
 "3 
 
 
 
 M-l 
 
 5 S 
 
 0) 
 
 £<S 
 
 o 
 
 
 
 'G 
 
 ^a 
 
 •v 
 
 ^l 
 
 o 
 
 
 
 3 
 
 3 
 
 f 
 
 '■A 
 
 
 
 Pisces — contimced. 
 
 
 
 
 
 
 
 Strepsodus, Huxley and Young 
 
 
 
 
 
 
 
 „ VoTtlooki {ex Ag. MS.) 
 
 
 X 
 
 
 
 
 18. 
 
 ,, striatulus, Traq. 
 
 X 
 
 
 
 X 
 
 
 22, 27, 29. 
 
 Actinopterygii. 
 
 
 
 
 
 
 
 Aorolepis, Agassiz 
 
 
 
 
 
 
 
 sp 
 
 
 
 
 X 
 
 
 29. 
 
 Eloniobthys, CHehel 
 
 
 
 
 
 
 
 „ Eobisoni (^i6. ) 
 
 
 X 
 
 
 
 
 25. 
 
 sp 
 
 
 X 
 
 
 
 
 17. 
 
 Rhadinichthys, Traquair 
 
 
 
 
 
 
 
 „ ornatissimus {.<4fl'.) ■ ■ 
 
 
 • X 
 
 
 
 
 25. 
 
 PalEeoniscid scales 
 
 X 
 
 X 
 
 
 X 
 
 
 16, 22, 29- 
 
 ,, clavicle 
 
 
 X 
 
 
 
 
 34. 
 
 Fish remains, indt 
 
 X 
 
 
 
 X 
 
 
 22, ,S6. 
 
 C. SPECIAL LISTS OP THE POSSILS FOUND IN EACH 
 SUBDIVISION OP THE OARBONIPEROUS SYSTEM. 
 
 Calciferous Sandstone Series- 
 
 Cordaites sp. 
 Fern rachis. 
 Lepidodendron sp. 
 Lepidophloios wiinschianus. 
 
 sp. 
 Rachopteris sp- 
 Sphenopteris crassa. 
 
 ,, (Rhodea) moravica. 
 
 ,, ( „ ) patentissima. 
 
 sp. 
 
 Stigmaria sp. 
 AUorisma sulcata. 
 Edmondia pentonensis. 
 Sedgwickia gigantea. 
 Palseoniscid scales. 
 Rhizodus Hibberti. 
 
 ,, ornatus. 
 Strepsodus striatulus. 
 Fish bones, teeth, scales, indt- 
 
 Hurlet Limestone. 
 
 Lepidodendron veltheimianum- 
 
 sp. 
 Chert nodules with sponge spicule 
 Montioulipora tumida. 
 
 sp. 
 Syringopora ramulosa. 
 
 „ sp. 
 
 Zaphrentis sp. 
 Crinoid stems. 
 Asteroid, part of. 
 Arohseocidaris Urei. 
 Echinus plates. 
 Spirorbis sp. 
 
 Worm tubes. 
 Beyriohia sp. 
 Phillipsia Eichwaldi. 
 
 var. mucronata. 
 
 „ sp. 
 Fenestella plebeia. 
 
 Glauconome sp. 
 Polypora sp. 
 Rhabdomeson rhombiferura. 
 
 „ sp. 
 
 Athyris arabigua. 
 ,, lamellosa. 
 
Appendix. 
 
 165 
 
 Athyris sp. 
 Chonetes laguessiana. 
 Lingula mytiloides. 
 Orthis resupinata. 
 
 „ sp. 
 Productus aculeatus. 
 , , fimbriatus. 
 
 giganteus (abundant). 
 
 latissimus. 
 
 longispinus. 
 
 probosoideus, 
 
 puuctatus. 
 
 pustulosus. 
 
 soabrioulus. 
 
 semireticulatus. 
 
 youugianus. 
 
 HuRLET Limestone — continued. 
 
 Lithodomus lingualis. 
 Myalina Fleming!. 
 ,, peralata. 
 sp. 
 Nuoiila gibbosa. 
 Nuculana attenuata. 
 
 „ brevirostris. 
 Pinna fiabelliformis. 
 , , mutioa. 
 
 Retzia sp. 
 
 Rh3Tichonella acuminata. 
 „ pleurodon. 
 
 ,, pugnus. 
 
 sp. 
 Spirifera duplicicosta. 
 ,, glabra. 
 „ grandioostata. 
 ,, laminosa. 
 ,, lineata. 
 
 trigonalia. 
 „ ,, var. 
 
 bisulcata. 
 
 „ sp. 
 Spiriferina cristata. 
 
 var. ootoplicata. 
 „ sp. 
 
 Streptorhynchus crenistria. 
 Terebratula hastata. 
 AUorisma sulcata. 
 Aviculopecten ccelatus. 
 fallax. 
 
 knockonniensis. 
 semicircularis. 
 sp. 
 
 (very tumid species), 
 (with colour bands). 
 Cardiomorpha parva. 
 Cypricardella rectangularis. 
 Edmondia Josepha. 
 
 „ pentonensis. 
 , scalaris. 
 . , sulcata. 
 , , unioniformis ? 
 sp. 
 Entoliuni (Pecten) Sowerbyi. 
 Leiopteria (Avioula) lunulata. 
 ,, „ recta. 
 
 , , , , squamosa, 
 
 sp. 
 
 „ sp. 
 Protoschizodus axiniformis. 
 
 „ obliquus. 
 
 sp. 
 Pteronites latus. 
 Sanguinolites tricostatus. 
 
 ,, variablis. 
 
 Bellerophon decussatus. 
 
 ,, ,, var. striatus. 
 
 „ Urei. 
 
 „ sp. 
 Dentaliutn ingens. 
 Euomphalus carbonarius. 
 
 ,, nodosus. 
 
 „ pentangulatu 
 
 „ sp. 
 
 Loxonema constriotum. 
 
 sp. 
 Macrooheilus sp. 
 Microdoma biserrata. 
 Murchisonia angiilata. 
 Narioa variata. 
 Natioopsis plicistria. 
 
 sp. 
 Pleurotomaria monilifera. 
 
 , , turaida. 
 
 , . Yvani. 
 
 ,, sp. 
 
 Porcellia Puzosi. 
 Actinoceras sp. 
 Cyrtoceras sp. 
 Nautilus (Discites) subsulcatus. 
 
 ,, sp. 
 Orthoceras annulare. 
 
 „ insequiseptum. 
 
 „ sp. 
 
 Trigonoceras meyeranium. 
 Eloniclithys Robisoni. 
 
 sp. 
 Megalichthys tooth. 
 Poeoilodus Jonesi. 
 Polyrhizodus magnus. 
 Rhadinichthys oruatissimus. 
 Strepsodus Portlooki. 
 Xystrodus striatus. 
 Coohliodont tooth ? 
 
 Hosies Limestone. 
 
 Cardiopteris nana. 
 Sphenopteris ? 
 Stigmaria sp. 
 Arohseooidaris Urei. 
 Echinoid lantern tooth. 
 Athyris ambigua. 
 Chonetes buohiana ? 
 
 Chonetes laguessiana. 
 Disoina nitida. 
 Lingula mytiloides. 
 
 „ squaraiformis. 
 Productus longispinus. 
 
 „ sp. 
 
 Retzia radialis. 
 
166 
 
 The Geology of North Arran. 
 
 HosiES Limestone — continued. 
 
 Spirifera glabra. 
 ,, trigonalis. 
 „ „ var. bisulcata. 
 
 Streptorhynchus crenistria. 
 Allorisma sulcata. 
 Aviculopecten knookonniensis. 
 Ctenodonta pentoneusls. 
 Edmondia Josepha. 
 
 „ rudis. 
 
 ,, soalaris? 
 
 „ sp. 
 
 Entolium (Pecten) Sowerbyi. 
 Leiopteria (Pteronites) sulcata. 
 Lithodomus lingualis. 
 Nuculana brevirostris. 
 
 Pecten sp. 
 
 Pinna flabelliformis. 
 
 Sanguinolites tricostatus. 
 
 ,, variablis. 
 
 Bellerophon hiulous ? 
 
 ,, Urei. 
 
 Euomphalus carbonarius. 
 
 „ catillus. 
 
 Macroclieilus acutus. 
 Naticopsis canaliculata. 
 Nautilus (Discites) subsulcatus. 
 Orthooeras smooth sp. 
 
 » sp. 
 
 Megalichthys sp. 
 Palaaoniscid scales. 
 
 Edge Coal Series. 
 
 Lepidodendron veltheimianum. 
 Archseocidaris Urei. 
 Retepora undata. 
 Camarophoria crumena. 
 Lingula mytiloides. 
 
 „ aquamiformis. 
 Productus giganteus. 
 
 „ latissimus? 
 Rhynchonella pleurodon. 
 Streptorhynchus crenistria. 
 Allorisma sulcata. 
 Aviculopecten knockonniensis. 
 Edmondia rudis. 
 sp. 
 
 Entolium (Pecten) Sowerbyi. 
 Myalina Verneuili. 
 
 sp. 
 Nucula gibbosa. 
 Nuculana attenuata.. 
 Pecten (Streblopteria) Ifevigata. 
 
 .. sp. 
 Protoschizodus axiniformis. 
 Sanguinolites tricostatus. 
 Bellerophon hiulcus. 
 
 , , Urei. 
 
 Orthoceras annulare. 
 
 „ sp. 
 
 Cladodus striatus. 
 
 Index Limestone. 
 
 Montioulipora tumida. 
 
 Zaphrentis sp. 
 
 Crinoid ossicles. 
 
 Archseocidaris Urei. 
 
 Phillipsia Eichwaldi, var. mucronata. 
 
 Fenestella sp. 
 
 Athyris ambigua. 
 
 „ Roy si? 
 Camarophoria crumena. 
 Chonetes laguessiana. 
 Lingula mytiloides. 
 Orthis resupinata. 
 Productus costatus. 
 
 „ latissimus (abundant). 
 
 , , longispinus. 
 
 „ mesolobus. 
 
 „ semireticulatus. 
 sp. 
 Rhynohonella pleurodon. 
 Spirifera glabra. 
 
 ,, triradialis. 
 Spiriferina cristata, var. octoplicata. 
 Streptorhynchus crenistria. 
 Allorisma sulcata. 
 
 Edmondia Josepha. 
 
 ,, rudis. 
 Entolium (Pecten) Sowerbyi. 
 Lithodomus lingualis. 
 Nucula gibbosa. 
 ,, luoiniformis. 
 „ sp. 
 Nuculana attenuata. 
 Protoschizodus sp. 
 Sanguinolites striatus. 
 „ variablis. 
 
 Bellerophon decussatus. 
 
 ,, Urei. 
 
 Dentaliura ingens. 
 Euomphalus carbonarius. 
 Loxouema constrictum. 
 
 „ Lefebvrei. 
 Macrooheilus acutus. 
 
 „ imbricatus 
 
 Murchisonia angulata. 
 Pleurotomaria atomaria. 
 Nautilus globatus. 
 Orthooeras sp. 
 Fish remains. 
 
 Limestones and Shales above Index Limestone. 
 
 Lithostrotion Porllooki. 
 Crinoid ossicles. 
 Athyris sp. 
 Lingula mytiloides. 
 
 Lingula squamiformis. 
 Orthis resupinata. 
 Productus fimbriatus ? 
 , , giganteus. 
 
Appendix. 
 
 167 
 
 Limestones and Shales above Index Limestone — continued. 
 
 Produotus latissimus. 
 
 , , muricatus ? 
 
 .. sp. 
 Spirifera glabra. 
 
 ,, lineata. 
 
 ,, trigonalis. 
 
 ,, ,, var. bisulcata. 
 
 Streptorhynchus crenistria. 
 Terebratula sp. 
 AUorisma sulcata. 
 Carbonicola sp. 
 Edmondia rudis. 
 
 „ sp. 
 
 Myalina sp. 
 Nuciila gibbosa. 
 ,, luoiniformis. 
 ,, scotica. 
 Nuoulana acuta. 
 
 ,, atteuuata. 
 Pecten sp. 
 Pinna flabeUlfo'rmis. 
 
 Protoschizodus axlniformls. 
 Sanguinolites clavus. 
 Solenomya primaBva. 
 Solenopsis minor. 
 Aclisina elongata. 
 „ striatula. 
 Bellerophon decussatus. 
 
 ,, Urei. 
 
 Dentalium ingens. 
 Macrocheilus aoutus. 
 
 „ imbricatus. 
 
 Metoptoma elliptica. 
 Murchisonia angulata. 
 
 „ cincta. 
 
 ,, quadricarinata. 
 
 Nautilus nodiferus. 
 
 ,, (Acanthonautilus) bispinosus. 
 Orthooeras sp. 
 Aorolepis sp. 
 Strepsodus striatulus. 
 Palaeonisoid scales. 
 
 Coal Measures. 
 
 Artisia approximata. 
 Calamites ramosus. 
 
 „ Suekowi. 
 
 „ varians. 
 
 „ sp. 
 
 Cordiates principalis. 
 Lepidodendron sp. 
 Lepidostrobus sp. 
 Mariopteris muricata. 
 Neuropteris gigantea. 
 
 „ heterophylla. 
 
 „ sp. 
 
 Sphenopliyllum myriophyllum. 
 
 „ sp. 
 
 Stigraaria sp. 
 
 Anthracomya modiolaris ? 
 Carbonicola acuta. 
 
 ,, „ var. rhomboidalis. 
 
 ,, aquilina. 
 
 „ sp. 
 
 Edmondia Josepha ? 
 Myalina sp. (? Verneuili). 
 Naiadites crassa ? - 
 „ modiblaris. 
 J, quadrata. 
 „ (periostracum of). 
 „ sp. 
 Megalichthys Hibberti. 
 Rhizodopsis sauroides. 
 
 D. NOTES ON THE MESOZOIC FOSSILS FOUND IN THE 
 ISLAND OF ARRAN, BY E. T. NEWTON, F.R.S. 
 
 The history of the discovery, under pecuHar circumstances, of 
 Mesozoic Fossils in Arran has already been fully described in the 
 earlier part of this Memoir. 
 
 It was in the beginning of the year 1900 that Rheetic fossils were first 
 discovered near Shiskine by Messrs. Macconochie and Gunn, and sub- 
 mitted to me for examination. Some remarks upon them will be 
 found in the Director-General's "Summary of Progress" for 1899 
 (published 1900), and a further account of them and of more recent 
 discoveries of Mesozoic fossils in Arran appeared in the Quarterly 
 Journal of the Geological Society. ' 
 
 i. Bhaetic. 
 
 The following is a list of the Rhsetic fossUs found at locality d, near 
 Shiskine. The species marked with an asterisk (*) have also been found 
 I Quart. Journ. Geol. See, vol. Ivii. (1901), p. 229. 
 
168 The Geology of North Arran. 
 
 in the Avimila contorta beds of the North-east of Ireland, i and it is 
 evident that this series of fossils must represent the Avicvla contorta zone. 
 
 *Avicula contorta, Portioch 
 
 *Pecten valoniensis, Defrance 
 
 *Schizodus eloaoinua, Quenstedt (= Isodonta Ewaldi, Boniemann). 
 
 *Protocardiuni philippianum ? Dunker ( = G. rhietioum, Merian). 
 
 •Modiola minima ? Sowerby (= C. mirmta,. Gold/.). 
 
 Estheria minuta ? Goldf. 
 
 Gyrolepis Alberti ? Agassiz 
 
 ii. Lower Lias. 
 
 Another and larger series of fossUs was obtained somewhat later from 
 Bally michael Glen, and forwarded to me. These were in a much 
 decomposed rock, and the fossils were only represented by internal and 
 external casts; but by means of wax impressions a considerable 
 series of determinable species was reproduced, the Liassic age of which 
 is clearly demonstrable. A careful examination led to the conclusion 
 that the fossils correspond most nearly with those of the Ammonites 
 angulatus beds of the North-east of Ireland (see Tate, referred to 
 above), as will be clearly seen from a study of the following list of species. 
 
 List of Liassic Fossils from Ballymichael Glen (Locality c). Those 
 marked with an asterisk have been found also in the North-east of 
 Ireland. 
 
 CEPHAIiOPODA. 
 
 *Ammomtes (Aegooeras) angulatus, ScMotheim 
 
 Gasteropoda. 
 Amberleya acuminata, Chapius and Dewalque 
 *Cerithium semele ? Martin 
 
 „ sp. (c/. C. Falsani, Dumortier). 
 *Pleurotomaria tectaria, Tate 
 
 Lambllibranchiata. 
 Area sp. 
 Astarte sp. 
 
 Avioula lanceolata, Soiverby 
 *Garduiia Listeri, Sowerby 
 *Cardita Heberti, Terquem 
 
 *Gomomya sp. (c/. 6. rhombifera, Goldf. and sinemuriensis, Oppd). 
 *GryphsBa arcuata, Lamarch 
 Inoceramus (Orenatula) sp. 
 *Lima pectinoides ? Sowerby 
 
 * ,, succincta, ScMolheim (= L. antiquata, Sow.). 
 Modiola sp. 
 *Myoeoncha psilonoti ? Queiistedt 
 Nucula sp. (two forms). 
 *Nuoulana (Leda) Tatei, Newton ( = L. Renevieri, Tate), 
 
 ,, ,, (c/. L. Quenstedti, Tate). 
 
 *Ostrea irregularis ? Quenstedt 
 Pecten (Chlamys) subulatus ? Goldfuss 
 Pholadomya ? 
 
 Protooardium truncatum ? Sowerby 
 Tancredia? Peachi, Newton 
 *Umcardium cardioides, Phillips 
 
 Annelida. 
 Ditrupa globiceps, Queiistedt 
 
 „ sp. 
 *Serpula sp. 
 
 Ceinoidea. 
 Pentaorinus basaltiforniis. Miller 
 
 PrjANT.a;. 
 Wood. 
 
 > See Tate, " Irish Liassic Fossils," Report Belfast Nat. Field Club, Appendix I., 1870. 
 
Appendix. 169 
 
 iii. Cretaceous. 
 
 The following list of Cretaceous fossils is based upon the examination 
 of blocks of grey limestone and chert found in the volcanic agglomerate 
 in Ballymichael Glen, not far from the fossiliferous Liassic masses 
 (Localities a and b). A series of specimens having been forwarded to 
 me, sections for the microscope were prepared, and these showed such 
 a close agreement with examples of Chalk from the North of Ireland 
 that there could be little doubt as to the Arran specimens being of a 
 like age. This was confirmed by the detection of the organisms detailed 
 in the following list. It is satisfactory to be able to say that Dr. G. J. 
 Hinde, who is so weU acquainted with the fossils of the Chalk, 
 fully agrees with the reference of these specimens to that formation. 
 
 Inocerarmis (piece of shell showing prisms). 
 
 Polyzoa (several specimens, perhaps Mntalophora and Escharina). 
 
 Echinoderms (fragments of). 
 
 Porosphaira globularis, d'Orhigny. 
 
 Hexactinellid sponge fragments (? Plocoscyphia). 
 
 Tetractinellid and other spicules. 
 
 Giobigerina cretacea, d'Orhigny (and other species). 
 
 Textularia, etc. 
 
 iv. Conclusion. 
 
 The following remarks on these collections of fossils from Arran is 
 taken from the Quarterly Journal of the Geological Society, vol. 57, 
 p. 239 :— 
 
 " The island of Arran is far from any locality where strata of Jurassic 
 or Cretaceous age are now found in place, the nearest locality being in 
 the North-east of Ireland, which is about 40 miles away, where there 
 are strata corresponding in a remarkable degi'ee with the masses met 
 with in Arran. 
 
 " The Secondary rocks of the North-east of Ireland, which had already 
 been made known by Portlock, ^ were described more fully by Prof. Tate 
 in 1863,- and in still greater detail in 1867.^ In these papers it is 
 shown that Rhsetic beds, including the Avicula contorta-shsles and 
 the White Lias, rest upon older Triassic rooks and are overlain by 
 Lower Lias, in which four distinct zones have been distinguished, 
 namely, those of Ammonites planorhis, Amm. angulatus, Amm. Buck- 
 lamdi, and Belemnites aoutus. The uppermost of these zones is succeeded 
 by Upper Cretaceous beds, Greensand, and hard Chalk,'' and this again 
 by basalt. Prof. Tate^ has recorded undoubted Middle Liassic fossils 
 from Ballintoy, but apparently from Drift, as hitherto they have not 
 been found in place. 
 
 " In 1870 Prof. Tate'^ published a revised list of the Liassic fossils of 
 Ireland, and from this it will be seen that nearly all the Ehsetic and 
 Liassic species found in Arran have been met with likewise in the 
 neighbourhood of Belfast. The Rhsetic fossils of Arran indicate the 
 former existence of strata corresponding with the Avicula oontorta- 
 shales, but at present there is nothing to represent the White Lias in 
 particular. 
 
 " That the Liassic fossils of Arran are from the earlier beds of that 
 
 ^ ' Keport on Geol. of Londonderry, &c.," 1843. 
 
 2 Quart. Journ. Geol. Soo. vol. xx. (1864), p. 103. 
 
 » Ibid. vol. xxiii. (1867), p. 297. 
 
 * Ibid. vol. xxi. (1865), p. 15. 
 
 = Ibid. vol. xxvi. (1870), p. 324. 
 
 » " Irish Liassic Fossils," Bep. Belfast Nat. Field Club, App. i. (1870). 
 
170 The Qeology of North Arran. 
 
 formation is evident, and broadly speaking, they are equivalent to the 
 Lower Lias of the Belfast area ; but I think that we may take another 
 step with almost equal certainty. There seems no valid reason for 
 supposing that the Liassic specimens hitherto found in Arran belong to 
 more than one bed ; for although some of the specimens are very friable 
 and others tolerably hard, this is due to different degrees of decomposi- 
 tion. Now, among the fossils collected are several examples of 
 Ammonites angulatus, while the characteristic ammonites of the Amm. 
 planorbis- and Amm. BticMandi-zones have not been met with ; neither 
 is there any fragment of a belemnite to indicate the ' Belemnite-shales.' 
 It seems evident, therefore, that our Arran specimens belong to the 
 Amm,onites angulatus-zone. Many of the species range into higher or 
 lower zones, but all of them have been met with in Amm. angulatiis-heds 
 elsewhere. Quite possibly representatives of the other Liassic zones of 
 the Belfast area may yet be found in A.rran ; but, as it is the Ammonites 
 angulatus-zone which attains the greatest thickness around Belfast, so 
 it may have been in Arran. The similarity of the Chalk of Arran to 
 that of Antrim has already been remarked upon. 
 
 " But for the preservation of the remnants above described the presence 
 of Mesozoic strata in Arran, other than the New Red rocks, would have 
 been unknown, and their preservation is due to the accident of portions 
 of the rocks having fallen into the neck of a volcano. Being thus 
 removed to some distance below the surface of the country, they escaped 
 the denuding influences that have so effectually removed the other parts 
 of the parent rocks which there is every reason to believe formerly 
 spread over the island of Arran, and were doubtless continuous to the 
 south-west with the corresponding strata of the North-east of Ireland : 
 forming also a link between that district and the Liassic and Cretaceous 
 areas of the Western Islands of Scotland and the smaU Liassic district 
 near Carlisle. The still further extension of Cretaceous deposits in 
 Scotland is indicated by the well-known remains of Greensand age near 
 Moorseat (Aberdeenshire). 
 
 " The Liassic and Cretaceous rocks of the Western Isles of Scotland are 
 perhaps 100 miles north-west of Arran, and have been noticed in part 
 by the earlier writers mentioned in the more recent works of Sir 
 Archibald Geikie,! Thomas Wright,^ and Prof. Judd^ ; but the fossils 
 of the Lower Lias which have been recorded from that area do not 
 correspond so nearly with the Arran specimens as do those from the 
 neighbburhood of Belfast. The zone of Avicula contorta does not seem 
 to be distinctly developed in the Western Isles, according to Prof. J udd, 
 although he had seen some indications of its presence, and only last year, 
 under Mr. Horace B. Woodward's directions, some obscure fossils were 
 obtained fi-om Skye which it is thought may represent these beds. The 
 numerous other horizons of Jurassic strata described in the Western 
 Isles, having no representatives among the Arran fossils, need be no 
 further alluded to. Above them, however, are Cretaceous rocks which 
 Prof. Judd refers to the Lower, Middle, and Upper Chalk ; the last- 
 named horizon being that of Belemnitella munronata, and apparently 
 corresponding with the White Limestone of Antrim. If this correlation 
 be correct, it seems highly probable that the Arran limestone will prove 
 to be on the same horizon." 
 
 * Quart. Journ. Geol. Soc, vol. xiv. (1868), p. 1. ^ Hid. p. 2i. 
 
 » Ibid. vol. xxxiv. (1878), p. 696. 
 
PAET II.— PETEOGEAPHICAL. 
 
 ARRAN. 
 
 Notes on the Petrography of Old Red Sandstone Igneous Rocks, 
 BY H. Kynaston, B.A. 
 
 Upper Old Red Sandstone. 
 
 6370, (93) Near Fallen Rocks, Arran. A dark purplish, fine-grained 
 rock, apparently considerably decomposed. The microscope shows 
 numerous small pseudomorphs after idiomorphic olivine, consisting of a 
 pale yellowish, and sometimes almost colourless, serpentine (?), which 
 appears almost isotropic, and is surrounded by a deep opaque border of 
 iron-oxide (reddish-brown by reflected light), which also fills cracks in 
 the pseudomorphs. A few felspar phenocrysts appear to have been 
 present, but are too highly altered foi' satisfactory recognition. The 
 groundmass is much obscured by decomposition products, though 
 numerous small lath-shaped plagioclases may be recognised. Iron-ores 
 lie scattered throughout the slide, and fill narrow branching cracks. The 
 rock is probably an altered olivine-hasalt. 
 
 9394. (267) Near Fallen Rocks, on hillside. A dark purplish rock 
 with somewhat greenish patches. Too decomposed for satisfactory 
 description. In its main features the rock is similar to the last. 
 Olivine pseudomorphs are common, and the groundmass is of similar 
 type. Black opaque iron-ores, leucoxene, and pyrites (?) may be seen, 
 and calcite in patches. Altered basalt (!). 
 
 9395. (268) HiU side above Laggantuin. The microscope shows 
 numerous pseudomorphs after olivine, some consisting in part of a 
 reddish-brown to pale yellow, slightly dichroic, mineral resembling 
 iddingsite ; some calcite pseudomorphs after a more or less idiomorphic 
 pyroxene (probably augite) ; and a groundmass of unorientated felspar 
 microlites, carbonates, and interstitial matter. Altered oUvine-basalt. 
 
 Lower Old Red Sandstone. 
 Volcanic Series. 
 
 In this series the rocks occurring in the field as lava flows are of a 
 decidedly basic facies, and appear to be more closely allied to the basalts 
 than to the typical andesites. It is probable, however, that typical 
 andesites also occur. On the other hand, an examination of some of the 
 fragments from the conglomerate, which is found overlying these lavas, 
 shows that they belong to the more acid class of andesites, and may be 
 referred in part to hornblende-andesite. It thus appears that a more 
 acid series of andesites were undergoing denudation at the time of the 
 formation of the conglomerate, while the earlier outpourings partook of 
 a more basic character. A similar range in the composition of the 
 lava-flows is exemplified in many other Lower Old Red volcanic areas 
 and the sequence from basic to more acid is common and characteristic. 
 
 In the more basic series pseudomorphs after olivine are often very 
 common, but in no case has the unaltered mineral been observed. 
 Augite is frequent in both types. In the more basic rocks phenocrysts 
 
172 The Geology of North Arran. 
 
 of felspar appear to be almost entirely absent, while in the more acid 
 series they are exceedingly numerous. The groundmass of the basic 
 rocks consists mainly of felspar microlites, amongst which pyroxene 
 granules may sometimes be distinguished, and occasionally a small 
 quantity of interstitial matter. In the more acid series the matrix 
 usually shows felspar microlites together with a varying proportion of 
 felsitic matter. 
 
 9388. (261) Auchencar burn, 70 yards east of the moor fence. The 
 microscope shows numerous pseudomorphs after olivine in a ground- 
 mass of small lath-shaped felspars, sometimes showing a tendency to 
 flow-orientation, grains of altered pyroxene (?), and iron-ores. Small 
 scattered flakes of biotite are also seen in the groundmass. Altered 
 basic lava — olwine-hasalt (?). 
 
 9389. (262) 300 yards north of Oreagan Geala, Garbh Thor, Mony- 
 quil. Pseudomorphs, mainly of iron-oxide, after olivine, and grains and 
 crystals of augite occur in a groundmass mainly composed of felspar 
 microlites and iron-ores, with some small ill-defined patches of secondary 
 quartz. Altered basic lava, probably basalt. 
 
 9390. (263) Same loc. Purplish lava with well-defined amygdules. 
 The microscope shows pseudomorphs of iron- oxide after idiomorphic 
 olivine, grains of augite, mostly more or less altered, and amygdules of 
 calcite in a groundmass of small lath-shaped felspars, pyroxene granules, 
 iron-ores, and some interstitial matter. Altered basic lava. Basalt (?). 
 
 9391. (264) Scar, east of Creag Mhor, Auchencar. Pebble in Lower 
 Old Eed conglomerate. A reddish purple lava with irregular amygdules 
 of calcite, and showing small porphyritic felspars. This is evidently a 
 more acid type of rock than any of the preceding. The microscope 
 shows numerous idiomorphic crystals and crystal-groups of brownish 
 hornblende, for the most part now almost entirely replaced by pseudo- 
 morphs" of iron-oxide. Sometimes the inner portion of the crystal 
 retains some of the original brown colom", but there is invariably a deep 
 opaque border of iron-oxide. Pleochroism is scarcely noticeable. The 
 characteristic cleavages of the original hornblende may_be seen in one or 
 two cases. The felspar phenocrysts are fairly numerous. They are 
 evidently mainly plagioclase, probably an acid variety, though some 
 individuals only show the Carlsbad twinning. Apatite is accessory, and 
 of a brownish tint. The matrix consists mainly of small felspar micro- 
 lites (traohytic type)^ though a good deal obscured by small flecks of 
 iron-ore. Sm-nhlende-Andesite. 
 
 9392 (265) Sannox Burn, one mile west of mouth. Boulder in Lower 
 Old Red conglomerate. A dark bluish-grey lava, with patches of epidote. 
 Shows phenocrysts of turbid plagioclase, and pseudomorphs after a 
 f erromagnesian constituent, some of which suggest hornblende, and some 
 biotite, in a groundmass mainly formed of epidote, chloritic (?) matter, 
 and iron-ores. The rock is rather decomposed and characterised by 
 an extensive liberation of iron-oxide, and development of epidote. 
 Altered Andesite. 
 
 9393 (266) A and B. Sannox Burn, one mile west of mouth. Boulder 
 in Lower Old Red conglomerate. A dark purplish lava, showing what 
 appears like an inclusion of a paler coloiu?. The microscope shows 
 numerous idiomorphic plagioclases of two generations, grains and aggre- 
 gates of epidote and chloritic (?) matter, sometimes in the form of 
 pseudomorphs after a ferromagnesian mineral, in a groundmass of felspar 
 microlites, iron-ores, and felsitic matter. A portion of 9393A has the 
 appearance of an inclusion of a more acid rock, but the microscope 
 
Appendix. 173 
 
 shows that there is no difference between the two portions except in the 
 relative poverty in disseminated iron-ores of the lighter portion, the 
 high proportion of which in the darker part gives it a black appearance 
 in the hand-specimen. Moreover, felspar phenocrysts may often be 
 observed lying partly in one portion and partly in the other. Scattered 
 throughout both portions of the slide are some small colourless Hakes 
 resembling white mica, doubtless secondary, seen perhaps more 
 frequently in the paler portion. Apatite is accessory. 9393B shows a 
 portion of the matrix of the conglomerate, consisting chiefly of frag- 
 ments of altered andesite, quartzite, quai'tzose-schist, quartz grains, 
 felspars, chlorite, and a considerable quantity of epidote. Altered 
 andesite. 
 
 Intrusive Rocks. 
 
 9401. (274) East end of big dyke — west of Farchan Mor. 
 
 9402. (275) 200 yards west of AUt-a-Chapuill. 
 
 9403. (276) West end of dyke near Cioch-nah-Oighe. 
 A fairly coarse-grained holocrystalline rock of doleritic appearance. 
 The microscope shows more or less lath-shaped turbid plagioclases, 
 
 grains of pale augite (malacolite or salite), of earlier consolidation than 
 the felspar, patches of pale greenish — (sometimes yellowish in the 
 more weathered parts of the rock) — secondary fibrous amphibole, with 
 some chlorite, and occasionally [9401] a little brown hornblende may 
 be seen associated with the augite. There is also some interstitial 
 alkali-felspar and quartz. Magnetite, ilmenite, and apatite needles are 
 accessory. 
 
 The rock appears to be intermediate between the typical dolerites and 
 the augite-diorites. It may be termed a mcdacolite (salite) — dolerite. 
 
 7444. (162) Torr Breac, Glen Rosie. 
 
 7519. (186) Torr Breac, Glen Rosie. 
 
 7520. (187) Rosie Burn, Glen Rosie, 400 yards north of wood. 
 These three specimens closely resemble one another. They are dark 
 
 greenish-grey finegrained rocks, and are practically merely finer- 
 grained varieties of the intrusive rock already noticed. They consist 
 essentially of more or less lath-shaped felspars, grains and aggregates of 
 pale augite, patches of chlorite, and some secondary quartz. Apatite 
 and iron-ores are accessory. Grains of epidote are sometimes seen, and 
 the rock is occasionally traversed by narrow veins of epidote and calcite. 
 MalacoUte-dolerite (or diabase). 
 
 Doubtful Tuffs. 
 
 7542. (224) Merkland Burn, west branch, 500 feet above junction. 
 A dark greenish rook, in which numerous small irregular fragments are 
 easily seen with the naked eye. The microscope shows numerous small 
 fragments of andesite and felsite (?) up to about g-in. in diameter, broken 
 plagioclases, and quartz grains, grains of epidote, chlorite, etc., in a fine 
 matrix consisting apparently of smaller fragments of a similar nature, 
 though much obscured by greenish alteration products and iron-ores. 
 The quartz and epidote often tend to form in patches and irregular veins 
 
 7542. (225) Merkland Burn. Similar to the preceding, but consisting 
 of larger fragments, which are mainly andesitic, and showing very little 
 matrix. These rocks do not resemble the matrix of the conglomerate 
 as seen in 9393B ; but suggest rather rocks of pyroclastic origin, such as 
 tuffs or agglomerates. 
 
174 
 
 The Geology of North Arran. 
 
 < 
 
 
 Ph 
 
 
 S 
 
 N 
 
 < 
 
 tes 
 
 O 
 
 
 
 &? 
 
 
 
 \—\ 
 
 N 
 
 m 
 
 So 
 
 P 
 
 
 rn 
 
 
 
 «M 
 
 M 
 
 
 P5 
 
 |<1 
 
 O 
 
 o 
 
 h^ 
 
 
 O 
 
 t^ 
 
 ^ 
 
 fcl 
 
 o 
 
 ^is 
 
 PI 
 
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 Ph 
 
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 00 03 O 1— I C<) CO 
 
 00 cx} cn OS a> o> 
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Afpendwa, 175 
 
 Notes on the Petrography op the Oabbonifbrous Igneous Rocks 
 OF Abran, Bute, and the Cumbrabs, by H. J. Seymour, B.A. 
 
 (1) Late Carboniferous Sills (2609, 4633, and 4634) and Dyke 4592. 
 
 These rocks are medium to coarse grained olivine dolerifes, showing a Sills. 
 well- developed ophitic st/rvjctv/re between the augite and plagioclase. 
 They contain a good deal of hypidiomorphic olivine crystals usually 
 under 0'5 mm. in longer diameter, which are more or less altered along 
 their edges and cracks into serpentinous material, their central parts 
 remaining clear. Augite occurs as brownish pink faintly pleochroic 
 granules and allotriomorphic crystals moulded on the olivine and some- 
 times completely enclosing it (4633). Some of those crystals intergrown 
 with the plogioclases are up to 2 or 3 mm. in length. The plagioclases 
 (1'5 mm. average length) show repeated twinning and give symmetrical 
 extinction angles up to 27°, indicating labradorite. Magnetic iron ore is 
 present in small quantity Secondary products are chlorite, actinolite, 
 and serpentinous material. These rocks are like tertiary dolerites. 
 
 4592. Is a much altered rock. The plagioclase is still fairly fresh and Dyke, 
 contains abundant apatite needles. The orginal ferro-magnesian 
 constituents are almost completely altered to secondary chloritic material. 
 Vesicular structure is noticeable, and the rock probably originally 
 possessed a more or less glassy base. — Basalt. 
 
 (2) Carboniferous Volcanic Series, "Upper." 
 
 Nos. 6371, 6994, 7051, and 7738 to 7743 inclusive. 
 
 These include two types of rocks — viz., basalts Nos. 7051, 7739, 
 7740, and 7741, and volcanic tufifs and giits Nos. 6371, 6994, 7738, 
 7742, and 7743. All these rocks occur in or near the burns at Sliddery 
 Water Head, Arran (Sheet 1 3). The basic rocks have already been Basic 
 described in the Summary of Progress for 1897, pp. 119 and 120, as rooks, 
 basaltic andesites. They are all much altered and stained red with 
 ferric oxide, and original ferro-magnesian constituents (olivine and 
 augite) are merely suggested now by the shapes of the iron-stained 
 pseudomorphs noticeable in the sections. The tuffs and volcanic grits Tuffs and 
 or sandstones are also stained red with ferric oxide, and the compact grits, 
 varieties present a very close resemblance to some of the igneous rocks. 
 In section they are seen to consist of very numerous quartz granules, 
 mostly sub-angular, associated in different slides with a greater or less 
 amount of basic volcanic lapilli. The latter are mostly in a glassy 
 (altered) and scoriaceous or pumiceous condition, and less seldom finely 
 crystalline. Pieces of quartzite and a few odd plagioclase crystals are 
 also noticeable, the whole being cemented into a compact mass with 
 ferric oxide. 
 
 (3) Carboniferous Volcanic Series, "Lower." 
 
 Nos. 2148?, 2463?, 2603 to 2607, 4593, 4594, 4596, 4616 to 4022, 
 4625, 6373?, 6995 to 6997, and 9396 to 9398. 
 
 Of the above rocks the great majority are basic, two of them are 
 porph3rritic trachytes (2606 and 4617), and one (6996) is a tuff. 
 
 These include olivine basalts with and without plagioclase pheno- Basic 
 crysts, porphyritic dolerites, and diabase. The ohvine basalts without rocks, 
 
176 The Geology of North Arran. 
 
 plagioclase phenocrysts are compact and fine grained as a rule, and do 
 not differ essentially from the basic types described already except 
 that they are much fresher and their constituents more readily 
 determinable. No. 6995, from Benlister Glen, may be taken as repre- 
 sentative. This in section is seen to be finely crystalline, and contains 
 abundant olivine crystals altered to iddingsite. The other ferro- 
 magnesian constituent is chloritized, and the plagioclase crystals are 
 mostly coated with nearly opaque calcareous matter. The rock from 
 the west side of St. Blane's Hill (4625) is the most basic type examined, 
 containing much less felspar than usual. It contains phenocrysts of 
 augite and olivine (iddingsite), the former being much corroded by the 
 ground and frequently forming " glomero-porphyritic " groups. The 
 ground, which is very minutely crystalline, consists chiefly of more or less 
 idiomorphic augite micro-crystals, with a good deal of magnetic iron ore, 
 a subordinate proportion of the ground being composed of plagioclase 
 microlites and some glass. Specimen No. 4621, from east of Port TJisg, 
 South Bute, is a basalt, veined with a httle calcite and a good deal of 
 red stilbite or heulandite. 
 
 The basalts with plagioclase phenocrysts contain on the whole a 
 smaller proportion of olivine crystals, and approximate closely to the 
 Lion's Haunch type. The specimen from the east side of Port 
 Luchdach, South Bute (4618), is fairly representative. This contains 
 numerous phenocrysts of a basic plagioclase giving rather high extinc- 
 tion angles, and being probably labradorite. These frequently have 
 included in them portions of the glassy base. The ground is made up 
 of a finely crystalhne aggregate of abundant hypidiomorphic augite 
 crystals and plagioclase laths with a good deal of magnetite. A little 
 interstitial glassy matter occurs here and there. Numerous greenish 
 pseudomorphs after olivine are noticeable in the section, also several 
 augite phenocrysts, the larger ones (2 mm. diameter) being much 
 corroded. 
 
 The rock (2463) south of Millstone Point is an altered dolerite or 
 diabase. It is somewhat amygdaloidal, the amygdales being now filled 
 in with calcite. The ferromagnesian minerals are completely altered to 
 a greenish chloritic product. The remaining basic rocks of this series 
 are porphyritic dolerites (^2603-2605, 2607, and 4622), similar generally 
 in composition to those rocks above described, but with a ground more 
 definitely and coarsely crystalline. The coloured phenocrysts (augite 
 and olivine) are almost completely altered to secondary materials, but 
 the plagioclases are quite fresh. Olivine phenocrysts are rather scarce, 
 and augite also is not very conspicuous. The ground, which is of the 
 anamesite dolerite type, is much finer in grain than the ophitic dolerite 
 described above, e.g. 4633 or 4634. It usually contains abundant 
 partially chloritized augite, plagioclase, magnetite, and a little secondary 
 biotite, with abundant accessory apatite, as inclusions in the felspathic 
 constituents. 
 Acid The acid rocks (2606 and 4617) of this group are pale greyish and 
 
 rocks. slightly porphyritic trachytes. The phenocrysts are pinkish coloured 
 
 simply twinned orthoclases about 0"5 cm. long. The specimen (461 7) from 
 the west side of Port Luchdach is the most typical. In section it consists 
 of a plexus of simply twinned felspar micro-crystals, in the form of long 
 laths, and showing well-marked flow orientation. Many of them are 
 stained slightly with red iron oxide. Between <he crystals occur 
 abundant specks of hematite, some of which appears to be pseudo- 
 morphic after an original ferromagnesian mineral, traces of which in 
 
Appendix. 177 
 
 the form of minute green granules are still noticeable in the ground. 
 The section of the other rock (from the east of North Garrochty) is 
 similar generally, but the flow structure is not quite so tjrpically 
 developed. 
 
 The remaining rock included in this series is (No. 6996) one from the T"ff- 
 north of Creag-na-Fitheach (?), Glen Dubh, Arran. This rock is a 
 quartzose Uiff indentical with those described from the " Sliddery 
 Water " area. ' The qu.artz grains contain abundant fluid cavities with 
 a moving bubble in each. 
 
 (4) Sills oe Bosses of Eaely Oarbonifeeous Age. 
 Nos. 4573, 4574, 4576, 4583, 4588, 2608, 4587, and 4627 to 4629. 
 
 These include examples of trachytes (4576, 4588, and 4583) and 
 basalts (2608, 4587, 4627-4629) and two rocks (4573 to 4574) which are 
 tentatively referred to the Bostonite type. Another rock included in 
 this set (4626) is a tuff. 
 
 These are reddish and yellowish coloured rocks, which are considerably Trachytes, 
 altered and stained with iron oxide. One of the rocks (4583) is 
 porphyritic, the phenocrysts being altered orthoclase" or sanidine. In 
 Ihe ground, which is typically trachytic, occur greenish pseudomorphs 
 in gi'ains and ophitic patches, after augite (segirine) probably. Some 
 interstitial secondary quartz is also present. These rocks recall the 
 types described by Hatch from the Garlton Hill, Haddingtonshire. 
 {Trans. Roy. Soc. Ed., Vol. 37, also Vol. 29.) 
 
 Two specimens (4573 and 4574) from Millport Bay, Great Cumbrae. Bos- 
 These are creamy brown coloured, slightly porphyritic, rocks. In tomtes? 
 section they consist of small felspar laths, which are much altered and 
 kaolinized on their surfaces. The porphyritic mineral is an untwinned 
 felspar with a low refractive index, and is probably orthoclase. Some 
 of the small felspars of the ground are repeatedly twinned, but have a 
 lower refractive index than Canada balsam, and hence are alkali varieties. 
 The majority of the felspar laths show simple twinning. In the absence 
 of any analyses the rocks are tentatively referred to the bostonites, as 
 they correspond very closely with the t3rpe of that rock described by 
 Kemp and Marsters (in the Bulletin of the U.S. Geol. Survey, No. 107), 
 both macroscopically and microscopically. 
 
 These rocks occur at Suidhe Hill (2608 and 4627-4629) and at Basalts. 
 Sheughends, Great Cumbrae (4587). They are porphyritic olivine 
 basalts verging towards compact dolerites. They are quite similar to 
 types already described, and do not call for any special remarks here. 
 Most of the ferromagnesian constituents are altered, but the plagioclase 
 is quite fresh usually. 
 
 (5) Dykes of Eaelt Oaebonifeeous Age. 
 Nos. 4577 to 4579, 4586, 4589 to 4591, and 2595 to 2600. 
 
 Of these rocks two are trachytes (4577 and 4578) and the remainder 
 basalts and dolerites. 
 
 The trachytes are fine-grained types, consisting of a felt of orthoclase Trachytes, 
 laths somewhat stained with ferric oxide, and showing very typical flow 
 orientation. Orthoclase phenocrysts are scarce, and some interstitial 
 and secondary quartz is noticeable in the sections. The rock from top 
 
 1 Summary of Progress, 1897, pp. 119 and 120 
 
178 
 
 The Geology of North Arran. 
 
 Basic 
 rocks. 
 
 of crag near Hawk's Nest, Great Cumbrae (4578), contains a few flakes 
 of biotite mica orientated in the same direction as the felspars of the 
 ground. 
 
 The basic rocks are chiefly altered basalts and compact dolerites, 
 usually with olivine, and generally porphyritic (Lion's Haunch type). 
 The phenocrysts are usually labradorite, and less often augite or olivine. 
 A good many of the roclcs show the lateritic type of weathering, which 
 characteristic is shared with many of the trachytes of this area. 
 
 List of Sliced Rocks from One-inch Sheets 21 and 13 (Scotland), 
 WITH Localities and Determinations. 
 
 Eeg. 
 
 No. 
 
 Locality. 
 
 1" 
 No. 
 
 Name. 
 
 2148 
 
 Bed above red tuffs, south of High 
 
 
 
 
 Oorrie, Arran, 
 
 21 
 
 Altered olivine basalt. 
 
 2463 
 
 South of Millstone Point, east 
 
 
 
 
 side of Arran, .... 
 
 jj 
 
 Diabase. 
 
 2595 
 
 South of Bruchag Point, Bute, . 
 
 3) 
 
 Dolerite. 
 
 2596 
 
 Same locality 
 
 )) 
 
 Dolerite. 
 
 2597 
 
 Wood, south of Kerrylamont, 
 
 
 
 
 Bute, ..... 
 
 J) 
 
 Dolerite altered. 
 
 2598 
 
 North of Lubas Point, Isle of Bute, 
 
 JJ 
 
 Diabase. 
 
 2599 
 
 Dyke on Keixytonlia shore, Bute, 
 
 JJ 
 
 Olivine dolerite. 
 
 2600 
 
 Dyke on Kerrytonlia shore, Bute, 
 
 )) 
 
 Porphyritic dolerite. 
 
 2603 
 
 West of Dunstrone Fort, Bute, . 
 
 29 
 
 Porphyritic dolerite. 
 
 2604 
 
 From west of Branzet ?, Bute, 
 
 21 
 
 Porphyritic dolerite or 
 andesite. 
 
 2605 
 
 North of Tor Mor, Bute, . 
 
 J) 
 
 Porphyritic dolerite. 
 
 2606 
 
 East of North Garrochty, Bute, . 
 
 JJ 
 
 Porphyritic trachyte. 
 
 2607 
 
 Garroch Head, Bute, . 
 
 V 
 
 Porphyritic dolerite. 
 
 2608 
 
 Suidhe Hill, Bute, 
 
 7) 
 
 Porphyritic dolerite. 
 
 2609 
 
 East of Tor Mor, Bute, 
 
 J, 
 
 Olivine dolerite. 
 
 4573 
 
 The Clack, Millport Bay, Great 
 
 
 
 
 Cumbrae, .... 
 
 yj 
 
 Bostonite 1 
 
 4574 
 
 Miller's Thumb, Millport Bay, . 
 
 JJ 
 
 Bostonite ? 
 
 4576 
 
 Barbay Hill, Great Cumbrae, 
 
 JJ 
 
 Trachyte. 
 
 4577 
 
 Farland Point, Great Cumbrae, . 
 
 J> 
 
 Trachyte. 
 
 4578 
 
 Top of crag near Hawk's Nest, 
 
 
 
 
 Great Cumbrae, 
 
 JJ 
 
 Biotite-trachyte. 
 
 4579 
 
 South of the Hawk's Nest, Great 
 
 
 
 
 Cumbrae, .... 
 
 JJ 
 
 Porphyritic basalt. 
 
 4583 
 
 Shore west of Creag nan Fith- 
 
 
 
 
 each. Great Cumbrae, 
 
 J? 
 
 Porphyritic trachyte. 
 
 4586 
 
 West of Creag nan Fitheach, 
 
 
 
 
 Great Cumbrae, 
 
 JJ 
 
 Porphyritic basalt. 
 
 4587 
 
 Sheughends, Great Cumbrae, 
 
 II 
 
 Porphyritic olivine 
 basalt. 
 
 4688 
 
 Terrach Hill, Great Cumbrae, 
 
 JJ 
 
 Porphyritic trachyte. 
 
Appendix. 
 
 179 
 
 Eeg. 
 
 No. 
 
 Locality. 
 
 1" 
 No. 
 
 Name. 
 
 4589 
 
 Dyke, Little Skate Bay, Great 
 
 
 
 
 Cumbrae, .... 
 
 21 
 
 Altered basalt. 
 
 4590 
 
 Dyke, Little Skate Bay, Great 
 
 
 
 
 Cumbrae, .... 
 
 ;; 
 
 Altered basalt (por- 
 phyritic). 
 
 4591 
 
 Dyke, Little Skate Bay, Great 
 
 
 
 
 Cumbrae, .... 
 
 )) 
 
 Altered basalt (por- 
 phyritic). 
 
 4592 
 
 North side of Fintray Bay, Great 
 
 
 
 
 Cumbrae, .... 
 
 ;j 
 
 Basalt. 
 
 4593 
 
 South end of Little Cumbrae, 
 
 )) 
 
 Basalt. 
 
 4594 
 
 Best and be Thankful, Little 
 
 
 
 
 Cumbrae, .... 
 
 
 Porphyritic basalt. 
 
 4596 
 
 Little Cumbrae, 
 
 )) 
 
 Basalt. 
 
 4616 
 
 Dunagpil Fort, South Bute, 
 
 
 Porphyritic basalt. 
 
 4617 
 
 West side of Port Luchdach, 
 
 
 
 
 South Bute, .... 
 
 )) 
 
 Porphyritic trachyte. 
 
 4618 
 
 East side of Port Luchdach, 
 
 
 
 
 South Bute, .... 
 
 ?J 
 
 Porphyritic olivine 
 basalt. 
 
 4619 
 
 Dunstrone, South Bute, 
 
 )i 
 
 Porphyritic olivine 
 basalt. 
 
 4620 
 
 South of Barr Hill, South Bute, 
 
 jf 
 
 Altered porphyritic 
 basalt. 
 
 4621 
 
 East of Port TJisg, South Bute, . 
 
 5) 
 
 Porphyritic basalt. 
 
 4622 
 
 Barr Point, North of Dunagoil 
 
 
 
 
 Bay, South Bute, . 
 
 7) 
 
 Porphyritic dolerite. 
 
 4625 
 
 West side, St. Blanes (?) Hill, 
 
 
 
 
 South Bute, .... 
 
 )) 
 
 Basalt. 
 
 4626 
 
 South-west end of Suidhe Hill, 
 
 
 
 
 South Bute, . 
 
 )J 
 
 Tuff. 
 
 4627 
 
 South-east side of Suidhe Hill, 
 
 
 
 
 South Bute 
 
 " 
 
 Porphyritic olivine 
 basalt. 
 
 4628 
 
 West side of Suidhe Hill, South 
 
 
 
 
 Bute, 
 
 )J 
 
 Porphyritic olivine 
 basalt. 
 
 4629 
 
 South-east side of Suidhe Hill, 
 
 
 
 
 South Bute, .... 
 
 ?J 
 
 Porphyritic olivine 
 basalt. 
 
 4633 
 
 On shore south of Barr Hill, 
 
 )5 
 
 Ophitic olivine dolerite 
 
 4634 
 
 South-west of Barr Buidhe, South 
 
 
 
 
 Bute, . ' . 
 
 )J 
 
 Ophitic olivine dolerite 
 
 6371 
 
 Head of Sliddery Water, Burn 
 
 
 
 
 B, Arran, . . ; . 
 
 13 
 
 Sandstone. 
 
 6373 
 
 
 
 
 6994 
 
 Sliddery Water Head, Burn B, 
 
 
 
 
 Arran, ..... 
 
 13 
 
 Tuff. 
 
 6995 
 
 Benlister Glen, east of Lagna 
 
 
 
 
 Croise, Arran, 
 
 21 
 
 Olivine basalt, 
 
180 
 
 The Geology of North Arran. 
 
 Reg. 
 No- 
 
 Locality, 
 
 1" 
 No. 
 
 Name. 
 
 6996 
 
 North of Creag na Fitheach, Glen 
 
 
 
 
 Dubh, Arran, .... 
 
 21 
 
 Tuff. 
 
 6997 
 
 500 yards north-east of Windmill 
 
 
 
 
 Hill, Arran, .... 
 
 Jj 
 
 Olivine basalt. 
 
 7051 
 
 Sliddery Water, Burn B, 400 yds.- 
 
 
 
 
 north-west of Cnoc Dubh, 
 
 13 
 
 Altered basalt. 
 
 7738 
 
 Sliddery Water, Burn C, . 
 
 57 
 
 Tuff. 
 
 7739 
 
 Sliddery Water Head, upper part 
 
 
 
 
 of Burn 0, . . . . 
 
 ;j 
 
 Basaltic andesite. 
 
 7740 
 
 Sliddery Water Head, Burn B, . 
 
 J) 
 
 Olivine basalt junction 
 
 
 _- 
 
 
 with quartz-felsite. 
 
 7741 
 
 " Trap " bed in shale. Burn B, 
 
 
 
 
 Sliddery Water, 
 
 )' 
 
 Basaltic andesite. 
 
 7742 
 
 "Coarse ash" in Burn B, 
 
 
 
 
 Sliddery Water, 
 
 )) 
 
 Tuff. 
 
 7743 
 
 Fossiliferous ironstone horizon, 
 
 
 
 
 Burn B, Sliddery Water, 
 
 7J 
 
 Tuff or ash ? 
 
 9396 
 
 Base of Carboniferous "trap," 
 
 
 
 
 north of Corrie, Arran, , 
 
 21 
 
 Porphyritic olivine 
 basalt. 
 
 9397 
 
 Top of Carboniferous "trap," 
 
 
 
 
 near Corrie, Arran, 
 
 )J 
 
 Porphyritic olivine 
 basalt. 
 
 9398 
 
 Small " trap " bed opposite Corrie 
 
 
 
 Established Church, 
 
 JJ 
 
 Porphyritic olivine 
 
 
 ; basalt (altered). 
 
PART III.— BIBLIOGRAPHICAL. 
 
 1774. Pennant, Thomas. A Tour to the Hebrides. 2nd Journey to 
 Scotland. 
 
 1795, Button, James. Theory of the Earth, with proofs and illustra- 
 tions. 2 vols., 8vo, Edinburgh. {See pp. 429, 467, and 480 
 of Vol. I. For 3rd volume of this work see under 1899.) 
 
 1797. St. Fond, Faujas de. Voyage en Angleterre, en Ecosse, et aux 
 
 iles Hebrides. 2 vols., 8vo. Paris, (Translation in 1799,) 
 
 1798. Jameson, Robert. An Outline of the Mineralogy of the Shetland 
 
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 1799. St. Fond, Faujas de. Travels in England, Scotland, and the 
 
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 1800. Jameson, Robert. Mineralogy of the Scottish Isles; with 
 
 mineralogical observations made in a tour through different 
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 1802, Playfair, John. Illustrations of the Huttonian Theory of the 
 Earth. 8vo. Edinburgh. (Arran, pp. 215, 314-316, 334.) 
 
 Jameson, R. Mineralog, Reisend. Schottland, n.d. Schottischen 
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 1807. Headrick, James. View of the Mineralogy, Agriculture, 
 Manufactures, and Fisheries of the Island of Arran, 8vo. 
 Edinburgh, 
 
 1814. Jameson (Robert). On Porphyry. Mem. Wern. Soc, Vol. II., p. 
 217. 
 
 MaccuUoch, John, Miscellaneous Remarks accompanying a 
 Catalogue of Specimens transmitted to the Geological Society. 
 Trans. Geol. Soc, 1st Ser., Vol. II„ p. 388, (Goatfell, Arran.) 
 
 1819. Macculloch, John. A Description of the Western Islands of 
 
 Scotland, including the Isle of Man, London. 2 vols., 8vo,, 
 and 1 vol., 4to,, with plates. 
 
 1820. Boue, Ami. Short Comparison of the Volcanic Rocks of France 
 
 with those of a similar nature found in Scotland. Edin. Phil. 
 Journ., Vol. II., p. 326. 
 
182 The Geology of North Arran. 
 
 1820 (about). Bou^, Ami. Essai Geologique sur I'Ecosse. 8vo, Paris. 
 (Another edition in 1829.) 
 
 1821. MaccuUoch, John. A Geological Classification of Rocks. 8vo. 
 London. (Arran Pitchstones, p, 524, etc) 
 
 Necker de Saussure, L.A. Voyage en Ecosse et aux iles 
 Hebrides. 3 vols. Geneve et Paris. 
 
 1824, Macullocli, John. The Highlands and Western Isles of Scotland, 
 containing descriptions of their scenery and antiquities. 4 vols. 
 8vo. London. 
 
 MaccuUoch, John. List of the Localities of some of the rarer 
 Scottish Minerals. Edin. Journ. Sci., Vol. I., p. 225. 
 
 1828. Landsborough, David. Arran. A Poem in six cantos. 12mo. 
 
 Edinburgh. 
 Sedgwick, Adam, and Murchison, (Sir) Roderick Impey. On the 
 Geological Relations of the Secondary Strata in the Isle of 
 Arran. Trans. Geol. Sac. Lond. 2nd Series, Vol. III., 
 p. 21, (Not puhlished tUl 1835.) 
 
 1829. Geynhausen, Karl von, and Dechen, Heinrich von. Die Insel 
 
 Arran. Karstein Arohiv. I. (2 Heft), pp. 316-356. Tab. 
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 1836. Thomson, Thomas. Outlines of Mineralogy, Geology, and 
 
 Mineral Analvsis ... 2 vols. 8vo. (Arran, Vol. I., 
 p. 392.) 
 
 1837. Patei'son, John. (Factor to his Grace the Duke of Hamilton and 
 
 Brandon.) Account of the Island of Arran with a map ; in 
 Prize Essays and Trans, of Highland and Agricultural Society 
 of Scotland, 8vo. Edinburgh, Vol. XL, p. 125 (or New 
 Series, Vol. V.) 
 
 1839. Smith, James (of Jordanhill). On the Last Changes in the 
 
 Relative Levels of Land and Sea in the British Islands, with 
 Catalogues of Recent Shells in the Basin of the Clyde and 
 N. Coast of Ireland, and of Shells from the newer Pliocene 
 Deposits in the British Islands. Edinh. Mem. Wern. Sac, 
 Vol. VIIL, p. 49. 
 
 1840. MaccuUoch, John, M.D, A Geological Map of Scotland with 
 
 Memoir on ditto. (Published several years after Macculloch's 
 death.) 
 
 Necker de Saussure, L.A. Documents sur les Dykes de Trap 
 d'une Partie de I'ile d' Arran. Trans. Roy. Sac. Edinh. Vol. 
 XIV., part 2, p. 684. 
 
 Ramsay, (Sir) A. C, Geological Model of the Island of Arran. 
 
 1841. The Statistical Account of Buteshire, by the ministers of the 
 
 respective parishes. 8vo. Edinburgh and London. (Generally 
 known as the New Statistical Account.) 
 
Appendix. 183 
 
 1841. Kamsay, (Sir) A. C. Notes taken during the Surveys for the 
 
 Construction of the, Model Maps and Sections of the Island of 
 Arran. -Eep. Brit. Ass. for 18Jfi. Trans. Sect., pp. 92-94. 
 
 Ramsay, (Sir) A. C. The Geology of the Island of Arran from 
 Original Survey. 8vo, Glasgow, p. 78. 
 
 1842. Rhind, William. The Geology of Scotland and its islands, with 
 
 a coloured Geological Map and numerous Sections. 8vo. 
 Edinburgh. 
 
 1844. Nicol, James. Guide to the Geology of Scotland with Geological 
 
 Map and Plates. 8vo. Edinburgh. 
 
 1845. The New Statistical Account of Ayrshire, by the ministers of the 
 
 respective parishes — (Parishes of Largs and West Kilbride, 
 pp. 786 and 243.) 8vo. Edinburgh and London. 
 
 1847. Landsborough, Rev. David. Arran. A Poem; and Excursions to 
 
 Arran, with reference to the Natural History of the Island. 
 8vo. London and Edinburgh. 
 
 1848. Wilson, John. Guide to Rothesay and the Island of Bute. Also 
 
 separately, the Geology of Bute with Map. New edition, 
 1856. Chapter on Geology p. 159, with account of Fossil 
 Shells by Hugh Miller. 
 
 Chambers, Robert. Ancient Sea Margins. 8vo. Edinburgh, 
 (pp. 197-199.) 
 
 1844-48. Bryce, James. On the Geology of the Island of Bute. Proc. 
 Phil. She. Glasg., Vol. II., 198-208. 
 
 1849. Bryce, James. Note on the Altered Dolomites of the Island of 
 
 Bute. Phil. Mag., Vol. XXXV., pp. 81-92, and Proc. Phil. 
 Soc, Glasg., Vol. III., p. 20. 
 
 1850. Grierson, Rev. Thomas. Autumnal Rambles among the Scottish 
 
 Mountains, or Pedestrian Tourists' Friend. 8vo. Edinburgh. 
 
 1852. Nicol, James. On the Geology of the Southern Portion of the 
 Peninsula of Cantyre, Argyllshire. Quart. Journ. Geol. Soc, 
 Vol. VIII., 426-425. At p. 424 Arran rocks compared with 
 those of Cantjrre. 
 
 Landsborough, Rev. David. Excursion to Arran, Ailsa Craig, 
 and the Two Cumbraes, with reference to the Natural History 
 of these Islands. 2nd series. Edinburgh. 
 
 1855. Napier, James. Dykes between Brodick and Lamlash. Edin. 
 New Phil. Jom-n, New ser.. Vol. II., No. 1, p. 81. 
 Bryce, James. Geological Notices of the Environs of Glasgow, 
 the Shores of the Clyde, and the Isle of Arran. 8vo. 
 Glasgow. (A pamphlet of pp. 24.) 
 
 ' Notice of Discovery of a New Granite in Arran. 
 
 Proc. Phil. Soc. Glasg., Vol. IV., p. 18. 
 
184 The Geology of North Arran. 
 
 1855. Bryce, James. On a Lately Discovered Tract of Granite in Arran 
 Rep. Brit. Ass. Trans. Sect., p. 80. (Title only.) 
 
 Phillips, Prof. John. Remarks on Certain Trap Dykes in Arran. 
 Bep. Brit. Ass. Trans. Sect., p. 94. 
 
 Manual of Geology, Practical and Theoretical. 8vo. 
 
 London. (Arran, pp. 503-506.) 
 
 Bryce, James. On the Geological Relations of certain Copper 
 Veins Recently Discovered in Bute. Proc. Phil. Sac. Glasg., 
 Vol. IV., p. 51. 
 
 1858. Sorby, Henry. On some Peculiarities in the Microscopical 
 Structure of Crystals applicable to the Determination of the 
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 -Journ. Geol. Sac., Vol. XIV., pp. 452-500. (Arran Pitch- 
 stones, p. 476, et seq., and Plate XVIII.) 
 
 1858. Mackinlay, John. Notice of Two Crannoges or Palisaded Islands 
 
 in Bute, with Plans. Proc. Antiq. Sac. Scotlcmd. Vol. III., 
 p. 43. 
 
 Delesse, Achille. Ettides sur le Metamorpbisme. Ann. des Mines, 
 Ser. 5. Vol. XIII., pp. 349, 350, 368-370. 
 
 Nicol, Prof. James. Geological Map of Scotland. 
 
 1859. Miller, Hugh. Sketchbook of Popular Geology. 8vo. Edin. 
 
 (Edited by Mrs. Miller.) Account of Glacial Shells in Bute, 
 pp. 321, et seq. 
 
 1859. Bryce, James. The Geology of Clydesdale and Arran. 8vo. 
 Glasgow. 
 
 1861. Jamieson, T. P. On the Structure of the South- West Highlands 
 
 of Scotland. Qucm-t. Journ. Geol. Soc. Vol. XVII., p. 133. 
 
 1862. Murchison, (Sir) Roderick, and Geikie, (Sir) Archibald. First 
 
 Sketch of a New Geological Map of Scotland, with Explana- 
 tory Notes. 
 
 Bryson, Alexander. On the Aqueous Origin of Granite. Edin. 
 New Phil. Journ. (N.S.), Vol. XV., p 52. 
 
 Smith, James (of Jordanhill). On a Split Boulder in the Island 
 of Little Cumbrae. Quart. ■Journ. Geol. Soc. Vol. XVIII., 
 p. 162. 
 
 Researches in Newer Pliocene and Post- Tertiary 
 
 Geology. 8vo. Glasgow. 
 Jamieson, T. F. On the Iceworn Rocks of Scotland. Quai-t, 
 
 Journ. Geol. Soc. Vol. XVIII., p. 164. 
 
 1863. Nicol. Prof. James. On the Geological Structure of the Southern 
 
 Grampians. Qumi,. Journ. Geol. Soc. Vol XIX., 180. 
 
 Geikie, (Sir) Archibald. On the Phenomena of the Glacial 
 Drift of Scotland. Trans. Geol. Soc. Glasgow. Vol. I., Part 
 2. (Glaciation in Bute, pp. 22 and 23 ; Kilchattan Clays, 
 p. 132.) 
 
Appendix. 185 
 
 18(>3. Zirkel, Ferdinand. Mikroskopische Gesteinsstudien. Sitz. Akad. 
 Wiss. Wien, Vol. XLVII., p. 226. (Arran, pp. 260-262, and 
 plates.) 
 
 1864. Boog Watson, Rev. E. On the Great Drift Beds with Shells in 
 
 the South of Arran. Trains. Roy. Soc. Edin. Vol. XXIII., 
 523, and Proceedings do., Vol. V., p. 157. 
 
 1865. Geikie, (Sir) Archibald. The Scenery of Scotland Viewed in 
 
 connection with its Physical Geology. 8vo. London and 
 Cambridge. 
 
 Bryce, James. The Geology of Arran and Clydesdale. 8vo. 
 Glasgow, Enlaiged edition of work of 1859. 
 
 On the Order of Succession in the Drift Beds of the 
 
 Isle of Arran. Quart. Journ. Geol, Soc. Vol. XXI., p. 204. 
 Crosskey, Rev. H. W. Glacial Deposits of the Clyde District. 
 
 Trans. Geol. Soc. Glasg. Vol. II., p. 45. 
 Campbell, J. F. Frost and Fire . . 2 vols., 8vo. (Glaciation 
 
 of Arran, Vol. II., pp. 65-71.) 
 Jamieson, T. F. On the History of the Last Geological Changes 
 
 in Scotland. Quart. Journ. Geol. Soc. Vol. XXL, p. 161. 
 
 (Kilchattan Tile Works, pp. 173, 174, and 202.) 
 Lyell, Charles (Sir). Elements of Geology. 8vo. London. 
 
 (Arran Granites, pp. 719-723.) 
 
 1866. Wiinsch, E. A. On the Occurrence of Fossil Trees Imbedded in 
 
 Trappean Ash in Arran. Trans. Geol. Soc. Glasgow. Vol. 
 II., p. 97 and p. 160. 
 
 1867. Forbes, David. The Microscope in Geology. Popular Science 
 
 Review (October). Vol. XXV., pp. 355-368. 
 Bolton, Henry E. On the Occurrence of Slickensides in the Trap 
 
 Dykes of Arran Island, Scotland. Journ. Roy. Geol. Soc. 
 
 Irel. (N.S.), Vol. I., p. 242. 
 Bryce, James. Account of Recent Researches into the Age of 
 
 the Arran Granites. Geol. Mag., Vol. IV., p. 552. (Paper 
 
 read at Meeting of Brit. Assoc.) 
 Wiinsch, E. A. On some Carboniferous Fossil Trees imbedded 
 
 in Trappean Ash in the Isle of Arran. Geol. Mag., Vol. IV., 
 
 p. 551, and Report Brit. Ass. Trams. Sect., p. 73. (Title only.) 
 Zirkel, Ferdinand. Mikroskopische Untersuchungen liber die 
 
 glasigen und halbglasigen Gesteine. Zeits. deuts. geol. Ges., 
 
 Vol. XIX., p. 737. (Arran Pitchstones, pp. 785-788, and 
 
 pi. XIV.) 
 
 1868. Crosskey, Rev. H. W., and Robertson, David. The Post-Tertiary 
 
 Fossiliferous Beds of Scotland (Cumbrae College). Trans. 
 Geol. Soc. Glasg. Vol. III., p. 113. 
 Forbes, David. Researches in British Mineralogy. Phil. Mag. 
 
 1869. Haswell, James. On Columnar Structure Developed in Mica 
 
 Schist from a Vitrified Fort in the Kyles of Bute. Trans, 
 Geol. Soc. Edin. Vol. I., p. 229. 
 
186 The Geology of North Arran. 
 
 1869. Potts, Rev. John F. On the Airan Olaystones. Tram. Geol. Sac. 
 
 GUs. Vol. III., p. 244. 
 
 1870. Coutts, James. On the Post-Tertiary Clay Beds at Kilchattan 
 
 Bay, Isle of Bute. Proc. Nat. Hist. Soc. Glasg. Vol. II., 
 p. 33. 
 
 Young, John, and Armstrong, James. On the Carboniferous 
 Fossils of the West of Scotland, their Vertical Range and 
 Distribution. Published by Glasgow Geol. Soc. as Supplement 
 to Vol. III. of their Transactions. 8vo, pp. 1-103. 
 
 1871. Binney, Ed. Wm. Observations on the Structure of Fossil 
 
 Plants found in the Carboniferous Strata. Paiceont. Soc. 4to, 
 pp. 55-59 and pi. XI. 
 
 Bell, Dugald. On the Aspects of Clydesdale during the Glacial 
 Period. Trails. Geol. Soc. Glasg. Vol. IV., p. 63. 
 
 Wunsch, E. A. On a Section of the Northern Shore of Arran. 
 Ibid., p. 95. 
 
 Zirkel, Prof. F. Geologische Skizzen von der Westkiiste 
 Schottland. Zeits. d, Deutsche. Geol. Ges., Vol. XXIII., 
 pp. 1-124, with 4 plates. 8vo. Leipzig, and separately. 
 
 1872. Allport, S. On the Microscopic Structure of the Pitchstones 
 
 of Arran. Geol. Mag., Vol. IX., pp. 1-10. 
 
 On the Microscopic Structure of the Pitchstones and 
 
 Felsites of Arran. Ihid. Vol. IX., pp. 536-545. 
 
 Bell, Dugald. Note on the Pitchstone at Oorriegills, Arran. 
 
 Trans. Geol. Soc. Glasg. Vol. IV., p. 190. 
 Bryce, James. The Geology of Arran and the other Clyde 
 
 Islands. 4th ed., 8vo. Glasgow and London. 
 B. (Anon.) Review of Bryce's Geology of Arran. Geol. Mag., 
 
 Vol. IX., pp. 552-556. 
 Orosskey, Rev. H. W., and Robertson, David. The Post-Tertiary 
 
 Fossiliferous Beds of Scotland (Kilchattan, Bute), Trans. 
 
 Geol. Soc. Glasgow. Vol. IV., p. 128. 
 
 1873. Geikie, (Sir) A. On some Points in the Connection between 
 
 Metamoi'phism and Volcanic Action. Trans. Geol. Soc. 
 Edin. Vol. II., pt. 3, p. 287. (Arran Granites, pp. 305, 306.) 
 M'Arthur, John. The Antiquities of Arran, with a Historical 
 Sketch of the Island. 8vo. Edinburgh. (2nd ed.) 
 
 1874. Vogelsang, Herman. Die Krystalliten. 8vo. Bonn (dated 
 
 1875), nachdem Tode des Verfassers herausgeben von F. 
 Zirkel. 
 
 . Allport, S. On the Microscopic Structure and Composition of 
 British Carboniferous Dolerites. Quart. Jowrn. Geol. Soc. 
 Vol. XXX., p. 529. (Arran, pp. 534, 547, 562-564.) 
 Thomson, James, and Wiinsch, E. A. Discovery of Derived 
 Carboniferous Fossils in the Conglomerates at the North End 
 of Arran. Trams. Geol, Soc. Glasgow. Vol. V., p. 313. 
 
Appendix. 187 
 
 1874. Brady, G. S., Rev. H. W. Crosskey, and D. Eobertson. A 
 
 Monograph of the Post-Tertiary Entomostraca of Scotland. 
 PalcBontograph. Soo., pp. 52, 53, 56, and 90. 
 
 1875. Crosskey, Eev. H. W., and Robertson, David. The Post- 
 
 Tertiary Fossiliferous Beds of Scotland (Kyles of Bute, etc.) 
 Trans. Qeol. Soo. Glasg. Vol. V., p. 29. 
 
 Glen, David Corse. Notes from the Island of Bute. On a Tract 
 of Columnar Sandstone and a Perched Boulder near Kil- 
 chattan. Trans. Oeol. Soo. Glasg. Vol, V., p. 154. 
 
 On a Magnetic Sand from East Bay, Rothesay. Ihid., 
 
 p. 158. 
 
 Landsboroughs, Father and Son. Arran, its Topography, 
 Natural History, and Antiquities. 8vo. Ardrossan and 
 London. 
 
 1876. Armstrong, James ; Young, John; and Robertson, David. Cata- 
 
 logue of the Western Scottish Fossils, with Introduction by 
 Prof. Young, M.D., on the Geology and Paleontology of the 
 District. Svo. Glasgow. 
 
 Bonney, T. G, On Columnar, Fissile, and Spheroidal Structure. 
 Quart. Joum. Geol. Soo., Vol. XXXII., p. 140. (Arran, 
 p. 142.) 
 
 Gooch, Frank A. Bemerkungen ilber die Pechsteine von Arran. 
 Tsch. Min. Petr. Mitth., p. 185. 
 
 Robertson, David. Notes on a Raised Beach at Cumbrae. Trans. 
 Geol. Soo. Glasg. Vol. V., p. 192. (Read May 1875.) 
 
 Geikie, (Sir) A. A New Geological Map of Scotland. 
 
 1877. Bonney, Rev. T. G. On Certain Rock Structures as Illustrated 
 
 by Pitchstones and Felsites in Arran. Geol. Mag., Dec. 2. 
 Vol. IV., p. 499. 
 
 Wiinsch, E. A. On the Junction of Granite and Old Red Sand- 
 stone at Corrie and Glen Sannox, Arran. Report Brit. Ass. 
 for 1876. Trans. Sect., p. 98. See also Trans. Geol. Soo. 
 Glasg. Vol. V., p. 162. 
 
 • Columnar Sandstone in Arran. Ihid. Vol. V., p. 
 
 324. 
 
 Glen, D. C. Remarks on a Porphyritic Quartziferous Felstone, 
 Bute. Trans. Geol. Soo. Glasg. Vol. V., p. 324. 
 
 1878. Lasaulx, Prof. A. von. Aus Irland. Bonn. 
 
 Wiinsch, E. A. A German Professor's View of the Geology of 
 Arran. Translated from Prof. A. von Lasaulx's " Aus 
 Irland." Trams. Geol. Soc. Glasg. Vol. VI., pp. 165 and 
 
 289, 
 
 Thomson, Prof. James. On the Jointed Prismatic Structure in 
 Basaltic Rocks. With three plates. Ibid. Vol. VI., pp. 95 
 and 117. (Columnar Sandstone in Bute, p. 110.) 
 
188 The Geology of North Arrwn. 
 
 1881. Allporfc, S. Note on the Pitchstones of Arran. Geol. Mag. 
 
 New Series, Vol. VIII., p. 438. 
 
 Lee, John Edward. Note-Book of an Amateur Geologist. Svo. 
 (Arran, pp. 50, 51, pi. LXV.-LXVIII.) 
 
 Milne Home, David. Seventh Report of the Boulder Committee 
 of the Royal Society of Edinburgh. Proceedings for the Session 
 1880-1881. Vol. XL, p. 246. 
 
 1882. Cadell H. M. Prof. Geikie in Arran. Nature, Vol. XXVL, 
 
 p. 39. 
 
 Geikie, (Sir) Archibald. Textbook of Geology. 8vo. London. 
 (Arran, pp. 716 and 739.) 
 
 Heddle (M. F.). Minerals New to Britain. Min. Mag., Vol. V., 
 p. 1. (Analyses of pitchstone and spherulite from Corrygills.) 
 
 1883. Heddle (M. P.). The Geognosy and Mineralogy of Scotland. 
 
 Sutherland. Part IV. Min. Mag., Vol. IV., p. 133. 
 (Murchisonite from Arran, p. 162.) 
 
 Judd, Prof. J. W., and Cole, (Prof.) Grenville A. J, On the Basalt 
 Glass (Tachylyte) of the Western Isles of .Scotland. Quart. 
 Joivi-n. Geol. Sac. Vol. XXXIX., p.' 444. Lamlash, and 
 Castle Grounds, Brodick. 
 
 1884. Bell, Dugald. On the Geology of Ardrossan arid West Kilbride. 
 
 Trans. Geol. Sac. Glasg. Vol. VII., p. 342. 
 Glen, David Corse. Notes on the Spherulitic Rock of Oorrie- 
 gills and the Banded Pitchstone of Invercloy, Arran. Ihid. 
 Vol. VII., p 352. 
 
 1886. Macadam, W. Ivison. Notice of a new Fossiliferous Bed in 
 
 the Island of Arran. Trails. Geol. Sac. Edhib. Vol. V., p. 
 316. 
 
 Rutley, Frank. Notes on Alteration induced by Heat in certain 
 Vitreous Rocks . . . Proc. Roy. Sac, Vol. XL., p. 430. 
 (Arran Pitchstones.) 
 
 1887. Macadam, W. Ivison. Notes on the Ancient Iron Industry ot 
 
 Scotland. Proc. Antiq. Soc. Scotland. Vol. XXI., p. 89. 
 (Skipness, p. 96. Arran, several localities, pp. 98 and 99.) 
 
 1888. Teall, J. J. H. British Petrography. Large 8vo. London. 
 
 Arran, pp. 15, 184, 185, 194, 195, 263, 264, 265, 328, 344-347. 
 Plates, 34 and 39. 
 
 1891. Smith, John. Note on the Occm'rence of Footprints in the 
 
 Calciferous Sandstone between West Kilbride and Fairlie. 
 Trans. Geol. Soc. Glas. Vol. IX., p. 201. 
 
 1892. Geikie, Sir A. Geological Map of Scotland. 
 
 Presidential Address to Geological Society on the 
 
 Volcanic Rocks of Great Britain. Quart. Journ. Geol. Soc, 
 Vol. XLVIII. (pp. 107, 111, 115, 119, 120, 122, 123.) 
 
Appendix. 189 
 
 1893. Blair, M. (Two large boulders near King's Cross, Arran.) 
 
 Trans. Geol. Soc. Glasg. Vol. IX., p. 427. 
 
 Judd, (Prof,) J. W. On Composite Dykes in Arran. Quart. 
 Journ. Geol. Soc. Vol. XLIX., pp. 536-565. 
 
 Murdoch, J. B. Columnar Fused Rock from the Vitrified Fort 
 at Burnt Islands, Kyles of Bute. Trans. Geol. Soc. Glasg. 
 Vol. IX., p. 418. 
 
 Neilson, James. A Visit to the Island of Little Cumbrae, with 
 some notes on its minerals. Ibid. Vol. IX., p. 373. 
 
 1894. Smith, John. Large Spherulites from Dun Fionn, Arran. Proc. 
 
 Geol. Soc. Glasg. Vol. X., p. 166. 
 
 China Clay from the Schrevin Clun Shaune, Arran. 
 
 Ibid., p. 168. 
 
 Smith, John. Rock fragments from near the centre of the 
 Arran Granite area. Ibid., p. 168. 
 
 Blair, Matthew. Arctic Shells from the Clay Bed near Lag, 
 Arran. Ibid., p. 169. 
 
 Young, John, LL.D. On the occurrence of Pyroxene or Augite 
 in large crystals in two localities in Western Scotland. Ibid. 
 p. 13. (Fairlie). 
 
 Milner, George. Studies of Natm-e on the Coast of Arran. 8vo. 
 London. 
 
 Zirkel, Ferdinand. Lehrbuch der Petrographie ; 2nd ed. ; 3 vols. 
 8vo. (Arran Pitchstones, Vol. II., pp. 223-225.) 
 
 1895. Corstorphine, Geo. S. Ueber die Massengesteine der Siidlichen 
 
 Theiles der Insel Arran, Schottland. Tscherinah, Min. u. pet. 
 
 Mitth. Vol. XIV., pp. 443-470 ; and separately. Wien. 
 Douglas, W. The Granite Peaks of Arran. Scott. Mount. Club 
 
 Journ. Vol. III., p. 195. 
 Geological Survey. Annual Report for the year 1894, pp. 
 
 284-286. 
 
 Thomson, Gilbert. Cir Mhbr. Scott. Mount. Club Journ., Vol. 
 III., p. 212. 
 
 1896. Smith, John. A New View of the Arran Granite Mountains. 
 
 Trans. Geol. Soc. Glasgow. Vol. X., p. 216. 
 Neilson, Jas. On the Old Red Sandstone and Carboniferous 
 
 Rocks of the North End of the Isle of Arran. Trans. Geol. 
 
 Soc. Glasg. Vol. X., pp. 280-301, and p. 367. 
 Geological Survey. Annual Report for the year 1895., p. 29. 
 Geikie, Sir Archibald. Scottish Mountains. Scott. Mount. Club 
 
 Journ., Vol. IV., p. 113. (Gcatfell, with plate.) 
 Rosenbusch, H. Mikroskopische Physiographic der Massigen 
 
 Gesteine ; 3rd ed. ; 8vo. (Arran, pp. 683, 692, 693, 699-703, 
 
 1144, 1157.) 
 Young, John. (A peculiar cream-coloured Felspathic Rock, from 
 
 a boulder on the shore of Brodick Bay in Arran.) Trans, 
 
 Geol. Soc. Glasg., Vol. X., p. 380. 
 
190 The Geology of North Arran. 
 
 1897. Geikie, Sir Archibald. The Ancient Yoloanoes of Great Britain. 
 
 2 vols. 8vo. London, pp. 307 and 411, Vol. I.; and pp. 
 368 and 418-420, Yol. II. 
 
 Geological Survey. Annual Report for the year 1896, pp. 53, 63, 
 66, 75, 76. 
 
 Thomson, James. On the Stratified Rocks of the Shore-line 
 from Clachland Point to the Cock of Arran. Trans. Geol. Sac. 
 Glas. Vol. XI., pp. 12-30, with a section. (The greater part 
 of this paper was i-ead in January 1875, and the section pre- 
 pared for the Meeting of the British Association in 1876.) 
 
 Young, Dr. John. Specimen of Felsite near Whiting Bay. 
 Trans. Geol. Soe. Glasg. Vol. XI., p. 32. 
 
 Gunn, WiUiam. Notes on the Geology of the Isle of Arran. 
 Trans. Geol. Soe. Edinburgh. Yol. YII., pt. 3, pp. 268-276. 
 
 1898. Geological Survey. Summary of Progress for the year 1897, pp. 
 
 81, 112-123. 
 
 Seward, A. 0. Fossil Plants for Students of Botany and Geology. 
 8vo. Cambridge, pp. 88-90. 
 
 1899. Hutton, James. Theory of the Earth, with Proofs and Illustra- 
 
 tions. Vol. III. (Edited by Sir A. Geikie). Arran, pp. 
 191-267.) 
 
 Geological Survey. Summary of Progress for the year 1898. 
 (Arran, pp. 52, 53, 93, 131, 150-152, 168, 169, 185, 186, 187.) 
 
 Cohen, E. Sammlung von Mikrophotographien . . 3rd ed. 
 (Arran, pi. IV.) 
 
 1900. Blair, Matthew. Andersonian Naturalists' Society. (Report of 
 
 paper on "The Circuit of Arran, with special reference to the 
 Ancient Sea Levels.") North Brit. Daily Mail, Sept. 13th. 
 
 Geological Survey. Summary of Progress for tlie year 1899. 
 (Arran, pp. 67-71, 82, 133, 134, 147, 148.) 
 
 1901. Geological Survey. Summary of Progress for the year 1900, pp. 
 
 Ill, 123-126, 168, 169. 
 
 Peach, B. N., Gunn, W., and E. T. Newton. On a Remarkable 
 Volcanic Vent of Tertiary Age in the Island of Arran, 
 enclosing Mesozoic Fossiliferous Rocks. Quart. Journ. Geol. 
 Soe. Vol. LVIL, pp. 226-241. 
 
 Gunn, WiUiam. On the Old Volcanic Rocks of the Island of 
 Arran. Trans. Geol. Soe. Glasg. Yol. XI., pp. 174-191 . 
 
 Smith, John. The Barite Veins of South-west Scotland. Ihid., 
 p. 232. 
 
 . Detached Microliths from the Pitchstone Sill at 
 
 Corriegills, Arran. Ibid., p. 275. 
 
 Cowie, Charles R. The Glacial Phenomena of Loch Ranza Glen, 
 Arran. Ibid., p. 282, 
 
191 
 
 INDEX 
 
 Aeeefoyle, black' shales and cherts of, 
 
 18. 
 Abhuinn Bheag, 14. 
 Achag, 28, 38. 
 A'Chir, 3, 9 ; basic dykes in the granite 
 
 of, 101. 
 A'Chruach, 2, 79, 87, 88, 98, 144. 
 Agates, 64. 
 Agglomerate, volcanic, 19, 20, 57, 59. 
 
 60, 61, 65, 66, 79-81. 
 Agriculture, 150. 
 
 Allpobt, S., 92, 97, 111, 117, 120, 127. 
 AUt a Bhuic, 102. 
 
 a Chapuill, 27, 86, 173, 174. 
 
 Airidh Niall, 95. 
 
 an Dris, 75, 78, 80 ; Rhsetio rocks 
 
 in Tertiary volcanic vent, 73. 
 
 an Siorrain, 135. 
 
 an Slaic, 120. 
 
 Beidh, 4. 
 
 Beith, pitchstone dyke at, 93. 
 
 Carn Bhain, Arenig cherts, 20, and 
 
 igneous rooks in, 20, 21, 22. 
 
 Dhepin, 111. 
 
 Domach, Arenig igneous rocks, 20, 
 
 21. 
 
 Gobhlach, 2, 14, 135. 
 
 Mor,24, 51, 129; 153. 
 
 na h-Airidh, 13. 
 
 na Meanie, 90, 91. 
 
 nan Calaman, 104 ; quartz-diorite 
 
 in, 88. 
 
 nan Eirreanach, 14, 90, 103. 
 
 Euadh, 81. 
 
 Alluvial flats, 150. 
 
 Alluvium, fresh- water, 5; in Arran, 
 
 142-143 ; in Ayrshire district, 144 ; 
 
 in Kintyre district, 17, 144, 145. 
 
 marine, 5, 11, 142. 
 
 Am Binnein, 3, 135. 
 
 Ambrisbeg, 54, 60 ; coal at, 48, 146. 
 
 AmmcmitRS angidatus zone, 76, 168, 169, 
 
 170. 
 
 Buddandi zone, 169, 170. 
 
 planorbis zone, 169, 170. 
 
 Amygdaloidal andesite, 64 ; pebble of, 
 
 in Tertiary volcanic agglomerate, 80. 
 
 lava, 26, 29, 57, 59. 
 
 oli vine-basalts, 62. 
 
 Amygdules in pillowy lava, 20. 
 
 Analcime diabase, 112. 
 
 Analysis of limestones, 40, 78, 148-149. 
 
 Ancient lakes, 143. 
 
 An Cumhann, 71, 92, 95, 139. 
 
 Andalusite developed by action of 
 
 granite, 86, 87. 
 
 Andesite, as lavas, 60, 64 ; as sills, 98, 
 99, 120 ; as necks, 65, 66 ; as dykes, 
 119 ; as fragments in Lower Old Red 
 Sandstone grit and conglomerate, 23, 
 26, 27 ; also in Tertiary volcanic 
 agglomerate, 80, 81. 
 
 Ann's Lodge, 35. 
 
 An Sgriob, landslip near, 144 ; lime- 
 stone quarries, 40, 148. 
 
 Anthracite coal at Ambrisbeg, 54, 146 ; 
 at Ascog, 146 ; at Cock of Arran, 49, 
 146. 
 
 An Tunna, 8, 13, 144. 
 
 Ard Bheinn, 2, 9, 70, 75, 78, 83, 88, 
 98, 153 ; acid sills, 91 ; breociated 
 conglomerate, 80 ; Cretaceous lime- 
 stone, 77 ; fault, 131 ; fragments of 
 Trias in Tertiary volcanic vent, 67, 
 72 ; granite, 87, 88 ; magnetic rock, 
 82, 98 ; Tertiary volcanic vent, 
 79-82. 
 
 Ardneil Bay, 35. 
 
 Ardrossan, 1, 10 ; raised beach at, 140 ; 
 Upper Old Red Sandstone rocks at, 
 35 ; volcanic necks near, 65. 
 
 Ardscalpsie, 129, 133. 
 
 House, 128. 
 
 Point, 54, 128, 129. 
 
 Arenig rocks, in Arran, 4, 8, 13, 15, 16, 
 18-22 ; in Bute, 22 ; intrusive igneous, 
 4, 21-22 ; metamorphism of, 18. 
 
 Argyllshire, area embraced within the 
 map, 1. 
 
 Arran, Arenig rocks of, 4, 13, 18-22 
 Bibliography of, 181-189; Carboni 
 ferous igneous rooks of, 56-58, 60, 61 
 Carboniferous strata of, 4, 8, 37-52 
 Coal Measures, strata of, 4, 41, 43, 45, 
 46 ; Cretaceous rocks of, 4, 76-78, 
 169 ; economic geology of, 146-151 , 
 faults (chief), 128-132 ; glaciation 
 and glacial deposits of, 133-136 
 granite, granophyre, and granitic 
 dykes, 84-91 ; Liassic rocks of, 4, 
 75-76, 168 ; metamorphic rooks of, 
 
 7, 12-16, Old Red Sandstone of, 4, 6', 
 
 8, 23-31 ; Old Red Sandstone igneous 
 rocks of, 26, 27, 28 ; physical features 
 of, 2-4 ; pitchstones of, 92-96 ; raised 
 beaches and recent deposits of, 
 139-140, 142-144, Rh^tic rocks in, 4, 
 73-75, 167-168; sills and dykes in, 
 91-101 ; Tertiary volcanic vent in, 
 4, 8, 9, 79-83; Trias or New Red 
 Sandstone of, 4, 8, 67-72. 
 
 Ascog, coal worked at, 48, 146. 
 Ash, volcanic, trees and plant remains 
 in, 48. 
 
192 
 
 Index. 
 
 Auchagalloii, 25 ; boundary between 
 Upper and Lower Old Red Sandstone, 
 31 ; pitohstone dykes, 95 ; Triassic 
 rocks 70 71 
 
 Auchenoar,'24,'26, 27, 134, 172, 174. 
 
 Burn, 25, 26, 172, 174. 
 
 Auchinhew, 114. 
 
 Auohmore, 94 ; faults in schists at, 14. 
 
 Augite andesites, 100 ; petrography of, 
 119. 
 
 porphyrite, 96. 
 
 Avicula coniorta zone, 168, 169, 170. 
 
 Ayrshire (part of, in sheet 21), 68 ; 
 alluvium, 11 ; area embraced within 
 the map, 1, 9, 10 ; Arenig rooks in, 4, 
 18, 20, 21 ; black shales and cherts in, 
 18 ; blown sand, 1 1 ; Caloif erous Sand- 
 stone series of, 63-64 ; Carboniferous 
 rocks of, S, 10 ; faults, 63 ; general 
 geological description of, 9-11 ; glacial 
 deposits of, 11, 136-137 ; igneous 
 rocks of, 10, 35, 63, 64-66, 101-102; 
 passage beds from Old Red Sandstone 
 to Carboniferous, 63; peat in, 11; 
 physical features of, 2, 9 ; raised 
 beaches of, 11, 140-141, 142; 
 Tertiary dykes of, 10, 65, 101 ; Upper 
 Old Red Sandstone of, 8, 10, 34-36 ; 
 volcanic necks of, 10, 64-66. 
 
 B 
 
 Ballantrae, Arenig volcanic rocks of, 
 
 4. 
 Ballarrie, 140, 149. 
 Balliekine, 14, 100, 133, 150. 
 Ballintay, 169. 
 Ballochmyle, resemblance of Triassic 
 
 sandstones of Arran to Permian 
 
 strata at, 67. 
 Ballykellet, cornstone, 31, 53; faxalt, 31 ; 
 
 nodular basalt dyke, 62. 
 Ballymichael, 72, 136. 
 Burn, 71, 75, 135, 136, 143. 
 
 Glen, 72, 76, 81, 87, 88, 89, 98 ; 
 
 Lias fossils from, 153, 168, 169. 
 
 Baniorlach, 25, 26. 
 
 Bank, The, 141. 
 
 Barefield, 133. 
 
 Barr Bnidhe, deviation of ice-sheet, 
 
 133. 
 Barr Hill, 99, 116. 
 Barr Point, 55, 60. 
 Barytes workings, old, in Glen Sannox, 
 
 27, 147. 
 Basalt, as lavas, 34, 59, 171, 172 ; as 
 
 dykes, 62, 85, 91, 101, 102. 
 Basic sills and dykes in Arran, 97-101 ; 
 
 in Ayrshire district, 101-102 , Kintyre 
 
 district, 102. 
 Beaches, raised, 5 ; in Arran, 139, 140 ; 
 
 Ayrshire district, 140-142 ; Little 
 
 Cumbrae, 139 ; Skipness, 142 ; South 
 
 Bute, 128, 139. 
 Beinn a' Chliabhain, 3, 94, 101. 
 
 Bharrain, 2, 85. 
 
 Bhreac, 2, 25, 31, 78, 79, 81, 83, 
 
 87, 88, 94, 100, 144.' 
 Chaore^ch, 13. 
 
 Beinn, Loehain, 13, 129, 131. 
 Nuis, 3, 65, 85, 94. 
 
 Tharsuinn, 3, 92, 94. 
 
 Belemnitdla mucronata zone, 170. 
 Belemnites acutus zone, 169. 
 Belemnite shales, 170. 
 
 Belfast, Rhastio and Liassic rocks near, 
 
 169, 170. 
 Bell Bay, 32. 
 Benan Head, 99. 
 Ben Ledi grits, metamorphic rocks of 
 
 Kintyre district correlated with, 16. 
 Benlister Burn, 2, 44, 45. 
 Glen, 8, 38, 44, 56, 58, 61, 67, 69, 
 
 81, 92, 97, 130, 155, 176. 
 Bessy's Port, 32, 134. 
 Biglees Hill, 66. 
 Binnein nah-Uaimh, 82. 
 Biotite granite, 81. 
 
 developed by contact alteration, 
 
 86, 87. 
 
 Birch Burn, 70, 72, 100. 
 
 Birgidale Butts, 2. 
 
 Birk Glen, 92, 93, 97, 131. 
 
 Black Rock, 66, 134. 
 
 schist or shales, Arenig, in Arran, 
 
 4, 18, 19, 20, 21. 
 
 Blackshaw Hill, 65, 101. 
 
 Blackwater, 2. 
 
 Blown sand, 5, 11, 142, 144. 
 
 Bloomeries, old, in Arran, 147. 
 
 Blue Rock, 30. 
 
 Bog iron ore, 147. 
 
 BoNNEY, Professor T. G., 127. 
 
 Bostonite, 62. 
 
 " Bottle rock," 92. 
 
 BouE, A., 115, 118. 
 
 Boulder clay, 5, 36, 135, 138, 140. 
 
 Boulders, 133, 134-135. 
 
 Boydston, 141. 
 
 Branzet Moss, 143. 
 
 Breccia, fault, 129. 
 
 volcanic (Arenig), 19, 20. 
 
 Brecknock, 143, 144. 
 
 Brisderg, 44, 45, 58, 69, 87, 97. 
 
 Broad Island, 119. 
 
 Broadford Bay, 35. 
 
 Brodick, 1, 23, 25, 27. 37, 67, 68, 72, 
 79, 87, 92, 97, 99, 100, 101, 118, 120, 
 123, 135, 139, 142, 147, 149, 150. 
 
 Bay, 3. 68, 69, 70, 100, 151. 
 
 Castle, 25, 37, 42, 43, 56, 58, 60, 
 
 67, 68, 132. 
 
 Manse, fault, 130. 
 
 Pier (old), 68. 
 
 Schoolhouse, pitchstone dyke, 93, 
 
 94. 
 
 Woods, boundary between Upper 
 
 and Lower Old Red Sandstone, 31. 
 
 Brooraoraig Park, 140. 
 
 Bruce's Castle, 70. 
 
 Bruchag Point, 33. 
 
 Brtce, J., 55, 86, 87, 117, 148. 
 
 Building stone, 148. 
 
 Bute, 1, 3, 4, 9, 10, 64, 134, 139, )50; 
 altered sandstone and conglomerate 
 in, 33 ; area of, embraced within the 
 sheet, 1 ; Arenig rocks of, 22; boulders 
 in, 134 ; Calciferous Sandstone Series 
 of, 53 ; Carboniferous rooks of, 8, 53, 
 
Index. 
 
 193 
 
 56 ; columnar sandstone in, 33 ; clays 
 and sands with glacial shells in, 136 ; 
 clays worked for tile-making in, 149 ; 
 dykes and sills in, 54, 62, 63, 99 , 
 faults, 34, 54, 60, 128, 129; glacial 
 deposits of, 133, 136; iprneous rooks 
 of, 8, 54, 56, 59-60, 61, 62; meta- 
 morphio rocks, 7, 12 ; Old Red Sand- 
 stone (Upper) of, 8, 28, 31, 32 ; physical 
 features of, 2 ; population of, 149 ; 
 quarries in, 54, 148 ; raised beaches 
 of, 139 ; Tertiary basic sills of, 98, 
 99 ; volcanic vents in, 55, 56, 61. 
 Butter Lump, 32. 
 
 Caistbal Aehah,, 3, 85, 92, 94, 100, 
 101, 122, 135, 151. 
 
 an Fhionn, 85. 
 
 Calciferous Sandstone Series of Ayr- 
 shire, 10, 63 ; Arran, 57 ; Bute, 53 ; 
 Cumbraes, 53 ; thickness of, in Arran, 1 
 46 ; igneous rocks of, 56, 57, 63-64 ; 
 trachyte dykes and sills of, 62. 
 
 Calcite, 21, 62, 70 ; in amygdaloidal 
 basalts, 59. 
 
 veins, 43 ; in pillowy lavas, 58. 
 
 Campbeltown district, " Green Beds " 
 and " Loch Tay limestone " of, 17. 
 
 Carboniferous formation of Arran, 4, 
 8, 37-52 ; Ayrshire, 8, 10, 63 ; Great 
 and Little Cumbrae, 8, 9, 31, 53-54 ; 
 Bute, 8, 33, 53, 54-56 ; boundary 
 between Old Red Sandstone and, 31, 
 34, 53, 54, 63 ; boundary between 
 Trias and, 68 ; boundary fault between 
 schists and, 19, 129 ; conglomerates, 
 39, 63 ; cornstone at base of, 46 ; 
 faults, 18, 34, 37, 38, 39, 40, 41, 42, 
 43, 44, 45, 46, 47, 48, 50, 54, 57, 58, 
 61 , 128, 129, 130, 132 ; fossils from, 
 39, 40, 41, 42, 43; fossil localities, 
 153-154 ; Laggan section, 45-51 ; 
 plants in shaly tuff, 48, 57 ; thickness 
 of, in Arran, 37, 46 ; igneous rocks 
 of, in Arran, 4, 8, 9, 38, 39, 44, 47, 
 56-58, 60-61, 97; in Ayrshire, 64- 
 66 ; in Bute, 8, 9, 53, 54, 56, 59, 61 ; 
 in Great Cumbrae, 9, 61 ; Little 
 Cumbrae, 8, 53, 56, 58. 
 
 Limestone Series, 48-51. 
 
 petrography of, 175-178. 
 
 Carlisle, Lias.<iic rooks near, 170. 
 
 Carlung, 65, 142. 
 Moss, 11, 142, 144. 
 
 Cam Ban, pitchstone dyke, 94. 
 
 Casteal an Fhionn, 85. 
 
 Castle Island, 53, 69. 
 
 Carradale, 137. 
 
 Catacol, 15, 52, 90, 99, 133, 138, 140, 
 142. 
 
 Bay, 15. 
 
 Bridge, 14. 
 
 Burn, 52, 90, 133. 
 
 — — Cairn, 52. 
 
 Glen, 2, 84, 86, 144. 
 
 Caves, water- worn, on edge of raised 
 beach, 139. 
 
 Cement-stones (Carboniferous), 43, 47, 
 
 48, 57, 58, 63, 64. 
 Ceum na Caillich, 3, 9, 101, 134, 135. 
 Chalk of England, 76. 
 
 of Ireland, 76, 77, 169. 
 
 Cherts, Arenig, in Arran, 4, 18, 19, 20, 
 21 ; absence of radiolaria in, 18 ; 
 altered by granite, 18 : correlated 
 with those of Southern Uplands, 18. 
 
 fossiliferous, in Tertiary volcanic 
 
 neck 77 
 Cioch na h-Oighe, 3, 27, 30, 31, 86, 129, 
 
 173, 174. 
 CirMh6r, 3, 85, 92, 94, 116, 119, 120, 
 
 125, 136, 151. 
 Claoh, 62. 
 
 a Chait, 135. 
 
 Clachan, 90. 
 
 Glen, 8, 23, 25, 31, 132. 
 
 Claoh an Fhionn, 39, 57, 134. 
 Clauchlands Burn, 37. 
 
 Hills, 70, 93, 97, 130, 146. 
 
 Point, 70, 97. 
 
 Shore, 93, 135. 
 
 Clach Mhor, 134. 
 Claonig Bay, 142. 
 
 Water, 1, 102, 138, 144. 
 
 Clashfarland Point, 32. 
 
 Clays, laminated, 5 ; with glacial shells, 
 
 136 ; used for tile-making, 49. 
 Olaystone, 125. 
 Clyde Basin, 138. 
 
 Firth of, 138. 
 
 Cnoc Ballygown, 112. 
 
 a' Chapuill, 38. 
 
 a Moine Raibert, 102. 
 
 an Biorach, 23, 81. 
 
 Bum, 3, 13, 23, 86, 117, 129, 
 
 135. 
 
 Donna, 20. 
 
 Donn, 14. 
 
 Dubh, 72, 79, 87, 88, 91, 97. 
 
 na Ceille, 25, 95, 136. 
 
 Croise, 8, 23, 81. 
 
 nan Sgrath, 15. 
 
 Coal, 48; anthracite, 49. 54: at the 
 Cock of Arran, 40, 49, 146; bonnf; 
 for, in Arran, 146; in Bute, 48, 54, 
 146 ; (thin) at base of Carboniferous 
 volcanic series, 48. 
 Coalfin, 138, 144. 
 
 Coal-measures in Arran, 4, 41, 42, 43, 
 44, 45, 67, 129, 130 ; thickness of, 46 ; 
 fossils from, 41, 42, 43, 44, 45, 51 ; 
 volcanic rocks of, 56, 60, 61. 
 Coast line, extent of, within the map, 1. 
 Cock of Arran, 15, 50, 99, 105, 129, 150 ; 
 Carboniferous rooks, 8, 37, 45 ; fossil 
 localities at, 153, 154 ; New Red Sand- 
 stone or Trias at, 8, 67, 70 71, 138. 
 
 Farm, 45, 51, 146, 147. 
 
 Cohen, E., 122. 
 
 Coillemore, old bloomeries at 147. 
 
 Coire Fhraoich, 151. 
 
 nan Ceum, 135. 
 
 Larach, 135. 
 
 hkn, 136. 
 
 Cole, G. A. J., 118. 
 Columnar structure, 33, 34, 59, 91, 92, 
 99. 
 
194. 
 
 Index. 
 
 Composite dykes, 116. 
 
 sills, 114. 
 
 Concretionary sandstone, 71. 
 Conglomerates [see the respective for- 
 
 matio-is). 
 " Coral'' limestone, 50. 
 Corlooh, 7, 8, 15, 20, 23, 28, 45, 56, 57, 
 
 129. 
 Cornstone, 29, 33, 38, 39, 46, 47, 48, 
 
 129. 
 
 at base of the Carboniferous in 
 
 Arran, 46, 52 ; Bute, 33 ; Great 
 Cumbrae, 31, 53. 
 
 Corrie, 1, 99, 136, 146, 150, 151 ; Car- 
 boniferous rocks at, 8, 37, 38, 39, 45, 
 46 ; Coal Measures near, 41, 45 ; 
 faults, 130, 131 ; fossil localities near, 
 154 ; igneous rocks of, 38, 56, 57 ; 
 marine shells in raised beach south of, 
 139; Old Red Sandstone, 8, 23, 28, 30, 
 31, 38, 68; "pillow" structure in 
 lavas, 57, 58 ; thickness of Calciferous 
 Sandstone at, 46 ; Trias, 8, 37, 67, 68, 
 70 ; water-worn caves on edge of 
 raised beach, 147. 
 
 — Burn, 134. 
 
 — Church Burn, 13. 
 
 Cravie, 117. 
 
 Hotel, 37, 68. 
 
 — limestone, 37, 38, 39, 40, 42, 43, 
 44, 45, 48 ; analysis of, 40 ; thickness 
 of, 39 ; Trias resting on, 67 ; uncon- 
 formability of Trias to, 44. 
 
 North High, 150. 
 
 Schoolhouse, 30, 38. 
 
 Corrygills, 93 110, 122, 123, 125, 127, 
 130. 
 
 North, 91, 93. 
 
 South, 91, 93, 151. 
 
 Point, 69, 91, 99. 
 
 Shore, 70, 91, 100, 135. 
 
 COESTOBPHINE, G. S., 99, 111, 112, 113, 
 
 114, 115, 120. 
 Cosson, 32. 
 Cour, 17. 
 
 CouTTS, James, 136. 
 Cowal, 12, 15, 131, 138. 
 CowiE, James, 49. 
 Ckampton, Dr. C. B., 153. 
 Creag a Mhaid, 61. 
 Creagan a' Choilich, 15. 
 Creag an Feidh, 77. 
 Creagan Geala, 172, 174. 
 
 Liatha na Cluain Monaidh, 98. 
 
 Creag Dubh, 3, 82, 85, 87, 94, 135, 151. 
 
 Ghlas Cuithe, 15. 
 
 Mh6r Derenenach, 107. 
 
 nam Fitheach, 43, 44, 70, 119, 130, 
 
 177. 
 
 nam Mult, 87, 88, 96. 
 
 Rosie, 13, 120. 
 
 Shocach, 80. 
 
 D 
 
 Db Ut. Beeche, 33. 
 Delbssb, a., 104, 115, 118,1123. 
 Derenenach, 70, 73, 77, 80 81 82 87, 
 91, 98, 136, 146, 153, 
 
 Devil's Dyke, 100, 119. 
 
 Diamond Hill, volcanic neoka, 66. 
 
 Diorite, 81, 89 ; felsite veins in, 96 ; 
 granite veins in, 87, 88, 89, 96 ; grano- 
 phyre veins in, 89, 96 ; intrusions in 
 Old Red Sandstone, 23, 96 ; intrusions 
 in Tertiary volcanic vent, 81 ; mass 
 in Glen Dubh, 96. 
 
 Dippin, HI, 112, 113, 119. 
 
 Doire na Ceardich, 150. 
 
 Dolerite, 99, 148 ; altered, 86 ; ophitic, 
 82, 96 ; porphyritic, 60. 
 
 dykes, 35, 62, 64, 69, 101 ; sand- 
 stone hardened and bleached by, 35 ; 
 shifted by fault, 130; Tertiary, 
 cutting schists, 102. 
 
 sills, 10, 63, 97 ; compound, 98 ; 
 
 Tertiary, cutting dolerite sill, 98. 
 
 Dolomitio limestone, 33, 54 ; in contact 
 
 with igneous rock, 54. 
 Doughend Hole, 31, 32, 53, 62. 
 Dougrie, 7, 12, 23, 24, 25, 129, 135, 140, 
 
 150. 
 
 Lodge, 140. 
 
 Downcraig Ferry, 32, 62. 
 
 Drift deposits, 5, 11, 26,27, 44, 54, 134. 
 
 Drumadoon, 110, 115. 
 
 Drumlins, 5, 134. 
 
 DrummilUng Hill, 65. 
 
 Dubh Loch, 3, 94. 
 
 Dun, 22. 
 
 Dunagoil Bay, 33, 55, 61. 
 
 Fort, 60. 
 
 Dun Dubh, 91, 93. 
 
 Fionn, 93, 96, 97. 
 
 Dunoon, dyke, 62 ; metamorphic rooks 
 
 of, 12 ; slates of, 13, 15. 
 Dimstrone, 56. 
 
 Fort, olivine basalt of, 60. 
 
 Dykes, 9, 25, 27, 33, 84, 85, 100, 101 
 
 102 ; acid, 44 ; andesite, 64 ; basalt, 
 10, 19, 43, 91 ; basic, 40, 44, 99, 101 
 composite, 95 ; dolerite, 35, 64 
 granitic, 90-91 ; granophyrio, 90 
 quartz-felsite, 92 ; pitchstone, 92-96 
 
 Tertiary, 58, 73, 87, 101, 102. 
 
 E 
 
 Easan Bioeach, 2, 133, 142. 
 
 Eas Geal, 45, 61. 
 
 Economic geology, 146-151. 
 
 Edinburgh, porphyritic olivine basalt of 
 Arthur's Seat, 62. 
 
 Elvans, 88, 91. 
 
 England, chalk of, 76 ; Trias of, 67. 
 
 Epidiorite, 18, 20, 22. 
 
 Epidote, 20, 22, 24, 26, 27, 86. 
 
 Erratic blocks, 5 ; in Arran, 133, 
 134-135 ; in Bute, 134; in Great Cum- 
 brae, 134 ; in Kintyre, 137. 
 
 Escairt, 5, 142. 
 
 Point, 142. 
 
 Eskers, 5, 136. 
 
 Estuarine deposits, 5. 
 
 Bun Point, 117. 
 
 Euritp, 99 
 
Index. 
 
 195 
 
 F 
 
 Fairlie, 10, 63, 64, 137. 
 
 Burn, 63. 
 
 Castle, 63. 
 
 Glen, 63, 64. 
 
 Roads, 142. 
 
 Fairy Dell, 144. 
 
 Fallen Rocks, 8, 23, 28, 29, 34, 37, 45, 
 46, 99, 100, 129, 139, 144, 171, 174. 
 
 False-bedding in sandstones, 32, 35, 38, 
 53, 63, 67, 68. 
 
 FarohaTi Mor, 28, 30, 130, 133. 
 
 Farland Head, 35. 
 
 Point, 32, 62, 128. 
 
 Faults (chief), 128-132 ; relative ages 
 of, 131-132. 
 
 Felsite, banded, 82 ; magnetic, 82, 98 ; 
 pebble, in agglomerate of Tertiary 
 volcanic vent, 81 ; veins in diorite, 96. 
 
 dykes, 43, 85. 
 
 sills, 72, 74, 91, 92, 149; age of, 91. 
 
 Felstone, spherulitic, 93. 
 
 Fence Bay, 66, 140, 142. 
 
 Ferry Rock, 40. 
 
 Figgatooh, 62, 148. 
 
 Fintray Bay, 32, 62. 
 
 Fireclays, 40. 
 
 Firth of Clyde, 10, 137, 140. 
 
 Flett, Dr., 16, 21. 
 
 Flow structure in rhyolite, 82. 
 
 Foraminifera in Cretaceous limestone, 
 77. 
 
 Forfarshire, Old Red Sandstone of, 24. 
 
 Formations, table of, 5-7. 
 
 Fossils, derived, in Triassic conglomer- 
 ate, 71-72. 
 
 general list of, 156-170. 
 
 lists of, in Carboniferous strata, 41, 
 
 42, 43, 45,. 46, 48, 49, 50, 51, 52 ; in 
 Rhsetic, Lias, and Cretaceous, of Ter- 
 tiary volcanic vent, 75, 76, 77, 167- 
 170. 
 
 localities for, 153-155. 
 
 Foul Port, 53-54. 
 
 Gabbro, 82 ; petrography of, 107. 
 Garbh AUt, 24, 47, 101, 129, 131, 136. 
 
 -choire, 118. 
 
 Dubh, 136, 151. 
 
 Thorr, 24, 25, 26, 131, 172, 174. 
 
 Garlton Hills, 177. 
 
 Garroch Head, 2, 54, 61, 63. 
 Garrochty, North, 60, 177. 
 
 South, 55, 60. 
 
 Garveoline, 102. 
 
 Gbikie, Sir Archibald, 24, 51, 52, 67, 
 103, 136, 170. 
 
 Glacial shell-beds, 136. 
 
 Glaciation and glacial deposits, 5 ; in 
 Arran, 133-136 ; Ayrshire district, 
 11,136-137; Bute, 133; Cumbraes, 
 133 ; Kintyre district, 137-138. 
 
 Glaid Stone, 32. 
 
 Glaister, 136. 
 
 Gleann ant Suidhe, 87, 88, 96, 134. 
 
 Easbuig, 13. 
 
 Glen Burn, 63. 
 
 Glen, D. C, 33. 
 
 Glen, The (Ayrshire), 64. 
 
 Glenoallum, 2, 56, 60, 143. 
 
 Bay, 56, 98. 
 
 Glen Catacol, 2, 14, 84, 86, 104, 108. 
 
 Chalmadale, 15, 90, 105. 
 
 Cloy, 68, 69, 70, 94, 66, 125, 135, 
 
 136, 139-140, 143, 147, 150. 
 
 Burn, 2, 4, 135. 
 
 Craigag, 9, 82, 83, 87. 
 
 Dubh, 8, 14, 23, 25, 31, 38, 43, 69, 
 
 87, 88, 89, 92, 96, 106, 111, 126, 130, 
 135, 136, 150, 177. 
 
 Easan Biorach, 14, 85, 86. 
 
 Fyne granite, boulder of, near 
 
 Cock of Arran, 134. 
 
 Glenhead, 141. 
 Glenkiln, 147. 
 Glenloig, 9, 75, 77, 80, 82, 87, 88, 108. 
 
 Burn, 89, 95, 96. 
 
 - Farm, 81. 
 
 House, 83. 
 
 Glen Ormidale, 8, 43, 69, 88, 91, 92, 97, 
 
 126, 135. 
 Glenrickard, 147. 
 Glen Rosie, 13, 23, 24, 27, 43, 68, 92, 
 
 101, 118, 120, 129, 136, 140, 150, 155, 
 
 174. 
 Burn, 3, 37, 68, 86, 101, 173, 
 
 174 ; old course of, 143. 
 
 Sannox, North, 3, 4, 7, 8, 18, 20, 
 
 21, 23, 24, 28, 34, 57, 84, 86, 129, 
 131, 140, 150, 151. 
 
 South, 3, 7, 23, 24, 27, 85, 
 
 101, 117, 129, 131, 135, 140. 
 
 Burn, 172, 174. 
 
 North, 8, 19, 142. 
 
 South, 27, 142, 147. 
 
 Scaftigill, 13, 87. 
 
 Glenshant Hill, 7, 13. 
 
 Glen Shurig, 23, 24, 31, 43, 46, 58, 92, 
 94, 132, 149, 151, 165. 
 
 Struey, 115. 
 
 Glentane Hill, 64, 66. 
 Goatfell, 3, 104. 
 
 Gogo Burn, 137, 140, 141. 
 
 Glen, 10. 
 
 Granite, general description of, 84-91 ; 
 affecting the strike of metaniorphic 
 rocks, 12, 14; areas occupied by, 84, 
 85, 87 ; age of, 87, 90 ; boulders in 
 Kintyre, 137 ; denudation of, 9 ; 
 fragments of, in agglomerate of Ter- 
 tiary volcanic neck, 80 ; intrusions in 
 Tertiary volcanic neck, 81, 82, 103 ; 
 raetamorphism produced by, 7, 12, 
 13, 14, 86 ; petrography of, 104 ; 
 veins in diorite, 87-88, 89, 96. 
 
 Granite dykes, 90-91. 
 
 Granitite, 89. 
 
 Granophyre, 87, 8S, 89 ; causing meta- 
 morphism of Old Red Sandstone, 23, 
 25, 31, 89 ; gradation into granite and 
 quartz-diorite, 87; intrusive in diorite, 
 89, 96 ; intrusive in Tertiary volcanic 
 vent, 81, 82 ; petrography of, 104. 
 
 Granophyric dyke, 90. 
 
 Gravel, 5, 136. 
 
 " Green Beds," 15, 16, 17, 20. 
 
196 
 
 Index. 
 
 Greensand, 169, 170. 
 Greenside Hill (Ayrshire), 66. 
 Grejrffaoke in Arran correlated with 
 Dunoon series, 15 ; schistose, 13. 
 
 H 
 
 Haddingtonshike, 177. 
 
 Haematite, 49. 
 
 Halifax, 33. 
 
 Haswell, Jambs, 34. 
 
 Hatch, Dr. F., 177. 
 
 Hawk's Nest, 62, 177. 
 
 Haystack, 128. 
 
 Hbadbiok, Rev. J., 40, 49, 78. 
 
 Heat causing columnar structure in 
 
 sandstone, 33. 
 Highland border, black shales and 
 
 cherts of, 18 ; fault, 19, 128, 131. 
 Highlands, metamorphio series of, 18. 
 
 Southern, "Green Beds" of, 20. 
 
 Hill House, 141. 
 
 Hind, Dr. Wheelton, 153, 169. 
 HiNDE, Dr. G. J., 169. 
 Holy Island, 1, .S, 9, 70, 91, 92, 135. 
 Hornblende-gabbro, 21. 
 
 schist, 7, 22. 
 
 Homstone, 125, 126. 
 Horse Island, 1, 13. 
 Hosie limestone, 48. 
 Huddersfield, 33. 
 Hunterston, 64, 141, 142. 
 
 House, 1, 14, 66. 
 
 Hurlet limestone, 39, 48, 64. 
 HCTTON, J., 51, 84. 
 Hyperite, 81, 96, 108. 
 
 Ioe-Sheet, direction of movement of, 
 133, 134, 136, 137. 
 
 Igneous rooks of Arran, 4, 8, 34, 39, 
 56-58, 60-61 ; 79-98, 99-101 ; Ayr- 
 shire, 8, 10, 35, 64-66, 101-102 ; 
 Bute, 54, 55, 56, 69-60, 61, 63, 98-99 ; 
 (Jumbrae (Great), 54, 61 ; Cumbrae 
 (Little), 58-59; Kintyre district, 102; 
 petrography of, 103-127, 171-180. 
 
 Imaohar, 12. 14, 100, 133, 134, 147. 
 
 Inchmamook Island, 1, 2, 7, 12, 139, 
 148. 
 
 Index mestone, 40, 41, 49. 
 
 Innellan, 22. 
 
 Inveroloy, 93, 94, 99, 100, 120. 
 
 lorsa, 13, 85. 
 
 Glen, 85, 86. 
 
 Loch, 85, 95, 142, 143. 
 
 Valley, 13, 94, 95, 131,. 133, 136, 
 
 . 142, 143. 
 
 Water, 2, 86, 135, 139, 140. 
 
 Ireland, Ammonites angulatus zone of, 
 
 168; Avicida contorta zone of, 168; 
 chalk of, 76, 77, 169 ; granite of, 87 ; 
 Secondary rocks of, correlated with 
 those of Arran, 169, 170 ; unconform- 
 abllity of Cretaeous rocks to Lower 
 Lias, 76. 
 
 Ironstone, at Cock of Arran, 49, 147 ; 
 
 at Corrie, 40, 147 ; and musselband, 
 
 in Glen Rosie, 43. 
 Islay. 138. 
 Isle of Man, 148. 
 
 Jamieson, Professor R. , 88, 117, 120, 126. 
 Joints, in Triassic sandstones, 68, 69 ; 
 
 in granite, 84, 85 ; in schists, 13, 14, 
 
 15. 
 JUDD, Professor, 94, 100, 117, 118, 119, 
 
 120, 121, 125, 170. 
 
 K 
 
 Kaim Hill, 63, 66. 
 Kames, 136. 
 Kel Burn, 141. 
 Kelburn, 63. 
 
 Glen, 10. 
 
 Park, 141. 
 
 Kelspoke Castle, 54, 55. 
 Kemp, J. F., 177. 
 
 Kcuper strata, 67, 71, 72 ; in Tertiary 
 
 volcanic neck, 74. 
 KiDSTON, R., 24, 153. 
 Kilchattan, 1, 2, 32, 33, 54, 63, 136, 
 
 148, 149. 
 
 Bay, 2, 4, 33, 62, 134. 
 
 Little, 32. 
 
 King's Cove, 111, 125, 139, 151. 
 
 Kintyre district, area embraced within 
 the map, 1 ; boulder clay of, stained 
 by Triassic rocks, 138 ; boulders of 
 Arran granite in drift, 137 ; glacial 
 deposits of, 137 ; metamorphio rocks 
 of, 16-17 ; physical features of, 1 ; 
 Tertiary basic dykes of, 102. 
 
 Kippen Burn, 63. 
 
 Kirkland Glen, 35. 
 
 Kirkton, Upper, 54. 
 
 Knowe, 135. 
 
 Kyles of Bute, 34. 
 
 Ktnaston, H.,26, 27, 34, 152, 171. 
 
 Lag a Bheidh, 93. 
 
 a' Bheith, 70. 
 
 Laggan, 37, 56, 57, 150. 
 Laggantuin, 34, 150, 154, 171, 174. 
 Lag na Croise, 58. 
 
 Lairside Hill, 66. 
 
 Lakes, ancient fresh-water, 143. 
 
 Laralash, 1, 93, 118, 147, 149. 
 
 Bay, 3, 70, 100, 135, 139, 140 
 
 142, 146. 
 
 Landslips, 68, 139, 144, 
 Larach Mor Burn, 102. 
 Largs, 1, 10, 64, 65, 102, 137, 141, 142. 
 Lava flows, brecoiated, slaggy, or 
 scoriaoeous surfaces of, 59, 64. 
 
 forming terraces, 8, 58, 59. 
 
 Law Hill, volcanic neck, 65. 
 Leacan Ruadha, 71, 95. 
 Leac an Tobair, 151. 
 
Index. 
 
 197 
 
 Lias, former extension of, in Arran, 4 ; 
 fragments of, in Tertiary volcanic 
 neck, 4, 5, 8, 73, 75-76, 79, 153, 168, 
 169-170 ; in Ireland, 169 ; near 
 Carlisle, 170 ; of Western Islands of 
 Scotland, 170. 
 
 Limestone, altered, 77, 78 ; analyses of, 
 40, 78 ; Coral, 51 ; dolomitic, 33 , 
 fragments of, in Tertiary volcanic 
 neck, 61 ; " White" of Antrim, 170. 
 
 Lion Rook, 32, 100. 
 
 Lion's Haunch, Arthur's Seat, Edin- 
 ■ burgh, 62, 176, 178. 
 
 Lochan a Mhill, 86, 133. 
 
 Loch Chorein Lochain, 3. 
 
 Dubh'(or Dubh Loch), 3, 94. 
 
 Locherim Burn, 31, 41, 42, 58, 151, 154. 
 Loch Fad, 22, 60. 
 
 Fyne, 138. 
 
 lorsa, 3. 
 
 na Davie, 2, 3, 86, 90, 100. 
 
 na Leighe, 98, 119. 
 
 na Leirg, 111. 
 
 Nuis, 3. 
 
 Quien, 3, 99. 
 
 Ranza, 1, 3, 12, 52, 99, 148, 150; 
 
 former extent of, 140 ; old bloomeries 
 near, 147 ; succession in the schists 
 near, 13 ; workable peat at, 146 ; 
 unconformable junction near, 51-52. 
 
 Castle, 15. 
 
 Tanna, 3, 135. 
 
 Tay limestone, 16, 17. 
 
 Lubas, 63, 134. 
 
 Bay, 55. 
 
 Port, 33, 56. 
 
 M 
 
 Macadam, Professor W. IvisoN, 42, 
 
 147. 
 Maoookoohie, a., 24, 75, 76, 77, 153, 
 
 167. 
 Macoulloch, John, 33, 105. 
 Machrie Bay, 144. 
 
 Bridge, 136. 
 
 Burn, 25, 31, 71, 95, 136. 
 
 Water, 2, 8, 25, 31, 67, 70, 71, 79, 
 
 136, 139, 142, 143, 146. 
 
 Madadh Lounie, 84. 
 
 Maol Don, 8, 40, 41, 68, 144, 148, 155. 
 
 Marble, 77, 78, 79, 149. 
 
 Marls, Old Red Sandstone, containing 
 
 doubtful traces of plants, 25 ; Keuper, 
 
 4, 67, 71, 72, 74, 79. 
 Maksteks, V. F., 117. 
 Meall Biorach, 3. 
 Mor, 2, 9. 
 
 nan Damh, 2, 3, 9, 84. 
 
 Merkland Burn, 25, 27, 42, 151, 155, 
 
 173, 174. 
 
 Mesozoic strata in Arran, 67-78, 
 167-170. 
 
 Metamorphio rocks, 7, 12-17 ; frag- 
 ments of, in conglomerate, 28, 68 ; 
 table of, 6. 
 
 Metamorphism of Arenig rocks, 18 ; 
 of dolerite dykes, 117 ; of fragments 
 in agglomerate, 103 ; of Old Red 
 
 Sandstone rooks, 28, 31 ; of syenite 
 
 dyke, 109. 
 Metamorphism caused by basic dykes, 
 
 101 ; round the granite, 7, 12, 13, 
 
 14, 86, 89, 90, 96. 
 Miller's Thumb, 62, 133. 
 Millport, 1, 144 ; freestone quarries at, 
 
 148 ; marine shells in raised beach 
 
 near, 139. 
 
 Bay, 4, 32, 53, 100, 128, 177. 
 
 Harbour, 62, 119, 133. 
 
 Millstone Grit, 41, 67, 97 ; igneous 
 
 rocks of, 56, 57- 
 
 Point, 45, 47, 97, 144, 150, 176. 
 
 Minuemoer, 32. 
 
 Misty Law, 64. 
 
 Monyquil, 24, 26, 129, 131, 135, 136, 
 
 172, 174. 
 Moor dyke, 174. 
 Moraines, 134, 135-136. 
 Moss-holes, 71. 
 Mourne Mountains, granite of the, 87, 
 
 104, 105. 
 Mudstones, metamorphism of, 90. 
 Musselband ironstone in Glen Rosie 
 
 Bum, 43. 
 
 N 
 
 NEC.KER, L. A., 117- 
 
 Necks, volcanic, 4, 5, 10, 64, 65-66, 69, 
 
 73, 79-83. 
 New Red Sandstone (see Trias). 
 Newton, B. T., 75, 76, 77, 153, 167. 
 Newton, North, 15, 37, 51, 52, 129, 148; 
 
 unconformability of Carboniferous 
 
 strata to schists, 61, 52. 
 Noddisdale Glen, 10. 
 Norite, 108. 
 North Mound, volcanic neck at, 65. 
 
 
 
 Old Red Sandstone, table of strata, 6 ; 
 in Arran, 7-8, 23-26, 28-31 ; doubtful 
 traces of plants in, 28 ; boundary 
 between Lower and Upper, 25, 31 ; 
 faulted boundary between Trias and, 
 131 ; fossil localities, 153, 155. 
 
 in Ayrshire, 8, 10, 34- 
 
 36 ; passage beds into Carboniferous, 
 63 ; boundary between Carboniferous 
 and, 34. 
 
 in Bute, 8, 32-34; thick- 
 ness of, 32, 33 ; patches of Carbonifer- 
 ous trap in, 33 ; passage beds into 
 Carboniferous, 33 ; boundary between 
 Carboniferous and, 54. 
 
 Old Red Sandstone, igneous rooks of, 4, 
 8, 26-27, 34, 54; petrography of, 
 171-174. 
 
 Olivine basalt, 60, 62, 100, altered, 58, 
 61, 171. 
 
 dolerite dykes and sills, 54, 117. 
 
 petrography of, 112. 
 
 Ophitio dolerite, 82, 96; altered, 97. 
 
 Orthoclase crystals in drusy cavities, 86. 
 
 Overtonshore, 35. 
 
198 
 
 Index. 
 
 Peach, B. N., 62, 76, 77, 152, 153. 
 Peat, 5 ; in Arran, 143-144, 146, 147 ; 
 in Ayrshire district, 11, 142. 
 
 filling up old lochans, 143, 145. 
 
 Penriooh, 14, 94, 131, 133. 
 
 North, 14, 100. 
 
 Perthshire, Ben Ledi grits, 16 ; Old Red 
 
 Sandstone of, 24. 
 Permian, 67. 
 Petrography of Old Red Sandstone 
 
 igneous rooks, 171-174. 
 
 of Carboniferous igneous rooks, 
 
 175-180. 
 
 of Tertiary igneous rocks, 103-127. 
 
 Phillips, J. A., 125. 
 
 Phyllites, 12, 16, 18; contorted Arenig, 
 
 18 ; gradation from schists into, 16. 
 Phyllitic schist, 14, 90. 
 Physical features, 1-4. 
 Piper Hall, 32. 
 
 Pirnraill, 12, 14, 131, 135, 150. 
 Pitchstones, list of, in Arran, 93-96. 
 
 banded, 92; dykes and sills, 72, 
 
 82, 85, 92-93 ; porphyry, 92 ; spheru- 
 litic, 92. 
 
 petrography of, 120. 
 
 Plants, Carboniferous, in brecciated 
 rock, 46; in Calciferous Sandstone 
 shales of Ayrshire, 64 ; in Old Red 
 Sandstone, 24, 25 ; in trappean ash, 
 
 - 48, 57. 
 
 Player, J. H. , 125. 
 Playbill, 54. 
 Ploverfield, 87. 
 Population, 149-150. 
 Porcellanite, 75, 79, 90. 
 Portachur Point, 53. 
 Port Alisdair Ruadh, 102. 
 
 Dornach, 65. 
 
 Portincross, 2, 35, 101, 137, 141. 
 Port Leithue, 55, 60. 
 POKTLOCK, J. E., 169. 
 
 Port Luchdach, 60, 176. 
 
 Uisg, 55, 117, 176. 
 
 Post-Tertiary and recent deposits, 5. 
 Poteath, 141. 
 
 ProducUis giganteus in Corrie limestone, 
 39. 
 
 latissimns limestone, 4) , 44, 49. 
 
 Pailophyton in Lower Old Red Sand- 
 stone of Arran, 24. 
 
 Pyroxene, green, 160. 
 
 Q 
 
 Quarries, limestone, in Arran, 14, 37, 
 38, 39, 40, 42, 43, 54, 55, 78, 148, 
 149 ; in Bute, 33, 148 ; millstone, 63 ; 
 road-metal, 23, 92 ; sandstone, in 
 Arran, 68, 71, 148 ; in Great Cumbrae, 
 32, 53, 148 ; slate, in Arran, 15, 148. 
 
 Quoohag, 134. 
 
 R 
 
 Radiolabia, absence of, in Arran 
 cherts, 18. 
 
 Raised beaches, 5 ; in Arran, 52, 57, 69, 
 134, 139-140, 150; in Ayrshire dis- 
 trict, 11, 140 ; in Bute, 22, 55, 128, 
 139 ; in Great Cumbrae, 139, 144 ; in 
 Inohmarnock, 139 ; Skipness district, 
 17. 
 
 marine shells in, 139. 
 
 Rainfall, 151. 
 
 Ramsay, Sir A. C, 86, 88, 117, 139, 147. 
 
 Recent and Post-Tertiary deposits, 5 ; 
 in Ayrshire, 11. 
 
 Rhsetic, 4, 5, 8, 73-75 ; fossils from, 75, 
 167-168, 169. 
 
 rocks in Ireland correlated with 
 
 those of Arran, 168, 169, 170. 
 
 Rhyolite, 91, 99 ; with flow structure, 
 82. 
 
 Road-metal, 92, 149. 
 
 Robertson, D., 136. 
 
 Roinn Clurahaoh, 98, 99. 
 
 RosENBrrscH, H., 120. 
 
 Rosie (see Glen Rosie). 
 
 Ross, The, 97. 
 
 Rothesay, 2, 62, 128. 
 
 Rudha Ban, 100. 
 
 Rum, Island of, 33, 148. 
 
 Runnan Eun Point, 60, 61, 63, 117. 
 
 S 
 
 Saddle, The, 94, 101. 
 
 Sail Chalmadale, 3, 85. 
 
 Salite diabase, 27. 
 
 dolerite, 27. 
 
 Salt-pans (old), 146. 
 
 Sand, laminated, with glacial shells, 
 136. 
 
 Sandstone, altered, 26, 33, 35, 54, 61, 
 68, 69, 77, 97, 101 ; fragments and 
 blocks of, in volcanic agglomera,te, 60, 
 61, 65, 66, 73, 80; columnar, 33; 
 false bedding in, 63, 67, 68, 69, 70, 
 71 ; ripple-marked, 35. 
 
 Sannox (see Glen Sannox). 
 
 Scaftigill Glen, 87. 
 
 Scalpsie, 22. 
 
 Bay, 4, 22, 128, 144. 
 
 Schist, detailed description of, 12-17. 
 
 ScHoriELD, J. A., 125. 
 
 Scotland, Western Islands of, 170. 
 
 Sea Mill, 65. 
 
 Bridge, 140, 141. 
 
 Serpentine, 7 ; altered, 22. 
 
 Serpent Mound, 136. 
 
 SEYMOirR, H. J., 152, 175. 
 
 Sgeir na Luinge, 102. 
 
 Shale, black, Arenig, 18, 19, 65. 
 
 Lias and Rheetic in Tertiary 
 
 volcanic neck, ^Z^ 74, 75, 79, 81. 
 
 Sheeans, 97. 
 
 Sheriff Port, 62. 
 
 Sheughends, 54, 177. 
 
 Shiskine, 8, 9, 79, 87, 130, 131, 132, 147, 
 149, 150. 
 
 district, 131 ; Rhsetic fossils from, 
 
 75, 167. 
 
 Plain, 142, 143 ; old sea loch, 140. 
 
 Sills, acid, 91-92; basic, 97-98; com- 
 pound, 98 ; dolerite. 111 ; epidiorite 
 or hornblende, 22 ; felsite, 64, 91-92, 
 
Index. 
 
 199 
 
 93 ; orthophyrio, 64 ; pitchstone, 
 92-96 ; quartz-felsite, 91 ; quartz- 
 porphyry, 91 ; rhyolite, 91 ; trachyte, 
 62. 
 
 Silurian, Lower ? , table of strata, 
 6-7. 
 
 in Arran, 4, 18-22. 
 
 igneoua rooks, 4, 8, 21-22 ; 
 
 petrography of, 20-21. 
 
 Skipness district, 1; glaciation and 
 glacial deposits of, 137-138; meta- 
 raorphio rocks of, 16-17 ; raised 
 beaches of, 142 ; alluvium of, 144. 
 
 Bay, 142. 
 
 Castle, 142. 
 
 Point, 102. 
 
 Water, 1, 102, 138, 142, 144. 
 
 Skye, 105, 107, 116 ; Lias of, 170. 
 Sliddery Water, 110, HI. 
 
 Head, 60, 175, 177. 
 
 Soils, 150. 
 
 SOKBY, H, C, 120. 
 
 Southannan, 142. 
 
 Southern Uplands, cherts of, altered by 
 
 granite, 18. 
 pillow structure in lavas, 19, 
 
 20. 
 Springbank, 69, 130. 
 Springs, water supply from, 151. 
 St. Annan's Chapel, 66. 
 St. Blane's Hill, 98, 99, 176. 
 Stone circles, 97, 143. 
 Strabane, old course of Rosie Burn, 
 
 near, 143. 
 Stravanan Bay, 2, 62, 143. 
 Streams in Arran, 1, 2, 3, 4. 
 String Road, 8, 23, 24, 43, 97, 149; 
 
 granite area south of, 87. 
 Suidhe Chatain, 2, 9. 
 
 Hill, 61, 177. 
 
 Fhearghas, 3, 18, 150. 
 
 PJantation, 56, 117, 134. 
 
 Syenite, 88. 
 
 dykes, 90 ; petrography, 108. 
 
 Syncline, in Carboniferous rocks, 8, 44, 
 
 48, 54, 59 ; in schists, 15, 
 
 Table of Fobmations, 5-7. 
 
 Tachylyte, 118. 
 
 Tailorleap Bridge, 36. 
 
 Tait, D., 24,40, 46, 52, 153. 
 
 Tarbert Hill, 65. 
 
 Tate, Professor, 168, 169. 
 
 Team., J. J. H., 20, 21, 34, 63, 90, 104, 
 
 120. 
 Terraces, lava flows forming, 8, 58-59. 
 Terrach Hill, 31. - 
 
 Tertiary igneous rocks in Arran, 4, 9, 
 
 58, 73, 79-101 ; in Ayrshire, 10, 65, 
 
 101-102. 
 Teschenite, 112. 
 Thomson, J., 44, 67, 72. 
 
 Dr. R. D., 149. 
 
 T., 125. 
 
 Thundergay, 12. 
 
 Mid, 151. 
 
 North, 14. 
 
 South, 94. 
 
 Throughlet, 35. 
 
 Tilemaking, clays used for, 142, 149. 
 
 Till or boulder clay, 5, 49, 135. 
 
 Tir Dubh, 96. 
 
 Tobar Challumohille, 151. 
 
 Tormore, 71, 110, 116, 122, 123, 125, 
 126. 
 
 Shore, 93, 95. 
 
 Tor Nead an Eoin, 84. 
 
 Torr Breao, 27, 173, 174. 
 
 Dubh, 27. 
 
 Meadhonach, 15, 133. 
 
 Mor, 2, 60, 98. 
 
 na Lair Brice, 21. 
 
 Righ Beag, 91, 95, 140. 
 
 Mor, 126, 140. 
 
 Trachyte, 54 ; analysis of, 62 ; dykes 
 and sills of, 61, 62. 
 
 Traighliath, 71. ' 
 
 Trail Isle, 59. 
 
 Trappean ash, trees and plant remains 
 in, 48. 
 
 Traquaik, Dr. R. H., 153. 
 
 Trias, 4, 8, 67-72 ; boimdary between 
 Carboniferous and, 68, 130; boundary 
 (faulted) between Old Red Sandstone 
 and, 131 ; derived Carboniferous 
 fossils in, 71-72; fossil locality, 153 ; 
 in Tertiary volcanic neck, 73, 79 ; of 
 England, 67 ; of Skye, 35 ; sub- 
 divisions of, 6, 67; thickness of, 68, 
 70. 
 
 U 
 
 Uamh CAPUiLt,, 98, 99, 115, 116. 
 
 Uisge nam Fear, 58. 
 
 Urie-Loch Bum, 110. 
 
 Unconformability between Carboniferous 
 igneous rocks and Old Red Sandstone, 
 54 ; between Carboniferous rocks and 
 schist, 51-52; between Carboniferous 
 rocks and Old Red Sandstone, 38-39 ; 
 between Old Red Sandstone and 
 Arenig lavas, 129; between Old Red 
 Sandstone and schist, 128; between 
 Upper and Lower Old Bed Sandstone, 
 8 ; between Trias and Carboniferous 
 rocks, 4, 44, 67; between Trias and 
 metamorphic rocks, 129. 
 
 Upper Kirkton, 31. 
 
 Valleys, drift-filled, 17. 
 
 Vent, Tertiary volcanic, in Arran, 4, 8, 
 79-83 ; fragments of Rhaetio, Liassic, 
 and Cretaceous rocks in, 5, 72, 73-78, 
 167-170 ; fragments of Trias in, 67, 
 72. 
 
 in Ayrshire, 10, 64, 65-66 ; in 
 
 Bute, 61. 
 
 Vogelsang, H., 120. 
 
 Volcanic agglomerate, petrography of, 
 103. 
 
 rocks (>ee Igneous rocks). 
 
200 
 
 Index. 
 
 W 
 
 Water Supply, 151. 
 
 Wells, 151. 
 
 West Bay, 54. 
 
 Western Islands, Liassic and Cretaceous 
 
 areas of the, 171. 
 West Kilbride, 1, 65, 101. 
 West Port, 54. 
 Whitefarland, 17, 134, 151. 
 White Port, 33. 
 Whiteside Hill, 66. 
 White Water, 3, 31, 86, 136. 
 Windmm Hill, 38, 43, 58, 91, 92, 131. 
 Wood, artificial, in Arran, 151 ; in Bute, 
 
 150; in Great Cumbrae, 151. 
 
 Wood, natural, in Arran, 150. 
 WOODWAED, H. B., 170. 
 Weight, T., 170. 
 WtJNSCH, E. A., 48, 67, 67, 72. 
 
 Xenocrysts in basic sills, 114. 
 Xenoliths in granite, 107. 
 
 Zeolites, 64. 
 
 ZiKKEL, F., 88, 97, 104, 106, 107, HI, 
 113, 117, 120, 121, 126. 
 
 GLASGOW : FEINTED BY JAMES HEDDEEWICK AND SONS, 
 FOR HIS majesty's STATIONERY OFFICE. 
 
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