The Estuary of the Forth and adjoining districts viewed geologically

Front matter

■ ■ m I ■ ■ THE ESTUARY OF THE FORTH AND ADJOINING DISTRICTS VIEWED GEOLOGICALLY. Edinburgh: Printed by Thomas and Archibald Constable, FOR EDMONSTON AND DOUGLAS. LONDON ........ HAMILTON, ADAMS, AND CO CAMBRIDGE MA.CMILLAN AND CO. GLASGOW ....... JAMES MACLEHOSE. J Explanation (}/</ St;i Margins t/uu . Whale •Skefemnt . w Boulders , bio Bairns 4H_Bfc O/// Though brtn-frii /'br//i tuut f'/vde- . , Direction, <>r Stria* mi rorktf ' * \ THE EMrflBAlY U-P" TTSOII IFfflIBTIW AND DISTRICTS ADJOININC IT TO THE WESTWARD Showing OLD HEX MARGIN and l'o sit ions of Kaims, RoiiI<I-tk. Sk.lolons of Whales *e. o I 2 .. •» S Etu> UOm At A.M. JOHN-TON, L ITM V THE ESTUARY OF THE FORTH AND ADJOINING DISTRICTS VIEWED GEOLOGICALLY BY DAVID MILNE HOME OF WEDDERBURN. EDINBURGH EDMONSTON AND DOUGLAS 1871.

Preface

. Some explanation of the circumstances which have led to the publication of this Memoir may not be inap propriate. It embraces the discussion of several questions of much geological interest, on which it is hoped that the facts presented in the Memoir may throw some gleams of light. These facts are the result of the author's observation and investigations, carried on occasionally for many years past, as he had opportunity. He will not say that all the facts brought forward in the Memoir are new. Most of them, indeed, only confirm what fellow-labourers in the same field had already ascertained and made known ; but, if they have no other merit, they may serve to strengthen and enlarge the basis on which important truths are established. In the course of this Memoir, the author has avaded himself of some of the observations by other persons who have preceded him ; and it is only fitting that, besides acknowledging the Hberty so taken, he should specially notice their publications.

The first person who drew up any account of the dis trict to which the following Memoir refers, was Mr. Alexander Blackadder, civil engineer. In the year 1824 he published a Memoir in the Wernerian Society's Trans-

PREFACE.

. VI actions, "On the Superficial Strata of the Forth Dis trict," illustrating it by a small map, extending from Grangemouth to Gartmore and Callander. This Memoir described the beds of clay and sand found in that upper district, and specified some of the extraneous bodies found in these beds. Mr. Blackadder, however, made no allusion to the old sea-cliffs bordering the district, or to any change in the relative levels of sea and land. In the year 1839, the late Mr. Charles Maclaren published his instructive little volume on the Geology of Fife and the Lothians. Most of the information con tained in this work was the result of excursions by the author to the different districts embraced by it ; and the author was known to be very searching in all his investigations. It is believed that Mr. Maclaren was the first to take notice of the beds of sea-shells found along several portions of the shores of the Firth of Forth ; and of the old escarpment more or less parallel with the existing coast line.

Of these localities he gave accounts from time to time in the Scotsman newspaper, and also at greater length in the journal conducted by the late Professor Jameson. Mr. Maclaren has in his book a concluding chapter entitled " Eise in the Bed of the Forth." This chapter consists of only seven pages. In it he intimates his opinion, " that the bed of the Firth of Forth, and the land on both sides of it, have been raised 2 0 feet or more, at an epoch which, though very recent geologically, is probably long anterior to the records of history." In the same short chapter, Mr. Maclaren adverts to the discovery of an oyster-bed near Bo'ness, "36 or 38 feet above the high-water level." With this discovery he seems to have been greatly puzzled. He says it imphes

PREFACE.

. VII " a rise of not less than 60 feet, but which may be twice as much. The other facts appear to be at variance with so great a change. It seems therefore probable, that the remarkable elevation here, was the consequence of a dislocation, and merely local. In the coal-fields (he says) there are often several faults within the space of a mile, so that there is nothing unreasonable in assuming that more than one may have been produced in the 20 miles between Leith and Bo'ness." " It is probable that the river Avon runs in the fissure, which divides the raised beds from the depressed" (page 234). This suggestion was at the time extremely reasonable. But subsequent investigations have demonstrated its fallacy. The next person who seems to have described these shell-beds and old sea-cliffs along the shores of the Firth of Forth, was the late Hugh Miller.

About the year 1842, he is said to have given several public lectures in Edinburgh, and also to have published some articles in the Witness newspaper, explaining his views on these points. I have lately seen the work published by his widow, which contains these lectures ; and I observe in them a particular account of three portions of the coast, viz., at Portobello, Fillyside, and Queensferry. He specifies the kinds of shells found at these places, and refers to them as evidence of a considerable eleva tion of the land out of the sea. At this time, and indeed for some years previously, I was myself studying the subject. I took every opportunity, when visiting different parts of Scotland, to note the places where old sea-escarpments were visible, and also to ascertain their heights above the sea. It was about the same time that I visited the Parallel Eoads of

PREFACE.

. VIII Glenroy, which Mr. Darwin had shortly before declared to be old sea-beaches. After about a week's examination of the Lochaber valleys, I satisfied myself that the shelves which so singularly mark their sides, were not marine but lacustrine. I thought that I could distinguish between the two kinds of beaches, and very much in consequence of my previous study of the old sea cliffs along the existing coasts. The result of my investigations on both subjects, was submitted to the Eoyal Society of Edinburgh in a paper1 which was sent to the Council of the Society in the year 1847. It was read in March and April of that year. In this paper an account was given of the traces in various maritime counties of four separate sea-cliffs, with flats extending from each, the lowest being that now generally recognised as 10 or 12 feet above the present high-water mark, and the highest at a level of about 300 feet.

Abstracts of two papers by me, regarding these old sea-cliffs, will be found in the Proceedings of the Eoyal Society for 1838 and 1847. The next person who published on the subject was the late Dr. Chambers. His book, On Ancient Sea- Margins, appeared in 1848. It opened a still wider field of inquiry; for besides giving tables of old sea cliffs and terraces in Scotland, he gave the results of his investigations in England, Ireland, and some parts of the Continent. I do not at this moment remember any other works or papers bearing on the old sea-margins of the Firth of Forth — except one by Professor Geikie which re- 1 I have still the original mss., bearing a docquet by Professor Forbes, as Secretary, dated 15th February 1847.

PREFACE.

. IX lated to the time of the last upheaval of the land, and which was published in the 18th volume of the Journal of the London Geological Society. The information contained in the following pages, having been scattered through a number of rough note books, some of them many years old, the author has found a little difficulty in putting it into proper order ; and his only excuse for not doing more in that respect, is the desire of his pubbsher to bring out the Memoir in time to be of use to the members of the Geological Section of the British Association, when they visit Edinburo-h next month. It may be added that these note-books contain many facts, observed in other parts of Scotland, which would probably throw fight on some of the general questions discussed in the Memoir. It would have been desirable to have embraced these facts in the Memoir.

Possibly a second edition may be called for, in which case there would be an opportunity of supplying the omission. Edinburgh, 14th July 1871. CONTENTS. PACE I. Form and Physical Features of Estuary, . . . . .1-2 II. Formation or Origin of Estuary, . . . . . .2-9 III. Pleistocene Strata, or Superficial Beds of Estuary— Materials of these Beds, whence derived, . .... 9-12 1. Borings at various Localities, .... . 12-18 2. Particular Beds, Description of— (1.) Sleech or Mud, ....... 19 (2. ) Brick or Laminated Clay, ' . . . . .19 (3.) Peat, Beds of, ....... 20 3. Shells in these Superficial Beds, ... 23 4. Bones of Whales and Seals, ...... 25 5. Sand and Gravel Beds, . ...... 27 Extraneous Bodies found in them, ..... 30 6. Kames, or long Banks of Sand and Gravel, . . . .32 They are Ancient Submarine Banks, ..... 37 7.

Erratic Blocks or Boulders — Particular Boulders described, . . 39-57 8. Forms of Hills and Rocky Cliffs, ..... 57 Rocks Smoothed, Grooved, and Striated, . . . .66 " Crag and Tail," 69 9. Boulder Clay, 70 Boulders in the Clay, ....... 71 Elephants' and Reindeers' Horns in it, . . . . 72 Sea-shells in it, . . . . . . . .72 Beds of Sand below, above, and in it, . . . . .73 Colour of Boulder Clays, ...... 75 Probable Origin and Formation of, . . . . .75 Alternation of Boulder Clay with Marine Deposits, . . .77 Opinion and Testimony of Mr. Robert Brown, . . .79 Reasons for Iceberg Theory stated, ..... CONTENTS. PAGE 10. Ancient Kyle or Sea-strait connecting the Firths of Forth aud Clyde, 87 Mr. Croll's Theory that this is a River Channel, . . .89 Opinion advocated, that the Channel scooped out by Sea-currents loaded with Ice, ....... 90 Objections to River Theory stated, ..... 94 Reasons for Iceberg Theory stated, . . . . .95 Evidences of a similar Kyle or Sea-strait in the Valley west of Stirling, 98 Transport Eastward, of Boulders and Boulder Clay, stopped by Trap Rock, 98 Cases of Boulders supposed to have been carried on Ice, . . 99 11.

Old Sea Cliffs and Terraces, . . . . . .100 (1.) Terraces or Base of Cliffs 140 to 180 Feet above Sea Level, . 101 (2.) Do. do. 100 to 120 do. . 102 (3.) Do. do. 50 to 60 do. . 103 (4.) Do. do. 10 to 40 do. . 104 Slope of Line of Sea Cliffs up towards Head of Estuary, Explained, . 106 River Cliffs and Terraces, when Rivers flowed at Higher Level, . 107 Why Difficult to obtain exact Measurements of Line of Old Sea Margin, ........ 108 Old Sea Bars and Deltas, ...... 110 Loch Lubnaig once at a Higher Level, . . . . .110 12. Has Land risen, or has Sea sunk ?..... 112 13. When did last change in relative Levels of Sea and Land take place? ........ 113 Probably in Human Period, before the Romans were in Scotland, . 114 14. Precis or Programme of Changes in History of the Estuary, . .117

Appendix

. Direction of Striæ on Rocks and on Boulders, ..... 121 Why Striæ on Boulders Less Uniform in direction than on Rocks, . . 122 Deflection of Current indicated by Change in Direction of Striæ, . . 123 Depth and Breadth of Current indicated by Uniformity of Striæ, . . LIST OF ILLUSTEATIONS. Map of the Estuary of the Forth and Districts adjoining it to the Westward, showing Old Sea-Margin, Positions of Kames, Boulders, etc., ..... Frontispice. Plate I. ....... to face p. & Figs. 1-3. Stratified carboniferous rocks before and after being fractured. Fig. 4. Shell-bed in a sandstone quarry on the east of the river Avon, and about three-quarters of a mile from the Firth. Fig. 5. Position of the shell-bed relatively to the Carse land and the Firth. Figs. 6 and 7. Sections of Railway Cirttings through Sand and Gravel Beds.

Plate II. 29 »> Fig. 8. Section on Sea-shore near Granton Quarry. Figs. 9-11. Sections of Railway Cuttings. Plate III. 32 Fig. 12. Cutting for Turnpike Road at east end of Musselburgh Links. Fig. 13. Section of a Railway cutting near Glasgow, showing a mass of Boulder Clay with stratified sand on each side. Fig. 14. Transverse Section of Kame near Polmont. Fig. 15. Structure of Kame near Carstairs. Fig. 16. GrouDd-plan of Kame near Polmont. Plate IV. 39 Fig. 17. Ancient Deltas at foot of Ochil Hills. Fig. IS. Kilbride Boulder. Fig. 19. Landrick Stone. Fig. 20. The Herd Stone, near Tullibody. LIST OF ILLUSTRATIONS. XIV Plate V. to face p. 46 Fig. 21. Position of Boulder on the Barrhill, near Stirling. Fig. 22. Section of the north slope of a valley south of the Sauchie Hills, and showing peculiar position of a large Boulder.

Fig. 23. Shapes and position of a remarkable assemblage of Boulders recently exposed by a railway cutting on the estate of Plean, Stirlingshire. Plate VI. 59 Fig. 24. The Castle Rock of Stirling (Section and Plan). Fig. 25. Bridge of Allan and Airthrey Crags. Plate VII. 04 Fig. 26. (1.) The rocky prominence near Stirhng, on which the ruins of Bruce Castle stand, and the trench round its west base. (2.) Ground-plan showing the configuration of the trench. Fig. 27. Caves between Crail and Anstruther, Fifeshire. Plate VIII. 99 Fig. 28. Section of stratified beds of Sand and Gravel, containing several Angular Boulders, at Strathblane Railway Station. Fig. 29. Cemetery south of Stirling Castle. Fig. 30. Sketch of a case in which layers of sand and gravel occur in the very heart of the Boulder clay.

Fig. 31. Submarine Kames off Yarmouth. MEMOIR AND ADJOINING DISTRICTS VIEWED GEOLOGICALLY. I. The form and dimensions of this Estuary will be best understood from any correct map ; but the following statistics deserve special notice : — The distance of the Isle of May, situated at the mouth of the estuary, to the town of Stirling, which is the highest point reached by tidal action, is about 60 mdes. The width is, at its mouth, about 1 0 miles ; at Leith, about 5 miles ; at Queensferry, about li mdes. Above this last-mentioned point the estuary widens, chiefly in consequence of the concave curvature of the south shore. Near Alloa, the estuary no longer possesses the appearance of an arm of the sea. It is there merely a navigable river, and with numerous windings, due, no doubt, to the flatness of the district and the soft sedi mentary strata, through which the river has to cut its way between AUoa and Stirling.

The depth of water in the estuary, is at its mouth, about 26 fathoms; at Queensferry, 39 fathoms; and opposite Bo'ness, where a great raflway bridge was projected, 9 fathoms. The water is deepest, generally speaking, along the A north shores of the estuary, illustrating the well-known rule, that the ocean is deep along a coast where the land is high — shallow, where the land is low. The reason for this condition of things in the estuary of the Forth is obvious, when regard is had to the slope of the country on the two sides, and their geological structure. On the south side, there is an extensive area of land, comparatively low and flat, lying between the estuary and the ranges of hills. On the north side, the area between the estuary and the hills, is comparatively narrow. Therefore the area for rain-fall is much greater on the south side, producing larger and more numerous rivers, by which sediment can be carried into the estuary.

Moreover, the rocks calculated to yield sediment are more abundant in the districts to the south of the estuary, than in the districts adjoining it on the north. Hence, banks of sand, gravel, and mud are more numerous along the south shores, making the water shaUower. In explanation of these general state ments, it may be added that, whdst the range of hills which lie between the estuary and the Tweed, is from 15 to 20 mdes distant, the range of hills between the estuary and the Tay, is only from 3 to 8 mdes dis tant ; and, though the geological formations in the Lothians and in Fife are the same, the proportion of hard trap rocks to the soft and crumbling strata of the coal measures is far greater in Fife than in the Lothians. In regard to the general direction of the Estuary, it may be stated that, viewing it as an oblong trough, its axis or medial line between the mouth, at the Isle of May, and Queensferry, is about due east and west; above Queensferry, about w.N.w.1 1 All the bearings in this Memoir are magnetic.

In adverting to the probable origin of the Estu ary, I would observe that the great fractures of the earth's crust in this part of Scotland, run nearly parallel with the medial line of the estuary. If a geological map which shows these fractures in the districts bordering on the estuary be examined, it will be seen that, in the counties of Mid Lothian and Haddington, there are five greenstone dykes situated near the coast, running nearly parallel to one another, and in a direction about w.N.w.1 In Linlithgowshire, at Bo'ness, as Professor Geikie states,2 " the faults are numerous," — " in a general way trending east and west, or rather E. by s." In Stirlingshire, at or near Grangemouth, a greenstone dyke,3 about 36 yards in width, has been traced for several miles, running w. by N. through the coal workings.

The chief slips or faults in these workings observe the same direction. In a map by Mr. Landale, published in 1837,4 showing the principal features of the Fife coal-fields, many greenstone dykes and lines of faults are laid down, all running in directions from w. to w.N.w. One of these dykes has been traced from the coast, near Largo, through several parishes; and one of the faults for nearly 15 miles.5 Whdst the great dislocations of the earth's crust on both sides of the estuary are paraUel with its axis, or 1 Coal-fields of the Lothians, by Milne, p. 24, and accompanying map. 2 Memoir on the Geology of Edinburgh, p. 69. 3 Mr. Stirling, coal-manager, Grangemouth, kindly gave me this information. 4 Highland and Agricultural Society's Transactions for 1837, vol. xi. 6 These dykes and faults are also well shown in the Geological Maps published by the Ordnance Survey. nearly so, there is another important fact, which shows even more clearly the connexion between these faults or fractures, and the origin of the estuary.

To these faults or fractures the provincial name of " slips " is given ; a name not unsuitable, as it suggests what ready happened. It is found that the whole strata along the line of these fractures have slipped down on one side, or (what would produce the same effect) slipped up on the other side ; so that whereas before the fault or fracture the strata were continuous on each side, after it was produced the edges of the strata on each side became separated verticaUy by an interval of many feet or fathoms. There is another provincial phrase applicable to these faults, not less significant. When the miner discovers on which side of the fault the dislocated strata are lower than on the other side, the former are described by him as being on the "downcast" side of the fault, and the former on the " upcast " side.

Now, with reference to the bearing of these principles on the origin or formation of the estuary of the Forth, it is a fact alike remarkable and interesting, that the " downcast " strata along the " faults " in the counties of Fife and Clackmannan are, in a great majority of cases, on the side of the faults which are next to or face the estuary ; and that the " downcast " strata along the " faults " in the districts bordering the south coast of the estuary are, in like manner, on the side of the faults next to the estuary. In other words, the sink ing of the strata composing the earth's crust, when dis located, has been towards the estuary, producing there fore a trough or longitudinal depression in the country paradel with the faults. In proof of these statements it is only necessary to refer to a few of the more remarkable faults or slips on both sides of the estuary.

The late Eobert Bald, mining engineer, a native of AUoa, and intimately acquainted with the workings of the Clackmannan coal measures, was the first to point out the great dislocation of the earth's crust in that quarter. He states, that if a line is drawn from the Ochil Hills at Alva, in a southerly direction, to the river Forth, a distance of about six miles, two faults or slips would be crossed, both running nearly east and west. The one near the hills, which he called the Great North Slip, throws down the strata, along the south side or face of the slip, to the extent of 700 feet. The other, which he called the Great South Slip, throws down the strata along its south side or face, no less than 1300 feet. By reason of these two faults alone, the whole surface of the land, in what is now the upper or westermost part of the estuary, has been made to sink 2000 feet below the level which it occupied before the faults were formed.

To the eastward, in the Fife coal-field, the following faults or slips are known :— one in Salines parish, throwing down 150 feet ; another in Culross parish, throwing down 240 feet ; and several near Dunferm line, whose united " downcasts " amount to 1020 feet. AU these " downcasts " are on the side or face of the faults or slips next to the estuary.1 StiU farther eastward, viz., in the Leven district, the great " slip " before mentioned, which traverses the coal workings for 1 5 miles and more, throws them down 1 Report on the Coal-fields of Dunfermline, by Rev. Mr. Chalmers, in Highland Society's Essays for 1841, vol. feet, and another throws them down 192 feet ; the " downcasts " in both cases being on the south or estuary side of the " slips." Both " slips " are indicated on the valuable Geological Map lately published by Professor Geikie.

This map shows a slip in the Dysart district, throwing down 180 feet, and several slips in the LochgeUy district, whose united "downcasts" amount to no less than 1200 feet. AU these "down casts" are like the others, on the sides of the slips facing the estuary. Mr. Landale in his Memoir says, in regard to the Fife coal-fields generally, " Faults or slips are innumer able, and, with one exception, aU the large ones throw up to the north, and point out in the most decisive manner the very steps by which the country has been raised to its present level" (page 346). The general rule existing in the districts along the north shores of the estuary, prevails also in the districts adjoining the south shores. AU the principal faults or sUps in these last-named districts throw down the strata on the north or estuary side.

Thus near Grangemouth several great slips running east and west exist to the south, about Falkirk and Callan der Park, which dislocate the coal measures, aU casting the strata down on the north. But cross to the north of Grangemouth, about half a mde or more, and we come to slips which throw down to the south.1 The 1 Mr. F. Stirling, the managing engineer of Grangemouth Colliery, gave to me the following particulars of dykes and slips situated to the north of the river Carron : — 1st, Whinstone dyke running w. by n. for several miles, 36 yards wide. The sides of dyke vertical, throwing strata down on south, 40 feet. 2<_, Zetland pit fault, having same direction, throws strata down on north, 44 feet. between these two sets of slips is probably the centre of the trough forming the estuary ; it is there, at all events, that the river Carron is now found flow ing, its general course being here nearly east and west.

At and near Bo'ness, as I was informed by Mr. Cadell, the principal slips run from w. to w.N.w., and throw down on the north or estuary side. Professor Geikie in his Memoir specifies two faults in the submarine coal workings of Bo'ness, each throwing the strata clown on the north, to the extent altogether of 186 feet (page 69). He also refers to others on the land, producing a downcast towards the north of 500 feet (page 118). In the Mid-Lothian coal-field the slips in like manner throw down principally on the north side. In my Memoir on this field (page 98), it is shown that the " downcasts " on the north exceed the " downcasts " on the south sides of the slips by no less than 2760 feet. In East Lothian, as Professor Geikie in his Ordnance Survey Memoir reports, the slips near Tranent run east and west, with north " downcasts" of from 100 to 150 feet ; and near Dunbar the slips have exactly the same features (page 56) as regards direction and "down cast."

Thus, by means of these dislocations, a great sinking or depression must have taken place along the area 3d, About 20 chains north of preceding fault, another fault, having same direction, throwing down on south, 78 feet. 4th, About 18 chains farther north, another fault, having same direction, throwing down on south, more than 30 feet. The result of these four dislocations of the strata in this part of the estuary is a downcast towards the south, that is towards the centre of the trough, of more than 100 feet. now occupied by the estuary of the Forth — forming a long valley — which would allow the sea to enter, if the levels suited, and draw towards it the rivers on either side. - The effects of the dislocations before referred to may be the better understood, by referring to the subjoined diagram, in which Fig. 1 represents the stratified car boniferous rocks before being fractured, and Fig. 2 these rocks after being fractured.

The slips on the south or Lothian side of the estuary are at the letters a, those on the north or Fife side at the letters b. It will be observed that these slips are drawn not vertically, but with a slope towards the central parts. This is in accordance with the fact generally observed, that a slip or fault slopes towards the side on which the "downcast" has taken place, as if the strata had slipped down on the upper side of the fault ; and in accordance with this explanation it not unfrequently happens, that the ends of the downcast strata are turned up, as if they had rubbed violently upon the adjoining strata when in the process of sinking. The ends of the corresponding strata, on the opposite side of the fault, are on the other hand turned down. When these dislocations took place, by which large portions of the earth's crust in our part of Europe sunk down, and in long bands or stripes, what would be the appearance presented ?

In this district of Scotland there would be ranges of cliffs, some of them 600 or 700 feet high. These mural precipices would exhibit sections of exposed strata, which for a time would retain the jagged outline presented in Fig. 2. But that jagged outline would in time become obliterated by the FIFE LOTHIANS Fl C. I (PA SE 8 ) FIFE yr. L0TH1ANS Fl C. 2 | Fl G. 3 |F( Fl C. A- ( PA SE 24) EAST OF RIVER AVON, 1 ABOUT SiOFA MILE FROM THE FIRTH Surface Sloping ru?ro\ t/Jivccr&s setz. FIC. 5 (P. Fl G. 6 ( BETWEEN FIG. 7 I P« & F _ 9 > CUTTINC ON RAILWAY BETWEEN DALRY 4LEITH J..rJi,rA„ UJouJLajeri-'^Aj A Gir/jrel ahouct Qffiliijck. B ■Saxui.& clAiy?w,rau,ri/arlliJ saxc/i/Oxl, containmp peXbUrs or Oral., shale.,&po,-pTiyry action of the weather if they were above the sea level, or by the more powerful action of the waves and tides of the ocean, if below the sea level.

These rocky pre cipices would gradually crumble down and produce something like uniformity of surface, — the materials taken from them being spread over extensive areas, and filling up previously existing hollows. In Fig. 3 an attempt is made to indicate the effects of the level ling process referred to. In the counties bordering the estuary towards the eastward, there are no traces left of these long ranges of cliff which marked the lines of fault. The rocks there were so soft that they readily crumbled under the abrading agency to which they were exposed. In the western parts of the estuary, however, several ranges of cUff on the south side of the axis of the estuarean trough still remain, running east and west, and presenting vertical precipices towards the north. Examples of these occur to the south of Polmont, and on the Touch or Gargunnock hills.