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40 0 W. W. WATTS AND W. j, HARRISON ON chief constituents are characters linking the two types, while the freshness of many of the minerals, and especially of the olivine, gives the rock a very new aspect. It would be scarcely possible for a petrologist to discriminate the coarse varieties of rock seen at Hailstone Hill from that of Killala Bay, in Sligo. on the one hand, or from the coarse dolerites of Portrush and Fair Head on the other> Again the finer grained dolerite lavas of the Giant's Causeway, and the Tertiary dykes of Lisnaskea and elsewhere in Ireland would be very difficult to distinguish from the normal rocks of Pouk Hill and Rowley. When we recollect that some of the faults which bound the South Coalfield traverse Jurassic rocks, one is tempted to ask whether it may not be possible that those move­ ments which post-date the Rowley Rag in the South ­ Coalfield are in reality of Tertiary date. If Dot, the similarity of pre-Tertiary and post-Tertiary volcanic rocks is closer even than Allport suspected, when he was struggling for a recognition of the identity of the rocks of these different ages.

THE ANCIENT GLACIERS OF THE MIDLAND OF .

By W. JEROME HARRISON, F.G.S. As far as their glacial phenomena are concerned, the Midland Counties offer to the geologist one of the most interesting and important fields of research in the British Isles. And this for three main reasons: (I) Three great glaciers met here. (2) The contains examples of the terminal and lateral moraines, and also of the" fringe "t of these g;aciers. (3) But little detailed work has as yet been done in mapping out the precise courses and limits of the great streams of ice by which the district was formerly invaded. No SUBMERGENCE. It may be said at once that there is no evidence in the of any great depression since the close of the Mesozoic Era. The so-called " sea cliffs," " coast lines," etc., can be shown to be but the ordinary results of sub-aerial denudation; the finely-stratified, often false-bedded, gravels, sands. and loams of the surface deposits are for the most part the results of the sub­ glacial, englacial, and supra-glacial drainage-systems of the glaciers. Some loams were deposited in ice-dammed glacial lakes, while * Guide to fhe Collections of Rocks, etc., belonging to the Geological Sun'ey oflreland. Dubtin, 1895, pp. 51 and 78. t I apply the term l4 fringe" to the dubious region which lay just at or in front of the original margin of the ice. It is usually occupied by gravels and sands, the results of the melting of the ice. The glacier-ice sometimes made temporaryexcursions into the "fringe" in Romeregions, but it was never permanently glaciated. THE GEOLOGY OF THE BIR:\IINGHAM DISTRICT. 401 extensive sheets of gravel were formed along the "fringe," especially at the time of the final disappearance of the ice. The broken and fragmentary sea-shells which have been found in some sections never lived where they now occur, but were scraped off the bottom of the Irish Sea by the advancing ice. Of the earlier deposits formed by the old rivers, which appear to have crossed the Midlands from west to east during Tertiary times, only scanty traces remain. They were largely interfered with, and destroyed or covered up by the action of the glaciers. LOCAL ICE. During the Glacial Period several of the Midland hills-such as Charnwood Forest, the Rowley Hills, the Hartshill Range, etc.­ appear to have been permanently capped by ice. This ice enabled them to more or less successfully resist the invasion of foreign ice, which consequently glided round them. The result is that we find little or no foreign drift upon the summits of these hills, although each such elevation has a stream or tail of boulders, which can be traced proceeding from it to the southward. And the upper portion of the glacial ice-by which alone these hill-tops would in any case be traversed-would be comparatively" clean" ice, con­ taining but little debris.

THE THREE GREAT GU.CIERS WHICH INVADED THE MIDLANDS. There is clear evidence of the entrance of "rivers of ice" (glaciers) into the Midlands from at least three external sources. These glaciers may be named: (i.) The Arenig Glacier. (ii.) The Irish Sea Glacier. (iii.) The North Sea Glacier, 1. THE ARENIG GLACIER.-The Arenig Hills of lie south-east of Snowdon, and attain a height of 2,817 ft. They are very favourably placed to arrest the south-west winds, and the precipitation of snow upon them during the Glacial Period must have been enormous. There is the clearest evidence that a glacier descended eastward from the Arenigs, passing down the Vale of Llangollen and debouching into the plain near Ruabon, Overton, and Ellesmere. Great moraine heaps occur here. The Welsh ice then pursued a south-easterly course across Shropshire and Staffordshire, and terminated its career in the tract of country lying between Bromsgrove and Birmingham, some of its boulders (felspathic Arenig ashes and felsites) occurring on the top of Romsley Hill (one of the Clent Hills, in North ) at the remarkable elevation of 897 ft. This Arenig Glacier presents several remarkable features, and 402 W. j, HARRISON ON THE appears to have retained the characteristics of a true" Alpine "­ type glacier throu ghout its course . It did not follow what might have been thought its normal course on emerging from the Vale of Llangollen, either along the present Dee Valley to the north , or the Severn Valley to the south .. The former was blocked by the Ir ish Sea ice ; while Welsh ice from Plinlimmon, the Malverns, etc., occupied much of the Severn Valley to the south. The Welsh ice had, as we know from many sections on the coast of North Wales, attained a conside rable extension before the arrival in its distri ct of the Irish Sea Glacier. It is thus probable that the Arenig Glacier was the first of the thre e great glaciers ment ioned above to enter the Midland s. But it is doubtful if it would have obtained tbe extension which it actually did (the distance from Bromsgrove to the Arenigs is abo ut 100 miles), or if its boulders would have attained the remarkable height on the Clent Hills of 897 ft. had it not been for the extraneous impelling force which its ice received from the ice of the Irish Sea Glacier, which must have united with the Welsh Arenig ice and forced it onward and forward. Welsh boulders (often accompanied by basalt boulders from the Rowley Hills) occur along a line about 15 or 20 miles in length, extending from the south-west of Bromsgrove to the north-east of Birmingham. But this indicates a comparatively small amount of "fanning-out" as compared with the length of this glacier. A fine Arenig bould er lies in Cannon-H ill Park, Birmingham, close to the spot from which it was dug out (Fig. 1 2 ). Dur ing the excursion to the Lickey Hills several Areni g bould ers will be noted near Rubery, and a fine group of similar boulders lies close by upon till capping Frankley Lower Hill. At this point is .the section which revolutionised the ideas of the late Prof. Carvill Lewis, when he visited it not long before his death. Th ere is also a classical section of the till, gravels, etc., of the Arenig Glacier exposed in the brickyards at California, a spot about four miles south-west of Birmingham. And the railway cutting at Moseley (a southern suburb of Birmingham) shows a magnifi­ cent section of false-bedded sands and gravels, 80 ft. in thickness, constituting an esker and proba bly mark ing an important point of discharge of the waters draining the glaciers which lay to the north-west (PI. XII, Fig. 2). The railway cuttings excavated in recent years at Soho, :K ing's Norton, etc., near Birmingham, have revealed extensive sections of boulder-clays containing Welsh rocks. But in no case has any trace--not even a fragment-of a shell been found. The reason evidently is, that the Aren ig Glacier did not cross allY portion oj a sea bottom during its course from Wales to Birmin gham. The Keuper Sandstone at Weoley Castle (near the California brick­ pits) showed striations running south-west; and the Bunter Sandstone ridge, adjoining Icknield Street; Birmingh am, bears GLACIAL GEO LOGY OF T H E BI RI\H NGH AI\! D ISTR ICT. 40 3

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~'" '"<::' '"I1 ~.;: ?i {. .... ;:,. "" -e<>- I ..,. :J> ::: ::0 :;;. '"z ~ B ~ t::l 0 " c: ::t: r- ::l'" e ~ . 1"'1 ::0 ?' 2 l::l o <:;- :>- ;;. z ~ z ::. 0z <>- :r: "~ t=: ~ t""' '-> "1:l ~ > i:l:l r-'" ;;. '";;:. if ~ <, W. ]. HARRI SON ON THE along its course the signs of enormous ice pressure acting from the north-west, which has forced Arenig boulders into the sand­ stone, and torn off great slices from it.'*' The Rowley Hills (highest point about 890 ft.) of lie directly in the path of the Arenig Glacier. I have found no foreign drift upon their summits, but a train of basalt bould ers can be traced from them to the south and east, extending to the Clent Hills, to Harborne, and to the north-western suburbs of Birmingham. Where the surface soil on the Rowley hi11s has been removed during quarrying opera­ tions, well-striated platforms of the basalt have been exposed, the striations running from N.W . to S.E. The general contour of these hills is that of a great roche moutonnee. II. THE IRISH SEA GLA CIER. - The ice from the South of Scotland, uniting with the Lake district ice and with ice from Ir eland, advanced southwards durin g the Glacial Period until it completely filled the basin of the Irish Sea, and overrode the highest summit (Snaefell, 2,024 ft.) of the Isle of Man. Passing southwards, this great body of ice received such a stout resistance from the mountains and glaciers of North Wales that it was divided into two great lobes. The western lobe passed on down St. Georg e's Channel, while the eastern lobe swept over and , and then , invading Shropshire, Staffordshire, and the adja cent counties, came to its final melting point along a line which has not as yet been precisely mapped out, but which is roughly indicated by great concen­ trations of boulders at such points as Much Wenlock, Burton, Bridgnorth, Env ille, Wolverhampton, Bloxwich, Chase, , and . The western lateral moraines of this grand glacier lie on the eastern slopes of the Welsh hills, as at Hope Mountain, Balkin Mountain, " the Gloppa," etc., ranging up to r ,400 feet ; while its eastern morai nes range up to a similar height on the western flanks of the Pennine Range. The boulders brought by this Irish Sea glacier lie in amazing numbers at the places mentioned above in South Staffordshire and Shropshire, and can be traced thence northwards through Che shire and Lancashire. Lake district rocks-such as granites from Buttermere, Eskdale, Syning Gill, etc., with and esites, volcanic ashes, etc.­ are most plentiful (as might be expected) on the eastern side of the district, where Mountain limestone and Car boniferous sand­ stone boulders also abound ; while Scotch rocks - Criffel granites, etc.- are commoner on the west. But there is much intercrossing of these rocks, as might naturally be expected when we consider the changing conditions which affected the growth and progress of this Iri sh Sea Glacier. See Dr. Crosskey's paper in Proc. Birm, P ltil. Soc. vol. iii, 1883, p. 209. GLACIAL GEOLOGY OF THE BIRMINGHAM DISTRICT. 405

Recent marine shells-usually in a very fragmentary state­ have been found at several points in the path of the Irish Sea Glacier, as at Wolverhampton, Bushbnry, Ketley, Lilleshall, Madeley, Worcester, etc.; not to mention the many points at which such shells have been found further to the north and west. These shells appear to have been scraped by the ice from off the bed of the Irish Sea. The tract of country extending from Wolverhampton by Trescott, , and to Enville, may be described as an open-air petrological museum on a grand scale, but devoid of arrangement! Here rocks from the Lake district are mingled with the Kirkcudbrightshire granites of the South of Scotland, while an occasional "Welshman" tells that we are on the Arenig " trail." In Wolverhampton Park a grand boulder of Lake district (?) andesite over eleven feet in length is reared up like a monolith (Fig. 13),while close by a fine mass of grey Criffel granite bears it company. To the north, west. and south-west of Wolver­ hampton the erratics are to be numbered by the thousand, and some of them bear striations which they probably received while still in sitti, and before removal from their native places. About thirty or forty years ago Mr. Mander, of The Mount, Tettenhall, Wolverhampton, preserved many fine local erratics from destruction by removing them to his grounds, where he formed them into a " bouldery." III. THE NORTH SEA GLACIER. - This name seems pre­ ferable to that of" Scandinavian Glacier," which is frequently used. For both Scotland and the North of England contributed largely to the mighty mass of ice of which this glacier consisted; and there is also evidence to show that at some period of its history this glacier-or its southern part-crossed to England, not direct from Scandinavia, but by way of Holland and Denmark. The foreign portion of the ice of the North Sea Glacier impinged upon the English coast just north of Flambro' Head, and it filled the basin of the North Sea down to the mouth of the Thames. Passing over the Wolds it left much of its debris on the eastern side of these hills; but it took up a new burden from the chalk, and in its further course over East Anglia and the Midlands its characteristic deposit is known as the "Great Chalky Boulder-Clay." Crossing the Trent near Gainsborough the ice pressed up the valley of this river past Nottingham and Derby to Burton-on­ Trent. Here it came quite close to -if not into actual contact with-the Irish Sea Glacier. No section here shows clearly the relations of the respective boulder-clays of the two glaciers, but the ice from the east appears to me to be the later arrival. Charnwood Forest formed a buttress which offered a stout resistance to the passage of this ice from the north-east. Twenty W. ]. HARRISON ON THE

[Copyri.tu. 1 FIG. I3.-BoULDER IN WOLVERHAMPTON PARK. (Flom a Photograph by vv. Jerome Harrison. Block lent by Messrs. Blackie & Co.] GLACIAL GEOLOGY OF THE BIRMINGHAM DISTRICT. 407 years ago I described" the fine section then exposed on the flanks of Mount Sorrel, where the Chalky Boulder-Clay lay upon the striated and mammillated granite. Pressing down the Soar Valley the main body of the ice passed by Leicester'[ and Rugby to Buckingham, and thence its margin can be traced through to the northern heights of (Finchley, etc.), and eastwards still to Romford and South . A lobe of ice crossed South and entered the Valley. The district immediately to the south-west of Charnwood, in N. W. Leicestershire and N. , has no foreign drift, but it was surrounded in such a way by ice-dams and high land that a considerable lake was formed in N.W. Leicestershire, extending from Hinckley to Market Bosworth and Ashby-de-Ja . [As Bosworth Field stands on a part of this old glacial lake-basin, it might, perhaps, be called" Lake Bosworth."] The loarns of this lake are well shown in the brick-pits at Hinckley, and lying upon them are a few syenite boulders from the South Leicestershire Hills (Stoney Stanton, etc.), carried by bergs, detached from the ice-front. The members of the Geologists' Association will have constant views during their two days' work in the Nuneaton district of the area once occupied by this old lake lying between the Hartshill Range and the Charnwood Hills. At Nuneaton a few years ago the Trias marls in a brick-pit exhibited a typical section, showing the reversal of the marl­ beds (producing the typical "hook-form") due to the passage of ice, apparently a local glacier pressing southwards from the Harts­ hill Range. CONCLUSION. It is not possible to mention here more than a few of the principal conclusions to which I have been led during a study of the glacial deposits ofthe Midlands during the past thirty years; and it is quite impossible to give the evidence and the arguments by which these conclusions may be supported. But to the points mentioned above I may add: (a) The district affords no proof of any" interglacial" period. (b) The glacial deposits tell of one continuous but not un­ varying period of cold, during which fluctuations of the ice-front took place. (c) The freshness of the glacial deposits, and the small amount of denudation to which they have been subjected, show that no long period of time (probably not more than 10,000 years) has elapsed since the close of the Glacial Period. (d) No exact divisions of the drift-beds can be made out; indeed it is probable that no two sections which are more than a few yards apart ever reveal exactly the same sequence. * "Geology of Leicester and ," with photographs. J.and T. Spencer, Leicester. t When the railway between Leicester and Wigston was widened in I87.h a section more than a quarter of a mile in length was exposed, showing a beautifully striated pavement of Lias Limestones, covered by the Chalky Boulder-Clay. 408 THE GEOLOGY OF THE BIR?IINGHAM DISTRICT,

There is evidence, however, that at the bottom of the drift­ deposits we usually find: (I) A bed of-it may be a tough reddish or bluish clay (= till), or even a mass consisting mainly of sand mixed with stones, whose compactness is due to the passage over it and pressure upon it of some heavy body (= the glacier-ice). Above this till we often find (2) sandy and gravelly beds, generally false-bedded, caused by the drainage-system of the glacier, and deposited by water running either under the glacier, or through the glacier (in pipes or tunnels in the ice), or upon the glacier. Finally, we often find (3) an upper, looser, and more incoherent deposit of clay, stones, etc., consisting of material contained in and upon the ice, which settled down during the final melting of the glacier. This arrangement corresponds with the three-fold division of the drift into Upper and Lower Boulder-Clays with the intervening " Middle Sands and Gravels," which has so often been described elsewhere. But anyone, or even two, of these divisions are as often absent as present ; and it is only by accident if the various deposits in any two sections are of exactly the same age.

LITERATURE OF THE MIDLAND DRIFT. The Proceedings 0/ the Birmingham Nat. Hist. and Phi]. Soc. for 1895 contains a "Bibliography of Midland Glaciology," by W. Jerome Harrison, vol. ix, pp, II6-200, in which the titles (and an ahstract of each paper) of more than 150 books and papers are given. From these the following may be selected: 1858. "Memoirs of H. E. STRICKLAND." Published by Van Voorst. 1864. MAW, G.-" Severn Valley Drifts." Quart. J6urn, Geoi. Soc., vol. xx, p. 130. 1869. LISTER, Rev. W.-" Drift at Wolverhampton." Quart. Younz. Geol. Soc., vol. xx, p. 159. 1869. MACKINTOSH, D.-" Scenery of ." Longmans and Co. 1870. CROSSKEYandWOODWARD, C, J.-" Post-Tertiary Beds of Midlands." Proc. Birm, N.H. and M. Soc., part ii, p. 42. 1870. LLOYD, T. G. B.-" Drifts of the Avon and Severn Valleys." Quart. Journ. Geol, Soc., vol. xxvi, p. 202, 1870. WOODWARD, C. ].-" Mapping the Midland Boulders." Proc. Bsrm, N.H. and M. Soc., part ii, p. 55. 1878. HARRISON, W. J.-" Scheme for Examination of Glacial Deposits of Midlands." Mid. Naturalist, vol. i, pp. 181, 242, 312. 1879, etc. CROSSKEY, Rev. H. W.-" Reports of Erratic Blocks Committee" (B,·it. Assoc.), especially for 1879, 1883, 1886, 1887, and 1890. 1886. CROSSKEY, Rev. H. W.-" Glacial and Post-Glacial Deposits [of th.e Midlands.]" Britzsh AssociationHandbook, p. 248 (Birmingham). 1886. DEELEY, R. M.-" Pleistocene Succession in the Trent Basin." Quart. Yourn. Geol. Soc., vol. xlii, p. 437. 1888-9. MARTIN,F. W.-" Report on Shropshire and Staffordshire Boulders" (with map). Proc, Birm. Phi!. Soc., pp. 93 and 85. 1894. LEWIS, Prof. C.-" Glacial Geology of Great Britain and Ireland." Longmans and Co.