On the Glacial Phenomena of Western Lancashire and Cheshire

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Summary and General Conclusions: From an examination of the facts and inferences brought forward it appears probable:— 1. that before the Glacial epoch the N.W. of England was higher above the sea-level than it is at present, and that the sea stood further out, possibly forming a narrow channel between England and Ireland, which were probably more or less connected from Miocene times down to the period immediately preceding the Glacial epoch. Before the commencement of this epoch the land commenced gradually subsiding, the Irish Channel was no longer narrow, and the waves were rapidly denuding across the ends of the various longitudinal hills and valleys, wearing them back and back, until the plains of Wirral and Western Lancashire came into existence, part of the great plain, extending from Liverpool to Lancaster, being since obscured by the deposition of Glacial deposits 200 feet thick. These longitudinal valleys, running in the strike of the Triassic strata, appear to have been formed by the agency of running water, aided by atmospheric causes; and wherever, by natural sequence or subsequent faulting, hard beds rest upon or are thrown against soft, on the eastern sides of these valleys, or on the western sides of the hills, there the dissolving power of western storms of wind and rain have formed long lines of escarpment, running parallel with the strike. 2. That the Mersey occupies at Liverpool a longitudinal valley, or rather a tidal channel excavated at the bottom of one; but its outfall, in Preglacial times, appears from some reason to have been checked or closed, forcing it to turn abruptly westward, flowing over what is now Wallasey-pool gorge, a transvers evalley terminating to the west by escarpments running north and south respectively, which were continuous before the river Mersey cut the transverse gorge in question. The river must have thrown itself over the escarpment, wearing its bed backwards and downwards at the same time. This action probably began to take place before the sea had removed the western side of the valley of which the escarpment lying north of the gorge was the eastern slope. 3. That when the Glacial period commenced, the hilly country became covered with immense glaciers, or possibly an ice-sheet, which, as the cold increased and the land sank, gradually extended over the lower country and reached the sea, by this time covering the lowland plains above referred to, and that the Lower Boulder-clay, with angular local fragments, is due to this land-ice, and may be called terrestrial Lower Boulder-clay. 4. That this portion of the N.W. of England continued subsiding until the land stood 100 feet lower than at present, and that the lowlands of Lancashire and Cheshire were submerged to a depth of rather less than 20 fathoms. The coast-line, especially near the base of the Cumberland mountains, appears to have been surrounded by an ice-foot, which in winter not only caught up the beach formed in summer and before its formation, scratching the pebbles in every direction as the ice was lifted by the tide, but received on its surface vast quantities of lake-district pebbles, and boulders, brought down from the interior by land-ice, which, at the breaking up of the iceefoot, were spread in confused heap-like masses over the Lancashire and Cheshire lowlands, forming the marine Lower Boulder-clay. 5. Middle Drift .—That at the close of the period of deposition of the Lower Boulder-clay, the climate ameliorated, the subsidence of the land still continuing, the influx of muddy sediment ceasing, owing to the cessation of glaciers grinding the rocks on the land, and that of sand commencing, owing to the pulverizing of pebbles by the action of breakers on the coast-lines of the Middle-drift sea. 6. That the sand and shingle of the Middle Drift, though found at all elevations from 40 to 100 feet between Blackpool and Preston, to 1200 feet on the Buxton Eoad near Macclesfield, was everywhere deposited in comparatively shallow water of the same depth, being deposited round the ever-sinking coast-lines, on higher and higher ground, in the form of sand-banks, whose crests mark the level of the mean high water of the immediate period of their deposition,— the sinking of the land causing the present elevation of these crests to gradually rise from west to east, or from the sea to the Penine chain, and everywhere (in West Lancashire) to show a marked uniformity of level in a north and south direction. In the Manchester district, owing to the curving round of the high hills of the Penine chain, the Glacial sea extended further east than in West Lancashire, though it does not appear ever to have passed over the ridge dividing it from the Yorkshire area, the eastern edge of which ridge is shown in fig. 1 of Mr. S. V. Wood's paper on the “Boulder-clays of Yorkshire” in the February number of the Quarterly Journal. 7. That if the Middle Drift was thrown down in the form of sand-banks surrounding a gradually subsiding coast, it follows that though the Middle-drift beds at Blackpool, at an elevation of 80 feet, and the Middle Drift at Macclesfield at 1200 feet, must have been formed during one set of conditions, and in the same geological epoch, yet a considerable period of time must have elapsed between the formation of the two deposits; or, in other words, the Macclesfield beds must be newer than those of Blackpool. 8. That the extreme lamination and current-bedding in the Middle Drift would, without the littoral character of the shells found in it, point to shallow-water conditions; but this current-bedding is often so intense as to preclude the idea of its being entirely due to ordinary tidal streams, and to suggest rather the sudden currents which would be caused by the occasional melting of ice altering the temperature of the water. That ice was occasionally present in the Middle-drift sea is proved by the fact that beds with scratched pebbles are occasionally found in it, both in the Blackpool, Preston, and Chorley districts; and the contorted and folded Middle Drift seen on the northern Bide of Morecambe Bay is no doubt due to the stranding of ice-bergs. 9. That the surface of the Middle Drift in Lancashire appears to have been everywhere eroded into small hollows and undulations, apparently caused by subaerial denudation; if this be so (and there are many reasons to believe it was), the country must have risen above the Middle-drift sea, become land, have suffered denudation, and again sunk beneath the sea before the deposition of the Upper Boulder-clay. Be that as it may, there can be no doubt that the Upper Till invariably rests on an eroded surface of Middle Drift, the two formations being unconformable. 10. That at the close of the period during which the Middle Drift became eroded, the climate again became cold, and that portion of land which stood above the sea more or less covered with ice; this tract was probably considerable, as the land during the deepest submergence of the Upper-till period does not appear to have been more thon 800 feet lower than at present, the clays in the deeper valleys of the Penine chain, at greater elevations, probably belonging to the high-level Lower Boulder-clay. With the change of climate came an alteration in the character of the deposits; sands and gravels were no longer thrown down, owing probably to the coasts being again surrounded by an ice-foot; and the grinding of glaciers over the land caused vast quantities of clay to be carried out to sea, held in suspension by the water, and spread over the country, where stratification is now but faintly visible, probably from the extreme fineness of the grains of matter of which the Upper Till is composed: the included stones in it, though erratic, are always more or less rounded; and at whatever height, so far as I have seen it, this formation occurs, it invariably contains more or less perfect shells of marine mollusca. None of these are of an extremely arctic character, Turritella communis, Buccinum undatum, Purpura lapillus, Cardium edule , and Tellina balthica being the commonest. All these occur in the Middle Drift, as well as many others. The first also occurs in the marine Lower Boulder-clay, and also in the Upper Till. 11. That before the surface of the Upper Boulder-clay became land, and probably before any upward movement commenced, the climate appears to have ameliorated, the ice-foot to have disappeared, the formation of shingle to have recommenced, and the glaciers to have sufficiently retreated to no longer send down vast quantities of clay to the sea, the dust, so to speak, of their gigantic sawing of the valleys of the country; for on the surface of the Upper Till, in the north of Lancashire, often at elevations of 500 or 600 feet, occur mounds of water-worn gravels, similar to those known as Kames in Scotland, and Eskers in Ireland. 12. That the glaciers appear to have lingered especially in the deep valleys of the Cumberland and Westmoreland lake district, where, in many cases (Borrodale, Langdale, Liza valley), they have excavated out the marine drift, and shed their moraines in the space thus left vacant. In the latter valley I found the moraine-mounds to be peculiarly numerous and well preserved.

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