266 WELSH GLACIAL DRIFT. CHAP. XIV, covered with glaciers, which radiated from the central heights through the seven principal valleys of that chain, where stria and flutings are seen on the polished rocks directed towards as many different points of the compass. He also described the 'moraines' of the ancient glaciers, and the rounded masses of polished rock, called in Switzerland 'roches moutonnées.' His views respecting the old extinct glaciers of North Wales were subsequently confirmed by Mr. Darwin, who attributed the transport of many of the larger erratic blocks to floating ice. Much of the Welsh glacial drift had already been shown by Mr. Trimmer to have had a submarine origin, and Mr. Darwin maintained that when the land rose again to nearly its present height, glaciers filled the valleys, and swept them clean of all the rubbish left by the Professor Ramsay, in a paper read to the Geological Society in 1851, and in a later work on the glaciation of North Wales, described three successive glacial periods, during the first of which the land was much higher than it now is, and the quantity of ice excessive; secondly, a period of submergence when the land was 2,300 feet lower than at present, and when the higher mountain tops only stood out of the sea as a cluster of low islands, which nevertheless were covered with snow; and lastly, a third period when the marine boulder drift formed in the middle period was ploughed out of the larger valleys by a second set of glaciers, smaller than those of the first period. This last stage of glaciation may have coincided with that of the parallel roads of Glen Roy, spoken of in the last chapter. In Wales it was certainly preceded by submergence, and the rocks had been exposed to glacial polishing and friction before they sank. Fortunately the evidence of the sojourn of the Welsh * Philosophical Magazine, ser. 3, vol. xxi. p. 180. CHAP. XIV. PROOFS OF SUBMERGENCE. 267 mountains beneath the waters of the sea is not deficient, as in Scotland, in that complete demonstration which the presence of marine shells affords. The late Mr. Trimmer discovered such shells on Moel Tryfane, in North Wales, in drift elevated 1,392 feet above the level of the sea. It appears from his observations, and those of the late Edward Forbes, corroborated by others of Professor Ramsay and Mr. Prestwich, that about twelve species of shells, including Fusus bamfius, F. antiquus, Venus striatula (Forbes and Hanley), have been met with at heights of between 1,000 and 1,400 feet, in drift, reposing on a surface of rock which had been previously exposed to glacial friction and striation. The shells, as a whole, are those of the glacial period, and not of the Norwich Crag. Two localities of these shells in Wales, in addition to that first pointed out by Mr. Trimmer, have since been observed by Professor Ramsay, who, however, is of opinion that the amount of submergence can by no means be limited to the extreme height to which the shells happen to have been traced; for drift of the same character as that of Moel Tryfane extends continuously to the height of 2,300 feet.* Rarity of Organic Remains in Glacial Formations. The general dearth of shells in such formations, below as well as above the level at which Mr. Trimmer first found them, deserves notice. Whether we can explain it or not, it is a negative character which seems to belong very generally to deposits formed in glacial seas. The porous nature of the strata, and the length of time during which they have been permeated by rain-water, may partly account, as we hinted in a former chapter, for the destruction of organic remains. * Ramsay, Quarterly Geological Journal, vol. viii. p. 372, 1852. 268 LIFE IN THE OCEAN AT GREAT DEPTHS. CHAP. XIV. But it is also possible that they were originally scarce, for we read of the waters of the sea being so freshened and chilled by the melting of ice-bergs in some Norwegian and Icelandic fiords, that the fish are driven away, and all the mollusca killed. The moraines of glaciers are always from the first devoid of shells, and if transported by ice-bergs to a distance, and deposited where the ice melts, may continue as barren of every indication of life, as they were when they originated. Nevertheless, it may be said, on the other hand, that herds of seals and walruses crowd the floating ice of Spitzbergen in lat. 80° north, of which Mr. Lamont has recently given us a lively picture, and huge whales fatten on myriads of pteropods in polar regions. It had been suggested that the bottom of the sea, at the era of extreme submergence in Scotland and Wales, was so deep as to reach the zero of animal life, which, in part of the Mediterranean (the Egean, for example), the late Edward Forbes fixed, after a long series of dredgings, at 300 fathoms. But the shells of the glacial drift of Scotland and Wales, when they do occur, are not always those of deep seas; and, moreover, our faith in the uninhabitable state of the ocean at great depths has been rudely shaken, by the recent discovery by Captain M'Clintock and Dr. Wallich, of starfish in water more than a thousand fathoms deep (7,560 feet!), midway between Greenland and Iceland. That these radiata were really dredged up from the bottom, and that they had been living and feeding there, appeared from the fact that their stomachs were full of globigerina, of which foraminiferous creatures, both living and dead, the oozy bed of the ocean at that vast depth was found to be exclusively composed.† Whatever may be the cause, the fact is certain, that over large areas in Scotland, Ireland, and Wales, I might add * Seasons with the Sea-Horses, 1861. + See Appendix B. On life at great depths in arctic and antarctic seas. CHAP. XIV. GLACIAL FORMATIONS IN ENGLAND. 269 throughout the northern hemisphere cn both sides of the Atlantic, the stratified drift of the glacial period is very commonly devoid of fossils, in spite of the occurrence here and there, at the height of 500, 700, and even 1,400 feet, of marine shells. These, when met with, belong, with few exceptions, to known living species. I am therefore unable to agree with Mr. Kjerulf that the amount of former submergence can be measured by the extreme height at which shells happen to have been found. Glacial Formations in England. The mountains of Cumberland and Westmoreland, and the English lake district, afford equally unequivocal vestiges of ice Dome-shaped rocks, or 'roches moutonnées,' in the valley of the Rotha, near Ambleside, from a drawing by E. Hull, F.G.S.* action not only in the form of polished and grooved surfaces, but also of those rounded bosses before mentioned, as being so abundant in the Alpine valleys of Switzerland, where glaciers exist, or have existed. Mr. Hull has lately published a faithful account of these phenomena, and has given a representation of some of the English 'roches moutonnées,' which * Edinburgh New Philosophical Journal, vol. xi. pl. i. p. 31, 1860. 270 GLACIAL FORMATIONS IN IRELAND. CHAP. XIV. precisely resemble hundreds of dome-shaped protuberances in North Wales, Sweden, and North America.* The marks of glaciation on the rocks, and the transportation of erratics from Cumberland to the eastward, have been traced by Professor Phillips over a large part of Yorkshire, extending to a height of 1,500 feet above the sea; and similar northern drift has been observed in Lancashire, Cheshire, Derbyshire, Shropshire, Staffordshire, and Worcestershire. It is rare to find marine shells, except at heights of 200 or 300 feet; but a few instances of their occurrence have been noticed, especially of Turritella communis (a gregarious shell), far in the interior, at elevations of 500 feet, and even of 700 in Derbyshire, and some adjacent counties, as I learn from Mr. Binney and Mr. Prestwich. Such instances are of no small theoretical interest, as enabling us to account for the scattering of large erratic blocks at equal or much greater elevations, over a large part of the northern and midland counties, such as could only have been conveyed to their present sites by floating ice. Of this nature, among others, is a remarkable angular block of syenitic greenstone, four feet and a half by four feet square, and two feet thick, which Mr. Darwin describes as lying on the summit of Ashley Heath, in Staffordshire, 803 feet above the sea, resting on new red sandstone.† Signs of Ice-action and Submergence in Ireland during the Glacial Period. In Ireland we encounter the same difficulty as in Scotland, in determining how much of the glaciation of the higher mountains should be referred to land glaciers, and how much Hull, Edinburgh New Philoso phical Journal, July 1860. Ancient Glaciers of Caernarvon shire, Philosophical Magazine, series 3, xxi. p. 180. |
