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Show 10-! ISLAND LIF.K [l'AUT I. mi o·mtions and actual distribution of the animal world, a brief outline of the more important facts and of the conclusions they lead to must be here given. P?·oofs of the Recent Occurrence of a Glacial Epoch.-Tho phenomena that prove the recent occurrence of glacial epochs in the temperate regions are exceedingly varied, and extend over very wide areas. It will be well therefore to state, first, what those facts are as exhibited in our own country, referring afterwards to similar phenomena in other parts of the world. Perhaps the most striking of all the evidences of glaciation are the grooved, scratched, or striated rocks. These occur abundantly in Scotland, Cumberland, and North Wales, and no rational explanation of them has ever been given except that they were formed by glaciers. In many va.lleys, as, for instance, that of Llanberris in North Wales, hundreds of examples may be seen, consisting of deep grooves several inches wide, smaller furrows, and stri::e of extreme fineness wherever the rock is of sufficiently close and hard texture to receive such marks. Those grooves or scratches are often many yards long, they are found in the bed of the yaJley as well as high up on its sides, and they are almost all without exception in one general direction-that of the valley itself, even though the particular surface they are upon slopes in another direction. When the native covering of turf is cleared away from the rock the grooves and strire are often found in great perfection, and there is reason to believe that such markings cover, or have once covered, a large part of the surface. Accompanying these markings we find another, hardly less curious phenomenon, the rounding off or planing down of the hardest rocks to a smooth undulating surface. Hard crystalline schists with their strata nearly vertical, and which one would expect to find exposing jagged edges, are found ground off to a perfectly smooth but never to a flat surface. These rounded surfaces are found not only on single rocks but over whole valleys and mountain sides, and form what are termed 1·oclzes nwutonnees, from their often having the appearance at a distance of sheep lying down. Now these two phenomena are actually produced by existing glaciers, while there is no other known or even conceivable cause CHAP. Vll.] 'l'IIE GL!\CIAL EPOCU. 105 that could have produced them. Whenever the Swiss glaciers retreat a little, as they sometimes do, the rocks in the bed of the valley they have passed over are found to be rounded, grooved, and striated just as are those of Wales and Scotland. The two sets of phenomena are so exactly identical that no one who has ever compared them can doubt that they are due to the same causes. But we have fnrther and even more convincing evidence. Glaciers produce many other effects besides these two, and. whatever effects they produce in Switzerland, in Norway, or in Greenland, we find examples of similar effects having been produced in our own country. The most striking of these arc moraines ancl tmvollecl blocks. A OLACIE!t WITH MOHAINfS. Moraines.-AJmost every existing glacier carries d.own with it great masses of rock, stones, and earth, which fall on its surface from the precipices and mountain slopes which hem it in, or the |
