104 



ISLAND LIFE. 



[part r. 



migrations 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. 



Proofs of the Recent Occurrence of a Glacial Epoch. — The 

 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 valleys, 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 striae of extreme fineness wherever the rock is of 

 sufficiently close and hard texture to receive such marks. These 

 grooves or scratches are often many yards long, they are found 

 in the bed of the valley as well as high up on its sides, and they 

 are almost all without exception in one general direction — that 

 of the vahey 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 strise 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 crys- 

 talline 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 

 roclies moutonnees, 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 



