104 
ISLAND LIFE. 
[part t. 
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 m.ost 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 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 striae 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 
roches 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 
