this moving debris, and as they were crowded along they
would now and then grate over another piece of stone more firmly
seated, and so their surface would be deeply scratched in the
direction of their greatest length. There is always more or less
water circulating under the Alpine glaciers, and the streams
that flow from them are always very muddy, containing, as they
do, quantities of crushed rock, sand, and clay.


Illustration of Scratched Stone---------


If, for any reason, this earthy matter was not washed out it
would form a bed of hard clay, in places packed with these
striated stones. Such beds of clay are known as "till" or
bowlder clay.<21>

This is descriptive, though in a very general way, of the
glaciers as they exist to-day. Geologists have long been aware
of the fact that they have convincing proofs of the former
presence of glaciers in Northern Europe, where now the climate
is mild. The mountains of Scotland and Wales show as distinct
traces of glaciers as do those of the Alps. It is not necessary,
in this hasty sketch, to enumerate the many grounds on which
this conclusion rests. It is sufficient to state that by the
united labors of many investigators in that field we are in
possession of many conclusions relating to the great glaciers of
this age which almost surpass belief; and yet they are the
results of careful deductions. The former presence of this ice
sheet itself is shown in a most conclusive manner by the bowlder