MECHANICAL ACTION OF GLACIERS. 157 
covering the face of the country, filling up the valleys, 
mounting over the hills, and pressing with constant resist- 
less force upon all the rocks over which it advances; and 
blocks of stone, either loosened from the mountain by 
frost, or torn off by the moving glacier, are jammed in in 
the rear, and pressed along the rocky bed or sides of the 
valley ; and the stones, mud, gravel, and sand thus borne 
along act like files, scratching and scoring the hardest 
rocks, and being themselves scratched by the same process. 
As it is now in North Greenland so must it have been 
during the glacial period in Scotland. There we find the 
rounded, filed-down projections on the mountain top and 
on the mountain sides, and the parallel striae. So must it 
have been at the same period, and on to a later time, in 
Norway; and thus many numerous phenomena, presented 
by the mountains and the rocks there be satisfactorily 
accounted for. 
The rasping of the ice, charged with fragments of stone, 
and gravel, and sand, would occasion striae and markings 
on the rocks, and by the direction of these may be traced 
the direction of the movement, while variations in the 
direction of these can be accounted for. 
The striae produced by glaciers are generally.apparently 
parallel and straight. The normal erial currents, popu- 
larly known as the ‘ trade winds,’ produced by well-known 
causes, follow a curved direction, throwing off eddies both 
upward and horizontal. Similar currents and eddies have 
been observed in the ocean. Like eddies may be seen in 
the river, and even in the cup of tea, produced by upward 
currents from the dissolving sugar ; and strdae may be seen 
following a curve more or less expanding, and more or less 
contracting, and variations in their direction may have 
been similarly produced. 
Another of the results of the flux of a glacier is the for- 
mation of a deposit of stones at the extreme edge of it; 
stones which have been borne along on its surface, or, it 
may be, in some cases a little way beneath this by the slow 
massive advance of the body of ice, on reaching the ex- 
