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 serial 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 striae maybe 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- 



