46 



the ice moves. Kestin^ on the i-ock are boulders and pebbles 

 (Fig. 22), sometimes on the bare rock, sometimes imbedded in 



a clay as they are 

 with us. As we 

 found when study- 

 ing the soil in our 

 own region, so here 

 the pebbles are often 

 scratched, and many 

 of them are quite 

 ditt'erent from the 

 rock on which they 

 rest. 



Going nearer to 



2i. — A part of the edge of the Oreenland glacier, clean ^he Ice we find the 



white ice above, and dark discolored bands beloio ichere lower part loaded 



laden with rock fragments. In the foreground is a ^yji-jj pebbles, boul- 



boulder-strewn nwraine. ^^^,^ ^^^ ^.^^ ^^ ^^^^ 



quite like those on the rocks near by. Fig. 23 shows one of these 

 scratched and grooved, which I once dug from the ice of this 

 very glacier. The bot- 

 tom of the ice is like a ; ^ " ' ' 

 huge sandpaper, being 

 dragged over the bed 

 rock with tremendous 

 force. It carries a load 

 of rock fragments, and 

 as it moves obtains more 

 by grinding or prying 

 them from the rocks be- 

 neath. These all travel 

 on toward the edge of 

 the ice, being constantly 



ground finer and finer as wheat is ground when it goes through tlie 

 mill. Indeed the resemblance is so close that the clay coming from 

 this grinding action is often called rock flour. 



438 



25. — Hummocky surface of the boiildrr-.s/rcini 

 moraine of Oreeiiland. 



