Trans. N. V. Ac. Sci. 52 Jan. 14, 



thus seem that in the culmination of the Ice Period, the whole coun- 

 try from Greenland to Bismarck, St. Louis, Cincinnati and New York, 

 was covered with snow- fields and sheets of ice. The ice also seems 

 to have been thick enough to overtop the highest mountains in all this 

 region ; hence it pressed upon the underlying rocks with a weight of 

 from 50,000 to 300,000 lbs. to the square foot, and having been also in 

 motion and underlain by sand, gravel, and boulders, during the thou- 

 sands of years of its continuance, it wore away the surface rocks in 

 places hundreds of feet, and, as it retreated, left behind it the great 

 sheet of debris which it had scraped off and moved southward. In the 

 advent and decline of the Ice Period local glaciers occupied in suc- 

 cession different portions of the glaciated area, and there did their 

 special work in deepening valleys and excavatmg lake basins. In the 

 far West during the Ice Period, the more elevated portions of the 

 Rocky Mountains, the Wasatch and the Sierra Nevada, were occupied 

 by glaciers as far south as the 36th parallel. North of the Columbia 

 the glaciers reached the sea, and all the Puget Sound region was a 

 basin tilled with ice. In Southern Colorado and in California, about 

 the Yosemite, the evidences of glacial action are as striking as any- 

 where else, and thence northward are almost continuous to Alaska, 

 where great glaciers now exist. 



The erosive power of ice has been positively denied by a number 

 of American geologists, Prof. J. P. Lesley, Prof. J. D. Whitney, and 

 others ; but the facts cited, as well as others, show that ice is, over the 

 region it occupies, a much more powerful eroding agent than water. 

 The streams which drain glaciers are always turbid from the quantity 

 of sediment they receive, through the grinding action of ice resting on 

 sand and stones. 



The streams which drain the glaciers of the Cascade range in Wash- 

 ington Territory — the Cowlitz, Puyallup, White River, etc. — are opaque 

 and milky the year round ; while other streams, fed only by rains, are 

 turbid only at intervals when the rains are unusually heavy. In the 

 Alps, all the streams which flow from the glaciers are so white from 

 the sediment they transport that their water is called Gletscher Milch; 

 and the opalescence of the lakes into which these streams flow is due 

 to the fine particles ground up by the glaciers and held in suspension. 

 Measurements have been made of the amount of solid material trans- 

 ported by these glacier streams, and it is shown to be much greater 

 than that carried away by mere rain-fed rivers. For example, the 

 stream which drains the Aar glacier carries off daily 280 tons of sedi- 

 ment, and that which drains the Justedal glacier of Norway removes 

 69,000 cubic metres of rock annually ; and these are only partial 

 measurements of the eroding power of two small glaciers. 



