Trans. N. Y. Ac. Sci. 52 Fan. 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 excavating 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 filled 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. 
