1884. 51 Trans. N. Y. Ac. Sci, 
A paper was then read by Dr. Joun S. NEWBERRY, illustrated by 
lantern views and a map, on the subject of 
THE EROSIVE POWER OF GLACIER-ICE, AND ITS INFLUENCE ON 
THE TOPOGRAPHY OF NORTH AMERICA. 
(Abstract. ) 
Ice being a comparatively soft substance, seems at first sight inca- 
pable of doing much toward the wearing away of solid rock or changing 
topography. But the facts observed in connection with all glaciers 
prove that ice is a powerful eroding agent. Where several hundred or 
several thousand feet in thickness, as some glaciers have been, the ice 
rests upon the underlying surface with a weight of hundreds and even 
thousands of pounds to the square foot. Such a mass in motion, 
impinging against obstacles, has often crushed and removed them, 
gathering beneath it fragments of all sizes, from sand to boulders ; these 
have been the instruments of powerful grinding action, which over 
great surfaces has planed down the rocks, removed or rounded over 
asperities, filled valleys with debris, and thus produced a marked 
effect upon the topography. Local glaciers broaden and deepen the 
valleys in which they move, and having a positive excavating power, 
have often increased the irregularities of topography ; while broad, con- 
tinental glaciers have produced just the opposite effect, as we have 
evidence on a stupendous scale. Over all that portion of North 
America lying north and east of Bismarck, St. Louis, Cincinnati and 
New York, the surface bears marks of extensive erosion by ice, con- 
sisting of planed, scratched, and undulated rock surfaces, the inscrip- 
tion made by glaciers and nothing else, and sheets of transported 
material, which has been brought a greater or less distance from the 
north southward. This sheet of drift material extends from the Banks 
of Newfoundland, which are formed of glacial debris, over Nova Scotia, 
Canada, New England, New York, Northern Pennsylvania, over most 
of Ohio, Indiana, Illinois, Michigan, Wisconsin, and Minnesota. From 
the British line it extends northward, parallel with the Canadian High- 
lands, probably to the Arctic Sea. Over all this area, which embraces 
not less than a million of square miles, the surface of the eroded rocks 
is covered with a sheet from ten to three hundred feet in thickness, 
averaging thirty or forty feet of glacial debris, boulder clay, boulders, 
gravel, sand, etc., all of which have been moved a greater or less dis- 
tance southward. North and east of the Canadian Highlands, which 
extend from Labrador to the great Lakes, and then to the Arctic Sea, 
the country has been but partially explored; yet it apparently every- 
where bears evidence of having been covered with glaciers, and it would 
