QUATERNARY AGE. — GLACIAL PERIOD. 537 



the depositions, lateral moraines are not a characteristic feature, while 

 under-glacier moraines, or linear ranges of stones and gravel are very 

 common. 



3. Probable summit and limit of the ice of Eastern North America. 

 — The direction of the scratches, and the extent of the country they 

 cover, appear to show (since they indicate the direction of movement, 

 and therefore the slope of the surface of the ice) that, over New Eng- 

 land and Eastern Canada, there was a gradual rise in the surface of 

 the glacier toward the northwest, and over Western New York and 

 Western Canada, toward the northeast ; and that the ice-summit, or 

 the region toward which the directions converge — and therefore the 

 opposite slopes rise — was over the Canada Water-shed, nearly north 

 of Montreal. From this its southern portion the broad ice-range 

 stretched northward and northeastward ; for this is proved by the 

 southwest direction of the drift and scratches over the country from 

 Lake Huron to and beyond Lake Winnipeg. Since evidences of the 

 great southward moving glacier fail over the region west of a line 

 passing from a few degrees west of Winnipeg, southeastward through 

 Western Minnesota and Iowa, near the meridians of 98°-100°, and 

 all the way westward to the borders of California and Oregon if not 

 to the Pacific coast, the ice thinned out toward the interior of the 

 Continent and was mostly absent except about the higher parts of 

 the Rocky Mountains. 



The glacier of the Northern Hemisphere was, therefore, not a great 

 enveloping ice-cap extending far southward about the sphere. On the 

 contrary, the polar ice had a broad and lofty southward prolongation 

 toward the eastern border of the Continent ; another narrow and 

 shorter one on the western border ; and also a southward extension, 

 through local glaciers, along the higher portions of the Rocky Moun- 

 tains. 



The accumulation of ice, under a like degree of cold, depends on the 

 amount of precipitation. Hence it is that the largest ice-range was on 

 the Atlantic border ; and, for the same reason, in connection with the 

 high summer temperature, ice was mostly absent from the western in- 

 terior, the annual amount of precipitation there being not over sixteen 

 inches, which is less than half that of New England. 



The height of the ice-surface at the White Mountains, as scratches and bowlders 

 show, was at least 6,000 feet above the sea; and thence the surface rose toward the 

 summit of the ice-range, and fell away toward (he ocean which lay to the southeast, 

 where was the place of discharge of the ice-stream. It is probable that the lofty ice- 

 range of Eastern North America so intercepted the moisture from the ocean that Green- 

 land and other Arctic lands had less precipitation than now, and perhaps less thickness 

 of ice. 



The conditions were similar in Europe. The Scandinavian mountain range, as made 

 known by the Swedish Geologists, was the course of the great ice-mass, and hence, it 



