536 



CENOZOIC TIME. 



ridges. At the same time, as above stated, the under layers of the 

 ice will follow, to some extent, the general slopes of the country passed 

 over. 



A glacier filling the St. Lawrence valley could not move down the valley (northeast- 

 ward) if the ice were highest about its mouth; but it might, in such a case, move up 

 the valley, or across New England; and, if the latter, the portion in the bottom of the 

 valley would be likely to move up stream, because the valley, a groove in the land, 

 might give direction to the bottom layer. Dr. Dawson has observed evidence that, in 

 some parts of the St. Lawrence valley, the ice of the Glacial period did actually move 

 up stream. 



(6.) The glacial phenomena of the higher Rocky Mountain ranges, 

 the Sierra Nevada, and other heights on the Pacific Border, and of the 

 mountains of Virginia and North Carolina on the Atlantic, are all in 

 harmony with the Glacier theory. The several regions, as recognized 

 by all observers, are simply examples of glacier centres, like that of 

 the Alps, where the mountains were lofty enough to determine the 

 surface slope of the ice, in which case the glaciers of the region would 

 necessarily have been local glaciers. They point to the Glacial period 

 of the Continent as the time of , their origin. A few traces of the old 

 glaciers still linger about Mount Shasta, Mount Hood, and some other 

 of the loftier summits ; and two branches of the Saskatchewan head 

 in glaciers, one of which is nine miles long and three wide. 



Similarly, the glacial phenomena of Great Britain, the Alps, the 

 Pyrenees, Mount Lebanon, and the Himalayas, are those of Alpine 

 glacier centres, and cannot be explained without reference to the exist- 

 ence and action of glaciers. Geikie has shown that the great glacier 

 from the Highlands of Scotland extended northwestward over the Heb- 

 rides, and southward and south westward through the Irish Channel 

 and over Ireland ; and it probably reached northeastward to the Ork- 

 neys and Shetlands. The occurrence, in southern South America, of 

 bowlders from the Cordilleras, scores of miles to the east of the moun- 

 tains, as well as to the west on Chiloe, observed by Darwin, re- 

 quires the same explanation. 



The absence of glacier action, over a large part of the region from 

 Virginia to Georgia and Alabama, is shown by the great depth 

 of decomposed rock, covering in situ the crystalline rocks in many 

 places ; at the north, all such soft superficial material was scraped off 

 and carried away by the glacier. 



It hence appears that the glacier theory is alone capable, as first 

 shown by Agassiz, of explaining all the facts. 



The surface of the glacier in North America must have been of 

 unblemished whiteness ; for, from New England west to the Missis- 

 sippi, there was not a peak above its surface, excepting the White 

 Mountains, and these probably had their cap of snow. Hence among 



