536 CENOZOIC TIME. 



accounted for on the view of an era of glaciers, and not on that of 

 icebergs. 



(5.) The objection urged against the glacier theory, that the north- 

 ern part of the continents does not afford a slope southward, to favor 

 the movement, is of no weight, since no such slope was required. All 

 that was needed was a general southward slope in the upper surface 

 of the glacier ; or simply a greater accumulation of ice to the north 

 than to the south. The case is just like that of heaped-up pitch. If 

 stiff pitch be gradually dropped over a horizontal surface it will 

 spread, and continue so to do so long as the supply is kept up ; and, 

 if that surface rises at an angle in one direction, and there is no escape 

 in any other, it will first fill the space to the level of the edge, and 

 then drop over and continue onward its flow. So Glaciers, if the 

 accumulation is adequate, may go across valleys and over elevated 

 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. 



8. 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 southwestward 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 



