544 CENOZOIC TIME MAMMALIAN AGE. 



The submarine valley of the Hudson River (p. 441) may have been formed 

 during the same elevation of the continent in which the fiords originated. The 

 Connecticut River valley is also distinct over the same submerged plateau, run- 

 ning south from the channel east of Long Island. 



(6.) That an elevation of the continent over its northern regions 

 of a few thousand feet is sufficient to account for the existence of 

 a Glacial epoch in the earth's later history ; and an elevation of 

 5000 feet is as probable as a subsidence of 5000 feet. 



The main difficulty encountered by the Glacier theory is that the 

 land to the north has not the slope supposed necessary to give 

 glaciers a southward movement, and it would not acquire this 

 slope by any probable elevation. 



During a Glacial epoch of the kind here supposed, the whole 

 northern portion of the continent down to the southern limit of 

 the Drift would have been covered by a vast and almost uninter- 

 rupted glacier. This is now the case in North America with the 

 return of nearly every winter. But the depth, instead of being, as 

 now, but a few feet, and that mostly of snow, must have been, 

 judging from the height on the hills to which the strise extend, at 

 least 4000 or 5000 feet, and the material, as in all such thick accu- 

 mulations, would have been ice ; and above this there may have 

 been other hundreds of feet of snow. Glaciers of so vast extent 

 and thickness would have moved downward wherever the condi- 

 tions would permit, like the glaciers of the Alps, — and all the more 

 readily for their enormous weight. 



There are two conditions to be considered : — First, the one already 

 mentioned, — the existence of some degree of slope in the surface ; 

 second, the absence of barriers to prevent descent along the slope. 



Now, to the northward over the continent, with no lofty ranges, 

 there would have been a universal barrier in the ice and snow of 

 the universal glacier. But on the south the ice would have had a 

 limit, caused by the climate. Motion would therefore have been 

 mainly to the southward, if it took place in any direction. 



The requisite slope exists now in New England and eastern New 

 York, along the Connecticut valley, east of the summit of the 

 Green Mountains, and along the Hudson River valley west of the 

 summit. The motion of a great glacier along either valley would 

 have given the same direction to the striae and to the lines of 

 boulders which actually exists. It would also have scored the 

 sides and tops of the minor valleys and ridges, regardless of their 

 courses and declivities ; and as the glacier finally melted away it 

 might have left its moraines as trains of stones on the surface, cross- 

 ing deep valleys obliquely, or in any direction, and blocks of thou- 



