MODERN GEOLOGY 



along the Hudson, and such elevations as Mount Hoi- 

 yoke in western Massachusetts. 



Still there remained a vast interior sea, which later 

 on, in the tertiary age, was to be divided by the slow 

 uprising of the land, which only yesterday that is to 

 say, a million, or three or five or ten million, years ago 

 became the Rocky Mountains. High and erect these 

 young mountains stand to this day, their sharp angles 

 and rocky contours vouching for their youth, in strange 

 contrast with the shrunken forms of the old Adiron- 

 dacks, Green Mountains, and Appalachians, whose low- 

 ered heads and rounded shoulders attest the weight of 

 ages. In the vast lakes which still remained on either 

 side of the Rocky range, tertiary strata were slowly 

 formed to the ultimate depth of two or three miles, en- 

 closing here and there those vertebrate remains which 

 were to be exposed again to view by denudation when 

 the land rose still higher, and then, in our own time, to 

 tell so wonderful a story to the paleontologist. 



Finally, the interior seas were filled, and the shore 

 lines of the continent assumed nearly their present out- 

 line. 



Then came the long winter of the glacial epoch per- 

 haps of a succession of glacial epochs. The ice sheet 

 nded southward to about the fortieth parallel, driv- 

 ing some animals before it, and destroying those that 

 were unable to migrate. At its fulness, the great ice 

 mass lay almost a mile in depth over New England, as 

 attested by the scratched and polished rock surfaces 

 and deposited erratics in the White Mountains. Such 

 a mass presses down with a weight of about one hun- 

 dred and twenty-five tons to the square foot, according 



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