CHAPTER VIII. 



DEPTH OF THE ICE DURING THE GLACIAL PERIOD. 



There are two sources of information concerning the 

 depth attained by the ice in North America during the Gla- 

 cial period : First, we have direct evidence in the height of 

 the mountains which have marks of glaciation upon their 

 summits ; secondly, calculations can be made, with some 

 approximation to truth, from the distance through which 

 bowlders have been transported. 



Very conveniently for the glacialist, the mountains of 

 New England and the Middle States serve the purpose of 

 glaciometers, preserving upon their flanks and summits in- 

 dubitable evidence of the great depth of the ancient ice-sheet 

 over that portion of the country. 



It requires but a cursory examination to see that the 

 highest point of Mount Desert Island, on the coast of Maine, 

 was completely covered by the glacier, showing that at the 

 very margin of the ocean the ice must have been consider- 

 ably more than 1,500 feet deep. Even Mount Washington, 

 in New Hampshire, was either wholly enveloped by the ice- 

 current, or if a pinnacle projected above the glacier it could 

 have been no more than 300 or 400 feet higher, Professor 

 Hitchcock having found transported bowlders to within that 

 distance of the summit. The ice-current passed over the 

 Green Mountains where they are from 3,000 to 5,000 feet in 

 height in a course diagonal to that of their general direction, 

 showing that such a mountain-chain made scarcely more of a 

 ripple in the moving mass than a sunken log would make in 

 a shallow river. Farther south, Mounts Monadnock, Tom, 



