Icy Plateau, the source of the New England Glacier. 327 
summits and also scored surfaces on the White Mountains that are 
full 5200 feet above the sea, the propelling slope, or those of the 
Icy Plateau, must have certainly been higher than 5200 feet. 
e cannot assume that the rate of descent from the top of the 
Icy Plateau to the 5200 foot level on the White Mountains, a 
distance of about 400 miles, was as great as seventeen feet a mile ; 
ut we may reasonably infer it to have been at least three feet. 
This rate for 400 miles would make the height of the Plateau 
to average 6400 feet. The watershed is now about 1500 feet 
above the sea; accordingly, the average height of this region 
should have been at least 4900 feet greater than now. 
grade of two feet a mile would diminish this estimate 
wh making the required average height of the Icy Plateau 
fee 
was stegy 4 higher—at least 4500 feet on an average—than at 
t 
tl 
tion. All that the case demands is simply a bending upward of 
the surface over a wide area through a general continental 
ing its greatest results to the north ; 
imilar oscillations 
tain chains went forward on a stupendous scale over Euro ; 
Asia, and both ecu Guough ahe whole era of the Ter. 
tary; and this later upward movement in 
_ of the continent followed on as the close of the long series, 
