208 J. D. Dana on the Glacial and 
give about 2,700 feet for the mean thickness of the ice. But 
the rate of precipitation over the northern border of New 
England being to that of Connecticut as 3 to 4, the thick- 
ness of the ice over the latter, considering this condition alone, 
should have been 8,700 feet instead of 2,700: there was thence 
a loss of more than two-thirds of all the snow, which loss we can 
attribute only to melting and evaporation. If the waste from 
this cause over the northern border of New England was one- 
fourth of the whole precipitation, that in southern Connecticut 
would have been over three-fourths; just three-fourths, if the 
ice-cliff were assumed to be 500 instead of 200 feet. 
Whatever doubt exists with regard to the height attributed to 
the glacier about Mt. Washington also attaches more or less to 
the preceding calculations. But, to sustain our conclusion, we 
have now, in addition to the facts there observed, evidence that 
all the requisites of the Glacial era for the region from the At- 
lantic shoals to the Canadian watershed are satisfied by it. 
This is reason for believing that the error connected with the 
deduced height of 6,000 feet cannot be large. Moreover the 
Gulf Stream washes the margins of the banks in which the 
glacier has been supposed to have terminated, and would have 
determined a limit in height as well as length. 
The evidence of a large amount of melting in southern New 
esent level, is afforded by the height of sea-border terraces an 
beaches around New England and on the St. Lawrence, their 
height being nearly 50 feet on Long Island Sound, and 500 feet 
in the vicinity of Montreal, on the St. Lawrence ; in the height, 
equally, of the upper terrace-plain along the rivers and lakes; 
and in the additional fact, that the old alluvium beneath this 
plain was a direct result, as above stated, of the deposition by 
the rivers of material afforded by the melting glacier. The 
greater height of the river and lake terraces as we go north, 
and also of sea beaches, indicates that the depression nc 
