1872.] 85 [Perry. 
slowly advanced southward. And, as thus advancing, it would tend 
constantly to repair the wasting edge, bringing in a high and almost 
precipitous wall of ice to take the place of the melting parts, there 
would, therefore, doubtless be considerable abruptness on the south- 
ern limits of the ice-field, maintained in connection with the inces- 
sant strife between the wasting and the replacement of the mass 
along its slowly receding border. 
The exact conditions under which this wasting occurred are not 
yet known with certainty. That there was a change of climate is 
generally admitted; but how it was brought about is a question which, 
though it has been often discussed, is still waiting for a satisfactory 
answer. According to Professor Dana, “there was a sinking of the 
‘ land below its present level, resulting in a mild climate and the 
melting of the great glacier.”! Patient and long-continued examina- 
tion of the drift phenomena has failed to bring to light any evidence 
of such a subsidence, while it has wakened great doubt as to its oc- 
currence. It is true that the mass of ice overspreading the country 
would tend to depress it, but such tendencies by no means result 
invariably in actual subsidence, or at least in subsidences great in 
amount. But aside from this one point, viz., the antecedent proba- 
bility that the weight of ice would depress the region in whole or in 
part, I know of no evidence that there was any considerable sub- 
mergence of New England during the closing, or indeed any part of 
the Glacial period. 
That small portions of the country were perhaps slightly depressed 
during subsequent times is freely admitted; for there is evidence that 
parts of the region were at one time lower, relatively to the sea-level, 
than they are to-day. But they may have been a trifle lower at the 
beginning of the Post-Tertiary times, and thus there has been little 
if any subsequent depression; or the apparent change of level may 
have been, as it probably was, due to another cause, to be mentioned 
in the sequel. Meanwhile there seems to be no satisfactory proof 
that this subsidence, if there really was one, equalled 500 feet in 
any part of New England. But, granting that there was such a sub- 
sidence, and that it actually occurred, as Prof. Dana seems to think, 
~ during the glacial period, we are to remember that so far as can be 
yet shown, it did not extend far to the west, and so far as the evi- 
dence goes that it was very slight—in the New Haven region, accord- 
1 Paper cited, p. 48. 
