1872). 15 [Perry. 
the Atlantic.t Not positively asserting that such were the facts, I 
simply suggest them as points for consideration ; points which read- 
ily occur when it is supposed that this region was once covered by an 
immense blanket of ice ; points which indicate that what is regarded 
as necessary proof of elevation may be explained without resort to 
an extravagant assumption, of which there is not a shadow of direct 
evidence. It is scarcely needful to add that the submarine valleys 
of the Connecticut and of the Hudson — valleys which extend out 
under the sea from the existing mouths of these rivers — receive an 
easy explanation in the light of the views propounded. Also that 
mud-flats, during the depression of the ocean, would be very natu- 
rally laid down as sub-aerial deposits, at various points which are 
to-day beneath the level of the sea; and that thus the subject is 
readily relieved of the main difficulties with which Prof. Dana seems 
_to find it invested. 
There is, accordingly, little, if any, satisfactory proof of an eleva- 
tion of the land during the glacial period. Meanwhile no one 
should infer, on this account, that there was no special preparation 
for a change of temperature, and that there was not an adequate 
cause for the more or less intense cold supposed to have prevailed 
during the Glacial times. On this point, indeed, we are very igno- 
rant. ‘There are, however, certain facts which have a bearing upon 
it. Having reference to these, though without being able, or intend- 
ing to assign an exact value to their influence, I proceed to notice 
§ 5. The Preconditions of the Ice-sheet. 
Respecting the climate of the later Tertiary times, many conjec- 
tures have been made, while some important facts have been brought 
forward. Such quantities of snow as must have fallen in order to 
the formation and maintenance of a continental ice-sheet, imply the 
existence of not a little moisture in the atmosphere, a moisture 
which could not be readily produced in a vaporous form without a 
considerable degree of heat, accompanied by an immense amount of 
evaporation. Are there then any facts, or series of facts, suggestive 
of an adequate explanation of what is thus brought before us ? 
1%t is certainly probable that the glacial mass reached as far as the most 
distant islands along our sea-board, since they bear the peculiar striz ascribed 
to glaciers, as well as typical drift. Says Prof. Agassiz, “‘I have missed these 
marks nowhere upon the coast islands of New England.’’ 
