Upham.] 
138 
[Dec. 19, 
tion # , the North American coast in this latitude was not higher than 
now in relation to the sea ; for in that case no marine deposits 
and shells could have existed here to be eroded by the southeast- 
erly moving ice-slieet and incorporated in its drift accumulations. 
Conversely, we know that the land then was not appreciably lower 
than now, in other words, that there was no considerable submer- 
gence of the border of our present land area ; for this would have 
led to the intermingling of such broken sea-shells with the glacial 
drift farther inland, where no trace of them is found. So it ap- 
pears that the relative levels of land and sea here were closely the 
same before the last glacial epoch as at the present time. 
The chief element of my interest in this subject has been a hope 
that its bearing thus on the oscillations of land and sea during the 
Quaternary period would contribute to the solution of the question 
whether the northward ascent of the beaches of the glacial Lake 
Agassiz, assigned to me for investigation in the United States Geo- 
logical Survey, is to be explained mainly by northward attraction 
of the water of that lake in gravitation toward the ice-sheet, or 
mainly by a depression of the earth’s crust beneath the vast weight 
of the ice and its re-elevation when that weight was removed. In 
this study of our Atlantic coast, I have therefore sought to con- 
nect these observations near Boston with the allied evidence sup- 
plied by other Pleistocene marine fossils both south and north of 
our latitude. Some of the conclusions to which this correlation 
seems to lead I will endeavor to state briefly. 
As before noted, it is only toward the south that we find Pleis- 
tocene fossiliferous beds antedating the last epoch of glaciation, 
when an ice-sheet covered all New England. They occur in San- 
koty Head and on Gardiner’s island at elevations respectively about 
30 and 15 feet above the sea, and in numerous localities on Long 
Island from the sea level up to elevations of about 200 feet. But 
at least the higher of these beds appear to have been “upheaved 
by the lateral pressure of the ice-sheet and thrown into a series of 
marked folds at right angles to the line of glacial advance,” as 
shown by Merrill j 1 and he finds that this uplifting and folding 
is also very distinctly seen in the strata underlying the glacial drift 
on Gardiner’s island, so that the fossiliferous layer there, though 
raised little above the sea level, is probably higher than its origi- 
1 Annals of the New York Academy of Natural Sciences, vol. iii, 1886, pp. 341-364, 
with sections and map. 
