PROCEEDINGS OF SCIENTIFIC SOCIETIES. 509 
sheet might thus be formed. Great cold prevailing on its northern limits 
and serving as a barrier to its motion in that direction, there being at the 
same time a partial melting of its southern face, the waters from the 
wasting S on its surface percolating the icy mass, there also being 
MSS AAA and expansions cons ru ent upon alternations in the temper- 
ature; all these being connected with the gravitating force of a mass 
from five thousand to ten thousand ria in thickness, motion to the south 
would pd result, even on a horizontal surface, and much more if 
there were a southward inclination of the country. Under these circum- 
stances we n e an instrumentality fully able to plane, smooth, and striate 
the rocky floor of the continent as it now áppears, and thus to account 
for the debris almost everywhere met with in great c RR 
But if there were no elevation of the country, how are we to explain 
the ocean. Thus its waters must have undergone a great depression, per- 
haps one of several hundred feet; and this enables us to account for the 
mud-flats and other like deposits, which were probably laid down when 
the ocean was at a dud level than it is to-da 
It has been, moreover, thought necessary to suppose that a depression 
of the tuque na. do followed its conjectured elevation. The land 
havi ing been lifted up, it must be got down again, in order that there 
cause a return of Rx while the cosmical agencies already referred 
summer of the ages thus coming on, the ice-sheet as gradually melting 
must retreat northward. And the waning of the glacial mass wou 
accompanied by results which require an explanation. 
