14 
MUSEUM BULLETIN NO. 24. 
portion of the Ottawa valley . 1 No evidence is known which 
would suggest that depression of the land subsequently affected 
the northern portion of the Great Lakes region or the upper 
portion of the St. Lawrence valley near the foot of Lake Ontario. 
It seems improbable that depression of the land took place in 
the Ottawa valley during the time of the retreat of the ice-sheet 
from this region, for the results of investigations by numerous 
geologists, of the raised beaches of the Great Lakes region, has 
shown that differential uplift took place almost continuously 
as the ice withdrew, but probably proceeded from south to north, 
so that the region well outside the borders of the retreating ice- 
sheet was affected by uplift before the more northerly regions 
were affected. The evidence so far as known suggests that the 
rise of sea-level which, apparently, took place in the Ottawa 
valley was due to a return to the sea of the waters which had been 
bound up in the ice-sheet and was not due to depression of the 
land. 
1 Taylor, F. B., Monograph LIII, U.S. Geol. Surv. 
