116 Canadian Record of Science. 
tion in the heart of the Laurentian ridge there to admit of 
the necessary ice flow, not merely there but onwards to the 
south-westward over the ice-grooved limestones at Kingston 
and Wolfe Island. During the glacial epoch, and its inter- 
glacial periods, if any, here, the outlet was, the American 
geologists insist, so completely blocked with ice that the 
flow was necessarily by way of the Mohawk Valley to the 
ocean, but it does not seem requisite to assume that there 
was this ice blockade, as the already existing elevation 
probably formed a more than ample barrier to the lake 
waters. 
If this view of Laurentian depression be correct, then the 
St. Lawrence, immediately before the commencement of the 
jce age, was a modest stream, taking its rise here in the 
Adirondacks or Canadian Laurentians and flowing towards 
the sea in very much the same course as now, for this 
course was not much altered by the subsequent ice flow 
north-eastward from the Laurentians. The river from 
Brockville, immediately above which the Laurentian ridges 
under the river disappear, downwards to the first rapid near 
Edwardsburg, has, on the whole, a considerable uniformity 
of depth in the channel, and flows through a low, compara- 
tively level valley, unobstructed by islands. The river 
Ottawa, on the other hand, was, probably, at this time a 
much larger stream, as the great limestone escarpments 
and the terraces along its course seem to indicate. The 
oscillations of the earth’s surface in eastern Ontario and in 
Quebec had led to its being at one time an arm of the 
sea, and at another, perhaps later time, a great river, 
which Mr. J. K. Gilbert even thinks found its rise in the 
Georgian Bay and drained the upper Great Lakes. During 
the ice age, and the subsequent Champlain times, the path 
of the icebergs and glaciers was, in a general sense, down 
the valley of the Ottawa, and this, no doubt, occasioned 
much of the wear of the strata in the river’s course. 
The oscillations in level over great stretches of country 
or local warpings of the strata, will explain many of the 
physical features of a district. Thus, around the outlet of 
