52 TRANSACTIONS OF THE CANADIAN INSTITUTE. [VoL. VI. 
scale. If the horizontal distance be represented by one yard, we shall 
find it difficult to draw two lines on paper close enough together to 
show the difference between the surface and the bottom of the lake. In 
geological as well as engineering profiles we are accustomed to see the 
vertical measurements so greatly exaggerated that we are apt to over- 
look the true proportions. 
To unscientific persons who have not given the matter a thought, it 
may be a surprise to learn that our great lakes with their present 
outlines and areas, and their existing outlets or connections with one 
another are all very new, geologically speaking. Indeed all lakes, 
whether great or small, and in whatever continent they may be situated, 
are necessarily unstable and transient even in their very existence, 
owing to the movements which are going on perpetually in the crust of 
the earth and which tend to either raise or lower their outlets—in the 
latter case tipping the water out—and partly to the fact that the 
discharging streams are constantly wearing their beds to lower levels. 
The present great lakes of the St. Lawrence are only remnants lying 
in the deeper recesses of much larger ones which existed in compara- 
tively recent times. There is plenty of evidence to show that in 
post-tertiary times a fresh water sea extended from the front of our 
Laurentian highlands southward to the Middle States, and that only a 
ridge west of Lake Superior separated it from another fresh-water sea 
which covered over all the lakes of the Winnipeg basin and also 
extended as one sheet, far up the low and level Saskatchewan and Red 
River valleys. The great valley of the Mississippi has been the site of 
numerous wide lakes, in the bottoms of which have been preserved the 
bones of a large number of species of curious and interesting mammals, 
all of which are now extinct. If the northern part of Hudson’s Bay 
were raised a very little, and its southern part slightly depressed, so as 
to flood the low lands around it, we should have a fresh-water lake of 
unexampled extent, rivalling the Mediterranean Sea in area. It is 
possible that such a lake did really exist for a short time. Indeed the 
central part of our continent, all the way from the Rocky Mountains to 
the Appalachians and the Labrador Peninsula has been the region of 
the greatest lakes of the world in tertiary and post-tertiary times, and 
even their degenerate successors of the present day retain respectable 
proportions. : 
So far as | am aware, Professor Chapman, late of Toronto University, 
was the first to recognize the former extension of the great lakes in one 
sheet as the probable explanation of the phenomena of the superficial 
geology of the whole lake region and surrounding country. 
