50 THE ICE AGE IN CANADA. 



should not be neglected by geologists. I thus referred to 

 it in 1864.* 



" Our American lake-basins are cut out deeply in the 

 softer strata. Kunning water on the land could not have 

 done this under the present geographical conditions, 

 though it could effect it with a higher level and better 

 drainage ; nor could the result be effected by ocean 

 breakers, though the levelling power of these is enormous. 

 Glaciers could not have effected it; for even if the 

 climatal conditions for these were admitted, there is no 

 height of land to give them momentum. But if we 

 suppose the land submerged so that the arctic current, 

 flowing from the north-east, should pour over the Laur- 

 entian rocks on the north side of lake Superior and lake 

 Huron, it would necessarily cut out of the softer Silurian 

 strata just such basins, drifting their materials to the 

 south-west. At the same time, the lower strata of the 

 current would be powerfully determined through the 

 strait between the Adirondac and Laurentide hills, and 

 running over the ridge of hard rock which connects them 

 at the Thousand Islands, would cut out the long basin of 

 lake Ontario, heaping up at the same time in the lee of 

 the Laurentian ridge, the great mass of boulder-clay 

 which intervenes between lake Ontario and Georgian 

 bay. Lake Erie may have been cut by the flow of the 

 upper layers of water over the Middle Silurian escarp- 

 ment ; and lake Michigan, though less closely connected 

 with the direction of the current, is, like the others, due 

 to the action of a continuous eroding force on rocks of 

 unequal hardness. 



* Presidential Address to Nat. Hist. Soc. of Montreal, Canadian 

 Naturalist, 1864. 



