1864.] NATURAL HISTORY SOCIETY. 227 



of the present arctic current along the American coast has its 

 deep hollows as well as its sand banks. Our American lake- 

 basins are cut out deeply into the softer strata. Running water 

 on the land would not have done this, for it could have n > outlet; 

 nor could this result be effected by breakers. 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 northeast, should pour over the Laurentian 

 rocks on the north side of Lake Superior and Lake Huron, 

 it would necessai'ily cut out of the softer Silurian strata just such 

 basins, drifting their materials to the southwest. At the same 

 time, the lower strata of the current would be powerfully 

 determined through the strait between the Adirondac and 

 Laurcntide hills, and, flowing 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 escarpment ; 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. 



The predominant southwest striation, and the cutting of the 

 upper lakes, demand an outlet to the west for the Arctic current. 

 But both during depression and elevation of the land, there must 

 have been a time when this outlet was obstructed, and when the 

 lower levels of New York, New England, and Canada were still 

 under water. Then the valley of the Ottawa, that of the Mohawk, 

 and the low country between Lakes Ontario and Huron, and the 

 valleys of Lake Champlain and the Connecticut, would be straits 

 or arms of the sea, and the current, obstructed in its direct flow, 

 would set principally along these, and act on the rocks in north 

 and south and northwest and southeast directions. To this portion 

 of the process I would attribute the northwest and southeast stria- 

 tion. It is true that this view does not account for the southeast 

 striae observed on some high peaks in New England ; but it must 

 be observed that even at the time of greatest depression, the 

 Arctic current would cling to the northern land, or be thrown so 



