T. F. Jamicson — Oscillation of Land in Glacial Period. 459 



investigation by Mr. Whittlesey and others soon overthrew this 

 notion, for no recent marine fossils could anywhere be found, and all 

 the organic remains that were detected turned out to be land and 

 freshwater sliells, together with some bits of trees and plants. It is 

 also manifest that had the warm waters of the Gulf penetrated so 

 far into the interior of the Continent the effect would have been to 

 carry such an amount of heat thither that glacial conditions would 

 have been impossible. American geologists are now agreed that the 

 glacier at one time filled the basins of all the great lakes and even 

 stretched a good way beyond them, while Dr. Newberry and others 

 suppose that as the ice melted and shrank back to the north a body 

 of fi-eshwater formed in front of it and filled the area that the ice 

 abandoned ; in this lake which bathed the southern margin of the 

 glacier the sediment was deposited that now forms the stratified 

 clay and sand. Such a sheet of water would at present escape down 

 the St. Lawrence and out by the Mohawk and Hudson valleys to the 

 Atlantic ; but during the Glacial period its exit in that direction 

 appears to have been barred by the ice that lay across its path and 

 blocked all the outlet to the north and east. It seems probable that 

 the thicker ice which lay to the north and north-east would continue 

 to fill up that outlet for a long time after the thinner ice melted away 

 from the southern shores of the western lakes ; and it has been as- 

 certained that as the lake was gradually lowered, its waters found 

 their way out into the valleys of the Mississippi, the Wabash, and 

 the Ohio by channels which can still be traced with the gTeatest 

 clearness. That the ice was thicker to the east of the lakes is proved 

 by the fact that the glacier moved along the basins of Lake Ontario 

 and Lake Erie from N.E. to S.W., as appears from the ice-marks on 

 the rocks. On this point the American geologists seem to have no 

 doubt.^ This shows that the glacier must have been heavier at the 

 eastern extremity of Lake Ontario than it was at the west end. 



It is clear, thei'efore, that if a lake existed, such as Dr. Newberry 

 maintains, its escape to the southward must have been prevented by 

 the relative level of the land in that direction having been higher 

 than it is now. In other words, the northern area must have been 

 relatively lower. But this northern area was just that which was 

 longest occupied by the ice, and as it gradually melted away the 

 land seems to have regained, to some degree, its former height. My 

 idea therefore is that the immense weight of ice, which accumulated 

 over the basin of the lakes and the region to the north and east, 

 occasioned a depression of the area on which it lay, and, after this 

 weight was taken off by the ice melting, the depressed tract slowly 

 rose again. I think, however, that the recovery of level was not 

 complete, and that the Canadian ridge has never regained the height 

 it had at the commencement of the Glacial period. Dana in the 

 2nd edition of his Manual expressly says that the amount of depression 

 increased northward so that the beds of rivers flowing southward 

 had a diminished slope. 



' See Newberry's Surface Geology of Ohio, p. 76 ; also, G. J. Hinde in the 

 Canadian Journ. for April, 1377 ; and Dana's Manual, 2nd edition, p. 536. 



