30 BEPOET— 1886. 



glaciers as nothing but the southern limit of the ice-drift of a period of 

 submergence. In such a period the southern margin of an ice-laden sea 

 where its floe-ice and bergs grounded, or where its ice was rapidly melted 

 by warmer water, and where consequently its burden of boulders and other 

 debris was deposited, would necessarily present the aspect of a moraine, 

 which by the long continuance of such conditions might assume gigantic 

 dimensions. Let it be observed, however, that I fully admit the evidence of 

 the great extension of local glaciers in the Pleistocene age, and especially 

 in the times of partial submergence of the land. 



I am quite aware that it has been held by many able American 

 geologists ^ that in North America a continental glacier extended in tem- 

 perate latitudes from sea to sea, or at least from the Atlantic to the 

 Rocky Mountains, and that this glacier must, in many places, have 

 exceeded a mUe in thickness. The reasons above stated appear, however, 

 sufficient to compel us to seek for some other explanation of the observed 

 facts, however difficult this may at first sight appear. With a depression 

 such as we know to have existed, admitting the Arctic currents along the 

 St. Lawrence Valley, through gaps in the Laurentian watershed, and 

 down the great plains between the Laurentian areas and the Rocky 

 Mountains, we can easily understand the covering of the hills of Eastern 

 Canada and New England with ice and snow, and a similar covering of 

 the mountains of the west coast. The sea also in this case might be 

 ice-laden and boulder-bearing as far south as 40°, while there might still be 

 low islands far to the north on which vegetation and animals continued 

 to exist. We should thus have the conditions necessary to explain all the 

 anomalies of the glacial deposits. Even the glaciation of high mountains 

 south of the St. Lawrence Valley would then become explicable by the 

 grounding of floe-ice on the tops of these mountains when reefs in the sea. 

 In like manner we can understand how on the isolated ti'appean hill of 

 Beloeil, in the St. Lawrence Valley, Laurentian boulders far removed from 

 their native seats to the north are perched at a height of about 1,200 feet 

 on a narrow peak where no glacier could possibly have left them. The 

 so-called moraine, traceable from the great Missouri Coteau in the west, to 

 the coasts of New Jersey, would thus become the mark of the«western 

 and southern limit of the subsidence, or of the line along which the cold 

 currents bearing ice were abruptly cut ofi" by warm surface waters. I 

 am glad to find that these considerations are beginning to have weight 

 with European geologists in their explanation of the glacial drift of the 

 great plains of Northern Europe. 



Whatever difiiculties may attend such a supposition, they are small 

 compared with those attendant on the belief of a continental glacier, 

 moving withont the aid of gravity, and depending for its material on the 

 precipitation taking place on the interior plains of a great continent. 



' Report of Mr. Carvill Lewis in Penmylvania Geological Survey, 1884; also 

 Dana's Manual. 



