NORTH AMERICA IN THE ICE PERIOD. 237 



The writings of Moseley and Croll recall the utterances of Agassiz 

 as respects the motion of the glacier, lie himself modestly avows his 

 physical researches upon the glacier as inferior to those of his succes- 

 sors, Forbes, Tyndall, etc. ; yet he could not shut his eves to the fact 

 that those physicists had not satisfactorily solved the problem. While 

 ascribing the motion to expansion by freezing, Agassiz insisted tbat 

 heat was largely concerned, asserting that its presence was more con- 

 sequential than that there should be an inclined plane that the ice 

 might move up-hill toward the sun ; and particularly that a great 

 thickness of it could make its way over such level territory as the 

 prairies of Indiana and Illinois. The ice along the southern melting 

 edge would be charged with moisture percolating through the pores 

 and capillaries, descending the icy slopes obedient to gravity, and no 

 longer requiring the shearing force. The amount of motion would in 

 these circumstances be like that of the Greenland sheet, sixty feet per 

 diem, rather than the sluggish crawl of one to three feet in the same 

 time of the comparatively poorly developed Alpine glaciers. In agree- 

 ment with these views we find the motion northward toward the pole 

 to be very slight, though the land may be inclined northerly as in 

 Grinnell Land. 



Now, if we apply these principles to the territory in question, we 

 would say that the ice began to accumulate in Canada from an unu- 

 sual precipitation of moisture, gradually filling up the St. Lawrence 

 Valley, and at first moving southwesterly. But, the supply still con- 

 tinuing plentiful, the valley fills up and runs over. It does not need 

 to accumulate to the thickness of several miles upon the Laurentian 

 highlands so as to have a downward slope all the way to Mount Wash- 

 ington. A mass only a few thousands possibly hundreds of feet 

 thick miwht soften before the southern sun and the influence of the At- 

 lantic Ocean off our coast, and lead the plastic material southeasterly 

 over the Montalban water-shed. Once started upon the seaward slope, 

 the ice could not fail to reach its destination. The southwest motion 

 would likewise continue, and accomplish greater results, transporting 

 blocks much farther because commencing earlier, continuing longer, 

 and pushing forward in a thicker sheet. This Canadian ice would 

 have resembled the present mer de glace of Greenland, confluent over 

 hill, valley, and island, dragging the reluctant erratics up hill and 

 down, accumulating ground moraines and lenticular hills, hollowing 

 out pot-holes and discharging clouds of mud into the edge of the sea. 

 Hence, instead of saying that the land rose three or four miles above 

 its present level in Labrador in order to give the required impetus to 

 the ice-movement in New England, it is easy to see how the same 

 work could be accomplished by the action of much simpler causes. 



Messrs. Torell and Dana have advocated the notion that the Green- 

 land and Eastern American areas are one, and that Greenland was the 

 source of the ice that has covered the eastern part of our continent. 



