322 SURFACE GEOLOGY. 



that the general slope of the land is to the south-west, and in exact direction of the 

 glacial markings of what is known to have been the course of the transported boulders 

 in north-western America. Moreover, if we bear in mind the certainty that during the 

 glacial period the glaciers moving from the height of Greenland towards the sea could 

 not have formed detached icebergs as now, but must have for the time blocked up all 

 avenues except the one of easiest escape for the immense accumulations of ice, we 

 may easily assume this avenue was south-westward across British America and the 

 north-eastern part of the United States. 



Prof. Dana accepts this theory, saying that "we [self and Torell] agree 

 in all essential points." A few suggestions have occurred to me, to the 

 effect that the Greenland theory is untenable, (i) Accepting the notion 

 that the ice moves as Croll proposes, on the molecular theory, there must 

 be a piling up of ice to an enormous thickness, as much as twenty-two 

 miles, to account for a motion from Greenland to the extreme south- 

 west known limit of the ice-sheet. (2) The bridging of Davis straits 

 seems very difficult to explain. The water is deep, and the straits or bay 

 (Baffin's) wide, sufficiently so, it would seem, to discharge all the glacial 

 products poured into it from either side. (3) Good instances of a north- 

 ward transportation have been mentioned, the best known being north- 

 ward from Hudson's bay. The great lack of observations of such a 

 nature everywhere to the north of the Laurentian water-shed renders 

 affirmation of their presence or absence valueless. Some have said that, 

 on account of the cold, there would be little motion northerly. (4) The 

 Labrador peninsula seems to me to offer a good situation for the accum- 

 ulation of an ice-cap large enough to account for all the phenomena. The 

 fiords on the east indicate north-east movements of the ice; and three 

 other courses have been mentioned, so that we find good evidence of 

 motion in four directions from the central table land. Supposing this a 

 centre, Greenland would have been a second, of equal or greater height, 

 and the two would discharge their surplusage into the Atlantic. A cap 

 of thirteen miles would be required for the thickness of this ice, if there 

 were a flow from it to the western edges of the plains. (5) The growth 

 of Greenland and the neighboring parts of the continent suggests the 

 origin of the great basins, as of Baffin's bay, in Eozoic times, and a prob- 

 able submergence ever since. The Hudson's Bay depression is similar 

 (see Fig. i, Vol. H). The Miocene deposits of Baffin's bay were made 



