E. MINERALOGY AND GEOLOGY. 95 



east and west of the Connecticut, the great continental gla- 

 cier had a southeastward course, varying somewhat in par- 

 ticular latitudes, and that it moved over the elevated lands 

 to the east of the river, keeping right onward, with little va- 

 riation in its main movement, notwithstanding the ridges in 

 its course, and probably following the general slope of the 

 surface of New England. This being true of the movement 

 of the main mass, other facts show that the bottom ice of the 

 great glacier often followed the courses of the valleys be- 

 neath it. 



He also discusses the question whether the scratches in the 

 valleys were made in the glacial era, while the glacier was 

 of nearly or quite its maximum thickness, or during the de- 

 cline of the glacier, when its thickness was so diminished as 

 to make the ice of the valleys essentially independent gla- 

 ciers, and comes to the conclusion that the valley ice in the 

 Connecticut had, throughout its southern half, its own inde- 

 pendent southward motion, mostly unmodified, during the 

 whole progress of the glacial era, but that among the more 

 northern part of the valley there were modifications in the 

 valley movement referred to, and also scratches made by the 

 general glacier. 4 2>, October, 1871,233. 



GREAT CONTINENTAL GLACIERS. 



In the preceding article we give an abstract of Professor 

 Dana's paper in the American Journal of Science upon the 

 great continental glaciers of North America, and in the No- 

 vember number of that magazine he continues this highly 

 interesting topic, and proceeds to investigate its source, or 

 the position of the great plateau which constituted the start- 

 ing-point of the glacier movement. After a. full discussion 

 of the direction of the rock scratches at different points in 

 New- England and Canada, he comes to the conclusion that 

 the region of greatest elevation in question along the water- 

 shed and that of the icj? plateau must have been situated 

 between Lake Temiscaming and Lake Mistissinny, and that 

 its trend was consequently northeast and southwest, this be- 

 ing nearly that of the water-shed between the lakes a trend 

 just right for a southeast movement of the ice. The height 

 of this Canadian water-shed must have been at least four 

 thousand five hundred feet greater than at the present time. 



