lOi BELT ON THE GLACIAL PERIOD IN NORTH AMERICA. 



dence the highest points rose above the ice, rocks would be under- 

 mined and carried away. As the ice diminished and the ranges 

 emerged, a time would arrive when the passes would become icy- 

 straits through which flowed ice fi'om behind. It could not move 

 down the valleys, for at that time the great north and south valleys 

 of the Hudson and the Connecticut must have been filled with the 

 ice that dammed up the lateral valleys. 



The first stage in the formation of the trains began when the 

 two valleys were filled with ice, and glaciers streamed through the 

 passes in the most southern range bearing blocks from those behind. 

 As the glaciers Avasted the boulders would be left in lines marking 

 the retrogressive pomts to which they reached. When the passes 

 of the third range were free from ice it would still flow through those 

 of the second, and as it receded it would leave step by step the 

 monuments that now mark the direction it took. The resemblance 

 of many of the phenomena of the drift to those that might have been 

 produced by floating ice, proceeds from this, — that the valleys were 

 filled with ice as they would have been by water in the former case, 

 and that glaciers flowing through the gorges in the hills took the 

 place of the suppositious icebergs. 



o. Drift of the St. Lawrence. — Dr. Dawson of Montreal, has 

 pointed out that the drift of the valley of the St. Lawrence has been 

 carried up the valley. He argues that it ought to have been carried 

 down it if the transporting agent had been land and not floating ice. 



This objection is again rather against a theory of local glaciers 

 conforming to the slope of the valleys, than that of continental ice. 



The great valley runs from south west to north east, and the ice 

 coming from the north must have flowed up it, if it was influenced 

 by it at all. The general direction of the ice flow was from IST. N. 

 W. to S. S. E., but it could scarcely fail to be somewhat influenced 

 by such a wide and deep valley running obliquely to its course. 

 The valley must have filled from the bottom upwards, and drift 

 would be carried from the high grounds on the sides to the bottom 

 of the valley farther up, even if the ice was not pushed up by the weight 

 of the mass behind. Again, Avhcn the ice from the north reached 

 the bottom of the valley of the St. Lawrence, it would dam it up, and 

 a great inland fresh water sea might be formed, up which would float 



