102 BELT— ON THE GLACIAL PERIOD IN NORTH AMERICA. 



as the whole of a sandy beach is rippled between high and low water 

 marks by the retiring tide, so during the gradual retrogression of the 

 continental ice, every portion of the country that had been covered, 

 — from the valleys of the Ohio and the Missouri to the Arctic hills, 

 and from the summits of the hills to the bottoms of the deepest 

 valleys, — became again for a time, as they had been during the ad- 

 vance of the ice, the shore of an ice sea, or the boundary of an ice 

 stream. Again the ice wore into its rising banks and carried off 

 stones and gravel and formed terminal and lateral moraines. 



The transportation of drift from any region began as soon as any 

 of its mountain tops emerged above the subsiding ice. The highest 

 peaks would send the farthest carried fragments, and lower and 

 lower as the ice flow ebbed, so nearer and nearer to their source 

 would its burdens be deposited. 



Like its advance, the retreat of the ice was probably slow and 

 fluctuating. During some seasons it would diminish greatly ; during 

 others advance again, but taking a number of years together there 

 would be a decided retreat. The ice would act on the rocks during 

 its subsidence as it had done during its rise, but the drift formed 

 and deposited instead of being destroyed by the advancing mass, 

 was left in the valleys and on the hills as we now find it. The only 

 differences on the southern coast of Nova Scotia that we can detect 

 are, that the moraines in the valleys have often been cut through 

 either by the streams that issued from beneath the retiring glaciers, or 

 by those that now run through them, and that large stones and grain 

 gold have been concentrated on the surfaces of drift-beds on the 

 hill sides. 



v.— APPLICATION OF THE THEORY TO SOME OF THE PHENOMENA 



OF THE DRIFT. 



1. Local character of the drift. — Having thus sketched out the 

 probable action of the ice during its advance, culmination and 

 retreat, and explained the general distribution of the drift, it only 

 remains to apply the theory to a few of its more striking features. 

 The local character of most of the drift stones in Nova Scotia is one 

 of these. Here and there a few blocks of granite are found, that 

 have been brought two, four, or even eight miles, but the great 

 majority of fragments belong to the rock formation over which they 

 lie. Boulders of slate occur where bands of slate cross the countrv. 



