276 WALKS AND TALKS. 



near Boston, one hundred feet; onNantucket, eighty-five feet. 

 Northward, on the contrary, the submergence increased in 

 depth. On the coast of Labrador, it was five hundred feet ; 

 in Barrows' Strait, it was over one thousand feet. The usual 

 opinion is that this submergence occurred after the dissolution 

 of the glacier; but I incline to the conviction that it was 

 coincident with the glacier. I have already suggested, follow- 

 ing Croll and general opinion, that a load of northern ice 

 would very probably cause submergence of northern shores 

 though I think it resulted from depression of the crust, rather 

 than a shifting of the center of gravity. Such submergence 

 would be greatest northward. The facts observed seem to 

 show that it was a submergence of the glacial epoch, instead 

 of the post-glacial. If the sunken shores were already buried 

 in ice, the temperature of the sea would dissolve it, and the 

 sea-bottom would be of the usual character of a submerged 

 beach. 



The depths of submergence just mentioned are far less than 

 would have taken place, if the crust of earth had yielded 

 readily to the pressure of five thousand feet of ice. To have 

 influenced the temperature, there must have been a much 

 greater subsidence from the point of maxim urn- elevation. It 

 is reasonable to conclude that the action which caused the 

 original elevation was now reversed, and much greater subsi- 

 dence took place than was due to the load of ice. 



Whatever the amount of subsidence; whatever its cause; 

 whatever the cause of the climatic amelioration, there is no 

 question about the return of a geological spring. The glacier 

 began to waste more than its annual growth. A steady re- 

 cession began along its southern margin. A series of inoniinic 

 loops was left to mark its farthest advance. They were com- 

 posed of bowlders and sand. The materials were accumulated 

 in hills and ridges, with intervening "pot-holes" and valleys. 

 The dissolution of the ice-field proceeded with rapidity. Lively 

 rills flowed over the surface of the ice, and turbid streams 

 sprang from the foot of the glacier such streams as make the 

 Aar (Talk VIII) and the Arve (Talk IV). The moraine de- 



