258 PROCEEDINGS OP THE ACADEMY OF [1883. 



amount of silt has been deposited, as moraine material, by the 

 receding glacier, as far north as Trenton Falls, in New York, but 

 not much farther. On the north side of the Mohawk Valley, 

 from Utica to Schenectady, vast deposits of glacial drift may be 

 seen. North of Trenton Falls the deposits appear to diminish 

 rapidly in quantity, so that I observed no large accumulations 

 near the St. Lawrence River or north of it. The farther north I 

 proceeded the smaller the deposits appeared to be, including the 

 ordinary surface soil. 



From the above facts I consider there are reasonable grounds 

 for suspecting that the glacier receded slowly from Fenns3dvania 

 until its southern limit was not far north of the Mohawk River, 

 and then it was withdrawn more rapidly, with increasing speed, 

 as it proceeded north. 



Some geologists consider that there was not a great amount of 

 glacial erosion accomplished upon the rocks in Pennsylvania. I 

 believe that the erosion proceeded with much greater effect in 

 Canada than in this State. While progressing from the north 

 the glacier would operate on the rocky surface of Canada during 

 a long time before it would reach the latitude of Pennsylvania. 

 Also during its decline it would still continue its abrasion in 

 Canada long after it had retreated from our State. 



I have observed, in northern New York and Canada, that where 

 the country is level it is often covered with Silurian limestones or 

 sandstones, but where it is hilly the Laurentian rocks usually 

 prevail. In the latter case the Silurian rocks maj^ have formerly 

 existed and been removed, as they were more effectually' exposed 

 to the glacial erosion. 



Many sharp, angular stones are scattered over the ground in 

 Canada among the rounded boulders. These evidently have not 

 been transported far from the parent i"ock, but they are suggestive 

 of the fact that, even near the close of the glacier's career, rocks 

 were still being torn into fragments. These fragments were 

 chiefly broken loose from the southwestern portions of the rocks. 



As a shallow soil prevails in the district referred to, the trees 

 do not obtain a deep, substantial hold upon the ground ; conse- 

 quently they are easily blown down by the storms, and the forests 

 are filled with prostrate trees, which make travel a difficult oper- 

 ation there. When the forests are cleared off, the ground is in a 



