DECAY PRECEDING GLACIATION. 75 



of ice action in shaping the area. The facts presented in this report clearly 

 indicate that the bed rocks have been cast into exceedingly varied flexures 

 and faultings. As these disturbances involved a great thickness of strata 

 and were made apparently in a geologically short period, the result must 

 have been the formation of mountains of high relief. Yet these elevations 

 have been so completely effaced that, as is shown in the maps, the region 

 is now in the state of a great plain, the trifling differences of elevation 

 being due to the action of the rivers and the subglacial streams. As before 

 remarked, the modern school of geographers would attribute this topographic 

 character to the process of base-leveling, by which, through the atmospheric 

 agents of erosion, a surface, however diversified, tends inevitably to be low- 

 ered to near the level of the sea. Making what seems to be due allow- 

 ance for the effect of repeated elevation in refreshing the work of the 

 streams and thus promoting the degradation of a country, a cause which 

 most likely operated in the West Appalachians more effectively than on this 

 seashore, there still seem to be needed some agents to explain the remark- 

 able planation of the district we are considering. It is likely that glaciation 

 has been one of those auxiliary agents. We will now consider the way in 

 which it may have operated to bring planation about. 



The evidence has been noted which goes to show that the rocks of this 

 basin were deeply decayed at the time the work of the last Glacial period 

 began. Acting on such a surface, the ice would quickly become burdened 

 with an excess of debris, in which state it would resemble an ordinary stream 

 of water which has a charge of sediments much greater than it can carry. 

 In this case both the fluid and the viscous streams necessarily tend to 

 deposit a part of their burden and to flow over the accumulations, being 

 thus in part excluded from contact with the bed rock. The deposits of the 

 overburden would naturally take place in the valleys, the floors of which, 

 except when attacked by the subglacial streams, would remain uneroded, 

 while the higher-lying parts of the field would be cut away. As the process 

 of erosion advanced and the waste from the elevated places became smaller 

 in quantity, the glacier would be free to attack the lower levels. The result 

 of this succession of events would be to level off the inequalities of a country 

 which, owing to the decayed state of the rocks at the time the ice came 

 upon it, afforded detritus more rapidly than the machinery of transporta- 

 tion could bear it away. It may be remarked that the apparently excessive 



