DESCRIPTION OF THE REGION 281 



features eastward and correlate them definitely with those whose dates 

 of origin have been well determined, it is necessary to depend largely on 

 the characters which these forms possess. In entering on such a study 

 it is well to bear in mind that the region has been glaciated, that the 

 hilltops have been abraded to a certain extent by the ice-sheet, and that 

 the valleys suffered a large amount of filling from the same source; but 

 the region in question is near the outermost margin of the glacial ice, 

 and it was not seriously affected by the abrading action. Although the 

 topography has been slightly modified, it has not been changed in its 

 essential characteristics, and hence we may safely compare the surface 

 features here shown with those of other regions whose dates of origin are 

 fairly well determined. 



Interpretation of Surface Features 



Although the writer began the study of this region with the impres- 

 sion that the surface features are very old, he was soon impressed with 

 the fact that the hilltops composing the lower peneplain are distinctly 

 rounded, and in many places flat — features which are not characteristic 

 of extreme age. The drainage of the region also is incomplete and the 

 dissection has not advanced to that stage which characterizes the Cretace- 

 ous peneplain in other parts of the country. In studying its topography 

 the writer has instinctively compared it with the Coal Measures plateau 

 of the central Appalachian region. This plateau is generally regarded 

 as being of Cretaceous age, and hence there should be a similarity 

 between the two features, if the plateau of northern Pennsylvania and 

 southern New York is of the same age. The Appalachian plateau is 

 composed of harder rocks than the Chemung formation, and conse- 

 quently if the two features are of the same age the plateau character 

 should be better preserved in the central Appalachian region than in 

 northern Pennsylvania, but a comparison of the topographic map of the 

 two regions shows at a glance that dissection is much more complete in 

 the Appalachian region than in northern Pennsylvania. In the former 

 locality the hilltops are rudely conical and no fiat land remains to mark 

 the former surface of the peneplain. In the New York region, as here- 

 tofore shown, the hilltops are gently rounded and in many cases flat, 

 and presumably such tops are direct remnants of the peneplain surface. 

 The conclusion, therefore, seems inevitable that the peneplain formed 

 upon the Chemung rocks of northern Pennsylvania and southern New 

 York is much younger than that which marks the surface of the Coal 

 Measure plateau in the central Appalachian region. From this evidence 

 it seemed to the writer probable that the Jura-Cretaceous peneplain may 



