292 NEW YORK STATE MUSEUM 



tive inducement to valley-making, and the principal remaining 

 lines of weakness are structural, lines of faulting and of repeated 

 jointing. The main joint directions vary somewhat in different 

 parts of the region, but there is always an important set with 

 a direction approaching parallelism with that of the main faults, 

 and many of the main valleys of the region have this trend, this 

 being specially noteworthy in the eastern district where faulting 

 has been most pronounced. 



Because of the dome-shaped character of the uplift, the tend- 

 ency has been to locate the main watershed of the region at its 

 apex, with a radial arrangement of the main streams with respect 

 to it. Moreover, since the sides of the dome have a slightly 

 greater slope than the graded slope of the streams, the valleys are 

 cut to greater depth in the heart of the region than on its flanks. 

 The vertical distance between the cJld and new base levels is 

 greatest there. 



When we pass to the Paleozoic rocks which everywhere sur- 

 round the region, dipping slightly away from it, the stream 

 adjustments necessarily differ, owing to the different character 

 and arrangements of the rocks, which lie with their exposed edges 

 parallel to the border of the region. The original radial streams 

 flowed acrofss these bfeds, but the tributaries which developed to 

 these radial streams flowed along them and would develop 

 mainly on the softer belts. With successive uplifts of the region, 

 these adjusted streams would be more advantageously situated 

 than many of the radial streams, and would increase in isize at 

 their expense, converting them into tributaries. This process 

 has had much to do with the production, on all sides of the 

 region of main drainage valleys parallel with its sides, though 

 by no means the only factor involved. 



Glacial history 



This long erosion period was terminated by the great change 



in conditions which ushered in the Glacial period. The long and 



complicated history of the region during Glacial times is but 



imperfectly known. It was well within the field of action of the 



