SEDIMENTATION^. 323 



some cases it appears pi'obable that the local drainage of the hillside would 

 furnish all the water required to deposit the gravel. But there are other 

 cases (as that found near Wilton, elsewhere described) where the stream was 

 of good size at the top of the hill. In such cases the streams mu.st have 

 had a gathering ground to the north. Of course such streams ceased to flow 

 when the hills rose to the surface of the ice, but thus far I have found no 

 traces of deflection channels into which they turned after their original 

 channel was interrupted. 



Summary. — Some of the streams that deposited the hillside kames appear 

 to be instances of glacial streams whose career was cut short hj the lower- 

 ing of the ice to the tops of transverse hills. Thus far I can not identify 

 them with any of the long rivers, nor trace any channels they abandoned 

 for others. In the case of delta branches the glacial rivers may have 

 abandoned one channel for another, but such branches obey the same law 

 respecting low passes as the main rivers. In case of the larger rivers pene- 

 trating low passes, there is as yet no field proof that the rivers even flowed 

 anywhere except whei'e the osars were deposited. The general inference 

 follows that the courses of the great glacial rivers were determined to the 

 low passes before the osars were deposited or the adjoining hills were bare 

 of ice. 



SEDIMENTATION IN PLACES FAVORABLE OR UNFAVORABLE TO THE 

 FORMATION OF CREVASSES. 



The discontinuous gravel deposits found near the coast region often 

 form on a lenticular hill or drumlin, as near Belfast, or on the tops of low 

 hills, as near Portland. Both the Kennebec and the Penobscot rivers for 

 many miles are flanked by osars, somewhat discontinuous, that are for the 

 most of the distance found at the flanks of the valleys or near the top of 

 the steep bank 50 to 100 feet above the rivers, just where crevasses would 

 naturally form. Near Lewiston the Androscoggin River shows the same 

 peculiarity for a few miles. 



On the other hand, some of the discontinuous gravels are in the bot- 

 toms of valleys or on level ground where there appears to be no inequality 

 of the ground to cause crevasses. So, also, the long osars love to zigzag 

 over broad plains, often through swamps, where the land is very level and 

 even and there is no apparent cause for crevasses. They often follow the 



