PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 435 



As was previously said, they mostly lie in a north and south 

 direction. Some of them begin in the middle of the silurian and 

 are continued through the upper silurian, the whole of the devo- 

 nian, and the lower coal series, and are connected with the valleys 

 which terminate in the Atlantic. Most of them terminate in the 

 devonian. Cayuga and Seneca cut through the flinty limestone 

 of the Onondaga group, and the harder sandstone which lies below, 

 while the Owasco reposes entirely within the soft shales of the 

 lower devonian; Ontario is scooped out of the lower silurian, Erie 

 out of the upper silurian and lower devonian; Huron and Michi- 

 gan through the lower devonian, into the lower silurian, while 

 Superior is geologically lower, cutting through the lower silurian, 

 taconic and huronian, if this is not the equivalent of the former, 

 and into the laurentian; Chautauque, rarest of ail, reposes entirely 

 within the upper devonian. 



Are these valleys of subsidence? I answer, no. Why? Because 

 in their neighborhood, no signs of fault, fracture, downthrow, syn- 

 clinal, or anticlinal, can be found, with the single exception of 

 Superior. Here, there are abundant signs of Plutonic agency, and 

 which may, and probably has materially altered its profound bot- 

 tom. What other agent is competent to such mighty work? De- 

 nudation with removal of detritus. What was the power, what the 

 tools, in the hiind of this agent ? Prof. Forbes and other glacial- 

 ists answer, Glaciees. 



There is another sj^stem of valleys seldom noticed, because now 

 filled with drift, peat, marls, and dense growth of swamp trees. 

 I allude to a deep valley in New York State, which, beginning 

 near Rome, extends with the Erie canal, to or beyond Lyons, in 

 Wayne county. 



Oneida lake. Salt lake and Cross lake, lie within this valley. 

 Beneath the bed of the canal, in Onondaga county, it is over one 

 hundred feet deep. The red shales of the salt group bound it 

 on the south ; and it appears to be mainly scooped out of this 

 group. 



I am not aware of any similar valley in any other State. 



The next system of valleys to which I draw attention, is that 

 of our river systems. The Ohio will illustrate the phenomena of 

 all the others. 



Standing at its head springs, in the county of Potter, Pa., from 

 the same plateau of Devonian strata, the Allegany, Genesee and 

 Susquehanna issue as springs. The plateau is speedily cut down, 



