360 H. L. FAIRCHILD — GLACIAL LAKES OP WESTERN NEW YORK. 



Perkinsville, it may be called the Perkinsville lake. The evidences of 

 this highest level have not been studied. 



The main Lake. — Before the ice had melted back as far as the mouth 

 of the present Stony Brook glen, the Canaseraga tributary valley was the 

 basin of a small lake with its overflow near Burns into the Canisteo 

 creek, which remained the lowest outlet of the enlarged or Dansville 

 lake. This earlier episode of the lake may be called the Poags Hole 

 episode, using the local name applied to the narrow, picturesque middle 

 part of the Canaseraga valley. The lake remained at this level while 

 the ice-dam was melting back at least to Mount Morris, 18 miles from 

 the head of the main valley, and perhaps much longer, or even after it 

 reached the Genesee valley. During this time the other streams above 

 named brought down a great amount of detritus and built large deltas 

 at the south end of the broad valley. These have been spread out over 

 the north slope of the moraine, and being principally fine and incoherent 

 material they have been eroded into forms which resemble at first glance 

 the hummocky, morainic drift. Indeed the larger part of the deltas has 

 been removed, and the remnants arc so eroded that the terraces or water- 

 levels are not conspicuous, although clear upon examination. A fine 

 view of the head of the valley is obtained from either the Delaware, 

 Lackawanna and Western railroad or the Central New York and West- 

 ern railroad, the latter connecting with the former at Wayland. 



The altitude of the valley-bottom at Dansville is given by the Mount 

 Morris and Dansville railroad as 691 feet. Hence at its full height the 

 lake was more than 500 feet deep, and this lasted for a time sufficiently 

 long to allow the ice-lobe to recede at least 20 miles. 



When the ice-barrier was so far removed as to permit a lower outlet 

 of the waters northward, probably to the northwest by Caledonia and 

 Le Roy, then the middle Canaseraga creek came into existence and the 

 reversed drainage began to fill the valley and eventually joined forces 

 with Stony brook in the building of the delta southwest of Dansville. 

 When the Dansville lake was much lowered the Canaseraga was com- 

 pelled to reexcavate its middle valley and has produced the rough and 

 peculiar topography of the narrow, deep gorge, six miles long, which has 

 been locally called Poags Hole. In cutting down near the present mouth 

 of the gorge the stream fell upon an angle of rock projecting from the 

 west side of the great valley, and was compelled to make a rock-cutting 

 which gives a singular postglacial exit to an old preglacial valley. 



The Scottsburg Lake. 



CONES us VALLEY. 



Conesus lake is eight miles long and about one mile wide. The valley 

 extends south as a swampy area for more than two miles, and then rises 



