OUTLET AND WATER-LEVELS OP DANSVILLE LAKE. 441 



divide, the channel is somewhat swampy and uneven, and the vegetable 

 growth has not covered the old river gravels. The divide is under poor 

 cultivation, the soil being coarse sand and gravel with low mounds and 

 longitudinal bars of washed gravel. The material is so porous that no 

 recognizable stream is seen above Burns. The altitude is about 1,210 

 feet. The plain of the divide ends suddenly to the north in the deep 

 Poags Hole gorge, which has been cut out of the drift-filling which appar- 

 ently occupies a great depth of the ancient valley. Upon the west side 

 of the channel, along by Burns, there still remains about one-half mile 

 in width of the moraine and kame filling. At Arkport there is a group 

 of drift hills on the east side of the channel. Detrital or flood plains are 

 seen all the way from Burns to Hornellsville, at a height of 15 to 30 feet 

 over the channel. 



Water-levels. — This stage of the glacial waters began when the receding 

 ice-sheet uncovered the ridge between the Nunda and the Dansville val- 

 leys down to an altitude lower than the Swains divide. Gradually the 

 Swains channel was abandoned as the waters fell to the level of the Dans- 

 ville lake, and the Burns col became the direct and only outlet. 



With this fall of the Genesee waters the local Portageville morainal 

 lake was established. The moraine dam was left at a height of 1,323 to 

 1,340 feet, east of Portageville, but we have no means of knowing the 

 amount of drift-filling which has been cut away by the river OA^er the 

 head of the Portage gorge. The fall of water surface from the fifth to 

 the sixth stage was about 100 feet, as the Burns outlet had been partially 

 cleared by the local lake drainage. 



Perhaps the local Portageville lake cut down the drift top of its dam 

 so rapidly as to retain a level not far above the subsiding glacial waters, 

 but when the rock was reached the morainal lake was certainly left be- 

 hind. The top of the rock at the head of the Portage gorge, beneath the 

 Erie trestle, is 1,240 or 1,250 feet. The numerous and conspicuous lower 

 plateaus in the Genesee valley, from Portageville up as far as Caneadea, 

 ranging from 1,160 to 1,270 feet, undoubtedly belong to the local morainal 

 lake and not to the glacial waters. 



The undoubted terraces of the sixth stage must be found north of or 

 below the Portageville moraine. Such are to be seen in the present 

 valle,y of the Genesee (the Saint Helena valley), in the Kishawa valley 

 and in the Dansville valley. The only strong plateaus that have been 

 closely estimated in the Genesee valley are the delta terraces at the mouth 

 of Wolf creek, on the west side, a few miles north of the Portage ravine. 

 The summit was estimated from aneroid measurements at 1,275 feet. 

 Some three miles north of Wolf creek a broad clay terrace or silted plain 

 Avas measured by aneroid at 1,225 feet. 



