OUTLETS OF PORTAGEVILLE-NUNDA LAKE. 439 



ceased to be effective it is probable that Poags Hole and the Dansville 

 valley were the site of a local glacial lake,* the Dansville lake, overflow- 

 ing past Barns to the Chemung river. When the ice uncovered the 

 region of Portage ville the Genesee waters found an avenue of escape, 150 

 feet lower than Cuba, over the morainic dam east of Portageville and 

 filled the upper Nunda (Kishawa) valley to the height of the col north 

 of Swains. Overflowing by the Swains-Canaseraga channel into the 

 Dansville lake, the water ultimately escaped by the Poags Hole col past 

 the sites of Burns and Hornellsville to the Susquehanna. 



Primary outlet. — The present water-parting between the Nunda valley 

 and the Swains-Canaseraga channel is at Ross crossing on the Central 

 New York and Western railroad, four miles north of Swains. This point 

 is the southern limit or head of a heavy moraine which fills the head of 

 the Kishawa valley and descends rapidly to the north toward Nunda. 



The rock channel begins immediately south of the divide and extends 

 past Swains, Garwoods and Canaseraga to the head of Poags Hole, two 

 miles north of Burns, a length of 12 miles, being traversed the whole 

 distance by the Erie and the Central New York and Western railroads. 

 At Garwoods and at Canaseraga other valleys join and the channel is 

 there expanded and indefinite, but with these exceptions the channel 

 preserves its fine and uniform characters as an old river-course (see plate 

 20, figure 1). It has a very steady width of one-fourth to one-third of a 

 mile, with abrupt banks of Portage shales and curvatures of large radius. 

 The bottom of the channel is now flat and swampy, the stream being 

 insignificant. The mouths of side ravines are left higher than the channel 

 bottom, and bisected deltas, 20 to 40 feet high, are frequent. The altitude 

 of the divide is 1,320 feet. The fall from there to Swains, four miles, is 

 13 feet; from Swains to Garwoods, two miles, is 30 feet ; from Garwoods 

 to Canaseraga, two miles, is 20 feet ; or 60 feet fall for the first eight miles 

 below the divide. This channel terminates one mile east of Canaseraga. 



Ultimate outlet. — The waters of the fifth stage were poured into the 

 Dansville local lake one mile east of Canaseraga village. The second, or 

 ultimate outlet to the Susquehanna w^aters, will be described in connec- 

 tion with the sixth stage of the Genesee waters. 



Water-levels. — The erosion plane of this lake extends as far up the valley 

 as Belfast, but it is the highest or summit level only north of a parallel 

 cutting the valley just south of Portageville. Being lower and nearer 

 the center of the valley, these are the most conspicuous levels visible 

 from the railroad throughout the extent from Portageville to Belfast. 

 They have been measured at numerous points, as follows : Two miles 



* Described in a former paper, Bull. Geol. Soc. Am., vol. 6, pp. 358, and now believed to have been 

 later joined with the Genesee waters of the sixth stage. 



LII— Bull Geol. Soc. Am., Vol. 7, 1895. 



