PLEISTOCENE HISTORY OF THE GENESEE VALLEY 77 



middle of the valley they are the most conspicuous levels visible 

 from the railroad between Portageville and Belfast. 



Stage 6. Dansville lake. Outlet was at Burns past Arkport and 

 Hornell to the Canisteo-Chemung-Susquehanna. Present altitude of 

 the head of channel about 12 lo feet. Present altitude of the lake 

 plane at Portage about 1230 feet. 



The first cutting by the waters as they fell below the fifth stage 

 level is to be seen on the north point of the high ground in West 

 Sparta and about one mile southeast of Union Corners. Here was 

 the critical locality where the Portage lake waters first escaped be- 

 tween the receding ice wall on the north and the land slope on the 

 south. The notching on the nose of the hill is evident, though not 

 very conspicuous, at about 1300 feet and downward. .When the 

 waters came to a standstill as the Dansville lake, they produced the 

 smoothing, leveling and shoreline work that is plainly seen at about 

 1200 feet around the nose of the hill. 



This sixth stage lasted until the ice recede;! so as to uncover 

 ground below 1210 feet in the vicinity of Linden and Attica, south 

 of Batavia. As this new escape is on a meridian so far away from 

 the Burns outlet no estimate of the duration of the waters can be 

 made based on distance of the ice front retreat. Undoubted terraces 

 of this level m.ay be seen about Glen Iris at 1240 and higher; on the 

 delta of Wolf creek at 1220 to 1240; and a plateau east of Bishop 

 Corners and east of the river at 1230. 



Portageville morainal lake. With the fall of the glacial waters 

 below the Portage terraces, about 1320 feet, a local lake was left in 

 the valley above Portage, being hel 1 up by the drift barrier. This 

 water we have called the Portageville morainal lake. It was con- 

 temporaneous with the sixth stage of the glacial waters (lying north- 

 ward), which from this time touch only the areas on the north. 



It will now be seen that the gorge cutting at Portage began only 

 with the overhow of the Portageville morainal lake, and that the 

 glacial Dansville waters had no relation to the gorge except as pos- 

 sibly determining the base level for the stream and as the receiving 

 body for the detritus. The initiation of the gorge cutting probably 

 began at about 1320 feet, as it seems likely that the via^luct plain 

 originally extended entirely across the valley. The top of the rock 

 at the head of the canyon is at about 1240 to 1250 feet. 



It will also be seen that the Portage river, draining the morainal 

 lake, conl i not cut its channel lower than about 1230 feet during the 

 life of the Dansville glacial waters, or only some 10 or 20 feet into 



