76 NEW YORK STATE MUSEUM 



iMississippi. (3) Canisteo-Chemung-Susquehanna. (4) Glacial 

 lakes Warren and Chicago to Mississippi. (5) Mohawk-Hudson 

 (6) Gilbert gulf (sea level waters in Ontario basin). (7) St 

 Lawrence. 



In the present knowledge of the glacial and postglacial history of 

 the Genesee drainage the writer recognizes at least 17 distinct stages 

 or episodes. The first three stages involve only the upper 

 (southern) part of the valley, the Portage district being then under 

 the glacier. The Portage-Mount Morris region is involved in the 

 history of stages 4 to 13. The subsequent stages concern only the 

 valley north of Mount Morris. The history will be given very con- 

 cisely in its relation to the district under present study. 



Stage 4. Belfast-Fillmore lake.^ Outlet was at Cuba, to the 

 Allegheny-Ohio-Mississippi. Present altitude of outlet 1496 feet. 

 Present altitude of the lake plain on the Portage parallel about 1530 

 feet. 



During this stage the ice front receded as far as Portage, and 

 lingering there deposited the Portage moraine which blocks the old 

 valley in that district. South of Portage the valley was occupied by 

 the lake which has left conspicuous evidences of its presence in the 

 many water-leveled plains and terraces in the upper valley, with 

 deltas at the mouths of side streams, having elevations of 1500 feet 

 and upward. 



Stage 5. Portage-Nunda lake. Outlet was by the Dalton-Swains 

 rock gorge to the Canisteo-Chemung-Susquehanna. Altitude of the 

 channel head, at Rosses, 1320 feet. 



This stage endured while the ice front receded from Portage, 

 Hunts and Dalton to Union Corners and Tuscarora, or through 

 about 5 miles of meridional distance. However, the time involved 

 was sufficient to allow the escaping waters to cut the steep rock 

 bluffs south of Hunts and southeast of Dalton and the splendid 

 rock gorge leading through Rosses and Swains to Canaseraga. As 

 an example of an abandoned glacial river channel these features are 

 unusually fine. 



During this stage the Portage district was submerged in the lake 

 waters which by their leveling action produced the level stretches 

 and terraces of sand and gravel at and east of Portage with eleva- 

 tion from 1300 to 1325 feet. The plain at the Erie Railroad viaduct, 

 1325 feet, belongs in this category. The erosion plane of this lake 

 extends up the valley to Belfast, and being lower and nearer the 



• A fuller description of these early stages is printed in Geol. See. Am. Bui. 7:436-43. 



