OUTLET OF WARREN TRIBUTARY LAKE. 443 



found leading down the slope into the Tonawanda valley, but narrow, 

 steep channels occur in the shales. The latter decompose rapidly under 

 atmospheric agencies, and the ancient channel has probably been cut and 

 obscured by later erosion. 



In the region of East Bethany the ground consists of broad stretches 

 of level silts or sand plains, apparently spread out by lacustrine waters. 



North of the East Bethany channel is a low east and west ridge of 

 irregular and morainic character, which apparently marks the location of 

 the ice-front during the time the East Bethany channel was effective- 

 Between that ridge and Batavia, four miles northwestward, the drift sur- 

 face is shaped into east and west forms, at least partially due to the 

 erosion by water currents subsequent to the ice occupation. The alti- 

 tudes of the scourways are from 950 feet down to 900 feet near Batavia. 



The broad plain of sand and gravel on which Batavia lies, with an 

 altitude of 890 feet, is probably the effect of the leveling of the kame 

 and moraine drift by these lake waters during the close of the seventh 

 stage. The ice-front was then north of Batavia and the seventh-stage 

 waters had blended with the local Attica lake which occupied the Tona- 

 wanda valley. This episode was probably contemporary with the last 

 phase of the ice-dam holding the Warren waters in check west of 

 Batavia.* 



The altitude of the blended Genesee and Tonawanda waters, which 

 was not far above 900 feet, was determined by the height of some hypo- 

 thetical channels over the western border of the Tonawanda valley into 

 the Warren waters, which latter waters lay only a few miles to the west 

 at an altitude of 860 feet. 



Water-leveU. — The water-levels of this stage have not been closely stud- 

 ied. Various planes with altitudes from 1,200 down to 900 feet may 

 probably be correlated with this episode. 



The western and southern limits of the lake were not very different 

 from those of the preceding stage. The eastern and northern limits are 

 unknown, being dependent upon the position of the edge of the ice-sheet. 



EIGHTH STAGE: WARREN WATERS. 



Outlet by Chicago to the Mississippi. 



During the time covered by the lacustrine history of the Genesee valley 

 as described above other glacial lakes were formed on the north slope of 

 the continental divide both east and west of the Genesee valley. The 

 greatest of all the glacial lakes in the Laurentian basin was lake Warren, 

 which had its outlet past the site of Chicago to the Mississippi drainage, 



*See article by Mr Frank Leverett on "Correlation of New York Moraines with Raised Beaches 

 of Lake Erie," Amer. Jour. Sei., vol. 1, July, 1895, pp. 1-2U. 



