690 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



TOPOGRAPHY. 



. On the east border of Tonawanda Swamp the moraine rises into a stout 

 till ridge 30 to 50 feet in height, which has a well-defined crest and gently 

 undulating surface and is a jjroininent feature for at least 4 miles Its con- 

 tours are to some extent shown on the topographic map, PL III. 



Upon rising to the Corniferous escarpment the moraine breaks up into 

 a series of knolls and short ridges, rather sharp in contour, which inclose 

 basins and winding sloughs. This phase becomes conspicuous at the place 

 where the moraine rises above the level of Lake Warren, though a few 

 knolls and basins appear southwest of Oakfield at a considerably lower 

 level. The northwest side of this till ridge, just discussed, is fully 200 feet 

 below the level of that lake, and is a remarkably strong feature to have 

 been formed in such a depth of water. The contours of the part of this 

 moraine which was formed above the level of Lake Warren are partly 

 brought out by the topographic maps, the course of the moraine being 

 through the northeast part of the Medina quadrangle and the southwest 

 part of the Batavia. It will be observed that the height of the knolls and 

 ridges ranges from 60 feet down to less than 20 feet. Many small knolls 

 less than 10 feet in height are not represented on the maps, and this 

 detracts greatly from their expression. 



The moraine holds its sharp features as far east as the valley of Aliens 

 Creek, near Leroy, but within a few miles east from that creek the sharp 

 knolls change to very small swells and the prominent knolls and ridges 

 present smoother slopes than to the west. The ridges are not so long nor 

 so definite as in the district below the Corniferous escarpment, but they are 

 fully as high. This part of the moraine was also formed in water, for a 

 glacial lake occupied the Grenesee Valley at the time it was forming. 



STEUCTUEE OF THE DEIFT. 



The portion of the Batavia moraine between the Corniferous escarpment 

 and the Tonawanda Swamp contains a large amount of compact till, but 

 the portion on the escarpment carries a loose stony till and also considerable 

 gravel and sand. The gravelly ingredients are more conspicuous from 

 Batavia northwest to the brow of the escarpment than east from that city. 

 The portion of the moraine which stood above the level of Lake Warren 

 carries a large number of svirface bowlders, but bowlders are not a con- 

 spicuous feature on the part formed below the level of the lake. 



