682 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



Tonawauda Creek the crest generally stands between 950 and 1,000 feet, 

 while the inner border in places extends down to less than 900 feet. 



TOPORRAPHY. 



Along this moraine there is generally a definite ridging in line with the 

 trend of the moraine. In places two or more parallel ridges appear in close 

 succession, but quite as often there is a single main ridge, on the inner slope 

 of which there may be subordinate ridges. The relief of the ridges seldom 

 exceeds 40 feet, and is generally 30 feet or less. 



The undulations range from low, gentle swells to rather sharp knolls 

 West from the Erie-Genesee county line the crest is in places nearly free 

 from swells, and there are very few sharp knolls; but in Genesee County 

 the surface is generally sharply undulating, with knolls 15 to 30 feet in 

 height, which cover but a few acres each. The knolls are also more closely 

 associated in Genesee than in Erie County. There are only a few well- 

 defined basins, but winding sloughs are common among the knolls. 



There is a small esker situated in this moraine in the northeast part of 

 Darien Township, Genesee County. It is less than a half mile long and 

 only 50 to 75 feet wide, yet it rises generally to a height of fully 15 feet. 

 The trend is nearly north to south, though the esker is slightly winding. 

 It terminates at the south in a small gravel delta, which stands about as high 

 as the crest of the ridge. This delta rises abruptly above low ground on 

 the east, but is continued toward the west in a gravel plain which is at 

 nearly the same level as the delta, and which is probably an outwash 

 from the portion of the ice sheet immediately west of the esker, it being 

 on the south border of the moi-aine. 



STRUCTURE OF THE DRIFT. 



The Marilla moraine carries much less gravel than the Hamburg, there 

 being only an occasional knoll in which gravel is known to occur. The 

 surface of the moraine, both on knolls and in depressions, is a rather clayey 

 till, liberally strewn with bowlders. Large limestone slabs, gathered from 

 the formations which outcrop between this moraine and Lake Ontario, are 

 conspicuous both on the surface and in the midst of the till. Such slabs 

 are rare on moraines oiitside of this one, but are common on those which 

 lie between it and the lake. 



