658 GLACIAL FORMATIONS OF ERIE AND OHIO BASINS. 



but drops to less tlian 1,400 feet on the borders of the main Cattaraugus 

 Valley. 



In the portion which follows the divide north of Cattaraugus Creek the 

 altitude ranges between 1,400 and 1,800 feet in crossing the sags and 

 ridges, there being a variation similar to that in the portion between Lake 

 Chautauqua and the Conewango Valley. As this district has not been 

 covered by the topographic survey, only general statements can be made. 

 Near the head of Cattaraugus Creek, in the interlobate belt, a still greater 

 altitude is attained, some points being nearly 2,000 feet. 



Between the interlobate belt and the Grenesee the moraine descends 

 several hundred feet, the altitude in the vicinity of Portage Falls being 

 between 1,150 and 1,350 feet. The original level of the crest of the moraine 

 in the Genesee seems to have been fully 1,300 feet. 



From the data just given it seems probable that the ice sheet had 

 greater thickness in the eastern portion of the Lake Erie Basin at the time 

 it was forming this morainic system than in the central or western portions. 

 This seems due to its having had at that time an axial movement westward 

 into the Lake Erie Basin. The eastern portion, being nearer the center 

 of dispersion, would naturally carry a thicker sheet of ice than the more 

 remote western portion. 



It may not be possible to compute the thickness definitely, but a rude 

 approximation may perhaps be reached by considering the altitude and 

 position of the moraine. The moraine-covered hill near Arkwright, 1,740 

 feet above tide, is but 3 miles distant fi-om the base of the steep escarpment, 

 which stands 900 feet lower, or only 840 feet, but 7 miles distant from 

 the shore of Lake Erie at Dunkirk, where the altitude of the lake bed is 

 less than 670 feet, and 24 miles distant from the axis or deepest part of the 

 Lake Erie Basin, where the altitude is only 380 feet. Were the ice sheet 

 no higher in the midst of the lake basin than this moraine-covered hill, 

 its thickness opposite Arkwright and Dunkirk would have been nearly 

 1,400 feet. But it is probable that the ice margin rose considerably above 

 this moraine-covered hill, and that there was a gradual ascent from the 

 margin northward to the midst of the lake basin. The thickness of the ice 

 sheet, probably reached fully 2,000 feet in the midst of the lake basin 

 nor:th of Dunkirk. If the ice sheet had had a similar thickness opposite 

 the north end of the Grand River Basin, there should have been a decided 



