DRUMLINS OF CENTRAL WESTERN NEW YORK 403 



Tonawanda valley. This distribution of the drumlins indicates that 

 altitude and grosser topography are not alone controlling factors in 

 the drumlin formation. 



The most massive development of the drumlins is on the low 

 ground north of the Finger lakes, and chiefly under 500 feet altitude. 

 This great development of the drumlins on the low Ontario plain and 

 their comparative absence on the higher ground facing the ice 

 sheet is most striking in the central and eastern part of the drumlin 

 belt. 



It is important to note that the district of highland drumlins, the 

 western extension of the drumlin area, is where the later ice move- 

 ment and the drumlin direction coincide with the general direction 

 of the main ice movement, that is, toward the southwest ; while the 

 district of no elevated drumlins, east of Seneca valley, is where the 

 drumlin direction is oblique or nearly at right angles to the direction 

 of flow of the thicker ice. 



The production or nonproduction of drumlins is believed to 

 depend in part on the abundance and character of the bottom 

 drift of the ice sheet, but chiefly on the active movement of the 

 bottom ice, due to thrust from the rear. The absence of strong 

 drumlins on the gently ascending slopes between Seneca and 

 Owasco lakes may be partly due to the capacious preglacial val- 

 leys in the area north of the Finger lakes, which served as catch- 

 ment for the lower drift. The absence of any large amount of 

 drift, in the form of either drumlins or moraines, in the belt of 

 open valleys [pi. 2] suggests that the last ice which lay on this 

 territory was comparatively clear of drift. It would seem that the 

 greater burden of drift had been either rafted over the level of the 

 open valleys to the higher valley heads moraine farther south, or 

 was held in the lowest ice, and built into the drumlins farther 

 north. 



As stated above [p 369] the land surface east of Syracuse never 

 felt the rubbing action of the ice sheet The Syracuse district 

 was subjected to the thrust of a tongue of ice pushed southeast- 

 ward from the spreading Ontarian mass. The southeastward and 

 southward flow was not sufficient to reach the land surface over the 

 Oneida lake region nor over the high ground east of Seneca valley. 

 However, the land surface west of the Seneca valley, lying where the 

 latest ice movement was the same as the principal ice movement, 



