DRUMLINS OF CENTRAL WESTERN NEW YORK 393 



direction are the striking superficial characters ; but along with these 

 elements the composition and subglacial origin must be recog- 

 nized. Omitting reference to the precise manner of their amass- 

 ing, they may be defined as smooth-surfaced hills of till, elongated 

 in the direction of ice movement by the rubbing action of the ice 

 sheet. Or, more briefly, they may be defined as smooth drift hills 

 shaped by ice molding. 



The topographic expression of drumlins is so emphatic that any 

 group with fairly developed forms is readily distinguished on maps 

 in 20 foot contours. Plate 3 affords a comparison of drumlinized 

 drift with other forms of glaciated topography. 



It appears that the molding effect of the overriding ice was not 

 restricted to the drift masses deposited during the rubbing process 

 by the ice itself, but was felt by moraines or even by rock masses 

 which were exposed to the ice rubbing. The latter effect is seen 

 specially along the summits of the rock ridges that were buried under 

 the glacier [^see pi. 10]. The name drumlin can not appropriately 

 be applied to ice-shaped rock masses, though the relationship to 

 drumlins may be evident. The term " drumloid " is fully appropriate 

 but the word has long been used in a rather loose and indefinite way 

 for hills of drift having merely a formal and perhaps accidental 

 resemblance to drumlins. A distinctive term with obvious meaning 

 is desirable, and it is proposed to call these forms Rocdrumlins^ 

 using as a prefix the Celtic word for rock. In the case of ice-worn 

 hills or summits of rock which suggest the drumlin form but do not 

 fully attain it we may use the term rocdrmnloid. 



It should be emphasized that rocdrumlins are an effect of a 

 moderate amount of erosion, or the removal of material, while the 

 drumlins are a product of upbuilding and shaping at the same time 

 [j^(?p. 432] The genetic distinction is important. 



It seems probable that hill summits of rock should receive under 

 favorable conditions a drumloid expression, that is, a roches 

 moutonne form on a large scale. Plate 16 shows quite as good an 

 example as the published topographic sheets of western New York 

 supply, and even this is somewhat equivocal. Eastern New York 

 can probably furnish better examples. However, it may be said 

 that the erosional work of the continental ice sheet was commonly 

 insufficient, at least in western New York, to strongly mold the hill- 

 tops. The absence of such effect is seen in plate 3, figure i. 



