420 NEW YORK STATE MUSEUM 



Considering the great volume of water-laid drift commonly- 

 associated with the New York moraines, amounting in many cases 

 to almost the entire mass, it would seem certain that the drumlins 

 in the same territory, if overridden and reshaped moraines, should 

 frequently if not habitually hold sands and gravels as a part of their 

 mass ; in other words they should have the irregular structure and 

 miscellaneous Composition of the moraines. Indeed it would seem 

 likely that with the volume of deep-sealed waters in the marginal 

 portions of the ice sheet (the streams either subglacial or in deep 

 trenches) aqueous deposits might not infrequently be left beneath 

 the ice in such position as to be incorporated into the drumlin mass. 

 However, as stated above [p. 412], this feature is remarkably rare. 

 Drumlins may be built on other antecedent drift, and stream or lake 

 deposits may occur on their surface, but the drumlin material in the 

 area under discussion is very compact till, and may be distinctly 

 bedded. 



The facts pertaining to the drumlins of New York are only con- 

 sistent with the theory of their constructional origin. And now 

 we have the sufficient proof that at least a great number of them 

 were slowly built up by a plastering-on process, as described above 

 [p. 416]. 



Since we know that the Sodus bay-Oswego drumlins are con- 

 structional it is a legitimate assumption that other drumlins in 

 contiguous areas have the same origin. In the further discussion 

 of the New York drumlins their constructional origin will be 

 assumed.^ 



In the theoretical discussion of the mechanics of drumlin con- 

 struction three sets of factors are recognized : (a) those pertaining to 

 the ice itself, (<^) those relating to the drumlin-forming drift, and {c) 

 the external influences of topography and climate. These will be 

 briefly considered in the above order. 



a Dynamic factors pertaining to the ice body ^ 



1 Vertical pressure^ which is directly proportionate to the vertical 

 thickness of the ice sheet. 



2 Horizontal presswe. At the periphery of the continental" ice 

 sheet the horizontal pressure necessary to produce flow on level 



I Since these lines were written it has been found that sections of drumlins in Oakfield 

 cemetery, Syracuse, exhibit excellent bedding. 



yrnr ^ w i 



