4l6 NEW YORK STATE MUSEUM 



west outcrop they have been eroded by weathering and ice rubbing 

 and the belt of outcrop deeply covered with drift. Their more 

 common appearance on the Newark-Syracuse parallel is partly due 

 to greater thickness and also to the postglacial excavation by the ice 

 border drainage. The Salina shales as a whole, many hundreds of 

 feet in thickness throughout the drumlin area, have supplied a large 

 amount of plastic and adhesive material for the drumlin con- 

 struction process, and may be one factor in the production of the 

 drumlins. 



Concentric bedding. If drumlins are constructional forms, 

 that is, were built up by a plastering-on process, then it should be 

 expected that on cross-section they would reveal some concentric 

 bedding or onion structure, with the upper layers parallel to the 

 drumlin surface. Theoretically the bedding need not be con- 

 spicuous as there could not have been great variation in the con- 

 structive process, as compared with the work of water, in either 

 kind or quality of material or in rate of deposition. The com- 

 parative uniformity in the work of the ice, taken in connection 

 with the heterogeneous character of the till, would seem unfavorable 

 to any conspicuous structure. 



Few cuttings in drumlins expose large sectional areas, and such 

 as do occur can commonly be seen only at close range, which is 

 unfavorable to inspection of indefinite and large-scale structures. 

 To recognize the general structure it is necessary to have a com- 

 prehensive view, yet not so distant as to obscure all details. 



Bedded structure in drumlins has been casually noted in a few 

 instances but the only description of such feature (in the writer's 

 knowledge) has been given by Upham, of a few drumlins on the 

 Massachusetts coast at Scituate and in the neighborhood of Boston, 

 which have been dissected by wave erosion. 1 



The most favorable exposure of interior structure of drumlins 

 known to the writer is found along the south shore of Lake Ontario, 

 and specially between Sodus bay and Oswego. In this stretoh of 

 about 28 miles not less than a score of drumlins, many of large size, 

 are dissected to their core by the wave erosion. The constant 

 undercutting by the waves [pi. 3, 43-46] yields continually fresh 

 sections from top to bottom, and fortunately in different directions. 

 Some drumlins are cut in direct cross-section ; some in oblique 



I See titles on page 438 for the years iSSS, 18S9 and 1892. 



