DRUMLIN STRUCTURE AND ORIGIN 703 



DlSTBIBUTION 



Typical drumlins or drumlin ridges are the most emphatic of a variety of 

 forms produced by the rubbing action of the ground-contact ice under thrustal 

 motion. On the one hand these forms shade off into indefinite flutings or 

 moldings of the drift, and on the other hand are represented by scoured or 

 rounded rock hills (drumloids). The requisite conditions for production of 

 distinct drumlins do not seem to have been commonly fulfilled, as vast areas 

 of glaciated territory seem never to have been subjected to the drumlinizing 

 movement of the ground-contact ice. 



The land surface included in the drumlin area of New York is a belt about 

 35 miles wide, bordering the south side of lake Ontario, and about 140 miles 

 long (from Niagara river to Syracuse), with a total area of about 5,000 square 

 miles. At least half of this area carries numerous well developed drumlins. 

 An eastward extension of the area swings around the east end of lake Ontario 

 as a belt 5 to 10 miles wide, reaching past Watertown into the Saint Lawrence 

 valley. 



The New York drumlin area probably includes not less than 10,000 drumlin 

 crests, of which at least 6,000 are indicated on the topographic sheets. On the 

 216 square miles of the Palmyra quadrangle an actual count shows 955 indi- 

 cated on the map. Probably hundreds of minor ridges are beneath the recog- 

 nition of the contour lines, with 20 feet interval. 



Obientation 



The longer axis of the drumlins indicate the direction of the latest vigorous 

 movement of the ice-sheet in their locality, and their variant directions through- 

 out the New York area prove a radial or spreading flow of the ice-mass during 

 the stage of waning which is represented by the drumlin formation. The 

 angular directions cover nearly a half circle. East of lake Ontario they point 

 east — that is, they were shaped by a movement of the ice from the west. Pass- 

 ing westward around the south side of Ontario the directions of the drumlins 

 gradually shift to southeast, then to south, and in western New York to south- 

 west. 



The axial direction is not always uniform along the same meridian, but 

 records any change in the direction of the ice movement due to the topographic 

 control over the waning edge of the ice-sheet in its different positions. A 

 confirmation of this genetic relation between drumlin attitude and ice-flow 

 direction is found in the Pulaski region. As we pass eastward around Mexico 

 bay we find the direction toward which the drumlins point changes from 

 southeast to east ; but passing on 10 miles to the north we find the drumlins 

 pointing southwest, or at right angles to those near Mexico. These varied 

 directions represent ice-flow movement during successive stages of the waning 

 ice body. 



Relation to Topogbaphy and Rock Stbata 



The most massive development of drumlins is on the low Ontario plain north 

 of the Finger lakes and mainly under 500 feet altitude. They are comparatively 

 absent on the higher ground which faced toward the ice body. This dominant 

 drumlin area is underlain by the Cayugan (Salina), Niagaran, and Oswegan 



LXIII — Bull. Geol. Soc. Am., Vol. 17, 1905 



