290 TEE ICE AGE IN NORTH AMERICA. 



made at the same time,* namely, that these hills perhaps 

 represent an earlier moraine than that on the sooth shore of 

 .New England — i. e., one which was formed when, on the first 

 advance of the ice, it had reached the latitude of Boston, and 

 where for some reason it paused until great accumulations 

 had taken place along its front ; that afterward, upon a fresh 

 advance, these accumulations were overrun bj the ice with- 

 out being leveled ; being merely sculptured by it, and read- 

 justed to the changing line of general movement; and that, 

 finally, the retreat of the ice was so rapid over this region 

 that there were no marked terminal accumulations ; but the 

 superglacial debris settled gently over the whole country, 

 constituting the more highly colored superficial blanket of 

 debris called by Hitchcock " upper till," and furnishing the 

 larger and more angular bowlders characteristic of the super- 

 ficial deposits. I find also that Professor Charles Hitchcock 

 had made the same suggestion as early as 1876.f 



The long discussion concerning the origin of these singu- 

 lar hills would seem to have been brought to a close by the 

 careful summary and discussion of facts given by Professor 

 Davis, from which we have already quoted : 



The first clear reference to drumlins, as directly dependent 

 on glacial action for their form, was made by M. H. Close. J 

 They are here said to be parallel to the neighboring striae, and 

 hence, like these, dependent on the ice-sheet for their present 

 attitude and form. The same conclusion is presented in a 

 paper of 1866, when the name drumlin was first specially pro- 

 posed for them. Still later, when describing the physical 

 geography of the neighborhood of Dublin, Close writes, "It 

 is perfectly certain that it must have been the rock-scoring 

 agent which produced the bowlder-clay ridges." Besides this, 

 Kinnahan and Close, in a pamphlet of 1872, stated their opin- 



* "Proceedings of the Boston Society of Natural History," vol. xx, p. 218; 

 also, " Prehistoric Andover," p. 4. 



+ Ibid., vol. xix, p. 66. Professor N". S. Shaler now favors this view ; see the 

 "Seventh Annual Report of the United States Geological Survey," 1888, p. 821. 



\ "Journal of the Royal Geological Society of Ireland," vol. i, 1864, p. 3. 



