866 GEOLOGY 



York, in some parts of New England, 1 and in some other places. 

 The drumlins of New York (Fig. 577) are, in general, longer and 

 narrower than those of Wisconsin. 



The origin of drumlins has been much discussed without reach- 

 ing a final conclusion. Opinion is chiefly divided between the 

 views (1) that they were accumulated beneath the ice under special 

 conditions, and (2) that they were developed by the erosion (by 

 the ice) of earlier aggregations of drift. 2 



A terminal moraine is made where the edge of the ice remains 

 nearly stationary in position for a considerable period of time. In 

 constitution, it may be very like the adjacent ground moraine, 

 though there is often a larger proportion of stratified drift asso- 

 ciated with it. It sometimes constitutes a more or less well-defined 

 ridge, but it is more accurately characterized as a belt of thick 

 drift. Its most distinctive feature does not lie in its importance 

 as a topographic feature, but in the details of its own topography. 

 Its surface is often characterized by hillocks and hollows, or by 

 interrupted ridges and troughs, following one another in rapid 

 succession, and without apparent order (Figs. 227,228, and 570). 

 Many of the hollows and troughs contain marshes, ponds, and la! 

 The shape and abundance of round and roundish hills, and of short 

 and more or less serpentine ridges, often closely huddled together, 

 have locally given rise to such descriptive names as "knobs," 

 "short hills," etc.; but it is the association of "knobs" or "short 

 hills" with " kettles," and not either feature alone, which is especially 

 characteristic of terminal moraine topography. 



The "knobs" vary in size, from low mounds but a few feet 

 across, to considerable hills half a mile or more in diameter, and a 



1 For the topography of the drumlins, see the following topographic 

 sheets U.S. Geol. Surv.: Wisconsin: Sun Prairie, Watertown, and Waterloo. 

 New York: Oswego, Palmyra, Clyde, Brockport, ami Wri-dsport ; MM 

 chusetts: Boston. 



2 Some of the more important papers on drumlins arc: T'ph:im. IW. 

 Bos. Soc. Nat. Hist., 1879, pp. 220-234, ibid., Vol. XXIV (1SS<M. pp. 228 2 !J 

 Chamberlin, Third Ann. Kept., U. S. Geol. Surv., iss:;. ,. :{()<>, and -lour. 

 Geol., Vol. I, pp. 255-267; Davis, Am. Jour. Sci., Vol. XXVIII (issh. pp. 

 407-416: Salisbury, Glacial Geology of New Jersey. I'.MVJ: Lincoln. Am. 

 Jour. Sci., Vol.XLIV (1802), pp.29:; -29ii: Tvm-11, Bull. ( J.-ol. Soo. Am.. Vol. 

 I C1890) p 402; Leverett, Monogrs. XXXVIII and XLI, U. S. Geol. Surv , 

 and Russell, Amer. Geol., Vol. XXXV (1905), p. 177. 



