628 THE PLEISTOCENE PERIOD 



in some parts of New England, and in some other places. The 

 drumlins of New York are, in general, longer and narrower than 

 those of Wisconsin. 



The origin of drumlins has been much much discussed. Opinion 

 is divided chiefly between the views (i) 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. 1 



A terminal moraine (p. 149) may be very like the adjacent ground 

 moraine in constitution, though in many places there is more strati- 



Fig. 520. A Wisconsin drumlin seen from the side; two miles north of Sullivan. 

 (Alden, U. S. Geol. Surv.) 



fied drift associated with it. It commonly constitutes something of 

 a 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, as a rule, characterized by hillocks and hollows, or 

 by interrupted ridges and troughs (Figs. 168 and 514). Many 

 of the hollows and troughs contain marshes, ponds, and lakes. The 

 shape and abundance of round and roundish hills, and of ?hort 

 and more or less serpentine ridges closely huddled together, have 

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

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



1 Some of the more important papers on drumlins are: Upham, Proc. Bos. 

 Soc. Nat. Hist., 1879, pp. 220-234, ibid., Vol. XXIV (1889), pp. 228-242; Chamber- 

 lin, Third Ann. Kept., U. S. Geol. Surv., 1883, p. 306, and Jour. Geol., Vol. I, 

 pp. 255-267; Davis, Am. Jour. Sci., Vol. XXVIII (1884), pp. 407-416; Salisbury, 

 Glacial Geology of New Jersey, 1902; Lincoln, Am. Jour. Sci., Vol. XLIV (1892), 

 pp. 293-296; Tyrrell, Bull. Geol. Soc. Am., Vol. I (1890), p. 402; Leverett, Monogrs. 

 XXXVIII and XLI, U. S. Geol. Surv., and Russell, Amer. Geol., Vol. XXXV 

 (1905), p. 177. 



