630 



THE PLEISTOCENE PERIOD 



rods, or even furlongs in diameter. They may be so shallow that 

 the sagging at the center is hardly seen, or they may be scores of 

 feet in depth. Where steep-sided depressions are closely associated 

 with abrupt hillocks, the topography is notably rough. The topog- 

 raphy of the terminal moraine may be well developed, even where 

 the moraine as a whole does not constitute much of a ridge. 1 



The surface of the terminal moraine, where well developed, is 

 generally rougher than that of the ground moraine, but because the 



Fig. 522. Topography of drift shown in contours; an area near Minneapolis, 

 Minn. Scale about one inch to the mile. (U. S. Geol. Surv.) 



sags and swells are of smaller area and steeper slopes, rather than 

 because the relief is notably more. It is not to be understood, 

 however, that the topography described affects all terminal mo- 

 raines, or that it is confined strictly to them. The elevations and 

 depressions of terminal moraines grade from strength to weakness, 

 and locally even disappear, while the features characteristic of ter- 

 minal moraines are found, now and then, in other parts of the drift, 



1 References to papers on terminal moraines: Chamberlin, Third Ann. Rept., 

 U. S. Geol. Surv., 1881-2, pp. 291-402, and Amer. Jour. Sci., Vol. XXIV (1882), 

 pp. 93-97; Salisbury, Glacial Geology of New Jersey, pp. 92-100 and 231-260. 



