THE PLEISTOCENE OR GLACIAL PERIOD. 367 



tendency for the surface debris to be clumped at the edge along a defi- 

 nite line. Locally, where the debris clumped was mainly bowlders, 

 a wall-like riclge (Geschiebewall) was developed in such a position. 

 Such bowlder-walls have received little emphasis in America, although 

 they are known to exist at various points. 



The ridges and mounds of debris brought to the surface of the ice 

 near its edge by the upturning layers (Fig. 271, Vol. I) may be a fur- 

 ther, though very subordinate, element in the development of terminal 

 moraine topography. 1 



Where an ice-sheet or a glacier halted in its retreat, its edge or 

 end remaining in a constant or nearly constant position for a suffi- 

 ciently long period, a terminal moraine was developed. Such a ter- 

 minal moraine is often called a recessional moraine. Some caution 

 is needful in the use of this term lest it be the occasion of misinter- 

 pretation. While formed in a general time of retreat, some of these 

 later moraines represent appreciable advances, while others appa- 

 rently represent halts merely, and some may possibly signify only 

 an unusually slow rate of recession, by reason of which a deeper accu- 

 mulation of drift took place. The not uncommon impression that a 

 terminal moraine is one which, by its very name, marks the terminus 

 of the drift, is fundamentally erroneous and very objectionable, since 

 the word terminal merely relates to the terminus of the ice which formed 

 the moraine, and is contrasted with medial and lateral. It has no 

 relation to the stage of advancement or of retreat of the terminus 

 of the ice. No one moraine marks the border of the drift throughout 

 its entire extent, and confusion arises from the attempt to substitute 

 the border of the drift, for the edge of the ice, in the significance of the 

 word terminal. 2 



1 Jour, of Geol., Vol. IV, 1896, pp. 793-800. 



2 References on terminal moraines: Whittlesey, Smiths. Contr., 1866; Dawson, 

 G. M., Q. J. G. S., Nov. 1875, p. 614; Chamberlin, Trans. Wis. Acad. Sci., Vol. IV, 

 (1876-7), pp. 201-234, Proc. Int. Cong. Geologists, Paris, 1878, Third Ann. Rept. 

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

 pp. 93-97; Irving, Wis. Geol. Surv., Vol. II (1877), pp. 615-634; Cook and Smock, 

 New Jersey Geol. Surv., 1876-7, and 1877-8; Hitchcock, N. H. Geol. Surv., Vol. Ill 

 (1878), pp. 218, 230-236, 246, 301-5, 337; Upham, Amer. Jour. Sci., 1879, pp. 81-92, 

 197-209, Minn. Geol. Surv., Vol. I (1884), Can. Geol. Sun-., Vol. IV, 1889, pp. 44-5 E, 

 Proc. Amer. Assoc. Adv. Sci., Vol. XXXII (1883 ), pp. 213, 232, and Rept. Minn. 

 Geol. Surv., 1880, pp. 281-356; Sweet, Wis. Geol. Surv., Vol. Ill (1880), p. 384; 

 White, I. C, Penn. Geol. Surv., 1880, p. 26; W T inchell, N. H., Ohio Geol. Surv., Vol. II. 



