124 



PHYSIOGRAPHY 



is sometimes very thick, as already noted. The surface of glacial 

 drift is often marked by hillocks, mounds, and ridges, and by basin- 



Fig. 130. A lateral moraine left by a former glacier in the Bighorn Mountains 

 of Wyoming. (From photo, by Blackwelder.) 



Fig. 131. Sketch of drift (terminal moraine) topography near Hackettstown, 

 N. J. (N. J. Geol. Surv.) 



like or trough-like depressions (Fig. 131). Some of the latter 

 give rise to lakes, ponds, and marshes. The surface of drift 

 is therefore very unlike the surface developed by the erosion of 





