338 



GEOLOGY. 



(1) The constitution of the drift. — One of the striking character- 

 istics of the drift, taken as a whole, is its heterogeneity, both physical 

 and lithological. It is made up, at one extreme, of huge bowlders 

 (Figs. 474 and 475), and at the other of impalpable earthy matter. 

 Between these extremes there are materials of all sizes, and the pro- 

 portions of coarse and fine are subject to the greatest variations. Coarse 

 materials are, on the whole, most abundant in regions of rough topog- 

 raphy where the underlying formations are resistant, and in the le 



Fig. 472. — A section of stratified drift. 



of such situations. Fine materials, on the other hand, are most abun- 

 dant where the underlying formations, and especially the neighbor- 

 ing formations in the direction whence the ice came, are weak. The 



miliar that it is unnecessary to give extended references to the literature of the sub- 

 ject. They were emphasized in many of the early publications concerning the drift, 

 The striae and other scorings of the ice. are elaborated in the 5th Ann. Rept. U. S 

 Geol. Surv. The study of the drift from the standpoint of genesis is given in the 

 Jour of Geol.. Vol. II, pp. 708-724, and 837-851, and Vol. Ill, pp. 70-97, and in 

 Glacial Geology of New Jersey, pp. 3-33. The geological reports of all the states 

 affected and of Canada contain descriptions of the phenomena. 



