850 



GEOLOGY 



it, and (3) the relations of the drift to its bed. Some of the prin- 

 cipal considerations are the following: 1 



1. The constitution of the drift. One of the striking charac- 

 teristics of the drift is its heterogeneity, both physical and lit 1 id- 

 logical. It is made up at one extreme, of huge bowlders (Fig. 562), 

 and at the other of impalpable earthy matter. Between these ex- 



Fig. 562. "Pilot Rock." 



A glacial bowlder near Coule City, Wash. (( iar- 

 rey.) 



tremes there are materials of all sizes, and the proportions of 

 coarse and fine are subject to the greatest variations. Co. 

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

 topography, where the underlying and neighboring formations in 

 the direction from which the drift came are resistant; fine material- 



1 The phenomena pointing to the glacial origin of the drift IKIAT l>rr<>mr 

 so familiar that it is unnecessary to give extended references to the literature 

 of the subject. They were emphasized in many of the early publication* 

 concerning the drift. The striae and other scorings of the ice are elaborated 

 in the 7th Ann. Kept., U. S. Geol. Stirv. The study of the drift fn.m tin- 

 standpoint of genesis is given in the Jour. Geol., Vol. II. pp. 70S 7'J 1 and S07 

 835, and Vol. Ill, pp. 70-97, and in Glacial Geology of \e\v .JeiNi-y. pp. :; 33, 

 The geological Reports of all the states affected, and of Canada, contain de- 

 scriptions of the phenomena. 



