THE PLEISTOCENE OR GLACIAL PERIOD. 339 



fine material of the drift is made up, in large part, of the same mate- 

 rials as the gravel and bowlders, but of these materials in a finer 

 state of subdivision, and often in different proportions. The coarse 

 materials and the fine are often mixed without trace of assortment 

 or arrangement. 



Fig. 473. — A section of unstratified drift — till or bowlder clay, on bed-rock. 



Newark, N. J. 



The drift of any locality is likely to contain rock material from 

 every formation over which the ice which reached that locality had 

 passed; but the larger part of the drift of any place is composed of 

 materials derived from formations near at hand. Probably 75% of 

 the material of the drift has on the average not been moved 50 miles. 1 



No agent except glacial ice can impress these precise features on 



1 The Local Origin of the Drift, Jour, of Geol., Vol. VIII, p. 126. 



