340 THE EEGOLITH 



under conditions widely variable. Following Professor Salis- 

 bury^ and others, we may, according to its physical charac- 

 ters and method of deposition, separate the deposits into 

 two general groups: (1) the stratified or assorted drift,^ and 

 (2) the unstratified or unassorted, the first having been laid 

 down under the influence of water and hence showing a more 

 or less stratified condition, while the second, deposited directly 

 from the ice, consists of a heterogeneous aggregate of coarse and 

 fine materials without evident marks of stratification. The two 

 forms are not always readily separable nor is their relative posi- 

 tion always the same, either one occurring uppermost, and '^not 

 rarely they alternate with each other several times between the 

 surface and the bottom of the drift. ' ' 



A large part of the drift is composed of this unstratified and 

 unassorted material, consisting of clay, sand, gravel, and boulders 

 in ever- varying proportions, to which the name fill or boulder 

 clay is commonly applied, or from its mode of deposition, 

 that of ground moraine. As already noted, it is the material 

 carried along beneath the ice sheet and left in the position it now 

 occupies on its final retreat. This, entirely unmodified except 

 upon the immediate surface where it has become converted into 

 soil through the agencies elsewhere described, forms the regolith 

 over large areas of the northeastern portion of America and of 

 northern Europe as well. Where as yet unaffected by oxidation, 

 it is of a gray or blue-gray color, and often so intensely tough and 

 hard as to necessitate, in process of excavation, recourse to blast- 

 ing. The upper portion, through percolation of meteoric waters, 

 is as a rule of a buff or brownish color, owing to oxidation of the 

 ferruginous constituents. Through the combined agencies of 

 this oxidation, of plant and animal life and of cultivation, 

 considerable contrasts in both physical and chemical properties 

 are brought about between the superficial and deeper-lying 

 portion, which are commonly recognized by the terms soil and 

 subsoil respectively applied to them, though originally they 

 may have been one and the same thing. The composition of 

 this till naturally varies with the character of the rocks from 

 whence it was derived. It may have, and indeed probably has, 

 in most eases travelled but a short distance, and its constituent 

 particles may be the same as that of the rocks which it overlies, 



^Ann. Eep. State Geologists of New Jersey, 1891. 



* Here included in large part with the aqueo-glaeial deposits. 



