2 Frank Carney 



drift is under way, that is, it has reached an appreciable stage of 

 metamorphism ; furthermore, that this fact may be used in differ- 

 entiating the drifts of some of the Pleistocene epochs. 



In this paper the term "metamorphism" includes all alterations 

 concerned in the transition from degradational products to solid 

 rock again.*' It is not possible to observe many stages in this cycle 

 because of the fact that so far as present investigation goes, the 

 glacial periods are separated by long lapses of time, and because of 

 the further fact that most phases of metamorphism require a 

 physical environment that precludes observation. 



FIELD DATA 



The glacial deposits that occasioned this study are character- 

 ized by the following features : 



1. Color. — All the unmodified drift concerned is bluish; it is 

 felt that this is the constant color of the deposits because the obser- 

 vations were made either along stream banks that were being un- 

 dercut, thus giving fresh exposures, or along shore cliffs where the 

 waves are undermining the drift. In most of the exposures the 

 'color condition is emphasized by contact with drift which differs 

 in color; the usual association is a yellow and sometimes oxidized 

 horizon of more recent glacial accumulation beneath which is the 

 zone of bluish drift. So far as can be ascertained, the color is 

 not dependent upon the content of the drift. The surfaces of the 

 included bowlders, large and small, and the entire matrix of clay, 

 are uniformly of a bluish cast. This characterization applies equally 

 to these deposits in widely separated parts of Ohio as well as 

 throughout a considerable region of central New York. Because 

 of a lithological difference in the rock formations that were eroded, 

 as sho-wn by a study of the bowlders and pebbles in the drift, one 

 would expect some variation in color ; this, however, is not the case. 



2. Texture and strnctitre. — As is the case with nearly all types 

 of glacial deposits, we have here a great variety in texture. The 

 till of some exposures is very fine, and quite free of even small 

 bowlders ; other exposures contain many, and large, erratics. More 

 uniformity in texture, however, is found in the water-laid drift be- 

 longing to this study; usually, it is fine, even silty. 



All these deposits apparently show the eft'ects of great and 

 long-continued pressure. They are dense in structure. This com- 



6C. K. Leith, Journal of Geology, vol. XV (1907), p. 313. 



