CLASSIFICATION OF ARKOSE DEPOSITS 449 



conditions. But even if the premises of this classification should 

 be seriously disputed, it still remains a fact that most formations 

 lying unconformably on a former granitic terrane have arkose at 

 or near the base, and there seems to be a more or less general rule 

 that, whenever a period of deposition is inaugurated over a granitic 

 terrane, arkose is the first or one of the first deposits to be laid down, 

 whatever the prevailing conditions. This basal arkose commonly 

 shows but slight effects of wear and is apparently near the point 

 of origin of its constituent material. At higher horizons, there 

 often is yet other arkose, in most cases showing more signs of wear 

 and apparently having been transported for a greater distance; 

 and in still other cases, as has been noted, arkose composes the whole 

 of a formation, thousands of feet in thickness. The deposits are 

 of such differing types and have such different associations with 

 coal measures, with mud-cracked red beds, with beds containing 

 faceted pebbles, and with beds carrying marine fossils, that the old 

 conception of the limited significance of arkose is manifestly 

 incorrect, and arkose must be significant of several types of 

 conditions. 



