494 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



southwest, a distance of about 200 miles, and from bottom to top, a thick- 

 ness of 1,900 feet in the center and with all the oblique layers pointing 

 to the northwest. Such a type of cross-bedding has never yet been ob- 

 served on the seashore, nor is it conceivable how such a type can be 

 formed in subaqueous deposits. This cross-bedding is, however, exactly 

 the type which would be be formed if the deposit in question were formed 

 by torrential rivers. 



Eighth. The shale layers. These might, of course, also occur in marine 

 beds. 



Xinth. The character of the overlap of the strata which is away from 

 the source of supply. An overlap away from the source of supply may 





Figure 11. 



-Diagram showing the Relationship of a Seashore Delta of coarse Clasties 

 and the replacing Overlap 



occur in subaqueous delta deposits, but it would invariably be a replacing 

 one — that is to say, while the coarse river-borne detritus is deposited on 

 the shore other purely marine deposits are forming farther away. Now. 

 the base of the series is open for examination for a length of nearly 200 

 miles, and in no case is there any finer, purely marine deposit replacing 

 the lower coarser detrital beds away from the center. If the deposits 

 were forming in the sea and gradually spreading out, their relationship 



Figure 1: 



-Diagram showing Diameter and Overlap of a stihacrial delta Fan 



to the underlying rocks should be as shown in the following diagram 

 (figure 11), whereas the actual relationship is as shown in figure 12, the 

 successively overlapping clastic beds resting directly on the old erosion 

 surface. 



Tenth. The absence of undoubted marine fossils. 



The argument from contemporary salt deposits and from the occur- 

 rence of Eurypterids. — There are, then, none of the lithic and structural 

 characters known to be possessed by the Shawangunk which are not also 



