228 E. M. Kvn.dk — Criteria of Continental Deposits. 



fauna could live. Professor Moseley has indicated the destruc- 

 tive nature of wave action on the sea bottom in the following 



words : 



" With respect to enemies, the waves themselves are, perhaps, 

 the most formidable, as they attack and occasionally destroy 

 whole colonies at once, whereas predatory foes rather affect the 

 individual."* 



As an example of an environment which doubtless some of 

 the factors named above made uninhabitable by marine faunas 

 we may cite one of the Carboniferous sandstones. The irregu- 

 larity of the distribution of sea bottom life in the Paleozoic is 

 illustrated in the Riverside sandstone of the "Knobstone" 

 group of Southern Indiana. The most careful search over 

 scores of square miles of outcrops of this formation, over a 

 portion of its area of distribution, will fail to discover a single 

 fossil. In other areas they occur in abundance. In the areas 

 where fossils appear to be entirely wanting in this formation 

 there is a total absence of cross-bedding or any other physical 

 features which might suggest to some a continental origin. 

 Both the fossiliferons and the barren areas are clearly marine 

 beds and afford one of many possible examples of the " absence 

 of fossils in a rock which elsewhere carries them."f 



Another example which may be given of barren beds at a 

 horizon which is abundantly fossiliferons in other areas occurs 

 in central New York. Thus far 80 feet or more of the Gene- 

 see shale of the Oayugan section has failed to yield any fossils 

 tothe most persistent collectors. 



The barren areas of the Paleozoic seas are duplicated in the 

 present seas. They occur along various parts of the present 

 coasts of North America. The writer has traversed several 

 hundred miles of the northwestern and northeastern coasts of 

 the continent in small boats which gave excellent opportunities 

 for observing the contrasts between different areas of the coast 

 with respect to the relative abundance of marine life. On the 

 Alaskan coast contrasts are often abrupt and most striking. 

 Along the beach at Nome one may search for hours without 

 finding a single shell. In that vicinity the writer has scanned 

 the bottom in depths of 6 to 15 feet from the side of a small 

 boat, when the water was exceptionally smooth and favorable 

 for observation, for miles without seeing a single sea shell. 

 Northwest- of Nome 100 miles, however, the abundance of 

 marine life is such that the beach is strewn with thousands of 

 shells. A special effort was made at Nome to secure repre- 

 sentatives of the present marine fauna, but not a single mollus- 



*Else Rectus' New Physical Geograpihy, vol. ii, p. 376. 

 f Jour. Geology, vol. xvii, 1909. 



