402 T. C. CHAMBERLIN 



and so again in the Waterlime group of America in which the 

 Pteraspis Americana of Claypole occurs. The physical conditions 

 in all these cases seem to have been peculiar, and in the case of 

 the Waterlime group they were singularly so, for they permitted 

 a host of these large Eurypterids and other Crustaceans to flourish 

 in seeming luxuriance, while only a meager and pauperate marine 

 fauna found an occasional entrance into the series. The con- 

 ditions seem to have been congenial to the fish and Eurypterids 

 but not to a typical marine fauna. 



In the Old Red Sandstone phase of the Devonian both in 

 Europe and America a similar association obtained. A most 

 extraordinary group of fishes and a family of most gigantic 

 Crustaceans flourished where marine life found only an occasional 

 and meager presence. These few marine forms, here and there 

 in a massive deposit, no more imply prevalent salt water than 

 the present marine species in the -Bay of San Francisco imply 

 that the gravels, sands and silts of the valley of California and 

 of the Great Basin, which seem to be analogues of the Old Red 

 Sandstone, are prevailingly marine. The further association of 

 the fishes and Eurypterids with land plants and fresh water 

 mollusks, together with a total absence of marine relics from the 

 same beds, leaves no solid ground for hesitating to accept the 

 dominant view of English and other geologists that the typical 

 Old Red Sandstone and its homologues are the deposits of fresh 

 waters and that both the fishes and the Eurypterids found con- 

 genial conditions of life in them. As fishes and Eurypterids 

 were found both earlier and later in marine deposits the question 

 arises : Were the fishes a?id Eurypterids primarily marine a?id later 

 became adapted to fresh water, or were they primarily fresh-water 

 forms which were occasionally carried out to sea, a?id which later 

 became adapted to salt water? The two cases do not necessarily 

 require an identical answer, but the singular association of the 

 two in unusual display under peculiar conditions and on both 

 continents strongly implies a community of habit, at least at the 

 stages in question. The association is one of the most unique 

 faunal and physical combinations of geologic history. 



