THE EURYPTERIDA OF NEW YORK Q7 
In describing the geologic occurrence of the fish and eurypterids, 
Chamberlin lays special stress on the abrupt appearance of both groups of 
fossils in the Siluric, heralded by very scanty remains in the preceding 
formations, and gives the following account of the phenomena of their 
distribution in the rocks. : 
In the Ludlow “ bone bed ”’ of England, where they first make their 
appearance in abundance, the fish remains are associated with eurypterids, 
probably the most gigantic crustaceans that have ever lived, some of them 
attaining two meters in length. There is the same association on the 
continent, notably in the island of Oesel in the Russian Baltic and in Podolia 
and Galicia, and so again in the waterlime group of America in which the 
Pteraspis |[Palaeaspis] 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 larger 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 conditions seem to have 
been congenial to the fish and eurypterids but not to a typical marine 
fauna. | 
In the Old Red sandstone 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 meagér 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 pre- 
vailingly 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 congenial conditions 
of life in them. As fishes and eurypterids were found both earlier and 
later in marine deposits the question arises: Were the fishes and euryp- 
tertds primarily marine and later became adapted to fresh water, or were they 
primarily fresh-water jorms which were occasionally carried out to sea, and 
which later became adapted to salt water? The two cases do not necessarily 
