DISTRIBUTION AND OCCURRENCE OF EURYPTERIDS 521 



a shallow homohaline epicontinental body, has an average salinity of 11 

 permille, but in the northeast, where fresh-water streams enter the basin, 

 the salinity may be as low as 7 permille. Seasonal variations is shown in 

 the Adriatic, where in the spring, when the land waters pour in abun- 

 dantly, the salinity sinks to 18 or even 16 permille in the neighborhood 

 of the land, while in the winter the salinity is 38 permille even at the 

 mouths of streams.* 



It can not be doubted that the great deposits of clastic sediments seen 

 in the Shawangunk formation implies a great influx of fresh water from 

 the land. If the late Magaran or early Salina Sea was restricted into a 

 lagoon-like body, as is generally conceded, this body must at times have 

 suffered extensive reduction in salinity even to complete freshening. 

 Certainly if this sea was at any time cut off from the ocean, it must have 

 been converted into a fresh-water lake, in which the Eurypterids may 

 have flourished. Without, therefore, attributing to these creatures ex- 

 cessive euryhalinity, we may conceive of their having nourished in abun- 

 dance in the early Salina basins, which, however, if they were cut off 

 from the sea, must have been fresh-water lakes as long as the great land 

 streams poured into them. Increased aridity, brought about by a rising 

 in the land on the east, would dry the streams near their headwaters or 

 cause them to dwindle away after the manner of modern streams in arid 

 regions. The fresh-water lakes would then suffer desiccation and finally 

 be replaced by salinas, in which no life could flourish. The remarkable 

 fauna associated with the Eurypterids in the Pittsford shales might well 

 be taken as indicative of fresh-water lake conditions, while the inter- 

 calated marine layers may be taken as indicating periodic destruction of 

 the barrier and incursion of the sea, with consequent extermination of 

 the rich lacustrine fauna. 



We must now turn to a consideration of the rich Eurypterid faunas of 

 the Bertie water-lime. From their finely preserved state, one is tempted 

 to hold that this was the region where these organisms flourished. In- 

 deed, Clarke and Euedemann expressly consider that the two "pools" of 

 New York — the Buffalo and Herkimer pools — constituted the area of ex- 

 treme development of these creatures, the latter being especially character- 

 ized as the breeding area of these types. We may approach the discussion 

 of this problem from the side of the organisms themselves, scrutinizing 

 the remains and the other organic contents of the rock in an attempt to 

 solve their bionomic conditions of existence, and again we may approach 



* For further details, see Principles of Stratigraphy, chapter lv. 



