302 NEW YORK STATE MUSEUM 



several feet., proportions hardly exceeded in Beecher's well known, 

 restoration of the Catskill Stylonurusexcelsior and only 

 surpassed by a great, but little known Pterygotus from the Bertie 

 waterlimes in Herkimer county. 



In the descriptive account -of these fossils, we have indicated an 

 affinity with the fauna of the Pittsford shales of western Xew York 

 which is emphasized by the character of the deposit in which they 

 are involved. It is entirely safe to say that the fauna carries suffi- 

 cient evidence of an historic stage earlier than the predominant 

 Eurypterus fauna of the Bertie or final stage of the Salina. 



The evidence to be drawn from the Arthrophycuslike fossil from 

 this grit as indication of approximation in age to the Medina for- 

 mation of western New York is entirely negligible as its signi- 

 ficance is not material as an index fossil. 



The presence of this crustacean fauna in the Shawangunk 

 deposits thus may be taken as conclusive of the Salina age of the 

 entire series of conglomerates and sandstones. This inference, if 

 substantially grounded, brings us to an enlarged and modified 

 conception of the coastal physiography during the phases of the 

 Salina period. 



The Shawangunk mountains and their extension into the Kitta- 

 tinny range of Xew Jersey lie on the eastern boundary of the 

 Appalachian gulf and their sediments while depositing were 

 embraced in it. 



Referring again to the normal Salina succession in western Xew 

 York, we recognize the introductory, culminant and decadent stages 

 of the Salina sea representing respectively the gradual shoaling- 

 of the shore waters with the formation of bars, brackish lagoons 

 and salt pools, the complete abscission of the waters within the 

 barriers forming a salt lake of saturated brine in which no organism 

 has left a trace, and finally the breaking down of the barriers and 

 restoration of normal marine conditions. 



X^o such consecutive conditions present themselves at the eastern 

 boundary of the gulf during this period. Here rapid deposition 

 was in continuous progress with no further evidence of seclusion 

 from the main gulf waters than is afforded by the presence of these 

 black shale layers and their fauna. We have had occasion else- 

 where in discussing the bathymetric value of bituminous shales, to 

 bring forward the very strong evidence for their formation at 

 great depths, arguments abundantly supported by the writings of 

 others, but it is probably needless to state that certain dark shales 

 not necessarily bituminous carry accessory evidence of deposition 



