THE EURYPTERUS SHALES OF THE SHAWANGUNK 

 MOUNTAINS IN EASTERN NEW YORK 



JOHN M. CLARKE 



In the recent efforts to correlate the stratigraphy of the Paleo- 

 zoic rocks of eastern New York with the more lucid succession 

 in the central and western portions of the State, the present view- 

 point indicates some unsettling of long recognized values which 

 have been ascribed to the formational units of the former. 



In eastern New York we have to deal with paleogeographic 

 conditions which were doubtless diverse from those further west 

 in the old open Paleozoic gulf and until the recognition of the 

 difference in these conditions no trustworthy correlation could 

 be approximated. 



Briefly summarized for our present purpose, these old physi- 

 ographic differences are evinced first by the existence of an iso- 

 lated tongue of late Siluric and early Devonic deposits beginning 

 at Skunnemunk mountain in Orange county and running south- 

 westward into New Jersey, the Skunnemmik basin as it has been 

 termed by Ulrich and Schuchert. For this area which has been 

 carefully studied by several geologists we must employ the term 

 basin with reserve as it is an area of very steep dips, at the north 

 separated from the more western band of the same formations 

 by a broad area of the " Hudson River " (Lorraine, Utica and 

 Trenton) shales, and at the south by the crystallines and intru- 

 sives of the protaxis. There are many excellent reasons to regard 

 this area as the eastward branch of a broadened anticline whose 

 decapitation has exposed both the Lower Siluric beds and the 

 crystallines, and its actual present outcrops may eventually be 

 shown to merge toward the north in the vicinity of Kingston with 

 the parallel western band of contemporaneous deposits. This is 

 a point requiring more refined investigation. The other factor 

 in this divergence of physical conditions is the fairly demonstrated 

 existence in the early Paleozoic of a rising barrier at the head of the 

 Appalachian gulf, occupying the present site of the Llelderberg 

 mountain and forcing deposition at as early a period as the late 



