WATERLIME GROUP. 385 



GEOLOGICAL POSITION AND GEOGRAPHICAL DISTRIBUTION OF THE 

 AMERICAN SPECIES OF EURYPTERUS. 



• 



The true geological position of the rocks containing Eurypteeus in this 

 country is well determined in the series ; and in order to present its 

 relations the more clearly, I give below the names of several groups in 

 their order, that the sequence may be seen without referring to any other 

 table of formations. 



Hamilton group. -i 



Upper Helderbero limestoneb, \ DEVONIAN; 



including Schoharie grit. J 



Caudaoalli grit. 



oriskanr sandstone. 



Upper Pentamerus limestone. 



Encrinal limestone. 



Shalt limestone. 



Lower Pentamerus limestone. 



Stromatopora limestone. 



Tentaculite limestone. 



These constitute the limestones of the 

 LOWER HELDERBERG GROUP. 



A aingle small carapace of a Eurypterus is 

 known from the Tentaculite limestone. 



Wa-tvbitmv mtnjjv iVoiltian of E. remipea, E.lacuatris and othori, 



WATERLIME GROUP J with Pterygotut and Ceratiocaris. 



ONOJiDAGA-SAtT GROUP. 



Niagara group. 



This series is found full and unbroken in the central part of the State 

 of New- York, as in Oneida county, where the Eurypterus beds containing 

 £. rentipes, etc. are easily traceable passing beneath the Tentaculite lime- 

 stone ; while in "Western New- York, and in the locality where E. lacustris 

 occurs, the strata of the Lower Helderberg group are absent, and the 

 beds bearing these fossils, together -W^ith Pterygotus and Ceratiocaris, pass 

 directly beneath the limestones of the Upper Helderberg group which 

 contain the remains of fishes. In the absence, therefore, of that very im- 

 portant group of strata, the Lower Helderberg limestones, the Eurypterus 

 might seem to belong to the uppermost Silurian rocks of our country ; 

 while in fact, where the series is complete, the position of these fossils 

 is beneath a well-marked and persistent gi'oup having intimate relations 



[ PALiEONTOLOOy III. J 49 



