50 GEOLOGY OF THE EUEEKA DISTRICT. 



all the characteristic Cambrian fauna have passed away and genera equiv- 

 alent to the Chazy horizon of New York have taken their place, and near 

 the top a grouping of fossils comes in strongly indicating the Trenton hori- 

 zon. In the collections made from the Pogonip beds at Eureka, nearly 

 eighty species have been determined, a large proportion of them forms 

 found for the first time either at Eureka or White Pine, while many of 

 them are common to both localities and from the same stratigraphies! posi- 

 tion in the beds. Many of them are identical with species found in New 

 York and Canada and along the Atlantic border. 



Fifteen species comprise all those forms which have been recognized 

 as common to both the Cambrian period, and Pogonip epoch of the Silu- 

 rian, and several of these present a wide vertical range extending downward 

 to the summit of the Prospect Mountain limestone. 



The list is as follows: 



Lingnlepis maera. Agnostus neon. 



Lingulepis minuta. Ptychoparia affinis. 



Lingula manticula. Ptychoparia oweni. 



Obolella discoidea. Ptychoparia granulosus. 



Acrotreta gemma. Ptychoparia haguei. 



Leptajna melita. Ptychoparia unisulcatus. 



Agnostus conununis. Arethusina americaua. 

 Agnostus bidens. 



Only two species of the genus Dicellocephalus have been recognized as 

 yet in the Pogonip group at Eureka, D. finalis and D. inexpectans, both new 

 to science. They occur associated together several hundred feet above the 

 base, at a horizon where many of the Cambrian species have already dis- 

 appeared. Of the genus Dicellocephalus only two species are known from 

 the corresponding beds at White Pine. Near the base of the Pogonip in a 

 limestone northeast of Adams Hill, a decided mingling of both Cambrian 

 and Silurian occur, as seen by the following list: 



Lingulepis maera. Agnostus neon. 



Obolella discoidea. Ptychoparia (Euloma) affinis. 



Acrotreta gemma. Ptychoparia oweni. 



Leptsena melita. Ptychoparia haguei. 



Triplesia calcifera. Ptychoparia unisulcatus. 



Hyolithes vauuxemi. Illsenurus eurekeusis, 

 Asaphu.s caribouensis. 



