4 PALEONTOLOGY OF THE EUEEKA DISTRICT. 



Lower Trenton and indicating an horizon that is considered to be in a 

 measure the equivalent of that of the Chazy formation of New York and 

 Canada. The fauna of the lower portion of the Pogonip Group corre- 

 sponds in the same manner to that of the Calciferous sand-rock of the same 

 region. The large number of individuals of the species of Receptaculites, 

 E. mammillaris especially, gives the fauna of the upper beds a character 

 that this horizon has not hitherto had. This, united with several of the 

 Trenton species, viz, Orthis testudinaria, 0. tricenaria, 0. perveta, Tellinomya 

 contracta, two species of Modiolopsis allied to Trenton forms, and Eaphis- 

 toma Nasoni, strongly foreshadows the opening of the Trenton period. 



The fauna between that of the Pogonip and the Devonian horizon is 

 so meager that the only reference made to it is in the systematic list and in 

 the lists of the geologic report (Geology of the Eureka District). As the 

 determination of a higher Silurian horizon than that of the Trenton-like 

 fauna in the limestone above the quartzite capping the Pogonip Group 

 rested mainly on the presence of the genus Halysites, the opinion of Prof. 

 James Hall was requested as to the generic relations of the specimens that 

 had been referred to Halysites in the field. While he did not say positively 

 that the form represented was Halysites, he expressed the opinion that it 

 was of organic origin, and that he knew of nothing else but Halysites to 

 which it could be referred. This conclusion has since been fully proven by 

 the discovery of fine specimens of Halysites catenulatus at the same horizon 

 in the White Pine District, Nevada, associated with specimens in a similar 

 state of preservation as those from Lone Mountain. 



The fauna of the Devonian is large and representative, notwithstand- 

 ing some species have reversed their relative position in the group as they 

 have been known heretofore, and others have a greater vertical range. 

 Among the brachiopods, Orthis Tulliensis, of the Tully limestone of New 

 York State, is found at the summit of the Devonian limestone, and Orthis 

 impressa, a Chemung species of New York, at the base, associated with 

 eastern Upper Helderberg limestone species; and a variety of Atrypa reti- 

 cularis, characteristic of the Niagara limestone, and unknown heretofore 

 elsewhere, occurs with the former in the upper beds. Among the corals, 

 Cladopora pulchra, Syrmgopora Hisingeri, and Cyaihophyllum corniculum, of 



