SILURIAN AT WHITE PDTE. 191 



with a heavy bed of quartzite that forms the western central spur of Po- 

 gonip Ridge. As the Hamburg shales are wanting, the Hamburg limestone 

 and the included fauna continue to the base of the Pogouip. Here, as well 

 as at Eureka, the base of the Pogonip is determined by a commingling of 

 Cambrian and Silurian species, the line of demarcation resting wholly upon 

 paleontological evidence. Mr. Walcott examined the beds from the lower 

 quartzite across the Pogonip, Eureka quartzite, and Lone Mountain, until 

 the upper beds of the latter epoch were lost beneath the detritus of the 

 plain. 



The section is as follows: 



NIAGARA. 



Feet. 



1. Yellowish shaly limestone 50 



2. Light colored, massive bedded siliceous limestone, with plates of cri- 



noids, etc 650 



3. Light blue siliceous limestones with impressions of corals, Halysites caten- 



ulatus, Stromatopora f 150 



4. Light gray siliceous limestones 50 



TRENTON. 



5. Evenly bedded pure bluish gray limestones 50 



Fossils: Cystidian plates, Bryozoa 3 sp., Rhynchonella capax, Trinu- 

 cleus concentricus, Streptorkynchus filitexta, Orthis subquadrata, 

 Pterinea. 



6. Dark colored siliceous limestone in massive beds 500 



EUREKA. 



7. Light vitreous quartxite, ferruginous near the base 350 



POGONIF. 



8. Dark blue and black limestones, with numerous shaly belts, characterized 



by the fossils of the Upper Pogonip as seen at Eureka, nearly all the 

 genera being recognized, with the exception of Receptaculites 900 



9. Dark evenly bedded limestones, with more or less siliceous bauds 4, 300 



Fossils: Acrotreta gemma, Ill&nus eurekensis Triplesia calcifera in 

 the lower portion, followed higher up by the siiine forms as found 

 at Eureka east of the Jackson mine and east of Hamburg Eidge. 



