160 THE CAMBRIAN. [dull. 81. 



except that in the region of Twin Peaks are some phlogopite schists and siliceous 

 zones carrying considerable muscovite. The phlogopite members recur in the Egan 

 Canon region. The prevailing colors of this member are gray, greenish gray, drab, 

 and pale brown ; never dark colors. Conformably overlying it are 2,500 to 3,000 leet 

 of cream-color and salmon- color and white quartzites and quartzo-feldsites. Occa- 

 sional sheets of conglomerate are seen in the quartzites not far below the summit of 

 the Cambrian. 1 



The details of the Cottonwood Canon section to this point have not 

 been quoted, as these rocks are beneath the line provisionally drawn 

 between the Cambrian and pre-Cambrian rocks. This will be noticed 

 under the description of the Cambrian rocks of the Eocky Mountain 

 province. Above the quartzite series there is a thin series of green 

 siliceous argillites which are usually not more than 75 or 80 feet thick, 

 in which fossils of a Primordial type have been found. A description is 

 given of the Cambrian as recognized in central Nevada, and a compari- 

 son made between it and the Cambrian of the Mississippi Valley and 

 the Wasatch section. A complete list of the fossils of the Utah and 

 Nevada Cambrian is given on page 231, and on page 233 a list of those 

 from the Quebec group, eight of which are from the Middle Cambrian 

 zone, and will be mentioned under the description of the Cambrian 

 fauna of the Kocky Mountain province. The geographic distribution 

 of the Cambrian rocks and their mode of occurrence, as shown in cross- 

 section, is represented on the sheets of the atlas accompanying the 

 report. 



In 1882 Mr. Arnold Hague published a preliminary report on the 

 geology of the Eureka district, 2 which was followed in 1883 by the 

 abstract of a report on the geology of the district. 3 In this latter re- 

 port a detailed description is given of the Cambrian rocks of the Pros- 

 pect Mountain section. It is accompanied by a map of the district and 

 a plate of sections showing the relation of the Cambrian rocks to the 

 superjacent formations. 



The fauna of the Cambrian rocks of the Eureka district was de- 

 scribed and illustrated by Mr. C. D. Walcott in 1884. A short descrip- 

 tion of the range of the species is given, also a tabulation of the Paleo- 

 zoic section of Central Nevada, showing the vertical range of genera. 4 

 This was republished in 18S6 with greater detail, 5 accompanied by an 

 original description of the Big Cottonwood Canon section (pp. 38, 39), 

 and a section in the Highland range, 125 miles south of the Eureka 

 section (pp. 33-35), with notes upon the section at Pioche and Ophir 

 City. 



• Op. cit , pp. 229, 230. 



2 Report [on work in Eureka district]. 2d annual report U. S. Geol. Survey, 1880-81. pp. 21-35, 1882. 

 :H Hague, Arnold: Abstract of report on geology of the Eureka district, Nevada. U. S. Geol. Surv., 

 3d annual report, 1881, 1882, pp. 237-290, 1883. 



4 Paleontology of the Eureka district. U. S. Geol. Survey, Monograph vol. 8, 1884. 



5 Second contribution to the studies of the Cambrian faunas of North America. TJ. S. Geol. Surv., 

 J3ull. No. 30, 1886, pp. 30-33. 



