



wakott.1 UTAH AND NEVADA. 159 



tion Primordial fossils, showiug beyond doubt that the two series of 

 beds are the same and equivalent to the Potsdam sandstone of Wiscon- 

 sin. This statement is followed by a list of fifteen species, all of which 

 belong to the Upper Cambrian fauna. 1 



The collections made by the officers of the Fortieth Parallel Survey 

 were studied and reported upon by Messrs. Hall and Whitfield. Of 

 the fauna referred to the Potsdam period they say : " Although there is 

 not a single species common to the two regions, yet there is such a close 

 generic resemblance as to leave no doubt whatever of the positive iden- 

 tity of the formations." They mention the resemblance between the 

 fauna referred to the Potsdam zone in Texas and the Upper Mississippi 

 .Valley, Wisconsin, Minnesota, etc. 2 In speaking of the trilobites from 

 the base of Ute Peak, Wasatch range, Utah, they state that the fauna 

 is referred to the Quebec group on the evidence of the Brachiopodus 

 and Molluscan fauna. 3 There must have been some confusion in rela- 

 tion to the occurrence of trilobites and the Molluscan fauna, as the tri- 

 lobites belong to the Lower Cambrian zone, and have nothing in com- 

 mon with the fauna which they refer to the Quebec group. 



In the comprehensive review of the geology of the fortieth parallel, 

 Mr. Clarence King describes the Cambrian and Silurian rocks largely 

 from the data published in the volume of Messrs. Hague and Emmons 4 

 and in the recapitulation of the Paleozoic he gives a condensed descrip- 

 tion of the Cambrian as known to him in Utah and Nevada. The base 

 of the Cambrian is never seen. This is explained by the fact that the 

 Cambrian sediments accumulated in the deep valleys between the Ar- 

 chean ridges, and that the lower beds have not subsequently been brought 

 up to the surface. Under the term Cambrian he includes all of the rocks 

 of the lowermost Paleozoic exposures up to and including the whole of 

 the Primordial, thus following approximately the eastern nomencla- 

 ture. In describing the rocks referred to the Cambrian he says : 



Thus far, among the reported occurrences of the rocks of this horizon in the Cor- 

 dilleras, the locality at the mouth of Big Cottonwood Caiion must remain as the finest 

 example and the stratigraphical type. The lowest member— the Cottonwood slates, 

 a group about 800 feet thick, which here rest upon highly metatriovphic Archeau 

 schists — has thus far yielded no organic forms. Though searched by us with consid- 

 able care, it presented no indications of life. The rocks are dark blue, dark purple, 

 dark olive-green, and blackish argillites, all highly siliceous, and as a group sharply 

 defined from the light-colored quartzitic schists which conformably overlie them. 

 This second group, by far the greatest of the, whole Cambrian series, is a continuous 

 zone of schists which have a prevailing quartzitic character, though varied with con- 

 siderable amount of argillaceous matter. It would seem to be the product of a fine- 

 grained arkose formation, simply compressed into dense schists. From 8,000 to 9,000 

 feet thick, it has a general uniformity of lithological condition from bottom to top, 



1 Op. cit., pp. 547, 548. 



2 Hali, James, and B. P. Whitfield : Paleontology (of the 40th Parallel). General remarks. U.S. 

 Geol. Survey of the 40th Parallel, vol. 4, 1877, pp. 199, 200. 



3 Op. cit, p. 200. 



4 Systematic Geology: TJ. S. Geol. Exploration of the 40th Parallel, Clarence King, geologist in 

 charge, vol. 1, 1878, pp. 154-189. 



