walcott.] SUMMARY UTAH AND NEVADA. 319 



The presence of the Pleurotoinaria-like shells and the species just mentioned corre- 

 lates the fimua with that of the upper horizon of the Potsdam faunas of Wisconsiu 

 and Nevada. 1 



We have no details of the section of Silver Peak, Nevada, to which 

 attention was called by Prof. J. D. Whitney. The fossils are from a 

 limestone and silico-argillaceous shale and identical with species found 

 elsewhere. The most noteworthy occurrence is that of Archceocyathus = 

 Spirocyathus atlanticus and a large brachiopod like Kutorgina cingulata, 

 both of which occur on the Labrador coast over 3,000 miles to the north- 

 east on the opposite side of the continent. The abundant and pecul- 

 iar type of sponge Archceocyathus profundus of the L'Anse au Loup 

 locality is represented by the nearly identical species Ethmophyllum 

 'whitneyi of Silver Peak, and the tribolite Olenellus gilberti is scarcely 

 distinguishable from 0. thompsoni, as it occurs in L'Anse au Loup. 

 The species now known from Silver Peak are : 2 



Spirocyathus atlanticus. Kutorgina (like K. cingulata). 



Archaeocyathus undt. sp. Hyolithes princeps. 



Ethmophyllum whitneyi. Olenellus gilberti. 

 Strephochetus ? sp. ? 



The Cambrian rocks of Utah, as determined by the presence of the 

 Cambrian fauna, form a narrow horizon in the vast series of sedi- 

 ments of which they are a conformable portion. Messrs. Emmons and 

 King refer the 12,000 feet of siliceous slates and quartzites of the Big 

 Cottonwood section to the Cambrian. If we provisionally drew the 

 basal line of the Cambrian at the base of the strata known to contain 

 the Olenellus fauna, all but 250 feet of this section would be referred to 

 the Algonkian, but from the known range of Olenellus in the strati- 

 graphically equivalent series to the north in British Columbia, the view 

 is no longer tenable. The upper portion of the sectiou consists of 250 

 feet of hard silico-argillaceous shale, a little sandy in places. At the 

 base a species of Cruziana was found, associated with Olenellus gilberti, 

 and 100 feet higher in the section a band of shale afforded Lingulella ella, 

 Kutorgina pannula, Hyolithes billingsi, Leperditia argenta, Ptychoparia 

 quadrans, and Bathyuriscus producta. This list was published in 1886, 

 along with Cruziana and Olenellus gilberti, as characterizing the shales 

 at the summit of the great series of quartzites and slates. As in the 

 Eureka and Highland Range sections, the Olenellus zone is confined to 

 a very narrow belt just above the quartzite. The silico-argillaceous 

 shales above occupy the position of the 4,650 feet of Prospect Mountain 

 limestone and Secret Canon shale of the Eureka section. The Ham- 

 burg limestone and Hamburg shale of the latter are absent in the 

 Big Cottonwood section, causing an unconformity by nondeposition. 3 

 The section in the Oquirrh liange above Ophir City has a quartzite at 

 the base with shales above it carrying Lingulella ella, Olenellus gilberti, 

 and Bathyuriscus producta, as determined by the collections brought in 



»Op. cit., pp. 35, 36. 2 Op. cit., p. 38. »Op. cit,, p. 39. 



