EARLY CAMBRIAN STRATIGRAPHY. 
121 
The list quoted in the first column has been copied and 
recopied with little or no modification until 1912 1 when examina- 
tion of the original material in the collections of the U. S. National 
Museum resulted in the withdrawal from the list of Obolus 
( Westonia ) ella and Eocystites ? longidactylus and the insertion 
of Olenoides sp., Ptychoparia sp., and Ory otocephalus primus. 
Why the latter species, which was described in 1886 2 , has not 
been included in previous lists is more or less of a mystery. 
Its presence is important, see page 103. 
In the following discussion of the beds in question the term 
Pioche formation will be used though it was not so applied until 
1908, see page 120. It will be shown that this formation is 
divisible into two zones: (1) a low r er, characterized from 
eastern Nevada to northeastern Utah by the trilobite Olenellus 
gilberti, which will be called the Olenellus gilberti zone and 
assigned to the Lower Cambrian; and (2) an upper, which, from 
the collections at our disposal, appears not to belong to the 
same portion of the Middle Cambrian in the different sections 
from which the Pioche has been identified. In the Big Cotton- 
wood Canyon and Oquirrh Range sections this upper zone will be 
called the Bathyuriscus productus zone and correlated with the 
Spence-Stephen-Titkana fauna; at Pioche and in the Highland 
range (Bennett Spring) it will be called the Crepicephalus zone 
and tentatively correlated w'ith the Albertella fauna and the 
Burton formation. 
The rocks of the Pioche formation as they were first described 
for the Big Cottonwood Canyon section of Utah 3 were given a 
thickness of 250 feet and listed as carrying the following fauna: 
ll Cruziana sp., Lingulella ella, Kutorgina pannula, Hyolithes 
billingsi , Leperditia argenta, Olenellus gilberti, Ptychoparia 
quadrans, and Bathyuriscus productus.” 
The commingling of Lower and Middle Cambrian types 
exhibited by this fauna was first admitted by Walcott in 1891 4 
and the presence of the error has been noted 5 , but there appears 
J Mon. U. S. Geol. Survey, vol. LI, 1912, p. 192. 
2 Walcott: Bull. U. S. Geol. Survey, No. 30, 1886, p. 210. 
3 Idem, pp. 38-39. 
* Idem, No. 81, 1891, p. 319. 
* e.ff.: Mon. U. S. Geol. Survey, vol. LI, 1912, p. 189. 
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