EARLY CAMBRIAN STRATIGRAPHY. 
123 
the suggestion that the Pioche formation at Pioche includes 
two faunas, a lower zone with Olenellus discovered by the 
Wheeler Survey, and an upper zone with Crepicephalus which 
was mingled with the lower faunas by the subsequent collectors. 
Even this conclusion may be wrong, however, and we should 
be loth to adopt it if it had not already been forecasted by Mr. 
Walcott (see page 122). 
At Pioche, Olenellus gilberti is still typical of the lower zone 
and that horizon may for convenience receive the same name 
as in the Big Cottonwood section (the Olenellus gilberti zone) ; 
the Middle Cambrian horizon may be called the Crepicephalus 
zone from its typical fossil. It is separated by 600 feet of lime- 
stone from what has been described as a distinct though unnamed 
upper shale series (see page 96) which can be definitely correlated 
with the Bathyuriscus productus zone of the Pioche formation 
in Big Cottonwood canyon. (See the section on the strati- 
graphy at Pioche and in the Highland range, pages 95-98.) 
In the Highland Range and Pioche sections, therefore, the 
Pioche formation does not appear to include faunas so distinct 
as those comprised in the same formation in Big Cottonwood 
canyon (the Lower Cambrian and the Spence-Stephen) unless 
there is a duplication in the Highland Range section or the 
two shales at Pioche are of the same age. Locally, that is 
between sections 50 miles or less apart, the Spence shale 
exhibits marked variations in both the number and the types 
of species of which it is composed, differences hardly less pro- 
nounced than those (a) between the fauna of No. 21 of the 
Highland Range section and that of the Middle Cambrian 
portion of the “Pioche shale” in the Big Cottonwood Canyon 
section, or (6) between the two Middle Cambrian shales near 
Pioche — the one southeast of the town on the road to Panaca 
where the apparent inclusion of an underlying Olenellus horizon 
has complicated its age relationships, and the other typically 
exposed in the mine dumps west of Pioche in the Ely mountains. 
The equivalent of the Spence in the British Columbia section, 
the Stephen, is, however, separated by nearly 1,600 feet of 
strata from the Mount Whyte, to which the Alberlella fauna 
