EARLY CAMBRIAN STRATIGRAPHY. 
103 
by the Middle Cambrian Spence shale which is of interest in 
this connexion because of the similarity in lithologic position 
between it and the Pioche formation. The error resulting from 
admixture of Lower and Middle Cambrian forms in the lists of 
fossils credited to the Pioche formation (see pages 122-123) has 
been perpetuated for years and has still further accentuated 
the resemblance of the Pioche to the Spence. The presence of 
Olenellus in the Pioche has been the “insurmountable” barrier 
to this correlation, but the division of the Pioche into two zones 
referable to the Lower and Middle Cambrian respectively 
permits the true correlation of the Spence with the upper or 
Bathyuriscus produetus zone. See the discussion of the Pioche 
formation on pages 120-125. 
Idaho , Malade. — In Two Mile canyon, southeast of Malade, 
Idaho, the relations of the Langston limestone to the Brigham 
quartzite closely approximate those in the Mill Canyon section of 
the Bear River range. The limestone is much thinner, however, 
only 5 or 6 feet, and is very fossiliferous, thirty species having 
been identified. 1 Of these Oryctocephalus is perhaps the most 
interesting in this connexion, because of the very limited 
stratigraphic distribution of this most striking form. It has 
been found not only in the Langston limestone and the overlying 
Spence shale at Malade, in the Spence in Mill canyon, Idaho, 
and in the Stephen formation on Mount Stephen, British Colum- 
bia, all localities which appear to be referable to one remarkably 
uniform though widespread Middle Cambrian horizon, but it 
was included in the collections which have been assigned to the 
“Lower Cambrian” Pioche formation. This occurrence has 
been used on page 124, as an argument for the correctness 
of the proposed division of the Pioche. 
Montana, Big Belt and Little Belt Mountains. — The lowest 
rocks referred to the Cambrian in the Big Belt and Little Belt 
mountains of Montana are the Flathead sandstones which are 
stated 2 to carry fossils in the lowest horizons “comparable with 
the oldest part of the Middle Cambrian fauna as the latter occurs 
a short distance above the Olenellus horizon in Utah and Nevada.” 
1 Walcott: Smithsonian Misc. Coll., vol. 53, No. 5, 1908, pp. 198-199. 
1 Walcott: Bull. Geol. Soc. America, vol. X, 1899, pp. 209-245. 
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