﻿C. D. Walcott — Cambrian System of North America. 143 



is passed through. In the upper 250 feet of silico-argillaceous 

 shales that rest on a massive band of quartzite, 3,000 feet in 

 thickness, the following fossils occur : Gruziana f, Lingulella 

 Ella, Kutorgina pannula, Hyolithes Billingsi, Leperditia Argenta, 

 Olenellus Gilberti, Ptychoparia quadrans and Bathyuriscus pro- 

 ducta. This fauna is also found at a similar horizon in several 

 localities in Nevada; and the lithologic, stratigraphic and 

 paleontologic evidence, as found in the Oquirrh and Tintic 

 ranges of Utah and the House, Eureka and Highland ranges 

 of Central Nevada, extends the same horizons throughout the 

 western and southern portions of the Great Basin area. 



The entire absence of fossils in the lower portions of the 

 Wasatch section may be owing to the character of the sedi- 

 ments ; but an attempt is made further, to explain the absence 

 of the Lower Cambrian fauna of the Atlantic area. 



The second section (fig. 3), that of the Eureka District, by 

 Mr. Arnold Hague, stratigraphically overlaps that of the 

 Wasatch, the lower 1,500 feet of quartzite corresponding to the 

 upper-half of the 3,000 feet of quartzite of the Wasatch sec- 

 tion, and the Olenellus shales occurring at the same horizon on 

 the summit of the quartzite ; but here the Lower Silurian 

 (Ordovician) strata do not rest on the siliceous Olenellus-bear- 

 ing shales, but are separated by over 6,000 feet of limestone 

 that carries a fauna uniting the Middle Cambrian fauna with 

 the Upper Cambrian or Potsdam fauna, which begins in its 

 characteristic forms 4,500 feet above the Olenellus horizon. 

 One hundred miles south of Eureka, in the Highland Kange, I 

 found the Eureka section essentially repeated and identical spe- 

 cies occurring at the same relative horizons in each section. 

 The vertical range of the Eureka section embraces the corres- 

 ponding strata of the Highland Kange section and several sec- 

 tions that occur in Nevada and Western Utah. 



Section No. 3, fig. 4, is unlike either of the first two sections 

 in having the Upper Cambrian well developed, and the Middle, 

 and probably the Lower Silurian (Ordovician), entirely absent. 

 This section is beautifully exposed in the deeper portions of 

 the Grand Canon of the Colorado, Arizona, and was first made 

 known in a general way, through the explorations of Major J. 

 W. Powell in 1875. During the winter of 1882-83, Major 

 Powell instructed me to make a detailed section of the strata 

 in the depths of the canon, and fig. 4 is one of the results of 

 the work. The Upper Cambrian, or Tonto formation is 1,000 

 feet in thickness, composed of siliceous and calcareous strata 

 and carries a fauna that unites it closely with that of the Upper 

 Cambrian of Nevada, Texas and the Upper Mississippi Yalley. 

 Beneath the Tonto there is a great mass of strata, over 12,000 

 feet in thickness, that are unconformable to the horizontal Tonto 



