CAMBRIAN FAUNA. 41 



inclined at a much lower angle and have undergone much less movement 

 and compression, stratification may be frequently observed. 



Hamburg shale. This shale body in general resembles the one underlying 

 the Hamburg limestone, except that it is by no means as uniform in com- 

 position, showing very rapid changes in conditions of deposition, becoming 

 more or less arenaceous or calcareous throughout its entire thickness as 

 well as in its lateral extension It is characterized by cherty nodules, and 

 near the top by more or less persistent layers of chert and sand, followed 

 by calcareous shales which pass into the overlying Pogonip limestone of 

 the Silurian. Across its broadest development it measures 350 feet, yet it 

 rarely maintains a uniform thickness for any long distance. The best 

 exposures are seen opposite the Hamburg and Dunderburg mines, and 

 again in the ravine north of Adams Hill, where it attains as great a thick- 

 ness as anywhere on the eastern slope, and is in every way as well shown. 

 This group is not as thick as the Mountain shale in its broadest develop- 

 ment in the Prospect Mountain limestone, yet its persistency, stratigraphi- 

 cal position, and its relations to the fauna of the Cambrian render it of 

 far greater importance. 



Cambrian Fauna. As has already been mentioned, no evidences of organic 

 remains have been observed in the Prospect Mountain quartzite, and the 

 conditions under which the beds were deposited could hardly be considered 

 favorable to life. In the overlying Prospect Mountain limestone obscure 

 fragments of fossils may be detected at various places throughout the 

 epoch, but localities showing any grouping of species or forms, sufficiently 

 well preserved for identification, are limited to three horizons. The lower 

 of these horizons occurs at the base of the limestone, in a narrow belt rest- 

 ing on the quartzite; the second is found in strata of calcareous shales 

 several hundred feet higher up, while the third horizon, which may be two 

 or three hundred feet in thickness, lies at the top of the limestones just 

 below the Secret Canyon shale. 



Directly overlying the quartzite, in strata which may be regarded as tran- 

 sition beds between it and the Prospect Mountain limestone, occur the low- 

 est organic forms obtained in the district, and the equivalent of the lowest 

 Cambrian fossiliferous strata in the Great Basin. Along the east side of 



