CAMBRIAN FAUNA. 41 



iiifliiu'd at a imicli Iowit aiiyk' and have undergdUc iiuicli k-ss mdvt'nii'Ut 

 and comprL'ssiuii, stralitication 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 dejjosition, becoming 

 more or less arenaceous or calcareous throughout its entire thickness as 

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

 near the top bv more or less persistent lavers of chert and sand, followed 

 by calcareous shales which pass into the overlying I'ogonip limestime of 

 the Silurian. Across its bi-oadest development it measures SoO 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 develo[)- 

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

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

 far greater importance. 



Cambrian Fauna.— As luis already bceu mentioned, no evidences of organic 

 remains have been observed in the Prospect ^[ountain cpiartzite, and the ~ 

 conditions under which the beds were dejiosited could hai'illy be considered 

 favorable to life. In the overh'ing Prospect ^lountain 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. Tlie lower 

 of these horizons occiu's at the ba.se of the limestone, in a narrow l)elt rest- 

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

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

 or three hundred feet in thickness, lies at the top of the limestones ju.st 

 below the Secret Canyon shale. 



Directly ovei'lving the (piartzite, 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 Basiu. Along the east side of 



