46 GEOLOGY OF THE EUREKA DISTRICT. 



forms closely allied to the Olenellus grouping of species have been found 

 in four places in the Great Basin: in the Oquirrh Range, in Utah; in the 

 Highland and Timpah-Ute Ranges, and at Silver Peak, in Nevada. In all 

 these they are described as occurring in a similar arenaceous shale conforma- 

 ble to and overlying a body of quartzite, the base of which is not exposed. 



As early as 1874, Mr. F. B. Meek', in a letter to Dr C. A. White, described 

 the two species, Olenellus gilberti and 0. howelli, from Pioche, Nevada. He 

 called attention to the relationship existing between them and Olenellus ver- 

 montana and 0. thompsoni, Hall, from the Georgia slates of Vermont, and 

 to him belongs the honor of first correlating these widely separated beds. 



Quite recently, after a careful review of all the material at his com- 

 mand, and a comparative examination in the field of the well known New 

 York, Vermont, and Newfoundland regions with the more recently studied 

 Great Basin areas in Nevada and Utah, Mr. C. D. Walcott' suggests dividing 

 the Cambrian into three divisions, namely : Lower Cambrian, Middle Cam- 

 brian, and Upper Cambrian. These three primary divisions are recognized 

 in the Cambrian of Europe, and each of them has received local designa- 

 tions derived from the name of the region where the terrane is typical and 

 well exposed. Thus, in the Cordillera, the Lower Cambrian is designated 

 as the Prospect Mountain group, whereas in New York and New England 

 it is best known as the Georgia shale, from the well known locality in Ver- 

 mont. The Middle Cambrian has as yet no better typical locality than the 

 slates and shales of St. John, New Brunswick. The Upper Cambrian is 

 usually spoken of as the Potsdam so well recognized all the way from the 

 Atlantic coast to central Nevada. At Eureka the latter epoch is represented 

 by the Hamburg Ridge. 



Wherever in the Great Basin, so far as known to the writer, the genus 

 Olenellus has been discove 'ed, the beds do not attain a development of more 

 than 400 feet; at least they pass from shale and shaly limestone to lime- 

 stone, in which as yet no organic forms have been recognized. Only at 

 Eureka and in the Highland Range are their structural relations with both 

 the overlying and underlying beds clearly made out. We have very little 



1 U. S. Geographical Surveys, West of 100th Meridiau, vol. iv, Paleontology, 1877, p. 47. 

 2 Stratigraphic Position of the Olenellus Fauna in North America and Europe. Am. Jour. 

 Sci., 3d ser., vol. xxxvn, May and July, 1889. 



