250 C. W. TOM LIN SON 



described. In the absence of an adequate description of the fauna 

 of the typical Ozarkian, it is difficult to make comparison therewith. 

 The base of the Ordovician was placed by Walcott 1 at Blacksmith 

 Fork at the first appearance of cephalopods. As determined by 

 Richardson 2 in the Randolph quadrangle, the base of the Garden 

 City formation there is marked by the appearance of several genera 

 of coiled gastropods. The post- Cambrian, pre-Swan Peak (see 

 below) series thus defined has a thickness on Blacksmith Fork of 

 1,272 feet, which is 68 per cent greater than the total thickness of 

 the overlying Ordovician, including the Richmond. As above 

 noted, Richardson describes a marked unconformity at the top of 

 the Cambrian in the Randolph area. These faunal distinctions and 

 this physical evidence may warrant the recognition of the series 

 in question as a separate system ; but there is no evidence yet at 

 hand to suggest its subdivision into two systems, Ozarkian and 

 Canadian. It is possible that the St. Charles formation includes a 

 representative of the former. 



Up to the present, however, the Ozarkian has not been recog- 

 nized in the Rocky Mountains. 



THE ORDOVICIAN QUARTZITES AND SANDSTONES 



The Eureka and Swan Peak quartzite. — In eastern Nevada the 

 unfossiliferous Eureka quartzite, ranging from 200 to 500 feet in 

 thickness, lies in apparent conformity upon the Pogonip limestone. 

 The upper surface of the Eureka quartzite is clearly an irregular 

 erosion surface. It is overlain by the Lone Mountain limestone, 

 which carries a Trenton fauna near its base. 3 



The Eureka quartzite corresponds closely in stratigraphic rela- 

 tions to the quartzite at Geneva 4 and to the Swan Peak 5 quartzite, 

 both in northern Utah, which attain a similar thickness. Uncon- 

 formity is evident above the Swan Peak quartzite in the Randolph 

 quadrangle, 6 and farther south the post-Swan Peak erosion locally 



1 C. D. Walcott, "Cambrian Cordilleran Sections," Smithsonian Misc. Coll., 

 LIII (1910), 191. 



2 Op. cit., pp. 408-9. 3 Hague, op. cit., pp. 58-59. 



4 Eliot Blackwelder, "New Light on the Geology of the Wasatch Mountains, 

 Utah," Bull. Geol. Soc. Amer., XXI (1910), 526-27. 



5 Richardson, op. cit., p. 408. 6 Ibid. 



