46 C. R. Longwell — Geology of 



having finer plications), and PlatyscMsmaf amhiguum 

 Walcott. 



If the writer's field determinations are correct, the 

 fauna also contains Spirifer tvhitneyi. Dr. Ulrich states 

 that this fauna evidentl}^ represents that of the Devonian 

 Nevada limestone found at Eureka, Nevada. The hori- 

 zon is Upper Devonian. 



Mississippian System. — A plain disconformity sepa- 

 rates the Muddy Peaks limestone and higher sediments. 

 Above this break at least 1,500 feet of carbonaceous lime- 

 stone, containing an abundance of chert at many horizons, 

 yields fossils of Mississippian age. No physical break 

 was seen in this series of beds, but the faunas of the upper 

 and lower portions are so strikingly different that the 

 limestone may be separated into two formations. The 

 following forms were found in the lower 600 feet : Trip- 

 lophyllum sp., Leptopora aff. typa, Leptcena analoga, 

 Schuchertella aff. ckemungensis, Chonetes loganensis, 

 Productus sp., Camarotoschia metaUica, Spirifer centro- 

 natus, Spiriferina solidirostris, and Reticularia cooper- 

 ensisf 



Dr. G. H. Girty, who identified the forms, refers this 

 fauna definitely to the Lower Mississippian, correlating 

 the horizon with the Madison limestone. This formation 

 is prominently exposed near Rogers Spring, and will be 

 called the Rogers Spring formation in this paper. In 

 addition to its faunal peculiarities it is characterized by 

 the presence of a considerable thickness of dark quartzite 

 in the upper half. 



The younger Mississippian formation yielded the fol- 

 lowing forms: Triplophyllmn sp., Cyathaxonia sp., 

 Fenestella sp., Derhya aff. hashashiensis , Chonetes aff. 

 loganensis, Composita aff. suhquadrata, Productus aff. 

 scitulus, Pustula aff. indianensis, P. aif. arhansana, Spiri- 

 fer sp., Conocardium n. sp., Leptodesma aff. spergenensis, 

 Pleurotomaria n. sp., Paraparchites sp., and Bairdia sp. 

 Dr. Girty pronounces this fauna Upper Mississippian, 

 corresponding to the fauna of the Brazer limestone of 

 northern Utah. The formation will be referred to as 

 the Bluepoint limestone, because it forms the corner of 

 Callville Mountain which is locally called Bluepoint. 



Pennsylvanian System. — In Callville Mountain the 

 Bluepoint limestone is overlain by at least 1,100 feet of 

 dark gray, heavy bedded limestone containing the follow- 



