382 C. W. TOMLINSON 



The occurrence of such great thicknesses at four distinct local- 

 ities renders it unlikely that the true thickness has been greatly 

 overestimated because of duplication by faulting. 



The two chief fossiliferous horizons in the Nevada limestone are 

 near the base and near the top, and are separated by from 2,000 to 

 4,000 or more feet of strata which have yielded no diagnostic fossils. 

 The fauna described by Kindle from the Jefferson limestone includes 

 10 forms 1 (2 of which are specifically identified) which occur only in 

 the lower part of the Nevada limestone, 4 2 (3 of which are spe- 

 cifically identified) which occur in both the upper and the lower 

 horizons, and 5 s (2 of which are specifically identified) which occur 

 in the upper part of the Nevada only. Although this evidence is 

 meager, it suggests that the Jefferson limestone includes represent- 

 atives of both the basal and upper parts of the Nevada limestone. 

 It is possible that the disconformity between Members 14 and 15 

 of the Jefferson, for which evidence is cited on page — , represents 

 a large part of the barren middle portion of the Nevada. This 

 would mean that the greater thickness of the Nevada, as com- 

 pared with the Jefferson, was due, at least in part, to the presence 

 in the Nevada of members which either never were deposited in the 

 Rocky Mountain province or were eroded from that region in 

 Devonian time; that during the Devonian period the eastern part 

 of the Great Basin was more persistently submerged or less ele- 

 vated in emergent intervals (or both) than was the central Rocky 

 Mountain Region. 



In the Pahranagat Range, west of Hiko, in southeastern Nevada, 

 Walcott 4 measured a section including 5,400 feet of strata which he 

 assigned to the Devonian. From this sequence he obtained 22 

 fossil forms, to 9 of which he assigned definite specific names. All 

 of these forms are identical, according to Walcott's lists, with 



1 Favosites sp., Chonetes cf. macro striata, Stropheodonta sp., Sckuchertella che- 

 mungensis , Athyris sp., Platyceras sp., Actinopteria sp., Loxonema approximatum?, 

 Loxonema nobile, Bythocypris? (Leperditia?) sp. 



2 Stromatopora sp., Productella cf. spinulicosta (Productus subaculeatus) , Atrypa 

 reticularis, Martinia maia. 



3 Spirifer utahensis Meek (S. disjunctus Sowerby), S. engelmamii Meek, Pteri- 

 nopecten sp., Naticopsis sp., Pleurotomaria sp. 



4 Arnold Hague, op. cit. ult., pp. 197-99. 



