THE MIDDLE PALEOZOIC STRATIGRAPHY OF THE 

 CENTRAL ROCKY MOUNTAIN REGION 



C. W. TOMLINSON 



University of Chicago 



PART III 



stratigraphy — continued 



THE SILURIAN SYSTEM 



In Utah. — This system, not including the Richmond series, is 

 not known with certainty in the central Rocky Mountain region, 

 except in northern Utah, where it was included by Weeks 1 under 

 the name ''Paradise limestone," which has been supplanted in 

 official usage by the "Laketown dolomite" of Richardson. 2 Its 

 fauna does not comprise many species, but is ample to demonstrate 

 that the system is Silurian. 3 It is closely allied to the Niagaran 

 faunas of other regions. 



In Nevada. — This system may be represented in the upper part 

 of the Lone Mountain limestone of western Nevada, although no 

 diagnostic Silurian fossils have been reported from that formation. 

 The following is an extract from Iddings' section near Modoc Peak, 

 in the Eureka district: 



3. Shaly limestone, rich in fossils. Lower part of Nevada limestone. 



2. 550 feet. Light-gray siliceous limestone, with fine lines of bedding; in 



upper portion weathering in almost rectangular fragments; growing less 



siliceous toward the bottom. 

 1. 140 feet. Light-gray, highly crystalline, saccharoidal dolomite; not 



siliceous. 4 



1 F. B. Weeks, unpublished manuscript, U.S. Geol. Survey. 



2 G. B. Richardson, "The Paleozoic Section in Northern Utah," Amer. Jour. Set., 

 4 th Ser., XXXVI (1913), 406-15. 



3 Cf. E. M. Kindle, "Occurrence of Silurian Faunas in Western America," Am. 

 Jour. Sci., 4th Ser., XXV (1908), 125 ff. 



4 Arnold Hague, op. cit., p. 66. Section measured by J. P. Iddings. 



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