PALEOZOIC STRATIGRAPHY OF ROCKY MOUNTAINS 381 



well down in the Jefferson formation, which explains their likeness 

 to the Jefferson fauna known from other regions. 1 The variability 

 of the Three Forks formation from shale to limestone along the 

 strike has been overestimated because of this same erroneous 

 correlation. 



Correlation of the Jefferson dolomite with the Nevada limestone. — 

 The Jefferson dolomite, as known in Montana and northern Utah, 

 has been correlated definitely by Kindle 2 with the Nevada limestone 

 of eastern Nevada, on paleontological grounds. Of the eleven 

 specifically identified forms described by Kindle from the Jefferson 

 formation, other than new species, seven were described by Walcott 3 

 from the Nevada limestone. Of the 32 forms partially or com- 

 pletely identified by Kindle from the Jefferson Limestone, only 

 three are of genera not described by Walcott from Nevada. 



The total thickness of the Nevada limestone is estimated by 

 Hague 4 at 6,000 feet. Although accuracy is not claimed for this 

 figure, it cannot be doubted that the Nevada is very much thicker 

 than any described section of the Jefferson limestone. The follow- 

 ing figures are given by Hague for the thickness of the Nevada 

 limestone at various localities in the Eureka district: 



Newark Mountain 5 (Bed 5): 3,500 feet. Considered by Hague 6 to be 

 less than (the upper) half of the total thickness of the formation. A small 

 Upper Devonian fauna was collected "several hundred feet below the top." 



Near Modoc Peak 7 (Beds 3-18): 4,710 feet. (Hague regarded the Nevada 

 as including more than 700 feet of lower strata also.) Rich Lower Devonian 

 fauna in lower 425 feet (Beds 3-4); no fossils other than "Stromatopora" and 

 "Chaeletes" found at higher horizons. 



East of Lamoureux Canyon 8 (Beds 1-5) : 3,000 feet, top not exposed. 

 Basal 200 feet carries a rich Lower Devonian fauna. 



County Peak: ' 4,500 feet. Fossils at three horizons. 10 



1 Cf. E. M. Kindle, "Fauna and Stratigraphy of the Jefferson Limestone in the 

 Northern Rocky Mountain Region," Bull. Amer. Pal., IV, No. 20 (1908), 22. 



2 Ibid., pp. 20-21. 



3 C. D. Walcott, "Paleontology of the Eureka District," U.S. Geol. Survey, 

 Monographs, VIII (1884). 



4 Arnold Hague, "Geology of the Eureka District, Nevada," U.S. Geol. Survey, 

 Monographs, XX (1892), 13, 63-64. 



s Ibid., pp. 82, 158. ^ jbid., p. 66. 9 ibid., p. 68. 



6 Ibid., p. 158. 8 Ibid., p. 67. I0 Ibid., pp. 78-80. 



