CARBONIFEROUS UNDIVIDED. 365 



The Carboniferous rocks have been subdivided into four epochs — ^first, Diamond Peak 

 quartzite; second, Lower Coal-measure limestone; third, Weber conglomerate; fourth. Upper 

 Coal-measure limestone. 



At the base of the [Diamond Peak] horizon fine conglomerates firmly cemented together 

 lie next the argillaceous shale of the White Pine epoch, " but quickly give place to a more massive, 

 usually vitreous quartzite with a characteristic grajdsh-brown color and breaking irregularly 

 with a flinty fracture. Intercalated black cherty bands, carrying a more or less ferruginous 

 matter, occur near the middle portion of the horizon. Near the summit the beds pass into 

 thinly laminated green, brown, and chocolate-colored schists and clay shales. The Carbon- 

 iferous age of the epoch is determined by a narrow belt of blue limestone, which occurs inter- 

 stratified in the quartzite about 200 feet above its base, in which the widespread species 

 Productus semireticulatus occurs associated with an undetermined species of Athyris. As the 

 fauna at the top of the black shales foreshadows the coming in of the Carboniferous, the presence 

 of this characteristic Productus, with only a Carboniferous fauna higher up in the series, deter- 

 mines without question the geological position of the quartzite between the black shale and 

 Coal-measure limestone. 



In the Diamond Range the Lower Coal-measure limestone overlies conformably the Diamond 

 Peak quartzite, the transition beds passing rapidly from siliceous to calcareous sediments. In 

 their lithological character and physical habit they do not differ essentially from the same beds 

 elsewhere, except, perhaps, at their base, where they carry intercalated beds of chert, argUlite, 

 and gritty, pebbly limestone, with evidences of shallow-water deposition. They pass rapidly, 

 however, into purer gray and blue limestone, for the most part heavily bedded and distinctly 

 stratified at varying intervals. In broad masses they resemble the Upper Nevada limestone 

 but are rather lighter in color in distinction from the dark blue and black of the latter horizon. 

 No true dolomite beds of any considerable thiclaiess have been recognized, 9.21 per cent being 

 the largest amount of magnesium carbonate obtained in any of the rocks subjected to chemical 

 analysis. Across their broadest development they measure about 3,800 feeet in thickness, 

 which is much less than has usually been assigned to this horizon in other mountain uplifts, 

 more especially those lying eastward. 



As the term Lower Coal-measure has been employed by most geologists to designate this 

 epoch throughout the Great Basin, it has been thought best to retain the name provisionally, 

 although not exactly applicable, as the epoch includes such a commingling of species from both 

 the Upper and Lower Coal measures that a separation of the beds seems quite impossible. 

 ****** *** 



Three salient features in the life of the Lower Coal measures at Eureka call for special 

 mention, and each is worthy of still further investigation — ^first, the occurrence near the base 

 of the limestone of a fresh-water fauna; second, the yaried development of the lameUibranch- 

 iates, a class which has heretofore been but sparingly represented in the collection of Carbon- 

 iferous fossils from the Cordillera; third, the mingling near the base of the horizon of Devonian, 

 Lower Carboniferous, and Coal measure species in gray hmestone directly overlying beds 

 characterized by a purely Coal measure fauna. 



* ******** 



Conformably overlying the Lower Coal measures comes the Weber conglomerate [probably 

 of PottsviUe age], one of the most persistent and weU-defined horizons over wide areas of the 

 Cordillera, stretching westward all the way from the Front Range in Colorado to the Eureka 

 Mountains. It varies in the nature of the sediment with every changing condition, but it is 

 nearly everywhere easily recognized as a siliceous formation between two great masses of Car- 

 boniferous limestone. In places it is made up of an admixture of calcareous and sandy beds; 

 in others of fine grits and shales; and again of nearly pure sUiceous sediment, varying from 

 fine to coarse grained, dependent largely upon the distance from any land area and depth of 



Mississippian, according to G. H. Girty (comment on manuscript). 



