a King— Geology of the 4:0th Parallel 481 



measure limestones, where there can be no doubt of its true 

 strati graphical relations. 



Conformably overlying this is a body of about 2,000 to 2,500 

 feet of limestones, chert-beds, calcareous and argillaceous shales, 

 and some beds of calcareous sandstones and arenaceous lime- 

 stones, the whole constituting a very variable series, and carry- 

 ing from the bottom to the top distinct Coal-measure forms. In 

 middle and eastern Nevada the shales and arenaceous beds are 

 wanting, and the whole series is a continuous body of limestone. 



In the broken and dislocated exposures of the desert country 

 of Nevada there are many outcrops of limestone disconnected 

 from other formations and only referable by their fossils to the 

 Coal-measures. In such cases it is sometimes impossible to de- 

 termine whether the body should be strictly referred to the Up- 

 per Coal-measures or to the Coal-measure part of the Wahsatch 

 limestone. In consequence of this uncertainty, it is impossible 

 at present to say what species are common to both Coal-measure 

 limestones and to group those which are restricted to the two 

 different horizons. From localities where the data is complete, 

 it is evident that both limestones have many species in common. 

 The combined list of the two is too extensive to be published 

 here but will be found in full in the Paleozoic chapters of our 

 reports. 



Overlying the true Upper Coal-measures is a variable body of 

 argillaceous and calcareous shales and mud rocks, with limited 

 beds of limestone and sandstone, containing many ripple marks 

 and unquestionably a deposit of very shallow water. It is 

 composed altogether of fine silted material and contains forms 

 which have been referred unhesitatingly by Meek, and Hall 

 and Whitfield to the Permo-Carboniferous. This series is ex- 

 tremely variable and reaches a maximum of 500 feet. While 

 through the Upper Coal-measures there is more or less evidence 

 in the country east of the Wahsatch of a progressive shallow- 

 ing, there is a decided difference between the Coal measure 

 proper and the Permo-Carboniferous. The two are apparently 

 quite conformable, yet at the same time a very great change of 

 condition has taken place and it is possible that subsequent 

 study will show a slight discordance of position. If so, the 

 extent of the disturbance of the pre-Permian members has been 

 very slight east of the Wahsatch, while to the west of that range 

 the Permian is wanting. 



The following are some of the characteristic fossils : 

 Aviculopecten curtocardinales, n. sp. Aviculopecten "Weberensis, ep. n. 



McCoyi Meek. Eumicrotis Hawni M. & H. 



, " 8p., i/ee/c, (Pal. Up. Mo., " sp. undet. 



plate 2, fig. 10). Myalina permiaDa Meeli. 



Aviculopecten occidaneus Meek. Myacites Weberensis Meek. 



" parvulus, sp. n. " aviculoides Meek. 



^, " sp.? resembling Pecten " inconspicuus Metk. 



Clerelandicus SwaOow. Schizodus, sp.,=S. orata Jfte*. 



