PEOQUOP EANGE. 509 



The formation, like that of the southern end of the Gosi-Ute Range, consists 

 of limestone, and has, in like manner, been referred to the Lower Coal- 

 jyieasure series. The prevailing dip is westerly, and along the foot-hills, 

 which rise above Gosi-Ute Valley, varies in angle from 8° to 40°. Heavily- 

 bedded, dark-gray strata, many of them highly siliceous and seamed with 

 calcite, characterize the hills ; interstratified between them are frequent 

 layers of calcareous and cherty shales and thin beds of quartzite. 



A highly siliceous limestone, from the slopes of Grand Peak, on being 

 submitted to analysis, yielded Mr. B. E. Brewster the following : 



Insoluble residue 34.912 



Alumina^ ) _ _, ^^^^ 



Ferric oxide ) 



Lime - - 34.333 



Magnesia 1.116 



Carbonic acid 27.769 



Phosphoric acid trace 



Water 1.249 



99.765 

 This indicates a carbonate of lime with 2.34 per cent, of carbonate of 

 magnesia. Of the 34.912 of insoluble residue, 31.51 per cent, consisted of 

 silica. 



Organic remains of Brachiopoda, crinoidal columns, and fragments of 

 stems and roots, highly metamorphosed, in general too poor for specific 

 determinations, are abundant throughout the region, but only the two fol- 

 lowing forms have been recognized : 



Athyris subtilita. 

 Fusilina cyUndrica. . 



But for its intimate topographical and geological connection with the 

 extreme southern end of the Peoquop uplift. Spruce Mountain, with its long 

 ridge stretching to the northward, might almost be regarded as a separate 

 range. As it is, the mountain, one of the loftiest in this region, presents, for 

 a limestone summit, a striking appearance, rising steeply for nearly 4,000 feet 

 above Butte Valley, and again falling away abruptly in the opposite direc- 



