WEST HUMBOLDT RANGE. 725 



Star Canon furnished : 



Ammonites Blakei. 

 Halohia dubia. 

 Arcestes perplanus. 



In addition to the above, there have been described from Star Canon, 

 by Prof. W. M, Gabb/ the following forms : 



Spirifera Homfrayi. 

 Terebratula Sumholdtensis. 

 Bhynchonella lingulata. 

 Posidonomya stella. 

 Monotis suhcircularis. 

 Avicula Romfro,yi. 



And, from Buena Vista Canon : 



Myacites {Panopma) Humholdtensis. 



The total thickness of this lower limestone cannot be less than 1,200 

 or 1,500 feet. • , . 



Overlying the limestones occurs a belt of siliceous rocks, which crosses 

 Star Canon just above Star City, and Buena Vista Caiion above the 

 junction of the two main branches, where they strike about north 12° 

 east. 



In Star Canon, where the beds are well exposed, they present a varied 

 group of slaty quartzites alternating with greenish schistose rocks having 

 a resinous lustre and talcose habit, but apparently free from carbonate 

 of lime, passing up, in the region of the Sheba Mine, into an earthy argil- 

 laceous rock with a distinct slaty bedding, and gradually becoming cal- 

 careous, with the calcite crystals plainly visible under the microscope. 

 This series of beds is about 1,500 feet thick. 



In thin sections, under the microscope, the green talcose rock 

 reveals considerable chlorite scattered through it, and in places also frag- 



' Geological Survey of California, Palseontology, vol. i, 18G4. 



