ANALYSES OF LIMESTONE. 



37 



mites in thin layers have been recognized in several localities, but the per- 

 centage of carbonate of magnesia in most instances is too low to allow the 

 beds, for any considerable thickness, to be classed as dolomite, neither is 

 there any evidence that dolomitic rock is characteristic of any particular 

 portion of this great thickness of beds. Both dolomite and pure limestone 

 have been shown to occur near the large ore bodies, analyses demonstrat- 

 ing, however, that there exists no possible relation between the chemical 

 composition of the limestone and the occurrence of ore. Analyses of lime- 

 stone from the neighborhood of several large ore bodies situated in widely 

 separated localities along the ridge and from different geological horizons 

 throughout the epoch give the following results : 



An analysis of the stratified limestone from the seventh level of the 

 Richmond mine may be taken as a fair sample of the limestone body. It 

 yielded as follows: 



Carbonate of lime 88-34 



Carbonate of magnesia 4-98 



Iron 1-59 



Silica.. 4-83 



Total 99-74 



Mr. Thomas Price, of San Francisco, made a careful chemical study of 

 the limestones of Ruby Hill, collecting his samples for examination from the 

 most important points on the surface and from different levels in the mines. 

 Amono- the localities from which the rocks were selected, were the contact 



O 



beds between the limestone and the overlying Secret Canyon shale, strati- 

 fied beds on the seventh and eighth levels of the Richmond mine, the under- 

 lying rocks of Potts Chamber, the mouth of the Bell Shaft, and near the ore 

 body of the Tiptop Incline. In sixteen analyses the amount of carbonate 



