ANALYSES OF LIMESTONE. 



37 



mites in thin lavors luivc been recog'nized in several localities, l)nt the per- 

 centag'e 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 e%'idence that dolomitic rock is characteristic of any ])artieular 

 portion of this j^reat thickness of beds. Both dolomite and pure limestone 

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

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

 composition of the limestone and the occun-ence of ore. Analyses of lime- 

 stone from the neiglil)orhood of several large ore bodies situated in widely 

 se2)arated localities along the ridge and from different geological horizons 

 throughout the epoch give the following- results : 



Mine. 



Hodgson 



Geddes & Bertrand 



Dugout 



Jackson 



Insoluble 

 residue. 



Carbonate 

 ofmagnesia. 



0-36 

 13-83 

 5-79 

 0-20 



14-00 

 109 

 1-84 



26-32 



An analysis of the stratified limestone from tlie seventh hivcl 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 ofmagnesia 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 Ruljy Hill, collecting his samples for examination from the 

 most important points on tlie sui-face and from different levels in the mines. 

 Among the localities from which the rocks were selected, were the contact 

 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 ro(-ks 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 



