REPLACEMENT ORE DEPOSITS IN THE SIERRAS 397 



Dr. Stokes states that the residual C0 3 is the excess above 

 that required for CaC0 3 and MgC0 3 , and is in 1508 at least 

 clearly present as FcC0 3 . Assuming the residual C0 2 is in 

 the form of FeC0 3 in 1509 and 15 12 also, I have calculated 

 the amount of this in each case and inserted it in the analysis. 

 The analysis as completed by Dr. Stokes contained no estimate 

 of the FeC0 3 . 



No. 1 521 is a specimen of the Moccasin Creek dike, and com- 

 posed of nearly pure soda-feldspar. The rock contains no car- 

 bonates. 



No. 1509 is from one of the soda-feldspar dikes in argillite 

 just east of the Bachelor mine deposit. 



No. 1 5 12 is a more altered specimen of the soda-feldspar rock 

 from another branch of the multiple dike of the Bachelor mine. 



No. 1508 is the Bachelor lode material itself, composed of 

 quartz, carbonates, and mariposite. 



In this series there is the clearest evidence of a diminution 

 of silica and sodium and an increase of carbonates from the fresh 

 dike rock represented by No. 1521 to the lode material repre- 

 sented by No. 1508. There is, however, a decided jump in the 

 magnesian carbonates in Nos. 1509 and 1512, which are cer- 

 tainly altered soda-feldspar dikes, to the magnesian carbonate 

 in the lode material 1508. There being a mass of serpentine 

 immediately west of the lode, and magnesium being readily soluble 

 in carbonated waters, no one will doubt that the magnesium, both 

 in the lode and in the dikes, came orginally from the serpentine. 

 The possibility therefore arises that the association of the dikes 

 and the carbonate lode is merely accidental. In that case we 

 are forced to adopt Lindgren's hypothesis as to the origin of the 

 lode itself, and to suppose that the alteration of the dikes is 

 merely due to its proximity to the lode, itself formed by the 

 alteration of serpentine. A case entirely similar is that of 

 a mass of shale adjacent to serpentine. An analysis of the 

 shale next to the serpentine may show a decided content of 

 magnesia, but this does not prove the origin of the serpentine 

 from the shale, but merely that waters charged with magnesium 



