130 Hillebrand and Ransome — Carnotite and Associated 



been deposited by solutions in their present position are not 

 known. Dr. Hillebrand has shown,* however, that vanadium 

 in small amounts is widely distributed in sandstones, limestones, 

 and igneous rocks. It is perhaps present in very small amounts 

 in the bulk of the sandstone, and the deposits described may 

 simply represent a concentration of this material under certain 

 favorable conditions of solution and re-deposition. 



In the absence of exploitation it is manifestly impossible to 

 predict the probable shape and size of ore-bodies formed in 

 this manner. The roscoelite as seen near Placerville appears, 

 however, to be much more persistent than the carnotite. 

 There is no apparent reason why a mass of sandstone, impreg- 

 nated with roscoelite, which is continuously exposed for several 

 hundred feet along a cliff, should not extend for a considerable 

 distance inward from the cliff face. The carnotite, on the 

 other hand, appears to be a much more superficial occurrence 

 and, in fact, to have a not yet fully understood connection with 

 the present surface of the ground. This would indicate that 

 the carnotite results from a local concentration of material 

 already existent in the sandstone, and the deposition of this 

 material in the form of carnotite under conditions determined 

 by proximity to the surface, and probably partly dependent 

 upon a semi-arid climate. 



Chemical Analyses and Discussion. 



W. F. HILLEBRAND. 



I. The Green Coloring Constituent of the Placerville Sandstone. 



As noted by Mr. Ransome, the greener the sandstone, the 

 greater has been the replacement of the calcareous cementing 

 material by the crystalline vanadiferous mineral. Fortunately 

 the greenest available specimen was entirely free from carbo- 

 nate, and this was used for analysis, 10 grams being taken for 

 the main portion. 



The green substance was but slightly attacked by cold acids 

 and not rapidly by hot ones ; nevertheless after 12-24 hours 

 digestion on the water-bath with diluted nitric acid, the green- 

 ish color had been transferred to the liquid, the residue of sand 

 was nearly white, and a rather voluminous separation of non- 

 gelatinous silica had taken place. The nitration and washing 

 of the insoluble matter was accomplished without difficulty. 

 The free silica in it was extracted by two or three digestions of 

 15 minutes each on the water-bath with sodium carbonate solu- 

 tion of 5 per cent strength. The flocculent matter had 

 entirely disappeared and the sandy residue was collected in a 



* This Journal, IY, vol. vi, pp. 209-216, 1898. 



