xANsoME.J CARNOTITE AND ASSOCIATED MINERALS. 17 
ORIGIN OF THE DEPOSITS. 
That the bodies of earnotite and roscoelite were formed subsequently 
to the deposition of the sandstones is evident from the facts presented 
in the preceding pages. It is equally plain that the minerals could not 
have resulted from the alteration, in place, of other compounds of 
vanadium and uranium originally contained in the sands. The shape 
ind position of the deposits indicate clearly that the ores have been 
brought to their present position by transportation. Moreover, the 
recency of the deposits and the fact that they are sometimes directly 
3onnected with faults and dislocations in the sandstones show that the 
vanadium and uranium compounds could not have been the original 
cementing material of the quartz grains, but in all probability they 
have locally replaced the calcite that acts as matrix to the ordinary 
ight-colored sandstone in which the ore bodies occur. The deposits 
)f roscoelite appear to be comparable to impregnations formed in 
sandstones by cupriferous solutions — such impregnations as ma}^ be 
ieen at many places in this region, particularly on La Sal Creek near 
]ashin and in Sinbad Valley — whereby the sandstone becomes colored 
>right green with carbonate of copper. In these places, however, the 
opper appears to have been previously deposited in part as chalcocite. 
Ln analogy might also be drawn with the green chromiferous sand- 
tone near Placerville, already referred to. In all these cases the 
ctual sources of the materials which have been deposited by solu- 
ons in their present position are not known. Doctor Hillebrand 
as shown, a however, that vanadium in small amounts is widely dis- 
ibuted in sandstones, limestones, and igneous rocks. It is perhaps 
resent in very small amounts throughout the sandstone, and the 
eposits described ma} r simply represent a concentration of this mate- 
al under certain favorable conditions of solution and redeposition. 
In the absence of exploitation it is manifestly impossible to predict 
le probable shape and size of ore bodies formed in this manner, 
he roscoelite seen near Placerville appears, however, to be much 
I ore persistent than the earnotite. There is no apparent reason why 
mass of sandstone, impregnated with roscoelite, which is continu- 
ity exposed for several hundred feet along a cliff, should not extend 
r a considerable distance inward from the cliff face. The earnotite, 
1 the other hand, appears to be of much more superficial occurrence, 
d its connection with the present surface of the ground is not yet 
lly understood. This would indicate that the earnotite results from 
ocal concentration of material already existent in the sandstone, and 
e deposition of this material in the form of earnotite under condi- 
>ns determined by proximity to the surface, and probably partly 
pendent upon a semiarid climate. 
«Am. Jour. Sci., 4th scr., vol. »;, 1898, pp. 209-216. 
Bull. 262—05 2 
