ransome.J CARNOTITE AND ASSOCIATED MINERALS. 13 
lemon-yellow substance occurs sporadically in the section as an inter- 
stitial material between the quartz grains. This is probably the car- 
notite, which was seen as small, yellow specks in the hand specimen. 
It is very minutely crystalline, recalling' the habit of some obscure 
chloride aggregates in decomposed igneous rocks, and is too indistinct 
for successful optical study. Small crystal grains of zircon are scat- 
tered through the sandstone, and are readily concentrated in the resi- 
due after treating with hydrofluoric acid. 
Within the next 2 feet below the zone where it exhibits the fore- 
going facies, the sandstone becomes pinkish in consequence of the 
presence of ferric oxide, and in this pinkish rock the lens fails to 
reveal any roscoelite or carnotite. But just below the pink zone the 
sandstone begins to show yellow and green specks. The latter espe- 
cially become more numerous and larger, until at from 3 to 4 feet 
below the limestone the sandstone has a decided green tint. Farther 
downward this deepens, until near the floor of the tunnel the sandstone 
is a uniform deep olive-green. This green rock is rich in roscoelite 
over 20 per cent) and shows many small yellow specks of carnotite. 
This is regarded as the first-class ore, and the chief value of the deposit 
s supposed to be in its vanadium, the uranium being very subordinate. 
[n this respect the Placerville deposit differs from those on La Sal and 
Joe creeks, presently to be described, where the mineral sought for 
md occurring most abundantly is carnotite. 
Thin sections of the green-spotted sandstone, when examined micro- 
copically, resemble those of the light-buff sandstone just above it, as 
ar as character of quartz grains and relative abundance of matrix are 
oncerned. But the character of the matrix or cement is different. 
Jalcite is much less abundant and its place is largely taken by roscoe- 
Jte. This is grass-green in thin section, and might readily be mis- 
jaken for indistinct wisps and areas of chlorite. It sometimes forms 
distinct envelope around the quartz grains, showing an indistinct 
foliated or fibrous structure, with the fibers normal to the surface of 
e grains. 
The uniformly dark-green sandstone, richest in roscoelite, does not 
I ffervesce with acids and shows no calcite cement in thin section. 
fhe usual quartz grains are held together by roscoelite. This is crys- 
, illine, but the highest available powers show only an indistinct and 
linute foliation, such as may be observed in some very finely crys- 
Jillize,d chlorites. 
Close to the floor of the tunnel is a fairly regular, nearly horizontal 
reak of carnotite, varying in width, but usually less than an inch 
ide, and showing noticeable diminution in thickness in the face of 
e tunnel. This small seam is not solid carnotite, but is merety a 
ne in the sandstone impregnated with the bright-fellow uranium 
lineral. It is not nearly so continuous as the main vanadiferous belt, 
tad was seen only at three or four places along the outcrop of the 
