J. A, PHILLIPS ON MINERAL VEINS. 391 
sophical Magazine,’ a paper advocating the probability of certain 
mineral deposits having been the result of hydrothermal or solfataric 
action *, 
For some years subsequent to my visit this solfatara was worked 
as a source of sulphur only; but during these operations so large 
an amount of cinnabar was discovered, both in the decomposed 
basaltic rock and in the Cretaceous strata through which it has been 
erupted, as ultimately to lead to the opening up of the cooler por- 
tions of the Sulphur Bank as a mercury-mine. This has long 
yielded large quantities of quicksilver, and affords a striking and 
instructive example of a recently formed mineral deposit resulting 
from agencies still somewhat actively in operation; on the table 
before me will be found not only specimens of this cinnabar but 
also a specimen of a thin section of recently formed quartz from the 
face of a fissure in the decomposed basaltic rock. 
Many years since, Mr. Oxland found a notable amount of silver 
in the sinter-like deposit from a hot spring in the county of Colusa ; 
and Professor Whitney, previous to 1865, had been shown at Clear 
Lake some peculiar and interesting specimens of water-worn cin- 
nabar enclosing specks of gold, said to have been found near Sul- 
phur Springs in the same county of Colusa‘. 
These, from being water-worn, and from not haying been found 
in situ, had necessarily lost a certain portion of the interest which 
would have otherwise been attached to them; but through the 
kindness of Mr. Melville Attwood, of San Francisco, a Fellow of 
this Society, I am enabled to lay before you this evening a specimen 
of cinnabar from Colusa County, which, having been formed upon 
one of the surfaces of a fissure, has subsequently become covered by 
a brilliant deposit of metallic gold. 
Steamboat Springs, in the State of Nevada, are situated near 
the base of a volcanic hill seven miles, in a direct line, north-west 
of Virginia City and of the famous silver-mines on the Great Com- 
stock lode. 
The rock at this place is traversed by several parallel fissures, 
which either give issue to heated waters or simply throw off clouds 
of steam. The most active group of these crevices comprehends 
five parallel longitudinal openings extending, nearly in a straight 
line, for a distance exceeding a thousand yards; their general 
direction is nearly north and south, and all of them are included 
within a zone two hundred yards in width. These crevices are 
sometimes filled with boiling water which overflows in the form 
of a rivulet; while at others violent ebullition is heard to be taking 
place at a short distance below the surface. 
These fissures are lined with a siliceous incrustation, which is 
being constantly deposited, while a central longitudinal opening 
allows of the escape of gases, steam, and boiling water. The 
water is slightly alkaline, and contains carbonate of sodium, sul- 
* “Notes on the Chemical Geology of the Gold-fields of California,” by J. 
Arthur Phillips, Phil. Mag. 1868, vol. xxxvi. p. 321. 
t Geological Survey of California, vol. i. p. 92. 
