390 J. A. PHILLIPS ON MINERAL VEINS. 
31. A-Conrrisution to the History of Minprat VErnNs. 
By J. Artnur Puitiips, Ksq., F.G.S. (Read April 30, 1879.) 
Cerrar districts in California are remarkable for their hot springs ; 
and in some of the counties included between the 38th and 40th 
parallels, and consequently north of the city of San Francisco, 
sources of this description are of such frequent occurrence that, 
when viewed from elevated ground, almost every valley is seen to 
be more or less occupied by wreaths of steam rising from a flow of 
highly heated waters. 
The vents giving issue to these heated waters usually evolve 
carbonic acid, which is frequently accompanied by various sulphurous 
gases; such waters are generally alkaline, containing carbonate 
and sulphate of sodium, as well as, occasionally, alkaline borates. 
They generally give rise to abundant local incrustations of either 
silica or calcite, usually more or less mixed with free sulphur. 
These deposits of sinter often extend, in nearly horizontal layers, 
to a considerable distance from the orifices from which the waters 
issue. 
When water is ejected from such vents in the form of steam and 
spray only, while gases are abundantly given off and large amounts 
of sulphur deposited, the aperture becomes a solfatara. 
One of the largest known deposits of sulphur in California occurs 
in Lake County, a mile beyond the ridge which bounds Borax Lake 
on its north-eastern side, and is many acres in extent. This ‘‘ Sul- 
phur Bank,” as it is called, is composed of a much decomposed 
volcanic rock, traversed by numerous fissures, from which gases, 
steam, and water, either in the form of spray or of vapour, constantly 
issue; and upon and throughout the entire mass sulphur has been 
deposited in such large quantities that, at a short distance, the whole 
appears to consist of that substance. In the immediate neighbourhood 
of this solfatara are springs which give off carbonic acid, and of 
which the waters contain carbonates of sodium and of ammonium, 
chloride of sodium, borax, &e. 
The sulphur from this locality always contains a small amount 
of mercury in the form of cinnabar, and the sides of the fissures in 
the volcanic rock through which the gases and water make their 
escape are sometimes coated with gelatinous silica, beneath which is 
a layer of chalcedony resting upon a stratum of crystalline quartz. 
This siliceous deposit frequently contains pyrites and a notable per- 
centage of cinnabar, or is stained by a tarry hydrocarbon ; while the 
crystals of quartz often enclose liquid-cavities in which the usual 
bubbles are distinctly visible. 
In the year 1866 I visited Borax Lake and the neighbouring 
Sulphur Bank in company with Mr. R. Oxland, of Plymouth, who 
was the first to call attention to the presence of cinnabar in the 
sulphur from this locality ; and in 1868 I published, in the ‘ Philo- 
