

On the Chemical Geology of the Gold-fields of California. 123 



On the sides of the cavities gelatinous silica is found coating 

 chalcedony and opalescent silica in various stages of formation, 

 from the gelatinous state to that of the hardest opal. This indu- 

 rated silica is sometimes colourless, but is more frequently per- 

 meated by cinnabar and iron pyrites, or blackened by the tarry 

 matter before referred to. Cinnabar is also found in striae, and 

 occasionally even in veins and concretionary masses of conside- 

 rable thickness; where the bituminous matter occurs in the largest 

 quantity, and the mass consequently becomes black and friable, 

 cinnabar is replaced by globules of metallic mercury. 



On the edge of Clear Lake near the sulphur bank is a hot 

 spring, of which the outlet, even when the water is low, is par- 

 tially beneath the lake, so that the amount which flows from it 

 cannot be ascertained. Hot water, however, rises through the 

 sand at various points, extending over a considerable area ; and 

 Mr. Moore, of San Francisco, who analyzed the water from this 

 locality, has found that, in addition to chloride of sodium and 

 carbonate of soda, it contains a large quantity of borax, and 

 above a hundred grains of ammoniacal salts per gallon. Lying 

 immediately at the foot of the sulphur bank are several springs of 

 cold water, some of which contain carbonate and sulphate of soda> 

 whilst others yield boracic acid. All these springs evolve large 

 quantities of carbonic acid. 



The chalcedony and semi-opal from this place, when examined 

 under the microscope, are seen to enclose cubical pyrites, together 

 with crystalline cinnabar; but the latter mineral appears to have 

 been generally deposited in an amorphous state. Specimens of 

 chalcedony taken from the fissures in the sulphur bank were, 

 when first broken, so extremely soft as to readily receive an im- 

 pression of the nail ; but on reaching England they had become 

 hardened, and had assumed the ordinary characteristics of that 

 mineral. 



Thin sections of these specimens showed a structure like that 

 of fortification-agate, and were traversed by numerous fissures 

 parallel to lines of incipient crystallization, besides which they 

 were in places stained by oxide of iron. 



Boiling Spinngs. — About fifteen miles east of Little Lake, 

 situated in lat. 35° 50' north and long. 18° 10' west from Green- 

 wich, 200 miles north of Los Angeles, are numerous boiling- 

 springs. The first group covers several acres of the southern 

 declivity of a granitic hill, and is no longer in a state of great 

 activity, although numerous apertures are giving off an abun- 

 dance of steam and acid vapours, and small quantities of sulphur 

 are being deposited around the various openings. In the imme- 

 diate neighbourhood of these springs the granite has been reduced 

 to the state of a soft hot mud very dangerous to walk over ; and 



