1868.] 



Geology of the Gold-fields of California. 



297 



by crystalline iron pyrites ; and sometimes this cementing material consists 

 either of carbonate of lime or silica. The silica is rarely met with in a 

 crystaUine form ; but near Kenebeck Hill a cavity, resulting from the junc- 

 tion of several pebbles, was found completely lined with well-defined crystals 

 of quartz. These did not show, under the microscope, the usual fluid- 

 cavities of quartz of the ordinary quartz veins of the country. 



Where the cementing material of the conglomerate chiefly consists of 

 pyrites, the enclosed trunks of trees are usually replaced by that mineral, 

 although, of two pieces of wood lying in close proximity to each other, 

 one may have become silicified, whilst the other is replaced by iron 

 pyrites. 



The assay of several specimens of the cementing pyrites showed that it 

 invariably contained a certain but very variable amount of gold. In 

 order to ascertain whether this exists in the form of water- worn grains 

 mechanically enclosed within the sulphide, or in the form of spongy, crys- 

 talline, and filamentary particles, similar to those met with in the pyrites 

 of auriferous veins, various samples were dissolved in nitric acid, and 

 the residues afterwards subjected to microscopical examination. In this 

 way granules of the precious metal, which had evidently been worn by the 

 action of water, were detected, whilst others appeared not to have been 

 subjected to such attrition. Mr. Ulrich states that in the gold-drifts of 

 Australia pyrites is often found replacing roots and driftwood, and that 

 samples have, on assay, yielded from a few pennyweights to several ounces 

 of gold per ton. 



Hot Springs. — Hot and boiling springs are exceedingly numerous 

 throughout California ; and considerable accumulations of sulphur, to- 

 gether with evidences of extensive solfatara action, are met with in diff*erent 

 sections of the State. 



The most remarkable instance on the Pacific coast of the actual growth, 

 on a large scale, and at the present time, of mineral veins is probably that 

 afforded by the boiling springs in Steamboat Valley, about seven miles 

 north-west of the great Comstock silver vein in the State of Nevada. 



These springs are situated at a height of about 5000 feet above the 

 level of the sea, at the foot of the eastern declivity of the Sierra Nevada. 

 The rock in this locality presents several straight and parallel fissures, 

 either giving out heated water or simply ejecting steam. The first group 

 of crevices comprises five longitudinal springs extending in a straight line, 

 and parallel to each other, for a distance of above 3000 feet. These 

 fissures are partially filled by a siliceous incrustation, which is being con- 

 stantly deposited on the sides, whilst a longitudinal central crevice allows 

 of the escape of boiling water or steam. On the most eastern of these 

 lines of fracture are five active centres of eruption, from which boiling 

 water is sometimes ejected by the force of steam to a height of from 8 to 

 10 feet. These waters are alkaline, and contain, in addition to carbonate 

 of soda, the sulphate of that base, together with chloride of sodium. 



