of the Gold-fields of California. 427 



This silica presents itself in the form of a compact rock, much 

 resembling in appearance the quartz of ordinary veins, with 

 chalcedony, and occasional nodules of hyalite. This rock is, to 

 a certain extent, metalliferous, and, in addition to oxide of iron, 

 contains oxide of manganese, together with iron and copper 

 pyrites. M. Laur states that he discovered metallic gold in 

 this deposit, although I was myself unable to detect its pre- 

 sence. 



These phenomena of the Steamboat Valley appear to indicate 

 that metalliferous veins may be produced by mineral waters, 

 in the fissures through which they circulate. On taking into 

 consideration the principal circumstances connected with these 

 veins, it will be observed that their eruptive activity is by no 

 means equal throughout their longitudinal extent. This ac- 

 tivity is concentrated around certain points, which appear to 

 be the sources from which are principally discharged the 

 waters holding various mineral substances in solution, and 

 whence they subsequently become distributed throughout the 

 fissures existing in the rock. It has been observed by M. 

 Laur* that the slowness with which these incrustations are 

 formed in the interior of the cavities, as compared with the 

 great mass of mineral waters which escape over the edge of 

 the various fissures, also shows that a large proportion of the 

 metalliferous emanations may thus have been carried beyond 

 them ; so that, should they contain a non-oxidizable metal, such 

 as gold, the superficial deposits may occupy a considerable sur- 

 face and contain a great amount of wealth, although the vein 

 from which it originally issued may be small and comparatively 

 unimportant. 



The rock enclosing the veins of Steamboat Springs is a granite, 

 which in their vicinity is much decomposed, being often reduced 

 to a cavernous skeleton of silica containing only a few scales of 

 mica. The granite in this locality is poor in quartz, and chiefly 

 consists of oligoclase, but contains magnetic oxide of iron, titani- 

 ferous iron, &c. 



This rock, forming the bottom of Steamboat Valley, is over- 

 lain on its eastern and western flanks by a compact basalt con- 

 taining magnetic oxide of iron together with various zeolitic 

 minerals. 



Examination of the siliceous deposit at Steamboat Springs. — A 

 specimen of the siliceous deposit taken from the side of a fissure 

 from which steam and carbonic acid were issuing in considerable 

 quantities had a specific gravity of 1*99, slightly scratched fel- 

 spar (orthoclase), and afforded by analysis the following re- 

 sults : — 



* Annates des Mines, sixierae serie, torn. hi. p. 424. 



