298 Chemical Geology of the Gold-fields of California. [Mar. 12, 



There is also everywhere an escape of carbonic acid, whilst from some 

 places sulphuretted hydrogen is also evolved. These products, on arriving 

 at the surface, give rise to the deposition of sulphur, silica, and anhydrous 

 oxide of iron. The silica and oxide of iron form semicrystalline bands 

 parallel with the walls of the fissures ; and spongy deposits accumulate 

 around some of the points of most active emergence. 



At a considerable distance to the west of those above described, a fissure 

 having the same origin is observed ; but this is no longer traversed by 

 currents of hot water, although it still gives off steam and carbonic acid 

 at various points throughout its extent. At its northern extremity a central 

 fissure still remains open ; but in other localities it is, for the most part, ob- 

 structed by siliceous concretions. This siliceous rock is metaUiferous, and, 

 in addition to oxide of iron and manganese, contains iron and copper py- 

 rites. M. Laur states that he also discovered metalhc gold in this deposit. 



The rock enclosing the veins of Steamboat springs is granite, which in 

 their vicinity is much decomposed, being often reduced to a cavernous 

 skeleton of silica containing a few scales of mica. 



Alkaline Lakes. — In that portion of California lying on the east of the 

 Sierra Nevada are Mono Lake and Owen's Lake, both considerable sheets 

 of water, highly impregnated with alkaline salts. Owen's Lake lies in lat. 

 36° 20" south, long. 118° west from Greenwich, and is about twenty miles 

 in length and eight in width. 



The waters of this lake have a specific gravity of 1 "076, and contain 

 7128-24 grs. of solid matter per gallon. The salts held in solution are 

 chiefly carbonate and sulphate of soda, with chloride of sodium; but 

 potash, silica, and phosphoric acid are also present. 



The incrustations, which at certain seasons of the year are found to 

 the extent of many hundreds of tons, consist of a white spongy efflo- 

 rescence, and are, as will be seen from the results of the analysis given in 

 the paper, chiefly composed of carbonate of soda, mixed with a little chlo- 

 ride of sodium and sulphate of soda. 



General deductions. — The author remarks that, in the present state of 

 our knowledge, the results of a careful examination of the gold-regions of 

 the Pacific coast would appear to lead to the following conclusions : — 



a. Quartz veins have generally been produced by the slow deposi- 

 tion from aqueous solutions of silica on the surfaces of the enclosing 

 fissures. 



b. From the general parallelism with its w^alls of the planes of any frag- 

 ments of the enclosing rock which may have become imbedded in a vein, 

 it is to be inferred that they were mechanically removed by the growth of 

 the several layers to which they adhered, and that a subsequent deposition 

 of quartz took place between them and the rock from which they had 

 become detached. In this way were introduced the masses of rock known 

 as " horses." 



c. The formation of quartz veins is due to hydrothermal agencies, of 



