392 J. A, PHILLIPS ON MINERAL VEINS: 
phate of sodium, common salt, &c. Carbonic acid. escapes nearly 
along the whole line; while sulphuretted hydrogen is evolved and 
sulphur deposited at certain points. The fissures, which appear to 
have been subjected to a series of repeated widenings, such as 
would result from an unequal movement of their walls, are lined, 
sometimes to a thickness of several feet, by incrustations of silica 
of various degrees of hydration, containing hydrated ferric oxide 
and, exceptionally, crystals of iron pyrites. This silica exhibits the 
ribbon-like structure so frequently observed in mineral veins, and 
when examined under the microscope is observed to consist of alter- 
nately amorphous and crystalline bands, sometimes enclosing druses 
lined with crystals of quartz. 
At a distance of nearly a mile, in a westerly direction, from the 
locality above described is a second group of fissures In every respect 
similar to those of Steamboat Springs, excepting that they are no 
longer traversed by hot water, although still at various points giving 
off steam and carbonic acid. Towards the southern extremity of 
the principal fissure of this group the siliceous deposit extends con- 
siderably beyond the edges of the cleft, and has accumulated to a 
distance of some ninety yards on each side of the opening. 
The silica of this deposit is sometimes chalcedonic and contains 
nodules of hyalite; by far the larger proportion of it, however, although 
somewhat friable, is distinctly crystalline, the crystals containing 
numerous liquid-cavities and exhibiting the usual optical and other 
characteristics of ordinary quartz. Besides oxides of iron and 
manganese, this quartz contains small quantities of iron and copper 
pyrites; and in a paper on the Gold Regions of California, pub- 
lished in the ‘ Annales des Mines’ in 1863, Mr. Laur states that he 
had found it to contain distinct traces of gold. With regard to these 
deposits, this gentleman remarks that, so far as auriferous quartz 
yeins are concerned, Steamboat Springs appear to place before us a 
sort of practical verification of the theory which regards a certain 
class of metalliferous deposits as being produced by mineral waters 
in the fissures through which they circulate*. 
For many years local attention does not appear to have been 
directed to this portion of the Steamboat Valley; but in the year 
1878 this older fissure was opened by a tunnel to a depth of fifty 
feet from the surface, and the veinstone was there found so im- 
pregnated with cinnabar as to yield large quantities of mercurial 
ore of considerable commercial valuey. At this depth the tem- 
perature was not sufficiently high to cause inconyenience to the 
workmen, and five samples of the ore subjected to assay gave an 
average yield of 2:90 per cent. of mercury. 
Samples taken from the nearly horizontal flats produced by the 
overflow of the water yielded, on the contrary, traces only of that 
metal. 
Steamboat Springs thus afford another striking example of the 
* Annales des Mines, 1863, p. 423. 
t+ Messrs. Humbert, Mining Engineers, San Francisco. Private communi- 
cation. 
