ransome.] ORIGIN OF THE LODE AND STOCK ORES. 135 
metals and their sulphides. Some solutions are undoubtedly more 
efficient than others under like conditions, but where so many unknown 
elements, such as degree of heat, amount of pressure, relative mass 
of solvent and solute, and duration of the process, enter into the 
problem, it is rarely possible to arrive at even approximate quantitative 
results. 
As the lode and stock ores wee deposited from solutions, it follows 
that the chemical action of these solutions on the wall rocks offers a 
very important mode of attacking the problem of their chemical char- 
acter. The nature of this metasomatic alteration has been discussed 
at some length on pages 114-131 of this report. It is concluded that 
the solutions producing it were chemically different in different por- 
tions of the quadrangle. The very slight development of carbonates 
in connection with some lodes, and their entire absence in others, indi- 
cate that carbon dioxide or alkaline carbonates were not abundant 
in the mineralizing waters, although probably not wholly absent in 
the case of deposits such as those of Silver Lake- Basin. The silicifi- 
cation observed in connection with the Red Mountain deposits, with 
the removal of most of the bases, including in some cases part of the 
alumina and the addition of sulphur and water, indicate the action of 
acid waters, probably containing free sulphuric acid. But here 
another element, which can not be ignored, (niters the problem. 
Water containing sulphuric acid and ferric sulphate is known in the 
Red Mountain region to-day — not as ascending thermal water, but as 
(in pari at least) descending water, which owes its acidity to the 
oxidation of previously deposited iron pyrite. Tin 1 capacity of this 
water to effect some changes in the country rock is beyond doubt. It 
is not unlikely, therefore, that much of the alteration visible in the 
! Red Mountain region is the result of complex processes involving the 
action of solutions of different characters and origin and acting upon 
any given mass of the rock at different times. 
Writers on the genesis of ore deposits very commonly speak of 
the ''circulation," "currents," or "flow" of the ore-bearing solutions 
within the fissures. Although the use of these terms is convenient 
and can not be regarded as entirely incorrect, yet it is believed that 
it has tended to give artificial or false conceptions in regard to the 
actual processes of ore deposition in many veins, particularly in large 
veins. Ore deposited by solutions having obvious movement through 
a fissure should exhibit the phenomenon called by Posepny erustifica- 
tion — i. e., it should be deposited in successive layers or coatings upon 
the walls of the fissure. l But this structure, formerly so much insisted 
upon as evidence of deposition in open fissures, is, as a matter of 
fact, of comparatively rare occurrence even in veins which on other 
evidence are demonstrablj 7 simple fissure fillings. In most of the 
1 It is perhaps hardly needful to point out that the converse of this proposition is not necessa- 
rily true. 
