1212 KANSAS CITY REVIEW OF SCIENpE. 
sulphides are now being deposited there, along with silica, from solution. Ad- 
mitting, then, as established the view that metalliferous veins have been deposited 
from solutions, the most difficult questions still remain : What are the conditions 
under which deposit takes place? and what, in addition to simple water, have 
been the solvents? 
' In answering the first question it must be remembered that the chemistry of 
nature is far more subtle and refined that that of the laboratory ; that substances 
which are regarded as practically insoluble in the latter cannot be so regarded in 
the tormer. The infinite patience of nature and the infinite slowness of her 
operations must be taken into account. In the perpetual circulation of subter- 
ranean waters infinitesimal deposits, continued and accumulated through almost 
infinite time, produce large results. Thus mineral veins may be composed of 
substances of extremest insolubility, and yet be deposited from solutions. In 
fact, such extreme insolubility, or at least very feeble solubifity, would seem to 
be a condition of mineral vein formation, for otherwise 'the minerals would be in 
most cases brought to the surface instead of being deposited below. 
Again, it must be borne in mind that solubility, even the feeblest, is notably 
increased by heat, especially super-heat, and by pressure. The latter is gener- 
ally regarded only as a necessary condition of super heat and not as itself an active 
agent. But in fact pressure acts directly as an active agent in increasing the 
solubility of nearly all substances. Mr. Sorby has not only proven this by actual 
experiment on a great variety of substances, but has shown that it is a necessary 
consequence and beautiful illustration of the law of correlation and conservation of 
natural forces, and that we have in this as in the case of fusibility an example of 
the equivalency of mechanism and molecular forces. For, as in the matter of 
fusibility in all cases in which expansion takes place in fusion, pressure by resist- 
ing expansion raises the fusing point, while only in those exceptional cases like 
ice, in which contraction takes place in fusion, pressure by arresting contraction 
lowers the fusing point. So also in the matter of solubility, in all cases in which 
contraction takes place in solution, namely, in which the volume of the solution 
is less than the combined volumes of constituents, pressure by arresting contrac- 
tion increases solubility, while only in very exceptional cases as, for example, sal 
ammoniac, in which expansion takes place in solution, pressure by resisting ex- 
pansion diminishes solubility. These latter cases are so extremely rare that we 
may assume as a law the increased solvent power of water in proportion to pres- 
sure. It is even possible by experiment thus to determine the mechanical equiv- 
alent of the chemical force of solution of any given substance; and, in fact, this 
has been so determined for several substances by Mr. Sorby. There can be no 
doubt, then, that the solvent power of water may be increased without limit by 
corresponding increase of heat and pressure. It is quite certain, therefore, that 
water deep in the interior of the earth, especially in volcanic regions, and there- 
fore under heavy pressure and super-heat, would have its solvent power greatly 
increased, not only by the super-heat but also by the pressure. It is believed 
-that few substances could resist entirely its solvent power. Such waters, coming 
