FUTURE OF THE DISTRICT. 
231 
a solution of hydrogen sulphide to permeate the rocks with more ease than a solution 
of salts of the heavy metals. The same applies in a less degree to carbon dioxide 
and to the ordinary alkaline salts. Hydrolysis of many salts of the heavy metals 
has a tendency to transform the bases into colloid solutions or suspensions, and for 
this reason also such substances are more apt to remain in the fissures. Fluorite 
is common in the altered rocks, but only in very small amounts, indicating that 
diffusion of alkaline fluorides has taken place. 
In general, then, the acids will permeate the rock more extensively than the 
bases and, as Van Hise says,° “in underground solutions the alkalies and alkaline 
earths, with the exception of magnesia, will largely take possession of the acids. To 
a less extent this is true of magnesia and to a still smaller degree of alumina and 
iron. Thus we have the partial explanation of the relative solubility of the bases. 
The alkalies are dissolved to the greatest extent; next in order comes lime, then 
magnesia, and finally iron and alumina.” 
It is not denied that solutions of heavy metals may freely permeate many 
porous rocks—there are, of course, many degrees of porosity—but they will not do 
so if open fissures are available and if there is no very strongly pronounced chemical 
reaction between the rock and the solution. How conditions may change in this 
case is well shown by the energetic metasomatic action of lead solutions on limestone. 
We believe that the waters ascended in the deeper part of the volcano with 
comparatively great velocity on the fewer fissures and in the smaller areal space 
there available. Nearing the surface it spread through a much larger space in a 
more complicated fissure system. The speed of the current became checked; in 
places conditions no doubt approached stagnation; locally the solutions even 
became descending instead of rising; deposition and chemical action on the country 
rock changed their composition; and mingling with fresh ascending waters, possibly 
also with atmospheric waters, induced further precipitation. In this manner we 
would account for the smaller amount of ores deposited in depth and the richness 
and abundance of ore nearer to the old surface. The portion of the volcano 
removed by erosion may have contained still richer deposits. 
FUTURE OF THE DISTRICT. 
To predjct the future yield of any mining district is no easy task; the conditions 
under which most ores are deposited are as yet too imperfectly understood and the 
deposits themselves are usually too erratic in form and distribution to give certitude 
to such predictions, even when these are based upon a careful study of the history 
and present condition of a district. Nevertheless, it is part of the duty of the geolo¬ 
gists who have officially investigated the Cripple Creek district to interpret to the 
best of their ability the bearing of ascertained facts upon future mining develop¬ 
ment. For such a forecast of the future moderate probability is all that can be 
claimed. 
As has been pointed out in the preceding pages, the largest known ore bodies 
of the district are apparently confined within a zone which extends from the surface 
to a depth of 1,000 feet. In general, explorations below that depth have been much 
less satisfactory as regards quantity of ore than explorations above. It is certainly 
a A treatise on metamorphism: Mon. U. S. Geoi. Survey, vol. 47, 1904, p. 92. 
