214 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
of different waters. It is also to be remembered that a single local precipitation of 
tellurides will instantly act as an incentive to further precipitation and that the 
law of mass action is apt to produce cumulative effects. 
INFLUENCE OF DEPTH. 
Of the known ore bodies, as few exceed 1,000 feet in horizontal width, so very 
few exceed 1,000 feet in length or extend more than 1,000 feet from the surface. 
To speak broadly, explorations below that limit have not proved very satisfactory. 
With the lines drawn a little closer, it may be said that in proportion to the amount 
of exploration the upper 700 or 800 feet have yielded more than the interval from 
that limit to the lowest levels reached—-about 1,500 feet. It must not be over¬ 
looked, however, that four or five mines still have good ore bodies at a depth of 
1,200 to 1,400 feet from the surface. The developments of the next year or two 
will probably give a safer basis for generalization. 
In a general way, the above-mentioned distribution holds good for any eleva¬ 
tion within the district. In other words, the principal productive zone everywhere 
occupies the space from the surface down to about 1,000 feet below it, and its 
lower limit forms a curved surface approximately parallel to the surface of the 
ground. The fact that one mine situated in a low part of the district may have an 
ore body 2,000 feet below the shaft collar of another mine in a high part of the 
district is thus entirely in harmony with this statement. 
The question now arises, How far does the distribution of known pay shoots 
represent the distribution of all the pay shoots in the district? In other words, 
How far has exploration been impartial in revealing ore bodies near the surface 
and at depths greater than 1,000 feet? 
It requires but little examination to make clear the fact that ore bodies within 
1,000 feet of the surface are far more likely to be discovered than those at greater 
depth. While shafts have been sunk for a few hundred feet without any indica¬ 
tion of ore and have ultimately been developed into productive mines, such a pro¬ 
cedure is considered bold prospecting, and few well-informed mining men would 
seriously contemplate sinking a shaft over 1,000 feet solely on the expectation of 
finding possible ore bodies below that depth. Most of the large mines in the district 
have started upon some indication of ore near the surface and have grown by the 
subsequent discovery of other lodes and ore bodies in the course of their underground 
development. As few individual ore bodies persist for more than 1,000 feet in 
depth, by far the greater part of the underground prospecting is at less depths, 
there being usually little inducement to go deeper, unless, as in the case of the 
Gold Coin and Portland mines, lodes are discovered in which the ore, beginning 
several hundred feet below the surface, extends deeper than the pay shoot upon 
which the mine was originally opened. Thus deep prospecting is usually confined 
to the vicinity of the larger and more persistent pay shoots which have been fol¬ 
lowed down from near the surface. Underground water has also proved a most 
serious obstacle to deep prospecting, few properties being able to develop below the 
1,000-foot zone unless there is abundant and high-grade ore in sight. 
