UNDERGROUND WATER. 
249 
1 foot near Beacon Hill may be compared to part of an exceedingly irregular hori¬ 
zontal lens 1 foot thick near Beacon Hill and thinning to an edge in the northern and 
central parts of the productive area. Within such a mass, however, would be 
pockets of water undrained because not connected by fissures with the artificial 
channel of discharge. Furthermore, certain persistent fissures would probably 
contribute water from points outside of the recognized limit of general drainage. 
It is thus impossible to determine with any approach to accuracy what area a plate 
of rock 1 foot thick and possessing the same water-bearing capacity as the Cripple 
Creek rocks should have in order to contain the quantity of water removed from the 
district when the water in the Elkton is lowered 1 foot. It may be assumed that the 
area of such a plate is equal to that part of the volcanic neck lying south of Globe 
Hill and west of Bull Hill, plus a projecting area to include the phonolite plug of 
Beacon Hill. (See fig. 23.) In such case the volume of rock drained is approxi¬ 
mately 80,000,000 cubic feet. If the water discharged for each foot of subsidence 
is taken at 35,000,000 gallons, the drained water-bearing cavities in the rock con¬ 
stitute about 6 per cent of the whole. If Mr. Mudd’s estimate of approximately 
66,700,000 gallons be accepted as the average discharge per foot of drop above the 
level of the Standard tunnel, then the water-bearing cavities, on the same assump¬ 
tion as before with regard to the area drained, constitute about 13 per cent of the 
rock volume. These rough estimates, it should be observed, relate merely to spaces 
of visible size, due chiefly to fracture, but probably in some cases, as in the Elkton 
mine, enlarged by solution. If the assumption as to area drained is anywhere near 
the truth, even the lower figure of 6 per cent indicates that the aggregate water 
capacity of the fissured rock of the volcanic neck is unusually large for texturally 
nonporous rocks. Similar or more accurate estimates for other regions are lacking, 
so that no close comparisons are possible. The original pore space in coarse assorted 
gravel probably ranges, according to Van IIise, a from 32 to 40 per cent. The water¬ 
bearing spaces in some of the shattered rock in the Moose, Midget, Moon-Anchor, 
and Conundrum mines are probably nearly as porous as coarse gravel, and the large 
water capacity or such portions of the volcanic neck considered in connection with 
the remarkably abundant fissures suggests that the assumed area of the hypothet¬ 
ical plate 1 foot in thickness is not excessive. 
It is probable that at a depth of 1,000 to 1,500 feet below the El Paso tunnel 
open fissures and shattered zones in the breccia will still be sufficiently abundant to 
contain in the aggregate a large body of water, though the amount is likely to be 
smaller than that at the El Paso level. It is probable, also, that the greater part of 
this water can be drawn off by a tunnel, provided that the main tunnel or crosscuts 
are run through fissure zones known to carry abundant water at higher levels. 6 
From a tunnel driven to a point under the Blue Bird shaft it would not be difficult to 
crosscut into the water basin of the Vindicator and Golden Cycle mines. The valu¬ 
able bearing on this problem of the careful record that has been kept of the El Paso 
water can hardly be overestimated. 
a A treatise on metamorphism: Mon. U. S. Geol. Survey, vol. 47, 1904, p. 127. 
6 Press dispatches from Cripple Creek, dated March 27, 1900, bring news that the El Paso mine, which has been opened to 
the 1,000-foot level, or 400 feet below the drainage tunnel, has been flooded. On breaking through the El Paso phonolite dike 
(see fig. 39, p. 3-50) the miners encountered an unexpected flow of water, estimated at from 5,000 to 7,000 gallons per minute, 
which drowned the pumps and in six hours filled the mine to the GOO-foot level. This event shows that the Assuring along the 
C. K. & N. vein constitutes an open and.effective waterway to a depth of at least 400 feet below the present drainage tunnel. 
