244 GEOLOGY AND GOLD DEPOSITS OF THE CRIPPLE CREEK DISTRICT. 
great flow in the tunnel. The water later encountered in the tunnel is apparently 
not connected with the Elkton mine by any important open channels. 
The history of the water of the Elkton mine thus well illustrates the fact that 
the portion of the underground water which need be considered in mining opera¬ 
tions is confined to fissures. It also explains the frequent difference in water 
level in neighboring mines. The few springs in the district appear in some cases 
to be unaffected by the unwatering of deep mines in their vicinity, showing that 
they are not necessarily supplied from a general bod}" of underground water. At 
Arequa, for example, is a spring that has not disappeared in spite of the deep work¬ 
ings at Elkton and under Beacon Ilill. 
All of the existing drainage tunnels have tapped the breccia-filled volcanic 
neck from the west or southwest, and it is from the latter quarter that future tun¬ 
nels, in all probability, will be driven. The effect of each tunnel has naturally 
been most quickly and decisively apparent in what may be called the west-side 
group of mines (PI. XX, p. 242). That the Ophelia tunnel, driven far into the 
breccia and through a number of previously known fissure zones, would drain the 
mines of Raven and Gold hills approximately to its level was almost a foregone 
conclusion. But in the case of the Standard tunnel, directed not for the breccia 
but for the phonolite plug of Beacon Hill, no such result could confidently be pre¬ 
dicted. Fortunately the phonolite proved to be connected by open fissures with 
the main volcanic neck, and there can be no question that it lowered the water 
levels of most of the west-side mines. The Eclipse seems to have been the only 
wet mine not clearly affected. The peculiar behavior of the water in this mine, 
which should perhaps be grouped with the Battle Mountain or Victor mines, has 
already been pointed out and is shown diagrammatically in PI. XX (p. 242). The 
Eclipse water seems to occupy an impervious pocket in the breccia, for which no 
geological explanation has been found. The Standard tunnel undoubtedly drained 
the Gold Hill and Povert}" Gulch mines. 
The effect of the Standard tunnel on the mines of the Victor group is not clear. 
It is supposed to have lowered their water surfaces to some extent, but the con¬ 
tinuous pumping of the Stratton's Independence, Gold Coin, and Strong mines 
has probably been the dominant factor in lowering the water in this part of the 
district. At all events, the effect of the tunnel drainage is not clearly distinguish¬ 
able from that of pumping. As may be seen from PI. XX (p. 242), the pumping 
levels of the Gold Coin and Stratton’s Independence mines are far below the flow 
gradient of the tunnel. 
As regards underground water, the east-side group of mines is divisible into 
two subgroups. One of these includes the mines lying on the western and south¬ 
western slopes of Bull Hill, particularly the American Eagle, John A. Logan, Orpha 
May, Blue Bird, and Last Dollar mines. The shafts of these mines are among 
the deepest in the district, the American Eagle shaft being second only to the 
Lillie (see PI. XI, p. 148), though its sump is 806 feet above that of the Stratton's 
Independence shaft. Notwithstanding their depth, these shafts have had little 
trouble with underground water. This is due to the fact that they were not sunk 
to their present depth until this part of Bull Hill had been drained by the mines 
and tunnels to the west. The American Eagle, John A. Logan, and Orpha May 
