662 The American Naturalist. [July, 
hypothesis, numerous diamond-drill-holes and shafts have been sunk, 
and those that were continued to a sufficient distance (seldom more 
than 150 feet) have encountered the iron-flint blanket, but invariably 
with its silver-contents lacking. 
“ A later and more probable hypothesis is that the silver of the mines 
was originally contained in a great overflow of silver-bearing porphy- 
rite, perhaps coming from Monument Peak, which covered a square 
mile or more in the immediate vicinity of the mines. In the erosion 
of this porphyrite, the silver in it was leached out, the greater portion 
segregating itself in the Bridal Chamber and the workings connected 
with it, and the remainder going to the Bunkhouse and the connected 
Incline and Bella workings. The greatest distance that any large 
body of ore has been found from the line of the porphyrite is 500 feet, 
and most of the workings are within 200 feet of that line. 
“ The writer’s own observations have shown him that a distance of 
about 250 feet from the porphyrite the ore decreases in grade, and 
that at a distance of 300 feet there is little that can be profitably 
shipped. The Bunkhouse workings appear to have been in a cavern, 
in which the ore was deposited rapidly, and not by the slower process 
of a dissolution of the limestone and a synchronous substitution of the 
silver-bearing manganese. In many places in this working the man- 
ganese is pulverulent and non-adherent to the limestone walls; and 
when thoroughly cleaned off by brushing, the face of the limestone has 
precisely the same weathered appearance as that of an outcrop, and 
looks as though it had been freely acted upon by the atmosphere, pos- 
sibly assisted by the rays of the sun. Something of the same sort may 
be studied in the Last Chance workings at a depth of 20 feet from the 
surface, while the Bunkhouse workings lie at a depth of from 50 to 60 
eet. 
“ The evidences of a previous cavern or cavity in the blue limestone 
at the Bridal Chamber are not so marked, but the indications are such 
that in the writer’s opinion a comparatively rapid deposition appears 
more probable than a gradual substitution, such as was very likely the 
case in the Incline workings, the Bella Chute, the Thirty Slope and 
the Twenty-five Cut workings. 
“In a property of the extent of the Lake Valley mines, which has 
yielded at least $5,000,000, there always remains the possibility of new 
finds through the expenditure of small amounts of money. The con- 
tact between the two limestones is an established fact ; and there are 
but few places on the southeastern portion of the property where this 
contact cannot be reached at the moderate depth of 150 feet. Thus 
