pockets of ore, if they have been
exposed to the same agencies as those which have so changed the under
surface.

Accepting all the facts reported by Mr. Emmons, and without questioning
the accuracy of any of his observations, or depreciating in any degree
the great value of the admirable study he has made of this difficult and
interesting field, his conclusion in regard to the source of the ore
cannot yet be insisted on as a logical necessity. In the judgment of the
writer, the phenomena presented by the Leadville ore deposits can be as
well or better accounted for by supposing that the plane of contact
between the limestone and porphyry has been the conduit through which
heated mineral solutions coming from deep seated and remote sources have
flowed, removing something from both the overlying and underlying
strata, and by substitution depositing sulphides of lead, iron, silver,
etc., with silica.

The ore deposits of Tybo and Eureka in Nevada, of the Emma, the Cave,
and the Horn Silver [1] mines in Utah, have much in common with those of
Leadville, and it is not difficult to establish for all of the former
cases a foreign and deep seated source of the ore. The fact that the
Leadville ore bodies are sometimes themselves excavated into chambers,
which has been advanced as proof of the falsity of the theory here
advocated, has no bearing on the question, as in the process of
oxidation of ores which were certainly once sulphides, there has been
much change of place as well as character; currents of water have flowed
through them which have collected and redeposited the cerusite in sheets
of "hard carbonate" or "sand carbonate," and have elsewhere produced
accumulations of kerargyrite, perhaps thousands of years after the
deposition of the sulphide ores had ceased and the oxidation had begun.
In the leaching and rearrangement of the ore bodies, nothing would be
more natural than that accumulations in one place should be attended by
the formation of cavities elsewhere.

[Footnote 1: The Horn Silver ore body lies in a fault fissure between a
footwall of limestone and a hanging wall of trachyte, and those who
consider the Leadville ores as teachings of the overlying porphyry would
probably also regard the ore of the Horn Silver mine as derived from the
trachyte hanging wall; but three facts oppose the acceptance of this
view, viz., let, the trachyte, except in immediate contact with the ore
body, seems to be entirely barr