en; 2d, the Horn Silver ore "chimney,"
perhaps fifty feet thick, five hundred feet wide, and of unknown depth,
is the only mass of ore yet found in a mile of well marked fissure; and
3d, the Carbonate mine opened near by in a strong fissure with a bearing
at right angles to that of the Horn Silver, and lying entirely within
the trachyte, yields ore of a totally different kind. Both are opened to
the depth of seven hundred feet with no signs of change or exhaustion.
If the ore were derived from the trachyte, it should be at least
somewhat alike in the two mines, should be more generally distributed in
the Horn Silver fissure, and might be expected to give out at, no great
depth.

If deposited by solutions coming from deep and different sources, the
observed differences in character would be natural; it would accumulate
as we find it in the channels of outflow, and would be as time will
probably prove it, perhaps variable in quantity, but indefinitely
continuous in depth.]

Another question which suggests itself in reference to the Leadville
deposits is this: If the Leadville ore was once a mass of sulphides
derived from the overlying porphyry by the percolation of surface
waters, why has the deposit ceased? The deposition of galena, blende,
and pyrite in the Galena lead mines still continues. If the leaching of
the Leadville porphyry has not resulted in the formation of alkaline
sulphide solutions, and the ore has come from the porphyry in the
condition of carbonate of lead, chloride of silver, etc., then the
nature of the deposition was quite different from that of the similar
ones of Tybo, Eureka, Bingham, etc., which are plainly gossans, and
indeed is without precedent. But if the process was similar to that in
the Galena lead region, and the ores were originally sulphides, their
formation should have continued and been detected in the Leadville
mines.

For all these reasons the theory of Mr. Emmons will be felt to need
further confirmation before it is universally adopted.

From what has gone before it must not be inferred that lateral secretion
is excluded by the writer from the list of agencies which have filled
mineral veins, for it is certain that the nature of the deposit made in
the fissure has frequently been influenced by the nature of the adjacent
wall rock. Numerous cases may be cited where the ores have increased or
decreased in quantity and richness, or have otherwise changed character
in passing fro