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UNITED STATES, CANADA AND MEXICO 289
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gems
occur in somewhat irregular veins running in a northeast and southwest
direction, and with a nearly perpendicular dip. The veins are not
continuous, but branch off and disappear at short intervals ; neither
are the contents of uniform quantity, but the valuable parts are
usually in belts in the vein, and limited on each side by portions of
ordinary opal without play of colors. These lines of light are
sometimes numerous and narrow, alternating with the common opal,
forming a very beautiful gem. Many again, even of large size, are
uniform in structure, and exhibit as brilliant a play of colors as do
the finest opals from Hungary. The hill where they are found is about
250 feet high, and two or three miles in length, and for the width of
half a mile for its whole length opals have been found wherever
excavations have been made. The rock in which they occur is a hard,
brittle trachyte with a vitreous lustre, splintering into acute
fragments when struck. A bed several feet in thickness overlying this
rock, of a gray color and soft consistency, probably a trachyte changed
by atmospheric action, also contains opal veins. Other localities
within two leagues of Erandique have furnished fine opals, but as they
are not now worked, Dr. LeConte did not visit them. Many places between
Intibucat and Las Pedras appear favorable to the existence of opal
mines, but these can be discovered only by careful scrutiny of a number
of explorers. As most worthy of future attention, the vicinity of Le
Pasale and of Yucusapa and the ascent of the great mountain of Santa
Rosa may be mentioned. Almost certain success will attend the search
for opal mines in the valley leading from Tambla towards the pass of
Guayoca, nearly on the line of the proposed road. Within half a mile of
Tambla are immense beds of common opal of various shades of color. Near
Guayoca are banded opals of alternate layers of opaque and
semi-transparent white, having the appearance of onyx. They occur in a
red, vitreous trachyte, and sometimes in contact with the masses of
petrified wood which strew the ground for a considerable distance.
Veins of a pearl-colored opal, with red reflections, are also found
here. They have no commercial value, but serve as indications of better
things in the neighborhood. Between the two localities mentioned, near
Tambla and about Guayoca, W. W. Wright, chief assistant of
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