Ch. 14: Mexico and Central America

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	UNITED STATES, CANADA AND MEXICO 289

	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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