Page:Popular Science Monthly Volume 71.djvu/191

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185
SOME LITTLE KNOWN MEXICAN VOLCANOES

To watch the change in vegetation from the plain to the summit of the mountain is a constant pleasure. On the dry plain cactus and other desert plants are common, hut on the flanks of the mountain pines begin and many bright-colored flowers. These, as one continues the ascent, become shorter and more stunted, until in the crater the flower blossoms an inch or thereabouts from the ground instead of one or two feet from the ground, as is the case lower down. On the highest portions of the rim vegetation is almost lacking.

The Crater.—The crater of the volcano is somewhat elliptical in form, being a little more than a mile in its longest diameter and about a third of a mile in its shortest. The crater rim is complete on all sides, but is low on the side through which entrance is made. In the bottom of the crater and 1,000 feet below the highest portion of the rim are two beautifully clear lakes, the larger of which is almost one fifth of a mile in diameter and has a maximum depth of thirty feet. These two lakes are separated by a dome of compact andesite of considerable height (see illustration). This dome is of especial interest, because of its bearings upon the origin of the Mt. Pelée spike. There seems to be little doubt, as T. Flores points out, that it is composed of the lava which was forced up and out of the vent after the last eruption and which now closes it and stands above the floor of the crater.

Comparison with Mt. Pelée.—It was suggested by Dr. E. O. Hovey that the Pelée plug was formed in this way also, i. e., that instead of a solid mass of lava being pushed up bodily, as Heilprin believed, very

PSM V71 D191 Crater of toluca showing lake and andesite cone.png

Fig. 8. Crater of Toluca, showing Lake and Andesite Cone.