Page:Appleton's Guide to Mexico.djvu/261

Rh more cautiously, unupheared soil. Its beautiful vegetation, in which a multitude of salvias bloom beneath the shade of a new species of fan-palm (Corypha pumas), and of a new alder (Alnus Jonillensis), contrasts with the desert, naked aspect of the Malpais.

"The comparison of the height of the barometer, at the point where the upheaval commences in the Playas, with that at the point immediately at the foot of the volcano, gives 473 feet of relative perpendicular elevation. The house that we inhabited stood only about 500 toises (3, 197 feet) from the border of the Malpais. At that place there was a small perpendicular precipice of scarcely twelve feet high, from which the heated water of the brook (Rio de San Pedro) falls down.

"The portion of the inner structure of the soil, which I could examine at the precipice, showed black, horizontal, loamy strata, mixed with sand (lapilli). At other points which I did not see, Burkart has observed 'on the perpendicular boundary of the upheaved soil where the ascent of this is difficult, a light gray and not very dense (weathered) basalt, with numerous grains of olivine.'

"This accurate and experienced observer has, however, like myself, on the spot, conceived the idea of a vesicular upheaval of the surface effected by elastic vapors, in opposition to the opinion of celebrated geognosists, who ascribe the convexity, which I ascertain by direct measurement, solely to the greater effusion of lava at the foot of the volcano.

"The many thousand small eruptive cones (properly rather of a roundish or somewhat elongated oven-like form), which cover the upheaved surface pretty uniformly, are on the average four to nine feet in height. They have risen almost exclusively on the western side of the great volcano, as, indeed, the eastern part toward the Cerro de Cuiche scarcely constitutes one twenty-fifth of the entire area of the vesicular elevation of the Playas.

"Each of the numerous hornitos is composed of weathered basaltic spheres, with fragments separated like concentric shells; I was frequently able to count from twenty-four to twenty-eight such shells. The balls are flattened into a somewhat spheroidal form, and are usually fifteen to eighteen inches in diameter, but vary from one to three feet. The black basaltic mass is penetrated by hot vapors and broken up into an earthy form, although the nucleus is of greater density; while the shells, when detached, exhibit yellow spots of oxide of iron. Even the soft, loamy mass which unites the balls is, singularly enough, divided into curved lamcllce, which wind through all the interstices of the balls.

"At the first glance I asked myself whether the whole, instead of weathered basaltic spheroids, containing but little olivine, did not perhaps present masses disturbed in the course of their formation. But in