Page:Appleton's Guide to Mexico.djvu/262

234 to this we have the analogy of the hills of globular basalt, mixed with layers of clay and marl, which are found, often of very small dimensions, in the central chain of Bohemia, sometimes isolated and sometimes crowning long basaltic ridges at both extremities.

"Some of the hornitos are so much broken up, or have such large internal cavities, that mules, when compelled to place their fore-feet upon the flatter ones, sink in deeply, while in similar experiments which I made the hills constructed by the termites resisted. In the basaltic mass of the hornitos I found no immersed scoriæ, or fragments of old rocks which had been penetrated, as in the case of the lavas of the great Jorullo. The appellation hornos or hornitos is especially justified by the circumstance that in each of them (I speak of the period when I traveled over the Playas de Jorullo and wrote my journal, 18th of September, 1803) the columns of smoke break out, not from the summit, but laterally.

"In the year 1780, cigars might still be lighted, when they were fastened to a stick and pushed into a depth of two or three inches; in some places the air was at that time so much heated in the vicinity of the hornitos, that it was necessary to turn away from one's proposed course.

"Notwithstanding the refrigeration which, according to the universal testimony of the Indians, the district had undergone within twenty years, I found the temperature in the fissures of the hornitos to range between 199° and 203°; and, at a distance of twenty feet from some hills, the temperature of the air was still 108•5° and 116•2° at a point where no vapors reached me, the true temperature of the atmosphere of the Playas being at the same time scarcely 77°.

"The weak sulphuric vapors decolorized strips of test-paper, and rose visibly for some hours after sunrise, to a height of fully sixty feet.

"The view of the columns of smoke was most remarkable early in a cool morning. Toward midday, and even after eleven o'clock, they had become very low and very visible only from their immediate vicinity. In the interior of many of the hornitos we heard a rushing sound, like the fall of water. The small basaltic hornitos are, as already remarked, easily destructible. When Burkart visited the Malpais twenty-four years after me, he found that none of the hornitos were still smoking, their temperature being in most cases the same as that of the surrounding air, while many of them had lost all regularity of form by heavy rains and meteoric influences. Near the principal volcano, Burkart found small cones, which were composed of a brownish-red conglomerate, of rounded or angular fragments of lava, and only loosely coherent.

"In the midst of the upheaved area covered with hornitos, there is still to be seen a remnant of the old elevation on which the buildings of the