In the bottom of the crater are four fumaroles, whence vapors escape, which in issuing produce slight hissing sounds. Abundant deposits of sulphur exist near these. Besides the fumaroles mentioned, there are seven points at the borders of the crater, where gases escape, though in less abundance; six of these points lie to the east of the major diameter, and the seventh on the opposite side. All are inaccessible. The interior of the crater is formed by sheets, which form a regular wall with vertical sides. In some places these layers are profoundly shattered and there various species of rocks, of notably different natures are seen; first, below, are sheets of trachyte, very compact and rich in crystals of striated feldspar and partly decomposed amphibole; above these more or less regular trachytic layers are beds of well-characterized basalt--also very compact and rich in peridote; lastly, above these layers are porous scoriæ, of dark purple color, which indicates the presence of a considerable quantity of iron oxide. These scoriæ must have originated from the fusion of the porphyritic rocks. Every little while, at the summit, rage violent storms of snow, which falls in thick sheets; at such times the atmospheric clouds do not permit objects to be seen at a metre’s distance and the temperature falls to 20° and 22° below 0 C. The exploitation of the sulphur is insignificant since only some forty-eight or fifty tons are taken out, in a year; this sulphur is distilled at the ranch of Tlamacas; it is sold in Mexico and Puebla at the same price as that of Sicily--that of Popocatepetl being superior in quality. The snow, too, on the side of Ozumba, is exploited, but this exploitation is on the smallest scale. Various expeditions have been organized for the ascent of Popocatepetl, some scientific in nature, others for amusement. The first was made in 1519 by Diego de Ordaz, one of the soldiers of Cortes; others followed. In our own day, such expeditions are frequent and their results happily verify each other. Ixtaccihuatl,--“white woman”--connected to Popocatepetl by a ridge of graceful outline, rises to 5,288 m. altitude above sea-level. Down the slopes of this mountain, several torrents, derived from the melting snows, pour and form cascades and falls up to forty-five metres in height. These same slopes, covered by a sheet of astonishingly rich and luxuriant vegetation are gashed by deep crevices, in which are enormous masses of porphyritic and basaltic rocks. Conifers form dense forests up to 3,000 m. altitude; from there the vigor of arborescent vegetation diminishes and at 4,000 m. it completely ceases; from that point on there are only stretches of brambles, which completely disappear at about 4,200 m.; then follow the sands, and, lastly, the perpetual snows, which begin at 4,300 m.