From Proceedings of the Geological Society of London, Volume 1 (November 1826 to June 1833)

An extract of a letter was read from Lieutenant William Glennie, R.N., dated Mexico, May 6th, 1827, entitled “The Ascent of Popocatapetl.”

Many contradictory reports having long existed respecting the volcanic nature of this mountain, the author felt desirous of ascertaining its actual condition in person.

The ascent commenced during the month of April 1827, from the village of Ameca, situated in the province of Puebla, and near the N.W. foot of the volcano, at an elevation of 8216 feet above the level of the sea, and distant 14 leagues from Mexico.

The author describes the sides of the mountain as thickly wooded with forests of pines, extending to the height of near 12,693 feet, beyond which altitude vegetation ceased entirely. The ground consisted of loose black sand of considerable depth, on which numerous fragments of basalt and pumice-stone were dispersed. At a greater elevation, several projecting ridges, composed of loose fragments of basalt, arranged one above another, and overhanging precipices 600 or 700 feet deep, presented formidable impediments to the author’s progress; and, in one direction only, a ravine was observed to pass through these ridges, having its surface covered with loose black sand, down which fragments of rocks ejected from the crater continually descended.

After twelve hours of incessant fatigue the author gained the highest point of the mountain on the western side of the crater, 17,884 feet above the sea; at which station the mercury in the barometer subsided to 15.63 inches, and the temperature indicated by the attached and detached thermometers, was respectively 39° and 33° Fahr. at 5 o’clock P.M., when exposed to the direct rays of the sun. The plain of Mexico was enveloped in a thick haze, and the only distant objects visible at that time, were the volcanoes of Orizaba and Iztaccihuatl. The crater of Popocatapetl appeared to extend one mile in diameter, and its edges of unequal thickness descended towards the east. The interior walls consisted of masses of rock arranged per- . pendicularly, and marked by numerous vertical channels, in many places filled with black sand. Four horizontal circles of rock differently coloured were also noticed within the crater; and from the edges of the latter, as well as from its perpendicular walls, several small columns of vapour arose smelling strongly of sulphur. The noise was incessant, resembling that heard at a short distance from the sea shore during a storm; and at intervals of two or three minutes the sound increased, followed by an eruption of stones of various dimensions; the smaller were projected into the ravine before mentioned, the larger fell again within the crater.

The sensations experienced by the author were analogous to those usually felt by travellers at considerable elevations; viz. weariness, difficult respiration, and headache, the latter inconvenience having been first perceived at a height of 16,895 feet. Tobacco smoke and spirituous liquors were also found to produce an unusually rapid effect upon the sensorium.