TRUE VOLCANOES. 807 



mentioned — the Loma de Tablas, and the much broader Mal- 

 pais. Those of the country people who are well acquainted 

 with the district assert that the band of scoriae is elongated 

 toward the south-southeast, and consequently toward the 

 Cofre de Perote. As I have myself ascended the Cofre and 

 made many measurements on it,* I have been but little in- 



* The Cofre de Perote stands nearly isolated to tlie southeast of 

 the Fuerte or Castillo de Perote, near the eastern slope of the great 

 plateau of Mexico ; but its great mass belongs to an important range 

 of heights, which, forming the margin of the slope, extends in a north 

 and south direction, from Cruz Blanca and Rio Frio toward Las Vigas 

 (lat. 19° 37' 37") past the Cofre de Perote (lat. 19° 28' 57", long. 97° 

 T 20"), to the westward of Xicochimalco and Achilchotla, to the Peak 

 of Orizaba (lat. 19° 2' 17", long. 97° 13' 56"), parallel to the chain (Po- 

 pocatepetl — Iztaccihuatl) which separates the cauldron valley of the 

 Mexican lakes from the plain of La Puebla. (For the grounds of 

 these determinations, see my Recueil d'Observ. Astron., vol. ii., p. 529- 

 532 and 547, and also Analyse de t At las du Mexique, or Essai Politique 

 swr la Nouvelle Espagne, t. i., p. 55-60). As the Cofre has raised itself 

 abruptly in a field of pumice-stone many miles in width, it appeared 

 to me in my winter ascent (the thermometer fell at the summit, on 

 the 7th of February, 1804, to 28°-4) to be extremely interesting that 

 the covering of pumice-stone, the thickness and height of which I 

 measured barometrically at several points both in ascending and de- 

 scending, rose more than 780 feet. The lower limit of the pumice- 

 stone, in the plain between Perote and Rio Frio, is 1187 toises (7590 

 feet) above the level of the sea ; the upper limit, on the northern de- 

 clivity of the Cofre, 1309 toises (8370 feet) ; thence through the Pina- 

 huast, the Alto de los Caxones (1954 toises = 12,496 feet), where I 

 could determine the latitude by the sun's meridian altitude, up to the 

 summit itself, no trace of pumice-stone was to be seen. During the 

 upheaval of the mountain a portion of the coat of pumice-stone of the 

 great Arenal, which has probably been leveled in strata by water, was 

 carried up. I inserted a drawing of this zone of pumice-stone in my 

 journal (February, 1804) on the spot. It is the same important phe- 

 nomenon which was described by Leopold von Buch in the year 1834 

 on Vesuvius, where horizontal strata of pumice-tufa were raised by the 

 elevation of the volcano to a greater height indeed, 1900 or 2000 feet 

 toward the Hermitage del Salvatore {Poggendorff' s Annalen, bd.xxxvii., 

 s. 175-179). The surface of the dioritic trachyte rock on the Cofre, at 

 the point where I found the highest pumice-stone, was not withdrawn 

 from observation by snow. The limit <5f perpetual snow lies in Mex- 

 ico, under the latitudes of 19° or 19^°, only at the average elevation 

 of 2310 toises (14,770 feet); and the summit of the Cofre, up to the 

 foot of the small, house-like cubical rock where I set up the instru- 

 ments, reaches 2098 toises, or 13,418 feet, above the sea level. Ac- 

 cording to angles of altitude the cubical rock is 21 toises, or 134 feet, 

 in height; consequently, the total altitude, which can not be reached 

 on account of the perpendicular wall of the rock, is 13,552 feet above 

 the sea. I found only single spots of sporadic snow, the lower limit of 

 which was 12,150 feet, about 700 or 800 feet below the upper limit of 

 forest trees, in beautiful pine-trees : Pinus occidentalism mixed with Cu- 



