TRUE VOLCANOES. 307 



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 the 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 

 7' 20"), to the westward of Xicochimalco and Achilchotla, to the Peak 

 of Orizaba (lat. 19 2' IT', 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 Atlas du Mexique, or Essai Politique 

 sur la Nouvelle Espayne, t. i., p. 55-GO). 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 = 12,49G 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 hy 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 of perpetual snow lies in Mex- 

 ico, under the latitudes of 19 or 19|r , 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 : Pimis occidentcdis, mixed with Cu~ 



