326 COSMOS. 



myself ascended the Cofre and made many measurements 

 on it, 19 I have been but little inclined to conclude, from a 

 19 The Cofre de Perote stands nearly isolated to the south-east of 

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

 great plateau of Mexico; but its great mass belongs to an impor- 

 tant range of heights, which, forming the margin of the slope, 

 extends in a north and south direction, from Cruz Blanca and Rio 

 Frio towards 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' 17", long. 

 97 13' 56"), parallel to the chain (Popocatepetl 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, pp. 529532 and 547, and 

 also Analyse de I 'Atlas du Mexique, or Essai Politique sur la Nou- 

 velle Espagne, t. i, pp. 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 February, 1804, to 28'4) to be extremely interesting, that 

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

 measured barometically 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 

 i'eet) above the level of the sea ; the upper limit on the northern 

 declivity of the Cofre 1309 toises (8370 feet); thence through the 

 Pinahuast, the Alto de los Caxones (1954 toises = 12,4 96 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 levelled 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 impor- 

 tant phenomenon 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 towards the Hermitage del Salvatore (Pog- 

 gendorfs 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 Mexico under the latitudes 

 of 19 or 191, 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 instruments, reaches 2098 

 toises, or 13,418 feet above the sea level. According to angles of 

 altitude the cubical rock is 21 toi.ses or 134 feet in height ; conse- 

 quently the total altitude, which cannot 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 



