TRUE VOLCANOES. 279 



canoes, and unopened trachytic cones, together with the 

 non-volcanic masses which have been broken through by 

 both ; the subsequent chemical analyses, and the chemico- 

 geological inferences deduced from the analyses, would open 

 a field equally wide and fertile. Central America and Java 

 have the unmistakeable superiority over Mexico, Quito, and 

 Chili, that in a greater space they exhibit the most variously 

 formed and most closely approximated stages of volcanic 

 activity. 



At the point where the characteristic series of the vol- 

 canoes of Central America terminates on the borders of 

 Chiapa with the volcano of Soconusco (lat. 16 2'), there 

 commences a perfectly different system of volcanoes the 

 Mexican. The isthmus of Huasacualco and Tehuantepec, 

 so important for the trade with the coast of the Pacific, 

 like the state of Oaxaca, situated to the north-west, is en- 

 tirely without volcanoes, and, perhaps, even destitute of un- 

 opened trachytic cones. It is only at a distance of 160 geog. 

 miles from the volcano of Soconusco, that the small volcano of 

 Tuxtla rises near the coast of AJvarado (lat. 18 28'). Situated 

 on the eastern slope of the Sierra de San Martin, it had a 

 great eruption of flames and ashes on the 2nd of March, 1793. 

 An exact astronomical determination of the position of the 

 colossal snowy mountains and volcanoes in the interior of 

 Mexico (the old Anahuac) led me, after my return to 

 Europe, while inserting the maxima of elevations in my 

 chart of New Spain, to the exceedingly remarkable result, 

 that there is in this place, from sea to sea, a parallel of the 

 volcanoes and greatest elevations which oscillates by only 

 a few minutes to and from the parallel of 19. The only 

 volcanoes and, at the same time, the only mountains covered 

 with perpetual snow in the country, and consequently ele- 

 vations varying from 12,000 to 3,000 feet, the volcanoes 

 of Orizaba, Popocatepetl, Toluca, and Colima, lie between 

 the latitudes of 18 59' and 19 20', and thus indicate the 

 direction of a fissure of volcanic activity of 360 geog. miles 

 in length 69 . In the same direction (lat. 19 9'), between the 



69 See all the bases of these Mexican local determinations, and 

 their comparison with the observations of Don Joaquin Ferrer, in my 

 Recueil d Observations Astron. vol. ii, pp. 521, 529, and 536 550, and 

 gsai Politique sur la Nourelle-Espagne, t. i, pp. 55 59, and 176, t. ii. 



