402 COSMOS. 



IX. MEXICO. 



The six Mexican Volcanoes, Tuxtla,* Orizaba, Popoca- 

 tepetl,* Toluca, Jorullo* and Colima,* four of which have 

 been in a state of igneous activity within the historical era, 

 were enumerated in a former place, 6 and described in their 

 geognostically remarkable relative position. According to 

 recent investigations by Gustav Rose, the formation of 

 Chimborazo is repeated in the rock of Popocatepetl, or 

 Great volcano of Mexico. This rock also consists of oligo- 

 clase and augite. Even in the almost black beds of 

 trachyte, resembling pitch-stone, the oligoclase is recognis- 

 able in veiy small acute-angled crystals. To this same Chim- 

 borazo and Teiieriffe formation belongs the volcano of Co- 

 lima, which lies far to the west, near the shore of the South 

 Sea. I have not myself seen this volcano, but we are indebted 

 to Herr Pieschel * (since the spring of 1855) for a very 

 instructive view of the different kinds of rocks collected by 



6 See above, pp. 279 281. 



7 See Pieschel, Ueber die Vullcane von Mexico, in the Geitschrfft fur 

 allgem. Erdkunde, Bd. vi, 1856, s. 86 and 489532. The assertion 

 there made (p. 86) " that never mortal has ascended the steep summit 

 of the Pico del Fraile," that is to say, the highest Peak of the Volcano 

 of Toluca, has been confuted by my barometrical measurement made 

 upon that very summit, (which is, by the way, scarcely 10 feet in width,) 

 on the 29th September, 1803, and published first in 1807, and again 

 recently by Dr. Gumprecht in the same volume of the journal above 

 referred to (p. 489). The doubt raised on this point was the more sin- 

 gular as it was from this very summit of the Pico del Fraile, whose 

 tower-like sides are certainly not very easy to climb, and at a height 

 scarcely 600 feet less than that of Mont Blanc, that I struck off the 

 masses of trachyte which are hollowed out by the lightning, and which 

 are glazed on the inside like vitreous tubes. An essay was inserted so 

 early as 1819 by Gilbert in volume Ix of his Annalen der Physik, 

 (s. 261) on the specimens placed by me in the Berlin Museum as well 

 as in several Parisian collections (see also Annales de Chimie et de 

 Physique, t. xix, 1822, p. 298). In some places the lightning has bored 

 such regular cylindrical tubes (as much as 3 inches in length,) that they 

 can be looked through from end to end, and in those cases the rock 

 surrounding the openings is likewise vitrified. I have also brought 

 with me pieces of trachyte in my collections, in which the whole sur- 

 face is vitrified without any tube-like perforation, as is the case at the 

 little Ararat and at Mont Blanc. Herr Pieschel first ascended the 

 double-peaked volcano of Colirna, in October, 1852, and reached the 



