Humboldt' '« Theory of the Volcano qfJorulh. 57 



balls, separating into concentric leaves, imbedded in a black 

 clay. These hillocks, as well as some large fissures which 

 traverse the intermediate plain, act as so many fumarole, giv- 

 ing out thick clouds of aqueous vapour combined with sulphu- 

 ric acid, and at a very high temperature. 



The two first mentioned products of this eruption are of 

 ordinary occurrence, and testify that, at least for the greater 

 part, the volcanic action took effect here in the usual mode. 



The phenomena of the third class are remarkable, and de- 

 serving of the greatest consideration, as appearing at first 

 sight to differ materially from any hitherto observed, and as 

 referred for this reason by M. de Humboldt to a mode of vol- 

 canic action invented by him for the occasion, and of which 

 no other recorded eruption has ever afforded a parallel. 



And here, with the utmost respect for the great talents of 

 this first of scientific travellers, and giving all due weight to 

 the impression which appears to have been made upon him on 

 the spot, I own myself still unable to coincide in his opinion 

 as to the mode of formation of this remarkable plain. And 

 this for the two following reasons : 



1st. In the first place, the appearances presented can be 

 without the least difficulty explained by the ordinary mode of 

 operation of volcanoes. In which case we are bound to dis- 

 miss one so extraordinary and unparalleled as that brought 

 forward for the purpose by M. de Humboldt, and which, 

 however brilliant or seducing to the imagination, it would be 

 unwarrantable to persevere in. 



%dly. All the supplementary arguments which M. de H. 

 adduces, are completely invalid, and, instead of supporting his 

 theory rather tell against it, as will be proved directly. 



1. What are the positive facts with which we are acquainted 

 relative to this eruption, divested of all theoretical assumptions? 



In the month of September 1759, prodigious volcanic erup- 

 tions took place from six different openings, arranged on a 

 single line of very little extent, upon the Mexican plateau. 

 Their fragmentary projections produced six large volcanic 

 cones ; the central one being 1700 feet in height. A massive 

 current of lava projects from the side of this last hill, having 

 evidently flowed out of the crater at its summit. If any lava 



