TRUE VOLCANOES. 319 



near S. N. The fissure lias consequently been curved, 

 and has changed its strike throughout its total length 

 of 10,871 feet. The direction here indicated of the linear 

 but not contiguous mountains is certainly nearly at right 

 angles with the line upon which, according to my observation, 

 the Mexican volcanoes follow each other from sea to sea. 

 But this difference is the less surprising if we consider that 

 a great geognostic phenomenon (the relation of the principal 

 masses to each other across a continent) is not to be con- 

 founded with the local conditions and direction of a single 

 group. The long ridge of the great volcano of Pichincha 

 also, is not in the same direction as the series of volcanoes 

 of Quito ; and in non- volcanic chains, for example in the 

 Himalaya, the culminating points are often situated, as 

 I have already pointed out, at a distance from the general 

 line of elevation of the chain. They are situated upon par- 

 tial snowy ridges which even form nearly a right angle with 

 this general line of upheaval. 



Of the six volcanic hills which have risen upon the above- 

 mentioned fissure, the first three, the more southern ones, 

 between which the road to the copper mines of Inguaran 

 passes, appear, in their present condition, to be of least im- 

 portance. They are no longer open, and are entirely covered 

 with grayish white, volcanic sand, which however does not 

 consist of pumice-stone, for I have seen nothing either of 

 pumice or obsidian in this region. At Jorullo also, as at 

 Vesuvius according to the assertion of Leopold von Buch and 

 Monticelli, the last covering-fall of ashes appears to have been 

 the white one. The fourth, more northern mountain is the 

 large, true volcano of Jorullo, the summit of which, not- 

 withstanding its small elevation (4265 feet above the sea 

 level, 1151 feet above the Malpais at the foot of the volcano, 

 and 1681 feet above the old soil of the Playas), I had 

 some difficulty in reaching, when I ascended it with Bon- 

 pland and Carlos Montufar on the 19th September, 1803. 

 We thought we should be most certain of getting into the 

 crater, which was still filled with hot sulphurous vapours, 

 by ascending the steep ridge of the vast lava-stream, which 

 burst forth from the very summit. The course passed over a 

 crisp, scoriaceous, clear-sounding lava, swelled up in a coke- 

 like, or rather cauliflower-like form. Some parts of it have 



