TRUE VOLCANOES. 301 



culminating points are often situated, as I have already point- 

 ed out, at a distance from the general line of elevation of the 

 chain. They are situated upon partial snowy ridges, which 

 even form nearly a right angle with this general line of up- 

 heaval. 



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

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

 tween which the road to the copper mines of Inguaran pass- 

 es, appear, in their present condition, to be of least import- 

 ance. 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 Bonpland and 

 Carlos Montufar on the 19th of September, 1803. We 

 thought we should be most certain of getting into the crater, 

 which was still filled with hot sulphurous vapors, by ascend- 

 ing the steep ridge of the vast lava stream, which burst forth 

 from the very summit. The course passed over a crisp, sco- 

 riaceous, clear-sounding lava, swelled up in a coke-like, or 

 rather cauliflower-like form. Some parts of it have a metal- 

 lic lustre: others are basaltic and fall of small granules of 

 olivin. When we had thus ascended to the upper surface 

 of the lava stream at a perpendicular elevation of 711 feet, 

 we turned to the white ash cone, on which, from its great 

 steepness, we could not but fear that during frequent and 

 rapid slips we might be seriously wounded by the rugged 

 lava. The upper margin of the crater, on the southwestern 

 part of which we placed the instruments, forms a ring of a 

 few feet in width. We carried the barometer from the mar- 

 gin into the oval crater of the truncated cone. At an open 

 fissure air streams forth of a temperature of 200*6. We 

 now stood 149 feet in perpendicular height below the margin 

 of the crater ; and the deepest point of the chasm, the attain- 

 ment of which we were compelled to give up on account of 

 the dense sulphurous vapors, appeared to be only about twice 

 this depth. The geognostic discovery which had the most 



