300 KEACTION OF THE INTERIOR OP THE EARTH 



Jorullo, whose summit, notwithstanding its small eleva- 

 tion (4265 feet above the sea, 1150 feet above the 

 Malpais at its foot, and 1680 feet above the old surface 

 of the playas), was not attained without difficulty by 

 Bonpland, Carlos Montufar, and myself, Sept. 19th, 

 1803. We thought we should be most sure of reaching 

 the crater, then still filled with hot sulphurous vapours, 

 by climbing the steep side of the great lava-stream 

 which had burst forth from the summit itself. Our way 

 lay over a curled scoriaceous cauliflowerlike lava, which 

 gave a clear ringing sound when struck. Parts of it 

 have a metallic lustre ; others are like basalt, and are full 

 of fine grains of olivine. When we had thus gained 

 the top of the lava by an ascent of 721 feet in vertical 

 height, we turned to the very steeply inclined white cone 

 of cinders (on which, from its great steepness, the tra- 

 veller is liable to painful hurts from the sharp jagged 

 lava). The upper margin of the crater, on the south- 

 western part of which we placed our instruments, forms 

 a ring only a few feet in breadth. We afterwards took 

 the barometer down into the oval crater of the truncated 

 cone, where we found the temperature of the air issuing 

 from a cleft 200*7. We were now 150 feet below the 

 margin ; and the depth of the deepest part of the hollow, 

 which the thick sulphurous vapours forbade our reaching, 

 appeared to us to be about as much again. The discovery 

 which interested us most was that of several sharply 

 defined white fragments of a rock containing felspar, 

 three or four inches in size, baked into the black basaltic 

 lava. I took them at first for syenite ( 43G ) ; but by Cfus- 

 tav Eose's accurate examination of a specimen which I 

 brought home, they belong rather to the granite forma- 



