232 



semble rhomboidal fragments of pumice stone^ 

 disseminated in a domite deprived of color. 



The color of the pumice stones of the Peak 

 leads to another important observation. The sea 

 of white ashes, which encircles the Piton, and co- 

 vers the vast plain of Retama, is a certain proof 

 of the ancient activity of the crater : for in all 

 volcanoes, even when there are lateral eruptions, 

 the ashes and the rapilli issue jointly with the 

 vapours only from the opening* at the summit of 

 the mountain. Now, at Teneriffe, the black ra- 

 pilli extend from the foot of the Peak to the sea- 

 shore; while the white ashes, which are only 

 pumice ground to powder, and among which I 

 have discovered, with a lens, fragments of vitre- 

 ous feldspar and pyroxene, exclusively occupy 

 the region next to the Peak. This particular 

 distribution seems to confirm the observations 

 made a long time ago at Vesuvius, that the white 

 ashes are thrown out the last, and indicate the 

 end of the eruption. In proportion as the elasti- 

 city of the vapors diminishes, the matter is 

 thrown to a less distance ; and the black rapilli., 

 which issue the first, when the lava has ceased 

 running, must necessarily reach farther than the 

 white rapilli. The last appear to have under- 

 gone the action of a more intense fire.. 



I have now examined the exterior structure of 

 the Peak, and the composition of it's volcanic 

 productions, from the region of the coast to the 



