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- 

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

 shore ; while the white ashes, which are only 

 pumice ground to powder, and among w T hich 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 rapillL 

 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 



