For In All Volcanoes, Even When There Are Lateral Eruptions, The Ashes And The Rapilli Issue Conjointly With The Vapours Only From The Opening At The Summit Of The Mountain.

Now, at Teneriffe, the black rapilli 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 vitreous feldspar and pyroxene, exclusively occupy the region next to the Peak. This peculiar distribution seems to confirm the observations made long ago at Vesuvius, that the white ashes are thrown out last, and indicate the end of the eruption. In proportion as the elasticity of the vapours diminishes, the matter is thrown to a less distance; and the black rapilli, which issue first, when the lava has ceased running, must necessarily reach farther than the white rapilli. The latter appear to have been exposed to the action of a more intense fire.

I have now examined the exterior structure of the Peak, and the composition of its volcanic productions, from the region of the coast to the top of the Piton: - I have endeavoured to render these researches interesting, by comparing the phenomena of the volcano of Teneriffe with those that are observed in other regions, the soil of which is equally undermined by subterranean fires. This mode of viewing Nature in the universality of her relations is no doubt adverse to the rapidity desirable in an itinerary; but it appears to me that, in a narrative, the principal end of which is the progress of physical knowledge, every other consideration ought to be subservient to those of instruction and utility.

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