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Such was the crater of Teneriffe before the last peak rose within its basin. Now retama, a hardy bitter shrub, grows in these plains of pumice; the flats of it are pumice and rapilli, white and brown. But the ancient crater walls stand unbroken for miles, though here and there they have been swept away, some say by floods of water belched from the pit.
A cloud hangs over it all the time, which is occasioned by the column of steam that issues from its crater. The entire upper part of the peak is perfectly bare of vegetation, and covered with fine cinders, rapilli, &c., through which escapes a gas that almost suffocates the ascending traveler.
From the lava and ash ejected from this focus, the whole soils of the island have been formed; soils of still unexhausted fertility, save when as must needs be in a volcanic region patches of mere rapilli and scoriae occur.
The sea of white ashes which encircles the Piton, and covers the vast plain of Retama, is a certain proof of the former activity of the crater: 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.
From a plain of whitish-grey soil, covered with concentric shells as large as a nut, rises a circular embankment with gently-sloping sides, intersected only by a small cleft which serves as an entrance, and which shows, on its edges denuded of vegetation, the loose rapilli of which the embankment is formed. The sides of this natural amphitheatre tower more than a hundred feet above its flat base.
The soil, like that of the embankments of the other volcanic lakes, consists of rapilli and lava, and is thickly wooded. Its banks are from thirty to one hundred feet high. From its north-western edge San Cristobal lifts its head 70° to the northeast. Its waters are easily reached, and are much frequented by fishermen.
Where level, Las Canadas is a floor of rapilli and pumice-fragments, none larger than a walnut, but growing bigger as they approach the Pike. The picture is made brighter by the leek-green vegetation and by the overarching vault of glaring blue. Nor are the forms less note-worthy.
Only of those which returned to recover valuables, &c., were overtaken and covered by the shower of red hot rapilli, or fragments of pumice-stone, which, with succeeding showers of ashes, covered the town to the depth of 7-8 feet. "The present superincumbent mass is about 20 feet in thickness." In the one third of the town already excavated the skeletons of some 500 have been found.
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.