Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/310

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Mr. Bennet on the Island of Teneriffe.

which we ascended; from this side flowed the basaltic lavas of 1704, and of the last eruption in 1797; this latter stream of lava flowed in a remarkably slow current, for notwithstanding the sharp descent of the mountain, and the length of the lava not exceeding three miles, several days elapsed before it reached the spot where it stopped; how little fluid this lava must have been is evident, when it is remembered that the lava of Vesuvius in 1794, which destroyed Torre del Greco, reached the sea from the bottom of the cone, a distance of eight miles, in little more than six hours. M. Escolar further told me that there is on this south-western side of the Peak an ancient lava, at present not at all decomposed, of several miles in length, and in a perfect state of vitrification; the whole of this stream has the appearance of obsidian. All these lavas appear to have flowed from the bottom of the cone, and to have run from its base in the same manner as that of Vesuvius in 1794, the crater of which vomited out ash and pumice, and large pieces of rock, while the current of lava issued from its side. It is not however improbable that the cone itself is of anterior formation to this vitrified lava, as the summit of the Peak is similar to the lava of the Mal Pais, and that being porphyritic is considered as of more ancient date than the one above mentioned, which is basaltic.

If one might hazard a conjecture upon a subject where the data are so few, I should be inclined to suspect that the Peak itself, as well as the whole of the country around it which forms its base, were produced by that immense crater called Las Canales, the shape and magnitude of which I have before taken notice of when traversing the pumice plains; it is also well worthy of remark that there is no volcano in action at all to be compared in size of crater to those that are extinct. The ancient crater of Vesuvius is considerably