Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/304

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Mr. Bennet on the Island of Teneriffe.

is here no appearance of columnar formation, the lava being earthy and porphyritic; this continuity of wall, at present so easy to be traced, may be considered as forming the sides of one immense crater, from which perhaps originally the lavas of the island flowed, which might have thrown up the cone of the peak, and covered these wide-spreading plains or clanuras with the deep beds of ashes and pumice. On this plain or desart, for we had long left all shew of vegetation, except a few stunted plants of Spanish broom, a sensible change was felt in the atmosphere; the wind was keen and sharp, and the climate like that of England in the months of autumn. All here was sad, silent, and solitary. We saw at a distance the fertile plains on the coast, lying as it were under our feet, and affording a cheerful contrast to the scenes of desolation with which we were surrounded; we were already 7 or 8000 feet above the level of the sea, and had reached the bottom of the second region of the peak. Immense masses of lava, some of them many hundred tons in weight, lie scattered on these pumice plains. Some are broken by their fall, and all wear the appearance of having been projected by volcanic force. Their composition is uniformly porphyritic, with large masses of feldspar; the whole compact and heavy, and bearing no resemblance to the earthy lava we had seen in such abundance prior to our entering these pumice plains. Many of these masses are completely vitrified, while others only shew marks of incipient vitrification; but from their site and fracture, from the insulated state in which they lie, from there being no appearance of lava in a stream, from the pumice bed being very deep, (and in one place I saw it exposed to a depth of between 20 and 30 feet) from all these facts taken together, there can be little doubt that these masses were thrown out of the mountain when that lava flowed, which is of similar substance, and which is called by the Spaniards El Mal Pais.