Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/307

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297
Mr. Bennet on the Island of Teneriffe.

surprising that the lava should have flowed so short a distance; as it does not exceed 21/2 or three miles from the base of the cone to the point of union with the pumice hill; the mass of lava as well as its depth is prodigious; M. Escolar told me that its greatest breadth was above two miles, its depth it is not easy to determine, there are however several ravines or valleys in the course of the stream, some of which may be from 60 to 100 feet deep. The fusion of the mass does not appear to have been perfect; it is very earthy, and though vitrified pieces are found, there is no general appearance of vitrification; there are some pieces that exhibit an union with the pumice and the gradation from the stony structure to the vitrified, and thence to pumice. Immense heaps of this latter lie scattered on the surface of the lava, some of them containing large crystals of felspar, which abounds in, or more properly forms the constituent part, of the lava of the Mal Pais.

We halted several times during the ascent, and at last reached a spot called La Cueva, one of the numerous caves that are found on the sides of the mountain; this is the largest of them, and is filled with snow and the most delicious water, which was just at the point of congelation, the descent into it is difficult it being thirty or forty feet deep. One of our party let himself down by a rope, he could not see the extent of the cave, but the guides declared it to be 300 feet in length and to contain thirty or forty feet of water in depth, the roof and sides are composed of a fine stalactitic lava similar to that found on Vesuvius, and it is of the same nature as that which flowed on the surface. We rested here about half an hour, during which we had an opportunity of observing the rising of the sun and that singular and rapid change of night into day, the consequence of almost an entire absence of twilight. As we ascended the north-east side of the mountain this view was strikingly beautiful,

Vol. II.2 p