Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/298

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Mr. Bennet on the Island of Teneriffe.

point itself being very low and projecting as a promontory into the sea. The declination of the strata is similar from the Peak to Puerto de los Christianos. This south-westerly chain is broken into many abrupt ridges, and is cut nearly perpendicular down to the sea. I could not perceive any base or shelf as on the other sides of the Peak, from which the cone arose, but the fall is regular though steep. From Puerto de los Christianos to Santa Cruz, comprising the southern and south-eastern sides of the island, the form is similar so that in the vicinity of Orotava, but it is barren and desolate, laid warm by screams of lava. In the short space of a few leagues I counted no less than seven cones of extinct volcanoes, and the country is covered with scoria, exhibiting no appearance of culture, and hardly any vegetation; it is more broken into ravines and more intersected by lava torrents than on any of the other sides of the island. Numerous peaked and conical mountains rise upon the slope of the chain, and the whole country is covered by scoria, and is one continued stream of lava. The Montana Roxa itself is a singular example of the dislocation of strata so commonly found in countries of volcanic formation; it is evidently a slip or fall of semi-columnar lava, and slopes into the sea at an highly inclined angle.

The ordinary strata of the island are as follows, reckoning from below upwards: 1st. the porphyritic lava covered by scoria and sometimes by pumice. This lava is composed of hornblende and feldspar, and contains no other substance. The next stratum graduates into what the Spaniards call Roccaverde or greenstone, and is composed of feldspar and hornblende; upon this is generally a thick stratum of pumice, and last of all towards the surface is the basaltic lava covered also by tufa and ash. This lava decomposes the soonest. It also contains the greatest variety of extraneous substances, and is sometimes divided by a layer of large crystals of olivine some inches