(* These Petrosiliceous Masses Contain Vitreous And Often Calcined Crystals Of Feldspar, Of Amphibole, Of Pyroxene, A Little Of Olivine, But Scarcely Any Quartz.

To this very ambiguous formation belong the trappean porphyries of Chimborazo and of Riobamba in America, of the Euganean

Mountains in Italy, and of the Siebengebirge in Germany; as well as the domites of the Great-Sarcouy, of Puy-de-Dome, of the Little Cleirsou, and of one part of the Puy-Chopine in Auvergne.)

In the island of Teneriffe, strata of tufa, puzzolana, and clay, separate the range of basaltic hills from the currents of recent lithoid lava, and from the eruptions of the present volcano. In the same manner as the eruptions of Epomeo in the island of Ischia, and those of Jorullo in Mexico, have taken place in countries covered with trappean porphyry, ancient basalt, and volcanic ashes, so the peak of Teyde has raised itself amidst the wrecks of submarine volcanoes. Notwithstanding the difference of composition in the recent lavas of the Peak, there is a certain regularity of position, which must strike the naturalist least skilled in geognosy. The great elevated plain of Retama separates the black, basaltic, and earthlike lava, from the vitreous and feldsparry lava, the basis of which is obsidian, pitch-stone, and phonolite. This phenomenon is the more remarkable, inasmuch as in Bohemia and in other parts of Europe, the porphyrschiefer with base of phonolite* (* Klingstein. Werner.) covers also the convex summits of basaltic mountains.

It has already been observed, that from the level of the sea to Portillo, and as far as the entrance on the elevated plain of the Retama, that is, two-thirds of the total height of the volcano, the ground is so covered with plants, that it is difficult to make geological observations.

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