These Reflections Occurred To Me On Descending From The Summit Of The Peak Of Teneriffe, The First Unextinct Volcano I Had Yet Visited.

They returned anew whenever, in South America, or in Mexico, I had occasion to examine volcanic mountains.

When we reflect how little the labours of mineralogists, and the discoveries in chemistry, have promoted the knowledge of the physical geology of mountains, we cannot help being affected with a painful sentiment; and this is felt still more strongly by those, who, studying nature in different climates, are more occupied by the problems they have not been able to solve, than with the few results they have obtained.

The peak of Ayadyrma, or of Echeyde,* (* The word Echeyde, which signifies Hell in the language of the Guanches, has been corrupted by the Europeans into Teyde.) is a conic and isolated mountain, which rises in an islet of very small circumference. Those who do not take into consideration the whole surface of the globe, believe, that these three circumstances are common to the greater part of volcanoes. They cite, in support of their opinion, Etna, the peak of the Azores, the Solfatara of Guadaloupe, the Trois-Salazes of the isle of Bourbon, and the clusters of volcanoes in the Indian Sea and in the Atlantic. In Europe and in Asia, as far as the interior of the latter continent is known, no burning volcano is situated in the chains of mountains; all being at a greater or less distance from those chains. In the New World, on the contrary, (and this fact deserves the greatest attention,) the volcanoes the most stupendous for their masses form a part of the Cordilleras themselves. The mountains of mica-slate and gneiss in Peru and New Grenada immediately touch the volcanic porphyries of the provinces of Quito and Pasto. To the south and north of these countries, in Chile and in the kingdom of Guatimala, the active volcanoes are grouped in rows. They are the continuation, as we may say, of the chains of primitive rocks, and if the volcanic fire has broken forth in some plain remote from the Cordilleras, as in mount Sangay and Jorullo,* (* Two volcanoes of the Provinces of Quixos and Mechoacan, the one in the southern, and the other in the northern hemisphere.) we must consider this phenomenon as an exception to the law, which nature seems to have imposed on these regions. I may here repeat these geological facts, because this presumed isolated situation of every volcano has been cited in opposition to the idea that the peak of Teneriffe, and the other volcanic summits of the Canary Islands, are the remains of a submerged chain of mountains. The observations which have been made on the grouping of volcanoes in America, prove that the ancient state of things represented in the conjectural map of the Atlantic by M. Bory de St. Vincent* (* Whether the traditions of the ancients respecting the Atlantis are founded on historical facts, is a matter totally distinct from the question whether the archipelago of the Canaries and the adjacent islands are the vestiges of a chain of mountains, rent and sunk in the sea during one of the great convulsions of our globe. I do not pretend to form any opinion in favour of the existence of the Atlantis; but I endeavour to prove, that the Canaries have no more been created by volcanoes, than the whole body of the smaller Antilles has been formed by madrepores.) is by no means contradictory to the acknowledged laws of nature; and that nothing opposes the supposition that the summits of Porto Santo, Madeira, and the Fortunate Islands, may heretofore have formed, either a distinct range of primitive mountains, or the western extremity of the chain of the Atlas.

The peak of Teyde forms a pyramidal mass like Etna, Tungurahua, and Popocatepetl. This physiognomic character is very far from being common to all volcanoes. We have seen some in the southern hemisphere, which, instead of having the form of a cone or a bell, are lengthened in one direction, having the ridge sometimes smooth, and at others bristled with small pointed rocks. This structure is peculiar to Antisana and Pichincha, two burning mountains of the province of Quito; and the absence of the conic form ought never to be considered as a reason excluding the idea of a volcanic origin. I shall develop, in the progress of this work, some of the analogies, which I think I have perceived between the physiognomy of volcanoes and the antiquity of their rocks. It is sufficient to state, generally speaking, that the summits, which are still subject to eruptions of the greatest violence, and at the nearest periods to each other, are SLENDER PEAKS of a conic form; that the mountains with LENGTHENED SUMMITS, and rugged with small stony masses, are very old volcanoes, and near being extinguished; and that rounded tops, in the form of domes, or bells, indicate those problematic porphyries, which are supposed to have been heated in their primitive position, penetrated by vapours, and forced up in a mollified state, without having ever flowed as real lithoidal lavas. To the first class belong Cotopaxi, the peak of Teneriffe, and the peak of Orizava in Mexico. In the second may be placed Cargueirazo and Pichincha, in the province of Quito; the volcano of Puracey, near Popayan; and perhaps also Hecla, in Iceland. In the third and last we may rank the majestic figure of Chimborazo, and, (if it be allowable to place by the side of that colossus a hill of Europe,) the Great Sarcouy in Auvergne.

In order to form a more exact idea of the external structure of volcanoes, it is important to compare their perpendicular height with their circumference. This, however, cannot be done with any exactness, unless the mountains are isolated, and rising on a plain nearly on a level with the sea. In calculating the circumference of the peak of Teneriffe in a curve passing through the port of Orotava, Garachico, Adexe, and Guimar, and setting aside the prolongations of its base towards the forest of Laguna, and the north-east cape of the island, we find that this extent is more than 54,000 toises.

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