Reseña de las Rocas de la Isla Volcánica Gran Canaria

Abstract

IN this work, which is appropriately dedicated to M. Berthelot—to whom we owe one of the earliest descriptions of the geology of these interesting islands—the author gives some valuable information concerning the relations of the different classes of volcanic rocks to one another. He also describes some of the vast “Calderas” or craters so characteristic of this group of islands, and notices the theories which have been proposed to account fer their origin. Of especial interest, however, is the account which he furnishes of the nature and composition of the different varieties of volcanic rocks, and the classification which he proposes for them. It would appear from this work of Senor Calderon, that the true or “sanidine-trachytes” have not yet been found in these islands, but that the predominant felspathic constituent of the more acid rocks is always plagioclastic. Hence they are described under the names of Andesite, Trachy-dolerite, and Trachy-diorite. The first of these would appear, from the definition given, to correspond with the well-known lavas of Hungary, the last to resemble the greenstone trachytes or “propylites” of the same country. These trachytic rocks are found to assume at times a vitreous character, thus passing into obsidian; and they occasionally exhibit the perlite modification of structure. The basaltic rocks, noticed by the author, do not appear to offer any features of special interest.

Reseña de las Rocas de la Isla Volcánica Gran Canaria.

Por Don Salvador Calderon. (Reprinted from the Anales de la Sociedad Española de Historia Natural. Tomo iv.) Madrid 1876.