Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/300

290 which constitute the central chain of the island, and which stretch out as headlands like those of las Horcas and San Ursula.

I never found in situ those masses of columnar basaltic rock that are so common in the island of Madeira: but in the valley of las Esperanzas, in the chain of hills to the north-eastward of the town of Santa Cruz, they lie scattered about in considerable numbers, and M. Escolar told me that he had seen strata of them to a considerable extent, exhibiting with precision the columnar basaltic form; the modern lavas of the peak are all basaltic, that of 1704 is decidedly so, as well as that of 1798, though not exhibiting any prismatic form. Prisms of basaltic lava are yet found on the peak: I picked up one, though there are no strata of them to be met with. The metals are rare, and afford but little variety: specular and micaceous iron, black and grey manganese are all that have hitherto been discovered. The salts that are so common on Vesuvius, are here seldom met with. Augite is also rare, and mica and leucite, though carefully sought after, have hitherto not been found.

In that part of the island between Laguna and Tacaronte, where there are few streams of lava, the soil is evidently volcanic. I examined many of the clods that were turned up by the plough, and found them all alike: they contained much strong clay, with crystals of feldspar, olivine, and specular iron. Dr. Gillan, who accompanied Mr. Barrow and Sir G. Staunton, has advanced an opinion, that between Laguna and Matanzos there are no signs of volcanic formation. That the currents of lava occur but seldom is most true; but the mountains in the vicinity of Laguna are all volcanic, and one has a visible crater; besides, the assertion would prove too much; for it would go to maintain that the Campagna Felice, as well as the plains of Catania, were not created by the