253 



The direction and position of the dikes in the Val del Bove is then 

 spoken of, both in reference to the two ancient centres of eruption, 

 and to the question of the altered inclination of the intersected beds. 

 In regard to the arrangement also of the lateral cones of eruption, 

 the question is entertained, whether they are disposed in linear zones, 

 or are in some degree independent of the great centre of Mongibello. 



The origin of the Val del Bove has been variously ascribed to 

 engulfment, explosion, and aqueous erosion. Admitting the probable 

 influence of the two first causes, the author calls attention to the 

 positive evidence in favour of aqueous denudation afforded by the 

 accumulation of alluvium in the low country at the eastern base of 

 Etna between the Val del Bove and the sea. This rudely stratified 

 deposit, 1 50 feet thick and several miles in length and breadth, con- 

 tains at Giarre, Mangano, Riposto and other places, fragments, both 

 rounded and angular, of all the rocks, ancient and modern, occurring 

 in the escarpments of the Val del Bove, and it implies the con- 

 tinuance there for ages of powerful aqueous erosion. The alluvium 

 of Giarre is therefore supposed to bear the same relation to the Val 

 del Bove that the conglomerate of the Barranco de las Angustias 

 bears to the Caldera of Palma in the Canaries ; and those two crater- 

 like valleys, as well as the Curral of Madeira, are believed to have 

 been shaped out in great part by running water. But to render this 

 possible, the suspension, for a long period, of the outpouring of lava 

 on the eastern flank of Etna must be assumed. 



The author fully coincides in the generally received opinion that 

 the accessible parts of Etna are of subaerial origin, and refers to some 

 fossil leaves presented to him by MM. Gravina and Tornabene, of 

 Catania, as well as to others collected by himself in situ, from the 

 volcanic tuffs of Fasano and Licatia, which have been determined by 

 Prof. Heer to belong to terrestrial plants, of the genera Myrtle, 

 Laurel, and Pistachio, now living in Sicily. These tuffs, together with 

 the general mass of Etna, repose on marine strata of the newer Pli- 

 ocene period, in which 150 species of shells, nearly nine-tenths of 

 them identical with species now existing in the Mediterranean, have 

 been found. A very modern marine breccia, with shells of living 

 species extending to the height of thirty feet on the coast along the 

 eastern base of Etna, was pointed out to the author by Signer G. 

 G. Gemmellaro near Trezza, and in the Island of the Cyclops. The 



