249 



upward and outward pressure on beds originally horizontal or nearly 

 horizontal. For in all such mountains there are found to exist some 

 stony layers dipping at 10, 15, 25, or even higher angles; and 

 according to the assumed law, such an inclined position of the beds 

 must have been acquired subsequently to their origin. 



After giving a brief sketch of the controversy respecting " Craters 

 of Elevation," the author describes the results of his recent visit 

 (October, 1857) to Mount Etna, in company with Signer Gaetano 

 G. Gemmellaro, and his discovery there of modern lavas, some of 

 known date, which have formed continuous beds of compact stone 

 on slopes of 15, 36, 38, and, in the case of the lava of 1852, more 

 than 40. The thickness of these tabular layers varies from 1^ foot 

 to 26 feet ; and their planes of stratification are parallel to those of 

 the overlying and underlying scoriae which form part of the same 

 currents. The most striking examples of this phenomenon were 

 met with 1st, at Aci Reale ; 2ndly, in the ravine called the Cava 

 Grande near Milo, where a section of the lava of 1 689 is obtained ; 

 3rdly, in the precipice at the head of the Val di Calanna, in the lava 

 of 1852-53; and 4thly, at a great height above the sea near the 

 base of the Montagnuola. 



Sir C. Lyell then alludes to the extraordinary changes which had 

 taken place in the scenery of the Valley of Calanna and the Val del 

 Bove since his former visit to Mount Etna in 1828 changes effected 

 by the eruption of 1852-53, one of the greatest recorded in history. 

 A brief account is given, extracted from contemporary narratives and 

 illustrated by a map, compiled with the assistance of Dr. Giuseppe 

 Gemmellaro, of the course taken in 1852-53 by various streams of 

 lava, some of them six miles in length, flowing during nine succes- 

 sive months from the head of the Val del Bove to the suburbs of 

 Zafarana and Milo. The present aspect of this lava-field, parts of 

 it still hot and emitting vapour, and the numerous longitudinal ridges 

 and furrows on its surface are described. As to the origin of these 

 superficial inequalities, the author inquires whether they may be due 

 to the flowing of lava in subterranean tunnels, or whether they be 

 anticlinal and synclinal folds caused by fresh streams pouring over 

 preceding and half-consolidated ones, so that these last may be bent 

 and crumpled by the newly superimposed weight, like soft yielding 

 ground on which a railway embankment has been made. The cas- 



