266 Geological Gleanings. 



ward of the crust by subterranean force has long been agitated, 

 and Sir Charles Lyell has long upheld the former view. In the pre- 

 sent paper Sir Charles removes an objection derived from the steep 

 slopes of the beds of lava and scoriae in some volcanic cones. 

 In connection with this subject, the remains of a more ancient 

 vent than the present crater of Etna and the probable antiquity 

 of the mountain, are noticed. 



" The question whether lava can consolidate on a steep slope, 

 so as to form strata of stony and compact rock, inclined at angles 

 of from 10° to more than 30°, has of late years acquired consider- 

 able importance, because geologists of high authority have affirmed 

 that lavas which congeal on a declivity exceeding 5° or 6° are 

 never continuous and solid, but are entirely composed of scoria- 

 ceous and fragmentary materials. From the law thus supposed 

 to govern the consolidation of melted matter of volcanic origin, 

 it has been logically inferred that all great volcanic mountains 

 owe their conical form principally to upheaval or to a force acting 

 from below and exerting an upward and outward pressure on beds 

 originally horizontal or nearly horizontal. For in all such moun- 

 tains 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 

 " Craterrs of Elevation," the author describes the results of his 

 recent visit (October, 1857) to Mount Etna, in company with 

 Signor 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 phe- 

 nomenon were met with — 1st, at Aci Reale ; 2ndly, in the ravine 

 called the Cava Grande near Milo, where a section of the lava of 

 1689 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 — 



