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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 considerable 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 scoriaceous 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 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 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 1½ foot to 26 feet; and their planes of stratification are parallel to those of the overlying and underlying scoriæ 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 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.

proceedings of the royal society of london

I. On the formation of continuous tabular masses of stony lava on steep slopes; with remarks on the mode of origin of Mount Etna, and the theory of 'craters of elevation.'