124 PROCEEDLN'GS OF THE GEOLOGICAL SOCIETY. [June 23, 



frequent in the walls of the Yal di Bove. Applying this observation 

 to the gigantic group of dykes concentrated in the huge masses of 

 Eocca Giannicola and Musarra, I think that we must not give too 

 great a value to the dip of the beds of tufa and the crystalline 

 layers of the older formation of Etna in the immediate neighbour- 

 hood of the said Rocca, St. Nuolo, and Musarra. 



I have still to say some words about the dotted line and the 

 theoretical view which it points out. The first time I approached 

 Mount Etna (it was on the road from Palermo to Catania, some 

 hours before the moment I escaped with my life from the murderous 

 hands of robbers, who killed my poor guide instead of myself), I 

 admired for a long time the beautiful and regular shape of the chief 

 body of the mountain, which presented itself, at the distance of 

 about 40 Italian miles, as a flattened dome with a base " doucement 

 bombe ; " and the vertex corresponded, in the midst of the smoking 

 summit-cone, exactly to that point from whence a perpendicular 

 reached the centre of the imaginary circle, the segment of which 

 was projected before my eyes, as by the dotted line of fig. 9 (a, h). 

 Coming in a straight line from west to east, I saw the mountain in 

 the exact extension of south to north. On my return from Sicily 

 to Naples, Etna presented itself with admirable clearness at a some- 

 what greater distance from the sea in a direction of about S. 25° W. 

 Fig. 8 gives a copy of this view, which I made with as much ex- 

 actness as I could, by taking the chief angles by means of my pocket- 

 sextant. The shape of the mountain corresponds here exactly to a 

 natural profile obtained by cutting the mountain in the direction of 

 N.W.-S.E., namely the mean direction of the longitudinal axis of 

 the Yal di Bove. You will remark here the coincidence in the 

 nature of both curves (a b, fig. 8, and a h, fig. 9), which is best 

 perceivable by the equal abscisses a c and b d, at equal distances 

 from the central vertical line passing through the top of the under 

 cone. Seek now the centre of that second superior circle which cir- 

 cumscribes the contour of the dome-shaped upper half of the moun- 

 tain in the view fig. 8 ; you will see that its position does not exactly 

 coincide with the former, but it lies a little more to the east. 



Suppose that upper portion which is dotted to be absent, and you 

 get the old Etna as it probably was before the establishment of the 

 modem cone in that second period when the volcanic outbursts from 

 eruptive fissures became concentrated into one single vent, by which 

 the commimication between the atmosphere and the volcanic focus 

 continued now to take place only. Our late excellent mutual friend, 

 Gemmellaro, at Nicolosi, — the first who pointed out the interesting 

 fact of the excentrical position of the actual modern cone of Etna 

 with all its dependencies (with regard to the central axis of the older 

 Etna), — certainly never had an idea of the acuteness and subtility by 

 which this geological manner of viewing it is justified by projections 

 of the general shape of that mountain, taken at considerable distances 

 round the cardinal points of the horizon and compared together. 



Thus supplying the profiles fig. 8 and fig. 9, I give in fig. 10 



