1861.] GEMMELIARC — VOLCANIC CONES. 21 



according to Hoffmann, rises to the height of 620 metres above the 

 level of the sea, and is distant about 12 miles from the existing axis 

 of Etna. After a careful examination of it, the circumference being 

 about a mile, we can make out the central nucleus, the lava, and the 

 broken or fragmentary materials, — all of which are elements con- 

 curring to the formation of a volcanic cone. 



The central doleritic nucleus rises up directly from below ; its hard 

 crests, still rugged and angular, are exhibited at the rock of St. Mark, 

 that of La Scala, and near the old N^orman tower, and on the S.W., 

 "W., and 'N.W. sides of the rock, which are entirely exposed and 

 perpendicular, and are denuded of all the fragmentary materials 

 which formed the corresponding flanks of the cone. This consists 

 of a compact dolerite of a dark- ashy colour, tending to black, with 

 conchoidal fracture and poi-phyritic structure, in which olivine 

 occurs, varying in quantity in different portions of the same rock ; 

 nor is it difficult to find augite and labradorite. Some blocks of this 

 rock, broken away from the sides of the cliff, have fallen down on 

 splitting at the surface, which shows itself with an earthy fracture ; 

 whilst christianite in small crystals abounds in the vesicular hollows, 

 as well as in the incomplete fractures, together with incrustations of 

 blue phosphate of iron, which I have not found in the rock in situ 

 and not decomposed. The character of this dolerite is that of large 

 ovoidal masses laterally depressed, the larger diameter varying from 

 2 to 4 metres ; they chiefly occur on the S.W. side of the cliff, near 

 the Eock of St. Peter; and here, as well as imder the Norman Tower, 

 it assumes a prismatic form, which in the former locahty is in large 

 irregular prisms from 1 to 3 metres, whilst in the latter they are 

 smaller and more regular. On the ]!^.W. side of the cliff the dolerite 

 is impregnated with petroleum. 



In a kind of articiilated junction between the crests of the nodular 

 dolerite, there is found on the Kock of St. Peter a projecting mass of 

 clay with pebbles of sandstone (gresj, and another smaller one on 

 the south side of the liock, in the same matrix ; and these sediment- 

 ary rocks, anterior in age to the volcanic, have been metamorphosed 

 and transported, during the very act of the intrusion of the dolerite, 

 at the commencement of this volcanic action. 



The lava in this volcanic cone is easily distinguished. It comes 

 out from the upper part of the cone, from the very spot where now 

 stand the Church and Garden of the Capuchines, which is the most 

 elevated portion of the Eock, and in which are found large quantities 

 of scorios and volcanic bombs. The lava, when issuing from the 

 crater, flowed in two directions, the one due east, and the other 

 S.W. This latter stream near its mouth of eruption is seen to bi- 

 furcate into two branches, one of which forms the Eock of Calacala, 

 and the other flows due south. The eastern stream extends as far as the 

 Chiesa della Consolazione, in the neighbourhood of which it has been 

 cut through by the road also called that of the Consolation. During 

 the whole of this course, which is about 60 metres, it appears scoriated 

 on the upper surface, to a varying depth of from 3 decimetres to a 

 metre, while the rest of the mass is compact and of great thickness, 



