J. W. Judd — On Volcanos. 



15 



craters, but are sometimes cut up by denudation into isolated masses, 

 capping hills composed of tuffs, like the plateaux of Ischia and the 

 Auvergne. The lavas everywhere exhibit the characteristic slaggy 

 or scoriaceous upper and under surfaces, and are often seen to rest 

 on beds which are burnt to a bright red colour. The masses composed 

 of soft tuffs are often furrowed by deep ravines, which render some 

 parts of the islands almost impassable, but which, when accessible, 

 afford the most beautiful illustrations of the structure of the volcanos. 

 But it is in the sea-cliffs of some of the islands, and more espe- 

 cially in those of the southern and older part of Vulcano, that we 

 find the most instructive examples of that interlacing of agglomerates, 

 lava-streams and dykes, which constitutes the characteristic archi- 

 tecture of volcanos. Not even the cliffs of Somma or the pre- 

 cipices of the Val del Bove can compare, in this respect, with the 

 faces presented to the sea on the eastern, southern, and western sides 

 of Vulcano, where the mountain has been deeply eaten into by the 

 encroaching waves (see Fig. 4). For anything approaching in beauty 

 and completeness to the wonderful sections here exhibited, we must 

 go to the ruined and dissected volcanos of the Hebrides. 



Fig. 4. — Section near Quaglia on the south-west coast of Vulcano. 

 a. Rudely stratified tuffs, b. Upper scoriaceous surface of lava stream, c. Compact central 

 part of same. d. Scoriaceous under-surface of lava stream, e. Bed of burnt tuff of bright 

 red colour, f. Tuffs traversed by many dykes. 



That periods of great duration must have elapsed since the forma- 

 tion of the series of volcanic products which we have been describ- 

 ing, is indicated alike by the great amount of denudation which they 

 have undergone and by the fact that they are covered by a younger 

 series of deposits, some of which have themselves suffered not in- 

 considerably from the same cause. That, on the other hand, they 

 are of no great antiquity, from a geological point of view, is shown 

 by the fact that the vegetable remains imbedded in them all belong 

 to well-known species of the Mediterranean area. 



That movements of subsidence, similar in kind but less in degree 

 than that which appears to have submerged the great central volcano 

 of the group, must have taken place, in the case of the smaller and 

 encircling cones, is shown by the relations which many of the lava- 

 streams bear to them, as is particularly well seen in the coulees 

 which form the peninsula of Monte Bosa, and which have evidently 

 flowed from Monte Sant' Angelo. But that the movements which 

 have taken place in them have not been uniformly those of depres- 

 sion, is also demonstrated by the existence around the shores of 

 some of the islands of beautiful raised beaches, some of which are at 

 least 100 feet above the sea-level. Of such raised beaches we have 



