146 J. W. Judd — On Volcanos. 



soundings of from 300 to 700 fathoms, we must remember that the 

 several islands are only the upper portions of great volcanic cones ; 

 at least one-half of the height of these, and by far the greater part 

 of their bulk being concealed beneath the waves. Stromboli is 

 completely made up of volcanic materials, and presents, not only 

 some obscure traces of a greatly ruined crater at its summit, but 

 numerous indications, in craters and lava-streams, of lateral outbursts 

 on its flanks. But the most striking and interesting feature about 

 the mountain is that on its north-western side there exists a crater 

 in a state of constant activity, which, besides giving off vapours and 

 gases, — either in explosive puffs, in continuous blasts, or in quietly 

 issuing wreaths, — discharges at more or less regular intervals showers 

 of scoria? and volcanic ashes. Occasionally, also, small streams of 

 lava flow from the crater itself or at some lower point on the moun- 

 tain ; and that a reservoir of incandescent material exists within the 

 crater, is proved by the fact that, at night, the clouds of vapour and 

 dust abo^ve the mountain reflect a fiery glow, either at the moment 

 of the explosion and for a short interval afterwards, or, during times 

 of more intense activity, almost continuously. 



With regard to the position and relations of the several parts 

 of the mountain, we have numerous measurements of accurate 

 observers to guide us ; and the recently published map of the 

 Italian Government enables us to verify their various barome- 

 trical and other determinations. The active crater of Stromboli 

 (Cratere la Fossa) is situated rather more than 600 feet below the 

 summit of the mountain, that is, at a height of considerably more 

 than 2000 feet above the level of the Mediterranean. The diameter 

 of the crater is about 400 feet, and its bottom, which is several 

 hundred feet below the rim on its southern or landward side, ap- 

 pears to be bounded by a crater- wall of but little elevation towards 

 the sea. From this depressed portion of the crater-rim a long slope, 

 called the Sciarra del Fuoco, leads down to the sea, with so steep an 

 incline (35°) that all materials ejected from the crater are unable to 

 rest upon it, but roll down into the sea. The Sciarra of Stromboli 

 constitutes one of the most striking features of the mountain ; its 

 length from the crater to the sea-level is more than 1200 yards, and 

 the breadth of its seaward edge is about 1000 yards. The walls 

 bounding the inclined plane of the Sciarra, and which gradually 

 converge towards the crater, are steep cliffs, seen to be composed 

 of lava-streams, agglomerates, and dykes, presenting their usual 

 relations with one another ; indeed, the whole may be regarded as a 

 miniature representative of the grand Val del Bove of Etna. Its 

 general appearance is well seen in the view (copied from Abich) 

 given as an illustration to Mr. Scrope's paper in the Volume of this 

 Magazine for 1874, page 532. On the slope of the Sciarra may 

 be observed several well-marked ridges of lava, which are either 

 lava-streams that have flowed down it, or great dykes, formed by 

 lava rising through fissures which have been produced in it during 

 paroxysmal eruptions. We may remark that the Italian word 

 "Sciarra" seems to be derived from the same root as our northern 

 term " Scaur," and to have nearly the same significance. Having 



