G. Poulett Scropc — The Mechanism of Stromboli. 539 



general the amount supplied from beneath. Were it not so, the ac- 

 cumulation of matter in and above the crater would probably so far 

 increase the pressure on the steam in the chimney of the volcano as to 

 proportionately check its expansive force, and cause the eruptions to 

 cease for a time far longer than the present intervals, and to be 

 more violent when they did occur, and thus bring the volcano into 

 the more common phase of alternate great activity and prolonged 

 repose. The maintenance of this ^ 

 equilibrium between the expan- 

 sive and repressive forces is pro- 

 bably due (as I long since sug- 

 gested) to the peculiar shape 

 of this volcanic mountain (see 

 Woodcut rig. 3) ; its axial vent 

 being so close to the ridge of 

 the steeply inclined plane that 

 occupies the breached crater and 

 reaches down to and far below 

 the sea-level, as to admit of 

 a considerable portion of the 

 ejected fragments falling into 

 deep water, instead of accumu- 

 lating over the vent, as would be 

 the case if the circuit of the 



, , , ,1 , • T Fig. q. Plan OF THE Island OF Stromboli. 



crater was complete on that Slde.^^^,,^ ^;^^ official Map of the Italian Government. 

 Any excess of lava produced by a Highest summit of the mountain. 



the vent in a liquid form escapes I '^^:^^^^;,^^l^S^^,,^ ,ith its 

 in like manner, either through ndges of lava. 



, T • J. T J. J.1 D The furrowed slopes of the mountain. 



or over this crater-Jip, to the ex- 

 terior of the slope, and thence into the sea. In this explanation Hoffmann 

 expresses his concurrence. In 1831, this observer saw several minor 

 streams of lava issuing from the summit of the slope, and making 

 their way down towards the sea; and the same fact has been noticed 

 by others. The great depth of the Mediterranean at the base of 

 this slope, assisted by currents, would prevent the accumulation 

 of the ejected matters on that side. 



It is evident, on the whole, that Mr. Mallet's theory cannot stand 

 serious examination. Stromboli is only one of a string of volcanic 

 islands (the LijDaris), arranged along radiating lines evidently mark- 

 ing some subterranean fissures, which have all apparently been in 

 eruption within Post-Tertiary times. One of them, indeed (Vulcano), 

 has been several times violently eruptive within the historical period, 

 and is even now in the Solfatara state of activity, sending forth 

 volumes of acid vapours and steam. Last autumn, indeed, a 

 veritable eruption on a small scale broke out at the bottom of its 

 immense crater, luckily not at the point where the sulphur and borax 

 works, established by an enterprising Scotch firm, are situated. 

 It would need, therefore, a very strong proof to lead geologists to 

 believe that the action of Stromboli is essentially different in its 

 character and cause from that of the other ordinary volcanic vents of the 

 series, and such Mr. Mallet, as has been seen, fails entirely to produce. 



