510 Mr. R. Mallet on the 



the slope, are slowly removed and carried out into deeper water by the 

 under tow of the heavy seas in winter, and are lost in the chinks and 

 crevices between the huge blocks at the bottom, which I found to be so 

 deep and tortuous as often to render the extraction of the sounding-lead 

 which had entered them difficult. The lava ejected by Stromboli, whether 

 in the solidified or half-melted state, is extremely dark-coloured, almost 

 black. It is highly pyroxenic and crystalline, and its fusibility is greatly 

 increased by an intimate intermixture of dark obsidianic glass, of which 

 particles as well as strings are met with everywhere. It is still leathery 

 or plastic at a temperature considerably below a red heat, visible in day- 

 light, and is probably in tolerably liquid fusion at a temperature not 

 much exceeding 1200 Fahr. Its composition is by no means invariable, 

 as may be seen on the slope of debris ; and when the glassy material is 

 very abundant, as from time to time seems to be the case, or from 

 any of the causes which influence periodically the fluctuations of tempe- 

 rature more or less observable at all volcanic vents, this lava would become 

 extremely liquid and be blown about by the outbursts in the way some- 

 what obscurely described by Hoffman, as well as urged in liquid flakes 

 over the brim of the crater. The crystals of augite which are deposited 

 in such abundance with the dust blown out may preexist in the lava, but 

 appear to me, more probably, to be mainly formed by the disintegration of 

 the hot lava by contact and churning up with water, under a considerable 

 pressure and therefore high boiling-point, and perhaps by separation and 

 recombination from solution of its constituents. The crystals, which 

 are often an inch or more in length and frequently macled or cuneiform, 

 have scarcely any lustre ; and when the surfaces are closely examined with 

 a lens, they are often seen to be minutely pitted with microscopic cavities. 

 We now come to collect and correlate our facts and draw such conclusions 

 as they warrant in explanation of the mechanism which produces the 

 phenomena of Stromboli. The supply of water producing the immense 

 volumes of steam constantly blown off at the rate, on the average, of three 

 or four outbursts per hour may be derived in part from percolated fresh 

 water ; but this source alone, derived from the small gathering area of 

 the island, would be wholly insufficient; and, were that the sole source, it 

 would almost wholly fail towards the end of the dry season, so that a 

 marked annual change in the volcanic phenomena must result, and could 

 not fail to be observed. The supply of water, however, is manifestly 

 regular, and very nearly constant at all times, and therefore is derived 

 from the sea, and thus must enter the tube of the volcano below the sea- 

 level that is to say, more than 400 feet below the lip of the tube at the 

 bottom of the crater-funnel. Whatever be the source of supply of the 

 lava, therefore, it can never fill the tube as a solid column of melted mat- 

 ter reaching up to its lip ; for in that case, whatever be the mechanism 

 of the volcano at each outburst, the whole of this immense column of 

 melted matter of more than 400 feet in height must be blown completely 



