212 J. W. Judd — On Volcanos. 



shores of Stromboli, while within a few miles of the island soundings 

 of more than 700 fathoms occur. 



Mr. Mallet's hypothesis of " the Mechanism of Stromboli " is 

 based entirely on these grossly inaccurate " measurements ;" and as 

 it has already been criticized by Mr. Scrope in the pages of the 

 Geological Magazine, I am spared the necessity of dwelling longer 

 upon this painful subject. 



Nearly every observer who has studied the phenomena presented 

 by Stromboli, has been convinced that the permanent character of 

 its action is connected with the existence of the steep slope of the 

 Sciarra, which enables the ejected materials, sooner or later, to roll 

 down into the sea, instead of accumulating around the vent and 

 stifling its action for a time, only to lead to more violent paroxysms. 

 The formation of the present crater, with the steep slope of the 

 Sciarra leading down from it to the sea, was ascribed by Mr. Scrope 

 in 1825 to some violent paroxysm, which had destroyed a large 

 portion of that side of the mountain. This explanation is accepted 

 by Hoffmann, and nearly every other geologist who has examined 

 the question. Abich, indeed, not unjustly compares the destruction 

 of one side of the mountain and the formation of an eruptive centre 

 at a lower level, to the catastrophe which in the year 79 a.d. resulted 

 in the blowing away of one side of the ancient Somma, and the rise 

 of the modern cone of Vesuvius in its midst. 



Let us now proceed to notice the character of the operations going 

 on within this still active crater of Stromboli. These operations 

 appear to have been, during the last 2000 years at least, of a com- 

 paratively moderate character. We have no record or tradition of 

 the activity of the mountain becoming so violent as, in the case of 

 Vulcano, to drive away the inhabitants, who have formed settlements 

 (having a population in 1871 of 1,999) on the lower slopes of the 

 island, at a distance of two miles from the crater. On the other 

 hand, that the action is sometimes so energetic as to shake the 

 whole island, to cover every part of it with showers of ashes, and 

 to result in outflows of lava from the active crater and other portions 

 of the flanks of the volcano, we have the clearest evidence. 



With regard to the condition of the interior of the crater of Strom- 

 boli, we have also proofs of the occurrence of continual changes, 

 similar to those which have been noticed in Vesuvius, and all other 

 volcanos that have been systematically studied. That the bottom of 

 the crater is a thin and variable crust, which covers a mass of incan- 

 descent and liquefied material, and that this heated mass communi- 

 cates with the atmosphere by openings in the crust, which are 

 continually changing in number, size, form, and position, no one can 

 doubt who reads the account of the appearances presented by the 

 interior of the crater at different periods. According to the nature 

 of these openings, and their relations to the incandescent fluid mass 

 beneath, they are found quietly giving off jets of vapour and gas, — 

 violently discharging columns of steam, — permitting liquid lava to 

 rise and fall within them, and to be dispersed by sudden and inter- 

 mittent explosions, — or giving origin to small streams of lava. That, 



