J, W. Judd — On Vokanos. Ill 



The floor of the crater of Vulcano is about 200 yards in diameter; 

 but its level area is much encroached upon by the talus that leans 

 against its sides, and especially by the series of irregular cones 

 which were thrown up on its northern edge during the late eruptions. 

 The walls of the crater, which rise to heights of from 400 to 600 

 feet above its floor, are in their lower part vertical, but higher up 

 slope outwards at an angle of about 45°. The diameter of the crater- 

 rim is about 600 yards. The sides of the crater of Vulcano exhibit 

 a series of admirable sections of the masses of agglomerate composed 

 of materials of all sizes, often well stratified, and sometimes exhibit- 

 ing the series of anticlinals all round the crater, which has been 

 described by Mr. Scrope as so characteristic of the structure of 

 volcanic cones. Some portions of lava-streams and dykes of 

 vitreous lava can also be detected in the sides of the grand crater ; 

 but it is evident that the mountain has been mainly built up by 

 fragmentary ejections. 



The floor of the great crater of Vulcano, and also of the little 

 crater of the Fossa Anticcha, to be hereafter noticed, is covered by a 

 hard, compacted mass of pumiceous materials, which, when stamped 

 upon or struck with any heavy body, gives forth a dull sound ; this, 

 as in the case of the well-known Solfatara of Naples, is vulgarly 

 supposed to indicate the existence of vast cavernous hollows below 

 the mountain. A much simpler explanation of the phenomenon has 

 been suggested by Mr. Scrope (see Trans. Geol. Soc, 2nd series, 

 vol. v.) ; and that there is no foundation for the popular notion is 

 shown by the fact that many masses of compact tufaceous materials 

 give forth, when struck, precisely the same rimbombo sound, even 

 when situated at a distance from any crater. 



All over the sides and bottom of the crater of Vulcano fumaroles are 

 seen discharging acid vapours and gases. Many of these are of insig- 

 nificant proportions ; but very large ones exist on the north-western 

 rim of the crater and at a number of points at its bottom. The sides 

 of the fissures from which the vapours issue are sometimes red-hot ; 

 Fouque found that zinc was melted by the jets of issuing gas, and 

 Mallet that the temperature of the lips of the principal fissure was 

 in 1864 " sufficient to melt brass wire, but not sufficient to fuse 

 a similar wire of bronze." It is not surprising therefore to find 

 that, with this elevated temperature, the more inflammable products 

 of the fumaroles are ignited directly they reach the atmosphere. 

 This would seem to be the origin of the feebly-luminous flames, 

 usually of a blue colour, which are seen at night playing over some 

 of the fumaroles ; the existence of these will not of course be 

 thought to give any support to the popular notion of masses of red 

 flame rushing out of a volcanic crater during eruption, which has 

 been clearly demonstrated to be an optical illusion. Around all 

 the larger fumaroles are crusts of salts, usually of a white or pale 



estimate given in the text is that of M. Salino, and appears to be derived from the 

 official survey. Possibly some irregularity in the action of Mr. Mallet's barometer 

 may account for the very inaccurate results -which he was so unfortunate as to obtain, 

 not only on this occasion, but in other observations about the same time at Stromboli. 



