262 Notice of Active and Extmct Volcanos. 



in autumn ; it is in continual and violent ebullition from the rise oi' 

 much sulphuretted hydrogen gas, the odour of which is very per- 

 ceptible at a distance. Besides this there are given out from clefts 

 in the rock near the lake much sulphurous acid, carburetted hydro- 

 gen, and carbonic acid gases. These being wafted to different pla- 

 ces, according to the direction of the wind, become fatal to the ani- 

 mals in the lower parts of the valley, the specific gravity of the 

 sulphureous and carbonic acid gases causing them to accumulate 

 near the surface of the ground. As no injurious effects are caused 

 to the windward of the spots from whence the vapour issues, we 

 may readily explain the seemingly capricious action of the rno- 

 fetle upon animals in different parts of the valley, by the direc- 

 tion towards which the wind blows. The waters of the lake be- 

 ing impregnated with hepatic air are celebrated in many diseases 

 of cattle, and provided there be the slightest movement in the 

 atmosphere, the gases do not accumulate around its borders in suf- 

 ficient quantity to be pernicious. 



" There is one spot however in the midst of a torrent which 

 flows along the valley, called the " Vado Mortale," from the na- 

 ture of the mofette existing there. This, which consists entirely 

 of carbonic acid, attains usually to the height of four or five feet, 

 so that it is constantly fatal to the auimals that pass the stream 

 at that point. 



" A vast accumulation of sulphur takes place in this valley, 

 owing doubtless to the decomposition of the sulphuretted hydro- 

 gen, which is emitted in such quantities that it has been proposed 

 to collect it for commerce ; and petroleum has likewise been met 

 with intermixed with the former combustible. Volcanic products 

 occur in the neighborhood." 



Vesuvius. — To the east of the bay of Naples, rises the most 

 recent of the volcanos in this region, and the only one that 

 is in activity. 



The present cone probably dates from the year 79 of the 

 Christian era, when Pompeii, Herculaneum and Stabio3 were 

 destroyed, as is believed on strong evidence, by the explosion 

 of the ancient Somma, a vastly larger volcanic mountain, a 

 part of the walls of whose ancient crater still remain. Vesu- 

 vius is in the centre of this ancient volcanic amphitheatre, 

 and is supposed to be only the subsidiary cone, which was 

 thrown up after the grand explosion of Sorrima. We must 

 refer to Professor Daubeny's work, and to the ancient authors 

 whom he quotes, for the details of the evidence which go to 

 establish the above positions. 



