
‘Parr I. Sxcr.i.§ 2] VOLCANIC VAPOURS. 235 
- more than a foot high, and might be carefully removed as museum 
_ specimens. 
Mud-voleanoes occur in Iceland, Sicily (Macaluba), in many 
districts of northern Italy, at Tamar and Kertch, at Baku on the 
Caspian, near the mouth of the Indus, and in other parts of the 
lobe.? 
: Exhalations of Vapours and Gases.—In volcanic districts, 
sometimes from the craters and sides of dormant or extinct cones, some- 
times ata distance from them, heated vapours and gases are given off 
from orifices continuously and without eruptive discharges. Numerous 
examples occur among the volcanic tracts of Italy, where they have 
been termed sufiont. Steam, sulphuretted hydrogen, hydrochloric 
acid, and carbonic acid are particularly noticeable at these orifices. 
The vapours in rising condense. The sulphuretted hydrogen becomes 
_ sulphuric acid, which powerfully corrodes the surrounding rocks. 
The lava or tuff through which the hot vapours rise is bleached into 
a white or yellowish crumbling clay, in which, however, the less 
easily corroded crystals may still be recognised in situ. At the same 
time, sublimates of sulphur or of chlorides may be formed, or the 
sulphuric acid attacking the lime of the silicates gives rise to gypsum, 
- which spreads in a network of threads and veins through the hot, 
er Bi So 
steaming, and decomposed mass. In this way at the island of 
Volcano, obsidian is converted into a snow-white, dull, clay-stone- 
like substance, with crystals of sulphur and gypsum in its crevices. 
_ Silica is likewise deposited from solution at many orifices, and coats 
ph pede tie” edt oes Pe ot Wet ae 
the altered rock with a crust of calcedony, hyalite, or some form of 
' siliceous sinter. As the result of this action masses of rock are 
decomposed below the surface, and new deposits of alum, sulphur, 
sulphides of iron and copper, &c., are formed above them. Examples 
have been described from Iceland, Lipari, Hungary, Terceira, 
Teneriffe, St. Helena, and many other localities.? 
Another class of gaseous emanations betokens a condition of 
- volcanic activity further advanced towards final extinction. In 
these the gas is carbon dioxide, either issuing directly from the rock 
or bubbling up with water which is often quite cold. The old 
volcanic districts of HKurope furnish many examples. ‘Thus on the 
shores of the Laacher See—an ancient crater lake of the Hifel— 
the gas issues from numerous openings called moffette, round which 

dead insects, and occasionally mice and birds, may be found. In 
the same region occur hundreds of springs more or less charged 
a with this gas. The famous Valley of Death in Java contains one of 
1 On mud-voleanoes, see Bunsen, Liebig’s Annal, lxiii. (1847), p. 1; Abich, Mem. 
Acad. St. Petersburg, 7° sér. t. vi. No. 5, ix. No. 4; Daubeny’s Volcanoes, pp. 264, 539 ; 
Buist, Trans. Bombay Geograph. Suc. x. p. 154; Roberts, Journ. Roy. Asiatic Soc., 
1850 ; De Verneuil, Mem. Soc. Geol. France, iii. (1838), p. 4; Stiffe, Q. J. Geol. Soc. xxx. 
- p. 50; Von Lasaulx, Z. Deutsch. Geol. Ges. xxxi. p. 497; Giimbel, Sitzb. Akad. Miinch. 
1879. 
2 Von Buch, “Canar. Inseln,’” 232. Hoffman, Pogg. Ann. 1832, pp. 38, 40, 60. 
. Bunsen, Ann. Chem. Pharm, 1847 (xii.), p. 10. Darwin, “ Volcanic Islands,”’ p. 29. 
