914 GEOGNOSY AND GEOLOGY. 
Volcanic sublimates are not only of great extent, but are often of great 1m- 
portance to mineralogists. These are bodies which continue in the form of 
vapor until condensed into the solid state by cooling, in which case they gen- 
erally coat the walls of the crater and the cavities in the lava with a crystal- 
lization of greater or less perfection. Volcanic sublimations are met with not 
only in active volcanoes, but also in such as are nearly extinct, or the Solfata- 
ras. The principal sublimates are, combinations of chlorine, sulphur and sul- 
phuric acid combinations, and metallic oxydes. 
The gaseous exhalations and deposits from volcanic waters stand in in- 
timate connexion with these sublimates. Among the gases are carbonic acid, 
sulphurous acid, and chloride of hydrogen or hydrochloric acid. Sulphites 
are formed by the action of the sulphurous acid upon the neighboring 
rocks, which by further oxydation, are converted into sulphates. In this 
manner are formed sulphate of ammonia, sulphate of soda (glauber salts), 
sulphate of alumina, sulphate of iron, alum, and alum stone. The deposits 
from volcanic waters consist generally of silicious sinter, more rarely of 
borax. Naphtha springs appear likewise to stand in a certain connexion with 
volcanoes. 
Besides the primary phenomena of volcanoes, as lava currents and 
ejectamenta, there are others of secondary or derivative character, as 
earthquakes. A striking feature presented to us in our examination of a 
volcano mountain, is the great homogeneity of its character; furthermore, 
that its shape is almost always conical, with a crater upon the summit, and 
the entire mass different in petrographical character from the region above 
which it projects. All these circumstances, with the fact that no crater is 
found upon the summit of a mountain not volcanic, clearly evince that an 
exceedingly intimate connexion must exist between the formation of the 
crater with its central throat and that of the mountain itself. The 
mountain in which the crater is situated must first have originated by 
volcanic upheaving ; eruptions then followed, whose ejecta accumulated and 
gradually increased the size of the cone. After this heaping up around the 
mouth of the volcano had increased to a certain amount, the internal forces 
were no longer capable of raising the volcanic matters to the level of the 
mouth ; fissures were then formed in the sides of the mountain, through 
which the lava was emitted. These phenomena are met with in the highest 
volcanoes. ‘The formation of volcanic mountains has indeed been actually 
observed ; striking instances of which are exhibited in the case of Monte- 
Nuovo near Naples, of Jorullo in Mexico, and of various volcanic islands 
elevated in the sea. 
_ The formation of Monte-Nuovo took place in September of 1538. (See 
the chart of the Bay of Naples and its volcanic district, pl. 45, fig. 8.) It 
rose up from a plain of inconsiderable elevation above the level of the sea, 
after premonitory quakings of the earth of two years’ duration. On the 
28th of September flames burst forth from the earth, the ground cracked 
open, and a considerable quantity of water escaped, while the sea retreated 
about three hundred paces. On the following day, soon after the sun of a 
fiery red had set behind the western waters, a cavity opened near the sea, 
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