aad Volcanic Substances. B13 
not appear that any characteristic effect of Volcanoes de- 
pends on their proximity to the ocean. Breisl. § 644 et oa 
Volcanic eruptions usually co-exist with Earthquakes. 1 
Humb. per. nar. 227. 2 Ib. 226. Breisl. § 567. Bakewell’s 
Geol. p. 234. 51 Phil. trans. pt. 2p. 566 ann. 1760. 49 
Ib. 1755 p. 351 to the end of the volume. Art. Volcano 
and Earthquake, Rees’ Encyc. 
The exit for the ejected matter is usually the top or sides 
of a conical mountain, of which the top opening is the Cra- 
ter. In process of time, the craters of mountains that have 
long ceased to be active, fall in, by being undermined, or 
by atmospheric action, and are gradually obliterated ; in 
‘which case the volcano becomés extinct, and the traces of 
its existence rest upon the evidence of the volcanic char- 
acter of the ejections in its vicinity. 
A volcano in operation, gives out smoke and flame. Bibl. 
‘Britan. tom 30. derived from its contact with coal strata ; 
for we know of no substances capable of combustion and of 
giving out smoke and flame from the Granite or beneath it, 
ull we arrive at Werner’s independent coal formation. 
__ Itis usually accompanied by electric light ; I know not 
from what source derived. 
_ The ejections are Lava, _ ‘consisting of fluid, or half fused, 
“or softened minerals, or stones ienited only, and stones un- 
acted on, from the Granite rock below through the whole 
series of formations whose edges are exposed to volcanic 
action. What has taken place “at Chaud Coulant, between 
Buzene and Fraissinet in Auvergne. 2 Soulav. § 1166, must 
take place more or less inevery active voleana: © “You find 
ejected spongy ‘basalts, solid basalts, granite, calcareous 
rocks, mud lava, and confused mixtures of all kinds of mat- 
ter in the valley below: calcareous matter in Lava, in all 
degrees of vitrification, and all kinds of substances volcanic 
and non-yolcanic ea together. 
The Lava is glass (Obsidian) or partly fused and imper- 
“fect glass as ‘the 1 resinites, Spalan. tr. 250. V. 3. or porcela- 
nous substance, or cinders, or roughhackly slag or scoria, or 
columnar basalt, or vesicular basalt, or compact basalt; with 
stones of various kinds acted on by fire in various desrees. 
The basaltic Lava, is often columnar, both in the sea, 
and in places where no water could have reached; in figu- 
rate prisms of 3, 4,5 or 6 sides: rarely more; generally of 
Vor. IV.....No. 2. 
