264 Natural History of Volcanos and Earthquakes. 
means a necessary condition in the production of volcanic phe- 
nomena? But all that has been said respecting the channels by 
which the seo-water is admitted to the volcanic focus, holds 
equally good with respect to those admitting springs or rain-wa- 
ter; only with this difference, that, in the more lofty volcanos of 
America, the volcanic focus may be imagined much higher, and 
yet columns of water of considerable pressure will not be want- 
ing, provided those accumulations of water be situated at a great 
height in the mountains. 
The same power by which masses of lava are forced up, some- 
times so as to reach the surface and flow over it, or in other cases 
becoming solidified in their channels, will also raise whole moun- 
tains. These elevations may take place through rents of more 
or less considerable width ; and partly form dykes, or mountains 
of some magnitude ; or raise up or break through the upper strata 
of the earth. Thus Von Buch* informs us that on the island of 
Lancerote, during an eruption in 1730, a rent was formed above 
two German miles in length, on which about twelve conical hills 
had risen, whose summits were from 6U0 to 800 feet in height. 
In like manner basaltic cones (also even porphyritic and granitie 
hills) are situated in a line, and of which two or more are come 
nected by rents, which are filled up by basalt. Remarkable phe- 
nomena of the kind are seen near Mural in Auvergne.t 
We have abundance of proofs of the rising of masses of melted 
or at least semifluid matter,{ out of the interior of the earth, 1 
the filling up of dykes with compact crystalline rocks, in all o 
which, as in the rocks of undoubted voleanic origin, felspar forms 
a necessary and principal ingredient.§ We find these rocks 12 
contact with all the stratified and superficial formations, ls 
with those which are going on at the present day. But similar 
masses, which have evidently flowed in streams from eraters, 4° 
ee ee ee 
* Leonhard’s Taschenbuch, 1824, Abth. ii, p. 439. 
t Leonhard die Basalt Gebilde, t.i, p. : 
{ Cones of basalt, trachyte, and phonolite, whose inclination i 
siderable, cannot have risen in such a thin liquid state, as that in which I 
from volcanos; for, according to the observations of Elie de Beaumont, 
mentioned, lava streams having an inclination of only 6° cannot form @ com 
ass. e on this subject, Leonhard, loco cit, t. i, 17, &e. 
§ Felspar may certainly be considered as a characteristic sign of ap 
gin in rocks, as this mineral is never found in rocks, in the formation of 
the action of volcanic power can be proved to have been wholly excluded. 
s often very con 
ava issues 
already 
tinuous 
jgneous rage 
which 
