2 64 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 sea-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 granitic 

 hills) are situated in a line, and of which two or more are con- 

 nected by rents, which are filled up by basalt. Remarkable phe- 

 nomena of the kind are seen near Mural in Auvergne.\ 



We have abundance of proofs of the rising of masses of melted 

 or at least semifluid matter,^ out of the interior of the earth, in 

 the filling up of dykes with compact crystalline rocks, in all of 

 which, as in the rocks of undoubted volcanic origin,.felspar forms 

 a necessary and principal ingredient. *§> We find these rocks in 

 contact with all the stratified and superficial formations, even 

 with those which are going on at the present day. But similar 

 masses, which have evidently flowed in streams from craters, are 



* Leonhavd's Taschenbuch, 1824, Abth. ii, p. 439. 



t Leonliard die Basalt Gebilde, t. i, p. 408. 



X Cones of basalt, tracbyte, and pbonolite, whose inclination is often very con- 

 siderable, cannot have risen in such a thin liquid state, as that in which lava issues 

 from volcanos; for, according to the observations of Elie de Beaumont, already 

 mentioned, lava streams having an inclination of only 6° cannot form a continuous 

 mass. See on tliis subject, Leonhard, loco cit. t. i, p. 417, &c. 



§ Felspar may certainly be considered as a characteristic sign of an igneous ori- 

 gin in rocks, as this mineral is never found in rocks, in the formation of which 

 the action of volcanic power can be proved to have been wholly excluded. 



