372 VIEWS OF NATURE. 



within the earth, broke through its erust, everywhere 

 intersected with fissures, and became solidified as granular 

 veins, or were spread out in broad superimposed strata. 

 The products that may be termed exclusively volcanic, which 

 have come down to us from the primitive ages of the world, 

 have not flowed in streams or bands like the lava of our 

 isolated conical mountains. The mixtures of aus;ite. titanic 

 iron, feldspar, and hornblende, may have been the same at 

 different periods, sometimes allied to basalt, sometimes 

 to trachyte ; while chemical substances, (as we learn 

 from Mitscherlich's important labours and the analogies 

 presented by artificial igneous products,) may have ranged 

 themselves in layers according to some definite laws of 

 crystallization. In all cases we perceive that substances 

 similarly composed have come to the surface of the earth 

 by very different means, either by being simply upheaved, 

 or escaping: through temporary fissures : and that break- 

 ing through the older rocks, that is to say, through the 

 earlier oxidized earth's crust, they have flowed in the form of 

 lava streams from conical mountains having a permanent 

 crater. If we do not sufficiently distinguish between these 

 various phenomena, our knowledge of the geology of volcanos 

 will again be shrouded in that obscurity, from which nume- 

 rous comparative experiments are now beginning gradually 

 to release it. 



The questions have often been asked, what is it that burns 

 in volcanos, what generates the degree of heat capable 

 of mixing earths and metals together in a state of fusion ? 

 Modern chemistry has attempted to reply that it is the earths, 

 metals, and alkalies themselves, that is to sav, the metal- 

 loids of these substances, which burn. The solid and already 

 oxidized crust of the earth separates the surrounding atmo- 

 sphere, with the oxygen it contains, from the combustible 

 unoxidized substances in the interior of our planet. By the 

 contact of these metalloids with the atmospheric oxygen 



