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POPULAE SCIENCE REVIEW. 
sulpliur and clean iron-filings wliich he had contrived^ and 
whichj when hnried^ and exposed to the humidity of the soil, 
in a few hours grew warm, raised the ground, emitting sul- 
phurous vapours and flames through the cracks and crevices, 
sometimes bursting into explosion with a vivid fire, which 
would continue for some time when the quantity of the ma- 
terials used had been very large. Breslac ^‘^went in for what 
we may term the rock-oil notion, imagining that volcanos 
might arise from masses of petroleum collected in those 
favourite receptacles of imaginative geologists, underground 
caverns, and fired through the presence of other substances, 
such as sulphur and phosphorus, or even spontaneously, as 
coal mines occasionally are. 
Now the main and insuperable difficulty, as Dr. Daubeny 
very pointedly remarks, attendant on these and all other 
hypotheses which assumed the combustion of bodies such as 
those above mentioned, is the absence of the products which 
constantly arise from such combustion under ordinary circum- 
stances, together with the presence of others which could not 
in such a case be expected. 
And he further well points out that the carbonic acid evolved 
should be accompanied with unburnt carbon, with carbonic 
oxide, and so on ; as also that sulphuretted hydrogen would 
not be disengaged in large volumes from a crater where car- 
bonaceous matters were freely burning ; and, finally, he urges 
that water could not be as abundantly present as it evidently 
sometimes is, without extinguishing the flame of mere carbon- 
aceous combustion, or cooling down the temperature below the 
fusing point of lava. 
When Davy discovered in 1807 the metallic bases of 
soda, potash, and magnesia, he suggested that masses of 
pure alkaline metals might exist in the depths of the earth, 
and give rise — by their ready combination with oxygen and 
the violence of their combustion — to that intense action 
required as the prime motor of volcanic eruptions. But 
then there was, opposed to this idea, the difficulty of Nature^s 
obtaining sufficient quantities in store, or even any quan- 
tities at all of such volatile metals. Daubeny, however, 
supported this doctrine in a modified form in his memo- 
rable ^‘’Description of Active and Extinct Volcanos 
repeated it in the second edition of that work, in 1848; and, 
so far as I know, adheres to it still. 
There is yet another, the most widely accepted theory, that 
all volcanos have a common origin in the supposititious molten 
interior of our globe. The asserted deep-seated location of 
the volcanic force ; the exhibition of volcanic eruptions along 
long lines extending across large geographical areas; the 
