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III. Volcanic Energy : an attempt to develop its true Origin and Cosmical Relations. 
By Robert Mallet, A.M., C.E., F.R.S. 
Received May 13, — Read June 20, 1872. 
1. Plutonic action has long been loosely applied by geologists as a term for forces of some 
sort, of whose nature little was known, acting deep beneath the surface of our globe, 
and either not directly manifesting themselves at all at the surface, or, if so, chiefly in 
the form of earthquakes, thermal springs, &c. ; while volcanic action, showing itself 
at the surface in the phenomena of extinct, dormant, or active volcanoes, has been very 
generally regarded as something different in nature as well as in degree of activity. 
Some relations have always, more or less vaguely, been admitted between these ; but each 
has in turn been placed in the relation of cause and effect to the other. A third class 
of actions, those of “ forces of elevation,” though assumed to have some relations with 
the preceding, have very commonly been regarded by geologists as differing in nature 
from both, in degree as well as in kind. It is true that all these phenomena have been 
linked together by such wide and vague phrases as that of Humboldt, who speaks of 
them as “ the reaction of the interior of a planet upon its exterior ; ” but I am not 
aware of any attempt having previously been made to colligate them all as effects origi- 
nating in one common cause, and that referable to the admitted cosmical facts and 
mechanism of our globe. 
Sir William Thomson, regarding all these phenomena from the lofty point of thermo- 
dynamics (from which the writer also is about to view them in this paper), has distinctly 
colligated them as referable to dissipation of energy existing in our planet in the form 
of terrestrial heat, and has given to all its play of phenomena the title of “Plutonic 
action,” which he defines as “ any transformation of energy going on within the earth” 
(Trans. Geolog. Soc. of Glasgow, vol. iii. pt. ii.). 
2. The writer accepts Sir William Thomson’s above views, so far as he is yet acquainted 
with them through publication, as the broad basis for future physical geology. 
Sir William Thomson, however, has not attempted, so far as the writer knows, to 
bring his general view, that volcanoes, earthquakes, &c. result from transformations of 
terrestrial heat, so to bear upon the facts known respecting these as to explain in any 
way the immediate mechanism from the play of which within our globe these grand 
phenomena of nature are produced ; nor to connect these with the “ elevation theories ” 
of geologists, so as to substitute a precise and true one for the current and erroneous 
notions as to the nature of those forces which have elevated mountain-ranges and 
generally produced the inequalities of our globe, apart from the subsequent moulding- 
actions of water and other surface agencies. 
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