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 originating 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 thermodynamics (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.).
Explaining coincidences
