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ME. EOBEBT MALLET ON VOLCANIC ENEBGT. 
The attempt to do this, in outline at least, which is all, perhaps, that existing 
knowledge admits of, is the object of the present paper. The term “ Plutonic action ” 
is objectionable, as already and long used by geologists in a loose and different sense. 
Vulcanicity is preferable, as proposed by the writer (4th Report on Earthquakes, 
Brit. Assoc. Rep. 1858), as comprehending all energy resulting either in volcanoes 
( Vulcanology) or in earthquakes ( Seismology ). In the former of these, forces of elevation 
generally may be comprehended, and in the latter thermal springs, though, as will 
appear when the intimate relations of the mechanism of all of these are better understood, 
the boundaries of these divisions at some points grow indistinct. 
3. The phenomena seen at volcanic vents, and those experienced in earthquakes, have 
been tolerably well observed ; and the immediate mechanism of the latter may be con- 
sidered as understood, though the cause or causes of commotion, and it may be very 
different at different times and places, are still somewhat obscure. 
The deeper mechanism of volcanic vents, all nearly except what is visible and tangible, 
is so far quite obscure ; and this mainly because no rational origin has ever yet been 
assigned for the production of the high temperature manifested at volcanic vents. 
To assign a true origin for this is to possess the key of the whole ; for given a 
veritable cosmical mechanism for the production of the heat that shall square with its 
local distribution, and with the capricious, non-periodic phenomena of eruptive vents, 
and all the other observed phenomena of volcanoes, from the largest to the most minute 
of these, become explicable and fall into place upon a cooling terraqueous globe. As 
respects a presumed connexion, if not identity, save as to degree of intensity, between 
volcanic and seismic mechanism, however vaguely referred to some common force of 
origination, it can scarcely be said hitherto to have advanced beyond this. 
Volcanoes, notwithstanding Von Buch’s unsound distinction into linear and central 
groups, have long been observed to follow the lines of surface-elevations, i. e. mountain- 
chains, the exceptions being only apparent. (4th Report on Earthquakes, Brit. Assoc. 
Rep. 1858). 
So also the writer has shown (Earthquake Catalogue, Brit. Assoc, and Seismic Map of 
the world thereof) that earthquakes on the whole are found to occur within the area of 
great seismic bands which follow and extend at either side of the mountain-chains of 
the world. Again, though thermal springs occur everywhere (just as earthquakes may 
occur anywhere), yet on the whole they are chiefly manifested in regions which have 
been or are greatly disturbed by mountain elevation or by volcanic and seismic activity. 
Thus we find this local relationship binding together the whole, viz. that volcanoes, 
earthquakes, and hot springs follow the lines of mountain elevation or dislocation. 
And this is almost all that we can certainly affirm connects them as having some 
common origin beneath. 
4. Any subterranean impulse may produce an earthquake ; and for those impulses 
there must be more than one nature of origin, for the impulse producing a shock like 
that of Riobamba cannot be the same as those producing the tremors of Pignerol or of 
Comrie, lasting for years. 
