214 
ME. ROBERT MALLET ON VOLCANIC ENERGY. 
1st. The crushing of the earth’s solid crust affords a supply of energy sufficient to 
account for terrestrial vulcanicity * ; 
2nd. That the necessary amount of crushing falls within the limits that may be 
admitted as due to terrestrial contraction by secular refrigeration; 
and if so, that the cause thus assigned is probably the true cause of existing volcanic 
action, will further appear on comparing the conditions, or some of them, that we can 
predicate must follow from such crushing action going on locally within the earth’s 
solid crust, with some of the best known facts of observation of volcanoes themselves, to 
which we now proceed. 
202. A primary characteristic of the view of volcanic action here proposed is, that it 
is only one phase of a unique force which has always been in action, though always 
decreasing in energy, since our planet was nebulous. 
It introduces no hazy hypotheses of “ reaction of the interior against the exterior,” of 
internal distension by unknown gases, of chemical actions in the interior unsupported by 
proof of their existence. 
It simply postulates an always cooling globe subjected to gravitation, and through 
these two undeniable premises it links together as the successive products of two forces 
only, refrigeration and gravitation, the formation of the land and ocean-beds, the eleva- 
tion of mountain-chains, and volcanic action as now existing. Simplicity is the charac- 
teristic of every hypothesis upon which any true theory of the operations of nature has 
ever been produced. 
203. The long prevalent view of geologists, that volcanic heat and steam explosive 
power arose from w? icr making its way from the surface through an exceedingly thin solid 
crust to a universally liquid and fiery nucleus, is only tenable on the admission of such 
thinness of crust (probably 30 to 50 miles at most) as is quite incompatible with observed 
thermal conditions both on the surface and beneath it. 
But if we admit a very much thicker solid crust (from 300 to 800 miles), it is 
incredible that surface-water should ever find its way through such a depth of dense 
material to the liquid nucleus;’ yet without water we can have no volcano, steam being 
admitted on all sides to be the ejective agent. The wholly gratuitous hypotheses of 
Schaleb, of Boston (Proc. Bost. Nat. Hist. Soc. 186G), of a liquid spherical shell between 
a solid nucleus and a solid crust, and of Hopkins, of isolated liquid subterraneous lakes 
of lava within an otherwise solid globe, do not remove the difficulties as to their connexion 
with the surface-waters, and are exposed to insuperable objections to their existing at all. 
204. Schaler’s nucleus must be in unstable equilibrium as to position. Objections 
* As this paper cannot be extended so as to include any special considerations of the effects as to fusion, 
chemical combination, or decomposition producible by a given amount of thermal energy acting on the sub- 
stances within our earth’s crust, it is here only possible to remark that in such considerations the effects of 
heating substances under pressure, as pointed to in the recent experiments of Deville and Gernez and of 
Eraxklaxd, all tending to show that the same amount of heat is more effective chemically as the pressure under 
which it acts is greater, must not be neglected; nor, on the other hand, those of M. Caellelet (Les Mondes, 
1869) on the limits to chemical action set by its taking place under pressure. 
