[ 468 ] 

 LVII. Proceedings of Learned Societies. 



ROYAL SOCIETY. 



[Continued from p. 394.] 

 June 20, 1872.— Sir James Paget, Bart., D.C.L., Vice-President, in 



the Chair. 

 nPHE following communications were read : — • 

 -*- " Volcanic Energy : an attempt to develone its true Origin and 

 Cosraical Relations." By Robert Mallet, F.R.S. 



The author passes in brief review the principal theories which in 

 modern times have been proposed to account for volcanic activity. 



The chemical theory, which owed its partial acceptance chiefly to 

 the fame of Davy, may be dismissed, as all known facts tend to 

 show that the chemical energies of the materials of our globe were 

 almost wholly exhausted piior to the consolidation of its surface. 



The mechanical theory, which finds in a nucleus still in a state of 

 liquid fusion a store of heat and of lava &c., is only tenable on the 

 admission of a very thin solid crust ; and even through a crust but 

 30 miles thick it is difficult to see how surface-water is to gain access 

 to the fused nucleus ; yet without water there can be no volcano. 

 More recent investigation on the part of mathematicians has been 

 supposed to prove that the earth's crust is not thin. Attaching 

 little value to the calculations as to this based on precession, the 

 author yet concludes, on other grounds, that the solid crust is pro- 

 bably of great thickness, and that, although there is evidence of 

 a nucleus much hotter than the crust, there is no certainty that any 

 part of it remains liquid ; but if so, it is in any case too deep to 

 render it conceivable that surface-water should make its way down 

 to it. The results of geological speculation and of physico-mathe- 

 matical reasoning thus oppose each other ; so that some source of 

 volcanic heat closer to the surface remains to be sought. The 

 hypothesis to supply this, proposed by Hopkins and adopted by 

 some, viz. of isolated subterranean lakes of liquid matter in fusion 

 at no great depth from the surface remaining fused for ages, sur- 

 rounded by colder and solid rock, and with (by hypothesis) access 

 of surface-water, the author views as feeble and unsustainable. 



A source, then, for volcanic heat remains still to be found ; and if 

 found under conditions admitting to it water, especially of the sea, 

 all known phenomena of volcanic action on our earth's surface are 

 explicable. 



The author points out various relations and points of connexion 

 between volcanic phenomena, seismic phenomena, and the lines of 

 mountain elevation, which sufficiently indicate that they are all due 

 to the play of one set of cosmical forces, though different in degree 

 of energy, which has been constantly decaying with time. 



He traces the ways in which the contraction of our globe has been 

 met, from the period of its original fluidity to the present state : — 

 first by deformation of the spheroid, forming generally the ocean- 

 basins and the land ; afterwards by the foldings over and elevations 

 of the thickened crust into mountain-ranges &c. ; and lastly by the 



