128 R. Mallet — Reply to Mr. Poulett-Scrope. 



existence of a nucleus still in liquid fusion is a purely arbitrary assumption, anci Mr. 

 Scrope wholly misapprehends me when he affirms that the existence of such a 

 nucleus forms any necessary part of my theory. All that I postulate is, that ours is 

 a cooling globe, and that therefore the interior is hotter than the exterior. I know 

 nothing as to the liquidity of the interior ; and in so far as its existence can be 

 examined by the as yet imperfect approaches of science, I am obliged to suspend 

 my judgment, if not to disbelieve in it. Again, did such an enormous nucleus in 

 liquid fusion exist, coated over only by a thin solid crust of some thirty or 

 sixty rniles in thickness, I believe it proveable that the surface- temperature 

 of our globe must be greatly in excess of what it is — indeed, that the flood of 

 heat poured forth from such an incandescent nucleus through such a thin skin, 

 even were the conductivity of the latter as low as that of pipe-clay, would be 

 such as to roast every organized being off the present face of our earth. Yet this 

 gigantic incandescent nucleus and parenchymatous surface-skin Mr. Scrope and 

 the school to which he belongs must have, or their theories are impossible. Even 

 with such a thin skin, and the most rapid conceivable passage at its lower surface 

 from the solid to the liquid condition, I believe it proveable that neither water could 

 make its way through any channels that we are at liberty to suppose down to the 

 liquid nucleus, nor liquid lava from the latter make its way up to the surface. If 

 all this be so, then surely the time has come for substituting some theory that will 

 better square with the facts : and such is that which I have produced. I do not at 

 all expect that that theory will be accepted by many of the older school of Vulcan- 

 ology, without the usual struggle with which new views widely differing from the 

 old are always received by those holding preconceived and long-cherished opinions. 

 To compare small things with great, I cannot forget that Newton's theory of 

 Gravitation received but a partial acceptance even one hundred years after its 

 promulgation. My paper has been but a first "attempt," as I have called it, to 

 evolve a theory of volcanic heat and energy consistent with itself and with the 

 facts in nature. In treating so vast and complex a subject, it can scarcely be but 

 that future research may find numerical corrections necessary ; but I believe the 

 skeleton of the theory which I have sketched will be ultimately admitted as true : 

 for there is no surer test of the soundness of any theory than that it not only ex- 

 plains the principal phenomena, but often throws the most unexpected light upon 

 collateral ones before obscure, and with which it seemed to have no connexion ; 

 and this, as I have pointed out in my paper, is the case with my theory in several 

 remarkable particulars. 



Mr. Scrope's objections, if not very cogent or at all conclusive in my judgment, 

 are at least so numerous that I fear want of space must compel me for the 

 present to leave some of them unanswered. Several of his objections appear 

 to me to rest on no better basis than that of the very imperfect grasp he has 

 attained of the nature of my argument, and in some instances to misconcep- 

 tions as to the experimental facts and their relations referred to in rhy paper. 

 I do, indeed, adopt Prevost's view of mountain elevation by tangential thrusts, 

 to which I have made allusion in tracing the successive stages of refrigeration 

 of our planet ; but it is an error to say with Mr. Scrope (p. 29) that my theory 

 is "founded upon the assumed truth " of Prevost's views. My theory postulates 

 nothing more, so far as volcanic action is concerned, than that our globe is 

 still a cooling one, and subject to the known physical conditions of cooling bodies. 

 It would remain equally true, whatever view might be taken as to the mode of 

 elevation of mountain chains. It is a fact, however, that mountain elevation and 

 existing volcanic action are but successive phases of the same play of forces. 



It seems to have escaped Mr. Scrope's observation, that I have done more 

 than to merely adopt Prevost's views. I have, I believe, been the first to point 

 out the complete succession of connected phenomena produced by contraction 

 during the secular refrigeration of our globe from its condition of liquid fusion. 



It had not before been seen by any writer, so far as I know, that while the 

 solidified crust is very thin, the tangential strains therein were tensile, and that, as 

 the crust thickened, these were gradually reversed in direction, and became tangen- 

 tial thrusts. Admit this, which is rigidly demonstrable to be true, and it then 

 follows inevitably that in the earlier epoch the wellings up of fused material from 

 beneath were due to subsidences of the crust, and, as I have called it, hydrostatic, 

 and of a nature entirely distinct from existing explosive volcanic action. The 



