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



energy are due to the mechanical work and its transformation into heat incident 

 to the cooling of our globe — stands firm, and is wholly independent of these 

 numerical data. But to test the credibility of my theory, I bring it into contact 

 with these numerical data ; and it is only necessary to show that, making an ample 

 estimate of the amount of heat demanded by the volcanic action annually expended 

 upon our globe, its total amount does not exceed that due to the total heat annually 

 lost by radiation, or in any other way, measured in terms of melted ice or its 

 equivalent in crushed mean rock. If the annual volcanic heat were equal to or 

 exceeded the total heat annually lost by our globe, then the theory could not be 

 true ; but if, as I have shown, the total annual heat of volcanic action be but a minute 

 fraction (5^) of the total annually lost by radiation from our globe, then a strong 

 corroboration is afforded to the credibility of the theory itself, which really rests 

 upon the indisputable fact that crushing and its physical consequences 77iust take 

 place in the outer portions of a cooling globe such as ours. It is therefore mere 

 waste of time to cavil with the numerical data upon which I have based my 

 estimates of the heat annually expended in volcanic energy, unless it can be shown 

 that these are numerically defiicient and require correction, not by adding to them 

 to the extent of two or three fold, but to that of fifteen hundred fold or more. 

 No one will affirm that my estimates, which are in several respects ridiculously 

 ample and beyond all probable truth, are in error of deficiency to the above 

 enormous extent ; and if not, my argument remains untouched. 



Mr. Scrope also objects to the validity of my experimental results as to the heat 

 evolved by crushing rock specimens, as applied to our subject, in a way which I 

 cannot avoid saying betrays much want of clearness as to the physical conditions 

 involved. He says, "These crushing experiments being made upon small cubical 

 blocks in a dry state, at the temperature of 57") "^^^ subject on four of their 

 sides to no other resistance than that of the atmosphere, are wholly inconclusive 

 as to the effect of pressure on similar rocks miles under ground, permeated with 

 water, at temperatures probably far exceeding 1000°, and in contact on all sides 

 with resisting media at least as unyielding as themselves. How is it Mr. 

 Scrope does not see that if a cube of rock, crushed by pressure on two oppo- 

 site faces, the other four sides being in free air, requires a certain amount 

 of work, it will require more work in proportion when these four sides are sup- 

 ported by other material, and that if there be more work thus expended, there 

 must be more heat produced by its transformation ? Now the store of crushing 

 power in our globe is practically limitless, exceeding, as I have proved, the resist- 

 ance to crushing of the most resistant rocks known to us by nearly five hundred fold. 

 This objection therefore, rightly interpreted, is an a yb;Yw;-/ argument in favour of 

 my results. But then my crushed cubes were dry. They were not dryer than 

 rock not watersoaked usually is. What does Mr. Scrope know of the wetness or dry- 

 ness as to imbibed moisture, or even as to the veiy nature of any rock at even thirty 

 miles, not to say a hundred miles or more in depth ? They are certainly not likely 

 to be generally watersoaked, or even capable of imbibing water ; and if they were 

 so, can Mr. Scrope prove that they would necessarily require less work to crush 

 them ? But my experiments were conducted at the temperature of the atmosphere 

 only. Is Mr. Scrope prepared to prove that rocks heated to 1000° necessarily 

 require less work to crush them than at 57°? It is certain that fire-biick, which is 

 an artificial clay porphyry or a sandstone, millstone grits, and many granitic rocks, 

 and generally most neutral and basic silicates, offer about as much resistance to 

 crushing at temperatures of 1000° or even more, in fact up to within a few degrees 

 of their fusing points, as at ordinary temperatures. This is a fact illustrated every 

 day in the construction and use of our blast and other furnaces, and in the well- 

 known results of conflagration upon the materials of our architectural structures. 

 As to the further objection urged, that I have paid no regard in these experiments 

 to the effects of great pressure in raising or lowering the fusing point of rocks 

 exposed to it, I have not left that quite disregarded in my paper, and I feel that it 

 would be superfluous to seriously discuss the objection. The limits within which 

 the fusing temperature of rocks can be raised or lowered by differences of pressure 

 only are unquestionably extremely small, so small that I believe the results cannot 

 possibly play any important or leading part in geologic phenomena. The fact of 

 such differences existing at all is far from certain ; it has merely been analogically 

 inferred from a few experiments on spermacetti and wax, etc., and on ice, all, 



