by Rock-crushing and its Consequences. 3 



nomcna can be supposed to originate the last-mentioned factor 

 must exert a very considerable influence, reducing materially the 

 available heat-increment. Hence the numerical results of Mal- 

 let's laborious experiments on rock-crushing, however interesting 

 and useful as affording a definite measure of the thermal effects 

 producible by this means, yet fail to carry conviction as to the 

 efficacy of this particular modus operandi in reducing large masses of 

 solid rock to fusion, unless essentially supplemented by friction, 

 not so much of rock walls against each other, but more probably 

 by the heat produced within more or less comminuted detrital or 

 igneoplastic masses by violent pressure and deformation. 



" It may be doubtful what would be the physical and thermal 

 effect of enormously great pressures upon rock powder such as was 

 produced in Mallet's experiments ; but it would seem that if made 

 to yield, the frictional effect must produce very high temperatures. 

 A fortiori, solid detrital masses of variously sized fragments in- 

 termingled (such as, rather than powder, would be likely to 

 result from steady pressure), yielding rapidly under great pres- 

 sures, might, under the combined influence of friction and rock- 

 crushing, well be supposed to reach the temperature of fusion, 

 which a simple crushing of a solid mass by pressure would have 

 failed to produce. Mallet mentions the probable influence of 

 friction and of the squeezing of igneoplastic masses, but does not 

 attach to these agencies such importance as they seem to me to 

 deserve. 



u Of the complex thermal effects of the movements of detrital 

 masses under great pressure Mallet's figures of course offer no 

 measure whatsoever; nor is this, or even the thermal coefficients 

 resulting from his rock-crushing experiments, at all necessary 

 to the establishment, of the postulates of his theory/' 



Subsequently the Rev. 0. Fisher, in a paper read before the 

 Geological Society of London, May ] 2, 1875, entitled " Remarks 

 upon Mr. Mallet's Theory of Volcanic Energy," has repeated the 

 observations of Professor Hilgard, and extended his objections 

 to the author's theory in general in a way which appears not 

 warranted. It will be sufficient here to quote the following from 

 Mr. Fisher's paper : — " Indeed the form in which the objection 

 to Mr. Mallet's reasoning suggested itself to my mind on first 

 reading his paper was simply this. If crushing the rocks can 

 induce fusion, then the cubes experimented upon ought to have 

 been fused in the crushing; and I still adhere to this simple mode 

 of expressing my objection." Again : — " He considers that the 

 heat so developed may be localized, and that the heat developed 

 by crushing, say 10 cubic miles of rock, may fuse 1 cubic mile. 

 But I ask why so ? The work is equally distributed throughout ; 

 why should not the heat be so also ? or if not, what determines 



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