2 Mr. R. Mallet on the Temperature attainable 



of already crushed masses in the further progress of their defor- 

 mation and forced transport to points more or less distant from 

 those at which the crushing had taken place. The work of 

 crushing in free air was capable of rigid determination j the 

 work of subsequent deformation and transportation can only 

 admit of estimation upon assumed data, and these necessarily of 

 a somewhat arbitrary character, seeing how little we know accu- 

 rately of the nature and disposition of the rocky materials of our 

 earth's crust, except at the most inconsiderable depth from its 

 surface. Nor were any of the circumstances pointed out by 

 which high temperatures are capable of being attained locally 

 in rocky masses crushed beneath our surface and which we 

 must assume as those actually occurring in nature. The 

 writer's object here is to point out, 1st, that, taking the annual 

 supply of heat from transformed work of contraction, by expe- 

 riment in the way he has done, the result, though more than 

 sufficient to sustain his theory, affords alone no complete mea- 

 sure of the highest temperature that may through its means be 

 locally developed; 2ndly, to answer some doubts which have 

 been raised as to whether the temperature to which subter- 

 ranean rocky masses can become raised by the heat evolved in 

 their crushing and transportation of particles can be sufficient to 

 bring more or less of these at such foci of crushing and disloca- 

 tion to the fusing-point of such materials, which the author in 

 his original paper assumes to be 2000° Fahr. 



Professor Hilgard, occupying the chair of geology in the Uni- 

 versity of Michigan, U. S., in an able paper published in the 

 American Journal of Science, vol. vii. June 1874*, has, in terms 

 as clear as they are courteous, pointed out these lacuna in the 

 author's original paper in the following passage : — 



"One point, however, must strike every reader of the original 

 memoir, viz. the preeminence given by Mallet to the crushing of 

 solid rock as the means of producing heat and fusion. One 

 would naturally look to the results of his experiments on this 

 subject for the proof of the efficiency of this agency. But we 

 find that the maximum temperature resulting from the crushing 

 to powder of the hardest rock is something over 217° Fahr. 

 This, then, represents the maximum increment of temperature 

 that can be rendered efficient toward the fusing of rocks by the 

 crushing process under the most favourable circumstances, viz. 

 upon the supposition that it takes place instantaneously, or 

 under such circumstances that the heat cannot be conducted 

 away, and, further, that the resistance of the rock has not been 

 materially diminished by the downward increase of hypogeal 

 temperature. At the most moderate depths at which volcanic phe- 



* Phil. Mag. July, 1874, p. 11. 



