510 Reports and Proceedings — 



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I.— June 23rd, 1875.— John Evans, Esq., V.P.E.S., President, in 

 the Chair. 



1. " Some Observations on the Eev. 0. Fisher's Kernarks on 

 Mr. Mallet's Theory of Volcanic Energy, read May 12th, 1875." By 

 Kobert Mallet, Esq., F.K.S., F.G.S. 



The subject of the Eev. 0. Fisher's paper has been anticipated by 

 one from Prof. Hilgard (Geol. Univ. of Michigan) published in the 

 ' American Journal of Science ' (vol. vii. June, 1874). 



The pith of the Eev. 0. Fisher's communication is to a great 

 extent comprised in the two following sentences : — 



1st. That "if crushing the rocks can induce fusion, then the 

 cubes experimented upon ought to have been fused in the 

 crushing ? " 



2nd. " If the work (of crushing) is equally distributed through- 

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

 determines the localization ? " 



In his reply Mr. Mallet controverts the views of the Eev. 0. 

 Fisher by bringing them into contact with acknowledged physical 

 laws. He shows that " crushing alone of rocky masses beneath our 

 earth's crust may be sufficient to produce fusion. He also shows 

 that the heat developed by crushing alone cannot be equally diffused 

 throughout the mass crushed, but must be localized, and that the 

 circumstances of this localization must result in producing a local 

 temperature far greater than that due to crushing. Lastly, he 

 shows that after the highest temperatures have been thus reached, 

 a still further and great exaltation of temperature must arise from 

 detrusive friction and the movements of forcible deformation of the 

 already crushed and heated material." 



He therefore expresses his conviction that " there is no physical 

 difficulty in the conception involved in his original memoir, 1 but 

 not there enlarged upon in detail, that the temperatures consequent 

 upon crushing the materials of our earth's crust are sufficient locally 

 to bring these into fusion." 



Discussion. — Prof Duncan remarked that this reply to Mr. Fisher's paper, 

 which is not yet in print, was one which required careful thought and consideration. 

 He thought that Mr. Mallet had not considered sufficiently the effects of 

 tangential thrust. The curving of strata takes place along great planes, producing 

 main synclinal curves ; but there was another series of actions giving rise to thrusts 

 over smaller, areas. In any case the action of the thrust would be slow, and thus it 

 can furnish no parallel to experiments by crushing rocks, in which the effect is 

 rapidly produced. He further pointed out that volcanos do not follow mountain- 

 chains, and that the crust of the earth has no doubt become more rigid than formerly, 

 and that therefore tangential thrusts would now be less effective. Volcanic cones 

 are found in older rocks than the Eocene. 



Prof. Ramsay said that he agreed with Prof. Duncan in general, but thought that 

 the meaning of quick and slow was difficult to define in connexion with great thick - 

 nesses of strata. If the pressure was sufficient to maintain motion, this might be 

 quick in one sense and slow in another. Alterations may be gradually going on over 

 great areas, by which means metamorphism may be evidenced in different degrees in 

 different parts. 



1 Phil. Trans. 1873. 



