78 ON SOME POINTS IN DYNAMICAL GEOLOGY. [VII. 



ject, was published in 1866. In it, while recognizing with 

 Sorby the conversion of mechanical force into chemical action, 

 he insists that " the enormous pressure generated in the fold- 

 ing of masses of rocks the depth of which is measured ly 

 miles" is an agent potent to produce changes both mechanical 

 and chemical The causes of the conversion of sediments into 

 plutonic rocks like granite, he conceives to be "mechanical 

 compression, with the heat and chemical action which proceed 

 therefrom," and adds in a note, alluding to the view which 

 explains their conversion by the action of heat from beneath, 

 " we should prefer to get the heat needed by the compression 

 which accompanies the disturbance of the strata where meta- 

 morphism occurs." (Orographic Geology, pp. 129, 130.)* This 

 suggestion of Yose is sustained by the late researches of Kobert 

 Mallet, who concludes that, " as the solid crust sinks together 

 to follow down the shrinking nucleus, the work expended in 

 mutual crushing and dislocation of its parts is transformed into 

 heat, by which, at the places where the crushing sufficiently 

 takes place, the material of the rock so crushed and that adja- 

 cent to it are heated even to fusion. The access of water at 

 such points determines volcanic eruption." (American Journal 

 of Science, III. iv, 411.) To this it may be added, that, 

 inasmuch as the crushing process takes place in strata which, 

 from their depth, are already at an elevated temperature, the 

 heat developed by the mechanical process comes in to supple- 

 ment that derived by conduction from the igneous centre. 



* It was not until after the publication of this paper that I became aware 

 that Professor Henry Wurtz had previously enunciated the view suggested by 

 Vose and adopted anct applied by Mallet. In a paper read before the Amer- 

 ican Association for the Advancement of Science, at Buffalo, in August, 1866, 

 and published in the American Journal of Mining for January 25, 1868, umlcr 

 the title of Gold-Genetic Metamorphism, etc., Professor Wurtz concludes that 

 "the tremendous dynamic agencies whose effects of upheaval, sir 

 ruption and displacement we find so widely manifest, while doubtless them- 

 selves engendered of the pent-up heat-energy of the interior, must have given 

 birth to or been in part transmuted into heat-motion," and proceeds to say that 

 in the heat which must be evolved in these movements we may find an explana- 

 tion of metamorphic changes, and of "thermal springs and many like phe- 

 nomena." 



