218 On some Results of the Earth's Contraction from Cooling. 



by the observation that the lower of the forty thousand feet of 

 strata in the Appalachian region were, where measured by the 

 Professors Rogers, not metamorphic, the Chazy and Trenton 

 limestones being ordinary uncrystalline limestones. And yet 

 the temperature in these inferior beds, marked by the ascending 

 isogeotherrns, must have been before their disturbance, as calcu- 

 lated by Professor LeConte, not less than 800° ¥., and much 

 above this if more heat escaped from the earth then than now. 

 Thus seven miles of accumulations were not sufficient to bring 

 about metamorphism or crystallization even in the lowest stratum, 

 or any change beyond that of ordinary solidification*. 



It seems certain, therefore, that this method of obtaining the 

 heat, by blanketing the surface with strata, is not sufficient. 



Neither, as Mallet has observed (p. 303 of the last volume 

 of Silliman's American Journal), can heat be derived from simple 

 pressure or " mechanical compression," as the language of Vose 

 suggests f. But with movements in the strata, or progressive 

 plications, such as the metamorphic rocks themselves show they 

 have experienced, then, according to the principle of the trans- 

 formation of motion into heat, first suggested with reference 

 to metamorphism by Professor Henry Wurtz of New York in 

 1866 J, and recently applied to volcanoes and demonstrated by 

 Robert Mallet, Esq., the conditions for metamorphism might be 

 complete even with comparatively little help from a rise in the 

 isogeotherms. This result would certainly follow if the heat 

 from motion is great enough, as Mallet appears to show, to 

 produce fusion. Such a cause is capable, as others have urged, 



* The arguments here presented are the same that I urged in. 1866 (Silli- 

 man's American Journal, vol. xlii. p. 252). 



t Vose could hardly have intended to say in place of pressure the motion 

 produced by pressure ; for in one of his paragraphs he attributes the 

 changes distinctly to "the enormous pressure generated in the folding of 

 masses of rock the depth of which is measured by miles;" and this pres- 

 sure was that of gravitating sediments alone, while the additional heat re- 

 quired came from a rise in the isogeotherms in consequence of surface ac- 

 cumulations. The truth is, that instead of folding generating pressure, the 

 pressure generated the folding ; and the movement attending folding was 

 essential to the existence of the heat requisite for metamorphic changes. 

 Thus the views of Vose and Hunt are set aside by Mallet, instead of being, 

 as Professor Hunt says (the last volume of Silliman's Journal, p. 270), 

 " confirmed " by him. In a letter of May 10th to the writer, Mr. Mallet 

 refers to his opposition to Herschel's theory, and adds that he was " rather 

 amused " at finding himself brought forward by Professor Hunt in support 

 of it. Mr. Vose's views are contained in his work on Orographic Geology, 

 published in Boston in 1866 (136 pp. 8vo). 



% Silliman's Journal, vol. v. p. 385. Professor Wurtz's opinion was first 

 published in a paper on " Gold Genetic Metamorphism," in the 'American 

 Journal of Mining ' (New York), Jan. 25, 1868. The paper was read at the 

 Meeting of the American Association at Buffalo in August 1866. 



