364 



F. H. Lahee — Metamorp) 



lism and Geological 



Structure 





Conglomerates. 



Sandstones. 





Shales. 



General 



Stage of 



Stage of 





Stage of 



locality 



metamorphism 



metamorphism 



metamorphism 



H : 13 



C and B 



B 





— 



F : 10 



— 



C 





c 



H : 10 



D 



— 





c 



J : 5 



— 



A 





c 



J : 5 



— 



B 





A 



H : 9 



C 



C 





— 



B : 14 



— 



D 





c 



D : 14 



D 



— 





c 



G : 14 



C 



— 





B 



According to this table, (1) there are thirteen cases of like 

 metamorphism in specimens of different texture ; (2) there is 

 one case of conglomerate having higher metamorphism than 

 sandstone; (3) there are four cases of conglomerate having 

 higher metamorphism than shale ; (4) there are seven cases of 

 sandstone having higher metamorphism than shale ; and (5) 

 there are two cases of shale having higher metamorphism than 

 sandstone. Thus, out of twenty-seven comparisons, there are 

 only two instances of the finer rock having the greater meta- 

 morphism. The same lack of concordance between fact and 

 theory was also frequently observed in the field. 



As for the explanation of this condition, while we realize 

 that the definition of degree of metamorphism, as used in this 

 paper, is wholly arbitrary and that the opportunity for error 

 in assigning such degrees is therefore considerable, we believe 

 that the general conclusion which may be drawn will still 

 remain unmodified. Since the Purgatory conglomerate, the 

 uppermost member of the Carboniferous formation in this 

 region, shows evidence of intense metamorphism in the zone of 

 flow, it is clear that all these rocks must have been under a very 

 thick cover at the time of their deformation. Probably 

 adjacent beds, measuring but a few feet in thickness, are not 

 affected w T ith very marked differentiation according to texture, 

 under the great pressures existing at such depths. Shearing 

 is as apt to occur in a sandstone as in a shale. Moreover, as 

 has been stated by Daubree* and by Harker,f more heat is 

 developed by friction in the interstitial movements of coarse 

 rocks than in those of fine-grained rocks, and such heat no 

 doubt assists in the metamorphic processes. 



We infer, then, that, in single outcrops, differences of texture 

 have little or no direct influence upon the distribution of the 

 degrees of metamorphism in those outcrops. 



* Daubree, A., Synthetical Studies and Experiments on Metamorphism. 

 Translation by T. Egleston. Smith. Inst., An. Rept., pp. 463-465, 1861. 



f Harker, A., On Slaty Cleavage .... Brit. Assoc. Adv. Sci., Rept., 

 p. 848, 1885. 



