26 THE CHEMISTRY OF METAMORPHIC HOCKS. [III. 



might have been effected by hot springs ; which, rising along 

 certain lines of dislocation, and thence spreading laterally, 

 might produce alteration in strata near to the surface, while 

 those beneath would in some cases escape change.* This 

 ingenious hypothesis may serve in some cases to meet the 

 difficulty pointed out by ISTaumann ; but while it is undoubt- 

 edly true in certain instances of local metamorphism, it seems 

 to be utterly inadequate to explain the complete and universal 

 alteration of areas of sedimentary rocks, embracing many hun- 

 dred thousands of square miles. On the other hand, the study 

 of the origin and distribution of mineral springs shows that 

 alkaline waters (whose action in metamorphism I first pointed 

 out, and whose efficient agency Daubree has since so well shown) 

 are confined to certain sedimentary deposits, and to definite 

 stratigraphical- horizons ; above and below which saline waters 

 wholly different in character are found impregnating the strata. 

 This fact seems to offer a simple solution of the difficulty 

 advanced by Naumann, and a complete explanation of the 

 theory of metamorphism of deeply buried strata by the agency 

 of ascending heat ; which is operative in producing chemical 

 changes only in those strata in which soluble alkaline salts 

 are present, t 



When the sedimentary strata have been rendered crystalline 

 by metamorphism, their permeability to water, and their altera- 

 bility, become greatly diminished ; and it is only when again 

 broken down by mechanical agencies to the condition of soils 

 and sediments, that they once more become subject to the 

 chemical changes which have just been described. Hence, 



* It should be remembered that normal or regional metamorphism is in 

 no way dependent upon the proximity of unstratified or igneous rork*. which 

 are rarely present in metamorphic districts. The ophiolites, ampliibolitt-s, 

 euphotides, diorites, and granites of such regions, which it has been custom- 

 ary to regard as exotic or intrusive rocks, are in most cases indigenous. 



+ See Report of the Geological Survey of Canada, 1853 - 66, pp. 479, 480 ; 

 also Canadian Naturalist, Vol. VII. p. 262. For a consideration of the rela- 

 tions of mineral waters to geological formations, see General Report on the 

 Geology of Canada, 1863, p. 561, and also Chap. XIX. of the same Report, 

 on Sedimentary and Metamorphic Rocks ; where most of the points touched 

 in the present paper are discussed at greater length. 



