1859.] HUNT CHEMICAL GEOLOGY, 489 



Canada' for 1856, I have endeavoured to explain the theory of 

 the transformation of sedimentary deposits into crystalline rocks* 

 In considering this process we must commence by distinguishing 

 between the local metamorphism which sometimes appears in the 

 vicinity of traps and granites and that normal metamorphism which 

 extends over wide areas and is apparently unconnected with the 

 presence of intrusive rocks. In the former case, however, we find 

 that the metamorphic influence of intrusive rocks is by no means 

 constant, showing that their heat is not the sole agent in alteratioUj 

 while in the latter case different strata are often found affected in 

 very different degrees; so that fossiliferous beds but little altered 

 are sometimes found beneath crystalline schists, or even interca- 

 lated with them. 



We cannot admit that the alteration of the sedimentary rocks has 

 been effected by a great elevation of temperature, approaching, as 

 many have imagined, to that of igneous fusion ; for we find un- 

 oxidized carbon in the form of graphite both in crystalline lime- 

 stone and in beds of magnetic iron-ore ; and it is well known that 

 these substances, and even the vapour of water, oxidize graphite at a 

 red heat, with formation of carbonic acid or carbonic oxide. I havOj 

 however, shown that solutions of alkaline carbonates in presence of 

 silica and earthy carbonates slowly give rise to silicates, with disen- 

 gagement of carbonic acid, even at a temperature of 212° Pahr., — the 

 alliali being converted into a silicate, which is then decomposed by 

 the earthy carbonate, regenerating the alkaline salt which serves as 

 an intermediimi between the silica and the earthy base. I have 

 thus endeavoured to explain the production of the various silicates 

 of lime, magnesia, and oxide of iron so abundant in crystalline 

 rocks, and, with the intervention of the argillaceous element, the 

 formation of chlorite, garnet, and epidote *. I called attention to 

 the constant presence of small portions of alkalies in insoluble com- 

 bination in these silicates, both natural and artificial — -a fact which 

 had already led Kuhlmann to conclude that alkaline silicates have 

 played an important part in the formation of many minerals; and I 

 suggested f that, by combining with alkalies, clays might yield fel- 

 spars and micas, which are constantly associated in the rocks with 

 the silicates above mentioned. . This suggestion has since been veri- 

 fied by Daubree J, who has succeeded in producing felspar by heating 

 together for some weeks mixtures of kaolin and alkalme silicates in 

 the presence of water to 400° C. 



The problem of the generation, from the sands, clays, and earthy 

 carbonates of sedimentary deposits, of the various siliceous minerals 

 which make up the crystalline rocks may now be regarded as solved; 

 and we find the agent of the process in water holding in solution 

 alkaline carbonates and silicates, acting upon the heated strata. 

 These alkaline salts are constantly produced by the slow decomposi- 



^ Proceedings of the Eoyal Society, May 7, 1857. 



t Report Geol. Surv. Canada, 1856, p. 479. 



j Bull, de la Soc. Gr6ol. de France, 2 serie, vol. xv. p. 103, 



