300 ORIGIN OF CRYSTALLINE ROCKS. [XIII. 



of reactions which I had observed to take place in such admix- 

 tures in presence of heated alkaline solutions, and from the 

 composition of the basic silicates which I had found to be 

 formed in silicious limestones near their contact with eruptive 

 rocks, I was led to suppose that similar actions, on a grand 

 scale, might transform these silicious dolomites of the unaltered 

 strata into crystalline magnesian silicates. 



Further researches, however, convinced me that this view 

 was inapplicable to the crystalline schists of the Appalachians, 

 since, apart from the geognostical considerations set forth in 

 the previous part of this paper, I found that these same crys- 

 talline strata hold beds of quartzose dolomite and magnesian 

 carbonate, associated in such intimate relations with beds of 

 serpentine, diallage, and steatite, as to forbid the notion that 

 these silicates could have been generated by any transforma- 

 tions or chemical rearrangement of mixtures like the accom- 

 panying beds of quartzose magnesian carbonates. Hence it 

 was that already, in 1860, as shown above, I announced my 

 conclusion that serpentine, chlorite, and steatite had been de- 

 rived from silicates like sepiolite, directly formed in waters at 

 the earth's surface, and that the crystalline schists had resulted 

 from the consolidation of previously formed sediments, partly 

 chemical and partly mechanical in their origin. The latter 

 being chiefly silico-aluminous, took, in part, the forms of gneiss 

 and mica-schists, while from the more argillaceous strata, poorer 

 in alkali, much of the aluminous silicate crystallized as anda- 

 lusite, staurolite, cyanite, and garnet. These views were reit- 

 erated in 1863,* and further in 1864, in the following lan- 

 guage, as regards the chemically formed sediments : " Steatite, 

 serpentine, pyroxene, hornblende, and in many cases garnet, 

 epidote, and other silicated minerals, are formed by a crystalli- 

 zation and molecular rearrangement of silicates generated by 

 chemical processes in waters at the earth's surface." t Their 

 alteration and crystallization was compared to that of the 



* Geology of Canada, pp. 577 - 581. 



f American Journal of Science (2), XXXVII. 266 ; and XXXVII. 183. 



