36 THE CANADIAN NATURALIST. [Feb. 



the place of feldspar in a rock the other element of which is pyr- 

 oxene, and have shown how the occasional presence of a trichnic 

 feldspar connects euphotide with diabase. (Sillirnan's Journal [2], 

 xxvii, 336.) In the same paper are described rocks made up of 

 a white compact garnet with and without hornblende and feld- 

 spar, and also an epidosite, composed of epidote and quartz. 



By the disappearance of the aluminous silicate from the rocks 

 of the second and third groups, a passage is established to the am- 

 phibolites and pyroxenites ; and these, through diallage rock, offer 

 a transition to the ophiolites or serpentines. These relations are 

 well exhibited in Eastern Canada, where thediorites or greenstones, 

 which are sometimes highly feldspathic, pass into actinolite rock 

 and hornblende slate on the one hand, and into diallagic diabase 

 and diallagic ophiolite on the other. 



These greenstones, which contain a chloritic mineral, and are 

 often epidotic, pass gradually into compact or schistose chloritic 

 rocks, frequently enclosing modules or layers of epidote, either pure 

 or mingled with quartz. The relations between these various rocks 

 are such that after a prolonged study of them I find it difficult to 

 resist the conclusion that the whole series, from diorites, diallages, 

 and serpentines,to chlorites,epidosite3, and steatites, has been formed 

 under similar conditions, aud that they are all indigenous rocks. 

 (Geology of Canada, pp. 606, 612, 652.) I have elsewhere express- 

 ed the opinion that these silicates are probably of chemical origin, 

 and have been deposited from solutions at the earth's surface. The 

 sepiolite or hydrous silicate of magnesia, which occurs in beds in 

 tertiary rocks, the neolite of Scheerer, the silicates of lime, magnesia, 

 and iron-oxyd deposited during the evaporation of many natural 

 waters ; and the silicates of alumina like halloysite, allophane, and 

 colly rite, and that deposited by the thermal waters of Plombieres, 

 all show the formation and deposition at the earth's surface cf 

 silicates, whose subsequent alteration has probably given rise to 

 many minerals and rocks. (Sillirnan's Journal [2], xxxii, 286 ; and 

 Geology of Canada, pp. 559, 5Y7, 581). At the same time the 

 phenomena of local metamorphism furnish evidences that similar 

 compounds have resulted from the action of heat upon mechani- 

 cal mixtures in sedimentary deposits. (Ibid., p. 581.) A further 

 consideration of this subject, and of the two-fold origin of many 

 silicious minerals, is reserved for another place. 



(To be Continued.) 



