80 ROCK-METAMORPH1SM. 



and all-pervading, in deep-seated rocks, as repeatedly contended 

 for by the author, the fact may be taken as positive evidence 

 that the ' ' granitic veins 3> and the peculiar pyroxenic beds were 

 alike penetrated by such solutions, whose solvent powers were 

 exerted on the mineral silicates, whether belonging to the 

 beds or the veins. As to the " marked contrast " which it is 

 endeavoured to make out between the "rounded irregular 

 grains " of the former and the " rounded crystals " of the latter, 

 it seems extremely doubtful that the difference is more than 

 one of degree : it is not, however, beyond an explanation on 

 our view. As the veins are clearly posterior to the beds, the 

 latter have an important factor in their favour: time would 

 enable the corroding agents to act more decidedly and more 

 generally on the " grains " in the beds than on the " crystals " 

 in the veins. Moreover the "contrast" may also be due to 

 a difference in solvent power between the penetrating water in 

 the two cases. 



Again, the action of solvents, by rounding the " grains " or 

 " crystals," involves removal and displacement, whether it takes 

 place in beds or veins ; and as there are no openings surround- 

 ing either the grains or "crystals," but on the contrary an 

 environment of calcite, obviously the latter is the replacement 

 substance. And it may be equally affirmed that all the calcite 

 which occupies the interspaces between the grains and crystals 

 is in the same predicament, as in certain pseudomorphs whose 

 mineral silicates have been replaced by a mineral carbonate. 



Applying this reasoning to the solution of the problem in 

 regard to the origin of the Canadian bedded " crystalline lime- 

 stones" or hemithrenes, it will be understood that we have 

 simply to enlarge the field of solvent action. We may take a 

 region occupied by contorted granitoid, labradoritic, horn* 

 blendic, and other gneisses, permeated by thermal water charged 

 with a carbacid solution the water having gained admission 

 into the rocks either directly or indirectly from an overlying 

 ocean, along zones of outcrops, jointing, or porous beds, the 

 direction of such zones corresponding to the strike of the rocks : 

 by this means the gneisses would become regionally converted 

 into hemithrenes, the quartzo-feldspathic diorites, with their 

 admixtures of calcite and serpentine, being "beds of passage 

 between the two rocks." 



