40 Dr. Mac Culloch on the Origin, Materials, 



stances ; such as by their giving passage to granite veins, by the 

 change of chemical texture and composition which they present 

 in these cases, and by the crystallization within them of minerals 

 similar to those found in gneiss, such as garnet, hornblende, augit, , 

 and others, which could not have been deposited from water so as 

 to have entered into the confused crystalline arrangement of the 

 rock in the manner which they do. That limestone is actually 

 thus consolidated after fusion, even in large masses, is also 

 proved, as far as anything relating to the influence of trap is 

 proved, by the conversion of conchiferous secondary strata, in 

 those situations, into crystalline limestone ; a fact occurring very 

 extensively and demonstrably in Sky, and recorded in my work 

 on the Western Islands. 



With respect to serpentine, the whole question is as yet involved 

 5n darkness. It is not known that it can be formed from water, 

 and I have proved from observation, that, as it passes into trap, 

 forming part of a greenstone vein in Perthshire, it can be formed 

 by fusion. 



All the scaly schists, of which micaceous schist may here re- 

 present the whole, present characters which are scarcely explicable 

 without admitting the action of these two agents. The stratified 

 disposition, and the laminar form, both give indications of a depo- 

 sition from water ; and, if any doubt of that could remain, it is 

 removed by finding that, in many places, it contains fragments of 

 discordant rocks,— of granite, for example, limestone, and quartz 

 rock. It has further been held, that the parallel position of the 

 mica is, in itself, a sufficient proof of deposition, because it is the 

 necessary position, and because the same circumstance exists in 

 the micaceous sandstones, so analogous to it, which are actually 

 deposited from water. But this, if probable, is an equivocal cir- 

 cumstance: as I have shown, that in hypersthene rock, a member 

 of the trap family, and even in some rare trap veins that contain 

 mica in the Western Islands, the flat crystals of hypersthene in 

 one case, and the mica in the other, preserve that parallelism 

 which must here be attributed to the polarity of crystallization 

 operating extensively; an action which I have also elsewhere 



