3G6 



THE GEOLOGIST. 



llie movement, and in planes perpendicular, or rather dingonnl, to the 

 opposite pressures — the different crystalline elements separating into 

 more or less distinct bands or lamince, according as their forms 

 permitted them to move with greater or less freedom. The silex, if in 

 a gelatinous condition, would possess the greatest mobility, and act as 

 a lubricator to the other minerals. Eut the mica plates, likewise, would 

 probably slip or slide readily over one another when brought by pres- 

 sure and friction into parallel planes, and the rectangular crystals of 

 felspar would be likely to offer the greatest resistance to the motion, and 

 be therefore broken up in part, and dragged into those layers or stripes 

 which are characteristic of the position of this mineral in gneiss. Where 

 the pressure and friction was extreme, as towards the outer sides of the 

 erupted mass, the felspar might be so comminuted as to be undis- 

 tinguishable, or be taken up, perhaps, into the silicate, which, with the 

 mica, would then appear to constitute the entire rock, so as to present 

 ultimately the structure and composition of Ilica-scliist ; while the 

 irregularities of friction being equally extreme in the same parts would 

 be likely to occasion multiplied wavings and convolutions on the small 

 as well as large scale, such as we see in that rock, as well as in 

 serpentines and other of the so-called metamorphic schists. 



Further yielding of the mass to pressure, occasioning internal move- 

 ments, after more or less of consolidation, or even the mere shrinkage 

 during that process, might give rise to cracks and fissures, which, being 

 filled by infiltration of the silicate from the proximate parts, would 

 occasion the quartz veins so frequent in these crystalline schists. 



It is submitted whether such a purely mechanical re-arrangement 

 as is here indicated, and which would seem from a priori reasoning abso- 

 lutely a necessary accompaniment of the protrusion of any subterranean 

 granitic axis, by internal dilatation from increased temperature, through 

 disrupted overlying rocks, does not offer a more probable explanation of 

 the foliated structure of the (so-called) metamorphic schists than the 

 supposition that it is merely the original sedimentary bedding of other- 

 wise wholly metamorphosed strata ? It seems diflScult to understand 

 that exposure to an amount of heat and pressure infinitely greater tlian 

 that which, in the argillaceous schists, has nearly obliterated all traces 

 of the original bedding, should in mica-schist and gneiss have renlercJ 

 it only more distinct and decided. 



That these arc, or may be, metamorphic rocks, derived, that If, from , 



