346 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 23, 



to movement in the direction A B, while under vast pressure both 

 from above and below, that is in the opposite directions C and D. 

 Whether the surface, C, or D, or both, remained fixed, or merely- 

 moved, owing to resistances, at a slower rate than the other parts, 

 the crystals in the latter would be turned round by internal friction, 

 and rearranged and drawn out in stripes or planes in the direction of 

 the motion, while the proportionate dimensions of the mass would be 

 equally varied so as to produce a section something like E, F, G, H 

 (fig. 5), in fact, a rock which, if no further change occurred in it 

 except consolidation in place, would have all the characteristics of 

 gneiss. The same movement, if still further continued, might, it 

 appeared to me, be expected to disintegrate the angular crystals of 

 felspar altogether, so as to cause them to disappear, perhaps to force 

 their elementary molecules to melt into the intensely heated silicate, 

 to which they would impart their alkalies. And the resulting rock, 

 supposing the laminae of the mica-crystals to slide readily past each 

 other, when lubricated by the silicate, and not therefore to be so far 

 disintegrated as those of felspar (as from their peculiar form might 

 be expected), would put on a lamellar structure, and very much 

 resemble mica-schist, — especially since the great flexibility of the mica 

 would render its laminae extremely liable to yield to the irregularities 

 of pressure pervading the mass, in a variety of directions, and conse- 

 quently to take such wavings and contortions as are often exemplified 

 in that rock. Whoever will examine the tortuous way in which the 

 plates of mica envelope and bend round nodules of half-melted quartz 

 or crystals of garnet in mica-schist, will be convinced, I think, that 

 the whole mass has been subjected to great internal movement and 

 consequent friction in the direction of the layers of mica, while under 

 intense pressure, and in a comparatively softened state, the mica 

 being lubricated, as it were, by a vehicle of liquid or gelatinous quartz. 

 Whatever fissures or cracks were formed during this movement in 

 the semi-solid rock, or subsequently, so long as the silicate remained 

 unconsolidated, would be necessarily filled by it, and ultimately appear 

 in the shape of the quartz-veins so frequent in this class of rocks. 



Under this supposition gneiss and mica-schist would bear the same 

 relation to granite as the ribboned trachytes and schistose lavas (clink- 

 stone) to ordinary crystallized or granular trachyte ; and the quartz- 

 rocks associated with granite, represent the quartzose trachytes of 

 Hungary, Ponza, and the Andes. 



These views, developed by me in 1 825, I cannot but think, deserve 

 the attention of geologists engaged in investigating the origin of the 

 so-called "plutonic" and " metamorphic " rocks. It seems to me 

 more probable that some process of this kind may have metamor- 

 phosed granite into the laminated rocks of plutonic origin, gneiss, 

 and mica-schist, than that these rocks should have been formed by 

 the mere fusion and reconsolidation or crystallization in place of sedi- 

 mentary strata already laminated, according to the usual "meta- 

 morphic" doctrine. I can understand the clay-slates and other 

 fine-grained schists to have been formed through the mechanical dis- 

 integration of mica- schist, but not mica-schist by the baking or 



