The Gneissose- Granite of ilie Himalayas. 349 



regions and continued after its intrusion into the sedimentary rocks, had 

 progressed considerably, the still uncrystallized residuum, or mother 

 liquor, must have been, to some limited extent, capable of flow 

 or motion. Tangential pressure caused by earth movements, 

 continuously acting on the granite, would probably force some 

 of it into new fissures and newly-created planes of weakness, along 

 the margins of the intrusive mass ; and this marginal extension of 

 the intruded granite, combined with a continuance of the tangential 

 pressure, would create a slight flow in the unconsolidated mother 

 liquor, sufficient to allow the mica and other platy minerals to yield 

 to the pressure and orient themselves with their flat faces at right 

 angles to it. 



Further, it seems probable that the pressure exercised on the 

 granite by the molten mass below it fluctuated from time to time. 

 Deep-seated movements, such as laccolitio intrusions in neighbouring 

 areas, or the extrusion of acid lavas at the surface, would, for a time, 

 relieve this pressure and cause a small movement in or back flow of 

 the mother liquor. In other words, fluctuations in the resistance 

 offered by the molten mass under the granite would allow the 

 partially consolidated granite to be compressed by the tangential 

 pressure continuously exercised upon it. 



A very small amount of interstitial movement would suffice to 

 cause the flat leaves of mica to be arranged at right angles to the 

 pressure, while a back flow to any extent, by depriving the 

 crystallized minerals of the elastic support of the mother liquor, 

 would lead to their crushing and deformation. 



Those who have watched the operations conducted in a sugar 

 refinery will readily understand that the mother liquor may be 

 drained out of a mass of crystals without the crystals being carried 

 away with it. I do not wish to suggest that the mother liquor was 

 ever pumped out of the granite to any great extent : I only desire to 

 make it clear that small interstitial movements might result from the 

 causes above explained ; and that even small movements would 

 suffice to give the tangential pressure that was compressing the 

 partially consolidated granite a free hand, so to speak, and permit 

 it to impress a foliated structure upon the granite. 



Interstitial motion created in the two ways suggested above — 

 namely, by the marginal extension of the granite, ancl by a temporary 

 diminution of the resistance offered by the molten mass below it — 

 might be very local in its action, and hence some parts of a granite 

 might become foliated while other parts remained unfoliated. 



One more point remains to be mentioned. The earth movements 

 that produce faults often persist for some time, and though a rupture 

 in the folded strata gives temporary relief to the strain,, the stress 

 is sooner or later repeated, with the result that either the throw 

 of the fault gradually increases, or the walls of the fault are moved 

 up and down at intervals. Movements of the walls of a fault into 

 which an igneous rock had been intruded would, as the solidification 

 of the intruder approached completion, inevitably produce marginal 

 foliation and pronounced crush-structures. 



