750 A TREATISE ON METAMORPHISM. 



to suppose that a small amount of water may be the medium of rapid and 

 most profound modification of the rocks. 



We have already seen (pp. 690-691) that during the process of defor- 

 mation the material, if not dissolved, may be strained even to the point ot 

 granulation by the mechanical processes; also it has been seen that, so far as 

 strain occurs, or the particles are small, the minerals are in a state in which 

 solution is easier than for unstrained or larger mineral particles. But it is 

 probable that the solution of mineral particles and the deposition of the 

 material in an unstrained crystallized condition is considerably slower 

 than the solution of amorphous glass; for, among other reasons, it can not 

 be supposed that the same amount of energy is potentialized in the mineral 

 particles as in the glass. But the further the strain goes before fracture 

 the more energy is potentialized, or if fractures occur smaller particles are 

 produced. Moreover, the contained water is in small capillary or subcapil- 

 lary spaces, and therefore' a given volume is acting upon a much larger 

 surface than in the capillary tubes used by Barus in his experiments. In 

 so far as granulation occurs, the surface of action is still further increased. 

 All these conditions are favorable to solution and redeposition; therefore, 

 the greater the straining and resultant granulation, the more rapid the 

 process of recrystallization; hence, in the deep-seated zone, when water is 

 present in sufficient amount, mechanical disintegration never gets far in 

 advance of solution and redeposition. (See pp. 696-698.) 



At temperatures above 185° C, if it be supposed that in the capillary 

 and subcapillary spaces within the rocks the speed of solution of minerals 

 is 0.1 of that of glass, as ascertained by Barus, water would dissolve its own 

 volume of minerals in about five hours. If the deep-seated rocks be 

 supposed to contain 2 per cent of water by volume — that is, less than 1 per 

 cent by weight — the entire mass of rocks might be dissolved in about 250 

 hours, or little more than ten days, provided deposition went on at the 

 same rate as solution. The percentage of water premised is known to be 

 lower than the amount ordinarily found in the recrystallized schists and 

 gneisses (see pp. 742-743), and the rate suggested seems reasonable; but 

 if the speed of solution and deposition be decreased to 0.1 of that sug- 

 gested, or to 0.01 of that of the solution of glass, still the entire mass of 

 the rock might be dissolved and redeposited in about 100 days. Make the 

 rate 0.1 of this, or 0.001 of that of the solution of glass, and still recrystal- 



