88 Van Ilise — Metamorphism of Boohs and Rock Flowage. 



volume — that is, less than 1 per cent by weight — the entire 

 mass of rocks might be recrystallized in about 250 hours, or 

 little more than 10 <lays. The percentage of water premised 

 is known to be lower than the amount ordinarily found in the 

 crystalline schists, and the rate hypothesized seem- reasonable; 

 but if this speed be decreased to '1 of that suggested or -01 of 

 that of glass, still the entire mass of the rocks might be dis- 

 solved and reposited in about 100 days. Make the rate of *1 of 

 this or *001 of that glass, and still recrystallization might be 

 complete in about 1,000 days, or three years. It it be sup- 

 posed that a mountain-making period occupied 150,000 years, 

 and this is probably less rather than more than the time required 

 for most mountain-making movements, during this period, at 

 the slow rate suggested, the rocks could be recrystallized 50,- 

 000 times by 1 per cent of water, and this number certainly 

 seems adequate to fulfill the requirement that at any given 

 moment the crystalline rock shall exhibit but a slight strain 

 effect. 



Of course, it is not thought probable that any rock has 

 completely recrystallized 50,01)0 times. Indeed, it is well 

 known that many of the rocks in which recrystallization is 

 complete, in so far as the finer particles are concerned, contain 

 many larger particles which have not been completely recrys- 

 tallized or even granulated. 



If the case of a large grain of quartz or feldspar in a recrys- 

 tallizing rock be taken, we may suppose the process to go on 

 somewhat as follows : Because of the lack of homogeneity of 

 the rock the stresses are irregularly distributed. At the most 

 exposed places upon the mineral particles the conditions are 

 favorable for solution, for the following reasons: the particles 

 are there greatly strained, perhaps to the point of granulation, 

 and, so far as strain exists or small granules are formed, these 

 conditions are favorable to solution. At the places of great 

 strain the material is therefore taken into solution and trans- 

 ported to the parts of the particles less strained. At such 

 places the conditions are favorable to deposition, on account of 

 the relatively large size of the residual original grains as com- 

 pared with the granules. A mineral where least strained 

 separates from the solution material like itself, attaching it to 

 itself, in orientation with the core, in an unstrained or little 

 strained condition. The process of growth is analogous to 

 that of mineral growth by secondary enlargement. The entire 

 process is similar in several respects to that of the continuous 

 solution and deposition of calcium carbonate in the chemical 

 laboratory when water is passed through 'a layer of this 

 material under pressure. Where the pressure is greatest in 

 the upper part, the grains are taken into solution. At the 



