MEANING OF ROCK FLOW AGE. 751 



lization might be complete in about 1,000 days, or three years. If it be 

 supposed that a mountain-making period occupied 150,000 years — and tins 

 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 rock shall exhibit but a slight strain effect. 



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

 recrystallized 50,000 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 

 recrystallized. Perhaps one of the best instances of this is furnished by 

 the schist-conglomerates. The typical schist-conglomerates contain a 

 schist matrix, embedded in which are numerous large fragments. In many 

 of these the matrix is completely recrystallized, but the fragments, unlike 

 the matrix, show important strains, which not infrequently pass to the 

 point of partial granulation with partial recrystallization. To explain 

 the phenomena exhibited by the perfect schists which hrvo developed 

 during a continuous process of deformation it does not seem necessary to 

 suppose that complete recrystallization is necessary. If the Case of a large 

 grain of quartz or feldspar in a recrystallizing 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 

 transported to the parts of the particles less strained or to other particles. 

 At such places the conditions are favorable to deposition, on account of the 

 relatively large size of the residual original grains as compared with the 

 granules. (See pp. 74-76.) The mineral particles, where least strained, 

 separate from the solution materials like themselves and attach them in 

 orientation with the cores 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 



