FACTS CONCERNING RECRYSTALLIZATION. 687 



766-768); on the contrary, there is every gradation between the two. 

 The original rock may have varied greatly in the coarseness of its con- 

 stituent particles. If one passes from a place of granulation to a place of 

 recrystallization, one may find that recrystallization of the matrix begins 

 while granulation of the larger particles is still going on. In an inter- 

 mediate stage the matrix may have completely recrystallized and the 

 granulation of the coarser particles be still incomplete. As a consequence, 

 the mineral particles of the matrix are increasing in size at the same time 

 the larger particles are decreasing in size. 



At a certain stage the larger grains are granulated into particles which 

 average about the same magnitude as those which have crystallized out of 

 a fine-grained and perhaps irresolvable matrix, and, moreover, the grains 

 which have formed from the matrix approximate uniformity of size. Thus 

 there is a marked tendency toward uniformity in the size of the grains of 

 the metamorphosed rocks, and this tendency is ordinarily dominant in the 

 schists and gneisses so long as mass deformation continues. (PL XI, C.) 

 This statement is more nearly accurate in reference to the particles of each 

 mineral than to particles of different minerals. This tendency toward 

 uniformity controls notwithstanding the principle that under ordinary 

 conditions large minerals grow at the expense of smaller ones (see Chapter 

 III, pp. 74-76); for under mass-mechanical conditions a large grain, 

 whether original or produced by uneven growth, is especially exposed to 

 the mechanical stresses, and therefore is granulated in part or put into a 

 state of strain, and thus is more readily attacked by the solutions. Some 

 of the properly oriented smaller particles may themselves grow at the 

 expense of the larger ones or of the small ones not properly oriented or 

 happily placed. Thus is explained the characteristic uniformity in the size 

 of the particles of the schists and gneisses which have not been modified 

 since mass-mechanical action ceased. However, in some cases, where the 

 mineral particles are properly oriented, the tendency for large individuals 

 to grow at the expense of smaller ones may control, and porphyritic 

 textured schists and gneisses be produced. (PI. Ill, G, D.) 



Such an occurrence is beautifully illustrated by the albite-schist of 

 Hoosac Mountain, Massachusetts, described by Wolff." Here there are 



aPumpelly, Raphael, Wolff, J. E., and Dale, T. Nelson, Geology of the Green Mountains in 

 Massachusetts: Mon. IT. S. Geol. Survey, vol. 23, 1894, pp. 59-63. 



