THEORY OF RECRY STALL1ZATION. 693 



had recrystallized anew as a single individual and subsequently had been 

 somewhat strained. In some cases the flat individuals have a somewhat 

 curved form. (PI. Ill, B; also, see p. 753.) The phenomena are believed 

 to be due to solution and deposition, or recrystallization, as already 

 explained. The particles of the quartz not fortunately oriented or at places 

 of great strain are taken into solution and transported to fortunately ori- 

 ented individuals or those less strained, and redeposited; or, the material 

 dissolved from the more strained part of a grain may be deposited on another 

 part of the same grain where the strain is less. Thus the quartz of a given 

 flat granule may be largely the same quartz as that of the original grain, 

 but it has been dissolved and redeposited in part, perhaps repeatedly. 



Were the quartz grains to be granulated the volume of the rock would 

 be increased. (See pp. 674-675.) But by the process of solution and 

 deposition above described the form of the grain is changed and no increase 

 in volume results. Therefore, in the zone of anamorphism, where pressure 

 is the dominant force, recrystallization rather than granulation takes place 

 where it can, for by so doing the volume remains the same even if the 

 grains remain of the same average size, and heavier minerals are not 

 formed; and the volume is decreased where many grains merge, as cited 

 below, and where heavier minerals are produced. 



Micas, especially biotite and muscovite, are very abundant in the slates, 

 schists, and gneisses. Moreover, in proportion as the rocks approach typical 

 schists and gneisses the particles of these minerals are large, of approximately 

 uniform size, and. oriented crystallographically. (See PL XI, C.) In the 

 original pelites, from which the micaceous schists most extensively form, 

 the micas are not abundant constituents. Even in the psammites, where 

 allogenic micas occur, the particles are large, more or less irregularly 

 arranged, often somewhat decomposed, and are readily discriminated from 

 the regularly arranged, fresh micas of the schists. These facts are so well 

 known that nearly all petrographers who have studied thin sections of the 

 schists have regarded the micas as authigenic. Chemical analyses show 

 that soils, muds, clays, and shales contain the elements out of which mica 

 may develop/ 1 Many of these elements occur in hydrated compounds, such 

 as kaolinite, zeolite, chlorite, and limonite. In the schists which develop 



"Clarke, F. W., and Hillebrand, W. F., Analyses of rocks and analytical methods: Bull. U. S. 

 Geol. Survey No. 14S, 1897, pp. 277-301. 



