6o6 C. K. LEITH AND W. J. MEAD 



determined by their habit of crystal growth, rather than by any 

 growth or breaking giving other shapes, direct our attention to the 

 crystal habit of these minerals as essential reasons for their devel- 

 opment. Whether processes of rock flowage have been weak or 

 intense, the resulting minerals maintain their habit and dimensional 

 characteristics. 



If convergence toward certain characteristic minerals is estab- 

 lished in rock flowage, the question naturally arises whether these 

 end-products can be regarded purely as results of the great variety 

 of processes in anamorphism by rock flowage, or whether the 

 individual characters of the resulting minerals have exerted a 

 certain directive and controlling influence in converging the 

 various lines of anamorphism and rock flowage toward themselves, 

 and more particularly whether the crystal habit of these minerals 

 has exerted this influence. From this point of view it seems to 

 be something more than a coincidence that, under such a variety 

 of conditions and with such variety of available materials, that 

 which we call crystallizing force has been able to exert itself 

 to the extent of causing important mineralogical and chemical 

 changes toward a limited number of mineral forms. It has drawn 

 to itself the materials needed, eliminated those not needed, and has 

 developed crystals of uniform habit. Under given environment it 

 has had the capacity to organize the substances in a fashion best 

 adapted to environment in much the same way that organisms have 

 been supposed to adapt themselves to environment. The problem 

 before us may be similar to the biologic question whether organisms 

 are distinctly the results of physical and chemical environment or 

 whether that mysterious force we call life on occasion rises superior 

 to environment and to some extent modifies and controls external 

 conditions. It is sometimes said that man is the multiplier and 

 environment the multiplicand in the product determining history. 

 The attempt to apply the same reasoning to the development of 

 certain characteristic minerals in schists suggests the crystallizing 

 power of these crystal individuals as the multiplier and environ- 

 ment as the multiplicand in the product representing rock flowage. 



It is of interest also to note that the convergence here argued 

 is toward a group mineralogically and chemically different from 



