F. E. Wright — Schistosity by Crystallization. 229 



of the aggregate is that of an arrangement of the fibers in 

 layers parallel to 001 ; along this plane the cube also showed 

 a tendency to split. 



Figure 2 is part of a cross-section parallel to 010 of an 

 anorthite cube crystallized from glass under stress normal to 

 001. The photograph shows the upper part of a section which 

 was cut nearer the outer edge of the cube than that of the 

 preceding figure. The effect of crystallization proceeding 

 from the outer surface inwards because of the rapid heating 

 and in spite of the counteracting forces, is clearly marked in 

 this section. Only after the conditions of heating had become 

 more uniform could the effect of the unequal stress find expres- 

 sion in the parallel arrangement of the fibers in the central 

 portion of the cube as shown by fig. 1, and the lower part of 

 fig. 2. 



Magnification 25 x . Nicols crossed. 

 Fig. 3. — Section parallel to 100 and near exposed surface of a cube of 

 diopside crystallized from the glass under stresses indicated. The prismatic 

 fibers were normal to 100 and are cut, therefore, crosswise by the section. 



Figure 3 represents part of a thin slice taken from a crys- 

 tallized cube of diopside glass parallel to 100 and very close to 

 the exposed surface. The prismatic fibers which were the 

 first to crystallize were normal to the exposed surface and are 

 thus cut transversely by the section. 



