F. E. Wright — Schistosity by Crystallization. 227 



cut after the three faces of each cube and sections ground 

 from them. 



If the foregoing hypotheses are applicable in this case, the 

 prismatic minerals crystallizing out of the glass under a stress 

 acting in one direction only, should show in the center of the 

 cube an arrangement along planes which are approximately 

 perpendicular to the line of pressure ; while the influence of a 

 second stress at right angles to the first should cause the crys- 

 tallites to grow along the one line of least resistance and show 

 parallel orientation in consequence. Both of these textures 

 were produced roughly in the cubes and were visible not only 

 under the microscope, but also to the unaided eye. 



t 



Magnification 25 x . Nicols crossed. 

 Fig. 1. — Section parallel to 100 throngh the center of a cube of wollas- 

 tonite crystallized from the glass while under stresses acting in the direction 

 indicated by the arrows. 



For the sake of convenience in describing the phenomena 

 observed, the cubes will be considered as fixed in position rela- 

 tive to the stresses applied, and the six cube faces as those of 

 an isometric cube ; the first stress being applied vertically and 

 perpendicular to the basal planes (001) of the cube ; the 



Am. Jour. Sci. — Fourth Series, Vol. XXII, No. 129. — September, 1906. 

 16 



