230 F. F. Wright — Schistosity by Crystallization. 



Resume. 



The schistose and gneissose textures of many metamorphic 

 rocks have been ascribed by Yan Hise and others to the orient- 

 ing influence of pressures with a stress difference acting dur- 

 ing the recrystallization of the rock in its new environment, — 

 solution taking place along the line of greatest strain and 

 deposition along the line of least resistance and normal to the 

 maximum stress. In such cases the rock cleavage is due to the 

 parallel arrangement of its mineral components in planes per- 

 pendicular to the line of greatest stress. 



Conditions of experiment in which crystallization under 

 unequal strains could take place were effected by using cubes 

 of glasses made by chilling melts of different minerals rapidly, 

 and by heating these to the point at which crystallization first 

 began, the viscous glass at that temperature being still in a 

 state of fair rigidity, and capable of supporting a certain 

 amount of unequal strain. 



Textures similar to those of certain metamorphic rocks were 

 produced in this way, and an experimental confirmation of the 

 theoretical deductions thus obtained. 



Geophysical Laboratory, Carnegie Institution, Washington, D. C. 



