PLATE III. 



PHOTOMICROGRAPHS OF METAMORPHIC TEXTURES. 



A. Uneven texture developed by rnetasomatic alteration of feldspar to quartz and mica. From 

 biotite-slate of Penokee-Gogebic district, Michigan. 



B. Thin section of mashed quartz-porphyry, showing the quartzes elongated by recrystallization, 

 while the adjacent feldspar is little affected. After Futterer. 



C. Albite-schist, showing secondary porphyritic albites which include other mineral constituents 

 i >f the rock and their longer axes parallel to the prevailing schistosity. From Hoosac Mountain, 

 Massachusetts. After Leith. 



D. Porphyritic chloritoid developed after rock flowage has ceased. The chloritoid includes the 

 other constituents of the rocks with their longer diameters parallel to the prevailing cleavage. From 

 Black Hills, South Dakota. After Leith. 



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