Report of National Museum, 1890.— Merrill. 



Plate CXX. 



Fig. 1. Microstructure of granite. Fig. 4. Microstructure of porphyritic obsidian. 



Fig. 2. Microstructure of micropegmatite. Fig. 5. Microstructure of trachyte. 



Fig. 3. Microstructure of quartz porphyry. Fig. 6. Microstructure of serpentine. 



