PLATE XIX. 
Fig. a. — Augite-porphyrite. Specimen 69. Slide 69 D. Gettysburg Railroad, south- 
east of the Clermont House. In ordinary light, X 24. Ophitic structure outlined by 
iron oxide. Colorless areas are quartz, and the considerable irregular areas are 
epidote. 
Fig. b. — The same. In polarized light, X 24. The quartz breaks up into irregular 
areas, producing the mottled effect of the micropoikilitic structure. 
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