PLATE XV. 
Fig. a. — Quartzite. Specimen I. Slide 1 D. Between Waterloo and the Blue 
Mountain House. In polarized light, X 32. Illustrates the induration of a sand- 
stone by enlargment of the original grains. 
Fig. b. — Penetration Manebacher twin of anorthoclase in quartz-porphyry. Speci- 
men 23. Slide 23 D. From well, at depth of 40 feet near Clermont House. In 
polarized light, X 10 (about). 
Piedmontite tills the cavities in the crystal. 
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