PLATE XXI. 
Fig. a. — Perlitic parting in an aporhyolite. Specimen G. H. W. Slide G. II. W. 
(unnumbered). Raccoon Creek, Franklin County. In ordinary light, X 40. 
Fig. b. — Axiolites in an aporhyolite. Specimen 77. Slide 77. South Mountain. 
In ordinary light, X 40. 
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