PLATE XXIII. 
Fig. a.— Spherulitic aporhyolite. Specimen 226. Slide 226 D. South flank of 
mountain northeast of the junction of Copper Run and Toms Creek. In polarized 
light, X 28. 
The left-hand side of the figure shows the spherulites in ordinary light; the 
right-hand shows the same spherulites in polarized light. 
Fig. b. — Aporhyolite. Specimen 121. Slide 121 D. One-half mile heyond the 
Bigham copper mine, Old Furnace road. In polarized light, X 80. A crystal of feld- 
spar broken by the cleavage along the plane of former spherulitic crystallization. 
The figure shows the crystalline silica, which has replaced the spherulitic crystal- 
lization and which is much coarser in grain than that of the groundmass. 
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