PLATE SG: 
Fia. 1. Perlitic structure in red felsite-porphyry (apobsidian ) from Hammond 
River below Upham. The stippled part is microfelsite, which 
shows a flow-brecciated structure, the horizontal shading repre- 
sents secondary quartz and feldspar. The perlitic cracks are in 
fact preserved in a brightly polarizing substance, but this was not 
easy to represent in the drawing. >< 67 diam. 
Fia. 2. Skeleton crystals of magnetite in black felsite porphyry (petrosilex) 
from Hanford Brook. Spec. 570. > 67 diam. 
