56 CALIFORNIA ACADEMY OF SCIENCES. 



/')X'. /. Analcite Basalt, magnified 25 Diameters. 



A. Olivine. 1?. Augite. C. Analcite. 



Groundmass: augite, analcite, magnetite, apatite. 



In some specimens faintly double-refracting spots are 

 more frequent in the analcite crystals. I do not feel pos- 

 itive whether this is a result of a physical or a chemical 

 change in the isotropic substance. In the original paper 

 in Vol. XV, loth Census, these phenomena were regarded 

 as results of the anomalous double refraction so often 

 observed in the analcite (more frequently, though, in 

 free crystals, than in the mineral when enclosed in the 

 rock mass). 



In some specimens of the rock in question, the larger 

 part of the colorless mineral is faintly double-refracting, 

 showing bluish gray colors, between crossed nicols ; the 

 crystals are then not so well defined, and often take the 

 form of rounded spots separated by groundmass and small 

 porphvritic augites and olivines; these rounded spots, be- 

 tween crossed nicols, divide into irregular, sometimes also 

 into regular triangular fields. I regarded this (see Vol. 



