PLATE XXVIII. 

 Fig. a. 



(Sp. No. 32909c. Without analyzer, x 35.) 



Photomicrograph of section of fine-grained basalt with well-developed igneous texture. The 

 feldspar outlines are now occupied ohieily by flalies of muscovite and grains of zoisite. (Described, 

 p. 127.) 



Fig. B. 



(Sp. No. 32909c. With analyzer, x 35.) 



Photomicrograph of the same section when viewed between crossed nicols, showing the obliter- 

 ation of the igneous texture. The lath-shaped mineral is muscovite. (Described, p. 127.) 



