PLATE XXXI. 



Fig. a. 



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



Photomicrograph illustrating the igneou.s texture of the basalt from the center of an ellipsoid. 

 This has already untlergone advanced alteration, and the feldspars liave been replaced by a granular 

 aggregate of calcite, sericite, chlorite, epidote, quartz, and albite. With advancing alteration the 

 igneous texture is destroyed, and infiltrated calcite becomes more prominent. The photomicrograph 

 shows in the lower left-hand corner a portion of the section in which a large quantity of calcite is 

 present. (Described, p. 131.) 



Fig. B. 



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



Photomicrograph illustrating the igneous texture of the basalt from the center of an ellipsoid, 

 when viewed between crossed nicols. The igneous texture is almost completely destroyed by the 

 breaking up of the secondary aggregates. (Described, p. 131.) 



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