PLATE XI 



MAGNIFIED SECTIONS OF BASALT AND SECONDABY MINEBALS 



Fig. 1. Normal crystallization of dense basalt. X 24. Slide 18. 



Fig. 2. Dense basalt bordered by secondary albite. X 24. Slide 62. 



Fig. 3. Dense basalt bordered by secondary albite (Ab) with fanlike groups of 

 prehnite (Pr) and some calcite (Ca). x 24. Slide 62. 



Fig. 4. Groups of radiating quartz crystals surviving from an early period of 

 alteration in a slide in which zeolites and chlorite form the principal 

 features, X 24. Slide 59. 



Fig. 5'. Garnet (Gr), fibrous green amphibole (Am) and prehnite (Pr) encrust- 

 ing dense basalt. The garnet forms clear grains where it borders 

 the prehnite, but the greater portion is in masses which are nearly 

 opaque from dust of TiOj or MnOa. The circular markings are inter- 

 preted as due to nuclei of resorbed olivine in the original glass which 

 the secondary minerals have replaced. X 24. Slide 5-3. 



Fig. 6. Garnet grains (Gr), acicular amphibole (Am) and long needles of 

 pectolite (Pc) in prehnite (Pr). X 24. Slide 50a. 



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