EXPLANATION OF PLATE 5. 



Figure r. — Corroded quartz phenocryst with glassy border, x 30. 



Figure 2. — Illustrating porphyritic facies with microcrystalline ground-mass; 

 q, quartz;^ plagioclase. • 30. 



Figure 3. — Plagioclase phenocryst with border of spherulites in glassy ground- 

 mass. Nicols + , x 30. 



Figure 4. — Characteristic section of soda-rhyolite. Nicols + . q, quartz; 

 f, plagioclase. x 30. 



Figure 5. — Rhyolite glass with phenocrysts. Nicols +. q, quartz; /, feldspar. 



x 30. 



