EXPLANATION OF PLATE 30 

 Thin sections of radiolarian chert 



Fig. A. Mount Diablo. (Mag. 25 X.) 



Fig. B. North Berkeley. (Mag. 25 X.) 



Fig. C. Mount Diablo. (Mag. 15 X.) 



Fig. D. Mount Diablo. (Mag. 10X.) 



Fig. E. North Berkeley. (Mag. 12 X.) 



Fig. F. Spherulitic chert. (Mag. 12 X.) 



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