EXPLANATION OF PLATE 25 



Fig. A. Franciscan cherts in Golden Gate Park, San Francisco, showing 

 thin bedding and contortion of the cherts. 



Fig. B. Franciscan cherts exposed in quarry by cemetery, Piedmont. Shows 

 rhythmic alternation of cherts and shales, the pinching and swelling of the 

 chert beds, and wedging out of cherts and shales. 



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