EXPLANATION OF PLATE 27 



Fig. A. Franciscan chert near Tennessee Cove, Marin County. Shows 

 mounding of chert, pinching and swelling of chert beds, and the wedging out 

 of shale partings. 



Fig. B. Franciscan chert, Twin Peaks, San Francisco. Shows pinching and 

 swelling of beds and wedging out of shale partings. 



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