UNIVERSITY OF CALIFORNIA PUBLICATIONS 



BULLETIN OF THE DEPARTMENT OF 



GEOLOGY 



Vol. 11, No. 3, pp. 235-432, 16 text-figures, plates 25-36 December 23, 1918 



THE RADIOLARIAN CHERTS OF THE 

 FRANCISCAN GROUP 



BY 



E. F. DAVIS 



CONTENTS 



PAGE 



Introduction - - 239 



The Franciscan group 240 



The radiolarian cherts of the Franciscan group 241 



Nature of contacts between chert and sandstone 242 



Occurrence of chert in lenses — 243 



Bedding of the cherts 247 



Two types of chert , 247 



Contortion of cherts 248 



Breeciation of cherts 248 



Minor irregularities in bedding 248 



Concretionary cherts 252 



Petrographic features of the radiolarian cherts 253 



The red cherts 254 



Typical red cherts 254 



Shaly cherts 257 



Veining of the cherts 259 



Leaching of the red cherts 260 



Eesistance to chemical weathering 261 



Gray and green cherts 261 



Laminated black and white cherts 262 



Massive white cherts 263 



The matrix of the cherts 263 



Concretions in chert , 263 



Shale partings of the radiolarian cherts 264 



Bed shales „ 264 



Green and gray shales 266 



Carbonaceous shales 266 



