1918] Davis: The Radiolarian Cherts of the Franciscan Group 237 



PAGE 



Ural Mountains 324 



The Alps 325 



Harz Mountains 325 



Other occurrences in central Europe j 326 



Italy 327 



Borneo 329 



Malay Peninsula 331 



Dutch East Indian Archipelago 332 



The Philippines 332 



The novaculites of Arkansas, Oklahoma, and Texas 333 



Occurrences of bedded cherts and jaspers without radiolaria 336 



Cherts and jaspers of the Lake Superior district 336 



Jaspers of South Africa 342 



Contributions of earlier workers in California to the question of the origin of 



the radiolarian cherts 343 



Origin of the radiolarian cherts of the Franciscan group 353 



Statement of thesis 353 



Interpretation of cherts as volcanic or metamorphic rocks 355 



Interpretation of the cherts as fossil radiolarian oozes 355 



Hypothesis of abyssal origin 356 



Calcium carbonate 356 



Manganese oxide 357 



Bed color 358 



Chemical composition of shales * ., * 358 



Terrigenous minerals 359 



Absence from shales of certain things characteristic of red clay 359 



Bate of accumulation 359 



Bhythmic bedding 359 



Possibility that red shales may be red muds 360 



Doctrine of permanence of ocean basins 360 



Significance of carbon ._ 361 



Association of cherts with sandstones 362 



Nature of sandstone-chert contacts 362 



Occurrence of cherts in lenses 362 



Possibilities which might reconcile the hypothesis of abyssal origin 



with the known facts 363 



Interbedding of cherts with coarse mechanical sediments 364 



Bipple marks 364 



Conclusion 364 



Hypothesis of lagoon deposition 364 



The lagoon phase 364 



Absence of calcaerous organisms 365 



Variation in ocean waters 365 



Enclosed basins — -tropical weathering 365 



Solution of calcareous remains in shallow water 366 



Change in habits of life 366 



