28 University of California Publications in Geology [ VoL 11 



are not due to contact action of Franciscan igneous rocks, but are 

 members of a pre-Franciscan group of rocks : 



No one explanation seems to satisfactorily account for the many different 

 aspects and occurrences of the glaueophane and related schists. That there has 

 been some development of glaueophane at the contact of basic igneous masses 

 seems certain. It seems improbable, however, that the main portion of the normal 

 glaueophane and actinolite schists is a result of contact action. That the schists 

 have not resulted from contact action by peridoite masses seems probable, for at 

 some points the same masses have certainly produced but slight alteration in ad- 

 joining sandstones and shales, and the thickness and character of the schists is 

 such that they could only have been produced by metamorphosing agents acting 

 on a large scale. It seems difficult to believe, also, that the schists could be 

 formed by serpentine dikes which are smaller than the schist masses themselves. 

 Besides, the inclusions of schist in the Healdsburg and Angel Island serpentines 

 render it almost certain that the schists are the older of the two rocks. In addi- 

 tion, the evidence points to the massive glaueophane rocks and normal schists 

 being older than the Golden Gate or Franciscan series of rocks, for the schists are 

 unconformably beneath what appears to be the Golden Gate or Franciscan rocks 

 in the Calaveras Valley, and they probably have similar relations at Healdsburg. 

 Finally, serpentinized dikes are frequently found intrusive in Golden Gate or 

 Franciscan rocks, while at Mount Diablo, near Gilroy, and in San Luis Obispo 

 County there are serpentine dikes intrusive in the Knoxville beds. This would of 

 course make the dikes younger than the schists, if the schists are older than the 

 Golden Gate or Franciscan series. . . . 



It can hardly be doubted that glaueophane schists have been developed in rocks 

 of different ages, and older than the Knoxville. It seems probable, also, that 

 there is a series of glaueophane schists older than the Golden Gate or Franciscan, 

 and the possibility suggests itself that these may be but isolated outcrops of exten- 

 sive masses which underlie the Coast Ranges. 



The only hypothesis that seems to satisfactorily explain the occurrences of 

 these rocks is that they are the result of dynamic agencies, and may or may not 

 be the products of widespread regional metamorphism. 



However, Franciscan sandstones and radiolarian cherts have 

 actually been observed at many places to pass into glaueophane schists, 

 at their contacts with Franciscan igneous rocks. It is unlikely that 

 there is a pre-Franciscan formation of glaueophane schist in the 

 Coast Ranges. Glaueophane schists are rare in their occurrence and 

 appear to require special conditions for their production. In Cali- 

 fornia they are not found outside areas of the Franciscan group 

 and no one has ever reported an occurrence of glaueophane schist in 

 the Coast Ranges in any pre-Franciscan area. 



Similarly, it is not known that there are any older formations of 

 red and green radiolarian cherts in the California Coast Ranges or 

 formations of arkose sandstone. 



The presence of these conglomerates with boulders of many of the 

 typical rocks of the Franciscan group, implies that there are breaks 

 within the Franciscan itself. These represent periods when earlier 



