370 University of California Publications. [Geology 



GENEBAL DISCUSSION. 



Tlie Franciscan series extends with various interruptions for 

 about six hundred miles along the Coast Ranges of California 

 and Oregon and in it and its associated eruptives are found a 

 very great number of occurrences of vein deposits that lie among 

 similar surroundings, and a comparison of these with the 

 deposit now under consideration yields some general analogies 

 along with the striking differences. 



Very often in traversing the serpentine areas, so frequently 

 associated with the Franciscan, we come across included masses 

 of partly recrystallized basic rocks or irregular areas or lenses 

 of glaueophane, hornblende, or other basic schists. These are 

 often cut by veins of quartz, but of particular interest in the 

 present connection are the abundant veins of albite. Natrolite, 

 so far as known to the writer, has not been found under these 

 conditions except at the benitoite locality, but the analogous 

 albite veins are very common. 



Titanium is often found in the recrystallized rock, occasion- 

 ally in the veins, and occurs most commonly as titanite, some- 

 times as rutile. 



While minerals containing potassium (usually muscovite), 

 magnesium and iron (such as chlorite or more rarely talc) are 

 also found in veins cutting such rocks, an association represent- 

 ing so many metallic elements in essential quantities as occur in 

 the benitoite veins is exceptional : sodium, potassium, magnesium, 

 iron, manganese, copper, aluminum, barium. With this variety 

 it seems pecidiar that calcium is practically absent within the 

 veins proper. It is found generally in the veins in the schists 

 as lawsonite or the amphiboles. 



The occurrence of barium as an essential constituent is with- 

 out precedent. The only barium mineral that the writer has 

 found associated with such formations is barite in veins in the 

 serpentine of Mt. Diablo. While suggestive of the presence and 

 possible concentration of barium in such rocks, it is not an 

 analogous occurrence. 



Apart from the chemical differences, a comparison of the 

 chief gangue materials, albite and natrolite, would indicate that 



