184 SMITH— PARAGENESIS OF MINERALS. [Octobers 



from acid quartzites and diorites to very basic gabbros and dia- 

 bases. It is, therefore, clear that the chemical nature of the altered 

 rocks can have had little influence on the formation of the glauco- 

 phane, though of course it decided the petrographic character. 



The glaucophanes in the Coast Ranges of California are always 

 products of metamorphism, and never of crystallization out of a 

 magma. And while they are found in altered igneous rocks just 

 as often as in altered sedimentaries, they are always secondary in 

 both. It is thus clear that the petrographic character can have had 

 just as little influence as the chemical constitution on the formation 

 of glaucophane. It is true that the sedimentary rocks altered to 

 glaucophane schists are all acid, with the exception of tuffs, and that 

 the igneous rocks that have had glaucophane developed in them are 

 mostly basic. But then non-calcareous sediments are usually acid, 

 on account of the predominance of quartz sand ; and acid intrusive 

 rocks are rare in the Franciscan series. 



Ransome^ has shown that glaucophane has been developed on 



a small scale in chert at the contact with serpentine, and with meta- 

 basalts or '' fourchites." There are, however, in the Coast Ranges 

 extensive glaucophane schist masses near which neither serpentine 

 nor metabasalt has been found. And often where such schists are 

 near serpentine they are in much greater masses than the igneous 

 rocks to which the metamorphism might be ascribed. From this it 

 would seem illogical to assume that the formation of glaucophane 

 schists is due in every case to contact with basic intrusive rocks. 

 There are also numerous contacts of such basic intrusives with sedi- 

 ments where no schists have been formed. 



On the other hand, we might assume that dynamic metamorphism 

 has been the cause of the formation of the glaucophane schists, for 

 the Franciscan series is usually crushed, and zones of shearing are 

 common in it. But while the glaucophane rocks are extensively 

 developed for several hundred miles in the Coast Ranges, from 

 Oregon to San Diego, there are no continuous masses of schists. 

 Thus the cause of metamorphism can hardly have been regional. 

 And it is hard to see how this agency can have been intermittent or 

 local in its action, since the rocks of the Franciscan series are 



' " Geology of Angel Island," Bull. Dept. Gcol. Univ. Calif., Vol. I., p. 223. 



