226 SMITH— PARAGENESIS OF MINERALS. [Octobers, 



the original rock contained soda only in extremely small quantities 

 the blue hornblendes are developed only rarely in the secondary 

 rocks resulting from them. When soda was more abundant some of 

 it went to the formation of paragonite, and when there was an excess 

 of lime in the pyroxenes it went largely into margarite. Both of 

 these minerals are quite common in the basic schists and eclogites. 



In the medium-basic rocks, gabbros and diorites, which form the 

 bulk of the older igneous rocks of the Coast Ranges the products 

 of metamorphism are much more varied. The first step is simply 

 the formation of paramorphs of hornblende after pyroxene, uralitiza- 

 tion, without any fundamental chemical readjustment. But when 

 the lime-soda feldspars were partly broken down some of the soda 

 went into the amphibole molecule and actinoHte was formed. Since 

 this mineral contains no titanium, while the original hornblende 

 and pyroxene were often titaniferous, titanic oxide was set free, 

 and either crystallized out as rutile, or combined with lime to form 

 titanite. These are both very abundant in the basic metamorphics of 

 this group. 



The silica, lime, and alumina set free from the feldspars often 

 took up iron from the ferro-magnesian minerals to form more 

 basic silicate, usually epidote, and sometimes zoisite when the iron 

 was deficient. When the feldspars were more broken down and 

 more soda set free, or more soda added from outside sources, bluish 

 pargasite was formed, accompanied by large quantities of white 

 epidote. In other cases, but usually in the more acid diorites, the 

 bluish green soda-bearing hornblende, carinthine, has been formed 

 in considerable quantities. In the pargasite-bearing rocks there was 

 more of the albite molecule set free than was needed for the forma- 

 tion of pargasite, and this has crystallized out in veins of very pure 

 albite. 



When still more soda was released from the feldspars glauco- 

 phane was formed, while the excess of lime went into garnet, more 

 rarely into lawsonite, accompanied as before by white epidote. In 

 some of the basic eclogites diopside is common, and in this case little 

 epidote was formed, the excess of lime having gone into garnet. 



When the rocks are low in silica and rich in lime, lawsonite has 

 often been formed in great abundance by the plagioclase giving up 



