i9o6.] SMITH— PARAGENESIS OF MINERALS. 239 



phism has done nothing more than change the mineralogical asso- 

 ciation. Each sort of rock, whether igneous or sedimentary, has its 

 own peculiar chemical composition, and this is disclosed by a 

 chemical analysis, no matter what molecular readjustment has taken 

 place. Aletamorphism was once considered as a sort of magical 

 process by which almost any sort of rock might be made out of any 

 sort of material. But metamorphism such as we have to deal with in 

 the glaucophane-bearing rocks of the Coast Ranges may be defined 

 merely as recrystallization. A siliceous rock remains siliceous, a 

 basic ferruginous or magnesian rock remains ferruginous or mag- 

 nesian. Little is added and little is taken away, not enough in any 

 case to obscure the relations of the original material and the recrys- 

 tallized product. The only essential difference is the water of consti- 

 tution, which is always present in some mineral in the recrystallized 

 rocks. 



Analyses I., II. and III. in the foregoing table are of altered 

 siliceous sediments, and are clearly recognizable as such by their 

 chemical composition. Analysis IV. is of an arkose which corre- 

 sponds closely to a granodiorite. No. V. is a lawsonite gneiss, with 

 every mineral in it a product of recrystallization, but its chemical 

 constitution shows it to have been originally either a quartz diorite 

 or an arkose from such a rock. Analysis VI. is an albite crossite 

 gneiss, with every mineral of secondary origin, but chemically it is a 

 soda syenite, and it was originally such an igneous rock or an 

 arkose from a soda syenite. No. VIII. is a soda syenite porphyry, 

 showing a composition almost identical with No. VL, and glauco- 

 phane-like minerals have been observed at several places in the 

 Sierra Nevada in dynamically altered soda syenites. 



No. VII. is a little altered quartz diorite in which secondary 

 lawsonite and crossite have been developed by dynamic meta- 

 morphism. 



No. IX. is a mica glaucophane schist, but the chemical composi- 

 tion shows it to have been a normal diorite. 



Nos. X., XL, XIII. and XIV. are of metamorphosed medium 

 basic rocks, either diabases or gabbros, and the chemical composi- 

 tion shows only the addition of water, otherwise they are still 

 gabbros in composition. 



