168 FE. P. CAREY. AND W. J. MIELER 
In other instances the rock appears to be a mica schist, with free 
quartz intercolated irregularly between the planes of schistosity. The 
bands are crumpled, and the crystals of glaucophane are broken, dis- 
torted, and frequently healed with quartz. 
Suggestions as to origin.—The close association of the glauco- 
phanes with the jaspers and sandstones would suggest a genetic rela- 
tionship. According to F. L. Ransome,’ the glaucophane schists of 
Angel Island, San Francisco Bay, are the result of the metamorphism 
of the radiolarian cherts as well as the feldspathic sandstones. The 
schist there consists of quartz, albite, glaucophane, biotite, etc. Some 
of the Oak Hill rocks are very similar to those in composition. ‘This 
close association of the glaucophane schists and jaspers has been 
commonly observed in the Coast Ranges of California. 
Some of the Oak Hill glaucophane schist is rich in argillaceous 
matter. Near the border of this schist fairly large flakes of a light 
brown mica have been developed, while nearer the center of the mass 
little or no mica appears. 
Although no positive general statement can be made with refer- 
ence to the origin of the glaucophane schist, nevertheless it is certain 
that at least in some cases they are the products of the metamor- 
phism of sediments. ‘This is undoubtedly true of the more siliceous 
facies, while the more basic facies may have resulted from the altera- 
tion of tuffs of ingneous rocks. Ransome ascribed their origin to 
contact metamorphism, while Nutter and Barber? thought that 
dynamic metamorphism alone could account for the origin of the 
greater schist masses of the Coast Ranges. It would appear that 
further investigation along the line of mineralizing effects of solutions 
in metamorphic zones is necessary to explain the genesis of glau- 
cophane and associated minerals. 
MAGMATIC DIFFERENTIATION 
In the foregoing description of the gabbros, pyroxenites, and ser- 
pentines with their products, it has been pointed out that, while all the 
rock types are very distinctly shown, nevertheless the transitions are 
t Bulletin of the Department of Geology of the University oj California, 1894, pp. 
193-240. 
2 Journal of Geology, Vol. X, No. 7 (1902), p- 742. 
