14 CALIFORNIA ACADExMY OF SCIENCES. 



IV. — The Slate Series. 



In the vast granite area are inclosed smaller slate areas 

 which always appear to have suffered intense lateral com- 

 pression and are highly altered. 



Tiie specimens collected come from two of these areas, 

 one in the vicinity of Eeal del Castillo, the other between 

 this place and Ensenada, but petrographically speaking the 

 rocks from both are nearly identical. The material is not 

 sufficient for a thorough examination of the whole series, 

 and only the general character can be indicated. 



A division of the rocks may be made in — 1. Chloritic 

 slate; 2. Quartzite; 3. Carbonaceous slate. 



1. Chloritic Slate. 



Specimens of this from near Real del Castillo, are soft 

 and decomposed; it is very likely that the chlorite is sec- 

 ondary and has resulted from primary pyroxenic or amphi- 

 bolitic rocks. 



2. Quartzite. 



These are fine-grained, brown or grayish-brown rocks, 

 collected near the road from Ensenada to Real, in Gallo 

 Canon. Some are thoroughly crystalline, consisting of 

 sliarply defined, rounded or angular quartz grains of some- 

 what varying size. Orthoclase is, however, also present, 

 and even a few striated triclinic feldspars. Eilms of small, 

 parallel biotite foils and grains of iron pyrites are distrib- 

 uted through the mass. 



In other specimens the quartz and feldspar grains do not 

 always join each other directly, but are separated by a once 

 detrital, now microcrystalline mass of the same materials, 

 to which is usually added minute foils of chestnut-brown 

 biotite. The quartz grains frequently contain fluid inclu- 

 sions . 



