I9I0.] COAST RANGES OF CALIFORNIA. 329 



constituent of the original rock remaining behind. Diallage is not 

 present, but since it gives rise to antigorite and seems to be more 

 susceptible to decomposition than enstatite, it was probably also 

 a constituent of the- original rock. Traces of picotite with a broad 

 surrounding mass of chromite are seen (Plate XXXV, Fig. 4), and 

 veins of magnetite are in abundance. With an advance of decom- 

 position the carbonates dolomite, calcite and magnesite appear. 

 They have no crystalline form, but are either granules enclosed in 

 serpentine or vein filling. 



The serpentine found near Glenbrook Springs differs somewhat 

 from the above in structure and appearance. It is massive, well 

 preserved and slickensided fragments are rare. It appears to be 

 porphyritic, due to a yellowish brown ground mass which is very 

 uniform and dotted by numerous green phenocrysts of bastite stand- 

 ing out prominently. Thin sections show that this coloration is 

 caused by an abundance of oxide of iron. 



Analysis of Serpentine from Mayacmas Range. 

 H. E. Kramm, Analj-st. 



Per Cent. 



SiO. 39.98 



ALO3 1. 12 



Fe-jOa 13.19 



FeO 



1.05 



^IgO 30.49 



CaO 46 



Na^O og 



K=o ;;;;; 'i^ 



H20 13 26 



Cr^Oa trace 



TiOi- trace 



100.08 

 Serpentine is also found on the road from Aliddletown to Lower 

 Lake, about two miles south of Guenoc. The area has a northwest- 

 southeast trend, an average width of a quarter mile and a length of 

 about five miles, forming a low ridge which rises not more than a 

 few hundred feet above the surrounding country. The serpentine 

 is well preserved, and its similarity to the Knoxville serpentine 

 makes further comment unnecessary. Herewith is given an analysis 

 of a Mayacmas range serpentine made by the writer. It was taken 



