332 KRAMM— SERPENTINES OF THE CENTRAL [June 6, 



possibly some chromite. It would therefore correspond to a dial- 

 iagite. 



An analysis made by Ransome upon serpentine taken from a 

 nodule of the slickensided facies is given above : 



The Tihnron Peninsula Serpentine. 



Although a narrow channel of the San Francisco Bay separates 

 it the Angel Island serpentine is probably continuous with the one 

 which is found north of it at the extreme tip of the Tiburon penin- 

 sula. It covers an area of perhaps one square mile. The road fol- 

 lowing the western shore line exposes the slickensided facies about 

 100 yards east of the ferry station. 



The serpentine is much decomposed but the nodules, which often 

 are several feet in diameter show fairly fresh serpentine which is 

 very brittle. Vein serpentine is common. 



The outcrops of this part of the area are small. The soil is of a 

 reddish color and vegetation is scant. The crest of the ridge pre- 

 sents different features. 



Outcrops reach a height of about 15 feet and consist of the 

 siliceous mass, to which serpentine gives rise, and which is known 

 in the coast ranges as the quicksilver rock. From a distance they 

 resemble a conglomerate, close inspection however reveals the honey- 

 combed tough silicious mass with magnesite stains here and there. 

 Remnants of the serpentine can still be observed. The whole pre- 

 sents a rugged appearance. Magnesite float is abundant. 



Slides of the fresh serpentine show the following minerals bron- 

 zite, diallage chromite and magnetite. The mesh structure due to 

 olivine is prominent. 



V. The Coyote Creek and Black Mountain Serpentine. 



Serpentine is also found on what is known as the Los Lagrinas 

 ridge a part of the Mount Hamilton range south of San Jose east of 

 the Coyote Creek in Santa Clara County. The ridge consists of a 

 series of kidney-shaped hills bordering the valley in the east, and 

 reaching a maximum elevation of 300-400 feet above the valley 

 level. About four miles south of Coyote station is the extreme 

 southern end of the serpentine area, which covering the western 

 slope of the ridge extends north to within one half mile of Edenvale. 



