I9I0.] COAST RANGES OF CALIFORNIA. 331 



An analysis of a Presidio serpentine made by Easter is given on 

 account of the similarity with the one made by the writer on Sul- 

 phur Creek serpentine. 



The second belt of serpentine occupies the southeastern portion 

 of Buri-Buri ridge from San Andreas Lake to San ]\Iateo Creek, 

 and nearly the whole of Las Pulgas ridge, with a total length of ii^ 

 miles and a maximum width of over one mile. 



The third belt consists of a linear group of dike-like masses dis- 

 tributed along San Mateo Canyon between Sayer and Cahill ridges, 

 on the pass between Cahill and Fifield ridges, and thence obliquely 

 along Fifield ridge and across San Pedro Valley nearly to the ocean. 

 The linear extent is six miles. There are also some few minor out- 

 crops not referable to these belts. 



All these serpentines exhibit similar features to those which 

 Palache designated as Iherzolite serpentine. 



The Angel Island Serpentine. 

 Angel Island is situated in the bay of San Francisco 3^ miles 

 north of the city of San Francisco. The geology of the island has 

 been described by Ransome. Serpentine is found along the western 

 portion of the island as a large dike having a maximum width of 500 

 feet. Intrusive into the San Francisco sandstone, it has metamor- 

 phosed it to some extent. The two facies, the slickensided and the 

 massive are present. The slickensided differs from the one found 

 at the Potrero in that the nodules are not as large and the matrix 

 is less broken. 



Analysis of Serpentine from Angel Island. 

 F. L. Ransome, Analyst. 



Per Cent. 



SiO; 42.06 



AI.O3 ] 



Fe^Oaj '■'' 



FeO 2.88 



MgO 39.53 



H.0 12.04 



9923 



The massive facies is of unusual interest. It is made up of in- 

 terlocking crystals of diallage with small amounts of magnetite and 

 Proc. Amer. Phil. Soc, xlix, 196 v, Printed September 7, 1910. 



