294 



University of California. 



[Vol. r. 



Although the actual proof is not possible, it seems to the writer 

 that the conclusion is reasonable that some primary soda silicate 

 (probably nepheline) formerly occupied the wedge-shaped areas. 

 The description given by Rosenbusch and others of the teschenites 

 corresponds very closely with the facts observed in the rocks which 

 form the subject of this paper. 



OCEANIC DIKES. 



The most important development of this series of dikes is near 

 the Oceanic quicksilver mine, six miles east of Cambria. Two to four 

 dikes of varying width and separated by narrow strips of upturned Ter- 

 tiary strata were traced for at least twelve miles. There is a great 

 similarity in all, and they have undoubtedly issued from one parent 

 magma. At one locality an oil well was sunk nearly seven hun- 

 dred feet in a strip of Tertiary strata lying between two of these 

 dikes. In the bottom a crystalline rock was encountered which in 

 all probability marks the point at which junction takes place. 

 The degree of decomposition of these dikes appears to be very 

 great. Except in the bottom of the canons the rock is scarcely 

 more coherent than the main body of the Cuyamas dike. At the 

 foot of the «rade leading from Cambria across the mountains, there 

 are shown some remarkable examples of shelly spheroidal weather- 

 ing. Many of the spheroids are a foot in diameter with clayey 

 matter between them, and peel off in very regular concentric shells, 

 one-third of an inch in thickness down to a more solid core. 



A microscopic study of these rocks confirmed to a considerable 

 degree the appearance of decomposition. In a general way there 

 are two macroscopic differences, the lighter colored facies in struc- 

 ture and appearance much resembling the Cuyamas dike, except 

 that no analcite is visible to the unaided eye; and the dark-colored 

 facies, very rich in iron, in which the individual components cannot 

 be determined without the microscope. The most of the lighter- 

 colored specimens were collected from the most westerly dike. 

 Sections made from this dike showed the existence of feldspar, 

 augite, olivine decomposed to serpentine, analcite, magnetite, and 

 green decomposition products. The structure is typically diabase 

 granular, the feldspar crystals penetrating and frequently almost 



