UNIVERSITY OF CALIFORNIA 



Bulletin of the Department of Geology 



Vol. I, No. 9, pp. 273=300, Pis. 15-16. ANDREW C. LAWSON, Editor 



ON 



A N A L C I T E DIABASE 



FROM 



SAN LUIS OBISPO COUNTY, CALIFORNIA. 



BY 



Harold VV. Fairbanks. 

 CONTENTS. 



Field Relations 273 



Contact Metamorphism 275 



Macroscopical Character of the Cuyamas Occurrence 276 



Microscopical Petrography of the Main Dike 27S 



Microscopical Petrography of the Secondary Dikes 279 



Plagioclase 279 



Lamellar Pyroxene 2S1 



Analcite 283 



Secondary Minerals in the Analcite 289 



Titaniferous Magnetite 292 



Chemical Character 292 



Oceanic Dikes 294 



Eagle Ranch Occurrence 297 



Conclusion 297 



FIELD RELATIONS. 



San Luis Obispo County is situated in the Coast Ranees of 

 California, nearly midway between San Francisco and the southern 

 boundary of the State. The topography is characterized by a 

 series of mountain ranges extending northwest and southeast, con- 

 stituting the Coast Range system. The geology of this region is 



* These interesting rocks were discovered by the writer while engaged in 

 field work for the State Mining Bureau. Their petrographic investigation was 

 conducted in the geological laboratory of the University of California. 



