2 University of California. [Vol. 2. 



Spheroidal Basalt and Diabase-Gabbro Complex 



Field Relations 



Age of the Complex 



Microscopic Petrography 



Chemical and Mineralogical Character 



Volcanic Ash 



Gabbro, Peridotite, and Serpentine 



Field Relations 



Microscopic Petrography 



Age 



Comparison with other Peridotites of the State 75 



Relation between the Magnesian and the Feldspathic Rocks 77 



The Banded Structure 78 



Discussion of Magmatic Variation 85 



INTRODUCTION.* 



Point Sal is situated in the extreme northwestern portion of 

 Santa Barbara County. It forms the termination of a low range of 

 hills about midway between Point Arguello and Port Harford. North 

 and south there are many miles of continuous sandy beaches. 

 Although Point Sal does not form a very marked break in the reg- 

 ularity of the coast line, yet it shows several miles of rocky cliffs 

 which offer exceptional exposures for the study of its remarkably 

 interesting geology. 



The geographical features of the accompanying map have been 

 taken from the map of Santa Barbara County, the contours having 

 been added with the aid of an aneroid. The area included com- 

 prises all that portion of the region about Point Sal which presents 

 any marked geological interest. It is five and a half miles from 

 north to south and four and a half from east to west, containing 

 about sixteen square miles. 



As Point Sal lies away from the main lines of travel, none of the 

 parties of the earlier geological surveys ever visited the section, and 

 no references to its geology have been published except a brief 

 notice by the author, f 



*The author is indebted to Mr. C. H. Clark, of Point Sal, and to Mr. P. H. 

 Dallidet, Jr., of San Luis Obispo, for kindnesses shown during the field work. 



|XII Report of the State Mineralogist of California, p. 506. 



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