University of California. 



[Vol. 2. 



daloidal intrusions, in some cases at least, andesitic; gabbro with 

 diabasic facies; dikes in the gabbro; the lavas of the volcanic neck 

 and perhaps dikes of the same age. 



ANALYSES OF GABBRO, ANDESITE AND SPHEROIDAL BASALT. 





I. 



II. 



III. 



SiO, 



49.56 



55.80 



50.56 



A1.A 



20.09 



18.22 





FeO 



2.02 1 



8.98 





Fe 2 3 



2.32 j 





CaO 



1 5.62 



4.40 



6.24 



MgO 



7.01 



2.23 





Na. 2 



1.63 



6-34 





K,0 



•34 



1.90 





Ig 



2.25 



2.30 







100.84 



1 00. 1 7 





Sp. gr. 



2-93 



2.72 





Volcanic Ash. — A small area of volcanic ash occurs a little above 

 the foot of the grade on Corralito.s Creek. The exposures are not 

 good, and its relations to the spheroidal basalt are not revealed. In 

 the hand specimen it appears as a rather soft rock of light color, 

 containing fragments of pumice and dark pebbles. Viewed under 

 crossed nicols it appears to be almost entirely isotropic. There are 

 a few clear grains of feldspar. 



GABBRO, PERIDOTITE, AND SERPENTINE. 



Field Relations. — The most complicated and, in many respects, 

 the most interesting of all the eruptive masses which are found on 

 Point Sal extends from Point Lospie, three miles in a southeasterly 

 direction. For the first mile and a half it forms a narrow'fringe 

 along the coast, and where the latter begins to turn to the south, 

 the eruptive complex passes inland, terminating finally in a low 

 rounded hill, which rises to a hight of 700 feet at the southern 

 foot of a spur of the main ridge. 



A detailed description can be perhaps best given by beginning 

 at the western end, and following the coast line, also noting the 

 various sections in the gulches which cross it. For nearly half a 



