EXPLANATION OF PLATE 9 



Fig. 1. Thin section of norite. X 25. 



The relations between the hypersthene and the plagioclase are typical of the 

 rocks of the Cuyamaca Intrusive. 



Fig. 2. Thin section of norite. X 104. 



Brown hornblende separating grains of plagioclase. 



Fig. 3. Thin section of olivine norite. X 6.7. 



Plagioclase, light gray, hypersthene and olivine, darker gray. The hyper- 

 sthene may be distinguished from -the olivine by its lower relief and distinct 

 cleavage. The texture is typical of the Cuyamaca Basic Intrusive rocks. 



Fig. 4. Thin section of gabbro. X 25. 



Augite, darker gray, plagioclase, lighter gray. Note the extremely irregular 

 outlines of the augite. 



Fig. 5. Thin section of gabbro. X 32. 



Several augite sections, all parts of a single ophitic individual, associated with 

 plagioclase. The augite is altered to a slight extent to green hornblende. 



Within the augite are several magnetite grains, associated in such a fashion 

 with spinel, sp., that the two minerals appear contemporaneous. 



Fig. 6. Troctolite. Trains of olivine grains in plagioclase. X 6.95. 



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