1922] Hudson: Geology of the Cuyamaca Region of California 199 



Quarts norite (no. 114), from point one hundred yards north of contact in 

 northwest quarter of southwest quarter, section 21, township 13 south, range 4 



east. 



The mineral composition is as follows: 



Labradorite and Bytownite 52% 



Hypersthene 22% 



Quartz 20% 



Biotite 4% 



Magnetite 1.3% 



Pyrrhotite 0.4% 



The average grain is 0.5 mm., the maximum 1.6 mm. 



The hypersthene and feldspar occur as an aggregate of anhedral grains with 

 curving contacts. The quartz is sometimes molded against crystallographic 

 faces of feldspar, or the two minerals meet along irregular curving boundaries. 

 The biotite occurs as ragged grains and is penetrated along cleavages by the 

 feldspars. It is possible that the biotite represents grains picked up by the 

 norite from the wall rock, granite or schist, and that these grains were never 

 melted or dissolved by the norite. 



Most of the pyrrhotite occurs as very irregular masses, occupying the space 

 at the meeting place of three or more feldspar individuals. 



Quartz gdbbro (no. 180b), two hundred yards northeast of locality of speci- 

 men 151 in small area of basic rock east of Pine Hills. 



The mineral composition is as follows: 



Labradorite 31% 



Hypersthene 10% 



Hornblende 20% 



Augite 13% 



Biotite 19% 



Quartz 4% 



Magnetite 3% 



Average grain is 1.0 mm., maximum 2.0 mm. 



The textural relations of the feldspar, pyroxenes, hornblende, and biotite are 

 quite like those of specimen 114, and need no further comment. 



The quartz occurs in irregular veinlike masses, which are optically continuous 

 and may reach 5 mm. in length. Its boundaries against the various inclosing 

 minerals are such as would be produced if the quartz had corroded the pyroxenes 

 or feldspars. The contacts of the quartz against several of the bounding plagio- 

 clase crystals and also against individuals inclosed in the quartz are straight 

 lines. One set of these lines is the trace of the 010 plane of the plagioelase. 

 The other set does not seem to be related to any crystallographic properties of 

 the feldspars, but on the other hand often corresponds exactly with the c axis 

 of the quartz. These quartz masses, together with the bounding and included 

 feldspars, have then the properties of a pegmatitic intergrowth. 



Effect of marginal cliilling. — Norites with distinct porphyritic tex- 

 ture were found at three localities in the north half of section 21, 

 township 13 south, range 4 east. Two of these occurrences are within 

 one hundred yards of the eastern and western margins of the intru- 

 sive mass. They are, however, known to occur as dikes, cutting the 

 even-grained norites. At the third locality the structural relationship 



