154 



H. W. TURNER 



THE PORPHYRITIC QUARTZ-MONZONITE 1 



Forming large areas along the higher parts of the range is a 

 coarse granitic rock containing numerous porphyritic orthoclases 

 which are often more than two inches in length. This rock is in 

 sharp contact with the quartz-monzonite, above described, to the 

 northwest of Lake Tenaya in the Yosemite Park, and doubtless 

 at other points. While not differing much in chemical composi- 

 tion (see No. 39, table of analyses) from the latter rock, its 

 marked porphyritic character and the usual absence of amphi- 

 bole readily distinguish it. Along the contact, however, the por- 

 phyritic quartz-monzonite sometimes contains abundant amphi- 

 bole. The orthoclase phenocrysts are evidently formed at a 

 late period in the consolidation of the rock, for these contain as 

 inclusions most of the minerals of the groundmass, including 

 plagioclase, biotite, quartz, titanite, and iron oxide. The inclu- 

 sions have no definite arrangement in the phenocrysts. 



BRIDAL VEIL GRANITE 



In the drainage of Bridal Veil Creek, on Horse Ridge, and 

 at many other points in the Yosemite Park, there are consider- 

 able masses of a white, rather fine-grained granite which has 

 been designated Bridal Veil granite. It often shows an orbicular 

 structure, there being a central white nucleus composed of quartz 

 and feldspar, surrounded by a layer rich in biotite. This granite 

 is intrusive in the biotite granite and often contains near the con- 

 tact chunks of the latter. It also incloses fragments of dioritic 

 rocks, which are likewise found as nodules and small areas in 



ANALYSES OF BRIDAL VEIL GRANITE 



Fourteenth Ann. Rep. U. S. Geol. Surv., pp. 478-480. 



