GKAPHITE-BEARING QUARTZITE 



387 



Figure 9. — Photomicrograiih of sheared Granite, for Comparison with the Quartz-mica 

 Schist. X Nicols. (X 20) 

 Locality, 1% miles northeast of Hellertown, Allentown quadrangle. Specimen 6749. 

 Shows microperthite and quartz, much shattered, and surrounded by secondary micaceous 

 material (dark) ; a large grain of perthite on the left has resisted the force, but is trav- 

 ersed above by a tiny fault-crack containing angular, fragments. 



Figure 10. — Photomicrograph of Graphite-bearing Quartzite. Ordinary Light. (X 20) 

 Locality, three-fourths mile southwest of Vera Cruz, Allentown quadrangle. Specimen 

 7788. The pale mineral is quartz, the dark graphite ; carbonaceous dust spreads out 

 from some of the graphite plates into the quartz, appearing to cause a bluish color in 

 the latter. 



Figure 11. — Photomicrograph of basic Gneiss. Ordinary Light. (X 20) 

 Locality, 1% miles southwest of Lower Saucon, Allentown quadrangle. Specimen 

 6876. The dark mineral is hornblende, the white oligoclase feldspar, the .gray band 

 crossing horizontally below the center sericite with dark patches of augite ; there is no 

 indication that the hornblende is an alteration product of the augite, and both are 

 thought to have formed simultaneously in the course of feldspathization of a shale. 



Figure 12. — Photomicrograph of basic Gneiss shoioing rounded Zircons. Ordinary 



Light. (X 100) 



Locality, 3 miles northwest of Boyertown. The clear mineral is orthoclase feldspar, 

 and several zircons are visible, standing out in relief, near the center of the field ; they 

 are well rounded and of different sizes. 



