THE GEOLOGY OF SOUTH MOUNTAIN 337 
and age with the Losee, Byram, and Pochuck gneisses of eastern 
Pennsylvania and New Jersey.” 
Granite pegmatite occurs in isolated outcrops along the southern 
slope, and in the region of the valley southwest of the Insane 
Asylum. The exact manner of intrusion was not noted and no 
attempt was made to learn the direction of veins or dikes of this 
rock. Megascopically, the pegmatite is a coarse-grained binary 
granite composed of pink microcline and bluish quartz. That 
muscovite occurs sporadically in large bunches or pockets is evi- 
denced by the abandoned workings of a mica mine situated on 
southwestern part of the plateau near the Lebanon-Lancaster 
county line. 
PALEOZOIC ROCKS 
Cambrian System; Potsdam Formation 
The basal member of the Cambrian system is the Primal White 
Sandstone of Rogers, or the Potsdam Sandstone of the Second 
Geological Survey. 
On paleontologic evi- 
dence Walcott? cor- 
relates the Reading 
quartzite with the 
Chickies quartzite of 
Lancaster County, 
and with the quartz- 
ite of the South Fic. 2—South Mountain from a distance of 14 
Mountain in York, miles, looking southeast from Newmanstown. The 
northern flanking ridge of quartzite is here shown. 
Cumberland, and East of the notch it is known as Eagle Peak. 
Adams counties. The 
same rock in Lehigh and Northampten counties is correlated by 
Peck‘ with the Hellam quartzite of York County, and the Hardyston 
quartzite of northern New Jersey. 
t Personal communication, by Dr. E. T. Wherry and Mr. E. L. Estabrook. 
2H. B. Ktimmel, ‘‘ Geological Section of New Jersey,” Jour. Geol., XVII, No. 4, 
1909, 352-53. 
3 C. D. Walcott, “The Cambrian Rocks of Pennsylvania.” U.S. Geol. Surv., No. 
134, 1896, 29-33. - 
4F. B. Peck, “Basal Conglomerate in Lehigh and Northampton Counties, 
Pennsylvania,” Geol. Soc. Amer., Bull., XIV (1903), 521. 
