THE GEOLOGY OF SOUTH MOUNTAIN AT THE 
JUNCTION OF BERKS, LEBANON, AND LAN- 
CASTER COUNTIES, PENNSYLVANIA 
H. N. EATON 
School of Mines, University of Pittsburgh 
INTRODUCTORY 
The term South Mountain is applied in general to the range of 
high hills which enters the state of Pennsylvania from the east, 
extending in a southwest direction through the counties of Bucks, 
Northampton, Lehigh, Berks, Lancaster, and Lebanon, and thence, 
after a break, passing southwest through York, Cumberland, 
Adams, and Franklin counties into Maryland. It is a pre- 
Cambrian mountain range, the third or northern gneissic zone of 
Rogers, bounded on the north by the Paleozoic limestones and 
slates of the Great Valley, and on the south by the Trias. Several 
portions of the range, topographically prominent, bear individually 
the name of South Mountain and are so marked on the topographic 
maps issued by the United States Geological Survey. 
The South Mountain of the title of this article is a ridge or 
elongated knob-like hill extending about nine miles east and west 
and four miles north and south, whose center is nearly at the 
junction of Berks, Lebanon, and Lancaster counties and near the 
intersection of parallel 40° 20’ north latitude and meridian 76° 10’ 
west longitude. It is nine miles west of the city of Reading and 
directly south of the Harrisburg division of the Philadelphia and 
Reading railroad. The villages of Newmanstown, Womelsdorf, 
Robesonia, and Wernersville lie in the Great Valley at its northern 
base. Fritztown is situated between the mountain and an adjacent 
hill on the east. Blainsport, Cocalico, and Kleinfeltersville respec- 
tively lie in the lowland to the south, southwest, and west. 
The mountain crest is a divide between the drainage of the 
Schuylkill and the Susquehanna, streams flowing down the north- 
western, northern, and eastern slopes reaching the former river via 
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