THE SEDIMENTARY ROCKS OF SOUTH MOUNTAIN, 

 PENNSYLVANIA^ 



GEORGE W. STOSE 



The area described in this paper is the western portion of South 

 Mountain, Pa., and the adjacent part of the Cumberland Valley 

 from near the Maryland state Hne to the vicinty of Shippensburg, 

 Pa. It is about 15 miles in length. The accompanying topo- 

 graphic map of this area (Fig. i) is taken from the Chambersburg 

 sheet of the United States Geological Survey and the South Moun- 

 tain atlas of the Pennsylvania Geological Survey. South Mountain 

 is the local name for the Blue Ridge which parallels the Great 

 Valley of the Appalachian Province on the east, and Cumberland 

 Valley, a section of the Great Valley. 



TOPOGRAPHY 



The Cumberland Valley is a broad, rolhng lowland extending 

 from the Potomac River to the Susquehanna River. Its general 

 elevation is from 400 to 800 feet, and scattered, low eminences rise 

 to 1,100 feet. These hills are usually of the rounded form char- 

 acteristic of Umestone country, but in part they are shale tablelands 

 with steep escarpments. The valley has a width of approximately 

 13 miles in the vicinity of Harrisburg, but expands to 20 miles in 

 the area under discussion. The southern half of the valley is drained 

 by Conococheague Creek and its tributaries into the Potomac, 

 the northern half by Yellow Breeches Creek into the Susquehanna. 



South Mountain is a more or less irregular aggregate of ridges 

 with a general northeast-southwest trend. Although cut across 

 by numerous gaps, and deflected in places by sharp bends, the 

 ridges maintain a marked continuity. The mountain front rises 

 abruptly from the plain to elevations of 1,700 or 1,900 feet. The 

 interior ridges are generally higher, reaching 2,100 feet in places, 

 whence they decline again eastward into lower hills. 



I Published by permission of the Director of the U. S. Geological Survey. 



