THE 



JOURNAL OF GEOLOGY 



SEPTEMBER-OCTOBER, igo4 



PHYSIOGRAPHIC STUDIES IN SOUTHERN 

 PENNSYLVANIA.^ 



Cumberland Valley is the northward extension into Maryland 

 and Pennsylvania of the Shenandoah Valley of Virginia. It is 

 a broad hmestone valley, with low, shale hills, lying between South 

 Mountain on the east, and Tuscarora Mountain and associated 

 ridges on the west. The southern portion is drained chiefly by 

 Conococheague and Antietam creeks into the Potomac, and the 

 northern part by Conodoguinet and Yellow Breeches creeks into 

 the Susquehanna. The area discussed in this paper is that portion 

 of the Cumberland Valley and bordering mountains which is repre- 

 sented on the Mercersburg and Chambersburg, Pa., atlas sheets 

 of the U. S. Geological Survey, on the scale of i mile to i inch. Fig. i 

 is a contour map of the same area. 



Conococheague Creek, which enters the Potomac at WilUams- 

 port, Md., divides into two branches in the southern part of this 

 area. The West Conococheague heads in Tuscarora Mountain 

 to the northwest, and enters the main valley from Path Valley. 

 The East Conococheague reaches the valley through a narrow gap 

 in South Mountain in the eastern portion of the area, and after 

 flowing northward for 5 miles, turns southwestward. Before uniting 

 with the west branch it is joined by another prominent stream. Back 

 Creek, which drains the northern part of the area. 



It has been pointed out by Campbell^ that two, and possibly three, 



1 Published with the permission of the director of the U. S. Geological Survey. 



2 " Geographic Development of Northern Pennsylvania and Southern New York," 

 Bulletin of the Geological Society of America, Vol. XIV, pp. 277-96. 



Vol. XII, No. 6. 473 



