332 H. N. EATON 
the Tulpehocken and Cacoosing creeks; while the streams rising 
on the southern slope empty into Cocalico Creek whose waters 
eventually find their way to the latter river. 
TOPOGRAPHY 
South Mountain rises abruptly from the valleys on all sides and 
is isolated from the main chain at Reading. Its persistence as a 
topographic form is easily accounted for by the difference in hard- 
ness between its rocks and the rocks of the neighboring valleys. 
The highest altitude, 1,340 feet, is attained in the northwestern 
part of the mountain at a point one mile southwest of Eagle Peak, 
being 964 feet above the level of the valley at Wernersville. South 
of here and a trifle east of the intersection of the county boundaries, 
the summit roughly presents the appearance of a plateau with a 
mean altitude of 1,100 feet, dissected by the narrow gorges of 
Furnace Creek in the north and an unnamed stream farther east. 
The summit is partially cleared of trees and farming is carried on 
to a limited extent. Eastward the height slightly decreases and 
the plateau-like character gives place to a number of knobs of 
which Cushion Peak is the most prominent. 
West of Robesonia the northwestern part is a densely wooded 
ridge sloping steeply toward the valley with a low escarpment 
facing the interior. South of Wernersville the northern slope is 
cleared and is the site of several sanitariums. 
The southern slope is more gentle than the northern, the stream 
courses are not as deep, and the streams are not as long. .- 
Directly east of Fritztown, a ridge, 500 feet high and one-half 
mile wide, continues for over two miles eastward, finally merging 
into the valley. This ridge is very significant structurally as will 
appear later. 
HISTORY 
References to the mountain in geological literature are few, 
although Millbaugh Hill, as it was called, was known as early as the 
period of the Rogers Survey. H. D. Rogers,* in 1858 writes, 
‘“Westward a few miles from Reading there is an insulated tract of 
gneiss, forming, with the sandstone of Millbaugh Hill, an elevated 
t Henry Darwin Rogers, The Geology of Pennsylvania, Philadelphia, 1858, I, 93. 
