PRETz: FLoRA OF LEHIGH CouUNTY, PENNSYLVANIA 47 
Still farther south, approximately five miles, are the foothills 
of the South Mountain range, really a part of the main range 
which has here spread out to include the considerable area of the 
Saucon Valley. These hills are practically a continuation of that 
part of the South Mountain range which in Bucks County is known 
as the Durham Hills. To the southwest in the county these hills 
are more closely grouped and in this formation trend southwest into 
Berks County as far as the vicinity of Reading. In Cumberland 
County, where this range practically reappears and is properly 
called the South Mountains, it is a portion of the southern boun- 
dary of the Great or Kittatinny Valley. 
The greater part of the surface area of Lehigh County lies 
between these ranges in the Great or Kittatinny Valley. This 
long and broad valley, like the Kittatinny Range which it parallels, 
is an important geological as well as topographical feature in the 
East. The geological formations are of the Cambrian and Or- 
dovician periods of the Paleozic Era, and although they may be 
subdivided into various minor formations, fall naturally into two 
well marked divisions, lithologically as well as topographically, 
which may be characterized as the “‘slate’’ or ‘‘shale’’ and the 
“limestone” regions. Theshale occupies the greater surface area 
and overlies the limestone, which in turn overlies the Hardyston 
sandstone and quartzite that outcrops in the vicinity of the South 
Mountains and occupies relatively little surface area. 
This shale region differs very materially from the limestone 
region to the south. Its water courses greatly exceed those of 
the limestone region numerically, and by the mechanical cutting 
down of the hills have created numerous wide ravines with sharp 
rises to the uplands, creating a characteristic topography differing 
greatly from that of the limestone region to the south. 
As the shale region is approached the line of contact with the 
limestone plain is apparent in the landscape. Within the county 
this line is irregular on account of shale ridges that extend into 
the limestone region and widen the shale region westward as they 
join that formation in that direction. For this reason the shale 
region along the Lehigh River is about eight miles wide, but at 
the Berks County line it is twelve and one-half miles wide. Just 
south of the Kittatinny Range are high hills of approximately 
