46 Pretz: FLorRA OF LEHIGH COUNTY, PENNSYLVANIA 
is a part of the Appalachian chain and fin the “county trends to 
the southwest from Lehigh Water Gap, with an even crest at an 
altitude of about 450 m., broken only by a few depressions and 
‘one noteworthy prominence, Bake-oven Knob, 473 m. The 
Shawangunk* sandstone and conglomerate of which this range 
consists belongs to the Lower Silurian Period of the Paleozoic 
Era. Only the south slope of the range is included within the 
county. Unlike the north slope, which is long, the south slope is 
short and steep, from a comparatively sharp and narrow crest, 
and almost uniformly rocky. A plateaulike shelf, composed 
largely of fallen talus from the mountain and resting on the under- 
lying shale formation, leads gently away from this steep slope. 
Many small streams rise here, and there are occasional areas that 
are marshy or boglike in character, but usually of very limited 
extent. In the vicinity of the Bake-oven, there arise Trout 
Creek draining into the Lehigh at Slatington, the Jordan Creek 
draining into the Lehigh at Allentown, and the Antelawny drain- 
ing into the Schuylkill in Berks County. 
Approximately twenty miles to the south are the South Moun- 
~ tains, or Durham and Reading hills, usually known locally as the 
Lehigh Mountains. This is a range of gentle slopes and rounded | 
knobs with shallow intervening valleys quite unlike the long 
sharp-crested and rocky mountains to the north. In general 
within the county the north slopes are rather longer than the 
steeper south slopes, but small streams heading in the moist areas 
of marshy or boglike character in the shallow valleylike depres- 
sions between the ridges of the crests are found on both slopes. 
With the exception of some of the knobs, the average altitude is 
about 275 m. In New Jersey the region corresponding to this 
geological formation, which is topographical as well, is called the 
Highlands and from Pennsylvania southward forms a part of the 
so-called Piedmont Plateau. 
In the vicinity of these hills are outcrops of the Hardyston 
quartzite and sandstone of the Cambrian Period, which overlies 
the Pre-Cambrian rocks of which these hills are largely made up: 
* These rocks have been known as the ‘Onda: and Medina sandstones sae 
conglomerates se Spe apeierge L, Miller, of Lehigh University, has recently re- 
ferred them tot nd this later term is here used through his courtesy. 
