Lehigh. - Area, 360 square miles; population in 1880,
65,969. This county carries the geology of Berks county (already described)
eastward, along the Great Valley and South Mountains to the Lehigh
River, which issues from the Blue (Kittatinny) mountain through a
water-gap of surpassing beauty. The slate belt however, which is 17
miles wide at the Berks county line, contracts itself to 9 miles at
the river; and the limestone belt, which is only 4 ½ miles wide at
the Berks county line, widens to 9 miles. This change is effected
by a set of four anticlinals which cross the limestone belt diagonally
(E. and W.) and enter the slate belt making coves of lowland, walled
round by a slate escarpment about 200 feet high; the coves being separated
by projecting spur ridges of slate, one of which, just south of the
Jordan, is five miles long from root to point. In these coves are
large brown hematite iron deposits, mined by open quarries, one of
which in especial, the old Balliot mine at Ironton, is of vast size
and very famous. (See a map of it in Report D2). The excavation
is 2,000 feet long, 600 wide and 100 deep to the water level, with
walls of white, black and red clay, a deposit of oxide of manganese,
and much ore under foot. It lies in a limestone cove half a mile wide
cut off from the slate belt by a projecting strip of slate on the
south. Other deposits are mined in the vicinity. Two hundred and two
mines are marked upon the topographical map of the district published
in Report D2. Those at Trexlertown are also of large size,
and all have contributed to make the blast furnaces at Allentown,
Catasauqua, Hokendauqua, &c., on the river, among the largest
and most productive iron works of the world. The floor of the limestone
belt (No. II) is broken at two points by small projecting hills of
gneiss and Potsdam quartzite No. I; one on the Berks county line;
the other where the Little Lehigh passes out of Lower Macungie into
South Whitehall township. The South Mountain mass of gneiss separates
into two ridges, in Upper Saucon county, which enclose the head or
west end of the Saucon limestone valley, in which lie the world-famous
deep mines of carbonate and silicate of zinc, in layers of limestone.
The Friedensville mine of zincblende and pyrites disseminated throughout
a series of minutely fissured limestone beds (10` to 40` thick) is
1,000 feet long on the strike and 250` deep on a south-by-east dip
of 30º to 35º. The southern slope of the mountain (none of whose summits exceed
1,200` A.T.) is banked against by the northern edge of the great New
Red formation of Montgomery and Bucks counties, the loss of which
by erosion is plainly shown by the fact that its edge rises to 930`
A.T. overlooking a gneiss summit to the north of it which is only
803` A.T. The outcrops of Potsdam quartzite No. I, which are very
numerous at the foot, on the slope, and even at the summit of the
gneiss hills (not well exhibited on the small amp, but all laid down
in yellow on the Index map in D3 Atlas) are seen at Centre
Valley in the east corner of Upper Saucon township passing down under
the New Red; as is also the limestone at other places. The slate quarries
at Slatington and up Traut run (west of it) are described in D3,
Vol. I, with a section (on page 147) showing the two folds into which
the six sets of beds (in a total mass of 500` of the formation) have
been pressed. The Franklin beds (15`) overlie the Hess beds (50`)
63`; these overlie the Washington beds (60`) 12`; these overlie the
Blue vein (15`) 15`; these overlie the Pennlynn beds (25`) 222`; these
overlie the Blue mountain quarry beds (12`) 16`. (For pictures of
quarries; details of cleavage; notices of slate quarries elsewhere
in the county, &c., see report D3 Vol. I.)
From: A geological hand atlas of the sixty-seven
counties of Pennsylvania :embodying the results of the field work
of the survey, from 1874 to 1884. By J. P. Lesley. (Report of
progress (Geological Survey of Pennsylvania), v. X ) Harrisburg, PA
: Board of commissioners for the second geological survey, 1885.
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