Dauphin. Area, 520 square miles; population in 1880,
76,148. The two prongs of the fish-tail at the western end of the
southern Anthracite coal field penetrate the northern part of the
county; that of the Wiconisco coal basin for 5 miles; that of the
Dauphin County coal basin for 10 miles; and along its southern edge
runs the northern line of Lebanon County. This basin is narrow and
sharp, and the lowest coal beds are pinched into a groove along the
top of the mountain. The Wiconisco basin is broader, deeper, and very
productive. It differs from all other Anthracite coal fields in possessing
the magnificent Lykens Valley coal bed, at its maximum thickness of
10 to 15 feet, and of exceptionally fine quality; for everywhere else
this bed is a thin, poor streak in the lowest layers of the Conglomerate.
Wiconisco Creek issues from the coal basin through a gap in its southern
mountain rim, near its western end; which projects into a broad red
shale (XI) country, covering five townships, bordered on the north
by the Mahontongo Mountain (X); and on the south by Berry’s Mountain
(X.) From Berry’s mountain gap, 4 miles above Halifax, to Peter°
mountain gap, 7 miles below Halifax, there is a grand double rock-arch,
the highest crown of which crosses the river 1 ½ miles above Halifax,
and brings up Chemung rocks (VIII). Both mountains cross the county,
converging as the arch sinks eastward, and meet just inside of Schuylkill
County. From Berry’s mountain (X) to Second mountain (X) is 3 ½ miles,
and between them lies a red shale (XI) valley which, in Perry County,
heads up as the Cove; and in the other direction, is split by the
Third mountain into Clark’s Creek valley* on the north, and Stony
Creek valley on the south. The formations from Halifax to the mouth
of Clark’s Creek all dip south about 45°
. From Clark° Creek down through Second mountain and Blue mountain
gaps, they ought to dip north, but in reality they are thrown over
on their faces 20°
beyond the vertical, so that they dip southward 70°
; affording a superb section of formations XI, X, IX, (6000`), VIII
(5000`), except its lowest beds, V, and IV, down to the slates of
the Cumberland Valley, III. But the Oriskany (VII), Lower Helderberg
(VI), and Onondaga (upper of V), are also missing, in all about 1000
feet, in a section of nearly 20,000`. In all this thickness of strata
there is absolutely no mineral deposit of any value. The overturn
continues eastward along the mountain into Lebanon County. The southern
half of Dauphin County is (1) a belt of valley slate (III) six miles
wide; (2) a belt of limestone (II) three miles wide; (3) a belt of
Mesozoic red shale and sandstone and trap, seven miles wide, to the
Lancaster County line. The limestone belt, solid from the Lebanon
line to the Swatara, splits into two; one arm running up to Harrisburg,
the other keeping on straight to the river, a synclinal of slate lying
between them, and both arms being extensively quarried for lime and
furnace flux at the river bluffs. Brown hematite iron ore has been
extensively mined at Hummelstown, near the edge of the Mesozoic. A
good deal of graphite is disseminated throughout some of the limestone
layers. A few poor limestone beds, very earthy, appear in the heart
of the slate belt.
* A mistake in the map puts this creek on the south.
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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