Bucks.- Area, 590 square miles; population in 1880, 68,656. This
long and narrow county bordering on the Delaware river, stretches
from the old gneiss ridges of the Northhampton county South mountain
to the Cretaceous outcrop at Burlington, N.J., but most of its surface
is a gently rolling, highly cultivated country of Mesozoic new red
sandstone and shale, all dipping north-westward at angles varying
from 50 to 150, for 33 miles (in a straight
line) along the river, giving to the formation an apparent total thickness
of say 30,000 feet, which seems incredible for several reasons; especially
seeing that at half way of the distance, across Solebury and Buckingham
townships, a straight N.E.- S.W. fault, 10 miles long, brings the
sandstone No.I and limestone No. II floor up to the present surface
with so little disturbance of the topography that the amount of upthrow
cannot be considered large. The whole surface of Mesozoic country
has been reduced by erosion several hundred feet, and the upper deposits
must have once overspread the Potsdam-covered gneiss ridge at the
northern county line, for they still rise nearly to its top (1000'
A.T.), although they dip north towards it, and there is no evidence
for a fault; but why no trace of it exists in the Great Valley cannot
be explained, except on the supposition that the surface of the valley
has been lowered by erosion at least a thousand feet since Mesozoic
times; and this fact is proved at Hummelstown in Dauphin county. The
Mesozoic formation is of the same character throughout, an alternation
of hard and soft layers of reddish sand and mud, some fit for building
purposes, some conglomeritic, a few calcareous, and some (near the
middle of the formation) fossiliferous, containing numerous bones
of large sea-lizards, shells and plants. A range of trap four miles
long in Rockhill township forms a hill parallel with the strike; the
east ends of two other trap hills enter Bucks from Montgomery county
near the north-western corner; another in Southampton township; an
isolated mass of trap forms "Haycock Mountain"; and two others occur
back of Newhope and Brownsville. These traps may be interbedded with
the New Red strata. At the southern edge of the formation, its lowest
strata lie upon the Trenton range of gneiss and appear to be made
up of fragments of the older rock. At its northern edge, its uppermost
strata are also in places a cemented conglomerate of quartzite and
limestone fragments brought by mountain torrents from the once higher
lands of Northampton and Lehigh County. The limestone valley of Durham
creek at the north end of Bucks County, lying between two ridges of
gneiss and Potsdam quartzite, has furnished much brown-hematite iron
ore to the Durham blast furnaces. Prehistoric animal bones were obtained
from one of its numerous caverns, now quarried away. The same iron
ore has been mined along the limestone upthrow east of Doylestown.
The southern end of Bucks county is occupied by a belt, 5 miles wide,
of Philadelphia rocks, micaceous gneiss and mica-schists of unknown
age, dipping very gently northward and covered with gravels of recent
but various ages, ending with the present river mud. A remarkable,
very straight and very steep outcrop of the Edge Hill (itacolumite)
sandstone runs along the south edge of the older gneiss, separating
it everywhere from the Philadelphia gneiss and schists. (See Report
and Special Map C6.)
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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