Westmoreland. -Area, 1,040 square miles; population
in 1880, 78,036. The geology of this large and wealthy county is a
continuation of that of Fayette County already described. But in the
northern part of Ligonier valley on the Ligonier-Fairfield line the
Pittsburgh coal bed has been preserved in a long high ridge
and some isolated hill tops. Another remarkable diversity of structure
is presented along the west side of the valley in an extraordinary
steepening of the commonly 20º
to 30º east
dip of the rocks to 80º
, the Conglomerate, No. XII, forming a line of low sharp knobs on
the slope of the mountain; and this explains why the basin east of
it is locally deep enough to hold all the Barren measures and even
some of the beds above the Pittsburgh coal. Chestnut Ridge, finely-gapped
by the Loyalhanna, shows the usual arches of Conglomerate (XII) red
shale and iron ore (XI) and Pocono sandstones (X). West of Chestnut
Ridge runs the remarkably straight and regular Blairsville basin,
with the Derry and Latrobe mines to the north, and the Jacobs creek
mines to the south, in the Pittsburgh coal bed, as at Connellsville,
sustaining a vast number of coke ovens. Next west of this basin (5
miles wide at the south and 3 at the north, and 20 miles long) runs
the Blairsville anticlinal, crossing the Loyalhanna near Bradey’s
old mill and the Pennsylvania railroad just east of Carr’s tunnel;
the arch on the Loyalhanna being high enough to expose all the Barren
measures, and even the Freeport Upper coal bed, the stream cutting
deep between cliffs of Mahoning sandstone. Approaching the Sewickley,
with equal dips of 4*#186;
on both sides, it flattens away. West of it is the Greensburg basin
of Pittsburgh coal bed and overlying measures, (4 miles wide by 12
long) and another smaller patch north of New Alexandria. West of this
runs the Saltsburg anticlinal arch across the county exposing most
of the Barren measures, under which appear the Freeport coals in the
deep valley of the Loyalhanna; at the head of Little Sewickley creek;
and along Sewickley creek and its branches around Sewickely mills;
the anticlinal being very flat and only slightly represented on the
Youghiogheny above the mouth of Jacob’s creek. West of the Saltsburg
belt lies the great (Lisbon) basin of the Pittsburgh coal bed (12`
thick), the northern point of which overlooks the Kiskiminitas river
3 miles below Saltsburg, and widens southward to 3 miles in Franklin
Township, 4 miles in Penn, 7 miles across Huntingdon into Hempfield,
with its eastern edge running on south to the mouth of Jacobs Creek,
and spreading across the Youghiogheny and Allegheny rivers westward
into Allegheny and Washington counties. As it deepens southward the
basin begins to preserve patches of the Redstone coal (4` thick
and 50` above the Pittsburgh bed); then patches of the Fish-pot
limestone (25` thick); then the Sewickley coal (3`); then
the Great limestone (80`); then the Uniontown limestone
(12`); and its overlying coal (3`) then the Waynesburg limestone
(20`); and its overlying coal (6`), roofed with the Waynesburg
sandstone (70`), a total of Upper Productive coal measures overlying
the Pittsburgh bed of 425`. Even some of the still higher Upper Barren
Measures are preserved in a hill top in Huntingdon, and another at
Fulton P.O. and a large patch between the Big and Little Sewickley
creeks, a considerable area between the two rivers in the south-west
corner of the county. Although called "Barren measures" and holding
six coal beds only 1` thick, and a seventh only 2` thick, in 236 feet
of column to the top of the Upper Washington limestone (30`
thick), they have an eighth (Washington coal) lying 500` above
the Pittsburgh bed, of very poor quality, much parted with slate,
and rapidly varying from 4` to 9`. In the north-west the Waynesburg
anticlinal arch crosses the Kiskiminitas near Roaring run; Pucketta
creek west of Oakland P.O.; the Murraysville pike just east of Murrysville;
and the Pa. R.R. exactly midway between Carpenter’s and Stewart’s
stations. A continuation of this anticlinal roll runs down the county
line across the Yough to the Monongahela River near Webster; it is
so gentle as rarely to show a dip greater than 1º
. West of it lies the Waynesburg trough, not deep enough in
this county to hold the Pittsburgh bed, except in six hill tops west
and north of McLaughlinstown. West of it runs the Pinhook anticlinal
from 2 miles below Leechburg to the mouth of Patterson’s run. (See
Report K2, 1877.) The character of the Pittsburgh bed along
the Monongahela is amply illustrated in Report K4 1885.
In the Blairsville basin its top bench (c) varies from 0` to
5`, its main clay (b) from 6 inches to 2 ½ feet; its bottom
bench (a) from 6` to 9`. In the Greensburg basin, (c) varies
from 4 inches to 5`; (b) from ½ to 1 ½`; (a) from 6`
to 8`. In the Lisbon trough (b) varies from 1/3` to 6`; (c)
from ½` to 1 1/3`; (a) from 6` to 9`. Six analyses from the
Blairsville basin show 30 to 34 p.c. vol.; 59 to 64 carb.; 3.5 to
6 ash; 1 water; 1 sulphur; coke 65 to 69; and nearly the same
in the other basins, (see K2, p.59.)
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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