Page:The American Cyclopædia (1879) Volume XIII.djvu/267

 PENNSYLVANIA 257 only 4 ft.), but for the fact that it cuts trans- versely all the Silurian and Devonian forma- tions for a distance of many miles, passing Carlisle and the mouth of the Juniata river. The sandstones afford some good building stones, of which there are quarries on the Swatara, Schuylkill, and Delaware. The divi- sions of the palaeozoic series are given in the article GEOLOGY, vol. viii., p. 695 ; and they amount in aggregate thickness to over 35,000 ft. The lower members lie upon the N. W. flank and foot of the South mountain, and dip N. W. beneath the " auroral " magnesian lower Silu- rian limestones of the Kittatinny valley, which correspond to the Chazy, Birdseye, and Black river limestones of New York, and fill the broad valley between the Kittatinny and Blue mountains on one side and the South mountain on the other. Their range is marked by soil of great fertility, and the finest agricultural region of the state is this great limestone val- ley, occupying the chief portion of Northamp- ton, Lehigh, Berks, Lebanon, Dauphin, Cum- berland, and Franklin cos. ; the N. half of the valley, however, is of Utica and Hudson riv- er lower Silurian slate, containing the roof- ing slate quarries of the Delaware and Le- high. Beyond this to the northwest ranges the central belt of upper Silurian and Devo- nian mountains and valleys above described, as far as the main Alleghany mountain, and its picturesque topography much resembles that of the Jura mountains in Switzerland. Long narrow ridges parallel to each other, often run- ning many miles in straight lines and then curv- ing together, and varied by the occasional ter- mination of one of them upon the plain of the valleys that lie between them, are everywhere encountered over this region of middle Penn- sylvania. The rivers and the roads follow and cross them alternately, finding a passage from one to another by the numerous gaps and around the ends of the ridges. The great pile of the palaeozoic formations, raised and crum- pled in long folds, the bearing of which is with the mountain ranges, presents its various mem- bers in regular succession ; and each one of these along the line of its outcrop impresses its pe- culiar form of outline upon the surface. When the limestone belts, by reason of their enormous thickness or by their changing dips, are spread over a wide area, there is a valley between the steep ridges, in which the sandstones, that have more stoutly resisted the denuding action, form bold cliffs and give a sharp outline to the ridges. The same formations are frequently repeated until the main Alleghany mountain is reached, when the whole scene changes, and the traveller descending toward the west rides over and between innumerable rounded knobs and short irregular ridges, around the sides of which are the outcrops of the nearly horizontal bituminous coal beds. E. of the Alleghanies the coal measures are limited to the few deep, long, sharp, usually disconnected, but closely parallel anthracite basins, E. of the Susque- hanna river ; and to one semi-bituminous coal area occupying the high Broad Top mountain, S. of the Juniata river. Within each basin these strata present frequent changes of dip, the successive anticlinal and synclinal axes ly- ing nearly on the general range of the basin, and the flexures being often sharp. (See AN- THRACITE.) The summit of the Alleghany mountain has already been described as the E. margin of the great bituminous coal field. The highest points are capped by the conglomerate which underlies the coal formation, or by the lower members of this series, and the strata dipping gently toward the west, the formation gains in thickness in that direction, overspread- ing the whole western part of the state, except the N. W. corner. (See COAL.) The useful mineral beds found interstratified with the coal are fire clay, limestone, iron ore, and sandstone. Fire clay underlies every coal bed. Three or four limestone beds from 2 to 10 ft. thick oc- cur in the lower or Alleghany valley coal sys- tem, and heavy formations of limestone in the upper or Monongahela river coal system. Beds of clay ironstone are mined from between the lower coals at Johnstown and Brady's Bend, and from the base of the upper coal system in Westmoreland and Fayette counties. An im- portant stratum of limonite furnished ore to all the charcoal furnaces of Armstrong, But- ler, and Clarion cos. ; it overlies the most im- portant of the lower limestones. (See IKON.) Salt is obtained by boring through the coal formation of the western portion of the state, and this business is extensively carried on in the valley of the Kiskiminetas. The annual product of salt is estimated at about 1,000,000 bushels. Petroleum abounds in the upper De- vonian rocks at a depth of about 1,000 ft. be- low the lowest coal bed in the Alleghany val- ley country, but fails in the extreme N. W. counties, and also toward the east. (See PE- TROLEUM.) Among the mineral springs those of Bedford are the most celebrated. The soil of the state is generally rich, that of Lancaster co. on the limestone in the southeast, and of some of the counties bordering the Ohio river and also underlaid with limestone in the west, being particularly noted for productiveness. In the south and east, the abundance of lime constitutes good grain soils generally, and there are none of the thin tertiary sands, or of the weak soils lying on primary rocks, which be- long to other states of the seaboard. The moun- tain valleys of the interior generally contain limestone, which secures good soils. In the north grazing soils preponderate; these are rich on the upper Susquehanna in the north- east, thin and cold on the highlands of the cen- tral counties of the N. border, and again very rich and productive in the northwest. The whole W. border of the state is, like the Ohio valley generally, alike adapted to grain and grazing. The white pine forest of the Alle- ghany mountains has been a source of great wealth to the middle northern counties. Wil-