still one of the most common trees all over the State. For Fauna see this section under United States.
Geology. The great Archæan belt which forms the entire eastern flank of the Appalachian system from Alabama to Canada crosses the southeastern corner of the State in a band about 50 miles wide and consisting chiefly of gneisses with tracts of serpentine. It is exposed in two sections, one ending in a point near Trenton, and broadening southwestward along the Delaware, forming the hills near Philadelphia, the other running southwest from the confluence of the Lehigh River with the Delaware, and forming the South Mountain chain. Between these two cut-crops the Archæan belt is crossed by a band of Triassic red sandstone, which runs northeastward and extends across New Jersey. Both this and the Archæan belts are crossed by numerous dikes of trap-rock. Against the western flank of the South Mountain rests the lowest stratum of the great Paleozoic series which covers the entire remainder of the State as well as the whole of the Ohio and Upper Mississippi Valley. On the western plateau these strata lie nearly horizontal, but in the Appalachian uplift they are much tilted, folded, and broken, so that they outcrop in narrow successive bands. Here the hard sandstone strata generally form the ridges, while the softer limestone forms the valley floors. The series begins with a narrow belt of Cambrian running along the edge of the Archæan outcrop. West of this, between the South and the Blue or Kittatinny Mountains, the Kittatinny Valley runs across the State as a belt of Lower Silurian limestone, from which rise the Appalachian ridges of Devonian rocks, with some belts of Silurian. The great Devonian area of southwestern New York extends across the whole length of the boundary, and is especially prominent in the northeastern part of the State. It is overlaid with Carboniferous strata, which, with the exception of the Triassic belt in the east, is the most recent formation in the State, and covers the entire southwestern and west central regions, with isolated patches east of the Susquehanna.
Mineral Resources. In these isolated Carboniferous areas in the Appalachian valleys the coal seams were subjected to metamorphosis by the folding and crushing action of the older strata during the great upheaval, and were changed into invaluable beds of anthracite, while on the western plateau, where the strata were undisturbed, they remained in the bituminous form. The underlying Devonian sandstone strata in the west are heavily charged with petroleum and natural gas. Iron is found as brown hematite in the Silurian slates in the region of the Lehigh River, and as magnetite in the metamorphic rocks, while it is also imbedded with the Carboniferous strata. Other minerals found are zinc, cobalt, nickel, lead, copper, tin, chrome iron, salt, and soapstone. White marble is quarried in the Silurian limestone beds, and building stone, such as the trap and red sandstone in the east, is abundant.
Mining. No State in the Union compares with Pennsylvania as to mining. Its mineral wealth has been in a large measure the basis of its diversified and highly developed industrial life. The annual output of coal alone exceeds in value the total mineral product of any other State, and has annually, since 1880, been equal in amount to that of all the coal mined in the other States. Anthracite has been mined continuously since 1820. The demand and the output rapidly increased, particularly after 1840, when it came into use for smelting iron ore. The annual output of anthracite coal much more than doubled in both bulk and value from 1880 to 1901. The amount in short tons for 1880 was 28,649,811; for 1890, 46,468,641; and for 1901, 67,471,667, the value for the year 1901 being $112,504,020. The anthracite coal fields of Pennsylvania yield almost the entire product for the United States, and represent the only high-grade anthracite producing region in the world. These mining districts fall principally into three sections in the northeastern part of the State—the Northern Field, in the Wyoming and Lackawanna valleys, the Middle or Lehigh and Mahonoy Fields, and the Southern or Schuylkill Field. The bituminous coal is mined chiefly in six parallel valleys west of the Allegheny slope, in the southwestern corner of the State. It was not until about 1875 that bituminous coal began to be extensively used in iron-smelting, but since then it has far exceeded anthracite in annual tonnage. The tonnage increased from 19,416,171 short tons in 1880 to 82,305,496 in 1901, the value for the latter year being $81,397,586. In 1900 there were 92,692 employees engaged in coal-mining.
Pennsylvania has always ranked first in the production of coke, usually yielding about two-thirds of the total for the United States. The yield increased from 2,821,384 tons in 1880 to 8,560,245 in 1890 and to over 13,000,000 tons in 1900. The coal used requires little or no preparation before charging into the ovens, and the greater part of it is unwashed run-of-mine. Nearly three-fourths of the total product of coke is made in the Connellsville district.
The utilization of petroleum in the United States began in Pennsylvania in 1859. The output increased almost constantly until 1882, when the yield was 30,053,500 barrels. This figure was not exceeded until 1891, when the output was 33,009,236 barrels. The yield has since fallen off over half, being 12,625,378 barrels in 1901, valued at $15,430,609. Prior to about 1885 Pennsylvania produced almost the whole product for the United States, and up to 1900 had produced 60 per cent. of the total output for the country. However, since 1894 Ohio has annually outranked Pennsylvania, and it was also outranked by West Virginia in 1900. The first oil pipe lines were laid in 1865, and have been extended until they reach numerous distant points. Natural gas became prominent as a fuel in Pennsylvania earlier than in other gas States, and its annual sales of gas exceed those of any other State. Gas came into general use from 1880 to 1885, reaching its climax in 1888, in which year the sales amounted to $19,282,375. As the supply in certain regions became exhausted, the receipts decreased to less than $6,000,000 in 1895 and 1896; but the growing scarcity has resulted in a considerable rise in price, and this fact has largely been responsible for a recent gain in receipts, which amounted in 1900 to $12,688,161.
Iron-mining began early in the colonial period, and until 1850 the local product supplied the iron furnaces of the State with all the raw material required. And though the greater part of
