Atlantic State of the United States, situated at the apex of the arch formed by the coast States from North Carolina to New England, whence it is popularly called the ‘Keystone State.’ It lies between 39° 43′ and 42° 15′ north latitude, and between 74° 43′ and 80° 31′ west longitude. It is bounded on the north by New York State, and for about 50 miles in the west by Lake Erie, on the east by New York and New Jersey, on the south by a small part of Delaware and by Maryland and West Virginia, and on the west by West Virginia and Ohio. In shape it forms a rectangle. The north and south boundaries are straight lines running along parallels 157¾ miles apart, except for the small projection of the northwestern corner. The western boundary is a straight line running along the meridian, but the eastern boundary is formed by the Delaware River, which forms two large and regular zigzag bends, making the extreme length of the State 302 miles. The area is 45,215 square miles, of which 44,985 square miles, or 28,790,400 acres, are land surface. The State ranks twenty-ninth in size among the United States.
Topography. Three of the four topographical belts which form the Eastern United States may be recognized in this State, running across its territory from southwest to northeast. The Atlantic coastal plain does not come within the State limits, so that the first of the three belts is the Piedmont Plain (q.v.), which occupies the southeastern portion between the lower course of the Delaware and the Blue or Kittatinny Mountain range. It has a width of about 60 miles, and ascends by gentle undulations from sea-level at the Delaware estuary to an elevation of 500 feet at the base of the mountains. It is broken, however, by several low ridges in the southeast, and farther inland by the interrupted chain of semi-isolated groups of hills known as the South Mountain, which farther north becomes the Highlands of New Jersey and New York. The second belt is the Appalachian Mountain region. It crosses the State toward the northeastern corner as a system of more or less parallel ridges, together from 50 to 80 miles wide. The eastern ridge is the Blue Mountain, known farther north and in New Jersey as the Kittatinny Range. It rises abruptly from the plain to a uniform height of a little over 1000 feet, or about 1500 feet above the level of the sea. It is broken by but few river gaps, notably that of the Susquehanna (which pierces the entire mountain belt), and the Delaware Water-Gap, on the eastern boundary of the State. West of the Blue Mountain there follows a succession of low ridges bearing various names, and intersected here and there by transverse river valleys. They appear almost like waves on the ocean, turning their steep faces southeastward and sloping gently toward the northwest, and they inclose a number of fertile and populous valleys. North of the Susquehanna they pass in the west into irregular masses which merge with the western plateau, but in the southern half the undulating belt is sharply limited on the west by the high and steep face of the Allegheny Range. The western slope of the latter falls gradually toward the plateau, though it is flanked by a few minor ridges, the extreme western outliers of the system, chief among which is Laurel Hill in the southwestern part of the State. The highest point in the State is North Knob, 2084 feet above the sea. The third topographical region is the broad Allegheny Plateau, covering the entire western half of the State. Its horizon has an elevation of 1000 to 2000 feet, sloping gently to the south and west. But it has been reduced by erosion to a complicated hill-country, or rather valley-country, being intersected in all directions by river-valleys, some broad and open, others narrow, with abrupt slopes 500 to 800 feet deep. The line of 1000 feet elevation is only two to five miles from the shore of Lake Erie, so that there is here no lake-shore plain.
Hydrography. The three chief river systems are, in the order of their drainage areas, the Susquehanna, the Ohio, and the Delaware. These together drain over 90 per cent. of the State. An insignificant area in the south belongs to the Potomac system, and in the north to the Genesee, while the extreme northwestern corner is drained by short streams flowing into Lake Erie. The Delaware, which is navigable for the largest ships to Philadelphia, and for small steamers some distance above, drains the eastern slope through its right tributaries, chief of which are the Lehigh and the Schuylkill. The Susquehanna traverses the State in a large zigzag from north to south, receiving its two main tributaries, the West Branch and the Juniata, from the west. It is broad, but shallow and unnavigable. The western part of the State is drained by the Ohio and its two great headstreams, the Allegheny and Monongahela, both of which are navigable for some distance above their junction at Pittsburg.
Climate. The climate in the southeastern part along the Delaware is much warmer, both in summer and in winter, than in the western upland. The mean temperature for January at Philadelphia is 32.3°, and for July 76.2°. The corresponding figures for Wilkesbarre, among the mountains, are 27° and 72°; for Pittsburg, 31° and 75°; and for Erie, on the lake shore, 27° and 70°. The summer heat south of the Blue Mountain has been as high as 107°, and is prolonged far into autumn. Northwest of the mountains the snow sometimes lies several feet deep throughout the winter, and the temperature may fall to 28° below zero. The average annual rainfall for the State is 44.6 inches. It is evenly distributed both as to season and through the larger regions of the State, though it may range from 35 to 50 inches in isolated localities.
Soil and Vegetation. The soils are on the whole somewhat more fertile than those of the average Atlantic State, there being no Tertiary sand area, and comparatively small areas of primary rocks. The soil is to a large extent decomposed limestone material, which is a good grain soil, and, where least fertile, is well suited for pasturage. Pennsylvania was originally one of the most densely forested States, and there are still considerable forest areas on the western plateau. The predominating trees on the lowlands are white oak, hickory, chestnut, walnut, and cherry; on the higher ground are the white pine, hemlock, pitch pine, maple, beech, and black and yellow birch; and on the mountains above 1800 feet the black and red spruce, balsam fir, and larch predominate. On the western plateau the forests are mostly deciduous, with chestnut and oak abundant, and in the southwest the common trees of the State mingle with those characteristic of Kentucky, such as the honey locust and Kentucky coffee tree. The sugar-maple is
