Pittsburg (321), second city of Pennsylvania, is 350 m. by rail W. of Philadelphia, where the junction of the Alleghany and the Monongahela Rivers forms the Ohio; the city extends for 10 miles along the rivers' banks, and climbs up the surrounding hills; there are handsome public buildings and churches, efficient schools, a Roman Catholic college, and a Carnegie library; domestic lighting and heating and much manufacture is done by natural gas, which issues at high pressure from shallow borings in isolated districts 20 m. from the city; standing in the centre of an extraordinary coal-field—the edges of the horizontal seams protrude on the hillsides—it is the largest coal-market in the States; manufactures include all iron goods, steel and copper, glassware, and earthenware; its position at the eastern limit of the Mississippi basin, its facilities of transport by river and rail—six trunk railroads meet here—give it enormous trade advantages; its transcontinental business is second in volume only to Chicago; in early times the British colonists had many struggles with the French for this vantage point; a fort built by the British Government in 1759, and called after the elder Pitt, was the nucleus of the city.