PHYSICAL DivIsioNs. America is divided in to two continents, North and South America. separated in part by the Caribbean Sea and the Gulf of Mexico, and connected by the narrow Isthmus of Panama, 30 miles in width.
North America has an area of about S,300,000 square miles, and South America of 7,700,000. The mean altitude above sea level of both conti nents is not far from 2000 feet.
These two great continents are much alike in sonic respects, while differing in others. They are both triangular in shape, with the base of the triangle at the north and the opposite apex at the south. Each has its greatest length along meridians, and greatest breadth along parallels of latitude; each has a great mountain system running the whole length of the western side and parallel to it, and a shorter secondary and more disconnected mountain system in the eastern part, also parallel to the coast, the two moun tain systems in each case converging toward the lower apex of the continent. In both cases
the eastern ranges are the oldest geologically.
While the two American continents thus pre sent certain similarities of configuration, they are very differently placed on the sphere, and thus their climatic differences are marked, and the conditions dependent on climatic influences likewise differ. The broad part of North Ameri ca lies mainly within the north temperate zone, and only its apex extends into the tropical zone; thus causing a great portion of the continent to be dominated by comparatively low tempera ture conditions. In South America, on the con trary, the broad part lies within the tropics, and a comparatively small portion of it extends into the temperate zone.