National Geographic : 1896 May
180 GEOGRAPHIC RELATION OF THE THREE AMERICAS the lands bordering the gulf of Mexico and Caribbean sea; the former in its geognostic aspects and relations is North American, while the latter is distinctly Central American. The gulf of Mexico, with the single exception of its extreme southwestern indentation of the coast of Mexico, is surrounded by gently tilted plains, composed of great sheets of subhorizontal sediment, largely deposited by its own waters when they occu pied a larger area than at present. The Central American region as above outlined-i. e., that portion of the American hemisphere extending from the south ern termination of the Rocky Mountain region to the northern termination of the South American Andes, including the south ern border of Mexico, the Republics of Central America, and the isthmus of Panama proper-constitutes the western perimeter of the circle of mountains inclosing the Caribbean. As a whole it is called by some writers the American Isthmian region,* and can be genetically separated into two conspicuous regions: 1. The recent volcanic plateau lying nearer the Pacific coast from its commencement in Guatemala to its eastern termination in Costa Rica, which is composed of accumulated material ex truded across the western termini of the Antillean trends. 2. The lower but nevertheless mountainous portions of the Caribbean side, composed of folded mountain-axes extending east-west in conformable direction vith the Antillean uplifts, accompanied by old eruptive extrusions of past geologic time. The most conspicuous eminences are the grand volcanic peaks of Guate mala, San Salvador, and Costa Rica. These rise to an average height of 10,000 feet, in irregular masses standing nearer the Pacific coast than the Atlantic until reaching the borders of Costa Rica, when they sweep diagonally toward the Caribbean side, again assuming in the southern portion of that republic a central continental position. These great eminences are built up of accumulations of volcanic debris, which have buried and largely concealed a most interesting antecedent geologic structure that must be interpreted before the complete history of the re gion can be written. These mountains, being largely extrusions of volcanic material instead of regular folds or plications of stratified rock, produce irregularities of surface which defy the ordinary modes of classification. * The conspicuous features of this greater Isthmian (Central American) region are its narrow, elongated outlines relative to the broadening areas of the adjacent conti nent and the completely mountainous character of its entire area, which is void of coastal plains.