Central America is hardly a part of either great system. The Isthmus is a low plateau, succeeded by highlands rather than mountains in Costa Rica ; then comes the depression near ly filled by Lake Nicaragua, where the elevation sinks to less than 100 feet above the sea. The mountains begin in northern Nicaragua and occupy the entire breadth of Honduras, Guate mala and Salvador from ocean to ocean; but they are not of great height and consist of several detached ranges with active or extinct volcanic peaks. These sink to a broad plain at the Isthmus of Tehuantepec, forming the dividing line between the mass of North American and South American organic species; though zoologically the central plateau is a northern tongue thrust into two lines of tropic territory along the Gulf and Pacific coast.
The Rocky Mountain system, or northern Cordillera, begins with the plateau of Anahuac on which the City of Mexico is situated, the seat of the original culture overthrown by Cor tes. It is from 4,000 to 7,000 feet high, and is flanked by mountain ranges and isolated vol canic peaks, active or quiescent the highest summits in Mexico. Onzaba, tile loftiest, is 18,250 feet high; but the most remarkable and imposing is 1Popocatapetl, rising 17,520 feet from the floor of the valley, the highest peak of the world in practical isolation its whole height visible from sea-level. At this point the main ridge of the Rockies (the Mexican section is knoyrn also as the Sierra Madre, which prop erly is the name of the northeastern spur) sud denly turns far eastward from the Pacific and for the remaining 3,500 miles of its course steeps hundreds of miles from it, so that the broad western slope is drained by very large rivers, as the Columbia and Fraser, and in the extreme north the mighty Yukon. But it throws out lesser arms to the west nearly to the ocean. Between the main range and the great Sierra Nevada arm is enclosed the desert Great Basin of Utah and Nevada and northern Arizona and New Mexico: a waste of alkaline earth and naked rocks, of river courses dry except in the Infrequent rains, and roaring torrents then for a few hours or minutes; of the great canons, gulleys cut sometimes a mile deep into the solid rock by the swift sand-laden currents. It is drained to the Gulf of California by the only real stream of water of any size in the whole region, the Colorado. The Sierra Nevada has for its crowning summit Mount Whitney, in California, 14,898 feet high. Still farther west it throws out the Coast Range, running through California, Oregon and Washington up to Puget Sound. The Sierra Nevada is continued, both structurally and through more recent independent volcanic action, by the Cascade Range of Oregon, Washington and British Columbia, with Mount Shasta, 14,510 feet, in the south, rid Mount Rainier or Tacoma, 14,526 feet, in Washington. Puget Sound is a
submerged trough and the Valley of California a lowland lying between the Coast ranges and the Sierra Nevada-Cascade ranges. The system as a whole, across from California and Oregon to Colorado and Wyoming, is 1,000 miles wide, with a number of north-and-south ranges rising from a plateau from 5,000 to 10,000 feet high, and with a large number of peaks between 14,000 and 15,000 feet high. The main range in Colorado has for its chief divisions the Front, Sangre de Cristo, Park, Saguache and San Juan ranges ; Long's and Pike's Peaks, Blanca Peak, Mounts Lincoln and Harvard and Uncompahgre Peak are the best known of the summits.
The system follows the coast around nearly to Asia, rising in peaks all along the Aleutian Islands, the chief being the noble Shishaldin, 8,000 feet high; and north of Yakutat Bay, a great landmark, where the coast turns west and the greatest glaciers begin, the place where the temperate zone properly gives place to the semi Arctic — a branch continues straight on, runs far north to the Yukon watershed, then turns west again and rejoins the other in southwest Alaska. In the course of the latter it throws up mighty peaks, the monarchs of the northern continent, including Mount Saint Elias, 18,024 feet, and Mount Wrangell, a great isolated semi-active volcano, 17,524 feet; the altitude rising as it goes west, it culminates in Mount McKinley, 20,464 feet, the highest elevation in North America.
The Eastern Mountains and the Plains.— In North America the backbone and nucleus of the continent is locally known as the Alleghany system in the northern half of the United States an? the Appalachian in the southern; but for scientific purposes the latter name is commonly extended to the whole. It extends from Gaspe peninsula, between the lower Saint Lawrence and Chaleur Bay, below Quebec, through the United States to north Alabama and north Georgia, where the mountains sink,down to the great coastalplain which girdles the United States from 50 to 100 miles back from the shore. Between the mountain and plain is a foothill region usually known as the Piedmont region. The mountains are a plateau from 50 to 200 miles wide and averaging 1,500 to 3,000 feet high, but with peaks rising to 6,294 feet in Motuit Washington (New Hampshire) and 6,707 feet in Mount Mitchell (North Carolina). The range has many local names for the differ ent divisions, as the White and Green, the Adirondacks, the Taconic, Hoosac and Catskill, the Alleghany, the Blue Ridge and South Moun tain, the Black and Smoky, etc.