PACIFIC DRAINAGE. The Rocky Mountains in Colorado offer the most compact source of impor tant drainage within the United States. To the south they send forth the Rio Grande. To the east flows the Arkansas, while to the north and east pass important branches of the Missouri. From the southwest issues the San Juan, while farther north the Grand, White, and Yampa rivers leave the State. All these join the Colo rado River, and thus introduce us to the most southerly of rivers in the United States that reach the Pacific Ocean. Some of the chief facts concerning this river have been given in the de scription of the topography of the region. Its ultimate sources are in the Wind River Moun taMs of Wyoming. Thence it crosses the plateau of the southeastern part of that State and passes by a great gorge through the heart of the Uinta Mountain Range. It is here known as the Green River, but becomes the Colorado after receiving the Grand. Thence it threads its greater canons and crosses the low desert region to the Gulf of California. Not far from its mouth it receives the Gila from the east. The only remaining master stream is the Columbia, with its wide spread sources in the Rocky 'Mountains. These largely belong to its tributary, the Snake River, Nvbieh after passing the lava plateaus joins the trunk stream in s(rothern \\ ashington. The Columbia has an important tidal conrse before it enters the ocean, and this and the Saint Lawrence are the only rivers of the United States which receive great accessions to their waters from foreign territory.
The foregoing review ha; shown how various are the rivers of the United States in their physical features. The Hudson may be taken as the type of that great number of stream,3, es pecially on the Atlantic side, which have a tidal course. Within the glaciated district most rivers show serious inequalities in their beds, causing innumerable rapids and waterfalls. Such con centration of descent does not occur elsewhere, save in the mountainous belts. The greatness and destructiveness of floods depends upon rain fall, gradient, the porosity of the rocks or soil, and other features. Thus the Ohio has steep slopes, an impervious bed. and a moist climate, when eompared with the 1\lissouri taken as a whole. In its long course across the plains the latter loses by seepage, by evaporation, and by abstraction of water for irrigation.
The rivers exhibit great diversity in relation human uses. The :Merrimac and many other streams within the glacial belt are mainly useful for manufacturing or for water supply. The Mississippi is ehietly of value as a highway, while the Hudson eombines water and ice supply, and the furnishing of power. The Colorado is thus far almost purely scenic in its relation to loan, arousing interest by the origin and magnificence of its canons. A new era of utilization of these American river waters is now being entered upon. See IRRIGATION.