To the south of the rivers of the plateau the only considerable stream is the Guadalquiver, with its tributaries. The character of this river is entirely different to that of the former streams. Like the Ebro, it forms a true valley, instead of merely cutting its way through rocks, canons, and defiles. Its bed is on an average about 1200 feet below that of the Guadiana in the greater part of its course. It is also the only river in Spain of any utility for navigation; the tide is felt beyond Seville, and vessels of 200 to 300 tons ascend to that city. There are also several lines of steamboats trading thence directly with London, Marseilles, Bilbao, Cadiz, and Gibraltar. The Guadalquiver takes its rise from two sources--one, in the streams Guadalimar and Guadarmeno, rises in the Sierra Alcaraz, and not very far from the sources of the Guadiana; the other, which bears the name of the Guadalquiver, in the south-west of the Sierra Sagra; this latter branch is soon joined by the Guadiana Menor, coming down from the Sierra Nevada. The basin of the Guadalquiver presents this peculiarity, that its boundary is not formed by the line of the highest summits; on the contrary, many of its tributaries take their rise on the farther side of the Sierra Morena on the north, and of the Sierras de Granada and Nevada on the south, and have cut their way through these higher grounds to join the Guadalquiver in the plains of Andalusia. The upper part of its course is very rapid, and the junction of the two rivers Guadalimar and Guadalquiver, in the plains of Baeza, is about 5000 feet below the Punta de Almenara; but from thence to the sea the fall is very slight. After the junction the river passes by Andujar, Montoro, and Cordova, receiving on both banks the waters of many streams of but little importance; but between Cordova and Seville it is joined by its largest tributary, the Xenil, which rises in the Sierra Nevada, and flowing through the celebrated Vega of Granada, bursts through the Antequera mountains to enter the great plain of Andalusia, and loses itself in the Guadalquiver. From Seville downward the character of the stream is greatly changed; it wanders in large meanderings through low and marshy grounds for two or three leagues on each bank, mostly uninhabited, and used only for pasturing cattle. These low lands, which are called _Marismas_, in dry weather are covered with clouds of black dust, and in wet are an almost impassable slough of mud; mid these the river divides, and its winding beds form two islands--Isle Mayor and Menor, the former of which is wholly given to cattle, while the latter is inhabited and well cultivated; The river finally enters the Gulf of Cadiz, at San Lucar de Barameda, forcing its way with difficulty through low hills of sand, like those of the Landes in France. The marshes near the mouth are utilized as _Salinas_, for making excellent salt; and on the hills which overlook the _Marismas_