Outside of the mountainous districts thus described, the general surface of Cuba is a gently undulating plain, with altitudes varying from only a few feet above the sea level to 500 or 600 feet, near El Cristo in Oriente. In Pinar del Rio it forms a piedmont plain that entirely surrounds the mountain range. On the south this plain has a maximum width of about 25 miles and ascends gradually from the shores of the Caribbean at the rate of seven or eight feet to the mile until it reaches the edge of the foothills along the line of the automobile drive, connecting Havana with the capital of Pinar del Rio. North of the mountain range the lowland belt is very much narrower and in some places reaches a height of 200 feet as a rule deeply dissected, so that in places only the level of the hill tops mark the position of the original plain. The two piedmont plains of Pinar del Rio unite at the eastern extremity of the Organos Mountains and extend over the greater part of the provinces of Havana and Matanzas and the western half of Santa Clara. The divide as a rule is near the center of this plain, although the land has a gradual slope from near its northern margin towards the south. In the neighborhood of Havana, the elevation varies between 300 and 400 feet, continuing eastward to Cardenas. The streams flowing north have lowered their channels as the land rose, and the surface drained by them has become deeply dissected, while the streams flowing toward the south have been but little affected by the elevation and remain generally in very narrow channels. East of Cardenas the general elevation of the plain is low, sloping gradually both north and south from the axis of the Island. Considerable areas of this plain are found among the various mountain groups in the eastern half of Santa Clara province, beyond which it extends over the greater part of Camaguey and into Oriente. Here it reaches the northern coast between isolated mountain groups, extending as far east as Nipe Bay, and toward the south merges into the great Cauto Valley. From Cabo Cruz the plain extends along the northern base of the Sierra Maestra to the head of the Cauto valley. Its elevation near Manzanillo is about 200 feet, whence it increases to 640 feet at El Cristo. In the central section of Oriente, the Cauto River and its tributaries have cut channels into this plain from 50 to 200 feet in depth. In the lower part of the valley these channels are sometimes several miles across and are occupied by alluvial flats or river bottoms. They decrease in width towards the east and in the upper part of the valley become narrow gorges.