The drainage basin of the Amazon is remark ably level, and the slope from the outlying bounding highlands is very gradual. The height of land almost to the very sources of the branch rivers does not exceed 1000 feet, and as falls or rapids east of the Andes are almost unknown, these rivers are navigable for the greater part of their lengths. The Amazon and its tributaries form the most remarkable and extensive system of inland water highways in the world. The possibilities of future development in the chain of South American inland navigation are shown by the fact that on the north, the Amazon has water communnication with the Orinoco through the Rio Negro and the Casiquiare, while on the south the navigable waters of the Tapajos lack little of connecting it with the head waters of a tributary of the Plata River.
Within the basin of the Amazon there occur horizontal layers of argillaceous rocks and sand stone, which vary in height from feet to ten times that amount. These and other deposits seem to indicate that at one time a local med iterranean sea covered the present Amazonian lowlands, and the Maraiion had for its outlet into the western end of this sea a delta, which has gradually moved eastward as the shallow- sea beeame filled up.
Not only the source streams. but nearly all the tributaries of the Amazon, experience a succes sion of falls where their waters enter upon the floor of the main stream, and some branches have falls higher up. Above these falls, which vary from a succession of rapids to falls of 50 feet, or more, navigation is again resumed. On the Lower Amazon these rapids occur at a distance of only from 200 to 300 miles from the main stream; hut the distance increases toward the west, so that on the Madeira. and Rio Negro rivers the falls are far removed from the mouths. while most of the southern branch rivers west of the Madeira lie almost entirely within the unob structed low belt.
Where the Amazon enters Brazil its elevation is less than 300 feet above sea-level. Even at its
low stage its usual depth in its lower course is about 150 feet, and in places it is said to 1w much deeper still. It has been estimated that the Amazon discharges between four and five mil lion cubic feet of water per second; and with this enormous outflowing water there is carried every twenty-four hours a quantity of sediment sufficient to form a solid cube measuring 500 feet on each edge.
The Amazon is navigable by steamers for a distance of about 2200 miles. and for smaller boats to points considerably beyond: but at the entrance to the gorges of the eastern Andes, navigdtion is practically suspended, on account of the rapids occurring there. Steamboat navi gation of the Amazon began in 1853, but it wa4; not until 1867 that the navigation of the river was thrown open to the world. Now regular lines of steamers ply from the mouth of the Amazon to Yurimagnas on the Huallaga River in north central Peru. Vessels enter the Amazon through the estuary of the Para River, since the main mouth of the Amazon north of Marajo Island is shoal water filled with rocky islands.
At the mouth of the Amazon there is a con tinual battling of the river current, the tides, and the winds. The tidal influence is felt up the river to a distance of about 400 miles. The tidal bore is at times so pronounced as to form successive walls of water ten to fifteen feet in height, which noisily sweep everything before them in their mad rush against the river current. The latter is perceptible at a distance of fully 200 miles seaward from the mouth of the river.
The importance of the Amazon as a highway of foreign commerce will become greater and greater as time economic development of Brazil proceeds, when in exchange for the ever-increas ing quantities of tropical products exported from the Amazon basin, there will be returned the manufactures and products of the temperate zones.