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that as soon as the coast plain has been reached, where there are no further obstructions on the north side, the river assumes this position, its mouth being almost exactly bifurcated by the equator. The lateral expansion of the interior flood plain has been caused mainly by the tributaries, which are subject to the same laws of movement as those which have been so exhaustively studied in the case of the Mississippi.

Another striking feature of the Amazon is the large number of furos or side canals, which run approximately parallel to the river for hundreds of miles. With few exceptions these are confined to the south side of the stream, being evidently nothing more than former channels abandoned in its steady progress towards the equator. Bayous and abandoned channels along the tributaries are also found, but these are of far less gigantic proportions as to length than those which follow the Amazon proper. It will also be seen that the great estuary of the Pará extends westwardly, by a number of elongated lake-like expansions, almost to the junction of the Rio Xingú with the Amazon. Though not fully proven, it is almost certain that these indicate a former channel of the Amazon, when it emptied into the sea south of the huge island of Marajó. On this assumption the existence of the vast network of furos running north and south between the Rio do Pará and the lower Amazon can be easily explained as remaining vestiges of the northward movement of the great stream towards its normal equatorial position.

One more important feature of the Amazon remains to be noticed. This is the existence of what may be called the terrace basins, which are a peculiarity of its greater tributaries on both the north and south side of the valley. Following up either the Rio Madeira on the south or the Rio Negro on the north, a series of gigantic rapids occur at a distance of a few hundred miles from the Amazon. These rapids aggregate 40 or more miles in length in each case, the total descent being several hundred feet. Then an enormous plateau is found above the rapids in which the respective rivers have cut down to an elevated base level. Properly speaking, these belong in the curve of the terrain, for in the course of ages these rivers will have worked down and back from the edges of the plateaus, to the beginning of the upper terrain above

the plateaus. Here, again, lack of complete exploration, with respect particularly to the geology of the regions involved, introduces some uncertainty in the interpretation of the facts, but the evidence would seem to imply that the transverse South American uplifts were more recent than those parallel with the great oceans. Similar terrace basins occur on many other Amazonian tributaries below the junction of the Rio Javary, but less extensive as to area. The fact that they do not occur prominently west of the Javary is also significant as indicating the earlier and perhaps more gradual upheaval of the Andes, the eastern cordillera apparently being the oldest.

In another important respect the Amazonian basin is peculiar. It is divisible into an equatorial belt of nearly uniform annual precipitation, and of flanking areas, north and south, of variable precipitation. Thus, in spite of the enormous floods, which are conspicuous to every traveller, the Amazon is subject to far less serious fluctuations of level than any other great river in the world, in proportion to the volume of water discharged. The axial contributions being nearly constant, the variations are due to the change of seasons in its tributary basins. As the sun swings from one tropic to the other, the rainy period on one side is just ceasing as it begins on the other. Accordingly, the variations of stage in the tributaries are proportionately greater than in the main stream. The vast lowlands of the flood plain, of course, serve as an equalizer of floods in the Amazon, being all the more effective for this purpose from the fact that the entire interior basin is densely wooded.

The climate of the coastal plain and interior basin is remarkably equable. The temperature averages about 85° F. at 2 P. M. and about 76° F. at 6 A. M., these being the hours of maximum and minimum heat. The annual variation is apparently less than 8°, although exact data from à sufficiently wide area are wanting. The humidity, however, is excessive, varying between the limits of 60 per cent. and complete saturation. The trade winds are felt throughout the entire length of the valley from the sea to the Andes, and serve to freshen the atmosphere and render the climate more salubrious. The daily electrical storms are also efficient purifying agents. Notwithstanding these, the quantity of carbon dioxide in the atmosphere is large, and in some localities at a

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THE VALLEY OF THE AMAZON.

distance from the main river is enormous, giving rise to the pain. ful and dangerous disease of beri-beri. Malarial disorders are common upon the tributaries, but are not so frequent nor so dangerous along the windswept Amazon. Perfect acclimatization is probably impossible for persons of northern birth, without southern ancestry, except in individual cases. Persons having a normally rapid circulation of blood, with a correspondingly high average body temperature, are less liable to climatic disorders in this tropic valley than those having the opposite characteristics.

The products of the Amazon are so many that to name them would be to set forth a catalogue of dreary length. Predominant today is India rubber, the product mainly of the Syringa trees, (Hevea discolor, and H. brasiliensis), euphorbiaceous plants, having a height of about sixty feet, growing only in the low, highly heated basin, subject to periodical inundation. Under proper treatment these trees will produce several pounds of rubber each per annum for fifty years. Systematic cultivation is now an infant industry, but as the wild reserves become ruined by improvident tapping of the sap, rubber culture will grow in importance. Owing to the habits of the trees, only native-born workmen can ever perform the actual labor of the plantations with safety. From the upper Amazon, in addition to some rubber from the Heveas, a somewhat inferior grade is obtained from the Castilloa elastica, a tree belonging to the bread fruit family (Artocarpaceae). The Castilloa is common throughout Central America, the north and west coasts of South America, and the West Indies, but the two species of Hevea named are peculiar to the Amazon, and produce the most highly esteemed rubber of commerce.

Sarsaparilla, copaiba balsam, cacao (from which the cocoa of commerce is made), Brazil nuts, and hides are the more important products of this valley next in order after rubber. Sugar cane is extensively raised for the manufacture of rum, which is all locally consumed. The prevailing low prices for sugar afford little inducement to its production here for export. Rice is also grown to some extent, and might easily become an article of Amazonian commerce. All the fruits of the tropics are found abundantly, and no region in the world yields choicer bananas and oranges. The agricultural possibilities of the Amazon are very great, but it

is doubtful if they can be developed except by native Indian labor under intelligent superintendence. The difficulties in the way of a successful prosecution of such enterprises are the same as those common to all well watered and well wooded southern countries, but in this case enhanced by the enormous growth of timber, most of which is of the hard, close-grained varieties. The value of the timber, however, would be very great if it could be delivered in the markets of the United States and Europe. The future development of the Amazonian valley, so far as it may be accomplished by internally acting forces, will then be either by a slow growth of small plantations, carved out of the forests by natives at the cost of much labor and long and patient waiting for returns, or on a larger scale by wealthy operators or corporations, on a systematic plan, utilizing the timber product during the process of clearing land, and employing native labor for all tasks involving exposure to the severities of heat and rain.

The building of highways and railroads in a country requiring such heavy and expensive foundations, and so many bridges, often of great length, will be impossible until a comparatively dense population shall have occupied the region, and even then the cost of these conveniences will be so great as to limit for many decades any considerable advance in this direction. Fortunately water courses are so abundant, ramifying through the flood plain in so intricate a network, that the needs of a large population may be served by water transportation. High industrial development, however, is impossible where slow water communication is not supplemented by rapid land conveyance. This at once limits the central Amazonian valley to agricultural pursuits for a long period, and also ties her commerce to the chief fluvial cities, Pará and Manáos, which are accessible by sea-going vessels.

It would be possible to enter the Amazonian valley from the north by a railroad, coming across the Guiana highlands, which in part consist of open savannas, reaching the city of Manáos near the junction of the Rio Negro with the Amazon. Such a line would be about 750 miles in length, and would, in addition to opening up large areas of highland suitable for European colonization, save 1,250 miles of the journey from the center of the Amazonian basin to either New York or Liverpool. In time such a

road will be regarded as a necessity, and will result in partially conquering the valley of the Amazon by colonization working downward from the north. The persistent tendency of Brazilian railroad extension westward towards its natural goal at Cuyabá, the head of navigation on the Paraguayan river system, may result in a similar subjugation of a part of the great valley to productive industry by northward expansion from the salubrious Matto Grosso highlands. This development is already becoming realized by extensions of the industrial zone of Sao Paulo and Minas Geraes into Goyaz and down the Araguaya and Tocantíns. The determination of the Peruvians to unite the west coast with their eastern fluvial system by rail communication will produce a like result in the west, and evidences are increasing that a Bolivian industrial encroachment will manifest itself within the present decade. In this way the more material development of the resources of the Amazon, by forces working from the periphery, will probably be brought about. Thus an interchange of commodities between the elevated and the low-lying portions of the valley will be rendered feasible, giving to the valley as a whole greater commercial unity which will be an element of strength, leading to a permanent prosperity that could never be securely established while the conditions of trade prevented any considerable diversity of production. COURTENAY De Kalb.

SCHOOL OF MINES,

University of Missouri, Rolla, Mo.

TOPOGRAPHIC MAPS OF THE UNITED STATES.

Until very recently, there has been no formal provision for the distribution or sale of the topographic maps prepared by the United States Geological Survey and concerning which reference has several times been made in this JOURNAL. The maps have been used by geologists in the progress of their field studies; have been deposited in libraries and various public offices, and a certain number distributed to individuals having particular interests in the mapped areas. In 1894, the Director of the Survey authorized the statement that map sheets would be issued gratis to teachers and other school authorities "for use in teaching geography in

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