Page:EB1911 - Volume 04.djvu/460

 Compared with the number, length and volume of its rivers, Brazil has very few lakes, only two of which are noticeable for their size. There are a number of lakes in the lowland region of the Amazon valley, but these are mainly overflow reservoirs whose areas expand and contract with the rise and fall

of the great river. The coastal plain is also intersected by lagoons, lakes and inland channels formed by uplifted beaches. These inland channels often afford many miles of sheltered navigation. The lakes formed in this manner are generally shallow, and are sometimes associated with extensive swamps, as in southern Bahia. The lakes of the Alagôas coast, however, are long, narrow and deep, occupying valleys which were deeply excavated when the land stood at a higher level, and which were transformed into lakes by the elevation of the coast. The largest of these are the Lagôa do Norte, on whose margin stands the city of Maceió, and the Lagôa do Sul, a few miles south of that city. Both have outlets to the sea, and the former is salt There is a large number of these lakes along the coasts of Espirito Santo and Rio de Janeiro, some of them of considerable size. The two largest lakes of this class are on the coast of Rio Grande do Sul and are known as the Lagôa dos Patos and Lagôa Mirim. Both of these lakes lie nearly parallel with the coast line, are separated from the ocean by broad sand beaches filled with small lakes, and communicate with the ocean through the same channel. The Lagôa dos Patos is about 124 m. long with a maximum width of 37 m., and Lagôa Mirim is 108 m. long with a maximum width of 15 m. Both are navigable, though comparatively shallow and filled with sandbanks. So far as known, there are no lakes of noteworthy size in the interior of the country. There are a few small lakes in Maranhão and Piauhy, some in Goyaz in the great valley of the Araguaya, and a considerable number in Matto Grosso, especially in the Paraguay basin, where the sluggish current of that river is unable to carry away the rainfall in the rainy season.

The coast of Brazil is indented with a number of almost landlocked bays, forming spacious and accessible harbours. The larger and more important of these are Todos os Santos, on which is located the city of São Salvador or Bahia, and Rio de Janeiro or Guanabara, beside which stands the capital of the

republic. These two are freely accessible to the largest ships afloat. The bays of Espirito Santo, Paranaguá and São Francisco have similar characteristics, but they are smaller and more difficult of access. The first is the harbour for the city of Victoria, and the other two for ports of the same name in southern Brazil. The port of Pernambuco, or Recife, is formed by a stone reef lying across the entrance to a shallow bay at the mouth of two small rivers, Beberibe and Capibaribe, and is accessible to steamers of medium draught. Santa Catharina and Maranhão have well-sheltered harbours formed by an island lying in the mouth of a large bay, but the latter is shallow and difficult of access. Pará, Parnahyba, Parahyba, Santos and Rio Grande do Sul are river ports situated near the sea on rivers having the same name; but, with the exception of Pará and Santos, they are difficult of access and are of secondary importance. There are still other bays along the coast which are well adapted for commercial purposes but are used only in the coasting trade. Many of the Atlantic coast rivers would afford excellent port facilities if obstructions were removed from their mouths.

Geology.—Brazil is a region which has been free from violent disturbances since an early geological period. It has, indeed, been subject to oscillations, but the movements have been regional in character and have not been accompanied by the formation of any mountain chain or any belt of intense folding. From the Devonian onwards the beds lie flat or dip at low angles. They are faulted but not sharply folded. The mountain ranges of the east of Brazil, from Cape St Roque to the mouth of the river Plate, are composed chiefly of crystalline and metamorphic rocks. Some of the metamorphic rocks may belong to the older Palaeozoic period, but the greater part of the series is probably Archaean. Similar rocks cover a large area in the province of Goyaz and in the south of the Matto Grosso, and they form, also, the hills which border the basin of the Amazon on the confines of Venezuela and Guiana. They constitute, in fact, an incomplete rim around the basin of sedimentary beds which occupies the Amazonian depression. In a large part of this basin the covering of sedimentary deposits is comparatively thin. The crystalline floor is exposed in the valleys of the Madeira, Xingú, &c. Some of the rocks thus exposed are, however, eruptive (e.g. in the Tapajoz), and probably do not belong to the Archaean. The crystalline rocks are succeeded by beds which have been referred to the Cambrian and Silurian systems. In the valley of the Trombetas, one of the northern tributaries of the Amazon, fossils have been found which indicate either the top of the Ordovician or the bottom of the Silurian. In the Maecuru, another northern affluent, graptolites of Ordovician age have been discovered, and Silurian fossils are said to have been found in the Maraca. Elsewhere the identification of the Silurian and older systems does not rest on palaeontological evidence. Devonian beds cover a much more extensive area. They crop out in a band some 25 to 50 m. north of the lower Amazon and in another band at a still greater distance south of that river. These bands are often concealed by more recent deposits, but it is clear that in this region the Devonian beds form a basin or synclinal with the Amazon for its axis. Devonian beds also lie upon the older rocks in the Matto Grosso and other provinces in the interior of Brazil, where they generally form plateaux of nearly horizontal strata. Fossils have been found in many localities. They belong to either the lower or the middle division of the Devonian system. The fauna shows striking analogies with that of the Bokkeveld beds of South Africa on the one hand and of the Hamilton group of North America on the other. The Carboniferous system in Brazil presents itself under two facies, the one marine and the other terrestrial. In the basin of the Lower Amazon the Carboniferous beds lie within the Devonian synclinal and crop out on both sides of the river next to the Devonian bands. There is a lower series consisting of sandstone and an upper series of limestone. The former appears to be almost unfossiliferous, the latter has yielded a rich marine fauna, which belongs to the top of the Carboniferous or to the Permo-carboniferous. In southern Brazil, on the other hand, in Rio Grande do Sul, Paraná, &c., the beds of this period are of terrestrial origin, containing coal seams and remains of plants. Some of the plants are European forms, others belong to the Glossopteris flora characteristic of India and South Africa. The beds are homotaxial with the Karharbári series of India, and represent either the top of the Carboniferous or the base of the Permian of Europe. The only Mesozoic system which is represented in Brazil by marine beds is the Cretaceous, and the marine facies, is restricted to the coasts and the basin of the Amazon. In the province of Sergipe, on the east coast, the beds are approximately on the horizon of the Cenomanian; in the valley of the Amazon they belong to the highest parts of the Cretaceous system, and the fauna shows Tertiary affinities. In the interior of Brazil, the Palaeozoic beds are directly overlaid by a series of red sandstones, &c., which appear to be of continental origin and of which the age is uncertain. Tertiary beds cover a considerable area, especially in the Amazonian depression. They consist chiefly of sands and clays of aeolian and freshwater origin. Of the Pleistocene and recent deposits the most interesting are the remains of extinct animals (Glyptodon, Mylodon, Megatherium, &c.) in the caves of the São Francisco.

From the above account it will appear that, excepting near the coast and in the basin of the Amazon, there is no evidence that any part of Brazil has been under the sea since the close of the Devonian period. During the Triassic and Jurassic periods even the basin of the Amazon appears to have been dry land. Eruptive rocks occur in the Devonian and Carboniferous beds, but there is no evidence of volcanic activity since the Palaeozoic epoch. The remarkable “stone reefs” of the north-east coast are ancient beaches hardened by the infiltration of carbonate of lime. They are quite distinct in their formation from the coral reefs of the same coast.

Climate.—Brazil lies almost wholly within the torrid zone, less than one-twelfth of its area lying south of the tropic of Capricorn. In general terms, it is a tropical country, with sub-tropical and temperate areas covering its three southern states and a great part of the elevated central plateau. The forest-covered, lowland valley of the Amazon is a region of high temperatures which vary little throughout the year, and of heavy rainfall. There is no appreciable change of seasons, except that produced by increased rainfall in the rainy season. The average temperature according to Castelnau is about 78°F., or 82.40° to 84.20° F. according to Agassiz. There is an increase in the rainfall from August to October, and again from November to March, the latter being the regular rainy season, but the time varies considerably between the valley of the upper Amazon and those of the upper Madeira and Negro. There is usually a short dry season on the upper Amazon in January and February, which causes two annual floods—that of November-December, and the great flood of March-June. The subsidence of the latter usually lasts until October. The average rainfall throughout the whole Amazon valley is estimated by Reclus as “probably in excess of 2 metres” (78.7 in.), and the maximum rise of the great flood is about 45 ft. The prevailing winds in the Amazon valley are easterly and westerly (or south-westerly), the former warm and charged with moisture, the latter dry and cold. The easterly winds, which are deflections of the trade winds, blow upstream with great regularity and force, more especially in the winter or dry season, and are felt as far inland as the mouths of the Madeira and Negro. Above these they are less regular and are attracted northward by the heated llanos of Venezuela in winter, or southward by the heated campos of Matto Grosso in summer. The cold south-westerly winds are felt when the sun is north of the equator, and are most severe, for a few days, in the month of May, when a tempo da friagem (cold period) causes much discomfort throughout the upper Amazon region. There are winter winds from the Andes, but in the summer season there are cold currents of air from up-river (ventos da cima) which are usually followed by downpours of rain.

The coastal plain as far south as Santos is a region of high temperatures and great humidity. The year is usually divided into a winter (inverno) and summer (verão), corresponding approximately to a dry and wet season. The “dry” season, however, is a season of moderate rainfall, except on the north-east coast where arid conditions prevail. Another exception is that of the Pernambuco coast, where the rainy season comes between March and August, with the heaviest rainfall from May to July, which is the time of the southern winter. Going southward there is also a gradual decrease in the mean annual temperature, the difference between Rio de Janeiro and the Amazon being about 5°. The north-east coast, which is sandy and barren, shows an average mean annual temperature (at