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 BRAZIL 221 and much smaller. Though these lakes com- municate with each other and with the sea, the water of the Lagoa dos Patos is but slightly brackish, particularly in the N. por- tions, where its waters are constantly fresh- ened by the influx of several large rivers. The lakes of the coast region of Rio de Janeiro are very numerous, some being several leagues in diameter, but all exceedingly shallow. La- goa Feia, the largest, is 20 m. long; and another, called Rio Iguassfi, 15 m. Elsewhere on the coast similar lagoons are common. For a length of at least 2,000 m. along the coast of Brazil, and certainly for a consid- erable space inland, solid rock, wherever it occurs, belongs to a granitic formation. The serras do Mar and da Mantiqueira are wholly composed of gneiss of an orthoclase species, varying from schistose to coarse-grained and porphyritic or homogeneous and granitic. As one proceeds westward from the coast, the gneiss becomes finer, and finally gives way to heavy beds of mica slate, or mica-schistose gneiss with bands of quartz ; and this same suc- cession is said to obtain in most other parts of the empire. Strong lithological resemblances are observed between the gneisses of Brazil, which De Beaumont affirms to be among the very oldest stratified rocks on the globe, and the Laurentian rocks of Europe and North America ; and this resemblance is still more strongly marked by the absence of mica slate in both formations. The exact succession of the different members of the metamorphic se- ries in the gold-bearing region in Minas Geraes has not yet been thoroughly worked out. The clay and talcose schists, the itacolumite, itabi- rite, and other associated metamorphic rocks of this section are, in the opinion of Prof. Hartt, lower palreozoic in age. Some of these rocks, which resemble the auriferous rocks of Nova Scotia, may be Devonian ; they have been everywhere so metamorphosed that all trace of fossils has been obliterated. Great numbers of fossil plants of carboniferous genera occur in the empire; the coal basins lie just S. of the tropic, but within the range of the palm ; they are of coast formation; and carboniferous rocks also occur in the Rio Itenez. There do not appear to be any carboniferous strata on the coast N. of Rio de Janeiro, the depression of the shore allowing the accumulation of coal beds not having extended beyond the southern provinces. A thick series of triassic red sand- stone, unassociated with trap, underlies the cretaceous rocks in Sergipe, and extends over a large area. Cretaceous rocks are found along the coast from Bahia to Pianhy, but none occur S. of the parallel of the Abrolhos ; they are so largely covered by tertiary beds that it is diffi- cult to estimate their extent ; but it is quite probable that they underlie the tertiary de- posits throughout the whole Amazon valley. They show themselves on the Aquiry, an affluent of the Purfis, and have there been ex- amined, as reported by Prof. Agassiz. The cretaceous rocks seem to have been deposited in a shallow sea, have been very slightly dis- turbed, do not anywhere form remarkably high hills, and are at the Abrolhos associated with volcanic deposits. Prof. Hartt, though no fos- sils have been found in them, refers to the tertiary the clays and ferruginous sandstones forming the coast plains and overlying the cre- taceous rocks unconformably, inasmuch as they are themselves overlaid by the drift clays that descend from the mountains and cover their glaciated surfaces. Drift occurs in Brazil, and is considered by Prof. Agassiz to be due to the agency of glacier ice. The mineral p~roduc- tions of Brazil are immense ; they comprise diamonds, sapphires, emeralds, euclases, rubies, topazes, aquamarines, zircon, gold, silver, cop- per, tin, lead, iron, and other metals. Dia- monds have been found in various parts of the empire ; but the great diamond region is in Minas, and extends from E. to W. between lat. 17 and 19 S., the most celebrated mines being those of the Serra do Frio. Diamond washing was formerly a monopoly of the government, but in pursuance of a recent law for the ad- ministration and working of diamond mines, these'now belong exclusively to private indi- viduals. The diamond usually occurs among the sands produced by the disintegration of the sandstone rock. Some of the largest known diamonds were found on some of the small rivers flowing into the Sao Francisco on the left bank, between lat. 18 and 19 S. ; but search here has long since been abandoned. On one of these streams, the Abaet6, was found one of the largest diamonds of which we have any record; it weighed 138 carats. From 1740 to 1772 the average diamond extraction per annum was 52,080 carats; but this average has since suffered an enormous annual decrease, and the total value of the diamond washings during the first 100 years, perhaps $20,000,000 at the most liberal estimate, was far outstrip- ped by the exportation of the single article of coffee in the year 1856, $28,000,000. Dia- monds are also met with in Parana, near Cn- yaba in Matto Grosso, and in the Patinga dis- trict in Bahia. The annual production of dia- monds in this province is perhaps $3,000,000. The export of these stones from the port of Bahia in the year 1864-'5 amounted to nearly $760,000, and that of sugar alone to almost four times that sum. The other pre- cious stones above enumerated occur in Minas Geraes. Garnets, though not of the finest qual- ity, are found throughout the whole empire ; and beautiful amethysts are by no means rare. The gold of Brazil occurs in the metamorphic rocks, in drift gravels and clays, and alluvial sands and gravels. The formations richest in gold are clay slates traversed by auriferous quartz lodes, itacolumite rock veined with gold' bearing quartz, and certain iron ores various- ly known under the names itabirite and jacu- tinga. The richest gold mines in the empire are situated in the vicinity of Ouro Preto, in