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1866.] signs of stratification. It is also everywhere underlaid by coarse, well-stratified deposits, resembling somewhat the recife of Bahia and Pernambuco; whereas the unstratified drift of the south rests immediately upon the undulating surface of whatever rock happens to make the foundation of the country, whether stratified or crystalline. The peculiar sandstone on which the Amazonian clay rests exists nowhere else. Before proceeding, however, to describe the Amazonian deposits in detail, I ought to say something of the nature and origin of the valley itself.

The Valley of the Amazons was first sketched out by the elevation of two tracts of land; namely, the plateau of Guiana on the north, and the central plateau of Brazil on the south. It is probable that, at the time these two table-lands were lifted above the sea-level, the Andes did not exist, and the ocean flowed between them through an open strait. It would seem (and this is a curious result of modern geological investigations) that the portions of the earth's surface earliest raised above the ocean have trended from east to west. The first tract of land lifted above the waters in North America was also a long continental island, running from Newfoundland almost to the present base of the Rocky Mountains. This tendency may be attributed to various causes,—to the rotation of the earth, the consequent depression of its poles, and the breaking of its crust along the lines of greatest tension thus produced. At a later period, the upheaval of the Andes took place, closing the western side of this strait, and thus transforming it into a gulf, open only toward the east. Little or nothing is known of the earlier stratified deposits resting against the crystalline masses first uplifted in the Amazonian Valley. There is here no sequence, as in North America, of Azoic, Silurian, Devonian, and Carboniferous formations, shored up against each other by the gradual upheaval of the continent, although unquestionably older palæozoic and secondary beds underlie, here and there, the later formations. Indeed, Major Coutinho has found palæozoic deposits, with characteristic shells, in the valley of the Rio Tapajos, at the first cascade, and carboniferous deposits have been noticed along the Rio Guapore and the Rio Marnore. But the first chapter in the valley's geological history about which we have connected and trustworthy data is that of the cretaceous period. It seems certain, that, at the close of the secondary age, the whole Amazonian basin became lined with a cretaceous deposit, the margins of which crop out at various localities on its borders. They have been observed along its southern limits, on its western outskirts along the Andes, in Venezuela along the shore-line of mountains, and also in certain localities near its eastern edge. I well remember that one of the first things which awakened my interest in the geology of the Amazonian Valley was the sight of some cretaceous fossil fishes from the province of Ceara. These fossil fishes were collected by Mr. George Gardner, to whom science is indebted for the most extensive information yet obtained respecting the geology of that part of Brazil. In this connection, let me say that here and elsewhere I shall speak of the provinces of Ceara, Piauhy, and Maranham as belonging geologically to the Valley of the Amazons, though their shore is bathed by the ocean, and their rivers empty directly into the Atlantic. But I entertain no doubt, and I hope I may hereafter be able to show, that, at an earlier period, the northeastern coast of Brazil stretched much farther seaward than in our day; so far, indeed, that in those times the rivers of all these provinces must have been tributaries of the Amazon in its eastward course. The evidence for this conclusion is substantially derived from the identity of the deposits in the valleys belonging to these provinces with those of the valleys through which the actual tributaries of the Amazons flow; as, for instance, the Tocantins, the Xingu, the Tapajos, the Madura, etc. Besides the fossils above alluded to from the eastern borders of this