lso
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 palaeozoic and secondary beds underlie,
here and there, the later formations. Indeed, Major Coutinho has found
palaeozoic 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