eastward, the Bay of
Braganza has doubled its width in the last twenty years, and on the
shore, within the bay, the sea has gained upon the land for a distance
of two hundred yards during a period of only ten years. The latter fact
is ascertained by the position of some houses, which were two hundred
yards farther from the sea ten years ago than they now are. From these
and the like reports, from my own observations on this part of the
Brazilian coast, from some investigations made by Major Coutinho at the
mouth of the Amazons, on its northern continental shore, near Macapa,
and from the reports of Mr. St. John respecting the formations in the
valley of the Paranahyba, it is my belief that the changes I have been
describing are but a small part of the destruction wrought by the sea on
the northeastern shore of this continent. I think it will be found, when
the coast has been fully surveyed, that a strip of land not less than a
hundred leagues in width, stretching from Cape St. Roque to the northern
extremity of South America, has been eaten away by the ocean. If this be
so, the Paranahyba and the rivers to the northwest of it, in the
province of Maranham, were formerly tributaries of the Amazons; and all
that we know thus far of their geological character goes to prove that
this was actually the case. Such an extensive oceanic denudation must
have carried away not only the gigantic glacial moraine here assumed to
have closed the mouth of the Amazonian basin, but the very ground on
which it stood.

During the last four or five years I have been engaged in a series of
investigations, in the United States, upon the subject of the
denudations connected with the close of the glacial period there, and
the encroachments of the ocean upon the drift deposits along the
Atlantic coast. Had these investigations been published in detail, with
the necessary maps, it would have been far easier for me to explain the
facts I have lately observed in the Amazonian Valley, to connect them
with facts of a like character on the continent of North America, and to
show how remarkably they correspond with facts accomplished during the
same period in other parts of the world. While the glacial epoch itself
has been very extensively studied in the last half-century, little
attention has been paid to the results connected with the breaking up of
the geological winter and the final disappearance of the ice. I believe
that the true explanation of th