the deposition of the sandstone, and the currents which
gave rise to the denudation of the latter had ceased, the whole sheet of
water would naturally become much more placid. But the time came when
the water broke through its boundaries again, perhaps owing to the
further encroachment of the sea and consequent destruction of the
moraine. In this second drainage, however, the waters, carrying away a
considerable part of the new deposit, furrowing it to its very
foundation, and even cutting through it into the underlying sandstone,
were, in the end, reduced to something like their present level, and
confined within their present beds. This is shown by the fact that in
this ochre-colored clay, and penetrating to a greater or less depth the
sandstone below, are dug, not only the great longitudinal channel of the
Amazons itself, but also the lateral furrows through which its
tributaries reach the main stream, and the network of anastomosing
branches flowing between them; the whole forming the most extraordinary
river system in the world.

My assumption that the sea has produced very extensive changes in the
coast of Brazil--changes more than sufficient to account for the
disappearance of the glacial wall which I suppose to have closed the
Amazonian Valley in the ice period--is by no means hypothetical. This
action is still going on to a remarkable degree, and is even now rapidly
modifying the outline of the shore. When I first arrived at Para, I was
struck with the fact that the Amazons, the largest river in the world,
has no delta. All the other rivers which we call great, though some of
them are insignificant as compared with the Amazons,--the Mississippi,
the Nile, the Ganges, and the Danube,--deposit extensive deltas, and the
smaller rivers also, with few exceptions, are constantly building up the
land at their mouths by the materials they bring along with them. Even
the little river Kander, emptying into the Lake of Thun, is not without
its delta. Since my return from the Upper Amazons to Para, I have made
an examination of some of the harbor islands, and also of parts of the
coast, and have satisfied myself that, with the exception of a few
small, low islands, never rising above the sea-level, and composed of
alluvial deposit, they are portions of the mainland detached from it,
partly by the action of the river itself, and partly by the encroachment
of the ocean. In fact the sea is eating away the land much faster tha