den increases, the streams often overflow their usual banks, and
make their deposits laterally, until the constant succession of such
deposits raises the adjacent ground high enough to set bounds to the
further spreading of the stream. This deposit is remarkable for its
taking place in greatest quantity close to the usual bed of the stream;
and thus it speedily opposes natural dykes to its own redundant waters.
This action is most conspicuous at points where marked changes take
place either permanently or periodically in the rapidity of running
water: when streams descend from mountains into lines of less descent, a
deposit uniformly takes place, forming _flats_ or _intervals_, as they
are styled in the United States, of which we have such beautiful
instances in the valleys of the Connecticut and Mohawk, and that part of
the Hudson near Albany; again, where rivers meet the sea, they are
interrupted in their course by the rise of the tides of the ocean, and
here again deposits take place, sometimes forming shoals and banks in
the ocean itself; at other times, bars and obstructions at their own
mouths; and again, deltas of solid land, constantly encroaching upon the
sea. This action, which is continually going forward, is called
alluvial. The delta of greatest fame, and from which the others have
derived their generic name, is that of the Nile; this we have evidence,
almost historic, to prove to be wholly the gift of the river. And if it
no longer increase as rapidly as in former ages, the cause is obvious,
for the alluvion has been pushed so far forward as to meet a strong
current that sweeps along the African coast, and must carry off much of
the earth the Nile discharges into the Mediterranean. The great rivers
of Asia and of America carry still greater quantities of solid matter,
but we have not the same distant traditions to refer to for the amount
of the increase they have caused; still, however, we know that the mouth
of the Mississippi has been advanced into the Gulf of Mexico several
leagues since the settlement of Louisiana; and that islands of great
extent are frequently formed, in the course of a single year, by the
deposits of the Ganges.

We however find traces of aqueous action far more extensive and powerful
than those which are now taking place under our eyes by fluviatile
action. There is no part of the globe that has been examined, which does
not show that it has been subjected to the action of water, in