nk. In the one case we have
the swamps or an expanse of freshwater with the tops of trees appearing
above, in the other the bluish green surface of the Gulf of Mexico. An
opinion has very commonly prevailed that this narrow promontory, the
newest product of the river, has gained very rapidly upon the sea, since
the foundation of New Orleans; but after visiting the Balize in 1846, in
company with Dr. Carpenter, and making many inquiries of the pilots, and
comparing the present outline of the coast with the excellent Spanish
chart, published by Charlevoix 120 years before, we came to a different
conclusion. The rate of permanent advance of the new land has been very
slow, not exceeding perhaps one mile in a century. The gain may have
been somewhat more rapid in former years, when the new strip of soil
projected less far into the gulf, since it is now much more exposed to
the action of a strong marine current. The tides also, when the waters
of the river are low, enter into each opening, and scour them out,
destroying the banks of mud and the sand-bars newly formed during the
flood season.

An observation of Darby, in regard to the strata composing part of this
delta, deserves attention. In the steep banks of the Atchafalaya, before
alluded to, the following section, he says, is observable at low
water:--first an upper stratum, consisting invariably of bluish clay,
common to the banks of the Mississippi; below this a stratum of red
ochreous earth, peculiar to Red River, under which the blue clay of the
Mississippi again appears; and this arrangement is constant, proving, as
that geographer remarks, that the waters of the Mississippi and the Red
River occupied alternately, at some former periods, considerable tracts
below their present point of union.[366] Such alternations are probably
common in submarine spaces situated between two converging deltas; for,
before the two rivers unite, there must almost always be a certain
period when an intermediate tract will by turns be occupied and
abandoned by the waters of each stream; since it can rarely happen that
the season of highest flood will precisely correspond in each. In the
case of the Red River and Mississippi, which carry off the waters from
countries placed under widely distant latitudes, an exact coincidence in
the time of greatest inundation is very improbable.

The antiquity of the delta, or length of the period which has been
occupied in the deposition of so vast a