8]

By the confluence of the Rhone and the currents of the Mediterranean,
driven by winds from the south, sand-bars are often formed across the
mouths of the river; by these means considerable spaces become divided
off from the sea, and subsequently from the river also, when it shifts
its channels of efflux. As some of these lagoons are subject to the
occasional ingress of the river when flooded, and of the sea during
storms, they are alternately salt and fresh. Others, after being filled
with salt water, are often lowered by evaporation till they become more
salt than the sea; and it has happened, occasionally, that a
considerable precipitate of muriate of soda has taken place in these
natural salterns. During the latter part of Napoleon's career, when the
excise laws were enforced with extreme rigor, the police was employed to
prevent such salt from being used. The fluviatile and marine shells
inclosed in these small lakes often live together in brackish water; but
the uncongenial nature of the fluid usually produces a dwarfish size,
and sometimes gives rise to strange varieties in form and color.

Captain Smyth in his survey of the coast of the Mediterranean, found the
sea opposite the mouth of the Rhone, to deepen gradually from four to
forty fathoms, within a distance of six or seven miles, over which the
discolored fresh water extends; so that the inclination of the new
deposits must be too slight to be appreciable in such an extent of
section as a geologist usually obtains in examining ancient formations.
When the wind blew from the southwest, the ships employed in the survey
were obliged to quit their moorings; and when they returned, the new
sand-banks in the delta were found covered over with a great abundance
of marine shells. By this means, we learn how occasional beds of drifted
marine shells may become interstratified with freshwater strata at a
river's mouth.

_Stony nature of its deposits._--That a great proportion, at least, of
the new deposit in the delta of the Rhone consists of _rock_, and not of
loose incoherent matter, is perfectly ascertained. In the Museum at
Montpelier is a cannon taken up from the sea near the mouth of the
river, imbedded in a crystalline calcareous rock. Large masses, also,
are continually taken up of an arenaceous rock, cemented by calcareous
matter, including multitudes of broken shells of recent species. The
observations lately made on this subject corroborate the former