mous extent. If the event happened in the dry season, when
the ordinary channels of the Mississippi and its tributaries are in a
great degree empty, the inundation might not be considerable; but if in
the flood-season, a region capable of supporting a population of many
millions might be suddenly submerged. But even this event would be
insufficient to cause a violent rush of water, and to produce those
effects usually called diluvial; for the difference of level of 600 feet
between Lake Superior and the Gulf of Mexico, when distributed over a
distance of 1800 miles, would give an average fall of only four inches
per mile.

The second case before adverted to is where there are large tracts of
dry land beneath the mean level of the ocean. It seems, after much
controversy, to be at length a settled point, that the Caspian is really
83 feet 6 inches lower than the Black Sea. As the Caspian covers an area
about equal to that of Spain, and as its shores are in general low and
flat, there must be many thousand square miles of country less than 83
feet above the level of that inland sea, and consequently depressed
below the Black Sea and Mediterranean. This area includes the site of
the populous city of Astrakhan and other towns. Into this region the
ocean would pour its waters, if the land now intervening between the Sea
of Azof and the Caspian should subside. Yet even if this event should
occur, it is most probable that the submergence of the whole region
would not be accomplished simultaneously, but by a series of minor
floods, the sinking of the barrier being gradual.[237]

_Supposed universality of ancient deposits._--The next fallacy which has
helped to perpetuate the doctrine that the operations of water were on a
different and grander scale in ancient times, is founded on the
indefinite areas over which homogeneous deposits were supposed to
extend. No modern sedimentary strata, it is said, equally identical in
mineral character and fossil contents, can be traced continuously from
one quarter of the globe to another. But the first propagators of these
opinions were very slightly acquainted with the inconstancy in mineral
composition of the ancient formations, and equally so of the wide spaces
over which the same kind of sediment is now actually distributed by
rivers and currents in the course of centuries. The persistency of
character in the older series was exaggerated, its extreme variability
in the newer was assumed