Po were retained on their left or northern side by dikes near the
small city of _Ficarolo_, which is about 19,000 _metres_[390] to
the north-west of Ferrara, spreading themselves southwards over
the northern part of the territory of Ferrara and the _Polesine_
of Rovigo, and flowed through the two formerly mentioned canals of
_Mazzorno_ and _Toi_. It seems perfectly ascertained, that this
change in the direction of the waters of the Po had been produced by
the effects of human labours; and the historians who have recorded
this remarkable fact only differ from each other in some of the
more minute details. The tendency of the river to flow in the new
channels, which had been opened for the more ready discharge of its
waters when in flood, continually increased; owing to which the
two ancient chief branches, the _Volano_ and _Primaro_, rapidly
decreased, and were reduced in less than a century to their present
comparatively insignificant size; while the main direction of the
river was established between the mouth of the Adige to the north,
and what is now called _Porto di Goro_, on the south. The two
before-mentioned canals of _Mazzorno_ and _Toi_ becoming insufficient
for the discharge, others were dug; and the principal mouth, called
_Bocco Tramontana_, or the northern mouth, having approached the
mouth of the Adige, the Venetians became alarmed in 1604; when they
excavated a new canal of discharge, named _Taglio de Porto Viro_, or
_Po delle Fornaci_, by which means the _Bocco Maestra_, was diverted
from the Adige towards the south.
During four centuries, from the end of the twelfth to that of the
sixteenth, the alluvial formations of the Po gained considerably upon
the sea. The northern mouth, which had usurped the situation of the
_Mazzorno_ canal, becoming the _Rama di Trimontana_, had advanced
in 1600 to the distance of 20,000 _metres_[391] from the meridian
of Adria; and the southern mouth, which had taken possession of
the canal of _Toi_, was then 17,000 _metres_[392] advanced beyond
the same point. Thus the shore had become extended nine or ten
thousand _metres_[393] to the north, and six or seven thousand to
the south[394]. Between these two mouths there was formerly a bay,
or a part of the coast less advanced than the rest, called _Sacca
di Goro_. During the same period of four hundred years previous to
the commencement of the seventeenth century, the great and extensive
embankments of the Po were constructed; and also, during the same
period, the southern slopes of the Alps began to be cleared and
cultivated.
The great canal, denominated _Taglio di Porto Viro_, or _Po delle
Fornaci_, ascertains the advance of the alluvial depositions in the
vast promontory now formed by the mouths or delta of the Po. In
proportion as their entrances into the sea extend from the original
land, the yearly quantity of alluvial depositions increases in an
alarming degree, owing to the diminished slope of the streams, which
was a necessary consequence, of the prolongation of their bed, to the
confinement of the waters between dikes, and to the facility with
which the increased cultivation of the ground enabled the mountain
torrents which flowed into them to carry away the soil. Owing to
these causes, the bay called _Sacra di Goro_ was very soon filled
up, and the two promontories which had been formed by the two former
principal mouths of _Mazzorno_ and _Toi_, were united into one vast
projecting cape, the most advanced point of which is now 32,000 or
33,000 _metres_[395] beyond the meridian of Adria: so that in the
course of two hundred years, the mouths or delta of the Po have
gained about 14,000 _metres_[396] upon the sea.
From all these facts, of which I have given a brief enumeration, the
following results are clearly established.
_First_, That, at some ancient period, the precise date of which
cannot be now ascertained, the waves of the Adriatic washed the walls
of Adria.
_Secondly_, That, in the twelfth century, before a passage had been
opened for the waters of the Po at _Ficarrolo_; on its left or
northern bank, the shore had been already removed to the distance of
nine or ten thousand _metres_[397] from Adria.
_Thirdly_, That the extremities of the promontories formed by the
two principal branches of the Po, before the excavation of the
_Taglio di Porto Viro_, had extended, by the year 1600, or in four
hundred years, to a medium distance of 18,500 _metres_[398] beyond
Adria; giving, from the year 1200, an average yearly increase of the
alluvial land of 25 _metres_[399].
_Fourthly_, That the extreme point of the present single promontory,
formed by the alluvions of the existing branches, is advanced
to between thirty-two and thirty-three thousand _metres_[400]
beyond Adria; whence the average yearly progress is about seventy
_metres_[401] during the last two hundred years, being a greatly more
rapid proportion than in former times.
PRONY.
NOTE, p. 244.
_On the Universal Deluge._
Mr Cuvier in the present work, and more recently in a note to Mr
Lemaire’s edition of Ovid’s Metamorphoses, enumerates the Mosaic,
Grecian, Assyrian, Persian, Indian, and Chinese traditions,
concerning a universal deluge; and concludes from them, that the
surface of the globe, five or six thousand years ago, underwent a
general and sudden revolution, by which the lands inhabited by the
human beings who lived at that time, and by the various species of
animals known at the present day, were overflowed by the ocean; out
of which emerged the present habitable portions of the globe. This
celebrated naturalist maintains, that these regions of the earth
were peopled by the few individuals who were preserved, and that the
tradition of the catastrophe has been preserved among these new races
of people, variously modified by the difference of their situation
and their social disposition. According to Mr Cuvier, similar
revolutions of nature had taken place, at periods long antecedent
to that of the Mosaic deluge. The dry land was inhabited, if not by
human beings, at least by land animals at an earlier period; and must
have been changed from the dry land to the bed of the ocean; and it
might even be concluded from the various species of animals contained
in it, that this change, as well as its opposite, had occurred more
than once.
This opinion being brought forward in a geognostic work, especially
in a work abounding in such valuable matters of fact, and stated
as the result of geognostic investigation, we may be permitted, in
this point of view, to examine it; and to ask, whether, from the
phenomena exhibited by the present condition of the earth’s surface,
we are entitled to conclude that it owes its conformation to such a
universal deluge.
We know, from arguments suggested by chemistry and the higher
mechanics, that the globe was once in a state of fluidity; hence it
might be maintained with some appearance of probability, that the
condition of the earth, previous to the existence of organic matter,
depended upon fusion; and that the primitive rocks are of igneous
origin. Since, however, granite has been found above rocks of various
kinds which contain the remains of organic bodies, we are under no
necessity of ascribing to primitive rocks an origin different from
that of subsequent formations; and, without having recourse to other
arguments, the fact, that aquatic animals are the most abundant of
fossil organic remains from the earliest of the transition to the
latest of the secondary and tertiary formations, affords evidence
that they are precipitates from water.
Notwithstanding the great and daily advancement of science, our
knowledge of chemistry is still too imperfect for us to arrive at
an adequate knowledge of the state of this water, or rather sea,
as, from its universal expansion, it must be denominated. Did it
contain dissolved in it at the same time all the materials from
which the various beds of rock were formed; what were the solvents
of those materials which we find, either insoluble in water, or
at least not easily soluble; by what means were the precipitates
produced; and whence came this prodigious mass of waters? Upon these
unanswered questions depend others no less important. The aquatic
animals of a former world undoubtedly lived in this sea; otherwise,
we must admit of another sea free from heterogeneous materials. But
did these animals continue to live in it during the whole process
of precipitation; and did this process proceed so slowly and
imperceptibly, that animal life was not interrupted by it, and that
only remains of dead animals, such as the skeletons of fishes, and
the covering of shell-fishes, were enveloped in the precipitates?
Or, did animal life continue only during the state of solution; and
were the myriads of aquatic animals found in beds of rocks buried in
them alive? Many naturalists appear to entertain the latter opinion,
from observing the agonies of death depicted in the distorted
position of fishes in copper-slate, or from deriving the bituminous
properties of stink-stone, as well as of marl, from the decomposition
of animal bodies, of which such numerous vestiges are extant in these
beds? In this way a plausible explanation is given of the phenomena
of a former world that has perished. How, then, do they explain the
constant appearance of so many species, which have continued without
interruption for such an infinite length of time? Have these species
been propagated by individuals who accidentally escaped destruction:
or, Does a new race continually spring up again? But laying aside
the difficulty of this explanation, the violent destruction of so
many races of animals, is scarcely consistent with the general
order of the universe, according to which, we behold every animal
occupying its proper element, and fulfilling its particular destiny.
We, therefore, involuntarily revert to the opinion, that those
creatures, whose remains are preserved in beds of rocks, have lived
continually in the sea, out of which the rocks were precipitated, in
the same manner as the analogous species now living in the sea become
enveloped in deposits still taking place, although on a comparatively
small scale.
What has just been said does not entitle us to admit that the various
parts of the earth have been, from time to time, overflowed with
water. Yet are there other appearances which completely indicate
such a change, namely, beds of coal, and the fossil remains of land
animals. The carbonisation of roots of trees in clefts of rocks,
and of marsh plants in peat-bogs, which takes place, as it were,
under our own immediate observation; the transitions of bituminous
wood into pitch-coal, the frequent presence of vegetables partly
converted into coal, in the neighbourhood of beds of coal, and which
are more abundant the nearer they are to these beds; and, finally,
the chemical nature of coal, which is similar to that of vegetables,
go to prove the vegetable origin of the older and independent coal
formation.
Though some fossil vegetables might derive their origin, by being
floated to quarters more or less remote from their native soil, as we
find to be the case in many islands of the South Sea, and on other
shores; on the other hand, neither the breadth and extent of beds of
coal, nor the erect position in which fossil trees and reed plants
are not unfrequently found in their neighbourhood, coincide with such
an explanation. The plants, from which these beds were formed, once
stood and grew in the place where they were buried; and, from these
remains, we infer that they were entirely land plants, tree-ferns,
_Lycopodia_, and other cryptogamia. It also appears undeniable, that
the land, being once dry, was, during a longer or shorter time,
covered with luxuriant vegetation; that it was afterwards overflowed
with water, and then became dry land again. But, was this overflow of
water produced by a sudden, violent, and universal catastrophe, such
as we consider the deluge? Many circumstances leave room for opposite
conjecture. If it is probable that the older or black coal is of
vegetable origin, the plants from which it has originated, must have
suffered an incomparably greater change than those of more recent
coal formations. Their composition and their texture, afford evidence
of a long operation of the fluid in which the changes were produced;
and their situation, proves that the substance of the plants, though
not entirely dissolved, was yet much comminuted, and was kept
floating and swimming, and then precipitated. How can we, in any
other way, account for the layers of sandstone and slate-clay, with
which coal regularly alternates, so that from one to sixty alternate
beds have been enumerated? How can we explain the combination of
mineral coal with slate-clay, or account for the appearance of
bituminous shale, flinty slate, of iron-pyrites and iron-ore, in the
midst of mineral coal itself? We do not, however, admit of a repeated
uncovering and covering of the land with water, and of a renewal of
vegetation for every particular bed of coal; far from it, for violent
inundations exhibit very different phenomena. These formations, like
pure mineral formations, bear the evident impress of a lengthened
operation, and of gentle precipitations; and whoever still entertains
doubts regarding this, may have them completely removed by the
condition in which vegetable remains are frequently found in the
coal formations, by the perfect preservation of the most delicately
shaped fern leaves, by the upright position of stems, and by other
appearances of a similar character. It is also an important objection
against the universality of the cover of water, notwithstanding the
wide extent of beds of coal, that they are sometimes accompanied with
fossil remains of fresh-water shells, from which we are entitled to
draw the conclusion, that they must have been deposited in inclosed
basins of inland waters.
From the beds of coal found in various situations among _Alpine_
limestone, as well as in other secondary formations, under similar
circumstances, we are at liberty to maintain that they are not
indebted for their origin to any universal and sudden revolution.
When we proceed to the second division of coal formations, to
brown coal, or to _lignite_, the principal difference we discover
is, that the change which the vegetables have undergone, having
taken place at a time when the chemical power had lost much of its
energy, was incomplete; and besides, we observe in the different
brown coal formations the same repetition of single beds alternating
with other beds of rocks, the mixture of different minerals, and
not unfrequently of upright stems. Some appear to be derived from
sea plants, and others from fresh-water plants; but the greater
proportion from land plants. They, equally with the beds of black
coal, give evidence of a new overflow of water, and the water plants
themselves, which never thrive at a great depth, and which frequently
appear under prodigious beds of rocks, must have experienced such a
change. But that change was scarcely of the kind which we understand
by a deluge, and the frequent repetition of deluges indicated,
according to some, by the repeated beds of coal from the transition
to the newest tertiary periods, is hardly credible. It may be
maintained, with more certainty, of _brown coal_ than of _black
coal_, that they have been formed in land water, and hence in
limited and isolated basins of water, since fresh-water animals are
their constant attendants.
Although the beds of coal of our secondary formations appear to
have originated in a similar way with other mineral formations, and
not by violent catastrophes, it is otherwise with a part of those
vegetable remains which are met with in alluvial land. Subterranean
forests, whose circumference, in some instances, extends about 70
square leagues, partly in a state of good preservation, and partly
more or less decomposed, afford satisfactory proof of deluges, and
have undoubtedly been covered up with earth by a violent eruption of
standing or running water. But these are local effects, similar to
what take place in our own day, but on a larger scale.
There are abundant fossil remains of land animals, resembling those
of water animals, found in such a state of preservation, that we
cannot suppose them to have been brought hither from distant places,
and by means of currents. Their appearing in beds of rocks, or
generally in aqueous precipitates, proves that the soil they first
inhabited, must have been dry land, afterwards overflowed with water.
The appearance of what are called fresh water shells, in alternate
beds with marine animals, being sometimes observed in newer flœtz
rocks in great abundance, seems to indicate a reiterated retreat
and return of the sea. But however meritorious the labours of
naturalists, through whom attention has been directed to the
subject, may be in other respects, we are nevertheless disposed
to entertain doubts concerning their conclusions. In our own seas
and ponds upon the coasts, we observe the same testaceous animals
growing equally well in salt water, and in water nearly fresh; and,
again, fresh water animals living in salt water[402]. By artificial
means the inhabitants of the sea may be changed into inhabitants of
fresh water; as fresh-water animals are, in their turn, converted
into marine animals, so that, to decide concerning the proper
element of each individual species is often matter of difficulty.
Therefore, other circumstances besides that of containing salt
must be taken into account. The occasional plenty, scarcity, or
absolute want of food; the soil being sometimes sandy, slimy, or
rocky; the depth, extent, agitation or tranquillity of the water;
and, finally, the quality of the air contained in it, may be as
instrumental in determining the habitation of these animals, as the
materials which the water holds in solution. An excellent observer
has indeed very lately shewn in a treatise, which supports the idea
of fresh-water formations, that we possess no unerring character
for distinguishing sea shell-fish from those of fresh water; but
admitted, notwithstanding the transition above stated, we can draw
a line of distinction between them, we must not forget that this
investigation is neither regarding sea shell-fish now existing,
nor of our present waters. We indeed draw our conclusion, and
not without reason, from similar conformation, similar modes of
existence. But one of two things must be; either that the shell-fish,
whose remains are found in beds of rocks, lived in the water out
of which these beds were precipitated, or the water in which they
lived, was dislodged by other water containing the materials of the
precipitations. In the first and more generally admitted case, the
water was so different from the present water, whether salt or fresh,
that we cannot infer from the inhabitants of the latter any thing
concerning the inhabitants of the former; but we can confidently
maintain, that a greater resemblance prevails between our sea and
land water, than between either the one or the other, and that fluid
which was inhabited by the shell-fish. In other respects, there
remains no other difference between fresh and salt water formations,
but that the bottom upon which the former is placed once contained
land water; a fact worthy of observation: but the notion of enclosed
basins, and of isolated formations originating in them, the way
in which fresh water formations are supposed to have taken place,
remained a long time unsatisfactory. Finally, we may be permitted to
ask, upon what grounds they considered themselves entitled to ascribe
to the former sea the continual possession of a portion of salt,
while the salt precipitates appear only at particular intervals, and
after long interruptions? If the sea occasionally contained a great,
and sometimes a very small, quantity of salt, it might equally be at
times altogether without it. And yet it deserves to be remembered,
that the beds of rock, to which the salt formations are most nearly
related, contain no petrifactions; that, therefore, the so-called
marine animals are wanting in those periods during which we have any
direct evidence of the presence of salt water.
There is, however, a geognostic fact, which, in preference to all
others, has been cited in evidence of violent revolutions and
deluges, that is, the appearance of conglomerates or of reproduced
kinds of stone. Indeed, there might still be a wide field for
investigation here, and more than one formation, which now passes
for sandstone, might be acknowledged as an original and chemical
production; without having occasion to go so far as Mr Gerhard does
with greywacke,--that is, to consider them as immediate precipitates
from the atmosphere. But still conglomerates sufficiently genuine,
will remain from the transition period through all the subsequent
formations, to serve as acknowledged monuments of destruction, as
well as of the renovation of what was destroyed. These are the
Codices rescripti, in the archives of the Earth, out of which, the
antiquarian will one day decipher the almost obliterated traces of
her former condition, as well as the history of her changes. Though
these conglomerates deviate so much in their nature, and in the
character of their origin, from chemical productions, they have yet
among themselves this remarkable and common characteristic, that,
with few exceptions, the older are much less varied in character,
and more extensive in distribution, than the newer, and that, at
length, the newest conglomerates become mere local appearances.
But, in reference to the main question which engages our attention,
we may conjecture that the beds of rocks from which the sea had
never retreated, might be assailed by its floods and currents,
and shattered to pieces, as happens even in our own time, and the
fragments be again reunited into solid rocks, by means of the still
remaining dissolved matter in the water. But of many conglomerates it
is evident that they have been deposited on the dry land, in the same
way as our gravels. Jupiter, who took counsel with himself, whether
he would destroy the sinful world with fire or water, and at length
decided for water[403], may not be so justly considered the author of
these appearances, as Saturn, who devoured his children. Or, to be
less metaphorical in our language, it may perhaps have been with the
origin of conglomerates, as it is in our own day with the origin of
fragments of rock and boulders, in which the rock being fractured in
various places by the alternations of heat and cold, by the influence
of air and atmospheric water, falls into pieces of greater or smaller
magnitude, which are carried forward by the water, and gradually
rounded in their progress, so that they assume a more perfectly
globular shape the farther they are removed from their original
situation. Therefore, as regards the foregoing enquiry, it is not an
unimportant circumstance, that the long but continual rolling of the
boulders during their rounding, appears to be much more efficacious
than a rapid and violent impetus, and that, in this case, as in
many other geognostic appearances, time rather than force is to be
taken into account. Another circumstance, perhaps, corresponds with
this, that the change produced by the weather, not only by the first
disunion, but also by the progressive disintegration of the rocks,
by the blunting of the edges and corners, by the diminution of the
fragments, and generally in the origin of the boulders and fragments
of rocks of every description, has just as much influence as the
mechanical operation of the water; and that a great part of the land
called Alluvial, generally owes its existence to this cause[404]. But
if, upon farther consideration, the conglomerates appear to derive
their origin in a similar way with rolled masses of gravel, they
afford evidence, nevertheless, of the elevated station of the water
in the neighbourhood, from which they had been before removed; for
their conglomeration could take place only under water; and, with few
exceptions, they occupy an incomparably greater elevation than any of
the coal formations, or any of the beds of rocks which enclose the
remains of land animals.