_Further observations from the same Paper—Epoch of the destruction of the
said Forest—Agency by which it was effected_, _&c.—Similar appearances
eastward along the Norfolk coast_.
“Such a wide-spread assemblage of vegetable ruins, lying almost in
the same level, and that level generally under the common mark of low
water, must naturally strike the observer, and give birth to the
following questions: 1. What is the epoch of this destruction? 2. By
what agency was it effected?
“In answer to these questions I will venture to submit the following
reflections: The fossil remains of vegetables hitherto dug up in so
many parts of the globe, are, on a close inspection, found to belong
to two different states of our planet. The parts of vegetables and
their impressions, found in mountains, of a colaceous and schistous,
or even sometimes of a calcareous nature, are chiefly of plants now
existing between the tropics, which would neither have grown in the
latitudes in which they are dug up, nor have been carried and
deposited there by any of the acting forces under the present
constitution of nature. The formation indeed of the very mountains
in which they are buried, and the nature and position of the
materials which compose them, are such as we cannot account for by
any actions and re-actions which in the actual state of things take
place on the surface of the earth. We must necessarily recur to that
period in the history of our planet, when the surface of the ocean
was at least so much above its present level as to cover even the
summits of those secondary mountains which contain the remains of
tropical plants. The changes which these vegetables have suffered in
their substance is almost total; they commonly retain only the
external configuration of what they were. Such is the state in which
they are found in England by Lhwyd; in France by Jussicu; and in the
Netherlands by Burtin; not to mention instances in more distant
countries. Some of the impressions or remains of plants found in
soils of this nature which were, by the more ancient and enlightened
oryctologists, supposed to belong to plants actually growing in
temperate and cold climates, seem, on accurate investigation, to have
been part of exotic vegetables. In fact, whether we suppose them to
have grown near the spot where they are found, or to have been
carried thither from different parts by the force of an impelling
flood, it is equally difficult to conceive how organized beings,
which, in order to live, require such a vast difference in
temperature and seasons, could live on the same spot, or how their
remains could (from climates so widely distant) be brought together
in the place by one common dislocating cause. To this ancient order
of fossil vegetables belong whatever retains a vegetable shape found
in or near coalmines, and (to judge from the places where they have
been found) the greater part of the agatized woods. But from the
species and state of the trees which are the subject of this memoir,
and from the situation and nature of the soil in which they are
found, it seems very clear that they do not belong to the primeval
order of vegetable ruins.
“The second order of fossil vegetables comprehend those which are
found in the strata of clay or sand; materials which are the result
of slow depositions of the sea and of rivers, agents still at work
under the present constitution of our planet. These vegetable
remains are found in such flat countries as may be considered to be a
new formation. The vegetable organization still subsists, at least
in part; and their vegetable substance has suffered a change only in
colour, smell, or consistence; alterations which are produced by the
development of their oily and bitumenous parts, or by their natural
progress towards rottenness. Such are the fossil vegetables found in
Cornwall by Borlase; in Essex, by Derham; in Yorkshire by Dela Prime
and Richardson; and in foreign countries by other naturalists. These
vegetables are found at different depths; some of them much below the
present level of the sea, but in clayey and sandy strata (evidently
belonging to modern formation); and have, no doubt, been carried from
their original place and deposited there by the force of great rivers
or currents, as it has been observed with respect to the Mississippi.
In many instances, however, these trees and shrubs are found standing
on their roots, and generally in low or marshy places above, or very
little below the level of the sea.
“To this last description of fossil vegetables the decayed trees here
described certainly belong. They have not been transported by
currents or rivers; but though standing in their native soil, we
cannot suppose the level in which they are found to be the same as
that in which they grew. It would be impossible for any of these
trees or shrubs to vegetate so near the sea, and below the common
level of its water. The waves would cover such tracts of land, and
hinder any vegetation. We cannot conceive that the surface of the
ocean has ever been any lower than it is now; on the contrary we are
led, by numberless phenomena to believe that the level of the water
in our globe is now below what it was in former periods. We must
therefore conclude, that the forest here described grew in a level
high enough to permit its vegetation; and that the force (whatever it
was) which destroyed it, lowered the level of the ground where it
stood.
“There is a force of subsidence (particularly in soft ground) which
being a natural consequence of gravity, slowly, though imperceptibly
operating, has its action sometimes quickened and rendered sudden by
extraneous causes; for instance, by earthquakes. The slow effects of
this force of subsidence have been accurately remarked in many
places: examples also of its sudden action are recorded in almost
every history of great earthquakes.—In England, Borlase has given in
the Philosophical Transactions a curious observation of a subsidence
of at least sixteen feet in the ground between Sampson and Trecaw
islands in Scilly. The soft and low grounds between the towns of
Thorne and Gowle in Yorkshire, a space of many miles, has so much
subsided in latter times, that some old men of Thorne affirmed, “that
whereas they could before see little of the Steeples (of Gowle) they
now see the church yard wall.” The instances of similar subsidence
which might be mentioned, are innumerable.
“The force of subsidence, suddenly acting by means of some
earthquake, seems to me the most probable cause to which the usual
submarine situation of the forest we are speaking of may be ascribed.
It affords a simple easy explanation of the matter; its probability
is supported by numberless instances of similar events; and it is not
liable to the strong objections which exist against the hypothesis of
the ultimate depression and elevation of the level of the ocean; an
opinion which, to be credible, requires the support of a great number
of proofs less equivocal than those which have hitherto been urged in
its favour, even by the genius of Lavoisier.
“The stratum of soil, sixteen feet thick, placed above the decayed
trees, seems to remove the epoch of their sinking and destruction far
beyond the reach of any historical knowledge. In Cæsar’s time the
level of the north sea appears to have been the same as in our days.
He mentions the separation of the Wahal branch of the Rhine, and its
junction with the Meuse; noticing the then existing distance from
that junction to the sea, which agrees according to D’Anville’s
inquiries, with the actual distance. Some of the Roman roads,
constructed according to the order of Augustus, under Agrippa’s
administration, leading to the maritime towns of Belgium, still
exist, and reach the present shore. The description which Roman
authors have given of the coast, ports, and mouths of rivers, on both
sides of the North sea, agree in general with their present state;
except in places ravaged by the inroads of this sea, more apt from
its force to destroy the surrounding countries than to increase them.
“An exact resemblance exists between maritime Flanders and the
opposite coast of England, both in point of elevation above the sea,
and of the internal structure and arrangement of the soils. On both
sides strata of clay, silt, and sand, (often mixed with decayed
vegetables) are found near the surface; and in both, these superior
materials cover a very deep stratum of blueish or dark coloured clay,
unmixed with extraneous bodies. On both sides they are the lowermost
part of the soil, existing between two ridges of high lands, on their
respective sides of the same narrow sea. These two countries are
certainly coeval; and whatever proves that maritime Flanders has been
for many ages out of the sea, must, in my opinion, prove also that
the forest we are speaking of was long before that time destroyed and
buried under a stratum of soil. Now it seems proved from historical
records, carefully collected by several learned members of the
Brussels Academy, that no material change has happened in the
lowermost part of maritime Flanders during the period of the last two
thousand years.
“I am therefore inclined to suppose the original catastrophe which
buried this forest to be of very ancient date; but I suspect the
inroad of the sea which uncovered the decayed trees of the islands of
Sutton, to be comparatively recent. The state of the leaves and of
the timber, and also the tradition of the neighbouring people concur
to strengthen this suspicion.”
The reader, it is hoped, will excuse, and even approve the length of this
curious extract, as it seems so well calculated to account for and
elucidate divers striking phenomena in the natural history of the Fens.
Here it may not be improper further to observe, that the forest above
described seems to have extended from the coast of Lincolnshire a
considerable way along the Norfolk coast; as there is on the shore, near
Thornham in that county, at low water, the appearance of a large forest
having been, at some period, interred and swallowed up by the waves.
Stools of numerous large timber trees, and many trunks, are to be seen,
but so rotten, that they may be penetrated by a spade. These lie in a
black mass of vegetable fibres, consisting of decayed branches, leaves,
rushes, flags, &c. The extent of this once sylvan tract [on the Norfolk
coast] must have been great, from what is discoverable; and at high
water, now covered by the tides, is in one spot from five to six-hundred
acres. No hint of the manner, or the time, in which this submersion
happened, can be traced. Nothing like a bog is near, and the whole beach
besides is composed of a fine ooze, or marine clay. {49}