THE SANDS.
ORIGIN OF SAND--SAND NOW CARRIED DOWN TO THE SEA--THE SANDS OF EGYPT AND
THE ADJACENT DESERT----THE SUEZ CANAL----THE SANDS OF EGYPT--COAST DUNES
AND SAND PLAINS--SAND BANKS--DUNES ON COAST OF AMERICA--DUNES OF WESTERN
EUROPE--FORMATION OF DUNES--CHARACTER OF DUNE SAND--INTERIOR STRUCTURE
OF DUNES--FORM OF DUNES--GEOLOGICAL IMPORTANCE OF DUNES--INLAND DUNES--
AGE, CHARACTER, AND PERMANENCE OF DUNES--USE OF DUNES AS BARRIER AGAINST
THE SEA--ENCROACHMENTS OF THE SEA--THE LIIMFJORD--ENCROACHMENTS OF THE
SEA--DRIFTING OF DUNE SANDS--DUNES OF GASCONY--DUNES OF DENMARK--DUNES
OF PRUSSIA--ARTIFICIAL FORMATION OF DUNES--TREES SUITABLE FOR DUNE
PLANTATIONS--EXTENT OF DUNES IN EUROPE--DUNE VINEYARDS OF CAPE BRETON--
REMOVAL OF DUNES--INLAND SAND PLAINS--THE LANDES OF GASCONY--THE BELGIAN
CAMPINE--SANDS AND STEPPES OF EASTERN EUROPE--ADVANTAGES OF RECLAIMING
DUNES--GOVERNMENT WORKS OF IMPROVEMENT.
_Origin of Sand._
Sand, which is found in beds or strata at the bottom of the sea or in
the channels of rivers, as well as in extensive deposits upon or beneath
the surface of the dry land, appears to consist essentially of the
detritus of rocks. It is not always by any means clear through what
agency the solid rock has been reduced to a granular condition; for
there are beds of quartzose sand, where the sharp, angular shape of the
particles renders it highly improbable that they have been formed by
gradual abrasion and attrition, and where the supposition of a crushing
mechanical force seems equally inadmissible. In common sand, the quartz
grains are the most numerous; but this is not a proof that the rocks
from which these particles were derived were wholly, or even chiefly,
quartzose in character; for, in many composite rocks, as, for example,
in the granitic group, the mica, felspar, and hornblende are more easily
decomposed by chemical action, or disintegrated, comminuted, and reduced
to an impalpable state by mechanical force, than the quartz. In the
destruction of such rocks, therefore, the quartz would survive the other
ingredients, and remain unmixed, when they had been decomposed and had
entered into new chemical combinations, or been ground to slime and
washed away by water currents.
The greater or less specific gravity of the different constituents of
rock doubtless aids in separating them into distinct masses when once
disintegrated, though there are veined and stratified beds of sand where
the difference between the upper and lower layers, in this respect, is
too slight to be supposed capable of effecting a complete
separation.[409] In cases where rock has been reduced to sandy fragments
by heat, or by obscure chemical and other molecular forces, the sandbeds
may remain undisturbed, and represent, in the series of geological
strata, the solid formations from which they were derived. The large
masses of sand not found in place have been transported and accumulated
by water or by wind, the former being generally considered the most
important of these agencies; for the extensive deposits of the Sahara,
of the deserts of Persia, and of that of Gobi, are commonly supposed to
have been swept together or distributed by marine currents, and to have
been elevated above the ocean by the same means as other upheaved
strata.
Meteoric and mechanical influences are still active in the reduction of
rocks to a fragmentary state; but the quantity of sand now transported
to the sea seems to be comparatively inconsiderable, because--not to
speak of the absence of diluvial action--the number of torrents emptying
directly into the sea is much less than it was at earlier periods. The
formation of alluvial plains in maritime bays, by the sedimentary matter
brought down from the mountains, has lengthened the flow of such streams
and converted them very generally into rivers, or rather affluents of
rivers much younger than themselves. The filling up of the estuaries has
so reduced the slope of all large and many small rivers, and,
consequently, so checked the current of what the Germans call their
_Unterlauf_, or lower course, that they are much less able to transport
heavy material than at earlier epochs. The slime deposited by rivers at
their junction with the sea, is usually found to be composed of material
too finely ground and too light to be denominated sand, and it can be
abundantly shown that the sandbanks at the outlet of large streams are
of tidal, not of fluviatile origin, or, in lakes and tideless seas, a
result of the concurrent action of waves and of wind.
Large deposits of sand, therefore, must in general be considered as of
ancient, not of recent formation, and many eminent geologists ascribe
them to diluvial action. Staring has discussed this question very fully,
with special reference to the sands of the North Sea, the Zuiderzee, and
the bays and channels of the Dutch coast.[410] His general conclusion
is, that the rivers of the Netherlands "move sand only by a very slow
displacement of sandbanks, and do not carry it with them as a suspended
or floating material." The sands of the German Ocean he holds to be a
product of the "great North German drift," deposited where they now lie
before the commencement of the present geological period, and he
maintains similar opinions with regard to the sands thrown up by the
Mediterranean at the mouths of the Nile and on the Barbary coast.[411]
_Sand now carried to the Sea._
There are, however, cases where mountain streams still bear to the sea
perhaps relatively small, but certainly absolutely large, amounts of
disintegrated rock.[412] The quantity of sand and gravel carried into
the Mediterranean by the torrents of the Maritime Alps, the Ligurian
Apennines, the islands of Corsica, Sardinia, and Sicily, and the
mountains of Calabria, is apparently great. In mere mass, it is
possible, if not probable, that as much rocky material, more or less
comminuted, is contributed to the basin of the Mediterranean by Europe,
even excluding the shores of the Adriatic and the Euxine, as is washed
up from it upon the coasts of Africa and Syria. A great part of this
material is thrown out again by the waves on the European shores of that
sea. The harbors of Luni, Albenga, San Remo, and Savona west of Genoa,
and of Porto Fino on the other side, are filling up, and the coast near
Carrara and Massa is said to have advanced upon the sea to a distance
of 475 feet in thirty-three years.[413] Besides this, we have no
evidence of the existence of deep-water currents in the Mediterranean,
extensive enough and strong enough to transport quartzose sand across
the sea. It may be added that much of the rock from which the torrent
sands of Southern Europe are derived contains little quartz, and hence
the general character of these sands is such that they must be
decomposed or ground down to an impalpable slime, long before they could
be swept over to the African shore.
The torrents of Europe, then, do not at present furnish the material
which composes the beach sands of Northern Africa, and it is equally
certain that those sands are not brought down by the rivers of the
latter continent. They belong to a remote geological period, and have
been accumulated by causes which we cannot at present assign. The wind
does not stir water to great depths with sufficient force to disturb the
bottom,[414] and the sand thrown upon the coast in question must be
derived from a narrow belt of sea. It must hence, in time, become
exhausted, and the formation of new sandbanks and dunes upon the
southern shores of the Mediterranean will cease at last for want of
material.[415]
But even in the cases where the accumulations of sand in extensive
deserts appear to be of marine formation, or rather aggregation, and to
have been brought to their present position by upheaval, they are not
wholly composed of material collected or distributed by the currents of
the sea; for, in all such regions, they continue to receive some small
contributions from the disintegration of the rocks which underlie, or
crop out through, the superficial deposits. In some instances, too, as
in Northern Africa, additions are constantly made to the mass by the
prevalence of sea winds, which transport, or, to speak more precisely,
roll the finer beach sand to considerable distances into the interior.
But this is a very slow process, and the exaggerations of travellers
have diffused a vast deal of popular error on the subject.
_Sands of Egypt._
In the narrow valley of the Nile--which, above its bifurcation near
Cairo, is, throughout Egypt and Nubia, generally bounded by precipitous
cliffs--wherever a ravine or other considerable depression occurs in the
wall of rock, one sees what seems a stream of desert sand pouring down,
and common observers have hence concluded that the whole valley is in
danger of being buried under a stratum of infertile soil. The ancient
Egyptians apprehended this, and erected walls, often of unburnt brick,
across the outlet of gorges and lateral valleys, to check the flow of
the sand streams. In later ages, these walls have mostly fallen into
decay, and no preventive measures against such encroachments are now
resorted to. But the extent of the mischief to the soil of Egypt, and
the future danger from this source, have been much overrated. The sand
on the borders of the Nile is neither elevated so high by the wind, nor
transported by that agency in so great masses, as is popularly supposed;
and of that which is actually lifted or rolled and finally deposited by
air currents, a considerable proportion is either calcareous, and,
therefore, readily decomposable, or in the state of a very fine dust,
and so, in neither case, injurious to the soil. There are, indeed, both
in Africa and in Arabia, considerable tracts of fine silicious sand,
which may be carried far by high winds, but these are exceptional cases,
and in general the progress of the desert sand is by a rolling motion
along the surface.[416] So little is it lifted, and so inconsiderable
is the quantity yet remaining on the borders of Egypt, that a wall four
or five feet high suffices for centuries to check its encroachments.
This is obvious to the eye of every observer who prefers the true to the
marvellous; but the old-world fable of the overwhelming of caravans by
the fearful simoom--which, even the Arabs no longer repeat, if indeed
they are the authors of it--is so thoroughly rooted in the imagination
of Christendom that most desert travellers, of the tourist class, think
they shall disappoint the readers of their journals if they do not
recount the particulars of their escape from being buried alive by a
sand storm, and the popular demand for a "sensation" must be gratified
accordingly.[417]
Another circumstance is necessary to be considered in estimating the
danger to which the arable lands of Egypt are exposed. The prevailing
wind in the valley of the Nile and its borders is from the north, and it
may be said without exaggeration that the north wind blows for three
quarters of the year.[418] The effect of winds blowing up the valley is
to drive the sands of the desert plateau which border it, in a direction
parallel with the axis of the valley, not transversely to it; and if it
ran in a straight line, the north wind would carry no desert sand into
it. There are, however, both curves and angles in its course, and hence,
wherever its direction deviates from that of the wind, it might receive
sand drifts from the desert plain through which it runs. But, in the
course of ages, the winds have, in a great measure, bared the projecting
points of their ancient deposits, and no great accumulations remain in
situations from which either a north or a south wind would carry them
into the valley.[419]
_The Suez Canal._
These considerations apply, with equal force, to the supposed danger of
the obstruction of the Suez Canal by the drifting of the desert sands.
The winds across the isthmus are almost uniformly from the north, and
they swept it clean of flying sands long ages since. The traces of the
ancient canal between the Red Sea and the Nile are easily followed for a
considerable distance from Suez. Had the drifts upon the isthmus been as
formidable as some have feared and others have hoped, those traces would
have been obliterated, and Lake Timsah and the Bitter Lakes filled up,
many centuries ago. The few particles driven by the rare east and west
winds toward the line of the canal, would easily be arrested by
plantations or other simple methods, or removed by dredging. The real
dangers and difficulties of this magnificent enterprise--and they are
great--consist in the nature of the soil to be removed in order to form
the line, and especially in the constantly increasing accumulation of
sea sand at the southern terminus by the tides of the Red Sea, and at
the northern, by the action of the winds. Both seas are shallow for
miles from the shore, and the excavation and maintenance of deep
channels, and of capacious harbors with easy and secure entrances, in
such localities, is doubtless one of the hardest problems offered to
modern engineers for practical solution.
_Sands of Egypt._
The sand let fall in Egypt by the north wind is derived, not from the
desert, but from a very different source--the sea. Considerable
quantities of sand are thrown up by the Mediterranean, at and between
the mouths of the Nile, and indeed along almost the whole southern coast
of that sea, and drifted into the interior to distances varying
according to the force of the wind and the abundance and quality of the
material. The sand so transported contributes to the gradual elevation
of the Delta, and of the banks and bed of the river itself. But just in
proportion as the bed of the stream is elevated, the height of the water
in the annual inundations is increased also, and as the inclination of
the channel is diminished, the rapidity of the current is checked, and
the deposition of the slime it holds in suspension consequently
promoted. Thus the winds and the water, moving in contrary directions,
join in producing a common effect.
The sand, blown over the Delta and the cultivated land higher up the
stream during the inundation, is covered or mixed with the fertile earth
brought down by the river, and no serious injury is sustained from it.
That spread over the same ground after the water has subsided, and
during the short period when the soil is not stirred by cultivation or
covered by the flood, forms a thin pellicle over the surface as far as
it extends, and serves to divide and distinguish the successive layers
of slime deposited by the annual inundations. The particles taken up by
the wind on the sea beach are borne onward, by a hopping motion, or
rolled along the surface, until they are arrested by the temporary
cessation of the wind, by vegetation, or by some other obstruction, and
they may, in process of time, accumulate in large masses, under the lee
of rocky projections, buildings, or other barriers which break the force
of the wind.
In these facts we find the true explanation of the sand drifts, which
have half buried the Sphinx and so many other ancient monuments in that
part of Egypt. These drifts, as I have said, are not primarily from the
desert, but from the sea; and, as might be supposed from the distance
they have travelled, they have been long in gathering. While Egypt was a
great and flourishing kingdom, measures were taken to protect its
territory against the encroachment of sand, whether from the desert or
from the sea; but the foreign conquerors, who destroyed so many of its
religious monuments, did not spare its public works, and the process of
physical degradation undoubtedly began as early as the Persian invasion.
The urgent necessity, which has compelled all the successive tyrannies
of Egypt to keep up some of the canals and other arrangements for
irrigation, was not felt with respect to the advancement of the sands;
for their progress was so slow as hardly to be perceptible in the course
of a single reign, and long experience has shown that, from the natural
effect of the inundations, the cultivable soil of the valley is, on the
whole, trenching upon the domain of the desert, not retreating before
it.
The oases of the Libyan, as well as of many Asiatic deserts, have no
such safeguards. The sands are fast encroaching upon them, and threaten
soon to engulf them, unless man shall resort to artesian wells and
plantations, or to some other efficient means of checking the advance of
this formidable enemy, in time to save these islands of the waste from
final destruction.
Accumulations of sand are, in certain cases, beneficial as a protection
against the ravages of the sea; but, in general, the vicinity, and
especially the shifting of bodies of this material, are destructive to
human industry, and hence, in civilized countries, measures are taken to
prevent its spread. This, however, can be done only where the population
is large and enlightened, and the value of the soil, or of the
artificial erections and improvements upon it, is considerable. Hence in
the deserts of Africa and of Asia, and the inhabited lands which border
on them, no pains are usually taken to check the drifts, and when once
the fields, the houses, the springs, or the canals of irrigation are
covered or choked, the district is abandoned without a struggle, and
surrendered to perpetual desolation.[420]
_Sand Dunes and Sand Plains._
Two forms of sand deposit are specially important in European and
American geography. The one is that of dune or shifting hillock upon the
coast, the other that of barren plain in the interior. The coast dunes
are composed of sand washed up from the depths of the sea by the waves,
and heaped in knolls and ridges by the winds. The sand with which many
plains are covered, appears sometimes to have been deposited upon them
while they were yet submerged, sometimes to have been drifted from the
sea coast, and scattered over them by wind currents, sometimes to have
been washed upon them by running water. In these latter cases, the
deposit, though in itself considerable, is comparatively narrow in
extent and irregular in distribution, while, in the former, it is often
evenly spread over a very wide surface. In all great bodies of either
sort, the silicious grains are the principal constituent, though, when
not resulting from the disintegration of silicious rock and still
remaining in place, they are generally accompanied with a greater or
less admixture of other mineral particles, and of animal and vegetable
remains,[421] and they are, also, usually somewhat changed in
consistence by the ever-varying conditions of temperature and moisture
to which they have been exposed since their deposit. Unless the
proportion of these latter ingredients is so large as to create a
certain adhesiveness in the mass--in which case it can no longer
properly be called sand--it is infertile, and, if not charged with
water, partially agglutinated by iron, lime, or other cement, or
confined by alluvion resting upon it, it is much inclined to drift,
whenever, by any chance, the vegetable network which, in most cases,
thinly clothes and at the same time confines it, is broken.
Human industry has not only fixed the flying dunes, but, by mixing clay
and other tenacious earths with the superficial stratum of extensive
sand plains, and by the application of fertilizing substances, it has
made them abundantly productive of vegetable life. These latter
processes belong to agriculture and not to geography, and, therefore,
are not embraced within the scope of the present subject. But the
preliminary steps, whereby wastes of loose, drifting barren sands are
transformed into wooded knolls and plains, and finally, through the
accumulation of vegetable mould, into arable ground, constitute a
conquest over nature which precedes agriculture--a geographical
revolution--and, therefore, an account of the means by which the change
has been effected belongs properly to the history of man's influence on
the great features of physical geography. I proceed, then, to examine
the structure of dunes, and to describe the warfare man wages with the
sand hills, striving on the one hand to maintain and even extend them,
as a natural barrier against encroachments of the sea, and, on the
other, to check their moving and wandering propensities, and prevent
them from trespassing upon the fields he has planted and the habitations
in which he dwells.
_Coast Dunes._
Coast dunes are oblong ridges or round hillocks, formed by the action of
the wind upon sands thrown up by the waves on the beach of seas, and
sometimes of fresh-water lakes. On most coasts, the supply of sand for
the formation of dunes is derived from tidal waves. The flow of the tide
is more rapid, and consequently its transporting power greater, than
that of the ebb; the momentum, acquired by the heavy particles in
rolling in with the water, tends to carry them even beyond the flow of
the waves; and at the turn of the tide, the water is in a state of
repose long enough to allow it to let fall much of the solid matter it
holds in suspension. Hence, on all low, tide-washed coasts of seas with
sandy bottoms, there exist several conditions favorable to the formation
of sand deposits along high-water mark.[422] If the land winds are of
greater frequency, duration, or strength than the sea winds, the sands
left by the retreating wave will be constantly blown back into the
water; but if the prevailing air currents are in the opposite direction,
the sands will soon be carried out of the reach of the highest waves,
and transported continually farther and farther into the interior of the
land, unless obstructed by high grounds, vegetation, or other obstacles.
The tide, though a usual, is by no means a necessary condition for the
accumulations of sand out of which dunes are formed. The Baltic and the
Mediterranean are almost tideless seas, but there are dunes on the
Russian and Prussian coasts of the Baltic, and at the mouths of the Nile
and many other points on the shores of the Mediterranean. The vast
shoals in the latter sea, known to the ancients as the Greater and
Lesser Syrtis, are of marine origin. They are still filling up with
sand, washed up from greater depths, or sometimes drifted from the coast
in small quantities, and will probably be converted, at some future
period, into dry land covered with sand hills. There are also extensive
ranges of dunes upon the eastern shores of the Caspian, and at the
southern, or rather southeastern extremity of Lake Michigan.[423] There
is no doubt that this latter lake formerly extended much farther in that
direction, but its southern portion has gradually shoaled and at last
been converted into solid land, in consequence of the prevalence of the
northwest winds. These blow over the lake a large part of the year, and
create a southwardly set of the currents, which wash up sand from the
bed of the lake and throw it on shore. Sand is taken up from the beach
at Michigan City by every wind from that quarter, and, after a heavy
blow of some hours' duration, sand ridges may be observed on the north
side of the fences, like the snow wreaths deposited by a drifting wind
in winter. Some of the particles are carried back by contrary winds, but
most of them lodge on or behind the dunes, or in the moist soil near the
lake, or are entangled by vegetables, and tend permanently to elevate
the level. Like effects are produced by constant sea winds, and dunes
will generally be formed on all low coasts where such prevail, whether
in tideless or in tidal waters.
Jobard thus describes the _modus operandi_, under ordinary
circumstances, at the mouths of the Nile, where a tide can scarcely be
detected: "When a wave breaks, it deposits an almost imperceptible line
of fine sand. The next wave brings also its contribution, and shoves the
preceding line a little higher. As soon as the particles are fairly out
of the reach of the water they are dried by the heat of the burning sun,
and immediately seized by the wind and rolled or borne farther inland.
The gravel is not thrown out by the waves, but rolls backward and
forward until it is worn down to the state of fine sand, when it, in its
turn, is cast upon the land and taken up by the wind."[424] This
description applies only to the common every-day action of wind and
water; but just in proportion to the increasing force of the wind and
the waves, there is an increase in the quantity of sand, and in the
magnitude of the particles carried off from the beach by it, and, of
course, every storm in a landward direction adds sensibly to the
accumulation upon the shore.
_Sand Banks._
Although dunes, properly so called, are found only on dry land and above
ordinary high-water mark, and owe their elevation and structure to the
action of the wind, yet, upon many shelving coasts, accumulations of
sand much resembling dunes are formed under water at some distance from
the shore by the oscillations of the waves, and are well known by the
name of sand banks. They are usually rather ridges than banks, of
moderate inclination, and with the steepest slope seaward; and their
form differs from that of dunes only in being lower and more continuous.
Upon the western coast of the island of Amrum, for example, there are
three rows of such banks, the summits of which are at a distance of
perhaps a couple of miles from each other; so that, including the width
of the banks themselves, the spaces between them, and the breadth of the
zone of dunes upon the land, the belt of moving sands on that coast is
probably not less than eight miles wide.
Under ordinary circumstances, sand banks are always rolling landward,
and they compose the magazine from which the material for the dunes is
derived. The dunes, in fact, are but aquatic sand banks transferred to
dry land. The laws of their formation are closely analogous, because the
action of the two fluids, by which they are respectively accumulated and
built up, is very similar when brought to bear upon loose particles of
solid matter. It would, indeed, seem that the slow and comparatively
regular movements of the heavy, unelastic water ought to affect such
particles very differently from the sudden and fitful impulses of the
light and elastic air. But the velocity of the wind currents gives them
a mechanical force approximating to that of the slower waves, and,
however difficult it may be to explain all the phenomena that
characterize the structure of the dunes, observation has proved that it
is nearly identical with that of submerged sand banks. The differences
of form are generally ascribable to the greater number and variety of
surface accidents of the ground on which the sand hills of the land are
built up, and to the more frequent changes, and wider variety of
direction, in the courses of the wind.
_Dunes on the Coast of America._
Upon the Atlantic coast of the United States, the prevalence of western
or off-shore winds is unfavorable to the formation of dunes, and, though
marine currents lodge vast quantities of sand, in the form of banks, on
that coast, its shores are proportionally more free from sand hills than
some others of lesser extent. There are, however, very important
exceptions. The action of the tide throws much sand upon some points of
the New England coast, as well as upon the beaches of Long Island and
other more southern shores, and here dunes resembling those of Europe
are formed. There are also extensive ranges of dunes on the Pacific
coast of the United States, and at San Francisco they border some of the
streets of the city.
The dunes of America are far older than her civilization, and the soil
they threaten or protect possesses, in general, too little value to
justify any great expenditure in measures for arresting their progress
or preventing their destruction. Hence, great as is their extent and
their geographical importance, they have, at present, no such intimate
relations to human life as to render them objects of special interest in
the point of view I am taking, and I do not know that the laws of their
formation and motion have been made a subject of original investigation
by any American observer.
_Dunes of Western Europe._
Upon the western coast of Europe, on the contrary, the ravages
occasioned by the movement of sand dunes, and the serious consequences
often resulting from the destruction of them, have long engaged the
earnest attention of governments and of scientific men, and for nearly a
century persevering and systematic effort has been made to bring them
under human control. The subject has been carefully studied in Denmark
and the adjacent duchies, in Western Prussia, in the Netherlands, and in
France; and the experiments in the way of arresting the drifting of the
dunes, and of securing them, and the lands they shelter, from the
encroachments of the sea, have resulted in the adoption of a system of
coast improvement substantially the same in all these countries. The
sands, like the forests, have now their special literature, and the
volumes and memoirs, which describe them and the processes employed to
subdue them, are full of scientific interest and of practical
instruction.[425]
_Formation of Dunes._
The laws which govern the formation of dunes are substantially these. We
have seen that, under certain conditions, sand is accumulated above
high-water mark on low sea and lake shores. So long as the sand is kept
wet by the spray or by capillary attraction, it is not disturbed by air
currents, but as soon as the waves retire sufficiently to allow it to
dry, it becomes the sport of the wind, and is driven up the gently
sloping beach until it is arrested by stones, vegetables, or other
obstructions, and thus an accumulation is formed which constitutes the
foundation of a dune. However slight the elevation thus created, it
serves to stop or retard the progress of the sand grains which are
driven against its shoreward face, and to protect from the further
influence of the wind the particles which are borne beyond it, or rolled
over its crest, and fall down behind it. If the shore above the beach
line were perfectly level and straight, the grass or bushes upon it of
equal height, the sand thrown up by the waves uniform in size and weight
of particles as well as in distribution, and if the action of the wind
were steady and regular, a continuous bank would be formed, everywhere
alike in height and cross section. But no such constant conditions
anywhere exist. The banks are curved, broken, unequal in elevation; they
are sometimes bare, sometimes clothed with vegetables of different
structure and dimensions; the sand thrown up is variable in quantity and
character; and the winds are shifting, gusty, vortical, and often
blowing in very narrow currents. From all these causes, instead of
uniform hills, there rise irregular rows of sand heaps, and these, as
would naturally be expected, are of a pyramidal, or rather conical
shape, and connected at bottom by more or less continuous ridges of the
same material.
On a receding coast, dunes will not attain so great a height as on more
secure shores, because they are undermined and carried off before they
have time to reach their greatest dimensions. Hence, while at sheltered
points in Southwestern France, there are dunes three hundred feet or
more in height, those on the Frisic Islands and the exposed parts of the
coast of Schleswig-Holstein range only from twenty to one hundred feet.
On the western shores of Africa, it is said that they sometimes attain
an elevation of six hundred feet. This is one of the very few points
known to geographers where desert sands are advancing seaward, and here
they rise to the greatest altitude to which sand grains can be carried
by the wind.
The hillocks, once deposited, are held together and kept in shape,
partly by mere gravity, and partly by the slight cohesion of the lime,
clay, and organic matter mixed with the sand; and it is observed that,
from capillary attraction, evaporation from lower strata, and retention
of rain water, they are always moist a little below the surface.[426] By
successive accumulations, they gradually rise to the height of thirty,
fifty, sixty, or a hundred feet, and sometimes even much higher. Strong
winds, instead of adding to their elevation, sweep off loose particles
from their surface, and these, with others blown over or between them,
build up a second row of dunes, and so on according to the character of
the wind, the supply and consistence of the sand, and the face of the
country. In this way is formed a belt of sand dunes, irregularly
dispersed and varying much in height and dimensions, and some times many
miles in breadth. On the Island of Sylt, in the German Sea, where there
are several rows, the width of the belt is from half a mile to a mile.
There are similar ranges on the coast of Holland, exceeding two miles in
breadth, while at the mouths of the Nile they form a zone not less than
ten miles wide. The base of some of the dunes in the Delta of the Nile
is reached by the river during the annual inundation, and the
infiltration of the water, which contains lime, has converted the lower
strata into a silicious limestone, or rather a calcareous sandstone, and
thus afforded an opportunity of studying the structure of that rock in a
locality where its origin and mode of aggregation and solidification are
known.
_Character of Dune Sand._
"Dune sand," says Staring, "consists of well-rounded grains of quartz,
more or less colored by iron, and often mingled with fragments of
shells, small indeed, but still visible to the naked eye.[427] These
fragments are not constant constituents of dune sand. They are sometimes
found at the very summits of the hillocks, as at Overveen; in the King's
Dune, near Egmond, they form a coarse calcareous gravel very largely
distributed through the sand, while the interior dunes between Haarlem
and Warmond exhibit no trace of them. It is yet undecided whether the
presence or absence of these fragments is determined by the period of
the formation of the dunes, or whether it depends on a difference in the
process by which different dunes have been accumulated. Land shells,
such as snails, for example, are found on the surface of the dunes in
abundance, and many of the shelly fragments in the interior of the
hillocks may be derived from the same source."[428]
J. G. Kohl has some poetical thoughts upon the origin and character of
the dune sands, which are worth quoting:
"The sand was composed of pure transparent quartz. I could not observe
this sand without the greatest admiration. If it is the product of the
waves, breaking and crushing flints and fragments of quartz against each
other, it is a result which could be brought about only in the course of
countless ages. We need not lift ourselves to the stars, to their
incalculable magnitudes and distances and numbers, in order to feel the
giddiness of astonishment. Here, upon earth, in the simple sand, we find
miracle enough. Think of the number of sand grains contained in a single
dune, then of all the dunes upon this widely extended coast--not to
speak of the innumerable grains in the Arabian, African, and Prussian
deserts--this, of itself, is sufficient to overwhelm a thoughtful fancy.
How long, how many times must the waves have risen and sunk in order to
reduce these vast heaps to powder!
"During the whole time I spent on this coast, I had always some sand in
my fingers, was rubbing and rolling it about, examining it on all sides,
holding a little shining grain on the tip of my finger, and thinking to
myself how, in its corners, its angles, its whole configuration, it
might very probably have a history longer than that of the old German
nation--possibly longer than that of the human race. Where was the
original quartz crystal, of which this is a fragment, first formed? To
what was it once fixed? What power broke it loose? How was it beaten
smaller and ever smaller by the waves? They tossed it, for aeons, to and
fro upon the beach, rolled it up and down, forced it to make thousands
and thousands of daily voyages for millions and millions of days. Then
the wind bore it away, and used it in building up a dune; there it lay
for centuries, packed in with its fellows, protecting the marshes and
cherished by the inhabitants, till, seized again by the pursuing sea, it
fell once more into the water, there to begin the endless dance
anew--and again to be swept away by the wind--and again to find rest in
the dunes, a protection and a blessing to the coast. There is something
mysterious about such a grain of sand, and at last I went so far as to
fancy a little immortal spark linked with each one, presiding over its
destiny, and sharing its vicissitudes. Could we arm our eyes with a
microscope, and then dive, like a sparling, into one of these dunes, the
pile, which is in fact only a heap of countless little crystal blocks,
would strike us as the most marvellous building upon earth. The sunbeams
would pass, with illuminating power, through all these little
crystalline bodies. We should see how every sand grain is formed, by
what multifarious little facets it is bounded, we should even discover
that it is itself composed of many distinct particles."[429]
Sand concretions form within the dunes and especially in the depressions
between them. These are sometimes so extensive and impervious as to
retain a sufficient supply of water to feed perennial springs, and to
form small permanent ponds, and they are a great impediment to the
penetration of roots, and consequently to the growth of trees planted,
or germinating from self-sown seeds, upon the dunes.[430]
_Interior Structure of Dunes._
The interior structure of the dunes, the arrangement of their particles,
is not, as might be expected, that of an unorganized, confused heap, but
they show a strong tendency to stratification. This is a point of much
geological interest, because it indicates that sandstone may owe its
stratified character to the action of wind as well as of water. The
origin and peculiar character of these layers are due to a variety of
causes. A southwest wind and current may deposit upon a dune a stratum
of a given color and mineral composition, and this may be succeeded by a
northwest wind and current, bringing with them particles of a different
hue, constitution, and origin.
Again, if we suppose a violent tempest to strew the beach with sand
grains very different in magnitude and specific gravity, and, after the
sand is dry, to be succeeded by a gentle breeze, it is evident that only
the lighter particles will be taken up and carried to the dunes. If,
after some time, the wind freshens, heavier grains will be transported
and deposited on the former, and a still stronger succeeding gale will
roll up yet larger kernels. Each of these deposits will form a stratum.
If we suppose the tempest to be followed, after the sand is dry, not by
a gentle breeze, but by a wind powerful enough to lift at the same time
particles of very various magnitudes and weights, the heaviest will
often lodge on the dune while the lighter will be carried farther. This
would produce a stratum of coarse sand, and the same effect might result
from the blowing away of light particles out of a mixed layer, while the
heavier remained undisturbed.[431] Still another cause of
stratification may be found in the occasional interposition of a thin
layer of leaves or other vegetable remains between successive deposits,
and this I imagine to be more frequent than has been generally supposed.
The eddies of strong winds between the hillocks must also occasion
disturbances and re-arrangements of the sand layers, and it seems
possible that the irregular thickness and the strange contortions of the
strata of the sandstone at Petra may be due to some such cause. A
curious observation of Professor Forchhammer suggests an explanation of
another peculiarity in the structure of the sandstone of Mount Seir. He
describes dunes in Jutland, composed of yellow quartzose sand intermixed
with black titanian iron. When the wind blows over the surface of the
dunes, it furrows the sand with alternate ridges and depressions,
ripples, in short, like those of water. The swells, the dividing ridges
of the system of sand ripples, are composed of the light grains of
quartz, while the heavier iron rolls into the depressions between, and
thus the whole surface of the dune appears as if covered with a fine
black network.
_Form of Dunes._
The sea side of dunes, being more exposed to the caprices of the wind,
is more irregular in form than the lee or land side, where the
arrangement of the particles is affected by fewer disturbing and
conflicting influences. Hence, the stratification of the windward slope
is somewhat confused, while the sand on the lee side is found to be
disposed in more regular beds, inclining landward, and with the largest
particles lowest, where their greater weight would naturally carry them.
The lee side of the dunes, being thus formed of sand deposited according
to the laws of gravity, is very uniform in its slope, which, according
to Forchhammer, varies little from an angle of 30 deg. with the horizon,
while the more exposed and irregular weather side lies at an inclination
of from 5 deg. to 10 deg.. When, however, the outer tier of dunes is formed so
near the waterline as to be exposed to the immediate action of the
waves, it is undermined, and the face of the hill is very steep and
sometimes nearly perpendicular.
_Geological Importance of Dunes._
These observations, and other facts which a more attentive study on the
spot would detect, might furnish the means of determining interesting
and important questions concerning geological formations in localities
very unlike those where dunes are now thrown up. For example, Studer
supposes that the drifting sand hills of the African desert were
originally coast dunes, and that they have been transported to their
present position far in the interior, by the rolling and shifting
leeward movement to which all dunes not covered with vegetation are
subject. The present general drift of the sands of that desert appears
to be to the southwest and west, the prevailing winds blowing from the
northeast and east; but it has been doubted whether the shoals of the
western coast of Northern Africa, and the sands upon that shore, are
derived from the bottom of the Atlantic, in the usual manner, or, by an
inverse process, from those of the Sahara. The latter, as has been
before remarked, is probably the truth, though observations are wanting
to decide the question.[432] There is nothing violently improbable in
the supposition that they may have been first thrown up by the
Mediterranean on its Libyan coast, and thence blown south and west over
the vast space they now cover. But whatever has been their source and
movement, they can hardly fail to have left on their route some
sandstone monuments to mark their progress, such, for example, as we
have seen are formed from the dune sand at the mouth of the Nile; and it
is conceivable that the character of the drifting sands themselves, and
of the conglomerates and sandstones to whose formation they have
contributed, might furnish satisfactory evidence as to their origin,
their starting point, and the course by which they have wandered so far
from the sea.[433]
If the sand of coast dunes is, as Staring describes it, composed chiefly
of well-rounded quartzose grains, fragments of shells, and other
constant ingredients, it would often be recognizable as coast sand, in
its agglutinate state of sandstone. The texture of this rock varies from
an almost imperceptible fineness of grain to great coarseness, and
affords good facilities for microscopic observation of its structure.
There are sandstones, such, for example, as are used for grindstones,
where the grit, as it is called, is of exceeding sharpness; others where
the angles of the grains are so obtuse that they scarcely act at all on
hard metals. The former may be composed of grains of rock, disintegrated
indeed, and recemented together, but not, in the meanwhile, much rolled;
the latter, of sands long washed by the sea, and drifted by land winds.
There is, indeed, so much resemblance between the effects of driving
winds and of rolling water upon light bodies, that there would be
difficulty in distinguishing them;[434] but after all, it is not
probable that sandstone, composed of grains thrown up from the salt sea,
and long tossed by the winds, would be identical in its structure with
that formed from fragments of rock crushed by mechanical force, or
disintegrated by heat, and again agglutinated without much exposure to
the action of moving water.[435]
_Inland Dunes._
I have met with some observations indicating a structural difference
between interior and coast dunes, which might perhaps be recognized in
the sandstones formed from these two species of sand hills respectively.
In the great American desert between the Andes and the Pacific, Meyen
found sand heaps of a perfect falciform shape.[436] They were from seven
to fifteen feet high, the chord of their arc measuring from twenty to
seventy paces. The slope of the convex face is described as very small,
that of the concave as high as 70 deg. or 80 deg., and their surfaces were
rippled. No smaller dunes were observed, nor any in the process of
formation. The concave side uniformly faced the northwest, except toward
the centre of the desert, where, for a distance of one or two hundred
paces, they gradually opened to the west, and then again gradually
resumed the former position.
Poeppig ascribes a falciform shape to the movable, a conical to the fixed
dunes, or _medanos_, of the same desert. "The medanos," he observes,
"are hillock-like elevations of sand, some having a firm, others a loose
base. The former [latter], which are always crescent shaped, are from
ten to twenty feet high, and have an acute crest. The inner side is
perpendicular, and the outer or bow side forms an angle with a steep
inclination downward. When driven by violent winds, the medanos pass
rapidly over the plains. The smaller and lighter ones move quickly
forward, before the larger; but the latter soon overtake and crush them,
whilst they are themselves shivered by the collision. These medanos
assume all sorts of extraordinary figures, and sometimes move along the
plain in rows forming most intricate labyrinths. * * A plain often
appears to be covered with a row of medanos, and some days afterward it
is again restored to its level and uniform aspect. * * *
"The medanos with immovable bases are formed on the blocks of rocks
which are scattered about the plain. The sand is driven against them by
the wind, and as soon as it reaches the top point, it descends on the
other side until that is likewise covered; thus gradually arises a
conical-formed hill. Entire hillock chains with acute crests are formed
in a similar manner. * * * On their southern declivities are found vast
masses of sand, drifted thither by the mid-day gales. The northern
declivity, though not steeper than the southern, is only sparingly
covered with sand. If a hillock chain somewhat distant from the sea
extends in a line parallel with the Andes, namely, from S. S. E. to N.
N. W., the western declivity is almost entirely free of sand, as it is
driven to the plain below by the southeast wind, which constantly
alternates with the wind from the south."[437]
It is difficult to reconcile this description with that of Meyen, but if
confidence is to be reposed in the accuracy of either observer, the
formation of the sand hills in question must be governed by very
different laws from those which determine the structure of coast dunes.
Captain Gilliss, of the American navy, found the sand hills of the
Peruvian desert to be in general crescent shaped, as described by Meyen,
and a similar structure is said to characterize the inland dunes of the
Llano Estacado and other plateaus of the North American desert, though
these latter are of greater height and other dimensions than those
described by Meyen. There is no very obvious explanation of this
difference in form between maritime and inland sand hills, and the
subject merits investigation.[438]
_Age, Character, and Permanence of Dunes._
The origin of most great lines of dunes goes back past all history.
There are on many coasts, several distinct ranges of sand hills which
seem to be of very different ages, and to have been formed under
different relative conditions of land and water.[439] In some cases,
there has been an upheaval of the coast line since the formation of the
oldest hillocks, and these have become inland dunes, while younger rows
have been thrown up on the new beach laid bare by elevation of the sea
bed. Our knowledge of the mode of their first accumulation is derived
from observation of the action of wind and water in the few instances
where, with or without the aid of man, new coast dunes have been
accumulated, and of the influence of wind alone in elevating new sand
heaps inland of the coast tier, when the outer rows are destroyed by the
sea, as also when the sodded surface of ancient sands has been broken,
and the subjacent strata laid open to the air.
It is a question of much interest, in what degree the naked condition of
most dunes is to be ascribed to the improvidence and indiscretion of
man. There are, in Western France, extensive ranges of dunes covered
with ancient and dense forests, while the recently formed sand hills
between them and the sea are bare of vegetation, and are rapidly
advancing upon the wooded dunes, which they threaten to bury beneath
their drifts. Between the old dunes and the new, there is no
discoverable difference in material or in structure; but the modern sand
hills are naked and shifting, the ancient, clothed with vegetation and
fixed. It has been conjectured that artificial methods of confinement
and plantation were employed by the primitive inhabitants of Gaul; and
Laval, basing his calculations on the rate of annual movement of the
shifting dunes, assigns the fifth century of the Christian era as the
period when these processes were abandoned.[440]
There is no historical evidence that the Gauls were acquainted with
artificial methods of fixing the sands of the coast, and we have little
reason to suppose that they were advanced enough in civilization to be
likely to resort to such processes, especially at a period when land
could have had but a moderate value.
In other countries, dunes have spontaneously clothed themselves with
forests, and the rapidity with which their surface is covered by various
species of sand plants, and finally by trees, where man and cattle and
burrowing animals are excluded from them, renders it highly probable
that they would, as a general rule, protect themselves, if left to the
undisturbed action of natural causes. The sand hills of the Frische
Nehrung, on the coast of Prussia, were formerly wooded down to the
water's edge, and it was only in the last century that, in consequence
of the destruction of their forests, they became moving sands.[441]
There is every reason to believe that the dunes of the Netherlands were
clothed with trees until after the Roman invasion. The old geographers,
in describing these countries, speak of vast forests extending to the
very brink of the sea; but drifting coast dunes are first mentioned by
the chroniclers of the Middle Ages, and so far as we know they have
assumed a destructive character in consequence of the improvidence of
man.[442] The history of the dunes of Michigan, so far as I have been
able to learn from my own observation, or that of others, is the same.
Thirty years ago, when that region was scarcely inhabited, they were
generally covered with a thick growth of trees, chiefly pines, and
underwood, and there was little appearance of undermining and wash on
the lake side, or of shifting of the sands, except where the trees had
been cut or turned up by the roots.[443]
Nature, as she builds up dunes for the protection of the sea shore,
provides, with similar conservatism, for the preservation of the dunes
themselves; so that, without the interference of man, these hillocks
would be, not perhaps absolutely perpetual, but very lasting in
duration, and very slowly altered in form or position. When once covered
with the trees, shrubs, and herbaceous growths adapted to such
localities, dunes undergo no apparent change, except the slow occasional
undermining of the outer tier, and accidental destruction by the
exposure of the interior, from the burrowing of animals, or the
upturning of trees with their roots, and all these causes of
displacement are very much less destructive when a vegetable covering
exists in the immediate neighborhood of the breach.
Before the occupation of the coasts by civilized and therefore
destructive man, dunes, at all points where they have been observed,
seem to have been protected in their rear by forests, which served to
break the force of the winds in both directions,[444] and to have
spontaneously clothed themselves with a dense growth of the various
plants, grasses, shrubs, and trees, which nature has assigned to such
soils. It is observed in Europe that dunes, though now without the
shelter of a forest country behind them, begin to protect themselves as
soon as human trespassers are excluded, and grazing animals denied
access to them. Herbaceous and arborescent plants spring up almost at
once, first in the depressions, and then upon the surface of the sand
hills. Every seed that sprouts, binds together a certain amount of sand
by its roots, shades a little ground with its leaves, and furnishes food
and shelter for still younger or smaller growths. A succession of a very
few favorable seasons suffices to bind the whole surface together with a
vegetable network, and the power of resistance possessed by the dunes
themselves, and the protection they afford to the fields behind them,
are just in proportion to the abundance and density of the plants they
support.
The growth of the vegetable covering can, of course, be much accelerated
by judicious planting and watchful care, and this species of improvement
is now carried on upon a vast scale, wherever the value of land is
considerable and the population dense. In the main, the dunes on the
coast of the German Sea, notwithstanding the great quantity of often
fertile land they cover, and the evils which result from their
movement, are, upon the whole, a protective and beneficial agent, and
their maintenance is an object of solicitude with the governments and
people of the shores they protect.[445]
_Use of Dunes as a Barrier against the Sea._
Although the sea throws up large quantities of sand on flat lee-shores,
there are, as we have seen, many cases where it continually encroaches
on those same shores and washes them away. At all points of the shallow
North Sea where the agitation of the waves extends to the bottom, banks
are forming and rolling eastward. Hence the sea sand tends to accumulate
upon the coast of Schleswig-Holstein and Jutland, and were there no
conflicting influences, the shore would rapidly extend itself westward.
But the same waves which wash the sand to the coast undermine the beach
they cover, and still more rapidly degrade the shore at points where it
is too high to receive partial protection by the formation of dunes upon
it. The earth of the coast is generally composed of particles finer,
lighter, and more transportable by water than the sea sand. While,
therefore, the billows raised by a heavy west wind may roll up and
deposit along the beach thousands of tons of sand, the same waves may
swallow up even a larger quantity of fine shore earth. This earth, with
a portion of the sand, is swept off by northwardly and southwardly
currents, and let fall at other points of the coast, or carried off,
altogether, out of the reach of causes which might bring it back to its
former position.
Although, then, the eastern shore of the German Ocean here and there
advances into the sea, it in general retreats before it, and but for the
protection afforded it by natural arrangements seconded by the art and
industry of man, whole provinces would soon be engulfed by the waters.
This protection consists in an almost unbroken chain of sand banks and
dunes, extending from the northernmost point of Jutland to the Elbe, a
distance of not much less than three hundred miles, and from the Elbe
again, though with more frequent and wider interruptions, to the
Atlantic borders of France and Spain.[446] So long as the dunes are
maintained by nature or by human art, they serve, like any other
embankment or dike, as a partial or a complete protection against the
encroachments of the sea; and on the other hand, when their drifts are
not checked by natural processes, or by the industry of man, they become
a cause of as certain, if not of as sudden, destruction as the ocean
itself whose advance they retard.
_Encroachments of the Sea._
The eastward progress of the sea on the Danish and Netherlandish coast,
and on certain shores of the Atlantic, depends so much on local
geological structure, on the force and direction of tidal and other
marine currents, on the volume and rapidity of coast rivers, on the
contingencies of the weather and on other varying circumstances, that no
general rate can he assigned to it.
At Agger, near the western end of the Liimfjord, in Jutland, the coast
was washed away, between the years 1815 and 1839, at the rate of more
than eighteen feet a year. The advance of the sea appears to have been
something less rapid for a century before; but from 1840 to 1857, it
gained upon the land no less than thirty feet a year. At other points of
the shore of Jutland, the loss is smaller, but the sea is encroaching
generally upon the whole line of the coast.[447]
_The Liimfjord._
The irruption of the sea into the fresh-water lagoon of Liimfjord in
Jutland, in 1825--one of the most remarkable encroachments of the ocean
in modern times--is expressly ascribed to "mismanagement of the dunes"
on the narrow neck of land which separated the fjord from the North Sea.
At earlier periods, the sea had swept across the isthmus, and even burst
through it, but the channel had been filled up again, sometimes by
artificial means, sometimes by the operation of natural causes, and on
all these occasions effects were produced very similar to those
resulting from the formation of the new channel in 1825, which still
remains open.[448] Within comparatively recent historical ages, the
Liimfjord has thus been several times alternately filled with fresh and
with salt water, and man has produced, by neglecting the dunes, or at
least might have prevented by maintaining them, changes identical with
those which are usually ascribed to the action of great geological
causes, and sometimes supposed to have required vast periods of time for
their accomplishment.
"This breach," says Forchhammer, "which converted the Liimfjord into a
sound, and the northern part of Jutland into an island, occasioned
remarkable changes. The first and most striking phenomenon was the
sudden destruction of almost all the fresh-water fish previously
inhabiting this lagoon, which was famous for its abundant fisheries.
Millions of fresh-water fish were thrown on shore, partly dead and
partly dying, and were carted off by the people. A few only survived,
and still frequent the shores at the mouth of the brooks. The eel,
however, has gradually accommodated itself to the change of
circumstances, and is found in all parts of the fjord, while to all
other fresh-water fish, the salt water of the ocean seems to have been
fatal. It is more than probable that the sand washed in by the irruption
covers, in many places, a layer of dead fish, and has thus prepared the
way for a petrified stratum similar to those observed in so many older
formations.
"As it seems to be a law of nature that animals whose life is suddenly
extinguished while yet in full vigor, are the most likely to be
preserved by petrification, we find here one of the conditions favorable
to the formation of such a petrified stratum. The bottom of the
Liimfjord was covered with a vigorous growth of aquatic plants,
belonging both to fresh and to salt water, especially _Zostera marina_.
This vegetation totally disappeared after the irruption, and, in some
instances, was buried by the sand; and here again we have a familiar
phenomenon often observed in ancient strata--the indication of a given
formation by a particular vegetable species--and when the strata
deposited at the time of the breach shall be accessible by upheaval, the
period of eruption will be marked by a stratum of _Zostera_, and
probably by impressions of fresh-water fishes.
"It is very remarkable that the _Zostera marina_, a sea plant, was
destroyed even where no sand was deposited. This was probably in
consequence of the sudden change from brackish to salt water. * * It is
well established that the Liimfjord communicated with the German Ocean
at some former period. To that era belong the deep beds of oyster shells
and _Cardium edule_, which are still found at the bottom of the fjord.
And now, after an interval of centuries, during which the lagoon
contained no salt-water shell fish, it again produces great numbers of
_Mytilus edulis_. Could we obtain a deep section of the bottom, we
should find beds of _Ostrea edulis_ and _Cardium edule_, then a layer of
_Zostera marina_ with fresh-water fish, and then a bed of _Mytilus
edulis_. If, in course of time, the new channel should be closed, the
brooks would fill the lagoon again with fresh water; fresh-water fish
and shell fish would reappear, and thus we should have a repeated
alternation of organic inhabitants of the sea and of the waters of the
land.
"These events have been accompanied with but a comparatively
insignificant change of land surface, while the formations in the bed of
this inland sea have been totally revolutionized in character."[449]
_Coasts of Schleswig-Holstein, Holland, and France._
On the islands on the coast of Schleswig-Holstein, the advance of the
sea has been more unequivocal and more rapid. Near the beginning of the
last century, the dunes which had protected the western coast of the
island of Sylt began to roll to the east, and the sea followed closely
as they retired. In 1757, the church of Rantum, a village upon that
island, was obliged to be taken down in consequence of the advance of
the sand hills; in 1791, these hills had passed beyond its site, the
waves had swallowed up its foundations, and the sea gained so rapidly,
that, fifty years later, the spot where they lay was seven hundred feet
from the shore.[450]
The most prominent geological landmark on the coast of Holland is the
Huis te Britten, _Arx Britannica_, a fortress built by the Romans, in
the time of Caligula, on the main land near the mouth of the Rhine. At
the close of the seventeenth century, the sea had advanced sixteen
hundred paces beyond it. The older Dutch annalists record, with much
parade of numerical accuracy, frequent encroachments of the sea upon
many parts of the Netherlandish coast. But though the general fact of an
advance of the ocean upon the land is established beyond dispute, the
precision of the measurements which have been given is open to question.
Staring, however, who thinks the erosion of the coast much exaggerated
by popular geographers, admits a loss of more than a million and a half
acres, chiefly worthless morass;[451] and it is certain that but for the
resistance of man, but for his erection of dikes and protection of
dunes, there would now be left of Holland little but the name. It is, as
has been already seen, still a debated question among geologists whether
the coast of Holland now is, and for centuries has been, subsiding. I
believe most investigators maintain the affirmative; and if the fact is
so, the advance of the sea upon the land is, in part, due to this cause.
But the rate of subsidence is at all events very small, and therefore
the encroachments of the ocean upon the coast are mainly to be ascribed
to the erosion and transportation of the soil by marine waves and
currents.
The sea is fast advancing at several points of the western coast of
France, and unknown causes have given a new impulse to its ravages since
the commencement of the present century. Between 1830 and 1842, the
Point de Grave, on the north side of the Gironde, retreated one hundred
and eighty metres, or about fifty feet per year; from the latter year to
1846, the rate was increased to more than three times that quantity, and
the loss in those four years was above six hundred feet. All the
buildings at the extremity of the peninsula have been taken down and
rebuilt farther landward, and the lighthouse of the Grave now occupies
its third position. The sea attacked the base of the peninsula also, and
the Point de Grave and the adjacent coasts have been for twenty years
the scene of one of the most obstinately contested struggles between man
and the ocean recorded in the annals of modern engineering.
It cannot, indeed, be affirmed that human power is able to arrest
altogether the incursions of the waves on sandy coasts, by planting the
beach, and clothing the dunes with wood. On the contrary, both in
Holland and on the French coast, it has been found necessary to protect
the dunes themselves by piling and by piers and sea walls of heavy
masonry. But experience has amply shown that the processes referred to
are entirely successful in preventing the movement of the dunes, and the
drifting of their sands over cultivated lands behind them; and that, at
the same time, the plantations very much retard the landward progress of
the waters.[452]
_Drifting of Dune Sands._
Besides their importance as a barrier against the inroads of the ocean,
dunes are useful by sheltering the cultivated ground behind them from
the violence of the sea wind, from salt spray, and from the drifts of
beach sand which would otherwise overwhelm them. But the dunes
themselves, unless their surface sands are kept moist, and confined by
the growth of plants, or at least by a crust of vegetable earth, are
constantly rolling inward; and thus, while, on one side, they lay bare
the traces of ancient human habitations or other evidences of the social
life of primitive man, they are, on the other, burying fields, houses,
churches, and converting populous districts into barren and deserted
wastes.
Especially destructive are they when, by any accident, a cavity is
opened into them to a considerable depth, thereby giving the wind access
to the interior, where the sand is thus first dried, and then scooped
out and scattered far over the neighboring soil. The dune is now a
magazine of sand, no longer a rampart against it, and mischief from this
source seems more difficult to resist than from almost any other drift,
because the supply of material at the command of the wind, is more
abundant and more concentrated than in its original thin and widespread
deposits on the beach. The burrowing of conies in the dunes is, in this
way, not unfrequently a cause of their destruction and of great injury
to the fields behind them. Drifts, and even inland sand hills, sometimes
result from breaking the surface of more level sand deposits, far within
the range of the coast dunes. Thus we learn from Staring, that one of
the highest inland dunes in Friesland owes its origin to the opening of
the drift sand by the uprooting of a large oak.[453]
Great as are the ravages produced by the encroachment of the sea upon
the western shores of continental Europe, they have been in some degree
compensated by spontaneous marine deposits at other points of the coast,
and we have seen in a former chapter that the industry of man has
reclaimed a large territory from the bosom of the ocean. These latter
triumphs are not of recent origin, and the incipient victories which
paved the way for them date back perhaps as far as ten centuries. In the
mean time, the dunes had been left to the operation of the laws of
nature, or rather freed, by human imprudence, from the fetters with
which nature had bound them, and it is scarcely three generations since
man first attempted to check their destructive movements. As they
advanced, he unresistingly yielded and retreated before them, and they
have buried under their sandy billows many hundreds of square miles of
luxuriant cornfields and vineyards and forests.
_Dunes of Gascony._
On the west coast of France, a belt of dunes, varying in width from a
quarter of a mile to five miles, extends from the Adour to the estuary
of the Gironde, and covers an area of three hundred and seventy-five
square miles. When not fixed by vegetable growths, they advance eastward
at a mean rate of about one rod, or sixteen and a half feet, a year. We
do not know historically when they began to drift, but if we suppose
their motion to have been always the same as at present, they would have
passed over the space between the sea coast and their eastern boundary,
and covered the large area above mentioned, in fourteen hundred years.
We know, from written records, that they have buried extensive fields
and forests and thriving villages, and changed the courses of rivers,
and that the lighter particles carried from them by the winds, even
where not transported in sufficient quantities to form sand hills, have
rendered sterile much land formerly fertile.[454] They have also
injuriously obstructed the natural drainage of the maritime districts by
choking up the beds of the streams, and forming lakes and pestilential
swamps of no inconsiderable extent. In fact, so completely do they
embank the coast, that between the Gironde and the village of Mimizan, a
distance of one hundred miles, there are but two outlets for the
discharge of all the waters which flow from the land to the sea; and the
eastern front of the dunes is bordered by a succession of stagnant
pools, some of which are more than six miles in length and breadth.[455]
_The Dunes of Denmark and Prussia._
In the small kingdom of Denmark, inclusive of the duchies of Schleswig
and Holstein, the dunes cover an area of more than two hundred and sixty
square miles. The breadth of the chain is very various, and in some
places it consists only of a single row of sand hills, while in others,
it is more than six miles wide. The general rate of eastward movement of
the drifting dunes is from three to twenty-four feet per annum. If we
adopt the mean of thirteen feet and a half for the annual motion, the
dunes have traversed the widest part of the belt in about twenty-five
hundred years. Historical data are wanting as to the period of the
formation of these dunes and of the commencement of their drifting; but
there is recorded evidence that they have buried a vast extent of
valuable land within three or four centuries, and further proof is found
in the fact that the movement of the sands is constantly uncovering
ruins of ancient buildings, and other evidences of human occupation, at
points far within the present limits of the uninhabitable desert.
Andresen estimates the average depth of the sand deposited over this
area at thirty feet, which would give a cubic mile and a half for the
total quantity.[456]
The drifting of the dunes on the coast of Prussia commenced not much
more than a hundred years ago. The Frische Nehrung is separated from the
mainland by the Frische Haff, and there is but a narrow strip of arable
land along its eastern borders. Hence its rolling sands have covered a
comparatively small extent of dry land, but fields and villages have
been buried and valuable forests laid waste by them. The loose coast row
has drifted over the inland ranges, which, as was noticed in the
description of these dunes on a former page, were protected by a surface
of different composition, and the sand has thus been raised to a height
which it could not have reached upon level ground. This elevation has
enabled it to advance upon and overwhelm woods, which, upon a plain,
would have checked its progress, and, in one instance, a forest of many
hundred acres of tall pines was destroyed by the drifts between 1804 and
1827.
_Control of Dunes by Man._
There are three principal modes in which the industry of man is brought
to bear upon the dunes. First, the creation of them, at points where,
from changes in the currents or other causes, new encroachments of the
sea are threatened; second, the maintenance and protection of them where
they have been naturally formed; and third, the removal of the inner
rows where the belt is so broad that no danger is to be apprehended from
the loss of them.
_Artificial Formation of Dunes._
In describing the natural formation of dunes, it was said that they
began with an accumulation of sand around some vegetable or other
accidental obstruction to the drifting of the particles. A high,
perpendicular cliff, which deadens the wind altogether, prevents all
accumulation of sand; but, up to a certain point, the higher and broader
the obstruction, the more sand will heap up in front of it, and the more
will that which falls behind it be protected from drifting farther. This
familiar observation has taught the inhabitants of the coast that an
artificial wall or dike will, in many situations, give rise to a broad
belt of dunes. Thus a sand dike or wall, of three or four miles in
length, thrown in 1610 across the Koegras, a tide-washed flat between
the Zuiderzee and the North Sea, has occasioned the formation of rows of
dunes a mile in breadth, and thus excluded the sea altogether from the
Koegras. A similar dike, called the Zijperzeedijk, has produced another
scarcely less extensive belt in the course of two centuries.
A few years since, the sea was threatening to cut through the island of
Ameland, and, by encroachment on the southern side and the blowing off
of the sand from a low flat which connected the two higher parts of the
island, it had made such progress, that in heavy storms the waves
sometimes rolled quite across the isthmus. The construction of a
breakwater and a sand dike have already checked the advance of the sea,
and a large number of sand hills has been formed, the rapid growth of
which promises complete future security against both wind and wave.
Similar effects have been produced by the erection of plank fences, and
even of simple screens of wattling and reeds.[457]
_Protection of Dunes._
The dunes of Holland are sometimes protected from the dashing of the
waves by a _revetement_ of stone, or by piles; and the lateral
high-water currents, which wash away their base, are occasionally
checked by transverse walls running from the foot of the dunes to
low-water mark; but the great expense of such constructions has
prevented their adoption on a large scale.[458] The principal means
relied on for the protection of the sand hills are the planting of their
surfaces and the exclusion of burrowing and grazing animals. There are
grasses, creeping plants, and shrubs of spontaneous growth, which
flourish in loose sand, and, if protected, spread over considerable
tracts, and finally convert their face into a soil capable of
cultivation, or, at least, of producing forest trees. Krause enumerates
one hundred and seventy-one plants as native to the coast sands of
Prussia, and the observations of Andresen in Jutland carry the number of
these vegetables up to two hundred and thirty-four.
Some of these plants, especially the _Arundo arenaria_ or _arenosa_, or
_Psamma_ or _Psammophila arenaria_--Klittetag, or Hjelme in Danish, helm
in Dutch, Duenenhalm, Sandschilf, or Huegelrohr in German, gourbet in
French, and marram in English--are exclusively confined to sandy soils,
and thrive well only in a saline atmosphere.[459] The arundo grows to
the height of about twenty-four inches, but sends its strong roots with
their many rootlets to a distance of forty or fifty feet. It has the
peculiar property of nourishing best in the loosest soil, and a sand
shower seems to refresh it as the rain revives the thirsty plants of the
common earth. Its roots bind together the dunes, and its leaves protect
their surface. When the sand ceases to drift, the arundo dies, its
decaying roots fertilizing the sand, and the decomposition of its leaves
forming a layer of vegetable earth over it. Then follows a succession of
other plants which gradually fit the sand hills, by growth and decay,
for forest planting, for pasturage, and sometimes for ordinary
agricultural use.
But the protection and gradual transformation of the dunes is not the
only service rendered by this valuable plant. Its leaves are nutritious
food for sheep and cattle, its seeds for poultry;[460] cordage and
netting twine are manufactured from its fibres, it makes a good material
for thatching, and its dried roots furnish excellent fuel. These useful
qualities, unfortunately, are too often prejudicial to its growth. The
peasants feed it down with their cattle, cut it for rope making, or dig
it up for fuel, and it has been found necessary to resort to severe
legislation to prevent them from bringing ruin upon themselves by thus
improvidently sacrificing their most effectual safeguard against the
drifting of the sands.[461]
In 1539, a decree of Christian III, king of Denmark, imposed a fine upon
persons convicted of destroying certain species of sand plants upon the
west coast of Jutland. This ordinance was renewed and made more
comprehensive in 1558, and in 1569 the inhabitants of several districts
were required, by royal rescript, to do their best to check the sand
drifts, though the specific measures to be adopted for that purpose are
not indicated. Various laws against stripping the dunes of their
vegetation were enacted in the following century, but no active measures
were taken for the subjugation of the sand drifts until 1779, when a
preliminary system of operation for that purpose was adopted. This
consisted in little more than the planting of the _Arundo arenaria_ and
other sand plants, and the exclusion of animals destructive to these
vegetables.[462] Ten years later, plantations of forest trees, which
have since proved so valuable a means of fixing the dunes and rendering
them productive, were commenced, and have been continued ever
since.[463] During this latter period, Bremontier, without any knowledge
of what was doing in Denmark, experimented upon the cultivation of
forest trees on the dunes of Gascony, and perfected a system, which,
with some improvements in matters of detail, is still largely pursued
on those shores. The example of Denmark was soon followed in the
neighboring kingdom of Prussia, and in the Netherlands; and, as we shall
see hereafter, these improvements have been everywhere crowned with most
flattering success.
Under the administration of Reventlov, a little before the close of the
last century, the Danish Government organized a regular system of
improvement in the economy of the dunes. They were planted with the
arundo and other vegetables of similar habits, protected against
trespassers, and at last partly covered with forest trees. By these
means much waste soil has been converted into arable ground, a large
growth of valuable timber obtained, and the further spread of the
drifts, which threatened to lay waste the whole peninsula of Jutland, to
a considerable extent arrested.
In France, the operations for fixing and reclaiming the dunes--which
began under the direction of Bremontier about the same time as in
Denmark, and which are, in principle and in many of their details,
similar to those employed in the latter kingdom--have been conducted on
a far larger scale, and with greater success, than in any other country.
This is partly owing to a climate more favorable to the growth of
suitable forest trees than that of Northern Europe, and partly to the
liberality of the Government, which, having more important landed
interests to protect, has put larger means at the disposal of the
engineers than Denmark and Prussia have found it convenient to
appropriate to that purpose. The area of the dunes already secured from
drifting, and planted by the processes invented by Bremontier and
perfected by his successors, is about 100,000 acres.[464] This amount of
productive soil, then, has been added to the resources of France, and a
still greater quantity of valuable land has been thereby rescued from
the otherwise certain destruction with which it was threatened by the
advance of the rolling sand hills.
The improvements of the dunes on the coast of West Prussia began in
1795, under Soeren Bjoern, a native of Denmark, and, with the exception of
the ten years between 1807 and 1817, they have been prosecuted ever
since. The methods do not differ essentially from those employed in
Denmark and France, though they are modified by local circumstances,
and, with respect to the trees selected for planting, by climate. In
1850, between the mouth of the Vistula and Kahlberg, 6,300 acres,
including about 1,900 acres planted with pines and birches, had been
secured from drifting; between Kahlberg and the eastern boundary of
West-Prussia, 8,000 acres; and important preliminary operations had been
carried on for subduing the dunes on the west coast.[465]
_Trees suited to Dune Plantations._
The tree which has been found to thrive best upon the sand hills of the
French coast, and at the same time to confine the sand most firmly and
yield the largest pecuniary returns, is the maritime pine, _Pinus
maritima_, a species valuable both for its timber and for its resinous
products. It is always grown from seed, and the young shoots require to
be protected for several seasons, by the branches of other trees,
planted in rows, or spread over the surface and staked down, by the
growth of the _Arundo arenaria_ and other small sand plants, or by
wattled hedges. The beach, from which the sand is derived, has been
generally planted with the arundo, because the pine does not thrive well
so near the sea; but it is thought that a species of tamarisk is likely
to succeed in that latitude even better than the arundo. The shade and
the protection offered by the branching top of this pine are favorable
to the growth of deciduous trees, and, while still young, of shrubs and
smaller plants, which contribute more rapidly to the formation of
vegetable mould, and thus, when the pine has once taken root, the
redemption of the waste is considered as effectually secured.
In France, the maritime pine is planted on the sands of the interior as
well as on the dunes of the sea coast, and with equal advantage. This
tree resembles the pitch pine of the Southern American States in its
habits, and is applied to the same uses. The extraction of turpentine
from it begins at the age of about twenty years, or when it has attained
a diameter of from nine to twelve inches. Incisions are made up and down
the trunk, to the depth of about half an inch in the wood, and it is
insisted that if not more than two such slits are cut, the tree is not
sensibly injured by the process. The growth, indeed, is somewhat
checked, but the wood becomes superior to that of trees from which the
turpentine is not extracted. Thus treated, the pine continues to
flourish to the age of one hundred or one hundred and twenty years, and
up to this age the trees on a hectare yield annually 350 kilogrammes of
essence of turpentine, and 280 kilogrammes of resin, worth together 110
francs. The expense of extraction and distillation is calculated at 44
francs, and a clear profit of 66 francs per hectare, or more than five
dollars per acre, is left.[466] This is exclusive of the value of the
timber, when finally cut, which, of course, amounts to a very
considerable sum.
In Denmark, where the climate is much colder, hardier conifers, as well
as the birch and other northern trees, are found to answer a better
purpose than the maritime pine, and it is doubtful whether this tree
would be able to resist the winter on the dunes of Massachusetts.
Probably the pitch pine of the Northern States, in conjunction with some
of the American oaks, birches, and poplars, and especially the robinia
or locust, would prove very suitable to be employed on the sand hills of
Cape Cod and Long Island. The ailanthus, now coming into notice as a
sand-loving tree, may, perhaps, serve a better purpose than any of them.
_Extent of Dunes in Europe._
The dunes of Denmark, as we have seen, cover an area of two hundred and
sixty square miles, or one hundred and sixty-six thousand acres; those
of the Prussian coast are vaguely estimated at from eighty-five to one
hundred and ten thousand acres; those of Holland at one hundred and
forty thousand acres;[467] those of Gascony at about three hundred
thousand acres.[468] I do not find any estimate of their extent in other
provinces of France, in the duchies of Schleswig and Holstein, or in the
Baltic provinces of Russia, but it is probable that the entire quantity
of dune land upon the eastern shores of the Atlantic and the Baltic does
not fall much short of a million of acres.[469] This vast deposit of sea
sand extends along the coast for a distance of several hundred miles,
and from the time of the destruction of the forests which covered it, to
the year 1789, the whole line was rolling inward and burying the soil
beneath it, or rendering the fields unproductive by the sand which
drifted from it. At the same time, as the sand hills moved eastward, the
ocean was closely following their retreat and swallowing up the ground
they had covered, as fast as their movement left it bare.
Planting the dunes has completely prevented the surface sands from
blowing over the soil to the leeward of the plantations, and though it
has not, in all cases, arrested the encroachments of the sea, it has so
greatly retarded the rapidity of their advance, that sandy coasts, when
once covered with forests, may be considered as substantially secure, so
long as proper measures are taken for the protection of the woods.
_Dune Vineyards of Cap Breton._
In the vicinity of Cap Breton in France, a peculiar process is
successfully employed, both for preventing the drifting of dunes, and
for rendering the sands themselves immediately productive; but this
method is applicable only in exceptional cases of favorable climate and
exposure. It consists in planting vineyards upon the dunes, and
protecting them by hedges of broom, _Erica scoparia_, so disposed as to
form rectangles about thirty feet by forty. The vines planted in these
enclosures thrive admirably, and the grapes produced by them are among
the best grown in France. The dunes are so far from being an unfavorable
soil for the vine, that fresh sea-sand is regularly employed as a
fertilizer for it, alternating every other season with ordinary manure.
The quantity of sand thus applied every second year, raises the surface
of the vineyard about four or five inches. The vines are cut down every
year to three or four shoots, and the raising of the soil rapidly
covers the old stocks. As fast as buried, they send out new roots near
the surface, and thus the vineyard is constantly renewed, and has always
a youthful appearance, though it may have been already planted a couple
of generations. This practice is ascertained to have been followed for
two centuries, and is among the oldest well-authenticated attempts of
man to resist and vanquish the dunes.[470]
_Removal of Dunes._
The artificial removal of dunes, no longer necessary as a protection,
does not appear to have been practised upon a large scale except in the
Netherlands, where the numerous canals furnish an easy and economical
means of transporting the sand, and where the construction and
maintenance of sea and river dikes, and of causeways and other
embankments and fillings, create a great demand for that material. Sand
is also employed in Holland, in large quantities, for improving the
consistence of the tough clay bordering upon or underlying diluvial
deposits, and for forming an artificial soil for the growth of certain
garden and ornamental vegetables. When the dunes are removed, the ground
they covered is restored to the domain of industry; and the quantity of
land, recovered in the Netherlands by the removal of the barren sands
which encumbered it, amounts to hundreds and perhaps thousands of
acres.[471]
_Inland Sand Plains._
The inland sand plains of Europe are either derived from the drifting of
dunes or other beach sands, or consist of diluvial deposits. As we have
seen, when once the interior of a dune is laid open to the wind, its
contents are soon scattered far and wide over the adjacent country, and
the beach sands, no longer checked by the rampart which nature had
constrained them to build against their own encroachments, are also
carried to considerable distances from the coast. Few regions have
suffered so much from this cause in proportion to their extent, as the
peninsula of Jutland. So long as the woods, with which nature had
planted the Danish dunes, were spared, they seem to have been
stationary, and we have no historical evidence, of an earlier date than
the sixteenth century, that they had become in any way injurious. From
that period, there are frequent notices of the invasions of cultivated
grounds by the sands; and excavations are constantly bringing to light
proof of human habitation and of agricultural industry, in former ages,
on soils now buried beneath deep drifts from the dunes and beaches of
the sea coast.[472]
Extensive tracts of valuable plain land in the Netherlands and in France
have been covered in the same way with a layer of sand deep enough to
render them infertile, and they can be restored to cultivation only by
processes analogous to those employed for fixing and improving the
dunes.[473] Diluvial sand plains, also, have been reclaimed by these
methods in the Duchy of Austria, between Vienna and the Semmering ridge,
in Jutland, and in the great champaign country of Northern Germany,
especially the Mark Brandenburg, where artificial forests can be
propagated with great ease, and where, consequently, this branch of
industry has been pursued on a great scale, and with highly beneficial
results, both as respects the supply of forest products and the
preparation of the soil for agricultural use.
As a general rule, inland sands are looser, dryer, and more inclined to
drift, than those of the sea coast, where the moist and saline
atmosphere of the ocean keeps them always more or less humid and
cohesive. No shore dunes are so movable as the medanos of Peru described
in a passage quoted from Poeppig on a former page, or as the sand hills
of Poland, both of which seem better entitled to the appellation of sand
waves than those of the Sahara or of the Arabian desert. The sands of
the valley of the Lower Euphrates--themselves probably of submarine
origin, and not derived from dunes--are advancing to the northwest with
a rapidity which seems fabulous when compared with the slow movement of
the sand hills of Gascony and the Low German coasts. Loftus, speaking of
Niliyya, an old Arab town a few miles east of the ruins of Babylon, says
that, "in 1848, the sand began to accumulate around it, and in six
years, the desert, within a radius of six miles, was covered with
little, undulating domes, while the ruins of the city were so buried
that it is now impossible to trace their original form or extent."[474]
Loftus considers this sand flood as the "vanguard of those vast drifts
which, advancing from the southeast, threaten eventually to overwhelm
Babylon and Baghdad."
An observation of Layard, cited by Loftus, appears to me to furnish a
possible explanation of this irruption. He "passed two or three places
where the sand, issuing from the earth like water, is called
'Aioun-er-rummal,' sand springs." These "springs" are very probably
merely the drifting of sand from the ancient subsoil, where the
protecting crust of aquatic deposit and vegetable earth has been broken
through, as in the case of the drift which arose from the upturning of
an oak mentioned on a former page. When the valley of the Euphrates was
regularly irrigated and cultivated, the underlying sands were bound by
moisture, alluvial slime, and vegetation; but now, that all improvement
is neglected, and the surface, no longer watered, has become parched,
powdery, and naked, a mere accidental fissure in the superficial stratum
may soon be enlarged to a wide opening, that will let loose sand enough
to overwhelm a province.
_The Landes of Gascony._
The most remarkable sand plain of France lies at the southwestern
extremity of the empire, and is generally known as the Landes, or
heaths, of Gascony. Clave thus describes it: "Composed of pure sand,
resting on an impermeable stratum called _alios_, the soil of the Landes
was, for centuries, considered incapable of cultivation. Parched in
summer, drowned in winter, it produced only ferns, rushes, and heath,
and scarcely furnished pasturage for a few half-starved flocks. To crown
its miseries, this plain was continually threatened by the encroachments
of the dunes. Vast ridges of sand, thrown up by the waves, for a
distance of more than fifty leagues along the coast, and continually
renewed, were driven inland by the west wind, and, as they rolled over
the plain, they buried the soil and the hamlets, overcame all
resistance, and advanced with fearful regularity. The whole province
seemed devoted to certain destruction, when Bremontier invented his
method of fixing the dunes by plantations of the maritime pine."[475]
Although the Landes had been almost abandoned for ages, they show
numerous traces of ancient cultivation and prosperity, and it is
principally by means of the encroachments of the sands that they have
become reduced to their present desolate condition. The destruction of
the coast towns and harbors, which furnished markets for the products of
the plains, the damming up of the rivers, and the obstruction of the
smaller channels of natural drainage by the advance of the dunes, were
no doubt very influential causes; and if we add the drifting of the sea
sand over the soil, we have at least a partial explanation of the
decayed agriculture and diminished population of this great waste. When
the dunes were once arrested, and the soil to the east of them was felt
to be secure against invasion by them, experiments, in the way of
agricultural improvement, by drainage and plantation, were commenced,
and they have been attended with such signal success, that the complete
recovery of one of the dreariest and most extensive wastes in Europe may
be considered as both a probable and a near event.[476]
_The Belgian Campine._
In the northern part of Belgium, and extending across the confines of
Holland, is another very similar heath plain, called the Campine. This
is a vast sand flat, interspersed with marshes and inland dunes, and,
until recently, considered wholly incapable of cultivation. Enormous
sums have been expended in reclaiming it by draining and other familiar
agricultural processes, but without results at all proportional to the
capital invested. In 1849, the unimproved portion of the Campine was
estimated at little less than three hundred and fifty thousand acres.
The example of France has prompted experiments in the planting of trees,
especially the maritime pine, upon this barren waste, and the results
have been such as to show that its sands may both be fixed and made
productive, not only without loss, but with positive pecuniary
advantage.[477]
_Sands and Steppes of Eastern Europe._
There are still unsubdued sand wastes in many parts of interior Europe
not familiarly known to tourists or even geographers. "Olkuez and
Schiewier in Poland," says Naumann, "lie in true sand deserts, and a
boundless plain of sand stretches around Ozenstockau, on which there
grows neither tree nor shrub. In heavy winds, this plain resembles a
rolling sea, and the sand hills rise and disappear like the waves of the
ocean. The heaps of waste from the Olkuez mines are covered with sand to
the depth of four fathoms."[478] No attempts have yet been made to
subdue the sands of Poland, but when peace and prosperity shall be
restored to that unhappy country, there is no reasonable doubt that the
measures, which have proved so successful on similar formations in
Germany, may be employed with advantage in the Polish deserts.
There are sand drifts in parts of the steppes of Russia, but in general
the soil of those vast plains is of a different, though very varied,
composition, and is covered with vegetation. The steppes, however, have
many points of analogy with the sand plains of Northern Germany, and if
they are ever fitted for civilized occupation, it must be by the same
means, that is, by planting forests. It is disputed whether the steppes
were ever wooded. They were certainly bare of forest growth at a very
remote period; for Herodotus describes the country of the Scythians
between the Ister and the Tanais as woodless, with the exception of the
small province of Xylaea between the Dnieper and the Gulf of Perekop.
They are known to have been occupied by a large nomade and pastoral
population down to the sixteenth century, though these tribes are now
much reduced in numbers. The habits of such races are scarcely less
destructive to the forest than those of civilized life. Pastoral tribes
do not employ much wood for fuel or for construction, but they
carelessly or recklessly burn down the forests, and their cattle
effectually check the growth of young trees wherever their range
extends.
At present, the furious winds which sweep over the plains, the droughts
of summer, and the rights and abuses of pasturage, constitute very
formidable obstacles to the employment of measures which have been
attended with so valuable results on the sand wastes of France and
Germany. The Russian Government has, however, attempted the wooding of
the steppes, and there are thriving plantations in the neighborhood of
Odessa, where the soil is of a particularly loose and sandy
character.[479] The trees best suited to this locality, and, as there is
good reason to suppose, to sand plains in general, is the _Ailanthus
glandulosa_, or Japan varnish tree.[480] The remarkable success which
has crowned the experiments with the ailanthus at Odessa, will, no
doubt, stimulate to similar trials elsewhere, and it seems not
improbable that the arundo and the maritime pine, which have fixed so
many thousand acres of drifting sands in Western Europe, will be,
partially at least, superseded by the tamarisk and the varnish tree.
_Advantages of Reclaiming the Sands._
If we consider the quantity of waste land which has been made productive
by the planting of the sand hills and plains, and the extent of fertile
soil, the number of villages and other human improvements, and the value
of the harbors, which the same process has saved from being buried under
the rolling dunes, and at last swallowed up forever by the invasions of
the sea, we shall be inclined to rank Bremontier and Reventlov among the
greatest benefactors of their race. With the exception of the dikes of
the Netherlands, their labors are the first deliberate and direct
attempts of man to make himself, on a great scale, a geographical power,
to restore natural balances which earlier generations had disturbed, and
to atone, by acts guided by foreseeing and settled purpose, for the
waste which thoughtless improvidence had created.
_Government Works._
There is an important political difference between these latter works
and the diking system of the Netherlandish and German coasts. The dikes
originally were, and in modern times very generally have been, private
enterprises, undertaken with no other aim than to add a certain quantity
of cultivable soil to the former possessions of their proprietor, or
sometimes of the state. In short, with few exceptions, they have been
merely a pecuniary investment, a mode of acquiring land not economically
different from purchase. The planting of the dunes, on the contrary, has
always been a public work, executed, not with the expectation of reaping
a regular direct percentage of income from the expenditure, but dictated
by higher views of state economy--by the same governmental principles,
in fact, which animate all commonwealths in repelling invasion by
hostile armies, or in repairing the damages that invading forces may
have inflicted on the general interests of the people. The restoration
of the forests in the southern part of France, as now conducted by the
Government of that empire, is a measure of the same elevated character
as the fixing of the dunes. In former ages, forests were formed or
protected simply for the sake of the shelter they afforded to game, or
for the timber they yielded; but the recent legislation of France, and
of some other Continental countries, on this subject, looks to more
distant as well as nobler ends, and these are among the public acts
which most strongly encourage the hope that the rulers of Christendom
are coming better to understand the true duties and interests of
civilized government.