Genesis and Development of Sand Forma-
tions on Marine Coasts
Pehr Olsson-Setfer, Ph. D.
Sand formations in general 10
Genesis and development 14
Sandy beaches ; 20
Their sculptural forms 27
Polygenetic origin of a dune-complex 32
Sand fields near the coasts 33
Conditions for plant life 34
Genesis and Development of Sand Forma-
tions on Marine Coasts.
Pehr Olsson-Seffer, Ph. D.
Since the year 1891 I have been studying the sand formations on
marine coasts and their flora and vegetation. During the years 1891
to 1899 my investigations were confined to the coasts of the Baltic.
The last mentioned year I also investigated the dunes on the Danish
North Sea Coast, in Holland, and in certain parts of Scotland -and
France. In 1900 1901 observations were made in Southern Sweden,
in various places in Denmark, on the South Coast of England, in
Southern Italy, at Port Said, in Egypt, in Western Australia, and in
Various coasts in Australia, from Central Queensland to Western
Australia, through New South Wales, Victoria and S'outh Australia,
were visited and re-visited during 1902. In New Zealand only part
of the North Cape was made subject to a brief and hurried visit and
notes of the strand vegetation were taken during stays in various
islands of the Pacific, such as the New Hebrides, Solomon Islands,
S'amoa and Hawaii.
On the Pacific coast of North America the dunes at San Francisco
and Monterey Bay were studied in 1903 05. During 1905, I also
visited the coastal sands at Santa Barbara and Santa Monica, in
Southern California, as well as several sand dune districts on the Pacific
coast of Mexico, such as Salina Cruz, in the innermost part of the
Gulf of Tehuantepec, and San Benito, near the Guatemalan border.
The extensive sand dunes near Vera Cruz, in Mexico, on the Gulf side,
were investigated in August of the same year. In December, sand
strands were studied at Mazatlan, a Mexican port on the eastern shore
of the Gulf of California, as well as at San Bias in Mexico and
Champerico in Guatemala.
The large field these observations cover have given me ample oppor-
tunity to make comparisons of the coastal sands in various climates
Library Publications. 1
10 GENESIS AND DEVELOPMENT
and under the most different natural conditions. In the present paper
I propose to deal briefly with some of the marine sand formations, their
origin, development, and classification, so far as it is necessary to
demonstrate the most fundamental facts of this subject and the principles
on which they are based. I also give short comments upon the principal
dune districts visited in the course of my studies.
To PROFESSOR WM. E. DUDLEY of Leland Stanford Junior University
I am greatly indebted for many favors in connection with my work,
and I have also to express my acknowledgments to DR. JOHAN ERIKSON,
Karlskrona, Sweden, DR. K. K. KTJPPFER, Eiga, Eussia, DR. W. J.
SMITH, Leeds, England, B. H. WOODWARD, ESQ., F. E. G. S'., Perth,
Western Australia, C. E. BENBOW, ESQ., C. E., Sidney, New South
Wales, DR. L. COCKAYNE, Christchurch, New Zealand, and various other
persons, who have assisted me with information and photographs.
SAND FORMATIONS IN GENERAL.
When we consider the factors which have given rise to the formation
of sand, the principal ones are the atmospheric and the aqueous agen-
cies, which also are the most important in transportation and distribu-
tion of the material. It will therefore be convenient to distinguish
between the following general classes of sand deposits:
1. Eolian sand formations.
2. Neptunian sand formations.
The term eolian in this connection was to my knowledge first used in
1835 by R. J. Nelson *) and it signifies the agency of wind. Eolian
deposits exhibit a different composition and structure from the nep-
tunian, those sediments which have been built up by the water. The
transporting power of water being considerably greater than that of
wind, it necessarily follows that the material moved by aqueous agencies
varies more in size than that which is carried by the wind. We will
have ample opportunity to note this difference as we proceed in our
No rational nomenclature for the different kinds of soil constituents,
neither of inorganic nor of organogenetic origin, has yet been agreed
upon, and it will thus be necessary to give here the designations which
have been used during my observations in the field.
1) Proceedings of Geological Society of London, Vol. II., p. 160.
OF SAND FORMATIONS ON MABINE COASTS. 11
Diameter of grains in millimeters.
Fine dust or silt 0.02 0.03
Medium dust or silt 0'. 03 . 05
Coarse dust or silt . 05 . 1
Finest sand 0.1- 0.2
Fine sand 0.2- 0.3
Medium sand 0.3 0.5
Coarse sand 0.5- 1
Grits 1 2
Gravel 2 4
Coarse gravel 4 6
Pebbles 6 - 10
Coarse pebbles 10 20
S'hingle 20 - 50
Stones 50 250
Boulders 250 Upwards.
The limit of the coarseness of sand grains is here considered as
0.2 0.1 mm. When the grains are finer than 0.05 mm., the soil 1 )
has lost the physical properties of sand. It does not feel gritty to the
fingers, and if it is dropped on a level and hard surface the grains
will not separate but congregate in small heaps. It needs several minutes
to sink in water to the bottom of a test tube. When over 0.05 mm.
the soil has, however, more of the characteristics of real sand. It is
then gritty, when pulverized between the fingers. If scattered dry, it
will separate into grains conspicuous to the naked eye. When mixed
with water in the test tube, it sinks rapidly, usually in less than one
minute, and it is to a noticeable degree conductive of water. It is
difficult in practice to draw the lower limit for sand of a certain coarse-
ness, because the soil is more or less mixed. On account of the difference
in specific gravity of the grains many samples contain grains of different
In the above table the measurements of diameter refer to the average
sized grains in each class. The term sand has here been applied to soil,
the grains of which are under 1 mm., while a coarseness of 1 2 mm.
has entitled the soil to the name of grits. When the chief ingredient
is particles larger than 2 mm. and below 6 mm. the soil has been
designated as gravel.
Common sand is 2,100 times heavier than dry air, while only 2.5 to
1) The term soil is in this paper used in its broadest technical sense to
designate the loose material constituting the disintegrated superficial layer?
of the earth's surface.
12 GENESIS AND DEVELOPMENT
2.7 times heavier than water. A strong breeze is therefore required
to raise the dust of a road for transportation by the wind, and a still
stronger breeze to raise quartz sand; while large pebbles are seldom
lifted from the ground. The winds are also extremely irregular in their
movements and action. The trades over the ocean have a higher degree
of uniformity than other winds, but the velocity is generally only 10 to
20 km. an hour. The winds that do the chief part of eolian geological
work are those of storms, whose velocity per hour is from 50 to more
than 100 km. Such winds are very unsteady in their action, blowing
in gusts, in which there is a sudden increase to a maximum and a slower
decline to a minimum. There is no constancy in force even for an
hour, and no uniformity over large areas.
The transporting power of water, on the contrary, is very great;
strong waves or torrents being able to move rocks weighing hundreds
of tons. By experiments it has been found that a current moving at
the rate of 25 cm. per second is able to carry fine sand, while a velocity
of 50 cm. is sufficient to transport coarse gravel. The action of water
is, moreover, very constant as a rule, and the waves on a long coast,
for instance, exert their uniform influence over a considerable area.
We must not, however, confound the transporting power of these
agencies, wind and water, with their erosive power. In one case it is
the weight, in the other the cohesion, that offers the resistance. Neither
wind nor water has any greater erosive power by itself. It is where
mud or sand is carried by the wind or water, that a friction arises which
removes the particles, loosened by decaying and other processes, from
their original place.
Water is efficient in denudation by 1) dissolving of rocks, 2) trans-
portation of the material which assists in the eroding work, and 3) car-
rying away the debris. The analogous functions of wind are : 1 ) trans-
portation of the material which triturates and erodes all substances in
its way, and 2) distribution.
A water current when overloaded with solids will deposit ; when under-
loaded it will erode. A sandladen wind always both cuts and deposits.
Dry sand, wind borne, is an unobtrusive agent, working silently but
diligently on the task of paring away the surface. It leaves no monu-
ments to show the magnitude of its results, as does denudation by
water. Kiver beds and sandbanks are examples of the excavating and
building up through sedimentation by the water.
Water is a base leveler in the sense that it transfers material from
higher places to lower ; but where it erodes, it always works more rapidly
OF SAND FORMATIONS ON MARINE COASTS. 13
along the lowest lines and leaves ridges and islands, by which its results
can be measured. The water currents have, at any one spot, but a
single direction, and the furrows and mouldings of the curved surface
are grouped in a single system; but the wind may blow in many direc-
tions, and produces series of corresponding complexity.
It is a well known law in dynamical geology that all sedimentary
deposits are stratified. This lamination is somewhat different when
caused by eolian influence than when resulting from the action of water.
The sorting power of water is more distinct than that of wind, because
of the greater regularity of water currents.
As a consequence of the rapid variations to which the transporting
power of the wind is subjected, eolian deposits are generally straticulate,
finer and coarser laminae succeeding each other in indefinite alterations.
But there is not the evenness of layer characterizing aqueous deposits,
even when made over level surfaces. To make beds without straticula-
tion would require winds without these irregularities, little varying
and long continuing, such as few regions have, except those that have
winds of too moderate velocity to carry any but the finest particles.
The gusty winds also tend, by their denuding as well as transporting
work, to make wavy rather than plane upper surfaces. Moreover, any
barrier, as a projecting rock or a stump, or a tuft of grasses, causes
a heaping of the sands around the obstacle, and makes curving surfaces
in the heaps, owing to the eddies in the air.
We must here consider the following kinds of lamination :
3) flow- and plunge
Horizontal strata are developed in water only, especially in non-
running water. Each lamination here represents different conditions
of the water in which the sediment is deposited, and oblique lamination
or cross-bed structure is a result of deposition by rapid shifting currents,
carrying material of varying coarseness. While strictly horizontal lami-
nation cannot be formed by winds, obliquely laminated layers occur in
eolian deposits, indicating that somewhat regular winds have blown
for some time.
This cross-bed structure of the sediments is characterized by a lami-
nation in a plane, oblique to the horizon. It results from the pushing
along of the sand by currents, causing at first a little elevation, and
14 GENESIS AND DEVELOPMENT
then the deposition of successive layers over the front slope of the
elevation. If the currents are transient, alternating with conditions of
still water, the obliquely laminated beds will alternate with others
horizontally laminated. Such laminations may be due to changes of
wind or tide, or to the periodical or occasional fluctuations in the
volume of rivers.
The flow- and plunge structure has been caused by plunging waves
accompanying the rapid flow of a current, through which action the
oblique laminae have been broken up into short, wavelike parts. This
lamination bears evidence of being the result of an agent less variable,
and moving slower than that which has formed the irregular structure
so characteristic of most eolian deposits.
THE DEVELOPMENT OF COASTAL SAND FORMA-
The sand formations, which will come under discussion in connection
with our present subject, all have their origin ultimately due to the
action of the sea. We can conveniently divide these marine formations
into following groups:
1. Submarine sand banks.
2. Sandy islands.
3. Sandy spits.
4. Sandy beaches.
1. The first class of formations or submarine sand banks are formed
by the combined action of streams and the waves of the sea, or by the
latter alone. Most of these accumulations contain more or less of river
detritus, which is brought .down to the sea during floods. The ocean's
waves and currents meet it as the tide sets in, with a counter action,
or one from the sea landward; between the two the waters, as they
lose their velocity, drop the detritus over the bottom. Where the river
is very large and the tides feeble, the banks and reefs extend far out
to sea. Where the tide is strong, sand bars are formed, and the stronger
the tide, the closer are the sand bars to the coast. Where the stream
is small, the ocean may throw a sand bank quite across its mouth, so
that there may be no egress to the river waters except by percolation
through the sand; or, if a channel is left open, it may be only a
In other cases the material constituting the sand banks is derived
OF SAND FOBMATIONS ON MARINE COASTS. 15
from the land through the erosion and transportation of waves and cur-
rents. This material consists usually of coarse or fine sand, but may
include some beds of pebbles or stones when the currents are strong.
The stratification is comparatively regular and nearly horizontal.
2. When the accumulations just spoken of increase under wave-
action in shallow water, until they rise above low tide level, they form
3. S'andy spits are the lengthwise extensions of beaches formed
through the waves throwing material on shoals at the turn of the shore.
Their composition is similar to that of the above formations.
4. Sandy beaches are made by material thrown up on the shore by
waves. This material is coarse where the waves break heavily, because,
although trituration is going on at all times, the powerful wave action
and the undertow carry off the finer material seaward into the offshore
shallow waters, where it settles over the bottom or is distributed by
currents. It is fine where the waves are gentle in movement, as in
sheltered bays, or estuaries, the triturated material accumulating in
such places near where it is made.
As soon as the accumulations of eroded material have increased so
far as to rise above the surface of the water, the further growth is
similar to that of the beaches, and from these latter other coastal sand
formations such as dunes and sand fields are developed by the influence
of wind. The development of these two kinds of eolian sand formations
will be discussed in detail under separate headings.
It is a well known fact that the salts of seawater hasten the deposi-
tion of sediments, and consequently the shape and formation of sand
banks and beaches on marine coasts is somewhat different from those
of corresponding freshwater deposits. I have not been able to ascertain
whether the seawater acts differently on siliceous material than on clay
sediments. We usually find that deposits nearer the shore or the source
of the material contain more silica than further out in the deep water,
but this may depend on the usually large size and the greater weight
of the siliceous fragments, which causes them to sink sooner.
In order to determine this, experiments were conducted in the labora-
tory. I tried ordinary seawater from the Baltic, of a salinity of 0.6%
measured with areometer, and artificially prepared solutions of resp.
2.7% and 3% corresponding to the salt content of ocean water. Finely
ground clay and beach sand were stirred in the water samples, and
allowed to settle in vessels 25 cm., 50 cm., and 100 cm. deep, all being
42 cm. in diameter. The following results were obtained:
GENESIS AND DEVELOPMENT
Depth of vessel.
No. of vessel.
Hours for settling-.
As will be seen from this table, silica in all cases both in salt and
fresh water settled faster than clay. Whether this fact was merely a
result of a greater weight of the siliceous particles, or whether other
factors influenced the sedimentation, I was unable to decide. At all
events it was evident that the salt produces a considerable flocculation
in the water. The primary cause of the growth of the deposit in water
is sedimentation, but in many cases the rising of the level of the coast-
line has to be taken into consideration as a secondary factor. It is
often difficult to determine to what extent the rate of growth of a
deposit is due to one of these factors or the other. Especially is this
the case on a low coast, where the growth always takes place more rap-
idly than on a steeper shore. The horizontal growth of the deposit is
also much greater on coasts protected by islands than on open coasts
with deep water, where the material is more easily carried away.
With regard to the position of the marine sediments it will be
noticed that they are apparently horizontal, and the tendency is to level
the beds through filling all depressions. The coarser sediments are
always nearer the shore in comparatively narrow lines, parallel to the
coast, whereas the finer sediments are spread over a larger area further
off the shore. Banks and beaches are always sloping gently seawards,
and they are, perhaps, somewhat steeper on marine coasts than on fresh
water shores, general conditions being equal.
OF SAND FORMATIONS ON MARINE COASTS. 17
We have here also to consider the peculiar results of the wave-action
of both water and wind, which are generally known by the name of
ripple marks, a term introduced by Lyell,
The phenomena of rippling have in recent times had a careful ob-
server in Cornish, and the following statements are principally based
on his studies of this problem, although the laws and facts presented by
him have been subjected to a detailed investigation in the field by the
present writer, and I am able in a few instances to bring forward some
evidence in support of Cornish's theories.
The same factor which causes the wave formation of water has a
similar influence on the sand. The resulting wave-forms or ripples
consist of alternate ridges and furrows made by the wash of the waters
over a sand flat or beach, or over the bottom within soundings. They
may also be made by the action of wind on a surface of sand. When
the ripples are formed through the action of water we can distinguish
1. wave formed ripples,
2. current made ripple marks, and
3. tidal sand ripples.
The parallel formations of wind made sand waves are
4. eolian sand ripples, and
Comparing waves of water with those of a more solid medium, such
as sand, we find that, while in the case of water two kinds of waves,
oscillatory and wind driven, can be recognized, wave formation in sand
is always connected with onward movement of the particles. In oscil-
latory waves the water particles on the crest are moving forward, but
those in the trough backward with the same velocity and consequently
the water body as such does not move in either direction. It is cus-
tomary to express this motion by saying that the particles move in a
circular orbit. When the waves are wind driven the forward velocity
is greater than the backward, and a bodily movement of the water in
the direction of the acting force is the result. The curve described by
the water particles is still closed, having a trochoidal form. In the case
of drifting sand the particles from the crest of the wave move in curves,
which are open.
Wave-formed sand ripples have an unsymmetrical form, always facing
with the waves. Current made ripple marks are similarly unsymmetrical
in form, the sheltered side being steeper, and the front facing the cur-
18 GENESIS AND DEVELOPMENT
rent. Tidal sand ripples, first described by Reynolds*) and later by
Cornish 2 ) occur in estuaries and also on some shores where the sand
is exposed to waves as well as currents. Cornish is of the opinion that
they do not require for their formation any cooperation between flood
and ebb currents. The size and form of these ripples is constantly
changing with the variations in the tide. Cornish describes this in the
"At neap tides the sands were nearly smooth, and as the tides in-
creased the tidal sand ripples appeared, short and relatively steep. The
amplitude increased steadily, the average wave-length also increased,
apparently by elimination of some of the ridges. When the highest
spring tide was passed the amplitude rapidly diminished, the wave-
length remaining nearly, but not quite constant, and the mean sand
level remaining practically unchanged."
Tidal sand ripples sometimes attain a considerable size, Cornish
giving the wave length of from 1 to 6.7 m. I have often noticed a finer
rippling of the proper tidal ripples, and in two instances, on the east-
ern coast of Australia, I observed the tidal sand ripples crossed by
another set of large ripples. These were formed by a sudden change of
the direction of the tide current through the overflow of a neighboring
stream. Both these sets of wave formations were then beautifully
rippled in the usual way by little current marks, facing almost trans-
versely the second set of larger ripples. Cornish attributes the forma-
tion of current marks to the pulsation of the fluid rather than to the
In the formation of eolian sand ripples it is the heterogeneity of the
material which is of the greatest importance. The sorting action of
wind is remarkable, and it is evident at the first glance on a group of
ripples that the heavier grains always constitute the crest, the lighter
the trough. A moderate range of sizes of grains seems therefore most
favorable to the formation of ripples.
Darwin 3 ) remarked the uniformity of pattern in the ripples formed
by wind, which uniformity, as a rule, is absent from ripples made in
1) Reports of committee appointed to investigate the action of waves
and currents on the beds and foreshores of estuaries by means of working
models. British Association for Advancement of Science, Reports '89,
2) The formation of wave surfaces in sand. Scot. Geogr. Mag. 17:
3) G. H. Darwin: On ripple mark. Proceedings of Royal Society,
London, vol. 36. 1883.
OF SAND FOBMATIONS ON MARINE COASTS.
water. When the wind blows upon the sand, a winnowing process takes
place, the finer particles being carried farther away than the coarser
material, which then produces the ridges of heavier grains mentioned
above. This uniformity of pattern connected with the fact that the
wave length increases with the time during which the force of the
wind is acting upon the sand led Cornish * ) to advance the following
law for rippling by wind: The rippling takes place when the eddy
in the lee of the larger grains is of sufficient strength to lift the smaller.
The systematically corrugated surface of loose sand can only be
produced by a wind that is not too strong for the larger grains to remain
on the ground. If the breeze is too strong no rippling whatever takes
place as all the particles of sand then will be transported. If on the
other hand the wind is too weak to make an eddy, the sand moves slowly,
but does not form ripples.
The height of the waves and their distances from each other is larger
the larger the grains are. The movement of the waves is of different
rapidity and depends on the force of wind and the size of the grains.
It is naturally more rapid when the wind is stronger and the sand fine.
Following results were obtained by the author from a number of meas-
urements of amplitude or height of ridge and wave-length of sand
ripples made by wind on the coast of West Australia. All measurements
are given in millimeters.
Number of measure
ments of which
sample is average.
These measurements serve to support the results obtained by Cornish
and the law advanced by him, that amplitude and wave-length increase
1 ) On the formation of sand dunes. Geographical Journal, vol. IX :
20 GENESIS AND DEVELOPMENT
in same proportion. His other conclusion that regular rippling has
an amplitude of three grains from trough to crest, seems to me rather
hasty. I have, however, not made any regular observations to test this
statement, it being of minor importance in connection with my present
For the study of wave forms, which as a legitimate subject for in-
vestigation has attracted the attention of several scientists since the
time of Newton, Cornish has proposed 1 ) the term Kumatology
Accepting this name for the sake of convenience, the writer has to
point out that the digressions here made into the domain of Kumatology
have been necessary in order to arrive at a better understanding of the
factors which control the movements of sand, the interpretation of
which is in many respects still contradictory.
The beach may be defined as that strip of the shore which is formed
by the agency of waves. As a rule, it is situated between the lowest
level of the water and the formations produced by other geological
The method of beach formation has already been indicated. It was
mentioned that the mechanical action of the sea is evidenced in the
phenomena of erosion, transportation and sedimentation. The eroding
action of the sea is especially prominent on steep rocky shores, and on
places where the difference between low and high tide is great.
The material from the rocks eroded by the waves as well as the sand
and silt carried down to the rivers, sinks to the bottom of the sea and
is again transported by the waves and currents to the coast, there to
be accumulated. Although the transporting power of the waves is im-
mensely great, the distances to which rocks or even sand can be carried
is limited. In sediments of a clastic nature a sifting takes place through
the action of the waves against the shore, the finer material being carried
farther away, while the coarser is left on the shore. On very steep
shores, only larger pebbles and gravel are found, on lower fine sand, and
on very low coasts, silt.
If we consider the movements of the sand on a low shore, we will
1) Geographical Journal, March 1897 and June 1898.
OF SAND FORMATIONS ON MARINE COASTS. 21
notice that the sand grains follow the movement of the waves, that
is roll up and down. The deposit of sand takes place only when the
returning current does not carry back all material brought forward by
the wave. It follows that the velocity of the forward movement must
be greater than that of the returning current which is possible only on
very low strands, the sloping angle of which is not greater than five
degrees. If the size of the grains is large, the angle naturally also
changes. At the limit to which the wave reaches, an instantaneous ab-
sorption of the very thin strata of water takes place in the sand, so
that the returning current does not begin at this limit, but at a place
lower down. It is easy to determine the width of this belt in which the
absorption takes place, as the sand surface first is shining by the water
and then quickly turns dull. The width is always varying, and is in
direct relation to the strength of the waves, and also to the sloping
angle of the beach. During a strong gale and on a very low strand,
this belt is from 2 m. upwards on the Baltic coast, and on the western
coasts of Australia and the Pacific coast of America, where the mighty
waves of the ocean strike the shore with all their force, this belt is still
much broader. Secondly, deposits take place only on coasts, the sloping
angle of which is not more than 5 to 10 degrees. This angle is about 5
degrees with a grain size of 0.5 to 1 mm. in diameter. With finer sand,
under 0.5 mm., as is the case on many places on sheltered shores on
the Baltic coasts, it sinks to between 1 and 2 degrees, while with larger
grains, from 1 to 3 mm., an angle of 7 or even 8.5 degrees is formed.
With a steeper slope, deposition does not take place, but a denudation
Sandy beaches afford a certain protection of the coast line against
the erosive action of waves and surf. During the constant landward
urging of the sediments the coarser ingredients of the arenaceous
material soon cease to roll, and come to rest, and as the deposits are
augmented they will offer sufficient resistance to reduce the energy
of the wave, and consequently the erosion is diminished.
That beach sands remain unworn depends to a great extent on the
fact that the particles do not touch each other, as each one is surrounded
by a film of water. The beating of the waves also compresses the inter-
stitial water, and the solitary grains are thus not tossed about and
therefore do not grind and wear.
The presence of a considerable amount of interstitial water in the
beach sand washed by the waves is demonstrated when through the
pressure of the foot on the sand this whitens because of the expulsion
22 GENESIS AND DEVELOPMENT
of water, while as soon as the foot is lifted the original dull color is
Very fine sand is angular, and the rounding by water is produced
only when the strength of the current is not sufficient to keep the grains
suspended, but yet capable of moving them. The specific gravity of the
volume of sand is always smaller than that of the solitary grains. The
latter leave between each other spaces which are filled with air and
water; if all the grains were of the same size and exactly spherical,
the specific gravity of the volume of sand would be independent of the
absolute size of the grains, but as soon as grains of different sizes are
mixed, the small grains fill the spaces between the larger and hence
increase the specific gravity. This latter is also, the mineral character
of the grains being equal, higher the more dissimilar the grains are.
The texture of the sand in each locality depends entirely upon the
nature of the rocks from which it was originally derived. Through
having a comparatively large mixture of different sizes, and consisting
of the most different minerals of different specific gravity, beach sands
exhibit considerable differences in texture. On almost every non-rocky
coast, however, some kind of accumulation of fine grained quartz sand
can be noticed.
By quartz sand we understand a soil consisting mainly of white or
yellowish quartz grains, among which only very seldom any organic mat-
ter is distributed. Being conspicuously free from foreign constituents,
quartz sand is very uniform. It is generally believed that the pure
quartz sand on marine shore is a special result of the action of the sea.
This is, however, not the case. I have examined many samples of the
littoral sediments on different coasts, but never found the clean white
quartz sand of the beach occuring on the bottom of the sea. On the
contrary, the sandy sediment under water is impure, mixed with organic
matter, and highly colored. As soon as the sand is thrown ashore by
the wave and current action, and left at the water level, it is picked
up by the wind and carried inland. And if we observe the sand of the
beach from the edge of the water landward, we will find that it becomes
cleaner the further it is from the sea. This fact is mentioned by several
authors; for instance, Serres,^ who speaks of it in discussing the
French Mediterranean coast. Beach formations are very irregular in
stratification in their upper portions, where they are made by the toss
1) Marcel de Serres: Der Treib- und Flugsand des MittellSndischen Meeres.
Peterm. Mitth. V : 197198. 1859.
OF SAND FORMATIONS ON MABINE COASTS. 23
of the waves combined with the drifting of the winds. But the sloping
part swept by the waves below high-tide level is very evenly stratified
parallel to the surface: This surface dips usually at an angle of 5 to
15. Generally speaking the coarsest beaches have the steepest slopes.
The sand of the beach is increased or decreased according to the weather
and the seasons, it being thickest in summer and thinnest in winter, and
sometimes the beach is almost stripped of sand after a series of gales.
On the beach, there is formed a ridge of sand during offshore winds.
The sand is readily raised by the breakers and usually an excavation
or trough is found at the back of the ridge. This is similar to the
excavation and elevation produced in ripples. When the wind goes
down, a succession of low ridges are formed concave on the side toward
the sea, but as soon as a wave reaches over the top of the ridge, the
concavity is filled and an edge with uniformly sloping sides is formed.
The height of this beach ridge is usually not very considerable on the
Baltic coasts; seldom more than 1.5 m. over the general level of the
beach, or 2.25 over the sea. On the Atlantic and Pacific coasts, the
height is not much greater, although the ridge is formed by breakers
of considerable strength.
When the breaker line has been stationary for some time, for
instance during a high tide, an excavation is dredged out, and at ebb a
lagoon is often left here. For our purposes the beach may be divided
into the following belts: 1. The submerged beach; 2. The front beach;
3. The middle beach; and 4. The upper beach. The first belt includes
that portion of the beach that lies below mean low tide, but which may
be exposed by neap tides. It is normally covered with water, and is
subjected to the constant beating of the waves, which carry the material
ashore in their landward advance. Some of the detritus is deposited,
while another part is returned seawards with the undertow. Where the
carrying power of the surf is great, the beach is often built up by
material containing a considerable amount of coarse gravel and pebbles.
On such beaches there is always a residue of mud after a storm or an
exceptionally high tide, while no such deposits occur on sand alone.
The front beach is the belt between mean low tide and mean high tide,
being alternately each day exposed to the air and submerged. It mostly
passes without any marked break into the submerged belt. Situated on
the border between the land and water the front beach offers very
unfavorable conditions, not allowing the deposits to remain stable or
resting, on account of the repeated washing of the waves and currents.
With the .term middle beach we would designate that portion of the
24 GENESIS AND DEVELOPMENT
shore which is continuously moistened by the spray from the sea, and
it may even occasionally become inundated. The sand of this formation
which has been piled up by the waves, is picked up by the wind and
carried inland. It is usually of a light color. The upper layers are
rapidly drying up, but the ground water keeps at a high level, and
moisture is usually found at a very slight depth.
The upper beach is limited on one side by the line of debris that
marks the highest water. This debris, cast up by the sea, consists of
lumber and other wooden articles, fruits and seeds, fragments of marine
plants, and a quantity of animal remains, rapidly decaying. The upper
beach is also characterized by a greater rise in elevation and contains
more organic matter than any other part of the beach. The development
of this formation is modified to a greater extent by the wind than by
water, and it is especially on this strip of the shore, where the sands
commence to drift, and where they usually form the first ridges of sand
parallel to the coast, which we know as dunes.
The windmade embankments on the beach have a remarkable con-
struction, somewhat different from the usual. When the shifting of the
sand is very rapid, the littoral dunes do not reach any remarkable height,
and their existence is then very precarious.
The etymology of the word dune is somewhat obscure. Generally
it is presumed that it is derived from the Celtic word dun, hill. In
Latin it is/called dunum, in Greek Sowov, and hence the modern lan-
guages haye acquired the use of the same term in more or less changed
dress. According to Grewingk, not every ridge of sand parallel to the
coast is a dune, as they can in some cases originally be sand-banks formed
under water, which later have been lifted above the surface of the water
through the elevation of the shore. Dunes are formed especially where
the sands are almost purely siliceous, and hence incoherent, and little
fit for any kind of vegetation. They reach their greatest height on
projecting coasts that receive the winds from different directions.
The source of the dune sand is usually either diluvial sand, which
has been laid bare, or sand which has been brought ashore by the sea.
On the Dutch and Danish west coasts almost all the sand which
forms the dunes traces its origin from the sea. It is here thrown up
on the beach by the waves, and as soon as it has been dried by the sun,
OF SAND FORMATIONS ON MARINE COASTS. 25
the wind carries it further inland. . On the coasts in question, the
westerly winds are the prevailing, and therefore the sand wanders in
an easterly direction. .
Because of their extreme shiftiness of soil, the dunes do not attain
any considerable elevation. The sand deposited by the wind on the
summit of the hill is always in a state of unstable equilibrium. It has
a constant tendency to be precipitated down the other side, and the
higher the summit, the greater is this tendency, so that the dune arrives
at last to a point when no further accumulation is possible. The dune,
however, still continues to grow, extending its base and generally
increasing in dimensions, but does not increase in elevation.
The size and the height of the dune depends on the distance from the
sea and on the strength of the wind. In some cases it has been observed
that during a strong wind a dune has decreased in height 5 cm., while
other dunes have increased 25 cm. Every dune has one side placed
against the prevailing wind. This front side has a lower grade than
that on the lee side, which is always more abrupt. As long as the same
wind prevails, and as long as the wind carries only so much sand as
it is able to take away from the top of the dune, so long will the dune
retain its position and form, just as a whirlpool in a river is constant,
so long as the river maintains the same velocity and volume. Because
the sand grains cannot be lifted to any greater height in the air, the
dunes, when they have reached a certain elevation, would present to the
sand grains an almost insurmountable obstacle, but they have very seldom
time to cohere. The wind modifies its work incessantly and the height
of the dune is very soon reduced by stronger winds.
The transporting power of the air is, as already mentioned, small
compared with that of water, because of its lightness and want of
cohesion. The size of the particles has, therefore, a great influence
not only on the degree to which the sand is liable to drift, but also
on the extent in which it may manifest properties relative to the
texture of the soil, among others that of retaining moisture, which is
so important to vegetation.
The amount of sand transportation is greatest, other things being
equal, where there is no cover of vegetation to keep down the sands,
and the deposits made are most extensive in the direction of the pre-
vailing currents. The coarser dune sand particles are pushed along the
ground, while the finer form clouds of dust in the air, and settle rapidly
or slowly near to or remote from the source of supply according to the
force of the wind and the size of the particles suspended.
Library Publications. 2
26 GENESIS AND DEVELOPMENT
The drifting of sand by wind takes place according to following
principles: If the force of the wind is great, the grains do not move
on the surface but are lifted by the wind to a certain height. The larger
grains make jumps, and touch the ground from time to time, while the
smaller grains often are carried forward in form of clouds at a con-
siderable height from the ground. At a velocity of 4.5 m. in the second,
grains of 0.25 mm. diameter slide on the ground, but at a velocity of
15 m., grains of 1 mm. diameter are lifted high in the air. As a
corollary of this fact it follows that the movement of the grains depends
on their volume. The greater part of the sand grains have an irregular
flat form, and hence their movement is not rolling but sliding. That
of the largest take place spasmodically and only during stronger gusts.
According to Sokoloff, a wind of a velocity of 10 12 m. in a second
cannot carry grains of 100 150 cubic mm. When the wind is not too
strong, the grains slide along the surface, but when they are lifted up
during the strong gusts, and fall down at a certain angle, they again
rebound at the same angle. Eagen has proved that coarser sand grains
are sometimes lifted up to 2 m. height, and in such a case they are
carried up to 12 m. from their original place.
Ridges or rim formed ripples advance almost entirely by the sliding
of the larger grains of the top layer of the crest, and Cornish estimates
the progress of the ridges at one foot per hour. Helmann found in
Chiwa that the ripples on the lee-side of the dunes move almost with
the same rapidity as on the windward side, and he was not able to
interpret this phenomenon. It has been ascertained that the movement
of the dunes landward goes on at the average rate of 4.30 m. a year,
and that the quantity of sand thus transported is about 75 cubic m. to
the running m. of the length of the dune.
The winds have a greater power at a higher elevation than near the
surface, and consequently more sand is removed from the summit than
the wind is able to lift from the ground. This difference in the strength
of wind exercises a modifying influence on the development of the
dunes. The effect of the wind is to diminish the maximum slope, but as
the formation of dunes is mainly regulated by the supply of sand, the
varying angle of the windward slope depends upon the varying density
of the sand shower pushed forth toward the summit. In cases where
the supply of sand has become scarce or exhausted, the front slope
of the dune soon will be almost as steep as the lee side, that is, approach
the natural limit of the angle of rest.
The leeward slope of the dune varies but slightly, provided a reverse
OF SAND FOEMATIONS ON MARINE COASTS. 27
of the dominant wind .does not take place. It is the gravity which here
exercises its force and reduces to the angle of rest any steeper slope
caused by the air currents or other factors. The development of a dune
is similar to that of a ripple, although it takes place on a larger scale.
In lee of the dune crest there is an eddy, the upward motion of which
lifts the fine sand particles, and in cooperation with the wind sends
them flying from the summit. Gravity acts upon these particles,
causing the fall across the stream lines of the air. The coarser sand falls
more steeply, and this pitch is further increased by the backward
motion of the eddy.
There are thus several factors which influence the formation of
dunes. Of these operating factors the force and direction of the wind,
the sand shower, the eddy in the lee of any obstacle, the gravity, the
configuration of the surface, and the moisture are the principal ones.
If the dune is formed at a certain constant sum-total of these factors,
it retains its form as long as these factors are constant.
THE SCULPTURAL FORM OF DUNES.
The forms of dunes have a greater variety than those of ripples,
because a dune is the result of many changing winds. While the dunes
do not owe their origin to the action of the sand grains, like the ripples,
still rippling plays a part in the shaping of every dune. Eeversible
winds produce dunes having both front and back slope very steep. The
first effect of reverse of winds is to turn the top of the dune. !) During
strong winds the troughs are always deeper. 2 ) On a hard ground, the
windward slope can be as steep as the angle of rest, in case the sand
supply fails and tne wind is strong. If such is the case the dunes are
widely separated. 3 ) This form differs from that of dunes produced
in deep sand by dominant wind. The angle of the windward slope in
this case decreases with the density of the sand shower, and increases
with the power of the wind.
The amplitude of the dune does not exceed one third of the wave-
length, and this limit is most nearly approached when the wind blows
1) Sven Hedin: A journey through the Takla-Makan Desert, Chinese
Turkestan. Geogr. Journ., VIII: 264278, 356372. 1896.
2) G. Grand jean: Les Landes et les dunes de Gascogne. Bull. Soc. G6ogr.
Coml. de Bordeaux, March 1896.
3) V. Cornish: On the formation of sand dunes. Geogr. Journ. IX., p.
28 GENESIS AND DEVELOPMENT
alternately from opposite quarters, but does not hold in one quarter
sufficiently long to reverse the work of preceding winds. Cornish*)
remarks that in speaking of amplitude instead of height of dunes,
one avoids the common confusion which results from the fact that the
vertical distance from the bottom of the trough to the summit may
increase even by raising of the crest or by deepening of the trough.
A dune sufficiently large is stationary, and it is an established law
that as the amplitude increases, the velocity of the dune wave decreases.
The velocity of the dune is the rate of advance of the crest which takes
place by accumulation of sand upon the lee slope. There is also a group
velocity of dunes to be recognized, that is, the rate of travel of the sand.
Increase of wind will increase formation of new dunes to leeward
rather than the rate of travel of the individual dune, and is usually
accompanied by a considerable lowering of the general level, especially
in the case of simultaneous diminution in the supply of sand.
The sorting action of wind already mentioned is supported by rain-
water which washes the finer particles down into the trough, and con-
sequently we find the summit of dunes to consist of coarser material.
But on the other hand the lower part of the eddy is gouging out the
trough and the finer material is carried away through the combined
action of the eddy and the wind. The sand is therefore finer in the
dunes generally than in the hollows between them. On a large sandy
surface the particles are finer at the extremity towards which the wind
Through this winnowing process the dust which consists of friable
matter, having been reduced to the size of powder by grinding between
the sands is carried away from the dune district and deposited beyond
its limit. It is especially in desert regions, where aridity excludes
vegetation and allows the wind to play with full force upon the finer
particles of the soil, that we notice the development of sandy deserts
covered with quartz sand, yet surrounded by grassy steppes consisting
of clay dust. This remarkable distribution of the products of rock
disintregration by wind and its effect on the physiography of Northern
Africa has been eminently shown by WaUher2) Already Buvay 3)
described the transition between the cultivated coast lands and the desert
of Africa, which must be called a steppe, and the genetical relation of
these formations is now a generally admitted fact.
1) 1. c. p. 287.
2) Die Denudation in der Wiiste.
3) Zeitschr. fur Allgemeine Erkunde, Berlin, 1857, p. 290.
OF SAND FORMATIONS ON MABINE COASTS. 29
If we consider the general appearance and composition of the drift
sands we find that they consist in a preponderating degree of somewhat
rounded grains of quartz sand with only a very small percentage of
other materials. The admixture consists primarily of felspar, of mica,
and of various other minerals, such as hornblende, augite and granite,
and to some extent of lime, mostly in form of fragments of shells.
In a crystallinic rock, such as granite, we find that the different con-
stituents, felspar, quartz and mica, are present in isolated crystals.
As soon as these elements are separated from each other, they acquire
a granulated form and constitute what we call quartz sand. The grains
of felspar and mica act, however, in a different way than those of quartz,
the latter representing crystallographically only one or a few individuals,
while felspar and mica consist of many thin lamellae. Hence, when
exposed to the decomposing agencies, disintegration of felspar and mica
is much more intensive than that of quartz. The different particles of
sand are moved more rapidly by the wind the lesser their gravity in
proportion to their surface. Mica is so light that the least gust of
wind carries its thin lamellae away, and it is further so brittle that
it is easily broken into small fragments against other sand particles.
The same can be said of felspar, although, perhaps, in a less degree.
Here we also have to consider the chemical facility for decomposition.
During the night and in the dewy mornings, the felspar which has been
opened through the many capillary spaces is chemically decomposed by
the moisture, while the quartz has a greater resistance against this
agency. Consequently the older the dune sand is and the longer time
and water have exerted their influence, the less felspar will be found
in it and the more dominant is the quartz over the other minerals.
As a rule, all the sand grains, however, exhibit more or less the rounded
appearance due to attrition and weathering.
Besides the sand, the wind carries all kinds of light plant remains,
thin shells, dry crabs, dead and living insects, and similar particles.
All these temporary constituents of the dune are, however, insignificant
in comparison with the sand, and are usually so rapidly decayed that
they are seldom found in the deeper parts of the dune. The separate
grains are mostly covered with a fine mold, in part due to the decomposi-
tion of the above organic remains, on which depends the fertility of
the sand. The drift sand, though varied with a sprinkling of somewhat
rare grains of darker colored substances, is generally a mass of a light
The stratification of dunes is usually very mixed, and in the same
30 GENESIS AND DEVELOPMENT
dune strata, cut in all the four directions of the compass, can be seen.
Successive layers dip in various directions, and are abruptly cut short,
showing that the growing dune hill was partly cut down by storms and
was again and again built up by such disasters. The consolidation
of sand is best observed in ripples and rarely well shown in dunes,
because the latter are the result of changing winds, and the time
involved in their formation is too great for observation.
The fundamental forms of sand dunes include the transverse and the
longitudinal. The former, which is the most common on sea coasts,
especially where the wind is of moderate strength or the sand strip
comparatively narrow, is that placed at right angles to the prevailing
wind; the latter, formed where the wind is so strong as to prevent free
lateral growth, is that following the direction of the wind; between
these two there is an intermediate form; when varying winds act upon
this latter form, conical dunes are produced. They are, as a rule,
stationary, while the longitudinal form represents the most rapidly
The dunes which are placed parallel to the direction of the prevailing
winds have originated quite differently from those which are placed at
right angles to the wind. As we have seen, the usual mode of develop-
ment of a dune is that the sand forms a ridge transverse to the direction
of the wind. The sand is blown up on the lower slope on the front, and
when it reaches the top it falls down along the lee slope; the ridge
growing until it has reached considerable height. The parallel longi-
tudinal dunes are, however, formed through the central part of the dune,
being blown further and further forward, while the ends are kept back
by various forces. The rule is that such a horseshoe-shaped or parabolic
dune on the seashore moves with the convex side in the direction of the
Apparently diverse, even opposing effect is produced in sandy deserts,
if the observations of Holland and many other travellers regarding the
dunes called Barchanes are correct. In Traite de Geologic of Lapparent,
3 Ed., 1893, p. 140, we find the following opinion expressed about these
wandering dunes: "Enfin la forme de dunes en marche doit etre
generalement celle d'un croissant tournant sa convexite vers le vent;
par les particules sableuses, ayant moins de hauteur a franchir sur les
bords de la dune qu'en son centre, cheminent plus vite a droite et a
gauche. La crete doit done se courber en projectant deux pointes vers
1'interieur. Cette forme en croissant a ete bien constate par tous les
voyageurs qui ont parcouru le Sahara et les deserts americains."
OF SAND FORMATIONS ON MARINE COASTS. 31
Now the question arises: How is this phenomenon to be explained?
Cornish 1) refers to the development of barchanes in the following
words: "They form here and there upon the desert floor where the
wind will let them. It appears that they neither occur in localities
where the sheet of wind has everywhere a complete mastery over the
sand, nor where the burden of all the flying sand is everywhere too great
for the carrying power of the wind ; they dot the desert plain in localities
where the sheet of wind has, for the most part, the mastery of the sand,
but drops its burden here and there at certain points or more probably
along certain strips."
"The horns or cusps of the barchanes, pointing to leeward, are readily
explained, for the lowest parts of the dune travel quickest. A form as of
the moon in her first quarter (i. e. that is to say with the cusps pointing
in the direction of motion) is the form of front proper to a traveling
sand-wave as viewed in plan. In this case gravity does not operate, so
that the incoherence of sand does not hinder the formation of the cusp
as it does in the profile of dunes."
This explanation seems negatived by the fact that the cusps generally
are very insignificant as compared with the body of the dune, and in
most cases a difference in size of the cusps can be recognized. Thus
Lessar 2 ) observed in the Kara-Kum desert in Central Asia that the
southwesterly cusp always was longer. This seems to indicate that the
cusps are formed in a way similar to that of the low ridges which have
often been noticed on the lee side of both stationary and wandering
dunes on sea coasts. These lee ridges are usually placed at right angles
to the length of the dune and are formed by the combined action of the
eddy in the lee and the current sweeping around the side of the dune.
If we accept this explanation for the formation of cusps in lee of the
barchanes, the original form of which tends to the oval, according to
SokoloffZ), we will find a satisfactory solution of the action of wind in
the development of the barchane without having to theorize about the
lower cusps of the dune moving more rapidly than the higher, which
cannot be correct, as we know that the force of the wind is considerably
greater on the higher parts of the dune hill than on the lower, and
that consequently the central and highest part travels quicker. Steen-
strup 4) has also shown that a parabolic dune never can move with the
1) On the formation of sand dunes, p. 290.
2) P. M. Lessdr: Die Wtiste Kara-Kum. "Izwestija" Russ. Geogr. Soc.
20: p. 115. 1884.
3) Die Diinen. 1894. p. 164.
4) Om Klitternes vandring. 1894. p. 14.
32 GENESIS AND DEVELOPMENT
closed side toward the wind, and I must subscribe to his opinion, as J
have not, on any of the dunes visited my me, been able to observe a
phenomenon of that kind.
Summing up the foregoing discussion on dune forms, we would say
1. Dunes are formed in lines transverse to wind in unobstructed
2. Dunes are formed in lines parallel with wind in places where
some kind of obstruction is in the path of the wind.
3. Wandering dunes have their convexity in the direction of the
POLYGENETIC ORIGIN OF A DUNE COMPLEX.
The fundamental principles of dune formation established in the
previous section must be recognized at the outset of this discussion in
order to facilitate an understanding of the conditions which cause the
origin and development of a dune complex. With this term, dune
complex or dune tract, as distinguished from a solitary dune or a dune
massiv, we signify a collection of secondary dune hills interspersed with
The dune complex is formed behind the chain of primary dunes,
when the rate of travel of the sand is locally diminished without a
corresponding decrease in the supply of sand. The formation takes
place either through older dunes having been broken up into rough
hummocks by the wind, or through secondary embryonic dunes being
started by the piling up of drifting sand around some obstacle, in most
cases a congregation of plants.
One of the most important factors determining the development of
a dune complex is the. presence of ground moisture. Without this factor
we would not be able to explain the apparent irregularity of formation
of a group of small dunes, where the quality of sand ought to have called
for a regular dune massiv. The action of wind alone is insufficient for
this modelling of the surface, but in connection with the greater co-
herence of the sand particles caused by the ground moisture the
phenomenon is easily explicable.
It is the irregularity in action of wind, caused by the breaking 'up
of the regular even surface of a dune or a sand field into small elevations
OF SAND FORMATIONS ON MABINE COASTS. 33
and depressions, that governs the development of such embryonic sand
hills into a dune complex. In almost every case the latter formation
has had such origin from a number of nuclei, while a dune massiv is
formed from a single embryonic dune.
If the plants should not influence the development of dunes the
ridges would, like large waves, roll over the land until they were
stopped either by water or by high mountains. In most cases it is the
plants which have caused the broken forms of the sea coast dunes.
Inland dunes have, as a rule, a more regular shape.
There is 'no other geological formation of the present time which
is the result of such a combination of factors from the organic and
inorganic nature. Dunes are developed wherever the winds can play
over the loose sands, and as soon as the sand begins to drift, the
ordinary vegetation is destroyed and plants which thrive in drifting
sand immigrate, and thus begins the co-operation between the drift
sand and the dune plants, the result of which is the dune. Although
there is a struggle for power between the moving sand and the plants,
it is remarkable with this strife that they both thrive best where they
are almost of equal strength. If the plants have gained a victory they
will soon be replaced by other plants, and then it can happen that the
wind again breaks open the soil and the sand starts to drift afresh.
SAND FIELDS NEAR THE COAST.
As long as an obstruction has caused the formation of a dune, one
.of these will act as a recipient for the sand, and in this way dunes after
dimes are formed until finally a whole sea of sand covered with dunes
The encroachment of dunes is due not only to the travel of the dunes
themselves, but also to the formation of new dunes to the leeward from
material supplied by the sand shower.
In some cases, however, when the dunes have not been fixed by a
vegetation, the sand skims along the surface like snow drifting before a
stiff breeze and accumulates rapidly, covering the plains without forming
any hills. Further, the fine material which has been lifted to a certain
height in the air, is deposited behind the dune region, and is quickly
covered with vegetation, as it offers better condition for plant life on
account of its greater coherence and capacity of retaining moisture
than the coarser dune sand. These sand fields sometimes cover con-
34 GENESIS AND DEVELOPMENT
siderable areas, and it seems often almost inexplicable that no rippling
or dune formation takes place. The explanation of their non-formation
is to be sought in the fact that the sand-sized particles are too small
in proportion to the mass of material, and further, the deposition of
dust takes place so rapidly that the wind is not able to carry it away,
leaving the coarser particles to accumulate.
CONDITIONS FOR PLANT LIFE.
There is a great variation in the conditions for plant life on different
sand formations. The climate has something to do with this result as
well as the quality of the soil. ' Sea air and saline constituents of the
soil destructive to some plants may be beneficial to others. The mobility
of a drifting sand dune on the coast may be a condition of life to one
plant, while dry atmosphere and the stability of an inland sand field may
be essential to the growth of another. Even Pinus maritima, which has
produced such wonderful results on the Landes of Gascony, does not
grow everywhere even on sand formations in France. It is therefore
necessary to study in every case the natural conditions of the locality be-
fore the problems of ecological relationship can be solved.
Some of the conditions of sand formations are, however, everywhere
the same and these will here be briefly considered. One of the most
important points in this connection is the relation to moisture. The
rain-water sinks easily into the sand, the better the coarser the grains are.
Generally speaking, the power of retention of water is very small and of
all soils sand ranges lowest in this respect. The sandy soil has also a
very low power of absorption, and is able to condense only a small por-
tion of the atmospheric moisture. This is especially the case with quartz
Further, sandy soil dries easily, and it is therefore heated quickly by
the sun ; but it also cools very soon at night. The difference between day
and night temperature can be as high as 40-50 C. In consequence of
this, sand is subjected to a considerable bedewing at night, a factor which
is important for its capability of carrying a vegetation cover. The great
variation of temperatures of the soil is disadvantageous to the plants in
one respect, they being more liable to injury by frost, than if growing on
any other soil. Sand floras, on the other hand, are always developed
earlier, because of the greater heat capacity of the soil.
OF SAND FORMATIONS ON MARINE COASTS. 35
The nutritive value of the sand is very different according to the
chemical character of the grains. The commonest form, or quartz sand,
is the most barren on account of the insolubility of the quartz grains, and
also because of their resistance to decomposing agencies, as already men-
tioned. S'and consisting of mica, felspar, limestone, and other minerals,
disintegrate, however, and have by reason of this a higher nutritive
Formation of mould takes place only to a small degree in dry sandy
soil, because the organic constituents are so easily decomposed through
the admittance of air, and the particles are further quickly distributed
and carried out of reach of the plants by sinking with the water through
the loose soil. The proportion between organic and inorganic constitu-
ents in this soil is too great, the quantity of the former being too small
to establish a sufficient supply for the demand of a more luxuriant growth
This scarcity of plant food results in a more or less open vegetation
consisting of low growing plants, which do not give each other the mut-
ual assistance against mechanical influence of wind and other factors,
that is evident in the arrangement of plants on most other soils. The
injurious effect of the intense light, both direct and reflected from the
surface of the sand, has to be guarded against. The transpiration of
open sand vegetation, especially on the seacoasts, is always considerable
because of the constantly changing atmosphere, resulting from the almost
continuous winds. The plants have to develop some means of reducing
this excessive transpiration.
Summing up, we may say that the competition for food is more in-
tense, the water supply less, the light stronger, the temperature higher,
the transpiration greater, the foothold more uncertain and difficult, the
conditions for plant life generally more adverse, than on any other soil.
30 .GENESIS AND DEVELOPMENT
Ackermanu, Carl Beitrage zur physischen Geographie der Ostsee. pp. IX
399. Hamburg, 1883.
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