industry of the Dutch nation--furnish a conspicuous example of the
sand-hills, or _dunes_, which are often found on low sandy coasts,
and which owe their origin to the action of prevailing winds upon
the loose drift-sand. Where no means are adopted to fix them to
the soil, the sand-hills become agents of destruction, sometimes
overwhelming whole villages in their slow but steady advance inland.
But this is not the case in Holland, where the ingenuity of the Dutch
has converted them from instruments of destruction into a means of
national preservation. In some of the provinces of the Netherlands,
a large portion of the land is actually lower than the level of
high-water mark, and is therefore exposed (it might appear) to the
ravages of the adjoining ocean. But from the channel of the Helder
southward, the coast is protected by a line of broad dunes, or
sand-hills, which are partially covered with grass or heath, and
are in some places from forty to fifty feet in height. These have
been formed by the natural process above adverted to, and still in
operation; the prevalent sea-winds raise banks or ridges of sand
at a short distance from the coast, which the inhabitants prevent
from proceeding further inland by sowing them with a kind of grass
(_arundo arenaria_), the long roots of which bind the whole mass
firmly together.
The district of the _Landes_, in the southwest corner of France,
offers an example of the combined action of sand and sea which is
widely different from the above in its results. The coast here
exhibits a line of shifting sand, backed toward the interior by a
belt of pine-forest. For a length of nearly two hundred miles, from
the mouth of the Garonne to that of the Adour, there stretches along
the extreme edge of the sea a range of hills composed of white sand,
as fine as though it had been sifted for an hour-glass. Every gale
changes the shape of these rolling masses of drift-sand. A strong
wind from the land flings millions of tons of sand per hour into
the sea, to be again washed up by the surf, flung upon the beach,
and with the first Biscay gale blown in whirlwinds inland. A water
hurricane from the west has been known to fill up with sand many
square miles of shallow lake, driving the displaced waters inland,
dispersing them among the pine-woods, flooding and frequently
destroying the scattered hamlets of the people, and burying forever
their fields of millet and rye. The shepherds of the Landes pursue
their avocation mounted upon stilts, which raise them above the
reach of the sand-blasts. The pine-forests yield annually a large
supply of resin, the only harvest of this wild region. Intermixed
with the pine-forests, a chain of shallow and marshy lakes stretches
in a direction parallel to the coast, and at a few miles inland.
[Illustration: Great Barrier Coral Reef, Queensland, Australia
This Reef is composed entirely of Stag’s Horn Coral (_Madrepora
Hebes_)]
The lowland plains of the New World are on a scale of vast magnitude,
and, if not superior in extent to those of the Eastern Hemisphere,
yet bear a much larger proportion to the entire area of the land.
They are watered, moreover, by the longest rivers of the globe, and
enjoy, for the most part, conditions of situation and climate in the
highest degree favorable to man. Both in North and South America, the
whole central expanse of the continent exhibits a vast succession
of lowland plains, the only division between the different portions
of which is that formed by the watersheds of its longer rivers--not
always to be traced without difficulty, owing to the generally
level nature of the entire plain. In North America, the prairies;
in South America, the tracts known as llanos, selvas, and pampas,
are included within the lowland region, and exhibit some of the most
characteristic among the aspects of nature in the Western world.
The prairies coincide, in a general sense, with the middle and upper
portion of the Mississippi Valley, embracing the vast region which
extends from the Great Lakes to the base of the Rocky Mountains. They
are covered in their natural state with a rich herbage, and exhibit a
waving sea of grass several feet high. At intervals, toward the banks
of the rivers, patches of forest vegetation break the uniformity
of the prospect, but the prairie itself is destitute of trees, and
(as the name implies) is merely a grassy plain, or meadow. Alternate
forest and prairie constitute the great features of natural scenery
in the New World. When the rich soil of the prairie-land is broken
up by the plow--an operation which is rapidly progressing, year by
year, within the Western States of America--it yields abundant crops
of corn. There are, however, within the vast extent of the North
American continent, immense regions which yet retain the aspect of
the wilderness. It was within these regions that the buffalo roamed,
in vast herds, and that the native Indian hunter pursued his game
ere the advancing footsteps of the white man had driven him from his
haunts.
The llanos, or savannahs, are vast grassy plains, which occupy nearly
the whole basin of the Orinoco River, excepting only toward its
highest portion, when they are succeeded by wooded plains. The llanos
resemble in general features the prairies of the Mississippi Valley,
but have for the most part a lower level, and (owing to the abundant
rains of the torrid zone) are annually inundated by the rivers to
an immense extent. Whole districts, embracing thousands of square
miles, are annually converted, within the interior plains of South
America, into lakes, or temporary seas of fresh water, to be rapidly
evaporated under the burning rays of a vertical sun. At the close of
the rainy season the llanos are covered with grass, and form rich
natural pasture-grounds. During the prolonged season of drought which
ensues, the verdure is entirely destroyed, and the parched earth
opens in wide and deep crevices--again to be laid under water with
the recommencement of the rains.
The selvas, or forest-plains, belong to the valley of the Amazon, and
include an immense area of Brazil, watered by the lower portion of
the great stream and its chief tributary, the Madera. Vast regions
are here covered by an uninterrupted forest, composed of trees of
giant growth, their boughs interlaced by immense creeping plants, and
the ground beneath thickly covered with a dense growth of underwood.
To the southward of the forest region are vast grassy plains, which
stretch in that direction into the valley of the Paraguay.
The pampas, or plains of the Paraguay and Paraná valleys, exhibit the
same luxuriant natural growth of herbaceous plants as other lowland
regions of the New World. They include an immense region, which
stretches from the neighborhood of the southern tropic far to the
southward of the river Negro (lat. 39° S.), and from the banks of the
Paraná to the eastern base of the Andes. The pampas are variously
covered with long coarse grass, mixed with wild oats, clover, and
other herbage. The tract of country known by the name of El Gran
Chaco, immediately to the westward of the upper Paraguay--scarcely
tenanted excepting by wild beasts--exhibits a luxuriant covering of
grass, which springs from a soil possessed of the highest natural
capabilities.
Further south, the plains that extend from Buenos Ayres to the foot
of the Andes are covered, during a great part of the year, with
gigantic thistles, which grow to the height of seven or eight feet,
and are so thick as to render the country almost impassable. For nine
months of the year the thistles are here the predominant (and almost
the sole) feature of the vegetable kingdom; but with the heats of
summer they are burned up, and their tall leafless stems are leveled
to the ground by the powerful blast of the pampero, or southwest
wind, which blows from the snowy ranges of the Andes, after which the
ground is covered for a brief season with herbage. This is destined,
with the returning spring, again to give place to the stronger
vegetation which it had succeeded, and for a time supplanted.
THE SMELL OF EARTH
--G. CLARKE NUTTALL
A bright fine evening after a day of rain is one of Nature’s
compensations. The air is peculiarly sweet and fresh, as though
the rain had washed all evil out of it. The mind, relieved from
the depressing influence of continuous rain, is exhilarated, and,
above all, the strong smell of the earth rises up with a scent more
pleasing than many a fragrant essence. In the town, indeed, this
earthy smell is often obscured by the bricks and mortar which cover
the land, and by the stronger, less wholesome, odors of human life,
but in the country it has full sway, and fills the whole air with
its presence. Even a slight shower, particularly after drought, is
sufficient to bring out the sweet familiar smell of the land and
thrust it upon our notice.
The smell of freshly turned earth is often regarded by country lovers
as one of the panaceas for the ills of the flesh, and “follow a
plowshare and you will find health at its tail” has proved a sound
piece of advice to many a weakly town-sick one, over whose head the
threatenings of consumption hung like the sword of Damocles, though
it is possible that it is the fresh air, and more especially the
sunshine, which are the saving media, and not the mere smell.
But what do we know about this characteristic smell of the soil? Can
we regard it as the mere attribute of the soil as a simple substance,
such an attribute as is, for instance, the peculiar smell of leather,
or the odor of india-rubber; or can we go deeper and find that it is
really an expression of complexity below?
Strangely enough this is the case, for the smell of damp earth is one
of the latest sign-posts we have found which lead us into a world
which, until recently, was altogether beyond our ken. It points us to
the presence, in the ground beneath us, of large numbers of tiniest
organisms, and not merely to their presence only, but to their
activity and life, and reveals quite a new phase of this activity.
A handful of loose earth picked up in a field by the hedgerow, or
from a garden, no longer represents to us a mere conglomeration of
particles of inorganic mineral matter, “simply that and nothing
more”; we realize now that it is the home of myriads of the smallest
possible members of the great kingdom of plants, who are, in
particular, members of the fungus family in that kingdom, plants so
excessively minute that their very existence was undreamed of until a
few years ago.
Some faint idea of their relative size, and of the numbers in which
they inhabit the earth, may be gleaned from the calculations of an
Italian, Signor A. Magiora, who, a short time ago, made a study of
the question. He took samples of earth from different places round
about Turin and examined them carefully. In ordinary cultivated
agricultural soil he found there would be eleven millions of these
germs in the small quantity of a gramme, a quantity whose smallness
will be appreciated when it is remembered that a thousand grammes
only make up about two and a quarter pounds of our English measure.
Thus, a shovelful of earth would be the home of a thousand times
eleven millions of bacteria--but the finite mind can not grasp
numbers of such magnitude. In soil taken from the street, and,
therefore, presumably more infected with germs, he calculated that
there was the incredible number of seventy-eight million bacteria to
the gramme. Sandy soil is comparatively free from them, only about
one thousand being discovered in the same amount taken from sandy
dunes outside Turin.
But though the workers were hidden yet their works were known, for
what they do is out of all proportion to what they are; in fact they
perform the deeds of giants, not those of veriest dwarfs. “By their
works shall ye know them” might be a fitting aphorism to describe
the bacteria of the soil. And the nature of their deeds is widely
various, for though the different groups are members of one great
family, yet, like the individuals of a human family that is well
organized, they have each of them their special vocation. In the
spring time, when the sun warms the chilly earth, they act upon the
husks that have protected the seeds against the rigors of the winter,
and crumble them up so that the seedling is free to grow; they
break down the stony wall of the cherry and plum which has hitherto
imprisoned the embryo; and then, when the young plant starts, they
attach themselves to its roots, assist it to take in all sorts of
nutriment from air and soil, and thus help it in its fight through
life, and when its course has run they decently bury it. They turn
the green leaves and the woody stem and the dark root back into the
very elements from which they were built up; they effect its decay
and putrefaction, and resolve it into earth again. “Dust to dust,
ashes to ashes,” is the great life work of the earth bacteria.
But up to about 1898 the fresh smell of the earth, the smell peculiar
to it, had not been in any way associated with these energetic
organisms, and it was quite a new revelation to find that it was
a direct outcome of their activity. Among the many bacteria which
inhabit the soil, a new one, hitherto unknown, has been isolated and
watched. It lives, as is usual with them, massed into colonies, which
have a chalky-white appearance, and as it develops and increases in
numbers it manifests itself by the familiar smell of damp earth,
hence the name that has been given it--_Cladothrix odorifera_.
Taken singly, it is a colorless thread-like body, which increases
numerically by continuous subdivisions into two in the direction of
its length. It derives its nutriment from substances in the soil,
which either are, or have been, touched by the subtle influence of
life, and in the processes of growth and development it evolves from
these materials a compound whose volatilizing gives the odor in
question. This compound has not yet been fully examined; it is not
named, nor have all its properties been satisfactorily elucidated,
but two facts concerning it stand out clearly. One is that it is the
true origin of the smell that we have hitherto attributed to earth
simply; and the other, that it changes into vapor under the same
conditions as water does. Therefore, when the sun, shining after the
rain, draws up the water from the earth in vapor form, it draws up,
too, the odorous atoms of this newly found compound, and these atoms,
floating in the air, strike on our olfactory nerves, and it is then
we exclaim so often, “How fresh the earth smells after the rain!”
Though moisture, to a certain extent, is a necessary condition of the
active work of these bacteria, yet the chief reason why the earthy
smell should be specially noticeable after the rain is probably
because this compound has been accumulating in the soil during the
wet period. We only smell substances when they are in vapor form,
and since the compound under consideration has precisely the same
properties in this respect as water, it will only assume gaseous form
when the rain ceases. The bacteria have, however, been hard at work
all the time, and when the sun shines and “drying” begins, then the
accumulated stores commence their transformation into vapor, and the
strong smell strikes upon our senses. For the same reason we notice a
similar sort of smell, though in a lesser degree, from freshly turned
earth. This is more moist than the earth at the surface, and hence,
on exposing it, evaporation immediately begins which quickly makes
itself known to us through our olfactory nerves.
It may also have been remarked that this particular odor is always
stronger after a warm day than after a cold one, and is much more
noticeable in summer than in winter. This is because moderate warmth
is highly conducive to the greater increase of these organisms, and,
in fact, in the summer they are present in far larger numbers and
exhibit greater vitality than in the winter, when they are often more
or less quiescent.
Two other characteristics of _Cladothrix odorifera_ are worthy of
notice as showing the tenacity with which it clings to life. It is
capable of withstanding extremely long periods of drought without
injury; its development may be completely arrested (for water in
some degree is a necessity with all living things, from highest to
lowest), but its vitality remains latent, and with the advent of
water comes back renewed activity. But besides drought it is pretty
well proof against poisons. It can even withstand a fairly large
dose of that most harmful poison to the vegetable world, corrosive
sublimate. Hence any noxious matter introduced into the soil would
harm it little ultimately; the utmost it could do would be to retard
it for a time.
This, then, is the history of the smell of earth as scientists have
declared it unto us, and its recital serves to further point the
moral that the most obvious, the most commonplace things of everyday
life--things that we have always taken simply for granted without
question or interest--may yet have a story hidden beneath them.
Like sign-posts in a foreign land, they may be speaking, though
in a language not always comprehended by us, of most fascinating
regions--regions we may altogether miss to our great loss if we
neglect ignorantly the directions instead of learning to comprehend
them.
DESERTS
--ÉLISÉE RECLUS
The most important group of deserts in the world is that of the
Sahara, which extends across the African continent from the shores
of the Atlantic to the valley of the Nile. This immense area is more
than 3,100 miles from east to west, and is, on an average, more than
600 miles in breadth; it is, in fact, equal in size to two-thirds
of Europe. In this region there is only one season, viz., summer,
burning and merciless. It is but rarely that rain comes to refresh
these regions, on which the solar rays dart vertically down.
The mean altitude of the Sahara is estimated at 2,000 feet; but the
level of the soil varies singularly in the different districts. To
the south of Algeria, the surface of the Chott Mel-R’ir, the remains
of an ancient sea, which communicated with the Mediterranean, is at
the present time more than 165 feet below the Gulf of Cabes; while to
the south and east, the ground rises into plateaus and mountains of
sandstone or granite to a height varying from 3,300 to 6,660 feet. In
the centre of the Sahara stands the Djebel-Hogger, the sides of which
are covered with snow during three months in the year; from December
to March, its picturesque defiles are traversed by streams which flow
some distance and lose themselves beneath the surrounding plains.
This group of lofty mountains is the great landmark which forms the
boundary between the eastern deserts, or the Sahara proper, and the
group of western deserts, designated under the general name of Sahel.
The Sahel is very sandy. Throughout the greater part of its extent
the soil is composed of gravel and large-grained sand, which does
not give way even under the foot of the camel. Some of the ranges
of sand-hills which rise in this desert are chains of small hills,
composed of heavy sand which resists the influence of the wind. But
in many districts of the Sahel, the arenaceous particles of the
soil are fine and small. The trade-winds which pass over the desert
distribute these sandy masses into long waves similar to those of
the ocean, and here and there raise them into movable sand-hills,
which overwhelm all the oases which lie across their path. Traveling
toward the southwest, in which direction they are driven by the wind,
the sands reach the northern shores of the Niger and Senegal at many
points of their course, and by their incessant deposits gradually
drive the waters of these rivers toward the south. To the west, the
sand of the desert encroaches also upon the ocean. Off the coast
which stretches between Cape Bojador and Cape Blanco--pointed out
from afar by the highest dunes in the world--a line of sand-banks
extends far out into the sea. A current of sand is, therefore,
constantly passing across the desert from northeast to southwest.
The débris of rocks in a state of decomposition, and the particles
brought to the coast of the Gulf of Cabes by the tide, which is very
powerful at this point, are driven before the wind into the plains of
the Sahel, and thence, after a journey lasting hundreds and perhaps
thousands of years, they at last reach the seashore of the Atlantic,
in order to recommence in the oceanic currents another eventful
odyssey.
Some parts of the eastern Sahara are equally sandy; but the principal
parts of the surface of this desert are occupied by plateaus of rock
or clay, and by groups of grayish or yellowish mountains. The chains
of sand-hills are numerous, and, like those of the west, they travel
incessantly under the impulse of the wind in a south or southwest
direction. The rocky plateaus are crossed and recrossed here and
there by wide and deep clefts, which are gradually filled by the
drifted sand, and into which the traveler runs the risk of sinking,
like the mountaineer into the _crevasses_ of a glacier. In the
hollows, patches of salt take the place of the lakes which in more
rainy countries would be found there.
Those districts of the Sahara which are destitute of oases present
a truly formidable aspect, and are fearful places to travel over.
The path which the feet of the camels have marked out in the immense
solitude points in a straight line toward the spot which the caravan
wishes to reach. Sometimes these faint footmarks are again covered
with sand, and the travelers are obliged to consult the compass, or
examine the horizon; a distant sand-hill, a bush, a heap of camels’
bones, or some other indications which the practiced eye of the
Touareg alone can understand, are the means by which the road is
recognized.
Terrible stories are told by the side of the watch-fires of caravans
being overtaken when amid the sand-hills by a sudden storm of wind,
and completely buried under the moving masses; they also tell of
whole companies losing their way in the deserts of sand or rocks,
and dying of madness after having undergone all the direst tortures
of heat and thirst. Happily such adventures are rare, even if the
accounts of them are at all authentic. Caravans, when led by an
experienced guide and protected by treaties and tribute against the
attacks of plundering Arabs and Berbers, nearly always arrive at the
end of their journey without having undergone any other sufferings
than those caused by the intolerable heat, the want of good water,
and the coldness of the nights; for the nights which follow the
burning days in the Sahara are in general very cold. In fact, the air
of these countries being entirely destitute of aqueous vapor, the
heat collected during the day on the surface of the desert is, owing
to the nocturnal radiation, again lost in space. The sensation of
cold produced by this waste of heat is most acute, and especially
so to the chilly Arab. Not a year passes without ice forming on the
ground, and white frosts are frequent.
In all those countries in the Sahara where the water gushes out in
springs or descends in streams from some group of mountains, there is
an oasis formed--a little green island, the beauty of which contrasts
most strikingly with the barrenness of the surrounding sands. These
oases, compared by Strabo to the spots dotted over the skin of
the panther, are very numerous, and perhaps comprehend altogether
an area equal in extent to one-third of the whole Sahara. In the
greater part of this region, the oases, far from being scattered
about irregularly, are, on the contrary, arranged in long lines in
the middle of the desert. The cause of this is either the higher
proportion of moisture contained in the aerial currents which pass in
this direction, or, and perhaps principally, the subterranean water
which follows this slope, and here and there rises to the surface.
The oases are, _par excellence_, the country of date-trees; in
the neighborhood of Mourzouk there are no less than thirty-seven
varieties. These trees form the riches of the tribe, for their fruit
supplies food to man as well as to beast--to dromedaries, horses, and
dogs. Below the wide fan of leaves, which quiver in the blue air, are
thickly growing clumps of apricot, peach, pomegranate, and orange
trees, their branches loaded with fruit, and vines intertwining round
the trunks; maize, wheat, and barley ripen under the shade of this
forest of fruit-trees, and, lower still, the modest trefoil fills
up the very smallest intervals of the soil which is capable of
irrigation.