situated on the banks of the Nile, the desert begins again, and
borders the whole extent of the Red Sea. A large part of Arabia
presents nothing but sands and rocks, and toward the southeast, in
the Dahna, there are solitudes which no traveler, either Arab or
Frank, seems yet to have crossed. To the north and east stretch
the _Nefouds_, or “daughters of the great desert,” which are much
smaller than the Dahna, but are nevertheless formidable tracts to
travel over. One of these regions, which was crossed by Palgrave,
is that in which the mass of sand, formerly deposited there by the
marine currents, affords the greatest depth; in certain places it is
330, 400, and even 500 feet deep. It can be measured by the eye by
descending to the bottom of the funnel-shaped cavities, which the
springs of water, spouting out of the adjacent granite or calcareous
rock, have gradually hollowed out in the bed of sand. This enormous
bed of material, which represents chains of pulverized mountains,
does not exhibit an even surface, as one would expect, but,
throughout its whole expanse, presents long symmetrical undulations,
similar to those waves which roll in the Caribbean Sea under the
even influence of the trade-winds. These waves stretch from north
to south, parallel to the meridian; it is probable that they are
owing to the movement of the earth round its axis. The solid rocks
beneath unresistingly obey the impelling force which carries them
toward the east, but the movable sands which are above them do not
allow themselves to be carried away with an equal rapidity; each day
an infinitesimal quantity remains behind and seems to glide toward
the west, like the waves of the ocean, the atmospheric currents, and
everything that is movable on the face of the globe. The parallel
furrows of sand in the Nefouds certainly rise to a greater height
than those of the other deserts, and differ much in their aspect from
the smaller waves of sand formed by the wind; but the reason is, that
the bed of sand in this region is of a very great bulk, and because
at this point the swiftness of the globe nearly attains its maximum
on account of its vicinity to the equator.
To the east of the Arabian peninsula, the chain of deserts is
prolonged obliquely across Asia. The principal part of the plateau
of Iran, occupying a quadrilateral space, surrounded by mountains
which stop the rains in their passage, consists of sterile solitudes,
some covered with saline beds, the remains of dried-up lakes,
others spread over with shifting sands, which the wind blows up
into eddies, or dotted over with reddish-colored hills, which the
mirage renders either nearer or more distant to the eye than they
really are, incessantly modifying them according to the undulations
of the atmosphere. This plateau is only separated from the steppes
of Turkestan by the Elburz Mountains, and is continued toward the
east by the deserts of Afghanistan and Beloochistan, which are not
so large, and much easier to travel over. Even the rich peninsula of
India is protected by a belt of sterile tracts situated on the right
and left of the Indus. Between each of the five rivers (Punjaub),
which, by the union of their waters, form the great river, stretches
a line of steppes in which the torrent-waters of the mountains are
soon lost. The soil of these steppes is nearly everywhere barren,
except on the edge of the irrigation canals constructed by the
inhabitants at a very heavy outlay.
Beyond the mighty central group, whence radiate far and wide
the mountain-chains of Asia, the steppes and deserts, mutually
alternating according to the topographical conditions, and the
abundance or scarcity of water, extend over a space of more than
1,850 miles between Siberia and China Proper. The eastern part
of this belt is called, according to the languages, Gobi or
Chamo, that is to say, the desert _par excellence_, and, from
its enormous dimensions, corresponds with the Sahara of Africa,
situated exactly at the opposite extremity of the long chain of
solitudes which stretches right across the Old World. The mirage,
the moving sand-hills blown up into eddies, and many other phenomena
described by African travelers, are found in certain districts of
the Gobi, just the same as in all other deserts. But the cold here
is exceptionally intense, on account of the great height of the
plateaus, which is on an average 4,950 feet, and the vicinity of the
plains of Siberia, which are crossed by the polar wind. It freezes
nearly every night, and often during the day. The dryness of the
atmosphere is extreme; there is hardly any vegetation, and a few
grassy hollows are the only oases of these regions. From Kiahkta to
Pekin, there are only five trees for a distance of 400 to 500 miles,
which is the width of the desert in this part of Mongolia. The Gobi,
however, like the Sahara, was formerly covered by the waters of the
ocean; even on the elevated plateaus, old cliffs may be noticed, the
bases of which are worn away by the waves, and long strands of round
shingle stretch around the area which was formerly occupied by a now
vanished gulf.
In North, as in South America, the deserts proper lie to the west of
the continent, and occupy the basins commanded by the parallel or
divergent walls of the Rocky Mountains.
The most northerly of these American deserts occupies, to the west
of Lake Utah, a part of the space called the “Great Basin,” and is
comprised between the principal chain of the Rocky Mountains and
the Sierra Nevada of California. The desert of Utah is an immense
surface of clay, dotted over with thin tufts of artemisia; in certain
places, however, it exhibits no trace of vegetation, and resembles
a causeway of concrete, intersected by innumerable clefts, forming
nearly regular polygons. In the midst of these solitudes no rivulet
flows, and no water-spring gushes forth; only after journeying for
many a long hour the traveler sometimes comes upon some field of
crystallized salt, a white expanse, on which the clouds and blue sky
are reflected as on the surface of a lake. On the extreme horizon
some volcanic rocks may be seen, like great scoriæ, half veiled by
warm atmospheric columns, quivering like the air over the flame of a
hot brazier. Across these vast plains, inhabited only by a prodigious
quantity of extraordinarily shaped lizards, the road employed by the
emigrants used to pass, which was so soon destined to be supplanted
by the Pacific Railway from New York to San Francisco.
The deserts of North America, crossed here and there by fertile
valleys, extend eastward toward the basins of the Red River and the
Arkansas, where they blend with the savannas, and to the south into
the Mexican states of Chihuahua, Sonora, and Sinaloa. But in the
tropical zone, which commences beyond these points, the heavy summer
rains and the much smaller extent of the Mexican territory between
the two oceans, have prevented the formation of deserts. Regions
destitute of trees and verdure are only again found on the coasts of
Peru, to the south of the Gulf of Guayaquil. The trade-winds, after
having discharged their moisture on the eastern slopes of the Andes,
pass away through the air far above the seashore on the western side
of the mountains, and then sweep far out to sea over the surface of
the Pacific.
The solitudes of the Andes most resembling the desert regions of
the Old World and of the United States are the elongated plateaus
which rise one above another between the sea and the principal chain
of the Andes, in southern Peru and on the frontiers of Bolivia and
Chili; such as the _pampas_ of Islay and Tamarugal and the desert of
Atacama. The _pampa_ of Tamarugal, so called from the _Tamarugos_,
or tamarisks, which grow in the hollows where some moisture oozes
out of the soil, has a mean altitude of from 2,900 to 3,900 feet. It
is a plain nearly covered with beds of salt, or _salares_, which are
worked like rock quarries. The strata of salt are so thick, and rain
is so rare upon the plateau, that the houses of the village of Noria,
which are inhabited by the workmen, are entirely constructed of
blocks of salt. Some deserts, situated to the east of the Tamarugal,
on more elevated plateaus, contain a still larger quantity of salt.
The _pampa_ of Sal, which is overlooked by the volcano of Isluga, has
a mean altitude of not less than 13,800 feet, and its whole extent,
which is 125 miles long and from nine to twenty-four miles wide, is
perfectly white. The depth of salt deposited upon this plateau varies
from five to sixteen inches, according to the undulations of the
ground.
Whence do these enormous masses of salt proceed? Doubtless from the
sea or ancient lakes which formerly covered these countries and have
been gradually emptied by the rising of the soil. Saline matter
saturates even the rocks and clays, for a film of salt again forms
by efflorescence on all the ground in the desert from which crops
have previously been taken. The district of Santa-Rosa, which was
completely cleared of salt in 1827, was all white again and fit for
working after a lapse of twenty-three years. Sea-salt is not the
only production of these immense natural laboratories; but nitrates,
sulphates, carbonate of soda, borates of soda and lime, are also
found there and increase every year in thickness, thanks to the
ephemeral torrents which sometimes descend loaded with débris from
the adjacent Cordilleras. Saltpetre is also procured from the _pampa_
of Tamarugal, and is the article which, during all the wars of Europe
and America, gave such great commercial importance to the town of
Iquique.
The desert of Atacama, the largest of all those in South America,
occupies a wide belt of plateaus between the shores of the Pacific
and the high rampart of the Andes, which separates Bolivia from
the Argentine Republic. This expanse of reddish-colored rocks, and
crescent-shaped shifting sand-hills, is so repulsively desolate a
place that the conquerors of Chili, whether Incas or Spaniards,
never made up their minds to venture into it, in going along the
sea-coast; they have been obliged to pass far into the interior, by
the plateaus of Bolivia, and to twice cross the Andes before entering
the Chilian valleys. Not long since, men of science were the only
travelers who dared to enter the desert of Atacama. Nevertheless
this formidable-looking country also possesses, like the _pampa_ of
Tamarugal, great natural riches, which will not fail to summon the
labor of man and all the progress of civilization to these desolate
regions. Besides salt and saltpetre, this desert produces guano--that
is, heaps of the almost exhaustless droppings of all the sea-birds
which settle down in clouds upon the seashore. During the course of
centuries the ordure has accumulated into perfect rocks which the sun
dries up, and the surface of which is but rarely softened by rain.
These masses of detritus, which are, to all appearance, useless upon
these barren shores, are life itself to the countries of England,
France, and Belgium, which have become exhausted by the extent of
cultivation; and, consequently, this substance constitutes a most
important element of national commerce.
II.--THE SEA
THE PRIMITIVE OCEAN
--G. HARTWIG
The greatest of all histories, traced in mighty characters by the
Almighty Himself, is that of the earth-rind. The leaves of this great
volume are the strata which have been successively deposited in the
bosom of the sea or raised by volcanic powers from the depths of
the earth; the wars which it relates are the Titanic conflicts of
two hostile elements, water and fire, each anxious to destroy the
formations of its opponent; and the historic documents which bear
witness to that ancient strife lie before us in the petrified or
carbonified remains of extinct forms of organic existence--the medals
of creation.
It is only since yesterday that science has attempted to unriddle
the hieroglyphics in which the past history of our planet reveals
itself to man, and it stands to reason that in so difficult a study
truth must often be obscured by error; but although the geologist is
still a mere scholar, endeavoring to decipher the first chapters of a
voluminous work, yet even now the study of the physical revolutions
of our globe distinctly points out a period when the molten earth
wandered, a ball of liquid fire, through the desert realms of space.
In those times, so distant from ours that even the wildest flight
of imagination is unable to carry us over the intervening abyss,
the waters of the ocean were as yet mixed with the air, and formed
a thick and hazy atmosphere through which no radiant sunbeams, no
soft lunar light ever penetrated to the fiery billows of molten
rock, which at that time covered the whole surface of the earth.
What pictures of desolation rise before our fancy at the idea of yon
boundless ocean of fluid stone which rolled from pole to pole without
meeting on its wide way anything but itself. Ever and ever in the
dark-red clouds shone the reflection of that vast conflagration,
witnessed only by the eye of the Almighty, for organic life could
not exist on a globe which exclusively obeyed the physical and
chemical laws of inorganic nature. But while the fiery mass with
its surrounding atmosphere was circling through the icy region of
ethereal space (the temperature of which is computed to be lower than
60° R. below freezing point) it gradually cooled, and its hitherto
fluid surface began to harden to a solid crust. Who can tell how many
countless ages may have dropped one after the other into the abyss of
the past, ere thus much was accomplished; for the dense atmosphere
constantly threw back again upon the fiery earth-ball the heat
radiating from its surface, and the caloric of the vast body could
escape but very slowly into vacant space?
Thus millions of years may have gone by before the aqueous vapors,
now no longer obstinately repelled by the cooling earth-rind,
condensed into rain, and, falling in showers, gave birth to an
incipient ocean. But it must not be supposed that the waters
obtained at once a tranquil and undisturbed possession of their new
domain, for, as soon as they descended upon the earth, those endless
elementary wars began, which, with various fortunes, have continued
to the present day.
As soon as the cooling earth-rind began to harden, it naturally
contracted, like all solid bodies when no longer subject to the
influence of expanding heat, and thus in the thin crust enormous
fissures and rents were formed through which the fluid masses below
gushed forth, and, spreading in wide sheets over the surface, once
more converted into vapors the waters they met with in their fiery
path.
But after all these revolutions and vicissitudes which opposed the
birth of ocean, perpetually destroying its perpetually renewed
formation, we come at last to a period when, in consequence of
the constantly decreasing temperature of the earth-rind and its
increasing thickness, the waters at last conquered a permanent abode
on its surface, and the oceanic empire was definitely founded.
The scene has now changed; the sea of fire has disappeared, and water
covers the surface of the earth. The rind is still too thin and the
eruptions from below are still too fluid to form higher elevations
above the general surface: all is flat and even, and land nowhere
rises above the mirror of a boundless ocean.
This new state of things still affords the same spectacle of dreary
uniformity and solitude in all its horrors. The temperature of
the waters is yet too high, and they contain too many extraneous
substances, too many noxious vapors arise from the clefts of the
earth-rind, the dense atmosphere is still too much impregnated with
poisons to allow the hidden germs of life anywhere to awaken. A
strange and awful primitive ocean rises and falls, rolls and rages,
but nowhere does it beat against a coast; no animal, no plant grows
and thrives in its bosom; no bird flies over its expanse.
But, meanwhile, the hidden agency of Providence is unremittingly
active in preparing a new order of things. The earth-rind increases
in thickness, the crevices become narrower, and the fluid or
semi-fluid masses escaping through the clefts ascend to a more
considerable height.
Thus the first islands are formed, and the first separation between
the dry land and the waters takes place. At the same time no less
remarkable changes occur, as well in the constitution of the waters
as in that of the atmosphere. The further the glowing internal heat
of the planet retires from the surface, the greater is the quantity
of water which precipitates itself upon it. The ocean, obliged to
relinquish part of its surface to the dry land, makes up for the loss
of extent by an increase of depth, and the clearer atmosphere allows
the enlivening sunbeam to gild here the crest of a wave, there a
naked rock.
And now also life awakens in the seas, but how often has it changed
its forms, and how often has Neptune displaced his boundaries since
that primordial dawn?
Alternately rising or subsiding, what was once the bottom of the
ocean now forms the mountain crest, and whole islands and continents
have been gradually worn away and whelmed beneath the waves of
the sea, to arise and to be whelmed again. In every part of the
world we are able to trace these repeated changes in the fossil
remains imbedded in the strata that have been successively deposited
in the sea, and then raised again above its level by volcanic
agencies, and thus, by a wonderful transposition, the history of the
primitive ocean is revealed to us by the tablets of the dry land.
The indefatigable zeal of the geologists has discovered no less
than thirty-nine distinct fossiliferous strata of different ages,
and as many of these are again subdivided into successive layers,
frequently of a thickness of several thousand feet, and each of them
characterized by its peculiar organic remains, we may form some idea
of the vast spaces of time required for their formation.
The annals of the human race speak of the rise and downfall of
nations and dynasties, and stamp a couple of thousand years with
the mark of high antiquity; but each stratum or each leaf in the
records of our globe has witnessed the birth and the extinction of
numerous families, genera, and species of plants and animals, and
shows us organic Nature as changeable in time as she appears to us in
space. As, when we sail to the Southern Hemisphere, the stars of the
northern firmament gradually sink below the horizon, until finally
entirely new constellations blaze upon us from the nightly heavens;
thus in the organic vestiges of the Palæozoic seas we find no form of
life resembling those of the actual times, but every class
“Seems to have undergone a change
Into something new and strange.”
Then spiral-armed Brachiopods were the chief representatives of the
mollusks; then crinoid star-fishes paved the bottom of the ocean;
then the fishes, covered with large, thick rhomboidal scales, were
buckler-headed like the Cephalaspis, or furnished with wing-like
appendages like the Pterichthys; and then the Trilobites, a
crustacean tribe, thus named from its three-lobed skeleton, swarmed
in the shallow littoral waters where the lesser sea-fry afforded them
abundant food. From a comparison of their structures with recent
analogies, it is supposed that these strange creatures swam in an
inverted position close beneath the surface of the water, the belly
upward, and that they made use of their power of rolling themselves
into a ball as a defence against attacks from above. The remains of
seventeen families of Trilobites, including forty-five genera and 477
species, some of the size of a pea, others two feet long, testify
the once flourishing condition of these remarkable crustaceans, yet
but few of their petrified remains, so numerous in the Silurian
and Devonian strata, are found in the carboniferous or mountain
limestone, and none whatever in formations of more recent date.
Thus, long before the wind ever moaned through the dense fronds of
the tree ferns and calamites which once covered the swampy lowlands,
and long before that rich vegetation began to which we are indebted
for our inexhaustible coal-fields, now frequently buried thousands of
feet below the surface on which they originally grew, the Trilobites
belonged already to the things of the past.
In the seas of the Mesozoic or medieval period, new forms of life
appear upon the scene. A remarkable change has taken place in the
cephalopods; for the chambered and straightened Orthoceratites
and many families of the order have passed away, and the spiral
Ammonites, branching out into numerous genera, and more than 600
species, now flourish in the seas, so that in some places the
rocks seem, as it were, composed of them alone. Some are of small
dimensions, others upward of three feet in diameter. They are met
with in the Alps, and have been found in the Himalaya Mountains
at elevations of 16,000 feet, as eloquent witnesses of the vast
revolutions of which our earth has been the scene. Carnivorous,
and resembling in habits the _Nautili_, their small and feeble
representatives of the present day, their immense multiplication
proves how numerous must have been the mollusks, crustaceans, and
annelides, on which they fed, all like them widely different from
those of the present day.
Then also flourished the Belemnites (Thunder-stones), supposed by
the ancients to be the thunder-bolts of Jove, but now known to
be the petrified internal bones of a race of voracious ten-armed
cuttle-fishes, whose importance in the Oolitic or cretaceous seas
may be judged by the frequency of their remains and the 120 species
that have been hitherto discovered. Belemnites two feet long have
been discovered, so that, to judge by analogies, the animals to
which they belonged as cuttle-bones must have measured eighteen to
twenty feet from end to end, a size which reduces the rapacious
Onychoteuthis of the present seas to dwarfish dimensions. But of all
the denizens of the Mesozoic seas, none were more formidable than
the gigantic Saurians, whose approach put even the voracious sharks
to flight. The first of these monsters that raises its frightful
head above the waters is the dreadful Ichthyosaurus, a creature
thirty or even fifty feet long, half fish, half lizard, and combining
in strange assemblage the snout of the porpoise, the teeth of the
crocodile, and the paddles of the whale. Singular above all is the
enormous eye, in size surpassing a man’s head. Woe to the fish
that meets its appalling glance! No rapidity of flight, no weapon,
be it sword or saw, avails, for the long-tailed, gigantic Saurian
darts like lightning through the water, and its dense harness bids
defiance to every attack. Not only have fifteen distinct species of
_Ichthyosauri_ been distinguished, but the remains of crushed and
partially digested fish-bones and scales which are found within their
skeleton indicate the precise nature of their food. Their fossil
remains abound along the whole extent of the Lias formation, from the
coast to Dorset, through Somerset and Leicestershire to the coast of
Yorkshire, but the largest specimens have been found in Franconia.
Along with this monster, another and still more singular deformity
makes its appearance, the Plesiosaurus, in which the fabulous
chimæras and hydras of antiquity seem to start into existence. Fancy
a crocodile twenty-seven feet long, with the fins of a whale, the
long and flexible neck of a swan, and a comparatively small head.
With the appearance of this new tyrant, the last hope of escape
is taken from the trembling fishes; for into the shallow waters
inaccessible to the more bulky Ichthyosaurus the slender Plesiosaurus
penetrates with ease.
A race of such colossal powers seemed destined for an immortal reign,
for where was the visible enemy that could put an end to its tyranny?
But even the giant strength of the Saurians was obliged to succumb to
the still more formidable power of all-changing time, which slowly
but surely modified the circumstances under which they were called
into being, and gave birth to higher and more beautiful forms.