have long since vanished from the bosom of the ocean, and cetaceans,
walruses, and seals, unknown in the primitive deep, now wander
through the waters or bask on the sunny cliffs. With them begins a
new era in the life of the sea. Hitherto it has only brought forth
creatures of base and brutal instinct, but now the Divine spark of
parental affection begins to ennoble its more perfect inhabitants and
to point out the dim outlines of the spiritual world.
During all these successive changes the surface of the earth has
gradually cooled to its present temperature, and many plants and
animals that formerly enjoyed the widest range must now rest
satisfied with narrower limits. The sea-animals of the North find
themselves forever severed from their brethren of the South by the
impassable zone of the tropical ocean; and all the fishes, mollusks
and zoophytes, whose organization requires a greater warmth, confine
themselves to the equatorial regions.
As the Tertiary period advances toward the present epoch, the species
which flourished in its prime become extinct, like the numberless
races which preceded them; new modifications of life, more and more
similar to those of the present day, start into existence; and,
finally, creation appears with increasing beauty in her present rich
attire.
Thus old Ocean, after having devoured so many of his children, has
transformed himself at last into our contemporaneous seas, with their
currents and floods, and the various animals and plants, growing and
thriving in their bosom.
Who can tell when the last great revolutions of the earth-rind took
place, which, by the upheaving of mighty mountains or the disruption
of isthmuses, drew the present boundaries of land and sea? or who
can pierce the deep mystery which veils the future duration of the
existing phase of planetary life?
So much is certain, that the ocean of the present day will be
transformed as the seas of the past have been, and that “all that
it inhabit” are doomed to perish like the long line of animal and
vegetable forms which preceded them.
We know by too many signs that our earth is slowly but unceasingly
working out changes in her external form. Here lands are rising,
while other areas are gradually sinking, here the breakers
perpetually gnaw the cliffs and hollow out their sides, while in
other places alluvial deposits encroach upon the sea’s domain.
However slowly these changes may be going on, they point to a
time when a new ocean will encircle new lands, and new animal and
vegetable forms arise within its bosom. Of what nature and how gifted
these races yet slumbering in the lap of time may be. He only knows
whose eye penetrates through all eternity; but we can not doubt that
they will be superior to the present denizens of the ocean.
Hitherto the annals of the earth-rind have shown us uninterrupted
progress; why, then, should the future be ruled by different laws?
At first the sea only produces weeds, shells, crustacea; then the
fishes and reptiles appear; and the cetaceans close the vista. But is
this the last word, the last manifestation of oceanic life, or is it
not to be expected that the future seas will be peopled with beings
ranking as high above the whale or dolphin as these rank above the
giant Saurians of the past?
THE FLOOR OF THE OCEAN
--JOHN JAMES WILD
If we wish to form a perfect idea of the distribution of land and
water, we must consider not only the length and breadth of the areas
occupied, but also the height of the land and the depth of the water;
in other words, the volume of those portions of the solid crust
of the earth which are raised above the level of the sea, and the
volume of the masses of water which fill up the depressed portions
of the earth’s crust. We are thus led to regard the surface of the
solid crust of our planet as composed of heights and hollows, of
areas of elevation and areas of depression, and, as a next step, to
discriminate between these areas--not according to the usual standard
of the level of the sea, but according to their relative distance
from the centre of the earth. In this sense we may conceive an area
of elevation--_i. e._, a raised portion of the earth’s surface,
which may be partially or entirely covered with water, and an area
of depression--_i. e._, a hollow in the same surface, which may be
raised above the level of the sea, and from dry land or the basin of
an inland sea or lake.
If we examine a chart of the world in the light which has been thrown
upon this question by all the reliable soundings obtained up to the
present, it will be found that continents and islands which we have
been in the habit of considering as separated from each other by
wide seas and deep straits virtually form part of the same area of
elevation; and, in a similar manner, that certain oceans and seas,
which we are accustomed to distinguish by separate names, form part
of the same area of depression. It will also appear that, with the
exception of the islands scattered over the face of the ocean and of
the Antarctic region, all the dry land at present existing may be
reduced to one large area of elevation gravitating to the North Pole,
as the common centre of the principal land masses; similarly, if we
except the Arctic region and other inland basins, all the oceans and
seas compose a single vast area of depression, with the South Pole
for common centre of the larger accumulations of water on this globe.
The Arctic region forms a distinct area of depression placed in the
centre of the great area of elevation, and the Antarctic region,
according to the evidence we at present possess, is an area of
elevation, surrounded on all sides by the above-described great area
of depression. The numerous small islands that crop up in the middle
of the oceanic basins are generally found associated in groups, and
they belong to areas of elevation at the present time submerged, that
is to say, in the condition in which we know the dry land to have
been at an epoch more or less remote in the history of our planet. In
support of the above generalization, we may point to the following
facts as established by recent soundings. The 100-fathom line, as is
well known, joins the whole of the British Islands, including the
Hebrides, Orkneys, and Shetland Islands, to the continent of Europe.
It forms a broad band connecting the Asiatic and American continents
across Behring Strait. It unites Australia, Papua, and Tasmania in
a single area of elevation, which, together with the intervening
archipelago of Java, Sumatra, Borneo, Celebes, the Moluccas, and the
Philippines, may be looked upon as a prolongation of the continent of
Asia. It joins Ceylon to Hindostan and the Falkland Islands to the
South American continent. The 500-fathom line connects North America,
Greenland, Iceland, the Faroe Islands, and the continent of Europe,
the only unexplored space being Denmark Strait, between Iceland
and Greenland, where the soundings may exceed the above depth. The
1,000-fathom line unites New Zealand with Australia, Madagascar with
Africa, and nearly exhausts the depth of the more or less landlocked
seas which lie between Australia and Asia, Africa and Europe, South
and North America, and of the seas situated within the Arctic and
Antarctic Circles. The Cape de Verde Islands and the Canaries belong
to Africa, Madeira to Europe, and less than 500 fathoms divide Norway
from Spitzbergen.
Depths from 100 to 1,000 fathoms may be considered as shallow in
comparison with the prevailing depths from 2,000 to 3,000 fathoms
of the principal oceanic basins, and sufficient to establish a
connection between islands and continents, the more so as we
generally find one or more islands occupying the intervening space,
thus betraying the common link between them.
The result of this examination is that all the larger land masses
compose an area of elevation which, after nearly completing the
circuit of the world in the latitude of the Arctic Circle, subdivides
itself into two parts, an eastern and a western one--the former
embracing Europe, Africa, Asia, and Australia, the latter North and
South America. In a similar manner, the different oceans combine
into an area of depression which, after making the circuit of the
world along the parallel of lat. 60° S. under the name of the
Southern Ocean, divides itself into three large basins, respectively
designated as the Pacific, the Atlantic, and the Indian Oceans. Thus
the two elements, land and water, starting from opposite hemispheres,
extend their arms across the equator, holding each other in close
embrace, like two champions wrestling for the mastery of the world.
A comparison of the deep-sea soundings obtained up to the present
date shows that, if we omit the seas situated beyond the parallels of
lat. 60° N. and lat. 60° S.--no depths exceeding 2,000 fathoms having
as yet been ascertained beyond these latitudes--the average depth of
the ocean between these parallels may be estimated at about 2,500
fathoms, or more roughly at three English miles, and the average
depth of all seas on the surface of the globe at probably two miles.
Contrary to the ideas formerly entertained of the enormous depth of
the ocean, the soundings of H.M.S. _Challenger_, S.M.S. _Gazelle_,
and of the U.S.S. _Tuscarora_ and _Gettysburg_, indicate that depths
of five miles, or even 4,000 fathoms, are but seldom met with, and
are as exceptional as heights of the same amount on land.
One of the greatest depths ascertained in the Atlantic was found by
H.M.S. _Challenger_, about eighty miles north of the island of St.
Thomas in the West Indies. It is 3,875 fathoms, or about four and a
half miles. In May, 1876, the _Gettysburg_ found 3,593 fathoms only
eleven miles south of the _Challenger_ sounding. A depth of 3,370
fathoms obtained by the American ship shows that the deepest area in
the Atlantic is placed to the northward of the Virgin Islands, and
extends over 400 miles along the meridian of 65° W.
The greatest depth observed in the Indian Ocean was discovered by the
_Gazelle_ in May, 1875. Two soundings of 3,020 and 3,010 fathoms were
taken in the eastern extremity of this ocean between the northwest
coast of Australia and the line of islands extending from Java to
Timor.
The greatest of all depths of which we have reliable evidence
was found by the _Challenger_ on the 23d March, 1875, in the
comparatively narrow channel which separates the Caroline Islands
from the Mariana or Ladrone Islands. This sounding amounts to 4,575
fathoms, or about five miles and a quarter. Several soundings
exceeding 4,000 fathoms were obtained by the _Tuscarora_ to the
eastward of the islands of Nippon and Yesso, and another close to
the most westerly of the Aleutian Islands. Two of these soundings
are over 4,600 fathoms, but as it appears that no sample of the
bottom was brought up, there is no evidence of the latter having
been reached. H.M.S. _Challenger_, shortly after her departure from
Yokohama, sounded 3,950 and 3,625 fathoms, and in doing so seems to
have just touched the southern border of this deep but narrow area of
depression, which runs parallel to the eastern coasts of Japan and
the Kurile Archipelago as far as the entrance to the Behring Sea.
It will be observed that the above exceptional depths in the
Atlantic, Indian, and Pacific Oceans are not placed, as one might
be inclined to conjecture, in or near the centre of these oceanic
basins, but, on the contrary, upon their confines and in close
proximity to the land. This remarkable circumstance suggests the idea
that such areas of maximum depression may be the effect of a sinking
of the bottom of the sea in compensation for an upward movement of
the land in their immediate vicinity.
Just as the results of the recent soundings have rendered the
existence of depths from six to nine miles, as formerly reported,
highly improbable, so have they modified our ideas of the shape
of the sea-bottom. The latter was generally represented as a
repetition of the dry land with its combination of mountain, valley,
and plain. No doubt the sea-bottom within a short distance of the
shore naturally forms a continuation of the leading features of the
adjoining land. Thus a large plain or a low-lying country will, as a
rule, continue its almost level slopes to a considerable distance out
to sea, while a range of hills or a chain of mountains often extends
its steep inclines below the surface of the water.
The alteration of level in mid-ocean between two points as much as
a hundred miles apart is generally so slight that to an observer
standing at the bottom of the sea, the latter would appear a perfect
plain. Thus the bottom of our oceanic basins is composed of gentle
undulations rising and falling from a few fathoms to two or three
miles, in distances extending over many hundred miles. This view
accords with the experience of the geologist who finds that the bulk
of the dry land consists of sedimentary strata originally laid down
in a horizontal, or nearly horizontal, position at the bottom of the
sea, and there can be little doubt but that the depths of the ocean
are at the present time the scene of the formation of sedimentary
strata which some day may be converted into dry land, and contain
imbedded in their folds traces of the animal life with which they
abound.
One of the most remarkable results in connection with the
exploration of the sea is the discovery of several extensive
submarine plateaus, which interrupt what was until lately supposed
to be an unbroken waste of fathomless abyss. One of these plateaus
traverses the Atlantic Ocean in its whole length from north to south,
repeating in its form the S-shaped contour of the eastern and western
shores of this ocean. After attaching itself by its northern end to
the plateau which connects Europe and Iceland, and separates the
Atlantic from the Arctic basin, it runs southward toward the Azores,
and, gradually contracting in width, sweeps round toward St. Paul’s
Rocks. Reduced, comparatively speaking, to a narrow ridge, it follows
the line of the equator as far as the meridian of Ascension Island,
where, resuming its southward course, it widens out until in lat.
30° S. it occupies nearly half the space between South America and
Africa, uniting the island of Ascension with St. Helena in the east,
Trinidad in the west, and the group of Tristan d’Acunha and Gough
Island at its southern end.
Considerable portions of this plateau are within 1,500 fathoms, or a
mile and a half, of the surface of the sea, and most of the islands
are of volcanic origin. An extinct volcano, 8,300 feet in height,
forms the island of Tristan d’Acunha; Ascension Island rises to 2,800
feet, and the summit of Pico in the Azores to 7,600 feet above the
level of the sea. The northern end of the plateau joins the plateau
of Iceland with its still active focus of eruption.
By this central plateau, the Atlantic Ocean is divided into two
longitudinal areas of depression or channels, one following the
shores of North and South America, the other the shores of Europe
and Africa. The depths vary from 2,000 to nearly 4,000 fathoms, the
average depth being about three miles. The deepest portion of the
eastern channel is situated to the westward of the Cape de Verde
Islands, and forms an area of depression of over 3,000 fathoms.
In the western channel there are two such depressions, one placed
between the Antilles, Bermudas, and the Azores, the other between
Cape St. Roque, Ascension, and Trinidad. They are divided from each
other by a submarine elevation, which apparently connects the central
plateau with the South American continent.
The soundings taken in the Indian Ocean prove the existence of a
submerged plateau on the limit between the Indian Ocean and the
Southern Ocean. It rises in many parts to within 1,500 fathoms of
the sea-surface, and forms the common foundation of all the islands
situated in this part of the world--viz., Prince Edward Island, the
Crozet Islands, the Kerguelen group, the Heard Islands, and the
islands of St. Paul and Amsterdam. The origin of all these islands is
probably volcanic.
The main basin of the Indian Ocean with an average depth of over
2,000 fathoms, stretches from the meridian of the Cape of Good Hope
toward the angle between Java and northwestern Australia, where it
attains its greatest depths, forming a depression of over 3,000
fathoms. It communicates with the Arabian Sea by two narrow channels
situated north and south of the Chagos Archipelago, being nearly
cut off from that sea by a line of islands and shallow soundings
which connect Africa, Madagascar, Bourbon, and Mauritius, the Chagos
Islands and the Maldive Islands with the Asiatic continent. The
2,500-fathom area of the Indian Ocean crosses the parallel of lat.
40° S. between St. Paul and Amsterdam Islands and Cape Leeuwin in
Australia, and forms, between the south coast of Australia and the
forty-fifth parallel, an area of depression which extends beyond the
southern end of Tasmania, includes the deepest portion of the basin
between New South Wales and New Zealand, and probably communicates
with the depths of the Pacific by a channel situated off the southern
extremity of New Zealand.
If we divide the Pacific Ocean into an eastern and a western half
by a line passing from Honolulu to Tahiti, or by the meridian of
long. 150° W., we observe a remarkable contrast between the two
portions thus formed. While the eastern half, extending toward
America, presents a vast unbroken sheet of water, almost devoid of
islands, the western half, toward Asia and Australia, and inclosed
between the parallels of lat. 30° N. and lat. 30° S., is composed
of a labyrinth of seas, separated from each other by chains of
islands, the projecting points of numerous submarine ridges. Although
extensive tracts in the Pacific Ocean remain as yet untouched by
the sounding-line, the observations made by the _Challenger_, the
_Gazelle_, and the _Tuscarora_ enable us to form an idea of the
general contours of its bottom. From the shores of North and South
America, the depths of the eastern half of the Pacific gradually
increase until, upon the line between Honolulu and Tahiti, they
attain 3,000 fathoms. The latter depth forms extensive areas of
depression in the western half of this ocean, and increases to
4,000 fathoms in the already described hollow extending along the
Japanese and Kurile Islands toward the entrance of the Behring Sea.
Thus the idea formerly entertained of the inferior depths of the
Pacific in comparison with the Atlantic, founded apparently upon the
large number of islands scattered over its surface, is proved to be
erroneous. Many of these islands, especially in the northwestern
half, rise immediately from depths of 3,000 fathoms and more.
In the southeastern portion of the Pacific there are indications
of a submerged plateau connecting the Society Islands, the Low
Archipelago, the Marqueses, and the intervening islands of Easter
Island and Juan Fernandez with the coast of Chili and Patagonia.
It seems as if an almost uninterrupted area of elevation crossed
the whole basin of the Pacific in a northwesterly direction from
Patagonia to Japan. The tendency of most of the submerged ridges of
this ocean to follow the same direction has been frequently commented
upon, and, as is the case with the submerged plateaus of the Indian
and Atlantic Oceans, their association with centres of volcanic
activity is equally evident.
A line passing from Kamtchatka over Japan, the Ladrone, Caroline,
Marshall, Gilbert, Ellice, Samoa, Tonga, and Kermadec Islands to
New Zealand, divides the main basin of the Pacific, of an average
depth of 3,000 fathoms, from the much shallower seas lying to the
westward, and may possibly have formed the coast-line of a large
continent which existed at a remote epoch in the history of the
surface of our planet, and the boundaries of which have since been
driven back to the present confines of Asia and Australia.
The Southern Ocean, which makes the circuit of the world along the
parallel of 60° S., in length equal to half the circumference of
the earth at the equator, may be considered as occupying the space
between the Antarctic Circle and the parallel of lat. 40° S. Owing to
the limited number of soundings as yet obtained within its limits, we
can only form a general idea of the distribution of its depths.
The boundary-line of the fortieth parallel, which separates the
Southern Ocean from the Pacific, Atlantic, and Indian Oceans, is
occupied alternately by areas of depression, with depths ranging
from 2,500 to nearly 3,000 fathoms, and by areas of elevation, or
submarine plateaus, approaching to within 1,500 fathoms of the
sea-surface. With regard to the general distribution of depth in the
Southern Ocean, its bottom appears to rise gradually from nearly
3,000 fathoms at the fortieth parallel (with the exception of the
intervening plateaus) to little over 1,500 fathoms at the Antarctic
Circle. There are also indications of an area of depression of an
average depth of 2,000 fathoms, making the circuit of the globe
between the parallels of 50° and 60° lat. S. The whole surface of the
Southern Ocean is strewn with masses of floating ice, some of them
forming islands many miles in extent, and rising from 100 to 300 feet
above the level of the sea--an imposing spectacle, but fraught with
much danger to the navigator in these regions. It is this central
ocean which supplies the masses of cold water that fill up nearly
two-thirds of the total depth of the Atlantic, Pacific, and Indian
Oceans.
We are indebted to Sir James Ross for the first soundings procured
within the Antarctic Circle. They are situated in the wide inlet,
discovered by that illustrious navigator in the year 1840, which
extends along the meridian of New Zealand, and terminates at the foot
of Mount Erebus and Mount Terror. These soundings, which are all
under 500 fathoms, viewed in combination with the above-mentioned
gradual rise of the bottom of the Southern Ocean toward the Antarctic
Circle, justify the assumption that the seas included within the
latter do not exceed 1,500 fathoms in depth, their average depth
probably falling below this estimate. The extensive formation of ice
in this region, as well as the numerous indications of land reported
by the daring sailors who have penetrated so far south, suggest the
hypothesis of the existence, if not of an Antarctic continent, at
all events of a considerable extent of land, rising in the mountain
ranges and volcanoes of Victoria Land to 10,000 and 15,000 feet above
the level of the sea.
The region inclosed within the Arctic Circle forms an area of
depression, almost completely surrounded by the land-masses of the
great eastern and western continents. A shallow strait of less than
fifty fathoms in depth connects it with the Pacific Ocean, and it is
separated from the depths of the Atlantic by the plateau between the
British Islands and Iceland, which rises to within 500 fathoms of the
sea-surface. Greenland is probably the largest land-mass belonging to
this basin, and next in importance we have the group of Spitsbergen,
of Franz Joseph Land, discovered by the Austrian expedition; Nova
Zembla, the Liakhov Islands, Kellett Land, off Behring Strait,
discovered by the Americans in 1867; and finally the extensive
archipelago, a continuation of the American continent.
The few soundings taken within the Arctic Circle leave much to
conjecture, but we are tolerably safe in stating that the average
depth of the Arctic basin is probably under 1,000 fathoms. The
immense plains of Northern Asia and America seem to continue beneath
the surface of the Arctic Sea, as indicated by the numerous islands
which skirt the coasts of these continents, and the greatest depths
to be found inside the Arctic Circle are probably confined to the
basin situated between Greenland and Norway, Iceland and Spitzbergen.
CORAL FORMATIONS
--CHARLES DARWIN