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force appears to be in the north of Lapland, and to diminish gradually to
the south toward Calmar and Solvitzborg. Lines marking the ancient level of
the sea in pre-historic times are indicated throughout the whole of Norway,*
from Cape Lindesnaes to the extremity of the North Cape, by banks of shells
identical with those of the present seas, and which have lately been most
accurately examined by Bravais during his long winter sojourn at Bosekop.
[footnote] *Keilhan, in 'Nyt Mag. fur Naturvid.', 1832, bd. i., p. 105-254;
bd. ii., p. 57; Bravais, 'Surles Lignes d'ancien Niveau de la Mer', 1843, p.
15-40. See, also, Darwin, "on the Parallel Roads of Glen-Roy and Lochaber,"
in 'Philos. Trans. for' 1839, p. 60.
These banks lie nearly 650 feet above the present mean level of the sea, and
reappear, according to Keilhau and Eugene Robert, in a north-northwest
direction on the coasts of Spitzbergen, opposite the North Cape. Leopold
von Buch, who was the first to draw attention to the high banks of shells at
Tromsoe (latitude 69 degrees 40'), has, however, shown that the more ancient
elevations on the North Sea appertain to a different class of phenomena,
from the regular and gradual retrogressive elevations of the Swedish shores
in the Gulf of Bothnia. This latter phenomenon, which is well attested by
historical evidence, must not be confounded with the changes in the level of
the soil occasioned by earthquakes, as on the shores of Chili and of Cutch,
and which have recently given occasion to similar observations in other
countries. It has been found that a perceptible sinking resulting from a
disturbance of the strata of the upper surface sometimes occurs,
corresponding with an elevation elsewhere, as, for instance, in West
Greenland, according to Pingel and Graah, in Dalmatia and in Scania.
Since it is highly probable that the oscillatory movements of the soil, and
the rising and sinking of the upper surface, were more strongly marked in
the early periods of our planet than at present, we shall be less surprised
to find in the interior of continents some few portions of the earth's
surface lying below the general level of existing seas. Instances of this
kind occur in the soda lakes described by General Andreossy, the small
bitter lakes in the narrow Isthmus of Suez, the Caspian Sea, the Sea of
Tiberias, and especially the Dead Sea.*
[footnote] *Humboldt, 'Asie Centrale', t. ii., p. 319-324; t. iii., p.
549-551. The depression of the Dead Sea has been successively determined by
the barometrical measurements of Count Berton, by the more careful ones of
Russegger, and by the trigonometrical survey of Lieutenant Symond, of the
Royal Navy, who states that the difference of level between the surface of
the Dead Sea and the highest houses of Jaffa is about 1605 feet. Mr.
Alderson, who communicated this result to the Geographical Society of London
in a letter, of the contents of which I was informed by my friend, Captain
Washington, was of opinion (Nov. 28, 1841) that the Dead Sea lay about 1400
feet under the level of the Mediterranean. A more recent communication of
Lieutenant Symond (Jameson's 'Edinburgh New Philosophical Journal', vol.
xxxiv., 1843, p. 178) gives 1312 feet as the final result of two very
accordant trigonometrical operations.
The level of the water in the two last-named seas is
p 297
666 and 1312 feet below the level of the Mediterranean. If we could
suddenly remove the alluvial soil which covers the rocky strata in many
parts of the earth's surface, we should discover how great a portion of the
rocky crust of the earth was then below the present level of the sea. The
periodic, although irregularly alternating rise and fall of the water of the
Caspian Sea, of which I have myself observed evident traces in the northern
portions of its basin, appears to prove,* as do also the observations of
Darwin on the coral seas,** that without earthquakes, properly so- called,
the surface of the earth is capable of the same gentle and progressive
oscillations as those which must have prevailed so generally in the earliest
ages, when the surface of the hardening crust of the earth was less compact
than at present.
[footnote] *'Sur la Mobilite du fond de la Mer Caspienne', in my 'Asie
Centr.', t. ii., p. 283-294. The Imperial Academy of Sciences of St.
Petersburgh in 1830, at my request, charged the learned physicist Lenz to
place marks indicating the mean level of the sea, for definite epochs, in
different places near Baku, in the peninsula of Abscheron. In the same
manner, in an appendix to the instructions given to Captain (now Sir James
C.) Ross for his Antarctic expedition, I urged the necessity of causing
marks to be cut in the rocks of the southern hemisphere, as had already been
done in Sweden and on the shores of the Caspian Sea. Had this measure been
adopted in the early voyages of Bougainville and Cook, we should now know
whether the secular relative changes in the level of the seas and land are
to be considered as a general, or merely a local natural phenomenon, and
whether a law of direction can be recognized in the points which have
simultaneous elevation or depression.
[footnote] **On the elevation and depression of the bottom of the South
Sea, and the diffrent areas of alternate movements, see Darwin's 'Journal',
p. 557, 561-566.
The phenomena to which we would here direct attention remind us of the
instability of the present order of things, and of the changes to which the
outlines and configuration of continents are probably still subject at long
intervals of time. That which may scarcely be perceptible in one
generation, accumulates during periods of time, whose duration is revealed
to us by the movement of remote heavenly bodies. The eastern coast of the
Scandinavian peninsula has probably risen
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about 320 feet in the space of 8000 years; and in 12,000 years, if the
movement be regular, parts of the bottom of the sea which lie nearest the
shores, and are in the present day covered by nearly fifty fathoms of water,
will come to the surface and constitute dry land. But what are such
intervals of time compared to the length of the geognostic periods revealed
to us in the stratified series of formations, and in the world of extinct
and varying organisms! We have hitherto only considered the phenomena of
elevation; but the analogies of observed facts lead us with equal justice to
assume the possibility of the depression of whole tracts of land. The mean
elevation of the non-mountainous parts of France amounts to less than 480
feet. It would not, therefore, require any long period of time, compared
with the old geognostic periods, in which such great changes were brought
about in the interior of the earth, to effect the permanent submersion of
the northwestern part of Europe, and induce essential alterations in its
littoral relations.
The depression and elevation of the solid or fluid parts of the earth --
phenomena which are so opposite in their action that the effect of elevation
in one part is to produce an apparent depression in another -- are the
causes of all the changes which occur in the configuration of continents.
In a work of this general character, and in an impartial exposition of the
phenomena of nature, we must not overlook the 'possibility' of a diminution
of the quantity of water, and a constant depression of the level of seas.
Thgere can scarcely be a doubt that, at the period when the temperature of
the surface of the earth was higher, when the waters were inclosed in larger
and deeper fissures, and when the atmosphere possessed a totally different
character from what it does at present, great changes must have occurred in
the level of seas, depending upon the increase and decrease of the liquid
parts of the earth's surface. But in the actual condition of our planet,
there is no direct evidence of a real continuous increase or decrease of the
sea, and we have no proof of any gradual change in its level at certain
definite points of observation, as indicated by the mean range of the
barometer. According to experiments made by Daussy and Antonio Nobile, an
increase in the height of the barometer would in itself be attended by a
depression in the level of the sea. But as the mean pressure of the
atmosphere at the level of the sea is not the same at all latitudes, owing
to meteorological causes depending upon the direction of the wind and
varying degrees of moisture, the
p 299
barometer alone can not afford a certain evidence of the general change of
level in the ocean. The remarkable fact that some of the ports in the
Mediterranean were repeatedly left dry during several hours at the beginning
of this century, appears to show that currents may by changes occurring in
their direction and force, occasion a 'local'' retreat of the sea, and a
permanent drying of a small portion of the shore, without being followed by
any actual diminution of water, or any permanent depression of the ocean.
We must, however, be very cautious in applying the knowledge which we have
lately arrived at, regarding these involved phenomena, since we might
otherwise be led to ascribe to water as the elder element, what ought to be
referred to the two other elements, earth and air.
As the 'external' configuration of continents, which we have already
described in their horizontal expansion, exercises, by their variously
indented littoral outlines, a favorable influence on climate, trade, and the
progress of civilization, so likewise does their internal articulation, or
the vertical elevation of the soil (chains of mountains and elevated
plateaux), give rise to equally important results. Whatever produces a
polymorphic diversity of forms on the surface of our planetary habitation --
such as mountains, lakes, grassy savannas, or even deserts encircled by a
band of forests -- impresses some peculiar character on the social condition
of the inhabitants. Ridges of high land covered by snow impede intercourse;
but a blending of low, discontinued mountain chains* and tracts of valleys,
as we see so happily presented in the west and south of Europe, tends to the
multiplication of meteorological processes and the products of vegetation,
and, from the variety manifested in different kinds of cultivation in each
district, even under the same degree of latitude, gives rise to wants that
stimulate the activity of the inhabitants.
[footnote] *Humboldt, 'Rel. Hist.', t. iii., p. 232-234. See also, the
able remarks on the configuration of the earth, and the position of its
lines of elevation in Albrechts von Roon, 'Grundzugen der Erd Volker und
Staatenkunde', Abth. i., 1837, s. 158, 270, 276.
Thus the awful revolutions, during which, by the action of the interior on
the crust of the earth, great mountain chains have been elevated by the
sudden upheaval of a portion of the oxydized exterior of our planet, have
served, after the establishment of repose, and on the revival of organic
life, to furnish a richer and more beautiful variety of individual forms,
and in a great measure to remove from the earth that aspect of dreary
p 300
uniformity which exercises so impoverishing an influence on the physical and
intellectual powers of mankind.
According to the grand views of Elie de Beaumont, we must ascribe a relative
age to each system of mountain chains* on the supposition that their
elevation must necessarily have occurred between the period of the
deposition of the vertically elevated strata and that of the horizontally
inclined strata running at the base of the mountains.
[footnnote] *Leop. von Buch, 'Ueber die Geognostischen Systeme von
Deutschland', in his 'Geogn. Briefen an Alexander von Humboldt', 1824, s.
265-271; Elie de Beaumont, 'Recherches sur les Revolutions de la Surface du
Globe', 1829, p. 297-307.
The ridges of the Earth's crust -- elevations of strata which are of the
same geognostic age -- appear, moreover, to follow one common direction.
The line of strike of the horizontal strata is not always parallel with the
axis of the chain, but intersects it, so that, according to my views,* the
phenomenon of elevation of the strata, which is even found to be repeated in
the neighboring plains, must be more ancient than the elevation of the chain.
[footnote] *Humboldt, 'Asie Centrale', t. i., p. 277-283. See, also my
'Essai sur le Gisement des Roches', 1822, p. 57, and 'Relat. Hist.', t.
iii., p. 244-250.
The main direction of the whole continent of Europe (from southwest to
northeast) is opposite to that of the great fissures which pass from
northwest to southeast, from the mouths of the Rhine and Elbe, through the
Adriatic and Red Seas, and through the mountain system of Putschi-Koh in
Luristan, toward the Persian Gulf and the Indian Ocean. This almost
rectangular intersection of geodesic lines exercises an important influence
on the commercial relations of Europe, Asia, and the northwest of Africa,
and on the progress of civilization on the formerly more flourishing shores
of the Mediterranean.*
[footnote] *'Asie Centrale', t. i., p. 284, 286. The Adriatic Sea likewise
follows a direction from S.E. to N.W.
Since grand and lofty mountain chains so strongly excite our imagination by
the evidence they afford of great terrestrial revolutions, and when
considered as the boundaries of climates, as lines of separation for waters,
or as the site of a different form of vegetation, it is the more necessary
to demonstrate, by a correct numerical estimation of their volume, how small
is the quantity of their elevated mass when compared with the area of the
adjacent continnents. The mass of the Pyrenees, for instance, the mean
elevation of whose summits, and the real quantity of whose base have been
ascertained by accurate measurements, would if scattered over
p 301
the surface of France, only raise its mean level about 115 feet. The mass
of the eastern and western Alps would in like manner only increase the
height of Europe about 21 1/2 feet above its present level. I have found by
a laborious investigation,* which from its nature, can only give a maximum
limit, that the center of gravity of the volume of the land raised above the
present level of the sea in Europe and North America is respectively
situated at an elevation of 671 and 748 feet, while it is at 1132 and 1152
feet in Asia and South America.
[footnote] *'De la hauteur Moyenne des Continents', in my 'Asie Centrale',
t. i., p. 82-90, 165-189. The results which I have obtained are to be
regarded as the extreme value ('nombres-limites'). Laplace's estimate of
the mean height of continents at 3280 feet is at least three times too high.
The immortal author of the 'Mecanique Celeste' (t. v., p. 14) was led to
this conclusion by hypothetical views as to the mean depth of the sea. I
have shown ('Asie Centr.', t. i., p. 93) that the old Alexandrian
mathematicians, on the testimony of Plutarch ('in Aemilio Paulo', cap. 15),
believed this depth to depend on the height of the mountains. The height of
the center of gravity of the volume of the continental masses is probably
subject to slight variations in the course of many centuries.
These numbers show the low level of norther regions. In Asia the vast
steppes of Siberia are compensated for by the great elevations of the land
(between the Himalaya, the North Thibetian chain of Kuen-lun, and the
Celestial Mountains), from 28 degrees 30' to 40 degrees north latitude. We
may, to a certain extent, trace in these numbers the portions of the Earth
in which the Plutonic forces were most intensely manifested in the interior
by the upheaval of continental masses.
There are no reasons why these Plutonic forces may not, in future ages, add
new mountain systems to those which Elie de Beaumont has shown to be of such
different ages, and inclined in such different directions. Why should the
crust of the Earth have lost its property of being elevated in the ridges?
The recently-elevated mountain systems of the Alps and the Cordilleras
exhibit in Mont Blanc and Monte Rosa, in Sorata, Illimani, and Chimborazo,
colossal elevations which do not favor the assumption of a decrease in the
intensity of the subterranean forces. All geognostic phenomena indicate the
periodic alternation of activity and repose;* but the quiet we now enjoy is
only apparent.
[footnote] *'Zweiter Geologischer Brief von Elie de Beaumont an Alexander
von Humboldt', in Poggendorf's 'Annalen', bd. xxv., s. 1-58.
The tremblings which still agitate the surface under all latitudes, and in
every species of rock, the elevation of Sweden, the appearance of new
islands of eruption, are all conclusive as to the unquiet condition of our
planet.
p 302
The two envelopes of the solid surface of our planet -- the liquid and the
aeriform -- exhibit, owing to the mobility of their particles, their
currents, and their atmospheric relations, many analogies combined with the
contrasts which arise from the great difference in the condition of their
aggregation and elasticity. The depths of ocean and of air are alike
unknown to us. At some few places under the tropics no bottom has been
found with soundings of 276,000 (or more than four miles), while in the air,
if, according to Wollaston, we may assume that it has a limit from which
waves of sound may be reverberated, the phenomenon of twilight would incline
us to assume a height at least nine times as great.*
[footnote] *[See Wilson's Paper, 'On Wollaston's Argument from the
Limitation of the Atmosphere as to the finite Divisibility of Matter.' --
'Trans. of the Royal Society of Edinb.', vol. xvi., p. 1, 1845.] -- Tr.
The aërial ocean rests partly on the solid earth, whose mountain chains and
elevated plateaux rise, as we have already seen, like green wooded shoals,
and partly on the sea, whose surface forms a moving base, on which rest the
lower, denser, and more saturated strata of air.
Proceeding upward and downward from the common limit of the aërial and
liquid oceans, we find that the strata of air and water are subject to
determinate laws of decrease of temperature. This decrease is much less
rapid in the air than in the sea, which has a tendency under all latitudes
to maintain its temperature in the strata of water most contiguous to the
atmosphere, owing to the sinking of the heavier and more cooled particles.
A large series of the most carefully conducted observations on temperature
shows us that in the ordinary and mean condition of its surface, the ocean
from the equator to the forty-eighth degree of north and south latitude is
somewhat warmer than the adjacent strata of air.*
[footnnote[ *Hamboldt, 'Relation Hist.', t. iii., chap. xxix., p. 514-530.
Owing to this decrease of temperature at increasing depths, fishes and other
inhabitants of the sea, the nature of whose digestive and respiratory organs
fits them for living in deep water, may even, under the tropics, find the
low degree of temperature and the coolness of climate characteristic of more
temperate and more northern latitudes. This circumstance, which is
analogous to the prevalence of a mild and even cold air on the elevated
plains of the torrid zone, exercises a special influence on the migration
and geographical distribution of many marine animals. Moreover, the depths
at which fishes live, modify, by the increase of pressure, their cutaneous
respiration, and the
p 303
oxygenous and nitrogenous contents of the swimming bladders.
As fresh and salt water do not attain the maximum of their density at the
same degree of temperature, and as the saltness of the sea lowers the
thermometrical degree corresponding to this point, we can understand how the
water drawn from breat depths of the sea during the voyages of the Kotzebue
and Dupetit-Thouars could have been found to have only the temperature of 37
degrees and 36.5 degrees. This icy temperatureof sea water, which is
likewise manifested at the depths of tropical seas, first led to a study of
the lower polar currents, which move from both poles toward the equator.
Without these submarine currents, the tropical seas at those depths could
only have a temperature equal to the local maximum of cold possessed by the
falling particles of water at the radiating and cooled surface of the
tropical sea. In the Mediterranean, the cause of the absence of such a
refrigeration of the lower strata is ingeniously explained by Arago, on the
assumption that the entrance of the deeper polar currents into the Straits
of Gibraltar, where the water at the surface flows in from the Atlantic
Ocean from west to east, is hindered by the submariine counter-currents
which move from east to west, from the Mediterranean into the Atlantic.
The ocean, which acts as a general equalizer and moderator of climates,
exhibits a most remarkable uniformity and constancy of temperature,
especially between 10 degrees north and 10 degrees south latitude,* over
spaces of many thousands of square miles, at a distance from land where it
is not penetrated by currents of cold and heated water.
[footnote] *See the series of observations made by me in the South Sea,
from 8 degrees 5' to 13 degrees 16' N. lat., in my 'Asie Centrale', t. iii.,
p. 234.
It has therefore, been justly observed, that an exact and long-continued
investigation of these thermic relations of the tropical seas might most
easily afford a solution to the great and much-contested problem of the
permanence of climates and terrestrial temperatures.*
[footnote] *We might (by means of the temperature of the ocean under the
tropics) enter into the consideration of a question which has hitherto
remained unanswered, namely, that of the constancy of terrestrial
temperatures, without taking into account the very circumscribed local
influences arising from the diminution of wood in the plains and on
mountains, and the drying up of lakes and marshes. Each age might easily
transmit to the succeeding one some few data, which would perhaps furnish
the most simple, exact, and direct means of deciding whether the sun, which
is almost the sole and exclusive source of the heat of our planet, changes
its physical constitution and splendor, like the greater number of the
stars, or whether, on the contrary, that luminary has attained to a
permanent condition." -- Arago, in the 'Comptes Rendus des Seances de
l'Acad. des Sciences', t. ii., p. 321, 327.
Great changes in the luminous disk of the sun would,
p 304
if they were of long duration, be reflected with more certainty in the mean
temperature of the sea than in that of the solid land.
The zones at which occur the maxima of the oceanic temperature and of the
density (the saline contents) of its waters, do not correspond with the
equator. The two maxima are separated from one another, and the waters of
the highest temperature appear to form two nearly parallel lines north and
south of the geographical equator. Lenz, in his voyage of circumnavigation,
found in the Pacific the maxima of density in 22 degrees north and 17
degrees south latitude, while its minimum was situated a few degrees to the
south of the equator. In the region of calms the solar heat can exercise
but little influence on evaporation, because the stratum of air impregnated
with saline aqueous vapor, which rests on the surface of the sea, remains
still and unchanged.
The surface of all connected seas must be considered as having a general
perfectly equal level with respect to their mean elevation. Local causes
(probably prevailing winds and currents) may, however, produce permanent,
although trifling changes in the level of some deeply indented bays, as for
instance, the Red Sea. The highest level of the water at the Isthmus of
Suez is at different hours of the day from 24 to 30 feet above that of the
Mediterranean. The form of the Straits of Bab-el-Mandeb, through which the
waters appear to find an easier ingress than egress, seems to contribute to
this remarkable phenomenon, which was known to the ancients.*
[[footnote] *Humboldt, 'Asie Centrale', t. ii., p. 321, 327.