ELEVATION AND SUBSIDENCE OF LAND WITHOUT EARTHQUAKES.
Changes in the relative level of land and sea in regions not
volcanic--Opinion of Celsius that the waters of the Baltic Sea and
Northern Ocean were sinking--Objections raised to his
opinion--Proofs of the stability of the sea level in the
Baltic--Playfair's hypothesis that the land was rising in
Sweden--Opinion of Von Buch--Marks cut on the rocks--Survey of these
in 1820--Facility of detecting slight alterations of level on coast
of Sweden--Shores of the ocean also rising--Area upheaved--Shelly
deposits of Uddevalla--Of Stockholm, containing fossil shells
characteristic of the Baltic--Subsidence in south of Sweden--Fishing
hut buried under marine strata--Upheaval in Sweden not always in
horizontal planes--Sinking of land in Greenland--Bearing of these
facts on geology.
We have now considered the phenomena of volcanoes and earthquakes
according to the division of the subject before proposed (p. 345), and
have next to turn our attention to those slow and insensible changes in
the relative level of land and sea which take place in countries remote
from volcanoes, and where no violent earthquakes have occurred within
the period of human observation. Early in the last century the Swedish
naturalist, Celsius, expressed his opinion that the waters, both of the
Baltic and Northern Ocean, were gradually subsiding. From numerous
observations, he inferred that the rate of depression was about fifty
Swedish inches in a century.[728] In support of this position, he
alleged that there were many rocks both on the shores of the Baltic and
the ocean known to have been once sunken reefs, and dangerous to
navigators, but which were in his time above water--that the waters of
the Gulf of Bothnia had been gradually converted into land, several
ancient ports having been changed into inland cities, small islands
joined to the continent, and old fishing-grounds deserted as being too
shallow, or entirely dried up. Celsius also maintained, that the
evidence of the change rested not only on modern observations, but on
the authority of the ancient geographers, who had stated that
Scandinavia was formerly an island. This island, he argued, must in the
course of centuries, by the gradual retreat of the sea, have become
connected with the continent; an event which he supposed to have
happened after the time of Pliny, and before the ninth century of our
era.
To this argument it was objected that the ancients were so ignorant of
the geography of the most northern parts of Europe, that their authority
was entitled to no weight; and that their representation of Scandinavia
as an island, might with more propriety be adduced to prove the
scantiness of their information, than to confirm so bold an hypothesis.
It was also remarked that if the land which connected Scandinavia with
the main continent was laid dry between the time of Pliny and the ninth
century, to the extent to which it is known to have risen above the sea
at the latter period, the rate of depression could not have been
uniform, as was pretended; for it ought to have fallen much more rapidly
between the ninth and eighteenth centuries.
Many of the proofs relied on by Celsius and his followers were
immediately controverted by several philosophers, who saw clearly that a
fall of the sea in any one region could not take place without a general
sinking of the waters over the whole globe: they denied that this was
the fact, or that the depression was universal, even in the Baltic. In
proof of the stability of the level of that sea, they appealed to the
position of the island of Saltholm, not far from Copenhagen. This island
is so low, that in autumn and winter it is permanently overflowed; and
it is only dry in summer, when it serves for pasturing cattle. It
appears, from the documents of the year 1280, that Saltholm was then
also in the same state, and exactly on a level with the mean height of
the sea, instead of having been about twenty feet under water, as it
ought to have been, according to the computation of Celsius. Several
towns, also, on the shores of the Baltic, as Lubeck, Wismar, Rostock,
Stralsund, and others, after six and even eight hundred years, are as
little elevated above the sea as at the era of their foundation, being
now close to the water's edge. The lowest part of Dantzic was no higher
than the mean level of the sea in the year 1000; and after eight
centuries its relative position remains exactly the same.[729]
Several of the examples of the gain of land and shallowing of the sea
pointed out by Celsius, and afterwards by Linnaeus, who embraced the same
opinions, were ascribed by others to the deposition of sediment at
points where rivers entered; and, undoubtedly, Celsius had not
sufficiently distinguished between changes due to these causes and such
as would arise if the waters of the ocean itself were diminishing. Many
large rivers descending from a mountainous country, at the head of the
Gulf of Bothnia, enter the sea charged with sand, mud, and pebbles; and
it was said that in these places the low land had advanced rapidly,
especially near Torneo. At Piteo also, half a mile had been gained in
forty-five years; at Luleo,[730] no less than a mile in twenty-eight
years; facts which might all be admitted consistently with the
assumption that the level of the Baltic has remained unchanged, like
that of the Adriatic, during a period when the plains of the Po and the
Adige have greatly extended their area.
It was also alleged that certain insular rocks, once entirely covered
with water, had at length protruded themselves above the waves, and
grown, in the course of a century and a half, to be eight feet high. The
following attempt was made to explain away this phenomenon:--In the
Baltic, large erratic blocks, as well as sand and smaller stones which
lie on shoals, are liable every year to be frozen into the ice, where
the sea freezes to the depth of five or six feet. On the melting of the
snow in spring, when the sea rises about half a fathom, numerous
ice-islands float away, bearing up these rocky fragments so as to convey
them to a distance; and if they are driven by the waves upon shoals,
they may convert them into islands by depositing the blocks; if stranded
upon low islands, they may considerably augment their height.
Browallius, also, and some other Swedish naturalists, affirmed that some
islands were lower than formerly; and that, by reference to this kind of
evidence, there was equally good reason for contending that the level of
the Baltic was gradually rising. They also added another curious proof
of the permanency of the water level, at some points at least, for many
centuries. On the Finland coast were some large pines, growing close to
the water's edge; these were cut down, and, by counting the concentric
rings of annual growth, as seen in a transverse section of the trunk, it
was demonstrated that they had stood there for four hundred years. Now,
according to the Celsian hypothesis, the sea had sunk about fifteen feet
during that period, in which case the germination and early growth of
these pines must have been, for many seasons, below the level of the
water. In like manner it was asserted, that the lower walls of many
ancient castles, such as those of Sonderburg and Abo, reached then to
the water's edge, and must, therefore, according to the theory of
Celsius, have been originally constructed below the level of the sea.
[Illustration: Fig. 91.]
In reply to this last argument, Colonel Hallstrom, a Swedish engineer,
well acquainted with the Finland coast, assured me, that the base of the
walls of the castle of Abo is now ten feet above the water, so that
there may have been a considerable rise of the land at that point since
the building was erected.
Playfair, in his "Illustrations of the Huttonian Theory," in 1802,
admitted the sufficiency of the proofs adduced by Celsius, but
attributed the change of level to the movement of the land, rather than
to a diminution of the waters. He observed, "that in order to depress or
elevate the absolute level of the sea, by a given quantity, in any one
place, we must depress or elevate it by the same quantity over the whole
surface of the earth; whereas no such necessity exists with respect to
the elevation or depression of the land."[731] The hypothesis of the
rising of the land he adds, "agrees well with the Huttonian theory,
which holds, that our continents are subject to be acted upon by the
expansive forces of the mineral regions; that by these forces they have
been actually raised up, and are sustained by them in their present
situation.[732]
In the year 1807, Von Buch, after returning from a tour in Scandinavia,
announced his conviction, "that the whole country, from Frederickshall
in Norway to Abo in Finland, and perhaps as far as St. Petersburg, was
slowly and insensibly rising." He also suggested "that Sweden may rise
more than Norway, and the northern more than the southern part."[733] He
was led to these conclusions principally by information obtained from
the inhabitants and pilots, and in part by the occurrence of marine
shells of recent species, which he had found at several points on the
coast of Norway above the level of the sea. He also mentions the marks
set on the rocks. Von Buch, therefore, has the merit of being the first
geologist who, after a personal examination of the evidence, declared in
favor of the rise of land in Scandinavia.
The attention excited by this subject in the early part of the last
century, induced many philosophers in Sweden to endeavor to determine,
by accurate observations, whether the standard level of the Baltic was
really subject to periodical variations; and under their direction,
lines or grooves, indicating the ordinary level of the water on a calm
day, together with the date of the year, were chiselled out upon the
rocks. In 1820-21, all the marks made before those years were examined
by the officers of the pilotage establishment of Sweden; and in their
report to the Royal Academy of Stockholm they declared, that on
comparing the level of the sea at the time of their observations with
that indicated by the ancient marks, they found that the Baltic was
lower relatively to the land in certain places, but the amount of change
during equal periods of time had not been everywhere the same. During
their survey, they cut new marks for the guidance of future observers,
several of which I had an opportunity of examining fourteen years after
(in the summer of 1834), and in that interval the land appeared to me to
have risen at certain places north of Stockholm four or five inches. I
also convinced myself, during my visit to Sweden, after conversing with
many civil engineers, pilots, and fishermen, and after examining some
of the ancient marks, that the evidence formerly adduced in favor of the
change of level, both on the coasts of Sweden and Finland, was full and
satisfactory.[734] The alteration of level evidently diminishes as we
proceed from the northern parts of the Gulf of Bothnia towards the
south, being very slight around Stockholm. Some writers have indeed
represented the rate of depression of the waters at Stockholm as very
considerable, because certain houses in that city which are built on
piles have sunk down within the memory of persons still living, so as to
be out of the perpendicular; and this in consequence of the tops of the
piles giving way and decaying, owing to a fall of the waters which has
exposed them to be alternately wet and dry. The houses alluded to are
situated on the borders of Lake Maeler, a large lake, the outlet of
which joins the Baltic, in the middle of Stockholm. This lake is
certainly lower than formerly; but the principal cause of the change is
not the elevation of the land, but the removal of two old bridges built
on piles, which formerly obstructed the discharge of the fresh water
into the sea. Another cause is the opening, in the year 1819, of a new
canal at Sodertelje, a place south of Stockholm, by means of which a new
line of communication was formed between Lake Maeler and the
Baltic.[735]
It will naturally be asked, whether the mean level of a sea like the
Baltic can ever be determined so exactly as to permit us to appreciate a
variation of level, amounting only to one or two feet. In reply, I may
observe, that, except near the Cattegat, there are no tides in the
Baltic; and it is only when particular winds have prevailed for several
days in succession, or at certain seasons when there has been an
unusually abundant influx of river water, or when these causes have
combined, that this sea is made to rise two or three feet above its
standard level. The fluctuations due to these causes are nearly the same
from year to year; so that the pilots and fishermen believe and
apparently with reason, that they can mark a deviation, even of a few
inches, from the ordinary or mean height of the waters.
There are, moreover, peculiarities in the configuration of the shores of
Norway and Sweden, which facilitate in a remarkable degree the
appreciation of slight changes in the relative level of land and water.
It has often been said, that there are two coasts, an inner and an outer
one; the inner being the shore of the main land; the outer one, a fringe
of countless rocky islands of all dimensions, called the skar (_shair_).
Boats and small vessels make their coasting voyages within this skar:
for here they may sail in smooth water, even when the sea without is
strongly agitated. But the navigation is very intricate, and the pilot
must possess a perfect acquaintance with the breadth and depth of every
narrow channel, and the position of innumerable sunken rocks. If on such
a coast the land rises one or two feet in the course of half a century,
the minute topography of the skar is entirely altered. To a stranger,
indeed, who revisits it after an interval of many years, its general
aspect remains the same; but the inhabitant finds that he can no longer
penetrate with his boat through channels where he formerly passed, and
he can tell of countless other changes in the height and breadth of
isolated rocks, now exposed, but once only seen through the clear water.
The rocks of gneiss, mica-schist, and quartz are usually very hard on
this coast, slow to decompose, and, when protected from the breakers,
remaining for ages unaltered in their form. Hence it is easy to mark the
stages of their progressive emergence by the aid of natural and
artificial marks imprinted on them. Besides the summits of _fixed_
rocks, there are numerous erratic blocks of vast size strewed over the
shoals and islands in the skar, which have been probably drifted by ice
in the manner before suggested.[736] All these are observed to have
increased in height and dimension with the last half century. Some,
which were formerly known as dangerous sunken rocks, are now only hidden
when the water is highest. On their first appearance, they usually
present a smooth, bare, rounded protuberance, a few feet or yards in
diameter; and a single sea-gull often appropriates to itself this
resting-place, resorting there to devour its prey. Similar points, in
the mean time, have grown to long reefs, and are constantly whitened by
a multitude of sea-fowl; while others have been changed from a reef,
annually submerged, to a small islet, on which a few lichens, a
fir-seedling, and a few blades of grass, attest that the shoal has at
length been fairly changed into dry land. Thousands of wooded islands
around show the great alterations which time can work. In the course of
centuries also, the spaces intervening between the existing islands may
be laid dry, and become grassy plains encircled by heights well clothed
with lofty firs. This last step of the process, by which long fiords and
narrow channels, once separating wooded islands, are deserted by the
sea, has been exemplified within the memory of living witnesses on
several parts of the coast.
Had the apparent fall of the waters been observed in the Baltic only, we
might have endeavored to explain the phenomenon by local causes
affecting that sea alone. For instance, the channel by which the Baltic
discharges its surplus waters into the Atlantic, might be supposed to
have been gradually widened and deepened by the waves and currents, in
which case a fall of the water like that before alluded to in Lake
Maeler, might have occurred. But the lowering of level would in that
case have been uniform and universal, and the waters could not have sunk
at Torneo, while they retained their former level at Copenhagen. Such an
explanation is also untenable on other grounds; for it is a fact, as
Celsius long ago affirmed, that the alteration of level extends to the
western shores of Sweden, bordering the ocean. The signs of elevation
observed between Uddevalla and Gothenburg are as well established as
those on the shores of the Bothnian Gulf. Among the places where they
may be studied, are the islands of Marstrand and Gulholmen, the
last-mentioned locality being one of those particularly pointed out by
Celsius.
The inhabitants there and elsewhere affirm, that the rate of the sinking
of the sea (or elevation of land) varies in different and adjoining
districts, being greatest at points where the land is low. But in this
they are deceived; for they measure the amount of rise by the area
gained, which is most considerable where the land descends with a gentle
slope into the sea. In the same manner, some advocates of the Celsian
theory formerly appealed to the increase of lands near the mouths of
rivers, not sufficiently adverting to the fact, that if the bed of the
sea is rising, the change will always be most sensible where the bottom
has been previously rendered shallow; whereas, at a distance from these
points where the scarped granitic cliffs plunge at once into deep water,
a much greater amount of elevation is necessary to produce an equally
conspicuous change.
As to the area in northern Europe which is subject to this slow
upheaving movement, we have not as yet sufficient data for estimating it
correctly. It seems probable, however, that it reaches from Gothenburg
to Torneo, and from thence to the North Cape, the rate of elevation
increasing always as we proceed farther northwards. The two extremities
of this line are more than a thousand geographical miles distant from
each other; and as both terminate in the ocean, we know not how much
farther the motion may be prolonged under water. As to the breadth of
the tract, its limits are equally uncertain, though it evidently extends
across the widest parts of the Gulf of Bothnia, and may probably stretch
far into the interior, both of Sweden and Finland. Now if the elevation
continue, a larger part of the Gulf of Bothnia will be turned into land,
as also more of the ocean off the west coast of Sweden between
Gothenburg and Uddevalla; and on the other hand, if the change has been
going on for thousands of years at the rate of several feet in a
century, large tracts of what is now land must have been submarine at
periods comparatively modern. It is natural therefore to inquire whether
there are any signs of the recent sojourn of the sea on districts now
inland? The answer is most satisfactory.--Near Uddevalla and the
neighboring coastland, we find upraised deposits of shells belonging to
species such as now live in the ocean; while on the opposite or eastern
side of Sweden, near Stockholm, Gefle, and other places bordering the
Bothnian Gulf, there are analogous beds containing shells of species
characteristic of the Baltic.
Von Buch announced in 1807, that he had discovered in Norway and at
Uddevalla in Sweden, beds of shells of existing species, at considerable
heights above the sea. Since that time, other naturalists have
confirmed his observation; and, according to Strom, deposits occur at
an elevation of more than 400 feet above the sea in the northern part of
Norway. M. Alex. Brongniart, when he visited Uddevalla, ascertained that
one of the principal masses of shells, that of Capellbacken, is raised
more than 200 feet above the sea, resting on rocks of gneiss, all the
species being identical with those now inhabiting the contiguous ocean.
The same naturalist also stated, that on examining with care the surface
of the gneiss, immediately above the ancient shelly deposit, he found
barnacles (_balani_) adhering to the rocks, showing that the sea had
remained there for a long time. I was fortunate enough to be able to
verify this observation by finding in the summer of 1834, at Kured,
about two miles north of Uddevalla, and at the height of more than 100
feet above the sea, a surface of gneiss newly laid open by the partial
removal of a mass of shells used largely in the district for making lime
and repairing the roads. So firmly did these barnacles adhere to the
gneiss, that I broke off portions of the rock with the shells attached.
The face of the gneiss was also incrusted with small zoophytes
(_Cellepora?_ Lam.); but had these or the barnacles been exposed in the
atmosphere ever since the elevation of the rocks above the sea, they
would doubtless have decomposed and been obliterated.
The town of Uddevalla (see Map, p. 523) stands at the head of a narrow
creek overhung by steep and barren rocks of gneiss, of which all the
adjacent country is composed, except in the low grounds and bottoms of
valleys, where strata of sand, clay, and marl frequently hide the
fundamental rocks. To these newer and horizontal deposits the fossil
shells above mentioned belong, and similar marine remains are found at
various heights above the sea on the opposite island of Orust. The
extreme distance from the sea to which such fossils extend is as yet
unknown; but they have been already found at Trollhattan in digging the
canal there, and still farther inland on the northern borders of Lake
Wener, fifty miles from the sea, at an elevation of 200 feet near Lake
Rogvarpen.
To pass to the Baltic: I observed near its shores at Sodertelje, sixteen
miles S. W. of Stockholm, strata of sand, clay, and marl, more than 100
feet high, and containing shells of species now inhabiting the Bothnian
Gulf. These consist partly of marine and partly of freshwater species;
but they are few in number, the brackishness of the water appearing to
be very unfavorable to the development of testacea. The most abundant
species are the common cockle and the common mussel and periwinkle of
our shores (_Cardium edule_, _Mytilus edulis_, and _Littorina
littorea_), together with a small tellina (_T. Baltica_) and a few
minute univalves allied to _Paludina ulva_. These live in the same water
as a _Lymneus_, a Neritina (_N. fluviatilis_), and some other
fresh-water shells.
But the marine mollusks of the Baltic above mentioned, although very
numerous in individuals, are dwarfish in size, scarcely ever attaining a
third of the average dimensions which they acquire in the salter waters
of the ocean. By this character alone a geologist would generally be
able to recognize an assemblage of Baltic fossils as distinguished from
those derived from a deposit in the ocean. The absence also of oysters,
barnacles, whelks, scallops, limpets (_ostrea_, _balanus_, _buccinum_,
_pecten_, _patella_), and many other forms abounding alike in the sea
near Uddevalla, and in the fossiliferous deposits of modern date on that
coast, supplies an additional negative character of the greatest value,
distinguishing assemblages of Baltic from those of oceanic shells. Now
the strata containing Baltic shells are found in many localities near
Stockholm, Upsala, and Gefle, and will probably be discovered everywhere
around the borders of the Bothnian Gulf; for I have seen similar remains
brought from Finland, in marl resembling that found near Stockholm. The
utmost distance to which these deposits have yet been traced inland, is
on the southern shores of Lake Maeler, at a place seventy miles from the
sea.[737] Hence it appears from the distinct assemblage of fossil shells
found on the eastern and western coasts of Sweden, that the Baltic has
been for a long period separated as now from the ocean, although the
intervening tract of land was once much narrower, even after both seas
had become inhabited by all the existing species of testacea.
As no accurate observations on the rise of the Swedish coast refer to
periods more remote than a century and a half from the present time, and
as traditional information, and that derived from ancient buildings on
the coast, do not enable the antiquary to trace back any monuments of
change for more than five or six centuries, we cannot declare whether
the rate of the upheaving force is uniform during very long periods. In
those districts where the fossil shells are found at the height of more
than 200 feet above the ocean, as at Uddevalla, Orust, and Lake
Rogvarpen, the present rate of rise seems less than four feet in a
century. Even at that rate it would have required five thousand years to
lift up those deposits. But as the movement is now very different in
different places, it may also have varied much in intensity at different
eras.
We have, moreover, yet to learn not only whether the motion proceeds
always at the same rate, but also whether it has been uniformly _in one
direction_. The level of the land may oscillate; and for centuries there
may be a depression, and afterwards a re-elevation, of the same
district. Some phenomena in the neighborhood of Stockholm appear to me
only explicable on the supposition of the alternate rising and sinking
of the ground since the country was inhabited by man. In digging a
canal, in 1819, at Sodertelje, about sixteen miles to the south of
Stockholm, to unite Lake Maeler with the Baltic, marine strata,
containing fossil shells of Baltic species, were passed through. At a
depth of about sixty feet, they came down upon what seems to have been a
buried fishing-hut, constructed of wood in a state of decomposition,
which soon crumbled away on exposure to the air. The lowest part,
however, which had stood on a level with the sea, was in a more perfect
state of preservation. On the floor of this hut was a rude fireplace,
consisting of a ring of stones, and within this were cinders and charred
wood. On the outside lay boughs of the fir, cut as with an axe, with the
leaves or needles still attached. It seems very difficult to explain the
position of this buried hut, without imagining, as in the case of the
temple of Serapis (see p. 486), first a subsidence to the depth of more
than sixty feet, then a re-elevation. During the period of submergence,
the hut must have become covered over with gravel and shelly marl, under
which not only the hut, but several vessels also were found, of a very
antique form, and having their timbers fastened together by wooden pegs
instead of nails.[738]
Whether any of the land in Norway is now rising, must be determined by
future investigations. Marine fossil shells, of recent species, have
been collected from inland places near Drontheim; but Mr. Everest, in
his "Travels through Norway," informs us that the small island of
Munkholm, which is an insulated rock in the harbor of Drontheim, affords
conclusive evidence of the land having in that region remained
stationary for the last eight centuries. The area of this isle does not
exceed that of a small village, and by an official survey, its highest
point has been determined to be twenty-three feet above the mean
high-water mark, that is, the mean between neap and spring tides. Now,
a monastery was founded there by Canute the Great, A. D. 1028, and
thirty-three years before that time it was in use as a common place of
execution. According to the assumed average rate of rise in Sweden
(about forty inches in a century), we should be obliged to suppose that
this island had been three feet eight inches below high-water mark when
it was originally chosen as the site of the monastery.
Professor Keilhau of Christiania, after collecting the observations of
his predecessors respecting former changes of level in Norway, and
combining them with his own, has made the fact of a general change of
level at a modern period, that is to say, within the period of the
actual testaceous fauna, very evident. He infers that the whole country
from Cape Lindesnaes to Cape North, and beyond that as far as the
fortress of Vardhuus, has been gradually upraised, and on the southeast
coast the elevation has amounted to more than 600 feet. The marks which
denote the ancient coast-line are so nearly horizontal that the
deviation from horizontality, although the measurements have been made
at a great number of points, is too small to be appreciated.
More recently (1844), however, it appears from the researches of M.
Bravais, member of the French scientific commission of the North, that
in the Gulf of Alten in Finmark, the most northerly part of Norway,
there are two distinct lines of upraised ancient sea-coast, one above
the other, which are not parallel, and both of them imply that within a
distance of fifty miles a considerable slope can be detected in such a
direction as to show that the ancient shores have undergone a greater
amount of upheaval in proportion as we advance inland.[739]
It has been already stated, that, in proceeding from the North Cape to
Stockholm, the rate of upheaval diminishes from several feet to a few
inches in a century. To the south of Stockholm, the upward movement
ceases, and at length in Scania, or the southernmost part of Sweden, it
appears to give place to a movement in an opposite direction. In proof
of this fact, Professor Nilsson observes, in the first place, that there
are no elevated beds of recent marine shells in Scania like those
farther to the north. Secondly, Linnaeus, with a view of ascertaining
whether the waters of the Baltic were retiring from the Scanian shore,
measured, in 1749, the distance between the sea and a large stone near
Trelleborg. This same stone was, in 1836, a hundred feet nearer the
water's edge than in Linnaeus's time, or eighty-seven years before.
Thirdly, there is also a submerged peat moss, consisting of land and
freshwater plants, beneath the sea at a point to which no peat could
have been drifted down by any river. Fourthly, and what is still more
conclusive, it is found that in seaport towns, all along the coast of
Scania, there are streets below the high-water level of the Baltic, and
in some cases below the level of the lowest tide. Thus, when the wind is
high at Malmo, the water overflows one of the present streets, and some
years ago some excavations showed an ancient street in the same place
eight feet lower, and it was then seen that there had been an artificial
raising of the ground, doubtless in consequence of that subsidence.
There is also a street at Trelleborg, and another at Skanor, a few
inches below high-water mark, and a street at Ystad is exactly on a
level with the sea, at which it could not have been originally built.
The inferences deduced from the foregoing facts are in perfect harmony
with the proofs brought to light by two Danish investigators, Dr. Pingel
and Captain Graah, of the sinking down of part of the west coast of
Greenland, for a space of more than 600 miles from north to south. The
observations of Captain Graah were made during a survey of Greenland in
1823-24; and afterwards in 1828-29; those by Dr. Pingel were made in
1830-32. It appears from various signs and traditions, that the coast
has been subsiding for the last four centuries from the firth called
Igaliko, in lat. 60 degrees 43 minutes N. to Disco Bay, extending to
nearly the 69th degree of north latitude. Ancient buildings on low rocky
islands and on the shore of the main land have been gradually submerged,
and experience has taught the aboriginal Greenlander never to build his
hut near the water's edge. In one case the Moravian settlers have been
obliged more than once to move inland the poles upon which their large
boats were set, and the old poles still remain beneath the water as
silent witnesses of the change.[740]
The probable cause of the movements above alluded to, whether of
elevation or depression, will be more appropriately discussed in the
following chapters, when the origin of subterranean heat is considered.
But I may remark here, that the rise of Scandinavia has naturally been
regarded as a very singular and scarcely credible phenomenon, because no
region on the globe has been more free within the times of authentic
history from violent earthquakes. In common, indeed, with our own island
and with almost every spot on the globe, some movements have been, at
different periods, experienced, both in Norway and Sweden. But some of
these, as for example during the Lisbon earthquake in 1755, may have
been mere vibrations or undulatory movements of the earth's crust
prolonged from a great distance. Others, however, have been sufficiently
local to indicate a source of disturbance immediately under the country
itself. Notwithstanding these shocks, Scandinavia has, upon the whole,
been as tranquil in modern times, and as free from subterranean
convulsions, as any region of equal extent on the globe. There is also
another circumstance which has made the change of level in Sweden appear
anomalous, and has for a long time caused the proofs of the fact to be
received with reluctance. Volcanic action, as we have seen, is usually
intermittent: and the variations of level to which it has given rise
have taken place by starts, not by a prolonged and insensible movement
similar to that experienced in Sweden. Yet, as we enlarge our experience
of modern changes, we discover instances in which the volcanic eruption,
the earthquake, and the permanent rise or fall of land, whether slow or
sudden, are all connected. The union of these various circumstances was
exemplified in the case of the temple of Serapis, described in the last
chapter, and we might derive other illustrations from the events of the
present century in South America.
Some writers, indeed, have imagined that there is geological evidence in
Norway, of the sudden upheaval of land to a considerable height at
successive periods, since the era when the sea was inhabited by the
living species of testacea. They point in proof to certain horizontal
lines of inland cliffs and sea-beaches containing recent shells at
various heights above the level of the sea.[741] But these appearances,
when truly interpreted, simply prove that there have been long pauses in
the process of upheaval or subsidence. They mark eras at which the level
of the sea has remained stationary for ages, and during which new strata
were deposited near the shore in some places, while in others the waves
and currents had time to hollow out rocks, undermine cliffs, and throw
up long ranges of shingle. They undoubtedly show that the movement has
not been always uniform or continuous, but they do not establish the
fact of any sudden alterations of level.
When we are once assured of the reality of the gradual rise of a large
region, it enables us to account for many geological appearances
otherwise of very difficult explanation. There are large continental
tracts and high table-lands where the strata are nearly horizontal,
bearing no marks of having been thrown up by violent convulsions, nor by
a series of movements, such as those which occur in the Andes, and cause
the earth to be rent open, and raised or depressed from time to time,
while large masses are engulfed in subterranean cavities. The result of
a series of such earthquakes might be to produce in a great lapse of
ages a country of shattered, inclined, and perhaps vertical strata. But
a movement like that of Scandinavia would cause the bed of the sea, and
all the strata recently formed in it, to be upheaved so gradually, that
it would merely seem as if the ocean had formerly stood at a higher
level, and had slowly and tranquilly sunk down into its present bed.
The fact also of a very gradual and insensible elevation of land may
explain many geological movements of denudation, on a grand scale. If,
for example, instead of the hard granitic rocks of Norway and Sweden, a
large part of the bed of the Atlantic, consisting chiefly of soft
strata, should rise up century after century, at the rate of about half
an inch, or an inch, in a year, how easily might oceanic currents sweep
away the thin film of matter thus brought up annually within the sphere
of aqueous denudation! The tract, when it finally emerged, might present
table-lands and ridges of horizontal strata, with intervening valleys
and vast plains, where originally, and during its period of submergence,
the surface was level and nearly uniform.
These speculations relate to superficial changes; but others must be
continually in progress in the subterranean regions. The foundations of
the country, thus gradually uplifted in Sweden, must be undergoing
important modifications. Whether we ascribe these to the expansion of
solid matter by continually increasing heat, or to the liquefaction of
rock, or to the crystallization of a dense fluid, or the accumulation of
pent-up gases, in whatever conjectures we indulge, we can never doubt
for a moment, that at some unknown depth beneath Sweden and the Baltic,
the structure of the globe is in our own times becoming changed from day
to day, throughout a space probably more than a thousand miles in
length, and several hundred in breadth.