IGNEOUS CAUSES.
Changes of the inorganic world, _continued_--Igneous
causes--Division of the subject--Distinct volcanic regions--Region
of the Andes--System of volcanoes extending from the Aleutian isles
to the Molucca and Sunda islands--Polynesian archipelago--Volcanic
region extending from Central Asia to the Azores--Tradition of
deluges on the shores of the Bosphorus, Hellespont, and Grecian
isles--Periodical alternation of earthquakes in Syria and Southern
Italy--Western limits of the European region--Earthquakes rarer and
more feeble as we recede from the centres of volcanic action.
Extinct volcanoes not to be included in lines of active vents.
We have hitherto considered the changes wrought, since the times of
history and tradition, by the continued action of aqueous causes on the
earth's surface; and we have next to examine those resulting from
igneous agency. As the rivers and springs on the land, and the tides and
currents in the sea, have, with some slight modifications, been fixed
and constant to certain localities from the earliest periods of which we
have any records, so the volcano and the earthquake have, with few
exceptions, continued, during the same lapse of time, to disturb the
same regions. But as there are signs, on almost every part of our
continent, of great power having been exerted by running water on the
surface of the land, and by waves, tides, and currents on cliffs
bordering the sea, where, in modern times, no rivers have excavated, and
no waves or tidal currents undermined--so we find signs of volcanic
vents and violent subterranean movements in places where the action of
fire or internal heat has long been dormant. We can explain why the
intensity of the force of aqueous causes should be developed in
succession in different districts. Currents, for example, tides, and the
waves of the sea, cannot destroy coasts, shape out or silt up estuaries,
break through isthmuses, and annihilate islands, form shoals in one
place, and remove them from another, without the direction and position
of their destroying and transporting power becoming transferred to new
localities. Neither can the relative levels of the earth's crust, above
and beneath the waters, vary from time to time, as they are admitted to
have varied at former periods, and as it will be demonstrated that they
still do, without the continents being, in the course of ages, modified,
and even entirely altered, in their external configuration. Such events
must clearly be accompanied by a complete change in the volume,
velocity, and direction of the streams and land floods to which certain
regions give passage. That we should find, therefore, cliffs where the
sea once committed ravages, and from which it has now retired--estuaries
where high tides once rose, but which are now dried up--valleys hollowed
out by water, where no streams now flow, is no more than we should
expect; these and similar phenomena are the necessary consequences of
physical causes now in operation; and if there be no instability in the
laws of nature, similar fluctuations must recur again and again in time
to come.
But, however natural it may be that the force of running water in
numerous valleys, and of tides and currents in many tracts of the sea,
should now be _spent_, it is by no means so easy to explain why the
violence of the earthquake and the fire of the volcano should also have
become locally extinct at successive periods. We can look back to the
time when the marine strata, whereon the great mass of Etna rests, had
no existence; and that time is extremely modern in the earth's history.
This alone affords ground for anticipating that the eruptions of Etna
will one day cease.
Nec quae sulfureis ardet fornacibus, AEtna
Ignea semper erit, _neque enim fuit ignea semper_,
(Ovid, _Metam._ lib. 15-340,)
are the memorable words which are put into the mouth of Pythagoras by
the Roman poet, and they are followed by speculations as to the cause of
volcanic vents shifting their positions. Whatever doubts the philosopher
expresses as to the nature of these causes, it is assumed, as
incontrovertible, that the points of eruption will hereafter vary,
_because they have formerly done so_; a principle of reasoning which, as
I have endeavored to show in former chapters, has been too much set at
naught by some of the earlier schools of geology, which refused to
conclude that great revolutions in the earth's surface are now in
progress, or that they will take place hereafter, _because_ they have
often been repeated in former ages.
_Division of the subject._--Volcanic action may be defined to be "the
influence exerted by the heated interior of the earth on its external
covering." If we adopt this definition, without connecting it, as
Humboldt has done, with the theory of secular refrigeration, or the
cooling down of an original heated and fluid nucleus, we may then class
under a general head all the subterranean phenomena, whether of
volcanoes, or earthquakes, and those insensible movements of the land,
by which, as will afterwards appear, large districts may be depressed or
elevated, without convulsions. According to this view, I shall consider
first, the volcano; secondly, the earthquake; thirdly, the rising or
sinking of land in countries where there are no volcanoes or
earthquakes; fourthly, the probable _causes_ of the changes which result
from subterranean agency.
It is a very general opinion that earthquakes and volcanoes have a
common origin; for both are confined to certain regions, although the
subterranean movements are least violent in the immediate proximity of
volcanic vents, especially where the discharge of aeriform fluids and
melted rock is made constantly from the same crater. But as there are
particular regions, to which both the points of eruption and the
movements of great earthquakes are confined, I shall begin by tracing
out the geographical boundaries of some of these, that the reader may
be aware of the magnificent scale on which the agency of subterranean
fire is now simultaneously developed. Over the whole of the vast tracts
alluded to, active volcanic vents are distributed at intervals, and most
commonly arranged in a linear direction. Throughout the intermediate
spaces there is often abundant evidence that the subterranean fire is at
work continuously, for the ground is convulsed from time to time by
earthquakes; gaseous vapors, especially carbonic acid gas, are
disengaged plentifully from the soil; springs often issue at a very high
temperature, and their waters are usually impregnated with the same
mineral matters as are discharged by volcanoes during eruptions.
VOLCANIC REGIONS.
_Region of the Andes._--Of these great regions, that of the Andes of
South America is one of the best defined, extending from the southward
of Chili to the northward of Quito, from about lat. 43 degrees S. to
about 2 degrees N. of the equator. In this range, however, comprehending
forty-five degrees of latitude, there is an alternation on a grand scale
of districts of active with those of extinct volcanoes, or which, if not
spent, have at least been dormant for the last three centuries. How long
an interval of rest may entitle us to consider a volcano as entirely
extinct is not easily determined; but we know that in Ischia there
intervened between two consecutive eruptions a pause of seventeen
centuries; and the discovery of America is an event of far too recent a
date to allow us even to conjecture whether different portions of the
Andes, nearly the whole of which are subject to earthquakes, may not
experience alternately a cessation and renewal of eruptions.
The first line of active vents which have been seen in eruption in the
Andes extends from lat. 43 degrees 28 minutes S.; or, from Yantales,
opposite the isle of Chiloe, to Coquimbo, in lat. 30 degrees S.; to
these thirteen degrees of latitude succeed more than eight degrees in
which no recent volcanic eruptions have been observed. We then come to
the volcanoes of Bolivia and Peru, reaching six degrees from S. to N.,
or from lat. 21 degrees S. to lat. 15 degrees S. Between the Peruvian
volcanoes and those of Quito, another space intervenes of no less than
fourteen degrees of latitude, said to be free from volcanic action so
far as yet known. The volcanoes of Quito then succeed, beginning about
100 geographical miles south of the equator, and continuing for about
130 miles north of the line, when there occurs another undisturbed
interval of more than six degrees of latitude, after which we arrive at
the volcanoes of Guatemala or Central America, north of the Isthmus of
Panama.[469]
Having thus traced out the line from south to north, I may first state,
in regard to the numerous vents of Chili, that the volcanoes of Yantales
and Osorno were in eruption during the great earthquake of 1835, at the
same moment that the land was shaken in Chiloe, and in some parts of the
Chilian coast permanently upheaved; whilst at Juan Fernandez, at the
distance of no less than 720 geographical miles from Yantales, an
eruption took place beneath the sea. Some of the volcanoes of Chili are
of great height, as that of Antuco, in lat. 37 degrees 40 minutes S.,
the summit of which is at least 16,000 feet above the sea. From the
flanks of this volcano, at a great height, immense currents of lava have
issued, one of which flowed in the year 1828. This event is said to be
an exception in the general rule; few volcanoes in the Andes, and none
of those in Quito, having been seen in modern times to pour out lava,
but having merely ejected vapor or scoriae.
Both the basaltic (or augitic) lavas, and those of the felspathic class,
occur in Chili and other parts of the Andes; but the volcanic rocks of
the felspathic family are said by Von Buch to be generally not trachyte,
but a rock which has been called andesite, or a mixture of augite and
albite. The last-mentioned mineral contains soda instead of the potash
found in common felspar.
The volcano of Rancagua, lat. 34 degrees 15 minutes S., is said to be
always throwing out ashes and vapors like Stromboli, a proof of the
permanently heated state of certain parts of the interior of the earth
below. A year rarely passes in Chili without some slight shocks of
earthquakes, and in certain districts not a month. Those shocks which
come from the side of the ocean are the most violent, and the same is
said to be the case in Peru. The town of Copiapo was laid waste by this
terrible scourge in the years 1773, 1796, and 1819, or in both cases
after regular intervals of twenty-three years. There have, however, been
other shocks in that country in the periods intervening between the
dates above mentioned, although probably all less severe, at least on
the exact site of Copiapo. The evidence against a regular recurrence of
volcanic convulsions at stated periods is so strong as a general fact,
that we must be on our guard against attaching too much importance to a
few striking but probably accidental coincidences. Among these last
might be adduced the case of Lima, violently shaken by an earthquake on
the 17th of June, 1578, and again on the very same day, 1678; or the
eruptions of Coseguina in the year 1709 and 1809, which are the only two
recorded of that volcano previous to that of 1835.[470]
Of the permanent upheaval of land after earthquakes in Chili, I shall
have occasion to speak in the next chapter, when it will also be seen
that great shocks often coincide with eruptions, either submarine or
from the cones of the Andes, showing the identity of the force which
elevates continents with that which causes volcanic outbursts.[471]
The space between Chili and Peru, in which no volcanic action has been
observed, is 160 nautical leagues from south to north. It is, however,
as Von Buch observes, that part of the Andes which is least known,
being thinly peopled, and in some parts entirely desert. The volcanoes
of Peru rise from a lofty platform to vast heights above the level of
the sea, from 17,000 to 20,000 feet. The lava which has issued from
Viejo, lat. 16 degrees 55 minutes S., accompanied by pumice, is composed
of a mixture of crystals of albitic felspar, hornblende, and mica, a
rock which has been considered as one of the varieties of andesite. Some
tremendous earthquakes which have visited Peru in modern times will be
mentioned in a subsequent chapter.
The volcanoes of Quito, occurring between the second degree of south and
the third degree of north latitude, rise to vast elevations above the
sea, many of them being between 14,000 and 18,000 feet high. The Indians
of Lican have a tradition that the mountain called L'Altar, or Capac
Urcu, which means "the chief," was once the highest of those near the
equator, being higher than Chimborazo; but in the reign of Ouainia
Abomatha, before the discovery of America, a prodigious eruption took
place, which lasted eight years, and broke it down. The fragments of
trachyte, says M. Boussingault, which once formed the conical summit of
this celebrated mountain, are at this day spread over the plain.[472]
Cotopaxi is the most lofty of all the South American volcanoes which
have been in a state of activity in modern times, its height being
18,858 feet; and its eruptions have been more frequent and destructive
than those of any other mountain. It is a perfect cone, usually covered
with an enormous bed of snow, which has, however, been sometimes melted
suddenly during an eruption; as in January, 1803, for example, when the
snows were dissolved in one night.
Deluges are often caused in the Andes by the liquefaction of great
masses of snow, and sometimes by the rending open, during earthquakes,
of subterranean cavities filled with water. In these inundations fine
volcanic sand, loose stones, and other materials which the water meets
with in its descent, are swept away, and a vast quantity of mud, called
"moya," is thus formed and carried down into the lower regions. Mud
derived from this source descended, in 1797, from the sides of
Tunguragua in Quito, and filled valleys a thousand feet wide to the
depth of six hundred feet, damming up rivers and causing lakes. In these
currents and lakes of moya, thousands of small fish are sometimes
enveloped, which, according to Humboldt, have lived and multiplied in
subterranean cavities. So great a quantity of these fish were ejected
from the volcano of Imbaburu in 1691, that fevers, which prevailed at
the period, were attributed to the effluvia arising from the putrid
animal matter.
In Quito, many important revolutions in the physical features of the
country are said to have resulted, within the memory of man, from the
earthquakes by which it has been convulsed. M. Boussingault declares his
belief, that if a full register had been kept of all the convulsions
experienced here and in other populous districts of the Andes, it would
be found that the trembling of the earth had been incessant. The
frequency of the movement, he thinks, is not due to volcanic explosions,
but to the continual falling in of masses of rock which have been
fractured and upheaved in a solid form at a comparatively recent epoch;
but a longer series of observations would be requisite to confirm this
opinion. According to the same author, the height of several mountains
of the Andes has diminished in modern times.[473]
The great crest or cordillera of the Andes is depressed at the Isthmus
of Panama to a height of about 1000 feet, and at the lowest point of
separation between the two seas near the Gulf of San Miguel, to 150
feet. What some geographers regard as a continuation of that chain in
Central America lies to the east of a series of volcanoes, many of which
are active in the provinces of Pasto, Popayan, and Guatemala. Coseguina,
on the south side of the Gulf of Fonseca, was in eruption in January,
1835, and some of its ashes fell at Truxillo, on the shores of the Gulf
of Mexico. What is still more remarkable, on the same day, at Kingston,
in Jamaica, the same shower of ashes fell, having been carried by an
upper counter-current against the regular east wind which was then
blowing. Kingston is about 700 miles distant from Coseguina, and these
ashes must have been more than four days in the air, having travelled
170 miles a day. Eight leagues to the southward of the crater, the ashes
covered the ground to the depth of three yards and a half, destroying
the woods and dwellings. Thousands of cattle perished, their bodies
being in many instances one mass of scorched flesh. Deer and other wild
animals sought the towns for protection; many birds and quadrupeds were
found suffocated in the ashes, and the neighboring streams were strewed
with dead fish.[474] Such facts throw light on geological monuments, for
in the ashes thrown out at remote periods from the volcanoes of
Auvergne, now extinct, we find the bones and skeletons of lost species
of quadrupeds.
_Mexico._--The great volcanic chain, after having thus pursued its
course for several thousand miles from south to north, sends off a
branch in a new direction in Mexico, in the parallel of the city of that
name, and is prolonged in a great platform between the eighteenth and
twenty-second degrees of north latitude. Five active volcanoes traverse
Mexico from west to east--Tu[\x]tla, Orizaba, Popocatepetl, Jorullo, and
Colima. Jorullo, which is in the centre of the great platform, is no
less than 120 miles from the nearest ocean--an important circumstance,
as showing that the proximity of the sea is not a necessary condition,
although certainly a very general characteristic of the position of
active volcanoes. The extraordinary eruption of this mountain, in 1759,
will be described in the sequel. If the line which connects these five
vents be prolonged in a westerly direction, it cuts the volcanic group
of islands called the Isles of Revillagigedo.
To the north of Mexico there are said to be three, or according to
some, five volcanoes in the peninsula of California; and a volcano is
reported to have been in eruption in the N. W. coast of America, near
the Colombia river, lat. 45 degrees 37 minutes N.
_West Indies._--To return to the Andes of Quito: Von Buch inclines to
the belief that if we were better acquainted with the region to the east
of the Madalena, and with New Granada and the Caraccas, we might find
the volcanic chain of the Andes to be connected with that of the West
Indian or Carribee Islands. The truth of this conjecture has almost been
set at rest by the eruption, in 1848, of the volcano of Zamba, in New
Grenada, at the mouth of the river Madalena.[475]
Of the West Indian islands there are two parallel series: the one to the
west, which are all volcanic, and which rise to the height of several
thousand feet; the others to the east, for the most part composed of
calcareous rocks, and very low. In the former or volcanic series, are
Granada, St. Vincent, St. Lucia, Martinique, Dominica, Guadaloupe,
Montserrat, Nevis, and St. Eustace. In the calcareous chain are Tobago,
Barbadoes, Mariegallante, Grandeterre, Desirade, Antigua, Barbuda, St.
Bartholomew, and St. Martin. The most considerable eruptions in modern
times have been those of St. Vincent. Great earthquakes have agitated
St. Domingo, as will be seen in the twenty-ninth chapter.
I have before mentioned (p. 270) the violent earthquake which in 1812
convulsed the valley of the Mississippi at New Madrid, for the space of
300 miles in length, of which more will be said in the twenty-seventh
chapter. This happened exactly at the same time as the great earthquake
of Caraccas, so that it is possible that these two points are parts of
one subterranean volcanic region. The island of Jamaica, with a tract of
the contiguous sea, has often experienced tremendous shocks; and these
are frequent along a line extending from Jamaica to St. Domingo and
Porto Rico.
Thus it will be seen that, without taking account of the West Indian and
Mexican branches, a linear train of volcanoes and tracts shaken by
earthquakes may be traced from the island of Chiloe and opposite coast
to Mexico, or even perhaps to the mouth of the Colombia river--a
distance upon the whole as great as from the pole to the equator. In
regard to the western limits of the region, they lie deep beneath the
waves of the Pacific, and must continue unknown to us. On the east they
are not prolonged, except where they include the West Indian Islands, to
a great distance; for there seem to be no indications of volcanic
disturbances in Buenos Ayres, Brazil, and the United States of North
America.
[Illustration: Fig. 89.
MAP OF ACTIVE VOLCANOES AND ATOLLS of THE INDIAN ARCHIPELAGO, and Part
of the adjoining PACIFIC OCEAN.]
_Volcanic region from the Aleutian Isles to the Moluccas and Isles of
Sunda._--On a scale which equals or surpasses that of the Andes, is
another line of volcanic action, which commences, on the north, with the
Aleutian Isles in Russian America, and extends, first in a westerly
direction for nearly 200 geographical miles, and then southwards, with
few interruptions, throughout a space of between sixty and seventy
degrees of latitude to the Moluccas, where it sends off a branch to the
southeast while the principal train continues westerly through Sumbawa
and Java to Sumatra, and then in a northwesterly direction to the Bay of
Bengal.[476] This volcanic line, observes Von Buch, may be said to
follow throughout its course the external border of the continent of
Asia; while the branch which has been alluded to as striking southeast
from the Moluccas, passes from New Guinea to New Zealand, conforming,
though somewhat rudely, to the outline of Australia.[477]
The connection, however, of the New Guinea volcanoes with the line in
Java (as laid down in Von Buch's map) is not clearly made out. By
consulting Darwin's map of coral reefs and active volcanoes,[478] the
reader will see that we might almost with equal propriety include the
Mariana and Bonin volcanoes in a band with New Guinea. Or if we allow so
much latitude in framing zones of volcanic action, we must also suppose
the New Hebrides, Solomon Isles, and New Ireland to constitute one line
(see map, fig. 39, p. 351).
The northern extremity of the volcanic region of Asia, as described by
Von Buch, is on the borders of Cook's Inlet, northeast of the Peninsula
of Alaska, where one volcano, in about the sixtieth degree of latitude,
is said to be 14,000 feet high. In Alaska itself are cones of vast
height, which have been seen in eruption, and which are covered for
two-thirds of their height downwards with perpetual snow. The summit of
the loftiest peak is truncated, and is said to have fallen in during an
eruption in 1786. From Alaska the line is continued through the Aleutian
or Fox Islands to Kamtschatka. In the Aleutian Archipelago eruptions are
frequent, and about thirty miles to the north of Unalaska, near the Isle
of Umnack, a new island was formed in 1796. It was first observed after
a storm, at a point in the sea from which a column of smoke had been
seen to rise. Flames then issued from the new islet which illuminated
the country for ten miles round; a frightful earthquake shook the
new-formed cone, and showers of stones were thrown as far as Umnack. The
eruption continued for several months, and eight years afterwards, in
1804, when it was explored by some hunters, the soil was so hot in some
places that they could not walk on it. According to Langsdorf and
others, this new island, which is now several thousand feet high, and
two or three miles in circumference, has been continually found to have
increased in size when successively visited by different travellers; but
we have no accurate means of determining how much of its growth, if any,
has been due to upheaval, or how far it has been exclusively formed by
the ejection of ashes and streams of lava. It seems, however, to be well
attested that earthquakes of the most terrific description agitate and
alter the bed of the sea and surface of the land throughout this tract.
The line is continued in the southern extremity of the Peninsula of
Kamtschatka, where there are many active volcanoes, which, in some
eruptions, have scattered ashes to immense distances. The largest and
most active of these is Klutschew, lat. 56 degrees 3 minutes N., which
rises at once from the sea to the prodigious height of 15,000 feet.
Within 700 feet of the summit, Erman saw, in 1829, a current of lava,
emitting a vivid light, flow down the northwest side to the foot of the
cone. A flow of lava from the summit of Mont Blanc to its base in the
valley of Chamouni would afford but an inadequate idea of the declivity
down which this current descended. Large quantities of ice and snow
opposed for a time a barrier to the lava, until at length the fiery
torrent overcame, by its heat and pressure, this obstacle, and poured
down the mountain side with a frightful noise, which was heard for a
distance of more than fifty miles.[479]
The Kurile chain of islands constitutes the prolongation of the
Kamtschatka range, where a train of volcanic mountains, nine of which
are known to have been in eruption, trends in a southerly direction. The
line is then continued to the southwest in the great island of Jesso,
and again in Nipon, the principal of the Japanese group. It then extends
by Loo Choo and Formosa to the Philippine Islands, and thence by Sangir
and the northeastern extremity of Celebes to the Moluccas (see map, fig.
39). Afterwards it passes westward through Sumbawa to Java.
There are said to be thirty-eight considerable volcanoes in Java, some
of which are more than 10,000 feet high. They are remarkable for the
quantity of sulphur and sulphureous vapors which they discharge. They
rarely emit lava, but rivers of mud issue from them, like the moya of
the Andes of Quito. The memorable eruption of Galongoon, in 1822, will
be described in the twenty-fifth chapter. The crater of Taschem, at the
eastern extremity of Java, contains a lake strongly impregnated with
sulphuric acid, a quarter of a mile long, from which a river of acid
water issues, which supports no living creature, nor can fish live in
the sea near its confluence. There is an extinct crater near Batur,
called Guevo Upas, or the Valley of Poison, about half a mile in
circumference, which is justly an object of terror to the inhabitants of
the country. Every living being which penetrates into this valley falls
down dead, and the soil is covered with the carcasses of tigers, deer,
birds, and even the bones of men; all killed by the abundant emanations
of carbonic acid gas, by which the bottom of the valley is filled.
In another crater in this land of wonders, near the volcano of Talaga
Bodas, we learn from M. Reinwardt, that the sulphureous exhalations have
killed tigers, birds, and innumerable insects; and the soft parts of
these animals, such as the fibres, muscles, nails, hair, and skin,
are very well preserved, while the bones are corroded, and entirely
destroyed.
We learn from observations made in 1844, by Mr. Jukes, that a recent
tertiary formation composed of limestone and resembling the coral rock
of a fringing reef, clings to the flanks of all the volcanic islands
from the east end of Timor to the west end of Java. These modern
calcareous strata are often white and chalk-like, sometimes 1000 feet
and upwards above the sea, regularly stratified in thick horizontal
beds, and they show that there has been a general elevation of these
islands at a comparatively modern period.[480]
The same linear arrangement which is observed in Java holds good in the
volcanoes of Sumatra, some of which are of great height, as Berapi,
which is more than 12,000 feet above the sea, and is continually
smoking. Hot springs are abundant at its base. The volcanic line then
inclines slightly to the northwest, and points to Barren Island, lat.
12 degrees 15 minutes N., in the Bay of Bengal. This volcano was in
eruption in 1792, and will be described in the twenty-sixth chapter. The
volcanic train then extends, according to Dr. Macclelland, to the island
of Narcondam, lat. 13 degrees. 22 minutes N., which is a cone seven or
eight hundred feet high, rising from deep water, and said to present
signs of lava currents descending from the crater to the base.
Afterwards the train stretches in the same direction to the volcanic
island of Ramree, about lat. 19 degrees. N., and the adjoining island of
Cheduba, which is represented in old charts as a burning mountain. Thus
we arrive at the Chittagong coast, which in 1762 was convulsed by a
tremendous earthquake (see chap. 29).[481]
To enumerate all the volcanic regions of the Indian and Pacific oceans
would lead me far beyond the proper limits of this treatise; but it will
appear in the last chapter of this volume, when coral reefs are treated
of, that the islands of the Pacific consist alternately of linear groups
of two classes, the one lofty, and containing active volcanoes, and
marine strata above the sea-level, and which have been undergoing
upheaval in modern times; the other very low, consisting of reefs of
coral, usually with lagoons in their centres, and in which there is
evidence of a gradual subsidence of the ground. The extent and direction
of these parallel volcanic bands have been depicted with great care by
Darwin in his map before cited (p. 351).
The most remarkable theatre of volcanic activity in the Northern
Pacific--or, perhaps, in the whole world--occurs in the Sandwich
Islands, which have been admirably treated of in a recent work by Mr.
Dana.[482]
_Volcanic region from central Asia to the Azores._--Another great region
of subterranean disturbance is that which has been imagined to extend
through a large part of Central Asia to the Azores, that is to say,
from China and Tartary through Lake Aral and the Caspian to the
Caucasus, and the countries bordering the Black Sea, then again through
part of Asia Minor to Syria, and westward to the Grecian Islands,
Greece, Naples, Sicily, the southern part of Spain, Portugal and the
Azores. Respecting the eastern extremity of this line in China, we have
little information, but many violent earthquakes are known to have
occurred there. The volcano said to have been in eruption in the seventh
century in Central Tartary is situated on the northern declivity of the
Celestial Mountains, not far distant from the large lake called
Issikoul; and Humboldt mentions other vents and solfataras in the same
quarter, which are all worthy of notice, as being far more distant from
the ocean (260 geographical miles) than any other known points of
eruption.
We find on the western shores of the Caspian, in the country round Baku,
a tract called the Field of Fire, which continually emits inflammable
gas, while springs of naphtha and petroleum occur in the same vicinity,
as also mud volcanoes. Syria and Palestine abound in volcanic
appearances, and very extensive areas have been shaken, at different
periods, with great destruction of cities and loss of lives. Continual
mention is made in history of the ravages committed by earthquakes in
Sidon, Tyre, Berytus, Laodicea, and Antioch, and in the Island of
Cyprus. The country around the Dead Sea appears evidently, from the
accounts of modern travellers, to be volcanic. A district near Smyrna,
in Asia Minor, was termed by the Greeks Catacecaumene, or "the burnt
up," where there is a large arid territory, without trees, and with a
cindery soil.[483] This country was visited in 1841 by Mr. W. J.
Hamilton, who found in the valley of the Hermus perfect cones of scoriae,
with lava-streams, like those of Auvergne, conforming to the existing
river-channels, and with their surface undecomposed.[484]
_Grecian Archipelago._--Proceeding westwards, we reach the Grecian
Archipelago, where Santorin, afterwards to be described, is the grand
centre of volcanic action.
It was Von Buch's opinion that the volcanoes of Greece were arranged in
a line running N. N. W. and S. S. E., and that they afforded the only
example in Europe of active volcanoes having a linear direction; but M.
Virlet, on the contrary, announces as the result of his investigations,
made during the French expedition to the Morea in 1829, that there is no
one determinate line of direction for the volcanic phenomena in Greece,
whether we follow the points of eruptions, or the earthquakes, or any
other signs of igneous agency.[485]
Macedonia, Thrace, and Epirus, have always been subject to earthquakes,
and the Ionian Isles are continually convulsed.
Respecting Southern Italy, Sicily, and the Lipari Isles, it is
unnecessary to enlarge here, as I shall have occasion again to allude to
them. I may mention, however, that a band of volcanic action has been
traced by Dr. Daubeny across the Italian Peninsula, from Ischia to Mount
Vultur, in Apulia, the commencement of the line being found in the hot
springs of Ischia, after which it is prolonged through Vesuvius to the
Lago d'Ansanto, where gases similar to those of Vesuvius are evolved.
Its farther extension strikes Mount Vultur, a lofty cone composed of
tuff and lava, from one side of which carbonic acid and sulphuretted
hydrogen are emitted.[486]
_Traditions of deluges._--The traditions which have come down to us from
remote ages of great inundations said to have happened in Greece and on
the confines of the Grecian settlements, had doubtless their origin in a
series of local catastrophes, caused principally by earthquakes. The
frequent migrations of the earlier inhabitants, and the total want of
written annals long after the first settlement of each country, make it
impossible for us at this distance of time to fix either the true
localities or probable dates of these events. The first philosophical
writers of Greece were, therefore, as much at a loss as ourselves to
offer a reasonable conjecture on these points, or to decide how many
catastrophes might sometimes have become confounded in one tale, or how
much this tale may have been amplified, in after times, or obscured by
mythological fiction. The floods of Ogyges and Deucalion are commonly
said to have happened before the Trojan war; that of Ogyges more than
seventeen, and that of Deucalion more than fifteen centuries before our
era. As to the Ogygian flood, it is generally described as having laid
waste Attica, and was referred by some writers to a great overflowing of
rivers, to which cause Aristotle also attributed the deluge of
Deucalion, which, he says, affected Hellas only, or the central part of
Thessaly. Others imagined the same event to have been due to an
earthquake, which drew down masses of rock, and stopped up the course of
the Peneus in the narrow defile between mounts Ossa and Olympus.
As to the deluge of Samothrace, which is generally referred to a
distinct date, it appears that the shores of that small island and the
adjoining mainland of Asia were inundated by the sea. Diodorus Siculus
says that the inhabitants had time to take refuge in the mountains, and
save themselves by flight; he also relates, that long after the event
the fishermen of the island drew up in their nets the capitals of
columns, which were the remains of cities submerged by that terrible
catastrophe.[487] These statements scarcely leave any doubt that there
occurred, at the period alluded to, a subsidence of the coast,
accompanied by earthquakes and inroads of the sea. It is not impossible
that the story of the bursting of the Black Sea through the Thracian
Bosphorus into the Grecian Archipelago, which accompanied, and, as some
say, caused the Samothracian deluge, may have reference to a wave, or
succession of waves, raised in the Euxine by the same convulsion.
We know that subterranean movements and volcanic eruptions are often
attended not only by incursions of the sea, but also by violent rains,
and the complete derangement of the river drainage of the inland
country, and by the damming up of the outlets of lakes by landslips, or
obstructions in the courses of subterranean rivers, such as abound in
Thessaly and the Morea. We need not therefore be surprised at the
variety of causes assigned for the traditional floods of Greece, by
Herodotus, Aristotle, Diodorus, Strabo, and others. As to the area
embraced, had all the Grecian deluges occurred simultaneously, instead
of being spread over many centuries, and had they, instead of being
extremely local, reached at once from the Euxine to the southwestern
limit of the Peloponnese, and from Macedonia to Rhodes, the devastation
would still have been more limited than that which visited Chili in
1835, when a volcanic eruption broke out in the Andes, opposite Chiloe,
and another at Juan Fernandez, distant 720 geographical miles, at the
same time that several lofty cones, in the Cordillera, 400 miles to the
eastward of that island, threw out vapor and ignited matter. Throughout
a great part of the space thus recently shaken in South America, cities
were laid in ruins, or the land was permanently upheaved, or mountainous
waves rolled inland from the Pacific.
_Periodical alternation of Earthquakes in Syria and Southern Italy._--It
has been remarked by Von Hoff, that from the commencement of the
thirteenth to the latter half of the seventeenth century, there was an
almost entire cessation of earthquakes in Syria and Judea; and, during
this interval of quiescence, the Archipelago, together with part of the
adjacent coast of Lesser Asia, as also Southern Italy and Sicily,
suffered greatly from earthquakes; while volcanic eruptions were
unusually frequent in the same regions. A more extended comparison,
also, of the history of the subterranean convulsions of these tracts
seems to confirm the opinion, that a violent crisis of commotion never
visits both at the same time. It is impossible for us to declare, as
yet, whether this phenomenon is constant in this and other regions,
because we can rarely trace back a connected series of events farther
than a few centuries; but it is well known that, where numerous vents
are clustered together within a small area, as in many archipelagoes for
instance, two of them are never in violent eruption at once. If the
action of one becomes very great for a century or more, the others
assume the appearance of spent volcanoes. It is, therefore, not
improbable that separate provinces of the same great range of volcanic
fires may hold a relation to one deep-seated focus, analogous to that
which the apertures of a small group bear to some more superficial rent
or cavity. Thus, for example, we may conjecture that, at a comparatively
small distance from the surface, Ischia and Vesuvius mutually
communicate with certain fissures, and that each affords relief
alternately to elastic fluids and lava there generated. So we may
suppose Southern Italy and Syria to be connected, at a much greater
depth, with a lower part of the very same system of fissures; in which
case any obstruction occurring in one duct may have the effect of
causing almost all the vapor and melted matter to be forced up the
other, and if they cannot get vent, they may be the cause of violent
earthquakes. Some objections advanced against this doctrine that
"volcanoes act as safety-valves," will be considered in the sequel.[488]
The northeastern portion of Africa, including Egypt, which lies six or
seven degrees south of the volcanic line already traced, has been almost
always exempt from earthquakes; but the northwestern portion, especially
Fez and Morocco, which fall within the line, suffer greatly from time to
time. The southern part of Spain also, and Portugal, have generally been
exposed to the same scourge simultaneously with Northern Africa. The
provinces of Malaga, Murcia, and Granada, and in Portugal the country
round Lisbon, are recorded at several periods to have been devastated by
great earthquakes. It will be seen, from Michell's account of the great
Lisbon shock, in 1755, that the first movement proceeded from the bed of
the ocean ten or fifteen leagues from the coast. So late as February 2,
1816, when Lisbon was vehemently shaken, two ships felt a shock in the
ocean west from Lisbon; one of them at the distance of 120, and the
other 262 French leagues from the coast[489]--a fact which is more
interesting, because a line drawn through the Grecian Archipelago, the
volcanic region of Southern Italy, Sicily, Southern Spain, and Portugal,
will, if prolonged westward through the ocean, strike the volcanic group
of the Azores, which may possibly therefore have a submarine connection
with the European line.
In regard to the volcanic system of Southern Europe, it may be observed,
that there is a central tract where the greatest earthquakes prevail, in
which rocks are shattered, mountains rent, the surface elevated or
depressed, and cities laid in ruins. On each side of this line of
greatest commotion there are parallel bands of country where the shocks
are less violent. At a still greater distance (as in Northern Italy, for
example, extending to the foot of the Alps), there are spaces where the
shocks are much rarer and more feeble, yet possibly of sufficient force
to cause, by continued repetition, some appreciable alteration in the
external form of the earth's crust. Beyond these limits, again, all
countries are liable to slight tremors, at distant intervals of time,
when some great crisis of subterranean movement agitates an adjoining
volcanic region; but these may be considered as mere vibrations,
propagated mechanically through the external covering of the globe, as
sounds travel almost to indefinite distances through the air. Shocks of
this kind have been felt in England, Scotland, Northern France, and
Germany--particularly during the Lisbon earthquake. But these countries
cannot, on this account, be supposed to constitute parts of the southern
volcanic region, any more than the Shetland and Orkney islands can be
considered as belonging to the Icelandic circle, because the sands
ejected from Hecla have been wafted thither by the winds.
Besides the continuous spaces of subterranean disturbance, of which we
have merely sketched the outline, there are other disconnected volcanic
groups, of which several will be mentioned hereafter.
_Lines of active and extinct Volcanoes not to be confounded._--We must
always be careful to distinguish between lines of extinct and active
volcanoes, even where they appear to run in the same direction; for
ancient and modern systems may interfere with each other. Already,
indeed, we have proof that this is the case; so that it is not by
geographical position, but by reference to the species of organic beings
alone, whether aquatic or terrestrial, whose remains occur in beds
interstratified with lavas, that we can clearly distinguish the relative
age of volcanoes of which no eruptions are recorded. Had Southern Italy
been known to civilized nations for as short a period as America, we
should have had no record of eruptions in Ischia; yet we might have
assured ourselves that the lavas of that isle had flowed since the
Mediterranean was inhabited by the species of testacea now living in the
Neapolitan seas. With this assurance, it would not have been rash to
include the numerous vents of that island in the modern volcanic group
of Campania.
On similar grounds we may infer, without much hesitation, that the
eruptions of Etna, and the modern earthquakes of Calabria, are a
continuation of that action which, at a somewhat earlier period,
produced the submarine lavas of the Val di Noto in Sicily. But on the
other hand, the lavas of the Euganean hills and the Vicentin, although
not wholly beyond the range of earthquakes in Northern Italy, must not
be confounded with any existing volcanic system; for when they flowed,
the seas were inhabited by animals almost all of them distinct from
those now known to live, whether in the Mediterranean or other parts of
the globe.