Chapter 6 (second part)

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ON THE GROUPING OF THE DIFFERENT
CLASSES OF REEFS.


Having made these preliminary
remarks, I will consider first
how far the grouping of the
different kinds of coral-islands
and reefs is corroborative
of the truth of the theory.
A glance at the map shows that
the reefs, coloured blue and red,
produced under widely different
conditions, are not indiscriminately mixed together.  Atolls
and barrier-reefs, on the other hand, as may be seen by the
two blue tints, generally lie near each other; and this would
be the natural result of both having been produced during the
subsidence of the areas in which they stand.  Thus, the largest
group of encircled islands is that of the Society Archipelago;
and these islands are surrounded by atolls, and only separated by
a narrow space from the large group of Low atolls.  In the midst
of the Caroline atolls,there are three fine encircled islands.  The northern
point of the barrier-reef of New Caledonia seems itself, as before remarked,
to form a complete large atoll.  The great Australian barrier is described
as including both atolls and small encircled islands.  Captain King (Sailing
directions, appended to volume ii. of his "Surveying Voyage to Australia.")
mentions many atoll-formed and encircling coral-reefs, some of which lie within
the barrier, and others may be said (for instance between latitude 16 deg and
13 deg) to form part of it.  Flinders ("Voyage to Terra Australis," volume
ii. page 336.) has described an atoll-formed reef in latitude 10 deg, seven
miles long and from one to three broad, resembling a boot in shape, with
apparently very deep water within.  Eight miles westward of this, and
forming part of the barrier, lie the Murray Islands, which are high and are
encircled.  In the Corallian Sea, between the two great barriers of
Australia and New Caledonia, there are many low islets and coral-reefs,
some of which are annular, or horse-shoe shaped.  Observing the smallness
of the scale of the map, the parallels of latitude being nine hundred miles
apart, we see that none of the large groups of reefs and islands supposed
to have been produced by long-continued subsidence, lie near extensive
lines of coast coloured red, which are supposed to have remained stationary
since the growth of their reefs, or to have been upraised and new lines of
reefs formed on them.  Where the red and blue circles do occur near each
other, I am able, in several instances, to show that there have been
oscillations of level, subsidence having preceded the elevation of the red
spots; and elevation having preceded the subsidence of the blue spots: and
in this case the juxtaposition of reefs belonging to the two great types of
structure is little surprising.  We may, therefore, conclude that the
proximity in the same areas of the two classes of reefs, which owe their
origin to the subsidence of the earth's crust, and their separation from
those formed during its stationary or uprising condition, holds good to the
full extent, which might have been anticipated by our theory.

As groups of atolls have originated in the upward growth, at each fresh
sinking of the land, of those reefs which primarily fringed the shores of
one great island, or of several smaller ones; so we might expect that these
rings of coral-rock, like so many rude outline charts, will still retain
some traces of the general form, or at least general range, of the land,
round which they were first modelled.  That this is the case with the
atolls in the Southern Pacific as far as their range is concerned, seems
highly probable, when we observe that the three principal groups are
directed in north-west and south-east lines, and that nearly all the land
in the S. Pacific ranges in this same direction; namely, N. Western
Australia, New Caledonia, the northern half of New Zealand, the New
Hebrides, Saloman, Navigator, Society, Marquesas, and Austral
archipelagoes: in the Northern Pacific, the Caroline atolls abut against
the north-west line of the Marshall atolls, much in the same manner as the
east and west line of islands from Ceram to New Britain do on New Ireland:
in the Indian Ocean the Laccadive and Maldiva atolls extend nearly parallel
to the western and mountainous coast of India.  In most respects, there is
a perfect resemblance with ordinary islands in the grouping of atolls and
in their form: thus the outline of all the larger groups is elongated; and
the greater number of the individual atolls are elongated in the same
direction with the group, in which they stand.  The Chagos group is less
elongated than is usual with other groups, and the individual atolls in it
are likewise but little elongated; this is strikingly seen by comparing
them with the neighbouring Maldiva atolls.  In the Marshall and Maldiva
archipelagoes, the atolls are ranged in two parallel lines, like the
mountains in a great double mountain-chain.  Some of the atolls, in the
larger archipelagoes, stand so near to each other, and have such an evident
relationship in form, that they compose little sub-groups: in the Caroline
Archipelago, one such sub-group consists of Pouynipete, a lofty island
encircled by a barrier-reef, and separated by a channel only four miles and
a half wide from Andeema atoll, with a second atoll a little further off.
In all these respects an examination of a series of charts will show how
perfectly groups of atolls resemble groups of common islands.

ON THE DIRECT EVIDENCE OF THE BLUE SPACES IN THE MAP HAVING SUBSIDED DURING
THE UPWARD GROWTH OF THE REEFS SO COLOURED, AND OF THE RED SPACES HAVING
REMAINED STATIONARY, OR HAVING BEEN UPRAISED.

With respect to subsidence, I have shown in the last chapter, that we
cannot expect to obtain in countries inhabited only by semi-civilised
races, demonstrative proofs of a movement, which invariably tends to
conceal its own evidence.  But on the coral-islands supposed to have been
produced by subsidence, we have proofs of changes in their external
appearance--of a round of decay and renovation--of the last vestiges of
land on some--of its first commencement on others: we hear of storms
desolating them to the astonishment of their inhabitants: we know by the
great fissures with which some of them are traversed, and by the
earthquakes felt under others, that subterranean disturbances of some kind
are in progress.  These facts, if not directly connected with subsidence,
as I believe they are, at least show how difficult it would be to discover
proofs of such movement by ordinary means.  At Keeling atoll, however, I
have described some appearances, which seem directly to show that
subsidence did take place there during the late earthquakes.  Vanikoro,
according to Chevalier Dillon (See Captain Dillon's "Voyage in search of La
Peyrouse."  M. Cordier in his "Report on the Voyage of the 'Astrolabe'"
(page cxi., volume i.), speaking of Vanikoro, says the shores are
surrounded by reefs of madrepore, "qu'on assure etre de formation
tout-a-fait moderne."  I have in vain endeavoured to learn some further
particulars about this remarkable passage.  I may here add, that according
to our theory, the island of Pouynipete (Plate I., Figure 7), in the
Caroline Archipelago, being encircled by a barrier-reef, must have
subsided.  In the "New S. Wales Lit. Advert." February 1835 (which I have
seen through the favour of Dr. Lloghtsky), there is an account of this
island (subsequently confirmed by Mr. Campbell), in which it is said, "At
the N.E. end, at a place called Tamen, there are ruins of a town, NOW ONLY
accessible by boats, the waves REACHING TO THE STEPS OF The HOUSES."
Judging from this passage, one would be tempted to conclude that the island
must have subsided, since these houses were built.  I may, also, here
append a statement in Malte Brun (volume ix., page 775, given without any
authority), that the sea gains in an extraordinary manner on the coast of
Cochin China, which lies in front and near the subsiding coral-reefs in the
China Sea: as the coast is granitic, and not alluvial, it is scarcely
possible that the encroachment of the sea can be owing to the washing away
of the land; and if so, it must be due to subsidence.), is often violently
shaken by earthquakes, and there, the unusual depth of the channel between
the shore and the reef,--the almost entire absence of islets on the reef,--
its wall-like structure on the inner side, and the small quantity of low
alluvial land at the foot of the mountains, all seem to show that this
island has not remained long at its present level, with the lagoon-channel
subjected to the accumulation of sediment, and the reef to the wear and
tear of the breakers.  At the Society Archipelago, on the other hand, where
a slight tremor is only rarely felt, the shoaliness of the lagoon-channels
round some of the islands, the number of islets formed on the reefs of
others, and the broad belt of low land at the foot of the mountains,
indicate that, although there must have been great subsidence to have
produced the barrier-reefs, there has since elapsed a long stationary
period.

(Mr. Couthouy states ("Remarks," page 44) that at Tahiti and Eimeo the
space between the reef and the shore has been nearly filled up by the
extension of those coral-reefs, which within most barrier-reefs merely
fringe the land.  From this circumstance, he arrives at the same conclusion
as I have done, that the Society Islands since their subsidence, have
remained stationary during a long period; but he further believes that they
have recently commenced rising, as well as the whole area of the Low
Archipelago.  He does not give any detailed proofs regarding the elevation
of the Society Islands, but I shall refer to this subject in another part
of this chapter.  Before making some further comments, I may observe how
satisfactory it is to me, to find Mr. Couthouy affirming, that "having
personally examined a large number of coral-islands, and also residing
eight months among the volcanic class, having shore and partially
encircling reefs, I may be permitted to state that my own observations have
impressed a conviction of the correctness of the theory of Mr. Darwin."

This gentleman believes, that subsequently to the subsidence by which the
atolls in the Low Archipelago were produced, the whole area has been
elevated to the amount of a few feet; this would indeed be a remarkable
fact; but as far as I am able to judge, the grounds of his conclusion are
not sufficiently strong.  He states that he found in almost every atoll
which he visited, the shores of the lagoon raised from eighteen to thirty
inches above the sea-level, and containing imbedded Tridacnae and corals
standing as they grew; some of the corals were dead in their upper parts,
but below a certain line they continued to flourish.  In the lagoons, also,
he frequently met with clusters of Madrepore, with their extremities
standing from one inch to a foot above the surface of the water.  Now,
these appearances are exactly what I should have expected, without any
subsequent elevation having taken place; and I think Mr. Couthouy has not
borne in mind the indisputable fact, that corals, when constantly bathed by
the surf, can exist at a higher level than in quite tranquil water, as in a
lagoon.  As long, therefore, as the waves continued at low water to break
entirely over parts of the annular reef of an atoll, submerged to a small
depth, the corals and shells attached on these parts might continue living
at a level above the smooth surface of the lagoon, into which the waves
rolled; but as soon as the outer edge of the reef grew up to its utmost
possible height, or if the reef were very broad nearly to that height, the
force of the breakers would be checked, and the corals and shells on the
inner parts near the lagoon would occasionally be left dry, and thus be
partially or wholly destroyed.  Even in atolls, which have not lately
subsided, if the outer margin of the reef continued to increase in breadth
seaward (each fresh zone of corals rising to the same vertical height as at
Keeling atoll), the line where the waves broke most heavily would advance
outwards, and therefore the corals, which when living near the margin, were
washed by the breaking waves during the whole of each tide, would cease
being so, and would therefore be left on the backward part of the reef
standing exposed and dead.  The case of the madrepores in the lagoons with
the tops of their branches exposed, seems to be an analogous fact, to the
great fields of dead but upright corals in the lagoon of Keeling atoll; a
condition of things which I have endeavoured to show, has resulted from the
lagoon having become more and more enclosed and choked up with reefs, so
that during high winds, the rising of the tide (as observed by the
inhabitants) is checked, and the corals, which had formerly grown to the
greatest possible height, are occasionally exposed, and thus are killed:
and this is a condition of things, towards which almost every atoll in the
intervals of its subsidence must be tending.  Or if we look to the state of
an atoll directly after a subsidence of some fathoms, the waves would roll
heavily over the entire circumference of the reef, and the surface of the
lagoon would, like the ocean, never be quite at rest, and therefore the
corals in the lagoon, from being constantly laved by the rippling water,
might extend their branches to a little greater height than they could,
when the lagoon became enclosed and protected.  Christmas atoll (2 deg N.
latitude) which has a very shallow lagoon, and differs in several respects
from most atolls, possibly may have been elevated recently; but its highest
part appears (Couthouy, page 46) to be only ten feet above the sea-level.
The facts of a second class, adduced by Mr. Couthouy, in support of the
alleged recent elevation of the Low Archipelago, are not all (especially
those referring to a shelf of rock) quite intelligible to me; he believes
that certain enormous fragments of rock on the reef, must have been moved
into their present position, when the reef was at a lower level; but here
again the force of the breakers on any inner point of the reef being
diminished by its outward growth without any change in its level, has not,
I think, been borne in mind.  We should, also, not overlook the occasional
agency of waves caused by earthquakes and hurricanes.  Mr. Couthouy further
argues, that since these great fragments were deposited and fixed on the
reef, they have been elevated; he infers this from the greatest amount of
erosion not being near their bases, where they are unceasingly washed by
the reflux of the tides, but at some height on their sides, near the line
of high-water mark, as shown in an accompanying diagram.  My former remark
again applies here, with this further observation, that as the waves have
to roll over a wide space of reef before they reach the fragments, their
force must be greatly increased with the increasing depth of water as the
tide rises, and therefore I should have expected that the chief line of
present erosion would have coincided with the line of high-water mark; and
if the reef had grown outwards, that there would have been lines of erosion
at greater heights.  The conclusion, to which I am finally led by the
interesting observations of Mr. Couthouy is, that the atolls in the Low
Archipelago have, like the Society Islands, remained at a stationary level
for a long period: and this probably is the ordinary course of events,
subsidence supervening after long intervals of rest.)

Turning now to the red colour; as on our map, the areas which have sunk
slowly downwards to great depths are many and large, we might naturally
have been led to conjecture, that with such great changes of level in
progress, the coasts which have been fringed probably for ages (for we have
no reason to believe that coral-reefs are of short duration), would not
have remained all this time stationary, but would frequently have undergone
movements of elevation.  This supposition, we shall immediately see, holds
good to a remarkable extent; and although a stationary condition of the
land can hardly ever be open to proof, from the evidence being only
negative, we are, in some degree, enabled to ascertain the correctness of
the parts coloured red on the map, by the direct testimony of upraised
organic remains of a modern date.  Before going into the details on this
head (printed in small type), I may mention, that when reading a memoir on
coral formations by MM. Quoy and Gaimard ("Annales des Sciences Nat." tom.
vi., page 279, etc.) I was astonished to find, for I knew that they had
crossed both the Pacific and Indian Oceans, that their descriptions were
applicable only to reefs of the fringing class; but my astonishment ended
satisfactorily, when I discovered that, by a strange chance, all the
islands which these eminent naturalists had visited, though several in
number, namely, the Mauritius, Timor, New Guinea, the Mariana, and Sandwich
Archipelagoes, could be shown by their own statements to have been elevated
within a recent geological era.

In the eastern half of the Pacific, the SANDWICH Islands are all fringed,
and almost every naturalist who has visited them, has remarked on the
abundance of elevated corals and shells, apparently identical with living
species.  The Rev. W. Ellis informs me, that he has noticed round several
parts of Hawaii, beds of coral-detritus, about twenty feet above the level
of the sea, and where the coast is low they extend far inland.  Upraised
coral-rock forms a considerable part of the borders of Oahu; and at
Elizabeth Island ("Zoology of Captain Beechey's Voyage," page 176.  See
also MM. Quoy and Gaimard in "Annales de Scien. Nat." tom. vi.) it composes
three strata, each about ten feet thick.  Nihau, which forms the northern,
as Hawaii does the southern end of the group (350 miles in length),
likewise seems to consist of coral and volcanic rocks.  Mr. Couthouy
("Remarks on Coral Formations," page 51.) has lately described with
interesting details, several upraised beaches, ancient reefs with their
surfaces perfectly preserved, and beds of recent shells and corals, at the
islands of Maui, Morokai, Oahu, and Tauai (or Kauai) in this group.  Mr.
Pierce, an intelligent resident at Oahu, is convinced, from changes which
have taken place within his memory, during the last sixteen years, "that
the elevation is at present going forward at a very perceptible rate."  The
natives at Kauai state that the land is there gaining rapidly on the sea,
and Mr. Couthouy has no doubt, from the nature of the strata, that this has
been effected by an elevation of the land.

In the southern part of the Low Archipelago, Elizabeth Island is described
by Captain Beechey (Beechey's "Voyage in the Pacific," page 46, 4to
edition.), as being quite flat, and about eighty feet in height; it is
entirely composed of dead corals, forming a honeycombed, but compact rock.
In cases like this, of an island having exactly the appearance, which the
elevation of any one of the smaller surrounding atolls with a shallow
lagoon would present, one is led to conclude (with little better reason,
however, than the improbability of such small and low fabrics lasting, for
an immense period, exposed to the many destroying agents of nature), that
the elevation has taken place at an epoch not geologically remote.  When
merely the surface of an island of ordinary formation is strewed with
marine bodies, and that continuously, or nearly so, from the beach to a
certain height, and not above that height, it is exceedingly improbable
that such organic remains, although they may not have been specially
examined, should belong to any ancient period.  It is necessary to bear
these remarks in mind, in considering the evidence of the elevatory
movements in the Pacific and Indian Oceans, as it does not often rest on
specific determinations, and therefore should be received with caution.
Six of the COOK AND AUSTRAL Islands (S.W. of the Society group), are
fringed; of these, five were described to me by the Rev. J. Williams, as
formed of coral-rock, associated with some basalt in Mangaia), and the
sixth as lofty and basaltic.  Mangaia is nearly three hundred feet high,
with a level summit; and according to Mr. S. Wilson (Couthouy's "Remarks,"
page 34.) it is an upraised reef; "and there are in the central hollow,
formerly the bed of the lagoon, many scattered patches of coral-rock, some
of them raised to a height of forty feet."  These knolls of coral-rock were
evidently once separate reefs in the lagoon of an atoll.  Mr. Martens, at
Sydney, informed me that this island is surrounded by a terrace-like plain
at about the height of a hundred feet, which probably marks a pause in its
elevation.  From these facts we may infer, perhaps, that the Cook and
Austral Islands have been upheaved at a period probably not very remote.

SAVAGE Island (S.E. of the Friendly group), is about forty feet in height.
Forster ("Observations made during Voyage round the World," page 147.)
describes the plants as already growing out of the dead, but still upright
and spreading trees of coral; and the younger Forster ("Voyage," volume
ii., page 163.) believes that an ancient lagoon is now represented by a
central plain; here we cannot doubt that the elevatory forces have recently
acted.  The same conclusion may be extended, though with somewhat less
certainty, to the islands of the FRIENDLY GROUP, which have been well
described in the second and third voyages of Cook.  The surface of
Tongatabou is low and level, but with some parts a hundred feet high; the
whole consists of coral-rock, "which yet shows the cavities and
irregularities worn into it by the action of the tides."  (Cook's "Third
Voyage" (4to edition), volume i., page 314.)  On Eoua the same appearances
were noticed at an elevation of between two hundred and three hundred feet.
Vavao, also, at the opposite or northern end of the group, consists,
according to the Rev. J. Williams, of coral-rock.  Tongatabou, with its
northern extensive reefs, resembles either an upraised atoll with one half
originally imperfect, or one unequally elevated; and Anamouka, an atoll
equally elevated.  This latter island contains (Ibid., volume i., page
235.) in its centre a salt-water lake, about a mile-and-a-half in diameter,
without any communication with the sea, and around it the land rises
gradually like a bank; the highest part is only between twenty and thirty
feet; but on this part, as well as on the rest of the land (which, as Cook
observes, rises above the height of true lagoon-islands), coral-rock, like
that on the beach, was found.  In the NAVIGATOR ARCHIPELAGO, Mr. Couthouy
("Remarks on Coral-Formations," page 50.) found on Manua many and very
large fragments of coral at the height of eighty feet, "on a steep hill-side,
rising half a mile inland from a low sandy plain abounding in marine
remains."  The fragments were embedded in a mixture of decomposed lava and
sand.  It is not stated whether they were accompanied by shells, or whether
the corals resembled recent species; as these remains were embedded they
possibly may belong to a remote epoch; but I presume this was not the
opinion of Mr. Couthouy.  Earthquakes are very frequent in this
archipelago.

Still proceeding westward we come to the NEW HEBRIDES; on these islands,
Mr. G. Bennett (author of "Wanderings in New South Wales"), informs me he
found much coral at a great altitude, which he considered of recent origin.
Respecting SANTA CRUZ, and the SOLOMON ARCHIPELAGO, I have no information;
but at New Ireland, which forms the northern point of the latter chain,
both Labillardiere and Lesson have described large beds of an apparently
very modern madreporitic rock, with the form of the corals little altered.
The latter author ("Voyage de la 'Coquille'," Part. Zoolog.) states that
this formation composes a newer line of coast, modelled round an ancient
one.  There only remains to be described in the Pacific, that curved line
of fringed islands, of which the MARIANAS form the main part.  Of these
Guam, Rota, Tiniam, Saypan, and some islets farther north, are described by
Quoy and Gaimard (Freycinet's "Voyage autour du Monde."  See also the
"Hydrographical Memoir," page 215.), and Chamisso (Kotzebue's "First
Voyage."), as chiefly composed of madreporitic limestone, which attains a
considerable elevation, and is in several cases worn into successively
rising cliffs: the two former naturalists seem to have compared the corals
and shells with the existing ones, and state that they are of recent
species.  FAIS, which lies in the prolonged line of the Marianas, is the
only island in this part of the sea which is fringed; it is ninety feet
high, and consists entirely of madreporitic rock.  (Lutke's "Voyage,"
volume ii., page 304.)

In the EAST INDIAN ARCHIPELAGO, many authors have recorded proofs of recent
elevation.  M. Lesson (Partie Zoolog., "Voyage de la 'Coquille'.") states,
that near Port Dory, on the north coast of New Guinea, the shores are
flanked, to the height of 150 feet, by madreporitic strata of modern date.
He mentions similar formations at Waigiou, Amboina, Bourou, Ceram, Sonda,
and Timor: at this latter place, MM. Quoy and Gaimard ("Ann. des Scien.
Nat." tom. vi., page 281.) have likewise described the primitive rocks, as
coated to a considerable height with coral.  Some small islets eastward of
Timor are said in Kolff's "Voyage," (translated by Windsor Earl, chapters
vi., vii.) to resemble small coral islets upraised some feet above the sea.
Dr. Malcolmson informs me that Dr. Hardie found in JAVA an extensive
formation, containing an abundance of shells, of which the greater part
appear to be of existing species.  Dr. Jack ("Geolog. Transact." 2nd
series, volume i., page 403.  On the Peninsula of Malacca, in front of
Pinang, 5 deg 30' N., Dr. Ward collected some shells, which Dr. Malcolmson
informs me, although not compared with existing species, had a recent
appearance.  Dr. Ward describes in this neighbourhood ("Trans. Asiat. Soc."
volume xviii., part ii., page 166) a single water-worn rock, with a
conglomerate of sea-shells at its base, situated six miles inland, which,
according to the traditions of the natives, was once surrounded by the sea.
Captain Low has also described (Ibid., part i., page 131) mounds of shells
lying two miles inland on this line of coast.) has described some upraised
shells and corals, apparently recent, on Pulo Nias off SUMATRA; and Marsden
relates in his history of this great island, that the names of many
promontories, show that they were originally islands.  On part of the west
coast of BORNEO and at the SOOLOO Islands, the form of the land, the nature
of the soil, and the water-washed rocks, present appearances ("Notices of
the East Indian Arch." Singapore, 1828, page 6, and Append., page 43.)
(although it is doubtful whether such vague evidence is worthy of mention),
of having recently been covered by the sea; and the inhabitants of the
Sooloo Islands believe that this has been the case.  Mr. Cuming, who has
lately investigated, with so much success, the natural history of the
PHILIPPINES, found near Cabagan, in Luzon, about fifty feet above the level
of the R. Cagayan, and seventy miles from its mouth, a large bed of fossil
shells: these, he informs me, are of the same species with those now
existing on the shores of the neighbouring islands.  From the accounts
given us by Captain Basil Hall and Captain Beechey (Captain B. Hall,
"Voyage to Loo Choo," Append., pages xxi. and xxv.  Captain Beechey's
"Voyage," page 496.) of the lines of inland reefs, and walls of coral-rock
worn into caves, above the present reach of the waves, at the LOO CHOO
Islands, there can be little doubt that they have been upraised at no very
remote period.

Dr. Davy describes the northern province of CEYLON ("Travels in Ceylon,"
page 13.  This madreporitic formation is mentioned by M. Cordier in his
report to the Institute (May 4th, 1839), on the voyage of the "Chevrette",
as one of immense extent, and belonging to the latest tertiary period.) as
being very low, and consisting of a limestone with shells and corals of
very recent origin; he adds, that it does not admit of a doubt that the sea
has retired from this district even within the memory of man.  There is
also some reason for believing that the western shores of India, north of
Ceylon, have been upraised within the recent period.  (Dr. Benza, in his
"Journey through the N. Circars" (the "Madras Lit. and Scient. Journ."
volume v.) has described a formation with recent fresh-water and marine
shells, occurring at the distance of three or four miles from the present
shore.  Dr. Benza, in conversation with me, attributed their position to a
rise of the land.  Dr. Malcolmson, however (and there cannot be a higher
authority on the geology of India) informs me that he suspects that these
beds may have been formed by the mere action of the waves and currents
accumulating sediment.  From analogy I should much incline to Dr. Benza's
opinion.)  MAURITIUS has certainly been upraised within the recent period,
as I have stated in the chapter on fringing-reefs.  The northern extremity
of MADAGASCAR is described by Captain Owen (Owen's "Africa," volume ii.,
page 37, for Madagascar; and for S. Africa, volume i., pages 412 and 426.
Lieutenant Boteler's narrative contains fuller particulars regarding the
coral-rock, volume i., page 174, and volume ii., pages 41 and 54.  See also
Ruschenberger's "Voyage round the World," volume i., page 60.) as formed of
madreporitic rock, as likewise are the shores and outlying islands along an
immense space of EASTERN AFRICA, from a little north of the equator for
nine hundred miles southward.  Nothing can be more vague than the
expression "madreporitic rock;" but at the same time it is, I think,
scarcely possible to look at the chart of the linear islets, which rise to
a greater height than can be accounted for by the growth of coral, in front
of the coast, from the equator to 2 deg S., without feeling convinced that
a line of fringing-reefs has been elevated at a period so recent, that no
great changes have since taken place on the surface of this part of the
globe.  Some, also, of the higher islands of madreporitic rock on this
coast, for instance Pemba, have very singular forms, which seem to show the
combined effect of the growth of coral round submerged banks, and their
subsequent upheaval.  Dr. Allan informs me that he never observed any
elevated organic remains on the SEYCHELLES, which come under our fringed
class.

The nature of the formations round the shores of the RED SEA, as described
by several authors, shows that the whole of this large area has been
elevated within a very recent tertiary epoch.  A part of this space in the
appended map, is coloured blue, indicating the presence of barrier-reefs:
on which circumstance I shall presently make some remarks.  Ruppell
(Ruppell, "Reise in Abyssinien," Band i., s. 141.) states that the tertiary
formation, of which he has examined the organic remains, forms a fringe
along the shores with a uniform height of from thirty and forty feet from
the mouth of the Gulf of Suez to about latitude 26 deg; but that south of
26 deg, the beds attain only the height of from twelve to fifteen feet.
This, however, can hardly be quite accurate; although possibly there may be
a decrease in the elevation of the shores in the middle parts of the Red
Sea, for Dr. Malcolmson (as he informs me) collected from the cliffs of
Camaran Island (latitude 15 deg 30' S.) shells and corals, apparently
recent, at a height between thirty and forty feet; and Mr. Salt ("Travels
in Abyssinia") describes a similar formation a little southward on the
opposite shore at Amphila.  Moreover, near the mouth of the Gulf of Suez,
although on the coast opposite to that on which Dr. Ruppell says that the
modern beds attain a height of only thirty to forty feet, Mr. Burton
(Lyell's "Principles of Geology," 5th edition, volume iv., page 25.) found
a deposit replete with existing species of shells, at the height of 200
feet.  In an admirable series of drawings by Captain Moresby, I could see
how continuously the cliff-bounded low plains of this formation extended
with a nearly equable height, both on the eastern and western shores.  The
southern coast of Arabia seems to have been subjected to the same elevatory
movement, for Dr. Malcolmson found at Sahar low cliffs containing shells
and corals, apparently of recent species.

The PERSIAN GULF abounds with coral-reefs; but as it is difficult to
distinguish them from sand-banks in this shallow sea, I have coloured only
some near the mouth; towards the head of the gulf Mr. Ainsworth
(Ainsworth's "Assyria and Babylon," page 217.) says that the land is worn
into terraces, and that the beds contain organic remains of existing forms.
The WEST INDIAN ARCHIPELAGO of "fringed" islands, alone remains to be
mentioned; evidence of an elevation within a late tertiary epoch of nearly
the whole of this great area, may be found in the works of almost all the
naturalists who have visited it.  I will give some of the principal
references in a note.  (On Florida and the north shores of the Gulf of
Mexico, Rogers' "Report to Brit. Assoc." volume iii., page 14.--On the
shores of Mexico, Humboldt, "Polit. Essay on New Spain," volume i., page
62.  (I have also some corroborative facts with respect to the shores of
Mexico.)--Honduras and the Antilles, Lyell's "Principles," 5th edition,
volume iv., page 22.--Santa Cruz and Barbadoes, Prof. Hovey, "Silliman's
Journal", volume xxxv., page 74.--St. Domingo, Courrojolles, "Journ de
Phys." tom. liv., page 106.--Bahamas, "United Service Journal", No. lxxi.,
pages 218 and 224.  Jamaica, De la Beche, "Geol. Man." page 142.--Cuba,
Taylor in "Lond. and Edin. Mag." volume xi., page 17.  Dr. Daubeny also, at
a meeting of the Geolog. Soc., orally described some very modern beds lying
on the N.W. parts of Cuba.  I might have added many other less important
references.)

It is very remarkable on reviewing these details, to observe in how many
instances fringing-reefs round the shores, have coincided with the
existence on the land of upraised organic remains, which seem, from
evidence more or less satisfactory, to belong to a late tertiary period.
It may, however, be objected, that similar proofs of elevation, perhaps,
occur on the coasts coloured blue in our map: but this certainly is not
the case with the few following and doubtful exceptions.

The entire area of the Red Sea appears to have been upraised within a
modern period; nevertheless I have been compelled (though on unsatisfactory
evidence, as given in the Appendix) to class the reefs in the middle part,
as barrier-reefs; should, however, the statements prove accurate to the
less height of the tertiary bed in this middle part, compared with the
northern and southern districts, we might well suspect that it had subsided
subsequently to the general elevation by which the whole area has been
upraised.  Several authors (Ellis, in his "Polynesian Researches," was the
first to call attention to these remains (volume i., page 38), and the
tradition of the natives concerning them.  See also Williams, "Nar. of
Missionary Enterprise," page 21; also Tyerman and G. Bennett, "Journal of
Voyage," volume i., page 213; also Mr. Couthouy's "Remarks," page 51; but
this principal fact, namely, that there is a mass of upraised coral on the
narrow peninsula of Tiarubu, is from hearsay evidence; also Mr. Stutchbury,
"West of England Journal," No. i., page 54.  There is a passage in Von
Zach, "Corres. Astronom." volume x., page 266, inferring an uprising at
Tahiti, from a footpath now used, which was formerly impassable; but I
particularly inquired from several native chiefs, whether they knew of any
change of this kind, and they were unanimous in giving me an answer in the
negative.) have stated that they have observed shells and corals high up on
the mountains of the Society Islands,--a group encircled by barrier-reefs,
and, therefore, supposed to have subsided: at Tahiti Mr. Stutchbury found
on the apex of one of the highest mountains, between 5,000 and 7,000 feet
above the level of the sea, "a distinct and regular stratum of semi-fossil
coral."  At Tahiti, however, other naturalists, as well as myself, have
searched in vain at a low level near the coast, for upraised shells or
masses of coral-reef, where if present they could hardly have been
overlooked.  From this fact, I concluded that probably the organic remains
strewed high up on the surface of the land, had originally been embedded in
the volcanic strata, and had subsequently been washed out by the rain.  I
have since heard from the Rev. W. Ellis, that the remains which he met
with, were (as he believes) interstratified with an argillaceous tuff; this
likewise was the case with the shells observed by the Rev. D. Tyerman at
Huaheine.  These remains have not been specifically examined; they may,
therefore, and especially the stratum observed by Mr. Stutchbury at an
immense height, be contemporaneous with the first formation of the Society
Islands, and be of any degree of antiquity; or they may have been deposited
at some subsequent, but probably not very recent, period of elevation; for
if the period had been recent, the entire surface of the coast land of
these islands, where the reefs are so extensive, would have been coated
with upraised coral, which certainly is not the case.  Two of the Harvey,
or Cook Islands, namely, Aitutaki and Manouai, are encircled by reefs,
which extend so far from the land, that I have coloured them blue, although
with much hesitation, as the space within the reef is shallow, and the
outline of the land is not abrupt.  These two islands consist of coral-rock;
but I have no evidence of their recent elevation, besides, the
improbability of Mangaia, a fringed island in the same group (but distant
170 miles), having retained its nearly perfect atoll-like structure, during
any immense lapse of time after its upheaval.  The Red Sea, therefore, is
the only area in which we have clear proofs of the recent elevation of a
district, which, by our theory (although the barrier-reefs are there not
well characterised), has lately subsided.  But we have no reason to be
surprised at oscillation, of level of this kind having occasionally taken
place.  There can be scarcely any doubt that Savage, Aurora (Aurora Island
is described by Mr. Couthouy ("Remarks," page 58); it lies 120 miles
north-east of Tahiti; it is not coloured in the appended map, because it does
not appear to be fringed by living reefs.  Mr. Couthouy describes its summit
as "presenting a broad table-land which declines a few feet towards the
centre, where we may suppose the lagoon to have been placed."  It is about
two hundred feet in height, and consists of reef-rock and conglomerate,
with existing species of coral embedded in it.  The island has been
elevated at two successive periods; the cliffs being marked halfway up with
a horizontal water-worn line of deep excavations.  Aurora Island seems
closely to resemble in structure Elizabeth Island, at the southern end of
the Low Archipelago.), and Mangaia Islands, and several of the islands in
the Friendly group, existed originally as atolls, and these have
undoubtedly since been upraised to some height above the level of the sea;
so that by our theory, there has here, also, been an oscillation of level,
--elevation having succeeded subsidence, instead of, as in the middle part
of the Red Sea and at the Harvey Islands, subsidence having probably
succeeded recent elevation.

It is an interesting fact, that Fais, which, from its composition, form,
height, and situation at the western end of the Caroline Archipelago, one
is strongly induced to believe existed before its upheaval as an atoll,
lies exactly in the prolongation of the curved line of the Mariana group,
which we know to be a line of recent elevation.  I may add, that Elizabeth
Island, in the southern part of the Low Archipelago, which seems to have
had the same kind of origin as Fais, lies near Pitcairn Island, the only
one in this part of the ocean which is high, and at the same time not
surrounded by an encircling barrier-reef.

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