by Captain Owen, and the accounts given by him and by Lieutenant
Boteler. Commencing at the S.W. extremity of the island; towards the
northern part of the _Star Bank_ (in latitude 25° S.) the coast for ten
miles is fringed by a reef; coloured red. The shore immediately S. of
_St. Augustine’s Bay_ appears fringed; but _Tullear_ Harbour, directly
N. of it, is formed by a narrow reef ten miles long, extending parallel
to the shore, with from four to ten fathoms within it. If this reef had
been more extensive, it must have been classed as a barrier-reef; but
as the line of coast falls inwards here, a submarine bank perhaps
extends parallel to the shore, which has offered a foundation for the
growth of the coral; I have left this part uncoloured. From _lat_. 22°
16′ _to_ 21° 37′, the shore is fringed by coral-reefs (see Lieutenant
Boteler’s “Narrative,” volume ii., page 106), less than a mile in
width, and with shallow water within. There are outlying coral-shoals
in several parts of the offing, with about ten fathoms between them and
the shore, and the depth of the sea one mile and a half seaward, is
about thirty fathoms. The part above specified is engraved on a large
scale; and as in the charts on rather a smaller scale the same fringe
of reef extends as far as latitude 33° 15′; I have coloured the whole
of this part of the coast red. The islands of _Juan de Nova_ (in
latitude 17° S.) appear in the charts on a large scale to be fringed,
but I have not been able to ascertain whether the reefs are of coral;
uncoloured. The main part of the west coast appears to be low, with
outlying sandbanks, which, Lieutenant Boteler (volume ii., page 106)
says, “are faced on the edge of deep water by a line of sharp-pointed
coral-rocks.” Nevertheless I have not coloured this part, as I cannot
make out by the charts that the coast itself is fringed. The headlands
of _Narrenda_ and _Passandava Bays_ (14° 40′) and the islands in front
of _Radama harbour_ are represented in the plans as regularly fringed,
and have accordingly been coloured red. With respect to the _East coast
of Madagascar_, Dr. Allan informs me in a letter, that the whole line
of coast, from _Tamatave_, in 18° 12′, to _C. Amber_, at the extreme
northern point of the island, is bordered by coral-reefs. The land is
low, uneven, and gradually rising from the coast. From Captain Owen’s
charts, also, the existence of these reefs, which evidently belong to
the fringing class, on some parts, namely N. of _British Sound_, and
near _Ngoncy_, of the above line of coast might have been inferred.
Lieutenant Boteler (volume i., page 155) speaks of “the reef
surrounding the island of _St. Mary’s_ at a small distance from the
shore.” In a previous chapter I have described, from the information of
Dr. Allan, the manner in which the reefs extend in N.E. lines from the
headlands on this coast, thus sometimes forming rather deep channels
within them, this seems caused by the action of the currents, and the
reefs spring up from the submarine prolongations of the sandy
headlands. The above specified portion of the coast is coloured red.
The remaining S.E. portions do not appear in any published chart to
possess reefs of any kind; and the Rev. W. Ellis, whose means of
information regarding this side of Madagascar have been extensive,
informs me he believes there are none.
EAST COAST OF AFRICA.—Proceeding from the northern part, the coast
appears, for a considerable space, without reefs. My information, I may
here observe, is derived from the survey by Captain Owen, together with
his narrative; and that by Lieutenant Boteler. At _Mukdeesha_ (10° 1′
N.) there is a coral-reef extending four or five miles along the shore
(Owen’s “Narr.” volume i, page 357) which in the chart lies at the
distance of a quarter of a mile from the shore, and has within it from
six to ten feet water: this then is a fringing-reef, and is coloured
red. From _Juba_, a little S. of the equator, to _Lamoo_ (in 2° 20′ S.)
“the coast and islands are formed of madrepore” (Owen’s “Narrative,”
volume i., page 363). The chart of this part (entitled _Dundas
Islands_), presents an extraordinary appearance; the coast of the
mainland is quite straight and it is fronted at the average distance of
two miles, by exceedingly narrow, straight islets, fringed with reefs.
Within the chain of islets, there are extensive tidal flats and muddy
bays, into which many rivers enter; the depths of these spaces varies
from one to four fathoms—the latter depth not being common, and about
twelve feet the average. Outside the chain of islets, the sea, at the
distance of a mile, varies in depth from eight to fifteen fathoms.
Lieutenant Boteler (“Narr.” volume i., page 369) describes the muddy
bay of _Patta_, which seems to resemble other parts of this coast, as
fronted by small, narrow, level islets formed of decomposing coral, the
margin of which is seldom of greater height than twelve feet,
overhanging the rocky surface from which the islets rise. Knowing that
the islets are formed of coral, it is, I think, scarcely possible to
view the coast, and not at once conclude that we here see a
fringing-reef, which has been upraised a few feet: the unusual depth of
from two to four fathoms within some of these islets, is probably due
to muddy rivers having prevented the growth of coral near the shore.
There is, however, one difficulty on this view, namely, that before the
elevation took place, which converted the reef into a chain of islets,
the water must apparently have been still deeper; on the other hand it
may be supposed that the formation of a nearly perfect barrier in
front, of so large an extent of coast, would cause the currents
(especially in front of the rivers), to deepen their muddy beds. When
describing in the chapter on fringing-reefs, those of Mauritius, I have
given my reasons for believing that the shoal spaces within reefs of
this kind, must, in many instances, have been deepened. However this
may be, as several parts of this line of coast are undoubtedly fringed
by living reefs, I have coloured it red.— _Maleenda_ (3° 20′ S.). In
the plan of the harbour, the south headland appears fringed; and in
Owen’s chart on a larger scale, the reefs are seen to extend nearly
thirty miles southward; coloured red.—_Mombas_ (4° 5′ S.). The island
which forms the harbour, “is surrounded by cliffs of madrepore, capable
of being rendered almost impregnable” (Owen’s “Narr.” volume i., page
412). The shore of the mainland N. and S. of the harbour, is most
regularly fringed by a coral-reef at a distance from half a mile to one
mile and a quarter from the land; within the reef the depth is from
nine to fifteen feet; outside the reef the depth at rather less than
half a mile is thirty fathoms. From the charts it appears that a space
about thirty-six miles in length, is here fringed; coloured
red.—_Pemba_ (5° S.) is an island of coral-formation, level, and about
two hundred feet in height (Owen’s “Narr.” volume i., page 425); it is
thirty-five miles long, and is separated from the mainland by a deep
sea. The outer coast is represented in the chart as regularly fringed;
coloured red. The mainland in front of Pemba is likewise fringed; but
there also appear to be some outlying reefs with deep water between
them and the shore. I do not understand their structure, either from
the charts or the description, therefore have not coloured
them.—_Zanzibar_ resembles Pemba in most respects; its southern half on
the western side and the neighbouring islets are fringed; coloured red.
On the mainland, a little S. of Zanzibar, there are some banks parallel
to the coast, which I should have thought had been formed of coral, had
it not been said (Boteler’s “Narr.” volume ii., page 39) that they were
composed of sand; not coloured.—_Latham’s Bank_ is a small island,
fringed by coral-reefs; but being only ten feet high, it has not been
coloured.—_Monfeea_ is an island of the same character as Pemba; its
outer shore is fringed, and its southern extremity is connected with
Keelwa Point on the mainland by a chain of islands fringed by reefs;
coloured red. The four last-mentioned islands resemble in many respects
some of the islands in the Red Sea, which will presently be described.—
_Keelwa_. In a plan of the shore, a space of twenty miles N. and S. of
this place is fringed by reefs, apparently of coral: these reefs are
prolonged still further southward in Owen’s general chart. The coast in
the plans of the rivers _Lindy_ and _Monghow_ (9° 59′ and 10° 7′ S.)
has the same structure; coloured red.—_Querimba Islands_ (from 10° 40′
to 13° S.). A chart on a large scale is given of these islands; they
are low, and of coral-formation (Boteler’s “Narr.” volume ii., page
54); and generally have extensive reefs projecting from them which are
dry at low water, and which on the outside rise abruptly from a deep
sea: on their insides they are separated from the continent by a
channel, or rather a succession of bays, with an average depth of ten
fathoms. The small headlands on the continent also have coral-banks
attached to them; and the Querimba islands and banks are placed on the
lines of prolongation of these headlands, and are separated from them
by very shallow channels. It is evident that whatever cause, whether
the drifting of sediment or subterranean movements, produced the
headlands, likewise produced, as might have been expected, submarine
prolongations to them; and these towards their outer extremities, have
since afforded a favourable basis for the growth of coral-reefs, and
subsequently for the formation of islets. As these reefs clearly belong
to the fringing class, the Querimba islands have been coloured
red.—_Monabila_ (13° 32′ S.). In the plan of this harbour, the
headlands outside are fringed by reefs apparently of coral; coloured
red.—_Mozambique_ (150° S.) The outer part of the island on which the
city is built, and the neighbouring islands, are fringed by
coral-reefs; coloured red. From the description given in Owen’s “Narr.”
(volume i., page 162), the shore from _Mozambique_ to _Delagoa Bay_
appears to be low and sandy; many of the shoals and islets off this
line of coast are of coral-formation; but from their small size and
lowness, it is not possible, from the charts, to know whether they are
truly fringed. Hence this portion of coast is left uncoloured, as are
likewise those parts more northward, of which no mention has been made
in the foregoing pages from the want of information.
PERSIAN GULF.—From the charts lately published on a large scale by the
East India Company, it appears that several parts, especially the
southern shores of this gulf, are fringed by coral-reefs; but as the
water is very shallow, and as there are numerous sandbanks, which are
difficult to distinguish on the chart from reefs, I have not coloured
the upper part red. Towards the mouth, however, where the water is
rather deeper, the islands of _Ormuz_ and _Larrack_, appear so
regularly fringed, that I have coloured them red. There are certainly
no atolls in the Persian Gulf. The shores of _Immaum_, and of the
promontory forming the southern headland of the Persian Gulf, seem to
be without reefs. The whole S.W. part (except one or two small patches)
of _Arabia Felix_, and the shores of _Socotra_ appear from the charts
and memoir of Captain Haines (“Geographical Journal,” 1839, page 125)
to be without any reefs. I believe there are no extensive coral-reefs
on any part of the coasts of _India_, except on the low promontory of
_Madura_ (as already mentioned) in front of Ceylon.
RED SEA.—My information is chiefly derived from the admirable charts
published by the East India Company in 1836, from personal
communication with Captain Moresby, one of the surveyors, and from the
excellent memoir, “Über die Natur der Corallen-Bänken des Rothen
Meeres,” by Ehrenberg. The plains immediately bordering the Red Sea
seem chiefly to consist of a sedimentary formation of the newer
tertiary period. The shore is, with the exception of a few parts,
fringed by coral-reefs. The water is generally profoundly deep close to
the shore; but this fact, which has attracted the attention of most
voyagers, seems to have no necessary connection with the presence of
reefs; for Captain Moresby particularly observed to me, that, in
latitude 24° 10′ on the eastern side, there is a piece of coast, with
very deep water close to it, without any reefs, but not differing in
other respects from the usual nature of the coast-line. The most
remarkable feature in the Red Sea is the chain of submerged banks,
reefs, and islands, lying some way from the shore, chiefly on the
eastern side; the space within being deep enough to admit a safe
navigation in small vessels. The banks are generally of an oval form,
and some miles in width; but some of them are very long in proportion
to their width. Captain Moresby informs me that any one, who had not
made actual plans of them, would be apt to think that they were much
more elongated than they really are. Many of them rise to the surface,
but the greater number lie from five to thirty fathoms beneath it, with
irregular soundings on them. They consist of sand and living coral;
coral on most of them, according to Captain Moresby, covering the
greater part of their surface. They extend parallel to the shore, and
they are not unfrequently connected in their middle parts by short
transverse banks with the mainland. The sea is generally profoundly
deep quite close to them, as it is near most parts of the coast of the
mainland; but this is not universally the case, for between latitude
15° and 17° the water deepens quite gradually from the banks, both on
the eastern and western shores, towards the middle of the sea. Islands
in many parts arise from these banks; they are low, flat-topped, and
consist of the same horizontally stratified formation with that forming
the plain-like margin of the mainland. Some of the smaller and lower
islands consist of mere sand. Captain Moresby informs me, that small
masses of rock, the remnants of islands, are left on many banks where
there is now no dry land. Ehrenberg also asserts that most of the
islets, even the lowest, have a flat abraded basis, composed of the
same tertiary formation: he believes that as soon as the surf wears
down the protuberant parts of a bank, just beneath the level of the
sea, the surface becomes protected from further abrasion by the growth
of coral, and he thus accounts for the existence of so many banks
standing on a level with the surface of this sea. It appears that most
of the islands are certainly decreasing in size.
The form of the banks and islands is most singular in the part just
referred to, namely, from latitude 15° to 17°, where the sea deepens
quite gradually: the _Dhalac_ group, on the western coast, is
surrounded by an intricate archipelago of islets and shoals; the main
island is very irregularly shaped, and it includes a bay seven miles
long, by four across, in which no bottom was found with 252 feet: there
is only one entrance into this bay, half a mile wide, and with an
island in front of it. The submerged banks on the eastern coast, within
the same latitudes, round _Farsan_ Island, are, likewise, penetrated by
many narrow creeks of deep water; one is twelve miles long, in the form
of a hatchet, in which, close to its broad upper end, soundings were
not struck with 360 feet, and its entrance is only half a mile wide: in
another creek of the same nature, but even with a more irregular
outline, there was no bottom with 480 feet. The island of Farsan,
itself, has as singular a form as any of its surrounding banks. The
bottom of the sea round the Dhalac and Farsan Islands consists chiefly
of sand and agglutinated fragments, but, in the deep and narrow creeks,
it consists of mud; the islands themselves consist of thin,
horizontally stratified, modern tertiary beds, containing but little
broken coral;[2] their shores are fringed by living coral-reefs.
[2] Rüppell, “Reise in Abyssinie,” Band. i., S. 247.
From the account given by Rüppell[3] of the manner in which Dhalac has
been rent by fissures, the opposite sides of which have been unequally
elevated (in one instance to the amount of fifty feet), it seems
probable that its irregular form, as well as probably that of Farsan,
may have been partly caused by unequal elevations; but, considering the
general form of the banks, and of the deep-water creeks, together with
the composition of the land, I think their configuration is more
probably due in great part to strong currents having drifted sediment
over an uneven bottom: it is almost certain that their form cannot be
attributed to the growth of coral. Whatever may have been the precise
origin of the Dhalac and Farsan Archipelagoes, the greater number of
the banks on the eastern side of the Red Sea seem to have originated
through nearly similar means. I judge of this from their similarity in
configuration (in proof of which I may instance a bank on the east
coast in latitude 22°; and although it is true that the northern banks
generally have a less complicated outline), and from their similarity
in composition, as may be observed in their upraised portions. The
depth within the banks northward of latitude 17°, is usually greater,
and their outer sides shelve more abruptly (circumstances which seem to
go together) than in the Dhalac and Farsan Archipelagoes; but this
might easily have been caused by a difference in the action of the
currents during their formation: moreover, the greater quantity of
living coral, which, according to Captain Moresby, exists on the
northern banks, would tend to give them steeper margins.
[3] Rüppell, “Reise in Abyssinie,” Band. i., S. 245.
From this account, brief and imperfect as it is, we can see that the
great chain of banks on the eastern coast, and on the western side in
the southern portion, differ greatly from true barrier-reefs wholly
formed by the growth of coral. It is indeed the direct conclusion of
Ehrenberg (“Uber die,” etc., pages 45 and 51), that they are connected
in their origin quite secondarily with the growth of coral; and he
remarks that the islands off the coast of Norway, if worn down level
with the sea, and merely coated with living coral, would present a
nearly similar appearance. I cannot, however, avoid suspecting, from
information given me by Dr. Malcolmson and Captain Moresby, that
Ehrenberg has rather under-rated the influence of corals, in some
places at least, on the formation of the tertiary deposits of the Red
Sea.
_The West Coast of the Red Sea between lat._ 19° _and_ 22°.—There are,
in this space, reefs, which, if I had known nothing of those in other
parts of the Red Sea, I should unhesitatingly have considered as
barrier-reefs; and, after deliberation, I have come to the same
conclusion. One of these reefs, in 20° 15′, is twenty miles long, less
than a mile in width (but expanding at the northern end into a disc),
slightly sinuous, and extending parallel to the mainland at the
distance of five miles from it, with very deep water within; in one
spot soundings were not obtained with 205 fathoms. Some leagues further
south, there is another linear reef, very narrow, ten miles long, with
other small portions of reef, north and south, almost connected with
it; and within this line of reefs (as well as outside) the water is
profoundly deep. There are also some small linear and sickle-formed
reefs, lying a little way out at sea. All these reefs are covered, as I
am informed by Captain Moresby, by living corals. Here, then, we have
all the characters of reefs of the barrier class; and in some outlying
reefs we have an approach to the structure of atolls. The source of my
doubts about the classification of these reefs, arises from having
observed in the Dhalac and Farsan groups the narrowness and
straightness of several spits of sand and rock: one of these spits in
the Dhalac group is nearly fifteen miles long, only two broad, and it
is bordered on each side with deep water; so that, if worn down by the
surf, and coated with living corals, it would form a reef nearly
similar to those within the space under consideration. There is, also,
in this space (latitude 21°) a peninsula, bordered by cliffs, with its
extremity worn down to the level of the sea, and its basis fringed with
reefs: in the line of prolongation of this peninsula, there lies the
island of _Macowa_ (formed, according to Captain Moresby, of the usual
tertiary deposit), and some smaller islands, large parts of which
likewise appear to have been worn down, and are now coated with living
corals. If the removal of the strata in these several cases had been
more complete, the reefs thus formed would have nearly resembled those
barrier-like ones now under discussion. Notwithstanding these facts, I
cannot persuade myself that the many very small, isolated, and
sickle-formed reefs and others, long, nearly straight, and very narrow,
with the water unfathomably deep close round them, could possibly have
been formed by corals merely coating banks of sediment, or the abraded
surfaces of irregularly shaped islands. I feel compelled to believe
that the foundations of these reefs have subsided, and that the corals,
during their upward growth, have given to these reefs their present
forms: I may remark that the subsidence of narrow and
irregularly-shaped peninsulas and islands, such as those existing on
the coasts of the Red Sea, would afford the requisite foundations for
the reefs in question.
_The West Coast from lat._ 22° _to_ 24°.—This part of the coast (north
of the space coloured blue on the map) is fronted by an irregularly
shelving bank, from about ten to thirty fathoms deep; numerous little
reefs, some of which have the most singular shapes, rise from this
bank. It may be observed, respecting one of them, in latitude 23° 10′,
that if the promontory in latitude 24° were worn down to the level of
the sea, and coated with corals, a very similar and grotesquely formed
reef would be produced. Many of the reefs on this part of the coast may
thus have originated; but there are some sickle, and almost
atoll-formed reefs lying in deep water off the promontory in latitude
24°, which lead me to suppose that all these reefs are more probably
allied to the barrier or atoll classes. I have not, however, ventured
to colour this portion of coast.—_On the west coast from lat._ 19° _to_
17° (south of space coloured blue on the map), there are many low
islets of very small dimensions, not much elongated, and rising out of
great depths at a distance from the coast; these cannot be classed
either with atolls, or barrier- or fringing-reefs. I may here remark
that the outlying reefs on the west coast, between latitude 19° and
24°, are the only ones in the Red Sea, which approach in structure to
the true atolls of the Indian and Pacific Oceans, but they present only
imperfect miniature likenesses of them.
_Eastern Coast_.—I have felt the greatest doubt about colouring any
portion of this coast, north of the fringing-reefs round the Farsan
Islands in 16° 10′. There are many small outlying coral-reefs along the
whole line of coast; but as the greater number rise from banks not very
deeply submerged (the formation of which has been shown to be only
secondarily connected with the growth of coral), their origin may be
due simply to the growth of knolls of corals, from an irregular
foundation situated within a limited depth. But between latitude 18°
and 20°, there are so many linear, elliptic, and extremely small reefs,
rising abruptly out of profound depths, that the same reasons, which
led me to colour blue a portion of the west coast, have induced me to
do the same in this part. There exist some small outlying reefs rising
from deep water, north of latitude 20° (the northern limit coloured
blue), on the east coast; but as they are not very numerous and
scarcely any of them linear, I have thought it right to leave them
uncoloured.
In the _southern parts_ of the Red Sea, considerable spaces of the
mainland, and of some of the Dhalac islands, are skirted by reefs,
which, as I am informed by Captain Moresby, are of living coral, and
have all the characters of the fringing class. As in these latitudes,
there are no outlying linear or sickle-formed reefs, rising out of
unfathomable depths, I have coloured these parts of the coast red. On
similar grounds, I have coloured red the _northern parts of the western
coast_ (north of latitude 24° 30′), and likewise the shores of the
chief part of the _Gulf of Suez_. In the _Gulf of Acaba_, as I am
informed by Captain Moresby there are no coral-reefs, and the water is
profoundly deep.
WEST INDIES.—My information regarding the reefs of this area, is
derived from various sources, and from an examination of numerous
charts; especially of those lately executed during the survey under
Captain Owen, R.N. I lay under particular obligation to Captain Bird
Allen, R.N., one of the members of the late survey, for many personal
communications on this subject. As in the case of the Red Sea, it is
necessary to make some preliminary remarks on the submerged banks of
the West Indies, which are in some degree connected with coral-reefs,
and cause considerable doubts in their classification. That large
accumulations of sediment are in progress on the West Indian shores,
will be evident to any one who examines the charts of that sea,
especially of the portion north of a line joining Yucutan and Florida.
The area of deposition seems less intimately connected with the
debouchement of the great rivers, than with the course of the
sea-currents; as is evident from the vast extension of the banks from
the promontories of Yucutan and Mosquito.
Besides the coast-banks, there are many of various dimensions which
stand quite isolated; these closely resemble each other, they lie from
two or three to twenty or thirty fathoms under water, and are composed
of sand, sometimes firmly agglutinated, with little or no coral; their
surfaces are smooth and nearly level, shelving only to the amount of a
few fathoms, very gradually all round towards their edges, where they
plunge abruptly into the unfathomable sea. This steep inclination of
their sides, which is likewise characteristic of the coast-banks, is
very remarkable: I may give as an instance, the Misteriosa Bank, on the
edges of which the soundings change in 250 fathoms horizontal distance,
from 11 to 210 fathoms; off the northern point of the bank of Old
Providence, in 200 fathoms horizontal distance, the change is from 19
to 152 fathoms; off the Great Bahama Bank, in 160 fathoms horizontal
distance, the inclination is in many places from 10 fathoms to no
bottom with 190 fathoms. On coasts in all parts of the world, where
sediment is accumulating, something of this kind may be observed; the
banks shelve very gently far out to sea, and then terminate abruptly.
The form and composition of the banks standing in the middle parts of
the W. Indian Sea, clearly show that their origin must be chiefly
attributed to the accumulation of sediment; and the only obvious
explanation of their isolated position is the presence of a nucleus,
round which the currents have collected fine drift matter. Any one who
will compare the character of the bank surrounding the hilly island of
Old Providence, with those banks in its neighbourhood which stand
isolated, will scarcely doubt that they surround submerged mountains.
We are led to the same conclusion by examining the bank called Thunder
Knoll, which is separated from the Great Mosquito Bank by a channel
only seven miles wide, and 145 fathoms deep. There cannot be any doubt
that the Mosquito Bank has been formed by the accumulation of sediment
round the promontory of the same name; and Thunder Knoll resembles the
Mosquito Bank, in the state of its surface submerged twenty fathoms, in
the inclinations of its sides, in composition, and in every other
respect. I may observe, although the remark is here irrelevant, that
geologists should be cautious in concluding that all the outlyers of
any formation have once been connected together, for we here see that
deposits, doubtless of exactly the same nature, may be deposited with
large valley-like spaces between them.
Linear strips of coral-reefs and small knolls project from many of the
isolated, as well as coast-banks; sometimes they occur quite
irregularly placed, as on the Mosquito Bank, but more generally they
form crescents on the windward side, situated some little distance
within the outer edge of the banks:—thus on the Serranilla Bank they
form an interrupted chain which ranges between two and three miles
within the windward margin: generally they occur, as on Roncador,
Courtown, and Anegada Banks, nearer the line of deep water. Their
occurrence on the windward side is conformable to the general rule, of
the efficient kinds of corals flourishing best where most exposed; but
their position some way within the line of deep water I cannot explain,
without it be, that a depth somewhat less than that close to the outer
margin of the banks, is most favourable to their growth. Where the
corals have formed a nearly continuous rim, close to the windward edge
of a bank some fathoms submerged, the reef closely resembles an atoll;
but if the bank surrounds an island (as in the case of Old Providence),
the reef resembles an encircling barrier-reef. I should undoubtedly
have classed some of these fringed banks as imperfect atolls, or
barrier-reefs, if the sedimentary nature of their foundations had not
been evident from the presence of other neighbouring banks, of similar
forms and of similar composition, but without the crescent-like
marginal reef: in the third chapter, I observed that probably some
atoll-like reefs did exist, which had originated in the manner here
supposed.
Proofs of elevation within recent tertiary periods abound, as referred
to in the sixth chapter, over nearly the whole area of the West Indies.
Hence it is easy to understand the origin of the low land on the
coasts, where sediment is now accumulating; for instance on the
northern part of Yucutan, and on the N.E. part of Mosquito, where the
land is low, and where extensive banks appear to be in progressive
formation. Hence, also, the origin of the Great Bahama Banks, which are
bordered on their western and southern edges by very narrow, long,
singularly shaped islands, formed of sand, shells, and coral-rock, and
some of them about a hundred feet in height, is easily explained by the
elevation of banks fringed on their windward (western and southern)
sides by coral-reefs. On this view, however, we must suppose either
that the chief part of the surfaces of the great Bahama sandbanks were
all originally deeply submerged, and were brought up to their present
level by the same elevatory action, which formed the linear islands; or
that during the elevation of the banks, the superficial currents and
swell of the waves continued wearing them down and keeping them at a
nearly uniform level: the level is not quite uniform; for, in
proceeding from the N.W. end of the Bahama group towards the S.E. end,
the depth of the banks increases, and the area of land decreases, in a
very gradual and remarkable manner. The latter view, namely, that these
banks have been worn down by the currents and swell during their
elevation, seems to me the most probable one. It is, also, I believe,
applicable to many banks, situated in widely distant parts of the West
Indian Sea, which are wholly submerged; for, on any other view, we must
suppose, that the elevatory forces have acted with astonishing
uniformity.
The shore of the Gulf of Mexico, for the space of many hundred miles,
is formed by a chain of lagoons, from one to twenty miles in breadth
(“Columbian Navigator,” page 178, etc.), containing either fresh or
salt water, and separated from the sea by linear strips of sand. Great
spaces of the shores of Southern Brazil.[4] and of the United States
from Long Island (as observed by Professor Rogers) to Florida have the
same character. Professor Rogers, in his “Report to the British
Association” (volume iii., page 13), speculates on the origin of these
low, sandy, linear islets; he states that the layers of which they are
composed are too homogeneous, and contain too large a proportion of
shells, to permit the common supposition of their formation being
simply due to matter thrown up, where it now lies, by the surf: he
considers these islands as upheaved bars or shoals, which were
deposited in lines where opposed currents met. It is evident that these
islands and spits of sand parallel to the coast, and separated from it
by shallow lagoons, have no necessary connection with coral-formations.
But in Southern Florida, from the accounts I have received from persons
who have resided there, the upraised islands seem to be formed of
strata, containing a good deal of coral, and they are extensively
fringed by living reefs; the channels within these islands are in some
places between two and three miles wide, and five or six fathoms deep,
though generally[5] they are less in depth than width. After having
seen how frequently banks of sediment in the West Indian Sea are
fringed by reefs, we can readily conceive that bars of sediment might
be greatly aided in their formation along a line of coast, by the
growth of corals; and such bars would, in that case, have a deceptive
resemblance with true barrier-reefs.
[4] In the “London and Edinburgh Philosophical Journal,” 1841, page
257, I have described a singular bar of sandstone lying parallel to
the coast off Pernambuco in Brazil, which probably is an analogous
formation.
[5] In the ordinary sea-charts, no lagoons appear on the coast of
Florida, north of 26°; but Major Whiting (“Silliman’s Journal,” volume
xxxv., page 54) says that many are formed by sand thrown up along the
whole line of coast from St. Augustine’s to Jupiter Inlet.
Having now endeavoured to remove some sources of doubt in classifying
the reefs of the West Indies, I will give my authorities for colouring
such portions of the coast as I have thought myself warranted in doing.
Captain Bird Allen informs me, that most of the islands on the _Bahama
Banks_ are fringed, especially on their windward sides, with living
reefs; and hence I have coloured those, which are thus represented in
Captain Owen’s late chart, red. The same officer informs me, that the
islands along the southern part of _Florida_ are similarly fringed;
coloured red. CUBA: Proceeding along the northern coast, at the
distance of forty miles from the extreme S.E. point, the shores are
fringed by reefs, which extend westward for a space of 160 miles, with
only a few breaks. Parts of these reefs are represented in the plans of
the harbours on this coast by Captain Owen; and an excellent
description is given of them by Mr. Taylor (Loudon’s “Mag. of Nat.
Hist.” volume ix., page 449); he states that they enclosed a space
called the “_baxo_,” from half to three-quarters of a mile in width,
with a sandy bottom, and a little coral. In most parts people can wade,
at low water, to the reef; but in some parts the depth is between two
and three fathoms. Close outside the reef, the depth is between six and
seven fathoms; these well-characterised fringing-reefs are coloured
red. Westward of longitude 77° 30′, on the northern side of Cuba, a
great bank commences, which extends along the coast for nearly four
degrees of longitude. In the place of its commencement, in its
structure, and in the “_cays_,” or low islands on its edge, there is a
marked correspondence (as observed by Humboldt, “Pers. Narr.” volume
vii., page 88) between it and the Great Bahama and Sal Banks, which lie
directly in front. Hence one is led to attribute the same origin to
both these sets of banks; namely, the accumulation of sediment,
conjoined with an elevatory movement, and the growth of coral on their
outward edges; those parts which appear fringed by living reefs are
coloured red. Westward of these banks, there is a portion of coast
apparently without reefs, except in the harbours, the shores of which
seem in the published plans to be fringed. The _Colorado Shoals_ (see
Captain Owen’s charts), and the low land at the western end of Cuba,
correspond as closely in relative position and structure to the banks
at the extreme point of Florida, as the banks above described on the
north side of Cuba, do to the Bahamas, the depth within the islets and
reefs on the outer edge of the _Colorados_, is generally between two
and three fathoms, increasing to twelve fathoms in the southern part,
where the bank becomes nearly open, without islets or coral-reefs; the
portions which are fringed are coloured red. The southern shore of Cuba
is deeply concave, and the included space is filled up with mud and
sandbanks, low islands and coral-reefs. Between the mountainous _Isle
of Pines_ and the southern shore of Cuba, the general depth is only
between two and three fathoms; and in this part small islands, formed
of fragmentary rock and broken madrepores (Humboldt, “Pers. Narr.”
volume vii. pages 51, 86 to 90, 291, 309, 320), rise abruptly, and just
reach the surface of the sea. From some expressions used in the
“Columbian Navigator” (volume i., part ii., page 94), it appears that
considerable spaces along the outer coast of Southern Cuba are bounded
by cliffs of coral-rock, formed probably by the upheaval of coral-reefs
and sandbanks. The charts represent the southern part of the Isle of
Pines as fringed by reefs, which the “Columb. Navig.” says extend some
way from the coast, but have only from nine to twelve feet water on
them; these are coloured red.—I have not been able to procure any
detailed description of the large groups of banks and “cays” further
eastward on the southern side of Cuba; within them there is a large
expanse, with a muddy bottom, from eight to twelve fathoms deep;
although some parts of this line of coast are represented in the
general charts of the West Indies, as fringed, I have not thought it
prudent to colour them. The remaining portion of the south coast of
Cuba appears to be without coral-reefs.
YUCUTAN.—The N.E. part of the promontory appears in Captain Owen’s
charts to be fringed; coloured red. The eastern coast, from 20° to 18°
is fringed. South of latitude 18°, there commences the most remarkable
reef in the West Indies: it is about one hundred and thirty miles in
length, ranging in a N. and S. line, at an average distance of fifteen
miles from the coast. The islets on it are all low, as I have been
informed by Captain B. Allen; the water deepens suddenly on the outside
of the reef, but not more abruptly than off many of the sedimentary
banks: within its southern extremity (off _Honduras_) the depth is
twenty-five fathoms; but in the more northern parts, the depth soon
increases to ten fathoms, and within the northernmost part, for a space
of twenty miles, the depth is only from one to two fathoms. In most of
these respects we have the characteristics of a barrier-reef;
nevertheless, from observing, first, that the channel within the reef
is a continuation of a great irregular bay, which penetrates the
mainland to the depth of fifty miles; and secondly, that considerable
spaces of this barrier-like reef are described in the charts (for
instance, in latitude 16° 45′ and 16° 12′) as formed of pure sand; and
thirdly, from knowing that sediment is accumulating in many parts of
the West Indies in banks parallel to the shore; I have not ventured to
colour this reef as a barrier, without further evidence that it has
really been formed by the growth of corals, and that it is not merely
in parts a spit of sand, and in other parts a worn down promontory,
partially coated and fringed by reefs; I lean, however, to the
probability of its being a barrier-reef, produced by subsidence. To add
to my doubts, immediately on the outside of this barrier-like reef,
_Turneffe_, _Lighthouse_, and _Glover_ reefs are situated, and these
reefs have so completely the form of atolls, that if they had occurred
in the Pacific, I should not have hesitated about colouring them blue.
_turneffe Reef_ seems almost entirely filled up with low mud islets;
and the depth within the other two reefs is only from one to three
fathoms. From this circumstance and from their similarity in form,
structure, and relative position, both to the bank called _Northern
Triangles_, on which there is an islet between seventy and eighty feet,
and to _Cozumel_ Island, the level surface of which is likewise between
seventy and eighty feet in height, I consider it more probable that the
three foregoing banks are the worn down bases of upheaved shoals,
fringed with corals, than that they are true atolls, wholly produced by
the growth of coral during subsidence; left uncoloured.
In front of the eastern _Mosquito_ coast, there are between latitude
12° and 16° some extensive banks (already mentioned, page 148), with
high islands rising from their centres; and there are other banks
wholly submerged, both of which kinds of banks are bordered, near their
windward margins, by crescent-shaped coral-reefs. But it can hardly be
doubted, as was observed in the preliminary remarks, that these banks
owe their origin, like the great bank extending from the Mosquito
promontory, almost entirely to the accumulation of sediment, and not to
the growth of corals; hence I have not coloured them.
_Cayman Island_: this island appears in the charts to be fringed; and
Captain B. Allen informs me that the reefs extend about a mile from the
shore, and have only from five to twelve feet water within them;
coloured red.—_Jamaica_: judging from the charts, about fifteen miles
of the S.E. extremity, and about twice that length on the S.W.
extremity, and some portions on the S. side near Kingston and Port
Royal, are regularly fringed, and therefore are coloured red. From the
plans of some harbours on the N. side of Jamaica, parts of the coast
appear to be fringed; but as these are not represented in the charts of
the whole island, I have not coloured them.—_St. Domingo_: I have not
been able to obtain sufficient information, either from plans of the
harbours, or from general charts, to enable me to colour any part of
the coast, except sixty miles from Port de Plata westward, which seems
very regularly fringed; many other parts, however, of the coast are
probably fringed, especially towards the eastern end of the
island.—_Puerto Rico_: considerable portions of the southern, western,
and eastern coasts, and some parts of the northern coast, appear in the
charts to be fringed; coloured red.—Some miles in length of the
southern side of the Island of _St, Thomas_ is fringed; most of the
_Virgin Gorda_ Islands, as I am informed by Mr. Schomburgk, are
fringed; the shores of _Anegada_, as well as the bank on which it
stands, are likewise fringed; these islands have been coloured red. The
greater part of the southern side of _Santa Cruz_ appears in the Danish
survey to be fringed (see also Prof. Hovey’s account of this island, in
“Silliman’s Journal,” volume xxxv., page 74); the reefs extend along
the shore for a considerable space, and project rather more than a
mile; the depth within the reef is three fathoms; coloured red.—The
_Antilles_, as remarked by Von Buch (“Descrip. Iles Canaries,” page
494), may be divided into two linear groups, the western row being
volcanic, and the eastern of modern calcareous origin; my information
is very defective on the whole group. Of the eastern islands, _Barbuda_
and the western coasts of _Antigua_ and _Mariagalante_ appear to be
fringed: this is also the case with _Barbadoes_, as I have been
informed by a resident; these islands are coloured red. On the shores
of the Western Antilles, of volcanic origin, very few coral-reefs
appear to exist. The island of _Martinique_, of which there are
beautifully executed French charts, on a very large scale, alone
presents any appearance worthy of special notice. The south-western,
southern, and eastern coasts, together forming about half the
circumference of the island, are skirted by very irregular banks,
projecting generally rather less than a mile from the shore, and lying
from two to five fathoms submerged. In front of almost every valley,
they are breached by narrow, crooked, steep-sided passages. The French
engineers ascertained by boring, that these submerged banks consisted
of madreporitic rocks, which were covered in many parts by thin layers
of mud or sand. From this fact, and especially from the structure of
the narrow breaches, I think there can be little doubt that these banks
once formed living reefs, which fringed the shores of the island, and
like other reefs probably reached the surface. From some of these
submerged banks reefs of living coral rise abruptly, either in small
detached patches, or in lines parallel to, but some way within the
outer edges of the banks on which they are based. Besides the above
banks which skirt the shores of the island, there is on the eastern
side a range of linear banks, similarly constituted, twenty miles in
length, extending parallel to the coast line, and separated from it by
a space between two and four miles in width, and from five to fifteen
fathoms in depth. From this range of detached banks, some linear reefs
of living coral likewise rise abruptly; and if they had been of greater
length (for they do not front more than a sixth part of the
circumference of the island), they would necessarily from their
position have been coloured as barrier-reefs; as the case stands they
are left uncoloured. I suspect that after a small amount of subsidence,
the corals were killed by sand and mud being deposited on them, and the
reefs being thus prevented from growing upwards, the banks of
madreporitic rock were left in their present submerged condition.
THE BERMUDA ISLANDS have been carefully described by Lieutenant Nelson,
in an excellent Memoir in the “Geological Transactions” (volume v.,
part i., page 103). In the form of the bank or reef, on one side of
which the islands stand, there is a close general resemblance to an
atoll; but in the following respects there is a considerable
difference,—first, in the margin of the reef not forming (as I have
been informed by Mr. Chaffers, R.N.) a flat, solid surface, laid bare
at low water, and regularly bounding the internal space of shallow
water or lagoon; secondly, in the border of gradually shoaling water,
nearly a mile and a half in width, which surrounds the entire outside
of the reef (as is laid down in Captain Hurd’s chart); and thirdly, in
the size, height, and extraordinary form of the islands, which present
little resemblance to the long, narrow, simple islets, seldom exceeding
half a mile in breadth, which surmount the annular reefs of almost all
the atolls in the Indian and Pacific Oceans. Moreover, there are
evident proofs (Nelson, Ibid., page 118), that islands similar to the
existing ones, formerly extended over other parts of the reef. It
would, I believe, be difficult to find a true atoll with land exceeding
thirty feet in height; whereas, Mr. Nelson estimates the highest point
of the Bermuda Islands to be 260 feet; if, however, Mr. Nelson’s view,
that the whole of the land consists of sand drifted by the winds, and
agglutinated together, were proved correct, this difference would be
immaterial; but, from his own account (page 118), there occur in one
place, five or six layers of red earth, interstratified with the
ordinary calcareous rock, and including stones too heavy for the wind
to have moved, without having at the same time utterly dispersed every
grain of the accompanying drifted matter. Mr. Nelson attributes the
origin of these several layers, with their embedded stones, to as many
violent catastrophes; but further investigation in such cases has
generally succeeded in explaining phenomena of this kind by ordinary
and simpler means. Finally, I may remark, that these islands have a
considerable resemblance in shape to Barbuda in the West Indies, and to
Pemba on the eastern coast of Africa, which latter island is about two
hundred feet in height, and consists of coral-rock. I believe that the
Bermuda Islands, from being fringed by living reefs, ought to have been
coloured red; but I have left them uncoloured, on account of their
general resemblance in external form to a lagoon-island or atoll.
INDEX.
The names not in capitals are all names of places, and refer
exclusively to the Appendix: in well-defined archipelagoes, or groups
of islands, the name of each separate island is not given.
ABROLHOS, Brazil, coated by corals.
Abrolhos (Australia).
ABSENCE of coral-reefs from certain coasts.
Acaba, gulf of.
Admiralty group.
AFRICA, east coast, fringing-reef of.
Madreporitic rock of.
Africa, east coast.
AGE of individual corals.
Aiou.
Aitutaki.
Aldabra.
Alert reef.
Alexander, Grand Duke, island.
ALLAN, Dr., on Holuthuriæ feeding on corals. On quick growth of corals
at Madagascar. On reefs affected by currents.
Alloufatou.
Alphonse.
Amargoura. (Amargura.)
Amboina.
America, west coast.
Amirantes.
Anachorites.
Anambas.
ANAMOUKA, description of.
Anamouka.
Anadaman islands.
Antilles.
Appoo reef.
Arabia Felix.
AREAS, great extent of, interspersed with low islands. Of subsidence
and of elevation. Of subsidence appear to be elongated. Of subsidence
alternating with areas of elevation.
Arru group.
Arzobispo.
ASCIDIA, depth at which found.
Assomption.
Astova.
Atlantic islands.
ATOLLS, breaches in their reefs. Dimensions of. Dimensions of groups
of. Not based on craters or on banks of sediment, or of rock. Of
irregular forms. Steepness of their flanks. Width of their reef and
islets. Their lowness. Lagoons. General range. With part of their reef
submerged, and theory of.
Augustine, St.
AURORA island, an upraised atoll.
Aurora.
AUSTRAL islands, recently elevated.
Austral islands.
Australia, N.W. coast.
AUSTRALIAN barrier-reef.
Australian barrier.
Babuyan group.
Bahama banks.
Balahac.
Bally.
Baring.
BARRIER-REEF of Australia. Of New Caledonia.
BARRIER-REEFS, breaches through. Not based on worn down margin of rock.
On banks of sediment. On submarine craters. Steepness of their flanks.
Their probable vertical thickness. Theory of their formation.
Bampton shoal.
Banks islands.
Banks in the West Indies.
Bashee islands.
Bass island.
Batoa.
Beaupre reef.
BEECHEY, Captain, obligations of the author to. On submerged reefs.
Account of Matilda island.
BELCHER, Captain, on boring through coral-reef.
Belize reef, off.
Bellinghausen.
Bermuda islands.
Beveridge reef.
Bligh.
BOLABOLA, view of.
Bombay shoal.
Bonin Bay.
Bonin group.
BORINGS through coral-reefs.
BORNEO, W. coast, recently elevated.
Borneo, E. coast. S.W. and W. coast N. coast. Western bank.
Boscawen.
Boston.
Bouka.
Bourbon.
Bourou.
Bouton.
BRAZIL, fringing-reefs on coast of.
BREACHES through barrier-reefs.
Brook.
Bunker.
Bunoa.
BYRON.
Cagayanes.
Candelaria.
Cargados Carajos.
Caroline archipelago.
Caroline island.
Carteret shoal.
CARYOPHYLLIA, depth at which it lives.
Cavilli.
Cayman island.
Celebes.
Ceram.
CEYLON, recently elevated.
Ceylon.
CHAGOS Great Bank, description and theory of.
CHAGOS group.
Chagos group.
CHAMA-SHELLS embedded in coral-rock.
CHAMISSO, on corals preferring the surf.
CHANGES in the state of Keeling atoll. Of atolls.
CHANNELS leading into the lagoons of atolls. Into the Maldiva atolls.
Through barrier-reefs.
Chase.
China sea.
CHRISTMAS atoll.
Christmas atoll.
Christmas island (Indian Ocean).
Clarence.
Clipperton rock.
COCOS, or Keeling atoll.
Cocos (or Keeling).
Cocos island (Pacific).
COCHIN China, encroachments of the sea on the coast.
Cochin China.
Coetivi.
Comoro group.
COMPOSITION of coral-formations.
CONGLOMERATE coral-rock on Keeling atoll. On other atolls. Coral-rock.
COOK islands, recently elevated.
Cook islands.
CORAL-BLOCKS bored by vermiform animals.
CORAL-REEFS, their distribution and absence from certain areas.
Destroyed by loose sediment.
CORAL-ROCK at Keeling atoll. Mauritius. Organic remains of.
CORALS dead but upright in Keeling lagoon. Depths at which they live.
Off Keeling atoll. Killed by a short exposure. Living in the lagoon of
Keeling atoll. Quick growth of, in Keeling lagoon. Merely coating the
bottom of the sea. Standing exposed in the Low archipelago.
CORALLIAN sea.
Corallian sea.
Cornwallis.
Cosmoledo.
COUTHOUY, Mr., alleged proofs of recent elevation of the Low
archipelago. On coral-rock at Mangaia and Aurora islands. On external
ledges round coral-islands. Remarks confirmatory of the author’s
theory.
CRESCENT-FORMED reefs.
Cuba.
CUMING, Mr., on the recent elevation of the Philippines.
Dangerous, or Low archipelago.
Danger islands.
DEPTHS at which reef-building corals live. At Mauritius, the Red Sea,
and in the Maldiva archipelago. At which other corals and corallines
can live.
Dhalac group.
DIEGO GARCIA, slow growth of reef.
DIMENSIONS of the larger groups of atolls.
DISSEVERMENT of the Maldiva atolls, and theory of.
DISTRIBUTION of coral-reefs.
Domingo, St.
DORY, Port, recently elevated.
Dory, Port.
Duff islands.
Durour.
Eap.
EARTHQUAKES at Keeling atoll. In groups of atolls. In Navigator
archipelago.
EAST INDIAN ARCHIPELAGO, recently elevated.
Easter.
Echequier.
EHRENBERG, on the banks of the Red Sea. On depths at which corals live
in the Red Sea. On corals preferring the surf. On the antiquity of
certain corals.
Eimeo.
ELEVATED reef of Mauritius.
ELEVATIONS, recent proofs of. Immense areas of.
Elivi.
ELIZABETH island. Recently elevated.
Elizabeth island.
Ellice group.
ENCIRCLED ISLANDS, their height. Geological composition.
EOUA, description of.
Eoua.
ERUPTED MATTER probably not associated with thick masses of coral-rock.
FAIS, recently elevated.
Fais.
Fanning.
Farallon de Medinilla.
Farson group.
Fataka.
FIJI archipelago.
FISH, feeding on corals. Killed in Keeling lagoon by heavy rain.
FISSURES across coral-islands.
FITZROY, Captain, on a submerged shed at Keeling atoll. On an
inundation in the Low archipelago.
Flint.
Flores.
Florida.
Folger.
Formosa.
FORSTER, theory of coral-formations.
Frederick reef.
Freewill.
FRIENDLY group recently elevated.
Friendly archipelago.
FRINGING-REEFS, absent where coast precipitous. Breached in front of
streams. Described by MM. Quoy and Gaimard. Not closely attached to
shelving coasts. Of east coast of Africa. Of Cuba. Of Mauritius. On
worn down banks of rock. On banks of sediment. Their appearance when
elevated. Their growth influenced by currents. By shallowness of sea.
Galapagos archipelago.
Galega.
GAMBIER islands, section of.
Gambier islands.
Gardner.
Gaspar rico.
GEOLOGICAL COMPOSITION of coral-formations.
Gilbert archipelago.
Gilolo.
Glorioso.
GLOUCESTER Island.
Glover reef.
Gomez.
Gouap.
Goulou.
Grampus.
Gran Cocal.
GREAT CHAGOS BANK, description and theory of.
GREY, Captain, on sandbars.
GROUPING of the different classes of reefs.
Guedes.
HALL, Captain B., on Loo Choo.
HARVEY islands, recently elevated.
HEIGHT of encircled islands.
Hermites.
Hervey or Cook islands.
Hogoleu.
HOLOTHURIAE (Holuthuriæ) feeding on coral.
HOUDEN island, height of.
Honduras, reef off.
Horn.
Houtman Abrolhos.
HUAHEINE; alleged proofs of its recent elevation.
Huaheine.
Humphrey.
Hunter.
HURRICANES, effects of, on coral-islands.
Immaum.
Independence.
INDIA, west coast, recently elevated.
India.
IRREGULAR REEFS in shallow seas.
ISLETS of coral-rock, their formation. Their destruction in the Maldiva
atolls.
Jamaica.
Jarvis.
JAVA, recently elevated.
Java.
Johnston island.
Juan de Nova.
Juan de Nova (Madagascar).
Kalatoa.
KAMTSCHATKA, proofs of its recent elevation.
Karkalang.
KEELING atoll, section of reef.
Keeling, south atoll. North atoll.
Keffing.
Kemin.
Kennedy.
Keppel.
Kumi.
Laccadive group.
LADRONES, or Marianas, recently elevated.
Ladrones archipelago.
LAGOON of Keeling atoll.
LAGOONS bordered by inclined ledges and walls, and theory of their
formation. Of small atolls filled up with sediment.
LAGOON-CHANNELS within barrier-reefs.
LAGOON-REEFS, all submerged in some atolls, and rising to the surface
in others.
Lancaster reef.
Latte.
Lauglan islands.
LEDGES round certain lagoons.
Lette.
Lighthouse reef.
LLOYD, Mr., on corals refixing themselves.
LOO CHOO, recently elevated.
Loo Choo.
Louisiade.
LOW ARCHIPELAGO, alleged proofs of its recent elevation.
Low archipelago.
LOWNESS of coral-islands.
Loyalty group.
Lucepara.
LUTKE, Admiral, on fissures across coral-islands.
LUZON, recently elevated.
Luzon.
LYELL, Mr., on channels into the lagoons of atolls. On the lowness of
their leeward sides. On the antiquity of certain corals. On the
apparent continuity of distinct coral-islands. On the recently elevated
beds of the Red Sea. On the outline of the areas of subsidence.
Macassar strait.
Macclesfield bank.
MADAGASCAR, quick growth of corals at. Madreporitic rock of.
Madagascar.
Madjiko-sima.
Madura (Java).
Madura (India).
MAHLOS MAHDOO, theory of formation.
MALACCA, recently elevated.
Malacca.
MALCOLMSON, Dr., on recent elevation of W. coast of India. On recent
elevation of Camaran island.
Malden.
MALDIVA atolls, and theory of their formation. Steepness of their
flanks. Growth of coral at.
Maldiva archipelago.
MANGAIA island. Recently elevated.
Mangaia.
Mangs.
MARIANAS, recently elevated.
Mariana archipelago.
Mariere.
Marquesas archipelago.
Marshall archipelago.
Marshall island.
Martinique.
Martires.
MARY’S ST., in Madagascar, harbour made in reefs.
Mary island.
Matia, or Aurora.
MATILDA atoll.
MAURITIUS, fringing-reefs of. Depths at which corals live there.
Recently elevated.
Mauritius.
MAURUA, section of.
Maurua.
MENCHIKOFF atoll.
Mendana archipelago.
Mendana isles.
Mexico, gulf of.
MILLEPORA COMPLANATA at Keeling atoll.
Mindoro.
Mohilla. (Mohila.)
MOLUCCA islands, recently elevated.
Mopeha.
MORESBY, Captain, on boring through coral-reefs.
Morty.
Mosquito coast.
MUSQUILLO atoll.
Mysol.
NAMOURREK group.
Natunas.
NAVIGATOR archipelago, elevation of.
Navigator archipelago.
Nederlandisch.
NELSON, Lieutenant, on the consolidation of coral-rocks under water.
Theory of coral-formations. On the Bermuda islands.
New Britain.
NEW CALEDONIA, steepness of its reefs. Barrier-reef of.
New Caledonia.
New Guinea (E. end).
New Guinea (W. end).
New Hanover.
NEW HEBRIDES, recently elevated.
New Hebrides.
NEW IRELAND, recently elevated.
New Ireland.
New Nantucket.
Nicobar islands.
Niouha.
NULLIPORAE at Keeling atoll. On the reefs of atolls. On barrier-reefs.
Their wide distribution and abundance.
OBJECTIONS to the theory of subsidence.
Ocean islands.
Ono.
Onouafu. (Onouafou.)
Ormuz.
Oscar group.
OSCILLATIONS of level.
Ouallan, or Ualan. (Oualan.)
OULUTHY atoll.
Outong Java.
Palawan, S.W. coast. N.W. coast. Western bank.
Palmerston.
Palmyra.
Paracells.
Paraquas.
Patchow.
Pelew islands.
PEMBA island, singular form of.
Pemba.
Penrhyn.
Peregrino.
PERNAMBUCO, bar of sandstone at.
PERSIAN gulf, recently elevated.
Persian gulf.
PESCADO.
Pescadores.
Peyster group.
Philip.
PHILIPPINE archipelago, recently elevated.
Philippine archipelago.
Phœnix.
Piguiram.
Pitcairn.
PITT’S bank.
Pitt island.
Platte.
Pleasant.
PORITES, chief coral on margin of Keeling atoll.
Postillions.
POUYNIPETE. Its probable subsidence.
Pouynipète.
Pratas shoal.
Proby.
Providence.
Puerto Rico.
Pulo Anna.
PUMICE floated to coral-islands.
Pylstaart.
PYRARD DE LAVAL, astonishment at the atolls in the Indian Ocean.
QUOY AND GAIMARD, depths at which corals live. Description of reefs
applicable only to fringing-reefs.
RANGE of atolls.
Rapa.
Rearson.
RED SEA, banks of rock coated by reefs. Proofs of its recent elevation.
Supposed subsidence of.
Red Sea.
REEFS, irregular in shallow seas. Rising to the surface in some lagoons
and all submerged in others. Their distribution. Their absence from
some coasts.
Revilla-gigedo.
RING-FORMED REEFS of the Maldiva atolls, and theory of.
Rodriguez.
Rosario.
Rose island.
Rotches.
Rotoumah.
Roug.
Rowley shoals.
RUPPELL, Dr., on the recent deposits of Red Sea.
Sable, ile de.
Sahia de Malha.
St. Pierre.
Sala.
Salomon archipelago. (Solomon.)
SAMOA, or Navigator archipelago, elevation of.
Samoa archipelago.
SAND-BARS parallel to coasts.
Sandal-wood.
SANDWICH archipelago, recently elevated.
Sandwich archipelago.
Sanserot.
Santa-Cruz group.
SAVAGE island, recently elevated.
Savage.
Savu.
Saya, or Sahia de Malha.
Scarborough shoal.
SCARUS feeding on corals.
Schouten.
Scilly.
SCORIAE floated to coral-islands.
Scott’s reef.
SECTIONS of islands encircled by barrier-reefs. Of Bolabola.
SEDIMENT in Keeling lagoon. In other atolls. Injurious to corals.
Transported from coral-islands far seaward.
Seniavine.
Serangani.
Seychelles.
SHIP-BOTTOM quickly coated with coral.
SMYTH island.
SOCIETY archipelago, stationary condition of. Alleged proofs of recent
elevation.
Society archipelago.
Socotra.
Solor.
SOOLOO islands, recently elevated.
Sooloo islands.
Souvaroff.
Spanish.
SPONGE, depths at which found.
Starbuck. (Slarbuck.)
STONES transported in roots of trees.
STORMS, effects of, on coral-islands.
STUTCHBURY, Mr., on the growth of an Agaricia. On upraised corals in
Society archipelago.
SUBSIDENCE of Keeling atoll. Extreme slowness of. Areas of, apparently
elongated. Areas of immense. Great amount of.
Suez, gulf of.
Sulphur islands.
SUMATRA, recently elevated.
Sumatra.
Sumbawa.
SURF favourable to the growth of massive corals.
Swallow shoal.
Sydney island.
TAHITI, alleged proofs of its recent elevation.
Tahiti.
TEMPERATURE of the sea at the Galapagos archipelago.
Tenasserim.
Tenimber island.
Teturoa.
THEORIES on coral-formations.
THEORY OF subsidence, and objections to.
THICKNESS, vertical, of barrier-reefs.
Thomas, St.
Tikopia.
TIMOR, recently elevated.
Timor.
Timor-laut.
Tokan-Bessees.
Tongatabou.
Tonquin.
Toubai.
Toufoa. (Toofoa.)
Toupoua.
TRADITIONS OF CHANGE in coral-islands.
TRIDACNAE embedded in coral-rock. Left exposed in the Low archipelago.
TUBULARIA, quick growth of.
Tumbelan.
Turneffe reef.
Turtle.
Ualan.
VANIKORO, section of. Its state and changes in its reefs.
Vanikoro.
Vine reef.
Virgin Gorda.
Viti archipelago.
VOLCANIC islands, with living corals on their shores. Matter, probably
not associated with thick masses of coral-rock.
VOLCANOES, authorities for their position on the map. Their presence
determined by the movements in progress. Absent or extinct in the areas
of subsidence.
Waigiou.
Wallis island.
Washington.
Well’s reef.
WELLSTEAD, Lieutenant, account of a ship coated with corals.
WEST INDIES, banks of sediment fringed by reefs. Recently elevated.
West Indies.
WHITSUNDAY island, view of. Changes in its state.
WILLIAMS, Rev. J., on traditions of the natives regarding
coral-islands. On antiquity of certain corals.
Wolchonsky.
Wostock.
Xulla islands.
York island.
Yucutan, coast of.
ZONES of different kinds of corals outside the same reefs.