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CORALS

AND

CORAL ISLANDS.

JAMES D.^DANA, LL.D.,

PROFESSOR OF GEOLOGY AND MINERALOGY IN YALE COLLEGE ; AUTHOR OF REPORTS IN
CONNECTION WITH THE WILKES U. S. EXPLORING EXPEDITION, ON GEOLOGY,
ZOOPHYTES, AND CRUSTACEA ; OF A SYSTEM OF MINERALOGY ;
MANUAL OF GEOLOGY, ETC.

"We wandered where the dreamy palm
Murmured above the sleeping wave ;
And through the waters clear and calm,
Looked down into the coral cave."

J. C. P.. U. S. N. Expl. Expd,

NEW YORK:
DODD & MEAD, PUBLISHERS.

No. 762 B ROADWAY.
1874.

Kntorod according:: to Act of Congress, in the ycnr 1872, by

JAMES D. DANA,
in tlie OiUce of the Librarian of Congress at Washington.

STEREOTYPED BY

WILLIAM McCREA & CO.,

NEWBURGH, N. Y.

John F. Trow & Son, Printers,
205-213 East i2Th St., New York.

PREFACE TO THE SECOND EDITION,

In the preparation of this work for a second edition, a few
emendations have Ijeen made, and new facts introduced from
recent publications on the subject. Among the latter, an
account is given of the arrangements by MM. Le Clerc and De
Benaze, on Tahiti, for marking, in the future, the rate of
growth of the Dolphin Shoal or reef.

The Pjeface to the first edition alludes to some points
in which the author differs from Mi*. Darwin. The reader
will find some additional remarks on these differences in the
Aynerican Journal of Science for October, 1874, called out
by the discussion of the subject in the new edition of Mr.
Darwin's '' Coral Reefs."

New Haven, Conn., October 1, 1874.

PREFACE

npHE object in view in the preparation of this work has been
to present a popular account of '' Corals and Coral
Islands," witliout a sacrifice of scientific precision, or, on the
main topic, of fulness. Dry details and technicalities have
been avoided as far as was compatible with this restriction,
explanations in simple form have been freely added, and
numerous illustrations introduced, in order that the subject
may have its natural attractiveness to both classes of readers.

I have opened the volume with a chapter on " Corals and
Coral makers," describing, under it, the forms and structure
of polyps ; how they live and grow and hold their own in a
world of enemies ; how coral-making species secrete their
coral; how they multiply, and develop their large clusters,
spreading leaves and branching forms, so much like those
among plants ; and in what seas they thrive, and under what
conditions produce the coral plantations.

All this is prefatory to the following part of the volume on
Coral Reefs and Islands, which comprises a description of the
features and structure of these reef-formations, an account of
their mode of accumulation and increase, and a discussion of

4 PREFACE.

the origin of the included channels and lagoons, and of the
distribution of reefs, together with a review of the facts with
reference to their geological bearing.

The observations forming the basis of the work were made
in the course of the cruise of the Wilkes Exploring Expedi-
tion, around the world, during the four years from 1838 to
1842. The results then obtained are published in my Report
on Zoophytes, which treats at length of Corals and Coral
Animals, and in a chapter on Coral Reefs and Islands form-
ing part of my Geological Report.

The opportunities for investigations in this department
afforded by the Expedition, were large. We visited a number
of the coral islands of the Paumotu Archipelago, to the north
of east from Tahiti ; also, some of the Society, Navigator, and
Friendly Islands, all remarkable for their coral reefs; the
Feejee Group, one of the grandest regions of growing corals
in the world, where we spent three months ; several islands
north of the Navigator and Feejee Groups, including the Gil-
bert or Kingsmill Group ; the Sooloo sea, between Borneo
and Mindanao, abounding in reefs ; and, finally, Singapore,
another East India reef-region.

Most agreeable are the memories of events, scenes and
labors, connected with the cruise : — of companions in travel,
both naval and scientific; of the living things of the sea,
gathered each morning by the ship's side, and made the study
of the day, foul weather or fair ; of coral islands with their
groves, and beautiful life, above and within the waters ; of
exuberant forests, on the mountain islands of the Pacific,
where the tree-fern expands its cluster of large and graceful
fronds in rivalry with the palm, and eager vines or creepers
intertwine and festoon the trees, and weave for them hangings
of new foliage and flowers ; of lofty precipices, richly draped,

PREFACE. 5

even the sternest fronts made to smile and be glad as delights
the gay tropics, and alive with waterfalls, gliding, leaping, or
plunging, on their way down from the giddy heights, and,
as they go, playing out and in amid the foliage ; of gorges ex-
f)lored, mountains and volcanic cones climbed, and a burning
crater penetrated a thousand feet down to its boiling depths ;
and, finally, — beyond all these, — of man emerging from the
depths of barbarism through christian self-denying, divinely-
aided, effort, and churches and school-houses standing as cen-
tral objects of interest and influence in a native village.

On the other hand, there were occasional events not so
agreeable.

Even the beauty of natural objects had, at times, a dark
back-ground. When, for example, after a day among the
corals, we came, the next morning, upon a group of Fee-
jee savages with human bones to their mouths, finishing ofT
the cannibal feast of the night ; and as thoughtless of any im-
propriety as if the roast were of wild game taken the day be-
fore. In fact, so it was.

Other regions gave us some harsh scenes. One — that of
our vessel, in a tempest, fast drifting toward the rocks of
Southern Fuegia, and finding anchorage under Noir Island,
but not the hoped-for shelter from either winds or waves ; the
sea at the time dashing up the black cliffs two and three hun-
dred feet, and shrouding in foam the high rocky islets, half-
obscured, that stood about us ; the cables dragging and clank-
ing over the bottom ; one breaking ; then another, the storm
still raging; finally, after the third day, near midnight, the
last of the four cables giving way, amid a deluge of waters
over the careering vessel from the breakers astern, and an in-
stant of waiting among all on board for the final crash ; then,
that instant hardly passed, the loud calm command of the

b P EFFACE.

Cai)tain, the spring of the men to the yard-arms, and soon the
.ship again on the dark, stormy sea, with labyrinths of islands,
and the Fuegian cliffs to leeward ; but, the wind losing some-
what of its violence and slightly veering, the ship making a
bare escape as the morning dawned with brighter skies.

And still another scene, more than two years later, on a
beautiful Sunday, in the summer of 1841, when, after a cruise
of some months through the tro{)ics, we were in full expecta-
tion of soon landing joyously on the shores of the Columbia;
of the vessel suddenly striking bottom ; then, other heavier
blows on the fatal bar, and a quivering and creaking among
the timbers; the waters rapidly gaining, in spite of the pumps,
through a long night ; the morning come, our taking to the
boats, empty handed, deserting the old craft that had been a
home for three eventful years, for " Cape Disappointment " — a
name that tells of other vessels here deceived and wrecked ;
and, twenty hours later, the last vestige of the '' Old Peacock "
gone, her upper decks swept off by the waves, the hulk buried
in the sands.

But these were only incidents of a few hours in a long and
always delightful cruise. If this work gives pleasure to any,
it will but prolong in the world the enjoyments of the " Ex-
ploring Expedition."

In explanation of some allusions in the following pages,
I may here state with regard to the Exploring Expedi-
tion, that Captain (now Admiral) Charles Wilkes, U. S. N.,
the Commander of the Expedition, was in charge of the Sloop-
of-war Vincennes; Capt. W31. L. HudsojN-, U. S. N., of tlie
Sloop-of-war Peacock; Capt A. K. Lono, U. S. N., of the
Storeship Relief (the vessel which encountered the dangers
in the Cape Horn sea, above related) ; and Lieut. Command-
ant C. Ringgold, of the Brig Porpoise ; and that my associates

PREFACE. 7

in the ''Scientific Corps" were Dr. Ciiakles Pickering, J. P.
CouTHOUY, and TixiAisr R. Peale, Zoologists ; Wm. Rich and
J. D. BiiECKEiNTaDGE, Botanists ; Houatio Hale, Philologist;
Joseph Draytoin' and A. T. Agate, Artists.

Our cruise led us partly along the course followed by Mr.
Charles Darwust during the years 1831 to 1836, in the Voyage
of the Beagle, under Captain Fitzroy ; and, where it diverged
from his route, it took us over scenes, similar to his, of coral and
volcanic islands. Soon after reaching Sydne}-, Australia, in
1839, a brief statement was found in the papers of Mr. Dar-
win's theory with respect to the origin of the atoll and barrier
forms of reefs. The paragraph threw a flood of light over the
subject, and called forth feelings of peculiar satisfaction, and of
gratefulness to Mr. Darwin, which still come up afresh when-
ever the subject of coral islands is mentioned. The Gambier
Islands, in the Paumotus, which gave him the key to the
theory, I had not seen ; but on reaching the Feejees, six
months later, in 1840, I found there similar facts on a still
grander scale and of more diversified character, so that I was
afterward enabled to speak of his theory as established with
more positiveness than he himself, in his philosophic caution,
had been ready to adopt. His w^ork on Coral Reefs appeared
in 1842, when my repoit on the subject was already in man-
uscript. It showed that the conclusions on other points, which
we had independently reached, were for the most part the
same. The principal points of difference relate to the reason for
the absence of corals from some coasts, and the evidence there-
from as to changes of level, and the distribution of the oceanic
regions of elevation and subsidence — topics which a wide
range of travel over the Pacific brought directly and constantly
to my attention.

In the preparation of the present work my former chapter

8 PREFACE.

on Coral Reefs and Islands has been greatly extended by the
addition of facts from numerous sources. The authorities
cited from are stated in the courrse of the volume, and need
not here be re-mentioned. I have occasion, however, for special
acknowledgments to our excellent Yale Zoologist, Professor
A. E. Verrill, who now stands first in the country in the de-
partment of Zoophytes. Through his recent memoirs on the
subject, and also by his personal advice, I have been greatly
aided in acquainting myself with the present state of the sci-
ence : — my own special labors in this branch of zoology having
ended in 1850, when both the Reports, referred to above, had
been published, and the last of my Expedition departments —
that of the Crustacea — forced my studies in another direction.
The illustrations of the following pages have been drawn
mainly from my Expedition Reports. Those not my own are
from the works or memoirs of Gosse, Mobius, Verrill, Pour-
tales, L. Agassiz, a. Agassiz, Smitt, Edwards and Haime,
Wilkes, and Hartt. In addition, the volume is indebted for
a few cuts to the beautifully illustrated popular works, '' Le
Monde du Mer " and " La Vie et les Moeurs des Animaux; ''
but nearly half of these were engraved from my plates. The
sources of all the figures are given in the List of Illustrations.

James D. Dana.

New Haven, Conn., February 12, 1872.

C O I^ T E! ]Sr T S .

CHAPTER L

CORALS AND CORAL MAKERS.

General Observations.

I. Polyps.

I. Actinoid Polyps. ----••

I. Non-Coral Making Actinoid Polyps. - - -

II. Coral-Making Actinoid Polyps. - - •

III. Classification. ------

II. Cyathophylloid Polyps. - - .

III. Alcyonoid Polyps. - - - - -

IV. Life and Death in Concurrent Progress. - - •
V. Composition of Corals. - . . • •

II. Hydroids. - . . • .

III. Bryozoans. - - - - ...

IV. Algje; or, Nullipores and Corallines.

V. The Reef-Forming Corals, and the Causes Influencing their
Growth and Distribution. - - - -

I. Distribution in Latitude. . • - •

II. Distribution in Depth. . - • . •

III. Local Causes Influencing Distribution.

IV. Rate of Growth of Corals.

PAGE.

17

20

21
21
42
61
79
80
94
98

101

105

. 107

. 108^

108
. 114

119
. 123

10 CONTENTS.

CHAPTER II.

STRUCTURE OF CORAL REEFS AND ISLANDS.

PAGE.

I. Coral Reefs. - - - - 128

I. General Features. - ... - 128
II. Outer Reefs. - - - - - - 136

III. Formations in the Sea outside of Barrier Reefs. - - 139

IV. Inner Reefs. - - - 144
V. Channels among Reefs. - - - . . 148

VI. Beach Sand-Rock. . - - - - - 152

VII. Drift Sand-Rock. - - 154

VIII. Thickness of Reefs. ...... 156

IX. A Good Word for Coral Reefs. - - - • - 159

II. Coral Islands. - - - - . - - - 161

I. Forms and General Features. ------ 161

II. Soundings about Coral Islands. - - - - - 171

III. Structure of Coral Islands. .-.-.- 174

IV. Notices of some Coral Islands. .... ig5

Maldive Archipelago. - - . - - - 186

Great Chagos Bank. - - - - - - 192

Metia, etc. -------- 193

Jarvis's Island. - - - - - 195

Birnie's and Swain's Islands. - , - - 195

Otuhu, Margaret, Tehu, Washington Island, Enderbury's Island. 197

Honden, or Henuake. - - - . > . 198

Taiara, Sydney's, Duke of York's. . - - - 199

Fakaafo, Ahii. ----..-. 200

Raraka. ..-.--.- 201

Kawehe. -------- 202

Manhii, Aratica, Nairsa or Dean's. .... 203

Florida Reefs and Keys. -.---- 204

Soundings between Florida Reefs and Cuba. - - - 211

Bahamas. - ..-.-. 213

Salt Key Bank. - - - - - 214

Bermuda or Somers' Islands. - - - 218

CONTENTS. 11

CHAPTER III.

FORMATION OF CORAL REEFS AXD ISLANDS, AND CAUSES OF THEIR FEATURES.

PAGE.

I. Formation of Reefs. - - - . - . 222

I. Origin of Coral Sands, and of tlie Reef-Rock. - - - - 222

II. Origin of tlie Shore Platform. - - - - ^ 230

III. Effects of Winds and Gales. ------ 235

II. Causes Modifying the Forms and Growth of Reefs. - - 238

I. Barrier and Fringing Reefs. ------ 239

II. Atoll Reefs. - - - 248

III. Rate of Growth of Reefs. , - - - - - - 249

IV. Origin of the Barrier Condition of Reefs, and of the Atoll

FORM OF Coral Islands. ------ 254

I. Old Views. -------- 254

II. Origin of Channels within Barriers. - - - - . 257

III. Origin of Lagoons of Atolls. - - - - - 266

V The Completed Atoll. ------- 273

CHAPTER IV.

geographical distribution of coral reefs and islands. 301 -

CIIAPTE!! y.

CHANGES OF LEVEL IN THE PACIFIC OCEAN.

I. Evidences of Change of Level. ---.-. 320

II. Subsidence indicated by Atolls and Barrier Reefs. - - - , 323

III. Effect of the Subsidence. ------ 332

IV. Period of the Subsidence. ------, 333

V. Elevations of Modern Eras in the Pacific. .... 334

CHAPTER VI.

GEOLOGICAL OONCLUSTONS.

I. Formation of Limestones. .... 350

II. Beds of Limestone with Liying Margins. ... 352

III. Making of Thick Strata of Limestones. - . • . 352

12 COJSrTUJ^TS.

PAGE.

IV. Subsidence Essential to the Making of Thick Strata. - 352

V. Deep-Sea Limestones seldom made from Coral Island or

Reef Debris .... - . 353

VI. Absence of fossils from Limestone Strata. - - - 354

VII. The wide range of the older Limestones not exemplified

IN Modern Coral-reef formations - - 854

VIII. Consolidation of Coral Rocks. - - - - 356

IX. Formation of Dolomite or Magnesian Carbonate of Lime. 358

X. Formation op Chalk. ..-.-- 359

XI. Rate of Increase of Limestone Formations, - - - 361

XII. Limestone Caverns. ---.-• 302

XIII. Oceanic Temperature. _ - - - - - 364

XIV. The Oceanic Coral-Island Subsidence. - - - - 366

APPENDIX.

I. Geological Time. - - ... - 373
II. Radiates. .-.-----374

III. Protozoans. ----.-.- 377

IV. Names of Species in the Author's Report on Zoophytes. 879
V. List of Works referred to, and of Abbreviations. - 389

Index. • - - . - - - 891

LIST OF ILLUSTRATIONS.

The following list contains a statement of tlie original sources of the illustrations
througli the volume. By " Author's Atlas " is to be understood the Atlas of his Re-
port on Zoophytes. The figures are of natural size, except when otherwise stated.
The new figures included have been made by Mr. Lockwood Sanford, a New Haven
artist, engraver of most of the wood-cuts of this volume.

frontispiece, fig. 1, Phymactis florida. Author's Zoophyte Atlas, Plate 2.
" " 2, Phymactis clematis. Author's Zoophyte Atlas, Plate 1.

** " 3, 3a, Bunodes gemma. Author's Zoophyte Atlas, Plate 4 ; 3a, the

polyp contracted.
Page 28, Paractis rapiformis. From a drawing by the Author, made in 1852.

24, Cancrisocia expansa. Verrill, Amer. Naturalist, from Proc. Essex Institute,
vol. vi.

26, fig. 1. Peachia hastata. Gosse's Actin. Brit., Plate viii.

fig. 2. Edwardsia callimorpha ; and 3. Halocampa chrysanthellum. Ibid.,
Plate 7.

27, Section of Actinia. From a drawing by the Author, made in 1856, on the

basis of a study (1852) of the Actinia figured on p. 23.
31, Lasso-cells. Dr. K. Mobius, Abh. Nat. Ver. Hamburg, vol. v., 1866.

42, Caryophyllia cyathus. Le Monde du Mer.

43, Thecocyathus cylindraceus. Pourtales on Deep Sea Corals, Plate 2.

45, Ctenactis echinata, one-third natural size. La Vie et les Moeurs des Ani-

maux.

46, Fungia lacera, living and expanded. Author's Zoophyte Atlas, Plate 18.

47, Enlarged view of tentacle of F. lacera, and profile, natural size, of one of

the calcareous septa. Ibid., Plate 18.

50, Madrepora aspera, living and expanded. Author's Zoophyte Atlas, Plate 38.

51, Dendrophyllia nigrescens, living and expanded. Author's Zoophyte Atlas,

Plate 30.

52, Goniopora columna. Ibid., Plate 56.

53, Porites mordax. Ibid., Plate 53.

54, Cladocora arbuscula. Ibid., Plate 30.

55, Orbicella cavernosa. L. Sanford, from specimen.

56, Spontaneous fission. Author's Report on Zoophytes.

57, Astrsea pallida. Author's Zoophyte Atlas, Plate 10.

58, CaulastrsBa furcata. Ibid., Plate 9.

62, Epizoanthus Americanus. Verrill, Amer. Naturalist, vol. iii., p. 248.

View of single polyp. From a drawing by Prof. Verrill.

63, Antipathes arborea. Author's Zoophyte Atlas, Plate 56.

Enlarged view of polyp of A. arborea. Ibid., Plate 56.

14 LIST OF ILLUSTRATIONS.

Page 64, Astreea pallida. Author's Zoophyte Atlas, Plate 10.
65, Diploria cerebriformis. Le Monde du Mer.

Q^, Fungia Dana3. L. Sanford, one-sixth the natural size ; from a photograph
by Prof. A. E. Verrill.

67, Caryophyllia Smithii, one of the figures with the animal expanded ; the

other with it contracted. Gosse's Actinologia Britannica, Plate 10.

68, Astrangia Danas ; fig. a. one of the polyps enlarged ; c. coral with the polyps

expanded, natural size. Agassiz, Seaside Studies,
fig. h. surface of corallum, natural size. L. Sanford, from specimen.

69, Phyllangia Americana, a Florida species. Edwards & Hairae, Corallieres.
fig. 1. Oculina varicosa, extremity of a branch. Author's Report on Zoo-
phytes, page 67, corrected from specimen.

fig. 2, 3. Stylaster erubescens ; 2. corallum, natural size ; 3. extremity of a

branch enlarged. Pourta^es, Deep-Sea Corals,
fig. 4, 5. Stylophora Danse ; 4. extremity of a branch ; 5. one of the calicles

enlarged. Author's Zoophyte Atlas, Plate 49.
fig. 6. Polyp, enlarged, of St. mordax. Author's Zoophyte Atlas, Plate 49.
fig. 7. Pocillipora grandis. L. Sanford ; from an Exploring Expedition

specimen ; portion of one of the large, flattened branches of the corallum.

An entire clump is figured in the Author's Zoophyte Atlas, Plate 51.
fig. 8. cell, enlarged, of Pocillipora elongata. Author's Zoophyte Atlas,

Plate 50.
fig. 9. cell, enlarged, of Pocillipora plicata. Ibid., Plate 50.
fig. 10. vertical section of corallum of P. plicata, showing the tabular

structure. Ibid., Plate 50.

72, Polyp of Madrepora cribripora, enlarged. Author's Zoophyte Atlas, Plate

31.

73, Madrepora formosa. Author's Zoophyte Atlas, Plate 38.

75, Polyp of Dendrophyllia nigrescens, enlarged. Ibid., Plate 30.

76, Dendrophyllia nigresceils, natural size. Ibid., Plate 30.

77, Alveopora Verrilliana, natural size ; the corallum covered below with a pe-

ritheca. Author's Zoophyte Atlas, Plate 48. The species is here named
after Prof. A. E. Verrill, as it is not the true A. dedalea.
Alveopora spongiosa, vertical section of corallum, and upper view of calicle,
much enlarged ; the diameter of the cell being about a fifteenth of an
inch. Author's Zoophyte Atlas, Plate 48.

78, Polyp of Porites levis, enlarged. Author's Zoophyte Atlas, Plate 54.

79, Porites levis, with the polyps of one of the branches expanded, natural

size. Author's Zoophyte Atlas, Plate 54.

82, Xenia elongata. Author's Zoophyte Atlas, Plate 57.

83, Anthelia lineata. Verrill, Proceedings of the Essex Institute, vol. iv.,

Plate 5. From a drawing by Dr. Stimpson.

84, Telesto ramiculosa. Verrill, Proc. Essex Inst., vol. iv., Plate 6; the second

figure, an enlarged view of expanded polyp. From drawings by Dr.

Stimpson.
Tubipora syringa; fig. 1. part of a clump, natural size ; 2. one of the pol-

yps expanded. Author's Atlas, Plate 59.
Tubipora fimbriata (3d. figure), polyp, expanded. Author's Zoophyte Atlas,

Plate 59.

85, Gorgonia ? flexuosa, part of zoophyte, natural size. Author's Zoophyte At-

las, Plate 60.

LIST OF ILLUSTRATIONS. 15

Page 86, Spicules of Gorgoniae, much enlarged. Verrill, Transactions of the Con-
necticut Academy of Sciences, vol. i.. Plates 4 and 5.

88, Isis Hippuris. La Vie et les Moeurs des Animaux.

89, Corallium rubrum, the coral, natural size. L. Sanford, from specimen.
Extremity of branch of C. rubrum, enlarged, with some of the animals ex

panded. Lacaze-Duthiers, from La Vie et les Moeurs des Animaux.
91, Cophobelemnon clavatum ; the small figure, enlarged view of one of the

polyps. Verrill, Proc. Essex Institute, vol. iv., Plate 5. From a drawing

by Dr. Stimpson.
Veretillum Stimpsoni, enlarged 3 diameters. Verrill, Proc. Essex Institute,

vol. iv., Plate 5. From a drawing by Dr. Stimpson.
95, Caulastroea furcata. Author's Zoophyte Atlas, Plate 9.

101, Hydra. Le Monde du Mer.

102, Hydrallmania falcata. Le Monde du Mer.

103, Millepora alcicornis. La Vie et les Ma3urs des Animaux.

104, Animals of M, alcicornis, enlarged. L. Agassiz, Contributions to the Nat

ural History of the United States ; vol. iii., Plate 15.
106, Hornera lichenoides : 1. natural size ; 2. part of branch enlarged. Smitt's

Mem. des Bryozoaires,
Discosoma Skenei, part of a group much enlarged. Ibid.
130, High Island, with Barrier and Fringing Reefs. Author's Geol. Report.
134, Map of New Caledonia. Darwin on Coral Islands.
140, The Lixo Coral Reef, Abrolhos. Ilartt's Brazil, p. 202.
149, Coral Reefs otf the North Shore of Tahiti. Author's Exp. Geological Re*

port, from the Wilkes Expl. Exp. Maps.
162, Coral Island or Atoll. Wilkes's Narr. Expl. Exped.
165, Map of Gilbert or Kingsmill Islands. Author's Geol. Rep. ; from Expl.

Exp. Maps.
168, Maps of Taiara, Henuake, Swain's Island, Jarvis's Island, and Fakaafo.

Author's Geol. Rep. ; from Expl. Exp. Maps.
170, Map of Menchicoff Atoll. Darwin on Coral Reefs ; from Kotzebue's

Atlas.
176, Section of the rim of an Atoll. Author's Exp. Geol. Report.
179, Blocks of Coral on the shore platform of Atolls. Author's Geol. Report.
187, Map of Maldive Archipelago. Darwin on Coral Reefs.
189, Map of Mahlos Mahdoo Atoll, one of the Maldives. Darwin on Coral

Reefs.

191, Map of Great Chagos Bank. Darwin on Coral Reefs.

192, East and West Section across the Great Chagos Bank. Ibid.

193, Metia, an elevated Coral Island. Wilkes's Narrative of Expl. Exp., vol. 1.
218, Map of the Bermuda Islands. Reduced from an English Chart.

231, The " Old Hat." Author's Exp. Geol. Report.

239, Harbor of Apia. Author's Exp. Geol. Rep. ; from charts of the Wilkes

Expl. Exped.
242, Part of North Shore of Tahiti. Ibid.
244, Harbor of Falifa. Ibid.
246, Whippey Harbor. Ibid.

260, Section illustrating the Origin of Barrier Reefs. Ibid.

261, Map and Ideal Section of Aiva Island. Ibid.

265, Map of Gambler Islands. Darwin on Coral Reefs.

266, Section illustrating the Origin of Atolls. Author's Exp. Geol. Rep.

16 LIST OF ILLUSTRATIONS.

Page 268, Mencliicoff Atoll. Darwin on Coral Reefs.

274, Cocoanut Grove, on Bowditch Island. Wilkes's Narrative of the Expl

Exped., vol. V.

275, Fakaafo. Author's Geol. Rep. ; from Charts of Expl. Exped.
279, Scene on the Lagoon side of Duke of York's Island. Ibid.

At close of volume.

Isocrymal Cliart of the World. Author's Report on Crustacea.
Map of the Feejee Islands. Wilkes's Narative of the Expl. Exped.
Map of the Florida Reefs, and the Seas between them and Cuba. De Pour-
tales on Deep-Sea Corals,

CORALS AND CORAL ISLANDS.

CHAPTER I.
CORALS AND CORAL MAKERS.

A SINGULAR degree of obscurity has possessed the popu-
lar mind with regard to the growth of corals and coral
reefs, in consequence of the readiness with which speculations
have been supplied and accepted in place of facts ; and to the
present day the subject is seldom mentioned without the qual-
ifying adjective mysterious expressed or understood. Some
writers, rejecting the idea which science had reached, that
reefs of rocks could be due in any way to ''animalcules,"
have talked of electrical forces, the first and last appeal of ig-
norance. One author, not many years since, made the fishes
of the sea the masons, and in his natural wisdom supposed
that they worked with their teeth in building up the great
reef. Many of those who have discoursed most poetically on
zoophytes have imagined that the polyps were mechanical
workers, heaping up the piles of coral rock by their united la- *
bors ; and science is hardly yet rid of such terms as polypary,
polypidom, which imply that each coral is the constructed
hive or house of a swarm of polyps, like the honey-comb of
the bee, or the hillock of a colony bf ants.

Science, while it penetrates deeply the system of things

2

18 CORALS AND COMAL ISLANDS.

about us, sees everywhere, in the dim limits of vision, the word
mystery. Surely there is no reason why the simplest of organ-
isms should bear the impress most strongly. If we are aston-
ished that so great deeds should proceed from the little and
low, it is because we fail to appreciate that little things, even
the least of living or physical existences in nature, are, under
God, expressions throughout of comprehensive laws, laws that
govern alike the small and the great.

It is not more surprising, nor a matter of more difficult
comprehension, that a polyp should form structures of stone
(carbonate of lime) called coral, than that the quadruped
should form its bones, or the moUusk its shell The pro-
cesses are similar, and so the result. In each case it is a sim-
ple animal secretion ; a secretion of stony matter from the
aliment which the animal receives, produced by the parts of
the animal fitted for this secreting process ; and in each, car-
bonate of lime is a constituent, or one of the constituents, of
the secretion.

This power of secretion is then one of the first and most
common of those that belong to living tissues ; and though dif-
fering in different organs according to their end or function, it
is all one process, both in its nature and cause, whether in the
Animalcule or Man. It belongs eminently to the lowest kinds
of life. These are the best stone-makers ; for in their simplici-
ty of structure they may be almost all stone and still carry on
the processes of nutrition and growth. Throughout geological
time they were the agents appointed to produce the material
of limestones, and also to make even the flint and many of the
siliceous deposits of the earth's formations.

Coral is never, therefore, the handiwork of the many-
armed polyps ; for it is no more a result of labor than bone-
making in ourselves. And again, it is not a collection of cells

CORAL AND CORAL MAKERS. 19

into which the coral animals may withdraw for concealment
any more than the skeleton of a dog is its house or cell ; for
every part of the coral — or corallum as it is now called in sci-
ence—of a polyp, in most reef-making species, is enclosed
within the polyp, where it was formed by the secreting pro-
cess.

It is not, perhaps, within the sphere of science to criticise
the poet. Yet we may say in this place, in view of the frequent
use of the lines even by scientific men, that more error in the
same compass could scarcely be found than in the . part of
Montgomery's " Pelican Island " relating to coral formations.
The poetry of this excellent author is good, but the facts nearly
all errors — if literature allows of such an incongruity. There
is no *' toil," no " skill," no " dwelling," no " sepulchre " in the
coral plantation any more than in a flower-garden ; and as lit-
tle are the coral polyps shapeless worms that "writhe and
shrink their tortuous bodies to grotesque dimensions."

The poet oversteps his license, and besides degrades his
subject, when downright false to nature. U^

Coral is made by organisms of four very diflferent kinds.
These are : Firs% Polyps, the most important of coral-making
animals, the principal source of the coral reefs of the world.

Second^ Animals related to the little Hydra of fresh waters,
and called Hydroids (a division under the Acalephs), which,
as Agassiz has shown, form the very common and often large
corals called Millepores.

Third^ The lowest tribe of Mollusks, called Bbyozoans,
which produce delicate corals, sometimes branching and moss-
like (whence the name from the Greek for moss cmimal), and at
other times in broad plates, thick masses, and thin incrusta-
tions. Although of small importance as reef-makers at the

20 COBALS AND CORAL ISLANDS.

present time, in a fornaer age of the world — the Paleozoic —
they so abounded over the sea bottom that some beds of lime-
stone are half composed of them.

JPourth^ Algae or sea^weeds, some kinds of which would
hardly be distinguished from corals, except that they have no
cells or pores.

I. POLYPS.

V

A good idea of a polyp may be had from comparison with
the garden aster ; for the likeness to many of them in external
form as well as delicacy of coloring is singularly close. The
aster consists of a tinted disk bordered with one or more series
of petals. And, in exact analogy, the polyp flower, in its
most common form, has a disk fringed around with petal-like
organs called tentacles. Below the disk, in contrast with the
slender pedicel in the ordinary plant, there is a stout cylindri-
cal pedicel or body, often as broad as the disk itself, and some-
times not much longer, which contains the stomach and inter-
nal cavity of the polyp ; and the mouth, which opens into the
stomach, is at the centre of the disk. Here then the flower-
animal and the garden-flower diverge in character, the dif-
ference being required by the diflferent modes of nutrition and
other characteristics in the two kingdoms of nature. The cor-
/ al polyp is as much an animal as a cat or a dog.

The figures of the frontispiece, and others on pages 23, 24.
26, sustain well the description here given, and afibrd some
idea also of the diversity of form among them.

The prominent subdivisions of polyps here recognized are
tibe following :

I. AoTiNOiD Polyps. — Related to the Actinia, or Sea-anem-
one, in tentacles and interior structure, and having, as m

CORAL AND COMAL MAKERS. 21

them, the number of tentacles and interior septa a multiple of
six. The name Actinia is from the Greek ray,

II. Cyathophylloii) Polyps. — Like the Actinoids in tenta-
cles and interior structure, except that the number of tentacles
and interior septa is a multiple of fov/r. Ludwig and De
Pourtales state that the number in the earliest young state is
six^ and that therefore the fundamental ratio is the same as in
the Actinoids ; and that they pass from this ratio by develop-
ments of tentacles and septa more rapidly on one side than the
opposite, and in such a manner that the number becomes after
the first stage a multiple of four. The Cyathophylloid polyps
hence combine this characteristic of the Actinoids with one
feature of the Alcyonoids. The Oyathophylloids were the ear-
liest of polyps, and the most abundant species in Paleozoic
time.

III. ALCYONom Polyps. — Having eight fringed tentacles,
and other characters mentioned beyond ; as the Gorgoniae and
Alcyonia.

I. ACTESrorD POLYPS.

The highest of Actinoid Polyps are those of the Actinia
TRIBE — the species that secrete no coral to clog vital action
and prevent all locomotion. The details of structure may be
best described from the Actinia or Sea-anemone, and after-
ward the distinguishing characters of the coral-making polyps
may be mentioned. In external aspect and in internal charac-
ters all are essentially identicaL

L NON-CORAL-MAKING POLYPS.

As the figures on the frontispiece, and also the following,
show, the external parts of an Actinia are — a subcylindrical

22 CORALS AND CORAL ISLANDS,

body — a disk at top — one or more circular series of tentacles
making a border to the disk — a mouth, a merely fleshy, toothless
opening, at the centre of the disk, sometimes at the summit
of a conical prominence — a basal disk for attachment. The
upper extremity is called the actinal end, since it bears the
tentacles or rays, and the lower or base, the ahactinal.

Sea-anemones vary greatly in color, and in the distri-
bution of their tints. The lower figure on the frontispiece rep-
resents one variety o{ the Phymactis clematis from Valparaiso.
Another variety of the same has a rich deep green color.
The upper species on the same plate is one of the gorgeous va-
rieties of the Phymactis fiorida from Callao, Peru, Another
is green throughout; and another has a pale bluish-green
disk with purplish tentacles, and the papillae of the body dark
sap-green on a pale reddish ground. The other species is the
Bunodes gemma^ from Porto Praya, Cape Verd. It is one of
the warty species, and is but partly expanded. The same is
shown unexpanded in figure 3a, on the right, with disk and
tentacles, as usual in this state, wholly Concealed.

Wliile often brilliantly colored, especially in the tropics,
other Actiniae are nearly colorless. This was the case with
that represented in the following cut, a species from Long
Island Sound near the New Haven Light-house, figured
some twenty years since by the author, but left undescribed.
The body in this species had a delicate texture throughout, its
walls being so transparent that the organs within could be
seen through them. It was exceedingly flexible and passed
through various shapes, imitating vases of many forms, wine
glasses, goblets, etc. It was generally very slow in its
changes, and sometimes continued in the same vase-attitude
for a whole day.

Actiniae vary immensly in size, — from an eighth of an inch

AGTimJS AND OTHER ACTINOID POLYPS.

23

and smaller in the diameter of the disk to over a foot, —
though commonly between half an inch and three inches.
One species from the Paumotu Coral Archipelago in the

PARACTIS RAPIFORMIS, EDW.

Pacific, a colored figure of which is given in the Atlas of the
Author's Report on Zoophytes (Plate III.), had a diameter
across its disk of fourteen inches; and it was also one of the
most beautiful in those seas, having multitudes of tentacles
vnth carmine tips and yellowish bases, around the open centre,
giathered into a number of large groups or lobes.

With rare exceptions, ActinisB live attached to stones,
shells, or the sea bottom, or are buried at base in the sand or
mud. The attached species have the power of locomotion,
through the muscles of the base, but only with extreme slow-

24

C0BAL8 AND CORAL ISLANDS.

ness. The loose stones on a sea-shore near low tide level
often have Actiniae fixed to their under surface. A very few
species swim or float at large in the ocean.

Now and then an Actinia puts itself on the back of a
crab, and thus secures rapid locomotion, but only at the will
of the crab, which may at times give it some hard rubs: — a

CANCRISOCIA EXPANSA ST., ON THE BACK OF DORIPPB FACCHINO.

kind of association styled commensalism by Van Beneden, as
the two in a sense live at the same table, without preying
one upon the other. In the above example, from the China
seas, the Actinia has mounted a Dorippe. The figure is from
the Proceedings of the Essex Institute^ where an account of it
is published by Prof. Verrill ; the specimen was collected by
the zoologist, Dr. W. Stimpson. As Prof. Verrill states, the
Dorippe carries, for its protection when young, a small shell over
its back, which it holds in this position by means of its two
reversed pairs of hind legs. The Actinia appears to have fixed
itself, when young, to the shell, and afterward, by its growth,
spread over the back of the crab, taking the place of the shell
This case of commensalism, like most others, is not a mere
chance association of species, for the two always go together,

ACTINIA AND OTHER AGTINOID POLYPS. 25

the Actinia, according to Dr. Stimpson, never being seen
except upon the crab's back, and the crab never without its
Actinia. The fact shows an instinctive liking on the part of
the Actinia for a Dorippe courser, and for the roving life
thus afforded it. And the crab is undoubtedly conscious that
he is carrying his fortress about with him. It is not a soli-
tary case ; for there are many others of Actiniae attaching
themselves to locomotives — ^to the claws or backs of crabs, or
to shells in possession of soldier crabs, or to a Medusa ; and
frequently each Actinia has its special favorite, proving an
inherited instinctive preference for rapid change of place, and
for just that kind of change, or range of conditions, which the
preferred commensal provides. Prof. Verrill has an interest-
ing article on this subject, with especial reference to crustace-
ans, in the third volume of the American Naturalist.

Species living in sand are often unattached ; and then the
base is rounded or tapering, and sometimes balloon-shaped ;
some of them are long and almost worm-like, and even burrow
like worms. ^

The following are figures of three species : one, figure 3,
exhibiting simply the tentacles and disk of the i^ctinia, the
only parts visible above the sand; the others showing the
whole body removed from the sand, and consequently a little
out of shape. They are from Gosse's " British Sea- Anem-
ones," in which they are given with the natural colors.
Figure 1 represents the jPeachia hastata of Gosse, a beautiful
species having twelve large tentacles ; fig. 2, the Edwardeia
calMmorpha G. ; fig. 3, Halocampa chrysanthellum G. Most
of these sand-dwellers bury themselves like the Halocampa,
and often hide all the disk but the mouth. The Edwardsia
is peculiar in having, above the hollow bladder-like basal
portion, a firm opaque exterior to the body, making for it

26 CORALS AND CORAL ISLANDS.

a kind of case or jacket, into which the upper extremity,
which is soft and delicate in texture, may be retracted. The
thickening of the epidermis in this middle portion is produced
through the entangling of disintegrated cells and minute for-

eign particles, sometimes in part spores of Confervsa, by
means of the mucus of the surface ; and if the layer is re-
moved, as it may be, the skin will again become covered.
This species, like others of the genus, lives buried to its neck
in the sand, that is, with the soft upper extremity protrud-
ing-. If disturbed, the head is suddenly drawn in, together
with more or less of the following jacketed part of the body.
The warty prominences on some warty species have the
power of clinging by suction to a surface, and such Actiniae
often cover their sides thus with bits of shell or of other sub-
stances at hand. Where there are no warts the contracted

ACTINIA AND OTHER AGTINOID POLYPS, 27

exterior skin, reticularly corrugated, occasionally becomes a
surface of suction- warts, as in many Sagartiae.

The internal structure of the Actinia is radiate like the ex-
ternal, and more profoundly and constantly so. The mouth,
a fleshy toothless opening in the disk, opens directly into a
stomach, which descends usually about a third of the way to
the base of the body; its sides are closed together unless
it be in use. The general cavity of the body around and be-
low the stomach is divided radiately by fleshy partitions, or
septa, into narrow compartments ; the larger of these septa

connect the stomach to the sides of the animal, and, besides
holding it in place, serve to pull it open or distend it for the
reception of food. The above figure represents in a gener-
al way a horizontal section of the body through the stomach,
and shows the position of the radiating septa and the interme-
diate compartments. It presents to view the fact that these
are in pairs, and another fact that the number of pairs of par-
titions in the ordinary Actinoid polyps is regularly some mul-
tiple of six, although other numbers occur during the succes-
sive developments that take place in the growth of a polyp,
and are occasionally persistent in the adult state. There are six
pairs in the first series ; six in the second ; twelve in the third ;
twenty-four in the fourth ; forty-eight in the fifth, and so on.

28 CORALS AND CORAL ISLANDS.

The compartment between the two septa of each pair opens
at top into the interior of a tentacle, and thus the cavity in
each tentacle has its special corresponding compartment below.
This tentacular compartment is properly, as first recognized by
Prof. Verrill, the amhulacral^ since each corresponds in posi-
tion and function to an ambulacral or tentacle-bearing section
in the Echinoderms and other Radiate animals.

Although polyps are true Radiates, they have something
of the antero-posterior (or head-and-tail) polarity, with also the
right-and-left, which is eminently characteristic of the animal
type. This is manifested in the occurrence in some polyps of
a ray on the disk different in color from the general surface :
of one tentacle larger than the others, and sometimes peculiar
in color; of two opposite septa in a calicle or polyp -cell larger
than the others, and sometimes meeting so as to divide the cell
into halves. The first of these marks the author has observed
in a Zoanthid, as mentioned in his Report on Zoophytes at
page 419, and represented on plate 30: and the last is very
strongly developed in the cells of many Pocilloporae (ib. p. 523).
Gosse and many other authors have drawn attention to the
one large tentacle, and the fact that it lies in the direction of
the line of the mouth. Prof. H. James Clark, in his Mind in
Nature, states that the order in which the fleshy septa and the
tentacles in an Actinia are developed has direct reference to the
right and left sides of the body, and that there is only one
plane in which the body can be divided into two halves, and
this is that corresponding with the longer diameter of the stom-
ach, or the direction of the mouth. Mr. A. Agassiz has
shown that in Actiniae of the genus Arachnactis, the new
septa and tentacles are developed either side of the one chief
or anterior tentacle; and Prof. Verrill, that in Zoanthids,
they are formed principally either side of this anterior tentacle

AGTimJS AND OTHER ACTINOID POLYPS. 29

and also of the opposite or posterior one, and much less
rapidly, if at all, along the sides intermediate. This chief-
tentacle mark properly the true front or anterior side of
the polyp. A fore-and-aft structure is also very strongly
marked in some of the ancient cyathophylloid corals, and
hence it belonged to the type from early Paleozoic time.

The way leading out from the Radiate structure is thus
manifested by these llower-like polyps. In fact perfect circu-
lar series in organs or parts do not belong to any living organ-
ism, not even to the true flower ; for growth is fundamentally
spiral in its progress, and there must be always an advance
end to the spiral of growth ; all apparent circles are only dis-
guised spirals.

The walls of the body contain two sets of muscles, a circu-
lar and a longitudinal, the latter becoming radial in the disk
and base. Similar muscles exist also in the tentacles, and cor-
responding muscles in the fleshy partitions or septa of the in-
ternal cavity.

By means of these muscles an Actinia, whenever disturbed,
contracts at once its body ; and most species make of them-
selves a spheroidal or conoidal lump, showing neither disk
nor tentacles. One example of this contracted state is presented
on the frontispiece in figure 3(^. After a brief period of quiet
the polyp commonly reassumes its full expansion. The ex-
pansion depends on an injection of the structure with salt wa-
ter, which is taken in mainly by the mouth. As the whole body
is thus filled and injected, the flower slowly opens out, and
shows its petal-like tentacles. On contraction the water is
suddenly expelled through the mouth, and by pores in the sides
of the polyps, and at the extremity of the tentacles, and the
tentacles disappear, along with the disk, beneath the adjoining
sides of the body which are drawn or rolled in over them.

30 CORALS AND CORAL ISLANDS,

The Actinia appears, at first thought, to be well prepared
for securing its prey through its numerous tentacles. But
these are generally too short for prehension. Yet the disk often
aids them by rolling over the captured animal, and pushing it
down into the stomach. At the same time, the mouth and
stomach are both very extensile, so that an Actinia may swal-
low an animal nearly as large as itself; it gradually stretches
the margins of the mouth over the moUusk or crab, until the
whole is enclosed and passed into the digestive sac ; and when
digestion is complete, the shell and any other refuse matters
are easily got rid of by reversing the process.

But the Actinia owes nearly all its power of attack to its
concealed weapons, which are carried by myriads. These
are what Agassiz has called lasso-cells^ because the little cell-
shaped sheath contains a very long slender tubular thread
coiled up, which can be darted out instantly when needed.
As first observed by Agassiz, the tubular lasso escapes from
the cell by turning itself inside out, the extremity showing it-
self last, and this is usually done " with lightning-like rapidi-
ty." Then follows the poison. The lasso-cells (called often
nettling cellsy and by Gosse cnidce^ and thread capsules) are
usually less than a two-hundredth of an inch in length ; but
they are thickly crowded in the larger part of the skin or walls
of the tentacles, and about the mouth ; also in the walls of the
stomach, and within the visceral cavity in white cords hanging
in folds from the edge of the septa. Thus the polyp is armed
inside and out. The moUusk or crab that has the ill luck to
fall, or be thrown by the waves, on the surface of the pretty
flower is at once pierced and poisoned by the minute lassos,
and is rendered incapable of resistance.

The following figures, by Dr. Karl Mobius, of Hamburg, il-
lustrate admirably these organs. The views are magnified

LAS80-CELL8,

AGTINIJE AND OTHER AGTINOID POLYPS. 33

700 diameters. Figure 1 represents one of the lasso-cells of
the Actinia, Oorynactis viridis^ with its lasso coiled up within,
its actual length is about a 350th of an inch. Figure 2 is the
same with the lasso out, though less than half of the long
thread is shown. Figure 3 is the lasso-cell of the polyps of a
European coral, the Caryophyllia Smithii. It differs from
figure 1 in having the ba.sal part of the lasso within the cell or
sheath strait and stout ; it is this part which makes the first
portion of the extended lasso. A view of part of the latter is
represented in figure 4, and of the extremity of the same in
(igure 5. The lasso-cells in the above species are from a 240th
to a 360th of an inch in length. In the Metridium margina-
tum^ an American Actinia occurring along the coast of the Uni-
ted States, north of New York, the length of one of the lasso-
cells, according to Dr. Leidy, was about a 400th of an inch,
and the character of the extended lasso was much like that of
figure 4. The lower part of the lasso, for a length 1^ times
or more longer than the cell or sheath, is usually thickened,
and sometimes slenderly spindle-shaped, while the rest is an
even slender thread ; and the thickened part and sometimes
all the rest, as above shown, is spirally wound by a slender
line, sometimes elevated, set with short hairs or bristles. The
thread-like portion may be wanting or very short. The lasso
is often twenty times as long as the cell or sheath, and occa-
sionally forty times ; but if the thread-like part is absent, only
one and a half to two times.

A lasso-cell once used is afterward worthless ; for the tube
cannot be returned to the sheath. But those thus expended
are not missed, as the polyp has indefinite supplies of such
weapons, and also ready means of refurnishing itself.

Figures 6, 7, 8, 9, 10, on the preceding page, illustrate
different stages in the development of a lasso-cell (fig. 10)

34 CORALS AND CORAL ISLANDS.

out of a common spherical cell, as made out by Dr. Mobius in
his careful microscopic investigations. The Actinia affording
the results was the Urticina crassicornis^ found in both Euro-
pean and American seas. The actual size of the cell represent-
ed in figure 6 is about a 5,000th of an inch. In fig. 7 the
lasso-cell has already taken form but is folded on itself; in 8,
there is a second infolding ; 9 shows a return to a single fold,
and further progress in the forming cell ; and 10, the straight-
ened lasso-cell. Thus the work of replenishing, throughout
the body wherever lassos are used, is always going on.

The radiating partitions or septa in the internal cavity
of the polyp have along the outer free edge what looks like a
slender white cord attached to it by a much convoluted or
mesentery-like membrane ; and this cord contains vast num-
bers of lasso-cells radiately arranged. These white cords
through the multiplied plaitings of the mesenteric membrane
have great length ; and they sometimes extend up through the
stomach and pass out of the mouth ; or they are extended in
loops through the walls wherever they may happen to be torn.

There are often also bunches of somewhat similar white cords
full of lasso-cells appended to the septa, which are extended
from the body through some natural orifices near the base of the
Actinia (especially those of the Sargartia family). Gosse calls
these cords Acontia. They extend out usually two or three
inches, and sometimes six inches, and thereby widen much the
stinging range of an Actinia, both for the purposes of defence
and attack.

Gosse, in his "British Sea- Anemones," gives the results of
some experiments with regard to the action of these lasso-cells
(cnidce)^ from which a few paragraphs may be here cited.

" It has long been known, that a very slight contact with
the tentacles of a polyp is sufficient to produce, in any minute

ACTINIA AND OTHER ACTINOID POLYPS. 35

animal so touched, torpor and speedy death. Since the discov-
ery of these cnidce (lasso-cells) the fatal power has been sup-
posed to be lodged in them. Baker, a century ago, in speak-
ing of the Hydra, suggested that "there must be something
eminently poisonous in its grasp ; " arid this suspicion received
confirmation from the circumstance that the JEntomost/raca
which are enveloped in a shelly covering frequently escape un-
hurt after having been seized. The stinging power possessed
by many MedusaB, which is sufficiently intense to be formida-
able even to man, has been reasonably attributed to the same
organs, which the microscope shows to be accumulated by mil-
lions in their tissues.

" Though I cannot reduce this presumption to actual cer-
tainty, I have made some experiments, which leave no reason-
able doubt on the subject. First — I have proved that the ecthor-
wum (tubular thread of the lasso-cell) when shot out, has the
power of penetrating, and does actually penetrate, the tissues
of even higher animals. Several years ago, I was examining
one of the purple acontia of Adamsia palliata ; no pressure
had been used, but a considerable number of cnidce had been
spontaneously dislodged. It happened that I had just before
been looking at the sucker-foot of an Asterina, which remained
still attached to the glass of the aquatic box, by means of its
terminal disk. The cilia of the acontium had, in their rowing
action, brought it into contact with the sucker, round which it
then continued slowly to revolve. The result I presently dis-
covered to be, that a considerable number of the cnidce had
shot their ecihorcea into the flesh of the sucking disk of the
Echinoderm, and were seen sticking all round its edge, the
wires (lassos) being embedded in its substance even up to the
very capsules, like so many pins stuck around a toilet pin-
cushion.

36 C0BAL8 AND CORAL ISLANDS.

" To test this power of penetration still farther, as well as
to try whether it is brought into exercise on the contact of a
foreign body with the living Anemone, I instituted the follow-
ing experiment. With a razor I took shavings of the cuticle
from the callous part of my own foot. One of these shavings
I presented to the tentacles of a ftilly expanded Tealia crassi-
cornis ( Urticina crassicornis of Europe and America). After
contact, and momentary adhesion, I withdrew the cuticle, and
examined it under a power of 600 diameters. I found, as I
had expected, cnidce standing up endwise, the wires in every
case shot into the substance. They were not numerous — in a
space of .01 inch square, I counted about a dozen. * * *

" These examples prove that the slightest contact with the
proper organs of the Anemone is sufficient to provoke the dis-
charge of the cnidce ; and that even the densest condition of
the human skin offers no impediment to the penetration of the
ecthorcea.

'' As to the injection of a poison, it is indubitable that pain,
and in some cases death, ensues even to vertebrate animals
from momentary contact with the capsuliferous organs of the
Zoophyta. * ^ * j have elsewhere recorded an instance
in which a little fish, swimming about in health and vigor,
died in a few minutes with great agony through the momen-
tary contact of its lip with one of the emitted acontia of Sor
gartia parasitica. It is worthy of observation, that, in this
case, the fish carried away a portion of the acontium sticking
to its lip ; the force with which it adhered being so great, that
the integrity of the tissues yielded first. The acontium severed,
rather than let go its hold.

" Now, in the experiments which I have detailed above, we
have seen that this adhesion is effected by the actual impene-
tration of the foreign body by a multitude of the ecthorcea^

AGTINIJE] AND OTHER AGTINOID POLYP 8, 37

whose barbs resist withdrawal. So that we can with certainty
associate the sudden and violent death of the little fish with
the intromission of barbed ecthoroear

The following observation by J. P. Couthouy, from the
author's Report on Zoophytes (p. 128), if it is beyond ques-
tion, shows power even in the Actinia's presence. '^ Having a
number of Monodontas (a genus of univalve Mollusca allied
to our Trochi) too much crowded in a large jar of water. I
took out half-a-dozen, and placed them in a jar with an Ac-
tinia {Anthea flagellifera). On looking at them about three
hours after, I found that, instead of climbing like the others
to the top of the water, they remained just where they had
fallen, closely withdrawn into their shells. Supposing them
to be dead, they were taken out, when they directly began to
emerge ; and when returned to the jar with the other Mono-
dontas, they were in less than five minutes clustered round
its mouth. On placing them again in the jar with the Ac-
tinia, though kept there for two hours, they did not once
show themselves out of the shell. Once more placing them
along witb the other shells, they exhibited their former signs of
life and activity. The experiment was repeated several times
with a large Littorina, with the same result, evincing fear of
the Actinia on the part of the MoUusks.*"

Gosse states the following fish story, which is much to the
point. Speaking of the Anthea cereus^ or Opelet, a British
species, he says (p. 168) : " I one day saw an amusing example
of its power of passive resistance. A beautiful little speci-
men of the variety alabast/i^ina^ which had been sent to me
by Mr. Gatehouse, I had occasion to remove from one tank
to another. There was a half-grown Bullhead {Cottus huhalis)
at the bottom, which had been in captivity rather more than
a fortnight. As he had not been fed during that time, I pre-

38 C0BAL8 AND COBAL ISLANDS.

sume he was somewhat sharp-set. He marked the Anthea
falling, and before it could reach the bottom, opened his cav-
ern of a mouth and sucked in the bonne houche. It was not
to his taste, however, for as instantly he shot it out again. Not
discouraged, he returned to the attack, and once more sucked
it in, but with no better success ; for, after a moment's rolling
of the morsel around his mouth, out it shot otice more ; and
now the Bullhead, acknowledging his master, turned tail, and
darted into a hole on the opposite side of the tank in manifest
discomfiture."

He adds : " But if you, my gentle reader, be disposed for
exploits in gastronomy, do not be alarmed at the Bullhead's
failure : only take the precaution to " cook your hare." Kisso
calls this species " edIitZis," and says of it, — " On le mange en
friture^'^ and I can say, ^^prohatum esV No squeamishness
of stomach prevents our volatile friends, the French, from
appreciating its excellence; for the dish called Rastegna^
which is a great favorite in Provence, is mainly prepared from
Anthea cereus, I would not dare to say that an Opelet is as
good as an Omelet; but chacun a son gout — ^try for your-
selves. The dish is readily achieved."

The stomach, although without a proper sphincter muscle
at its inner extremity, appears to be closed below during the
process of digestion. When digestion is complete, the refuse
from the food is pushed out through the mouth, the only ex-
ternal opening to the alimentary cavity, and the digested ma-
terial passes downward, into the interior cavity ; and there,
mixed with sea- water from without, it is distributed through
all the interior cavities of the polyp for its nutrition. The
polyp has no circulating fluid but the results of digestion
mixed with salt water, no blood-vessels but the vacuities among
the tissues, and no passage-way for excrements excepting the

AGTINIJEJ AND OTHER AGTINOID POLYPS. 39

mouth and the pores of the body that serve for the escape of
water on the contraction of the animal.

Actiniae have usually no gills or branchice for the aeration
of the blood, the whole surface of the body being ordinarily
sufficiently soft and delicate to serve in this function. Some spe-
cies live half buried in the sand, and, as this in large species
would prevent the skin of the sides from aiding in respiration,
there are sometimes very much lobed and crimpled organs,
attached to, or alongside of, the tentacles, which give the an-
imal-flower much greater beauty, and at the same time increase
the extent of surface for the purposes of asration ; they are
set down as branchial by Prof Verrill.

In one tribe of polyps closely related to the Actiniae, the
Zoanthids, in which the outer skin is usually somewhat cor-
riaceous, or is filled with grains of sand, there are narrow gills
arranged vertically, one either side of the larger radiating sep-
ta, figures of which are given in the author's Zoophyte Atlas.

As to senses^ Actiniae, or the best of them, are not quite
as low as was once supposed. For, besides the general sense
of feeling, some of them have a series of eyes, placed like a neck-
lace around the body, just outside of the tentacles. The yel-
low prominences in this position on the larger figures in the
frontispiece are these eyes. They have crystalline lenses, and
a short optic nerve. Yet Actiniae are not known to have a
proper nervous system : their optic nerves, where they exist,
are apparently isolated, and not connected with a nervous
ring such as exists in the higher Radiate animals.

Reproduction is carried forward both by ova and by buds,
though the latter method is mostly confined to the coral-mak-
ing polyps.

The ovarian and spermatic functions belong to the radia-
ting septa in the interior cavity of the Actinia, and to the part

40 CORALS AND CORAL ISLANDS

of a septum, mesenteric in character, at or near the outer mar-
gin. They have the aspect of a pulpy mass, or look like clus-
ters of ovules. The ova have no chance for escape except
through the stomach and mouth. They are covered with vi-
bratile cilia, and rove about free for a while. As the develop-
ment of the embryo goes forward, a depression begins at one
end, which deepens and becomes a stomach, with the entrance
to it as a mouth. Concurrently, septa grow out from the inner
wall, and a few tentacles commence to rise around the mouth.
Not unfrequently, the young has already some of its tentacles
before it leaves the parent. There is at first but a single row
of tentacles ; the number increases with the size until the full
adult limit is reached, the newer series being successively the
outer.

In the budding process, which is of rare occurrence. Acti-
niae grow young ones on their sides near the margin of the
base. A protuberance begins to rise and soon shows a mouth,
and then becomes surrounded by tentacles ; and, thus begun,
the new Actinia continues to grow, usually until its tentacles
have doubled their number, when finally it separates from the
parent, an independent animal. At times, as Prof. H. James
Clark has observed, small pieces of the base of an Actinia sep-
arate by a natural process before a trace of a tentacle has ap-
peared, and in this case " they do not at first show any signs
of activity, but on the contrary, remain for a long time in a
quiet state, having the appearance of artificially separated
pieces, seeming to be undergoing, as in the latter, a recupera-
tive process after the shock of a separation." After a while
they commence to develop and grow into perfect individuals.
Prof Verrill mentions the case of an Actinia from Puget's
Sound {the JEJpiactis prolif era, V.) which had three rows of
young individuals attached to it around the middle of itJi

L

CORAL-MAKING ACTINOID POLYPS, 41

body ; but whether the young Actiniae were produced by bud-
ding from this part of the body, or whether they had colonized
there after being produced in the ordinary way, he was un-
able to determine. In all cases the young ultimately sepa-
rate from the parent.

These polyps have also the faculty of reproducing lost
parts ; and to such an extent that a mere fragment, if it be
from the lower part and include a portion of the base, will re-
produce all the rest of the Actinia, even to the disk, tentacles
and stomach. Thus the mere forcible tearing of an Actinia
from the rock to which it is attached may result in starting a
crop of new Actiniae.

Although Actiniae have no internal coral secretions, they
sometimes make a thickened epidermic plate at the base, and
also in a few cases around a part of the body. This is how-
ever not a result simply of an epidermic secretion, but arises
from an exudation of mucus from the surface, and the entan-
gling thereb}^ of minute particles of foreign or dead matters.
A case of the kind, in an Edwardsia where the body is thus<^
encased, is mentioned and explained on page 25,

The above are the more prominent characters of the Actin-
ia tribe of polyps. The special features distinguishing them
from the coral-making polyps are the following: (1), They are
simple animals, or, if they bud, the buds early separate from
the parent ; (2), They have a muscular base ; (3), They are gen-
erally capable, more or less perfectly, of locomotion on the base
by means of its muscles ; (4), They sometimes possess rudimen-
tary eyes ; (5), They have no internal coral secretions. Each
of these characters is evidence of the superior grade of this di-
vision of Polyps.

42

CORALS AND CORAL ISLANDS.

II. CORAL-MAKIjSG ACTINOID POLYPS.

Of the form, tentacles, mouth, stomach, fleshy septa, lasso-
cells, food, digestion and respiration of the coral-making polyps
here included, nothing need here be said, these characters being
the same as in the Actiniae. Their more striking peculiarities
depend on the secretion of coral, making them fixed species,
and involving an absence of the base ; and, in the case of the
majority of the species, on the extent to which they multiply
by buds, in imitation of species in the vegetable kingdom.

The coral skeleton which the secretions of polyps form is
called the corallum. These secretions take place among the tis-

CARYOPHYLLIA CYATHUS.

sues of the sides and lower part of the polyp, but never in the
disk or stomach, as this would interfere with the functions of
these organs. In the above sketches of a simple coral,
from the Mediterranean, the upper extremity is a depression,
or calicle^ enclosed by a series of radiating calcareous (coral)

CORAL-MAKINQ POLYPS. 43

septa. Each of these septa is secreted between a pair of the
radiating fleshy partitions, or septa, of the polyp (see figure
p, 27); and thus the radiate structure of ordinary corals is
nothing but an expression of the internally radiate structure
of the polyp. When alive, the top, and usually the sides, of
the coral were concealed by the outer skin of the polyp, in-
cluding, above, the disk and tentacles ; and into the depression
or calicle at top, descended the stomach.

Whether these radiating septa of the coral are secreted
from the surfaces of the fleshy septa, or from a prolongation
inward of the membrane forming the walls of the internal
cavity, has not been directly ascertainea. The latter view is
sustained by Prof. Verrill, on the ground that the coral
septa contain fibres of animal tissue. The secretion does not
always commence at the central plane of a septum, for the
septa are sometimes hollow within, just as the surface spines
of some species {e. ^., McJiinopora rejlexa) are hollow. The

THECOCYATHUS CYLINDRACEUS ; FLABELLUM PAVONINUM.

exterior surface of the corallum, that is, the part outside of
the calicles, is often ribbed, and the ribs are ordinarily only
an outer extension of the interior septa; so that surface
spines are in fact but the outer margins of septa.

The first of the preceding figures exhibits another of the
forms of these simple corals. It is described by Pourtales

44 GOBALS AND GOBAL ISLANDS.

from specimens collected by him at a depth of 100 to 200
fathoms off the Florida reef. The actual size was one-third
that of the figure. The second figure represents a living
species.

The bottom of the calicle^ or polyp-cell, in the corallum is
sometimes made simply by the meeting of the radiating sep-
ta; occasionally by the same, with the addition of a point
or columella at the centre ; often by a twisting together of
this part of the radiated septa. Very often, also, it is a mere
porous mass. Sometimes there is a circle of prominent points
about the centre, as seen in the figure of a Caryophyllia on
page 42, which are the extremities of narrow vertical strips
(called pall) lying in the planes of the septa. Similar points
exist in the Thecocyathus on the preceding page, though not
in sight in the figure.

In many cases the bottom is quite solid ; and this may be
so either (1), because the coral secretions fill up all the pores
as the polyp increases in age, and thus make the inte-
rior of the corallum solid or nearly so ; or (2), because there are
formed periodically, as the polyp grows upward, solid horizon-
tal plates across the bottom, so that beneath, in the interior of
the corallum, there is a series of plates or tables with spaces
between. The Pocilloporae, among recent corals (p. 70), and the
Favosites among ancient, are examples. Increasing solidity
with the increasing age of the polyps is also produced at
times by additions to the exterior of a corallum. In many
species, the skin, over part or all of the exterior, gradually
disappears or dies away and leaves the corallum bare, while
all is living within ; and, in such cases, the skin, before disap-
pearing, often adds a layer of stony material to the exterior,
giving greater firmness to the whole. An example is shown
in the figure on p. 41. In such a case, there is no skin or

COBAL-MAKINQ POLYPS. 45

animal tissue over the outside of the corallum, excepting at
its upper extremity, above this calcareous coating.

Another form of a corallum, the secretion of a single
polyp, is illustrated in the following figure of a species of the
Fungia family, so-called in allusion to a resemblance to the
mushroom. The long mouth occupied a considerable part of
the longitudinal central line. From the line at the centre,

CTENACTIS ECHINATA.

there is the same radiated arrangement of calcareous septa
as in the preceding species, though the animal differs greatly
in its extreme shortness in proportion to the breadth. The
corals of this group are also peculiar in having the radiated
upper surface flat, or nearly so, instead of concave. The fig-
ure is a fourth the natural size. These corals, of the genus
Fungia, often exceed a foot in length ; and thus coral animals
are sometimes as large as the largest of Actiniae.

Another species of this genus, the Fungia lacera V. (for-
merly Fungia echinata D., from the Feejees), is represented as it
appears when living (excepting a part left off to suit the page)
in the following figure. The coral in the perfect state of the an-
imal, is wholly concealed, though often showing the points of the
teeth of the septa in consequence of the skin being broken.

^^ COJIALS AWD CORAL ISLANDS.

An enlarged view of one of the tentacles is given on the

FUNGIA LACKRA, V.

opposite page. They are very small, compared with the size of

COBAL-MAKINQ POLYPS, 47

the polyp ; and this is true of all the living Fungiae studied
by the author. It is plain that the power of such tentacles
must reside wholly in their lasso-cells.

TENTACLE OF FUNGIA LACBBA.

The tentacles are scattered over the disk, instead of being
in regular circles. It is evident, from the figure, that the ap-
parent circles, where there is more than one, in Actiniae,
arise from the crowding of the series of tentacles together ;
and also that the inner row of tentacles in polyps is the older.
It will be noticed also that each of the tentacles stands where
a new ridge (or calcareous septum in the coral) begins.

The Fungise, unlike most corals, are not fixed animals
except in the young state. They are common in coral-reef
seas, lying over the sandy or rocky bottom between the other
corals.

Other varieties of corals and coral animals are illustrated
in the figures on the following pages. They represent com-
pound groups^ in which great numbers of polyps are con-
nected in a single zoophyte — a result, in part, of the process
of budding already alluded to, and partly of different modes
of growth connected therewith.

This budding is very similar to the budding process in
vegetation. One common method is the same that is occa-
sionally met with in Actiniae, the description of which is
briefly given on page 40. The bud commences as a slight

48 CORALS AND COMAL ISLANDS.

prominence on the side of the parent. The prominence en-
larges, a mouth opens, a circle of tentacles grows out around
it, and increase continues till the young finally equals the
parent in size. Since in these species the young does not
separate from the parent, this budding produces a compound
group ; and the process often continues until in some instances
thousands, or hundreds of thousands, have proceeded from a
single germ, and the colony has increased to a large size,
sometimes many feet, or even yards, in breadth or height
Such is the species of Dendrophyllia represented in the fig-
ure on page 51, and the Madrepora figured on page 50 ; in
both of which, and in all such coral zoophytes, each stellate
cavity or prominence over the surface corresponds to a sepa-
rate one of the united polyps.

The compound mass produced by budding — which con-
sists of the united polyps with the corallum as their united
secretion — was called in the Author's Report, a Zoophyte, it
being truly animal in nature, though under a plant-like form
through the plant-like process of budding. But the word to
many minds conveys the idea that the species is something
between a plant and an animal, which is totally false ; and
besides, it is often used distinctively for the division of ani-
mals including the sponges. As a substitute the term Zoo-
thome may be employed, derived from the Greek ^oov, ani-
mal^ and Oiofiog^ a heap — a term applicable also to compound
groups in other classes, as, for example, those of Ehizopods,
Bryozoans and Ascidians. The term zoophyte, where employ-
ed beyond, signifies a zoothome formed of united polyps, or a
polyp-zobihome. The coral of the zoothome being the coral-
lurrij that of each polyp in the compound corallum may be
called a corallet — the term calicle^ formerly used by the
author for the same, being now restricted to the polyp-cell.

CORAL-MAKING POLYPS. 49

It is obvious that the connection of the polyps in all com-
pound groups must be of the most intimate kind. The sever-
al polyps have separate mouths and tentacles, and separate
stomachs ; but beyond this there is no individual property.
They coalesce, or are one, by intervening tissues ; and there is
a free circulation of fluids through the many pores or lacunes.
The zoothome is like a living sheet of animal matter, fed and
nourished by numerous mouths and as many stomachs.

Polyps thus clustered, constitute the greater part of the
flowering zoophytes of coral reefs. Onl}^ a few are simple
animals, like the Caryophyllia figured on page 42, or the
Thecocyathus, page 43, or the Fungia, page 46.

This kind of budding riiay take place from the sides of the
polyp at diiferent heights ; either (1), from the base, as in the
Actinia mentioned on page 40, when it is hasal ; or (2), above
the base, when it is called lateral ; or (3), at the upper mar-
gin outside of the tentacles, when it is called marginal or ^^^.
perior ; or (4), from the disk inside of the tentacles.

Sometimes a shoot grows out from one point only of the
base of a polyp, like the stoloniferous stem from a strawberry
plant, and at short intervals gives off buds ; and thus makes a
linear zoophyte with a row above of flower-animals. In other
cases, the base spreads in all directions and buds at the edge,
or in the upper surface near the edge, and so makes an in-
crusting plate, consisting of a multitude of polyps.

If the germ polyp, or that from which the compound zoo-
phyte proceeds, has the property of growing upward beyond
the adult height — which the existence of coral renders a possi-
bilit}^, and even to an indefinite degree — ^various other forms
may result.

Sometimes the first polyp gives out buds from its sides,
and continues so to do whoe it grows upward; and thus a

50 CORALS AND CORAL ISLANDS.

rising stem is formed with one parent polyp at the extremity
of the stem, and a terminal corallet to the corallum, or to each
branch of it. This is the case in the genus Madrepora, a

MADREPORA ASPERA, D.

species of which is here represented. Each branch in the
living state had at its extremity the parent polyp of the
branch, or that whose budding made the other polyps of the
branch. In such species, a new lateral branch is commenced
by one, among the many polyps over the surface of a branch,
beginning to grow and bud. Thus branch after branch is
added, and the little tree produced.

Another kind of coral, growing and budding in the same
manner, is represented on page 51. It is a species of Dendro-
phyllia, from the Teejees — a genus often presenting tree-like
forms, as the name implies.

In other cases, budding goes on until a cluster of some size

CORAL-MAKING POLYPS, 51

is formed, and then the older or marginal polyps of the cluster

DENDKOPHYLLIA NIGRB8CENS, D.

cease budding while the rest continue the process ; in this way

52 CORALS AND VORAL ISLANDS.

a stem rises, with the budding cluster of polyps at its summit,
and the more aged, or non-budding polyps, about its sides ; and
the breadth of the stem depends on the size of the budding

GONTOPORA COLITMKA, D.

cluster. Above a case of this kind is represented, in which
the stem is a large column.

The polyps, in this beautiful Pacific species, as seen, stand
up prominently over the coral when expanded, which is due

CORAL-MAKING AGTINOID POLYPS.

53

to the fact that only the lower parts of the polyp secrete coral^
as a moment's consideration will make apparent.

In other cases, the budding cluster is small, and hence

PORITES MORDAX, D.

makes small branches, as in the annexed figure of a species of
Porites, fi-om the Feejees. The cells in this genus are very
small and nearly or quite superficial, as the figure shows.

54 CORALS AND (JOIIAL ISLANDS.

New branches are made in such species by a forking of an
old one. The budding cluster enlarges as it grows, and, when
it is just beginning to pass the regular or normal size for the
species, a subdivision of the budding cluster commences at the
extremity of the branch. It is a process of spontaneous fis-
sion of a branch or stem. In this way the forking in the coral
of the figure on page 52 was produced, and also the branching
in that on page 53.

Sometimes, again, the budding cluster is a linear series ;
and then a coral with erect, flattened or lamellar branches is
made.

Again, sometimes each branch of the corallum is only
the corallet of a single polyp ; and new branches are added by
the budding of new polyps from its sides, each to lengthen out
into a new branchlet. In this manner the coral here figured,

CLADOCORA AKBUSCULA.

%id many like it, were grown. It is a common species of the
West Indies.

When the budding is not confined to any particular polyp,
or cluster of polyps, but takes place universally through the
growing mass, the coral formed is more or less nearlv hemi-
spherical ; and often the process goes on with such extreme

aORAL-MAKINQ AOTINOID POLYPS. 55

regularity that these hemispheres are perfectly symmetrical,
even when enlarged to a diameter of ten or fifteen feet. A
portion of the surface of one of these massive species, called
Orhicella cavernosa^ fi'om the West Indies, is represented in
the annexed figure. In the growth of these hemispheres, the
enlargement takes place in the spaces between the polyps ; and

ORBICELLA CAVERNOSA.

whenever these spaces begin to exceed the width usual to the
species, a new mouth opens, commencing a new polyp ; and
thus the growth of the mass involves multiplication by buds.
The small calicle near the centre of the figure is from one of
the new interstitial buds.

Species of Porites also grow into hemispheres and rude hil-
lock-like forms, through the same method of budding, and
some of the masses in the tropical Pacific have a diameter of
even twenty feet. Myriads of living polyps are combined in a
single such mass, for each is but a fifteenth or a twentieth of an
inch in diameter.

Often there is a lateral growth of the polyp and thereby of
the zoophyte without much upward growth; and spreading
leaves are thus made, and bowUike shapes. Where there is
lateral budding, the leaves have generally an edge of young,
polyps from the new buds that are there opening, as in the

56 CORALS AND CORAL ISLANDS.

Gemmipores, and some foliaceous Madrepores ; where there is
superior budding, and sometimes in the case of inferior, the
new polyps appear some distance from the edge, the growing
margin spreading on in advance of the buds that open in it,
as in the Echinopores.

Besides the method of budding explained in the above re-
marks, there is also a kind of superior budding called sponta-
neons fission^ which consists in a spontaneous subdivision of a
polyp, by which two are made out of one. In such cases the
disk of the polyp has not a distinct limit of growth, as in the
above, but tends to enlarge indefinitely ; and when there is a
beginning of an increase beyond the proper adult size, a new
mouth opens in the disk, a short distance from the old one, and
at the same time its edges extend downward and make a new
stomach beneath it ; finally tentacles are developed between
the two mouths, and then each polyp separates with its part of
the old tentacles as illustrated in the following figure. It is not

SPONTANEOUS FISSION IN POLYPS.

as is seen, a subdivision strictly into halves, as one carries ofi'
the old mouth and stomach. The figure to the left represents
a polyp of the Astr^a tribe, with already two mouths, throuo-b
a commencement of the process of subdivision. In the next
figure there are tentacles between the two mouths, so that each

CORAL-MAKING AUTINOIB POLYPS. 57

mouth has its own circle ; and in the third, the separation has
gone so far as to complete the circles and make two independ-
ent polyps. This dividing one's self in two, for the sake of an
increase of population, is the process called spontaneous fis-
sion or fissiparity.

This mode of budding does not belong exclusively to coral
polyps, for it has been observed among a few ActinioB. Gosse
describes its occurrence in a British species, the Anthea cereus^
in which it results in two distinct animals. He says "the
fission begins at the margin of the disk, and gradually extends
downward until the separation is complete, when each moiety
soon closes and forms a perfect animal." The same author al-
ludes to the occurrence of double-disked individuals of the gen-
era Actinoloba, and Actinia as illustrating the process without
a separation of the spontaneously developed pair.

This spontaneous fission is the common kind of budding
in the large Astraea tribe.

ASTKiBA PALLIDA, D.

The preceding figure represents a species of living coral of
the Astraea family, from the Feejees, the Astrcea pallida D,

58 CORALS AND CORAL ISLANDS.

which grew, and multiplied its polyps as it grew, by this meth-
od. In such species some of the disks of the polyps will be
found to have two mouths. This is the first step in the pro-
cess. In others, the two mouths will be found to be partly
divided from one another by new-formed tentacles ; and finally
eadi will have its own circle complete and all else in polyp
perfection.

Many of the Astraea hemispheres of the Pacific, grown by
this method, have a diameter of ten to fifteen feet.

In other Astraea-like species, this spontaneous fission ends
in a complete separation of the two polyps formed ; and conse-
quently in a forking of an old branch. The figure annexed,
of a CaulastraBa, from the Feejees, illustrates this mode of

CAULASTB2BA FURCATA, D.

branching. In the left hand polyp there are already two
mouths, and the work of subdivision is consequently begun ;
while in those to the right, which have a single mouth, the
subdivision has just been completed, and also the forking of

COBAL-MAKINQ AGTINOID POLYPS. 59

the old branch. Thus spontaneous fission goes forward, and
branches accordingly multiply. By this method some of the
most magnificent clumps of coral zoophytes found in tropical
seas have been, and are being, developed each from a single germ.
Many of them have the perfect hemispherical symmetry of the
solid Astraeas.

Sometimes, when a new mouth forms in an enlarging disk,
there is not at once a separation of the two, but the disk con-
tinues to enlarge in one direction and another, and then another
mouth opens, and so on until a string of mouths exists in one
elongated disk ; and finally, a separation occurs, but only to
commence or carry forward another long series. In this way
the corals with maeandrine furrows are made, some kinds of
which are popularly called Brain coral, and pertain to the
Meandrina family (figure on page 65). The same may take place
in the ramose corals, and so make flat branches, each with a
long sinuous line of polyp mouths at top. In all such species
the tentacles stand in a line either side of the line of mouths.

By the simple methods here explained all of the various
forms of Actinoid zoophytes have been produced ; and, equally
so, those of the Alcyonoids described beyond. The tree, shrub,
clusters of coral leaves, hemispheres, and coral net- work re-
quire for the explanation of their origin only the few principles
which have been mentioned. The germ-polyp, growing uj)-
ward and more or less outward, and budding as it grows,
makes thus the rising stem — that of the Madrepore or Den-
drophyllia, with its summit polyp (figures p. 50, 51), or that of
the Porites, with its terminal budding clusters (p. 53) ; or the
rising, massive dome of the Astraea and Maeandrina (pp. 57,
65), in case budding is symmetrical in all directions ; — or, if
growth in the germ-polyp is upward exclusively, it forms a ris-
ing stem bearing at top the single polyp that originated it, or

60 CORALS AND CORAL ISLANDS,

crowded clusters of such stems branching variously and having
each branch surmounted with its one polyp (figure p. 54) ; or, if
there is lateral growth and but little of upward, it produces
leaf-like forms and gracefiil groups or clusters of leaves, vases,
and other shapes ; or, if the germ-polyp is capable of lateral
growth alone, the results are simple lines of polyps creeping
over the supporting rock, like the creeping stolons of a plant,
or else encrusting plates, spreading outward like a lichen.

In the descriptions of corals the following terms have the significa-
tions annexed. Those already mentioned are here repeated to bring
them all together.

Zoothome. — The compound animal mass produced by budding.

Corallum, — The coral either of the compound mass, or of the solitary
polyp.

Corallet (In Latin, corallulum). — The coral of a single polyp in a com-
pound corallum.

Calicle, — The polyp cell in the top of a corallet, or of a solitary
corallum, within the walls of the cells ; it is sometimes flat at top, that is,
without the usual depression.

Septa, — The radiated plates of the cell or calicle.

Dissepiments, — Small cross plates between adjoining septa (sometimes
wanting).

SynapticuloB, — ^Minute cross bars uniting the surfaces of adjoining
septa.

Ccenenchyma, — The common mass of the corallum between its dif-
ferent polyp cells or corallets, as in the Madreporae, GemmiporsB and
Dendrophylliae.

Epitheca, — The coral layer sometimes deposited over the exterior of
the corallum during the life of the polyp by the outer skin before it dries
away, as explained on page 44.

Peritheca, — The epitheca of a compound group or zoothome (fig. p. 71).

Mcotheca, — The portion of the corallum outside of the walls of cells
in paany coralla of the Astrsea family, and some others, in which the polyps
of the mass are properly in contact, and there is consequently no true
ccBnenchyma.

Endotheca, — ^The portion of the corallum inside of the walls of the ceU,

We may now state briefly the characteristics of the
grander divisions of the Actinoid polyps, several of which
have been illustrated in the preceding figures.

SUBDIVISIOirS OF AGTINOID POLYPS, 61

The tribes adopted are those recognized by Prof. Verrill,
and have the limits he has assigned to them. The classification
diverges from his system in uniting the non-coral-making
and coral-making species into one grand division, that of the
Actinoids (on the ground of the close resemblance of the
polyps), and also in separating from the latter the Cyatho-
phylloid corals, for the reasons mentioned on page 21. Some
of the figures of corals on former pages are here repeated in
order to present together those of like relations.

1. Species without internal Coral Secretions* Actinaria of

Verrill.

1. Th^ Actinia trihe^ or Actinacea, secrete no coral inter-
nally, and moreover have a muscular base, with some degree
of locomotion by means of it The Actiniae of the frontis-
piece, and of pages 23, 26, are examples.

2. The Zoanthus tribe^ or Zoanthaoea. The species here
included are like the Actiniae in secreting no coral. But while
they have a base, it is not muscular, and they are never capable
of locomotion. The polyps have a thick or somewhat leath-
ery exterior, and, as already observed (p. 39), have gills, or
branchiae. Some of the species are solitary polyps ; but
generally they form compound masses or zoothomes,
by budding; sometimes making simple lines of polyps
over a supporting surface ; at other times incrusting plates,
or irregular masses. The following figure (from Verrill)
represents a species found in American seas oflF the coast of
New Jersey, in deep water, and also in Massachusetts Bay,
which has a habit of fixing on a shell for its support and of
always taking one containing a soldier crab. The shell
finally becomes dissolved away — ^how, it is not known, by

62 CORALS AND CORAL ISLANDS.

the growing Zoanthid ; but the crab holds on to its house
although at the expense of transporting wherever it goes a

EPTZOANTHUS AMI5RICANUS, V., WITH BUPAGURU8 P0BESCENS, St.

colony of flowering polyps. The polyps are but partly ex-
panded in figure 1, and wholly so in figure 2.

The animals of the Zoanthus tribe have broad, radiated
disks, with an edging of short tentacles, in one or more
rows. Although not secreting coral, the mucus of the sur-
face in some of the species entangles the sand that falls
on it, and thus gives a degree of firmness to the mass of the
zoophyte.

3. The Antipathus trihe^ or Antipathaoea. In this tribe
the polyps never have locomotion, and, as far as known, al-
ways produce compound groups by budding. These groups
have the forms of delicate shrubs and long twigs ; and some of
them are three feet or more in height. The branches consist of
a homy axis, usually spiny or hispid over its surface, surrounded
by an animal coating, which is made up of united polyps. An
example is shown in the following figure of a living species
from the Feejees. A view of one of the polyps, much enlarged, is
given in the following figure. Its tentacles are closely like
those of the Actinia. The height of the entire shrub, collected
by the author, was three feet, and the trunk at base was
half an inch thick. The polyps had a brownish-yellow color,
not particularly beautiful, and the tentacles were in general, as

SUBDIVISIONS OF AGTINOID POLYPS 63

in another species described by the author, rather awkwardly

iLNTIPATHES ARBOREA, D.

handled by the polyp. The number is commonly six ; but
in one genus, Gerardia, it is as great as twenty-four.

POLYP OF A. ARBOREA, MUCH ENLARGED.

64 CORALS AND CORAL ISLANDS.

2. Polyps having internal calca/reous secretions. Madbepo-
RARiA of Verrill. {The Cyathophylloid species eoo
chided. )

4. Asl/roea trihe^ or Astr^acea. — In this tribe the polyp-
cells or calicles are distinctly lamello-radiate within, and gen-
erally so outside. Moreover, budding is always by division
of the disks, or spontaneous fission. The figure of the Cau-
lastraea, on page 58, illustrates one section of this family, that
in which each branch of the corallum is made by a single
polyp, and branching is by furcation through spontaneous fis-
sion. In other related genera, as Mussa, the polyps sometimes
have a diameter of two inches, being as large as ordinary
Actiniae.

ASTRiSJA PALLIDA, D.

The Astrcea pallida is a good representative of the massive
Astraeas. The color of the polyps in this species is quite pale,
the disks being bluish-gray, and the tentacles whitish. In oth-
ers, the tentacles are emerald-green, or deep purple, or of other
shades.

SUBDIVISIOI^a OF AQTINOID POLYPS.

65

Another range of forms is represented by the following
figure of one of the Meandrine corals, already referred to as
often called '' Brain coral." In the figure, the coral is re-
duced one-half lineally. The difference between its mode of
formation and that of an Astraea, has been stated on page 59.
This species is common at the Bermudas, where it grows to a
diameter of three feet. It is also found in the West Indies. The
ridges in this species are double, and hence the nsLme I)iplo7na^

DIPLORIA CEREBHIFORMIS, E. AND H.

from the Greek for double. A common large West India
species of Brain coral is called Meandrina labyrinthica. It is
readily distinguished from the Diploria by the ridges between
the furrows, these being simple and triangular.

Still other forms of the Astrasa tribe are foliaceous, or such

as would result if the growing margin of an Astraea, or of a

Meandrina, were to spread out into folia instead of thickening

upward in the ordinary way. The groups of gracefully curv

5

66 00RAL8 AND CORAL I8LANDR

ing leaves thus made are sometimes very large and sym-
metrical.

2. Fungia trihe^ or Fukgaoea. — ^The general character
of the simple species of this tribe is mentioned on page 45, and
the character of the living Fungia, with its tentacles, is shown
in the figure of a Feejee species on page 46. Large, com
pound groups, both massive and foliaceous, are formed by
budding, and the budding is always superior. There are
no margins to the disk in this tribe, and in the corallum
of the compound kinds no wall or partition between the ad-
jacent stars, and no walls to adjoining polyps, or only im-
perfect ones. The polyps consequently coalesce throughout
by their disks. The simple Fungise are attached when young,

FUNOTA DANiB, E. & H., KBDUCBD TO ONE-SIXTH LimffiALLY; «, 6, TEETTt OF UPPKH
AND LOWER MABGINS OF SEPTUM, NATURAL SIZE.

and then would hardly be distinguished from a simple or
solitary species of the Astraea tribe.

3, Oculina trihe^ or Oculikacea. — These species occur
either simple or compound, and the latter are often branched,
massive, or encrusting, never thin, foliaceous. Budding is
either superior, lateral, or basal ; never by spontaneous fission.
The coralla are remarkable for the solid walls and lamellas
of the cells ; and often for having the ccBnenchyma nearly or

SUBDIVISIONS OF AGTINOID POLYPS, 67

quite solid. Transverse septa between the lamellae are some-
times wanting. The calicles are usually striated externally
but seldom dentate. The polyps, moreover, are small ; and
very commonly they stand prominent above the corallum when
expanded. The Orbicella, figured on page 55, is an example
of one, of the massive Astraea-like forms, constituting the Or-
bicella family, or OrhicelUdce^ in the Oculina tribe.

The Caryophyllia here figured is one of the solitary species

CAKYOPHTLLIA SMITHII, STOKBS.

of the tribe found in European Seas, and on the coast of
Great Britain. The figure is from Gosse's British Actinology.
It also grows much longer in proportion to the breadth. The
figure to the right is of one unexpanded. One of its lasso-
cells, in different states, is shown in figures 3, 4, 5, on page 81.

The corallum of a related species, Oaryophyllia cyaihus^
is given on page 42. The walls and septa are remarkably
solid. The Oaryophyllia flavus hdi.^ been found not only in
the Mediterranean, but also as far north as the British Isles,
and in the Florida Straits.

Another example of this tribe, as defined by Prof. Verrill,
is the species of Astrangia occurring alive along the southern
shores of New England, and on the coast of New Jersey.
Specimens are not uncommon in the vicinity of New Haven,
on the rocks by the Light-House, and at other places in Long
Island Sound, and when alive it is an exceedingly beautiful

68 CORALS AND COMAL ISLANDS.

object The accompanying figures of the animal are from the
drawings made to illustrate a yet unpublished memoir by
Prof. Agassiz. They are copied from the " Sea-Side Studies "
of Mrs. Agassiz and Alexander Agassiz. In fig. c, the polyps
are of the natural size, while fig. a represents one of them en-
larged. The polyps, as is observed, stand very projninent
above the cells of the corallum, because only the bases of
them secrete coral ; and the buds, which open between the
calicles, are hence lateral buds; the coral has much resem-
blance to that of an Orbicella, in which budding is margin-

A6TBAKGIA DAN^, AO.

al. The tentacles have minute warty prominences over
them, which are full of lasso-cells, each about a 500th of an
inch in length, or about two-thirds larger than those of the
white cords that edge the internal septa. The corallum,
though massive, is somewhat irregularly lobed above, and
grows to a diameter of two or three inches. It is covered
with stars an eighth of an inch to a sixth across (fig. J), which
are usually crowded together, the intervening wall being very
thin and solid. The author alluded to the crowd of stars in
the name Pleiadia, which he proposed for the genus in his
Report on Zoophytes (p. 722).

The genus Cladocora, containing slenderly branching ra-

SUBDIVISIONS OF ACTINOID POLYPS. 69

mose zoophytes, is closely related in its polyps, according to
Prof. Vemll, to the Astrangiaa, and belongs to that family.
Its cylindrical stems are gathered into crowded clumps. The
C. arhuecula is figured on page 54.

PHYLLANGTA AMERICANA, E. & H.

A West India species of another genus of the group, the
Phyllangia Americana^ is represented in the annexed figure.

In the following cut, figure 1 represents the extremity of a
branch of an Oculina, the 0. varicosa^ of the family OcuUnidw.

CORALS OF THE OCULINA TRIBK.

The species of this genus grow in clumps of round branches,
and have very solid coralla, so white and firm when bleached

70 CORALS AND CORAL ISLANDS,%

as to go by the popular name of '' white coral," and to be some-
times polished for beads and other such ornamental purposes.

Figure 2 is a branch of a beautiful little coral called Sty-
laster ervhescens Pourt., and 3, a portion of the same enlarged.
It has the firmness, and something of the habit of an Oculina,
but is rather like a miniature Oculina, its calicles never exceed-
ing a twentieth of an inch in breadth. There are a number of
genera in this Stylaster family, the Stylasteridce^ and the corals
are among the most delicate of species.

Figure 4, in the same cut, represents aportion of a branch of
the Stylophora Danced, and H. The corals of the genus are
remarkable for their small, crowded calicles, and for the very
distinct six-raj^ed star in each calicle (as shown magnified in
figure 5), and usually have a prominent point or columella at
the centre of the star. The polyp of a Feejee species, S,
mordax^ is represented in figure 6. The name of the family,
Stylophoridoe (signifying style-bearer), alludes to this colu-
mella. The corals grow in regular hemispherical clumps con-
sisting of flattened or rounded branches, and are sometimes a
foot or more across.

In another family under this tribe, the Pocilliporicke^ very
common in coral-reef seas, the cells of the corallum are always
very small and crowded, as shown in figure 7. The corals are
branching, and in Pocillipora, the surface is often irregular and
warty, the little prominences, like the rest, being covered with
poljrp cells ; while in Seriatopora, the branches are slender,
even, and pointed. The corallum in both is very firm and sol-
id. In the larger part of them the number of tentacles is only
twelve, and formerly they were referred on this account to the
Madrepore tribe ; a few have as many as twenty-four tenta-
cles.

The PocilliporaB form hemispherical clumps like the Stylo-

SUBDIVISIONS OF AGTINOID POLYPS. 71

phoraB ; and the branches vary from the flattened and broad
form shown in figure 7 (which represents the upper part of
a branch of the P. grandis D.), to irregularly cylindrical
branches, looking rough on account of the very short branch-
lets. The cells are usually stellate, as in figure 8, from P.
elongata D., and often one of the septa, and sometimes two
opposite ones, extend to a columella at the centre, as illustra-
ted in figure 9, from P. pUcata D. ; dividing the cell into
halves. The cell in the interior of the corallum is crossed by
thin plates or tables, as shown in figure 10, and hence they
have been called tabulate corals. Agassiz, after the discovery
of the Hydroid character of the animals of the Millepore corals,
whose cells also are tabulate, referred the Pocilliporae to the
same Hydroid type. But the recent study of the polyps has
shown that they are true polyps ; and Prof Verrill remarks
on the resemblance of the tentacles to those of the Oculin^.
The stellate character of the calicle also proves that the ani-
mals must be polyps.

Madrepore tribe^ or Madeeporaoea. — In this tribe the cor-
alla, even to the walls of the corallets, are remarkable for be-
ing porous, and the radiating lamellae of the polyp-cells are
narrow, often perforated or imperfectly developed, , and fre-
quently mere points. The coralla are either branched, mas-
sive, or foliaceous. Budding is lateral, and in the branching
species there is either a parent polyp, as in Madrepora and
Dendrophyllia, or a terminal budding cluster. This peculiar-
ity has been already illustrated in the figure of Madrepora
aspera^ on page 50. On the following page there is an out-
line sketch of another species, the Madrepora formosa D.,
common in the Feejees, and also in the East Indies. The two
species here mentioned give a good idea of the ordinary char-
acter of the Madrepore corals. One of the polyps of the Mad-

72 CORALS AND CORAL ISLANDS.

repora cribripora D., a species collected in the Feejees, is rep-
resented much enlarged in the accompanying figure. The nat-

POLYP OP M. CllIBIlirOUA, D.

ural size of the expanded polyp in this genus is generally
from an eighth to a twelfth of an inch across the star. The
disk of the polyp is quite small, and the number of tentacles is
always twelve. The most common color of the j)olyps is green,
while that of the general surface between is ordinarily a pale
or a dark umber. In many species of Madrepora the branch-
es spread out laterally from a central or lateral trunk, and co-
alesce together into a complete net^work, having the form of a
shallow vase ; and the interior of the vase is filled with multi-
etudes of short, cylindrical coral stems, rising from the reticula-
ting branches, which, when alive, have literally the aspect of
sprigs of flowers in the vase.

In certain kinds, closely related to Madreporae, the calicles
^re reduced to points, or spiniform or angular prominences, or
fail altogether, and there are sometimes rounded promi-
nences between the cells ; these degraded Madrepores belong
to the genus Montipora (Manopora of the Author's Report).

The genus Dendrophyllia is also referred to the Madre-
pore tribe. The budding, as already explained, is of the
same kind as in the Madrepores. But the tentacles exceed
twelve. One of the polyps of i?. nigrescens D., enlarged, is
shown in the figure, on page 75. This Pacific species grows to
A height of at least three feet, and is peculiar in having a very

MADBEPORA FORMOSA.

SUBDIVISIONS OF ACTINOID POLYPS, lb

dark blackish green or almost black color, while the polyps
have the tentacles nearly colorless, and the disk has a circle
of emerald green around the mouth. DendropJiyllia a/rborea is
the name of a common species of this genus found in deep

POTiYP OF DENDROPHYLLIA NTGRE8CENS.

water in the Mediterranean ; it is equally large Avith the pre-
ceding, and somewhat similar in its mode of branching, but
a little stouter. It has also been found in the Atlantic about
the Azores, Another common Mediterranean species is
the 2). cornigera. It is sparingly branched, and has very
long and stout corallets, sometimes as long and large as the
finger.

The genus Gemmipora contains porous corals, of f oliaceous,
bowl-like, and massive forms, covered by prominent cylindrical,
porous calicles, and having many short tentacles to the polyps,
usually in a single circle.

Here belongs also the large Porites family (Poritidae), the
corals of which are very porous, and sometimes almost spongy,
and whose polyp-cells are exceedingly shallow, and usually only
imperfectly radiated.

One of the genera in this family is Alveopora. It con-
tains the lightest of known corals, the texture being exceeding-

76 COBALS AND CORAL ISLANDS.

\j porous, and the walls of the cells, which are continued reg-

DBNDROPHYLLIA NIGRBSCBNS, D.

nlarly through the corallum, are like delicate lace-work. As
stated long since by the author, " they are intermediate in char-

SUBDIVISIONS OF AGTINOID POLYPS,

77

acter between the Montiporae and the Favosites group " — as
shown by the texture and the horizontal partitions across the

ALVEOPORA VERRILLIANA, I).

cells, giving them the "tabulate" character of the ancient
Favosites, as represented by the author in the annexed fio-ure

VERTICAL SECTION OF CORALLUM, AKD UPPER VIEW OP CALICLBS, ENLARGED OF
ALVEOPORA SP0NGI08A, D.

exhibiting a section of the corallum of a Feejee species. On
account of this tabulate structure, the genus was referred by
the author to the Favosites family. A related species, of un-
known locality, has been made the type of a new genus, called
Favoeitipora, by Mr. W. S. Kent, on the ground of its tabu-
late character (Ann. Mag. Nat. Hist, 1870), thus confirming,
though overlooking, the author's conclusions.

78 CORALS AND COEAL ISLANDS.

In the genus Porites, the corals are frequently branching, as
in the Porites mordax D., sometimes more slenderly, but oftener
less so, and at times massive and monticulose in form. An-
other species of Porites is repiesented on the following page,
with one of the branches fully expanded, but the others in
outline ; a polyp, much enlarged, having twelve tentacles as

POLYP OF PORITES LEVIS.

in the Madreporae, is shown in the following figure. The cells
of the corallum are superficial, and hence the name of the
species, Porites levis.

Another form, different in the size and character of its
polyps, is exemplified in the genus Goniopora. In the species
figured on p. 52, the color of the projecting polyps was lilac
or pale purple, and the number of tentacles eighteen to twenty-
four, yet all were in a single series. The columns grow to a
height of two feet or more, with only the summits for two or
three inches alive. ITie dead portion is usually encrusted with
nullipores. sponges, serpulae and various shells, which protect
the very porous corallum within from wear and solution by
the moving waters.

n. CYATHOPHYLLOIDS.

It is not necessary to dwell here at length upon the an-
cient Cyathophylloids. The corals have a close resemblance
to those of the Astrasa tribe in general aspect, varieties of form,
and range of size ; the methods of multiplication by buds were
the same that nre now known in the Oculina tribe. Some

SUBDIVISIONS OF ACTINOID POLYPS, 7!^

of the larger kinds of simple corals, such as those of the gen-
era Zaphrentis and Heliophyllum, had at times a diameter of

PORITES LBVIS, D.

three or four inches, so that the breadth of the polyp flower
was probably at least six inches. Hemispherical masses oi

80 aORALS AND CORAL ISLANDS.

solid corals attained, in some species, a diameter of several
feet. No doubt the colors, among the coral polyps and other
life of the ancient seas, were as brilliant as now exist.

Nature's economist here puts the question — Why all this
beauty when there were no eyes to enjoy it? But beauty ex-
ists because, "in the beginning," "the Spirit of God moved
upon the face of the waters ;" and man finds delight therein in-
asmuch as he bears the image of his Maker.

A single recent species has been obtained by Mr. L. F. de
Pourtales, in dredging at a depth of 324 fathoms, near the
Florida reef, which may be a Cyathophylloid, although it has
been supposed that the species of the tribe have been extinct
since the middle of the Mesozoic era. It was half an inch
high and broad, and the polyp-cell had eight septa — a mul-
tiple of four ^ as in the true Cyathophy Holds. The discoverer
has named it Haplophylha paradoxa. But he observes that
it may after all be only an abnormal Actinoid.

in. ALCYONOID POLYPS.

The name Alcyonium^ given to some of the species of this
group, is derived from Alcyone, the fabled daughter of Nep-
tune. It is sometimes written with an initial H, in conform-
ity with the aspirate of the Greek word; but Latin authors
usually omitted the H, and this has been good enough author-
ity for Linnaeus and the majority of later writers.

The Alcyonoids include some of the gayest and most deli-
cate of coral shrubs. Almost all are flexible, and wave with the
motion of the waters. They contribute but little to the mate-
rial of coral reefs, but add largely to the beauties of the coral
landscape. Not only are the polyps of handsome tints, but
the whole shrub is usually of a brilliant orange, yellow, scarlet,

ALOYONOID POLYPS. 81

crimson or purple shade. Dun colors also occur, as ash-
gray, and dark brown, and almost black. Some kinds, the
Sponggodise, are too flexible to stand erect, and they hang
from the coral ledges, or in the coral caves, in gorgeous clus-
ters of scarlet, yellow, and crimson colors.

The species of this order spread from the tropics through
the colder seas of the globe, and occur at various depths, down
to thousands of feet.

The two following are the most striking external peculiari-
ties of the polyps : the number of tentacles is always eight ;
and these tentacles are always fringed with papillae, though the
papillae are sometimes mere warts. Some of the various forms
of the polyps are shown in the figures on the following pages.

But besides these characteristics, there is also the follow-
ing : the existence of only eight internal septa, and these septa
not in pairs ; consequently, the interior is divided into only
eight compartments (octants), and with each a tentacle is con-
nected. Hence in the Alcyonoids, as Prof. Verrill has ob-
served, the areas externally, and the compartments within,
are all ainbulacral^ or tentacular, which makes a wide dis-
tinction between them and the Actinoids (p. 28) in which only
the alternate are tentacular.

The solid secretions of these polyps are of two kinds : Ei-
ther (1), internal and calcareous ; or (2), epidermic, from the
base of the polyp. The latter make an axis to the stem or
branch, which is either horney (like that in Antipathus, p. 62) or
calcareous. A few species have no solid secretions.

All the species are incapable of locomotion on the base ;
yet there are some that sometimes occur floating in the open
ocean.

The three following divisions of the Alcyonoids are those
now generally recognized :

82

CORALS AND CORAL ISLANDS,

1. The Alcyonium tribe or Alcyonacea. — One of the
forms under this tribe is represented in the annexed figure.
It is from the Peejees (like most of the zoophytes figured
by the author), and in the living state the polyps had the mid-
dle portion of the tentacles pale brown, with the fringe deep
brown. In another more beautiful species of the genus, fi:'om
the same region, the Xenia florida D. (made Xenia Dance by
Verrill, as it proved to be distinct from Lamarck's species to

XENIA ELONGATA, D.

which the author referred it), the polyps are as large, but short-
er, and the color is a shade of lilac. These species differ from
the larger part of the Alcyonia in having the polyps not re-
tractile ; the tentacles fold together, if the zoophyte is disturb*
de, but cannot hide themselves.

The following figure represents another related species

ALOYONOIB POLYPS. 83

obtained by Dr. W. Stimpson, near Hong Kong, and called by
its discoverer AntJielia lineata ; the polyps are but partly ex-
panded.

Other Alcyonoids are much branched, with the branches
thick and finger-like, and soft or flexible, and the polyps small
and wholly retractile into the mass. The branches, bare of
polyps, are usually of some dull pale color, and on account of
this fact some of these Alcyonia go by the common name of
dead-men's fingers.

ANTHELIA LINEATA, SX.

Some of the species form thick-lobed plates over the rocks ;
and occasionally they are brightly colored, even when the
polyps are unexpanded.

The above kinds secrete granules or spicules of carbonate
of lime in the tissues, and are harsher or softer in texture ac-
cording to the proportion of these granules.

Some species form branching tubes, rising from an in-
crusting base, which are rather firm owing to the calcareous
spicules present Such species are referred to the genus Te-
lesto— one of which, from Hong Kong, fi-om the coUection
made by Dr. Stimpson, is here figured (from Verrill). The
second figure shows the form of the expanded polyps. The
unbranched species of this kind make up the genus Cornularia.

In one family of this tribe the polyps form red calcareous
tubes ; sometimes a slender, creeping tube, with polyps at
intervals, as in a species referred by the author to the genus

84

V0RAL8 AND CORAL ISLANDS.

Aulopora ; but generally vertical tubes, grouped into large red
masses, called, popularly, Organ-pipe coral. A portion of one
of the latter — Tubipora syringa D, — ^is represented in the

TELESTO RAMICULOSA, V,

first of the following figures, with its expanded polyps ; and a
polyp from the group much enlarged in the second figure.
The papillae of the fringe are arranged closely together in a

TUBIPOKA BTBINGA, D. AND T. FIMBRIATA, D.

plane, so that it is not at first apparent that there is a fringe.
Tlie third figure represents, enlarged, the polyp of another Fee-
jee species, the Tubipora jfmnhriata D. Such coral masses
are sometimes a foot or more in diameter, and the living zoo-

ALGTONOID POLYPS. 85

phyte, with its lilac or purple polyps fully expanded, looks
much like a large cluster of flowers from a lilac bush. The
tubes are united by cross plates at intervals.

2. Gorgonia trihe^ or Gokgonacea. — The following figure
represents a species of this tribe from the Kingsmill or Gilbert

GOKGONIA? FLEXUOSA, D.

Islands. It is one of the net-like or reticulated species, the
reticulation being a result of the coalescence of the branchlets.
The general color of the species was crimson ; but when alive
and expanded it was covered throughout with yellowish polyps
of the form in figure a, though much smaller, the natural size
not exceeding a twelfth of an inch. The common sea-fan of
the West Indies, Gorgonia fiahellum^ is much more finely
reticulated, the meshes of the net-work being ordinarily not
over a fourth of an inch in breadth ; while the fan often grows
to a height and breadth of a yard.

Other species of the Gorgonia family are like clusters

86 CORALS AND CORAL ISLANDS.

of slender twigs, and others like many-branched shrubs or
miniature trees.

The exterior of the stem or branch in a Gorgonia is a
layer of united polyps, with minute calcareous spicules dis-
tributed through the tissues and giving the layer some firm-
ness. It is like a bark to the axis of the stem or branch, and may
be peeled off without difficulty, and hence is often called the
cortex. The outer surface of the dried cortex is often smooth,
or nearly so ; but sometimes covered with small prominences.
Over it there may be seen numerous oblong points (one to
each of the prominences if there are any ; each of these is
the spot where a polyp opened out its tentacles when the zoo-
phyte was alive.

Kolliker and others have shown that genera, and some-
times species, of the Gorgonacea, may be distinguished by the

SPICULES OF GOKaONIiB, MUCH ENLARGED.

forms of the calcareous spicules. Some of these knobby spi-
cules are represented in the annexed cut, from figures published
by Prof. Verrill. The most common forms are those of figures
1, 4, 5 ; they occur, with small differences, in the genera Gor-
gonia, Eugorgia, Leptogorgia, etc. Figure 1 is from the Le]>
togorgia eximia V. Figure 2, in which one side is smooth
(from the Gorgonia quercifolia V), is characteristic of the
genus Gorgonia, but occurs in the species along with forms
much like fig. 1. The forms represented in figures 3, 4, 5,

ALCTONOID POLYPS. 87

are all from Migorgia aurantiaca V., the peculiar kind shown
in fig. 3 occurring with the other more common form, in species
of this genus. In species of Plexaurella many of the spi-
cules are beautiful crosses of various fancy shapes. In Eu-
nicellaB the cortex is covered with an outside layer, in which
the spicules are club-shaped, though ornately so, and have the
smaller end pointed inward. These spicules afford valuable dis-
tinguishing characters also in all Alcyonoids.

The spicules are often brilliantly colored, and sometimes
variously so in the same individual. Yellow, crimson, scar-
let and purple are common colors, and they occur both of
(lark and pale shades. Viewed under a compound micro-
scope by transmitted light, a group of these spicules from
some species, part bright yellow and part crimson, or of
some other tints, produces an exceedingly beautiful effect.
It gives still greater interest to this subject that all Gor-
goniae owe the various colors they present to the colors of
their spicules.

Spicules are usually wholly internal, or they only come to
the surface so as to make the exterior slightly harsh. But in
other cases, as in the genus Muric^a, they project and give
a somewhat bristly look to the coral.

The calcareous spicules are internal secretions, like those
of ordinary coral, and the constitution is the same,— mere
carbonate of lime. But the secretion of the axis of the
branches is epidermic, from the inner surface of the cortex,
as in the Antipathus before described (p. 62). In the ordinary
Alcyonoids that make no horny axis, the stolons, or budding
stem or mass, creeps or spreads over the supporting body.
But in these Gorgoniae, the budding cluster, which would make
a stolon if there were no horny secretions, has the form of a
tube about a horny axis ; and as this tube elongates and se-

88

CORALS AND COBAL ISLANDS.

cretes the axis v/ithin, it gives out buds externally ; thus the
branch rises. New branches commence at intervals over the
sides of the rising stem or branch through the starting of new

ISIS HIPrURIS.

budding centres, and so, finally, the Gorgonia zoophyte is
completed.

In a few species, the axis is partly or wholly calcareous.
In the Isis family, it is made up of a series of nodes and
intemodes. The former, in the genus Isis, are white, calcare
ous, furrowed or fluted pieces ; and the latter are smaller and
horn-like in nature, as illustrated in the preceding figures.
In the branching stem here figured, the main stem and the
branch on the left are simply the axis, bare of the polyp-layer

ALCTONOID POLYPS.

89

or cortex ; whUe the branch on the right, with the surface
dotted, has the cortex complete, and the dots are the sites of
the contracted polyps. The circular figure below is a trans-
verse section of the stem enlarged, showing the cavities occu-
pied by the retracted polyps.

In the genus Melitaea, and some others related, the inter-

COBALLIUM KUBBUM.

nodes are porous and somewhat cork-like or subereous instead
of horny. The species of this group are often bright-colored
and much branched, and resemble, in aspect, ordinary Gorgon-
iaj ; but they are very brittle, breaking easily at the inter-
nodes.

90 VORALS AND CORAL ISLANDS.

In the Corallidoe^ the axis is wholly calcareous, and firm and
solid throughout, with usually a red color, varying from crim-
son to rose-red. Here belongs the Corallium ruhrum, or pre-
cious coral The polyp-crust or cortex, which covers the red
axis or coral, is thin, and contains comparatively few calcare-
ous spicules, and consequently it readily disappears when the
dried specimens are handled. In an uninjured state, the polyp
centres may be distinguished over it by a faint six-rayed star.
A branch from a specimen obtained by the author at Naples,
is represented, of natural size, in the cut on page 89. The pol-
yps, as the enlarged view, by Lacaze Duthiers, shows, are sim-
ilar to those of other Alcyonoids — the tentacles being eight in
number and fringed. The figure represents the extremity of
a branch, magnified about four times lineally, with one pol-
yp fully expanded, two partly, and the rest unexpanded. In
the living Corallium, they open out thickly over the branches,
and make it an exceedingly beautiful object. The coral gro^7s
in branching forms, spreading its branches nearly in a plane ;
and sometimes the little shrub is over a foot in height. The
author just mentioned states that, among the polyps, those
of the same branch are often all of one sex alone, and that, be-
sides males and females, there are a few that combine both

sexes.

The precious coral is gathered from the rocky bottom of
the borders of the Mediterranean, or its islands, and most
abundantly at depths of 25 to 50 feet, though occurring
also even down to 1,000 feet. There are important fisheries
on the coast of southern Italy ; of the island of Ponza, off^ the
Gulf of Gaeta ; of Sicily, especially at Trapani, its western ex-
tremity ; of Corsica and Sardinia, in the straits of Bonifacio ;
of Algeria, south of Sardinia, near Bona, Oran, and other
places, which in 1853 afforded 80,000 pounds of coral ; and on

ALCTONOID POLYPS.

91

the coast of Marseilles. The rose-colored is the most highly
valued, because the rarest.

Another species of Corallium was obtained by the author
at the Sandwich Islands (Atlas of Zoophytes, plate 60) ; but,
while probably from the seas of that region, its precise locality
is not known.

3. Pennatvla tribe, or Pennatulacea. These are com-

COPHOBELBMNON CLAVATUM, V., AND VKRETILLTJM 8TIMP80Nr, V.

pound Alcyonoids, that, instead of being attached to rocks or
some firm support, have the base or lower extremity free from
polyps and buried in the sand or mud of the sea-bottom, or
else live a floating life in the ocean. Their forms are very va-
rious.

In the Veretillum family (Veretillidae) they are stout
and short club-shape. One of the species from Hong Kong,
is shown in the figure on the left, with its polyps fully ex-

92 CORALS AND CORAL ISLANDS,

papded, and the small figure represents one of the polyps en-
larged. The third figure represents a polyp of another spe-
cies, from Hong Kong, a true Veretillum, enlarged three di-
ameters ; the specimens, obtained by Dr. Stimpson, and de-
scribed by Prof Verrill, were six to eight inches in length, and,
where thickest, were three inches or more in diameter.

A common Mediterranean species is the Veretillum cynom.0-
rium ; and it has been recently found, of a length of ten in-
ches, in the depths of the Atlantic off the coast of Spain. Mr
W. S. Kent observes, with regard to its polyps and their
phosphorescent qualities, as follows :

-' Nothing can exceed the beauty of the elegant opaline pol-
yps of this zoophyte when fully expanded, and clustered
like flowers on their orange-colored stalk ; a beauty, however,
almost equalled by night, when, on the slightest irritation, the
whole colony glows from one extremity to the other with un-
dulating waves of pale green phosphoric light. A large buck-
etful of these Alcyonaria was experimentally stirred up one
dark evening, and the brilliant luminosity evolved produced a
spectacle too brilliant for words to describe. The supporting
stem appeared always to be the chief seat of these phosphor-
escent properties, and from thence the scintillations travelled
onward to the bodies of the polyps themselves. Some of the
specimens of this magnificent zoophyte measured as much as
ten inches from the proximal to the distal extremity of the
supporting stalk, while the individual polyps, when fully ex-
serted, protruded upward of an inch and a half from this in-
flated stalk, and measured as much as an inch in the diameter
of their expanded tentacular discs."

In several genera of the Pennatula tribe there are two
kinds of polyps over the surface, and this was the case vnth the
Veretillum 8timpson% as observed by Prof. Verrill. Between

ALCYONOID POLYPS. 93

the large and well- developed polyps, there were multitudes
of small wart-like prominences, each of which proved to be
a polyp, but very small and imperfectly developed, having
only two lamellae in the interior instead of the usual eight,
and without distinct tentacles, or the ordinary nettling cords
within.

Among the other forms of Zoophytes in the Pennatula tribe
are those having a stout axis, with branches either side,
arranged regularly in plume-like style (the Pennatulidae) ;
or a very slender stem and very short lateral polyp-bearing
pinnules or processes along it (the Virgularidae) ; or a thin
renifonn shape (RenillidaB). Others differ from the preceding
in having the polyps not retractile ; and some of these have
a slender stem and the polyps arranged along one side of it
(the Pavonaridae) ; and still others a terminal cluster of polyps
(the Umbellularidse).

The most of the species secrete a slender, horny axis, and
have slender calcareous spicules among the tissues, somewhat
like those of the Gorgonidae.

In conclusion, it may here be stated that the reader
will find very full illustrations of most of the forms of re-
cent corals, and of their animals, with their natural colors, in
the au^or's Report on Zoophytes. It is with regret that he
has to add, that owing to the special action of the Congres-
sional Committee in charge of the publications of the Wilkes
Exploring Expedition, only one hundred copies of this Re-
port were published by the Government, and also of the others
of the series, and that but few have been issued besides. The
Atlas contains sixty-one folio plates, many of them colored.

The works on " British Sea Anemones," by Mr. Philip
Henry Gosse, contains figures and descriptions of a large

94 CORALS AND CORAL ISLANDS.

number of species, and gives an excellent idea of the most of
the forms of Actiniae, and also presents well their colors.
Prof. A. E. Verrill has published, in the Memoirs of the Bos-
ton Society of Natural History, Vol. I., a "Review of the
Polyps of the Eastern Coast of the United States," with a
plate illustrating a few of the species.

IV. LIFE AND DEATH IN CONCURRENT PROGRESS IN CORAL

ZOOPHYTES.

The large, massive forms of stony corals would not exist,
and the tree-shaped and other kinds would be of diminutive size,
were it not for the fact that, in the living zoophyte, death and
life are going on together, pari passu. This condition ot
growth is favored by the coral secretions ; for these give a
chance for the polyp to mount upward on the coral, as it
lengthens it by secretions at the top. But, to be successful in
this ascending process, either the polyp must have the power
of indefinite elongation, or it must desert the lower part of
the corallum as growth goes forward ; and this last is what
happens. In some instances, a polyp, but a fourth of an inch
long, or even shorter, is finally found at the top of a stem
many inches in height. The following figure represents a case
of this kind; for all is dead coral, excepting less than an
inch at the extremity of each branch. The tissues that once
filled the cells of the rest of the corallum have dried away,
as increase went on above. Another example is shown
on page 54, in which the living part had a length of one
eighth of an inch. The Goniopora, on page 52, is still an-
other example of the process ; but here the living part com-
bines a great number of polyps : these are growing and bud-
ding with all the exuberance of life, while below, the old pol-

LIFE AND DEATH IN CONCURRENT PROGRESS. 95

7ps gradually disappear, and even their cells become superfi-
cial and fade out. Trees of Madrepores may also have their
limits — all below a certain distance from the summit being
dead ; and this distance will diflfer for different species. But
this is not a limit to the existence of the zoothome, even

CAULASTR^A FURCATA, D.

though a slender tree or shrub, or of its flourishing state ; for the
dead coral below is firm rock itself, often stronger than ordinary
limestone or marble, and serves as an ever-rising basement
for the still expanding and rising zoophyte.

But this death is not in progress alone at the base of the
column or branch. Generally the whole interior of a corallum
is dead, a result of the same process with that just explained.
Thus, a Madrepora, although the branch may be an inch in
diameter, is alive only to the depth of a line or two, the grow-
ing polyps of the surface having progressively died at the low-
er or inner extremity as they increased outward.

The large domes of Astraeas, which have been stated to
attain sometimes a diameter of ten or fifteen feet, and are

96 CORALS AND CORAL ISLANDS.

alive over the whole surface, owing to a symmetrical and un-
limited mode of budding, are nothing but lifeless coral
throughout the interior. Could the living portion be sepa-
rated, it would form a hemispherical shell of polyps, in most
species about half an inch thick. In some Porites of the same
size, the whole mass is lifeless, excepting the exterior for a
sixth of an inch in depth.

With such a mode of increase, there is no necessary limit
to the growth of zoophytes. The rising column may increase
upward indefinitely, until it reaches the surface of the sea, and
then death will ensue simply from exposure, and not from any
failure in its powers of life. The huge domes may enlarge till
the exposure just mentioned causes the death of the summit,
and leaves only the sides to grow, and these may still widen,
it may be indefinitely. Moreover, it is evident that if the
land supporting the coral domes and trees were gradually
sinking, the upward increase might go on without limit.

In the following of death after life " aequo pede," there is
obedience to the universal law. And yet the polyps, through
this ever yielding a little by piecemeal, seem to get the better
of the law, and in some instances secure for themselves almost
perpetual youth, or at least a very great age. Of the polyps
over an Astraea hemisphere, none ever die as long as the dome
is in a condition of growth ; and the first budding individual,
or at least its mouth and stomach, is among the tens of
thousands that constitute the living exterior of the dome of
fifteen feet diameter. In the Madrepore, the terminal parent-
polyp of a branch grows on without being reached by the
death-warrant that takes off at last the commoners about the
base of the tree ; it keeps growing and budding, and the tree
thus continues its increase.

The death of the polyps about the base of a coral tree

PROTEGTION A GAINST INJUR T. 97

would expose it, seemingly, to immediate wear from the waters
around it, especially as the texture is usually porous.
But nature is not without an expedient to prevent to some
extent this catastrophe.

In the first place, there is often a peritheca over the
dead corallum — that is, an outer impervious layer of carbonate
of lime, secreted by the lower edge of the series of dying pol-
yps, a fact in the Goniopora columna figured on page 52.
Then, further, the dead surface becomes the resting-place of
numberless small encrusting species of corals, besides Nulli-
pores, Serpulas, and some MoUusks. In many instances, the
lichen-like NuUipore grows at the same rate with the rate of
death in the zoophyte, and keeps itself up to the very limit of
the living part. The dead trunk of the forest becomes covered
with lichens and fungi, or in tropical climes, with other foliage
and flowers ; so among the coral productions of the sea, there
are forms of life which replace the dying polyp. The process
of wear is frequently thus prevented.

The older polyps, before death, often increase their coral se-
cretions also within, filling the pores as the tissues occupying
them dwindle, and thus render the corallum nearly solid; and
this is another means by which the trees of coral growth,
though of slender form, are increased in strength and endur-
ance.

The facility with which polyps repair a wound, aids in
carrying forward the results above described. The breaking
of a branch is no serious injury to a zoophyte. There is often
some degree of sensibility apparent throughout a clump even
when of considerable size, and the shock, therefore, may occa-
sion the polyps to close. But, in an hour, or perhaps much
less time, their tentacles will again have expanded; and such
as were torn by the fracture will be in the process of com-

98 CORALS AND COMAL ISLANDS.

plete restoration to their former size and powers. The frag-
ment broken oflF, dropping in a favorable place, would become
the germ of another coral plant, its base cementing by means
of new coral secretions to the rock on which it might rest ; or,
if still in contact with any part of the parent tree, it would be
reunited and continue to grow as before. The coral zoophyte
may be levelled by transported masses swept over it by the
waves ; yet, like the trodden sod, it sprouts again, and contin-
ues to grow and flourish as before. The sod, however,
has roots which are still unhurt ; while the zoophyte, which
may be dead at base, has a root — a source or centre of life — in
every polyp that blossoms over its surface. Each animal
might live and grow if separated from the rest, and. would ul-
timately produce a mature zoophyte.

V. COMPOSITION OF CORAL.

Ordinary corals have a hardness a little above that of com-
mon limestone or marble. The ringing sound given, when cor-
al is struck with a hammer, indicates this superior hardness.
It is possible that it may be owing to the carbonate of lime be-
ing in the state of aragonite, whose hardness exceeds a little
that of ordinary carbonate of lime or calcite. It is a common
error of old date to suppose that coral when first removed from
the water is soft, and afterward hardens on exposure. For, in
fact, there is scarcely an appreciable diflference ; the live coral
may have a slimy feel in the fingers ; but if washed clean of the
animal matter, it is found to be quite firm. The waters with
which it is penetrated may contain a trace of lime in solution,
which evaporates on drying, and adds slightly to the strength
of the coral ; but the change is hardly appreciable. A branched
Madrepore rings on being struck when first collected; and a
blow in any part puts in hazard every branch throughout it,

COMPOSITION OF C0HAL8.

99

on account of its elasticity and brittleness. The specific gravi-
ty of coral varies from 2*5 to 2*8 : 2-523 was the average from
fifteen specimens examined by Prof. Silliman.

Chemically, the common reef-corals, of which the branch-
ing Madrepora and the massive Astraeas are good exam-
ples, consist almost wholly of carbonate of liiiie, the same in-
gredient which constitutes ordinary limestone. In 100 parts,
95 to 98 parts are of this constituent ; of the remainder, there
are li to 4 parts of organic matter, and some earthy ingredi-
ents amounting usually to less than 1 per cent. These earthy
ingredients are phosphate of lime, with sometimes a trace of
silica. A trace of fluorine also has b^pen observed.

S. P. Sharpies found the following constitution for the spe-
cies below named {Am. Jour. Sci.^ III., i. 168).

Oculma arbuscula, N. Car.
Manicina areolata, Florida
Agaricia agaricites
Siderastraaa radians
Madrepora cervicornis
Madrepora palmata

C^BONATE

PHOSPHATE

WATER AND 011-

OF LIME.

OF LIME.

GANIC MATTERS.

. . . 95.37 .

. 0.84 .

. 3.79

. . . 96.54 .

. 0.50 .

. 2.96

. . . 97.73 .

. 0.53 .

. 1.64

. . . 97.30 .

. 0.28 .

. 2.42

. . . 98.07 .

. 0.32 .

. . 1.93

. . . 97.19 .

. 0.78 .

. . 2.81

Forchhammer found 2*1 per cent, of magnesia in Coral-
lium rubrum, and 6*36 in Isis hippuris.

The sea- water, and the ordinary food of the polyps, are evi-
dently the sources from which the ingredients of coral are ob-
tained. The same powers of elaboration which exist in other
animals belong to polyps ; for this function, as has been re-
marked, is the lowest attribute of vitality. Neither is it at all
necessary to inquire whether the lime in sea-water exists as
carbonate, or sulphate or whether chloride of calcium takes the
place of these. The powers of life may make from the ele-

100 CORALS AND CORAL ISLANDS.

nients present whatever results the functions of the animal re-
quire.

The proportion of lime salts which occurs in the water of
the ocean is about gj to gg of all the ingredients in solution. The
lime is mainly in the state of sulphate. Bischof states that the
proportion of salts of all kinds in sea-water averages 3*527 per
cent.; and in 100 parts of this, 75*79 are chloride of sodium,
9-16 chloride of magnesium, 3*66 chloride of potassium, 1*18
bromide of sodium, 4*62 sulphate of lime or gypsum, and 5*597
sulphate of magnesia, = 100. This corresponds to about 16^
parts of sulphate of lime to 10,000 of water.

Fluorine has also been detected in sea-water ; so that all the
ingredients of coral are actually contained in the waters of the
ocean.

It has been common to attribute the origin of the lime of
corals to the existence of carbonic-acid springs in the vicinity
of coral islands. But it is an objection to such a hypothesis,
that, in the first place, the facts do not require it ; and, in the
sebond, there is no foundation for it. The islands have been
supposed to rest on volcanic summits, thus making one hy-
pothesis the basis of another. Carbonic-acid springs are by no
means a universal attendant on volcanic action. The Pacific
affords no one fact in support of such an opinion. There are
none on Hawaii, where are the most active fires in Polynesia ;
and the many explorations of the Society and Navigator Isl-
ands have brought none to light. Some of the largest reefs
of the Pacific, those of Australia and New Caledonia, oc-
cur where there is no evidence of former volcanic action.

The currents of the Pacific are constantly bearing new sup-
plies of water over the growing coral beds, and the whole ocean
is thus engaged in contributing to their nutriment. Fish, mol-
lusks, and zoophytes are thus provided with earthy ingredi-

HTDR0ID8, 101

ents for their calcareous secretions, if their food fails of giving
the necessary amount ; and, by means of the powers of animal
life, bones, shells, and corals alike are formed.

The origin of the lime in solution throughout the ocean is
an inquiry foreign to our present subject. It is sufficient here
to show that this lime, whatever its source, is adequate to ex-
plain all the results under consideration.

II. HYDEOIDS.

The annexed sketch represents a Hydra as it often occurs
attached to the under surface of a floating leaf — that of a spe-
cies of Lemna. The animal is seldom over half an inch

HYDRA.

long. It has the form of a pol)^, with long slender tentacles ;
and, besides these tentacles with their lasso-cells, it has no spe-
cial organs except a mouth and a tubular stomach. Like the
fabled Hydra, if its head be cut off another will grow out ; and
any fragment will, in the course of a short time, become a per-
fect Hydra, supplying head, or tail, or whatever is wanting ;
and hence the name given to the genus by Linnaeus.

102

CORALIS AND GOBAL ISLANDS.

The Hydra is the type of a large group of species. It buds,
but the buds drop off soon, and hence its compound groups
are always small, and usually it is single. But other kinds

HYDRALLMANIA FALCATA.

multiply by buds that are persistent, and almost indefinitely so ;
and they thus make membranous coralla of considerable size
and often of much beauty.

HTDR0ID8, 103

The species here figured, Hydrallmaniafalcata (formerly
called Flumularia falcaia), is one of them. Along the
branches, there are minute cells, each of which was the seat of
one of the little Hydra-like animals (in this not a fourth a
line long), and usually with short tentacles spread out star-like.
Other kinds are simple branching threads, and sometimes the

MILLEPORA ALCICORfiS

cells are goblet-shaped and terminal. The Tubulariae grow in
tufts of thread-like tubes, and have a star-shaped flower at top
often half an inch in diameter, with a proboscis-like mouth at
the centre. In Coryne, a closely-related genus, the tentacles are
shorter, and somewhat scattered about the club-shaped or pro-
bosciform head of the stem, so that the animal at top is far
from star-shaped or graceful in form ; it is in fact a very clum-
sy unshapen thing for a Radiate.

104 CORALS AND CORAL ISLANDS.

To the animal of the Coryne, that of the very common, and
often large, corals, called Millepore^, is closely related, as first
detected by Agassiz on one of his cruises to the reefs of Flori-
da. The author often had Millepore corals under study in the
Pacific, and waited long for the expansion of the animals, but
was never gratified by their making their appearance. Agas-
siz observes that they are very slow in expanding themselves.
When expanded, they have no resemblance to true polyps.
There is simply a fleshy tube with a mouth at top and a few

ANIMALS OF MILLEPOKA ALCICOKNIS, MUCH ENLARGED.

small rounded prominences in place of tentacles, four of them
sometimes largest. The preceding figure, tirom Agassiz, shows,
much enlarged, a portion of a branch of the Millepora alcicor-
nis with the animals expanded, and the small figure a, near
the top of the cut, gives the natural size of the same.

The corals of the Milleporae are solid and stony, as much
so as any in coral seas. They have generally a smooth sur-
face, and are always without any prominent calicles, there being
only very minute rounded punctures over the surface, from
which the animals show themselves. The cells in the corallum
are divided parallel to the surface by very thin plates or tables,
as in the Pocilliporae and Favosites ; and they were former-
ly classed, therefore, with other tabulate corals.

BBYOZOANa. 105

S. p. Sharpies found the coral of M. alcicornis to consist
of 97*46 per cent of carbonate of lime, 0*27 of phosphate of
lime, and 2 '54 of water and organic matters. The Millepores
are very abundant corals, and eminently so in the West In-
dia seas, contributing largely to the material of the reefs.

The Hydroids were long considered polyps. But they
have been found to give origin to Medusoe or jelly-fishes, and
it is now proved that they are only an intermediate stage in
the development of Medusae, between the embryo state and
that of the adult or Medusa state. The Millepores afford, there-
fore, examples of coral-making by species of the class of Aca-
lephs. Many of these Medusas and their Hydroids will be
found illustrated in the admirable work of Alexander and Mrs.
L. Agassiz entitled " Sea-Side Studies " — an excellent com-
panion for all who take pleasure in sea-shore rambles.

Another genus of corals referred to the Millepora group
occurs in the East Indies, the species of which is remarkable
for having within an indigo-blue color ; it is called Heliopora
ecerulea^ the generic name, from the Greek for sun^ alluding to
the minute round polyp-cells. This and the true Milleporae,
are coral-reef species. A few allied species occur in colder
waters, and for these the genus Pliobothrus has been instituted ;
one species has been described by de Pourtales, from the deep
waters off the Florida reef. The ancient corals of the Cha3-
tetes family may also be Acaleph corals, as suggested by
Agassiz, but more probably were Bryozoan.

m. BRYOZOANS.

The Bryozoans are very small animals, and look much like
Hydroids. Although belonging to the sub-kingdom of Mol-
lusks, they are externally polyp-like, having a circle or ellipse of

106 C0BAL8 AND COMAL ISLANDS,

slender tentacles around the mouth. But, in internal struc-
ture, and all of the animal below the head, they are Mollusks.
They form delicate corals, membranous or calcareous, made up
of minute, cabin-like cells, which are either very thin crusts on
sea- weeds, rocks, or other supports, or slender moss-like tufts,
or graceful groups of thin, curving plates, or net-like fronds ;
and sometimes thread-like lines, or open reticulations.

Occasionally they make large, massive corals, from the
growing of plate over plate.

The first of the following figures, represents one of the
delicately branching species, of natural size ; and the second,
a portion of the same, much enlarged. The latter figure
shows that the branches are made up of minute cells. From
each cell, when alive, the bryozoum extends a circlet of ten-
tacles, less than a line in diameter.

1, 2, HOKNEKA LICHENOroES ; 3, DISCOPOBA SKBNBI, SmITT.

The encrusting kinds are common in all seas. The crust
of cells they make is often thinner than paper. A portion of
such a crust is represented, enlarged, in figure 3. When ex-
panded, the surface is covered over with the delicate flower-like
bryozoa. A low magnifying power is necessary to observe them

NULLIPOBES, 107

distinctly. The animals, unlike true polyps and the Hydroids,
have two extremities to the alimentary canal, and in this, and
other points, they are Molluscan in type.

The cells of a group never have connection with a common
tube, as in the Hydroids ; on the contrary, each little Bryozoum,
in the compound group or zoothome, is wholly independent of
the rest in its alimentary canal.

Bryozoans occur in all seas and at all depths ; and in early
Paleozoic time they contributed largely to the making of lime-
stone strata.

IV. NULLIPORES.

The more important species of the Vegetable Kingdom that
afford stony material for coral reefs are called NuUipores.
They are true Algae or sea- weeds, although so completely stony
and solid that nothing in their aspect is plant-like. They form
thick, or thin, stony incrustations over surfaces of dead corals,
or coral rock, occasionally knobby or branching, and often
spreading lichen-like.

They have the aspect of ordinary coral, especially the Mil-
lepores, but may be distinguished from these species by their
having no cells, not even any of the pin-punctures of those
species.

Besides the more stony kinds, there are delicate species, of-
ten jointed, Qd^^QdiOoralUnes^ which secrete only a little lime in
their tissues, and have a more plant-like look. Even these
grow so abundantly on some coasts, that, when broken up and
accumulated along the shore by the sea, they may make thick
calcareous deposits. Agassiz has described such beds as hav-
ing considerable extent in the Florida seas.

108 VORALS AND CORAL ISLANDS.

V. THE REEF-FORMIISTG CORALS AND THE CAUSES INFLU
ENCING THEIR GROWTH AND DISTRIBUTION.

I. DISTRIBUTION IN LATITUDE.

Reef-forming species are the warm-water corals of the
globe. A general survey of the facts connected with the tem-
perature of the ocean in coral-reef seas appears to sustain the
conclusion that they are confined to waters which, through even
the coldest winter month, have a mean temperature not below
68^ F. Under the equator, the surface waters in the hotter
part of the ocean have the temperature of 85^ F. in the Pacific,
and 83^ F. in the Atlantic. The range from 68^ F. to 85« F.
is, therefore, not too great for reef-making species.

An isothermal line, crossing the ocean where this winter-
temperature of the sea is experienced, one north of the equator,
and another south, bending in its course toward or from the
equator wherever the marine currents change its position,
will include all the growing reefs of the world ; and the area
of waters may be properly called the coralrveef seas.

This isothermal boundary line, the isocryme (or cold-watei*
line) of 68^ F., extends, through mid-ocean, near the parallel of
28^ ; but in the vicinity of the continents it varies greatly from
this, as explained beyond in the course of remarks on the geo-
graphical distribution of reefs. It is to be observed that the
temperature of 68^ F. is a temporary extreme — ^not that under
which the polyps will flourish. Except for a short period, the
waters near the limits of the coral seas are much warmer ; the
mean for the year is about 73i^ F. in the North Pacific, and
70^ F. in the South ; from which it may be inferred that the
summer mean would be as high at le^st as 78^ and 74^ F.

Over the sea thus limited coral reefs grow luxuriantly, yet

GEOGBAPHIGAL DiaTRIBUTION OF CORALS. 109

in greatest profusion and widest variety through its hotter por-
tions. Drawing the isocryme of 74^ F. (that is, the isotherm
for 74^ R as the mean for the coldest month) around the
globe, the coral-reef seas are divided, both north and south of
the equator, into two regions, a torrid., and a subtorrid., as they
are named by the author (see Chart beyond, from the Author's
Report on Crustacea) ; and these correspond, as seen below,
to a marked difference in the corals which they grow.

Further, the torrid region should be divided, as the distri-
bution of corals show, into a warmer and a cooler torrid, the
isocryme separating the two being probably that of 78^.

But, before considering the facts connected with the geo-
graphical distribution of existing coral-reef species, it is impor-
tant to have a correct apprehension of what are these reef spe-
cies as distinct from those of colder and deeper seas.

The coral-reef species of corals are the following. —

1. In the AstraBa tribe (Astraeacea), all the many known
species.

2. In the Fungia tribe (Fungacea), almost all known spe-
cies, the only exceptions at present known being two free spe-
cies found much below coral-reef depths, in the Florida seas,
by C. F. de Pourtales, one of them, at a depth of 450 fathoms.

3. In the Oculina tribe (Oculinacea), all of the Orbicellids ;
part of the Oculinids and Stylasterids ; some of the Caryophyl-
lids, Astrangids and Stylophorids ; all of the Pocilloporids.

4. In the Madrepora tribe (Madreporacea), all of the Mad re-
porids and Poritids; many of the Dendrophyllia family or
Eupsammids.

6. Among Alcyonoids, numerous species of the Alcyonium
and Gorgonia tribes, and some of the Pennatulacea.

6. Among Hydroids, the Millepores and Heliopores.

7. Among Algae, many NuUipores and Corallines.

110 CORALS AND CORAL ISLANDS,

The corals of colder waters, either outside of the coral- reel
seas, or at considerable depths within them, comprise, accord-
ingly, the following: —

1. A very few Fungids.

2. Some of the Oculinids ; many of the Astrangids and
Caryophyllids ; many Stylasterids ; a few Stylophorids.

3. Many of the Eupsammids.

4. Some of the Gorgonia and Pennatula tribes, and a few
of the Alcyonium tribe.

5. A few Milleporids of the genus Pliobothrus.

A large proportion of the cold water species are solitary
polyps.

Through the torrid region, in the central and western Pa-
cific, that is, within 15^ to 18 "^ of the equator, where the tem-
perature of the surface is never below 74^F. for any month of
the year, all the prominent genera of reef-forming species are
abundantly represented — those of the Astraeacea, Fungacea,
Oculinacea, Madreporacea, Alcyonoids, Millepores and NuUi-
pores. The Feejee seas afford magnificent examples of these
torrid region productions. Astrseas and Maeandrinas grow
there in their fullest perfection ; Madrepores add flowering
shrubbery of many kinds, besides large vases and spreading
folia ; some of these folia over six feet in expanse. Mussae
and related species produce clumps of larger flowers ; Meru-
linse, Echinopor^, Gemmiporas and Montiporae form groups
of gracefully infolded or spreading leaves ; Pavonia?, Pocilli-
porse, Seriatopor^ and Porites branching tufts of a great vari-
ety of forms ; Tubipores and Xenise, beds or masses of the
most delicately-tinted pinks ; Sponggodiae, large pendant clus-
ters of orange and crimson ; and Fungise display their broad
disks in the spaces among the other kinds. Many of the
species may be gathered from the shallow pools about the reefs.

QEOGRAPHIGAL DISTRIBUTION OF CORALS. HI

But with a native canoe, and a Feejee to paddle and dive, the
scenes in the deeper waters may not only be enjoyed, but boat-
loads of the beautiful corals be easily secured.

The Hawaian Islands, in the north Pacific, between the^
latitudes 19^ and 22^, a,re outside of the torrid zone of oceanic
temperature, in the suhtorrid, and the corals are consequently
less luxuriant and much fewer in species. There are no Mad-
repores, and but few of the Astrsea and Fungia tribes ; while
there is a profusion of corals of the hardier genera, Porites and
Pocilliporae.

The genera of corals occurring in the East Indies and Eed
Sea are mainly the same as in the Central Pacific ; and the
same also occur on the coast of Zanzibar.

At the eastern of the Pacific coral islands, the Paumotus,
which are within the limits of the torrid region, the variety of
species and genera is large, but less so than to the westward.
Special facts respecting this sea have not been obtained. The
author's observations were confined to the groups of islands
farther west, the department of corals having been in the hands
of another during the earlier part of the cruise of the Govern-
ment Expedition with which he was connected.

The Gulf of Panama and the neighboring seas, north to the
extremity of the California peninsula and south to Guayaquil,
lie within the torrid region ; but in the cooler part of it. The
species have throughout a Pacific character, and nothing of
the West Indian; but they are few in number, and are much
restricted in genera. There are none, yet known, of the As-
trseacea, and no Madrepores. Prof. VerriU, through the study
of collections made by F. H. Bradley and others, has observed
that there are, near Panama, a few species of Porites and Den-
drophylli^, a Stephanaria (near Pavonia), two species of Po-
cilliporae, two of Pavonia, one of them very large and named

112 C0RAL8 AND CORAL ISLANDS.

P. gigantea V., several Astrangids, and a few other small
species, besides a large variety under the Gorgonia tribe. At
La Paz, on the California peninsula at the entrance to the Gulf,
occur a small but beautiful Fungia {F. elegansY.), three Pon-
tes, a Dendrophyllia, a Pocillipora, some Astrangids, and
many fine Gorgoniae. The character of the species is that of
the cooler torrid region, rather than that of the warmer
torrid.

Owing to the cold oceanic currents of the eastern border
of the Pacific — one of which, that up the South American
coast, is so strong and chilling as to push the southern isocryme
of 68^, the coral-sea boundary, even beyond the Galapagos,
and north of the equator — the coral-reef sea, just east of Pan-
ama, is narrowed to 20*^, which is 36^ less of width than it has
in raid ocean ; and this suggests that these currents, by their
temperature, as well as by tJieir usual westward direction^ have
proved an obstacle to the transfer of mid-ocean species to the
Panama coast.

In the West Indies the reefs lie within the limits of the
isocryme of 74^ F., or the torrid region ; and yet the variety
of species and genera is very small compared with the same in
the central Pacific. The region contains some large Madre-
pores, the M. palmata^ a spreading foliaceous species that
forms clumps two yards in diameter ; M. cervicornis^ a stout,
sparsely-branched tree-like species, which attains a height of
fifteen feet; M.prolifera^ a handsome shrub-like species, of rath-
er crowded branches ; besides others ; and these are marks of the
existence of the wa7*mer torrid region ; yet the sea has not as
high a temperature as the hottest part of the Pacific. The species
of the Astraea tribe are few in number, and among the largest
kinds are the Maeandrinse (the Diploria being here included).
None of the free Fungi daB are known excepting the two spe-

GEOQRAPHICJAL DISTRIBUTION OF CORALS, 113

cies in deep water, and none of the Pavonise among the com-
pound species ; but the massive Siderinae (Siderastroeas) are
common, and the foliaceous Agaricice and Mycedia. Of the
Oculina tribe, species of Oculina, Cladocora and Astrangia are
rehitively more numerous than in the central Pacific ; but
there are none of the Pocilliporids, which are common both in
the torrid and subtorrid regions of the Pacific. Millepores are
very common. Gorgoniae, are of many species.

Prof Verrill observes that not a single West Indian coral
occurs on the Panama coast, although, on the opposite coast, at
Aspinwall, there are found nearly all the reef-building species
of Florida, viz. : Porites astrceoides Lmk., P. clavania Lmk.,
Madrepora palmata L., M, cervicornis L., M, prolifera L.,
Mceandrma clivosa V., M, lahyrinthica^ M. sinuosa Les., with
other species of Maeandrina, Manicina areolata Ehr., Sider-
astrcea {Sideinna) radiata V., S. galaxea BL, Againcia agari-
cite^Sj OrbiceUa cavernosa V., 0. annularis D. Moreover no
West Indian species is known to be identical with any from
the Pacific or Indian ocean.

The reefs of the Brazilian coast south of Cape Roque lie in
the subtorrid region of oceanic temperature, or between the is-
ocrymes of 74^ and 68^. The reef corals extend as far south
as Cape Frio, according to Prof. C. F. Hartt. The species, as
determined by Prof. Verrill, from Prof Hartt's collections, re-
semble the West Indian. All species of Madrepora, Maean-
drina, Diploria, Manicina, Oculina, genera eminently charac-
teristic of the West Indies, appear to be wanting, while the
most important reef-making genera are Favia^ Acantliastroea^
Orhicella^ Siderastrcea^ Porites^ and Millepora, and also, of
less importance, Miissa and some others. A few species, viz. :
Siderasirma stellata V., OrbiceUa a^erta V., Astrma gravida
v., and Porites solida V., are very close to West Indian spe-

114 C0BAL8 AND COMAL ISLANDS.

cies; and Millepora alcicornis is an identical species, though
different in variety.

The Bermudas are in the North Atlantic subtorrid region,
in the range of the Gulf Stream. The few reef-making species
that occur there are all West Indian, viz. : The species of the
Astr^a tribe, Isophyllia dipsacea^ I. rigida^ Diploria cerebri-
formis; of the Oculina tribe, Oculina diffusa^ Oculina varicosa^
Oculina pallens^ Oculina Valenciennesii ; of the Fungia tribe,
Siderastrcea radians^ Mycedium fragile; of the Madrepora
tribe, Porites clavaria ; also the Millepora alcicornis^ and the
common West India Alcyonoids, Gorgonia flabellum^ Plexaura
crassa Lx., PI fiexuosa Lx., PL homomalla Lx., Pterogorgia
Americana Ehr., Pt acerosa^ Ehr.

The facts presented are sufficient to show that temperature
has much to do with the distribution of reef corals in latitude,
while proving also that regional peculiarities exist that are not
thus accounted for.

II. DISTRIBUTION IN DEPTH.

Quoy and Gaymard were the first authors who ascertained
that reef forming corals were confined to small depths, contrary
to the account of Poster and the early navigators. The mis-
take of previous voyagers was a natural one, for coral reefs
were proved to stand in an unfathomable ocean ; yet it was
from the first a mere opinion, as the fact of corals growing at
such depths had never been ascertained. The few species which
are met with in deep waters appear to be sparsely scattered,
and nowhere form accumulations or beds.

The above-mentioned authors, who explored the Pacific in
the Uranie under D'Urville (and afterward also in the As-
trolabe), concluded from their observations that five or six
fathoms (30 or 36 feet) limited their downward distribution.

RANGE IN DEPTH OF G0RAL8, 115

Ehrenberg, by his observations on the reefs of the Red Sea.
confirmed the observations of Quoy and Gaymard ; he conclud-
ed that living corals do not occur beyond six fathoms. Mr.
Stutchbury, after a visit to some of the Paumotus and Tahiti,
remarks, in Volume I. of the West of England Journal, that
the living clumps do not rise from a greater depth than 16 or
17 fathoms.

Mr. Darwin, who traversed the Pacific with Captain Fitz-
roy, R. N"., gives 20 fathoms as not too great a range.

In his soundings oflP the fringing reefs of Mauritius, in
the Indian ocean, on the leeward side of the island, he ob-
served especially two large species of Madrepores, and two
of Astr^ea ; and a Millepora down to fifteen fathoms, with
also, in the deeper parts, Seriatopora ; between fifteen and
twenty fathoms a bottom mostly of sand, but partly covered
with the Seriatopora, with a fragment of one of the Madre-
pores at twenty fathoms. He states that Capt. Moresby, in
his survey of the Maldives and Chagos group, found, at seven
or eight fathoms, great masses of living coral ; at ten fathoms,
the same in groups with patches of white sand between ; and,
at a little greater depth, a smooth steep slope without any
living coral ; and further, on the Padua Bank, the northern
part of the Laccadive group, which had a depth of twenty-five
to thirty-five fathoms, he saw only dead coral, while on other
banks in the same group ten or twelve fathoms under water,
there was growing coral.

In the Red Sea, however, according to Capt. Moresby and
Lieut. Wellstead, there are, to the. north, large beds of living
corals at a depth of twenty-five fathoms, and the anchors were
often entangled by them; and he attributes this depth, so
much greater than reported by Ehrenberg, to the peculiar pu-
rity, or freedom from sediment, of the waters at that place. Kot-

116 CORALS AND CORAL ISLANDS,

zebue states that in some lagoons of the Marshall group he ob-
served living corals at a depth of twenty-five fathoms, or one
hundred and fifty feet

Prof Agassiz observes that about the Florida reefs, the
reef-building coi-als do not extend below 10 fathoms. Mr. L.
F. de Pourtales states that he found species of Oculina and Clad-
ocora off" the Florida reefs living to a depth of 15 fathoms.

It thus appears that all recent investigators since Quoy and
Gaymard have agreed in assigning a comparatively small depth
to growing corals. The observations on this point, made dur-
ing the cruise of the Wilkes Exploring Expedition, tend to
confirm this opinion.

The conclusion is borne out by the fact that soundings in the
course qf the various and extensive surveys afford no evidence
of growing coral beyond twenty fathoms. Where the depth
was fifteen fathoms, coral sand and fragments were almost uni-
formly reported. Among the Feejee Islands, the extent of
coral-reef grounds surveyed was many hundreds of square
miles, besides the harbors more carefully examined. The reefs
of the Navigator Islands were also sounded out, with others
at the Society Group, besides numerous coral islands ; and
through all these regions no evidence was obtained of corals
living at a greater depth than fifteen or twenty fathoms.
Within the reefs west of Viti Lebu and Vanua Lebu, the anchor
of the Peacock was dropped sixty times in water from twelve
to twenty- four fathoms deep, and in no case struck among
growing corals ; it usually sunk into a muddy or sandy bottom.
Patches of reef were encouutered at times, but they w^ere at a
less depth than twelve fathoms. By means of a drag, occasion-
ally dropped in the same channels, some fleshy Alcyonia
and a few Hydroids were brought up, but no reef-forming
species.

RANGE m DEPTH OF CORALS. 117

Outside of the reef of Upolu, corals were seen by the writer
growing in twelve fathoms. Lieutenant Emmons brought up
with a boat-anchor a large Dendrophyllia from a depth of
fourteen and a half fathoms at the Feejees ; and this species
was afterward found near the surface. But Dendrophyllia, it
may be remembered, is one of the deep-water genera.

These facts, it may be said, are only negative, as the sound-
ing-lead, especially in the manner it is thrown in surveys, would
fail of giving decisive results. The character of a growing
coral bed is so strongly marked in its uneven surface, its deep
holes and many entangling stems, to the vexation of the sur-
veyor, that in general the danger of mistake is small. But al-
lowing uncertainty as great as supposed, there can be little
doubt after so numerous observations over so extended regions
of reefs.

The depth of the water in harbors and about shores where
there is no coral, confirms the view here presented. At Upo-
lu, the depth of the harbors varies generally from twelve to
twenty fathoms. On the south side of this island, off Falealili,
one hundred yards from the rocky shores. Lieutenant Perry
found bare rocks in eighteen and nineteen fathoms, with no ev-
idence of coral. There is no cause here which will explain the
absence of coral, except the depth of water; for corals arid
coral reefs abound on most other parts of Upolu. Below Fa-
lelatai, of the same island, an equal depth was found, with no
coral. Off the east cape of Falifa harbor, on the north side of
Upolu, Lieutenant Emmons found no coral, although the depth
was but eighteen fathoms. About the outer capes of Funga-
sa harbor, Tutuila, there was no coral, with a depth of fifteen
to twenty fathoms ; and a line of soundings across from cape
to cape, affbrded a bottom of sand and shells, in fifteen to
twenty-one and a half fathoms. About the capes of Oafonu

118 CORALS AND CORAL ISLANDS.

harbor, on the same island, there was no coral, with a depth
of fifteen fathoms.

Similar results were obtained about all the islands surveyed,
as the charts satisfactorily show. There is hence little room to
doubt that twenty fathoms may be received as the ordinary
limit in depth of reef corals in the tropics.

It may however be much less, possibly not over half this, on
the colder border of the coral-reef seas, as, for example, at the
Hawaian Islands and the atolls northwest of that group. It
is natural that regions so little favorable for corals on account
of the temperature should differ in this respect from those in
the warmer tropics.

It may be here remarked, that soundings with reference to
this subject are liable to be incorrectly reported, by persons
who have not particularly studied living zoophytes. It is of
the utmost importance, in order that an observation supposed
to prove the occurrence of living coral should be of any value,
that fragments should be brought up for examination, in order
that it may be unequivocally determined whether the corals
are living or not. Dead corals may make impressions on a
lead as perfectly as living ones.

As to the origin of this small range in depth — about 120
feet- — temperature must be admitted as one cause, it having
been proved to be predominant with regard to distribution of
life throughout the extent and depths of the ocean. Yet it can
hardly in this case be the only cause. The range of tempera-
ture 85^ to 74^ gives sufficient heat for the development of the
greater part of coral-reef species ; and yet the temperature at
the 100 foot plane in the middle Pacific is mostly above 74.^.

CAUSES AFFECTING THE GROWTH OF CORALS. 119

III. LOCAL CAUSES INFLUENCING DISTRIBUTION.

Coral making species generally require pure ocean water,
and they especially abound in the broad inner channels among
the reefs, within the large lagoons, and in the shallow waters
outside of the breakers. It is therefore an assertion wide from
the fact that only small corals grow in the lagoons and chan-
nels, though true of lagoons and channels of small size, or of
such parts of the larger channels as immediately adjoin the
mouths of freshwater streams.

There are undoubtedly species especially fitted for the open
ocean ; but as peculiar conveniences are required or the col-
lection of zoophytes outside of the line of breakers, we have
not the facts necessary for an exact list of such species. From
the very abundant masses of Astrseas, Mgeandrinas, Porites,
and Madrepores thrown up by the waves on the exposed reefs^
it was evident that these genera were well represented in the
outer seas. In the Paumotus, the single individuals of Porites
lying upon the shores were at times six or eight feet in diam-
eter. Around the Duke of York's Island the bottom was ob-
served to be covered with small branching and foliaceous
Montipores, as delicate as any of the species in more protected
waters.

Species of the same genera grow in the face of the breakers,
and some are identical with those that occur also in deeper wa-
ters. Numerous Astraeas, Mseandrinas and Madrepores grow
at the outer edge of the reefs where the waves come tumbling
in with their full force. There are also many Millepores and
some Porites and Pocillipores in the same places. But the
weaker Montipores, excepting incrusting species, are found in
stiller waters either deep or shallow.

120 C0BAL8 AND CORAL ISLANDS.

Again, the same genera occur in the shallow waters of the
reef inside of the breakers. Astrceas, M^anclrinas and Pocilli-
pores are not uncommon, though requiring pure waters. Tliere
are also Madrepores, some growing even in impure waters.
One species was the only coral observed in the lagoon of Hon-
den Island (Paumotus), all others having disappeared, owing
to its imperfect connection with the sea. Upon the reefs en-
closing the harbor of Eewa (Viti Lebu), where a large river,
three hundred yards wide empties, which during freshets en-
ables vessels at anchor two and a half miles off its mouth to
dip up fresh water alongside, there is a single porous species
of Madrepora (M. cribripora), growing here and there in
patches over a surface of dead coral rock or sand. In similar
places about other regions, species of Porites are most com-
mon. In many instances, the living Porites were seen stand-
ing six inches above low tide, where they were exposed to sun-
shine and to rains ; and associated with them in such exposed
situations, there were usually great numbers of Alcyonia and
Xenise. The Siderinse endure well exposure to the air.

The exposure of six inches above low tide, where the tide
is six feet, as in the Feejees, is of much shorter duration than
in the Paumotus, where the tide is less than half this amount ;
and consequently the height of growing coral, as compared
with low-tide level, varies with the height of the tides.

Porites also occur in the impure waters adjoining the
shores ; and the massive species in such places commonly
spread out into flat disks, the top having died from the depo-
sition of sediment upon it.

The effects of sediment on growing zoophytes are strongly
marked, and may be often perceived when a mingling of fresh
water alone produces little influence. We have mentioned
that the Porites are reduced to flattened masses by the lodg-

CAUSES AFFEGTINO THE GROWTH OF CORALS. 121

ment of sediment. The same takes place with the hemispheres
of Astrsea ; and it is not uncommon, that in this way large
areas at top are deprived of life. The other portions still live
unaffected by the injury thus sustained. Even the Fungise,
which are broad simple species, are occasionally destroyed over
a part of the disk through the same cause, and yet the rest re-
mains alive. It is natural, therefore, that wherever streams or
currents are moving or transporting sediment, there no corals
grow ; and for the same reason we find few living zoophytes
upon sandy or muddy shores.

The small lagoons, when shut out from the influx of the
sea, are often rendered too salt for growing zoophytes, in con-
sequence of evaporation, — a condition of the lagoon of Ender-
by's Island.

They also are liable to become highly heated by the sun,
which, likewise would lead to their depopulation.

Coral zoophytes sometimes suffer injury from being near
large fleshy Alcyonia, whose crowded drooping branches lying
over against them, destroy the polyps and mar the growing
mass. Again, the dead parts of a zoophyte, though in very many
cases protected by incrusting nuUipores, shells, bryozoaiis, etc.,
as already explained, in others is weakened by boring shells
and sponges. Agassiz states, in his paper on the Florida
Reefs (Coast Survey Report for 1851): "Innumerable bor-
ing animals establish themselves in the lifeless stem, piercing
holes in all directions into its interior, like so many augjirs,
dissolving its solid connection with the ground, and even pen-
etrating far into the living portion of these compact communi-
ties. The number of these boring animals is quite incredible,
and they belong to different families of the animal kingdom ;
among the most active and powerful we would mention the
date-fish or Lithodomus, several Saxicavae, Petricolae, A ca&,

X22 CORALS AND CORAL ISLANDS.

and many worms, of whicli the Serpula is the largest and most
destructive, inasmuch as it extends constantly through the liv-
ing part of the coral stems, especially in the Ma3andrina. On
the loose basis of a M^andrina, measuring less than two feet
in diameter, we have counted not less than fifty holes of the
date-fish — some large enough to admit a finger — besides hun-
dreds of small ones made by worms. But however efficient
these boring animals may be in preparing the coral stems for
decay, there is yet another agent, perhaps still more destruc-
tive. We allude to the minute boring-sponges, which pene-
trate them in all directions, until they appear at last com-
pletely rotten through."

On the other hand Serpulas and certain kinds of barnacles
(of the genus Creusia, etc.) penetrate living corals without in-
jury to them. They attach themselves when young to the sur-
face of the coral, and finally become imbedded by the increase
of the zoophyte, without producing any defacement of the sur-
face, or affecting its growth. Many of these Serpulas grow with
the same rapidity as the zoophyte, and finally produce a long
tube, which penetrates deep within the coral mass ; and, when
alive, they expand a large and brilliant circle or spiral of deli-
cate rays, making a gorgeous display among the coral polyps.
Instinct seems to guide these animals in selecting those corals
which correspond with themselves in rate of growth ; and
there is in general a resemblance between the markings of a
Creusia and the character of the radiations of the Astraea it in-

habits.

In recapitulation, the three most influential causes of the
exclusion of reef-forming corals from coasts are the following :

I. The too low temperature of the waters along shores.

II. The too great depth of the waters.

III. The proximity of th« mouths of rivers, on account of

RATE OF GROWTH OF CORALS. 123

which sediment is distributed along the coast adjoining and
over the sea bottom.

IV. BATE OP GROWTH OF CORALS.

The rate of growth of coral is a subject but little under-
stood. We do not refer here to the progress of a reef in for-
mation, which is another question complicated by many co-op-
erating causes ; but simply to the rapidity with which partic-
ular living species increase in size. There is no doubt that
the rate is different for diiferent species. It is moreover prob-
able that it corresponds with the rate of growth of other al-
lied polyps that do not secrete lime. The rate of growth of
Actinia" might give us an approximation to the rate of growth
in coral animals of like size and general character ; for the ad-
ditional function of secreting lime would not necessarily re-
tard the maturing of the polyp ; and from the rate of growth
of the same animals in the young state, we might perhaps
draw some inferences as to the rate in polyps of corresponding
size. But no satisfactory observations on this point have yet
been made.

Although the rapidity is undoubtedly far less than was
formerly reported, the following facts from different sources
seem to show that the rate is greater than has been of late be-
lieved. Mr. Darwin, citing from a manuscript by Dr. Allan,
of Forres, some experiments made on the east coast of Mada-
gascar, states that, in December, 1830, twenty corals were
weighed, and then placed by him apart on a sandbank, in three
feet water (low tide), and in the July following, each had nearly
reached the surface and was quite immovable ; and some had
grown over the others Mr. Darwin mentions also a state-
ment made to him by Lieut Wellstead, that "in the Persian

124 COEALS AND CORAL ISLANDS.

Gulf a ship had her copper bottom encrusted in the course of
twenty months, with a layer of coral two feet thick, — evi-
dently to be accepted hesitatingly. He also speaks of a chan-
nel in the lagoon of Keeling atoll having been stopped up in
less than ten years ; and of the natives of the Maldives find-
ing it necessary occasionally to root out, as they express it,
coral knolls from their harbors.

Mr. Stutchbury describes a specimen consisting of a spe-
cies of oyster whose age could not be over two years, encrust-
ed by an Agaricia weighing two pounds nine ounces ; but he
does not state whether the shell was that of a living oyster
or not.

Dr. D. F. Weinland states that on Hayti, in a small coral
basin between the town of Corail and the island Cay mites,
never disturbed by vessels on account of the small depth of
water, he observed several branches of the Madrepora cervi-
cornis projecting above the surface of the water from three to
five inches, all of which, down to the water level, were dead,
as a result evidently of exposure to the air. This was in the
month of June. He adds that all along the north shore of
Hayti, the water level is from four to six feet higher in the
winter season than during summer ; and suggests that the
growth of three to five inches, above referred to, might have
been made during the three winter months.

Duchassaing (in L'Institut, 1846, p. 117) observes that in
two months some large individuals of Madrepora prolifera
which he broke away, were restored to their original size.
More definite and valuable is the observation of Mr. L. F. de
Pourtales, that a specimen of Mceandrina lahyrinthica^ meas-
uring a foot in diameter, and four inches thick in the most
convex part, was taken from a block of concrete at Fort Jef-
ferson, Tortugas, which had been in the water only twenty

RATE OF GROWTH OF CORALS.* 125

years. Again, Major E. B. Hunt mentions, in the Americaii
Journal of Science for 1863,* the fact of the growth of a Maean-
drina at Key West, Florida, to a radius of six inches in twelve
years, showing an average upward increase in this hemispherical
coral of half an inch a year, if, as is evidently implied, this
radius was a vertical radius. Major Hunt deposited speci-
mens of corals of his collection near Fort Taylor, Key West,
in the Yale College Museum, and three of these are labelled
by him as having grown to their present size between the
years 1846 and 1860, or in fourteen years. Two are speci-
mens of Oculina diffusa; one is a clump four inches high
and eight broad ; and the other has about the same height.
The weight of the first of these clumps is forty-four ounces.
The rate of four inches in fourteen years would be equal to
about 3^ twelfths of an inch a year in height, or three and one-
seventh ounces a year of solid coral. The other specimen is
of the Moeandinna divosa V. ; it has a height of two and a
quarter inches and a breadth of seven and a half inches. This
is equivalent to about a sixth of an inch of upward growth
in fourteen years. The specimen weighs aboat eighteen ounces.
It is not certain that with either of these specimens the germs
commenced to grow the first year of this interval, and hence
there is much doubt with regard to these calculations.

The following observations are from a paper read by
Prof Verrill before the Boston Society of Natural History
in 1862. The wreck of a vessel, supposed to have been the
British frigate Severn, lost in 1793 near "Silver Bay," off
Turk's Islands, is covered witli growing corals. It lies (accord-
ing to the journal of Mr. J. A. Whipple, by whom specimens
were collected in 1857) in about four fathoms of water. One
of the specimens was a mass of the species Orhicella annula-
ris^ shaped somewhat like a hat ; it is attached to the top of a

126 " CORAL a AND CORAL ISLANDS.

bell and spreads outward on all sides. The thickness of the
coral at the centre is about eight* inches, and the breadth fifl
teen. Another specimen consisted of an olive jar and glass
decanters cemented together by a mass, of like size, of the same
species of coral. The interval since the wrecking of the ves-
sel, to 1857, was sixty-four years, and if the corals commenced
their growth immediately after the wreck the increase of this
species of coral is very slow.

The journal of Mr. Whipple, in the library of the same
society, contains the records of his observations on the spot,
and the efforts made to remove the corals in order to examine
the wreck. The following are a few extracts made from it by
Prof. Verrill :

April 21, 1857. — Moored our boat over the remains of a
large wreck, * * its depth being from three to ten fath-
oms. I made the first descent in the armor. I found the bot-
tom very uneven and covered with the remains of a man-of-
war, what appeared to be the bow lying in a gulch, with the
shanks of three large anchors, the palm of only one of which
projected out of the coral rock.

April 22. — Made a second descent and commenced exam-
ining in six fathoms of water on what appeared to be mid-
ships. All astern of this is thick branching coral (Madrepora),
and it must have made very fast, the branches being twelve
inches in diameter and sixteen feet in height. To look among
it from the bottom reminds one of a thick forest of a heavy
growth of timber. * * * This branched coral appears to
grow where there is but very little iron, as I could see no guns
or shot around its roots. Commenced examining the cannon
with hammer and chisel. * * * Near these cannon, which
must have been near the forward part of the ship, I com-
menced to work on a clear space between the cannon. After

RATE OF GROWTH OF CORALS. 127

breaking three inches of coral crust I found the collar bone
of a man, a brass regulating screw belonging to a quadrant
and some large lead bullets. * * * The magazine must
be under the branch-coral, which has been sixty-four years
growing. * * *

Here we have a height of sixteen feet in a Madrepora
attained in sixty-four years., or at the rate of three inches a
year. Madrepores evidently grow with much greater rapidity
than the massive corals.

Observations on the rate of growth of different species
might easily be made by those residing in coral seas, either in
the manner adopted by Mr. Allan (placing the specimens on
a platform which could be raised for examination from time
to time — say every five years), or by placing marks upon par-
ticular species where they are immovably fixed to the bottom.
By inserting slender glass pins a certain distance from the sum-
mit of a Madrepore, its growth might be accurately measured
from month to month. Two such pins in the surface of an
Astraea, would in the same manner, by the enlarging distance
between, show the rate of increase in the circumference of
the hemisphere ; or if four were placed so as to enclose an
area, and the number of polyps counted, the numerical in-
crease of polyps resulting from budding, might be ascer-
tained. If specimens are selected, as done by Mr. Allan, it is
important that they should be placed where other corals are
growing in luxuriance, so as to be sure that there are no dele-
terious influences to retard growth. It is to be hoped that
some of the foreign residents at the Sandwich, Society, Samo-
an or Feejee Islands will take this subject in hand. There are
also many parts of the West Indies where these investiga-
tions might be conveniently made.

128 C0BAL8 AND GOBAL ISLANDS.

CHAPTER II.

STRUCTURE OF OORAL REEFS AISTD
ISEAlSr33S.

Coral reefs and coral islands are structures of the same
kind under somewhat different conditions. They are made
in the same seas, by the same means ; in fact, a coral island
has in all cases been a coral reef through a large part of its
history, and is so still over much of its area. The terms how-
ever are not synonymous. Coral islands are reefs that stand
isolated in the ocean, away from other lands, whether now
raised only to the water's edge and half submerged, or covered
with vegetation ; while the term coral reef., although used for
reefs of coral in general, is more especially applied to those
which occur along the shores of high islands and continents.
There are peculiarities in each making it convenient to describe
them separately.

I. COEAL REEFS.

I. GENERAL FEATURES.

Coral reefs are banks of coral rock built upon the sea-bot-
tom about the shores of tropical lands. In the Pacific, these
lands, with the exception of New Caledonia and others of
large size to the westward, are islands of volcanic or igneous
rocks, and they often rise to mountain heights. The coral ;
reefs which skirt their shores are ordinarily wholly submerged
at high tide ; but, at the ebb, they commonly present to view a|
broad, flat, bare surface of rock, just above the water level,

8TBUCTUBE OF CORAL REEFS. 129

strongly contrasting with the steep slopes of the endrcled
island.

ISTearing in a vessel a coral-bound coast, the first sign of the
reef, when the tide is well in, is a line of heavy breakers, per-
haps miles in length, off a great distance from the land. On
closer view, some spots of bare reef may be distinguished as
the waves retreat for another plunge; but the next moment
all again is an interminable line of careering waters. Happy
for the cruiser in untried reef-regions, if the surging waves con-
tinue to mark the line of reef; for a treacherous quiet some-
times intervenes, which seems to be evidence of deep waters
ahead, and the unsuspecting craft dashes onward ; but soon it
is grinding over the coral masses, then thumping heavily at
short intervals, and, in a few moments more, is landed helpless
on the coral reef. The heavier billows as they roll by a vessel
lin such a plight — the author's experience attesting — ^have a
way of lifting it and then letting it drop with all its
weight against the bottom, and hence, unless prompt escape is
in some way secured, the assaulting waves gain speedy posses-
sion, and soon after make complete the work of destruction.
At low tide the breakers often cease, or nearly so. But the
reef for the most part, is then in full view, and, with a good
lookout aloft, favorable winds, and plenty of daylight, navi-
gation is comparatively safe.

Some idea of the features of a tropical island thus bor-
dered, may be derived from the following sketch. The reef
to the right is observed to fringe the shore, making a simple
broad platform, as an extension, apparently, of the dry land.
To the left there is the same coral platform at the surface, but
it is divided by a channel into an inner and an outer reef — a
fringing and a harrier reef, as these two parts are called. At
a single place the sea is faced by a cliff; and here, owing to

130 C0BAL8 AND CORAL ISLANDS.

the boldness of the shores and depth of waters, the reef is
wanting. The barrier reef at one point has a passage through
it, w4iich is an opening to a harbor ; and many such harbors
exist about coral-girt islands.

HIGH ISLAND WITH BAHRIEK AlTD FRINGING REEFS.

While some islands have only narrow fringing reefs, others
are almost or quite surrounded by the distant barrier, which
stands off like an artificial mole to protect the land from an
encroaching ocean. The barrier is occasionally ten or fifteen
miles from the land, and encloses not only one, but at times
several, high islands. From reefs of this large size, there are
all possible variations down to the simple fringing platform.

The inner channel is sometimes barely deep enough at low
tide for canoes, or for long distances may be wanting entirely.
Then again, it is a narrow intricate passage, obstructed by
knolls or patches of coral, rendering the navigation dangerous.
Again, it is for miles in length an open sea, in which ships
find room to beat against a head wind with a depth of ten,
twenty, or even thirty fathoms. Yet hidden reefs make caution
necessary. Patches of growing corals, from a few square feet
to many square miles in extent, are met with over the broad
area enclosed by these distant barriers.

These varieties of form and position are well exemplified
in a single group of islands — the Feejees ; and the reader is
referred to the chart of this Archipelago at the close of this
volume.

STRUGTUBE OF GOBAL BEEFS, 131

Near the middle of the chart is the island Ooro ; its shores,
excepting the western, are bordered by a fringing reef. The
island Angau^ south of Goro, is encircled by a coral breakwa-
ter, which on the southern and western sides runs far from the
shores, and is a proper barrier reef, while on the eastern side,
the same reef is attached to the coast and is a fringing reef
From these examples we perceive the close relation of barrier
and fringing reefs. While a reef is sometimes quite encircling,
in other instances it is interrupted, or wholly wanting, along
certain shores ; and occasionally it may be confined to a single
point of an island.

Above Angau lies Nairai ; although a smaller island than
Angau, the barrier reef is of greater extent, and stretches off
far from the shores. To the eastward of Nairai are Vatu
Rera^ OhicJiia^ and Naiaxi^ other examples of islands fringed
around with narrow reefs. Lahemha^ a little more to the
southward, is also encircled with coral ; but on the east side
the reef is a distant barrier. In Aiva^ immediately south of
Lakemba, the same structure is exemplified; but the coral
ring is singularly large for the little spots of land it encloses.
The Argo Reef^ east of Lakemba, is a still larger bai'rier, en-
circling two points of rock called Bacon's Isles. It is actually
a large lagoon island, twenty miles long, with some coral islets
in the lagoon, and two of basaltic constitution, of which the
largest is only a mile in diameter. Aiva and Lakemba are in
fact other lagoon islands, in which the rocky islands of the in-
terior bear a larger proportion to the whole area. The same
view is further illustrated by comparing the Argo reef with
Nairai, Angau, or Moala : these cases differ only in the great-
er or less distance of the reef from the shores and the extent
of the enclosed land.

Passing to the large islands Vanua Levu and Vtti LevUj

132 C0RAL8 AND CORAL ISLANDS.

we observe the same peculiarities illustrated on a much grand-
er scale. Along the southern shores of Viti Levu, the coral
reef lies close against the coast ; and the same is seen on the
east side and north extremity of Vanua Levu. But on the
west side of these islands, this reef stretches far off from the
land, and in some parts is even twenty-five miles distant, with
a broad sea within. This sea, however, is obstructed by reefs,
and along the shores there are proper fringing reefs.

The forms of encircling reefs depend evidently to a great
extent on that of the land they enclose. That this is the case
even in the Argo reef, and such other examples as offer now
but a single rock above the surface of the enclosed lagoon, Ave
shall endeavor to make apparent, if not already so, when the
cause of the forms of coral islands is under discussion. Yet it
is also evident that this correspondence is not exact, for many
parts of the shores, and sometimes more than half the coasts,
may be exposed to the sea, while other portions are protected
by a wide barrier.

In recapitulation, we remark, that reefs around islands may
be (1) entirely encircling ; or they may be (2) confined to a larg-
er or a smaller portion of the coast, either continuous or inter-
rupted ; they may (3) constitute throughout a distant barrier ;
or (4) the reef may be fringing in one part and a barrier in
another ; or (5) it may be fringing alone : the barrier may be
(6) at a great distance from the shores, with a wide sea within,
or (7) it may so unite to the fringing reef that the channel be-
tween will hardly float a canoe. These points are sustained
by all reef regions.

It is to be noted that the fringing and barrier reefs here
pointed out are not the whole of the coral reef; they are only
the portions that have been built up to the water's level. Be-
tween them, and also outside of all, there are the submerged

STRUCTURE OF CORAL REEFS.

13a

fl. ..:..,

\ >

I../ ..-.,

9\

^^t^-^^^:^

NKW CALEDONIA.
9/2^ inch to 60 miZeSx

STRUCTURE OF CORAL REEFS, 135

coral banks which are continuous with the higher portions, and
all together make up the coral reef-ground of an island.

A wide difference in the extent of reef-grounds, follows
from the above-mentioned facts. On some coasts there are only-
scattered groups of corals, or rising knolls, or mere points of
emerged coral rock ; but again, as for example, west of the two
large Feejee Islands, there may be three thousand square miles
of continuous reef-ground, occupied with coral patches and in-
termediate channels or seas. The enclosing barrier off Vanua
Levu alone is more than one hundred miles long. The Ex-
ploring Isles, in the eastern part of the Feejee group, have a
barrier eighty miles in circuit. New Caledonia has a reef
alonp; its whole western shores, a distance of two hundred and
fifty miles, and it extends one hundred and fifty miles further
north, adding this much to the length of the island. The
great Australian barrier forms a broken line, twelve hundred
and fifty miles in length, lying off the coast from the Northern
Cape to the tropical circle.

The seas outside of the lines of coral reef are often unfath-
omable within a short distance of the line of breakers.

In the further description of reef-grounds, or reef-forma-
tions, there are several distinct subjects for consideration, as
is obvious from the preceding remarks. These are —

1. Outer reefs^ or reefs formed from the grow^th of corals
exposed to the open seas. Of this character are all proper
barrier reefs, and such fringing reefs as are unprotected by a
barrier.

2. Inner reefs^ or reefs formed in quiet water between a
barrier and the shores of an island. ^

3. Channels^ or seas within harriers^ which may receive de-
tritus either from the reefs, or from the shores, or from both of
these sources combined.

136 CORALS AND CORAL ISLANDS,

4. Beaches and heach formations^ produced by coral accu-
mulations on the shores through the action of the sea and
winds.

The outer and inner reefs, channels, and beaches, act each
their part in producing the coral formations in progress about
islands.

II. OUTER REEFS.

The barrier and other outer reefs are always submerged at
high tide, except where elevated at surface by accumulations
of beach sands. The level is generally that of about one third
tide. The coral rock is built up by the agencies at w^ork to
this level, and hence the existence of the broad platform-like
top of the barrier. The surface is however not even, for there
are many pools of water over it, even at the lowest tides, espe-
cially toward its outer limits, where corals of various kinds are
oTOwing luxuriantly, Avith fit associates of shells, star-fishes,
echini, holothurias with their large flower-bearing heads,
sponges, corallines and sea- weeds, making scenes of rare beauty.
The growing corals are, however, most abundant along the outer
margin of the reef, and in the adjoining shallow seas. Here
they grow in profusion ; but yet the eager lover of coral land-
scapes will be often disappointed by finding among the crowd-
ed plantations, extensive areas of coral sand.

The outer margin of the reef receives the plunging waves,
and under this action, and the consequent unequal growth of
the corals, the outline is very irregular, being often deeply cut
into, and hence having sometimes long channels that give en-
trance to the surging tide, and to the currents that flow back
in preparation for the next breaker. From it, seaward, the
depth of water usually sinks off* rapidly from three to six fath-
oms, and then falls away more gradually for many rods, or it

STRUCTURE OF CORAL REEFS. 137

may be some hundreds of yards ; over the bottom in these shal-
low waters are spread out the coral plantations, down to a
depth of 80 or 100 feet. Finally there is a rather abrupt de
scent to depths beyond the reach of an ordinary sounding-lead.
The great difference in the rapidity with which the water deep-
ens depends chiefly on the varied character of submarine
slopes. Shallow waters may extend out for miles, especially
off the prominent points or angles ; but it is more common to
meet with the opposite extreme — great depths within a few
hundred feet.

The outer reef or coral platform is generally a little the
highest at its seaward margin, owing partly to the growth of
ordinary corals and other species on this part, and also to the
accumulations which naturally would there be piled up by
the waves and become cemented. This part is therefore first
laid bare by the retreating tide ; and though a tempting place
for a ramble, it is often a dangerous place on account of the
heavy breakers. There is not only greater height, but often
also a remarkably smooth surface to the reef-rock, looking as
if water-worn, and frequently a blotching of the rock with va-
rious shades of pink and purple. These colors and the smooth-
ness, as observed by Chamisso, are due to incrusting Nulli-
pores ; and to the same calcareous sea- weeds, as Darwin first
observed, is often owing the increased height. The material
of the incrusting plant is more solid than ordinary coral, for it
is without a pore ; and layer is added to layer until it has con-
siderable thickness. It is thus an important protection to the
reef against the wash of the waters.

Darwin states that on Reeling's Island, the Nullipore bed
has a thickness of two or three feet and a breadth of twenty
feet. NuUipores are abundant on the Paumotu reefs. Still,
they are not essential to the formation or protection of an

138 CORALS AND CORAL ISLANDS,

outer reef, and are not always present; the outer margin is
higher than the rest of the reef when they are absent.

The Nullipores are not alone on this outer edge, for there
are alwajs sprigs of Madrepores, small Astrgeas, and some oth-
er corals, lodged in the cavities, with many Echini, star-fishes
and sea-anemones, besides barnacles and serpulas ; and fish of
many colors dart in and out of the numerous recesses.

Outer reefs are far more liable than the inner to become
covered with accumulations of coral fragments and sand
through the force and inward movement of the waves. The
debris gathered up by the w^aters finds a lodgment some dis-
tance back from the margin — it may be one or two hundred
feet, or as many yards, and gradually increases, until in many
instances dry land is formed, and an islet covered with vegeta-
tion appears. Such effects are confined chiefly to the reef on
the sides open to the prevailing wind, and the final result, a
green islet, is not of common occurrence. But occasionally,
the reef for miles has become changed from the coral bank,
bare at low or middle tide, to habitable land, and makes liter-
ally, as at Bolabola, a green belt to the island of volcanic rocks
and lofty hills within. The causes and the result are much the
same as in a coral island, and the steps in the process are
more particularly described beyond where treating of atolls.

The rock of the outer reef, wherever broken, exhibits usu-
ally a compact texture. In some parts it consists of coral
fragments, rounded or angular, of quite large size, firmly ce-
mented. Other portions are a finer coral breccia or conglom-
erate. Still others, more common, are solid white limestones,
as impalpable and homogeneous in texture as the old limestones
of our continents. There are also other regions where the
corals in the rock retain the original position of growth. But
the rock in general consists of the d6bris of the coral fields,

8TRUGTURE OF COMAL REEFS, 139

consolidated by a calcareous cement ; and the great abundance
of the tiner variety of rock indicates that much of it has orig-
inated trom coral sand or mud. Wherever broken, it usually
presents the character here described, a texture indicating a
detrital or conglomeritic origin. Such a reef-rock is formed
in the midst of the waves ; and to this fact it owes many of its
peculiarities. Reef-rocks made of corals in the position of
growth are formed about the outer reefs wherever the corals
grow undisturbed.

Besides corals, the shells of the seas contribute to it, and it
sometimes contains them as fossils, along with bones of fishes,
exuvia of crabs, spines and fragments of Echini, Orbitolites
(disk-shaped foraminifers), and other remains of organic life
inhabiting reef-grounds.

in. FORMATIONS IN THE SEA OUTSIDE OF THE BARRIER REEFS.

While barrier reefs are mostly made up of coarse coral ma-
terial, owing to the rough action of the waves, the region im-
mediately outside of the breakers, where of much width, is, to a
depth of 100 feet, one of growing patches of coral and extended
surfaces of coral sands.

Isolated islets of reef-rock are not however of common oc-
currence in the middle Pacific, though occurring in large groups
like the Feejees. They are most likely to occur where there
are great regions of shallow water extending outward from the
barrier, and where the tides are not heavy or there is partial pro-
tection from them. In some seas, such isolated patches are shaped
somewhat like a great mushroom^ — ^having a narrow trunk
or column below, supporting a broad shelf of reef above. Mr.
J. A. Whipple, in his Journal, referred to on page 126, figures
and describes one of these " coral heads '' standing in water fif-
ty feet deep, near Turks Island. Its trunk, which made up

140

CORALS AND CORAL ISLANDS.

two thirds of its height (or of the fifty feet), was only fifteen
feet in diameter along its upper half; and it supported above a
great tabular mass one hundred feet in diameter, whose top was
bare at low tide. The tide at this place is but two feet, and
this is favorable to the preservation of such top-heavy struc-
tures. In many places, he says, these tops have joined together,
leaving arches between them ; and in some parts of the reef-re-
gion such united coral-heads cover acres in extent, being joined
together above and supported by their pillars. A case is re-
ported of a whale having gone through one of these under
passages after being struck with a harpoon. Mr. Whipple
also states that there are cavernous recesses in some of thfese
heads, some that are 200 to 300 feet across; and "when there
is a heavy swell on, the water is one entire sheet of white foam,
caused by its being forced through them and the air entering
as the heavy sea recedes from them."

THE LIXO CORAIi REEF, ABROLHOS.

Professor C. F. Hartt, in his '^ Geology, etc., of Brazil"
(1870), describes very similar coral-heads in his account of the
reefs of the Abrolhos, and represents a scene of coral-head tops
in a sketch, of which the preceding is a copy. Professor Hartt
speaks of it as giving simply a general view of the region with-

STRUCTURE OF CORAL REEFS. 141

out any attempt at accuracy of position. The patches of reef
in the view are of this coral-head kind, though not all as slen-
derly supported as that above described. A vessel is represent-
ed passing through a passage between two of them. Prof.
Hartt, after describing the fringing reefs of the Abrolhos, gives
the following account of the outside coral formations (p. 199)
'' Corals grow over the bottom in small patches, in the open sea,
and, without spreading much, often rise to a height of forty or
fifty or more feet, like towers, and sometimes attain the level
of low water, forming what are called on the Brazilian . coast
chapeiroes (signifying big hats). At the top these are usually
very irregular, and sometimes spread out like mushrooms, or,
as the fishermen say, like umbrellas. Some of these chapei-
roes are only a few feet in diameter. A few miles to the east-
ward of the Abrolhos is an area, with a length of nine to ten
and in some places a breadth of four miles, over which these
structures grow abundantly, forming the well known Parcel
dos Abrolhos, on which so many vessels have been wrecked."
^' Among these chapeiroes I measured a depth of sixteen to
twenty metres, and once, while becalmed, I found twenty me-
tres alongside of one and three metres on top. They are
rarely laid bare by the tide. They do not coalesce here to
form large reefs as they do to the west of the islands. * * *
Sometimes vessels striking heavily on small chapeiroes, break
them off and escape without injury, as has been remarked by
Mouchez. At other times a vessel may run upon one and stick
fast by the middle of the keel, to the amazement of the cap-
tain, who finds deep water all around, the vessel being perched
on the chapeirQes like a weather-cock on the top of a tower."

"In the northern part of the Parcel the chapeiroes so close-
ly unite as to form an immense reef, which has grown upward
to a level a little above low water, and is quite uncovered at

142 C0RAL8 AND CORAL ISLANDS.

low tide." " The northeastern part of the reef is called the
Recife do Lixo, that is, Reef of the lixo^ a shark-like ray which is
furnished with large crushing teeth and frequents the reef in
search of shell-fish."

The rock of the submerged coral-heads is but a loose a^*-
gregation of corals in the position of growth, except probably,
in their lower portion, where the open spaces may be filled
with sand and fragments and all cemented too-ether.

The deposits of sand or coral mud over the bottom of the
seas outside of barrier reefs are sometimes of great extent.
These sands are the fine detritus which the return flow of the
breaker bears seaward ; and, in still deeper water, the deposits
should be mainly of the finest calcareous sand or mud — fit ma-
terial for impalpable compact limestones. The waters outside
of the reef, especially when moved by heavy tidal currents or
storms, are often milky with the coral sand ; and while the
coarser sand is dropped near the shores, the finer may be
carried for miles and distributed far out to sea. As Major
Hunt, in his observations on the Florida Reeft remarks, this
'' white water " is one of the signs of proximity to a coral reef.
After storms, the white coral material subsides and the waters
become clear again.

Mr. Jukes, who made special examinations of the Australi-
an reef region, and others in that vicinity, in H. M. S. Fly,
states that in the deeper waters outside of the great barrier,
"and in all the neighboring East India seas, from Torres
Straits, north of Australia, to the Straits of Malacca, wher-
ever the bottom was brought up by the lead, it proved to
be a very fine-grained, impalpable, pale olive-green mud,
wholly soluble in dilute hydrochloric acid, and therefore essen-
tially carbonate of lime. The substance, when dried, looked
much like chalk, excepting in its greener tinge. How far this

8TBTIGTURE OF CORAL REEFS. 143

calcareous matter may be due to foraminifers, rather than cor-
als, is not known."

Since the tidal waves on any coast that is gradually shal-
lowing have a landward propelling power, the coral sands are
mostly gathered about the reef, and generally are not to any
great extent lost in the depths of the ocean. The great ocean-
ic currents, like that of the Gulf stream, might bear awaj^ the
lighter material for long distances, if it swept with full strength
over the shore reefs ; but it is generally true that such cur-
rents are little felt close in shore. Notwithstanding the prox-
imity of the Florida reefs, and the strength of the Gulf stream
in the channel between the Keys and Florida, the adjoining
sea-bottom consists mainly of common mud, with relics of deep
water life, and only sparingly of coral debris. According to
Mr. L. F. de Pourtales, between twelve fathoms and one
hundred, in the Florida channel, outside of the reef, coral frag-
ments occur, but are rare ; dead specimens of Cladocora and
Oculina occur to a depth of about 50 fathoms. But on the
other side of the channel, "along the Salt Key Bank, dead
corals were dredged up in 315 fothoms ; but this is at the foot
of a very steep slope washed by the edge of the Gulf stream ;
which is much better defined here than on the Florida side."
The bottom, in the Florida channel, of 100 fathoms, is a rocky
plateau, and outside of 200 fathoms, a mud full of foraminifers,
Globigerina mud^ as it is called from the species characterizing
it ; and yet this channel is situated beneath the Gulf stream and
close by the Florida reefs. The facts seem to show that in most
regions the reefs contribute little calcareous matter to the deep
ocean. This may be otherwise over the bottom, of compara-
tively little depth, of a great Archipelago like that of the East
Indies.

144 COMALS AND COBAL ISLANDS.

IV. INNER REEFS.

In the still waters of the inner channels or lagoons, when
of large extent, we find corals growing in their greatest per-
fection, and the richest views are presented to the explorer of
coral scenery. There are many regions — in the Feejees, ex-
amples are common — where a remote barrier encloses as pure
a sea as the ocean beyond ; and the greatest agitation is only
such as the wind may excite on a narrow lake or channel.
This condition gives rise to some important peculiarities of
structure in the inner reefs, in which the inner margin of the
barrier reef participates.

In the general appearance of the surface, the inner gener-
ally much resemble the outer reefs. They are nearly flat, and,
though mostly bare of life, and much covered with coral sand,
there are seldom any large accumulations of coral debris. The
margin is generally less abrupt ; yet there is every variety of
slope, from the gradually inclined bed of corals to the bluff de-
clivity with its clinging clumps. In different parts, there are
many portions still under water at the lowest tides ; and here
(as well as upon the outer banks) fine fishing sport is afforded
the natives, who wade out at ebb tide with spears, pronged
sticks, and nets, to supply themselves with food. The lover of
the marvellous may find abundant gratification by joining ui
such a ramble ; for besides living corals, there are myriads of
other beings which science alone has named, of various beauti-
ful forms and colors, as becomes the inhabitants of a coral world.

Between the large reefs, which spread a broad surface, at
the water's edge, of lifeless coral rock, sometimes of great ex-
tent, there are other patches, still submerged, that are cov-
ered with growing corals throughout. They are of different
elevations under the water's surface ; and though at times but

STRUCTURE OF CORAL REEFS. 145

a few yards in breadth, there is often alongside of them a
depth of many fathoms. The mushroom shape described
above is common among them ; and a ship striking one with
her keel may crush it and glide on. More frequently, they
are at bottom like the solid reef above described, and the con-
test is more likely to be fatal to the vessel than to the coral
patch. In a passage between two reefs near Tongatabu, called
the Astrolabe channel, the sloop-of-war Vincennes ran on a
coral patch, which had been laid down as a reef. It stopped
the ship for a moment, but broke away under her ; and in the
survey of the passage afterward, says Captain Wilkes, '' no shoal
was found in the place where the ship had struck, and we had the
satisfaction of knowing that we had destroyed it without injury
to the vessel." Corals grow over these patches, as in the shal-
low waters about other reefs ; and, as elsewhere, there are deep
cavities among the congregated corals, in which a lead will some-
times sink to a depth of many feet, or even fathoms. These
holes about growing reefs often give much annoyance to the
boat which may venture to anchor upon them ; and in many
an instance diving is found to be the only resource left for free-
ing the foul anchor.

The margins of the reefs in and about the inner channels
are often luxuriant with magnificent corals quite to the ed^-e,
so that while the reef is elsewhere solid rock to its very top,
here at the margin it is alive and may be said literally to be
growing.

The rock of the inner reefs seldom consists of rolled or
broken fragments of coral like a large part of that of the
outer reef. It is often made of dead corals, standing to a
great extent as they grew ; yet it is generally compact and
firm in texture. The cavities among the branches and masses

gradually become filled with coral sand, and the whole is
10

146 CORALS AND CORAL ISLANDS.

finally cemented and so made solid. At Tongatabu and
among the Peejee Islands, reefs thus formed of corals standmg
in their growing positions are common. Though now mere
dead rock, and exceedingly firm and compact, the limits of
the several constituent coral masses may be distinctly made
out. Some individual specimens of Porites in the rock of the
inner reef of Tongatabu are twenty-five feet in diameter ; and
Astraeas and Masandrinas, both there and in the Peejees, meas-
ure twelve to fifteen feet. These corals, when growing be-
neath the water, form, as has been stated, solid hemispheres,
or rounded hillocks ; but on reaching the surface, the top dies,
and enlargement takes place only on the sides ; and in this
manner the hemisphere is finally changed to a broad cylinder
with a flat top. This was the condition of the Astrseas and
Porites in the reef-rock referred to. Such a platform looks
like a Cyclopean pavement, except that the calcareous ce-
menting material, filling in between the huge masses, is more
solid than in any work of art : it even exceeds in compactness
the corals themselves. Other portions of reefs consist of
hranching corals, with the intervals filled in by sand and small
fragments ; for even in the stiller waters fragments are to some
extent produced. A rock of this kind is often used for build-
ings and for walls on the island of Oahu. It consists mainly
of Porites, and in many parts is still cavernous, or but imper-
fectly cemented.

There is also to be found about inner reefs, over large
areas, the solid white limestone already described, showing
internally no evidence of its coral origin, and containing rarely
a shell or other imbedded fossil. It is a result of the consoli-
dation of the fine coral sand or mud that is made and accu-
mulated through the action of the light waves that work over
the inner reefs. It has been said that large regions of barren

STRUCTURE OF CORAL REEFS. 147

sands or mud occur among the patches of growing corals, and
these would give origin to this compact limestone.

The formation of the inner reefs goes on at a less rapid
rate than that of the outer, because the process depends on the
growth of the corals with comparatively little aid from the
action of the waves. Moreover, as is explained more par-
ticularly in another place, impure or fresh waters and cur-
rents often operate to destroy the living corals or retard their
progress.

Owing to the last mentioned cause, the inner reefs are not
usually joined directly to the beach. They stand off a little,
separated by an interval of shallow water. At Mathuata, in
the Feejees, however, the reef extends quite up ; and it is
the more remarkable as the coast is flat, the site of a Feejee
village, and a mile or two back stands a high bluff. On an
island off this part of Vanua Lebu there is another exam-
ple of this fact, and many more might be cited. In such
cases, however, there is evidence that the shores upon which
the corals grew were bare rocks, instead of moving beach-
sands.

From these descriptions it appears that the main distinc-
tion between the inner and outer reefs consists in the less frao-- i

i
mentary character of the rock in the former case, the less fre- '«

quent accumulations of debris on their upper surface, and the
more varied features and slopes of the margin. Moreover,
the Nullipores, which seem to flourish best in the breakers,
are here but sparingly met with.

The variety of coral zoophytes is also greater in the stiller
waters, and there are species peculiar to the different regions.

148 C0BAL8 AND CORAL ISLANDS,

V. CHANNELS AMONG REEFS.

To complete this review of the general appearance and
constitution of reef formations, it remains to add some partic-
ulars respecting the channels which intervene between coral
patches, or separate them from the shores of an island, and
also to describe the coral accumulations forming beaches.

The reef of Australia has been instanced as affording an
example of one of the larger reef-channels, varying from twenty
to sixty miles in width, and as many fathoms in depth. Its
average distance from the land is twenty to thirty miles, and
the ordinary depth ten to twenty-five fathoms ; but toward the
southern end, where the channel is widest, the depth exceeds
sixty fathoms. " The new Caledonia barrier reefs, 400 miles in
length," says Darwin, " seldom Approach within eight miles of
the shore." The reefs west of the large Feejee Islands are
another remarkable example, the reef grounds being in some
parts twenty-five miles wide, and the waters within the bar-
rier, where sounded, twelve to forty fathoms in depth. The
barrier in this instance may be fi^om a few hundred yards to
half a mile in width ; and some of the inner patches are of
the same extent ; but by far the larger part of the reef-ground
is covered with deep waters, mostly blue like the ocean, and
as clear and pure. In the course of the cruise of the Wilkes
Exploring Expedition, the sloop of war Peacock sailed along
the west coast of both Viti Lebu and Vanua Lebu, within the
inner reefs, a distance exceeding two hundred miles.

The island of Tahiti, on its northern side, presents a^igood
illustration of a narrow channel, and at the same time one
that exhibits the usual broken or interrupted character of
reefs. This is seen in the following cut, in which the reefs,
both fringing and barrier, are the parts enclosed by dotted

STRUCTURE OF CORAL REEFS.

149

lines. The outer reef extends half to two-thirds of a mile
from the shore. Within it, between Papieti and Matavai,
there is an irregular ship channel, varying from three to

CORAL REEFS OFF THE NORTH SHORE OP TAHITI.

twenty fathoms in depth. Occasionally it enlarges into har-
bors ; and in other parts it is very intricate, though throughout
navigable by large vessels. The island of Upolu, of the Sa-
moan Group, is bordered by a reef nearly a mile wide on part
of its northern shore ; but the waters within are too shallow
for a canoe at low tide ; and therefore, notwithstanding its ex-
tent, the reef is rather a fringing than a barrier reef. Within
the green belt that encircles Bolabola (p. 138) there is a large
and deep channel navigable by ships.

Beneath these channels lies, in general, the coral rock of the
reef-region — the inferior part of the great reef formation whose
upper portions constitute the so-called barrier and fringing
reefs. The rock would necessarily resemble that of the inner
reefs already described ; but there should be a larger propor-
tion of the white compact limestone made from the fine coral
sands carried oif from the higher reefs by the currents.

150 CORALS AND CORAL ISLANDS.

Yet the bottoms of these channels are not always made up
of calcareous or coral sands and fragments ; for the volcanic
or basaltic lands they adjoin are a source of ordinary mud ;
and the river courses of the land and the tidal currents of the
sea will often determine the nature of the bottom, or may
cause in it alternate variations.

At Upolu the white coral sands of the reefs (or in more
general terms the reef debris), forms the bottom. In some
places this coral material had the consistence of mud, and it
was seldom observed to be covered with coarse material ;
there were some small patches of coral over it, and here and
there a growing mass of Porites. The fresh waters of the
shores do not flow over these wide reefs, as there is no proper
inner channel, and there is consequently no shore detritus
mingled with the reef debris.

At Tahiti, the sounding lead, where dropped in the channels,
usually brought up sand, shells, and fragments of coral. At
Tongatabu, the bottom where the Peacock anchored was a
grayish blue calcareous mud, appearing as plastic as common
clay ; it consisted solely of comminuted corals and shells, with
coloring matter probably from vegetable and animal decom-
position.

But to the west of the larger Feejee islands, in the channels
near the land, soundings commonly indicated a bottom of mud
made from the material of the rocks of the mountains, and the
same was freque^itly brought up with our dredges. On the
north side of Vanua Lebu, a stream had so filled with its de-
tritus the wide channel into which it empties, that for a mile
the depth is but two to three fathoms, although elsewhere the
depth is mostly from twelve to twenty fathoms ; and at least
half a dozen square miles of land had been added to the shores
from this source Though due principally to shore material,

STRUCTURE OF CORAL REEFS. 151

the reefs have probably added somewhat to these accumula-
tions ; yet little coral sand could be detected in the mud by
the eye, and the proportion is certainly very small. In many
places where the ships of the Wilkes Exploring Expedition an-
chored, having the reef not more than five hundred yards from
the ship, the material of the bottom was wholly mud from
the land, as much so as if there were no corals or shells with-
in many miles.

When the materials from both sources, the shore and the
reef, are mingled, the proportion will necessarily depend on
the proximity to the mouths of streams, the breadth of the
inner waters or channels, and the direction and force of the
currents. These tidal currents often have great strength, and
aie much modified and increased in force at certain places, or
diminished in others, by the position of the reef with reference
to the land. Sweeping on, they carry off* the coral debris
from some regions to others distant ; and again they bear along
and distribute only the shore detritus. It is thus seen that
the same region may diff^er widely in its adjacent parts, and
seemingly aff'ord evidence in one place that there is no coral
near, and in another no high land, although either is within a
few rods, or even close alongside.

The extent of the land in proportion to the reef will have
an obvious eff^ect upon the character of the channel or lagoon
depositions. When the island stands, like one of Bacon's isles
in the Feejees, as a mere point of rock in a wide sea en-
closed by a distant barrier, the streams of the land are small
and their detritus quite limited in amount. In such a case,
the reef, and the growing patches scattered over the lagoon, are
the sources of nearly all the material that is accumulated upon
the bottom.

The bottom between the inner reefs within the great Aus-

152 CORALS AND CORAL ISLANDS,

tralian barrier, according to Jukes, as brought up by the
dredge from depths of fifteen to twenty fathoms, often resem-
bles the unconsolidated mass of a shelly or coralline limestone.
At other times it consisted very largely of the small disk-shaped
foraminifers called Orbitolites, closely allied in form and na-
ture to the Nummulites of the Tertiary; and they seemed
in some places to make up the whole sand of the beaches, both
of the coral islets and of the neighboring Australian shores.

The facts show that the rock formed in such channels may
be of all the kinds that occur in reef regions — coral and shell
conglomerates, compact impalpable limestones, limestones full
of Orbitolites, or containing, as well, remains of other species of
the seas, and also rocks made of the clay, mud, sand or pebbles
of the mountains or high lands adjoining.

VI. BEACH SAND-ROCK.

Besides the ordinary coral rock, there are also beach for-
mations made of coral sands, worn shells, etc., thrown up by
the tides and waves. Their mode of formation is like that
of any sea-beach. The material is mostly like common sand in
fineness, but often much coarser. When the beach is fronted
by a distant barrier to shield it from the force of the waves,
the material is usually sand and small pebbles ; but if the reef
is narrow, so that the sea breaks over it with full force, it may
consist even of cobble stones, as on any other shore, and in-
clude also huge masses of coral rock.

These deposits become cemented by being alternately mois-
tened and dried, through the action of the recurring tides and
the wash of the sea on the shores. The waters take up some
carbonate of lime, and this is deposited and hardens among the
particles on the evaporation of the moisture at the retreat of
the tides. In some places the grains are loosely coherent, and

STRUCTURE OF CORAL REEFS, 153

seem to be united only by the few points in contact ; and with
a little care the calcareous coating which caused the union
may be distinctly traced out. In other cases, the sand has
been consolidated into a solid limestone rock, the interstices
having been filled till a compact mass was formed. Generally
even the most solid varieties show evidence of a sand origin, and
in this they differ from the reef rock. The pebbly beds pro-
duce a pudding stone of coral.

In most localities the rock is an oolite or oolitic limestone.
The grains become coated by the agglutinating carbonate of
lime, and each enlarges thus into a minute sphere — a spherical
concretion ; and the aggregation of these concretions makes
the oolite. The grains are usually much smaller than the roe
of most fishes, a resemblance which is alluded to in the name,
from the Greek wov, egg.

These beach deposits consist of regular layers, commonly
from a few inches to a foot in thickness, and are generally con-
solidated up to a line a little above high-tide mark. In all in-
stances observed, the layers dip at an angle of six to eight de-
grees down the beach. This dip is nothing but the slope of the
beach itself, and arises from the circumstance that the sands
are deposited by the incoming waves, or tides, on such a slop-
ing surface. Tutuila and Upoln, in the Navigator Group, and
Oahu in the Hawaiian, afibrd many examples of these beach
formations. At certain localities the beach sand-rock has been
washed away after it was formed ; and occasionally large mass-
es or slabs have been uplifted by the sea and thrown high up
on the beach.

Deposits of the same kind sometimes include detritus from
the hills. Black basaltic pebbles are thus cemented by the
white calcareous material, producing a rock of very singular
appearance. Near Diamond Hill, on Oahu, is a good locality

154 C0BAL8 AND CORAL ISLANDS.

for observing the steps in its formation. Many of the pebbles
of the beach are covered with a thin incrustation of carbonate
of lime, appearing as if they had been dipped in milk, and
others are actually cemented, yet so weakly that the fingers
easily break them apart.

The lime in solution in waters washing over these coral
shores is also at times deposited in the cavities or seams of the
volcanic rocks ; thus the cavities of a lava or basalt become
filled with white calcareous kernels, and the cellular lava is
changed into an amygdaloid. In large cavities, or caverns, it
often forms stalactites or stalagmitic incrustations. Similar
facts are stated by Mr. Darwin as observed on the shores of
Ascension; and many interesting particulars are given respect-
ing: calcareous incrustations on coasts in his work on Volcanic
[slands, some of which are cited beyond. They were observed
by the writer upon Madeira, in St. Jago, one of the Cape
Verds, as well as among the volcanic islands of the Pacific.

Jukes speaks of the oolitic character of the beach sand-rock
about islets connected with the Australian barrier, and states
'' that the fact that the rock was not consolidated under wa-
ter was proved by nests of turtles' eggs being found imbedded
in it, these evidently having been deposited by the animal
when the sand was above water and still loose and incoherent."

VII. DRIFT SAND-ROCK.

Still another kind of beach formation is going on in some
regions through the agency of the winds in connection with
the sea. It occurs only on the windward side of islands when
the reefs are narrow, and proceeds from the drifting of the
sand into hillocks or ridges by the winds.

The drifts resemble ordinary sand-drifts, and are often

STBUOTUBE OF CORAL BEEFS. 155

quite extensive. On Oahu, they occur at intervals around the
eastern shores, from the northern cape to Diamond Point,
Avhich forms the south cape of the island,— the part exposed to
the trades ; and they are in some places twenty to forty feet
in height. They are most remarkable on the north cape, a
prominent point exposed to the winds that blow occasionally
from the M^estward, as well as to the regular trades. They
also occur on Kauai, another of the Hawaian Islands. But
at Upolu (Samoa), where the protecting reefs are broad, the
author met with no instance worthy of mention.

These sand-banks, through the agency of infiltrating wa-
ters, fresh or sale, become cemented into a sand-rock, more or
less friable, which is frequently oolite. The rock consists of
thin layers or laminaj, which are very distinct, and indicate,
generally, every successive drift of sand which puffs of wind
had added in the course of its formation : and where a heavier
gale had blown off the top of a drift, and new accumulations
again completed it, the whole history is distinctly displaj'ed in
the rock. Several catastrophes of this kind may be made out
from the character of the lamination in the sand-blutfs on the
north side of Oahu. Since their formation, this island has
undergone an elevation of twenty-five or thirty feet ; these
hills, once on the shores, are now seventy feet above the level
of the sea, and they face the water with a bluff front (due to
degradation), in which the lamination is finely exposed to view.
The layers are but a fraction of an inch thick ; at one of the
hills large slate-like slabs may be obtained ; they have a sand-
ed surface, but are so hard within as to clink under the ham-
mer. About cavities over the surface, the rock is usually very
compact to a depth of half an inch or more, almost horny in
texture, owing to the infiltration of lime from the waters often
occupying them; but this is an exceptional variety of the

156 G0RAL8 AND CORAL ISLANDS.

rock. A particular description of these bluffs is given in the
author's report on the geology of the Hawaian islands.

One of the most interesting facts observed in connection
with these drift hills, is the absence of shells, and even of frag-
ments of shells or corals sufficiently large to be referred to ei-
ther of these sources. The material is sand, without organic
remains, although situated on shores off which, within a huo
dred yards, there are shells and corals innumerable. The grind-
in f^- action of the waves and winds reduces all the coral frag-
ments and shells, by mutual trituration, to a fine beach sand.

Oolitic beds appear to be confined to the superficial forma-
tions of a reef, that is, to the beach and wind-drift accumulations.
No example has come under the notice of the author of oolite
constituting the foundation rock of a reef or island. It is possi-
ble that such beds might in some cases be the basement rocks to a
considerable depth below ; for a reef-island might subside so
much more slowly than coral formations grow and accumulate,
that a succession of beach-made beds would be produced even
to a great thickness. Yet the probability is that the subsi-
dence would sink the surface beneath the water, and put an
end to beach and wind-drift work. The beach slope of 6"^ to
8"^ is an almost constant mark of beach-made beds.

VIII. THICKNESS OF REEFS.

We have considered in the preceding pages the peculiari-
ties of form and structure characterizing the reef formations
bordering islands and continents, and their influence upon the
enclosed land. Could we raise one of these coral-bound islands
from the waves, we should find that the reefs stand upon the
submarine slopes, like massy structures of artificial masonry ;
some forming a broad flat platform or shelf ranging around

STRUCTURE OF CORAL ISLANDS, 157

the land, and others encircling it like vast ramparts, perhaps a
hundred miles or more in circuit. The reefs that were near
the water-line of the coast would be seen to have stood in the
shallowest water, while the outer ramparts rested on the more
deeply submerged slopes. Indeed, it is obvious that with a
given slope to the declivity of the land, the thickness of the
reef resting upon it may be directly determined, as it would be
twice as great two hundred feet from the shore as at one hun-
dred feet. The only difficulty, therefore, in correctly determin-
ing the depth or thickness of any given reef, arises from the
uncertainty with regard to the submarine slope of the land.
It is, however, admitted as the result of extensive observation,
that in general these slopes correspond nearly with those of the
land above water. Mr. Dar^vdn has thus estimated the thick-
ness of the reefs of the Gambler Group (p. 265) and some other
Pacific islands, and he arrives at the conclusion, as his figures
iadicate, that some coral reefs, at their outer limits, are at least
two thousand feet in thickness.

The mountain slopes of the islands of the Pacific, except
when increased by degrading agents, do not exceed in angle
twelve or fourteen degrees, and they are often but half this
amount. The slopes of Mauna Kea and Maun a Loa, isl-
and of Hawaii, do not average over eight degrees. On the
north side of Upolu, where the reefs are wide, the inclination
is from three to six degrees. Throughout the Pacific, the
steeper slopes of the mountains are due to agencies which can-
not be shown to have affected the submarine slopes, excepting
in cases of disruption of islands by forces below.

Assuming eight degrees as the mean inclination, we should
have for the depth of reef (or water), one mile from the shore,
740 feet ; or assuming five degrees, 460 feet. Adopting the
first estimate, the Gambler Group would give for the outer

158 COBALS AND COBAL ISLANDS.

reef a thickness of at least 1,750 feet ; or with the second, 1, 150
feet. The island of Tahiti (taking the north side for data)
would give in the same manner 250 feet by the last estimate,
which we judge to be most correct ; UidoIu, by the same esti-
mate, 440 feet. The deduction for Upolu, may be too large :
taking three degrees as the inclination, it gives 260 for the
thickness at the outer margin. The results are sufficiently ac-
curate to satisfy us of the great thickness of many barrier
reefs.

These calculations, however, are liable to error from many
sources. Very different results might generally be obtained
from different sides of the same island ; and the same group
often contains islands without reefs, and others with reefs one
or even several miles from the shores. But since we may show
that the absence of a reef, or its limited extent, may be traced
to some causes restricting or modifying its formation, it is ob-
vious that the error would probably be on the side of too low
an estimate.

Adjacent to the larger islands, such as those of Vanua
Levu, and Australia, the error might be of the opposite kind ;
for the slopes of the land are of a more complex or irregular
character than on the smaller islands. In the latter, they may
be shown to belong generally to a single elevation of igneous
origin, or,at the most, to two or three combined ; while, in the
former, they may pertain to different ranges of hills or moun-
tains. For correct results in any instance, the land and its
declivities should be carefully studied beforehand, and the sys-
tem in its inclinations determined by observation. With re-
gard to Tahiti and Upolu, information bearing upon this point
was obtained, and the above conclusions may be received with
much confidence. Many of the Feejee reefs, on the same prin-
ciple, cannot be less than 2,000 feet in thickness.

STRUCTURE OF CORAL REEFS. 159

IX. A GOOD WORD FOR CORAL REEFS.

All coral-bound coasts, and especially those of islands in mid
ocean, derive great benefit from their reefs. The wide coral banks
and the enclosed channels greatly enlarge the limits tributary
to the lands they encircle. Besides being barriers against the
ocean, they are dikes to detain the detritus of the hills.
They stop the waters of the streams, and cause it to drop the
silt they were bearing off, and thus secure its addition to the land.
They prevent, therefore, the waste which is constantly going on
about islands without such barriers ; for the ocean not only en-
croaches upon the unprotected shores of small islands, but car-
ries off much of whatever the streams empty into it. The del-
ta of Rewa, on Viti Lebu, resulting from the detritus accumu-
lations of a large river, covers nearly sixty square miles. This
is an extreme case in the Pacific, as few islands are so large,
and consequently rivers of such magnitude are not common.
But there is rarely a coral-girt island which has not at leas^
some narrow plains from this source ; and upon them the vil-
lages of the natives are usually situated. Around Tahiti these
plains are from half a mile to two or three miles in width, and
the cocoa-nut and bread fruit groves are mostly confined to
them.

The reefs also provide extensive fishing-grounds for the na-
tives, and afford abundant fish, their main reliance in the way
of animal food. They also supply large interior waters for
practice in navigation and for safe communication between dis-
tant settlements. And the effect is evident in the spirit of
maritime enterprise which characterizes the islanders; for
these circumstances have favored the construction of large sail«
canoes in which they venture beyond their own land, and often
undertake voyages hundreds of miles in length. Comm.unica-

160 C0RAL8 AND CORAL ISLANDS.

tion between the Friendly Islanders and the Feejees has long
been kept up by means of these large rudely-rigged sail-canoes.

Instead of a rock-bound coast, harborless and thinly hab-
itable, like St. Helena, in the tropics, and nearly all extra-
tropical islands, the shores of these reef-bound lands are bloom-
ing to the very edge, and wide plains are spread out with
bread fruit and other tropical productions. Harbors, safe for
scores of vessels, are also opened by the same means ; and
some islands number a dozen, when the unprotected shores
would hardly have aiforded a single good anchorage. Jukes
remarks that the sea within the great Australian barrier is
'' one great natural harbor ; " and this harbor is as long as
from the extremity of Florida to Newfoundland.

Coral-reefs are sometimes viewed as only traps to sur-
prise and wreck the unwary mariner ; but whoever has vis-
ited the dreary prison-house, St. Helena, will have some appre-
ciation of the benefits derived from the growing zoophytes.

But in addition to these general benefits, there are also
contributions from the larger reef regions to the commerce
of the world. Besides pearls, there is the hiclie de mar
(called also, heche de me?'^ sea-ginseng^ and in China, tripa7ig)^
thousands of hundred-weight of which annually enter the
Chinese market from the reef-regions of the East Indies, Aus-
tralia, and the seas to the north, including the Feejee Archi-
pelago. This favorite material for Chinese dishes, either stews
or soups, etc., is dried Jiolothuria — large slug-like animals,
called often sea slugs^ and also sea cucumbers^ from their form
in the contracted state. They are not slugs, but are most
nearly related to the echinus, though having a thick flexible
skin, while the echinus has for its exterior a firm shell, armed
about with spines. The largest are only nine or ten inches
long when contracted ; but they lengthen out sometimes to

STRUCTURE OF CORAL ISLAITDS. 161

two feet or more. They live just under the sand in the shal-
low waters, with the head projecting and bearing a beautiful
feathery rosette or flower which is branchial in nature. To
fit them for exportation, the holothuria, of which half a dozen
different kinds are taken, are slit open, boiled, and then dried,
in which last state they look like " smoked sausages. Dr. S.
Wells Williams says, in his " Middle Kingdom," that " when
soaked in water, the material resembles pork rind, and is like
that in taste when stewed." They are brought to China by the
Malays from Macassar, and elsewhere. There are also large
drying-houses at the Feejees, and ships from America make
their occasional visits to collect them, with the aid of the Fee-
jees, and to dry and load up for China. The term hiche de mar,
and also the French form of it, heche de m,er, are corruptions of
the Portuguese bicho do mar, which means sea-worm, or sea-slug. ^

II. STRUCTURE OF CORAL ISLANDS.

I. FORMS AND GENERAL FEATURES.

Coral islands resemble the reefs just described, except that
a lake or lagoon is encircled instead of a mountainous island.
A narrow rim of coral reef, generally but a few hundred yards
wide, stretches around the enclosed waters. In some parts
the reef is so low that the waves are still dashing over it into
the lagoon ; in others it is verdant with the rich foliage of the
tropics. The coral-made land, when highest, is seldom more
than ten or twelve feet above high tide.

When first seen from the deck of a vessel, only a series of

dark points is descried just above the horizon. Shortly aftei

the points enlarge into the plumed tops of cocoa-nut trees, and

a line of green, interrupted at intervals, is traced along the

water s surface. Approaching still nearer, the lake and it^ belt
11

162

CORALS AND CORAL ISLANDS.

of verdure are spread out before the eye, and a scene of more
interest can scarcely be imagined. The surf, beating loud and
heavy along the margin of the reef, presents a strange contrast
to the prospect beyond, — the white coral beach, the massy
foliage of the grove, and the embosomed lake with its tiny
islets. The color of the lagoon water is often as blue as the
ocean, although but ten or twenty fathoms deep ; yet shades
of green and yellow are intermingled, where patches of sand
or coral-knolls are near the surface ; and the green is a delicate
apple-shade, quite unlike the ordinary muddy tint of shallow
waters.

CORAIi ISLAND, OR ATOLL.

ThB belt of verdure, though sometimes continuous around
the lagoon, is usually broken into islets separated by varying
intervals of bare reef ; and through one or more of these in-
tervals, a ship-channel often exists opening into the lagoon.
The larger coral islands are thus a string of islets along a
line of reef.

These laTOon islands are called atolls, a word of Maldive
origin. The king of the Maldives bears the high sounding
title of " Ibrahim Sultan, King of the thirteen Atollons and
twelve thousand Isles (see page 189); which 'Capt. W. F. W.
Owen, R. N., says is no exaggeration.

In the larger atolls, the waters within look like the ocean,
and are similarly roughened by the wind, though not to the

8TRUGTVRE OF CORAL ISLANDS. 163

same extent. Standing on the north shore of the Raraka la-
goon and looking southwest, nothing is seen but blue waters.
Far in the distance to the right, and also to the left, a few
faint dots are observed ; and as the eye sweeps around in
either direction, these dots gradually enlarge and pass into lines
of verdure, and finally, distinct groves near the observer. At
Dean's Island, another of the Paumotus, and at some of the
Carolines, the resemblance to the ocean is still more striking.
The lagoon is in fact but a fragment of the ocean cut off by
more or less perfect walls of coral reef-rock ; and the reef is
here and there surmounted by verdure, forming a series of
islets.

In many of the smaller coral islands, the lagoon has lost
its ocean character, and become a shallow lake, and the green
islets of the margin have coalesced in some instances into a
continuous line of foliage. Traces may perhaps be still de-
tected of the passage, or passages, over which the sea once com-
municated with the internal waters, though mostly concealed
by the trees and shrubbery which have spread around and
completed the belt of verdure. The coral island is now in its
most finished state ; the lake rests quietly within its circle of
palms, hardly ruffled by the storms that madden the sur-
rounding ocean.

From the islands with small lagoons, there is every variety
in gradation down to those in which there is no trace of a la-
goon. These simple banks of coral are the smallest of coral
islands. In all the larger islands the windward side is the
highest ; and sometimes it is wooded and habitable through-
out when the leeward reef is bare. The entrances to the la-
goons are accordingly on the leeward side.

A single group of islands, the Gilbert or Kingsmill, af-
fords good examples of the principal varieties. It is at once

164 CORALS AND CORAL ISLANDS,

seen from these examples that atolls are not annular. In the
southernmost, Tapateuea, the form is very narrow, the
leno-th being thirty-three miles, with the wndth of the soutliern
portion scarcely exceeding six miles, and that of the northern
more than one-half less. The emerged land is confined to one
side the eastern or windward, and consists of a series of islets
upon the eastern line of coral reef. The western side is for
the most part several feet under water, and there is hardly a
proper lagoon. Sailing by the island, to windward, the patch-
es of verdure, thus strung together, seem to rise out of a long
white line of breakers, the sea surging violently against the un-
seen coral reef upon which they rest.

Nonouti, the next island north, is about twenty miles
long by eight broad. The rim of land, though in fewer islets,
is similar to that of Tapateuea in being confined to the reef
fronting northeast. The reef of the opposite side, though bare
of vegetation, stands near low-tide level, and the whole en-
closes a large lagoon.

Aranuka and Apamama, though smaller than Nonouti,
have the same general character. Aranuka is triangular in
shape, and has an islet on the western point or cape, which is
quite prominent. Apamama differs from either of the preced-
ing in having two narrow ship entrances to the lagoon, one
through the northwestern reef, and another through the south-
western.

Kuria is a remarkable double island, without a proper
lagoon. It consists of two neighboring groves, each about a
square mile in extent, on adjacent patches of reef.

Maiana is quite regularly quadrangular, with an uninter-
rupted range of land on two of the four sides, and an exposed
reef constituting the other two.

Tarawa consists of two sides of a triangle. The western

/

■=\, ij Apaiaiig

\\ Tarawa

^- ^// Maiana.

. Marald

Kuria

-V

Ap ainaina^. ^

Aranuka

30 xyy' Tan

orFitU

17 a*

Maikixv

Tari

Island;

^f^\^ Nonouti

M

I ^*^

Taj uteouea

Jm

GILBERT OR KINGSMILL ISLANDS

'STRUCTURE OF CORAL ISLANDS. 167

reef is wanting, and the sea and lagoon have unbroken com-
munication. In place of it, there are two to ten fathoms of
water, and a bottom of coral sand. Small vessels may sail in
almost anywhere on this side to good anchorage, and there is
a passage for ships of the largest size. The depth within is
greater than on the bar, and these inner waters obviously cor-
respond to the lagoon of other islands.

Apaiang has much resemblance to Apamama in its forest
border and lagoon. Moreover, there is a ship entrance through
the southwestern reef.

Marakei is one of the prettiest coral islands of the Pacific.
The line of vegetation is unbroken. Tn a view from the mast-
head it lies like a garland thrown upon the waters ; the un-
practiced eye scarcely perceives the variation from a circular
form, however great it may be. The grove is partially inter-
rupted at one point, where there are indications of a former
passage through the reef.

Tari-tari, lying to the north of Apia, is a large triangular
atoll. It is wooded almost continuouslv on the side facinof
southeast, and has a few spots of verdure on the southwest,
with three entrances to the extensive lagoon. The northern
side is a naked reef throughout, scarcely apparent from a ship's
deck, except by the long line of breakers. Makin, just north
of Tari-tari, is a mere patch of coral reef without a lagoon.

We add a few more descriptions of Pacific islands, with
figures reduced from the maps of the Wilkes Expedition to a
scale of four- tenths of an inch to a mile.

Taiara and Henuake (figs. 1 and 2), are two small belts of
foliage, somewhat similar to Maraki. Ilenuake possessed an
additional charm in being tenanted only by birds ; and they
were so tame that we took them from the trees as if they had
been their flowers.

168

C0RAL8 AND CORAL ISLANDS.

Swain's and Jarvis's Islands (figs. 3 and 4), are of still
smaller size, and have no lagoon. The former is densely
covered with foliage, while the surface of the latter is sandy.
Both islands are a little depressed about the centre, a fact
indicating that there was formerly a lagoon.

■>-v-

f

[J

..■-< . '

HENUAKE, OR HONDEN.

Fakaafo, or Bowditch (fig. 5), 200 miles north of the
Navigator Islands, is the type of a large part of coral islands.
The bank of reef has only here and there emerged from the

N

jarvis's island.

u ....„ \\

swain's island.

FAKAAFO, OR BOWDITCH'S ISLAND.

waves and become verdant ; in other portions the reef is of
the usual height, — that is, near low-tide level, — exceptitig a
few spots elevated a little by the accunmlation of sand.

STRUCTURE OF CORAL ISLANDS.

169

The Paumotu Archipelago, the crowded cluster of coral
islands east and northeast of Tahiti, is a most instructive study
for the reader ; and a map of these islands by the Wilkes Ex-
ploring Expedition, inserted in the Narrative of the Expedi-
tion, and also in the Hydrographical Atlas, will well repay
close examination. Sailing among these islands, over eighty
in number, — only four of which are over twelve feet high exclu-
sive of the vegetation, — two or three are almost constantly in
sight from the mast-head.

The small amount of habitable land on these reef-islands
is one of their most peculiar features. Nearly the whole sur-
face is water ; and the land around the lagoon is but a narrow
rim, the greater part of which is usually under water at high
tide. This fact wall be rendered more apparent from the fol-
lowing table, containing a statement of the sizes and areas
of several islands, with the amount of habitable land. The
measures are given in geographical miles.

Carlshoff, Paumotus,
Wolchonsky, "
Raraka, "

Manhii, "

Nairsa or Deans, Paumotus.
Fakaafo, Union Group,
Duke of Clarence, "
Tapateuea, Kingsmills,
Tarawa, ''

Nonouti, "

Tari-tari, "

LENGTH.

GREATEST

AREA IN

BREADTH.

SQ. MILES.

..27 .

...13 .

... 200 ...

..15 .

... 3 .

40 ...

..15 .

...10 .

90 ...

..14 .

... ^ .

50 ...

s, 50 .

... 19 .

... 1000 ...

.. n .

... 4i .

20 ...

.. 8i .

... 5i .

27 ...

..33 .

... 6 .

60 ...

..20 .

...10 .

... 130 ...

..22 .

... 9 .

... 125 ...

..18 .

... 11 .

... 110 ...

HABITABLE
PARTS IN
SQ. MILES.

. 10
. 3

. 8

. 9

. 16

. 2i

. 2

. 6

. 8

. 7

. 4

The ten islands here enumerated have an aggregate area
of 1,852 square miles, while the amount of actual dry habit-
able land is but seventy-six miles, or less than one twenty-
fourth. In the Caroline Archipelago the proportion of land
is still smaller. Menchikoflf atoll covers an area of 500 square

170 CORALS AND CORAL ISLANDS.

miles, and includes hardly six square miles of wooded land.
In the Marshall Islands the dry land is not over one-hundredth
of the whole surface; while in the Pescadores the proportion
of land to the whole area is about as 1 to 200.

The distribution of the land upon the reef is obvious from
the sketches already given. It is seen, as long since remarked,

MENCHICOFF ATOLL.
1-20 of an inch to a mile.

that the windward side is, in general, the highest. It is also
apparent that there are not only great irregularities of form,
but that on one side the reef may at times be wholly wanting
or deeply submerged.

In many islands there is a ship-entrance through the reef,
sometimes six or eight fathoms deep, to the lagoons, where
good anchorage may be had; but the larger part have only
shallow passages, or none at all. In the Paumotus, out of the
twenty- eight visited by the Expedition, not one-half were
found to have navigable entrances. In the Carolines, where
the islands are large and not so much wooded, entrances are
of more common occurrence. About half of the Kingsmill
Islands afford a good entrance and safe anchorage. Through
these openings in the reefs, there is usually a rapid outward

STRUCTURE OF CORAL ISLANDS. 171

current, especially during the ebbing tide. At Depeyster
Island, it was found to run at the rate of two and a half miles
an hour. It was as rapid at Raraka, in the Paumotus, and, as
Capt. Wilkes remarks, it was difficult to pull a boat against
it into the lagoon.

II. SOUNDINGS ABOUT CORAL ISLANDS.

The water around coral islands deepens as rapidly and in
much the same way as off the reefs about high islands. The
atoll usually seems to stand as if stilted up in a fathomless sea.
The soundings of the Expedition afford some interesting re-
sults.

Seven miles east of Clermont Tonnerre, the lead ran out to
1,145 fathoms (6,870 feet), without reaching bottom. Within
three quarters of a mile of the southern point of this island, the
lead, at another throw, after running out for a while, brought
up an instant at 350 fathoms, and then dropped off again and
descended to 600 fathoms without reaching bottom. On the
lead, which appeared bruised, a small piece of white coral was
found, and another of red ; but no evidence of living zoo-
phytes. On the east side of the island, three hundred feet
from the reef, a bottom of coral sand was found in 90 fathoms ;
at one hundred and eighty feet, the same kind of bottom in 85
fathoms ; at one hundred and thirty feet, a coral bottom in 7
fathoms ; and from this it decreased irregularly to the edge of
the shore reef.

Off the southeast side of Ahii (another of the Paumotus),
about a cable's length from the shore, the lead, after descend-
ing 150 fathoms, struck a ledge of rock, and then fell off and
finally brought up at a depth of 300 fathoms.

Two miles east of Serle's Island, no bottom was found at
600 fathoms.

172 CORALS AND CORAL ISLANDS.

A mile and a half south of the larger Disappointment
Island, there was no bottom at 550 fathoms.

Near the eastern end of Metia, an island nearly north of
Tahiti, no bottom was found with a line of 150 fathoms ; and,
a mile distant, no bottom was reached at 600 fathoms.

In general, for one to five hundred yards from the margin
of the shore reef, the water slowl}^ deepens, and then there is an
abrupt descent at an angle of 40 or 50 degrees. The results
of earlier voyagers correspond with this statement. At con-
siderable depths, as would appear from the above facts, the
sides of the coral structure may be vertical or even may over-
hang the bottom below.

Beechey, whose observations on soundings are the fullest
hitherto published, states many facts of great interest. At
Carysfort Island, he found the depth, 60 yards from the surf
line, 5 fathoms ; — 80 yards, 13 fathoms; — 120 yards, 18 fath-
oms ; — 200 yards, 24 fathoms ; — and immediately beyond, no
bottom with 35 fathoms. At Henderson's Island, soundings
continued out 250 yards, where the depth was 25 fathoms,
and then terminated abruptly. Off Whitsunday, 500 feet
out, there was no bottom -at 1,500 feet.

Darwin states other facts bearing upon this subject, of
which we may cite the following : — At Heawandoo Pholo (one
of the Maldives), Lieutenant Powell found 50 or 60 fathoms
close to the edge of the reef. One hundred fathoms from the
mouth of the lagoon of Diego Garcia, Captain Moresby found
no bottom with 150 fathoms. At Egniont Island, 50 fath-
oms from the reef, soundings were struck in 150 fathoms. At
Cardoo Atoll, only 60 yards fi:*om the reef, no bottom was ob-
tained with a line of 200 fathoms. Off Keeling Island, 2,200
yards from the breakers. Captain Fitzroy found no bottom at
1,200 fathoms. Mr. Darwin also states that, at a depth between

STRUCTURE OF CORAL ISLANDS. 173

five aiid six hundred fathoms, the line was partly cut as if it
had rubbed against a projecting ledge of rock ; and deduces
from the fact "the probable existence of submarine cliffs."

Prof. Agassiz states that the Bahamas and the reefs
northeast of Cuba have very great depth close alongside.

There are examples also of less abrupt slopes. Northwest
of the Ilawaian Group, Captain Lisiansky, who commanded
the Russian ship Neva in a voyage round the world in the
years 1860-61, at the island bearing his name, found shallow
water for a distance of six or seven miles ; the water deepened
to ten or eleven fathoms the first mile, fifteen the second, and at
the last throw of the lead there were still but twenty-five fath-
oms. Christmas Island affords on its western side another exam-
ple of gradually deepening waters. Yet these shallow waters
terminate finally in a rapid declivity of forty or fifty degrees.

Off the prominent angles of an atoll, soundings gen-
erally continue much beyond the distance elsewhere, as was
first observed by Beechey. At Washington Island, mostly
abrupt in its shores, there is a bank, according to the surveys
of the Expedition, extending from the east point to a distance
of half a mile, and another on the west extending to a distance
of nearly two miles. At Kuria, one of the Kingsmills, sound-
ings continue for three miles from the north extremity, along
a bank stretching off from this point to the north-northwest.
Many other instances might be cited, though they are seldom as
remarkable ; yet nearly all islands, especially if the points are
much prominent, afford similar facts. The Florida reefs,
according to Prof. Agassiz, have a gradual slope to seaward
instead of the abruptness of the Bahamas. As corals may
grow on submerged land of any form, there is no reason
why the bottom around should not often deepen gradually
It has been said that the reef to leeward is generally less

174 CORALS AND CORAL ISLANDS

abrupt than that to windAvard, but facts thus far obtained are
not sufficiently definite or extensive to settle this question. It
is probably true, yet the difference, if any, must be small.

III. STRUCTURE OF CORAL ISLANDS.

The descriptions of reefs and their islets alreacjy given apply
with equal force to coral islands. By transferring here the
statements respecting the former, we should have a nearly
complete account of the latter. The same causes, with scarcely
an exception, are at work : — the growing of coral zoophytes, and
the action of the waves, of oceanic currents, and of the winds.
This resemblance will be rendered more apparent by a review
of their characters. The description will be found to be a sim-
ple recapitulation of a former paragraph.

The reef of the coral atoll, as it lies at the surface still
uncovered with vegetation, is a platform of coral rock, usually
two to four hundred yards wide, and situated so low as to be
swept by the waves at high tide. The outer edge, directly
exposed to the surf, is generally broken into points and
lao-o-ed indentations, along which the waters of the resurging
wave drive with great force. Though in the midst of the
breakers, the edge stands a few inches, and sometimes a foot,
above other parts of the platform ; the incrusting Nullipores
cover it with varied tints, and afford protection from the
abrading action of the waves. There are usually three to five
fathoms water near the margin ; and below, over the bottom,
which gradually deepens outward, beds of corals are growing
profusely among extensive patches of coral sand and frag-
ments. Generally the barren areas much exceed those flour-
ishing with zoophytes, and not unfrequently the clusters are
scattered like tufts of vegetation in a sandy plain. The grow-
ing corals extend up the sloping edge of the reef, nearly to

STRUCTURE OF CORAL ISLANDS. 175

low-tide level. For ten to twenty yards from the margin, the
reef is usually very cavernous or pierced with holes or sinuous
recesses, a hiding-place for crabs and shrimps, or a retreat for
the echini, asterias, sea-anemones and mollusks ; and over this
portion of the platform, the gigantic Tridacna, sometimes over
two feet long, and 500 pounds in weight, is often found lying
more than half buried in the solid rock, with barely room to
gape a little its ponderous shell, and expose to the waters a
gorgeously colored mantle. Further in are occasional pools
and basins, alive with all that lives in these strange coral seas.

The reef-rock, when broken, shows commonly its detritus
origin. Parts are of compact homogeneous texture, a solid
white limestone, without a piece of coral distinguishable, and
rarely an imbedded shell. But generally the rock is a breccia
or conglomerate, made up of corals cemented into a compact
mass, and the fragments of which it consists are sometimes
many cubic feet in size.

It is apparent that we are describing a second time an
outer reef. Without dwelling further upon its characters, we
may pass to the features of the reef when raised above the
waters and covered with vegetation.

Sections of coral islands and their lagoons have been given?
by Captain Beechey and Mr. Darwin. We add another, by
way of illustration, although little may be presented that is
novel after the excellent descriptions of these authors. Sketch-
es of several of these islands, showing the general relation of
the rim of land to the reef and the lagoon within, are given
in the maps of islands on pages 165, 168. The following sketch
represents a section of the rim of land from the sea on one
side (the left), to the lagoon on the other. In the view, the
part m a represents the shallow sea bordering an island, and
abruptly deepening one to six hundred feet from the line of

176

CORALS AND CORAL ISLANDS,

breakers. In these shallow waters are the growing corals;
yet, as before stated, a large part is often barren sand or coral
rock, especially where the depth is over fifty feet.

SECTION OF THE KIM OF AN ATOLL.

From atohi^ the shore platform or reef-rock, nearly at
low-tide level, with the margin {a) slightly elevated, and usually
mucih incrusted at top with Nullipores. From the platform
there is a rise, by a steep beach {b c), of six or eight feet, to
the wooded part of the coral belt represented between c and d.
From d to e there is a gently sloping beach bordering the
lagoon. Beyond 6, the waters of the lagoon at first deepen
gradually, and then fall off^ more or less abruptly.

In the Paumotus, the shore platform, the steep beach, and
the more gently sloping shore of the lagoon are almost con-
stant characteristics.

The width of the whole rim of land, when the island gives
no evidence of late elevation, varies from three hundred yards
to one-third of a mile, excepting certain prominent points, more
exposed to the united action of winds and waves and often
from opposite directions, which occasionally exceed half a mile.
The shore platform is from one to three hundred feet in
width, and has the general features of a half-submerged outer
reef. Its peculiarities arise solely from the accumulations
which have changed the reef into an island. Much of it is
commonly bare at low tide, although there are places where it
is always covered with a few inches or a foot of water ; and
the elevated edge, the only part exposed, often seems like an
embankment preventing the water from running off. The

STRUCTURE OF CORAL ISLANDS, 177

tides, as they rise, cover it with water throughout, and bear
over it coral fragments and sand, comminuted shells and other
animal remains, to add them to the beach. The heavier seas
transport larger fragments ; and at the foot of the beach there
is often a deposit of blocks of coral, or coral rock, a cubic foot
or so in size, which low tide commonly leaves standing in a
few inches of water. On moving these masses, which gener-
ally rest on their projecting angles and have an open space
beneath, the waters at once become alive with fish, shrimps,
and crabs, escaping from their disturbed shelter ; and beneath,
appear various Actiniae or living flowers, the spiny echini and
sluggish biche-de-mar, while swarms of shells, having a soldier
crab for their tenant, walk off with unusual life and stateliness.
Moreover, delicate corallines, Ascidiae and sponges tint with
lively shades of red, green and pink, the under surface of the
block of coral which had formed the roof of the little grotto.

Besides the deep channels cutting into the margin of the
reef and giving it a broken outline, there are in some instances
long fissures intersecting its surface. On Aratica (CarlshofF),
and Ahii (Peacock Island), they extended along for a fourth
to half a mile, generally running nearly parallel with the
shore, and at top were from a fourth to half an inch wide.
These fissures are not essential features of the reef. They are
probably a result of a subterranean movement or shaking.

The beach consists of coral pebbles or sand, with some
worn shells, and occasionally the exuviae of crabs and bones
of fishes. Owing to its whiteness, and the contrast it affords
to the massy verdure above, it is a remarkable feature in the
distant view of these islands, and often seemed like an arti-
ficial wall or embankment running parallel with the shores.
On Clermont Tonnerre, the first of these islands visited by us,
the natives seen from shipboard, standing spear in hand along

12

178 C0RAL8 AND CORAL ISLANDS.

the top of the beach, were believed by some to be keeping
patrol on the ramparts of a kind of fortification. This decep-
tion arose from the dazzling whiteness of the coral sand, in
consequence of which, the slope of the beach was not distin-
guished in the distant view.

The emerged land beyond the beach, in its earliest stage,
when barely raised above the tides, appears like a vast field of
ruins. Angular masses of coral rock, varying in dimensions
from one to a hundred cubic feet, lie piled together in the
utmost confusion ; and they are so blackened by exposure, or
from incrusting lichens, as to resemble the clinkers of Mauna
Loa ; moreover, they ring like metal under the hammer. Such
regions may be traversed by leaping from block to block, with
the risk of falling into the many recesses among the huge
masses. On breaking an edge from the black masses, the
usual white color of coral is at once apparent. Some of the
blocks, measuring five or six feet in each of their dimensions,
were portions of single individual corals ; while others had the
usual conglomerate character of the reef-rock, or, in other
words, were fragments torn by the waves from the reef-rock.

In the next stage, coral sand has found lodgment among
the blocks ; and although so scantily supplied as hardly to
be detected without close attention, some seeds have taken
root, and vines, purslane, and a few shrubs have begun to
grow, relieving the scene, by their green leaves, of much of
its desolate aspect.

Both of these stages are illustrated on the greater part of
coral islands.

In the last stage, the island stands six to ten feet out of
water. The surface consists of coral sand, more or less dis-
colored by vegetable or animal decomposition. Scattered
among the trees, stand, still uncovered, many of the larger

STRUCTURE OF CORAL ISLANDS, 179

blocks of coral, with their usual rough angular features and
blackened surface. There is but little depth of coral soil,
although the land may appear buried in the richest foliage.
In fact, the soil is scarcely any thing but coral sand. It is
seldom discolored beyond four or five inches, and but little of
it to this extent; there is no proper vegetable mould, but only
a mixture of darker particles with the white grains of coral
sand. It is often rather a coral gravel, and below a foot or
two, it is usually cemented together into a more or less com-
pact coral sand-rock.

One singular feature of the shore platform, occasionally
observed, remains to be mentioned. Huge masses of reef-
rock are sometimes found upon it, some of which lie loose
upon the reef, while others are firmly imbedded in it below,
and so cemented to it as to appear to be actually a part of the
platform rock. Sketches of two of these masses are here given.

1 " 2

BLOCKS OF OORAL ROCK ON THE SHORE PLATFORM.

Figure 1 represents a mass on the island of Waterland
(one of the Paumotus), six feet high and about five in diam-
eter ; it was solid with the reef-rock below, as though a part
of it, and, about two feet above its base, it had been so nearly
worn off by the waters as to have become irregularly top-
shaped. Another mass, similarly attached to the reef at base,
observed on Kawehe (Vincennes Island), was six feet high
above low- water level, and seven feet in its longest diameter

180 CORALS AND iJOllAL ISLANDS.

Below, it had been worn like the one just described, though
to a less extent. Another similar mass was ei<>:ht feet hio;h.
Figure 2 represents a block six feet high and ten feet in its
longest diameter, seen on Waterland ; it was unattached be-
low, and lay with one end raised on a smaller block. On
Aratica (Carlshoff), others were observed. One loose mass
like the last was eight feet high and fifteen feet in diameter,
and contained a,t least a thousand cubic feet, Raraka also
afforded examples of these attached and unattached blocks,
some standing with their tops six feet above high-water mark.

These masses are similar in character to many met with
among the fields of blocks just described, and differ only in
having been left on the platform instead of transported over it.
Some of them are near the margin of the reef, while others are
quite at its inner limit. The second mass alluded to above, on
Kawehe, was a solid conglomerate, consisting of large fragments
of Astraeas and Madrepores, and contained some imbedded
shells, among which an Ostrsea and a Cypraea were noticed.
This is their usual character. The other two were parts of
large individual corals (Porites) ; but there was evidence in the
direction of the cells that they did not stand as they grew ; on
the contrary, they had been upthrown, and were afterward
cemented with the material of the rock beneath them, probably
at the time this rock itself was consolidated. Below some of
the loose masses the platform was at times six inches higher
than on either side of the mass, owing to the protection from
wear given to the surface beneath it. These blocks are always
extremely rough and uneven, like those of the emerging land
beyond ; and the angular features are partly owing, in both
cases, to solution from rains and from the dashes of sea- water
to which, with every tide, they are exposed.

It should be distinctly understood that these masses here

STRUCTURE OF CORAL ISLANDS. 181

described were found isolated, and only at considerable inter-
vals. In no instance were they observed clustered. The loose
blocks and those cemented below had the same general charac-
ter, and must have been placed where they were by the same
cause, though it may have been at different periods.

Such blocks are of course not confined to coral island reefs,
but belong to barrier reefs generally.

Jukes says, " I once landed close to the edge of the Aus-
tralian barrier on the south side of the Blackwood channel, in
south latitude 11^ 45^, on a continuous mass of Poritcs ivhich
was at least twenty feet across^ and it seemed to pass down-
wards into the mass of the reef below water without any dis-
connection. It was worn into pinnacles above, so that two or
three of us could stand in the different hollows without seeing
each other ; and it was one of a line of such masses that at-
tracted our attention for a distance of three miles."

The shore of the lagoon is generally low and gently in-
clined, yet in the larger islands, in which the waters of the
lagoon are much disturbed by the winds, there is usually a
beach resembling that on the seaward side, though of less
extent. A platform of reef-rock at the same elevation as
the shore platform sometimes extends out into the lagoon ;
but it is more common to find it a little submerged and cov-
ered for the most part with growing corals ; and in either case,
the bank terminates outward in an abrupt descent, of a few
yards or fathoms, to a lower area of growing corals, or a bot-
tom of sand. Still more commonly, we meet with a sandy
bottom gradually deepening from the shores without growing
coral. These three varieties of condition are generally found
in the same lagoon, characterizing its different parts. The
lower area of growing corals slopes outward, and ceases where
the depth is 10 to 12 fathoms or sooner; from this there

182 CORALS AND COBAL ISLANDS

is another descent to the depth which prevails over the lagoon.
On some small lagoons the shore is a thick plastic mud,
either white or brownish, and forms a low flat which is very
gently sloping. On Henuake, these mud deposits are qnite ex-
tensive, and of a white color. At Enderbury's Island, another
having a shallow lagoon, the mud was so deep and thick that
there was some difficulty in reaching the waters of the lagoon ;
the foot sunk in eight or ten inches and was not extricated
without some difficulty. It looked like a dirty brownish clay.
This mud is nothing but comminuted coral, so fine as to be
almost impalpable.

The lagoons of the smaller islands are usually very shallow ;
and in some, merely a dry bed remains, indicating the former
existence of water. Instances of the latter kind are met with
only in islands less than three miles in diameter ; and those
with shallow lagoons are seldom much larger. These shallow
waters, when direct communication with the sea is cut off, be-
come, in some instances, very salt by evaporation, and contain
no growing coral, with few signs of life of any kind ; and in
other cases, they are made too fresh for marine life through
the rains. At Enderbury's Island the water was not only ex-
tremely saline, but the shores of the lagoon were in some
places incrusted with salt. But when there is an open channel,
or the tides gain access over a bare reef, corals continue to
grow, and a considerable portion of the lagoon may be obstruct-
ed by them. At Henuake, the sea is shut out except at high
water, and there were consequently but few species of corals,
and those of small size. At Ahii (Peacock's Island), there
was a small entrance to the lagoon, and though comparatively
shallow, corals were growing over a large part of it.

In the larger islands, the lagoons contain but small reefs
compared with their whole extent ; the greater part is an open

8TRUGTUUE OF CORAL ISLANDS. 183

sea, with deep waters and a sandy or muddy bottom. There
are instances, as at the southern Maldives, of a depth of 50
and 60 fathoms. From 20 to 35 fathoms is the usual depth
in the Paumotus. This was the result of Captain Beechey's
investigations ; and those of the Expedition, though few, cor-
respond. It is however probable that deeper soundings would
be found in the large island of Nairsa (Dean's). In Gilbert'^
Group, southeast of the Carolines, the depth, where examined
by the Expedition, varied from 2 to 35 fathoms. Mr. Darwin
found the latter depth at Keeling's Island. Chamisso found
25 to 35 fathoms at the Marshall Islands.

The bottom of these large lagoons is very nearly uniform,
varying but little except from the occasional abrupt shallow-
ings produced by growing patches of reef. Soundings bring
up sand, pebbles, shells, and coral mud ; and the last men-
tioned material appears to be quite common, even in lagoons
of considerable size. It has the same character as above de-
scribed. The bluish clay-like mud of the harbor of Tongatabu
may be classed with these deposits. Darwin describes this mud
as occurring at the Maldives, and at Keeling's Island (op. cit.
p. 26); Kotzebue mentions it as common at the Marshall
atolls, and Lieutenant Nelson observed it at the Bermudas.
It appears, therefore, that the finer coral material of the
shores prevails throughout the depths of the lagoon. The
growing reefs within the lagoons are in the condition of the
inner reefs about high islands. The corals grow but little
disturbed by the waves, and the reef-rock often contains them
in the position of growth. At Taputeouea (Kingsmill's or
Gilbert's Group), reefs very similar to those of the Feejees
occur ; they contain similar large Astrseas ten to twelve feet
in diameter, which once were growing where they stand, but
are now a part of the solid lifeless rock.

184 CORALS AND CORAL ISLANDS,

Beach formations of coral sand-rock are common on the
coral islands, and they present the same features in every re-
spect as those described. They were observed among the Pau-
motus, on Earaka, Honden, Kawehe, and other islands. The
stratified character is always distinct, and the layers slope to-
ward the water at the usual small angle, amounting to 5-7
degrees bordering the lagoon, and 6-8 degrees on the seashore
side of the land. Agassiz gives the same angle for the sea-
ward slope of similar deposits at Key West. The rock is
largely a fine oolite. They often occupy a breadth of thirty
to fifty yards, appearing like a series of outcrops ; yet they are
frequently covered by the sands of the steep part of the beach.
It is probable that they generally underlie the loose surface
material of the land. The rock is a fine or coarse sand-rock,
or an oolite, or a coral pudding-stone, and consists of beach
materials. Occasionally it is quite compact, and resembles
common limestone, excepting in its whiter color ; but gener-
ally its sand origin is very apparent. On the northern atolls
of the Maldives, the beach sand-rock is said to be quarried
out in square blocks and used for building.

In borings by Lieutenant Johnson, of the •Wilkes Explor-
ing Expedition, on Aratica or Carlshoff*'s Island, in the Pan-
motus, ten or eleven feet were passed through easily, and then
there was a sudden transition from this softer rock (probably
the beach sand-rock), to the solid reef-rock.

The drift sand-rock was not met with by the author on any of
the coral islands visited. The time for exploration on these
islands allowed by the Expedition was too short for thorough
work. It has been stated that the more exposed points toward
the trades, especially the northeastern and southwestern, are
commonly a little higher than other parts ; and it is altogether
probable that some of the sand heaps there formed will prove

STBUGTURE OF COBAL ISLANDS. 185

on examination to afford examples of this variety of coral-
rock. Such situations are exactly identical with those on
Oahu, where they occur on so remarkable a scale. Mr. H. H.
Schomburgh, in an article in the Journal of the Royal Geo-
graphical Society, vol. ii., p. 152, states that on the island of
Anegada, in the West Indies, the drift banks on the windward
shores are forty feet in height, and that behind the first range
there is a second, and even a third.

Although in these descriptions of atolls, some points have
been dwelt upon more at length than in the description of
barrier reefs, still it will be observed that the former have no
essential peculiarities of structure apart from such as necessar-
ily arise from the absence of high rocky lands. The encircling
atoll reef corresponds with the outer reefs that enclose high
islands; and the green islands and the beach formations, in the
two cases, originate in the same manner.

The lagoons, moreover, are similar in character and posi-
tion to the inner channels within barrier reefs ; they receive
coral material only from the action of degrading agents, be-
cause no other source of detritus but the reefs is at hand. The
accumulations going on within them are, therefore, wholly of
coral. The reefs within the lagoons correspond very exactly
in mode of growth and other characters to the inner reefs un-
der the lee of a barrier,

IV. NOTICES OF SOME CORAL ISLANDS.

The preceding descriptions represent the general character
of atolls, but are more especially drawn from the Paumotus.
There are some peculiarities in other seas, to which we may
briefly allude.

Among the scattered coral islands north of the Samoan

186 CORALS AND CORAL ISLANDS.

Group, the shore platform is seldom as extensive as at the
Paamotus. It rarely exceeds fifty yards in width, and is cut
up by passages often reaching almost to the beach. In some
places the platform is broken into islets. Enderbury's Island
is one of the number to which this description applies. The
beach is eleven or twelve feet high. For the first eight feet it
slopes very regularly at an angle of thirty to thirty-five degrees,
and consists of sand, coarse pebbles, or rounded stones of coral,
with some shells ; and there is the usual beach conglomerate
near the water's edge. After this first slope, it is horizontal
for eighty to two hundred feet, and then there is a gradual
rise of three to four feet. Over this portion there are large
slabs of the beach conglomerate, along with masses from the
reef-rock, and some thick plates of a huge foliaceous Madre-
pora ; and these slabs, many of which are six feet square, lie
inclining quite regularly against one another, as if they had
been taken up and laid there by hand. They incline in the
same direction with the slope of the beach. The large Madre-
pora alluded to has the mode of growth of the Madrepora
palmata ; and probably the entire zoophyte extended over
an area twelve or fifteen feet in diameter. The fragments
are three to four inches thick, and thirty square feet in surface.

As a key to the explanation of the peculiarities here ob-
served, it may be remarked that the tides in the Paumotus are
two to three feet, and about Enderby's Island five to six feet
in height.

Maldive Archipelago, — The Maldives have been often
appealed to in illustration of coral structures. They are par-
ticularly described by Mr. Darwin from information commu-
nicated to him by Captain Moresby, and from the charts of this
officer and Lieutenant Powell. A paper on the northern Mal-
dives, by Captain Moresby, is contained in the Journal of the

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STRUCTURE OF CORAL ISLANDS. 189

Royal Geographical Society, vol. v., p. 398 ; and another on
this group by J. J. Horsburgh, and W. F. W. Owen, in the
the same journal, vol. ii., pp. 72 and 81. As stated by Mr.
Darwin, the archipelago has a length of 470 miles, with an
average breadth of 50 miles ; and it consists for the most of
its length of two parallel lines of atolls. The large atoll at
the north end has a length of 88 miles, while Suadiva, one of
the southernmost, is 44 miles long from north to south, and
34 miles across.

The point of special interest in their structure is the oc-
currence of atolls or annular reefs within the larger atolls

Powells Is**

zoo

of cahiruk>U>aTniU

^^S^or^ur^ Atoll

MAHLOS MAHDOO ATOLL, WITH HORSBUKGH ATOLL.
Scale 1-20 of an inch to a mile.

The islets of the lagoon and those of the encircling reef, are
in many instances annular reefs, each with its own little lake,
Gems within gems are here clustered together.

190 CORALS AND CORAL ISLANDS.

This feature is well exhibited in the Mahlos Mahdoo atoll,
an enlarged map of which, from Darwin's work, is here in-
serted. The atoll consists of three main atoll-shaped portions ;
but in each of these, the border is made up in part of atolls.
Many of the subordinate atolls of the border are " three, and
some even five miles in diameter, while those within the lagoon
are usually smaller, few being more than two miles across, and
the greater number less than one. The depth of the little
lagoons within these small annular reefs is generally from five
to seven fathoms, but occasionally more; and in Ari atoll,
many of the central ones are twelve, and some even more than
twelve fathoms deep. These subordinate atolls rise abruptly
from the platform or bank on which they stand, with their
outer margin bordered by living corals." " The small atolls
of the border, even where most perfect and standing farthest
apart, generally have their longest axis directed in the line
which the reef would have held if the atoll had been bounded
by an ordinary wall," (Darwin, on Coral Reefs, pp. 33, 34.)
The Maldives are among the largest atoll reefs known ;
and they are intersected by many large open channels ; and
Mr. Darwin observes, that the interior atolls occur only near
these channels, where the sea has free access. We may view
each large island in the archipelago as a sub-archipelago of
itself. Although thus singular in their features, they illus-
trate no new principles with regard to reef-formations.

Mr. Darwin thus remarks (Op. cit. pp. 33, 34),—" I can
in fact point out no essential difference between these little
ring-formed reefs (which, however, are larger, and contain
deeper lagoons than many true atolls that stand in the open
sea), and the most perfectly characterized atolls, excepting
that the ring-formed reefs are based on a shallow foundation
instead of on the floor of the open sea, and that instead of being

8TBUCTUSM OF CORAL ISLANDS.

1:91

scattered irregularly, they are grouped closely together."—" It
appears from the charts on a large scale, that the ring-like
structure is contingent on the marginal channels or breaches
being wide, and, consequently, on the whole interior of the
atoll being freely exposed to the waters of tlie open sea.
When the channels are narrow, or few in number, although
the lagoon be of great size and depth (as in Suadiva), there
are no ring-formed reefs ; where the channels are somewhat
broader, the marginal portions of reef, and especially those
dose to the larger channels, are ring-formed, but the central
ones are not so : where they are broadest, almost every reef
throughout the atoll is more or less perfectly ring-formed. Al-
though their presence is thus contingent on the openness of
the marginal channels, the theory of their formation, as we

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GREAT CHAGOS BANK.

shall hereafter see, is included in that of the parent atolls, of
which they form the separate portions."

192 C0BAL8 AND GOBAL ISLANDS.

The Great Chagos Bank. This bank lies about ten degrees
south of the Maldives, and is ninety miles long and seventy in
its greatest breadth. It is a part of the Chagos Group, in which
there are some true atolls, some bare atoll-reefs, and others, like
the Great Chagos Bank, that are quite submerged, or nearly
so. Its rim is mostly from four to ten fathoms under water.

Mr. Darwin confirms the opinion of Captain Moresby, that
this bank has the character of a lagoon reef, resembling one
of the Maldives ; and he states, on the evidence of extensive
soundings, that, if raised to the surface, it would actually be-
come a coral island, with a lagoon forty fathoms deep. He
says that, in the words of Captain Moresby, it is in truth
"nothing more than a halt drowned atoll."

The form of the bank, its margin of shoals, and a line
of soundings across it, giving the depth of the central or
lagoon portion, are shown in the map on p. 191, from Darwin,
and for which, as well as for other information about the

<<
^

Level of {Re Sea.

76 miles in length-

EAST AND WEST SECTION ACK0S8 THE GKEAT CHAGOS BANK.

bank, he gives credit to Captain Moresby. The cross section
is still further illustrated in the annexed cut. The whole
length of the section (or width of the bank in the line of the
soundings) is seventy-six miles. From the outer rim of
the submerged atoll, there is a drop off to a deeper level, which
is mostly fifteen to eighteen fathoms below the surface ; and

STRUCTURE OF CORAL ISLANDS.

193

then to the bottom of what was once the lagoon, now for
the most part forty to fifty fathoms under water, though hav-
ing its shoals that are five to ten fathoms submerged. All
points in the map that are shaded, have a depth of less than
ten fathoms ; the only emerged parts are three or four spots
on the western margin, as indicated on the map above. The
bottom over the interior is muddy ; on the flat bordering it,
15 to 20 fathoms deep, there is coral sand with ''a very little
live coral ; the outer rim is coral rock Avith scarcely any live
coral;" while the shoals or knolls of the interior are ''cov-
ered with luxuriantly-growing corals." Darwin states also
that the rim is steep on both sides, and outward slopes abruptly
to unfathomable depths ; at a distance of less than half a mile
from one part no bottom was found with 190 fathoms ; and
off another point, at a somewhat greater distance, there was
none with 210 fathoms.

Metia and other elevated Coral Islands, — Metia, or Au-
rora Island, is one of the western Paumotus. It is a small
island about four miles by two and a half in width, and two
hundred and fifty feet in height ; and it consists throughout

METIA, OR AURORA ISLAND.

of coral limestone. Approached from the northeast, its hio-h
vertical cliffs looked as if basaltic, resembling somewhat the

13

194 CORALS AND CORAL ISLANDS.

Palisades on the Hudson. This appearance of a vertical
structure was afterward traced to vertical furrowings by the
waters dripping down its front, and the consequent formation
of stalagmitic incrustations. Deep caverns were also seen.

The cliff, though vertical in some parts, is roughly sloping
in others, and on the west side, the surface of the island grad-
ually declines to the sea.

The rock is a white and solid limestone, seldom presenting
any traces of its coral origin. In some few layers there were
disseminated corals, looking like imbedded fossils, along with
beautiful casts of shells ; but for the most part it was as com-
pact as any ancient limestone, and as uniform in texture. Oc-
casionally there were disseminated spots of crystallized calcite.

The caverns contain coarse stalactites, some of which are
six feet in diameter ; and interesting specimens were obtained
containing recent land shells that had been enclosed by a cal-
careous film while hibernating.

It is probable that more extensive caverns would have
been found had there been more than a few hours for the ex-
amination of the island. The Rev. Mr. Williams, in his work
on Missionary Enterprises in the Pacific, gives very interesting
descriptions of caverns in the elevated coral rock of Atiu,
one of the Hervey Group. In one, he wandered two hours,
without finding a termination to its windings, passing through
chambers with " fretwork ceilings of stalagmite and stalactite
columns, which, 'mid the darkness, sparkled brilliantly with
the reflected torch-light." This author remarks, " that while
the madrepores, the brain and every other species of coral are
full of little cells, these islands (including those resembling
Atiu), appear to be solid masses of compact limestone^ in
which nothing like a cdl can he detectedP

Beechey, in his description of Henderson Island, another

STRUGTUBE OF CORAL ISLANDS, 195

of this character, speaks of the rock as compact, and having
the fracture of a secondary limestone.

The surface of the island is singularly rough, owino- to
erosion by rains. The paths that cross it wind through nar-
row passages among ragged needles and ridges of rock as high
as the head, the peaks and narrow defiles forming a miniature
model of the grandest Alpine scenery. There is but little
soil, yet the island is covered with trees and shrubbery.

The shores at the first elevation of the island, must have
been worn away to a large extent by the sea ; and the cliff
and some isolated pinnacles of coral rock still standino- on the
coast are evidence of the degradation. But at present there
is a wide shore-platform of coral reef, two hundred or two
hundred and fifty feet wide, resembling that of the low coral
islands, and having growing coral, as usual, about its margin
and in the shallow depths beyond.

In the face of the cliff there are two horizontal lines,
along which cavities or caverns are most frequent, which con-
sequently give an appearance of stratification to the rock,
dividing it into three nearly equal layers.

We might continue this account of coral reefs and islands,
by particular descriptions of others in the Pacific. But the
similarity among them is so great, and their peculiarities are
already so fully detailed, that this would amount only to a
succession of repetitions. The characters of a few, briefly
stated, will suffice in this place.

Jarvis's Island.— {¥xg, 4, page 168.) Lat. 0^ 22' S. Long,
159^ 58' W. Two miles long by one mile wide, and trending
east and west. No lagoon, but a basin-like depression over
its interior, which at bottom is seven or eight feet above the
sea, and in which the lagoon once existed ; old beach lines

196 CORALS AND COBAL ISLANDS.

are distinguishable in it. Its surface is a low sandy flat, eigh-
teen or twenty feet high, without trees, and partly covered with
small shrubs. A high sloping beach continuous around. Has
a shore platform about 300 feet wide.

Birnie's.—L^<^t. 3^ 35' S. Long. 171^ 30' W. Four-
fifths of a mile by one- third, trending northwest. No lagoon.
A sandy flat about ten feet high, excej)t near the north-north-
east extremity, where it is about twelve feet. To the south-
southwest the submerged reef extends out nearly a mile, over
which the sea breaks. In passing it, distinguished no vegeta-
tion except the low purslane and some trailing plants.

Swain's.— (Fi^. 3, page 168.) Lat. 11^ 10' S. Long.
170^ 52' W. li miles by f; shape nearly rectangular;
trends east and west. No lagoon, but the centre a little lower
than the sides. Surface covered with shrubbery and large
trees, among the latter many cocoanuts; the centre more
sparsely wooded. Height fifteen to eighteen feet, excepting
on the middle of the western side, where the surface is covered
with loose fragments of coral of small size ; there appears to
have been a former entrance to the lagoon at this place. Shore
reef, or platform, one hundred yards in average width, and
one hundred and fifty yards at the place where we landed.
Beach high, ten to twelve feet. At lower part of beach, for a
height of two to three feet, the coral reef-rock was exposed,
indicating an elevation of the island. For three or four feet
above this, layers of the beach sand-rock Avere often in view,
consisting of coral pebbles firmly cemented, and having the
usual dip of seven or eight degrees seaward ; in many places
it was concealed by the beach sands and pebbles. There was
no growing coral on the platform, excepting NuUipores.
The outer margin of this platform was very uneven, and
much intersected by channels, though less so than at Ender-

STRUCTURE OF CORAL ISLANDS. 197

by's Island. Great numbers of Birgi (large Crustacea),
were burrowing over the island, some of which were six inch-
es in breadth.

Otuhu, Paumotu Archipelago. — 14° 5' S. 141° 30' W.
li miles by f, trending north and south. No lagoon.
Wooded.

Margaret, Paumotu Archipelago.— 20° 42' S. 143° 4'
W. Diameter one mile, nearly circular. A small shallow
lagoon with no entrance. Northeast side alone wooded, and
in two patches.

Teku or Four Cimvns, Paumotu Archipelago, 20° 28'

S. 143° 18' W. Diameter IJ miles, nearly circular. A
small lagoon with no entrance. Southwestern reef bare ; hve
patches of forest on the other part.

Washington Island. — Lat. 4° 41' N. Long. 160° 15' W.
3 miles by li, trending east and west. It is a dense cocoanut
gi-ove with luxuriant shrubbery. No lagoon. The shore
platform is rather narrow. A point of submerged reef, one
and a half miles long, stretches out from the southwest end.
Did not land on account of bad weather.

Enderhury's.—Z" 8' S. 171° 15 W. 2|- miles by 1 mile
nearly, trending N. N. W., and S. S. E. ; form trapezoidal or
nearly rectangular. Little vegetation on any part, and but i^v.-
trees. The lagoon very shallow, and containing no growing
coral ; its shores of coral mud, allowing the foot to sink in
eight or ten inches, and covered in places with salin2 incrus-
tations. Shore platform one hundred feet or less in width,
and surface inclined outward at a very small angle ; covered
with three or four feet of water at high tide, and with few
corals or shells ; beyond this, falls off four to six feet, and then
the bottom inclines for one hundred yards or more. The beach
very high and regular; rises eight feet at an inclination of

198 COBALS AND CORAL ISLANDS,

thirty to thirty-five degrees ; then horizontal for eighty to two
hundred, after which another rise of three or four feet. It
consists of pebbles and fine sand, but above of slabs and
blocks of coral rock and of the beach sand-rock, those of the lat-
ter nearly rectangular and flat. This beach sand-rock occurs
in layers from ten to twenty inches thick along the shore, and
is inclined from five to seven degrees seaward. Some portions
are very compact, and ring under the hammer, while others
enclose fragments of different sizes to a foot or more in diam-
eter. Large trunks of transported trees lay upon the island,
one of which was forty feet long and four in diameter. The
shore platform was much intersected by channels.

Captain Hudson obtained soundings half a mile off in two
hundred fathoms ; the lead struck upon a sandy bottom, but
was indented by coral.

Honden or Henuake^ Paumotu Archipelago. — Size 3 J
miles by 2 miles. Oblong, five-sided; trending west-north-
west. A small shallow lagoon, conununicating with the sea
only at high tide, on the west side. There are two other
entrances which are seldom if ever covered with water, and
appeared merely as dry beds of coral rock. Height of the
island twelve feet : lowest on the south side. Belt of verdure
complete, and consisting of large forest trees, with the Panda-
nus and other species, but no cocoanuts ; its breadth h^lf a
mile, and in some parts three-fourths. Among the trees large
masses of coral rock often exposed to view, and the surface in
many parts very rough. It seemed surprising at all these
islands that there should be so luxuriant a growth of trees and
shrubbery over so rocky a surface. Shores of the lagoon near-
ly flat. On one side there was a large area of extremely fine
coral sand and mud, which extended a long distance into the
lagoon. Elsewhere about the centre of the island, the reef-

STRUCTURE OF CORAL ISLANDS. 199

rock was bare, and contained numerous shells of Tridacnaa. A
few small Madrepores still growing in the lagoon. Beach on
the sea-shore side eight feet high. In lower part of beach, sev-
eral layers of white limestone (the beach sand-rock), formed of
coral fragments or sand, shells, etc., much of which was very
compact. The layers inclined toward the sea at an angle of
about six degrees. Shore platform as elsewhere in this archi-
pelago.

The facts above stated are evidence of a slight elevation,
probably not exceeding three feet.

Taiara. or Kincfs. Paumotu Archipelago. — 15^ 42^ S. ;
144^ 46' W. 2| miles by If, trending northwest. Has a
small lagoon with no entrance. Reef almost continuously
wooded around, somewhat broken into patches.

Sydney Island— L^t 4^ 20 S. Long. 171^ 15' W.
Trends northeast and southwest. Well wooded nearly all
round ; but on leeward side the forest in patches, with breaks
of bare coral. Lagoon narrow, without entrance. Width of isl-
and from sea to lagoon, one hundred to four hundred yards :
width greatest at south end. Beach ten feet high. The soil of
the island consisted of coral fragments and sand. Shore plat-
form fifty to eighty feet wide ; five or six feet of Wciter over it at
high tide. Cut up very irregularly by channels three to eight
or ten feet wide. Observed small corals growing on the bottom
outside of the platform. Shores of lagoon shallow for fifty
yards, and consisting of coral sand. Beyond this a slope cov-
ered with growing corals ; the corals rather tender species of
Madrepores. In the interior of the lagoon many knolls and
large patches of coral.

Duhe of York's,— S"" 38' S., 172^ 27' W. Form irregu-
larly oblong, trending northwest. Length Sf miles ; breadth
2 miles. Circuit 9^ miles, and about one-half wooded in

200 CORALS AND CORAL ISLANDS.

patches. Southwest reef mostly bare. A lagoon, but without
entrance except for canoes at high tide, on leeward side. Isl-
and ten feet high. Shore platform narrow, and intersected
by channels. Shores lined by reef-rock, two or three feet out
of water, indicating an elevation of the island. This reef-rock
consists of various corals firmly cemented. Within the lagoon,
knolls of coral, but none near the shore on the leeward side.

Fahaafo or Bowditch' s.—^'' 20' S., 171^ 5^ W. Gf miles
by 4. Shape nearly triangular. Circuit seventeen miles,
about six of which are wooded in several patches, separated by
long bare intervals. A large lagoon, but no ship entrance.
Height of island, fifteen feet. Width to the lagoon, one hun-
dred to two hundred yards. Soil of the island coral sand,
speckled black with results of vegetable decomposition. Shore
platform narrow. At outer edge a depth of three fathoms,
and from thence gradually deepens, and abounds in corals
for fifty yards, when it deepens abruptly. Coral reef -rock ele-
vated three or four feet, indicating an elevation of the isl-
and. Lagoon shallow, with some growing coral, but none
near the shore. Some corals growing on the platform, near
its margin, mostly small Madrepores, Astraeas, NuUipores.
Fragments of pumice were found among the natives ; which
had floated to the island.

AMi^ or Peacock's Island^ Paumotu Archipelago. — 14^
30' S., 146^ 20' W. 13 miles by 6, trending N. E. by E.
Shape irregularly oblong. A large lagoon, having an entrance
for small vessels on the west. Reef wooded throughout nearly
its whole circuit. Lagoon shallow, and much obstructed by
growing coral, the latter giving the water over it a clear light
green color. Platform, or outer coral shelf of the island,
about two hundred and fifty feet wide ; under water except at
the lowest tides. Margin highest, and covered with NuUi

STRUCTURE OF CORAL ISLANDS. 201

pore incrustations, which give it a variety of delicate shades of
color, mostly reddish, of peach-blossom red, rose, scarlet. For
thirty to fifty feet from the margin, very cavernous, and con
taining many Tridacna3, lying half imbedded, vrith the variously
tinted mantle expanded when the surface is covered with wa-
ter. Rock of the platform either a compact white limestone or
a solid conglomerate ; dead over its surface, excepting a few
Madrepore tufts or Astrasas near the margin in pools. In this
shelf there were long fissures, extending nearly parallel with the
shore, a quarter to half an inch wide at top, and continuing
sometimes a fourth of a mile or more. These fissures were com-
monly filled with coral sand. The higher parts of the island
either consisted of loose blocks of coral or were covered with
some soil ; the soil mostly of comminuted coral and shells, with
dark particles from vegetable decomposition intermingled. On
the bottom, exterior to the shore platform, observed the same
corals growing as occurred in fragments upon the island ; but
the larger part of the bottom was without coral, or consisted
only of sand.

Baraka, Paumotu Archipelago.— 16^ 10' S., 145^ W. 14
miles by 8, trending east and west. Shape somewhat trian-
gular. North side nearly continuously wooded ; south angle
and southwest reef bare. A large lagoon with an entrance
for small vessels on the north side. A rapid current flows
from the entrance, which it was difiicult for a boat to pull
against. Shore platform, as usual, about a hundred yards
wide, with the edge rather higher than the surface back ; the
platform mostly bare of water at low tide. Several large
masses of coral and coral rock, one to four hundred cubic feet,
on the platform and upon the higher parts of the island, some
of which stood five and six feet above high- water mark ; they
were cemented to the reef- rock below, and appeared like project-

202 GOEALS AND CORAL ISLANDS.

ing parts of the reef. Layers of beach sand-rock on the lagoon
shores, as well as on the seaward side, inclined at an angle of
six or seven degrees : characters as already described. Grow-
iDs: coral in the entrance to the lagoon, within two feet of the
surface, mostly a species of Millepora (M. squarrosa). Inte-
rior of the lagoon not examined, no time being allowed for it by
the Expedition. The water looked as blue as the ocean, and
was much roughened by the winds.

Kawehe^ or Viiicennes Island^ Paumotu Archipelago, 15^
30^ S., 145^ 10^ W. 13 miles by 9, trending north-north-
west. Shape irregularly oval. Having a large lagoon, and
mostly wooded around, least so to leeward. Between the
wooded islets (as on Raraka and elsewhere), surface consisted
of angular masses of coral rock (among which the Porites pre-
vail), strewed in great numbers together ; and in some parts
bearing a few vines and purslane among the blocks, though
scarcely any appearance of soil, or even of coral sand. In
other parts, not as high, no vegetation, and surface still wet
by high tide. A few large masses of coral on the shore plat-
form, either lying loose, or firmly attached below, as already
described; some of them were six feet cube, and one was
raised seven feet above high- water mark. Shore platform about
a hundred yards wide, rather highest at the edge, and much of
its surface two to four feet under Avater at low tide. As else-
where, this platform is nothing but a compact coral conglom-
erate or limestone, having no growing coral over it, except in
some shallow pools near its outer margin, where also there
are numerous -holes in which crabs are concealed, with small
fish and other animals of the shores. On the lagoon shore,
layers of beach sand-rock, six or seven in number, dipping at
an angle of seven degrees toward the lagoon, and outcropping
one above the other. Similar layers on the sea-shore side

8TBUGTUBE OF CORAL ISLANDS. 203

Manlii% WilsoribS or Waterlandt^ Pauraotu Archipelago,
14^ 25' S., 146^ W. 15 miles by 6, trending E. N. E. A
large lagoon with a deep entrance on the west side. Shape
oblong triangular.

Shore platform as usual ; mostly under water at low tide.
Large masses of coral here and there, standing on this reef;
either cemented to it, or loose. One top-shaped mass is figured
on p. 179. High water did not reach the part of it which was
most worn ; and this was evidently owing to the fact that the
action of the swell or waves is greatest above the actual level
of the tide at the time. The reef-rock is either a compact
limestone, showing no traces of its composite origin, or a con-
glomerate. Beach, regular as usual, six to ten feet high, con-
sisting of coral sand, and fragments of worn shells, with occa-
sional exuviae of crabs, remains of Echini, fish, etc. The en-
trance to the lagoon is deep and narrow, with vertical sides.

Amtica or Carlshoff, Paumotu Archipelago, 15'' 30' S.,
145^ 30' W. 17 miles by 10, trending N. E. Large lagoon
with a good entrance for vessels. The reef fronting south
bare for nine miles ; on northwest side, mostly very low, with
only here and there a clump of trees ; occasionally a line of
wooded land for a quarter of a mile on the east side ; more
continuously wooded on the north. The bare parts mostly
covered wdth blocks of coral, one to thirty cubic feet and larg-
er, tumbled together as on the preceding. Some blocks of
coral on the shore platform very large ; one eight feet high
and fifteen in diameter, containing at least 1,000 cubic feet.
Nairsa or Dean's^ Paumotu Archipelago, 15^ S.. 148"" W.
44 miles by 17, trending W. N. W. Northern shore mostly
wooded ; southern with only an occasional islet, connected by
long lines of bare reef. In these intervals, the reef stood
eight feet or so out of water, according to estimate from ship-

204 CORALS AND CORAL ISLANDS.

board, and was worn into a range of columns, or excavated
with caverns, so as to look very much broken, though quite
regularly even in the level of the top line.

We might continue these descriptions ; but the above,
with the details before given, will convey a general idea of the
whole.

Florida Beefs and Keys, — This region of coral formations
has been described by Prof. M. Tuomey {^American Jour-
nal of Science,^ vol. xi., 1851), Professor Agassiz (Coast Sur-
vey Reports for 1851 and 1866, and Bull. Mus. Comp. Zool.,
i., 363), and Captain E. B. Hunt {Am. J, Sol, xxxv., 1863).
A few paragraphs from the papers of the first two of these
observers are here cited. The map, at the close of the volume,
illustrating this Florida reef-region, is from the Report on
Deep-Sea Corals of L. F. de Pourtales, published in the Illus-
trated Catalogue of the Museum of Comparative Zoology in
1871. First, from Professor Tuomey:

" Key West is about six miles in length and two miles wide,
the highest point being fifteen or twenty feet above mean tide.
The deepest wells are about fifteen feet in depth ; the water in
them, which is slightly brackish, ebbs and flows with the tide."
'' The rock perforated in these wells, like that everywhere else
exposed, is sufficiently soft to yield readily to the axe, with
the exception of a thin crust of a few inches on the surface,
which is quite hard, especially where it is exposed alternately
to the action of the tides and atmosphere. This indurated
crust may be seen on the road between the town and the bar-
racks, and around the salt works. Below this crust the rock
is quite soft, and in some other respects resembles the Ala-
bama white limestone ; but the most striking difference next
to that of organic remains, consiss , m the distinctly oolitic

FLORIDA REEFS AND KEY8. 205

structure of the Florida limestone. This structure is seen
where one would be led to expect it, in the fine grained seams.
A few hundred yards from the hospital a quarry has been
opened where the rock may be examined. The organic re-
mains consist of broken shells and water-worn fragments of
corals, which, both in species and state of preservation, resemble
those on the shores of the island. Except in degree of hard-
ness, the rock does not differ from the calcareous sands thrown
up by the waves on the shore in the vicinity ; and the condi-
tions presented by the loose moving sands, are not favorable
to the habits of molluscous animals, nor are fossil shells very
abundant in the limestone of the island. Oblique or false
stratification is everywhere seen in the rock, the inclination of
the planes differing very little from the slope of the shore up
which the waves push dead shells, pieces of coral, etc. After
a breeze, coarse materials are found strewing the beach, a
light wind leaves a finer deposit, and in the succeeding calm
the sea appears milky from fine calcareous matter suspended
in the water; this is deposited in the form of free, impalpable
mud, which invests marine plants and other objects, to which
it adheres with great tenacity, and becomes a source of annoy-
ance to the collectors of Algo9. All these alternations of fine
and coarse materials may be observed in the limestone. [The
rock corresponds to the beach sand-rock.]

"Along the south beach, the sand is thrown up by the
waves to an elevation nearly equal to that of the highest point
of the island, and during the gale of Oct. 1841, the greater
part of it was submerged, so that, at first sight, it might ap-
pear that the whole island was the result of sand thrown up
at such times. But although I observed no beds in the lime-
stone that prove, like those of our Tertiary, that the animals,
whose remains they contain, lived and died on the spot, yet

206 CORALS AND CORAL ISLANDS.

in its structure it shows the result of long-continued, steady
wave-work that cannot be referred to any other cause.

" On Key West I found in the rocks, no beds of coral re-
taining their original position, although large fragments are
scattered through the mass.

" Some of the small Keys, such as the Mangrove Keys,
are the result of gradual deposition of sedimentary matter,
and many of those interspersed among the larger islands have
not yet reached the level of high water, but are nevertheless
covered by a dense growth of this curious tree. It would be
difficult to imagine a plant better adapted to island-making
than the mangrove. Its long, pendulous seeds fall into the
shallow water, stick in the soft mud, and take root ; the bud
proceedhig from the opposite extremity, soon shoots up above
water and sends down branches almost perpendicularly into
the mud, these take root and produce other trees, and so on.
Besides these, lateral shoots are given off, and, at a distance of
three or four feet, enter the water and take root ; from the
part above water others proceed and take a similar stride,
and in this way they often travel twenty or thirty yards
from the parent stem. Seaweeds and drift-wood become en-
tangled among the stems, and very soon a permanent island
is formed. Such islands are generally found under the lee of
the Keys.

"But the greater number, if not all the Keys, rest upon a
foundation of corals. At Sand Key, large rugged masses of
dead coral are seen bordering the Key on the windward side,
and rising above low water ; similar masses may be seen at
Sambo Key, and at other places along the outer reef. But
the Keys within this barrier present better opportunities for
studying the foundation upon which they rest. At Key
Vacca, corals rise to a height of four feet above high water.

FLORIDA REEFS AND KEYS. 207

and present not the slightest evidence of disturbance, beyond
the upward movement which raised them to their present
position. The rocky mass of coral along the margin of the
Key is undermined by the waves, and otherwise worn into
singularly rugged shapes, with sharp projecting points. Even
at some distance from the water, bunches of coral project
above the surface wherever the overlying sand is washed
awa}'.

'' On Bahia-honda similar appearances are presented, where
the coral rocks extend seaward ; on the lee of the island a
long sand-bank is thrown up, and a lagoon of considerable
extent is formed, in which the mans^rove tree is seen stridino*
about in the soft mud. Tliis island was washed in two by
the last hurricane, and the channel formed has three feet of
water at low tide. In the shallow water off many of the
Keys, very beautiful patches of Algije, interspersed with living
corals, are seen within six or eight inches of the surface. Off
Indian and Plantation Keys, dark knobs of coral are visible
upon the white mud of the bottom, which render the nav-
igation amongst these Keys dangerous. On lower Matacum-
ba I traced the rugged coral rocks for a mile in extent ; I
also found them on Conch Key, as I did indeed on nearly
every island that I examined, where a section could be found
on the shore, from which the overlying sands were washed."
Professor Agassiz gives the following general account of
the Keys and Reefs (see also map) :

" The Keys consist of an extensive range of low islands,
rising but a few feet, perhaps from six to eight or ten, or at
the utmost to twelve or thirteen feet, above the level of the
sea. They begin to the north of Cape Florida, when they
converge toward the main land, extending in the form of a
flat crescent in a southwesterly direction, gradually receding

208 CORALS AND GOEAL ISLANDS.

from the mainland until, opposite Cape Sable, they have so
tar retreated as to be separated from it by a shallow sheet of
water forty miles wide. Farther to the west they project in a
more westerly course, with occasional interruptions, as far as
the Tortugas [in longitude SS"" W.], which form the most
western group. They consist either of accumulated dead
corals, of coral rocks, or of coral sand, cemented together with
more or less compactness. Their form varies, but is usually
elongated and narrow, their greatest longitudinal extent fol-
lowing the direction of the main range, except in the group of
the Pine Islands, where their course is almost at right angles
with the main range — a circumstance which we shall hereafter
attempt to explain.

'' Most of these islands are small, the largest of them, such
as Key "West, and Key Largo, not exceeding ten or fifteen
miles in length ; others only two or three, and many scarcely
a mile. Their width varies from a quarter to a third or half
a mile, the largest barely measuring a mile across ; but what-
ever the difference in their size, tliey all agree in one respect-
that their steepest shore is turned toward the Gulf Stream,
while their more gradual slope inclines toward the mud fiats
which they encircle.

'' This is a point which it is important to notice, as it will
assist us in the comparison between the Keys and the shore
bluffs of the main-land, as well as with the outer reef and reefs
of other seas, in all of which we find that the seaward shore is
steeper than that turned toward the main-land, or, in case of
circular reefs inclosing basins (atolls), than that which borders
the lagoon.

" The reef proper extends parallel to the main range of
Keys, for a few miles south or southwest of it, following
the same curve, and never receding many miles from it.

FLORIDA REEFS AND KEYS, 209

The distance between the reef and the main range of Keys
varies usually from six to two or three miles, the widest sep-
aration being south of Key West, and east of the Eagged
Keys, where the space is about seven miles. Between this
reef, upon which a few small Keys rise at distant intervals,
and the main range of Keys already described, there is a broad
navigable channel, extending the whole range of the reef from
the Marquesas to Cape Florida, varying in depth from three to
six fathoms, and except Love Key, where the passage is not
more than fourteen feet deep at low water, averaging from
three to four fathoms.

''Farther east the average depth is again the same as at
Love Key, but it becomes gradually more and more shoal
toward the east, measuring usually about two fathoms or
even less to the east of Long Key and Key Largo, but deep-
ening again somewhat toward Cape Florida, where the reef
converges toward the main Keys and main-land. Protected
by the outer reef, this channel aflFords a very safe navigation
to vessels of medium size, and would allow a secure anchor-
age almost everywhere throughout the whole length of the
reef, were the numerous deep channels which intersect the
outer reef well known to navigators, and marked by a regu-
lar system of signals. As it is, however, the reef seems
to present an unbroken range of most dangerous shoal
grounds, upon which thousands of vessels, as well as millions
of property, have already been wrecked. These facts have a
stronger claim upon the attention of the Government, since
there are, as already remarked, numerous passages across the
reef, which might enable even the largest vessels to find
shelter and safe anchorage behind this threatening shallow
barrier. * * «

"The reef proper, as we have remarked above, runs al-

14

210 GOBALS AND CORAL ISLANDS.

most parallel to tlie main range of Keys from Cape Florida
to the Avestern extremity of the Marquesas, where it is lost
in the deep. It follows, in its whole extent, the same curve as
the Keys encircling, to the seaward, the ship-channel already
mentioned. This is properly the region of living corals.

"Throughout its whole range it does not reach the sur-
face of the sea, except in a few points where it comes almost
within the level of low-water mark, giving rise to heavy
breakers, such as Carysfort, Alligator Reef, Tennessee Reef,
and a few other shoals of less extent, but perhaps not less
dangerous. In a few localities, fragments of dead coral, and
coral sand begin to accumulate upon the edge of the reef,
forming small Keys, which vary in form and position accord-
ing to the influence of gales blowing from different direc-
tions — sometimes in the direction of the Gulf stream from
southwest to northeast, but more frequently in the opposite
direction, the prevailing winds blowing from the northeast.
Such are Sombrero Key, Love Key, the Sambos and Sand
Key. Here and there are isolated coral boulders, Avhich pre-
sent projecting masses above water, such as the Dry Rocks
west of Sand Key, Pelican Reef, east of it, with many others
more isolated. Though continuous, the outer reef is, however,
not so uniform as not to present many broad passages over
its crest, dividing it, as it were, into many submarine elongated
hillocks, similar in form to the main Keys, but not rising above
water, and in which the depressions alluded to correspond
to the channels intersecting the Keys. The broad passages
leading into the ship-channel, which may be available as en-
trances into the safe anchorage within the reef, are chiefly the
inlet in front of Key Largo, and to the west of Carysfort
reef, with nine feet of water ; a passage between French reef
and Pickle reef, with ten feet ; another between Conch reef

FLORIDA BEEFS AND KEYS. 211

and Crocus reef, also with ten feet ; another between Crocus
reef and Alligator reef, with two fathoms ; another between
Alligator reef and Tennessee reef, with two fathoms and a
half; and a sixth to the west of Tennessee reef varying in
depth from two and a half to three fathoms."

Through the labors of Mr. de Pourtales, in connection
with the soundings by the Coast Survey, interesting facts
have been brought to light respecting the sea between the
Florida reefs and the opposite shores or reefs along the Ba-
hamas and Cuba, called the Straits of Florida. A few par-
agraphs on these straits by Mr. de Pourtales, are cited from
his memoir referred to on page 204. The places described will
be found on the map at the close of this volume.

'' In transverse sections of the channel, the greatest depth
is nearest its southern or eastern shore, and in a longitudinal
section the depth diminishes in passing toward the north,
finding its minimum in the narrowest part between Cape
Florida and the Bemini Islands, after which it increases
again. In a transverse section between Key West and Ha-
vana, the greatest depth is 853 fathoms ; between Sombrero
Light and Elbow or Double-Headed Shot Key, on the Salt
Key Bank, 500 fathoms ; between Carysfort reef and Orange
Key, on the Great Bahama Bank, 475 fathoms; and between
Cape Florida and the Bemini Islands, 370 fathoms. In fol-
lowing a cross section from the emerged coral reef called the
Florida Keys, the so-called Hawk Channel is first crossed,
limited outside by the living coral reef Its greatest depth
is seldom more than six or seven fathoms, generally much less
toward its northern extremity ; it is often interrupted by
shoals, and so-called heads of live coral, and its bottom con-
. sists of calcareous mud from decomposed corals and corallines.
Next comes the reef, rising nearly to low-water mark, but by

212 CORALS AND CORAL ISLANDS.

no means continuous. It extends from Cape Florida, south
and west, to a short distance from beyond Key West, and
seems to be slowly increasing in that direction.

" Although the deep blue color of the water after passing
the reef seems to indicate a very abrupt slope, there is in no
part of it any thing to compare with the sudden deepening on
the edge of the coral reefs of the Pacific Ocean, or even of
the Bahamas or the coast of Cuba. The distance from the
reef to the 100-fathom line is not less than three miles, and
often as much as six. In this space the bottom consists
of calcareous mud, and is not particularly rich in animal
life. From ninety or a hundred fathoms to two hundred and
fifty or three hundred, the bottom slopes rather gently in the
shape of a rough rocky floor, without great inequalities ; this
formation obtains its greatest breadth, of about eighteen miles,
a little to the east of Sombrero Light, and tapers off to the
west, where it ends in about the same longitude as the end of
the reef; toward the east and north it approaches nearer the
reef, and ends gradually between Carysfort reef and Cape
Florida. This bottom, which is called ' Pourtales' Plateau '
in Prof Agassiz's report (see map), is very rich in deep-sea
corals, the greatest number of those described in these pages
[the memoir here cited from] having been dredged on this
ground.

" Outside of the rocky bottom the Globigerina mud pre-
vails and fills the trough of the channel.

" On the Cuba shore the bottom is rocky and the slope
very abrupt, particularly for the first four or five hundred
fathoms. Along the Salt Key and Bahama Banks, the slope
is also exceedingly abrupt, but the underlying rock is often
covered with mud."

Prof. Agassiz observes that the rocky bottom of the Pour-

THE BAHAMA ISLANDS. 213

tales' Plateau is a true coral-rag, in other words, ordinary cor-
al reef-rock, — being made up of an agglomeration of fragments
of corals and sand, cemented into a solid limestone.

Bahama Islands. — The Bahamas (the western margin of
which is shown on the map of the Florida Reefs), are coral
reefs and reef islands, essentially like atoll reefs. The northern
end of the group lies opposite southern Florida, and from this
point they stretch off to the west of southwest in a double se-
ries, nearly parallel to the trend of Cuba and San Domingo,
and terminate properly in Turk's Island and some other
reefs north of the latter, — the whole length above 600 miles.
The 100-fathom line of soundings extends around the
two northern ranges of reefs and islands, which, therefore,
make up one bank, the Little Bahama Bank ; and another
similar line embraces the next six islands as parts of a
second Bank, called the Great Bahama Bank; whose whole
length is about 300 miles. New Providence Island, the site
of the seat of government of the Group, Nassau, is the middle
one of the three northern islands of this Bank. The relation
of the eastern and western ranges of land in this Great
Bank is really analogous to that of the opposite sides of the
great Maldive Atoll Group. The remaining islands and reefs
are mostly isolated. In the triangular interval between the
Great Bahama Bank, Florida and Cuba, lies the reef called
Salt Key Bank. The northern coast of Cuba, south of this
Bank, and to the eastward, is bordered by coral reefs.

Prof. Agassiz gives the following account of a part of
these reefs in the first volume of the '' Bulletin of the Mu-
seum of Comparative Zoology."

" The Bahamas and the reefs to the northeast of Cuba exhib-
it very abrupt slopes, and a great depth is reached close to the
shores of the Banks, so that the Bahamas resemble the cora]

214 CORALS AND CORAL ISLANDS.

reefs of the Pacific much more than the reefs of the coast of
Florida.

•' The whole group of banks and keys embraced between
Double-Headed Shot Key, Salt Key, and Anguilla Key (all
on the Salt Key Bank), is a very instructive combination of
the phenomena of building and destruction. The whole
group is a flat bank covered by four or five, and occasionally
six, fathoms of water, with fine sandy bottom, evidently corals
reduced to oolitic, the grains, which are of various sizes,
from fine powder to coarse sand, mingled with broken shells,
among which a few living specimens are occasionally found.
The margin of the Bank is encircled on several points by rocky
ridges of the most diversified appearance, and at others edged
by sand-dunes. A close examination and comparison of the
different Keys show that these different formations are in fact
linked together, and represent various stages of the accumula-
tion, consolidation, and cementation of the same materials.
On the flat top of the bank the loose materials are pounded
down to fine sand ; in course of time this sand is thrown up
upon the shoalest portions of the Bank, and it is curious to
notice that these shoalest parts are its very edge, along which
corals have formed reefs which have become the basis of the
dry Banks. The foundation rock, as far as tide, wind and wave
may carry the coarser materials, consist of a conglomeration
of coarser oolitic grains, rounded fragments of corals, or
broken shells, and even larger pieces of a variety of corals
and conchs, all the species being those now found living upon
the Bank, among which Stromhus gigas is the most common ;
besides that, Astroea (^Orhicella) annularis^ Siderastrcea si-
derea and Mceandrina mammosa prevail. The shells of
Strombus are so common that they give great solidity and
hardness to the rock. The stratification is somewhat irregu-

SALT KEY BANE. 215

lar, the beds slanting toward the sea at an angle of about
seven degrees. Upon this foundation immense masses of
Strombus, dead shells, and corals have been thrown in banks,
evidently the beginning of deposits similar to those already
consolidated below ; but there is this difference in their forma-
tion, namely, that while the foundation rock is slightly inclined,
and never rises above the level of high water, the accumula-
tion of loose materials above water level forms steeper banks,
varying from fifteen to twenty and thirty degrees. In some
localities broken shells prevail ; in others, coarse and fine sand ;
and the ridges thus formed, evidently by the action of hio-h
Avaves, rise to about twelve and fifteen feet. This is evidently
the foundation for the accumulation of finer sand driven by
the wind over these ridges, and forming high sand-dunes,
held together by a variety of plants, among which a trailing
vine {Batatas littoralis)^ various grasses, and shrubs are the
most conspicuous. These dunes rise to about twenty feet ;
on their lee side and almost to their summits grow a little
palmetto. The sand of the dunes is still loose, but here
and there shows a tendency to incrustation at the surface.
The slope of these dunes is rather steep, sometimes over thir-
ty degrees, and steeper to the seaward than on the landward
side.

''In the interior of Salt Key there is a pool of intensely
salt water, the tint of which is pinkish or flesh -colored, owing
to the accumulation of a small alga. When agitated by the
wind, this pool is hedged all around by foam of the purest
white, arising from the frothing of the viscous water. Alono-
the edge the accumulation of this microscopic plant forms
large cakes, not unlike decaying meat, and of a very offensive
odor. The foundation rock of this Key is exactly like what
Gressly described as the 'fades coralUen' of the Jurassic

216 CORALS AND CORAL ISLANDS.

formation ; while the deposit in deep water, consisting chiefly
of muddy lime particles, answers to his 'fades vaseux.'

''Double-Headed Shot Key is a long, crescent-shaped
ridge of rounded knolls, not unlike ' roches moutonnees,' at
intervals interrupted by breaks, so that the whole looks like a
dismantled wall, broken down here and there to the water's
edge. The whole ridge is composed of the finest oolite, pretty
regularly stratified, but here and there like torrential depos-
its ; the stratification is more distinctly visible Avhere the rocks
have been weathered at the surface into those rugged and
furrowed slopes familiarly known as ' karren ' in Switzerland.
It is plain that we have here the same formation as on Salt
Key, only older, with more thoroughly cemented materials.
The uniformity in the minute grains of the oolites leaves no
doubt that the sand must have been blown up by the wind
and accumulated in the form of high dunes before it became
consolidated. The general aspect of Double-Headed Shot Key
is very different from that of Salt Key. The whole surface
is barren— not a tree, hardly a shrub, and the scantiest creep-
ing vegetation. The rock is very hard, ringing under the
hammer, and reminds one of the bald summits of the Jura,
such as Tete-de-Rang, near La-Chaux-de-Fond. It is evident
that what is beginning on Salt Key has here been not only
completed, but is undergoing extensive disintegration in
Double-Headed Shot Key, both by the action of atmospheric
agents over the surface, and by the action of tides and winds
against the base of the Kay.

"Among these older oolitic deposits, forming the main
range of Orange Key, and of Double-headed Shot Key, we
recognize formations of more recent date, occupying the cavi-
ties of ancient pot-holes, which have been gradually filled with
materials identical with those of the older deposits. The pot-

SALT KEY BANK. 217

holes themselves show nothing very peculiar ; there are many
such upon these Keys — some large ones many yards in diame-
ter, and others quite small — evidently formed by the wearing ac-
tion of loose pieces of harder coral rocks thrown upon the Key by
great waves, and only occasionally set in motion by the waters
dashing over the Keys during heavy storms. The pot-holes
nearest the water's edge are the most recent, and are mostly
clean excavations, either entirely empty or containing sand and
limestone pebbles lying loose at the bottom of the holes. Some
of these excavations are circular ; others oblong ; still others
have the form of winding caves opening toward the sea, or upon
the surface of the Key. Beyond the reach of ordinary tides,
and of the waves raised by moderate winds, the pot-holes are
generally lined with coatings of solid, compact, and hard lime-
stone, varying from a thin layer to a deposit of several inches
in thickness, and following all the sinuosities of the cavities in
which they are accumulating. It is plain from their structure
that these coatings are a sub-aerial formation, increasing b}^'
the successive accumulations of limestone particles left upon
the older rock by the evaporation of water thrown upon the
Key when the ocean is so violently agitated as to dash over
the whole Key. Frequently the hollow of these coated pot-
holes is further filled with consolidated oolite ; or thin layers
of fine-grained oolite alternate with a coat of compact lime-
stone, throughout the excavation, which often has been filled
in this way up to the general level of the surrounding surface.
Occasionally these regenerated surfaces are again hollowed
out by the action of storms, and the result is a dismantled
pot-hole, in which their structure and the mode of their filling
is distinctly exhibited.

" The stratification of the main mass of these Keys is very
peculiar. Though evidently the result of an accumulation of

218 C0RAL8 AND CORAL ISLANDS.

oolites through the action of high waves, the beds are pretty
regular in themselves, but slant in every direction toward the
sea, showing that they were deposited under the action of
winds blowing at different times from every quarter. It is
further noteworthy, that, while the thicker layers consist of
oolitic grains distinguishable by the naked eye, there are at
intervals thin layers of very hard, compact limestone, alterna-
ting with the oolitic beds, which have no doubt been formed
in the same manner as the coating of the pot-holes."

/

/

i

THE BERMUDA ISLANDS.

The oolitic limestones, referred to by Prof Agassiz as
the description states, are not the true coral reef-rock, the base-
ment rock of the reefs, but the superficial beach sand-rock and
drift sand-rock of the preceding pages, which are very gener-
ally oolitic in structure.

The Bermuda^ or Somers' /^ZaTzc^s.— The Bermudas are the

BERMUDA ISLANDS. 219

parts of a single atoll, as first announced by Lieut, (now
Major-General) Nelson, R. E., in liis paper in the Transac-
tions of the Geological Society of London, VoL V. (1840) ;
and this atoll is the most remote from the equator of any
existing. It lies between the parallels 32° and 32° 35^, and
the meridians 65° 45^ and 66° 55^ It is a living coral reef;
the principal species of corals are mentioned on page 114.

The general form and position of the reef and its islets are
shown in the accompanying map. The longer diameter of the
elliptical area trends nearly northeast-by-east, and is about
twenty-five miles in length, while the transverse diameter is
about fi^fteen miles.

Although an elevated atoll, the emerged land — about fif-
teen miles in length — is confined to the side facing southeast,
excepting a single isolated rock on the north (between c and d
in the map), called North Rock. It is broken into a hundred
and fifty or more islets — in consequence partly of degradation
since the elevation, and partly of the unequal height of the reef
formation before its elevation. The surface is made up of
hills and low basins. The highest point. Sears' Hill (E), is,
according to Lieut. Nelson, 260 feet in elevation above the sea,
and Gibbs Hill (D), the site of the lighthouse, 245 feet. Wreck
Hill (F), near the western point of the principal island, is about
150 feet high, and North Rock is 16 feet high. H is the posi-
tion of Hamilton, the seat of Government, and G of St.
George's, the other principal town. A (Castle Harbor), B
(Harrington Sound), and C (Great Sound), are three encir-
cled bays, looking as if once the lagoons of sub-atolls in a
Maldive-like compound atoll. The surface, about half way
between the sounds A and B, is low. Most of the land is
covered with cedar trees, where not cultivated or given over to
loose sand.

220 CORALS AND CORAL ISLANDS.

The rock of the surface is described as a calcareous sand-
rock, analogous evidently to the beach sand-rock and drift
sand-rock. Toward the shores the solid reef-rock outcrops
— a hard, white limestone. Lieut. Nelson speaks of that on
St. George's Island, as a " very hard, fine-grained or compact
limestone, in which scarcely a vestige of organic structure is
to be seen.'" In one place he observed a Ma^andrina (Di-
ploria) four feet above high-tide level.

The soil is calcareous, modified by vegetation and in part,
according to Lieut. Nelson, " a dry, aluminous earth." The
same observer mentions the occurrence on the land of oxide
of iron and manganese, and of some titanic iron ; but Mr. J.
Matthew Jones states (Canadian Naturalist, Feb. 1864) that
all stones not of coral and shell origin have undoubtedly
been brought in the roots of drift-trees ; and the West Indies
were probably their source.

The greater part of the old atoll is still a submerged reef.
Its outer border is mostly from one to three fathoms under
water at low tide, though in some parts laid bare at the ebb.
It has open channels at a (called the Chub cut), h (Blue cut,
shallow), c (N. W, Channel), d (N. E. Channel), e (Mills'
Breaker Channel), / (The Channels affording the nearest
routes to Murray Anchorage and St. George's Harbor), g
(Channel by St. David's Head, shallow), and h (Hog-fish cut).
The reef-grounds, inside, are encumbered with countless clumps
of corals and coral-heads, one to four fathoms under water with
intervals between of five to ten fathoms ; some large tracts are
without corals, and these have a nearly uniform depth of seven
or eight fathoms. To a vessel entering, the positions of the coral
clumps are made known by the brownish or discolored water
above them. The bottom, over large areas, is a calcareous clay
or mud ; that of Murray Anchorage, a fine chalky clay.

BERMUDA ISLANDS. 221

The wind for three-fourths of the year is from the south-
east or southwest, and this may in part account for the south-
east side of the atoll being highest. But this feature is probably
owing much to the configuration of the land upon which
the coral reefs were built up. The reefs along the south-
east and south sides are narrow, not over a fourth of a mile
wide, and the waters abruptly deep, and consequently we
may conclude that this southeastern side of the original island
was bold and high, while oiF to the north, the surface was rela-
tively low and flat.

Twenty miles southwest-by-west from the Bermudas, there
are two submerged banks or shoals, both reported as having a
''corally and rocky bottom ; " one has 22 to 40 fathoms over it,
and the other 33 to 47 fathoms. Dredging on these banks
might make some interesting disclosures.

222 C0BAL8 AND COHi L ISLANDS,

4

CHAPTER III.

FORMATIOlSr OF OORAL R.EEFS AND ISL-
ANDS, AND CAUSES OF THEIR FEA-
TURES.

I. FORMATION OF REEFS.

I. ORIGIN OF CORAL SANDS AND THE REEF-ROCK.

Very erroneous ideas prevail respecting the appearance of
a bed or area of growing corals. The submerged reef is
often thought of as an extended mass of coral, alive uniform-
Iv over its upper surface, and as gradually enlarging upward
through this living growth; and such preconceived views,
when ascertained to be erroneous by observation, have some-
times led to skepticism with regard to the zoophytic origin
of the reef rock. Nothing is wider from the truth : and this
must have been inferred from the descriptions already given.
Another glance at the coral plantation should be taken by
the reader, before proceeding with the explanations which

follow.

Coral plantation and coral field are more appropriate ap-
pellations than coral garden, and convey a juster impression
of the surface of a growing reef Like a spot of wild land,
covered in some parts, even over acres, with varied shrub-
bery, in other parts bearing only occasional tufts of vegeta-
tion in barren plains of sand, here a clump of saplings, and
there a carpet of variously-colored flowers in these barren
fields — such is the coral plantation. Numerous kinds of
zoophytes grow scattered over the surface, like vegetation

FORMATION OF CORAL REEFS AND ISLANDS. 223

upon the land ; there are large areas that bear nothing, and
others of great extent that are thickly overgrown. There is,
however, no green sward to the landscape ; sand and frag-
ments fill up the bare intervals between the flowering tufts:
or, where the zoophytes are crowded, there are deep holes
among the stony stems and folia.

These fields of growing coral spread over submarine
lands, such as the shores of islands and continents, where the
depth is not greater than theirhabits require, just as vegetation
extends itself through regions that are congenial. The germ
or ovule, which, when first produced, is free, finds afterward a
point of rock, or dead coral, or some support, to plant itself
upon, and thence springs i\m tree or other forms of coral growth.

The analogy to vegetation does not stop here. It is well
known that the debris of the forest, decaying leaves and
stems, and animal remains, add to the soil ; that in the marsh
or swamp— where decaying vegetation is mostly under water,
and sphagnous mosses grow luxuriantly, ever alive and flour-
ishing at top, while dead and dying below, — accumulations
of such debris are ceaselessly in progress, and deep beds of
peat are formed. Similar is the liistory of the coral mead.
Accumulations of fragments and sand from the coral zoo-
phytes growing over the reef-grounds, and of shells and other
relics of organic life, are constantly making; and thus a bed
of coral debris is formed and compacted. There is this dif-
ference, that a large part of the vegetable material consists of
elements which escape as gases on decomposition, so that there
is a great loss in bulk of the gathered mass ; whereas coral is
an enduring rock material undergoing no change except the
mechanical one of comminution. The animal portion is but
a mere fraction of the whole zoophyte. The coral debris and
shells fill up the intervals betAveen the coral patches, and the

224 C0BAL8 AND CORAL ISLANDS.

cavities among the living tufts, and in this manner produce
the reef deposit; and the bed is finally consolidated, while
still beneath the water.

The coral zoophyte is especially adapted for such a mode
of reef-making. Were the nourishment drawn from below, as
in most plants, the solidifying coral rock would soon destroy
all life : instead of this, the zoophyte is gradually dying be-
low while growing above ; and the accumulations of debris
cover only the dead portions.

But on land, there is the decay of the year, and that of old
age, producing vegetable debris ; and storms prostrate forests.
And are there corresponding effects among the groves of the
sea ? It has been shown that coral plantations, from which
reefs proceed, do not grow in the '^calm and still" depths of
the ocean. They are to be found amid the very waves, and
extend but little below a hundred feet, which is far within the
reach of the sea's heavier commotions. To a considerable ex-
tent they grow in the very face of the tremendous breakers
that strike and batter as they drive over the reefs. Here is an
agent which is not without its effects. The enormous masses
of up torn rock found on many of the islands may give some
idea of the force of the lifting wave ; and there are examples
on record, to be found in various treatises on Geology, of still
more surprising effects.

During the more violent gales, the bottom of the sea is
said, by different authors, to be disturbed to a depth of three
hundred, three hundred and fifty, or even five hundred feet,
and De la Beche remarks, that when the depth is fifteen fath-
oms, the water is very evidently discolored by the action of
the waves on the sand and mud of the bottom. M. Siau men-
tions (Comptes Rendus, t. xii. 744), that ripple-marks are
formed on the bottom by the motion of the water, which may

FOJRMATION OF COllAL REEF8 AND ISLANDS. 225

be readily distinguished at a depth of at least twenty metres.
The hollows between such ridges or zones are occupied by the
heavier substances of the bottom. Similar ripple-marks were
distinguished at a depth of one hundred and eighty-eight
metres, to the northwest of the St. Paul's Roads.

In an article on the Force of Waves, by Thomas Steven-
son, of Edinburgh, published in the Transactions of the Royal
Society of Edinburgh (vol. xvi., 1845), it is stated as a deduc-
tion from two hundred and sixty-seven experiments, extend-
ing over twenty-three successive months, that the averao-e
force for Skerryvore, for five of the summer months, durino-
the years 1843, 1844, was six hundred and eleven pounds per
square foot ; and for six of the winter months of the same
year, it was two thousand and eighty-six pounds per square
foot, or three times as great as during the summer months.
During a westerly gale, at the same place, in March, 1845, a
pressure of six thousand and eighty-three pounds w^as regis-
tered by Mr. Stevenson's dynamometer (the name of the in-
strument used). He mentions several remarkable instances of
transported blocks. One of gneiss, containing five hundred
and four cubic feet, was carried by the waves five feet from
the place where it lay, and there became wedged so as no
longer to be moved. Of the manner in which it was moved,
Mr. Reid (as cited by Mr. Stevenson) says : " The sea, when
I saw it striking the stone, would wholly immerse or bury it
out of sight, and the rqn extended up to the grass line above
it, making a perpendicular rise of from thirty-nine to forty feet
above high-water level. On the incoming waves striking the
stone, we could see this monstrous mass, of upwards of forty
tons weight, lean landward, and the back-run would uplift it
again with a jerk, leaving it with very little water about it,
when the next incoming wave made it recline again."

16

226 CORALS AND CORAL ISLANDS.

Mr. Stevenson states also that the Bell Rock Lighthouse,
in the German Ocean, though one hundred and twelve feet in
height, is literally buried in foam and spray to the very top,
during ground swells, when there is no wind. On the 20th
of November, 1827, the spray rose to the height of one hun-
dred and seventeen feet above the foundations or low- water
mark; and deducting eleven feet for the tide that day, it
leaves one hundred and six feet, which is equivalent to a pres-
sure o^ nearly three tons per square foot.

With such facts, any incredulity respecting the power of
waves should be laid aside. Moreover, it may be remarked
that the Pacific is a much wider ocean than the Atlantic, with
far heavier waves in its ordinary state.

We must, therefore, allow that some effect will be pro-
duced upon the coral groves. There will be trees prostrated
by gales, as on land, fragments scattered, and fragmentary
and sand accumulations commenced. Besides, masses of the
heavier corals will be uptorn, and carried along over the coral
plantation, which will destroy and grind down every thing in
their way. So many are the accidents of this kind to which
zoophytes appear to be exposed, that we might believe they
would often be exterminated, were they not singularly tenacious
of life, and ready to sprout anew on any rock where they may
find quiet long enough to give themselves again a firm attach-
ment.

But it should be observed, that the sea would have far
less effect upon the slender forms characterizing many zoo-
phytes, among which the water finds free passage, than on the
massive rock, against whose sides a large volume may drive
unbroken. Moreover, much the greater part of the strength
of the ocean is exerted near tide level, where it rises in break-
ers which plunge against the shores. Yet owing to the many

FORMATION OF CORAL REEFS AND ISLANDS. 227

nooks and recesses deep among the corals, Ihe rapidly moving
waters, during the heavier swells, must produce whirling ed-
dies of considerable force, tending to uproot or break the coral
clumps. These disrupting and transporting effects will be
less and less as we recede from the shores ; yet all coral depths
must experience them in some degree.

There is another process going on over the coral field, some-
what analogous to vegetable decay, though still very different.
Zoophytes have been described as ever dying while living. The
dead portions have the surface much smoothed, or deprived
of the roughening points which belong to the living coral, and
the cells are sometimes half obliterated, or the delicate lamellte
Avorn away. This may be viewed as one source of fine coral
particles ; and as the process is constantly going on, it is not
altogether unimportant. This material is in a fit condition to
enter into solution, and it cannot be doubted that the water
receives lime from this source, which is afterward yielded to
the reef

In the Alcyonia family, which includes semi-fleshy corals,
and in the Gorgoni^, the lime is often scattered through the
polyps in granules ; and the process of death sets these calca-
reous grains free, which are constantly added to the coral sands.
The same process has been supposed to take place in the more
common reef corals, the Madrepores and Astr^eas, and it is
possible that this may be to some extent the case. Yet it
would seem, from facts observed, that after the secretion has
begun within the polyp, the secretion of lime going on takes
place against the portions already formed and in direct union
with them, and not as granules to be afterward cemented.

The mud-like deposits about coral reefs (pp. 142, 183, 205)
have been attributed to the causes just mentioned, but with-
out due consideration. There is an unfailing and abundant

228 C0EAL8 AJ^I) COMAL ISLANDS.

source of this kind of material in the self -triturating sands of
the reefs acted upon by the moving waters. On the seaward
side of coral islands, and on the shores of the larger la-
goons, where the surface rises into waves of much magnitude,
the finer portions are carried off, and the coarser sand remains
alone to form the beaches. This making of coral sand and
mud is just like that of any other kind of sand or mud. It
takes place on all shores exposed to the waves, coral or not
coral, and in every case the gentler the prevailing movement
of the water, the finer the material on the shore. In the
smaller lagoons, where the water is only rippled by the winds,
or roughened for short intervals, the trituration is of the
gentlest kind possible, and, moreover, the finely pulverized
material remains as part of the shores. Thus the fine mater-
ial of the mud must be constantly forming on all the shores,
for the sands are perpetually wearing themselves out ; but the
particles of the fine mud, which is washed out from the beach
sands, accumulates only in the more quiet waters some dis-
tance outside of the reef, and within the lagoons and channels,
where it settles. This corresponds exactly with the facts ; and
every small lake or region of quiet waters over our continent.^
illustrates the same point.

Mr. Darwin, in discussing the origin of the finer calcareous
mud, (op. cit., p. 14), supposes that it is derived in part from
fishes and Holothurians ; and other authors have thrown out
the same suggestion. He cites as a fact, on the authority of
Mr. Liesk, that certain fish browse on the living zoophytes ;
and from Mr. Allan, of Forres, he learned also that Holothu-
rians subsisted on them. With regard to the facts here stated,
can be made no positive assertion. Small fish swarm about the
branching clumps, and when disturbed, seek shelter at once
among the branches, where they are safe from pursuit. The

FOJIMATION OF COllAL REEFS AND ISLANDS. 229

author has often witnessed this, and never saw reason to sup-
pose that they clustered about the coral for any other purpose.
It is an undoubted fact, as stated by Mr. Darwin, that frao-.
ments of coral and sand may be found in the stomachs of
these animals, but this is not sufBcient evidence of their
browsing on the coral. Fish so carefully avoid polyps of all
kinds because of their power of stinging (as illustrated on
p. 37), that we should wait for further and direct evidence
on this point. The conclusion deduced by him from the facts,
may be justly doubted. The fish and Holothurian^, though
numerous, are quite inadequate for the supply ; and, more-
over, we have, as explained above, an abundant source of the
finest coral material without such aid. Motion of particle
over particle will necessarily wear to dust, even though the
particles be diamonds; and this incessant grinding action
about reefs accounts satisfactorily for the deposits of coral
mud, however great their extent.

The coral world, as we thus perceive, is planted, like the
land, with a variety of shrubs and smaller plants, and the el-
ements and natural decay are producing gradual accumula-
tions of material, like those of vegetation. The history of the
growing reef has consequently its counterpart among the or-
dinary occurrences of the land about us.

The progress of the coral formation is like its commence-
ment. The same causes continue, with similar results, and
the reader might easily supply the details from the facts al-
ready presented. The production of debris will necessarily
continue to go on : a part will be swept by the waves, across
the patch of reef, into the lagoon or channel beyond, while
other portions will fill up the spaces among the corals along
its margin, or be thrown beyond the margin and lodge on its

230 CORALS AND COEAL ISLAND b.

surface. The layer of dead coral rock which makes the body
of the reef, has its border of growing corals, and is thus un-
dergoing extension at its margin, both through the increase in
the corals, and the debris dropped among them.

But besides the small fragments, larger masses will be
thrown on the reefs by the more violent waves, and commence
to raise them above the sea. The clinker fields of coral by
this means produced, constitute the first step in the formation
of dry land. Afterward, by further contributions of the
coarse and fine coral material, the islets are completed, and
raised as far out of the water as the waves can reach — that is,
about ten feet, with a tide of three feet; and sixteen to
eio-hteen feet with a tide of six or seven.

The Ocean is thus the architect, while the coral polyps af-
ford the material for the structure; and, when all is ready, it
sows the land with seed brought from distant shores, covering
it with verdure and flowers.

The growth of the reefs and islands around high lands is
the same as here described for the atoll. The reef-rock is
mainly a result of accumulations of coral and shell debris.
There are reefs where the corals retain the position of growth,
as has been described on a former page. But with these the
debris comes in to fill up the intervening spaces or cavities, and
make a compact bed for consolidation. There are other parts,
especially portions of the outer reef along the line of break-
ers, which are formed by the gradual growth of layer upon
layer of incrusting Nullipores ; but such formations are of
small extent, and only add to the results from other sources.

II. ORIGIN OF THE SHORE PLATFORM.

Among the peculiarities of coral islands, the shore plat-
form, appears to be one of the most singular, and its origin

FORMATION OF CORAL REEFS AND ISLANDS. 231

has not been rightly understood. It will be remembered that
it lies but little above low-tide level, and it is often over three
hundred feet in width, with a nearly flat surface throughout.

Though apparently so peculiar, the existence of this plat-
form is due to the simple action of the sea, and is a necessary
result of this action. On the shores of New South Wales,
Australia, near Sydney, as observed by the author, the same
structure is exemplified along the sandstone shores of this
semi-continent, where it is continued for scores of miles. At
the base of the sandstone cliff, in most places one or more hun-
dred feet in height, there is a layer of sandstone rock, lying,
like the shore platform of the coral island, near low-tide level,
and from fifty to one hundred and fifty yards in width. It is
continuous with the bottom layer of the cliff: the rocks which
once covered it have been removed by the sea. Its outer edge
is the surf-line of the coast. At low-tide it is mostly a naked
flat of rock, while at high tide it is wholly under water, and
the sea reaches the cliff.

New Zealand, at the Bay of Islands, affords a like fact in
an argillaceous sand-rock ; and there was no stratification in •
this case to favor the production of a horizontal surface; it

THE OLD HAT.

was a direct result from the causes at work. The shore shelf
stands about five feet above low water. A small island in this
bay is well named the ''Old Hat," the platform encircling it,
as shown in the above figure, forming a broad brim to a rude

232 CORALS AND CORAL ISLANDS.

conical crown. The water, in these cases, has worn away the
cliffs, leaving the basement untouched.

A surging wave, as it comes upon a coast, gradually rears it-
self on the shallowing shores; finally, the waters at top, through
their greater velocity, plunge with violence upon the barrier
before it. The force of the ocean's surge is therefore mostly
confined to the summit waters, which add weight to superior ve-
locity, and drive violently upon whatever obstacle is presented.
The loioer waters of the surge advance steadily but more
slowly, owing to the retarding friction of the bottom ; the
motion they have is directly forward, and thus they act with
little mechanical advantage ; moreover, they gradually swell
over the shores, and receive, in part, the force of the uppei'
waters. The wave, after breaking, sweeps up the shore till it
gradually dies away. Degradation from this source is conse-
quently most active where the upper or plunging portion of
the breaker strikes.

But, further, we observe that at low-tide the sea is compara-
tively quiet; it is during the influx and efflux that the surges
are heaviest. The action commences after the rise, is strongest
from half to three-fourths tide, and then diminishes again near
high tide. Moreover, the plunging part of the wave is raised
considerably above the general level of the water. From
these considerations, it is apparent that the line of greatest
wave-action must be above low-water level. Let us suppose a
tide of three feet, in which the action would probably be
strongest when the tide had risen two feet out of the three ;
and let the height of the advancing surge be four feet : — the
wave, at the time of striking, would stand, with its summit,
three feet above high-tide level ; and from this height would
plunge obliquely downward against the rock, or any obstacle
before it. It is obvious that, under such circumstances, the

FORMATION OF CORAL REEFS AND ISLANDS. 233

p-reatest force would be felt not far from the line of hio-h tide-

O O /

or between that line and three feet above it ; moreover, the
rise of the waters to half or two-thirds tide affords a protection
against the breaker to whatever is below this level. In re-
gions where the tide is higher than just supposed, as six feet
for exam[)le, the same height of wave would give nearly the
same height to the line of wave action, as compared with high-
tide level. Under the influence of heavier waves, such as are
common during storms, the line of wave-action would be at a
still higher elevation, as may be readily estimated by the
reader.

Besides a line of the greatest wave-action, we may also dis-
tinguish a height where this action is entirely null; and it is
evident, from facts already stated, that the point will be found
somewhat above low-tide level. The lower waters of the surere,
instead of causing degradation, are accumulative in their or-
dinary action, when the material exposed to them is movable :
they are constantly piling up, while the upper waters are
eroding, and preparing material to be carried off. The height
at which these two operations balance one another will be
the height, therefore, of the line of no degradation. As the
sea at low tide is mostly quiet, and the lower of the surging
Avaters swell on to receive the upper and parry the blow, and
moreover, there is next a return current outward, we should
infer that the line would be situated more or less above low
tide, according to the height of the tide and the surges ac-
companying it. We are not left to conjecture on this point ;
for the examples presented by the shores of Australia and
New Zealand afford definite facts. Degradation has there
taken place sufficient to carry off* cliffs of rock, of great ex-
tent ; yet below a certain level, the sea has had little or no ef-
fect. This height, on the eastern shores of Australia, is three

234 CORALS AND CORAL ISLANDS.

feet above ordinary low tide, and at New Zealand, about five
feet. With regard to the height varying with the tides, we
observe that in the Paumotus, where the water rises but two
or three feet, the platform is seldom over four to six inches
above low tide, which is proportionally less than at Austra-
lia and New Zealand, where the tide is six and eight feet.
From these observations it appears that the height of no wave-
action^ as regards the degradation of a coast under ordinary
seas, is situated near one-fifth tide in the Paumotus, and above
half-tide at New Zealand, showing a great difference between
the eff^ect of the comparatively quiet surges of the middle Pa-
cific, and the more violent of New Zealand. Within the Bay
of Islands, where the sea has not its full force, the platform,
as around the '• Old Hat," is but little above low-water level.
The exact relation of the height of the platform to the height
and force of the tides, and the force of wave- act ion, remains
to be determined more accurately by observation. While,
therefore, the height of the shore platform depends on the
tides, and the degree of exposure to the waves, the breadth
of it will be determined by the same causes in connection with
the nature of the rock material.

On basaltic shores it is not usual to find a shore platfi)rm,
as the rock scarcely undergoes any degradation, except from
the most violent seas ; such coasts are consequently often cov-
ered with large fragments of the basaltic rocks. But on sand-
stone shores, this gradual action keeps the platform of nearly
uniform breadth. Moreover, any up torn masses thrown upon
it, are soon destroyed by the same action, and carried off; and
thus the platform is kept nearly clean of debris, even to the
base of the cliff.

It is apparent that one single principle meets all the va-
rious cases. The rocky platform of some sea-shores, the low

FORMATION OF CORAL REEFS AND ISLANDS. 235

tide sand-spit on others, and the coral reef platform of others,
require but one explanation. The material of the coral plat-
form is piled up by the advancing surges, and cemented
throuo;h the infiltrating; waters. These suro-es, advancinsr to-
ward the edge of the shelf, swell over it before breaking, and
thus throw a protection about the exposed rocks; and as the
tide rises, this protection is complete. They move on, sweep-
ing over the shelf, but only clear it of sand and fragments,
which they bear to the beach.

The isolated blocks in the Paumotus which stand on the
platform, attached to it below, are generally most worn one or
two feet above high-tide level, a fact which corresponds with
the statement in a preceding paragraph with regard to the
height of the greatest wave-action.

III. EFFECTS OF WINDS AND GALES.

In addition to this ordhiary wave-action, there are also
more violent effects from storms ; and these are observed alike
on the Australian shores referred to, and on those of coral
islands. The waters as they move in, first draw away, and
then drive on with increased velocity up the shallowing shores,
or under shelving layers, and thus they easily break off great
rocks from the edge of the platform, and throw them on the
reef. Prom the observations of Mr. Stevenson, cited on a pre-
ceding page (p. 225), it appears that the force of the waves
during the summer and winter months diflfers at Skerryvore
more than 1,200 pounds to the square foot, — in the former it
averaging but 636 pounds, and in the latter 2,086 pounds,
while in storms it was at times equivalent to 6,083 pounds.
The seasons are not as unlike in the tropical part of the Pa-
cific. Still there must be a marked difference between the or-

236 CORALS AND CORAL ISLANDS.

dinary seas and those duiing stormy weather. We have,
therefore, no difficulty in comprehending how the ordinary
wave-action should build up and keep entire the shore plat-
form, while the more agitated seas may tear up parts of the
structure formed, and bear them on to the higher parts of the
island. Still more violent in action are the great earthquake-
waves, which move through the very depths of the ocean.

These principles offer an explanation also of the general
fact that the windward reef is the highest. The ordinary
seas both on the leeward and windward sides, are sufficient
for producing coral debris and building up the reef^ and in
this work the two sides will go on together, though at different
rates of progress. We may often find no very great dif-
ference in the width of the leeward and windward reefs, es-
pecially as the wind for some parts of the year, has a course
opposite to its usual direction. But seldom, except on the
side to windward, is a sufficient force brought to bear upon the
edge of the platform, to detach and uplift the larger coral
blocks. The distance to which the waves may roll on without
becoming too much weakened for the transportation of up-
torn blocks, will determine the outline of the forming land.
With proper data as to the force of the waves, the tides, and
the soundings around, the extent of the shore platform might
be made a subject of calculation.

The effect of a windward reef in diminishing the force of
the sea, is sometimes shown in the influence of one island on
another. A striking instance of this is presented by the
northernmost of the Gilbert Islands (see map, on page 165.)
All the islands of this group are well wooded to windward —
the side fronting east. But the north and northeast sides of
Tari-tari are only a bare reef, through a distance of twenty
miles, although the southeast reef is a continuous line of ver-

FORMATION OIT VORAL UEEFS AND ISLANDS. 237

dure. The small island of Makin, just north of Tari-tari, is
the breakwater which has protected the reef referred to from
the heavier seas.

Coral island accumulations have an advantage over all
other shore deposits, owing to the ready agglutination of cal-
careous grains, as explained on a following page. It has been
stated that coral sand-rocks are forming along the beaches,
while the reef-rock is consolidating in the water. A defence
of rock against encroachment is thus produced, and is in con-
tinual progress. Moreover, the structure built amid the
waves, will necessarily have the form and condition best fitted
for withstanding their action. The atoll is, therefore, more
enduring than hills of harder basaltic rocks. Reefs of
zoophytic growth but ''mock the leaping billows," while
other lands of the same height gradually yield to the assaults
of the ocean. There are cases, however, of wear from the
sea, owing to some change of condition in the island, or in
the currents about it, in consequence of which, parts once
built up are again carried off. Moreover, those devastating
earthquake-weaves which overleap the whole land, may occa-
sion unusual degradation. Yet these islands have within
themselves the source of their own repair, and are secure
from all serious injury.

The change of the seasons is often apparent in the distri-
bution of the beach sands covering the prominent points of an
island. At Baker's Island (near the equator, in long. 176°
23^, W.), this fact is well illustrated. J. D. Hague states
[Am. Joxiv. Sci.^ II., xxxiv, 237), that the shifting sands
change their place twice a year. " The western shore of the
island trends nearly northeast and southwest; the southern
shore, east-by -north. At their junction there is a spit of sand
extending out toward the southwest. During the summer,

238 CORALS AND CORAL ISLANDS.

the ocean swell, like the wind, comes from the southeast, to
the force of which the south side of the island is exposed,
while the western side is protected. In consequence, the sands
of the beach that have been accumulating during the summer
on the south side, are all washed around the southwest point
and are heaped up on the western side, forming a plateau
along the beach two or three hundred feet wide, nearly cover-
ing the shore platform, and eight or ten feet deep. With
October and November comes the winter swell from the north-
northeast, which sweeps along the western shore, and from
the force of which the south side is in its turn protected.
Then the sand begins to travel from the western to the south-
ern side ; and, after a month or two, nothing remains of the
great sand plateau but a narrow strip ; while on the south
side, the beach has been extended two hundred or three hun-
dred feet. This lasts until February or March, when the
operation is repeated."

IT CAUSES MODIFYING THE FORMS AND GROWTH OF REEFS.

Coral reefs, although (1) dependent on the configuration of
the submarine lands for many of their features^ undergo vari-
ous modifications of form, or condition, through the influence of
extraneous causes, such as (2) unequal exposure to the waves ;
(3) oceanic or local currents ; (4) presence of fresh or impure
waters. In briefly treating of these topics, we may consider
first, reefs around high islands, and afterward, atoll reefs.
The effect of the waves on different sides of reefs has already
been considered, and we pass on, therefore, at once to the
influence of oceanic or local currents, and fresh or impure
waters.

FORMATION OF CORAL REEFS AND ISLANDS. 239

I. BARRIER AND FRINGING REEFS.

The existence of harhors about coral-bound lands, and of
entrances through reefs, is largely attributable to the action of
tidal or local marine currents. The presence of fresh-water
streams has some effect toward the same end, but much less
than has been supposed These causes are recognized by
Mr. Darwin in nearly the same manner as here: yet the
views presented may be taken as those of an independent wit-
ness, as they were written out before the publication of his
work.

There are usually strong tidal currents through the reef
channels and openings. These currents are modified in char-
acter by the outline of the coast, and are strongest wherever
there are coves or bays to receive the advancing tides. The
harbor of Apia, on the north side of Upolu, affords a striking
illustration of this general principle. The coast at this place

HARBOR OF APIA, UPOLTT.

has an indentation 2,000 yards wide and nearly 1,000 deep,
as in the accompanying sketch, reduced from the chart by the
Expedition. The reef extends from either side, or cape, a mile
out to sea, leaving between an entrance for ships. The har-
bor averages ten feet in depth, and at the entrance is fifteen
feet. In this harbor there is a remarkable out-current alono:
the bottom, which, during gales, is so strong at certain states

240 CORALS AND CORAL ISLANDS.

of the tide that a ship at anchor, although a wind may be
blowing directly in the harbor, will often ride with a slack
cable; and in more moderate weather the vessel may tail out
against the wind. Thus when no current but one inward is
perceived at the surface, there is an undercurrent acting
against the keel and bottom of the vessel, which is of sufficient
strength to counteract the influence of the winds on the rig-
ging and hull. The cause of such a current is obvious. The
sea is constantly pouring water over the reefs into the harbor,
and the tides are periodically adding to the accumulation ;
the indented shores form a narrowing space where these waters
tend to pile up : escape consequently takes place along the
bottom by the harbor-entrance, this being the only means of
exit. There are many such cases about all the islands. In a
group like the Feejees, where a number of the islands are
large and the reefs very extensive, the currents are still more
remarkable, and they change in direction with the tides.
''Through the channels and among the inner reefs of the
Australian reef-region," says Jukes, "they run sometimes
with an impetuous sweep in the same direction even for two
or three days together, especially after great storms have
driven large quantities of water into the space between the
outer edge and the land."

A current of the kind here represented will carry out much
coral debris, and strew it along its course. The transported
material will vary in amount from time to time, according to the
force and direction of the current. It is therefore evident
that the ground over which it runs must be wholly unfit for
the growth of coral, since most zoophytes are readily destroy-
ed by depositions of earth or sand, and require, for most spe-
cies, a firm basement. Or if the flow is very strong, it will
scour out the channels and so keep them open. The existence

FORMATION OF CORAL REEFS AND ISLANDS. 241

of an opening through a reef may require, therefore, no other
explanation ; and it is obvious that harbors may generally be
expected to exist wherever the character of the coast is such
as to produce currents and give a fixed direction to them.

The currents, about the reef grounds west of the large
Feejee Islands, aid in distributing the debris both of the land
and the reefs. In some parts, the currents eddy and deposit
their detritus ; in others they sweep the bottom clean. Thus,
under these varying conditions, there may be growing corals
over the bottom in some places and not in others ; and the
reefs may be distributed in patches, when without such an
influence we might expect a general continuity of coral reef
over the whole reef-grounds.

The results from marine currents are often increased by
waters from the island streams ; for the coves, where harbors
are most likelv to be found, are also the embouchures of val-
leys and the streamlets they contain. The fresh waters poured
in add to the amount of water, and increase the rapidity of
the out-current. At Apia, Upolu, there is a stream thirty
yards wide ; and many other similar instances might be men-
tioned. These waters from the land bring down also much
detritus, especially during freshets, and the depositions aid
those from marine currents in keeping the bottom clear of
growing coral. These are the principal means by which fresh-
water streams contribute toward determining the existence of
harbors ; for little is due to their freshening the salt waters of
the sea.

The small influence of the lastrmentioned cause — the one
most commonly appealed to — will be obvious, when we con-
sider the size of the streams of the Pacific islands, and the
fact that fresh water is lighter than salt, and therefore, in-
stead of sinking, flows on over its surface. The deepest rivers

16

242

CORALS AND CORAL ISLANDS.

are seldom over six feet, even at their mouths ; and three or
four feet is a more usual depth. They will have little effect,
therefore, on the sea water beneath this depth, for they cannot
sink below it; and corals may consequently grow even in
front of a river's mouth. Moreover the river water becomes
mingled with the salt, and, in most cases, a short distance out,
would not be unfit for some species of coral zoophytes.

Fresh-water streams, acting in all the different modes
pointed out, are of little importance in harbor-making about
the islands of the Pacific. The harbors, with scarcely an ex-
ception would have existed without them. They tend, how-
ever, by the detritus which they deposit, to keep the bottom

o O

PART OP NORTH SHORE OF TAHITI.

more free from growing patches of coral, and consequently
produce better anchorage ground ; moreover, within the har-
bors they usually keep channels open through, or over, the shore
reef sufficiently deep and wide for a boat to reach the land,
and sometimes preserve a clean sand-beach throughout. That
this is their principal effect will appear from a few facts.
The map of the reef of North Tahiti, between Papieti on

FORMATION OF CORAL REEFS AND ISLANDS. 243

the left, and the west cape of Matavai harbor, on the right,
here reproduced, affords illustrations of this subject.

a. The harbor of Papieti is enclosed by a reef about
three-fourths of a mile from the shore. The entrance through
the reef is narrow, with a depth of eleven fathoms at centre,
six to seven fathoms either side, and three to five close to the
reef. This fine harbor receives an unimportant streamlet,
while a much larger stream empties just to the east of the east
cape, opposite which the reef is close at hand and unbroken.

b. Toanoa is the harbor next east of Papieti. . The en-
trance is thirty-five fathoms deep at middle, and three and a
half to five fathoms near the points of the reef. There is no
fresh-water stream, except a trifling rivulet.

c. Papaoa is an open expanse of water, harbor-like in
character, but is without any entrance ; the reef is unbroken.
Yet there are two streams emptying into it, one of which is
of considerable size.

d. Off Matavai, the place next east, the reef is inter-
rupted for about two miles. The harbor is formed by an ex-
tension of the reef off Point Venus, the east cape. There is
no stream on the coast, opposite this interruption in the reef,
except toward Point Venus, and at the present time the wa-
ters find their principal exit east of the Point, behind a large
coral reef, but a quarter of a mile distant.

From such facts, it is evident that the growth of coral
reefs is not much retarded about the Pacific Islands by fresh-
water streams. We cannot be surprised at the little influence
they appear to have exerted about Tahiti, when knowing that
none of these so-called rivers are over three feet in depth;
and the most they can do is to produce a thin layer of brackish
water over the sea within the channels.

e. The following figure of the harbor of Falifa, Upolu,

244 CORALS AND CORAL ISLANDS.

represents another coral harbor, as surveyed by Lieutenant
Emmons. At its head there is a stream twenty-five or thirty
yards wide and three feet deep. Notwithstanding the unusual
size of the river, the coral reef lies near its mouth, and pro-

HAKBOR OF FALIFA.

jects some distance in front of it. Its surface is dead, but
corals are growing upon its outer slope.

/. The harbor of Kewa, in the Feejees, may be again al-
luded to. The waters received by the bay amount to at least
500,000 cubic feet a minute. Yet there is an extensive reef
enclosing the bay, lying but three miles from the shores, and
with only two narrow openings for ships. The case is so re-
markable that we can hardly account for the facts without
supposing the river's mouth to have neared the reef by depo-
sitions of detritus since the inner parts of the reef were formed ;
and there is some evidence that this was the case, though to
what distance we cannot definitely state. With this admis-
sion, the facts may still surprise us ; yet they are explained on
the principle that fresh water does not sink in the ocean, but
is superficial, and runs on in a distinct channel ; its effect is al-
most wholly through hydrostatic pressure, increasing the force
of the underwater currents, and through their depositions of
detritus. Besides these instances, there are many others in
,the Feejees, as will be observed on the chart at the end of
this volume. Mokungai has a large harbor, without a
stream of fresh water ; — so also Vakea and Direction Island.

FORMATION OF CORAL REEFS AND ISLANDS, 245

The instances brought forward are a fair example of what
is to be found throughout coral seas ; and they establish, be-
yond dispute, that while much in harbor-making should be at-
tributed to the transported sand or earth of marine and fresh-
water currents, in preventing the growth of coral, but little
is due to the freshening influence of the streams of islands.

But while observing that currents have so decided an in-
fluence on the condition of harbors, we should remember an-
other prevalent cause already remarked upon, which is perhaps
more wide in its efi'ects than those just considered. I refer to
the features of the supporting land, or the character of sound-
ings off* a coast. We need not repeat here the facts, showing
that many of the interruptions of reefs have thus arisen.
The wide break off* Matavai may be of this kind. The widen-
ing of the inner channel at Papieti, forming a space for a har-
bor, may be another example of it; for the reef here extends
to a greater distance from tlie shores, as if because the waters
shallowed outward more gradually off* this part of the coast.

The same cause — the depth of soundings, on the principle that
corals do not grow where the depth much exceeds a hundred
feet — has more or less influence about all reefs in determining
their configuration and the outlines of harbors. A remark-
able instance of the latter is exemplified in the annexed chart
of Whippey harbor, Viti Levu, reduced from the chart of the
Wilkes Expedition to the scale of half an inch to the mile.

The existence of harbors should therefore be attributed, to
a great extent, to the configuration of the submarine land ;
while currents give aid in preventing the closing of channels,
and keeping open grounds for anchorage. This subject will be
further illustrated in the following pages.

The permanency of coral harbors follows directly from the
facts above presented They are secure against any immediate

246 CORALS AND CORAL ISLANDS.

obstruction from reefs. Any growing patches within thera
may still grow, and the margins of the enclosing reef may
gradually extend and contract their limits ; yet only at an ex-
tremely slow rate. Notwithstanding such changes, the chan-
nels will remain open, and large anchorage grounds clear, as

WHIPPET HARBOK, VITI LEVU.

long as the currents continue in action. Coral harbors are
therefore nearly as secure from any new obstructions as those
of our continents. The growing of a reef in an adjoining
part of the coast, may in some instances diminish or alter the
currents, and thus prepare the way for more important chan-
ges in the harbor; but such effects need seldom be feared, and
results from them would be appreciable only after long periods,
since, even in the most favorable circumstances, the growth
of reefs is very slow.

When channels have a bottom of growing coral, they form
an exception to the above remark ; for since the coral is acted
upon by no cause sufficient to prevent its growth, the reef will
continue to rise slowly toward the surface.

FORMATION OF CORAL REEFS AND ISLANDS. 247

Again, when the channels are more than twenty fathoms
in depth, they have an additional security beyond that from
currents, in the fact that corals will not grow at such a depth.
The only possible way in which such channels could close,
without first filling up by means of shore material, would be
by the extension of the reefs from either side, till they bridge
over the bottom below. But such an event is not likely to
happen in any but narrow channels.

In recapitulation, the existence of passages through reefs,
and the character of the coral harbors, may be attributed to
the following causes :

1. The configuration and character of the submarine land;
— corals not growing where the depth exceeds certain limits,
or where there is no firm rocky basement for the plantation.

2. The direction and force of marine currents, with their
transported detritus; — these currents having their course
largely modified, if not determined, as in other regions, by the
features of the land, the form of the sea-bottom, and the posi-
tions of the reefs, and being sometimes increased in force by
the contributions of island streams, which add to the detritus
and to the weight of accumulating waters.

3. Harbors which receive fresh- water streams, or submarine
springs of fresh- water, are more apt to be clear from sunken
patches ; and the same causes keep open shallow passages to
the shores, where there are shore reefs.

It should be remembered, that while the effects from fresh-
water strelEims are so trifling around islands, they may be of
very wide influence on the shores of the continents where the
streams are large and deep, and transport much detritus.
This point is illustrated beyond.

248 CORALS AND CORAL ISLANDS,

II. ATOLL REEFS.

The remarks on the preceding pages, respecting reefs around
other lands, apply equally to atoll reefs. There are usually
currents flowing to leeward through the lagoon, and out, over
or through the leeward reef, the waves with the rising tide
dashing over the windward side, and keeping up a large sup-
ply, which is greatly increased in times of storms ; and this ac-
tion tends to keep open a leeward channel for the passage of
the water. This is the common explanation of the origin of
the channels opening into lagoons. These currents are strong-
est when a large part of the windward reef is low, so as to
permit the waves to break over it ; and the coral debris they
bear along will then be greatest. When a large part of the
leeward reef is under water, or barely at the water's edge, the
waters may escape over the whole, and on this account large
reefs sometimes have no proper channels. When the land
to windward becomes raised throughout above the sea, so as
to form a continuous barrier which the waves cannot pass,
the current is less perfectly sustained, since it is then dependent
entirely upon the influx and efflux of the tides; and the leeward
channels, in such a case, may gradually become closed.

The action of currents on atolls is, therefore, in every way
identical with what has been explained. The absence of
coves of land to give force to the waters of currents, and to
dii'ect their course, and the absence also of fresh- water streams,
are the only modifying causes not present. It is readily un-
derstood, therefore, why lagoon entrances are more likely to
become filled up by growing coral, than the passages through
barrier reefs.

FORMATION OF CORAL REEFS AND ISLANDS. 249

m. RATE OF GROWTH OF REEFS.

The formation of a reef has been shown to be a very dif-
ferent process from the growth of a zoophyte. Its rate of
progress is a question to be settled by a consideration of
many distinct causes, none of which have yet been properly
measured.

a. The rapidity of the growth of zoophytes is an element
in this question of great importance, and one that should be
determined by direct observation with respect to each of the
species which contribute largely to reefs, both in the warmer
and colder parts of coral-reef seas.

h. The character of the coral plantation under consider-
ation should be carefully studied ; for it is of the greatest con-
sequence to know whether the clusters of zoophytes are scat-
tered tufts over a barren plain, or whether in crowded profu-
sion. Compare the debris of vegetation on the semi-deserts of
California with that of regions buried in foliage ; equally va-
rious may be the rate of growth of coral rock in different
places. An allowance should also be made for the shells and
other reef relics. The amount of reef-rock formed in a o;iven
time cannot exceed, in cubic feet, the aggregate of corals and
shells added by growth — that is, if there are no additions from
other distant or neighboring plantations.

c. It is also necessary to examine all conditions that are
connected with, or can influence, the marine or tidal currents
of the region — their strength, velocity, direction, where they
eddy, and where not, whether they flow over reefs that may
afford debris or not. All the debris of one plantation may
sometimes be swept away by currents to contribute to other
patches, so that one will enlarge at the expense of others. Or,

250 CORALS AND CORAL ISLANDS.

currents may carry the detritus into the channels or deeper
waters around a coral patch, and leave little to aid the plan-
tation itself in its increase and consolidation.

d. The course and extent of fresh waters from the land,
and their detritus, should be ascertained.

e. The strength and height of the tides, and general force
of the ocean waves, will have some influence.

Owing to the action of these causes, barrier reefs enlarge
and extend more rapidly than inner reefs. The former have
the full action of the sea to aid them, and are farther removed
from the deleterious influences which may affect the latter.

No results with reference to this question of the rate of
progress in reefs were arrived at by the author in the course
of his observations in the Pacific. The general opinion,
that their progress is exceedingly slow, was fully sustained.
The facts with regard to the growth of zoophytes, give some
data.

Allowing that the large Madrepora of the wreck, men-
tioned on page 126, may grow three inches in height a year,
and that other Madrepores increase in the same ratio, it is still
not easy to deduce from it the rate of increase of the reef. In
the first place, the whole Madrepore is growing over the sides
of its branches, at the rate, if we may judge from the size of the
trunk at base, of a tenth of an inch a year, thus increasing
annually the diameter a fifth of an inch a year, which, in a
large species, is a very great addition to the three inches per
year at the extremities of the branches. Again, the branches of
the large Madrepore of the wreck were widely spaced, those of J/i
cervicornisj having intervals of from six to eighteen inches or
more between the branches.

In fact it is impossible to make any exact estimate of the
amount of increase without a knowledge of the weight of the

RATE Of GEOWTH OF CORAL REEFS. 251

part annually added. This ascertained, it would be easy to
calculate how much the added coral would, if ground up, raise
the area that is covered by the Madrepora. A rough esti-
mate gives the author an average increase to this surface of
a fourth of an inch a year. But this fourth must be much
reduced, if we would deduce the rate of growth of the reef;
because a large part of the reef-grounds — ^that is, of the region
of soundings receiving the coral debris — is bare of growing
corals. This is the case with much the larger portion of all
lagoons and channels among reefs, the bottoms of which, as
already explained, are often sandy or muddy, and to a great
extent so because too deep for living corals ; and it is true
even of the coral plantations, these including many and large
barren areas. These unproductive portions of reef-grounds
constitute ordinarily at least two-thirds of the whole; and
making this allowance, the estimate of one-fourth of an inch
a year would become one-twelfth of an inch.

Again, shells add considerably to the amount of calcareous
material, perhaps one-sixth as much as the corals ; but against
this we may set off the porosity of the coral.

The rate of growth of the Mceandrina clivosa^ stated on
page 125, would make the rate of increase in the reef very
much less rapid. The specimen — the growth of fourteen
years — weighs 24 oz. avoirdupois, and has an average diameter
of 7 inches. This gives for the amount of calcareous material
— the specific gravity being 2*523 (p. 99) — 16*45 cubic inches;
which is sufficient to raise a surface seven inches in diameter
to a height of 0*428 inch ; and consequently the average yearly
increase would be about l-33d of an inch. Allowing for two-
thirds of the reef- ground being unproductive in corals, the
rate of increase for the whole would become 1-1 00th of an
inch. But supposing that shells add one-fourth as much as

252 CORALS AND CORAL ISLANDS.

the corals to the reef material, the rate of increase would be-
come about l-80th of an inch per year.

The specimen of Oculina diffusa^ referred to on page 125,
weighs 44 ounces, which is five-sixths more than that of the
Mseandrina, while the average diameter of the clump is the
same. The average annual increase would consequently cover
a circular area of seven inches diameter 1-1 8th of an inch
deep. And making the same allowances as above, the rate
for the year for the whole reet-grounds would be l-44th of an
inch. The specimen of Mseandrina mentioned by Major
Hunt, is not here made the basis of a calculation, because we
have not the specimen for examination, and it is not certain
that the diameter stated by him was not the horizontal di-
ameter.

These estimates from the Moeandrina clivosa and Oculina
diffusa have this great source of uncertainty, that the growth
of \h^ groups may not have been begun in the first year of the
fourteen. Further, the corals obtained by Major Hunt near
Fort Taylor, Key West, may not have been as favorably situ-
ated for growth as those of the outer margin of the reef.
Again, we have made no allowance for the carbonate of lime
that is supplied by the waters by way of cement, supposing
that this must come originally, for the most part, from the
reef itself. Besides, we have supposed, above, all the coral
reef-rock to be solid, free from open spaces; and, further,
it is not considered that much of it is a coral conglomerate,
in which the fragments have their original porosity.

On the other side, we have not allowed for loss of de-
bris from the reef grounds by transportation into the deep seas
adjoining, believing the amount to be very small.

Whatever the uncertainties, it is evident that a reef in-
creases its height or extent with extreme slowness. If the

BATE OF GROWTH OF CORAL REEFS. 253

rate of upward progress is one-sixteenth of an inch a year, it
would take for an addition of a single foot to its height, one
hundred and ninety years, and iov five feet a thousand years.

It is here to be considered, that the thickness of a growing
reef could not exceed twenty fathoms (except by the few feet
added through beach and wind-drift accumulations), even if
existing for hundreds of thousands of years, unless there were
at the same time a slowly progressing subsidence ; so that if
we know the possible rate of increase in a reef, we cannot
infer from it the actual rate for any particular reef; for it may
have been very much slower than that. Without a subsidence
in progress, the reef would increase only its breadth.

In order to obtain direct observations on the rate of in-
crease of reefs, a slab of rock was planted, by the order of Cap-
tain Wilkes, on Point Venus, Tahiti, and by soundings, the
depth of Dolphin shoal, below the level of this slab, was care-
fully ascertained. By adopting this precaution, any error
from change of level in the island was guarded against. The
slab remains as a stationary mark for future voyagers to test
the rate of increase of the shoal. Before, however, the results
can be of any general value toward determining the average
rate of growing reefs, it is still necessary that the growing
condition of the reef should be ascertained, the species of
corals upon it be identified, and the influence of the currents
investigated which sweep in that direction out of Matavai
bay.

The depth to which the shells of Tridacnas lie imbedded in
coral rock, has been supposed to affbrd some data for estima-
ting the growth of reefs. But Mr. Darwin rightly argues that
these mollusks have the power of sinking themselves in the
rock, as they grow, by removing the lime about them. They
occur in the dead rock, — generally where there are no growing

254 CORALS AND CORAL ISLANDS.

corals, except rarely some small tufts. If they indicate any
thing, it must be the growth of the reef-rock, and not of the
corals themselves. But the shore-platform where they are
found is not increasing in height ; its elevation above low-tide
being determined, as has been shown, by wave action (page
232). They resemble, in fact, other saxicavous mollusks, sev-
eral species of which are found in the same seas, some
buried in the solid masses of dead coral lying on the reef.
The bed they excavate for themselves is usually so complete
that only an inch or two in breadth of their ponderous shells
are exposed to view. Without some means like this of secur-
ing their habitations, these mollusks would be destroyed by
the waves ; a tuft of byssus, however strong, which answers
for some small bivalves, would be an imperfect security against
the force of the sea for shells weighing one to five hundred
pounds.

IV. ORIGIN OF THE BARRIER CONDITION OF REEFS, AND
OF THE ATOLL FORMS OF CORAL ISLANDS.

I. OLD VIEWS.

In the review of causes modifying the forms of reefs, no
reason is assigned for the most peculiar, we may say the most
surprising, of all their features, — that they so frequently take
a belt-like form, and enclose a wide lagoon ; or, in other cases,
range along, at a distance of some miles, it may be, from
the land they protect, with a deep sea separating them from
the shores.

This peculiar character of the coral island was naturally
the wonder of early voyagers, and the source of many specu-
lations. The instinct of the polyp was mnde by some the sub-
ject of special admiration; for the "helpless animacules"

ORIGIN OF THE BARRIER REEF. 255

were supposed to have selected the very form best calculated
to withstand the violence of the waves, and apparently with
direct reference to the mighty forces which were to attack the
rising battlements. They had thrown up a breastwork as a
shelter to an extensive working ground under its lee, " where,"
as Flinders observes, "their infant colonies might be safely
sent forth."

It has been a more popular theory that the coral struc-
tures were built upon the summits of volcanoes ; — that the
crater of the volcano corresponded to the lagoon, and the rim
to the belt of land ; that the entrance to the lagoon was over
a break in the crater, a common result of an eruption. This
view was apparently supported by the volcanic character of
the high islands in the same seas. But sinL:e a more satisfac-
tory explanation has been offered by Mr. Darwin, numerous
objections to this hypothesis have become apparent, such as
the following •

a. The volcanic cones must either have been subaerial and
then have afterward sunk beneath the waters, or else they
were submarine from the first. In the former case the cra-
ter would have been destroyed, with rare exceptions, during
the subsidence ; and in the latter there is reason to believe
that a distinct crater would seldom, if ever, be formed.

h. The hypothesis, moreover, requires that the ocean's bed
should have been thickly planted with craters — seventy in a
single archipelago, — and that they should have been of nearly
the same elevation ; for if more than twenty fathoms below the
surface, corals could not grow upon them. [But no records
warrant the supposition that such a volcanic area ever existed.
The volcanoes of the Andes differ from one to ten thousand
feet in altitude, and scarcely two cones throughout the world
are as nearly of the same height as here supposed. Moun

256 CORALS AND CORAL ISLANDS.

Loa and Mount Kea, of Hawaii, present a remarkable instance
of approximation, as they differ but two hundred feet ; but
the two sides of the crater of Mount Loa diifer three hundred
and fourteen feet in height. Mount Kea, though of volcanic
character, has no large crater at top. Hualalai, the third
mountain of Hawaii, is 4,000 feet lower than Mount Loa.
The volcanic summit of East Maui is 10,000 feet high, and
contains a large crater ; but the wall of the crater on one
side is 700 feet lower than the highest point of the mountain ;
and the bottom of the crater is 2,000 feet below the rim of
the crater. Similar facts are presented by all volcanic regions.

c. It further requires that there should be craters over
fifty miles in diameter, and that twenty and thirty miles
should be a common size. Facts give no support to such an
assumption.

d. It supposes that the high islands of the Pacific, in the
vicinity of the coral islands, abound in craters ; while, on the
contrary, there are none, as far as is known, in the Marquesas,
Gambler, or Society Group, the three which lie nearest to
the Paumotus. Even this supposition fails, therefore, of giv-
ing plausibility to the crater hypothesis.

Thus at variance with facts, the theory has lost favor, and
it is no longer sustained even by those who were once its
strongest advocates.

The question still recurs with regard to the basemeni
of coral islands, and the origin of their lagoon character.
Shall we suppose, with some writers, that these islands
were planted upon submarine banks, within one hundred
and fifty feet of the surface of the sea? As has been said,
there is no authority for the supposition. We nowhere find
regions over our continents with elevations so uniform in
height ; and submerged banks of this kind are of extremely

ORIGIN OF THE BARRIER REEF. 267

rare occurrence. If such patches of submerged land existed,
the lagoon structure would still be as inexplicable as ever ; for
the growing reefs of the Pacific show that corals may flour-
ish alike over all parts of the bank, where not too deep. The
zoophyte can by no means be said to prefer the declivity to
the central plateau of the submarine bank ; on the contrary,
the part nearest the surface below low-tide level, abounds in
the largest species of corals.

II. ORIGIN OF CHANNELS WITHIN BARRIERS.

A study and comparison of the reefs of different kinds, —
fringing, barrier and atoll, — throughout the oceans, is the only
philosophical mode of arriving at any conclusion on this sub-
ject. This course Mr. Darwin has happily and successfully
pursued, and has arrived, as we have reason to believe, at the
true theory of barrier reefs and coral islands. It is satisfac-
tory, because it is a simple generalization of facts. The ex-
plorations of the author afforded him striking illustrations of
its truth ; and elucidate some points which were still deemed
obscure, establishing the theory, as he believes, on a firm basis
of evidence, and exhibiting its complete correspondence with
observation.

The reader may turn again to the chart of the Feejee
Group, and glance successively at the islands Goro, Angau,
Nairai, Lakemba, Argo Eeef, Exploring Isles, and Nanuku.
It will be observed that in Goro, the reef closely encircles the
land upon whose submarine shores it was built up. In the isl-
and next mentioned, the reef has the same character, but is
more distant from the shores, forming what has been termed a
barrier reef ; the name implying a difiference in position, but

none in mode of formation. In the last of the islands enumer-
17

258 CORALS AND CORAL ISLANDS.

ated, the barrier reef includes a large sea, and the island it en-
closes is but a rocky peak within this sea.

Can we account for this diversity in the position of bar-
rier reefs, and in their extent as compared with the enclosed
land ? There is evidently one way, in accordance with Mr
Darwin's theory, in which these features might have been pro-
duced. If, for example, such an island as Angau were very
gradually to subside, from some subterranean cause, two results
would take place : — the land would slowly disappear, while the
coral reef, ever in constant upward increase, as has been ex-
plained, might retain itself at the surface, if the rapidity of
subsidence were not beyond a certain rate. This subsidence
might go on till the last mountain peak remained alone above
the waters. Should we not then have a Nanuku ? Suppose
the subsidence not to have proceeded to this extent, but to leave
still a single ridge and a few isolated summits above the
waves ; would not its condition in this case be that of the Ex-
ploring Isles ? On such a supposition, reefs of large size en-
circling a mere point of rock might be explained even to every
feature. The subsidence of Goro, on the same principle, would
produce an Angau, or, carried further, a Nanuku.

It may here be remarked, that the fact that changes of lev-
el over vast areas of the earth's surface have taken place is fully
proved, and accounts of some of them which are now in pro-
gress, as that of Sweden and that of Greenland, are to be
ibund in any geological treatise.

But it admits of direct demonstration that such a subsi-
dence has actually taken place. It has been stated that the
depth of the reef at different distances from the shore it encir-
cles may generally be estimated from the slope of the shore.
On this principle it has been shown on a former page (p. 156)
that the thickness of the distant barrier reef cannot be less in

ORIGIN OF THE BARRIER REEF. 259

some instances than a thousand feet ; and in many cases it is
probably much greater. Now as reef corals do not grow be-
low eighteen or twenty fathoms, there is no way in which
this thousand feet of reef could have been formed except by a
gradual subsiding of the land upon which it stands. The
large number of instances of distant barriers in the Pacific re-
move any donbt with regard to these conclusions. The map
of the Feejees abounds in them through its eastern part, and
we may infer with reason that over this extended area there
has occurred, since the reefs began to form, a slowly progress-
ing subsidence, like that which is now going on in Green-
land.

Again, the island of Metia is 250 feet in height, full twice
the coral-growing depth. At the island of Mangaia, in the
Hervey Group, the coral rock is raised 300 feet out of water.
Such thick beds could not have been made by corals growing
in depths not exceeding 120 feet without a sinking of many
scores of feet during their progress.

The fact that subsidence has actually taken place during
the formation of many reefs is therefore put beyond doubt. It
must form a part of any true theory of reefs, whether it be the
crater hypothesis, or the view here advocated. The latter has
this advantage, that it explains all the facts, and requires no
other element but this single one of subsidence. It rests on a
simple fact and demands no hypothesis whatever.

The manner in which subsidence would operate is shown in
the following sketches, representing ideal transverse sections of
an island and its reefs. In the annexed figure, if I be the wa-
ter line, the island, like Goro, has a simple fringing reei^f^f:
— it is a narrow platform of rock at the surface, dropping off
at its edge to shallow depths, and then some distance out, de-
clining more abruptly. Let the same island become sub-

260 CORALS AND CORAL ISLANDS.

merged till II is the water line : — the reef extends itself up-
ward, as submergence goes on, and may have the character at
the surface represented by h' f V f . There is here a fringing
reef and also a barrier reef, with a narrow channel between.

SECTION ILLUSTBATING THE OKIGIN OP BAKRIER REEFS.

such as we have described as existing on the shores of Tahiti
(see p. 242) ; 6Ms a section of the barrier, d of the channel, and
f of the fringing reef. Suppose a farther submergence, till III
is the water line : then the channel (d^ c") within the barrier be-
comes quite broad, as in the island of Nairai or Angau ; on one
side {f'') the fringing reef remains, but on the other it has dis-
appeared, owing, perhaps, to some change of circumstance as
regards currents, which retarded its growth, and prevented its
keeping pace with the subsidence. With the water at IV,
there are two islets of rock in a wide lagoon, along with other
islets {i'^' %'") of reef over two peaks which have disappeared.
The coral reef-rock by gradual growth has attained a great
thickness, and envelops nearly the whole of the former land
Nanuku, the Argo Reef, and Exploring Isles are here exem-
plified, for the view is a good transverse section of either of
them, y V^' are sections of the distant enclosing barrier, and
c '^ d'\ and other intermediate spots, of the water within.

The supposed similarity between these ideal sections and
existing islands is fully sustained by actual comparison. The
figure beyond is a map of the island of Aiva, in the Feejee Group.

ORIQIK OF THE BARRIER REEF, 261

There are two peaks in the lagoon-, precisely as above ; and
although we have no soundings of the waters in and about it
nor sketches of peaks, facts observed elsewhere authorize in
every essential point the transverse section here given, which
resembles closely, as is apparent, the preceding. The section
is made through the line h 6, V b\ of the map. It is unneces-
sary to add other illustrations. They may be made out from

ICAP, AND IDEAL SECTION, OP AIVA ISLAND.

anv of the eastern groups of the Feejees, the Gambier Group
of the Paumotus, or Hogoleu in the Carolines. Wallis's
Island is another example of islets of rock in a large lagoon
enclosed by a distant barrier.

It has been asked, why the interior channels do not become
filled by coral reef, as the island sinks, and thus a plane of
coral result^ instead of a narrow belt ; and this has been urged
against the theory. But it is a sufficient reply to such an argu-
ment to state the fact that the subsidence admits of no doubt,
and that the islands, referred to as exemplifications of it, pre-
sent this very peculiarity. It should be received, therefore,
as a consequence of it, instead of an objection to the view, for
it is the most common feature with all islands that have broad
reef-grounds, or in other words, that show evidence of subsi-
dence during the gro^^i;h of the reefs. Broad channels, and

262 C0RAL8 AND CORAL ISLANDS.

even open seas within, as in Nanuku and the Exploring Isles,
are therefore to be received as results of the subsidence, for
which explanations should be sought.

These explanations are at hand, and accord so exactly with
facts ascertained, that the existence of inner passages becomes
a necessary feature of such islands. It has been shown that
the ocean acts an important part in reef-making ; — ^that the
outer reefs, exposed to its action and to its pure waters, grow
more rapidly than those within which are under the influence
of marine and fresh-water currents and transported detritus.
It is obvious, therefore, that the former may retain themselves
at the surface, when through a too rapid subsidence the inner
patches would disappear. Moreover, after the barrier is once
begun it has growing corals on both its inner and outer
margins, while a fringing reef grows only on one margin.
Again, the detritus of the outer reefs is, to a great extent,
thrown back upon itself by the sea without and the cur-
rents within, while the inner reefs contribute a large propor-
tion of their material to the wide channels between them.
These channels, it is true, are filled in part from the outer
reefs, but proportionally less from them than from the inner.
The extent of reef-grounds within a barrier, raised by accumu-
lations at the same time with the reefs, is often fifty times
greater than the area of the barrier itself. Owing to these
causes the rate of growth of the barrier may be at least twice
more rapid than that of the inner reefs. If the barrier in-
creases one foot in height in a century, the inner reef, ac-
cording to this supposition, would increase but half a foot ; and
any rate of subsidence between the two mentioned, would sink
the inner reefs more rapidly than they could grow, and cause
them to disappear. There is therefore not only no objection to
the theory from the existence of wide channels and open seas ;

ORIGIN OF THE BARRIER REEF. 263

on the contrary, their non- existence is incompatible with the
mode of action going on. They afford the strongest support
to the theory.

A wide, flat reef, continuous over extensive reef-grounds,
could be formed only upon a nearly level bank, where there
were consequently no hills to pour in detritus and otherwise
retard growth over the interior portions; and even then it
would be liable to be cut up by the action of currents, destroy-
ing growing corals over its interior parts.

From these considerations it is evident that a barrier reef
indicates approximately the former limits of the land enclosed.
The Exploring Isles (Feejee chart), instead of an area of six
square miles, the whole extent of the existing land, once cov-
ered three hundred square miles ; and the outline of the for-
mer land is indicated by the course of the enclosing reef. A
still greater extent may be justly inferred. For a barrier,
as subsidence goes on, gradually contracts its area, o>ving to
the fact that the sea bears a great part of the material inward
over the reefs ; and, consequently, the declivity forming the
outer limit of the sub-marine coral formation has a steep angle
of inclination.

In the same manner it follows that the island Nanuku, in-
stead of one square mile, extended once over two lundied
square miles, or had two hundred times the present area of
high land. Bacon's Isles once formed a large triangular
island of equal extent, though now but two points of rock
remain above the water.

The two large islands in the western part of the group,
VanuaLevu and Viti Levu, have distant barriers on the west-
ern side. Off the north point of the former island, the reef be-
gins to diverge from the coast, and stretches off from the
shores till it is twenty and twenty-five miles distant; then,

264 C0RAL8 AFD CORAL ISLANDS.

after a narrow interruption, without soundings, the Asaua
islands commence in the same line, and sweep around to the
reef which unites with the south side of Viti Levu ; and, tra-
cing the reef along the south and east shores, we find it at last
nearly connecting with a reef extending southward from Vanua
Levu. Thus these two large islands are nearly encircled in a
single belt ; and it would be doing no violence to principles or
probabilities, to suppose them once to have formed a single
island, which subsidence has separated by inundating the low
intermediate area. The singular reef of Whippey harbor,
page 246, is fully explained by the hypothesis. We may thus
not only trace out the general form of the land which once
occupied this large area (at least 10,000 square miles), but
may detect some of its prominent capes, as in Wakaia and
Direction Island. The present area is not far from 4,500
square miles.

The whole Feejee Group, exclusive of coral islets, includes
an area of about 5,500 square miles of dry land ; while, at the
period when the corals commenced to grow, there were, at least,
as the facts show, 15,000 square miles of land, or nearly three
times the present extent of habitable surface.

III. LAGOONS OF ATOLLS.

We pass from these remarks on the channels and seas
within barrier reefs, to the consideration of the seas or lagoons
of coral atolls. The inference has probably been already made
by the reader, that the same subsidence which has produced
the distant barrier, if continued a step farther, would produce
the lagoon island. Nanukii is actually a lagoon island, with
a single mountain peak still visible ; and Nuku Levu, north
of it, is a lagoon island, with the last peak submerged. This

ORIGIN OF THE ATOLL, 265

mode of origin may evidently be true of all atolls ; for with
the exception of the points of high land in the inner waters,
there is no one essential character, distinguishing many of the
eastern Feejee Islands from the Carolines to the north. The
Gambler group, near the Paumotus, appears to have afforded
the philosophical mind of Mr. Darwin the first hint with re-

GAMBIBR ISLANDS.

gard to the origin of the atoll ; the contrast, and, at the same
time, the resemblance, were striking ; the conclusion was nat-
ural and most happy. Captain Beechey, in his Voyage in the
Pacific, implies this resemblance, when he says of the Gambler
group, which he surveyed, "It consists of five large islands
and several small ones, all situated i / a lagoon forme Ihy a
reef of coraV Balbi, the geographer, as Mr. Darwin remarks
(p. 41), describes those barrier reefs which encircle islands of
moderate size, by calling them atolls, with high lands rising
from their central expanse.

As some interest is connected with the history of new prin-
ciples, and the illustration afforded is highly satisfactory, we
give here a sketch of the Gambler group. The very features
of the coast of the included islands, — ^the deep indentations, —

266 C0RAL8 AND CORAL ISLANDS.

are sufficient evidence of subsidence to one who has studied
the character of the Pacific islands ; for these indentations cor-
respond to valleys or gorges formed by denudation, during a
long period while the island stood above the sea.

The manner in which a further subsidence results in pro-
ducing the atoll is illustrated in the upper of the following
figures. Viewing V as the water line, the land is entirely
submerged ; the barrier, V^^\ y"\ then encloses a broad area
of waters, or a lagoon.^ with a few island patches of reef over
the peaks of the mountains. A continuation of the subsi-

SECnON ILLUBTRATING THE ORIGIN OF ATOLLS.

dence would probably sink beneath the waters some of the
islets, because of their increasing in height less rapidly than
the barrier ; and this condition is represented along the upper
line of the above figure, VI, subsidence having taken place to
that level. The lagoon has all the characters of those of atoll
reefs.

Should subsidence now cease, the reefs, no longer increas-
ing in height, would go on to widen, and the accumula-
tions produced by the sea would commence the formation of
dry land, as exhibited in figure 2. Verdure may soon afler
appear, and the coral island will finally be completed. It is

Omom OF THE ATOLL. 267

not impossible that dry land might form in certain favorable
spots on the reef while the subsidence was still in progress, if
the sinking were not beyond a certain rate.

A cessation or diminution of subsidence, in the case of the
barrier reef about a high island, might result in its becoming
covered with verdure like the finished atoll.

All the features of atolls harmonize completely with
this view of their origin. In form the)' are as various and
irregular as the outlines of barrier reefs. Compare Angau of
the Feejees, with Tari-tari of the Gilbert Group (p. 165);
Nairai or Moala with Tarawa ; Nanuku with Maiana or Ap-
amama. The resemblance is close. In the same manner we
might find the many forms of lagoon reefs represented among
barrier reefs.

We observe, also, that the configurations are such as would
be derived from land of various shapes of outline, whether
a narrow mountain ridge (as in Taputeouea, one of the Gilbert
Islands), or wide areas of irregular slopes and mountain
ranges. Among the groups of high islands, we observe that
abrupt shores may occasion the absence of a reef on one side, as
on Moala ; and a like interruption is found among coral
islands. Many of the passages through the reefs may be thus
accounted for.

The fact that the submerged reef is often much prolonged
from the capes or points of a coral island, accords well with
these views. These points or capes correspond to points
in the original land, and often to the line of the prominent
ridge ; and it is well known that such ridge lines often ex-
tend a long distance to sea, with slight inclination com-
pared with the slopes or declivities bounding the ridge on
either side.

Coral islands or reefs often lie in chains like the peaks of

268 CORALS AND CORAL ISLANDS.

a single mountain range: — for example, the sickle-shaped line
of islets north of Nanuku. Tari-tari and Makin (Gilbert
Group, see map, page 165), lie together as if belonging to
parts of one island. MenchicofF atoll, in the Caroline Archi-
pelago, consists of three long loops or lagoon islands, united
by their extremities, and further subsidence might reduce it to
three islands.

ffi of ttOi imh' A» a, rtUU^.

MENCHICOFF ATOLL.

Darwin in his account of the Maldives (op. cit, p. 37),
points out indications of a breaking up of a large atoll into
several smaller. The land with many summits or ranges of
heights may at first have had its single enclosing reef; but as
it subsided, this reef, contracting upon itself, may have encircled
separately the several ranges of which the island consisted,
and thus several atoll reefs may have resulted in place of the
large one ; and, further, each peak may have finally become
the basis of a separate lagoon island, under a certain rate of
subsidence or variations in it, provided the outer reef were so
broken as to admit the influence of waves and winds. Some
of the large atolls of the "Maldives are properly atoll archipel-
agos.

The sizes of atolls offer no objection to these views, as they

ORIGIN OF THE ATOLL, 269

do not exceed those of many barrier reefs. Some of the larger
Maldives, according to the crater theory, would require a crater
forty to ninety miles in diameter, with a rim made up of sub-
ordinate craters. No hypothesis of such extravagance is ne-
cessary. The facts all fall in with known principles, and are
illustrated by known and established truths, without hypo-
theses of any kind.

Reefs surrounded by shallow seas, gradually deepening
outward, require no different principle for their explanation
from reefs with abrupt depths around. The explanation of
the peculiarities of the Bermudas, on page 221, can now be
fully understood. If the original island had a high, bold
mountain ridge along its southeastern front, and low sloping
land for the most part to the northward and westward, the
result would have been what we find in fact. Previous to
the elevation of 250 feet, indicated by the height of the liills,
the shallow region on the north and west of the high land
(the existing reef-region), must have been mostly bare of liv-
ing corals, because lying at too great a depth. The elevation
brought it near enough to the surface to again become a coral
plantation. This near enough^ in the Bermuda seas, means
forty to fifty feet, for soundings show that wherever the depth
is seven to eight fathoms the bottom is free from living corals.
If the three great bays, A, B, C (see map of the Bermudas,
p. 218), correspond to subordinate atolls, in a ring-group,
then the subsiding peaks of the land became the centres of
annular reefs ; and the two eastern of the peaks were evidently
quite close together.

It is of interest to follow still further the subsidence of a
coral island, the earlier steps in which are illustrated in the
preceding figures. One obvious result of its continuation is
a gradual contraction of the lagoon and diminution of the

270 CORALS AND CORAL ISLANDS,

size of the atoll, owing to the fact already noted, that the xie-
tritus is mostly thrown inward by the sea. The lagoon will
consequently become smaller and shallower, and the outline of
the island in general, more nearly circular. Finally, the reefs
of the different sides may so far approximate by this process,
that the lagoon is gradually obliterated, and the large atoll is
thus reduced to a small level islet, w^ith only traces of a for-
mer depression about the centre. Thus subsidence aids
detritus accumulations in filling up the lagoon ; and as filled
lagoons are found only in the smallest islands, such as Swain's
and Jarvis's, the two agencies have beyond d<»ibt been gen-
erally united.

This subsidence, if more rapid than the increase of the
coral reef, would become fatal to the atoll, by gradually sink-
ing it beneath the sea. Such a fate has actually befallen
two atoU-forraed reefs of the Chagos Group, in the Indian
Ocean (p. 192), as stated by Darwin; a third has only "two
or three very small pieces of living reef rising to the sur-
face," and the fourth has a portion nine miles long, dead and
submerged. Darwin calls such reefs dead reefs. The south-
ern Maldives have deeper lagoons than the northern, fifty
or sixty fathoms being found in them. This fact indicates
that subsidence was probably most extensive to the south, and
perhaps also most rapid. The sinking of the Chagos Bank,
which lies farther to the south, in nearly the same line, may
therefore have had some connection with the subsidence of
the Maldives.

In view of the facts which have been presented, it appears
that each coral atoll once formed a fringing reef around a high
island. The fringing reef, as the island subsided, became a bar-
rier reef, which continued its growth while the land was slowly
disappearing. The area of waters within finally contained the

THE COMPLETED ATOLL, 271

last sinking peak. Another period, and this had gone — the
island had sunk, leaving only the barrier at the surface and an
islet or two of coral in the enclosed lagoon. Thus the coral
wreath thrown around the lofty island to beautify and pro-
tect becomes afterward its monument, and the only record of
its past existence. The Paumotu Archipelago is a vast island
cemetery, where each atoll marks the site of a buried island.
The whole Pacific is scattered over with these simple memori-
als, and they are the brightest spots in that desert of waters.

V. THE COMPLETED ATOLL.

The atoll, a quiet scene of grove and lake, is admirably set
off by the contrasting ocean. Its placid beauty rises to grand-
eur when the storm rages, and the waves foam and roar about
the outer reefs ; for the child of the sea still rests quietly, in
unheeding and dreamy content. This coral-made land is firm,
because, as has been already explained, it is literally sea-horn^
it having been built out of sea-products, by the aid of the
working ocean. And so with the groves : they were planted
by the waves ; and hence the species are those that can defy
the encroaching waters, and meet the various conditions in
which they are placed. The plants therefore take firm hold of
the soil, and grow in all their natural strength and beauty.

Only an occasional coral island has a completely encircling
grove, and is hence a model atoll. But the many in which a
series of green islets surround the lagoon are often but little
less attractive, especially when the several islets present varied
groupings of palms and other foliage. To give perfection to
the coral island landscape there ought to be, here and there,
beneath the trees, a pretty cottage or villa, and other marks of
taste and intelligence ; and now and then a barge should be

272 CORALS AND CORAL ISLANDS,

seen gliding over the Avaters. As it is, the inhabitants are
swarthy and nearly naked savages, having little about them
that is pleasant to contemplate ; and their canoes with a clum-
sy outrigger to keep them right side up, as well as their
thatched huts, are as little in harmony as themselves with na-
ture's grace and loveliness.

Where the islets of a coral reef are heaped up blocks of cor-
al rock, blackened Avith lichens, and covered with barely
enough of trailing plants and shrubs to make the surface green
in the distant view, the traveller, on landing, would be greatly
disappointed. But still there is enough that is strange and
beautiful, both in the life of the land and sea, and in the his-
tory and features of the island, to give enjoj'inent for many a
day.

The great obstacle to communication with a majority of
atolls, especially the smaller, is the absence of an entrance to
the lagoon, and hence of a good landing-place. In that case
landing can be eifected only on the leeward side, and in good
weather ; and best, when the tide is low. Even then, the sea
often rolls in, so heavily, over the jagged margin of the reef, that
it is necessary for the boat to take a chance to mount an in-go-
ing wave and ride upon it over the line of breakers, to a stop-
ping-place somewhere on the reef or shore-platform.

Less easy is the return through the breakers, especially if
the sea has risen during the ramble ashore. The boat, in or-
der to get off again, would naturally take one of the narrow
channels or inlets indenting the margin of the reef. But,
with the waves tumbling in one after another, roughly lifting
and dropping it, as they pass, and with barely room between
the rocks for the oars to be used, there is a fair chance of its be-
ing dashed against the reefs to its destruction, or thrown
broadside to the sea and swamped under a cataract of waters.

THE COMPLETED ATOLL. 273

If another boat with its crew were lying at the time off the
reef, a line, carried to it through the surf by an expert swim-
mer, might prove a means of rescue: — and so, in 1840, we
safely reached our ship. To those approaching such a shore in
a boat, prudence would give the advice — first, drop, some dis-
tance outside of the breakers, a kedge or anchor, for aid both
in landing on, and leaving, the reef. But the bottom off a cor-
al island is often bad anchoring ground. And then, if the
kedge thus planted holds firm, in spite of the jerking waves,

well and good. If not .

The accompanying plate represents a scene on Bowditch or
Fakaafo Island, sketched by Mr. A. T. Agate, one of the artists
of the Wilkes Exploring Expedition, and copied from Volume
V. of Wilkes's Narrative of the Expedition. This island is

FAKAAFO, OB BOWDITCH ISLAND.

the easternmost of three small atolls, situated to the north of
the Samoan or Navigator Group, near the parallels of 8^^, 9^,
and 9i^ S., and between the meridians of 171'' and 172^^ W.,

18

274 CORALS AND CORAL ISLANDS.

and has already been described (p. 168). The grove of cocoa-
nut trees contains the sacred or public house of the island —
a well-made structure nieasurmg fifty feet by thirty- five in
1 ngth and breadth, and twenty feet in height. In front of
the building stands the deity of the place, consisting of a
block of stone fourteen feet high, enveloped in mats ; and also
near by, a smaller idol, partially covered with matting. In
the left corner there is a young cocoanut palm — usually a more
beautiful object than the full-grown tree.

This island and the two others near it were among the
few, perhaps the last, examples that remained until 1840,
of Pacific lands never before visited by the w^hite man.
The people therefore were in tJiat purely savage state which
Captain Cook found almost universal through the ocean in
the latter part of last century. A few words respecting our
reception at this coral island, may not, therefore, be an im-
proper digression.

The islanders knew nothing of any other land or people :
— an ignorance not surprising, since the lagoons of the group
have no good entrances, and a nation cannot be great in nav-
igation or discovery without harbors. As a consequence, our
presence was to them like an apparition. The simple in-
habitants took us for gods from the sun, and, as we landed,
came with abundant gifts of such things as they had, to pro-
pitiate their celestial visitors. They, no doubt, imagined that
our strange ship had sailed off from the sun when it touched
the water at sunrise, or sunset, and any child among them
could see that this was a reasonable supposition. The king,
after embracing Captain Hudson, as the latter states in his
Journal (Wilkes's Narrative), rubbed noses, pointed to the
sun, howled, moaned, hugged him again and again, put a mat
around his waist, securing it with a cord of human hair, and

THE COMPLETED ATOLL. 275

repeated the rubbing of noses and the howling; and the mo-
ment the captain attempted to leave his side, he set up again
a most piteous howl, and repeated in a tremulous tone, "Nofo
ki lalo, mataku au," ''Sit down, I am afraid." While thus
in fear of us, they showed a great desire that their dreaded
visitors should depart; some pointed to the sun, and asked
by their gestures about our coming thence, or hinted to us to
be off again.

But with all their reverence toward their mysterious guests,
they became after awhile quite familiar, and took advantao-e
of every opportunity to steal from us. Our botanist gave his
collecting-box to one of them to hold, and, the moment his
back was turned, off the native ran, and a hard chase was re-
quired to recover it — a most undignified run on the part of
the celestial.

Wiiile the men wore the maro, the equivalent of tight-fit-
ting breeches six inches or less in length, the women were at
tired in a simple bloomer costume, consisting solely of a petti-
coat or apron, twelve to eighteen inches long, made of a large
number of slit cocoanut leaves, and kept well oiled. Besides tliis
they had on, as ornaments, necklaces of shell or bone. The girls
and boys were dressed au nature^ after the style in the garden
of Eden. These primitive fashions, however, were not peculiar
to the group, being in vogue also in other parts of the Pacific.
As a set-off" against the geographical ignorance of these
islanders, we may state that Captain Hudson and the best
map-makers of the age knew nothing of the existence of Bow-
ditch Island until he discovered it ; and from him comes the
name it bears, given in honor of the celebrated author of
" Bowditch's Navigator " as well as of the translation of La-
place's Mecanique Celeste. ^
The annexed plate— also f I'om Wilkes's Narrative, Vol. V.

276* CORALS AND CORAL ISLANDS.

— represents a scene on Duke of York's Island, another of the
same solitary group of atolls. The view was taken on the
lagoon side, and exhibits the placid lake, the border of verdure
far away in the distance, and, near by, the margin of a native
village beneath its cocoa-nut grove. A few young plants of
the Pandanus stand along the point. The houses are like
those of other islands to the west and northwest. The point
in front of the village is one of three small quays, two feet out
of water. The house, resting partly upon it and partly on
poles in the water, and thatched with leaves of the Pan-
danus, was apparently a shelter for canoes and fishing-tackle.
The Gilbert Group affords an example of a less isolated
coral-island people. A beautiful view representing a part of
the village of Utiroa, on Drummond's Island, is contained in
the same volume of Wilkes's Narrative with the preceding.
The public-house of the island is even larger than that on
Bowditch's Island, measuring one hundred and twenty feet in
length, forty-five feet in width, and forty in height to the
ridge-pole. This island, unlike the Duke of York's, was
densely peopled, and, owing apparently to the scant supply of
fish and vegetables thus occasioned, many of the natives were
afflicted with leprosy, and also had bad teeth, both circum-
stances unusual for the Pacific. Lean in body and savage in
look and gesture, they strangely contrasted with their fat, jolly
kinsmen on some of the more northern islands of the same
group. An old, fat chief who came from one of these islands
to the ship's side in his canoe was actually too large to have
reached the deck except by the use of a tackle. It was evi-
dent that infanticide — a necessity according tp their system
of political economy^ — was more thoroughly practised than on
Drummond's Island, and that the population was thus kept
from becoming uncomfortably numerous. The obesity was

THE COMPLETE!) ATOLL. 279

probably owing to their having nothing to do, and plenty,
in the vegetable way, to eat; for these somewhat elevated
equatorial islands, as elsewhere observed, are unusually pro-
ductive for atolls,— just the place for a voluptuous barbarian.
The people on Drummond's Island were great thieves, and
knew the pleasures of a cannibal feast. Without metals, or
any kind of hard stone, they make, out of the teeth of the
sharks caught about the reefs, a sharp, jagged edging for long
knives, swords and spears ; and the women, jealous of one an°
other, sometimes, as Mr. Hale says, carry about with them for
months a small weapon of shark's teeth concealed under their
dress, watching for an opportunity to use it; and desperate
fights sometimes take place. The same author mentions, also,
some good points in them : observing that the women are, for
the most part, better treated than is common among unc'ivil-
ized people ; that the men do the hard out-door work, while
the women clear and weed the ground, and attend to the do-
mestic duties that naturally fall to them. " Custom also re-
quires that when a man meets a female he shall pay her the
same mark of respect that is rendered to a chief, by turning
aside to let her pass,"— a rule that probably does not al^
ways hold in practice. He adds: "The Avord raanda sig-
nifies among the Gilbert Islanders a man thoroughly accom-
plished in all their knowledge and arts, and versed in every
noble exercise; a good dancer, an able warrior, one who has
seen life at home and abroad, and enjoyed its highest excite-
ments and delights— in short, a complete man of the world.
In their estimation this is the proudest character to which any
person can attain; and such a one is fully prepared to enter,
at his death, on the highest enjoyments of their elysium."
Thus much for the human productions of coral islands.
Although the vegetation of coral islands has the luxuri-

280

CORALS AND CORAL ISLANDS.

ance that characterizes more favored tropical lands, the num-
ber of species of land plants is small. When " Gray's Botany
of the Paumotus " shall appear, it will contain descriptions of
only 28 or 30 species. The most common kinds are the fol-

lowing :

Portulacca oleracea L. (lutea

of Solander).
Triumfetta prociimbens Forst.
Tournefortia argent ea X.
Scaevola Konigii Vahl.
Ipomoea longiflora JR. JBr.
Lepidiura piscidium Forst,
Pemphis acidula Forst.
Pandanus odoratissimus L. f,
Pisonia grandis ParJcinson,
Morinda citrifolia X.
Guettarda speciosa L,

Cassytha filiformis X.
Gouldia Romanzoffiensis A, Gr,
Euphorbia Chamissonis J3oiss,
Boerhavia diffusa X.
Boerliavia hirsuta Wild.
Achyranthes canescens 7?. Xr.
Heliotropium prostratum JR. Br.
Nesogenes euphrasioides, ^. D(J,
Asplenium Kidus X.
A Polypodium, and a species of
Grass

Still, there is a better supply than might be supposed. For
the cocoanut, in view of its uses, is a dozen trees in one. Its
trunk furnishes timber for the houses of the natives, and the
best of wood, on account of its weight and strength, for clubs
and spears, weapons much in use, besides serving as ornamen-
tal side-arms. Its leaves supply material for thatching ; for
coarse matting to sit on, and beautiful fine mats for use in the
way of occasional dress ; also for the short aprons or petti-
coats of the women, above alluded to. The fruit, besides its
delicately-flavored hollow kerne\ affords, by the grating of
this kernel, a milky juice, that is richer than cream for pur-
poses of native cookery, and which we explorers often used
with satisfaction in coflfee, cows being unknown in those re-
gions ; also, from each nut, a pint of the thinner " cocoanut
milk," a more aoreeable drink in the land of cocoanuts than
in New York ; also an abundant oil, much valued for sleeking
down their naked bodies, and sometimes offered to a friendly

THE COMPLETED ATOLL, 281

visitor \yhora they would honor with a like anointing.
Further, from the young fruit, three-fourths grown, comes a
delightful beverage as brisk nearly as soda-water, besides a
rich creamy pulp ; both of these far better than the correspond-
ing products of the ripe fruit. The husk is excellent for cord-
age, twine, thread, fishing-lines ; and the smaller cord serves in
place of nails for securing together the beams of their domes-
tic and public buildings, and also for ornamenting the struc-
ture within, the cord being often wound with much taste and
diversity of figures. The nut is, when opened, a ready-made
drinking cup or cooking utensil. Finally, the developing bud,
before blossoming, yields a large supply of sweet juice, from
which molasses is sometimes made, and then, by fermentation,
a spirituous liquor, called among the Gilbert Islanders by
a name that sounded very much like toddy, and possessing
qualities that answer to the name ; but this is procured at
the expense of the fruit, and the good of the tree, and also
of the best interests of the natives.

It is doubted whether the ocean is ever successful in planting
the cocoanut on coral islands. The nut seems to be well fitted
for marine transportation, through its thick husk, which serves
both as a float and a protection ; but there is no known evi-
dence that any island never inhabited has been found supplied
with cocoanut trees. The possibility of a successful planting
by the waves cannot be denied ; but there are so many chances
that the floating nut will be kept too long in the water, or be
thrown where it cannot germinate, that the probability of a
transplanting is exceedingly small. This palm — the Cocas
nucifera of the botanists — is not included in the list of native
Coral Island species on page 278.

Another tree, peculiarly fitted for the region, is the Pan-
danus or Screw-Pine — well named as far as the syllable screw

282 C0RAL8 AND CORAL ISLANDS.

goes, but having nothing of a pine in its habit. Its long,
sword-like leaves, of the shape and size of those of a large
Iris, are set spirally on the few awkward branches toward
the extremity of each, and make a tree strikingly tropical in
character. It grows sometimes to a height of thirty feet. It
is well fitted for the poor and shallow soil of a coral island ;
for as it enlarges and spreads its branches, one prop after an-
other grows out from the trunk and plants itself in the ground ;
and by this means its base is widened and the growing tree
supported. The fruit, a large ovoidal mass made up of ob-
long dry seed, diverging from a centre, each near two cubic
inches in size, affords a sweetish husky article of food, which,
though little better than prepared corn stalks, admits of being
stored away for use when other things fail ; and at the Gilbert
Islands and others in that part of the ocean, is so employed.

The Pisonia is another of the forest trees, and is one of
handsome foliage and large and beautiful flowers, sometimes
attaining a height of forty feet, and the trunk twenty in girt.

Among the species that are earliest in taking root in the
emerging coral debris over the reef, there are the Portulaccae
(species of Purslane) ; the Triumplietta procumhens^ a creep-
ing, yellow-flowering plant of the Tilia family ; the Tourne-
fortia sericea^ a low, hoary shrub of the family Boraginaceae,
and Sccevola Konigii^ a sub-fleshy seashore plant.

On Rose Island, just east of the Navigator Group, Dr. C.
Pickering, of the Wilkes Exploring Expedition, found only a
species of Pisonia and of Portulacca. This is a small atoll,
under water at high-tide, excepting two banks, one of which
is covered with trees.

In the Marshall Group, on the contrary, where the vegetar
tion is more varied, and the islands have probably undergone
some elevation since they were made, Chamisso observed fifty-

THE COMPLETED ATOLL. 283

two species of land plants, and in a few instances the Banana,
Taro and Bread-fruit were cultivated. At the elevated coral
island, Metia, north of Tahiti (p. 193), 250 feet above the sea.
Sugar-cane and Bread-fruit and many plants of the Society
group, occur.

Water is to be found commonly in sufficient quantities for
the use of the natives, although the land is so low and flat.
They dig wells five*to ten feet deep in any part of the dry
islets, and generally obtain a constant supply. These wells
are sometimes fenced around with special care ; . and the
houses of the villagers, as at Fakaafo, are often clustered
about them. On Aratica (CarlshotF) there is a watering
place 50 feet in diameter, from which vessels of the Wilkes
Exploring Expedition obtained 390 gallons. The Gilbert
Islands are generally provided with a supply sufficient for
bathing, and each native takes his morning bath in fresh wa-
ter, which is esteemed by them a great luxury. On Tari-tari
(of the Gilbert Group, p. 165), as Mr. Horatio Hale, philolo-
gist of the same expedition, was informed by a Scotch sailor
by the name of Grey, taken from the island, there is a
trench or canal bcveral miles long, and two feet deep. They
have taro plantations (which is possible only where there is
a large supply of water), and besides some bread-fruit. He
spoke of the taro as growing to a very large size, and as being
in great abundance ; it was planted along each side of the pond.
Grey added further that ten ships of the line might water there,
though the place was not reached without some difficulty.
There were fish in the pond which had been put in while
young. The bottom was adhesive like clay. These islands
have been elevated a little, but are not over fifteen feet above
the sea.

Kotzebue observes, that " in the inner part of Otdia (one

284 CORALS AND CORAL ISLANDS.

of the Marshall Islands) there is a lake of sweet water ; and
in Tabual, of the Group Aur, a marshy ground exists. There
is no want of fresh water in the larger islands ; it rises in
abundance in the pits dug for the purpose." Voyage^ London,
1821, iii. 145.

The only source of this water is the rains, which, perco-
lating through the loose sands, settle upon the hardened
coral rock that forms the basis of the island. As the soil is
white or nearly so, it receives heat but slowly, and there is
consequently but little evaporation of the water that is once
absorbed.

Water is sometimes obtained by making a large cavity in
the body of a cocoanut tree, two feet or so from the ground.
At the Duke of York's Island, and probably also at the ad-
jacent Bowditch Island, this method is put in practice ; the
cavities hold five or six gallons of water.

The tropical birds of the islands are often more in keep-
ing with the beautiful scenery about them than the savage in-
habitants. On one atoll, — Honden Island, of the Paumotus,
— where no natives had ever dwelt — the birds were so inno-
cent of fear, that we took them from the trees as Aye would
fruit, and many a songster lost a tail feather, as it sat perched
on a branch, apparently unconscious that the world contained
an enemy. J. D. Hague gives an account of the birds of Jar-
vis's and some other uninhabited islands in the equatorial Pa-
cific, in which it appears that, after all, there is evil doing
even among tropical birds. He gives the following facts :

'' From fifteen to twenty varieties of birds may be dis-
tinguished among those frequenting the islands, of which the
principal are Gannets and Boobies, Frigate Birds, Tropic
Birds, Tern, Noddies, Petrels, and some game birds, as the
Curlew, Snipe and Plover. Of Terns there are several species,

THE COMPLETED ATOLL. 285

the most numerously represented of which is what I believe
to be the Sterna hirundo. These frequent the island twice in
the year for the purpose of breeding. They rest on the
ground, making no nests, but selecting tufts of grass, where
such may be found, under which to lay their eggs. I have
seen acres of ground thus thickly covered by these birds,
whose numbers might be told by millions. Between the
breeding seasons they diminish considerably in numbers,
though they never entirely desert the island. They are expert
fishers and venture far out to sea in quest of prey. The
Noddies {Sterna stolida) are also very numerous. They are
black birds, somewhat larger than pigeons, with much longer
wings, and are very simple and stupid. They burrow holes
in the guano, in which they live and raise their young, gen-
erally inhabiting that part of the deposit which is shallow-
est and driest. Their numbers seem to be about the same
throughout the year. The Gannet and Booby, two closely
allied species (of the genus Sula), are represented by two or
three varieties. They are large birds, and great devourers
of fish, which they take very expertly, not only catching those
that leap out of the water, but diving beneath the surface
for them. They are very awkward and unwieldy, on land,
and may be easily overtaken and captured, if indeed they at-
tempt to escape at all on the approach of man. They rest
on the trees wherever there is opportunity, but in these islands
they collect in great grou[)s on the ground, where they lay
their eggs and raise their young. One variety, not very nu-
merous, has the habit of building up a pile of twigs and
sticks, twenty or thirty inches in height, particularly on How-
lands, where more material of that sort is at hand, on which
they make their nest. When frightened, these birds dis-
gorge the contents of their stomachs, the capacity of which

286 CORALS AND CORAL ISLANDS,

is sometimes very astonishing. They are gross feeders, and I
have often seen one disgorge three or four large flying fish
fifteen or eighteen inches in length.

"The Frigate Bird (Ihchypetes aquilus) I have already
alluded to. It is a large, rapacious bird, the tyrant of the
feathered community. It lives almost entirely by piracy,
forcing other birds to contribute to its support. These frig-
ate birds hover over the island constantly, lying in wait for
fishing birds returning from the sea, to whom they give chase,
and the pursued bird escapes only by disgorging its prey,
which the pursuer very adroitly catches in the air. They also
prey upon flying fish and others that leap from sea to sea, but
never dive for fish and rarely even approach the water.

"The above are the kinds of birds most numerously repre-
sented, and to which we owe the existing deposits of guano.
Besides these are the Tropic Birds, which are found in consid-
erable numbers on Howland's Island, but seldom on Jarvis's
or Baker's. They prefer the former because there are large
blocks or fragments of beach rock, scattered over the island's
surface, under which they burrow out nests for themselves. A
service is sometimes required of this bird, which may, perhaps,
be worthy of notice. A setting bird w^as taken from her nest
and carried to sea by a vessel just leaving the island. On the
second day, at sea, a rag, on which was written a message,
was attached to the bird's feet, who returned to the nest,
bringing with it the intelligence of the departed vessel. This
experiment succeeded so well that, subsequently, these birds
were carried from Rowland's to Baker's Island (forty miles
distant), and, on being liberated there, one after the other,
as occasion demanded, brought back messages, proving them-
selves useful in the absence of other means of communication.
The game birds, snipe, plover and curlew, frequent the islands

THE COMPLETED ATOLL, 287

in the fall and winter, but I never found any evidence of theii
breeding there. They do not leave the island in quest of prey,
but may be seen at low-tide picking up their food on the reef
which is then almost dry.

'' Some of the social habits of these birds are worthy of re*
mark. The gannets and boobies usually crowd together in
a very exclusive manner. The frigate birds likewise keep
themselves distinct from other kinds. The tern appropriate to
themselves a certain portion of the island ; each family col-
lects in its accustomed roosting-place, but all in peace and har-
mony. The feud between the fishing birds and their oppres-
sors, the frigate birds, is only active in the air ; if the gannet
or booby can but reach the land and plant its feet on the
ground, the pursuer gives up the chase immediately."

The extensive reefs about coral islands, as already stated,
abound in fisli, which are easily captured, and the natives,
with wooden hooks, often bring in larger kinds from the deep
waters. From such resources a population of 7,000 persons
is supported on the single island of Taputeuea, whose whole
habitable area does not exceed six square miles.

There are also shell-fish of edible kinds, and others that
are the source of considerable activity in pearl-fishing.

An occasional log drifts to the shores, and at some of the
more isolated atolls, where the natives are ignorant of any
land but the spot they inhabit, they are deemed direct gifts
from a propitiated deity. These drift-logs were noticed by
Kotzebue, at the Marshall Islands, and he remarked also that
they often brought stones in their roots. Similar facts have
been observed at the Gilbert Group, and also at Enderby's
Island, and many other coral islands in the Pacific. The
stones at the Gilbert Islands, as far as could be learned, are

288 CORALS AND CORAL ISLANDS,

generally basaltic or volcanic, and they are highly valued
among the natives for whetstones, pestles, and hatchets. The
logs are claimed by the chiefs for canoes. Some of the logs
seen by the author, like those at Enderby's Island, were forty
feet or more long. Several large masses of compact cellular
lava occur on Rose Island, a few degrees east of the Navigator
Group: they were lying two hundred yards inside of the line
of breakers. The island is uninhabited, and the origin of the
stones is doubtful; they may have been brought there by
roots of trees, or perhaps by some canoe.

Fragments of pumice and resin are transported by the
Avaves to many of the islands in the Central Pacific. We
were informed at the Gilbert Islands that the pumice was
gathered from the shores by women and pounded up to fer-
tilize the soil of their taro patches ; and that it is common for
a woman to pick up a peck a day.

Where this pumice comes from is not ascertained. It is
probably drifted from the westward, and perhaps from vol-
canic islands of the Ladrones or Philippines. In addition,
volcanic ashes are sometimes distributed over these islands,
through the atmosphere. In this manner the soil of the Tonga
Islands has been improved, and in some places it has even re-
ceived a reddish color. This group has its own active volcano
to supply the ashes, and the volcanic group of the New Heb-
rides is not far distant to the southwest.

Notwithstanding all the products and all the attrac-
tions of a coral island, even in its best condition it is but a
miserable place for human develoj)ment, physical, mental, or
moral. There is poetry in every feature, but the natives find
this a poor substitute for the breadfruit and yams of more
favored lands. The cocoanut and Pandanus are, in general,
the only products of the vegetable kingdom afforded for their

THE COMPLETED ATOLL, 289

sustenance, and fish, shellfish, and crabs from the reefs their
only animal food. Scanty too is the supply ; and infanticide
is resorted to in self-defence, where but a few years would
otherwise overstock the half a dozen square miles of which
their little world consists — a world without rivers, without
hills, in the midst of salt water, with the most elevated point
but ten to twenty feet above high tide, and no part more than
three hundred yards from the ocean.

In the more isolated coral islands, the language of the na-
tives indicates their poverty as well as the limited productions
and unvarying features of the land. All words like those for
mountain, hill, river, and many of the implements of their an-
cestors, as well as the trees and other vegetation of the land
from which they are derived, are lost to them ; and as words
are but signs for ideas, they have fallen off in general intelli-
gence. It would be an interesting inquiry for the philosopher,
to what extent a race of men placed in such circumstances is
capable of mental improvement. Perhaps the query might
be best answered bj^ another. How many of the various arts of
civilized life could exist in a land where shells are the only
cutting instruments, — the plants of the land in all but twen-
ty-nine in number, — minerals but one, — quadrupeds none,
with the exception of foreign rats or mice, — fresh water barely
enough for household purposes, — no streams, nor mountains,
nor hills ? How much of the poetry or literature of Europe
would be intelligible to persons whose ideas had expanded
only to the limits of a coral island ; who had never conceived
of a surface of land above half a mile in breadth, — of a slope
higher than a beach, — of a change of seasons beyond a varia-
tion in the prevalence of rains ? What elevation in morals
should be expected upon a contracted islet, so readily over*
peopled that threatened starvation drives to infanticide, and

19

290 CORALS AND COBAL ISLANDS.

tends to cultivate the extremest selfishness ? Assuredly there
is not a more unfavorable spot for moral or intellectual pro-
orress in the wide world than the coral island.

Still, if well supplied with foreign stores, including a good
stock of ice, they might become, were they more accessible, a
pleasant temporary resort for tired workers from civilized
lands, who wish quiet, perpetual summer air, salt-water bath-
ing, and boating or yachting ; and especially for those who
could draw inspiration from the mingled beauties of grove, lake,
ocean, and coral meads and grottoes, where

" Life in rare and beautiful forms

Is sporting amid the bowers of stone."

But after all, the dry land of an atoll is so limited, its fea-
tures so tame, its sui)ply of fresh water so small, and of salt
water so large, that whoever should build his cottage on one
of them would probably be glad, after a short experience, to
transfer it to an island of larger dimensions, like Tahiti or
Upolu, one more varied in surface and productions ; that has
its mountains and precipices ; its gorges and open valleys ; leap-
ing torrents not less than surging billows ; and forests spread-
ing up the declivities, as well as groves of palms and corals by
the shores.

The mineral alluded to above as the one mineral product
of atolls is calcite or carbonate of lime, the material of the
coral rock ; and this is the only kind on the great majority of
them.

But on some of the smaller islands, in the drier equatorial
part of the ocean, there are, in addition to this, and the stones
brought by logs with the floating pumice, beds of gypsum
which have been made through the evaporation of sea- water
(which holds it in solution) in the gradually drying lagoon ba-

THE COMPLETED ATOLL, 291

sins ; and also large deposits of guano from the multitudes of sea
birds that occupy them. Such are Jarvis's, Baker's, Ho wland's,
Maiden's, McKean's, Birnie's, Phoenix's, Enderbury's, and
probably other islands in the dry central equatorial Pacific.
As these deposits are connected with the completion of the coral
island, and its accompanying reduction in size, and illustrate
one of the ways by which new minerals are added to a desti-
tute land, a few facts are here cited from an article in the
Ameincan Journal of Science^ volume xxxiv. (1862), by J. D.
Hague, who resided for several months on the islands he de-
scribes.

Baker's Island is situated in lat. 0"^ 13^ north, and long.
176^ 22' west from Greenwich, and excepting Ho wland's Island,
forty miles distant, is very remote from any other land. It is
about one mile long and two-thirds of a mile wide. The sur-
face is nearly level ; the highest point is twenty-two feet above
the level of the sea, showing some evidence of elevation.

Above the crown of the beach there is a sandy ridge
which encircles the guano deposit. This marginal ridge is about
one hundred feet wide on the lee side of the island, and is
there composed of fine sand and small fragments of corals and
shells mixed with considerable guano; on the eastern or wind-
ward side it is much wider, and formed of coarser fragments
of corals and shells, which, in their arrangement, present the
appearance of successive beach formations. Encircled by this
ridge lies the guano deposit occupying the central and greater
part of the island. The surface of this deposit is nearly even,
but the hard coral bottom which forms its bed has a gradual
slope from the borders toward the centre, or, perhaps more
properly, from northwest to southeast, giving the guano a va-
riable depth from six inches at the edges to several feet at the
deepest part.

292 CORALS AND CORAL ISLANDS.

Howland's Island is situated in lat. 0^ hV north, and 176^
32^ west from Greenwich. It is about a mile and a half long
by half a mile wide, containing, above the crown of the beach,
an area of some 400 acres. The highest point is seventeen
feet above the reef, and ten or twelve feet above the level of
high tide. The general features of the island resemble
those of Baker's. Its surface, at least on the western side, is
somewhat depressed, and much of it is covered by a growth
of purslane, grass, and other vegetation like that on Baker's
Island, but considerably more abundant. Near the centre of
the island there are one or two thickets of leafless trees or
brushwood, standing eight or ten feet high, and occupying an
area of several acres. The tops of these trees, in which the
birds roost, are apparently quite dead, but the lower parts, near
the roots, show signs of life after every rain. The windward
side of the island is formed by a succession of ridges com-
posed of coral debris with some sand and shells, running
parallel to the eastern beach, each one of which may, at
earlier stages of the island's growth, have successively
formed the weather shore. Occasionally among these ridges
a sandy bed is met with in which some little guano is mixed.
On the lee side there is also a sandy margin of considerable
width. Bits of pumice and pieces of driftwood are scattered
all over the island's surface.

The main deposit of guano occupies the middle part of
the island, and stretches, with some interruptions of interven-
ing sand, nearly from the north to the south end. Its surface
is even, and in many places covered by a thick growth of pur-
slane, whose thread-like roots abound in the guano where it
grows. The deposit rests on a hard coral bottom, and varies
in depth from six inches to four feet. The fact already ob-
served at Baker's, that vegetation flourishes most where the

THE COMPLETED ATOLL. 293

guano is shallow, is also quite apparent here, and the conse-
quent characteristic difference between the guano of the deep
and shallow parts is distinctly marked.

Some interesting pseudomorphs occur buried in the guano
of this island. Coral fragments of various species were found
that had long been covered up under the deposit, and in some
of which the carbonic acid had been almost entirely replaced
by phosphoric acid. In such I have found seventy per cent, of
phosphate of lime. In many others the change was only par-
tial, and, on breaking some of these, in the centre was usually
found a nucleus or coi^e of coral, still retaining its original
hardness and composition, while the external parts had been
changed from carbonate to phosphate, which, though soft and
friable, still preserved the structure and appearance of the
coral.

Jarvis's Island is situated in lat. 0^ 22^ south, and long.
159^ 58^ west from Greenwich. It is nearly two miles long
by one mile wide, trending east and west, and containing
about 1,000 acres. Like Baker's and Howland's, it has the
general features "of a coral island, but it differs from them
essentially in the fact that it once contained a lagoon which
has gradually been filled up with sand and detritus, while the
whole island has undergone some elevation. It therefore pre-
sents a basin-like form, the surface being depressed from the
outer edge toward the centre. It is encircled by a fringing
reef, or shore platform, about 300 feet wide ; from this a
gradually sloping beach recedes, the cro^vn of which is from
eighteen to twenty-eight feet high, forming a ridge or border,
of varying width, which surrounds the island like a wall, from
the in-shore edge of which the surface of the island is gently
depressed.

Within this depression there are other ridges, parallel to

294 CORALS AND CORAL ISLANDS.

the outer one, and old beach lines and water marks, the re-
maining traces of the waters of the lagoon, marking its gradual
decrease and final disappearance.

This flat depressed surface in the centre of the island is
about seven or eight feet above the level of the sea. It bears
but little vegetation, consisting of long, coarse grass, Mesem-
bryanthemum and Portulacca, and that is near the outer
edges of the island, where the surface is formed of coral sand
mixed with more or less guano. In the central and lower
parts the surface is composed of sulphate of lime (gypsum),
and it is on this foundation that the principal deposit of
guano rests.

In examining the foundation of the guano deposit on
Baker's or Howland's Island, by sinking a shaft vertically,
the hard conglomerate reef-rock is found directly underlying
the guano. Resting on this foundation the guano has under-
gone only such changes as the climate has produced. On
Jarvis's Island, however, after sinking through the guano, one
first meets with a stratum of sulphate of lime (sometimes com-
pact and crystalline, sometimes soft and amorphous), fre-
quently two feet thick, beneath which are successive strata of
coral sand and shells, deposited one above the other in the
gradual process by which the lagoon was filled up. These
horizontal strata were penetrated to a depth of about twenty
feet. They were composed chiefly of fine and coarse sand with
an occasional stratum of coral fragments and shells.

Of the origin of this sulphate of lime there can hardly be
any doubt. As the lagoon was nearly filled up, while, by the
gradual elevation of the island, the communication between
the outer ocean and the inner lake was constantly becoming
less easy, large quantities of sea water must have been evap-
orated in the basin. By this means deposits would be formed

THE COMPLETED ATOLL. 295

containing common salt, gypsum, and other salts found in the
waters of the ocean. From these the more soluble parts
would gradually be washed out again by the occasional rains,
leaving the less soluble sulphate of lime as we find it here.

Some additional light is thrown on this matter by the dif-
ferent parts of the surface, which, though nearly flat, shows
some slight variety of level. The higher parts, particularly
around the outer edges, are composed chiefly of coral sand,
either mixed with or underlying guano. Nearer the centre is
a large tract, rather more depressed, forming a shallow basin,
in which the bulk of the sea water must have been evapor-
ated, and whose surface (now partly covered with guano) is a
bed of sulphate of lime, while, further, there is a still lower
point, the least elevated of the whole, where the lagoon waters
were, without doubt, most recently concentrated. This latter
locality is a crescent-shaped bed, about 600 feet long by 200
or 300 feet wide, having a surface very slightly depressed
from the outer edge toward the middle. Around the borders
are incrustations of crystallized gypsum and common salt,
ripple-marks, and similar evidences of the gradually disappear-
ing lake. The whole is composed of a crystalline deposit of
sulphate of lime, which, around the borders, as already ob-
served, is mixed with some common salt, while near the cen-
tre, where rain water sometimes collects after a heavy shower,
the salt is almost entirely washed out, leaving the gypsum by
itself It is closely, but not hard, packed, and is still very
wet. By digging 18 or 24 inches down, salt water may gen-
erally be found.

These facts help us to understand the varying conditions
in which we now find the guano beds. The most impor-
tant part, and that from which the importations have thus far
come, rests on a bed of sulphate of lime, of an earlier but

296 CORALS AND CORAL ISLANDS.

similar origin to that just described above ; part rests on a
coral formation ; while still another part, covering a large
tract, has been by the action of water mixed with coral mud.

The first named deposit, lying on the sulphate of lime bed,
has a peculiar character. It is covered by, or consists of, a
hard crust, that is from one-fourth of an inch to an inch and
a half in thickness, beneath which lies a stratum of guano
varying in depth from one inch to a foot. In many places
where the guano was originally shallow, the whole is taken
up and formed into the hard crust which then lies immedi-
ately on the sulphate. This crust, when pure, is snow-white,
with an appearance somewhat resembling porcelain, but is
usually colored more or less by organic matter. Generally it
is very hard, and strongly cohesive, though sometimes friable,
and it lies unevenly on the surface in rough fragments that
are warped and curved by the heat of the sun. It consists
chiefly of phosphoric acid and lime, but, owing to the variable
amount of sulphate of lime with which it is mechanically mixed,
there is a lack of uniformity in different samples. Hence
the percentage of phosphoric acid varies from over 50 per
cent to less than 30 per cent.

The gypsum or sulphate of lime is usually soft and amor-
phous, sometimes crystalline, and, at a depth of eighteen
inches, or two feet, occurs in hard, compact, crystalline beds.
It is of a light snutf color, and where it underlies guano, is
mixed with considerable phosphate of lime, which has been
washed down from the surface. Similar deposits of sulphate
of lime occur on many other elevated lagoon islands of the
Pacific.

Starbuck's, Starve or Hero Island is an elevated atoll,
and is worthy of mention, because like Jarvis's, McKean's, and
other islands of similar structure, it centains a large deposit of

TEE COMPLETED ATOLL, 297

gypsum. Its supposed guano I have found to consist of the
hydrated sulphate of lime, containing about twelve per
cent, of phosphate of lime, and colored by a little organic
matter. So far as my observation extends, all elevated la-
goons have similar deposits of gypsum.

As regards the distribution of tliese phosphatic guano de-
posits, I believe them, in this region of the Pacific, to be con-
fined to latitudes very near the equator, where rain is compara-
tively of rare occurrence. In latitudes more remote from the
equator than 4*^ or 5^, heavy rains are frequent, and. this cir-
cumstance is not only directly unfavorable to the formation of
guano deposits, but it encourages vegetation, and when an
island is covered with trees and bushes, the birds preferring
to roost in them, there is no opportunity for the accumulation
of guano deposits.

An article in the same Journal (vol. xL, 1865) by A. A. Ju-
lien, gives an account of the various phosphatic minerals
formed from the guano deposits on a coral island. Sombrero,
in the Caribbean Sea.

Lord Byron, of the Blonde, mentions that phosphate of
lime (apatite) was collected by him on Mauke, an elevated
coral island of the Hervey Group, west of the Society Islands,
but its exact condition in the rock is not stated.

Coral islands are exposed to earthquakes and storms like
the continents, and occasionally a devastating wave sweeps
across the land. During the heavier gales, the natives some-
times secure their houses by tying them to the cocoanut trees,
or to a stake planted for the purpose. A height of ten or
twelve feet, the elevation of their land, is easily overtopped by
the more violent seas ; and great damage is sometimes expe-
rienced. The still more extensive earthquake-waves, such as

298 CORALS AND CORAL ISLANDS.

those which have swept up the coast of Spain, Peru, and the
Sandwich Islands, would produce a complete deluge over these
islands. We were informed by both Grey and Kirby, that effects
of this kind had been experienced at the Gilbert Islands ;
but the statements were too indefinite to determine whether
the results should be attributed to storms, or to this more vio-
lent cause.

But while coral islands have their storms, the region in
their vicinity is generally one of light winds and calms, even
when the trades are blowing strongly all around them. The
heated air which rises from the islands lifts the currents to
a considerable height above the island. J. D. Hague men-
tions that on Jarvis's and the two neighboring islands, under
the equator, near 180^ in longitude from Greenwich, he "often
observed the remarkable phenomenon of a rain squall approach-
ing the island, and, just before reaching it, separating into two
parts, one of which passed by on the north, the other on the
south side, the cloud having been cleft by the column of heated
air rising from the white coral sands."

GEOGBAPHIGAL DISTRIBUTION. 299

CHAPTER IV.

GEOG-RAPHICAL DISTRIBUTION OF
CORAL REEFS AISTD ISLANDS.

The distribution of coral reefs over the globe depends on
the following circumstances, arising from the habitudes of
polyps already explained.

1. The temperature of the ocean.

2. The character of coasts as regards (a) the depth of
water, — {b) the nature of the shores, — {p) the presence of
streams.

3. Liability to exposure to destructive agents, such as vol-
canic heat.

It has been stated (p. 108) that reef-growing corals will flour-
ish in the hottest seas of the equator, and over the ocean, wher-
ever the average temperature of the waters during the coldest
month of winter, is not below 68 "^F. The isothermal line of
this temperature (or isocryme) forms, therefore, the boundary
line of the coral-reef seas. Other corals not forming reefs
grow in colder seas (p. 109), but to those we do not now refer.

This line traverses the oceans between the parallels 26^ and
30^, or in general near 28^ But, as has been stated, in the
vicinity of the continents it undergoes remarkable flexures
from the influence of oceanic currents, the polar currents bending
it toward the equator, while the tropical cause a divergence.
From a comparison of the thermometrical observations of va-

300 C0RAL8 AND COMAL ISLANDS.

rious voyages with those o£ the Expedition, the author has
been enabled to draw these boundary lines with a consider-
able degree of accuracy, and they are laid down upon the chart
of the world published in his Report (Wilkes Exploring Ex-
pedition) on Geology, and, with other isocrymal lines, on a
full isocrymal chart of the globe, in his Report on Crustacea,
from which it was reproduced in volume xv. (1853) of the
second series of the American Journal of Science^ which is now
again issued at the close of this volume.

In the Pacific Ocean, this coral boundary, or isocryme of
68^, excludes the Galapagos from the coral seas, making a
bend around them, and passing for a short distance even
north of the equator, instead of near the parallel of 28^
south, its position in mid-ocean. Captain Fitzroy, R. N.,
found the surface temperature of the sea at the Galapagos,
from Sept. 16 to Oct. 18, 1835, 62^ to 70^F. Oct. 23, in lat.
0^ 30^ S., and long. 99^ 4' W., the temperature of the sea
was 66^ F. ; Oct. 24, lat. 0^ 23' N., long. 96^ 53' W., temp.
70^^, 71^^ F. While, under the equator, about the middle of
the Pacific, the range of surface temperature of the sea through
the year is 81^ to88^F.

On the side of Asia the boundary line bends far southward,
and reaches the coast of Cochin China within 15^ of the
equator, although 30^ from the equator a little to the east-
ward. On the west side of the Atlantic, the northern line
starts at Cape Florida, in latitude 15^ N., stretches abruptly
northward, and bends around the Bermudas in latitude 33^
N. On the African coast opposite, the northern line curves
downward to the latitude of the Cape Verds, and the south-
ern upward nearly to the equator. The following table gives
the positions of the coral boundary lines where they meet
the coasts of the continents.

GEOGRAPHICAL DISTRIBUTION 301

Pacific Ocean. Atlantic Ocean.

East side of ocean — Northern, Lat. 21'' IS" Lat. 10° N.

Southern. 4° S. 5° S.

West side of ocean — ^Northern. 15° K 26° N.

Q .1 S 30° S., K Holland. ) ^^^ ^

Southern. | 29° S.l Africa. f ^2° S.

It follows from the above, that while the coral-reef seas
are about fiftj^-six degrees wide in mid-ocean, they are

In the Pacific twenty-five degrees wide on the west coast
of America, and forty-five degrees on the Asiatic side.

Ill the Atlantic about fifteen degrees wide on the African
coast, and forty -eight degrees on the coast of America.

If we reckon to the extremity of the bend in the Gulf
Stream, the whole width of the coral reef sea off* the east
coast of America, will be over sixty-four degrees ; while off
the west coast of America, the width is hardly eighteen degrees.
It is obvious that these facts enable us to explain many seem-
ing anomalies in the distribution of coral reefs.

The other causes which influence the distribution of reefs,
operate under this more general one of oceanic temperature,
that is, within the coral-reef boundary lines. The efi'ect of a
deep abrupt coast on the distribution of reefs has been pointed
out (p. 114). The unfavorable character of sandy or muddy
shores, and the action of detritus, marine currents, and fresh
waters have also been stated (p. 119), and it is not necessary
to touch again upon these points.

Not less striking are the effects of volcanic action in pre-
venting the formation of reefs ; and instances of this influ-
ence are numerous throughout the Pacific. The existence of
narrow reefs, or their entire absence, may often be thus ac-
counted for. For example, in the Hawaian Group, the island
Hawaii, still active with volcanic fires, has but few traces of
corals about it, while the westernmost islands, which have

302 C0RAL8 AND CORAL ISLANDS.

been longest free from such action, have reefs of considerable
extent. The island of Maui exemplifies well the same gen-
eral fact. The island consists of two peninsulas : one the
eastern, recent volcanic in character, with a large crater at
summit, and the other, the western, presenting every evidence,
in its gorges and peaks and absence of volcanic cones, of hav-
ing become extinct ages since. In conformity with the view
expressed, the coral reefs are confined almost exclusively to the
latter peninsula. Other examples are afforded by the Samoan
or Navigator Islands. Savaii abounds in extinct craters and
lava streams, and much resembles Hawaii in character; it
bears proof in every part of being the last seat of the vol-
canic fires of the Samoan Group. Its reefs are consequently
few and small: there is but a narrow line on part of the
northern shores, although on the other islands they are very
extensive.

This absence of corals results obviously from the destruc-
tion of the zoophytes by heat, consequent on volcanic action.
Submarine eruptions, which are frequent as long as a vol-
cano near the sea is in action, heat the waters and destroy
whatever of life they may contain. After the eruption of Ki-
lauea, in 1840, there were numerous dead fish thrown on the
beach ; and many such instances in diflFerent regions are on
record.

The agencies affecting the growth of coral reefs being be-
fore the mind, we may proceed to notice the actual distribu-
tion of reefs through the coral seas. The review given is a
rapid one, as our present object is simply to explain the
absence or presence of reefs within the coral reef limits, by
reference to the above facts.

In the valuable work by Mr. Darwin, the geographical
distribution of reefs is treated of at length. The facts here

OEOGRAPHIGAL DISTBIBUTIOl^. 303

detailed have been obtained from independent soui'ces, except
where otherwise acknowledged. In accounting for the char-
acter and distribution of reefs, Mr. Darwin appears to attrib-
ute too much weight to a supposed difference in the change
of level in different regions, neglecting to allow the requis-
ite limiting influence to volcanic agency, and to the other
causes mentioned. His conclusion that the areas of active
volcanos in general, are areas of elevation, and not of subsi-
dence, and the inference that reefs are absent from the shores
of islands of recent volcanic action on this account, do not
accord with the facts above stated : for example, the condition
of Maui, that it has no reefs on the larger half, that of the
volcanic cone of recent action, but has them on the other
half whose fires were long since extinct ; for it is not prob-
able that one end has been undergoing elevation, and the
other subsidence.

Pacific Ocean. — The west coast of South America is
known to be without coral reefs even immediately beneath
the equator ; and the seas of the Galapagos also grow no
coral. The northward deflection of the coral boundary line
accounts, as has been shown, for their absence. In the Bay
of Panama, and elsewhere on the coast, north and south,
corals occur in patches, but there are no reefs. There are
corals also at La Paz, near the extremity of the Peninsula of
California (p. 112).

In Captain Colnett's voyage, allusion is made to a beach
of coral sand on one of the Revillagigedo Islands, in lati-
tude 18^ ; besides this statement we have met with no allu-
sion to corals on any of the islands off the Mexican coast.

Between the South American coast and the Paumotus are
two rocky islands, Easter or Waihu and Sala-y-Gomez, both
of which are stated to be without reefs.

304 CORALS AND CORAL ISLANDS.

Captain Beechey mentions, however, that at forty-one fath
oms, near Sala-y-Gomez, he found a bottom of sand and
coral.

The Paumotus commence in longitude 130*^ W., and em-
brace eighty coral islands, all of which, excepting about eight
of small size, contain lagoons. Besides these, there are, near
the southern limits of the archipelago, the Gambier Islands
and Pitcairn, of volcanic or basaltic constitution. The for-
mer in 23^ S., have extensive reefs. About the latter, in 25^^
S., there are some growing corals, but no proper reefs.

The Marquesas, in latitude 10° S., have but little coral
about them ; and this is the more remarkable, since they are
in close proximity to the Paumotus. But their shores are
mostly very abrupt, with deep waters close to the rocks. An
island which, before subsidence has commenced, has some ex-
tent of shallow waters around, might have very bold shores
after it had half sunk beneath the waves. This would be the
case with the island of Tahiti ; for its mountain declivities are
in general, singularly precipitous, except at base. The Mar-
quesas may, therefore, have once had barrier reefs, which were
sunk from too rapid subsidence; and afterward, on the ces-
sation of the subsidence, others failed to form again on ac-
count of the deep waters.

The Society Islands have extensive coral reefs, with dis-
tant barriers. The reefs of Tahiti extend, in some parts, a
mile from the shores. Tetuaroa, to the north of Tahiti, and
Tubuai, near Bolabola, are lagoon islands. Maitea, east of
Tahiti, is a sugar loaf truncated at summit, four miles in
compass, and is said by Forster to have an encircling reef.

South of the Society Islands, near 25° S., is Rapa, which
is represented as a collection of rugged peaks without coral
shores. The Rurutu and Hervey Islands, just northwest of

OEOORAPHIGAL DISTRIBUTION, 305

Kapa, have coral reefs fringing the shores. There is no evi-
dence of recent volcanic action among them. Some of them
are elevated coral islands, as Mitiaro, Atiu, Mangaia and
Mauki, and also, according to Stutchbury, Eurutu. Oka-
tutaia is a low coral island but six or seven feet out of
water.

Between the Paumotus and the longitude of Samoa are
numerous small islands, all of coral origin.

The Samoan or Navigator Islands have extensive reefs.
About Tutuila, owing to its abrupt shores, they are somewhat
less extensive than around TJpolu, and about Savaii they are
still smaller, as already explained. The influence of abrupt
shores may also be seen in some parts of Upolu; for example,
to the west of the harbor of Falifa, where, for several miles,
there is no reef, except in some indentations of the coast.
Manua is described as having only shore reefs.

The Tonga Islands, south of Samoa, for the most part
abound in coral reefs, and Tongatabu and the Hapai Group
are solely of coral. Eoa is a moderately high island, with a
narrow reef Tafoa an active volcano, and Kao, an extinct
cone, are without reefs. Vavau, according to Williams {Miss.
Enterprises^ p. 427, Amer. ed.), is an elevated coral island.
Pylstaarts, near Eoa, is a naked rock, with abrupt shores, and
little or no coral. Sunday Island, farther south (29^ 12^ S.),
is beyond the coral-reef limits.

North of Samoa are several scattered islands of small size,
all of coral.

The Feejee Group, already sufficiently described, abounds
in reefs of great extent. There are no active volcanoes,
and, where examined, no evidence of very recent volcanic
action. The many islands afford a peculiarly favorable re-
gion for the growth of zoophytes, and the displays of reefs

20

30 G CORAL 8 AND CORAL ISLANDS.

and living corals were the most remarkable seen by the author
in the Pacific.

North of the Feejees are numerous islands leading up to
the Carolines. They are all of coral, excepting Rotuma,
Home and Wallis's Islands, which are high, and have fringing
or barrier reefs. The reefs of Wallis's Island are very exten-
sive.

The Gilbert or Kings mill Islands, the Marshall Islands,
and the Carolines, about eighty in number, are all atolls, ex-
cepting the three Carolines, Ponape (Pouynipete of Lutke),
Kusaie (or Ualan), and Truk (or Hogoleu). Between Ponape
and Ualan, the McAskill Islands, three in number, are of
coral, but 60 to 100 feet high {Miss. Herald, 1856, p. 193).

The westernmost of the Sandwich Islands, Kauai and
Oahu, have fringing reefs, while eastern Maui and the island
of Hawaii have but few traces of corals. On Hawaii, the
only spot of reef seen by us, was a submerged patch off the
southern cape of Hilo Bay. We have already attributed the
absence of corals to the volcanic character of the island. The
small islands to the northwest of Kauai, are represented as
coral reefs, excepting the rocks Necker and Bird Island ; the
line stretches on to 28^ 30^ N., the northern limit of the coral
seas. Lisianshy's Voyage, 1803-6, in the Neva, 4to., Lon-
don, 1814, pp. 254, 256, contains an account of some of these
islands ; also the Hawaian Spectator, vol. i. ; and also a Re-
port to the U. S. Bureau of Navigation, December, 1867, by
Capt. Wm. Reynolds, U. S. N., partially reproduced in the
American Journal of Science for 1871, vol. ii., p. 380.

The Ladrones, like the Hawaian Group, constitute a line
or linear series of islands, one end of which has been long
free from volcanic action, while the other has still its smok-
ing cones. The appearances of recent igneous action increase

GEOGRAPHICAL DISTRIBUTION. 307

therefore as we go northward, and the extent of the coral
reefs increase as we go southward ; no reefs occur about the
northernmost islands, while they are quite extensive on the
shores of Guam. This group, consequently, like the Hawai-
an and Navigator, illustrates the influence of volcanic action
on the distribution of reefs.

A short distance southwest of the Ladrones, and nearly
in the same line, lie extensive reefs. Mackenzie's is an atoll
of large size. Yap (or Eap), Hunter's, Los Matelotas and
the Pelews (Palao), are high islands, with large reefs. In the
last mentioned, the reef grounds cover at least six times the
area occupied by the high land. Still farther south, toward
New Zealand, lie the large atolls Aiou, Asie and Los Guedes.

South of tlie equator again : — The New Hebrides consti-
tute a long group of high islands, remarkable for the absence
of coral reefs of any extent, though situated between two of
the most extensive coral regions in the world, — the Feejees
and New Caledonia. But the volcanic nature of the group,
and the still active fires of two vents in its opposite extremi-
ties, are a sufficient reason for this peculiarity. Tanna is one of
the largest volcanoes of the Pacific ; and nearly all the islands
of the New Hebrides, as far as known, indicate comparatively
recent igneous action, in which respect they difffer decidedly
from the Feejees.

The Vanikoro Group, north of the New Hebrides, accord-
ing to Quoy, has large barrier reefs about the southernmost
island, Vanikoro ; but at the northern extremity of the range
there is an active volcano, Tinakoro, and no coral. Tikopia,
to the southeast of Vanikoro, is high and volcanic, according
to Quoy, though not now with active fires ; and it appears from
the descriptions given, to have no reefs. Mendana, northeast
of Tinakoro, according to Kruesenstern, as stated by Darwin, ,

308 CORALS AND CORAL ISLANDS.

is low, With large reefs ; Duff's Islands have bold summits
with wide reefs.

New Caledonia, and the northeast coast of New Holland,
with the intermediate seas, constitute one of the grandest reef-
regions in the world. On the New Caledonia shores (p. 134),
the reefs are of great width, and occur not only along the
whole length of the western coast, a distance of 200 miles, but
extend to the south bej^ond the main land 50 miles, and north
150 miles, making in all a line of reef full 400 miles in length.
Toward the north extremity, however, it is interrupted or bro-
ken into detached reefs. This surprising extent is partly ex-
plained by the fact that New Caledonia is not a land of vol-
canoes; but on the contrary consists of older metamorphic
rocks. The streams of so large a land might be expected to
exclude reefs from certain parts : and in accordance with this
fact, we find the reefs of the windward or rainy side compara-
tively small, and scarcely indicated on the charts ; while on
the dry or western side, they often extend thirty miles from the
shores. The theory of subsidence accounts fully for the great
prolongation of the New Caledonia reefs. The reefs indicate
moreover, the existence of a former land near three times the
area of the present island.

Between New Caledonia and the New Hebrides are sev-
eral high islands, one of which, Lafu, has been described
{Quart. J. Geol Soc, 1847, p. 6l) by Rev. W. B Clarke as
an elevated coral island, with fringing reefs ; it appears also
from the remarks of this writer, that the other islets of what
is called the Loyalty Group, are of the same kind. Lafu, the
largest of the number, is about ninety miles in circumference.

South of New Caledonia lies Norfolk Island, in latitude
29® S., about which there is said to be some coral, which is
occasionally thrown on the beach, but no reefs.

GEOGRAPHICAL DISTRIBUTION. 309

Between Australia and New Caledonia the islands are all
of coral. The Australian reef extending south to the east
cape, in latitude 24^ S., has already been described. Such
long reefs on the shores of continents are not common. In
the case of Australia, the zoophytes are not exposed to the
destructive agents usual on continental shores, as the land has
a dry climate, the shores are mostly rocky, and there are no
streams of any extent emptying into the ocean. The east cape
is the southern limit, because here the tropical current, owing
to the direction of the coast above, trends off to the eastward
of south, away from the land, while a polar current follows up
the shores from the south as far as this cape. South of this
cape there are only a few scattered coral zoophytes.

Louisiade Group is described as a region of extensive
reefs.

The Salomon Islands, as far as ascertained, are but spar-
ingly fringed, except the two westernmost, which are said to
have large reefs. The peculiar character of these lands is too
imperfectly known to allow of our deducing the cause of so
restricted reefs. Off to the north of the Salomon Islands,
there are several islands of considerable size. New Ireland,
according to D'Urville, has distant reefs on part of its shores.

The Admiralty Islands, farther west, are enclosed by bar-
rier reefs, and beyond this group there are a few lagoon
islands.

The north side of New Guinea is mostly without coral.
There are several islands off this coast, which are conical vol-
canic summits, and one of them, near New Britain, and an-
other, Vulcano, near longitude 145^ E., are in action.

From the facts thus far detailed, the connection between
the prevalence or extent of reefs, and the various causes as-
signed as limiting or promoting their growth, is obvious.

310 CORALS AND CORAL ISLANDS.

The amount of subsidence determines in some cases the dis-
tance of barrier reefs from shore ; but it by no means accounts
for the difference in their extent in different parts of a single
group of islands. Indeed, if this cause be considered alone,
every grade of extent, from no subsidence to the largest amount,
might in many instances be proved as having occurred on a
single island. Of far greater importance, as has appeared, is
the vo'canic character of the land. At whatever time the ex-
isting reefs in the Pacific commenced their growth, they be-
gan about those of the igneous islands whose fires had become
nearly or quite extinct ; and as others in succession were ex-
tinguished, these became in their turn, the sites of corals, and
of coral reefs. Those lands whose volcanoes still burn, are
yet without corals, or there are only limited patches on some
favored spots. Zoophytes and volcanoes are the land-making
agents of the Pacific. The latter prepare the way by j)our-
ing forth the liquid rock, and building up the lofty summit.
Quiet succeeds, and then commences the work of the zoophyte
beneath the sea, while verdure covers the exposed heights.

"We may add a few more illustrations fiom other parts of
the coral-reef seas.

Along the north and northwest coast of Australia, there
appears to be little or no coral in the Gulf of Carpentaria,
while some extensive patches occur on the shores west of this
Gulf, as far as the northwest cape in latitude 23^ S.

In the East Indies, there are large, scattered reef-islands
south of Borneo and Celebes, about some of the Molluccas,
and near the west end of New Guinea. The islands of Timor-
laut, and Timor, with many of those intermediate, have large
reefs. The Arru Group consists wholly of coral. This sea,
from Arru, to the islands south of Borneo, is more thriving in
corals than any other in the East Indies. j

OEOORAPHIGAL DISTRIBUTION. 311

Another East Indian coral-reef region of some extent, is
the Sooloo Sea, between Mindanao and the north of Borneo-
Yet the reefs are mostly submerged. The author saw no wide
platforms bordering the high lands, like those of the Pacific.
There are, however, some small coral islets in the Balabac
Passage.

In other parts of the East Indies, coral reefs are quite in-
considerable. Occasional traces, sometimes amounting to a
fringing reef, occur along Luzon and the other Philippines.

The Wilkes Exploring Expedition coasted by the west
shore of Luzon to Manila, and thence by Luban, Mindoro,
Panay, to Caldera, near Samboangan in Mindanao; and
through this distance no reefs were distinguished, as would
have been the case, had there been any of much extent. At
the last-mentioned place we found coral pebbles on the beach,
and by dredging, obtained living specimens in six to eight
fathoms of water. The only large reefs were those between
Mindoro and the Calariinianes. There are fringing reefs at
Singapore. The islands of Borneo, Celebes, Java, and Su-
matra, according to all the authorities seen by the writer, have
but few coral patches about their shores, although affording
long lines of coast for their growth. In the China Seas,
there are numerous shoals, banks, and island reefs of coral.
Moreover, shore reefs occur about Loochoo, and the islands be-
tween it and Formosa. But the whole eastern coast of China
appears to be without coral. Quelpaert's island, south of Co-
rea, in 34"^ N., is described as having coral about it ; and this
has been confirmed by late information.

Why should the reefs of the East India Archipelago be so
limited in extent, and large parts be almost destitute, notwith-
standing their situation in the warmest seas of the ocean, and
in the most favorable region for tropical productions ? We are

312 CORALS AND CORAL ISLANDS,

not prepared for a full answer to this inquiry ; for it would de-
mand a thorough knowledge of the shores, as well as of the cur-
rents, and of the former and present condition of volcanic fires.
From personal observation we may reply satisfactorilj^, as far as
regards part of the southern half of the east coast of Su-
matra. This coast is low, and sandy, or muddy, and thus af-
fords the most unfavorable place for zoophytes. A strong
current sweeps through the Straits of Banka, which keeps the
water muddy, and the shores in constant change. The same
cause may operate on the coasts of other islands, but we can-
not say to what extent.

The East Indies have been remarkable for their volcanoes,
exceeding, for the area, every other part of the world ; and this
fact must have had influence on the formation of coral reefs,
though there are not data for fixing the extent of the influence.
Of the thousand vents which have been in action, several still
make themselves felt over wide areas. The Sooloo Islands are
about one hundred in number, and nearly all are pointed with
volcanic cones, and while some have the broken declivities that
are marks of age, others have regular slopes, as if but just now
extinguished ; a dozen of these cones may sometimes be seen
on a single island. These volcanic peaks often rise out of the
sea, as if their formation had begun with a submarine erup-
tion. In a region so extensively and so recently igneous, the
coral polyps would have found little chance for growth, until
volcanic action had become comparatively quiet, and deluges
of hot water ceased. There appears, therefore, to be some
reason for the fact that \\ve reefs are small, and have seldom
reached the surface. The Sooloo Sea is but one of the volcan-
ic clusters in these seas. Java, several of the Philippines, and
other islands south of these last, with the northern shore of
New Guinea, make up a wide region of fires, and it cannot be

OEOOBAPHIGAL DISTRIBUTION. 313

doubted that the frequent eruptions prevented the growth of
any thing more than isolated corals, for a long period, over
each of these areas. For other causes we must look to the na-
ture of the coasts, fresh-water streams, and marine currents ;
we leave it for other investigators to apply the explanation to
particular coasts.

The coast of China owes its freedom from corals to the
cool temperature of \hQ^ waters, the coast being wholly outside,
as has been stated, of the coral-reef seas.

One interesting^ fact should be noted : — the most extensive
reefs in the East Indies are to be found in \h^ open seas, be-
tween the large islands ; these islands, at the same time, often
being without proper reefs, or with mere traces of coral. This
is the case between Borneo and the range of large islands south ;
the China Sea is another instance of it ; north of New Guinea,
a few degrees, is another. How far this is due to their being
distant from \h^ scenes of igneous action, and from the detri-
tus and fresh water of island streams, remains to be deter-
mined. A sinking island becomes a more and more favorable
spot for the growth of coral, as it descends ; for as its extent
diminishes, its streams of fresh water and detritus also de-
crease. It might, therefore, be expected, on this account alone,
that such isolated spots of land, away from all impure waters,
in the open ocean, should become the bases of large reefs.
The existence of these reef-islands is, therefore, no necessary
proof of greater subsidence than the coast adjoining has un-
dergone. Still the fact of a greater subsidence is not im-
possible or improbable.

In the Indian Ocean^ the Asiatic coast is mostly free from
growing coral. The great rivers of the continent are probably
the most efficient cause of their absence, both directly, through
their fresh waters, and through the detritus they trans[)oii: and

514 CORALS AND COMAL ISLANDS.

distribute along the shores. It will be observed that this
agent, so ineffectual on small islands, is one of vast influence
upon larger lands. Mr. Darwin alludes to small patches of
coral in the Persian Gulf. Ceylon has some fringing reefs.

The islands of the Indian Ocean are, to a great extent,
purely of coral. Of this character are the Laccadives, Mal-
dives, Keeling's, Saya-de-Malha, Almirante, and Cosmoledo.
The Chagos Group is of the same character, and the shoal Car-
gados is probably similar. The Seychelles are small islands
with extensive reefs.

Madagascar has a fringing reef upon its southwestern
point, according to Mr. Darwin, and on some parts of the
coast above : also on the north and eastern shores far down as
latitude 18^ S. The Comoro Islands, between Madagascar and
the continent, have large barrier reefs.

The eastern coast of Africa has narrow reefs extendino;
north with some interruptions from Mozambique, in latitude
16^ S., to a short distance from the equator. Corals also
abound in the Red Sea, occurring in some parts on both shores,
though most frequent on the eastern, from Tor, in the Gulf of
Suez, to Konfodah. This long continental reef may at first be
deemed a little remarkable, after what has been stated about
such reefs elsewhere. Yet the surprise is at once set aside by the
striking fact that this whole coast, from the isthmus of Suez
south, has no rivers, excepting some inconsiderable streams. It
affords, therefore, an interesting elucidation of the subject un-
der consideration, and confirms the view taken to account for
the absence of reefs from many continental coasts. It is a fact
almost universal, that where there are large fresh-water
streams, there are earthy, or sandy shores ; and where there
are no such streams, rocky shores, though not uniformly occur-
ring, are common.

QEOORAPHICAL DISTEIBUTIOJV. 315

On the African coast there are coral reefs at Port Natal,
in latitude 30^ S. ; and here, owing to the warm currents from
the tropical regions, the mean winter temperature of the water
IS not below 68^ F.

Passing from the Indian to the Atlantic Ocean^ we find
little or no coral on the west coast of Africa. The islands of
Cape St. Ann and Sherboro, south of Sierra-Leone, are de-
scribed as coral by Captain Owen, R. N., in the Journal of
\he Geographical Society (vol. ii., p. 89) ; but this has been
since denied. The Island of Ascension, in 7^ 56^ S.^ and 14^
16'' W., must have been bordered by growing coral, as Quoy
and Gaymard mention that a bed of coral rock may be seen
buried beneath streams of lava. Quoy also states that the
corals which formed these reefs are no longer found alive, and
adds that volcanic eruptions have probably destroyed them.
The cold polar currents along the Vv^estern African coast are the
cause of the absence of corals from it, to within six or seven de-
grees of the equator; and these cold waters may at times ex-
tend still farther north. The same obstacle to the diffusion of
species eastward, mentioned as occurring in the Pacific — that is,
westward currents — exists also in the Atlantic, and probably
with the same effect.

On the American shores of the Atlantic, north of the
equator, there are few reefs, except in the West Indies. The
waters of the Orinoco and Amazon, and the alluvial shores
they occasion, exclude corals from that part of the coast.

In the West Indies, the reefs of Florida (p. 204), Cuba,
the Bahamas (p. 213), and of many of the eastern islands are
well known. On the east coast of Florida they continue up
as far as Cape Florida, in latitude 25^ 40' N. ; but the
west coast is free from them. There are also said to be patches
at intervals along the coast of Venezuela and Guatemala ; but

316 CORALS AND CORAL ISLANDS.

the west shores of the Gulf of Mexico, as well as the northern,
like West Florida, are mostly low, and without reefs ; they
are within the influence of the Mississippi and other large
rivers. Some species of reef corals however occur in the
vicinity of Aspinwall (p. 113). The Bermudas are of coral
origin, and the most northern point of growing reefs.

South of the equator, on the east coast of South America,
there are reefs at intervals, from the vicinity of Cape St.
Roque to the Abrolhos shoals in latitude 18^, as described by
Prof. C. F. Hartt, while reef corals extend south to Cape Frio.
Descriptions of part of the Abrolhos reefs are given on page
140. North of the Abrolhos reefs, there are others of coral
stretching on to Point Carumba ; again, off the Bay of Porto
Seguro, and across the Bay of Santa Cruz ; in the vicinity of
Camamu, around Quieppe Island ; along the shores of Ita-
parica Island ; and at Bahia and Periperi ; then, after an in-
terruption, off Maceio, in the vicinity of Pernambuco. More-
over the Koccas, a cluster of reefs in the latitude of Fernando
do Noronha, are, as Hartt observes, probably of coral.

It is thus seen that the >earth is belted by a coral zone,
corresponding nearly to the tropics in extent, and that the
oceans throughout it abound in reefs, wherever congenial sites
are afforded for their growth. It has also been shown that
the currents of extra-tropical seas, which flow westward, and
are interrupted and trended toward the equator by the con-
tinents, contract the coral seas in width, narrowing them to a
few degrees on the western coasts of the continents ; while
the tropical currents flowing eastward, diverge from the equa-
tor, and cause the belt to widen near the eastern shores. The
polar currents flow also by the eastern coasts, preventing the
warmer waters from increasing the width of the coral zone as

OEOQRAPHICAL DISTRIBUTION 317

much as it is contracted on the western coasts. Moreover, the
trend of the coast and its capes produce other modifications in
the direction of the currents, the most of which are apparent
in the actual distribution of coral reefs. On the shores of
the continents it is observed that there are few extensive
reefs, and the coasts on which they occur are those which,
owing to the dryness of the climate, have no great rivers to
pour freshwater and detritus into the sea. Thus the influence
of continental waters and detritus on the distribution of reefs,
is shown to be very marked. But about the Pacific Islands,
where streams are small, the same cause has had little eff^ect,
seldom doing more than modifying sojnewhat the shores and
bottom of a harbor. It has been further demonstrated that
in different groups, as the Ladrones, Sandwich Islands, Navi-
gators, New Hebrides, there is an inverse relation between
the extent of reefs and the evidences of recent volcanic ac-
tion in the island ; and that the largest reefs exist where
there is no proof of former igneous action, or where it has
long ceased. The existence of large reef-islands in open seas
Avhere the neighboring lands are mostly destitute of coral
reefs, harmonizes with the conclusions announced, since such
islands are in general removed from the deleterious influences
just mentioned; yet it is very possible that in some cases of
this kind the region of the open sea may have undergone a
subsidence not experienced equally by the lands either side.

The modifications of form and interruptions of reefs, aris-
ing from abrupt or sloping shores, and tidal or local cur-
rents, have also been exemplified.

318 VORALS AND COMAL ISLANDS.

A

CHAPTER V.

ON OHAlSraES OF LEVEL EST THE PACIFIC

OOEAlSr.

I. EVIDENCES OF CHANGE OF LEVEL.

It has been shown that atolls, and to a large extent other
coral reefs, are registers of change of level. From the evi-
dence thus afforded the bottom of a large part of the Pacific
ocean is proved to have undergone great oscillations in recent
geological time. In this direction, then, we find the grandest
teachings of coral formations. In treating the subject we
necessarily bring into connection with it evidences of change
of level from other sources. The proofs of change of level here
considered are the following: —

A. Evidences of elevation.

1. The existence on coral or other islands of patches of
coral reef and deposits of shells and sand from the reefs^
above the level where they are at present forming.

The coral reef-rock has been shown occasionally to increase,
by growth of coral, to a height of four to six inches above low-
tide level when the tide is but three feet, and to twice this
height with a tide of six feet. It may, therefore, be stated as
a general fact, that the limit to which coral may gro^v above
ordinary low tide, is about one-sixth the height of the tide,
though it seldom attains this height. Its existence on an
island at a higher level would be proof of an elevation of the
land. ^^

CHANGES OF LEVEL IN CORAL-BEEF REGIONS, 319

When the tide is three feet, beach accumulations of large
masses seldom exceed eight feet above high tide, and the finer
fragments and sand may raise the deposit to ten feet; but
with a tide of six feet twice this height may be attained.
With the wind and waves combined, or on prominent points
where these agents may act from opposite directions, such ac-
cumulations may h^ fifteen to twenty feet in height, and occa-
sionally thirty to forty feet. These latter are drift deposits,
finely laminated, generally with a sandy texture, and com-
monly without a distinguishable fragment of coral or shell ;
and in most of these particulars they are distinct from reef-
rocks.

2. On islands not coral, the existence of sedimentary de-
posits^ or layers of rolled stones^ interstratified among the
layers of igneous or other rocks constituting the hills,
I B. Evidence of subsidence.

1. The existence of ivide aiicl deep channels between an
island and any of its coral reefs ; or in other words, the exist-
ence of harrier reefs.

2. The existence of lagoon islands or atolls.

3. The existence of submerged atolls.

4. Deep bay-indentations in the coasts of high islands as
the terminations of valleys. — In the course of remarks upon the
valleys of the Pacific Islands, presented by the author in his
Geological Report, it is shown that they were in general
formed by the waters of the land, unaided by the sea ; that
the sea tends only to fill up bays, level off the coast, and so
give it an even outline. When, therefore, the several valleys
of an island continue down beneath the sea, and their enclosing
ridges standing out in long narrow points, with abrupt sides,
there is reason to suspect that the island has subsided
after the formation of its valleys. For such an island as

320 CORALS AND CORAL ISLANDS

Tahiti could not subside even a few scores of feet without
changing the even outline into one of deep coves or bays, the
ridges projecting out to sea on every side, like the spread legs
of a spider. On the contrary, the absence of such coves, or
deep-valley bays, may be evidence that no subsidence has taken
place, or only one of comparatively small amount.

C. Probable evidence of subsidence now in progress.

1. A.n atoll reef without green idets^ or with hut few small
spots of verdure, — The accumulation requisite to keep the reef
at the surface-level, during a slow subsidence, renders it im-
possible for the reef to rise above the waves and supply itself
with soil, unless the subsidence is extremely slow, or has whol-
ly ceased.

From the above review of evidences of change of level, it
appears that where there are no harrier reefs^ and only fring-
ing reefs^ the corals may afford no evidence of sithsidence. But
it does not follow that the existence of only fringing reefs, or
of no reefs at all, is proof against a subsidence having taken
place. For we have elsewhere shown that through volcanic
action, and at times other causes, corals may not have begun
to grow till a recent period, and, therefore, Ave learn nothing
from them as to what may have previously taken place.
While, therefore, a distant barrier is evidence of change of
level, we can draw no conclusion either one way or the other,
from the fact that the reefs are small or wholly wanting,
until the possible operation of the several causes limiting
their distribution has been duly considered.

The influence of volcanoes in preventing the growth of
zoophytes extends only so far as the submarine action may
heat the water, and it may, therefore, be confined within a few
miles of a volcanic island, or to certain parts only of its shores.

SUBSIDEN'GE IN PACIFIC COHAL BEQ10N8. 321

There are two epoclis of changes in elevation which may
be here distinguished and separately considered. 1. The sub-
sidence indicated by atolls and barrier reefs. 2. Elevations
during more recent periods. I/'"

n. SUBSIDENCE INDICATED BY ATOLLS AND BARRIER

REEFS.

Looking at atolls as covering buried islands, we obsereve,
that through the equatorial latitudes, such marks of subsidence
abound, from the Eastern Paumotu to the Western Carolines,
a distance of about six thousand geographical miles. In the
Paumotu Archipelago there are about eighty of these atolls.
Going westward, a little to the north of west, they are found
to dot the ocean at irregular intervals ; and at the Kino-smill
or Gilbert Group, the Marshall Group, and the Carolines
comprise seventy-five or eighty atolls.

If a line be drawn from Pitcairn's Island, the soiithern-
most of the Paumotus. by the Gambier Group, the north of
the Society Group, the Navigators, and the Salomon Islands
to the Pelcws, it will form nearly a straight boundary,
trending N. 70^ W., running between the atolls on one side
and the high islands of the Pacific on the other, the former
lying to the north of the line, and the latter to the south.

Between this boundary line and the Hawaian Islands, an
area nearly two thousand miles wide and six thousand lon^^-,
there are two hundred and four islands, of which only thi^ee are
higli^ exclusive of the eight Marquesas, and the Ladrones with
Yap, Hunter's and Los Matelotas in the line of the Ladrones
and Pelews. These three are Kusaie or Ualan, Ponape, and
Truk or Hogoleu, all in the Caroline Archipelago. South
of the same line, within three degrees of it, there is an occa-

21

322 CORALS AND CORAL ISLANDS.

sional atoll ; but beyond this distance, there are none except-
ing the few in the Friendly Group, and one or two in the Fee-
jees.

If each coral island scattered over this wide area indicates
a subsidence of an island, we may believe that the subsidence
was general throughout the area. Moreover, each atoll, could
we measure the thickness of the coral constituting it, would
inform us nearly how much subsidence took place where it
stands; for they are actually so many registers placed over the
ocean, marking out, not only the sight of a buried island, but
also the depth at which it lies covered. We have not the
means of applying the evidence; but there are facts at hand,
which may give at least comparative results.

a. We observe, ^^'5^, that the barrier reefs are, in general,
evidence of less subsidence than atoll reefs (p. 266). Conse-
quently, the great preponderance of the former just below the
southern boundary line of the coral island area, and farther
south the entire absence of atolls, while atolls prevail so uni-
versally north of this line, are evidence of some depression just
below the line ; of less, farther south ; and of the greatest
amount, north of the line or over the coral area.

h. The subsidence producing an atoll, when continued,
gradually reduces its size until it finally becomes so small that
the lagoon is obliterated ; and, consequently, a prevalence of
these small islands is presumptive evidence of the greater subsi-
dence. We observe, in application of this principle, that the
coral islands about the equator, five or ten degrees south, be-
tween the Paumotus and the Gilbert Islands, are the smallest
of the ocean ; several of them are without lagoons, and some
not a mile in diameter. At the same time, in the Paumotus,
and among the Gilbert and Marshall Islands, there are atolls
twenty to fifVy miles in length, and rarely one less than three

SUBSIDENCE IN PAGIFIG COBAL BEQIONS, 323

miles. It is probable, therefore, that the subsidence indicated
was greatest at some distance north of the boundary line,
over the region of small equatorial islands, between the me-
ridians of 150^ W. and 180^.

c. When, after thus reducing the size of the atoll, the sub-
sidence continues its progress, or when it is too rapid for the
growing reef, it filially sinks the coral island, which, there-
fore, disappears from the ocean. Now it is a remarkable
fact that while the islands about the equator, above alluded
to, indicate greater subsidence than those farther south, there
is over a region north of these islands, that is, between them
and the Hawaian Group, a wide blank of ocean without an
island, which is nearly twenty degrees in breadth. This area
lies between the Hawaian, the Fanning and the Marshall
Islands, and stretches off between the first and last of these
groups, far to the northwest.

Is it not then a legitimate conclusion that the subsidence
which was least to the south beyond the boundary line, and
increased northward, was still greater or more rapid over this
open area ; that the subsidence which reduced the size of the
islands about the equator to mere patches of reef, was further
continued, and caused the total disappearance of islands that
once existed over this part of the ocean ?

d. That the subsidence gradually diminished southwest-
wardly from some point of greatest depression situated to the
northward and eastward, is apparent from the Feejee Group
alone. Its northeast portion (see chart), consists of immense
barriers, with barely a single point of rock remaining of the
submerged land ; while in the west and southwest there are
mountain islands of great magnitude. Again, along the north
side of the Vanikoro Group, Salomon Islands, and New
Ireland, there are coral atolls, but scarcely one to the south.

324 COBALS AND CORAL ISLANDS.

In view of this combination of evidence, we cannot doubt
that the subsidence increased from the south to. the north-
ward or northeastward, and was greatest between the Navi-
gator and Hawaian Islands, near the centre of the area des-
titute of islands, about longitude 170^ to 175^ W., and 8"^
to 10^ N.

But we may dei'ive some additional knowledge respecting
this area of subsidence from other facts.

" Hawaian Range. — We observe that the western islands
in the Hawaian Range, beyond Bird Island, are atolls, and all
indicate a large participation in this subsidence. To the east-
ward in the range, Kauai and Oahu have only fringing reefs,
yet in some places these reefs are half a mile to three-fourths
in width. They indicate a long period since they began to
grow, which is borne out by the features of Kauai showing a
long respite from volcanic action. We detect proof of sub-
sidence, but not of a large amount. Moreover, there are
no deep bays; and, besides, Kauai has a gently-sloping
coast plain of great extent, with a steep shore acclivity of one
to three hundred feet, all tending to prove the smallness of
the subsidence. We should, therefore, conclude that these
islands lie near the limits of the subsiding area, and that
the change of level was greatest at the western extremity of
the range beyond Kauai.

The coral subsidence of the western islands of the range,
bear some evidence of having in recent times, commenced a
new subsidence. They all have little dry land and vegetation
about the reefs. Brooks's Island^ in latitude 28"^ 15^ and lon-
gitude 177^ 20' W., eighteen miles in circumference, has on its
north and east sides a compact coral wall of about five feet
elevation, which continues for four and a quarter miles, and then
becomes a line of detached rocks at tide level. This bare

SUBSIDENCE IN PACIFIC CORAL REOI0N8. 325

wall, thus described by Capt. Wm. Reynolds, U. S. N., ap-
pears to be an indication that the land was once finished off
under a cessation of subsidence, but that a sinking of small
amount has since taken place, amounting perhaps to four
OT five feet.

Ocean Island, in 28^ 25' N., 178^ 25' W., another of this
range, is very similar to Brook's in its wall of coral rock on
the east ; and so also is Pearl and Hevme^ reef, in 27^ 50'
N., 176^ W., though the wall of the latter is more a series of
detached rocks than a continuous parapet.

Marquesas, — The Marquesas are remarkable for their ab-
rupt shores, often inaccessible cliffs, and deep bays. The ab-
sence of gentle slopes along the shores, their angular features,
abrupt soundings close alongside the island, and deep inden-
tations, all bear evidence of subsidence to some extent ; for
their features are very similar to those which Kauai or Ta-
hiti would present, if buried half its height in the sea, leaving
only the sharper ridges and peaks out of water. They are
situated but five degrees north of the Paumotus, where eighty
islands or more have disappeared, including one at least fifty
miles in length. There is sufficient evidence that they partici-
pated in the subsidence of the latter, but not to the same ex-
tent. They are nearly destitute of coral, and apparently be-
cause of the depth of water about the islands.

Gambler Group, — In the southern limits of the Paumotu
Archipelago, where, in accordance with the foregoing views,
the least depression in that region should have taken place,
there are actually, as we have stated, two high islands, PiY-
cairvbS and Gamhier^s, There is evidence, however, in the ex-
tensive barrier about the Gamhier'^s (see cut on page 265),
that this subsidence, although less than farther north, was by
no means of small amount. On page 157, we have estimated

326 C0RAL8 AND CORAL ISLANDS,

it at 1,150 feet — possibly 1,750. These islands, therefore,
although toward the limits of the subsiding area, were still far
within it. The valley-bays of the islets of the lagoon are of
great depth, and afford additional evidence of the subsidence.

Taliitian Islands. — ^The Tahitian Islands, along with Sa-
moa and the Feejees, are near the southern limits of the area
pointed out. Twenty-five miles to the north of Tahiti, within
sight from its peaks, lies the coral island Tetuaroa, a register
of subsidence. Tahiti itself, by its barrier reefs, gives evidence
of the same kind of change ; amounting, however, as we have
estimated, to a depression of but two hundred and fifty or
three hundred feet. The northwestern islands of the group
lie more within the coral area, and correspondingly, they have
wider reefs and channels, and deep bays, indicating a greater
amount of subsidence.

Samoan or Navigator Group. — ^The island of Upolu has
extensive reefs, which, in many parts are three-fourths of a
mile wide, but no inner channel. The subsidence is estimated
on page 158, at one or two hundred feet. The volcanic land
west of Apia, declines with an unbroken gradual slope of
one to three degrees beneath the sea. The absence of a low
cliff is probable evidence of a depression, as has been else-
where shown. The island of Tutuila has abrupt shores, deep
bays and little coral. It appears probable, therefore, that it
has experienced a greater subsidence than Upolu. Yet the
central part of Upolu has very similar bays on the north,
which would afford apparently the same evidence ; and it is
quite possible that the facts indicate a sinking which either
preceded the ejections that now cover the eastern and west-
ern extremities of Upolu, or accompanied this change of level.
The large island of Savaii, west of Upolu, has small reefs,
small because, probably, of volcanic action ; for it bears, every-

SUBSIDENCE m PAGIFIG CORAL REGIONS. 327

where, evidence of comparative!}^ recent eruption ; from it,
therefore, we gather no certain facts bearing on this subject.
East of Tutuila is the coral island^ Rose. It maj^ be, there-
fore, that the greatest subsidence in the group was at its
eastern extremity.

JFeejee Islands. — We have already remarked upon this
group (p. 158). A large amount of subsidence is indicated
by the extensive reefs in every portion of the group, but it was
greatest beyond doubt in the northeastern part. The sub-
sidence, where least, could hardly have been less than 2,000
to 3,000 feet.

Ladrones. — The Ladrones appear to have undergone their
greatest subsidence at the northern extremity of the range,
the part nearest the centre of the coral area ; for although
the fires at the north have continued longest to burn, the
islands are the smallest of the group, the whole having dis-
appeared except the summits, which still eject cinders. The
southern islands of the group have wide reefs, which show
that they participated to some extent in the subsidence ; and
this is further indicated by the islands lying to the southwest,
in the line of the Ladrones.

We have thus followed around the borders of the coral
area ; and, besides proving the reality of the limits, have as-
certained some facts with reference to a gradual diminution
of the subsidence toward, and beyond, these limits. A line
through the Hawaian Group would pass along the northern
boundary line of the area ; and taking the southern boundary,
as given on page 319, the oblong area narrows eastward.
An axis nearly bisecting this space, drawn from the eastern
Paumotus toward Japan, passes through the region of greatest
subsidence, as above determined, and may be considered the
line of greatest depression for the great area of subsidence.

328 CORALS AND CORAL ISLANDS.

It is worthy of special note, that this axial line, or line
of greatest depression^ coincides in direction, ivith the mean
trend of the great ranges of islands, it having the course N.
52^ W. ; and it also corresponds approximately with the axial
line of the Pacific ocean.

The southern boundary line of the coral area, as we have
laid it down, lies within the area of subsidence, although near
its limits. This area has been prolonged southeastward in
some places beyond the boundary line. One of the regions of
this prolongation lies between tlie Samoan or Navigator
Group and the Feejees and Tonga Group ; another is east of
Samoa, along by the Hervey Group. Each of these extensions
trends parallel with the groups of islands. It would seem,
therefore, that the Society and Samoan Islands were regions
of less change of level than the deep seas either side of them ;
that, therefore, instead of a uniform subsidence over the
subsiding area, shading off toward the borders, there were
troughs of greater subsidence, whose courses were parallel to
the ranges of islands ; that, in other words, there were in
the ocean's bottom, a few broad synclinal and anticlinal
flexures, having a common direction nearly parallel to the
axial line of the Pacific. The Marquesas and Fanning Groups
lie in a common line, and thus n^ay mark the course of a
great central anticlinal in the oceanic basin.

The Hawaian range has experienced its greatest subsidence
to the northwest, where the islands are all atolls, and show some
evidences of recent sinking; and this northwestern extremity
of the range is nearer to the axis of the area of subsidence,
above laid down, than is the southwestern.

What is the extent of the subsidence indicated by the coral
reefs and islands of the Pacific ? It is very evident that the
sinking of the Society, Samoan, and Hawaian Islands has

SUBSIDEirCE m PAGIFIG CORAL REGIONS. 329

been small compared with that required to submerge all the
lands on which the Paumotus and the other Pacific atolls rest.
One, two, or five hundred ^qq\^ could not have buried the
many peaks of these islands. Even the 1,200 feet of de-
pression at the Gambier Group is shown to be at a dis-
tance from the axis of the subsiding area. The groups of
high islands above mentioned, contain summits from 4,000 to
14,000 feet above the sea ; and can we believe it possible
that throughout this large area, when the two hundred islands
now sunken were above the waves, there were none of them
equal in altitude to the mean of these heights, or 9,000 feet?
That none should have exceeded 9,000 feet in elevation, is
by no means probable. Hence, however moderate our esti-
mate, there must still be allowed a sinking of many thousand
feet. Moreover, whatever estimate we make that is within
probable bounds, we shall not arrive at a more surprising
change of level than our continents show that they have un-
dergone ; for since the Tertiary began (or the preceding period,
the Cretaceous, closed) more than 10,000 feet have been added
to the Rocky Mountains, and parts of the Andes, Alps and
Himalayas.

Between the New Hebrides and Australia, the reefs and
islands mark out another area of depression, which may have
been simultaneously in progress. The long reef of one hun-
dred and fifty miles from the north cape of New Caledonia,
and the wide barrier on the west, cannot be explained with-
out supposing a subsidence of one or two thousand feet at the
least. The distant barrier of Australia is proof of great sub-
sidence, even along the border of that continent. But the
greatest amount of sinking took place, in all probability, over
the intermediate sea, called the " Coral Sea," where there are
now a considerable number of atolls.

330 CORALS AND CORAL ISLANDS,

m. EFFECT OF THE SUBSIDENCE.

The facts surveyed give us a long insight into the past,
and exhibit to us the Pacific once scattered over with lofty
lands, where now there are only humble monumental atolls.
Had there been no growing coral, the whole would have
passed without a record. These permanent registers, exhibit
in enduring characters some of the oscillations which the
" stable " earth has since undergone.

From the actual size of the coral reefs and islands, we
know that the whole amount of high land lost to the Pacific
by the subsidence was at the very least fifty thousand square
miles. But since atolls are necessarily smaller than the land
they cover, and the more so, the further subsidence has pro-
ceeded ; — since many lands, owing to their abrupt shores,
or to volcanic agency, must have had no reefs about them,
and have disappeared without a mark ; and since others may
have subsided too rapidl)^ for the corals to retain themselves
at the surface ; it is obvious that this estimate is far below
the truth. It is apparent that in many cases, islands now
disjoined have been once connected, and thus several atolls
may have been made about the heights of a single subsiding
land of large size. Such facts show additional error in the
above estimate, evincing that the scattered atolls and reefs tell
but a small part of the story. Why is it, also, that the Pa-
cific islands are confined to the tropics, if not that beyond
thirty degrees the zoophyte could not plant its growing reg-
isters ?

The island of Ponape, in the Caroline Archipelago, affords
evidence of a suhsidence in progress^ as Mr. Horatio Hale, the
Philologist of the Wilkes Expedition, gathered from a for-
eigner who had been for a while a resident on this island.

SUBSIDENCE IN PACIFIC CORAL BEQIONS. 331

Mr. Hale remarks, after explaining the character of certain
sacred structures of stone : " It seems evident that the con-
structions at Ualan and Ponape are of the same kind, and
were built for the same purpose. It is also clear that when
the latter were raised, the islet on which they stand was
in a different condition from what it now is. For at j^resent
they are actually in the water ; what were once paths are now
passages for canoes, and as O'Connell [his informant] says,
' when the walls are broken down, the water enters the enclo-
sures. ' " Mr. Hale, hence infers " that the land, or the whole
group of Ponape, and perhaps all the neighboring groups,
have undergone a slight depression." He also states respect-
ing a small islet near Ualan, " From the description given of
Leilei, a change of level of one or two feet would render it
uninhabitable, and reduce it, in a short time, to the same state
as the isle of ruins at Ponape."

In some of the northern Carolines, the Pescadores, and
perhaps some of the Marshall Islands, the proportion of dry
land is so very small compared with the great extent of the
atoll, that there is reason to suspect a slow sinking even at the
present time ; and it is a fact of special interest in connection
with it, that this region is near the axial line of greatest de-
pression, where, if in any part, the action should be longest
continued.

Among the Kingsmills and Paumotus, there is no reason
whatever for supposing that a general subsidence is still in
progress ; the changes indicated are of a contrary character.

IV. PERIOD OF THE SUBSIDENCE.

The period during which these changes were in progress,
extends back to the Tertiary era, and perhaps still farther back.

332 CORALS AND CORAL ISLANDS.

In the island of Metia, elevated two hundred and fifty feet,
the corals below were the same as those now existing, as far
as we could judge from the fossilized specimens. At the in-
ner margin of shore reefs, there is the same identity with ex-
isting genera. We do not claim to have examined the base-
ment of the coral islands, and offer these facts as the only ev-
idence on this point that is within reach. We cannot know
with absolute certainty that the present races of zoophytes
may not be the successors of others that flourislied, on the same
sites, even before the Tertiary era in Cretaceous and Jurassic
times ; but as yet have little reason in facts observed, for such
a conclusion. For a long time volcanic action may have been
too general and constant over the Pacific, for the growth of
corals; and this may have continued to interfere till a com-
paratively late period, if we may judge from the appearance
of the rocks, even on Tahiti. The subsidence has probably for
a considerable period ceased in most, if not all, parts of the
ocean, and subsequent elevations of many islands and groups
have taken place.

V. ELEYATIOISrS OF MODERN ERAS IN THE PACIFIC.

Since th^ period of subsidence discussed in the preceding
pages, there has been no equally general elevation. Yet va-
rious parts of the ocean bear evidence of changes confined to
particular islands, or groups of islands. While the former
exemplify one of the grander events in the earth's history, in
which a large segment of the globe was concerned, the latter
exhibit its minor changes over limited areas. The instances
of these changes are so numerous and so widely scattered, that
they afford convincing evidence of a cessation in the previous
general subsidence.

ELEVATIONS IN PAGIFIG CORAL REGIONS. e333

The most convenient mode of reviewing the subject is to
state in order, the facts relating to each group.

a. Paumotu Arclii2:)elago, — The islands of this archipelago
appear in general to have that height which the ocean may
give to the materials. Nothing was detected indicating
any general elevation in progress through the archipelago.
The large extent of wooded land shows only that the islands
have been long at their present level ; and on this point the
author's observations confirm those of Mr. Darwin. There
are examples of elevation in particular islands, however, some
of which are of unusual interest. The instances examined by
the Expedition, are those of Honden Island (or Henuake),
Dean's Island (or Nairsa), Aurora (or Metia), and Clermont
Tonnerre. Besides these, Elizabeth Island has been^ described
by Beechey, and the same author mentions certain facts rela-
ting to Ducie's Island and Osnaburgh, which afford some sus-
picions of a rise.

Honden Island or Henuake. — ^This island is wooded on its
different sides, and has a shallow lao-oon. The beach is eio-ht
feet high, and the land about twelve. There are three entrances
to the lagoons, all of which were dry at low water, and one
only was filled at high water. Around the lagoon, near the
level of high tide, there were numerous deserted shells of the
huge Tridacna, often a foot long, lying in cavities in the coral
rock, precisely as they occur alive on the shore reef. As theso
Tridacnas evide!itly lived where the shells remain, and do not
occur alive more than six or eight inches, or a foot at the most,
above low tide, they prove, in connection with the other facts,
an elevation of at least two feet.

Nairsa or Dean^s Island, — The south side of Dean's
Island, the largest of the Paumotus, was coasted along by the
Peacock, one of the Sloops of War of the Wilkes Exploring

334 CORALS AND COMAL 18LAKD8.

Expedition, and from the vessel we observed that the rim of
land consisted for miles 6i an even wall of coral rock, appar-
ently six or eight feet above high tide. This wall was broken
into rude columns, or excavated with arches and caverns ; in
some places the sea had carried it away from fifty to one hun-
dred rods, and then there followed again a line of columns,
and walls, with occasional arches as before. The reef, for-
merly lying at the level of low tide, had been raised above the
sea, and subsequently had undergone degradation from the
waves. The standing columns had some resemblance in cer-
tain parts to the masses seen here and there on the shore plat-
forms of other islands ; but the latter are only distantly scat-
tered masses, while on this island, for the greater part of the
course, there were long walls of reef-rock. The height, more-
over, was greater, and they occurred too on the leeward side
of the island, ranging along nearly its whole course, while the
north side, according to the map, is luooded throughout

The elevation here indicated is at least six feet] but it
may have been larger ; the observations were made from ship-
board.

Thirty miles to the southward of Dean's Island, we came
to Metia, one of the most remarkable examples of elevation in
the Pacific.

Metia, — This island has already been described, and its el-
evation stated at two hundred and fifly feet (See page 193.)

Clermont Tonnerre shows the same evidence of elevation
from Tridacnas, as Honden Island. Clermont Tonnerre and
Honden are on the northeastern limits of the Paumotus,

Mizaheth Island was early shown to be an elevated coral
island by Beechey. This distinguished voyager represents
it as having perpendicular cliffs over fifty feet in height.
From his description it is obviously like Metia ; the elevation

ELEVATIONS IN PACIFIC CORAL REGIONS, 335

is eighty feet. It is one of the southeastern Paumotus, near
Ducie's.

Ducie^s Island is described by Beechey as twelve feet high,
which would indicate a probable elevation of one or two feet.

Osnaburgh Island^ according to the same author, affords evi-
dence of having increased its height since the wreck of the Matil-
da, in 1792. He contrasts the change from a "reef of rocks,"
as reported by the crew, to "a conspicuously wooded island,"
the condition when he visited it ; and states, further, that the
anchor, iron works, and a large gun (4-pounder) of this vessel
were two hundred yards inside of the line of breakers. Cap-
tain Beechey suggests that the coral had grown, and thus in-
creased the height. But this process might have buried the
anchor if the reef were covered with growing corals (which
is improbable), and could not have raised its level. If there
has been any increase of height (which we do not say is cer-
tain), it must have arisen from an upheaval.

6. Tahitian Group. — The island of Tahiti presents no
conclusive evidence of elevation. The shore plains are said to
rest on coral, which the mountain debris has covered; but
they do not appear to indicate a rise of the land.

The descriptions by different authors of the other islands
of this group do not give sufficient reason for confidently be-
lieving that any of them have been elevated. The change,
however, of the barrier reef around Bolabola into a verdant
belt encircling the island, may be evidence that a long period
has elapsed since the subsidence ceased; and, as such a change
is not common in the Pacific, we may suspect that it has been
furthered by at least a small amount of elevation. The observa-
tion by the Eev. D. Tyerman with regard to the shells found at
Huahine high above the sea, may be proof of elevation ; but
the earlier erroneous conclusions with regard to Tahiti (on

336 CORALS AND CORAL ISLANDS.

which island masses of coral are carried by natives up the
mountain, to leave at the highest point reached, and also to
mark the limits between the land of different chiefs, and are
common from these causes, up to a height of fifteen hundred
feet), teach us to be cautious in admitting it without a more
particular examination of the deposit. Moreover, shells, even
large ones, are carried far away from the sea by Hermit
Crabs (Pagurids).

c. Hervey and Rurutu Groups.-^-These groups lie to the
southwest and south of Tahiti.

Mangaia is girted by an elevated coral reef three Jmndred
feet in height. Mr. Williams, in his Misuonavy Enterprises^
pages 48, 50 and 249, speaks of it as coral, with a small quan-
tity of fine grained basalt in the interior of the island ; he states
again that a broad ridge (the reef) girts the hills.

Atiu (Wateoo of Cook) is a raised coral island. Cook
Foy., i. 180, 197, obs'erves, that it is "nearly like Mangaia."
The land near the sea is only a bank of coral ten or twelve feet
high, and steep and rugged. The surface of the island is cov-
ered with verdant hills and plains, with no streams. It is de-
scribed by Williams in his Missionary Enter^prises, Mauke is
a low elevated coral island according to Williams, and Mitiaro
resembles Mauke. Okatutaia is a low coral island, not more
than six or seven feet high above the beach, which is coral
sand. It has a light-reddish soil.

Iturutu has an elevated coral reef one Jiitndred and fifty
feet in height, as stated by Stutchbury, and also Williams.
Tyerman and Bennet describe the island as having a high cen-
tral peak with lower eminences, and speak of the coral rock as
two hundred, feet high on one side of the bay and tliree hun-
dred on the other (ii, 102). — Ellis says that the rocks of the in-
terior are in part basaltic, and in part vesicular lava, iii. 393.

ELEVATIONS Ilf PACIFIC CORAL REGIONS. 337

With regard to the other islands of these groups, Manual^
Aitiitald^ Barotonga^ Bimetara^ Tuhua^ and Baivavai^ tlie de-
scriptions by Williams and Ellis appear to show that they have
undergone no recent elevation.

cL Tonga or Friendly Islands^ and others in their vicinity.

All the islands of the Tonga group about which there are
reefs, give evidence of elevation : Tongatahu and the Hapaii
islands consist solely of coral, and are elevated atolls.

Eua^ at the south extremity of the line, has an undulated
mostly grassy surface, in some parts eight hundred feet in
height. Around the shores, as was seen by us from shipboard,
there is an elevated layer of coral reef-rock, twenty feet thick,
worn out into caverns, and with many spout-holes. Between
the southern shores and the highest part of the island, we ob-
served three distinct terraces. Coral is said to occur at a height
of tliree hundred feet. From the appearance of the land, we
judged that the interior was basaltic ; but nothing positive was
ascertained with regard to it.

Tongatahu (an island visited by us) lies near Eua, and is in
some parts fifty or sixty feet higii, though in general but twen-
ty feet. It has a shallow lagoon, into which there are two en-
trances ; some hummocks of coral reef -rock stand eight feet out
of water.

Namuka and most of the Hapaii cluster, are stated by Cook
to have abrupt limestone shores, ten to twenty feet in height,
Namuka has a lagoon or salt lake at centre, one and a half miles
broad; and there is a coral rock in one part twenty-five feet
high. It is described by Williams, p. 296.

Vavau^ the northern of the Group, according to Williams
(p. 427), is a cluster of elevated islands of coral limestone,
thirty to one hundred feet in height, having precipitous cliffs,
with manv excavations alonor the coast.

22

338 C0BAL8 AND CORAL ISLANDS.

JPylstaar(s Island, south of Tongatabu, is a small rocky
islet without coral. Tafua and Prohy are volcanic cones, and
the former is still active.

Savage Island^ a little to the east of the Tonga Group, re-
sembles Vavau in its coral constitution and cavernous cliffs. It
is elevated, according to Williams (pp. 275, 276), one liun-
dredfeet.

Beveridge Reef^ a hundred miles southeast of Savage, is low-
coral.

e. Samoan or Navigator Islands. — No satisfactory evi-
dences of elevation were detected about these islands.

f. Atolls^ north of Samoa.

On account of the high tides (4 to 6 feet), the sea may
give a height of twelve to sixteen feet to the land.

Swai7i'Sj near latitude 11° S., is fifteen to eighteen feet
above the sea where highest, and the beach is ten to twelve
feet high. It is a small island, with a depression at centre, but
no lagoon. Probably an elevation of two or three feet.

Fahaafo^ ninety miles to the north, is fifteen feet high. The
coral reef-rock is raised in some places three feet above the
present level of the platform. Elevation at least three feet.

Nukunono^ or Duke of Clarence, near Fakaafo, was seen
only from shipboard.

Oatafu^ or Duke of York's, is in some parts fourteen feet
high. Whether elevated or not is uncertain ; probably as
much so as Fakaafo.

g. ScaMered islands farther north^ near the equator^ east of
the Gilbe7't Gioup.

Of the Fanning Group, Washington Island^ in lat. 4° 41^
S., and 160° 15^ W., is three miles in diameter, and is without
a proper lagoon ; the whole surface is densely covered with co-
coanut and other trees. The height of the land is ten or twelve

ELEVATIONS IN PACIFIC CORAL REGIONS. 339

feet The unusual size of the island for one without a lagoon,
and the luxuriance of the forest vegetation, are probable evi-
dence of some elevation, but not beyond three feet.

Palmyra Island^ northeast of Washington, is described
by Fanning as having two lagoons, the westernmost with
twenty fathoms water.

Fanning' 8 Island^ southeast of Washington, according to
the same voyager, is lower than that island. The accounts
give no evidence of elevation in either Fanning's or Pal-
myra.

Christmas Island, in lat. 1^ 53' N., 157^ 32' W.,is thirty
miles long, and is described by Cook as having the rim of
land in some parts three miles wide. He speaks of narrow
ridges lying parallel with the seacoast, which ^'must have
been thrown up by the sea, though it does not reach within a
mile of some of these places." The proof of elevation is de-
cided, but its amount is uncertain. The account of J. D.
Bennett {Geogr. Journ., vii. 226), represents it as a low coral
island.

Jarvis's Island, in 0^ 22' S., and 159° 58' W., is, ac-
cording to J. D. Hague, eighteen to twenty-eight feet in
height, which would indicate an elevation of at least eight
or ten feet. See further page 291.

Maiden's, in 4° 15' S., 155° W., two hundred and fifty
miles southeast of Jarvis, visited by Lord Byron, is described
by him as not ovev forty feet high. It is ten miles long.

StarhucKs, or Hero Island, in 5° 40' S., 155° 55' W., is
an elevated lagoon island ; but the amount of elevation is not
stated. Like Jarvis's, it contains a large deposit of gypsum,
but not much guano. — (J. D. Hague.)

PenrhyrHs Island^ near 9° S. and 157° W., has a length
of nine miles, and an extensive lagoon with a boat entrance

340 CORALS AND CORAL ISLANDS.

into it According to Captain Einggold of the Wilkes Ex-
pedition, it has a height of fifty feet, which, if correct, Avould
indicate an elevation of full thirty-five feet The northwest
side is, throughout, a cocoanut grove.

Flint's Island, in 11^ 26' S., and 151^ 48' W., is only a
mile and a half long, but is thickly wooded, according to Cap-
tain Ringgold, which is unusual for so small an island.

Staver's Island, in 10° 05' S., and 152° 22^' W., is only
half a mile across, and yet is well wooded. Both of these
islands were passed bj^ Captain Ringgold, but he does not
state the height — (Wilkes's Narr., iv. 277.)

Bakei^'s Island, 0° 13' N., 176° 22' W., is one mile
long and two-thirds of a mile wide. The greatest height,
according to J. D. Hague, is twentj-two feet, '' showing some
evidences of elevation." (See further, p. 289.) It has prob-
ably been elevated at least six feet.

Howland's Island, 0° 51' N., and 176° 32' W., and about
forty miles north of Baker's. It is about one and one-half
miles long, and one-half mile wide. The highest point, accord-
ing to Hague, is ten or twelve feet above high-tide level;
which is evidence of but little if any elevation. It is a guano
island like Baker's.

McKean's Island, of the Phcenix Group (like Phoenix, En-
derbury, and Birnie's), in 3° 35' S., 174° 17' W., is a low
island, according to Hague, circular in form, one-quarter of a
mile in diameter, but less elevated than Jarvis Island, It has
a lagoon depression in which there is a gypsum and guano de-
posit ; and at high tides the guano is sometimes two feet under
water. Phoenix's Island, near McKean's, 3° 40' S., 170° 52'
W., is less than half a mile in diameter, and the border is only
eight or ten feet high ; so that there is no evidence in the
height of an elevation. It is also a guano island.

ELEVATIONS IN CORAL PACIFIC REGIONS. 341

Endevlury's, in 3° 8' S., 174^ 14' W., is eighteen feet
high. It has j)robably experienced some elevation. But the
height of the tides is such in the seas as to give the beach and
drift sands much greater height than they have in the Paumo-
tus. Birnie's Island is a small bank of coral, only six feet
above the sea, according to Wilkes (Narr., V. 4).

Gardner's^ IIuWs^ Sydney and Newmarket were visited
by the Wilkes Expedition. No satisfactory evidences of ele-
vation were observed on the first three. Newmarket is stated
by Captain Wilkes to have a height of twenty-five feet, which
would indicate an elevation of six or eight feet.

h. Sandivich or Ilaivaian Islands, — Oahu affords decisive
proof of an elevation of twenty-five or thirty feet. There is an
impression at Honolulu, derived from a supposed increasing
height in the reef off the harbor, that the island is slowly ris-
ing. Upon this point we have nothing satisfactory. The pres-
ent height of the reef is not suflSciently above the level to which
it might be raised by the tides, to render it certain, from this
kind of evidence, that the suspected elevation is in progress.

Kauai presents us with no evidence that the island, at the
present time, is at a higher level than when the coral reefs be-
gun ; or, at the most, no elevation is indicated bej^ond a foot or
two. The drift sand-rock of Koloa appears to be a proof of
elevation, from its resemblance to that of Northern Oahu ; but
if so, there must have been a subsidence since, as it now forms
a cliff on the shore that is gradually wearing away.

Molokai^ according to information from the Rev. Mr. An-
drews, has coral upon its declivities three hundred feet above
the sea.

Mr. Andrews, in his communication, informed the author
that the coral occurs " upon the acclivity of the eastern or high-
est part of the island, over a surface of more than twenty or

342 CORALS AND COJRAL ISLANDS.

thirty acres, and extends almost to the sea. We had no means
of accurately measuring the height ; but the specimens were ob-
tained at least three hundred feet above the level of the sea,
and probably four hundred. The specimens have distinctly the
structure of coral. The distance from the sea was two to three
miles."

Coral has been reported to occur on the western peninsula
of Maui^ in some places eight hundred feet above the sea ; but
according to C. F. Winslow, the supposed coral does not eflFer-
vesce with acids, and therefore is not calcareous.

There are large masses of coral rock, according to Mr. An-
drews, along the shores of Maui, from two to twelve feet above
high water. From his descriptions, this rock appears to be
the reef -rock, like the raised reef of Oahu, and is probably
proof of an elevation of at least tiuelve feet.

On page 324, it is suggested that the westernmost coral
islands of the Hawaian range. Ocean and Brooks's Islands,
may have undergone a small subsidence. Should the bro-
ken wall of emerged rock turn out, on examination, to be
coral reef -rock, instead of the beach sand-rock, the facts would
prove an elevation of a few feet, instead of a subsidence. The
islands differ from Dean's, in having no long range of wooded
land on the windward side.

i. Feejee Islands. — The proofs of an elevation of four to six
feet about the larger Feejee Islands, Viti Lebu and Vanua
Lebu, and also Ovalau, are given in the author's report on this
group. How far this rise affected other parts of the group, he
was unable definitely to determine ; but as the extensive bar-
rier reefs in the eastern part of the group, rarely support a green
islet, they rather indicate a subsidence in those parts than an
elevation.

j. Islands north of the Feejees. — Home Island, Wallis, EI-

ELEVATIONS IN PACIFIC CORAL REGIONS. 343

lice, Depeyster, and four islands on the track toward the Kings-
mills, were passed by the sloop of war Peacock of the Wilkes
Expedition ; but from the vessel, no evidences of elevation could
be distinguished. The first two are high islands, with bar-
riers, and the others are low coral. Rotuma (177° 15'' E.,
and 12° 30' N.), is another high island, to the west of Wal-
lis's. It has encircling reefs, but we know nothing as to its
chansres of level.

h Kirigsmill or Gilbert Group. (Map, p. 165.)
Tapateuea or Drumviond. — This is one of the southern
islands of the group. The reef-rock, near the village of Utiroa,
is a foot above low-tide level, and consists of large massive As-
traeas and Maeandrinas. The tide in the Kingsmill seas is seven
feet ; and consequently this evidence of a rise might be doubted,
as some corals may grow to this height where the tide is so high.
But these Astrseas and Maeandrinas, as far as observed by the
writer, are not among the species that may undergo exposure
at low tide, except it be to the amount of three or four inches ;
and it is probable that an elevation of at least one foot has
taken place.

Apaiang or Charlotte! s Island, one of the northernmost of
the group, has the reef-i'ock in some parts raised bodily to a height
of six or seven feet above low-water level, evidencing this
amount of elevation. This elevated reef was observed for long
distances between the several wooded islets ; it resembled the
south reef of Nairsa in the Paumotu Archipelago in its bare,
even top, and bluff, worn front. An islet of the atoll, where we
landed, was twelve feet high, and the coral reef -rock was five
or six feet above middle tide. A wall of this rock, having the
same height extends along the reef from the islet There was
no doubt that it was due to an actual uplifting of the reef to a
height of full six feet.

344 cohals and coral islands.

Nonouti^ Kuria^ Maiana^ and Tarawa^ lying between the
two islands above mentioned, were seen only from the ship, and
nothing decisive bearing on the subject of elevation was ob-
served. On the northeast side of Nononti there was a hill
twenty or thirty feet in height covered with trees ; but we had
no means of learning that it was not artificial. We were, how-
ever, informed by Kirby, a sailor taken from Kuria, that the
reef of Apamama was elevated precisely like that of Apaiang, to
a height of five feet ; and this was confirmed by Lieutenant De
Haven, who was engaged in the survey of the reef. We were
told, also, that Kuria and Nononti were similar in having the
reef elevated, though to a less extent. It would hence appear
that the elevations in the group increase to the northward.

Marakei^ to the north of Apaiang, is wooded throughout.
We sailed around it without landing, and can only say that it
has probably been uplifted like the islands south. Maldn^ the
northernmost island, presented in the distant view no certain
evidence of elevation.

The elevation of the Kingsmills accounts for the long con-
tinuity of the wooded lines of land, an unusual fact considering
the size of the islands. The amount of fresh water obtained
from springs is also uncommon, (p. 283).

I. The Marshall and Caroline Islands. — The facts in
reference to the islands of these groups, are not yet fully known.
The very small amount of wooded land on the Pescadores in-
clines us to suspect rather a subsidence than an elevation ; and
the same fact might be gathered, with regard to some of the
islands south, from the charts of Kotzebue and Kruesenstern.
But McAskill's, as stated on page 306, is an elevated coral
island, having a height of 100 feet.

m. Ladrones. — The seventeen islands which constitute this
group may all have undergone elevations within a recent pe-

ELEVATIONS IN CORAL PACIFIG REGIONS.

345

nod, but owing to the absence of coral from the northern, we
have evidence only with regard to the more southern.

Giiam^ according to Quoy and Gaymard, has coral rock upon
its hills more than six hundred feet (one hundred toises) above
the sea.

Rota^ the next island north, afforded these authors similar
facts, indicating the same amount of elevation.

71. PeleiU'9^ and neighhoring Islands, — The island Feis^ three
hundred miles southwest of Guam, is stated by Darwin, on the
authority of Lutke, to be of coral, and ninety feet high. Mack-
enzie Island, seventy-five miles south of Feis, is a low atoll,
as ascertained by the Expedition. No evidences of elevation
are known to occur at the Pelews.

0. Melanesian Islands, — Among the New Hebrides, New
Caledonia, Salomon Islands, the evidences of elevation have
not yet been examined.

The details given on the preceding pages are here present-
ed in a tabular form.

Paumotu Archipelago,

Tahiti

<c

u

an Group,

Hervey and Rurutu Groups,

(( u

«

(C

(C ((

((

((

(( ((

«

(C

U ((

(C

u

u u

a

C(

Tongan Group,

(C ((

(( ((

Honden, 2 or 3

Clermont Tonnerre, . • , . 2 or 3

Nairsa or Dean's, 6

Elizabeth, 80

Metia or Aurora, 260

Ducie's, 1 or 2?

Tahiti, 0?

Bolabola, ?

Atiu, 12?

Mauke, .... somewhat elevated.
Mitiaro, .... " "

Mangaia, 300

Rurutu, 150

Remaining Islands, ?

Eua, 300?

Tongatabu, 50 to 60

Namuka and the Hapaii, • • . 25
Vavau, 100

346 CORALS AND COBAL ISLANDS,

FEET.

Savage Island, lOO

Samoan or Navigator Islands,

North of Samoa, Swain's, 2 or 3

" " " Fakaafo, or Bowditch, 3

" " " Oatafu, or Duke of York's, . 2 or 3

Scattered Equatorial Islands, . Washington, 2 or 3 ?

" " Christmas, ?

" " " Jarvis's, 8 or 10

Maiden's, 25 or 30

" " « Starbuck's, ?

" " " Penrhyn's, 35

" " " Flint's and Staver's, ?

" " Baker's, 5 or 6

" " Rowland's, ?

" " " Pha3nix and McKean's, ....

" " " Enderbury's, 2 or 3 ?

" " " Newmarket, 6 or 8 ?

" " " Gardner's, Hull's, Sydney, Birnie's, ?

Feejee Islands, Viti Levu and Vanua Levu,

Ovalau, 5 or 6

Eastern Islands, ?

North of Feejees, Home, Wallis, Depeyster, . . . ?

Ellice 5 or 6

Sandwich Islands, Kauai, 1 or 2

" " Oahu, 25 or 30

" " Molokai, 300

" " Maui, 12

Gilbert Islands, Taputeuea, 2 or 3

" " Nonouti, Kuria, Maiana and

Tarawa, 3 or more.

Apamama, 5

Apaiang or Charlotte, . . . 6 or 7

Marakei, 3 or more.

Makin, ?

Carolines, McAskill's, 60

Ladrones, Guam, 600

" Rota, 600

Feis, 90

Pelews, 0?

New Hebrides, New Caledonia, Salomon Islands, ?

Several deductions are at once obvious: —

1. That the elevations have taken place in all parts of the

ocean.

((

a

u

a

<(

u

(C

u

ELEVATIONS IN PACIFIC CORAL REGIONS, 347

2. That they have in some instances affected single islands,
and not those adjoining. Metia is 250 feet high, and yet the
other Pauniotus in that part of the archipelago, and also the
Tahitian islands, have been but little, or not at all, elevated.

3. That the amount is often very unequal in adjacent
islands.

4. That in a few instances the change has been experienced
by a whole group or chain of islands. The Gilbert Group
is an instance, and the rise appears to increase from the south-
ernmost island to Apaiang, and then to diminish again to
the other extremity.

The Feejees may be an example of a rise at the west side
of a group, and possibly a subsidence on the east; while a
little farther east, the Tonga Islands constitute another ex-
tended area of elevation. We observe that while the Samoan
Islands afford no evidences of elevation, the Tonga Islands on
the south have been raised, and also the Fakaafo Group and
others on the north.

We cannot, therefore, distinguish any evidence that a gen-
eral rise is, or has been, in progress; yet some large areas ap-
pear to have been simultaneously affected, although the action
has generally been isolated. Metia and Elizabeth Island may
have risen abruptly ; but the changes of level in the Feejees
and the Friendly Islands, appear to have taken place by grad-
ual action.

348 COEALS AND GOBAL ISLANDS.

CHAPTER VI.
GEOLOGICAL coisrcLusioisrs.

The geological bearing of the facts that have been de-
tailed in the preceding pages, may have been already perceived
by our readers. A brief review of the points of more special
interest, may serve as a convenient recapitulation of the sub-
ject.

I. FORMATION OF LIMESTONES

Coral reefs are beds of limestone made of corals, with the
help of shells. The mode of formation is essentially the same,
whichever of the two kinds of organic products, corals, or
shells, predominate; although in one case the bed would be
called coral limestone, and in the other, shell limestone.

The reefs illustrate two different modes of origin of such
beds : (1), by undisturbed growth, with only additions of fine
material to fill up the intervals ; (2), by the grinding of the
corals, etc., to fragments, sand, or mud, through the agency
of the waves.

Beds made by the former method, have many open spaces
between the grouped masses or branches, and could not be
turned into a solid layer of limestone, if situated too deep in
the ocean to feel sensibly the move nent of the waves, — unless
Rhizopods, or minute shells of some kinds, multiplied so rap-
idly over the same sea-bottom, as to fill up the interstices.
There is no reason to believe that such aid from shells or

GEOLOGICAL C0NCLTISI0N8, 349

Rhizopods is consistent with the grouping of living corals
thickly enough to form reefs.

The other kind of limestone beds referred to, where un-
mixed with the former, grow up in compact layers to the
surface, as a necessary consequence of wave-action ; and lime-
stones are made in such regions, instead of sandstones and
shales, because the material exposed to degradation is corals
and shells, instead of common rocks.

The facts show that there are formed about coral reefs,
in indefinite amount, all the ordinary products of degrada-
tion by wave-action — fragments large and small, down to
sand, and even mud. With such an agent as the ocean's
waves, driven often by the storm, so powerful and so per-
sistent at lifting, rending, grinding, and transporting, it is of
little account, at least about outer reefs, that some coral
stems or masses are first weakened below by the boring
sponge or mollusk ; and neither fish, nor holothurian, nor alcy-
onoid is needed, in order to keep up the supply of particles
for sand or mud-beds. In accordance with these facts, the reef-
formations illustrate that not only coral conglomerates, or coral
rag^ may be made of corals, but also the Yery finest and most
compact unfossiliferous limestones ; that fine compact lime-
stone, as flint-like in fracture as any of Silurian time, is one of
the most common of coral-reef rocks, and is nothing but con-
solidated mud, or fine sand, of coral origin.

The elevated portion of the island of Matea, which con-
sists largely of this kind of white, compact, coral-made lime-
stone, appears to correspond to the interior of the original lar
goon of the island; it exemplifies the kind of rock making
which is going forward in most coral island lagoons. In
archipelagos like that of the Feejees, where the reef chan-
nels are very broad, there is an opportunity for the formation

350 CORALS AND CORAL ISLANDS,

of very large areas of this compact white limestone, and also
for others of impure or argillaceous limestones.

Besides the kinds of coral rocks above mentioned, there are
also the Beach and Drift Sand'roclc6\ which are accumulated
and consolidated above low- tide level. These formations illus-
trate one common mode of origin of oolitic limestones.
They also afford numerous examples of the formation of
coarse and fine conglomerates consisting of beach pebbles —
these pebbles being either worn corals, or shells, or sometimes
of other kinds, if other rocks are at hand.

The uniform slope of the beach sand-rock and oolite, and
the mixed stratification of the drift sand-rock, are identical re-
spectively with those of beach and drift-sand deposits in other
regions.

II. BEDS OP LIMESTONE WITH LIVING MARGINS.

The coral reef as it lies at the water's level is in fact a bed
of limestone with living margins ; and the living part fur-
nishes material for its horizontal extension outward, and also,
if a slow subsidence is in progress, for its increase upward.
It illustrates an ordinary mode of formation of coral, or of
shell, limestone, whatever the age.

III. MAKING OF THICK STRATA OF LIMESTONE.

The coral reef-rock has been sho^vn to have in some cases
a thickness of at least 2,000 feet (page 156.) The reefs are,
therefore, examples of great limestone strata, nearly as re-
markable in this respect as the largest of ancient times.

IV. SUBSIDENCE ESSENTIAL TO THE MAKING OF THICK STRATA.

The coral island reef-rock has been shown to depend for
its thickness on a slowly progressing subsidence (p. 258).

GEOLOOIGAL CONCLUSIONS. 351

This is the only method by which any thick stratum of lime-
stone could be made out of a single set of species, for all
such species have a narrow range in depth ; and the only way,
from any succession of species, if those species are alike in
range of depth. •

In the case of existing coral reefs, there is yet no evidence
that the species of the lower beds differ from those of the top.
There is also no evidence, in any part of any ocean, that there
is a set of cold-water corals fitted to commence a reef in deep
water and build it up to such a level that another set of
species may take it and carry it up higher; the facts thus far
gathered are all opposed to such an idea. Should it be here-
after proved that the corals of the inferior beds differ in
species from those now existing, it will probably be found that
the predecessors of those now living were also shallow-water
species ; so that the subsidence in any case was necessary.

V. DEEP-SEA LIMESTONES SELDOM IF EVER MADE FROM CORAL
ISLAND OR REEF DEBRIS.

This point has been discussed on pages 143, 211. The facts
show that the sediment or debris from a shore is almost wholly
thrown back by the waves against the land where it originated,
or over its submerged part in the shallow waters, and that it
is not transported away to make deep sea formations.

The facts have also a wider bearino;, for thev teach that
lands separated by a range of deep ocean cannot supply one
another with material for rocks. The existence of an Atlan-
tic ocean continent — an Atlantis — has sometimes been assumed
in order to make it a source of the mud, sand and gravel, out
of which the thick sedimentary formations of the Appalachian
region of North America were made. But if this Atlantis
were a reality, there would still have been needed, in addition

352 CORALS AND CORAL ISLANDS.

to the presence of such an ocean continent, a set of freight
carriers that could beat off the waves from their accustomed
work, and push aside the ordinary oceanic currents ; or else

Atlantis would get back all its own dirt.

i

VI. ABSENCE OF FOSSILS FROM LIMESTONE STRATA.

Absence of fossils has been mentioned as a frequent char-
acteristic of the fine compact coral reef-rock, and also of the
beach and drift sand- rock or oolite (pp. 153, 194). The rocks
are formed at the sea-level, and in the midst of abundant life,
and yet trituration by the action of the waves and winds has
in many places reduced all to the finest material, so that an em-
bedded shell is seldom to be found in the beach or drift oolite,
and rarely too in much of the fine-grained coral reef-rock.

The lagoon basin af)pears to be eminently the place for
making these non-fossiliferous limestones. This is the case in
two widely different conditions : first., over the portions that are
below the coral- growing depths, which are sometimes of great
area ; and second., in lagoons that have become so small and
shallow that corals and large shells have all disappeared, and
the trituration is of the finest kind, producing calcareous mud ;
such lagoons being properly in a marsh condition. These last
appear to illustrate on a small scale the conditions under which
many of the ancient non-fossiliferous, or sparingly fossiliferous,
limestones were formed.

VII. THE W^IDE RANGE OF THE OLDER LIMESTONES NOT EXEMPLIFIED
AMONG MODERN CORAL-REEF FORMATIONS.

Coral-reefs, though they may stretch along a coast for scores
of miles, are seldom a single mile in width at the surface ; and if
elevated above the sea, they would stand as broad ramparts
separated by passages mostly 20 to 200 feet deep, and often of

GEOLOGICAL CONCLUSIONS. 353

great width. The substratum, however, is, in general, contin-
uous coral-rock; and if these more elevated parts were re-
moved by any process, after an elevation, they would leave a
nearly level area of coral limestone often as extensive as the
whole reef-grounds. This is at once seen from the map of the
islands of the Gilbert Group (p. 165), or that of the Feejees.
In an island like Dean's, one of the Paumotus, these reef-
grounds are 1,000 square miles in extent.

But the most extensive reef-grounds of the oceans are after
all of small breadth compared with many of the ancient lime-
stones of the continents ; and the reef-rocks also are peculiar
in their very abrupt limits, the margins sometimes descending
at a steep angle a thousand feet or more. These differences
between the new and the old arise in part from the fact that
the coral reefs of the present era are made about small oceanic
lands, or along the edges of the continents, while the limestones
of ancient time were generally formed over the broad surface
of a continent as it lay slightly submerged.

The Abrolhos reefs of the Brazilian coast, described on page
140, illustrate one of the methods by which the coral banks ex-
tend and finally coalesce into beds of wide extent ; but these
are small compared with the great limestones of early time,
and owe their slight approximation to them as regards extent
to the wide range of shallow waters there afforded. These
Abrolhos reefs differ from most limestone beds also in being
formed largely of the corals in the position of growth.

The tendency of modern reefs to grow up to the surface in
narrow banks, separated by channels, appears to be unlike any
thing we discover in the old rocks ; and it seems to be an un-
avoidable result of growth in the sea, where the waves pile up
barriers, and the currents make, and keep open, channels. The
case of the Australian and Feejee reefs are good examples It

23

354 C0RAL8 AND CORAL ISLANDS,

is possil)le that such barriers may often have existed in ancient
time, and have disappeared through subsequent denudation of
the surface. But may not the difference between the great even
layers of the continental formations and those of a coral island
have proceeded from the difference in the depth of the seas?
Over the great shallow continental seas where the limestones
were in progress, the waves may have generally been feeble,
and therefore there may have been a less tendency to form nar-
row barriers and deep intervening channels.

The marsh condition of a drying-up lagoon with its forming
limestones has been compared above with that under which an-
cient unfossiliferous limestones were made. The narrow limits
of the former make the comparison unsatisfactory ; for, in the
coral island, coarsely fossiliferous beds are all the while form-
ing about the exterior of the island, but a few miles at the
most from the lagoon-marsh ; while the ancient limestones re-
tain their unfossiliferous character often through many thou-
sands of square miles. Still, the above mentioned difference be-
tween the continental sea and the existing deep oceans may
perhaps account for the diversity of results.

VIII. CONSOLIDATION OF CORAL ROCKS.

All true coral-reef rocks are examples of the consolidation
of material mainly of coral origin — either mud, sands, frag-
ments, or standing corals, tbe last with mud or sands inter-
mixed — ^by (1), an under-water process; (2), at the ordinary
temperature ; and they exemplify the mode in which all other
submarine limestones of organic origin have been consolidated.
The process appears to depend on the presence (proved by
chemical analysis) of carbonic acid in the sea waters that bathe
and penetrate the sands. This carbonic acid is derived from
three sources: from (1), the rains which wash it down from

GEOLOGICAL CONCLUSIONS. 355

the atmosphere ; (2) the respiration of all the animal life in
the waters, even down to the simplest and minutest ; and (3)
the decomposition of all vegetable or animal debris in the
waters or diffused through the sand or muds. This gas is set
free, therefore, just where it is needed for the work, and is
always ready to perform its part in the process of consolida-
tion. It enables the water to take up carbonate of lime from
the grains of the mass to be solidified, or from outside sources ;
and then the deposition of the same among the grains through
their attractions produces the cementation.

The beach and drift sand-rocks or oolites are different
from the reef-rock in being superficial deposits. The carbonic
acid of the waters performs the same part as in the latter ; but
with these, there is alternate wetting and drying during the
ebb and flow of the tides and the succession of gales and quiet
winds. By this means, the grains become incrusted, and every
new wetting and drying adds a new layer to the surface of each ;
and thus the oolitic structui'e is produced. Facts are men-
tioned on page 153 of pebbles of volcanic or basaltic rocks,
lying loose on a seashore, becoming incrusted in this way with
a milky layer ; and of basaltic conglomerates being made by
the same means, the carbonate of lime being added until all
the intervals between the stones were filled up and the whole
made solid ; and of an amygdaloidal volcanic rock on a coast
having derived its little calcareous kernels or amygdules from
the same source. The following additional facts are cited
from Mr. Darwin's Journal (p. 588) :

" Lieutenant Evans informs me that during the six years
he has resided on this island (Ascension) he has always ob-
served that in the months of October and November, when
the sand [of a calcareous beach] commences travelling to-
ward the southwest, the rocks which are situated at the end

356 CORALS And coral islands.

of the long beach become coated by a white, thick, and very
hard calcareous layer. I saw portions of this remarkable
deposit, which had been protected by an accunmlation of
sand. In the year 1831 it was much thicker than during any
other period. It would appear that the water charged with
calcareous matter, by the disturbance of a vast mass of calca-
reous particles only partially cemented together, deposits this
substance on the first rocks against which it impinges. But
the most singular circumstance is that, in the course of a
couple of months, this layer is either abraded or redissolved,
so that after that period, it entirely disappears. It is curious
thus to trace the origin of a periodical incrustation, on certain
isolated rocks, to the motion of the earth with relation to the
sun ; for this determines the atmospheric currents which give
direction to the swell of the ocean, and this again the arrange-
ment of the sea-beach, and this again the quantity of calcareous
matter held in solution by the waters of the neighboring sea."

Mr. Darwin, speaking of a large beach of calcareous sand
composed of comminuted and rounded fragments of shells and
corals at Ascension, says, " The lower part of this, from the
percolation of water containing calcareous matter in solution,
soon becomes consolidated and is used as a buildinsr stone :
but some of the layers are too hard for fracture, and when
struck by the hammer, ring like flint."

The surface of hills of drift sand-rock often has small de-
pressions that are coated with a smooth, solid crust, as al-
ready explained.

IX. FORMATION OF DOLOMITE OR MAGNESIAN CARBONATE OF LIME.

Analyses of the coral limestone of the elevated coral island
Matea, by Prof. B. Silliman, Jr., have determined the singular
fact that, although the corals themselves contain very little

OEOLOOICAL CONCLUSIONS. 357

carbonate of magnesia, magnesia is largely present in some
specrmens of the rock. The rock is hard (H. = 4), and splints
ery in fracture, with a specific gravity 2*690. It affords
on analysis, 38*07 per cent, carbonate of magnesia, and hence,
only 61*93 of carbonate of lime.

Another specimen from the same island, having the spe-
cific gravity 2*646, afforded 5*29 per cent, of carbonate of mag-
nesia.

The former was a compact homogeneous specimen, and the
latter was partly fragmentary. Recent examinations of coral
sand and coral mud from the islands, give no different com-
position, as regards the magnesia, from that for corals, which,
as the analyses on page 99 show, contain very little or no
magnesia. , The coral sand from the Straits of Balabac, af-
forded Prof. Silliman carbonate of lime 98*26, carbonate of
magnesia 1*38, alumina 0*24, phosphoric acid and ^ilicaa trace.

This introduction of magnesia into the consolidating
under-water coral sand ortnud, has apparently taken place (1)
in sea waters at the ordinary temperature; and (2) without
the agency of any mineral waters except the ocean. But the
sand or mud may have been that of a contracting and evap-
orating lagoon, in which the magnesian and other salts of the
ocean were in a concentrated state. It has been already ob-
served (p. 349), that this was probably the actual condition
of the elevated portion of the island of Matea, every thing
about it looking as if it corresponded to the lagoon part of
the old atoll ; and also that the idea of the existence of min-
eral springs there has no support in known facts.

X. FORMATION OF CHALK.

The formation of chalk from coral is known to be ex-
emplified at only one spot among the reefs of the Pacific.

358 CORALS AND CORAL ISLANDS.

The coral mud often looks as if it might be a fit material for
its production ; moreover, when simply dried, it has much the
appearance of chalk, a fact pointed out by Lieutenant Nel-
son in his Memoir on the Bermudas (1834), and also by Mr.
Darwin, and suggested to the author by the mud in the lagoon
of Honden Island. Still this does not explain the origin of
chalk ; for, under all ordinary circumstances, this mud solidi-
fies into compact limestone instead of chalk, a result which
would naturally be expected. What condition then is neces-
sary to vary the result, and set aside the ordinary process.

The one locality of chalk among the reefs of the Pacific,
referred to above, was not found on any of the coral islands,
but in the elevated reef of Oahu, near Honolulu, of which reef
it forms a constituent part. It is twenty or thirty feet
in extent, and eight or ten feet deep. The rock could not be
distinguished from much of the chalk of England : it is equal-
ly fine and even in its texture, as earthy in its fracture, and so
soft as to be used on the blackboard in the native schools.
Some imbedded shells look precisely like chalk fossils. It con-
tained, according to Professor Silliman, 92*80 per cent, of
carbonate of lime, 2*38 of carbonate of magnesia, besides
some alumina, oxyd of iron, silica, etc.

The locality is situated on the shores, just above high-tide
level, near the foot of Diamond Hill. This hill is an extinct
tufa cone, nearly seven hundred feet in height, rising from the
water's edge, and in its origin it must have been partly sub-
marine. It is one of the lateral cones of eastern Oaha, and
was thrown up at the time of an eruption through a fissure,
the lavas of which appear at the base. There was some coral
on the shores when the eruption took place, as is evident from
imbedded fragments in the tufa; but the reef containing the
chalk appeared to have been subsequent in formation, and

OEOLOOICAL CONGLUSIOFS. 359

afforded no certain proof of any connection between the firea
of the mountain and the formation of the chalk.

The fine earthy texture of the material is evidence that the
deposit was not a subaerial seashore accumulation, since only
sandstones and conglomerates, with rare instances of more
compact rocks, are thus formed. Sand-rock making is the
peculiar prerogative, the world over, of shores exposed to
waves, or strong currents, either of marine or fresh water. We
should infer, therefore, that the accumulation was produced
either in a confined area, into which the fine material from a
beach may have been washed, or on the shore of a shallow,
quiet sea ; in other words, under the same conditions nearly
as are required to produce the calcareous mud of the coral
island. But, although the agency of fire in the result cannot
be proved, it is by no means improbable, from the position
of the bed of chalk, that there may have been a hot spring at
the spot occupied by it. That there were some peculiar cir-
cumstances distinguishing this from other parts of the reefs, is
evident.

This, if a true conclusion, is to be taken, however, only as
one method by which chalk may be made. For there is no
reason to suppose that the chalk of the Chalk formation has
been subjected to heat. On the contrary, it is now well ascer-
tained that it is of cold-water origin, even to its flints, and that
it is made up largely of minute foraminifers, the shells of
Rhizopods. Professor Bailey found under his microscope
no traces of foraminifers, or of any thing distinctly organic,
in the Oahu chalk.

XI. RATE OF INCREASE OF LIMESTONE FORMATIONS.

On page 249 it is shown that coral-reef limestones are of
sloAV formation, the rate of increase in thickness, where all

360 CORALS AND CORAL ISLANDS.

is most favorable, not exceeding perhaps a sixteenth of an
inch a year, or five feet in a thousand years. And yet such
limestones probably form at a more rapid rate than those
made of shells, because the animals are to a larger extent
calcareous or make proportionally larger calcareous secretions ;
and in addition they have the property of rapid multiplica-
tion by budding. The mollusks that grow and multiply most
rapidly and have proportionally the largest shells are the
Lamellibranchs or bivalves, among which the oyster is a fa-
mous example ; and the Brachiopods were once the full equals
of the ordinary bivalves. Large banks of bivalves seldom
occur in regions of corals, the species there being to a great
extent Gasteropods (or univalves) ; and hence the contributions
of shells to coral reefs from mollusks are small compared
with the extent of the beds which, by themselves, they make
on other coasts. The coral seas of Florida nowhere have
shore shell-beds like those of St. Augustine in northern
Florida outside of the coral-reef seas. There is reason for
this in the fact that these bivalves that grow in large banks live
in beds of ordinary sand or mud, such as reef-regions do not
generally supply.

XII. LIMESTONE CAVERNS.

The elevated coral limestone, although in general a hard
and compact rock, abounds in caverns. They may be due in
part to open spaces, or regions of loose texture, in or between
the strata. But in most cases they are a result of solution
and erosion by the fresh waters of the land, or the waves and
currents of the ocean, subsequent to the elevation.

On the island of Metia, many caverns open outward in
the coral limestone cliff and in some were large stalactites, aa
stated on page 194.

GEOLOGICAL CONCLUSIONS, 361

In the raised coral rock of Oahu (p. 341) there are several
long winding horizontal chambers, some of which are the
sources of subterranean streams that open out on the shores
between the layers of the rock, or from the mouths of caverns.
These running waters, and others trickling from above, are
obviously the eroding agents that have made the caves.

As briefly remarked on page 194, caverns are still more re-
markable on the island of Atiu, on which the coral reef-rock
stands at about the same height above the sea as on Oahu,
Rev. John Williams states that there are seven or eight of
large extent on the island. Into one he entered by a descent
of twenty feet, and wandered a mile in one only of its branches
without finding an end '' to its interminable windings." He says,
'' Innumerable openings presented themselves on all sides as
we passed along, many of which appeared to be equal in height,
beauty and extent to the one we were following. The roof, a
stratum of coral rock fifteen feet thick, was supported by massy
and superb stalactitic columns, besides being thickly hung with
stalactites from an inch to many feet in length; some of these
pendents were just ready to unite themselves to the floor, or to
a stalagmitic column rising from it. Many chambers were
passed through whose fretwork ceilings and columns of stalac-
tites sparkled brilliantly, amid the darkness, with the reflected
light of our torches. The effect was produced not so much by
single objects, or groups of them, as by the amplitude, the
depth, and the complications of this subterranean world."

Other similar caves exist on the neighboring island of
Mauke.

The Bermudas are also noted for their caverns. The coral-
made land here stands in some places 260 feet above the sea.
Lieutenant Nelson speaks of the caverns as large and beauti
ful — one of them " a perfect bijou."

362 CORALS AND CORAL ISLANDS.

These are examples of the comparativel}' rapid formation
of caverns. The waters which run or percolate through them
must be charged with carbonic acid to accomplish such work,
and yet they have no source for this ingredient except the atmos-
phere, animal respiration, and vegetable and animal decom-
position in the soil. The flutings and stalactitic incrustations
of a precipice facing the sea must depend on the former alone,
with the aid perhaps of the spray from the sea brought over
the reef by storms.

Xni. OCEANIC TEMPERATURE.

Facts seem to indicate — though [)erhaps not sufficient to
demonstrate — that the Gulf Stream has had, from the Juras-
sic period in Geological history onward, the same kind of in-
fluence on the temperature of the North Atlantic Ocean which
it now has.

The existence of a coral reef made out of corals of the As-
traea tribe and others, during part of the Oolitic era (middle
Jurassic), in England, as far north as the parallel of 52"^ to
55^ is strong evidence that the isocryme of 68^ F., the coral-
reef boundary, extended then even to that high latitude ; for
species of the Astraea tribe are now confined to coral-reef seas
(p. 109). This isocryme now reaches along the course of the
Gulf Stream, to a point just north of the Bermudas, near
33^ N. ; and 55^ is 22° beyond this.

There are no marine fossils in any rocks of that period on
the American side of the Atlantic, so that facts fail for defi-
nitely locating the western terminus of this oolitic isocryme of
68° F. But it is highly improbable that the whole ocean
across, on, or near, the parallel of 55° N., should have had, as the
mean temperature for the coldest month of the year, one so high
as 68° F. ; the present average position of the isocryme of 68^ F.,

GEOLOGICAL CONCLUSIONS. 363

through the middle of the two oceans, the Pacific and Atlan-
tic, is near the parallel of 27^ or 28^, or one-half nearer the
equator than the parallel of 55^. It is difficult to account for
an oceanic temperature high enough to give England's seas
68^ F. as the average for the coldest winter month, even sup-
posing the Gulf Stream to have aided ; but it is vastly more
difficult if no such northeastward current existed, and the high
temperature extended equably so far from the equator. The
probability is therefore strong that the existence of coral reefs
in the Oolitic era in England was owing to the extension, by
the aid of the Gulf stream, of the isocryme of 68^ move than
30^ in latitude (and over 3,000 miles in distance) beyond its
present most extra-tropical position, just outside of the Ber-
mudas; in other words, that the whole ocean was just enough
warmer, to allow this oceanic current (part of the great
water-circulation of the glol)e) to bear the heat required for
corals as far north as northern Eno^land.

The present isocryme of 44^ F., as drawn on the chart of
the world accompanying this volume, has approximately the
course which that of 68^ F. probably had in Oolitic times. It
should have a little less northing, and the loop to the north
should lean more to the eastward. The latter would have been
a consequence of the submerged condition at the time of most
of the European continent.

The ocean's waters seem to have cooled somewhat before
the next period — the Cretaceous — ^began, since evidence fails
of any Cretaceous coral reefs in the British seas ; but such
reefs prevailed then in central and southern Europe, so that
the amount of cooling in the interval since the Oolitic era,
had not been large ; and as late as the Miocene Tertiary, there
were reef corals in the seas of Northern Italy, above latitude
45^ N., or that of Montreal, in Canada.

364 CORALS AND CORAL ISLANDS.

The absence from the American coast of the Atlantic,
of any coral reefs in the Cretaceous beds, and of any reef corals,
seem to show that the oceanic temperature off this coast was
not favorable for such corals; and if so, then the line of 68^
F. extended at least 20"^ farther north on the European side
of the ocean, than on the Atlantic — an inequality to be ac-
counted for in part by the existence of the Gulf Stream. But,
in addition, the whole range of life in the European Creta-
ceous, and its vastly greater variety of species, leave no doubt
as to the higher temperature of the ocean along its European
border ; so that the idea of a Cretaceous Gulf Stream must be
accepted. And that of a Tertiary is demonstrated by similar
facts.

If the Gulf Stream had its present position and force in
Oolitic, Cretaceous and Tertiary times, then the ocean had,
throughout these eras, its pi'csent extension and oceanic char-
acter ; and, further, no barrier of land extended across from
South America to the Canaries and Africa, dividing the South
from the North Atlantic, but all was one great ocean.
Such a barrier would not annul entirely the flow of the Gulf
Stream ; yet the North Atlantic is so small an ocean, that if
left to itself, its system of currents would be very feeble,

XIV. THE OCEANIC CORAL ISLAND SUBSIDENCE.

Coral islands have been shown to be literally monuments
erected over departed lands ; and, through the evidence from
such records, it is discovered that the Pacific has its deep-water
mountain chains, or lines of volcanic summits, not merely
hundreds, but thousands of miles in length. Some of the
ranges of high islands are proved by such records to have an
under- water prolongation, longer than that above water : the
Hawaian Islands for example, which have a length of only

THE OCEANIC CORAL-ISLAND SUBSIDENCE. 365

four hundred miles from Hawaii to Kauai, and five hundred
and thirty to Bird Island, the western rocky islet of the group,
stretch on westward, as the coral registers show, even to a dis-
tance of two thousand miles from Hawaii, or, as far as from
New York to Salt Lake City ; and how much farther is un-
known, as the line of coral islands here passes the boundary
of the coral reef seas, or the region where coral records are
possible.

Other ranges of submerged summits are shown to extend
through the whole central Pacific, even where not a rocky
peak remains above the surface; for all the coral islands from
the eastern Paumotus to Wakes' Island, near long. 170^ E.
and lat. 19^ N., north of the Ralick and Radack (or Marshall)
groups, are in linear ranges ; and they have, along with the
equally linear ranges of high islands just south, a nearly uni-
form trend, curving into northwest and north-northwest at the
western extremity. The coral islands consequently cap the sum-
mits of linear ranges of elevations, and all these linear ranges
together constitute a grand chain of heights, the whole over five
thousand miles in length. Thus, the coral islands are records
of the earth's submarine orography, as well as of slow changes
of level in the ocean's bottom.

This coral island subsidence is an example of one of the
great secular movements of the earth's crust. The axis of the
subsiding area — the position of which is stated on page 328,
has a length of more than six thousand miles — equal to one-
quarter of the circumference of the globe ; and the breadth,
reckoning only from the Sandwich Islands to the Friendly
Group (or to Tongatabu) is over twenty-five hundred miles,
thus equalling the width of the North American continent.
A movement of such extent, involving so large a part of the
earth's crust, could not have been a local change of level, but

366 CORALS AND CORAL ISLANDS.

one in which the whole sphere was concerned as a unit ; for
all parts, whether participating or not, must have in some
way been in sympathy with it.

This subsidence was in progress, in all probability, during
the Glacial era, the thickness of the reefs proving that in their
origin they run back through a very long age, if not also
into the Tertiary. It was a downward movement for the Trop-
ical Pacific, and perhaps for the warmer latitudes of all the
oceanic areas, wliile the more northern continental lands, or at
least those of North America, were making their upward
movement, preparatory to, or during that era of ice.

The subsidence connected with the origin of coral islands
and barrier reefs in the Pacific has been shown (p. 327) to have
amounted to several thousands of feet, perhaps full ten thou-
sand. And, it may be here repeated that, although this
sounds large, the change of level is not greater than the eleva-
tion which the Rocky Mountains, Andes, Alps and Himalayas
have each experienced since the close of the Cretaceous era,
or the early Tertiary ; and perhaps it does not exceed the
upward bulging in the Glacial era of part of northern North
America.

The author has presented reasons for believing (^Am. J, Sci.,
III. V. 1873) that in this Glacial era the watershed of Canada,
between the River St. LaAvrence and Hudson's Bay, was
raised somewhat above its present level (1,500 feet) ; and
that this plateau thus elevated was the origin of the great
glacier which moved southeastward over New England. This
region is the summit of the eastern arm of the great V-shaped
Archaean area of the continent, the earliest elevated land of
North America ; and it is not improbable that the other arm of
the V, reaching from Lake Superior and Huron, northwest-
ward, to the Arctic, was the source of glacial movements over

THE OGEANIG G0BAL-I8LAND 8UBSIDENGE. 367

the more central portions of tlie continent : — we cannot say
western portions also, since in tlie^r^^ place, the facts, accord-
ing to Prof. J. D. Whitney, do not sustain the statement ; and,
in the second^ the great mountain ranges of the west would
have been a barrier to all influences from any central conti-
nental elevation, and, besides, the slopes of these ranges, even if
the Pacific border were higher to the north than now, would
have determined the course of all western glacial movements.
The idea that both arms of the great Archaoan nucleus were
raised together, is not without some support. For the courses of
the two were the courses of great continental uplifts or move-
ments, again and again, through the successive subsequent ages ;
and the present outline of the continent is but the final expres-
sion of the great fact ; moi*eover, the elevations parallel to the
western arm of the V have been much the greatest. Even the
exceptional courses, such as the nearly north and south trend of
the Green Mountains, were marked out first in the Archa3an, the
Archa3an peninsula of northern New York with the line of the
Adirondacks being an exhibition of it. And all this uniformity
of movement, from the laying of the first stone in the develop-
ing continent to the last, has been shown by the author to be
directly connected with the fact that the continent has always
been bordered by the same two great oceanic depressions, the
Atlantic, and the larger Pacific, the same in trend of axis as
now, the North Atlantic having a northeast and southwest
trend, parallel with one arm of the Archaean, and the Pacific
a northwest and southeast parallel with the other arm of the
Archaean. It is therefore reasonable that, late in geological
history, during the Glacial era, after the great mountain chains
of the continent had been made and raised to their full height,
and the surface crust thickened over all the continent, except
that of the Archaean nucleus, by successive beds to a thickness of

368 COBALS AND CORAL ISLANDS.

thousands of feet, even thirty-five thousand by the close of the
Paleozoic along the Appalachians, and mu(^h beyond this on
the Pacific border; and when these thick sediments had in
many regions been stifi^ened by crystallization or metamor-
phism ; I say it is reasonable that, finally, changes of level,
through the working still of the old system of forces, should
again have affected most the old nucleal Arcluiean area of the
continent, where there had been no thickening excei^t what
had taken place internally ; and that, if one arm of the V,
that along the Canadian watershed, were raised at this time,
the other, northwestern in trend, should also have been raised.
This is at least probable enough to become a question for
special examination over the I'egion. See further the author's
Manual of Geology, 1874.

The northern continental upward movements which intro-
duced the Glacial era, carrying Arctic cold towarxl tlie tropics,
may have been a balance to the doionward oceanic move-
ments that resulted in the formation of the Pacific atolls. While
the ci'ust was arching upward over the former (not rising into
mountains, but simply arching upward) it may have been
bending downward over the va^^t central area of the great ocean.
The changes which took place, cotemporaneously, in
the Atlantic tropics, are very imperfectly recorded. The
Bahamas show by their form and position that they cover
a submerged land of large area stretching over six hun-
dred miles from northwest to southeast. The long line
of reefs and the Florida Keys, trending far away from
the land of southern Florida, are evidence that this Flor-
ida region participated in the downward movement, though
to a less extent than the Bahamas. Again, the islands
of the West Indies diminis/h in size to the eastward, being
quite small in the long line that looks out upon the blank

THE OCEANIC CORAL ISLAND SUBSIDENCE. 369

ocean, just as if the subsidence increased in that direction.
Finally, the Atlantic beyond is water only, as if it had been
made a blank by the sinking of its lands.

Thus the size of the islands, as well as the existence of
coral banks, and also the blankness of the ocean's surface, all
appear to bear evidence to a great subsidence.

The peninsula of Florida, Cuba, and the Bahamas look, as
they lie together, as if all were once part of a greater Florida
or southeastern prolongation of the continent. The northwest-
ern and southwestern trends, characterizing the great features
of the American continent, run through the whole like a warp
and woof structure, binding them together in one system ; the
former trend, the northwest, existing in Florida and the Ba-
hamas, and the main line of Cuba ; and the latter course, the
west-southwest, in cross lines of islands in the Bahamas (one
at the north extremity, another in the line of Nassau, and
others to the southeast), in the high lands of northwestern
and southeastern Cuba, and in the Florida line of reefs, and
even further, in a submerged ridge between Florida and Cuba.
This combination of the two continental trends shows
that the lands are one in system, if they were never one in
continuous dry land.

We cannot here infer that there was a regular increase of
subsidence from Florida eastward, or that Florida and Cuba
participated in it equally with the intermediate or ad-
joining seas; for the facts in the Pacific have shown that
the subsiding oceanic area, had its nearly parallel bands of
greater and less subsidence, that areas of greatest sinking al-
ternated with others of less, as explained on page 326 ; and that
the groups of high islands are along the bands of least sinking.
So in the Atlantic, the subsidence was probablj^ much greater
between Florida and Cuba than in the peninsula of Florida it-

24

370 COBALS AND CORAL ISLANDS.

self; and greater along the Caribbean Sea parallel with Cuba,
as well as along the Bahama reefs, than in Cuba.

The position of the lonely Bermuda atoll confirms these
deductions. Its solitary state is reason for suspecting that
great changes have taken place about it; for it is not na-
tural for islands to be alone. The tongue of warm water
due to the Gulf Stream, in which the Bermudas lie, is nar-
row, and an island a hundred miles or more distant to the
northeast-by-east, or in the line of its trend (p. 219), if
experiencing the same subsidence that made the Bermuda
land an atoll, would have disappeared without a coral mon-
ument to bear record to its former existence. Twenty miles
to the southwest-by-west from the Bermudas, there are two
submerged banks, twenty to forty-seven fathoms under water,
showing that the Bermudas are not completely alone, and
demonstrating that they cover a summit in a range of heights ;
and it may have been a long range.

In the Indian ocean, again, there is evidence that the coral-
island subsidence was one that affected the oceanic area more
than the adjoining borders of the continent, and most, the
central parts of the ocean. For, in the first place, the Archi-
pelago of the Maldives narrows and deepens to the south-
ward (p. 186). Further, the large Chagos Group, lying to the
south of the Maldives, contains but very little dry land in any
of its extensive reefs, while some of them, including the
Great Chagos Bank, are sunken atolls. Again, still other
large reefs nearly bare, lie to the southwest of the Chagos
Group ; while Keeling's is another outlying atoll southwest
of southern Sumatra and far out toward mid-ocean.

The probability is, therefore, that both the central Atlantic
and Indian Oceans were regions of this subsidence, like the
central Pacific, and that the absence of islands over a large

THE OGEANIG GORAL-ISLAND 8UB8IDENGE. 371

part of their interiors may be a consequence of it. A rate of
sinking exceeding five feet in a thousand years (if the estimate
on page 253 is right) would have buried islands and reefs to-
gether in the ocean ; while, with a slower rate, the reefs might
have kept themselves at the water's surface. So small may
have been the difference of rate in the great movement that
covered the Pacific with coral islands, but left the Indian
Ocean a region of comparatively barren waters, with some
'' half-drowned " atolls, and the central Atlantic almost wholly
a blank.

"While thus seeming to prove that all the great oceans have
their buried lands, we are far from establishing that these
lands were oceanic continents. For as the author has elsewhere
shown, the profoundest facts in the earth's history prove that
the oceans have always been oceans. These lands in all proba-
bility were, for the most part, volcanic islands or summits of
volcanic ranges, for of this nature are all the islands over the
interior of either ocean that are not of coral origin.

The course of argument leads us to the belief that a very
large number of islands, more than has been supposed, lie
buried in the ocean. Coral islands give us the location of
many of these lands ; but still we know little of the extent to
which the earth's ranges of heights, or at least of volcanic
peaks, have disappeared through oceanic subsidence. Recent
dredgings and soundings have proved that the bottom of the
oceanic basin has little of the diversity of mountain chains
and vallies that prevails over the continents; and, through
this observation (and also by the discovery that some ancient
types of animal life, supposed to have been long extinct, are
perpetuated there), they have afforded new demonstration of
the proposition, above stated, that the oceans have always been
oceans. But while the facts do not imply the existence deep

372 C0BAL8 AND CORAL ISLANDS,

in the ocean of many granitic mountain chains, they do teach
that there are long ranges, or lines, of volcanic ridges and
peaks, and some of these may be among the discoveries of
future dredging expeditions. A range of deep-sea cones, or
sunken volcanic islands, would be as interesting a discovery
as a deep-sea sponge or coral, even if it should refuse, ex-
cepting perhaps a mere fragment, to come to the surface in
the dredge.

We may also accept, with some confidence, the conclusion
that atolls and barrier reefs originated in the same great bal-
ance-like movement of the earth's crust that gave elevation
and cold, in the Glacial era, to high-latitude lands. If so, the
tropics and the colder latitudes were performing their several
works simultaneously in preparation for the coming era ; and
it is a gain to us in our contemplations, that we hence may bal-
ance the beauty and repose of the tropics, through all the pro-
gressing changes, against the prolonged scenes of glacial deso-
lation that prevailed over large portions of the continents.

APPENDIX

The following brief explanations are here added for the benefit of the
general reader.

I. GEOLOGICAL TIME.

The terms Paleozoic era, Oolitic period, and Glacial era or period
have been used in the preceding pages. The positions of these eras in
geological history, will be gathered from the following review of its
principal divisions.

Geological history begins with what has been called Azoic time, azoic
signifying the absence of all life. But the rocks supposed to be Azoic
have been found to afford evidence of the existence of the simplest kinds
of life during their formation; and the era they represent, is, therefore,
more correctly styled the Archeozoic, from the Greek for beginni7ig and
life.

The other grand subdivisions of geological time, are as follows :

Paleozoic time (named from the Greek for ancient life)^ in the course
of which the earliest Corals, Mollusks, Crustaceans, Insects, Fishes and
Reptiles existed. It includes three ages : (1), The Silurian ; (2), the De-
vonian^ or Age of Fishes ; and (3), the Carboniferous, or Age of Coal-
plants, when the most extensive beds of mineral coal of the world were
originated.

2. Mesozoic time, or that of mediceval life. It corresponds to the
Age of Reptiles — being the era, not of the earliest reptiles, but that of
their climax in number, size and variety. This age is divided into three
periods : first, or earliest, the Triassic ; second, the Jurassic, to which the
Oolitic era belongs ; and, third, the Cretaceous, or that of the Chalk.

3. Cenozoic time, or that of recent life, as the term signifies. It
is modern in the aspect of its species, compared with the Mesozoic, and
still more so compared with the Paleozoic. The highest and dominant
species were Mammals^ ending in Man.

374 APPENDIX,

Cenozoic time is divided into two ages, the Tertiary and the Qua-
TERNARY. The Quaternary age, the last in the geological series, com-
mences with the Glacial period, when, over Northern North America,
vast quantities of stones, gravel and sand, were transported by ice from
the north, and spread over the surface down to the parallel of about 40^,
and, of finer material still farther south along the great valleys, extend-
ing in the Mississippi Valley, as Prof. E. W. Hilgard has shown, even to
the Gulf of Mexico. The transportation was probably, for the most part,
the work of a continental glacier, covering a large part of the continent
north of 40^, and of the floods proceeding from its final melting. Europe
also had, at the same time, its northern glacier, reaching down to the
parallel of 50^, along which parallel the temperature is about the same
as on the parallel of 40^ in North America.

The Glacial period in North America was an era of greater continen-
tal elevation than now exists — at least for the glacial latitudes, that is,
from the parallel of 40° northward. It was followed by the Champlain
era, the era of a subsidence of the land below its present level, over the
same northern regions, which subsidence was accompanied by a modera-
ting of the climate, and a melting of the glacier. Next came tlie Terrace
era, marked by the elevation of the continent toward, and finally to, its
existing height, and a consequent making of terraces along river valleys,
around lakes, and on many sea borders.

n. RADIATES.

Polyps have been described as constituting one of the grand divisions
of Radiates,

Kadiates are characterized by a radiate system of structure, apparent
both externally and internally : in other words, they consist of difierent
series of similar parts repeated around a vertical axis. In polyps the
tentacles are thus repeated ; so, also, the internal septa ; the reproductive
system; the eyes, where these exist ; and so on through the structure. In
order to make this distinctive feature of Radiates more intelligible, a few
words are here presented on the other grand divisions of the Animal
Kingdom, or the Sub-Kingdoms as they are called. The number of
Sub-Kingdoms is ^yq^ as follows :

1. Sub-kingdom of Vertebrates. — ^This designation refers to a fun-
damental feature of the species, — ^the backbone or spinal column, con-
sisting of a series of bones (sometimes cartilaginous only), articulated to-
gether, called, in the Latin language, vertebrce. In connection with this,
they have a cavity above for the great nervous cord, and one below for
the viscera. Here belong Mammals (or Man, Quadrupeds, Whales, and
the like). Birds, Reptiles, Fishes. All other animals are invertebrates,
that is, have no vertebral column.

APPENDIX 375

2. Sub kingdom of Articulates — so named with reference to the
fact that the body consists of a series of segments or joints, articulated
together ; and that all the legs, antennae, and other appendages are
likewise jointed (articulated). The body has one cavity containing both
the viscera and the principal nervous cord, the latter situated below the
alimentary canal. The species included are Insects, Spiders, Centipedes,
Crustaceans (or Crabs, Lobsters, Shrimps and the li?ke), and Worms.

3. Sub-kingdom of Mollusks — or, as the name implies, species having
soft fleshy bodies, which are characterized also by a simple bag-like struct-
ure, and by the absence of joints both from the body and all appendages.
As in Articulates, similar organs are repeated on the right and left sides
of a median plane, instead of around a central axis ; but there is no succes-
sion of segments in the body, or of corresponding ganglia (nervous masses)
in the nervous system ; and, consequently, Mollusks have not that compo-
site feature that characterizes and distinguishes Articulates. Examples are
the Oyster, Clam, Snail, Cuttle-fish, and Bryozoans (mentioned on page
105). Many of the species have shells, as an external covering ; but
many also are without them.

4. Sub-kingdom of Radiates, the subject of this note.

5. Sub-kingdom of Protozoans, briefly described on a following page.
The division of Radiates is thus the lowest but one in the system

of animal life, and its species are strikingly distinct from the higher kinds
in the radiate arrangement of the parts within and without.

Radiates are of three Classes.

1st. Polyps^ whose characters have already been stated (p. 20 and be-
yond.)

2d. Acalephs, or Jelly-fishes, or Medusae as many of them are called.
Acalephs are often nearly transparent and jelly-like in aspect, though not
in consistence. They have sometimes the shape of a disk, convex above,
or a hemisphere, or a bell-shaped spheroid, and vary in diameter from a
fraction of an inch to three yards or more. Attached either to the margin,
or to the under concave surface about the mouth, there are usually four
tentacles or groups of tentacular appendages, or a continuous fringe of
tentacles ; or there are other tasselings beneath the pellucid body ; and
these organs, like the tentacles and some other parts of an Actinia, are fur-
nished with myriads of lasso-cells. The whole structure is as completely
radiate within and without as that of a Polyp ; but there are radiating,
and radiately branching, vessels passing outward from the stomach cavi-
ty instead of radiating compartments. Acalephs, or jelly-fishes, float in the
ocean, usually with the mouth downward, moving ordinarily by the con-
traction and expansion of the sides of the body. Hydroids (p. 101) are
sexless forms under one division of Acalephs ; they are usually attached,
and look like polyps.

3d. JSchinoderms, Examples of this class are^Jirst, the star-Jtshes^ or

376 APPENDIX.

five-fingers^ whose bodies, although containing calcareous plates, are some-
what flexible, and ordinarily either five-rayed (fingered) or five-angled
(but sometimes more than five) : — second^ the Echinus or sea-hedgehog^ so
called from the spines that stand out in all directions over the thin, but
firm, hollow shell ; third^ the Holothicrians^ or sea-slugs^ alluded to on
page 160, whose bodies are long and flexible, and the exterior is a fleshy
skin, usually thick, often with calcareous points or pieces in the skin, but
not enough to interfere with its slug-like flexibility. There are also other
lower kinds, which need not be here described.

In Polyps the number of similar radiate parts in the structure is typi-
cally a multiple either of six or oifour; in Acalephs, oifour; in Echino-
derms, oifive. Some variations occur under each of these divisions ; but
they may probably be regarded as modifications of the type by suppres-
sion in development, or the reverse.

The Echinoderms are the highest of Radiates. They show their su-
periority of rank in having more perfect nervous, digestive and branchial
systems, generally an anal opening to the alimentary canal instead of
only a mouth, and a better organized mouth ; also in the absence of lasso-
cells, this provision of a stinging apparatus in the skin being a special at-
tribute of inferiority. They have tentacles (under the form of suckers and
also of branchiae), but these organs are usually arranged along the body
radiately with reference to the mouth or the opposite extremity of the an-
imal ; and the tentacular (or ambulacral) compartments alternate with others
non-tentacular (inter-ambulacral). When the body is long, as in the Holo-
thurians, the ^\e ranges of tentacles extend along the sides of the body.

In many points, the Echinoderms are unlike Polyps ; and yet the two
are fundamentally similar in the radiate system at the basis of the struc-
ture ; in the alternation of tentacular and non-tentacular compartments
when both kinds exist ; in the annular character of the nervous system — -
for, although the nervous ring is not complete either in Polyps or Aca-
lephs, the isolated parts existing in these species are manifestly rudiments
of the nervous ring of the Echinoderms ; in the system of water-circula-
tion, which in Polyps diflers from that of Echinoderms only in being less
perfect ; and in other points which cannot here be dwelt upon.

To the more scientific reader a word is here added on the question
whether Echinoderms are true Radiates. They have been separated from
this sub-kingdom by some zoologists on the ground of their having a
better defined alimentary canal, with two extremities to it instead of
only a mouth ; also a more perfect nervous system and a more perfect
aquiferous system ; and their not being furnished with lasso-cells : — the
Polyps and Acalephs being distinctively designated by such systeraatists
Coelenterates, But the organs, or arrangements, for the purposes of
digestion, sensation, aeration, prehension, are only the means by which
the animal sustains itself and does its work, while the type of structure

APPENDIX. 377

is something fundamental to all these conditions of its exhibition. The
fact of the radiate structure, and of the general homology in the several
parts between the Echinoderms and other Radiates, is not affected by the
fact of tlie nutritive system having one or two open extremities, or by
the perfection of the nervous or branchial systems, or by the condition
* the general visceral cavity. Moreover some Echinoderms have only
one opening to the alimentary cavity, while some Acalephs have two, like
the highest Echinoderms, thus proving that such distinctions are of small
importance alongside of system of structure. Again, the nervous system
of Echinoderms, as already stated, is only the perfected state of the ner-
vous system of some Polyps and Acalephs.

Echinoderms appear to differ strikingly from Polyps in having
many tentacles from one tentacular compartment. But in Polyps, one
compartment has occasionally, besides its one tentacle, a series of them ;
thus evincing the same fundamental idea in the structure of the two, and
affording proof of their close relationship. The branchial rosette in a
Holothurian looks quite peculiar ; but Actiniae that live, like most Holo-
thurians, in the sand, have sometimes a similar branchial rosette, the
crimped or finely divided appendages among the tentacles of such Actinia)
being true branchiae, as Verrill has observed ; and, further, such appen-
dages have no compartment of their own, but grow out from one that
bears its normal tentacle (page 39). The group of tentacles and branchial
appendages in the Actinia constitute a rosette around the mouth wholly
analogous to that of a Holothurian. This peculiarity is therefore con-
firmatory evidence that Polyps and Echinoderms are one in system of
structure and alike Radiates.

III. PROTOZOANS.

Foraminifers, which include the Orbitolites (mentioned on page 152),
the Globigeringe (page 212), and also Sponges, are the secretions of
Protozoans, just as ordinary corals are the secretions of Polyps.

Protozoans, the lowest and simplest of animals, show their simplicity in
first, their minuteness, the animals being mostly between a 100th and a
10,000th of an inch in length ; secondly/, in having no external organs or
parts, excepting (1) a mouth, and (2) minute cilia or thread-like processes ;
thirdly, in having no distinguishable digestive apparatus excepting a
stomach ; fourthly, in the fact that the stomach and mouth are some-
times wanting, or exist only when extemporized for the occasion. The
species have, besides, a palpitating vesicle or vacuole within the body
which appears to serve the purpose of a heart. Part of the so-called
Infusoria are Protozoans.

In the lowest section of Protozoans — that of the Rhizopods — the
animal has a spheroidal body, if of any particular shape, but is generally

378 APPENDIX.

without a permanent mouth or stomach. It has the power of extending
out portions of its protoplasmic body in the form of thread-like processes,
and thence the name Rhizopod, signifying rooUlike feet. Many of the
species secrete shells, and although the shell of a single animal may not
be larger than the point of an ordinary pin, it has pores or foramina
through it which give exit to the thread-like processes; and the shells
are therefore called /bramm^ers.

Rhizopods occur often as solitary animals ; but generally, like polyps,
they multiply by budding, and thus make groups of cells, some of the
larger of which have the magnitude of a quarter of a head of a pin ; of
this nature are the Globigerinse, and various other kinds, common over
the bottom of the deep ocean, as well as in many shallow waters. A few
form, through the budding process, disk-like or coin-shaped foraminifers,
half an inch to an inch in diameter ; and such are the Orhitolites^ re-
ferred to, on page 152, as contributing largely to the coral reefs of the
Australian seas, while common throughout the reef regions of the Pa-
cific.

In one division of Rhizopods — that including the Globigerinse and
Orbitolites — the foraminifers are calcareous ; in another, they consist of
agglutinated sand ; in another (that of the Polycystines) they are sili-
ceous.

In another section of Protozoans called the Flagellate Infusoria^ and
including the Monad, there is a permanent mouth, and often a slender
process {Jiagellum) which appears to serve the mouth by pushing in
food. The animals are much more minute than the Rhizopods. In this
section, as Prof. H. James Clark has shown, belong the sponges — a
sponge being a compound group of these living infinitesimals, produced
by growth and budding.

A third division of Protozoans is that of the Vorticellse and related
forms. They have at top a circle or spiral of cilia, around a disk, in one
part of which disk the mouth is situated. These beautiful species — occa-
sionally large enough to be visible to the naked eye — often grow in clusters
resembling somewhat those of the Hydroids and Bryozoans.

«0 100 110 120 130 1+0 130 180

/^J> ,. /'^^— ^^." ^^Q ^^Q ^^Q 120 JIO lOO 90 80 7 60

±0 30 -iO lO

JO 20

50 ^0 70 ao '

j ' r-~ TEMPERATl

THE ISOTHERMS SHOWING THE AVERAGE
TEMPERATURE OF THE COLDEST MOhfTH.
I1.XITSTRATE THIE -

0.00 110

50 60 70 So

l?ixj-d(?rs 03-L & Cauft ay^i , ITf ^^/ Ha^: fa l, Ct

IV. NAMES OF SPECIES IN THE AUTHOR'S REPORT ON ZOOPHYTES.

The following catalogue contains the names that are now accepted for the species
of Actinoid Coral Zoophytes described in the Author's Report. The changes have
chiefly resulted from the subdivision of the old genera. The catalogue has been pre-
pared for this place by Prof. Verrill, and the explanatory notes have been added by
him.

NAMES m THE AUTHOR'B REPORT.

Page 159. Euphyllia pavonina

" anthophyllum
" spheniscus
*' rubra
** spinulosa
" glabrescens
** gracilis
" aspera
" aperta

costata(p. 720)
" rugosa
*' turgida

** meandrina
*' sinuosa
" cultrifera
170. Ctenophyllia pectinata (not of
quadrata
pachyphylla
profunda
174. Mussa* fastigiata
" carduus

" angulosa

** corymbosa

" cactus

" costata

*' fiinuosa (not of Ellis)

NAMES NOW ACCEPTED, WHEN DIPFERINS
TBOM THOSE OP THE REPORT.

Flabellum pavoninum Lesson,

anthophyllum E. d H.
" spheniscus E. & H,
" rubrum E. d H.

Desmophyllum spinulosum VerrUL

unchanged.

Eusmilia aspera E. <& H,

" fastigiata E. & H. (?)
" costata VerrUL

unchanged.

Euphyllia fimbriata E. & H.
Pterogyra sinuosa E, & H.
" cultrifera E. & K
Lam.) Pectinia Danae E. & H,

" quadrata E. & H.
" pachyphylla E. <& H,
" profunda E. <& H,

unchanged.

Mussa tenuidentata Ed H,

380

NAMES OF SPECIES.

NAMES IN THE AUTHOR'S REPORT.

174. Mussa cytlierea

*' multilobata

" cerebrifonnis

" regalis

" crispa (not of Lam)

* dipsacea
" fragilis
" , gyrofi
" recta
" nobilis
189. Manicina amarantum
" fissa
*' areolata ^
meandrites
Lispida
" prserupta
" dilatata

195, Tridacopliyllia lactuca

196. " pseonia

" manicina

198. Caulastraea furcata

199. " distorta

" undulata

205. Orbicella ' radiata
" argus

" glaucopis

" patula

•* curta

" rotulosa

*' coronata

" liyadea

" excelsa

" pleiades

annularis
stellukta
" stelligera

" crjspata

" microphtlialma (not of

Lam.)
" ocellina

720. " orion

205. Siderina galaxea
205. Astraea (Fissicella) speciosa
" " uva

" '* ananas

" ' pandanus

" * puteolina

" " pallida

* " dipsacea

NAMES NOW ACCEPTED, WHEN DIFFERING
FROM THOSE OF THE REPORT.

unchanged.

Mussa Indica Verrill, and Mussa ra

dians Verrill.
Isopliyllia dipsacea Verrill.

" fragilis Verrill.
Colpophyllia gyrosa B. & H.
unclianged.

Tracypliyllia amarantum E. & IL

Colpophyllia.

Manicina areolata Bhr,

unchanged.

Orbicella radiata Dana.
*' cavernosa Verrill.
" glaucopis Dana.
Acanthastraea patula E. & H.
Plesiastraea curta E. & H.
Astraea rotulosa Lam.
Plesiastraea coronata E. & H,
Solenastraea hyades Verrill.
" excelsa Pourtales.

'* pleiades Verrill.

Orbicella annularis Dana.
" stellulata Dana.
Plesiastraea stelligera E. & H.
Ulastraea crispata E. & H.

Cyphastraea Danae E. & H.

" ocellina E. & H.

Orbicella orion Dana.
Siderastraea radians Verrill.
Astraea^ speciosa Dana.
Dichocoenia uva E. & H.
Astraea ananas Lam.

" pandanus Dana.

" puteolina Dana.

" pallida Dana.
Acanthastraea dipsacea Verrill.

NAMES OF SPECIES.

381

KAME8 m THE AUTHOR'S REPORT.

NAMES NOW ACCEPTED, WHEN DIEFERINO
FROM THOSE OP THE REPORT.

205. Astraea (Fissicella) porcata (not of

Esper) Astraea Danae Verrill.

Prionastraea flexuosa Verrill.

" fusco-viridis E. & H.

" virens E. & H.

Acantliastraea ecliinata E, <& H,
Astraea fragilis Dana.
Acantliastraea tenella Verrill.

flexuosa

fusco-viridis

virens

ecliinata

fragilis

tenella

magnifica (not

of Bv.) Prionastraea spectabilis Verrill,
filicosa Orbicella filicosa Verrill,

versipora Astraea versipora Lam.

" (var.) " Putnami Verrill.

denticulata (not

of Lam.) " cellulosa Verrill.
pectinata " pectinata Dana.

deformis Aplirastraea deformis E. & H.

Coeloria daedalina Verrill.

Coeloria spongiosa, var. E. & H.

Isopliyllia rigida Verrill.

var. dedalina
varia
rigida
reticularis (not

of Lam.)
petrosa
purpurea
pulclira
pentagona
lavistella
var., from

Wakes I.
eximia
sinuosa
melicerum
parvistella
favulus
cerium

Prionastraea Agassizii E. & H.
Dicliocoenia petrosa Verrill.
Leptastraea purpurea Verrill.

** pulclira Verrill.

Goniastraea pentagona Verrill.

" favistella Verrill.

" lialicora

" " cyclastra

" " favosa

254. Meandrina dedalea (not of Ellis)
" spongiosa

" labyrinthica

Astraea Pacifica Verrill.
Goniastraea eximia E. & II.
Prionastraea sinuosa Verrill.

" melicerum E. & H,

Goniastraea parvistella E. d H.
Prionastraea favulus Verrill.
Goniastraea cerium E. & H.
intersepta (not of

Lam) Plesiastraea armata Verrill.
abdita Prionastraea abdita E. & H.

tesserifera " tesserifera E. & H.

robusta " robusta E. & H.

complanata (?) " complanata E. & H.

heliopora Orbicella heliopora Verrill.

" figured Prionastraea valida Verrill.
Hemprichii Prionastraea Hemprichii E. (& H,

" halicora E. & H.

Astraea cyclastrsea Dana,
Prionastraea favosa E. & H.
Coeloria daedalina, var. Verrill,

" spongiosa E. & H.
Maeandrina labyrinthiformis Verrill,

382

NAMES OF SPECIES.

NAMES m THE AUTHOR'S RBPOBT.

NAMES NOW ACCEPTED, WHEN DIFrBRINO
FROM THOSE OF THE REPORT.

205.

Meandrina strigosa

unchanged.

"

interrupta

i(

"

rustica

u

€t

valida

tt

a

phrygia (not of Ellis)

Maeandrina rudis Verrill.

"

gracilis

Leptoria gracilis E. cfc H.

€1

tenuis

tenuis E, & H.

U

filograna

Maeandrina clivosa (young) Verrill,

€t

cerebriformis

Diploria cerebriformis E. & H,

"

truncata

" truncata E. & H.

<<

mammosa

Maeandrina clivosa Verrill.

(<

cylindrus

Dendrogyra cylindrus EJir

*'

caudex

" caudex Ehr,

266

Monticularia microcona

Hydnophora microconos E. & H,

«

lobata

exesa E. & H.

it

polygonata

" polygonata^. (fc 5"

270.

Phyllastraea tubifex

unchanged.

271.

Merulina ampliata

**

'

regalis

it

t

speciosa

it

*

crispa

ft

*

folium

Hydnophora Demidoffi Fischer.

I

Bcabricula

Clavarina scabricula VerrilL

*

laxa

unchanged.

"

rigida

Hydnophora rigida E. & H.

278.

Ecliinopora undulata

unchanged.

"

rosularia

ft

it

ringens

*i

t

reflexa

tt

it

aspera

Trachypora aspera Verrill,

u

liorrida

Acanthopora horrid a Verrill,

289.

Fungia cyclolites

Cycloseris cyclolites E. & H,

((

tenuis

** tenuis Verrill

"

glans

" glans Verrill,

t<

discus

unchanged.

u- "

agariciformis

Fungia patella J^.cfe H,

"

var. tenuifolia

Fungia tenuifolia Dana (not E, & H,)

«

dentata

unchanged.

w "

echinata (not of Pallas)

Fungia Danae E. <& H,

it

var. from Feejees

" lacera VerrUl,

i "

repanda

unchanged.

f.

Integra

tt

€t

confertifolia

tt

tt

liorrida

tt

U

actiniformis

tt

tt

crassitentaculata

tt

1^ u

Paumoteneis

Lobactis Paumotensis VerrUl,

1 "

dentigera

" Danae Verrill.

n

scutaria

Pleuractis scutaria (Ag. MSS.) Ver-

nil

NAMES OF SPECIES.

383

JLOTES IN THE ATTTHOR's REPORT.

289.'*Tungia pectinata

Ehrenbergii
var. gigantea
asperata
Ruppellii
crassa
307. Herpetolitlius limacinus
Herpetolithus interruptus
" foliosus

" Btellaris

" strictus

" crassus

811. Halomitra pileug (not of Linn,)
813. Polyphyllia talpa

" leptophylla

" sigmoides

" pelvis

" fungia

" pileiformis

" galeriformis

319. Zoopilus echinatu3
821. Pavonia explanulata
crispa
papyracea

elepliantotus (not of Pallas)
cactus
praetorta
formosa
venusta
divaricata

boletiformis (not of Lam.)
frondifera
decussata
lata
crassa

var. loculata
eiderea
latistella
clavus
335. Agaricia (Undaria) undata

" rugosa (not of

Lam.)
** speciosa

" levicollis

** planulata

(Mycedia) cucullata
" purpurea

'* fragilis

" gibbosa

" agaricites

NAMES NOW ACCEPTED, WHEN DIPPERING
PROM THOSE OP THE REPORT.

Ctenactis ecbinata (Ag. MSS.) VerriU

'* Ehrenbergii VerriU,

" gigantea VerriU.

" asperata VerriU.

" echinata VerriU.
_^ crassa VerriU.
Herpetolitba limax Esch.

unchanged.
v«

Halomitra clypeus VerriU.
Cryptabacia talpina E. & H.

" leptophylla'^. cfeJ5.

" sigmoides VerriU,
unchanged. »

Lithactinia pileiformis E. & H.

" galeriformis E. <& H,
unchanged.

Podabacia Crustacea E. & H.
Haloseris crispa E. <& H.
Leptoseris papyracea VerriU,
Mycedium elegans E. <& H,
unchanged.

Pavonia Danse VerriU.
unchanged.

Pavonia loculata VerriU.
Siderastraea siderea Blainv,
unchanged.

Siderastraea clavus VerriU,
Undaria ^ undata Dana,

" monticulosa VerriU

" speciosa Dana,

" levicollis Dana.

Asteroseris planulata VerriU.

Mycedium elephantotus E. & H,

Agaricia purpurea Les.

Mycedium fragile VerriU,

Agaricia gibbosa Dana.
" agaricites E. <& H,

384

NAMES OF SPECIES.

NAMES IN THE AUTHOR'S REPORT.

835. Agaricia (Mycedia) cristata (not of

Lam.)
845. Psammocora obtusangula

" plicata (not of Lam,)

" fossata

" columna

" exesa

849. Monomyces anthophyllum

" eburneus

870. Cyatliina cyatlius
" pezita

Smitliii
" turbinata

375. Desmopbyllum dianthus

" Btellaria

376. Culicia etellata

** tenella
" truncata
879. Caryopliyllia cespitosa
" conferta

" flexuosa

" arbuscula

" cornigera

" antliophyllum

" solitaria

" pocillum

'* dilatata

885. Dendropliyllia ^ ramea

" micrantha

" nigrescens

" aurantiaca

'* coccinea

" diaphana

" rubeola

" scabrosa

891. Oculina hirtella

" horrescens
" prolifera
" axillaris
'* varicosa
" oculata
" pallens
" virginea
*' diffusa
899. Antliophyllum musicale

** fasciculatum

" astreatum

" cespitosum

" hystrix

" cuspidatum

NAMES NOW ACCEPTED, WHEN DIPFERINS
FROM THOSE OF THE REPORT.

Agaricia Danse E. cfe H,

unchanged.

Psammocora frondosa Verrill.

unchanged.

Flabellum antliophyllum E. & H,
Caryophyllia cyatlms Lam.

" Smitliii Stokes.

" clavus Scacchi.

Desmophyllum crista-galli E. & H. (?)
unchanged.

Cladocora cespitosa Forbes.

conferta E. & H.

stellaria E. a; H. (?)
" arbuscula Edw.
Dendropliyllia cornigera.
Lophohelia anthophyllites E. & 21.
Astrangia solitaria Verrill.
Phyllangia pocillum Verrill.

unchanged.

Dendrophyllia Danse Verrill.
unchanged.

Balanophyllia scabrosa Verrill.
Sclerohelia hirtella E. & H.
Acrohelia horrescens E. & H.
Lophohelia prolifera E. & H.
Cyathohelia axillaris E. <& H.
unchanged.

unchanged.

Lophohelia oculata Pourt.

unchanged.

Galaxea musical is Oken.

" fascicularis Oken (in part).

" astraeata E. & H.

" cespitosa Verrill.

" hystrix Verrill.

" cuspidata Oken.

NAMES OF SPECIES.

385

NAMES IN THE AUTHOR S REPORT.

399. Anthophyllum clavus
404. Stylina ecliinulata
406. Astroitis calicularis

" viridis
409. Gemmipora palifera
" peltata

" patula

" crater

" cinerascens

" frondens

" brassica

414. Astrseopora pulvinaria (not of

Lam.)
" punctifera

" fungiformis

" stellulata

418. Isaura Hemprichii
" Savignii
" aster
" speciosa
420. Zoantlia Ellisii
" sociata

Solandri
" dubia

Bertholetii
423. Palytlioa denudata
" auricula

" nympbaea

" fuliginosa

" mammillosa
" ocellata

" glareola
" flavo- viridis
" argus
" caBsia
435. Madrepora

Names of species unchanged ex-
cept the following :
No. 23, corymbosa (not of Lam.)
" 26., plantaginea (not of Lam.)
*' 28, acervata
" 56, secunda

" 90, deformis (not of Mich.)
491. Manopora

Names of species unchanged, except

the following :
No. 1, gemmulata
" 6, crista-galli (not of Ehr,)
" 7, spumosa (not of Lam.)
" 8, circumvallata
25

NAMES NOW ACCEPTED, WHEN DIPPERINO
FROM THOSE OP THE REPORT.

Galaxea clavus JS. & H,
unchanged.

Goniopora viridis E. & H.
Turbinaria palifera E. & H.
peltata E. & H.
patula E. & H.
" crater Oken.
*' cinerascens Oken.
" frondens Yerrill,
brassica E. & H.

Astraeopora profunda Verrill.

unchanged.

Turbinaria fungiformis Verrill,

" stellulata E. & H.
unchanged.

Zoanthus Ellisii Lam.
" sociatus Les.
" Solandri Les.
" dubius Les.
" Bertholetii Ehr.
Mammillifera denudata Ehr,
" auricula Les.

** nymphaBa Les.

fuliginosa Ehr,

unchanged.

Madrepora.

Madrepora convexa (young) Dana,

" appressa (var.) Dana.

** plantaginea Lam.

" nobilis (var.) Dana,

" Danse Verrill.

Montipora.

Turbinaria gemmulata VerriU,
Montipora aspera Verrill,
M. hispida (var.) Dana.
M. monasteriata E. & H.

386

NAMES OF SPECIES.

NAHSB IK THE AUTHOR'S HEPOBT.

No. 9, foliosa (not of Pallas)
" 21, nudiceps

" 25, tuberculosa (not of Lam.)
511. Alveopora retepora

" dedalea (from Red Sea)

" ** (specimen fig-

ured)
" Bpongiosa
" rubra

•• fenestrata

" viridis

615. Sideropora digitata
" elongata

" pistillata

•* siibdigitata

" palmata

" mordax

519. Seriatopora subulata
" lineata

" hystrix

** octoptera

" caliendrum

" var. gracilis

" valida

523. Podllopora

Names of species unchanged, ex-
cepting :
No. 3, brevicomis (var. from Sand-
wich Is.)
" 6, favosa (var. from Feejees)
" " (var. from Sandwich

Islands)
" 7, verrucosa (var. from Sand-
wich Islands)
" 15, plicata (var. from Sandwich
Islands)
540. Heliopora ccerulea
543. Millepora alcicornia

•• moniliformis
" ramosa
** pumila
" tortuosa
*• plicata
** complanata
** squarrosa
" platyphylla
" mordax
" compressa
" clavaria
*• flexuosa

NAMES NOW ACCEPTED, WHEN DrFPERING
FROM THOSE OP THE REPORT.

M. Elirenbergii Verrill,
M. crista-galli E. & H.
M. Danae E. & H.
unchanged.

Alveopora Verrilliana Dana*

unchanged.

Montipora rubra E. & H,

unchanged.
tt

Stylophora digitata E, & H.

U it

** pistillata Schweigger.
tt «

" Danae E. & ff.
" mordax Verrill,
unchanged.

Seriatopora gracilis Dana.

unchanged.

Pocillipora.

Pocillipora cespitosa Dana.
" Danae Verrill.

" aspera Verrill.

" nooilis Verrill.

" aspera (var. lata) Verrill,
unchanged.

Millepora alcicornis (var.) Linn,
unchanged.

A variety of plicata. (t)
unchanged.

NAMES OF SPECIES.

387

NAMES IN THE AUTHOR S REPORT.

551. Porites f areata

" recta

*' divaricata

" conferta

" nigrescens

" var. mucronata

" palmata

" levis

" cylindrica

" contigua (not of Esper)

" astrasoides

" conglomerata (not of Lam.)

" lobata

*' fragosa

" limosa

" favosa

" cribripora

'* inforinis

" erosa

" monticiilosa

** lichen — —

" reticulosa "—

" arenacea
569. Qoniopora pedunculata

" columna

" Savignyi

571. Errina aspera
575 Antipatlies "^ spiralis

" anguina

" larix

" eupteridea

" pectinata

" myriophylla

'* subpinnata

" reticulata
flabellura

" ericoides

" mimosella

•' pinnatifida

*' cupressus

" paniculata

" pennacea

" Bcoparia

" foeniculum

" corticata

" lacerata

*' pyramidata

" Boscil

" alopecuroides

" arborea

NAMES NOW ACCEPTED, WHEN DIFPERIKe
PROM THOSE OF THE REPORT.

unchanged.

Porites f urcata (var.) Lam,

unchanged.

Porites mucronata Dana,
unchanged.

Synarsea DanaB Verrill,

unchanged.

Porites lutea E, <& H,

unchanged.

Synaraea informis Yerrill.

" erosa Yerrill.

" monticulosa VerrUL
unchanged.

Porites arenosa E, & H,
unchanged.

Hyalopathes pectinata E. d H,
unchanged.

Hyalopathes corticata E. cfe ff,

unchanged.

Hyalopathes pyramidata E» dh H,

unchanged.

388 NAMES OF SPECIES,

NAMES m THE AUTHOR 8 REPORT. NAITES NOW ACCEPTED, WHEN DIFPERINO

FROM THOSE OP THE REPORT.

575. Antipathes dicliotoma unclianged.

" glaberrima Leiopathes glaberrima E, S H.

" compressa " compressa E. & H.

^ The genus, Mussa, as here restricted, includes both Mussa and Sympliyllia of
Milne-Edwards and Haime, — different specimens of the same species sometimes dif-
fering in the same way, and to the same extent, as do these two so-called genera. The
only difference given, is dependant upon the mode of growth.

* It is probable that this, and some of those following it, are only varieties of one
species.

2 The name OrbiceUa is now restricted to the genus of which 0. annularis and
0. cavernosa are types. This group is equivalent to Heliastrcea of Edwards and
Haime, of more recent date.

^ The genus, Astrma, is here restricted to the group of which A. rotulosa is the
type. This was the original type named by Lamarck, in 1801, when the genus As-
trma was first established. The genus, thus limited, is equivalent to Fadia of Oken,
1815.

^ The genus, Undaria, is equivalent to Pachyseris Edw. and Haime, of later date.

^ C(Bnopsammia is recombined with Dendropliyllia, because in certain species
part of the corallets have the structure of the former genus, and others that of the
latter, even in the same specimen. The only distinction made is that the former
genus has a smaller number of lamellae, — a character that is by itself seldom of gen-
eric value.

"^ The genus, Antipathes, as here adopted, includes CirrJdjmthes, Araclinopathes,
and Bhipidopatkes of Edwards and Haime. Those divisions were based only upon
the modes of growth and branching, which are quite insufficient for establishing gen-
era among Polyps.

APPENDIX, 389

YI. ADDITIONAL INFORMATION ON CORAL ISLANDS AND

REEFS.

1. J3aha7nas, j). 213. — The following notes, by Major-General Nelson,
R.E., are from an abstract of a paper by him in the Quarterly Journal oj
the Geological Society of JLondon^ for 1853.

The loftiest land in the Bahamas, according to the maps of the Hydrogra-
phical Office, is only 230 feet above the sea. Generally speaking, the hills
on the larger islands are much under 100 feet in height, and on the islets

from 50 to 10 feet The surface generally is occupied by low

rocky hills, either surrounding basins or forming parts of what may once
have been basins, and rarely by distinct hill and valley of the ordinary
character. The bottoms of these basins are usually flat and rocky, only a
few inches above the average high-w^ater level, and have a rough and cavern-
ous surface. Water, more or less brackish, rises and falls everywhere
throughout the lower parts of these flats, though not contemporaneously with
the tide,"^' or at a uniform rate. The surface is sometimes covered with grass
and low bush, and sometimes it consists of the bare rock, full of hollows,
which are coated or even arclied over with sub-stalagmitic substances. It is
in these cavities, locally termed " pot-holes," that most of the soil is found ;
and in the gardens made on such ground, fruit-trees, pine-apples, Indian
corn, sugar-cane, etc., grow luxuriantly. Besides these " rock-marshes "
there are also ordinary marshes and mangrove swamps, of no great extent or
dej)th, wliich are more or less in connection with the sea. On the larger
islands the rocky surface of the hills is very thinly and partially covered
with " red earth," mixed in varying proportions with vegetable matter.
This scanty soil is fertile, if well used. When uncleared, it is covered with
bush and forest trees. There are also sandy tracts termed '' pine-barrens,"
where the bush suddenly disappears and the palmettos become fewer in num-
bei', though enough remain to exhibit an intermixture of pines and palms,
respectively typical of the northern and southern floras. The lowest portions
of the flat grounds frequently contain small brackish water or salt lakes. In
the chalk-marsh of Andros Island, however, there is a freshwater lake, with
three streams as its outlets ; and it ap2)ears that there is no other freshwater

lake or stream in the Bahamas There are large caverns in

Long Cay and Rum Cay ; and probably caverns are as numerous in i\iQi
Bahama Islands as in the Bermudas ; but so few extensive excavations have

been made, that this cannot be positively affirmed One of the

most striking objects in the topography of the Bahamas is the very deep sub-
marine valley, forming the gulf known as '' the Tongue of the Ocean," which

* At Nassau, Bahamas, the tide rises from 3 to 4 feet (spring to neap) ; but at Ber-
muda it rises from 6 to 4^.

390 APPENDIX.

runs into the great Bahama Bank from its northern end. The color of the
water around the islands is usually that of the aqua-mai'ine variety of beryl ;
but the water of the Tongue of the Ocean has the deep blue color of oceanic
depths.

The author describes a coral-reef as consisting of masses of numerous
species of Madrepora^ Astrcea^ Doedalea, Oculina, bases and axes of Gorgo-
nia^ Millepora^ JSfxdlipora., Corallince^ &c., &c., growing confusedly together
without any apparent order than that of accidental succession and accretion,
both laterally and vertically. These are at times aided or even superseded

by Serjndcv-^ &c., as seen in the serpuline reefs

Capt. Nelson points out a few of the localities that exhibit most clearly
the character, source, and mode of aggregation of the materials of the ordi-
nary Bahama rock, such as is formed above the sea level ; at the same time
referring to the illustrative specimens in the Bahama collection. For in-
stance : the south side of Silver Cay and the beach extending westward from
Nassau afford rolled blocks, pebbles, and sand derived from the more massive
corals, mixed with remains of turtles, fish, crustaceans, echinoderms, and
mollusks. On the beach between Clifton Point and West Bay (specimen
No. 1), the shells of Stromhus gigas more esj)ecially accompany the rolled
corals. At East Point (specimens Nos. 2 and 3), the sand is derived from
corallines and nullipores ; the finer sand being often in approximately spheri-
cal grains, though not so perfectly as the White Cay (specimen No. 4), and
between Exuma and Long Cay. The beach near Charlotteville Point (sjieci-
men No. 5) consists principally of Lucina JPennsylvanica in various stages
of comminution. At Six Hills (Caicos Group) the mass of Conch shells
(Stromhus gigas) is so great and sufficiently cemented together as to form
not only rock, but an island several hundred feet in length. Along the
north-west beach at Gun Cay (sjiecimen No. 8), a hard, coarse, stratified
rock is formed of Conch and other shells, together with coral fragments.

The large fragments of corals and shells are never found much beyond the
surf-range of high-tide, and therefore always form rock at a low level ; whilst,
on the contrary, the fine calcareous sand is removed by the wind and depo-
sited in irregularly laminated beds, which, being consolidated in various

degrees, are converted into rock of different qualities The

ordinary Bahama rock everywhere consists of the above-mentioned calcareous
sandstone. It is somewhat similar to Portland stone in appearance, but softer
and more porous. When first exposed it is quite white, and is inconveniently
bright and dazzling under a tropical sun ; but it becomes of a dark ashen-
gray color along the sea-coast, and more or less so elsewhere, when exposed
to the weather. Its average weight, like that of the Bermuda stone, varies
from 65 to 145 pounds per cubic foot. Its inferior value as a building
material arises from the numerous sand-flaws (specimen No. 7), and con-
sequent ready failure when exposed to the weather. About the south-west
of New Providence, for some feet above the sea, the rock is hard and homo-

APPENDIX, 391

geneouM, and may be raised in good blocks for building purposes. The
looser and softer kinds of rock are found usually on the hill-tops. A variety
offering a singular counterfeit of true oolitic structure is found at or near
"White Cay, Exunia, and elsewhere; but the spherules are solid, and have
been derived apparently from the stems of corallines. ... A. chalk-
deposit is to be found, by all accounts, in the different basins or lagoon bot-
toms in every principal group, though nowhere so extensively as along the
westei'n coast of Andros Island, where it may almost be termed a young
clialk formation

The " red earth " previously mentioned as forming, generally speaking,
the scanty soil of the Bahamas, is at times interstratified with the rock, and
sometimes it is incorporated with it. It is identical with the *' red earth "
of the Bermudas (si)ecimen No. 15), which proved a considerable source of
embarrassment, especially with reference to Ireland Island, by seeming to
point out alternations of aqueous and other deposits, which were contradicted
by the presence of the characteristic Helix in all the beds. In visiting a
cave near Delaport in 1849, Capt. Nelson found the bottom of the cave for
many feet in depth covered with a loose, dry, " red earth," in grains varying
in size from coarse sand to fine dust (specimens 14 and 14 c/, h). Under the
microscope this appeared as a mass of insect-remains, the rejectamenta of
bats living in these caverns. Specimens of the earth from another j)art of
the same cave, however, were so much altered in character that they
resembled the Bermuda " red earth," and afforded a complete clue to the
characters of this substance. Some of the varieties from the Delaport cave
were examined microscopically and chemically by Professor Quekett, of the
Boyal College of Surgeons, who not only confirmed the above, but announced
that all the varieties gave off ammonia, whether retaining organic texture or
not. The author thinks it not unlikely that the " red earth," even in the
case of the five strata in Ireland Island, has been largely derived from bats
inhabitiug once-existing caverns; at the same time, he considers it probable
that birds, their droppings supplying a sort of guano, have also assisted in
the formation of this deposit.

The occurrence of pumice floated ashore at Watling Island, and else-
where in the Bahamas (as also at Bermuda), is briefly noticed.

T. S. Bland, in remarks on the Bahamas, states that they are not any-
where over 200 feet in height, and in general they are much below this.
Some of the shores, he says, are abrupt cliffs of 40 feet.

2. Arrangements for measuring the rate of growth of a Coral Reef at
Tahiti, p. 253. — A memoir, by MM. Le Clerc andDe Benaz6, was published
at Paris in 1872, giving account of their attempts to make use of the stone
planted by Captain (now Admiral) Wilkes for the determination of the rate
of growth of the Dolphin Shoal. They made various measurements; but
they observe that Wilkes does not state whether he measured from the top

392

APPENDIX.

of a head of coral, or from the solid bank on which the corals were growing ;
and, farther, that the use of our '^ excellent spirit-level " from a stone of so
little length is not sufficiently exact for correct results, and hence they draw
no conclusions from their trials.

Before leaving the region, they made the following arrangements with
reference to future measurements. They planted two blocks of coral, cement-
ing them below, nearly burying them in the soil, placing them 0. 2 1 metres
above the Wilkes' stone, which is between them. They then put a mark
upon them on plates of metal directed toward the place of observation on the
shoal. A third stone was placed forty metres from the south-west angle of
the Point Venus lighthouse, in order to give a second observation on the
position of the spot on which the soundings were to be made. This spot

was found to bear from the two new stones N. 77° 30' E. ; from the third
stone, N. 70*" 55' E. ; from the bell of the new Mission Church, S. 81° 40'

APPENDIX. 393

E. A horizontal line passing from the mark on the new stone is 7.460
metres above the medoeporic heads.

They also made observations which satisfied them that Tahiti* was not at
present undergoing any general elevation. Two maps accompany the
pamphlet : one is copied from Wilkes ; the other is from a chart by Lieuten-
ants Le Clerc and Minier, and contains lines showing the positions of the
points referred to above.

3. Islands of Quiros and lakena, p. 284. — The island of Quiros, or
Gente Hermosa, has, according to S. G. AVhitnell, a freshwater lagoon, only
slightly brackish, about three miles in diameter. This writer states that the
connection between the lagoon and the sea must have been closed at a com-
paratively recent date ; its level is not affected by the tides.

There is a freshwater lagoon, according to the same authority, also in the
neighboring island of Lakena.

4. decent Elevations in the Pacific ^ p. 332. — S. J. Whitnell states that at
Ellice's Island, or Furrafuti, on the windward side of the largest island of
the atoll, there is a small lagoon, dry at low water, which is shut in from the
sea by a wall twenty feet high, consisting of large masses of coral ; and he
regards this as evidence of some elevation. Moreover, on the reef, which is
a narrow ledge, compact masses of coral rock were observed by him in situ,
rising four feet above low- water mark.

Clipperton Rock, in lat. 10° 17' N., and long. 109° 19' W., is an ele-
vated atoll, at least 100 feet high, according to W. Harper Pease, of Hono-
lulu, as stated in the Proceedings of the California Academy of Sciences^
vol. iii. p. 199.

In the J^ew Hebrides there is ^' much coral at a great altitude," accord-
ding to Darwin's report of observations by G. Bennett.

One of the Loyalty Islands, according to W. B. Clarke, consists wholly
of coral rock, and has been raised to a height of 2.50 feet.

Peel Island, one of the Bonin Group, between the Ladrones and Japan,
has coral reefs raised 50 feet above the sea level, according to P. W. Graves
{Journ, Geol. Soc.y 1855, p. 532).

Former Extent of the Bermuda Group, p. 370. — The argument, on page
370, with regard to the former extent of the Bermuda group being much
greater than the present, has been recently sustained by facts observed by
Mr. J. Matthew Jones, published in Nature for A^igust 1,;1872 :

As my late visit to these islands has placed me in possession of facts
relating to their original aspect of a somewhat conclusive nature, I deem it
advisable to commimicate such in a brief form, instead of awaiting the time
requisite for the preparation of a more elaborate paper on the subject.

394 APPENDIX,

Ou previous occasions I have always regretted my inability, from lack of
time, to look more closely into their geological character, in the hope of dis-
covering so'hie satisfactory cine to their primitive condition. 1 was a^vare
that in different parts of the islands road cuttings and well borings had
revealed layers of red earth at certain depths below the surface, the consis-
tence of which was similar to that now forming the present surface soil, and
it did not require much force of imagination, after personal inspection, to
conceive that such layers of red earth were first foi'med by the decomposition
of vegetable matter which grew upon former surfaces, and became covered
to their respective depths by accumulated masses of drift sand, which from
natural causes hardened into more or less comjoact sandstone. But these
different layers were but a few feet beneath the surface, and so, although
interesting as throwing light upon the gradual elevation of the land by drift
material forming over them, yet they afibrded no evidence of a contrary
nature — viz. : the siihmergence of the Bermuda group. Indeed, I have always
been led to suppose from appearances that the whole group was the result of
an upheaval of the ocean bed slightly above the water level, and a gradual
elevation afterward by means of drift matter, aided by the consolidating
agency of reef-building zoophytes encircling the whole with a barrier reef,
and by isolated patches gradually filling up the space within. The investi-
gations, however, which I have recently been able to make, tend, I think, to
prove that the barrier reef encircling the islands, which has hitherto been
considered an atoll, is merely the remnant of the more compact calcareous
rock which formed the shore of a much more extensive island group than
that now existing.

My views in this respect are borne out by the following facts : — The
barrier reef, as far as I have inspected it, is merely ordinary calcareous rock
coated with Serpulse, Nullipores, &c., the reef builders working only in the
sheltered waters between the reef and the shore in three to eight fathoms.
About two years ago submarine blastings were carried on at the entrance
of Hamilton Harbor, and at a depth of over six fathoms a cavern was broken
into which contained stalactites and red earth. Again, within the last few
months I have, through the kindness of his Excellency Major-General
Lefroy, C.B., F.B.S., the present Governor, been placed in possession of still
more satisfactory information. During the past two years extensive submarine
blastings have taken place inside an artificial harbor, situated at the western
extremity of the islands, for the purpose of forming a bed of sufficient depth
for the reception of the Great J^erniuda Dock, which attracted so much
attention off Woolwich when launched some three or four years ago. The
excavations extended to a depth of fifty-two feet below low- water mark. At
forty-six feet occurred a layer of red earth two feet in thickness, containing
remains of cedar trees, which layer rested upon a bed of compact calcareous
sandstone. Here we have the first satisfactory evidence of the submergence
of an extensive deposit of soil once upon the surface, and that to the depth

APPENDIX, 395

of forty-eiglifc feet below the present low-water level, which consequently
grants an equal elevation above it in former times. Now, on carefully sur-
veying the Bermuda chart, we find that an elevation of forty-eight feet will
bring the w]iole space which intervenes between the present land and the
barrier reef, now covered with water, above the water level. This attained,
what more is required to prove the former extent of the island group, before
the present submergence, to the present barrier reef? But having clearly
ascertained beyond doubt tliat the Bermudas were once forty-eight feet higher
than at present, will any one be bold enough to deny tliem a greater eleva-
tion? I have reason to believe that they once extended in a south-westerly
direction — not only out to the reef, but to a greater distance. There are some
rocky ledges about twenty to twenty-five miles from land in that direction,
known as ''The Flatts," lying in about thirty- five to forty fathoms water ;
and, singularly enough, in the very oldest maps of the Atlantic, copies of
which I have consulted in the British Museum, '' The False Bermudas " are
put down about this position. Is it unreasonable to su])pose that a low-
lying group of islets did actually exist here in former times? Again, in
Smith's " History of Yirginia," which gives an excellent account of the
islands in the early part of the seventeenth century, it is stated, among other
notes u})on their natural history, that flocks of crows, no doubt the same
species ( Corvus jlmcricamis) which now inhabits them, were in the habit
every evening of winging their flight from the main island toward the north.
This observation, which from its sinq)licity I should the more readily believe
to be a true statement, would clearly prove the existence of land in that
direction at no great distance ; for the habit of this bird to leave its roosting
place for distant feeding grounds during the day, to return at random, is one
of its well-known characteristics.

Taking these matters into consideration, I see everything to support the
supposition that the Bermudas once presented a much more extensive aspect
than they do at present, and certain additional evidences which I ho2:>e to
bring forward shortly in a collected form, will, 1 conceive, tend to confirm
my impression that the restricted terraqueous area lying within the limits of
the outer barrier reef is mei'ely the summit of one of a range of islands
which extended in somewhat semicircular form for a distance of seventy or
eighty miles, and which have suffered submergence to a depth only to be cor
rectly ascertained by borings, which might be successfully 'accomplished
under the auspices of the Government at a trifling expense.

A paper, by Mr. Thomas Bland, on the Bahama Islands, presents other
facts, based both on the geographical distribution of species and soundings
between the islands, strongly favoring the view that the absence of islands
in the equatorial Atlantic is a consequence of subsidence. This paper is
contained in the Annals of the Lyceum of Natural History of New York for
1873 (vol. X. page 311), and an abstract in the American tTournal of Science
for September, 1874.

V. LIST OF WORKS AND MEMOIRS REFERRED TO, AND OF AB-
BREVIATIONS.

A. Ag. Alexander Agassiz, and Mrs. L. Agassiz. Seaside Studies in Natural His-
tory, 158 pp. 8vo., Boston, 1871. (J. R. Osgood & Co.)

Aa. L. Agassiz. Contributions to the Natural History of the United States. 4to.,
vols. iii. and iv., on Acalephs.
Report on Deep-Sea Dredgings in the Gulf Stream, during the third cruise
of the U. S. Steamer Bibb. Bulletin of Mus. Comp. Zool, No. 13.

Am. J. Sci. American Journal of Science and Arts, New Haven, Ct. 1st series of
50 vols., 1818-1845, incl. ; 2d series of 50 vols., 1846-1870, incl. ; 3d series
from 1871. Editors, Professors J. D. Dana, and B. Silliman.

Am. Nat. American Naturalist, Monthly, since March, 1867. Salem, Mass. Editors
A. S. Packard, Jr., and F. W. Putnam.

D. J. D. Dana. Report on Geology, U. S. Exploring Expedition, 756 pp. 4to., and

folio Atlas of 21 Plates. 1849.
Report on Zoophytes, U. S. Expl. Exp., 780 pp. 4to., and folio Atlas of 61

Plates. 1846.
Darwin. C. Darwin. Journal of Researches during H. M. S. Beagle's Voyage

around the World. 8vo., London, 1839 ; 2d edit.. New York, 1872.
On the Structure and Distribution of Coral Reefs. 8vo., London, 1842.

E. & H. H. Milne Edwards and Jules Haime. Histoire Naturelle des Coralliaires,

on Polypes proprement dits. 3 vols. 8vo., Paris, 1857-1860. Parts of the
work published earlier in the Annales des Sci. Nat., and Archives du Mus.,
since 1847. H. Milne Edwards also published 1 vol. on Zoophytes, in 2d
edition of Lamarck's Animaux sans Vertebres, Paris, 1834.

Ehr. Ehrenberg. Beitrage zur Kenntniss der Corallienthiere der rothen Meeres.,
Abh. der Konigl. Akad. d. Wiss. zu Berlin Abh. for 1832 (issued in 1836),
pp. 225-438.

Ellis. John Ellis and Solander. The Natural History of many Curious and Uncom-
mon Zoophytes. 1 vol. 4to., London, 1786.

EsPER. E. T. C. Esper. Die Pfianzenthiere, etc. 4 vols. 4to. Nuremberg, 1791
et seq,

GOSSE. Philip Henry Gosse, F. R. S. Actinologia Britannica ; a History of the
British Sea-Anemones and Corals, with Colored Figures of the species and
principal varieties. 362 pp. 8vo., London, 1860. (Van Voorst.)

Hartt. Oil. Fred. Hartt. Geology and Physical Geography of Brazil ; 620 pp.
8vo. With Illustrations and Maps. Boston, 1870. (Fields, Osgood & Co.)

JUKES. J. Beete Jukes. Voyage of H. M. S. Fly, 2 vols., 1847. Also The Student's
Manual of Geology. Edinburgh, 1862.

398 LIST OF WORKS REFERRED TO,

Leidy. Joseph Leidy, M. D. Contributions toward a Knowledge of the Marine In-
vertebrate Fauna of the Coasts of Rhode Island and New Jersey. 20 pp.
4to., with two Plates Journ. . Acad. Nat. Sci., Philad. ; vol. iii., 2d ser.,
1855.

Les. C. a. Lesueur. Description de plusieurs animaux appartenant aux Polypiers
lamelliferes de M. le Chev. de Lamarck, Memoirs du Museum, vol. vi.. pp.,
271-297.

Lmk. J. B. de M. Lamarck. Systeme des Animaux sans Vertebres. Paris, 1801,

1 vol. 8vo. Histoire Naturelle des Animaux sans Vertebres. Paris, 1815-
1822, 7 vols. 8vo.

Lamx. J. V. Lamouroux. Histoire des Polypiers flexibles. 1 vol. 8vo., with many

Plates. Caen, 181G.

Exposition Methodique des genres de I'Ordre des Polypiers. Quarto,

with 84 Plates, 63 of which are from Ellis and Solander. Paris, 1821.
MOBius. Dr. Karl Mobius. Ueber den Bau, den Mechanismus und die Entwick-

lung der Nesselkapseln einiger Polypen und Quallen. 24 j^p. 4to., w^ith

2 Plates ; Abh. Nat. Vereins zu Hamburg, erstes Heft des f linften Bandes.
Hamburg, 186G. (G. E. Nolte.)

POURT. C. F. de Pourtales. Deep-Sea Corals, 94 pp. 4to., with 8 Litliogra23hic
Plates. Cambridge, 1871. No. 4, of the Illustrated Catalogue of the Mu
seum of Comparative Zoology.

St. Stimpson, in papers, by A. E. Verrill.

V. A. E. Verrill. Revision of the Polyps of the Eastern Coast of the United States,
46 pp. 4to., with a Lithographic Plate. Cambridge, 1864. Mem. Bost. Soc.
Nat. Hist., vol. i.

List of Polyps and Corals sent by the Museum of Comparative Zoology
to ether Institutions, in exchange, with Annotations. Bulletin Mus. Comp.
Zocil., vol. i., No. 3. 1864.

Corals and Polyps of the North Pacific Exploring Expedition, undei
Commodore C. Ringgold, and Capt. John Rodgers, U. S. N,, from 1850 to
18."; 6, collected y Dr. Wm. Stimpson ; with descriptions of other Pacific
Ocean species. Proc. Essex Institute, vols., iv., v. and vi.

Notes on the Radiates in the Museum of Yale College ; No. 4, Notice of
Coials and Echinoderms collected by Prof. C. F. Hartt, at the Abrolhos
Reefs; No. 6, Review of the Corals and Polyps of the V^est Coast of
America ; No. 7, Memoir on the Geographical Distribution of the Polyps
and Corals of the West Coast of America. Trans. Connecticut Acad-
emy of Arts and Sciences, vol. i., 1868 to 1870, pp. 351-570 ; 8vo., with 7
Pli.tes. New Haven.

( n the Parasitic habits of Crustacea. American Naturalist, vol. iii., p.
289, July, 1869. Salem, Mass.

^Iso several other Papers on Corals, in the Proceedings of the Boston
So( iety of Natural History, and Amer. Journal of Science.

Wilkes, diaries Wilkes, U. S. N. Narrative of the United States Exploring Ex-
pedition, during the years 1838, 1839, 1840, 1841, 1842. 5 vols, royal 8vo.,
with many Illustrations and an Atlas.

Williams. Rev. John Williams. Narrative of Missionary Enterprises in the
South-Sea Islands, with Remarks upon the Natural History of the Islands,
Origin, Languages, Traditions and Usages of the Inhabitants. London.
Also an American Edition issued by D. Appleton & Co., New York, in
18b7.

INDEX.

AcALEPns, characters of, 375.
Acontia, 34.
Aiou, 307.
Actinacea, 61.
Actinaria, 61.
Actinoid Polyps, 21.
Adamsia palliata, 35.
Admiralty Islands, 309.
Africa, reefs of eastern, 318.
Agassiz, L., on Astrangia, 68.

" depth of reef corals, 116.

" coral borers, 121.

" on Florida reefs, 207.

" on Bahamas and Salt Key

Bank, 213.
Agassiz, A., on Arachnactis, 28.

Seaside Studies, 68, 105.
Ahii, 171, 177, 182, 200.
Aitutaki, 337.
Aiva, 261.
Alcyonacea, 82.

Alcyonium, derivation of term, 80.
Alcyonoid, polyps, 80.
Almirante, 314.
Alveopora, 75.

" spongiosa, 77.

" Verilliana, 77.
Andrews, on Molokai and Maui, 841.
Anguilla Key, 214.
Antipathacea, 62.
Antipathes arborea, 63.
Anthea cereus, 37, 57.
" flagellifera, 37.
Anthelia lineata, 83.
Apaiang, elevation of, 167, 343
Apamama, 164, P44.
Apatite on Mauke, 297.

Apia on Upolu, harbor of, 239.

Aratica, 177, 180, 203.

Arru Group, 310.

Ascension Island, 355.

Asia, temperature of ocean along the east

coast of, 300.
Asie, 307.

Astraea pallida, 57, 64.
Astra?acea, 64.

'' distribution of, 109.

Astrangia Dange, 68.
Atiu, 194, 305, 336, 361.
Atlantic Ocean, subsidence in, 368, 369.
Atolls, structure of, 162, 174.
Atoll reefs, origin of, 248.

" " origin of lagoons of, 254, 264.

" " completed, 271.
Aurora Island, 193.

Australian reefs, 135, 142, 148, 309, 310
329.

Bahamas, 213.

Bahama region, subsidence in, 368.

Bailey, J. W., on absence of foraminifers

from chalk of Oahu, 359.
Baker's Island, 291, 340.
Balbi, remarks on encircling reefs, 265.
Barrier reefs, origin of, 254, 257.
Beach formations, 184.
Beechey, on Henderson Island, 194.
" soundings by, 172.
" remarks on Gambler Islands,
265.
on Elizabeth Island, 334, 335.
" on Ducie's and Osnaburgh Isl
ands, 335.

400

INDEX.

Bermudas, structure of islands, 183, 218.

" corals of, 114.

" former extent of, 370.

" ' caverns of, 301.
Beveridge reefs, 338.
Biclie-de-Mar, IGO.
Birds of Coral Islands, 284.
Birnie's Island, 196, 291, 341.
Biscliof, composition of sea water, 100.
Bolabola, 335.
Borneo, 310.

Bowditcli's Island, 168, 169, 200, 273.
Brancliia? in Actiniae, 39.
Brazil, corals of, 113.
" reefs, 140, 316.
Brooks's Island, 324, 342.
Bryozoans, 105.
Budding in Actiniae, 40.
Budding in Coral Polyps, 48.
Bunodes gemma, 22.

Byron, of the Blonde, apatite on Mauke,
297.

Calaminianes, 311.
Calicle, 42, 44, 48.
California Gulf, corals of, 112
Cancrisocia expansa,24.
Cape St. Ann, 315.
CarlshofF, 169, 177, 180, 203.
Caroline Archipelago, 109, 170.

" " elevations in, 344.

Caryophyllia cyathus, 42.

" Smithii, lasso cell, 33.

animal of, 67.
Carysfort Island, 172.
Caulastraea furcata, 58, 64, 95.
Caverns in coral limestone, 194, 360.
Celebes, 310.
Ceylon, reefs of, 314.
Ch^tetes, 105.
Chagos Bank, 191, 192, 314.
Chalk, origin of, 358.
" of Oahu, 359.
Channels among reefs, 148.
Charlotte's Island, 343.
China, coast of, free from corals, 313.
Christmas Island, 173, 339.
Cladocora arbuscula, 54, 69, 95.
Clarke, H. J., on budding in Actiniae, 28.
Classification of Actinoid Polyps, Q\.
Clermont Tonnerre, 171, 334.

Cnid?e, 30.

Cocoanut Grove, on Bowditch Island, 274.

tree, 280.
Coenenchyma, 60.
Columella, 44.

Commensalism in polyps, 24, 62.
Cook, Capt., on Christmas Island, 339.
Cophobelemnon clavatum, 91.
Corals changed to a phosphate by guano

293.
Corals, rate of growth of, 123.
" temperature limiting, 108.
" influence of impure and fresh wa-
ters on distribution, 119.
" injured by boring animals, 121.
Coral, precious, 90.
Coral Heads, 139, 140, 145.

" islands, forms and features, 161.

" ' birds of the Pacific, 286.
" " poor place for human de-

velopment, 288.
Coral-makers, 19.
Coral mud and sand of bottom, 142, 150,

181, 182, 183, 231.
Coral reefs, rate of growth of, 249.
" benefits from, 159.

" geographical distribution of,

303.
Coral Reef Harbors, 160.

" seas, extent of, 300.

Coral rocks, consolidation of, 152, 354.
Coral sands, formation of, 142, 224, 348.
Coral sand-rocks, 152, 154, 348.
Corallet, 48, 60.
Corallldae, 90.
Corallines, 107.

Corallium from the Sandwich Islands, 91
Corallium rubrum, 89.
Corallum, 42, 48, 60.

'' composition of, 98, 105.
'• hardness of, 98.
Comora Islands, 314.
Corynactis viridis, lasso-cells, 33.
Coryne, 103.
Cosraoledo, 314.
Couthouy, J. P., on Anthea flageUifera,

37.
Ctenactis echinafca, 45, QQ.
Currents in Atoll channels, 170, 171.

" among reefs, 239, 240.
Cyathophylli£e, 42, 67.
Cyathophylloids, 78.

INDEX.

401

Dana's Report on Zoophytes, names of
species of, 375.

" '' size of edition of, 93.

Darwin on depth of reef corals, 115.

" rate of growth of corals, 123.

*' origin of coral mud, 228.

" thickness of reefs, 157.

" on soundings, 172.

" on the Maldives, 18G, 189.

" on the Great Chagos Bank, 192.

" on the Gambler Islands, 2G5.

" on the Maldives, 270.

" geographical distribution of coral
reefs, 302.

" on consolidation of coral sands,
and change of position with the
seasons, 355.
Dead men's fingers, 83.
Dean's Island, 1G9, 203, 333.
Depth of reef -corals, 114.
Dendrophyllia arborea, 75.
" cornigera, 75.

" nigrescens, 51, 75.

Depeyster Island, 171, 342.
Diego Garcia, 172.
Diploria cerebriformis, 65.
Disappointment Islands, 172.
Dissepiments, 60.
Distribution of corals, 108, 114.
Dolomite, formation of, 356.
Dolomitic nature of coral rock of Matea,

357,
Dorippe facchino, 24.
Drift sand-rock, 184.
Drummond's Island, 343.
Ducie's Island, 335.
Duke of Clarence's Islands, 169, 338,
Duke of York's Island, 199, 338.
Duff's Islands, 308.

Eap, 307.

Easter Island, 303.

Echinoderms, characters of, 375.

Echinopora reflexa, 43.

Echthoroea, 35.

Edwards & Haime, Phyllangia Americana,

69.
Edwardsia callimorpha, 25, 41.
Egmont Island, 172.
Elevations in the Pacific, 332.
Elizabeth Island, an elevated coral island

334.

Ellice's Island, 346.

Enderbury's Island, 182, 186, 197, 291,

341.
Endotheca, 60.
Eoa, 305, 337.
Epiactis prolifera, 40,
Epitheca, 60.
Eugorgia aurantiaca, 87.
Eunicella, 87.
Eupagurus pubescens, 62.
Evans, Lieut., consolidation of coral sands

of Ascension Island, 355.
Exotheca, 60.

Fanning Group, 338, 339.
Fakaafo, 168, 169, 196, 271.
Favosites, 104.

" relation to Alveopora, 76, 77.

Feejees, corals of, 110.

" delta of Rewa, 244.

" reefs of, 257, 204, 327.

" elevations among, 342.
Feis, 345.

Fission, fissiparity, ^Q,
Fissures in reef-rock, 177.
Fitzroy, Capt., soundings by, 172.

" temperature about the Gal-

apagos, 300.
Flint's Island, 340,
Florida Reefs, soundings, etc., 173, 204,

211.
Florida Region, subsidences in, 368.
Flustra, 105.

Foraminifers of reefs, 152, 377.
Forchammer, magnesia in some corals,

99,
Four Crowns, 197.
Fungacea or Fungia tribe, 66,

" distribution of, 109.

Fungia echinata, 45.

" lacera, 45, 46.

" Danae, 66.

Galapagos, temperature about, Fitzroy,

300.
Gambler group, 157, 265, 304, 329.
Gardner's Island, 341.
Gemmipora, 75.
Geographical distribution of coral reefs

299.
Geological time, subdivisions of, 373.

402

INDEX.

Gilbert Islands, 163, 170, 183, 276, 306.

" elevations in, 343.

Glacial era synchronous with the era of

the coral island subsidence, 366.
G^obigerina^, nature of, 378.
Globigerina mud, 143.
Goniopora columna, 52, 94, 97.
Gorgonacea, 85.
Gorgonia flabellum, 85.
" flexuosa, 85.
" quercifoiia, 87.
GorgonioB, spicules of, 86.
Gosse, P. H.. species of Peachia, Edward-
si a, etc., from his British
Sea-Anemones, 25.
" on lasso-cells, 34.

" on spontaneous fission in

Antliea, 57,
" mention of his work, Brit-

ish Sea-Anemones, 93.
Guam, 307.

" elevation of, 345.
Guano, birds contributing to, 286.
G uano islands of Pacific, 291.
Gulf Stream, influence of, in the Oolit-
ic and Cretaceous eras, on the tem-
perature of the Atlantic Ocean, 362.
Gypsum on coral islands, 294.

Hague, J. D., sands shifted in position
with the season, 237.
" on guano islands of Pa-

cific, 291, 298.
" on birds of Pacific coral

islands, 284.
Hale, H., on Gilbert Islanders, 279.

" on subsidence at Ponape, 331.
Halocampa chrysanthellum, 25.
Hapaii Group, 305, 337.
Haplophyllia paradoxa, 80.
Harbors and channels, conditions deter-
mining the formation and condition
of, 236, 247.
Hartt, C. F., corals of Brazilian coast, 113.

" Brazil reefs, 140,
Hawaian chain, length of, 365.

" " western coral atolls of,

306, 324, 328.
" " northwestern part, sound-

ings in, 173.
Hawaian Islands, corals of. 111.
" " elevations at, 841.

Hawaii, reefs of, 306

Heliopora, 105.

Henuake, 167, 182, 198, 333.

Henderson's Island, 172, 194.

Hero Island, 296, 339.

Hervey Group, elevations in, 336.

Hogoleu, 306.

Holothurians, characters of, 376.

Holothuria, dried, 160.

Honden, see Henuake.

Home Island, 306, 342.

Horsburgh, J. J., on the Maldives, 189.

Howland's Island, 294, 340.

Huahine, shells of, at elevations, 335.

Hull's Island, 341.

Hunt, E. B., rate of growth of corals,

125.
" " on Florida Reefs, reference

to paper by, 204.
Hunter's Island, 307.
Hydra, 101.
Hydroids, 101, 105.

Indian Ocean, reefs of, 313.

" subsidence in, 370.

Isis hippuris, 88.
Isothermal or isocrymal chart, 108, 300.

Jarvis's Island, 168, 195, 293, 339.
Jukes, xiustralian reefs, 141, 181.
Julien, on guano minerals, 297.

Kao, 305.

Kawehe, 179, 202.

Kauai, 306, 324, 341.

Reeling's Island, 172, 314.

Kent, W. S., on Veretillum cynomorium,

92.
Key West, 204.

Kingsmills, see Gilbert Group.
King's Island, 199.
Kophobelemnon, see Cophobelemon.
Kotzebue, on water of coral islands, 283.
Kuria, 164, 173, 344.
Kusaie, 306.

Lacaze Duthiers, on Corallium rubrum,

90.
Laccadives, 314.
Ladrones, 306, 327.

" elevations in, 344.

INDEX.

403

Lafu, 308

Lagoons of atolls 181, 182.

Lusso-cells, 30.

Leptogorg-ia, 80.

].(?vel, changes of, in the Pacific, 318.

Life and death in concurrent progress,

94.
Lime in sea-water, 100.
Limestones, formation of, 348.

" beds of, with living margins,

350.
" thick strata of, 350.

" subsidence essential to the

: making of thick strata of,

350.
" deep sea, from coral reef de-

bris, rarely made, 351.
" rate, of increase of, 359.

" unfossiliferoas, 353.

" difference of continental and

modern oceanic, 352.
" consolidation of, 354.

Lisiansky, soundings by, 173.

" on islands northwest of Kauai,

306.
Lixo coral reef, 140.
Logs on coral islands, 287.
Los G uedes, 307.
Los Matelotas, 307.
Loochoo, 311.
Louisiade Group, 309.
Loyalty Group, 308

McA SKILL Islands, 306.
xVTackenzie Island, 307, 345.
Madagascar reefs, 314.
McKean's Island, 291,290, 340.
Madrepora aspera, 50, 71.

" formosa, 73.

" cribripora, 72, 120.

" of wreck, amount of contribu-
tion from, to reef, 250.
Madreporacea, distribution of, 109.
Madreporaria, 64.

Mseandrina cerebriformis, see Diploria.
Mseandrina clivosa, rate of growth of, 125,

251.
Mseandrina labyrinthica, 65.
Magnesia in corals, 99.
Mahlos Mahdoo Atoll, 189.
Maitea, 304.

Maiana, 164, 344.
Makin, 167.

Maiden's Island, 291, 339.
Maldives, 162, 172, 186, 314.

" map of, 187.

Mangaia, elevation of, 336.
Marakei, 167, 344.
Mangaia, 305.
Manhii, 203.
Manopora, 72.
Manual, 337.
Margaret, 197.
Marquesas, 304, 325.
Marshall Islands, 170, 183, 344.
Matea, dolomitic nature of coral rock of

357.
Maui, elevation of, 342.
Mauke, 305, 336.
Melita^a, 89.

Menchicoff Island. 170, 268.
Mendana, 307.
Metia, 172, 193, 334.
Metridium marginatum, lasso-cell, 33.
Millepora alcicornis, 103, 104.
Mitiaro, 305, 345.
Minerals of coral islands, 290.
Mobius, K., on lasso-cells, 30.
Molluccas, 310.
Molokai, elevation of, 341.
Montipora, 72.
Moresby, Capt., on the Maldives and Clia-

gos Bank, 172, 186, 192.
Mountain chains buried in the ocean,

364.
Mud of channeiS and lagoons, 142, 15(,

181, 182, 183, 231.
Murica3a, 87.
Mussa, 64.

Nairsa, 169, 203, 333.

Namuka, 337.

Navigator Group, 305, 326, 338.

Necker Island, 306.

Nelson, Lieut., on Bermudas, 219.

Nettling cells, 30.

New Britain, 309.

New Caledonia reefs, 135, 148, 308.

New Guinea, 309. »

New Hebrides, 307.

New Ireland, 309.

Newmarket, 341.

404

INDEX,

New Zealand Old Ilat, 231.
Nonouti, 1G4, 169, 340.
Norfolk Island, 308.
Nukiinono, 338.
iXullipores, 107, 174.

Oaiiu, 306, 324.
" caverns in elevated coral reef of,
361.
clialk of, 359.
Oatafu, 338.

Oceanic currents carry away little detri-
tus from islands, 143.
Oceanic subsidence, proofs of, 364.
Ocean Island, 325, 342.
Oculinacea, 66, 109.
Oculina diffusa, growth of, 125, 252.

" varicosa, 69.
Okatutaia, 336.
Old Hat, 231.
Oolite, 153, 156.

Oolitic rocks of Florida Keys, 204, 216.
Orbicella cavernosa, 55.
OrbicellidEe, 67.

Orbitolites about Australian reefs, 152.
Orbitolites, relations of, 378.
Organ-pipe Coral, 84.
Otuhu, 197

Pacific, elevations in, 332.

" axis of subsidence in 319, 328.

" subsidence in by broad anticli-
nals and synclinals, 328.

" cliain, central lengtli of, 365.
, Pali, 44.
Palao, see Pelews.
Palmyra Island, 339.
Panama, corals of, 111.
Pandanus, 276, 281.
Paractis rapif ormis, 23.
Paumotus, 111, 169, 280, 304.
' ' elevations in, 332.
Pavonaridae, 93.
Peachia hastata, 25.
Peacock's Island, 171, 177, 182, 200.
Pearl and Hermes Keef , 325.
Penrhyn's Island, 339.
P^lewa, 307, 345.
Pennatulacea, 91.
Peritheca, 60, 97.
Persian Gulf, reefs in, 314.

Pescadores, 170, 331.
Phoenix's Island, 291, 340.
Phillippine Islands, 311.
Phymactis clematis, 22.

florida, 22.
Pitcairn's Island, 304, 325.
Plants of Paumotus, list of, 280.
Plexaurella, 87.
Pliobothrus, 105.
Plumularia falcata, 102.
Pocillipora, 70.
Pocillipora grandis, 71.

" elongata, cell of, 71.

•* plicata, cell of, 71.

Polyps, classification of, 20, 61, 80.
Ponape, 300, 330, 331 .
Porites family, Poritidae, 75.
*' size of some, 146.

levis, 78, 79.
" mordax, 53, 78.
Port Natal, 315.

Pourtales, L. F. de, on Thecocyatluis, 43.
" " on Haplophyllia, 80.

" " on rate of growth of

corals, 124.
** " bottom of Florida

reefs, 143.
** ** depth of reef corals,

116.
" " on Florida region, 211.

Pouynipete, 306.

Powell, Lieut., on the Maldives, 186.
Protozoans, characters of, 377.
Pumice on coral islands, 288.
Pylstaarts, 305,'838.

Qtjelpaekt's Island, 311.
Quoy and Gaymard, depth of reef corals,
115.

Radiates, characters of, 374,

Raivavai, 337.

Rapa, 304.

Raraka, 169, 171, 201.

Rarotonga, 337,

Red Sea corals. 111, 314.

Reefs, formation of, 222.

" causes modifying forms of, 238.

" rate of growth of, 249.

" of windward side highest, 236.

INDEX.

405

Renillidee, 93.

Reproduction in Actiniae, 39.

Revillagigedo Islands, 303.

Rimetara, 337.

Ringgold, Capt., on Penrhyn's and otlier

Islands, 340.
Rivers, eflects of, 241.
Rocks, consolidation of coral, 152, 354.
Rose Island, 327.
Rota, elevation of, 345.
Rotuma, 30G, 343.
Ruriitii, 304, 305.
Rurntu, an elevated island, 336.

Sa(;aktta parasitica, 36.

St Augustine shell rock, 360.

Sala-y-Gomez, 303.

Salomon Islands, 309.

Salt Key Bank, 212.

Samoa, see Navigator Group.

Sandwich Islands, elevations at, 341 ; see

further Hawaian.
Savage Island, 338.
Savaii, 326.
Saya-de-Malha, 314.
Schomburgh, R. H., drift sands of Anega-

da, 185.
Sea- cucumbers, 160,
Sea, depths of disturbance of, by waves,

224.
Sea-ginseng, 160.
Sea slugs, 160.

Sea-water, composition of, 100.
Seriatopora, 70.
Senses in Actiniae, 39.
Septa, 43, 60.
Serle's Island, 171.
Seychelles, 314.

Shar[)les, S. P., analyses of corals, 99.
Sherboro Island, 315.
Shore-platform, origin of, 230.
Siau, ripple marks on sea-bottom, 224.
Silliman, B., analysis of dolomitic coral
rock of Matea, 357.

" analysis Of coral sand of

Straits of Balabac, 357.
Society Islands, 304, 321, 328.
Somers Island, 218.
Sooloo Sea, 311.
Soundings about atolls, 171.
Siponges, nature of, 378.

f Spontaneous fission, 56.
Starbuck's Island, 296, 339.
Starve Island, 296.
Staver's Island, 340.
Stevenson, force of waves, 225
Stimpson, Wm., observations by, 24, 83,

84, 92.
Stones of basalt or other rocks on coral

islands, 288.
Stntchbury, on Rurutu, 336.
Stylaster erubescens, 70.
Stylophora Danae, 70.
Subsidence in the Pacific, 319, 328, 331.
amount of land lost by, 330.
** period and extent of, and ac-

companying changes over
the globe, 364.
Sunday Island, 305.
Swain's Island, 168, 196, 338.
Sydney Island, 199, 341.
Synapticulae, 60.

Tafoa, 305, 338.

Tahiti, north shore of, 242.

'* thickness of reef, 158.

" no elevation at, 335.
Taiara, 167, 199.
Tanna, 307.
Tapateuea, 164, 169, 183.

elevation of, 343, 344.
Tarawa, 164, 169.

Tarawan Archipelago, see Gilbert.
Tari-tari, 167, 169.
Tealia crassicornis, see Urticina.
Teku, 197.

Telesto ramiculosa, 84.
Temperature limiting distribution of cor-
als, 108.
*• of Atlantic Ocean in pa»t

time, 362.
chart, 300.
Tetuaroa, 304, 326.
Thecocyathus cylindraceus, 48.
Tikopia, 307.
Timor, 310.
Timorlaut, 310.
Tinakora, 307.
Tonga Islands, 337.
Tongatabu, 305, 337.
Tripang, 160.
Truk, 306.

40f>

INDEX.

Tabipora fimbriata, 84.

syringa, 84.
Tubuai, 304, 337.
Tubularia, 103.

Tuomey, M., on Florida reefs, 204.
Tutuila, 305, 320.
Tyerman on Hualiine, 335.
" on Rurutu, 330.

Ualan, 806, 331,
Umbellularidie, 93.
Upolu, 305, 326.

*' thickness of reef, 158.

" liarbor of, at Apia, 241 ; at Falifa
244.
Urticina crassicornis, lasso-cells, 34, 36.

Vanikoro Group, 807.

Vavau, 305, 337.

Veretillum Stimpsoni, 91,92.

*' cynomorium, pliospliorescence

of, 92.

Verrill, A. E., on Cancrisocia expansa, 24 ;
on Epiactis prolif era, 40 ; on
coral secretion, 43 ; classifi-
cation of Actinoid corals,
61 ; compartments in Alcy-
onia all ambulacral, 81 ;
Anthelia and Telesto, 84 ;
spicules of Oorgoniae, 86;
on a species of Veretillum
and Copliobelemnon, 91 ; on
corals of Panama, 111 ; co-
rals of La Paz, 112 ; corals
of the West Indies, 113;
corals of the Brazilian
coast, 113 ; corals of the
Bermudas, 114 ; Whipple's
observations on corals of a
wreck, 125 ; accepted names
for species in Dana's Zoo-
phytes, 379 -84.

Vincennes Island, 179, 202.
Virgularid*, 93.

Volcanic action, effect of, in limiting the
distribution of corals, 301, 310, 320.
Vorticellae, nature of, 374.
Vulcano, 309.

Waihu, 303.

Wallis's Island, 306, 342.

Washington Island, 173, 197, 338.

Wateoo or Atiu, 336.

Water on coral islands, 283.

Waterlandt, 203.

Waves, action of on coasts, 231.

" force of, Stevenson, 225. .
West Indies, corals of, 112.
Weinland, D. F., rate of growth of corals

124.
Whippey Harbor, 246.
Whipple, J. A., corals from a wreck, 126.
" " coral heads of Turk's

Island, 139.
Whitsunday Island, 172.
Williams's Missionary Enterprivses, 805,
" rock and caverns of Atiu, 194,

361.
*' on Mangaia, Atiu, and Ruru-

tu, 336.
Williams, S. W., on biche-de-mar, 161.
Wilson's Island, 203.
Winds about coral islands, 298,

" effects of, 235
Wolchonsky, 169.

Xenia Dan^:, 82.
" elongata, 82.
** florida, 82.

Yap or Eap, C07.

ZOANTIIACEA, 61.

Zoantlms Americana, 62.

Zoophyte, 48.

Zoophytes, names now used for species in

Dana's Report on, Verrill, 379.
Zoc;thome, 48, 60.

THE END.

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