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Full text of "Corals and coral islands"

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HARVARD UNIVERSITY 




LIBRARY 

OF THE 

MUSEUM OF COMPARATIVE ZOOLOGY 



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tiiiiS. COMP. ZOOL. 
UBRARY 

m ~G (950 

HAHVARD 
UNIVERSITY 



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CORALS ^^n^ 



CORAL ISLANDS 



L2.. ^<3 



BY ^ 

JAMES D.^ANA, LL.D, 

Professor of Geology and Mineralogy in Yale College; Author of Reports, in connection 

with the IVilkes U.S. Exploring Expedition, on Geology, Zoophytes, and Crustacea : 

of a System of Mineralogy ; Manual of Geology, etc. 



' We wandered where the dreamy pahn 
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 Exp. 



SAMPSON LOW, MARSTON, LOW AND SEARLE, 

CROWN BUILDINGS, i88, FLEET STREET. 

1875. 

[A// Rights Reserved. '\ 



u 



MUS. COMP. ZOOL 
UBRARY 

JAN -(•> 1350 

HARVARD 
UNIVERSITY 



/ * 



LONDON 
R. CI AY, SONF, AND TA\I.OR, PRINTERS, 
BREAD STREET HILL. 



PREFACE 
TO THE ENGLISH EDITION. 

In presenting this volume to English readers, the prominent 
part which the science of Britain has borne in the develop- 
ment of the subjects discussed comes naturally to mind. 
The remarkable works and memoirs of Ellis, from 1754 to 
1786, which forced Linn/eus and Pallas ultimately to admit 
that corals belong to the animal kingdom, gave the earliest 
great impulse to the study of this branch of Zoology. On 
the other hand, Darwin's admirable investigations first made 
known the true nature and theory of coral reefs and islands. 
The publications of Ellis were constantly by my side in the 
preparation of my " Report on Zoophytes ; " and the theory 
of Darwin — as I have stated in my general preface — gave 
mc, in my ocean journeyings, not only light, but delight, 
since facts found their places under it so readily, and derived 
from it so wide a bearing on the earth's history. In later 
years have appeared the works of Johnston, Gosse, and 
HiNCKS, and the many memoirs of Gray, Forbes, Wright, 
Duncan, and other workers in science, which have aided 
largely in giving this department of Zoology its present 
advanced position. Since the subject of polyps is only 
incidental to the main topic of this volume, I have not 
had occasion to refer to the details of these memoirs. But 
the name of Gosse appears often in connection with passages 
cited from his " British Sea-Anemones ; " and I heartily com- 
mend his work to all who would appreciate the beauties ot 



PREFACE TO THE ENGLISH EDITION. 

these flower-like animals, and are able to enjoy science 
when well set forth by a genial author. 

Justice to France requires that these allusions to the science 
of polyps in Great Britain should be followed by a mention 
of the eminent names of Milne Edwards and Jules Haimr, 
of Paris, chief among the makers of the science of polyp- 
corals ; and by a reference also to the fact that France, 
through Peysonxel, was ahead in establishing by investigation 
the animal nature of corals, this observer proving his point 
at Marseilles, in 1723, on specimens of the very species that 
had just before been declared to be flowering plants by 
Marsigli, and afterward confirming his results by thirty years 
of study among the reef-corals of Guadaloupe. It should be 
added, also, that the rest of P'.urope has made large contribu- 
tions to the science, through Pallas, Esper, Ehrenberg, and 
other later investigators. If France, in past times, has taken 
the lead, she has had the advantage of a sea-coast of more 
than a thousand miles on the ocean, and of a long line also on 
the warmer and more prolific Mediterranean. 

The discovery of deep-sea corals by recent dredging expedi- 
tions has opened up a new field for coral investigations, no 
less important to (icology than to Zoology. But while so 
much attention has been absorbed in this direction, it should 
be remembered that the interest of the old coral-fields is far 
from exhausted, and that one great and most important sub- 
ject, the rate of growth of corals, and of the increase of 
reefs, waits for investigators. 

James D. Dana. 

New Haven, Conn., March i, 1872. 



PREFACE 

TO THE SECOND EDITION. 

The principal additions wliich have been made to this work 
in the preparation of the second edition are : an abstract of 
an important paper on the Bahamas, by Captain (now Major- 
General) Nelson, R.E., read before the Geological Society of 
London in 1852 ; an account of the interesting observations of 
Mr. J. Matthew Jones, from Nature of August 1872, bearing 
on the former extent of the Bermudas; facts stated by 
Mr. S. J. Whitnell with regard to some Pacitic coral islands ; 
and a report of the planting, by MM. Le Clerc and De 
Benaze, of slabs of coral rock at Tahiti, near the slab placed 
by Admiral Wilkes, to aid in future determinations of the rate 
of growth of the Dolphin Shoal, together with a Map of the 
region. Other minor changes have been made which it is 
not important here to enumerate. 

James D. Dana. 

March, 1875, 



h 



PREFACE. 



The object in view in the preparation of tins work has been 
to present a popular account of " Corals and Coral Islands," 
without 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, explana- 
tions 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. 

1 have opened the volume with a chapter on " Corals and 
Coral Makers,"" describing, under it, the forms and structure 
of Polyps ; how they Hve and grow and hold their own in a 
world of enemies ; how coralmaking 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 structme of these reef-formations, an account of 
their mode of accumulation and increase, and a discussion of 
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. 



viii PREFACE. , 

The observations forming the basis of the work were made 
in the course of the cruise of tlie Wilkes Exploring Expedi- 
tion around the world during tlie 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 Cieological Report. 

The opportunities for investigations in this department 
afforded by the Expedition were large, ^^'e 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 
P'eejee Group, one of the grandest regions of growing corals 
in the world, where we spent three montlis ; several islands 
north of the Navigator and Feejee Groups, including the 
Gilbert or Kingsmill Group ; the Sooloo sea, between Borneo 
and Mindanao, abounding in reefs ; and, finally, Singaj)ore, 
another P^ast India reef-region. 

Most agreeable are the memories of events, scenes and 
labours, 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, 
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 
explored, mountains and volcanic cones climbed, and a burn- 
ing crater penetrated a thousand feet down to its boiling 



PREFACE. ix 

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 central 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 Feejee 
savages with human bones to their mouths, finishing off the 
cannibal feast of the night ; and as thoughtless of any impro- 
priety as if the roast were of wild game taken the day before. 
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 
Soutliern Fuegia, and finding anchorage under Noir Island, 
but not the hoped-for shelter Irom either winds or waves ; the 
sea at the time dashing up the black cliffs two and three 
hundred feet, and shrouding in foam the high rocky islets, 
half-obscured, that stood about us ; the cables dragging and 
clanking 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 
instant of waiting among all on board for the final crash ; then, 
that instant hardly passed, the loud calm command of the 
Captain, 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 cHffs 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 tropics, we were in full expecta- 
tion of soon landing joyously on the shores of the Columbia ; 



X PRE FACE. 

of the vessel suddenly striking bottom ; then, other heavier 
blows on the fatal bar, and a quivering and creaking among 
the timbers ; the waters rai)idly 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 oft" by the waves, the hulk buried 
in the sands. 

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

In explanation of some allusions in the following pages, I 
may here state with regard to the Exploring Expedition, that 
Captain (now Admiral) Charles Wilkes, U.S.N., the Com- 
mander of the Expedition, was in charge of the Slooi)-or-war 
Vincenucs ; Capt. W^l L. Hudson, U.S.N., of the Sloop-of- 
war Peacock; Capt. A. K. Long, U.S.N., of the Storeshi]) 
Relief (the vessel which encountered the dangers in the 
Cape Horn sea, above related) ; and Eieut.-Commandant C. 
RiNGGOi>D, of the Brig Porpoise ; and that my associates in 
the "Scientific Corps" were Dr. Charles Pickering, J. P. 
CouTHOUY, and Titian R. Pkale, Zoologists ; Wm. Rich and 
J. D. Breckenridge, Botanists; Horatio Hale, Philologist : 
Joseph Dravt(3N and A. T. Agate, Artists. 

Our cruise ltd us partly along the course followed by 
Mr. Charles Darwin during the years 183 1 to 1836, in the 
voyage of the Peagie, under Captain Fitzrov ; and, where it 
diverged from his route, it took us over scenes, similar to his. 
of corq,l and volcanic islands. Soon after reaching Sydney, 
Australia, in 1839, a brief statement was found in the papers 
of Mr. Darwin's theory with respect to the origin of the atoll 
and barrier forms of reefs. The paragraph threw a flood of 



PREFACE. xi 

light over the subject, and called forth feelings of peculiar 
satisfaction, and of gratefulness to Mr. Darwin, which still 
come up afresh whenever the subject of coral islands is men- 
tioned. The Gambler 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 slill grander scale and of more diversified character, so 
that I was afterward enabled to speak of his theory as estab- 
lished with more positiveness than he himself, in his philosophic 
caution, had been ready to adopt. His work on Coral Reefs 
appeared in 1842, when my Report on the subject was already 
in manuscript. 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 therefrom 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 
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 courseof the volume, and need not here 
be rementioned. I have occasion, however, for special ac- 
knowledgments to our excellent Yale Zoologist, Professor A. 
K. Vp:rrill, who now stands first in the country in the depart- 
ment of Zoophytes. Through his recent memoirs on the subject, 
and also by his personal advice, I have been greatly aided in 
acquainting piyself with the present state of the science : — my 
own special labours 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 



xii PREFACE. 

from the works or memoirs of Gosse, Mubius, 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 beautifidly ilhistrated popular works, " Le 
Monde du Mer " and '" La Vie et les Moeurs des Animaux ; " 
but nearly half of these were engraved from m.y plates. Tlie 
sources of all the figures are given in the List of Illustrations. 

James D. Dana. 
New Haven, Conn., Feb, 12, 1872. 



CONTENTS. . 



CHAPTER 



CORALS AND C(H<AL MAKERS 



General Observations 



I. Polyp 



I. Actinoid Polyps .... 

1. Non-Coral Making Actinoid Polype 

2. Coral-Making Actinoid Polyps 

3. Classification .... 
IL Cyathophylloid Polyps . 

111. Alcyonoid Polyps .... 
IV. Life and Death in Concurrent Progress 
V. Composition of Corals . 

TI. HVDRcnDS 

HI. Bryozoans 

IV. Alg.e; or Nullipores and Corallines 

V. The Reef-Forming Corals, and the Causes i 
encing their Growth and Distribu' 

I. Distribution in Latitude . 

II. Distribution in Depth 

III. Local Causes influencing Distribution 

IV. Rate of Growth of Corals 



PAGE 
I 

3 

5 
.5 

22 
40 
55 

57 
70 

74 

76 
81 
82 

S3 
S3 
89 

93 
96 



CONTENTS. 



CHAPTER II. 

STRUCTURE OF CORAL REEl-S AND ISLANDS. 



I. Coral Reefs 

1, General Features 

n. Outer Reefs 

in. Formations in the Sea Outside of Barrier Reefs 

IV. Inner Reefs 

V, Channels among Reefs 

VI. Beach Sand Rock 

VII. Drift Sand Rock 

VIII. Thickness of Reefs . 

IX. A flood word for Coral Reefs 



II. Coral Islands 

I. Forms and General Features 
II, Soundings about Coral Islands 

III. Structuic of Coral Islands . 

IV. Notices of some Coral Islands 

Maldive Archipelago . 

Great Chagos Bank 

Metia, etc. . 

Jar vis's Island 

Birnie's and Swain's Islands 

Otuhu, Margaret, Tehu, Was 

Island 
Ilonden, or Ilenuake . 
Taiara, Sydney's, Uuke of \ 
Fakaafo, Ahii 
Raraka 
Kawehe 

Manhii, Aratica, Nairsa or I 
Florida Reefs and Keys 
Soundings between Florida R 
Bahamas 

Salt Key Bank . 
Bermuda or Somcrs' Island 



)can s 



ngton Isl 



and C 



uba 



and, Ender 



bury' 



PAGE 
lOI 

lOI 

no 

114 
118 

122 

124 

127 

130 
130 

140 
156 

160 

160 
162 
162 
163 
164 
165 
165 
167 
172 

179 
182 



CONTENTS. 



CHAPTER III. 

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

I. Formation of Reefs 

I. Origin of Coral Sands, and of the Reef-Rock . 

II. Origin of tlie Sliore Platform ..... 

III. EflTects of Winds and Gales ..... 

II. Causes ModifvinCx the Forms and Growth of Reefs 
I. Barrier and P'riniiinji Reefs ..... 



II. Atoll Reefs 



III. Rate of Growth of Reefs 

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

THE Atoll Form of Coral Islands . 

1. Old Views 

II. Origin of Channels ^^•ithin Barriers .... 
III. Origin of Lagoons of Atolls ..... 

V. The Co.mpleted Atoli 

CHAPTER IV. 

GEOGRAPHICAL DISTRIBUTION OF CORAL REEFS AND ISLANDS. 



189 
196 
200 

203 

203 
211 

212 

218 

218 
220 

227 

233 



255 



CHAPTER V. 

CIIANGFS OF LEVEL IN THE PACIFIC OCE.A.N. 

I. Evidences of Change of Level 
II. Subsidence indicated by Atolls and Barrier Reefs 
III. Effect of the Subsidence .... 
IV. Period of the Subsidence .... 
V. Elevations of Moilern Eras in the Pacific 



272 
274 
282 
2 84 
2S4 



CHAPTER VL 

GEOLOGICAL CONCLUSIONS. 

I. Formation of Limestones .... 
II. Beds of Limestone with Living Margins . 



299 



xvi CONTENTS. 

III. Making of Thick Strata of Limestones . 

IV. Subsidence Essential to the Making of Thick 

Strata 

V. Deep-Sea Limestones seldom made from Corai 

Island or Reef Dehris .... 

VI. Absence of Fossils from Limestone Strata 

VII. The Wide Range of the older Limestones not 

Exemplified in Modern Coral-Reef Formations 
VIII. Consolidation of Coral Rocks . . . . 
IX. Formation of Dolomite or Magnesian Carbonate 

OF Lime 

X. Formation of Chalk 

XL Rate of Increase of Limestone Formations 
XII. Limestone Caverns 

XIII. Oceanic Temperature 

XIV. The Oceanic Coral-Island Subsidence 



PAGE 

301 



301 
302 



305 

307 
308 

309 
310 

311 
314 



APPENDIX. 

I. Geological Time 321 

II. Radiates 322 

III. Protozoans 325 

IV. Names of Species in the Author's Report on 

Zoophytes ......... 327 

V. List of Works referred to, and of Abbreviations . 337 



Index 



341 



LIST OF ILLUSTRATIONS. 

The following list contains a statement of the original sources of the 
illustrations through the volume. By "Author's Atlas" is to be under- 
stood the Atlas of his Report 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. i, Phymactis florida. Author's Zoophyte Atlas, Plate 2. 
,, ,, 2, Phymactis clematis. Author's Zoophyte Atlas, Plate I. 

,, ), 3> 3^> Bunodes gemma. Author's Zoophyte Atlas, Plate 

4, 3a, the polyp contracted. 

PAGE 

6. Paractis Rapiformis, Edw. From a drawing by the Author, made in 1852. 

7. Cancrisocia expansa. Verrill, Amer. Naturalist, from Proc. Essex 

Institute, vol. vi. 
9. fig. I, Peachia hastata. Gosse's Actin. Brit, Plate viii. 

fig. 2, Edwardsia callimorpha ; and 3, Halocampa chrysanthellum. 
Ibid., Plate 7. 
10. Section of Actinia. From a drawing by the Author, made in 1856, 

on the basis of a study ([852) of the Actinia figured on p. 6. 
14. Lasso-cells. Dr. K. Mobius, Abh. Nat. Ver. Hamburg, vol. v., 
1866. 

22. Caryophyllia cyathus. Le Monde du Met. 

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

Flabellum Povonium. 

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

Animaux. 

26. Fungia lacera, living and expanded. Author's Zoophyte Atlas, 

Plate 18. 

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

of the calcareous septa. Ibid., Plate 18. 
29. Madrepora aspera, living and expanded. Author's Zoophyte Atlas 
Plate 38. 

31. Dendrophyllia nigrescens, living and expanded. Author's Zoophyte 

Atlas, Plate 30. 

32. Goniopora columna. Ibid., Plate 56. 

33. Porites mordax. Ibid., Plate 53. 

34. Cladocora arbuscula. Ibid., Plate 30. 

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

36. Spontaneous fission. Author's Repoit on Zoophytes. 

37. Astraea pallida. Author's Zoophyte Atlas, Plate 10. 
37. Caulastrasa furcata. Ibid., Plate 9. 

b 



X vi ii LIST OF ILL USTRA TIONS. 

lAGE 

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

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

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

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

43. Astra-a pallida. Author's Zoophyte Atlas, Plate lo. 

44. Diploria cerebriformis. Le Monde du Mer. 

45. Fungia Danw. L. Sanford, one-sixth the natural size ; from a photo- 

graph by Prof. A. Y.. Verrill. 

46. Caryophillia Smithii, one of the figures with the" animal expanded ; 

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

47. Astrangia Uanae; fig. a one of the polyps enlarged; c, coral with 

the polyps expanded, natural size. Agassiz, Seaside Studies, 
fig. b, surface of corallum, natural size. L. Sanford, from specimen. 
69. Phyllangia Americana, a Florida species. Edwards and Haime, 

Corallieres. 
fig. I, Oculina varicosa, extremity of a branch. Author's Report on 

Zoophytes, page 67, corrected from specimen, 
figs. 2, 3, Stylaster erubescens ; 2, corallum, natural size ; 3, extremity 

of a branch enlarged. Pourtales, Deep-Sea Corals, 
figs. 4, 5, Stylophora Dana; ; 4, extremity of a branch ; 5, one of the 

calicles enlarged. Author's Zoophyte Atlas, Plate 4Q. 
fig. 6, Polyp, enlarged, of St. mordax. Author's Zoophyte Atlas, 

Plate 49. 
fig. 7, Pocillipora grandis. L. Sanford ; from an Exploring Expe- 
dition 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 

stnicture. Ibid., Plate 50. 

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

Plate 31. 

51. Madrepora formosa. Author's Zoophyte A.tlas, Plate 38. 

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

53. Dendrophyllia nigrescens, natural size. Ibid., Plate 30. 

54. Alveopora Verril.Uana, natural size ; the corallum covered below with 

a peritheca. 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. 

55. Polyp of Porites levis, enlarged. Author's Zoophyte Atlas, Plate 54. 
6. Porites levis, with the polyps of one of the branches expanded, natural 

size. Author's Zoophyte Atlas, Plate 54. 

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

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

Plate 5. From a drawing by Dr. Stimpson. 
60. Telesto ramiculosa. Verrill, Proceedings of the Essex Institute, vol. 
iv., Plate 6 ; the second figure an enlarged view of expanded polyp. 
From drawings by Dr. Stimpson. 



LIST OF ILLUSTRA TIONS. xix 

'6^ Tubipora syringa ; fig. i. part of a clump, natural size ; 2, one of the 
polvps expanded. Author's Atlas, Plate 59. . v •• 1 , 

Tubipora fimbriata (3rd figure) polyp, expanded. Author s Zoophyte 
Atlas, Plate 59. , • a .1 ' v •• 

62. Gorgonia (?) flexuosa, part of zoophyte, natural size. Author s Zoo- 

6:; SpFcSes^f c'orgo^^,''much enlarged. Verrill, Transactions of the 

Connecticut Academy of Sciences, vol. 1., Plates 4 and 5. 
6:;. Isis Hippuris. La Vie et les Moeurs des Annnaux. 
66. CoralUum rubrum, the coral, natural size. L. Sanford, from specimen. 
Extremity of branch of C. rubrum, enlarged, with some of the ani- 
mals expanded. Lacaze-Duthiers, from La Vie et les Moeurs des 

Animaux. , ^ 1 j • r ^„ 

68 Cophobelemnon clavatum ; the small figure, enlarged view of one 
of the polyps. Verrill, Proceedings of the Essex Institute, vol. 
iv , Plate «;. From a drawing by Dr. Stimpson. 
Veredllum Stimpsoni, enlarged 3 diameters. Verri 1, Proceedings 
of the Essex Institute, vol. iv., Plate 5. From a drawing by Dr. 
Stimpson. 
71. Caulastrrea furcata. Author's Zoophyte, Plate 9. 

77. Hydra. Le Monde du Mer. 

78. Hydramania falcata. Le Monde du Mer. 

79 Millepora alcicornis. La Vie et les Moeurs des Animaux. 

80. Animals of M. Alcicornis, enlarged. L. Agassiz, Contributions to 

the Natural History of the United States ; vol. 111., Plate 15. 

81. Hornera lichenoides: I, natural size ; 2, part of branch enlarged. 

Smitt's Mem. des Bryozoaires. , tt.- 1 

Discosoma Skenei, part of a group much enlarged, ibid 
103. High Island, with Barrier and Fringing Reefs. Author s Geol. 

Report, 
106 Map of New Caledonia. Darwin on Coral Islands. 
III. The Lixo Coral Abrolhos. Harrt's Brazil, p. 202. 
119. Coral Reefs off the North Shore of Tahiti. Author's Exp. Geolo- 

crical Report, from the Wilkes Expl. Maps. 
131. Coral Island, or Atoll. Wilkes's Narr. Expl. Exped. 
133. Map of Gilbert or Kingsmill Islands. Authors Geol. Rep.; from 

Expl. Exp. Maps. ^ . , t 1 i 1 

13=:. Maps ot Taiara, Henuake, Swain's Island, Jarvis s Island, and 

Fakaafo. Author's Geol. Rep. ; from Expl. Exp. Maps. ^ 

137. Map of Menchikofif Atoll. Darwin on Coral Reefs ; from Kotzebue s 

Atlas 
142. Section of the rim of an Atoll. Author's Exp. Geol. Report. 
145. Blocks of Coral on the shore platform of Atolls. Authors Geol. 

Report. 1 T> f 

1 1,2 Map of Maldive Archipelago. Darwin on Coral Reels. 
153. Map of Mahlos Mahdoo Atoll, one of the Maldives. Darwm on 

Coral Reefs. 
155. Map of Great Chagos Bank. Darwin on Coral Reels. 
I «;6. East and West Section across the Great Chago^Bank. Ibid. 
158. Metia, an elevated Coral Island. Wilkes's Narrative of Expl. Exp., 

183 Map of the Bermuda Islands. Reduced from an English chart. 
197. The "Old Hat." Author's Exp. Geol. Report. 



X X LIS T OF ILL US TRA TIONS. 

PAGE 

204. Harbour of Apia. Author's Exp. Geol. Rep. ; [from charts of the 

Wilkes Expl. Exped. 
206. Part of North Shore of Tahiti. Ibid. 
208. Harbour of Falifa. Ibid. 
210. Whippey Harbour. Ibid. 
217. Map of the Coral reefs in Matavai Bay, Tahiti; from a chart by MM. 

Le Clerc and Minier. 

223. Section illustrating the Origin of Barrier Reefs. Ibid. 

224. Map and Ideal Section of Aiva Island. Ibid. 
227. Map of Gambler Islands. Darwin on Coral Reefs. 

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

230. Menchicofif Atoll. Darwin on Coral Reefs. 

235. Fakaafo. Author's Geol. Rep., from Charts of Expl. Exped. 
At close of vohime : — 

Isocrymal Chart of the World. Author's Report on Crustacea. 
Map of the Feejee Islands. Wilkes's Narrative of the Expl. 

Exped. 
Map of the Florida Reefs, and the Seas between them and Cuba. 
De Pourtales on Deep-Sea Corals. 



( 



I 



CORALS AND CORAL ISLANDS, 



CHAPTER I. 

CORALS AND CORAL MAKERS. 

A SINGULAR degree of obscurity has possessed the popular 
mind with regard to the growth of corals and coral reefs, in 
consequence of the readiness with which speculations have 
been suppUed and accepted in place of facts ; and to the 
present day the subject is seldom mentioned without the quali- 
fying adjective mysterious expressed or understood. Some 
writers, rejecting the idea which science had reached, that reefs 
of rocks could be due in anyway to "animalcules," have talked 
of electrical forces, the first and last appeal of ignorance. 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 labours ; 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 honeycomb of the bee, or the hillock of a 
colony of ants. 

B 



2 CORALS AND CORAL LSL.AhWS. 

Science, while it penetrates deeply the system of things 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 foil 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 com- 
prehension, that a polyp should form structures of stone (car- 
bonate of lime) called coral, than that the quadruped should form 
its bones, or the mollusk its shell. The processes are similar, 
and so the result. In each case it is a simple 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, carbonate 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 simpli- 
city 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 ot 
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 labour than bone making in 
ourselves. And again, it is not a collection of cells 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 science — of a polyp, in 
most reef-making species, is enclosed within the polyp, where it 
was formed by the secreting process. 



i 



CORALS AND CORAL MAKERS. 3 

It is not, perhaps, within the sphere of science to criticise the 
poet. Yet we may say in this place, in view of tlie frequent 
use of the Hnes 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 little 
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. 

Coral is made by organisms of four very different kinds. These 
are : First^ 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. 

Thh'd, The lowest tribe of MoUusks, called Bryozoans, which 
produce delicate corals, sometimes branching and moss-like 
(whence the name from the Greek for moss animal), and at 
other times in broad plates, thick masses, and thin incrustations. 
Although of small importance as reef-makers at the present time, 
in a former age of the world — the Paleozoic — they so abounded 
over the sea bottom that some beds of limestone are half com- 
posed of them. 

Fourth, Algai or sea-weeds, some kinds of which would hardly 
be distinguished from corals, except that they have no cells or 
pores. 

I. POLYPS. 

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 colouring is singularly close. The 



4 CORALS AND CORAL LS LANDS. 

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 cylindrical pedicel 
or body, often as broad as the disk itself, and sometimes not 
much longer, which contains the stomach and internal 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 difference being required 
by the different modes of nutrition and other characteristics in 
the two kingdoms of nature. The coral polyp is as much an 
animal as a cat or a dog. 

The figures of the frontispiece, and others on pages 6, 7, 
9, sustain well the description here given, and afford some idea 
also of the diversity of form among them. 

The prominent subdivisions of polyps here recognized are the 
following : — 

I. AcTiNoiD Polyps. — Related to the Actinia, or vSea- 
anemone, in tentacles and interior structure, and having, as in 
them, the number of tentacles and interior septa a multiple 
of six. The name Actinia is from the Greek ray. 

II. CvATHOPHYLLOiu PoLYPS. — Like the Actinoids in tenta- 
cles and interior structure, except that the number of tentacles 
and interior septa is a multiple of four. 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 fea- 
ture of the Alcyonoids. The Cyathophylloids were the earliest 
of polyps, and the most abundant species in Paleozoic time. 

HI. Alcyonoid Polyps. — Having eight fringed tentacles, 
and other characters mentioned beyond ; as the Gorgonix and 
Alcyonia. 



CORALS AND CORAL MAKERS. 5 

I. ACTINOID POLYPS. 

'J'he highest of Actinoid Polyps are those of the Actinia 
iKiBE — 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 aftei- 
ward the distinguishing characters of the coral-making polyps 
may be mentioned. In external aspect and in internal charac- 
ters all are essentially identical. 

I. NON-CORAL-MAKING POLYPS. 

As the figures on the frontispiece, and also the following, 
show, the external parts of an Actinia are — a subcylindrical 
body— a disk at top — one or more circular series of tentacles 
making a border to the disk — a mouth, a merely fleshy, tooth- 
less 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 abadhial. 

Sea-anemones vary greatly in colour, and in the distribution 
of their tmts. The lower figure on the frontispiece represents 
one variety of the Fhy?tiaclis clematis from Valparaiso. Another 
variety of the same lias a rich deep green colour. The upper 
species on the same plate is one of the gorgeous varieties of 
the Phymadis florida 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 Biuiodcs 
ganma, from Porto Pray a. Cape Verd. It is one of the warty 
species, and is but partly expanded. The same is shown un- 
expanded m figure 3^;, on the right, with disk and tentacles, as 
usual in this state, wholly concealed. 

While often brilliantly coloured, especially in the tropics, 
other Actiniai are nearly colourless. This was the case with 
that represented in the following cut, a species from Long 
Island Sound near the New Haven Lighthouse, figured some 
twenty years since by the author, but left undescribed. The 



6 CORALS AXD CORAL ISLANDS. 

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, &C. It was generally very slow^ in its changes, and 
sometimes continued in the same vase-attitude for a whole 
day. 




I'AKACrib KAl'IFOK.MIS, KUW. 



Actiniae vary immensely in size— from an eighth of an inch 
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 



COKALS AND CORAL MAKERS. 7 

Pacific, a coloured figure of which is given in the Atlas of the 
Author's Report on Zoophytes (Plate HI.)? had a diameter 
across its disk o( four tee? i inches ; and it was also one of the 
most beautiful in those seas, having multitudes of tentacles 
with carmine tips and yellowish bases, around the open centre, 
gathered into a number of large groups or lobes. 

With rare exceptions. Actiniae 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 slowness. 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. 




CAXCRISOCIA EXPANSA St., ON THE BACK OF DORII'I'E FACCHINO. 



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 kind of 
association styled cotnmensalisju 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 



8 CORALS AND CORAL LSLANDS. 

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 afterwards, 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, 
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 solitary 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 favourite, proving an inherited 
instinctive preference for rapid change of place, and for just 
that kind of change, or range of conditions, which the pre- 
ferred commensal provides. Prof. Verrill has an interesting 
article on this subject, with especial reference to crustaceans, 
in the third volume of the Aino'ican 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 Actinia, 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-Anemones," 
in which they are given with the natural colours. Figure i re- 
presents the Peachia hastata of Gosse, a beautiful species hav- 
ing twelve large tentacles; figure 2 the Edwardsia callvnorpha 



COKALS AND COITAL MAKERS. 9 

().; figure 3, Halocampa chrysa?ithcUum 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 a kind of case or 
jacket, into which the upper extremity, which is soft and 
delicate in texture, may be retracted. I'he thickening of the 




epidermis in this middle portion is produced through the 
entanghng of disintegrated cells and minute foreign particles, 
sometimes in part spores of Confervae, by means of the mucus 
of the surface ; and if the layer is removed, as it may be, the 
skin will again become covered. This species, like others of 
the genus, Uves buried to its neck in the sand, that is, with the 
soft upper extremity protruding. If disturbed, the head is 
suddenly drawn in, together with more or less of the following 
jacketed part of the body. 



lO 



CORALS AND CORAL ISLANDS. 



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

The hiteriial sti'iidure oi 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 below 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 general way a horizon- 
tal section of the body through the stomach, and shows the 
posidon of the radiating septa and the intermediate compart- 
ments. It presents to view the fact that these are in pairs, and 
another fact that the number of pairs of partitions in the 
ordinary Actinoid polyps is regularly some multiple of six, 
although other numbers occur during the successive develop- 
ments that take place in the growth of a polyp, and are 



CORALS AND CORAL MAKERS. ii 

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. 

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

Although polyps are true Radiates, they have something ot 
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 colour from the general surface ; 
of one tentacle larger than the others, and sometimes peculiar 
in colour ; 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 Pocillopor^ (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 "Mmd 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 on either side of the one chief or anterior 
tentacle : and Prof. Verrill, that in Zoanthids they are formed 
principally on either side of this anterior tentacle and also ot 
the opposite or posterior one, and much less rapidly, if at all, 
along the sides intermediate. This chief-tentacle marks properly 



12 CORALS AND CORAL LS LANDS. 

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 mani- 
fested *by these flower-like polyps. In fact perfect circular 
series in organs or parts do not belong to any living organism, 
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 disguised 
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- 
])ansion depends on an injection of the structure with salt water, 
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. 

The Actinia appears, at first thought, to be well prepared for 
securing its prey through its numerous tentacles. Bat 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 swallow an 
animal nearly as large as itself; it gradually stretches the 



CORALS AND CORAL MAKERS. 13 

m.irgins of the mouth over the mollnsk or crab, until the 
^' .:oIe is inclosed and passed into the digestive sac ; and when 
tl, estion 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 itself last, and 
this is usually done " with lightning-like rapidity." Then 
follows the poison. The lasso-cells (called often nettling cells, 
and by Gosse cnidcs, and thi-ead capsules) are usually less 
than a 200th 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 mollusk 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 ren- 
dered incapable of resistance. 

The following figures, by Dr. Karl Mobius, of Hamburg, 
illustrate admirably these organs. The views are magnified 
700 diameters. Figure i represents one of the lasso-cells of 
the Actinia, Corynactis 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 I in having the basal 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 
figure 5. The lasso-cells in the above species are from a 240th 
to a 360th of an inch in length. In the Aletridmm viargina- 



CORALS AND CORAL LSLANDS. 




tum^ an American Acti- 
nia occurring along the 
coast of the United 
States, north of New 
York, the length of one 
of the lasso-cells, ac- 
cording to Dr. Leidy, 
was about a 400th of 
an inch, and the charac- 
ter of the extended lasso 
was much like that ot 
figure 4. The lower 
part of the lasso, for a 
length \\ times or more 
longer than the cell or 
sheath, is usually thick- 
ened, and sometimes 
slender ly 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 occasion- 
ally forty times ; but if 
the thread-like part is 
absent, only one and a 
half to two times. 
A lasso cell once used 



CORALS AXD CORAL MAKERS. 15 

is afterward worthless ; for the tube cannot be returned to 
tlie sheath. But those thus expended are not missed, as the 
])olyp has indefinite suppUes of such weapons, and also ready 
means of refurnishing itself 

Figures 6, 7,8, 9, 10, pp. 14, 15, illustrate different stages in 
the development of a lasso-cell (figure ro) out of a com ^^m 
mon spherical cell, as made out by Dr. Mobius in his j^B 
careful microscopic investigations. The Actinia afford- IH^ 
ing the results was the Urticina crassicornis, found in ■^|i 
both European and American seas. The actual size of B|y 
the cell represented in figure 6 is about a 5000th of an K^ 
inch. In figure 7 the lasso-cell has already taken form 1^9 
but is folded on itself; in 8, there is a second infold- iBI 
ing ; 9 shows a return to a single fold, and further ^SA 
progress in the forming cell; and 10, the straightened- Wtm 
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 ot 
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 ex- 
tended from the body through some natural orifices near the 
base of the Actinia (especially those of the Sagartia family), 
(iosse 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. 



i6 CORALS AND CORAL ISLANDS. 

" It has long been known, that a very slight contact with the 
tentacles of a polyp is sufficient to produce, in any minute 
animal so touched, torpor and speedy death. Since the dis- 
covery of these c/iida; (lasso-cells) the fatal power has been 
supposed to be lodged in them. Baker, a century ago, in 
speaking of the Hydra, suggested that ' there must be some- 
thing eminently poisonous in its grasp ; ' and this suspicion 
received confirmation from the circumstance that the Entomos- 
traca which are etiveloped in a shelly covej'lng frequently escape 
unhurt after having been seized. The stinging power possessed 
by many Medusae, which is sufficiently intense to be formid- 
able even to man, has been reasonably attributed to the same 
organs, which the microscope shows to be accumulated by 
miUions 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 
edhorceum (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 cnidcc 
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 acofitiiim had, 
in their rowing action, brought it into contact with the sucker, 
round which it then continued slowly to revolve. The result 
I presently discovered to be, that a considerable number of 
cnidce. had shot their ecthorcea into the flesh of the sucking-disk 
of the Echinoderm, and were seen sticking all round its edge, 
the wires (lassos) being imbedded in its substance even up to 
the very capsules, like so many pins stuck around a toilet pin- 
cushion. 

'' 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- 



CORALS AND CORAL MAKERS. 17 

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 fully-expanded Tealia crassi- 
cornis {Urlicina 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 1 
had expected, cnidce standing up endwise, the wires in every 
case shot into the substance. They were not numerous — in a 
space of -Qi 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 
cct/iorcea. 

"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. ... I have elsewhere recorded an instance in 
which a little fish, swimming about in health and vigour, died 
in a few minutes with great agony through the momentary con- 
tact of its lip with one of the emitted acontia of Sagai'tia para- 
sitica. 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 ecthonea 
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 edhorcea!' 

The following observation by J. P. Couthouy, from the 
author's Report on Zoophytes (p. 128), if it is beyond question, 
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, 1 

c 



i8 CORALS AND CORAL LSLANDS. 

took out half-a-dozen, and placed them in a jar with an Actinia 
{Ant/iea Jias;el/ifera). 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 w^hen returned to the jar with the other Monodontas, they 
were in less than five minutes clustered round its mouth. On 
placing them again in the jar with the Actinia, though kept 
there for two hours, they did not once show themselves out of 
the shell. Once more placing them along with the other shells, 
they exhibited their former signs of life and activity. The ex- 
periment was repeated several times with a large Littorina, 
with the same result, evincing fear of the Actinia on the part 
of the Mollusks." 

Gosse gives the following fish story, which is much to the 
point. Speaking of the Aiithca cercus, or Opelet, a British 
species, he says (p. i68) : — " I one day saw an amusing exam]jle 
of its power of passive resistance. A beautiful little specimen 
of the variety alabastrijia., which had been sent to me by Mr. 
Gatehouse, I had occasion to remove from one tank to another. 
There was a,half-growm Bullhead (Coitus bubalis) at the bottom, 
which had been in captivity rather more than a fortnight. As 
he had not been fed during that time, I presume he was some- 
what sharp-set. He marked the Anthea falling, and before it 
could reach the bottom, opened his cavern of a mouth and 
sucked in the hojine boucJie. It was not to his taste, however, 
for as instantly he shot it out again. Not discouraged, he re- 
turned 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 once more ; and now the Bull- 
head, 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.' Risso 
calls this species ' edidis^ and says of it — * On le mange en 



CORALS AND CORAL MAL'CERS. 19 

friture^ and I can say, ^ Probatum est.^ No squeamishness of 
stomach prevents our volatile friends, the French, from appre- 
ciating its excellence ; for the dish called Rastcgna, which is a 
great favourite in Provence, is mainly prepared from AntJiea 
cefeiis. I would not dare to say that an Opelet is as good as 
an Omelet ; but diacun a son goiit — try for yourselves. 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 
material 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 
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 bra?ichice for the aeration of 
the blood, the whole surface of the body being ordinarily 
sufficiently soft and delicate to serve in this function. Some 
species Uve half buried in the sand, and, as this in large spe- 
cies would prevent the skin of the sides from aiding in respira- 
tion, there are sometimes very much lobed and crimpled organs, 
attached to, or alongside of, the tentacles, which give the 
animal-flower much greater beauty, and at the same time in- 
crease the extent of surface for the purposes of aeration ; 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 corria- 
ceous, or is filled with grains of sand, there are narrow gills 
arranged vertically, one on either side of the larger radiating 
septa, figures of which are given in the author's Zoophyte 
Atlas. 

As to senses, Actinia, or the best of them, are not quite as 

C 2 



20 CORALS AND CORAL ISLANDS. 

low as was once supposed. For, besides the general sense of 
feeling, some of them have a series of eyes, placed like a 
necklace around the body, just outside of the tentacles. The 
yellow prominences in this position on the larger figures in the 
frontispiece are these eyes. They have crystaUine 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-making 
polyps. 

The ovarian and spermatic functions belong to the radiating 
septa in the interior cavity of the Actinia, and to the part of 
a septum, mesenteric in character, at or near the outer margin. 
They have the aspect of a pulpy mass, or look like clusters of 
ovules. The ova have no chance for escape except through 
the stomach and mouth. They are covered with vibratile cilia, 
and rove about free for a while. As the development 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. Actiniae 
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 and independent animal. At times, as Prof. H. James 
Clark has observed, small pieces of the base of an Actinia 
separate by a natural process before a trace of a tentacle has 



CORALS AND CORAL MAKERS. 21 

appeared, 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 Epiactis prolifera, V.) which had three rows of 
young individuals attached to it around the middle of its 
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 unable 
to determine. In all cases the young ultimately separate 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 repro- 
duce 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 entang- 
ling thereby 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 9. 

The above are the more prominent characters of the 
Actinia tribe of polyps. The special features distinguishing 
them from the coral-making polyps are the following : (i) They 
are simple animals, or, if they bud, the buds early separate 
from the parent; (2) They have a muscular base; (3) They 
are generally capable, more or less perfectly, of locomotion on 
the base by means of its muscles ; (4) They sometimes possess 
rudimentary eyes; (5) They have no internal coral secretions. 



22 CORALS AND CORAL LSLANDS. 

Each of these characters is evidence of the superior grade of 
this division of polyps. 

II. CORAL-MAKING 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 Actinise. Their more striking pecu- 
liarities depend on the secretion of coral, making them fixed 
species, and involving an absence of the base ; and, in the 




CAKVOPHYLLIA CYATHUS. 



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 coi-allum. These secretions take place among the 
tissues 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, 



CORALS AND CORAL MAA'ERS. 



from the Mediterranean, the upper extremity is a depression, 
or caliclc, inclosed by a series of radiating calcareous (coral) 
septa. Each of these septa is secreted between a pair of the 
radiating fleshy partitions, or septa, of the polyp (see figure ]). 
lo); and thus the radiate structure of ordinary corals is 
nothing but an expression of the internally. radiate structure ot 
the polyp. When aUve, the top, and usually the sides, of the 
coral were concealed by the outer skin of the polyp, including, 
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 sur- 
faces of the fleshy septa, or trom a 
]jrolongation inward of the mem- 
brane forming the walls of the inter- 
nal cavity, has not been directl}' ascer- 
tained. The latter view is sustained 
by Professor 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 




■HEC0CVATHL:S CVLINDKACCrS. 




FLABELLL'M I'AVONINUM. 



species (e.g., Echinopora irjfcxa) are hollow. The exterior 
surface of the corallum, that is, the part outside of the calicles, 



24 CORALS AND CORAL LSLANDS. 

is often ribbed, and the ribs are ordinarily only an outer ex- 
tension of the interior septa ; so that surface spines are in fact 
but the outer margins of septa. 

The first of the preceding figures, representing Thecocyathus 
cylindraceus, Sourt, exhibits another of the forms of these 
simple corals. It is described by Pourtales, from specimens 
collected by him at a depth of loo 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 Flabellutii 
pavonifiuf/i, described and figured by the author from specimens 
obtained at Singapore. 

The bottom of the calide, or polyp-cell, in the corallum is 
sometimes made simply by the meeting of the radiating septa ; 
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 22, which are the extremities of narrow vertical strips 
(called /(?//) 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 (i) because the coral secretions fill up all the pores 
as the polyp increases in age, and thus make the interior 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 (page 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. 



CORALS AND CORAL MAKERS. 25 

giving greater firmness to the whole. An example is shown 
in the figure on i)age 22. In such a case, there is no skin or 
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 longi- 
tudinal central line. From the line at the centre, there is the 
same radiated arrangement of calcareous septa as in the 
preceding species, though the animal difi"ers greatly in its 




LNACTIS ECHINATA. 



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 figure 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 Fimgia 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 animal is wholly concealed, though often showing the 
points of the teeth of the septa in consequence of the skin 
being broken. 




FUNGIA LACERA, V. 



CORALS AND CORAL MAKERS. 



27 



An enlarged view of one of the tentacles is given below. 
They are very small, compared with the size of the polyp ; 
and this is true of all the living Fungiae studied by the author. 
It is plain that the ])ovver of such tentacles must reside wholly 
in their lasso-cells. 




TENTACLE OF FUNGIA LACERA. 



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 Fungi?e, 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 compound 
gj'oups, in which great numbers of polyps are connected 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- 



28 CORALS AND CORAL LSLANDS. 

sionally met with in Actinias, the description of which is briefly 
given on page 20. The bud commences as a sHght prominence 
on the side of the parent. The prominence enlarges, 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 condnues 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 figure on page 31, and 
the Madrepora figured on page 29 ; in both of which, and in 
all such coral zoophytes, each stellate cavity or prominence 
over the surface corresponds to a separate one of the united 
polyps. 

The compound mass produced by budding — which consists 
of the united polyps with the corallum as their united secre- 
tion — 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 animals in- 
cluding the sponges. As a substitute the term Zoofhome may 
be employed, derived from the Greek L,u)oy, animal, and Ow/jiog, 
a /ieaj> — a term applicable also to compound groups in other 
classes, as, for example, those of Rhizopods, Bryozoans and 
Ascidians. The term zoophyte, where employed beyond, 
signifies a zoothome formed of united polyps, or a polyp- 
zoothome. The coral of the zoothome being the corallum, 
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. 

It is obvious that the connection of the polyps in all com- 
pound groups must be of the most intimate kind. The 
several polyps have separate mouths and tentacles, and separate 



CORALS AND CORAL MAKERS. 



29 



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 hke a living sheet of animal matter fed and 
nourished by numerous mouths and as many stomachs. 




MADREPORA ASPERA, D. 



Polyps thus clustered constitute the greater part of the 
flowering zoophytes of coral reefs. Only a few are simple 
animals, like the Caryophyllia figured on page 22, or the 
Thecocyathus, page 23, or the Fungia, page 26. 

This kmd of budding may take place from the sides of the 
polyp at different heights ; either (i) from the base, as in the 
Actinia mentioned on page 20 when it is basal ; or (2), above 



30 CORALS AND CORAL ISLANDS. 

the base, when it is called lateral ; or (3) at the upper margin 
outside of the tentacles, when it is called marginal ox superior ; 
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 stolon iferous stem from a strawberry 
plant, and at short intervals gives off biids ; 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 ^^g^., and so makes an in- 
crusting plate consisting of a multitude of polyps. 

If the germ polyp, or that from which the compound 
zoophyte proceeds, has the property of growing upward be- 
yond the adult height — which the existence of coral renders a 
possibility, and even to an indefinite degree — various otlier 
forms may result. 

Sometimes the first polyp gives out buds from its sides, and 
continues so to do when it grows upward ; and thus a 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 species of 
which is represented on the preceding page. 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 31. It is a species of Dendro- 
phyllia, from the Feejees — a genus often representing tree-like 
forms, as the name implies. 

In other cases, budding goes on until a cluster of some size 
is formed, and then the older or marginal polyps of the cluster 
cease budding while the rest continue the process ; in this 
way 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 




DENDROPHYLLIA NIGRESCENS, 



32 CORALS AND CORAL ISLANDS. 

the budding cluster. Below a case of this kind is represented, 
in which the stem is a laro:e column. 




GONIOPORA COLUMN A, D. 



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




POKITES MUKDAX, D. 

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

D 



34 CORALS AND CORAL ISLANDS. 

In other cases, the budding cluster is small, and hence 
makes small branches, as in the annexed figure of a species of 
Porites, from the Feejees. The cells in this genus are very 
small and nearly or quite superficial, as the figure shows. 

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 
fission of a branch or stem. In this way the forking in the 
coral of the figure on page 32 was produced, and also the 
branching in that on page t,-^. 

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 length- 
en out into a new branchlet. In 
this manner the coral here figured, 
and 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 univer- 

CLADOCORA ARBUSCULA. n i i i • i 

sally through the growmg mass, the 
coral formed is more or less nearly hemispherical ; and often 
the process goes on with such extreme 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 Orbicella cavernosa, from 
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 whenever these spaces 




CORALS AND CORAL MAKERS. 



35 




ORBICELLA CAVERNOSA. 



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 Pontes also grow 
into hemispheres and rude hil- 
lock-like forms, through the 
same method of budding, and 
some of the masses in the tropi- 
cal Pacific have a diameter ot 
even twenty feet. Myriads ot 
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 bowl-like 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 
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- 
neous Jission^ 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 

D 2 



36 CORALS AND CORAL LSLANDS. 

the old tentacles, as illustrated in the following figure. It is not, 
as is seen, a subdivision strictly into halves, as one carries off 
the old mouth and stomach. The figure to the left represents 
a polyp of the Astraea tribe, with already two mouths, through 
a commencement of the process of subdivision. In the next 
figure there are tentacles between the two mouths, so that each 




SPONTANEOUS KISSiON IN POLYPS. 



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

This mode of budding does not belong exclusively to coral 
polyps, for it has been observed among a few Actiniae. 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 
alludes to the occurrence of double-disked individuals of the 
genera Actinoloba, and Actinia as illustrating the process with- 
out a separation of the spontaneously developed pair. 

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

The following figure represents a species of living coral of 
the Astraea family, from the Feejees, the Astrcsa pallida, D. 
which grew, and multiplied its polyps as it grew, by this 
method. In such species some of the disks of the polyps will 



COKALS AND CORAL MAKERS. 37 

be found to liave two mouths. This is the first step in the 




ASTR.KA I'ALI.IDA, D. 

process. In others, the two mouths will be found to be partly 
divided from one another 
by new-formed tentacles ; 
and finally each will have 
its own circle complete 
and all else in polyp per- 
fection. 

Many of the Astr^ea 
hemispheres of the Paci- 
fic, grown by this method, 
have a diameter of ten 
to fifteen feet. 

In other Astraia-like 
species, this spontaneous 
fission ends in a complete 
separation of the two 
polyps formed ; and con- 
sequently in a forking of 
an old branch. The caulasth^a furcata, d. 

figure annexed, of a Caulastrsea, from the Feejees, illustrates 




38 CORALS AND CORAL LSLANDS. 

this mode of 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 
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 meandrine furrows are made, some 
kinds of ^\^hich are popularly called " Brain coral," and pertain 
to the Meandrina family (figure on page 4-4). 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 
require for the explanation of their origin only the few princi- 
ples which have been mentioned. The germ-polyp, growing 
upward and more or less outward, and budding as it grows, 
makes thus the rising stem — that of the Madrepore or Dendro- 
phyllia, with its summit polyp (figures p. 29, 31), or that of the 
Pontes, with its terminal budding clusters (p. 2iZ) 'i *^'* the 
rising, massive dome of the Astrsea and Mcneandrina (pp. 37, 
44), in case budding is symmetrical in all directions ; — or, if 
growth in the germ-polyp is upward exclusively, it forms a 
rising stem bearing at top the single polyp that originated it, 



CORALS AND CORAL MAKERS. 39 

or crowded clusters of such stems branching variously and 
having each branch surmounted with its one polyp (figure j). 
32) ; or, if there is lateral growth and but little of upward, it 
produces leaf-like forms and graceful groups or clusters of 
leaves, vases, and other shapes ; or, if the germ-polyp is capa- 
ble 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 significations 
annexed. Those aheady mentioned are here repeated to bring them all 
together. 

Zo'dthotne. — 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. 

Calide. — The polyp cell in the top of a corallet, or of a solitary coral- 
lum, 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.— '^xcidXX cross plates between adjoining septa (sometimes 
wanting). 

Synapticulce. — Minute cross bars uniting the surfaces of adjoining septa. 

Ccenenchyma. — The common mass of the corallum between its differ- 
ent polyp cells or corallets, as in the Madreporae, Gemmiporae and Den- 
drophyllioe. 

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 25. 

Peritheca. — The epitheca of a compound group or zoothome (fig. p. 50). 

Exotheca. — The portion of the corallum outside of the walls of cells in 
many coralla of the Astraea family, and some others, in which the polyps 
of the mass ai;e properly in contact, and there is consequently no true 
ccenenchyma. 

Endotheca. — The portion of the corallum inside of the walls of the cell. 

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. 

The tribes adopted are those recognized by Prof Verrill, 
and have the limits he has assigned to them. The classification 



SS COKALS AND CORAL ISLANDS. 

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 5. Some 
of the figures of corals on former pages are here repeated in 
order to present together those of like relations. 

1. Species iciifhont internal Coral Secretions. Actinaria of 

Verrill. 

1. The Actinia tribe, or Actinacea, secrete no coral inter- 
nally, and moreover have a muscular base, with some degree 
of locomotion by means *of it. The Acdniae of the frontis- 
piece, and of pages 6, 9, are examples. 

2. The Zoanthus tribe, or Zoanthacea. 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 i)olyps have a thick or somewhat lea- 





El'IZOANTHL'S AM ERICA ^• US, V., WITH EirACa'KrS Pi: BESCEIsS, Sx. 

thery exterior, and, as already observed (p. 19), have gills, or 
branchiae. Some of the species are solitary polyps ; but gener- 
ally the>' 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 preceding figure (from Verrill) re])resents a species found 
in American seas off the coast of New Jersey, in deep water, 
and also in Massachusetts Bay, v/hich has a habit of fixing on 
a shell for its support and of always taking one containing a 



COKALS AND COKAL MAKERS. 



41 



soldier crab. The shell finally becomes dissolved away — how, 
it is not known— by the growing Zoanthid ; but the crab holds 
on to its house, although at the expense of transporting wher- 
ever it goes a colony of flowering polyps. I'he polyps are but 
partly expanded in figure i, and wholly so in figure 2. 



i^<;r7!VWir 




ANTIPATHES AKIiOREA, D. 



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 surface in some 



42 CORALS AND CORAL ISLANDS. 

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 Aiitipathus tribe, or Antipathacea. In this tribe 
the polyps never have locomotion, and, as far as known, always 
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 horny axis, usually spiny or hispid over its surface, sur- 
rounded 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 




POLYP OF A. AKBOKEA, MUCH ENLARGED. 



shrub, collected by the author, was three feet, and the trunk at 
base was half an inch thick. The polyps had a brownish- 
yellow colour, not particularly beautiful, and the tentacles were 
in general, as in another species described by the author, rather 
awkwardly handled by the polyp. The number is commonly 
six ; but in one genus, Gerardia,.it is as great as hventy-fo2ii\ 

2. Polyps having infernal calcareous secretions. Madreporaria 
of Verrill. i^TJie Cyathophylloid species excluded). 

4. AstrcEa tribe, or Astr^.acea. — In this tribe the polyj)- 
cells or calicles are distinctly lamello- radiate within, and gener- 
ally so outside. Moreover, budding is always by division of the 
disks, or spontaneous fission. The figure of the Caulastraea, on 



CORALS AND CORAL MALy'ERS. 43 

page 37, illustrates one section of this family, that in which each 
branch of the corallum is made by a single' polyp, and branch- 
ing is by furcation through spontaneous fission. In other 
related genera, as Mussa, the polyps sometimes have a diameter 
of two inches, being as large as ordinary Actiniae. 




ASTK/KA PALLIDA, D 



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

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 reduced 
one-half lineally. The difference betw^een its mode of for- 
mation and that of an Astraja has been stated on page 38. 
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 name 
Diploria, from the Greek for double. A common large West 
India species of Brain coral is called Meandrina labyri7ithica. 



44 



CORALS AND CORAL ISLANDS. 



It is readily distinguished from the Diploria by the ridges 
between the furrows, these being simple and triangular. 

Still other forms of the Astraea tribe are foliaceous, or such 
as would result if the growing margin of an Astrsea, or of a 
Meandrina, were to spread out into folia instead of thickening 




DIPLORIA CEKEHRIFOKMIS, E. AND H. 

upward in the ordinary way. The groups ot gracefully curv- 
ing leaves thus made are sometimes very large and sym- 
metrical. 

2. Fungia tribe, or Fung ace a. — The general character of 
the simple species of this tribe is mentioned on page 25, and 
the character of the living Fungia, with its tentacles, is shown 
in the figure of a Feejee species on page 26. The corallum 
of another large species, the Fungia Dance, is represented 



CORALS AND CORAL MAKERS. 45 

in the annexed figure one-sixth the actual diameter. 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 




FCXGIA DAN^, E. & H., Rf-DICEI) TO ONE-SIXTH MNKAI.I.V; a,l>, TEETH OF UI'l'ER 
AND LOWER MARGINS OF SEPTUM, NATURAL SIZE. 

the compound kinds no wall or partition between the adjacent 
stars, and no walls to adjoinmg polyps, or only imperfect ones. 
The polyps consequently coalesce throughout by their disks. 
The simple Fungise are attached when young, and then would 
hardly be distinguished from a simple or solitary species of the 
Astraea tribe. 

3. Oadina tribe, or Oculinacea. — These species occur 
eitner 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 lamellae 
of the cells ; and often for having the coenenchyma nearly or 
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 35, is an example 
of one of the massive Astraea-like forms, constituting the 
Orbicella family, or OrbicellidcE^ in the Oculina tribe. 



46 CORALS AND CORAL ISLANDS. 

The Caryophyllia here figured is one of the solitary species 
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 




CARVOrHYI.I.IA SMITHII, StOKES. 

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 13. 

The corallum of a related species is given on page 22. The 
walls and , septa are remarkably solid. This species, the 
Caryophyllia cyat/ms, has been found not only in the Mediter- 
ranean, but also at the Azores. Another species, the C. davus, 
has a wide distribution, occurring in deep water in the 
Florida straits and off the British coasts as well as m the 
Mediterranean. 

Another example of this tribe, as defined by Professor 
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 object. The accompanying figures of the animal are 
from the drawings made to illustrate a yet unpublished memoir 
by Professor Agassiz. They are copied from the "Sea-Side 
Studies" of Mrs. Agassiz and Alexander Agassiz. In figure 



COKALS AND CORAL MAKERS. 



47 



c, the polyps are of the natural size, while figure a represents 
one of them enlarged, The polyps, as is observed, stand very 
j)rominent 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 marginal. 




ASTKANGIA DANyE, Ag. 

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 ivhite cords 
that edge the internal septa. 
The corallum, though mas- 
sive, 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 (figure b), 
which are usually crowded 
the intervening 
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 (page 722). 

The genus Cladocora, containing slenderly branching ram.ose 
zoophytes, is closely related in its polyps, according to 



together, 
wall 




PHYI.LANGIA AMEKICANA, E. & H. 



48 



CORALS AND CORAL LSLANDS. 



Professor Verrill, to the Astrangiae, and belongs to that family. 
Its cylindrical stems are gathered into crowded clumps. The 
C. arbtcscula is figured on page 34. 

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

In the following cut, figure i represents the extremity of a 
branch of an Oculina, the O. varicosa, of the family Ocnlinidce. 
The species of this genus grow in clumps of round branches, 
and have very solid corolla, so white and firm when bleached 




CORALS OF THP: OCl'LINy\ TRIIiF. 



as to go by the popular name of " white coral," and to be 
sometimes pohshed for beads and other such ornamental 
purposes. 

Figure 2 is a branch of a beautiful little coral called Sty- 
laster eriihescens 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. 



CORALS AND CORAL MAKERS. 49 

Figure 4, in the same cut, represents a portion of a branch 
of the Stylophora Dance E. and H. The corals of the genus 
are remarkable for their small, crowded calicles, and for the 
very distinct six-rayed 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, 6". 
mordax, is represented in figure 6. The name of the family, 
StylophoridcE (signifying style-bearer), alludes to this columella. 
The corals grow in regular hemispherical clumps consisting of 
flattened or rounded branches, and are sometimes a foot or 
more across. 

In another family under this tribe, the FocilliporidcB^ 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 polyp cells ; while in Seriatopora, the branches are 
slender, even, and pointed. The corallum in both is very firm 
and soHd. 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 
tentacles. 

The Pocilliporje form hemispherical clumps like the Stylo- 
phorae ; 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 branchlets. 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 illustrated in figure 9, 
from P. plicata 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 recent study of the polyps has shown that they are 



50 CORALS AND CORAL ISLANDS. 

true polyps ; and Professor Verrill remarks on the resemblance 
of the tentacles to those of the Oculinae. The stellate 
character of the calicle also proves that the animals must be 
polyps. 

Madrepore tribe, or Madreporacea. — In this tribe tlie 
coralla, even to the walls of the corallets, are remarkable for 
being porous, and the radiating lamellae of the polyp-cells 
are narrow, often perforated or imperfectly developed, and 
frequently mere points. The coralla are either branched, mas- 
sive, or foUaceous. 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 peculi- 
arity has been already illustrated in the figure of Madrepora 
aspera, on page 29. On the following page there is an outline 
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 character of 
the Madrepore corals. One of the polyps of the Madrepora 
cribripora D., a species collected in the Feejees, is represented 
much enlarged in the accompanying figure. The natural size 
of the expanded polyp in this genus is generally from an 




POLYP OF M. CKIDKIPOKA, D. 

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 colour of the polyps is green, 
while that of the general surface between is ordinarily a pale 
or a dark umber. In many species of Madrepora the branches 
spread out laterally from a central or lateral trunk, and coalesce 
together into a complete net-work, having the form of a shallow 
vase ; and the interior of the vase is filled with multitudes of 
short, . cylindrical coral stems, rising from the reticulating 




MADREPORA FORMOSA. 



E 2 



52 



CORALS AND CORAL LS LANDS. 



branches, which, when alive, have literally the aspect of sprigs 
of flowers in the vase. 

In certain kinds, closely related to Madreporae, the calicles 
are reduced to points, or spiniform or angular prominences, or 
fail altogether, and there are sometimes rounded prominences 
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 Madrepore 
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 D. nigresce?is D., 
enlarged, is shown in the accompany- 
ing figure. This Pacific species grows 
to a height of at le.ist three feet, and 
is peculiar in having a very dark 
blackish green or almost black colour, 
while the polyps have the tentacles 
nearly colourless, and the disk has a 
circle of emerald green around the 
mouth. DeiidrophyUia arborea is the 
name of a common species of his 
genus found in deep water in the 
Mediterranean ; it is equally large 
with the preceding, 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 spegies is the D. cor?ngera. 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 foliaceous, 
bowl-like, and massive forms, covered by prominent cylindri- 
cal, porous calicles, and having many short tentacles to the 
polyps, usually in a single circle. 

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




POLYP OF DENDROPHYLLIA 
NIGRESCENS. 




DENUKOl 



HYLLIA NIGRESCENS, D. 



54 



CORALS AND CORAL ISLANDS. 



One of the genera in this family is Alveopora. It contains 
the h'ghtest of known corals, the texture being exceedingly 

porous, and the walls 
of the cells, which 
are continued regularly 
through the coral! um, 
are like delicate lace- 
work. As stated long 
since by the author, 
" they are intermediate 
in character between 
the Montiporse and the 
Favosites group " — as 
shown by the texture 
and the horizontal par- 
titions across the cells, 
giving them the " tabu- 
late " character of the 
ALVEOPORA vEKRiLLiANA, D. aucicnt T avositcs, as 

represented by the au- 
thor in the annexed figure exhibiting a section of the coral- 
lum of a Feejee species. On account of this tabulate structure. 





VERTICAL SECTION OK CORALLUM, AND UPPER VIEW OF CALICLES, ENLARGED, OF 
ALVEOPORA SPONGIOSA, D. 

the genus was referred by the author to the Favosites family. 
A related species, of unknown locality, has been made the 



CORALS AND CORAL MAKERS. 



55 




type of a new genus, called Favositipora^ by Mr. W. S. Kent, 
on the ground of its tabulate character (Ann. Mag. Nat. 
Hist., 1870), thus confirming, though overlooking, the author's 
conclusions. 

In the genus Pontes, the corals are frequently branching, 
as in the Forites viordax D., sometimes more slenderly, but 
oftener less so, and at times massive and monticulose in form. 
Another species of Porites is represented on the following 
page, with one of the branches 
fully expanded, but the others in 
outline ; a polyp, much enlarged, 
having twelve tentacles as in 
the Madrepor^e, is shown in the 

accompanying figure. The cells ^^^^^ ^^ ^^^^^^^ ^^^,3 

of the corallum are superficial, 
and hence the name of the species, Forites levis. 

Another form, different in the size and character of its 
polyps, is exemplified in the genus Goniopora. In the species 
figured on page 32, the colour 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. The dead portion is usually 
encrusted with nullipores, sponges, serpulse and various shells, 
which protect the very porous corallum within from wear and 
solution by the moving waters. 

II. CYATHOPHYLLOIDS. 

It is not necessary to dwell here at length upon the ancient 
Cyathophylloids. The corals have a close resemblance to those 
of the Astraea tribe in general aspect, varieties of form, and 
range of size ; the methods of multiplication by buds were the 
same that are now known in the Oculina tribe. Some of the 
larger kinds of simple corals, such as those of the genera 
Zaphrentis and Heliophyllum, had at times a diameter of three 
or four inches, so that the breadth of the polyp flower was 
probably at least six inches. Hemispherical masses of soHd 



56 



CORALS AND CORAL ISLANDS. 




PORITES LEVIS, D. 



CORALS AND CORAL MAKERS. 57 

corals attained, in some species, a diameter of several feet. 
No doubt the colours, 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 
exists because, " in the beginning," " the Spirit of God moved 
upon the face of the waters;" and man finds delight therein 
inasmuch 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 multiple 
of four, as in the true Cyathophylloids. The discoverer has 
named it Haplophyllia paradoxa. F)Ut he observes that it may 
after all be only an abnormal Actinoid. 

III. ALCYONOID POLYPS. 

The name Alcyo?uum, 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 conformity 
with the aspirate of ihe Greek word ; but Latin authors usually 
omitted the H, and this has been good enough authority 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 
material 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, crimson or purple shade. Dun colours also occur, as 
ash-grey, and dark brown, and almost black. Some kinds, the 
Sponggodiae, are too flexible to stand erect, and they hang 
from the coral ledges, or in the coral caves, in gorgeous clusters 
of scarlet, yellow, and crimson colours. 



58 CORALS AND CORAL ISLANDS. 

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 peculiarities 
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 following : 
the existence of only eight internal septa, and these septa not 
m pairs; consequently, the interior is divided into only eight 
compartments (octants), and with each a tentacle is connected. 
Hence in the Alcyonoids, as Prof. Verrill has observed, the 
areas externally, and the compartments within, are all ambu- 
lacral, or tentacular, which makes a wide distinction between 
them and the Actinoids (p. ii) in which only the alternate are 
tentacular. 

The solid secretions of these polyps are of two kinds : Either 
(i), 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 horny (like that in Antipathus, p. 42) or cal- 
careous. 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 : — 

I. The Alcyo?iiu7n tribe, or Alcyonacea. — One of the forms 
under this tribe is represented in the annexed figure. It is 
from the Feejees (like most of the zoophytes figured by the 
author), and in the living state the polyps had the middle por- 
tion of the tentacles pale brown, with the fringe deep brown. 
In another more beautiful species of the genus, from the same 
region, the Xenia fioi'ida D. (made Xenia Dance by Verrill, as 
it proved to be distinct from Lamarck's species to which the 
author referred it), the polyps are as large, but shorter, and the 
colour is a shade of lilac. These species differ from the larger 



CORALS AND CORAL MAKERS. 



59 



part of the Alcyonia in having the polyps not retractile ; the 
tentacles fold together, if the zoophyte is disturbed, but cannot 
hide themselves. 




The following figure represents another related species 
obtained by Dr. W. Stimpson, near Hong Kong, and called 
by its discoverer Anthelia lineata; the polyps are but partly 
expanded. 



6o 



CORALS AND CORAL LS LANDS. 



Other Alcyonoids are much branched, with die branched 
thick and finger-like, and soft or tlexible, and the polyps small 

and wholly retractile into 

the mass. The branches, 

bare of polyps, are usually 

of some dull pale colour, 

and on account of this fact 

some of these Alcyonia go 

by the common name of 

dcad-jnetis fingers. 

Some of the species form thick lobed plates over the rocks ; 

and occasionally they are brightly coloured, 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 
according to the proportion of these granules. 

Some species form branching tubes, rising from an incrusting 
base, which are rather firm owing to the calcareous spicuh^s 
present. Such species are referred to the genus Telesto — one 




ANTHEl.IA LINEATA, S F 





TEI/fCSTO RAMICULOSA, V. 



of which, from Hong Kong, from the collection 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. 



CORALS AND CORAL MAKERS. 



6i 



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 
Aulopora ; but generally 
vertical tubes, grouped 
into large red masses, 
called, popularly, Orga?i- 
pipe coraL A portion of 
one of the latter — Tiibi- 
pora syringa D. — is re- 
presented in the first of 
the annexed figures, with 
its expanded polyps ; 
and a polyp from the 
group much enlarged in 
the sfcond figure. The 
papillse of the fringe are 
arranged closely together 
in a plane, so that it is 
not at first apparent that 
there is a fringe. The 
third figure represents, 
enlarged, the polyp of 
another Feejee species, 
the Tubipora fiinbriata 
I). Such coral masses 
are sometimes a foot or 
more in diameter, and 
the living zoophyte, with 
its lilac or purple polyps 
fully expanded, looks 
much like a large cluster 
of flowers from a lilac bush, 
plates at intervals. 
. 2. Gorgo/iia tribe, or Gorgonacea. — The following figure re- 
presents a species of this tribe from the Kingsmill or Gilbert 
Islands. It is one of the net-like or reticulated species, the 




The tubes are united by cross 



62 



CORALS AND CORAL LSLANDS. 



reticulation being a result of the coalescence of the branchlets. 
The general colour 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, Go?^goma fiabellum, is much more finely re- 
ticulated, the meshes of the net-work being ordinarily not over 



CORALS AND CORAL MALCERS. 63 

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

The exterior of the stem or branch in a Gorgonia is a 
layer of united polpys, 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 pro- 
minences. 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 zoophyte was alive. 




SPICULES OF GORGONI/E, MUCH ENLARGED. 



Kolliker and others have shown that genera, and sometimes 
species, of the Gorgonacea, may be distinguished by the forms 
of the calcareous spicules. Some of these knobby spicules 
are represented in the annexed cut, from figures published by 
Professor Verrill. The most common forms are those of 
figures i, 4, 5 ; they occur, with small differences, in the 
genera Gorgonia, Eugorgia, Leptogorgia, etc. Figure i is from 
the Leptogorgia 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 figure i. The forms represented in figures 



64 CORALS AND CORAL LSLANDS. 

3, 4, 5, are all from Eugorgia aiiraiitiaca V., the peculiar 
kind shown in figure 3 occurring with the other more common 
form, in species of this genus. In species of Plexaurella 
many of the spicules are beautiful crosses of various fancy 
shapes. In Eunicellae the cortex is covered with an out- 
side layer, in which the spicules are club-shaped, though or- 
nately so, and have the smaller end pointed inward. These 
spicules afford valuable distinguishing characters also in all 
Alcyonoids. 

The spicules are often brilliantly coloured, and sometimes 
variously so in the same individual. Yellow, crimson, scarlet, 
and purple are common colours, and they occur both of dark 
and pale shades. Viewed under a compound microscope 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 Gorgoniae owe the various 
colours they present to the colours 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 Muricaea, 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 car- 
bonate 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 (page 42). In the ordinary Alcy- 
onoids that make no horny axis, the stolons, or budding stem 
or mass, creeps or spreads over the supporting body. But 
in these Gorgonige, 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 
secretes the axis within, 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 budding centres, and so, finally, the Gorgonia zoophyte 
is completed. 



ALCYONOID POLYPS. 



^'5 



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 inter- 
nodes. The former, in the genus Isis, are white, calcareous, 
furrowed or fluted pieces ; and the latter are smaller and horn- 




ISIS HiriT 



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 smiply the axis, bare of the polyp-layer or cor- 
tex ; while the branch on the right, with the surface dotted, 
has the cortex complete, and the dots are the sites of the con- 
tracted polyps. The circular figure below is a transverse sec- 

F 



66 



CORALS AND CORAL LSLANDS. 



tion of the stem enlarged, showing the cavities occupied by 
the retracted polyps. 

In the genus Melitaea, and some others related, the inter- 
nodes are porous and somewhat cork-like or suberous instead 




CORALI.RTM RUBRUM. 



of horny. The species of this group are often bright-coloured 
and much brancherl, and resemble, in aspect, ordinary Gor- 
gonicX ; but they are very brittle, breaking easily at the inter- 
nodes. 



. ALCYONOID POLYPS. 67 

In the Corallidae, the axis is wholly calcareous, and firm and 
solid throughout, with usually a red colour, varying from crim.- 
son to rose-red. Here belongs the Corallium riibrum, or pre- 
cious coral. The polyp-crust or cortex, which covers the red 
axis or coral, is thin, and contains comparatively few calca- 
reous 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 66. The 
polyps, as the enlarged view, by Lacaze Duthiers, shows, are 
similar 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 
polyp 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 grows 
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 besides 
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 niost 
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 the coast of Marseilles. The rose-coloured 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. 

F 2 



68 



CORALS AND CORAL LSLANDS. 



3. Pennatnla tribe, or Pennatulacea. These are com- 
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 
various. 

In the Veretillum family (Veretillidae) they are stout and 
short club-shape. One of the species from Hong Kong is 




C01'H()I5K1.E.MN()X t I.AVATf.M, V. , AND VERETII.LI;M STIMl'SONI, V 



shown in the figure on the left, with its polyps fully expanded, 
and the small figure represents one of the polyps enlarged. 
The third figure represents a polyp of another species, from 
Hong Kong, a true ^'eretillum, enlarged three diameters ; the 
specimens, obtained by Dr. Stimpson, and described by Prof. 



ALCYONOID POLYPS. 69 

Verrill, were six to eight inches in lengtli, and, where thickest, 
were three inches or more in diameter. 

A common Mediterranean species is the Vcretillum cynonio- 
rium; and it has been recently found, of a length of ten inches, 
in the depths of the Atlantic off the coast of Spain. Mr. 
VV. S. Kent observes, with regard to its polyps and their phos- 
phorescent qualities, as follows : — 

" Nothing can exceed the beauty of the elegant opaline 
polyps of this zoophyte when fully expanded, and clustered 
like flowers on their orange-coloured stalk ; a beauty, however, 
almost equalled by night, when, on the slightest irritation, the 
whole colony glows from one extremity to the other with 
undulating waves of pale green phosphoric light. A large 
bucketful 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 support- 
ing stem appeared always to be the chief seat of these phos- 
phorescent 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 
exserted, protruded upward of an inch and a half from this 
inflated 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 with the 
Veretillum Stimpsoni^ as observed by Professor Verrill. Between 
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 instea<3 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 Pennatulidse) ; 
or a very slender stem and verv short lateral polyp-bearing 



70 CORALS AND CORAL ISLANDS. 

pinnules or processes along it (the Virgularidse) ; or a thin 
reniform shape (Renillidae). 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 Umbellularidce). 

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

In conclusion, it may here be stated that the reader will find 
very full illustrations of most of the forms of recent corals, 
and of their animals, with their natural colours, in the author's 
Report on Zoophytes. It is with regret that he has to add, 
that owing to the special action of the Congressional Commit- 
tee in charge of the publications of the Wilkes Exploring 
Expedition, only one hundred copies of this Report were pub- 
lished by the Government, and also of the others of the series, 
and that but i^\N have been issued besides. The Atlas contains 
sixty-one folio plates, many of them coloured. 

The works on " British Sea Anemones," by Mr. Philip 
Henry Gosse, contains figures and descriptions of a large 
number of Species, and gives an excellent idea of the most of 
the forms of Actiniae, and also presents well their colours. 
Professor A. E. Verrill has published, in the Memoirs of the 
Boston 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 of 
growth is favoured by the coral secretions ; for these give a 



LIFE A ND BE A TH IN CONCUR REN T PR OGRESS, 



71 



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 hap- 
pens. In some instances, a polyp, but a fourth of an incli 
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 34, in 
which the living part had 
a length of one eighth of 
an inch. The Goniopora, 
on page 32, is still another 
example of the process ; but 
here the living part com- 
bines a great number of 
polyps : these are growing 
and budding with all the 
exuberance of life, while 
below, the old polyps gra- 
dually disappear, and even 
their cells become superficial and fade out. Trees of 
Madrepores may also have their limits — all below a certain dis- 
tance from the summit being dead ; and this distance will differ 
for different species. But this is not a limit to the existence of 
the zoothome, even 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. 




CAULASTR^A FURCATA, D. 



72 CORALS AND CORAL LSLAXDS. 

But this death is not in progress alone at the base of the 
cokimn or branch. Generally the w/iole ititerior 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 surfoce having progressively died at the 
lower or inner extremity as they increased outw^ard. 

The large domes of Astrseas, which have been stated to 
attain sometimes a diameter of ten or fifteen feet, and are alive 
over the whole surface, owing to a symmetrical and unlimited 
mode of budding, are nothing but lifeless coral throughout the 
interior. Could the living portion be separated, 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 Hfeless, 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 fife. 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 sink- 
ing, 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 Astrsea 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 thou- 
sands 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 deatli- 



rROTECTION A GAINST INJUR ] ; 73 

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 
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 ot 
lime, secreted by the lower edge of the series of dying polyps, 
a fact in the Gouiopoi'a co/u?nna figured on page 32. Then, 
further, the dead surface becomes the resting-place of number- 
less small encrusting species of corals, besides NuUipores, 
Serpulas, and some Mollusks. In many instances, the lichen- 
like Nullipore 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 
secretions 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 en- 
durance. 

The facility with which polyps repair a wound, aids in 
carrying forward the results above descri' ed. 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 
occasion 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 
complete restoration to their former size and powers. The 



74 CORALS AND CORAL LSLANDS. 

fragment broken otf, dropping in a favourable 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 continues 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 ultimately 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 
coral is struck with a hammer, indicates this superior hardness. 
It is possible that it may be owing to the carbonate of lime 
being 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 difference ; 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 
water 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, on account of its elasticity and brittleness. 
The specific gravity 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 branching 
Madrepora and the massive Astr^eas are good examples. 



PHOSPHATE 


WATER AND OR- 


OF LIME. 


GAN 


IC MATTERS. 


. 0-84 . 




379 


• 0*50 • 




2-96 


. 053 . 




164 


. 0-28 . 




2-42 


. 0-32 . 




1-93 


. 078 . 




2-8i 



COMPOSITION OF CORAL. 75 

consist almost wholly of carbonate of lime, the same ingredient 
which constitutes ordinary limestone. In 100 parts, 95 to 98 
parts are of this constituent; of the remainder, there are i^ 
to 4 parts of organic matter, and some earthy ingredients 
amounting usually to less than i per cent. These earthy 
ingredients are phosphate of lime, with sometimes a trace of 
silic;a. A trace of fluorine also has been observed. 

S. P. Sharpies found the following constitution for the 
species below namec^ {Afji. Jou?\ Sci., III., i. 168). 



CARBONATE 
OF LIME. 

Oculina arbuscula, N. Car. . . . 95 '37 . 

Manicina areolata, Florida . . . 96'54 . 

Agaricia agaricites 9773 • 

Siderastrtea radians 97*30 . 

Madrepora cervicornis 98'07 . 

Madrepora palmata 97 "19 • 



Forchhammer found 2*1 per cent, of magnesia in Corallium 
rubriim, and 6*36 in Isis hippuris. 

The sea-water, and the ordinary food of the polyps, are 
evidently the sources from which the ingredients of coral are 
obtained. The same powers of elaboration which exist in 
other animals belong to polyps ; for this function, as has been 
remarked, 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 
elements present whatever results the functions of the animal 
require. 

The proportion of lime salts which occurs in the water ot 
the ocean is about -^V to ^^ 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, 7579 are chloride 
of sodium, 9-i6 chloride of magnesium, 3*66 chloride of 
potassium, I'lS bromide of sodium, 4-62 sulphate of lime or 



76 CORALS AND CORAL LSLANDS. 

gypsum, and 5*597 sulphate of magnesia, = 100. This cor- 
responds 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 
second, there is no foundation for it. The islands have been 
supposed to rest on volcanic summits, thus making one 
hypothesis 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 Islands have brought none to light. Some of the 
largest reefs of the Pacific, those of Australia and New 
Caledonia, occur where there is no evidence of former vol- 
canic action. 

The currents of the Pacific are constantly bringing new 
supplies of water over the growing coral beds, and the whole 
ocean is thus engaged in contributing to their nutriment. 
Fish, mollusks, and zoophytes are thus provided with earthy 
ingredients 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 
explain all the results under consideration. 

II. HYDROIDS. 

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



HYDRO IDS. 



77 



long. It has the form of a polyp, with long slender tentacles ; 
and, besides these tentacles with their lasso-cells, it has no 
special 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 perfect Hydra, supplying head, or tail, or whatever is want- 
ing : and hence the name given to the genus by Linnaeus. 

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

The species figured on p. 78, the 
Hydrallmania Falcata, is one of 
them ; in allusion to its deli- 
cate plumes, it is called Plumu- 
laria. 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 of a line long), and usually 
with short tentacles spread out 
star-like. Other kinds are simple 
branching threads, and sometimes hvuka. 

the 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 probosciform 
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 clumsy unshapen 
thing for a Radiate. 

To the animal of the Coryne, that of the very common, and 
often large, corals, called Millepores, is closely related, as first 




78 CORALS AND CORAL LSLANDS. 

detected by Agassiz on one of his cruises to the reefs of Florida. 




HYDRALLMANIA FALCATA. 



The autlror often had Millepore corals under study in the 



HYDROIDS. 



79 



Pacific, and waited long for the expansion of the animals, but 
was never gratified by their making their appearance. Agassiz 
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 
small rounded prominences in place of tentacles, four of 




KILLEPORA ALCICORNIS. 



them sometimes largest. The next figure, from Agassiz, 
shows, much enlarged, a portion of a branch ot the Millepora 
alcicoiiiis with the animals expanded, and the small figure <?, 
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 



8o 



CORALS AND CORAL ISLANDS. 



surface, 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 
formerly classed, therefore, with other tabulate corals. 

S. P. Sharpies found the coral of M. alciconiis 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 India seas, contributing largely to the material of 
the reef^. 

The Hydroids were long considered polyps. But they have 
been found to give origin to Medusae, or jelly-fishes, and it 
is now proved that they are only 
an intermediate stage in the deve- 
lopment of Medusse, between the 
embryo state and that of the adult 
or Medusa state. The Millepores 
afford, therefore, examples of coral- 
making by species of the class of 
Acalephs. Many of these Medusae 
and their Hydroids will be found 
illustrated in the admirable work 
of Alexander and Mrs. L. Agassiz, 
entitled " Sea-Side Studies," — an 
excellent companion 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 colour; it is called Helio- 
pora cmridca, the generic name, from the Greek for sun, 
alluding to the minute roiuid polyp-cells. This and the true 
Milleporas 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 




ANIMALS OF MILLEPORA ALCI- 
CORNIS, MUCH ENLARGED. 



BRYOZOANS. 



8i 



corals of the ChcXtetes family were possibly, like the Mille- 
pores, Acaleph corals, as suggested by Agassiz. Others 
have suggested, with perhaps better reason, that they were 
Bryozoan. 



III. 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 slender tentacles around the mouth. But, in internal 
structure, and all of the animal below the head, they are 
MoUusks. They form delicate corals, membranous or cal- 
careous, made up of minute, cabin-like cells, which are either 
very thin crusts on sea-weeds, rocks, or other supports, or 




2, HOKNERA LICHENOlUfCS ; 3, UlSCOPORA SKENEI ; SmITT. 



slender moss-like tufts, or graceful groups of thin, curving 
plates, or net-like fronds ; and sometimes thread-like lines, or 
open reticulations. 

G 



^2 CORALS AND CORAL ISLANDS. 

Occasionally they make large, massive corals, from the 
growing of plate over plate. One of these massive species, 
Escharella variabilis., is common on the coast of the United 
States from Cape Cod southward. 

The first of the foregoing figm-es, from Smitt's work on the 
Bryozoans, 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 tentacles, less than a line in 
diameter. 

The incrusting 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 
expanded, the surface is covered over with the delicate flower- 
like bryozoa. A low magnifying power is necessary to observe 
them 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 Bryo- 
zoum, in the compound group or zoothome, is wholly inde- 
pendent 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. The two specimens figured on the preceding 
page occur on the coast of New England, as well as in the 
seas of North Europe. 

IV. NULLIPORES. 

The more important species of the Vegetable Kingdom that 
afford stony material for coral reefs are called NulHpores. 
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 



GEOGRAPHICAL DISTRIBUTION OF CORALS. %i 

spreading lichen-like. Species of these forms belong to the 
genus Melobesia. 

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, 
often jointed, called Corallines, which secrete only a little 
lime in their tissues, and have a more plant-like look. P>en 
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 having considerable extent in the Florida seas. 



V. THE REEF-FORMING CORALS AND THE CAUSES IN- 
FLUENCING THEIR GROWTH AND DISTRIBUTION. 

I. Distribution in Latitude. 

Reef-forming species are the warm-water corals of the globe. 
A general survey of tlie facts connected with the temperature 
of the ocean in coral-reef seas appears to sustain the con- 
clusion 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 equa- 
tor, 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 coral-reef seas. 

This isothermal boundary line, the isocryme (or cold-water 
line) of 68° F., extends, through mid-ocean, near the parallel 

G 2 



84 CO.?.^/.S AND CORAL ISLANDS. 

of 28°; but in the vicinity of the continents it varies greatly 
from this, as explained beyond in the course of remarks on 
the geographical 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 731" F. in the North 
Pacific, and 70° F. in the South; from which it maybe in- 
ferred that the summer mean would be as high at least as 78° 
and 74° F. 

Over the sea thus limited coral reefs grow luxuriantly, yet 
in greatest profusion and widest variety through its hotter 
portions. Drawing the isocryme of 74° F. (that is, the iso- 
therm for 74° F. 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 distribu- 
tion 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 
important to have a correct apprehension of what are these 
reef species as distinct from those of colder and deeper seas. 

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

1. In the Astraea tribe (Astrseacea), ail the many known 
species. 

2. In the Fungia tribe (Fungacea), almost all known species, 
the only exceptions at present known being two free species 
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 Caryo- 
phyllids, Astrangids and Stylophorids ; all of the Pocillo- 
porids. 



GEOGRAPHICAL DISTRIBUTION OF CORALS. 85 

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

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

6. Among Hydroids, the Millepores and Heliopores. 

7. Among Alg?e, many Nullipores and Corallines. 

The corals of colder waters, either outside of the coral-reef 
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 
C'aryophyllids ; 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 Pacific, 
that is, within 15° to 18° of the equator, where the tempera- 
ture 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 Astr^acea, Fungacea, 
Oculinacea, Madreporacea, Alcyonoids, Millepores and Nulli- 
])ores. The Feejee seas afford magnificent examples of these 
torrid region productions. Astraeas 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. Mussa*. 
and related species produce clumps of larger flowers ; Meru- 
linae, Echinoponx, Gemmiporse and Montiporae form groups 
of gracefully infolded or spreading leaves ; Pavonise, Pocilli- 
porae, Seriatoporae and Pontes, branching tufts of a great 
variety of forms ; Tubipores and Xeniae, beds or masses of the 
most delicately-tinted pinks; Sponggodiae, large pendant 
clusters of orange and crimson ; and Fungiae display their 



86 CORALS AND CORAL LSLANDS. 

broad disks in the spaces among the other kinds. Many of 
the species may be gathered from the shallow pools about the 
reefs. 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°, are outside of the torrid zone of oceanic 
temperature, in the siibton'id^ and the corals are consequently 
less luxuriant and much fewer in species. There are no 
Madrepores, and but few of the Astraea 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 Red 
Sea are mainly the same as in the Central Pacific ; and the 
same also occur on the coast of Zanzibar. 

To the eastward 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 neighbouring seas, north to 
the extremity of the California peninsula and south to Guay- 
aquil, lie within the ior7'id 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 
Astra^acea, and no Madrepores. Prof. Verrill, 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 Dendrophyllise, a Stephanaria (near Pavonia), two species 
of Pocilliporae, two of Pavonise, one of them very large and 
named P. gigafitea 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 



GEOGRAPHICAL DISTRIBUTION OF CORALS. 87 

to. the Gulf, occur a small but beautiful Fungia {F. elegans V.), 
three Porites, 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 ot 
68^, the coral-sea boundary, even beyond the Galapagos, and 
north of the equator — the coral-reef sea, just east of Panama, 
is narrowed to 20°, which is 36° less of width than it has in 
mid-ocean ; and this suggests that these currents, by their 
temperature, as well as by iheir usual westwa7'd direction, have 
])roved 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 /)/. paimata, 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. proli/era, a handsome shrub-like species, of 
rather crowded branches ; besides others ; and these are marks 
of the existence of the warmer torrid region ; yet the sea has 
not as high a temperature as the hottest part of the Pacific. 
The species of the Astrsea tribe are few in number, and among 
the largest kinds are the Maeandringe (the Diploria being here 
included). None of the free Fungidae are known excepting 
the two species in deep water, and none of the Pavonioe among 
the compound species ; but the massive Siderinaj (Siderastr^ece) 
are common, and the foliaceous Agaricias and Mycedia. Of 
the Oculina tribe, species of Oculina, Cladocora and Astrangia 
are relatively more numerous than in the Central Pacific ; but 
there are none of the Pocilliporids, which are common bodi 
in the torrid and subtorrid regions of the Pacific. Millei)ores 
are very common. Gorgonice, are of many species. 



88 CORALS AND CORAL LS LANDS. 

Professor 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 asti-ceoides Lmk., P. davaria 
Lmk., Madi'epora pabnata L., M. cervicoi'nis L., M. prolifera L., 
MffMJidrida divosa V., M. /aby7'i?tthica, M. sinuosa Les., with 
other species of Mseandrina, Manidna areolata Ehr., Sider- 
astriEa {Sidcrind) radiata V., 6". galaxea BL, Agarida agari- 
dtes, OrbiceUa cavernosa V., O. ajimilaris 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 isocrymes of '74° and 68°. The reef corals extend as far 
south as Cape Frio, according to Professor C. F. Hartt. The 
species, as determined by Professor Verrill, from Professor 
Hartt's collections, resemble the West Indian. All species of 
Madrepora, Mseandrina, Diploria, Manicina, Oculina, genera 
eminently characteristic of the West Indies, appear to be want- 
ing, while the most important reef-making genera are Faina, 
Acanthastrcea^ Oflncelia, Siderastraa, Porites, and Millep07-a, 
and also, of less importance, Mussa and some others. A 
few species, viz. : Siderastrcea stdlata V., OrbiceUa aperta V., 
Astrcea gravida V., and Porites solida V., are very close to 
West Indian species ; and Millepora alcicoi'iiis 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 
Astrsea tribe, Isophyllia dipsacea, /. rigida, Diploria cerebri- 
for mis ; of the Oculina tribe, Oadina diffusa, Ocidina varicosa, 
Oculina pallens, Oculina Valenciejinesii ; of the Fungia tribe, 
Siderastrcea radians, Alycediurn fragile ; of the Madrepora tribe, 
Porites davaria; also the Millep07'a alcicornis, and the common 
West India Alcyonoids, Gorgojua flabellum, Plexaura a-assa 
Lx., PL flexuosa Lx., PL homomalla Lx., Pterogorgia Ameri- 
cana Ehr., Pt. ace?'osa, Ehr. 



RANGE IN DEPTH OF CORALS. 89 

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 Foster 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 scat- 
tered, 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. 
P^hrenberg, by his observations on the reefs of the Red Sea, 
confirmed the observations of Quo}' and Gaymard ; he con- 
cluded 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 
sixteen or seventeen fathoms. 

Mr. Darwin, who traversed the Pacific with Captain Fitzroy, 
R.N., gives twenty fathoms as not too great a range. 

In his soundings ofT 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 Astraea ; and a Millepora down to fifteen fathoms, with 
pIso, 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 



90 CORALS AND CORAL LSLANDS. 

his survey of the Maldives and Chagos group, found, at seven 
or eight fathoms, great masses of Hving coral ; at ten fathoms, 
the same in groups with patches of white sand between ; and, 
at a litde 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 
otlier banks in the same group, ten or twelve fathoms under 
water, there was growing coral. 

In the Red Sea, however, according to Captain Moresby 
and Lieutenant 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 purity, or freedom from sediment, of the waters at that 
place. Kotzebue states that in some lagoons of the Marshall 
group he observed living corals at a depth of twenty-five 
fathoms, or one hundred and fifty feet. 

Professor Agassiz observes that about the Florida reefs 
the reef-building corals do not extend below ten fathoms. 
Mr. L. F. de Pourtales states that he found species of Ocu- 
lina and Cladocora off the Florida reefs living to a depth of 
fifteen 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 during 
the cruise of the Wilkes Explormg Expedition, tend to confirm 
this opinion. 

The conclusion is borne out by the fact that soundings in 
the course of the various and extensive surveys afford no evi- 
dence of growing coral beyond twenty fathoms. Where the 
depth was fifteen fathoms, coral sand and fragments were 
almost uniformly reported. Among the Feejee Islands, the 
extent of coral-reef grounds surveyed was many hundreds of 
square miles, besides the harbours more carefully examined. 
The reefs of the Navigator Islands were also sounded out, 
with others at the Society group, besides numerous coral 



RANGE IN DEPTH OF CORALS. 



91 



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 Lebuand 
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 encountered 
at times, but they were at a less depth than twelve fathoms. 
By means of a drag, occasionally dropped in the same channels, 
some fleshy Alcyonia and a few Hydroids were brought up, but 
no reef-forming species. 

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 afterwards 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 
allowing 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 harbours and about shores where 
there is no coral, confirms the view here presented. At Upolu, 
the depth of the harbours 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 
evidence of coral. There is no cause here which will explain 
the absence of coral, except the depth of water ; for corals and 
coral reefs abound on most other parts of Upolu. Below 
Falelatai, of the same island, an equal depth was found, with 
no coral. Off the east cape of Falifa harbour, on the north 



92 CORALS AND CORAL ISLANDS. 

side of Upolu, Lieutenant Emmons found no coral, although 
the depth was but eighteen fathoms. About the outer capes of 
Fungasa harbour, Tutuila, there was no coral, with a depth of 
fifteen to twenty fathoms ; and a line of soundings across from 
cape to cape afforded a bottom of sand and shells, in fifteen 
to twenty-one and a half fathoms. About the capes of Oafonu 
harbour, 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 sadsfactorily 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 favourable 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 GROWTH OF CORALS. 93 

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 fLict that only small corals grow in the lagoons and chan- 
nels, though true of lagoons and channels of small si7e, or of 
such parts of the larger channels as immediately adjoin the 
mouths of fresh-water streams. 

There are undoubtedly species especially fitted for the open 
ocean ; but as peculiar conveniences are required for 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, Mseandrinas, 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 
diameter. Around the Duke of York's Island, the bottom 
was observed to be covered with small branching and folia- 
ccous Montipores, as delicate as any of the species in more 
])rotected waters. 

Species of the same genera grow in the face of the breakers, 
and some are identical with those that occur also in deeper 
waters. 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 Miile- 
l)ores 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. 

Again, the same genera occur in the shallow waters of the 
reef inside of the breakers. Astraeas. Mseandrinas and Pocilli- 
pores are not uncommon, though requiring pure waters. There 
are also Madrepores, some growing even in impure waters. 
One species was the only coral observed in the lagoon of 



94 CORALS AND CORAL ISLANDS. 

Honden Island (Paumotus), all others having disappeared, 
owing to its imperfect connection with the sea. Upon the 
reefs inclosing the harbour of Revva (Viti Lebu), where a 
large river, three hundred yards wide, empties, which during 
freshets enables 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. cribripord), 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 common. In many instances, the living Porites were 
seen standing six inches above low tide, where they were 
exposed to sunshine and to rains ; and associated with them in 
such exposed situations there were usually great numbers of 
Alcyonia and Xeniae. The Sideringe 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 dura- 
tion 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 deposition 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- 
ment of sediment. The same takes place with the hemispheres 
of Astraea ; 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 Fungiag, 
which are broad simple species, are occasionally destroyed 
over a part of the disk through the same cause, and yet the 
rest remains alive. It is natural, therefore, that wherever streams 
or currents are moving or transporting sediment, there no corals 



CAUSES AFFECTING GROWTH OF CORALS. 95 

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 
consequence of evaporation, — a condition of the lagoon of 
Knderby'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 nullipores, shells, bryo- 
zoans, &c., 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 185 1) : " Innumerable 
boring animals establish themselves in the lifeless stem, piercing 
holes in all directions into its interior, like so many augurs, 
dissolving its solid connection with the ground, and even pene- 
trating far into the living portion of these compact communi- 
ties. The number of these boring animals is quite incredible, 
and they belong to difterent families of the animal kingdom ; 
among the most active and powerful we would mention the 
date-fish or Lithodomus, several Saxicavae, Petricolce, Acae, 
and many w^orms, of which the Serpula is the largest and most 
destructive, inasmuch as it extends constantly through the 
living part of the coral stems, especially in the Mseandrina. On 
the loose basis of a Maeandrina, 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 completely 
rotten through. ' 

On the other hand, Serpulas and certain kinds of barnacles 



96 CORALS AND CORAL LSLANDS. 

(of the genus Creusia, &c.) penetrate living corals without 
injury to them. They attach themselves when young to the 
surface of the coral, and finally become imbedded by the in- 
crease of the zoophyte, without producing any defacement of 
the surface, or affecting its growth. Many of these Serpulas 
grow with the same rapidity as the zoophyte, and finally pro- 
<luce a long tube, which penetrates deep within the coral mass ; 
and, when alive, they expand a large and brilliant circle or 
spiral of delicate rays, making a gorgeous display among the 
coral polyps. Instinct seems to guide these animals in select- 
ing 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 Astrsea it inhabits. 

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. J 

II. The too great depth of the waters. 

III. The proximity of the mouths of rivers, on account of 
which sediment is distributed along the coast adjoining and 
over the sea bottom. 

IV. Rate of Growiii of Corals. 

The rate of growth of coral is a subject but Httle under- 
stood. We do not refer here to the progress of a reef in 
formation, which is another question complicated by many 
co-operating causes ; but simply to the rapidity with which 
particular living species increase in size. There is no doubt 
that the rate is different for different species. It is moreover 
probable that it corresponds with the rate of growth of other 
alHed polyps that do not secrete lime. The rate of growth 
of Actiniae might give us an approximation to the rate of 
growth in coral animals of like size and general character ; 
for the additional function of secreting lime would not neces- 
sarily retard the maturing of the polyp ; and from the rate of 
growth of the same animals in the young state, we might 



RATE OF GROWTH OF CORALS. 97 

{)erhaps draw some inferences as to the rate in polyps of cor- 
responding 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 
believed. 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 statement made to him by Lieutenant Wellstead, that 
*'in the Persian Gulf a ship had her copper bottom in- 
crusted in the course of twenty months, with a layer ot 
coral two feet thick," — evidently to be accepted hesitatingly. 
He also speaks of a channel in the lagoon of Keeling 
atoll having been stopped up in less than ten years ; and 
of the natives of the Maldives finding it necessary oc- 
casionally to root out, as they express it, coral knolls from 
their harbours. 

Mr. Stutchbury describes a specimen consisting of a spe- 
cies of oyster whose age could not be over two years, in- 
crusted 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. VVeinland 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 

H 



98 CORALS AND CORAL LSLANDS. 

growth of three to five inches, above referred to, might have 
been made during the three winter months. 

Duchassaing (in L Institute 1846, p. 117) observes that in 
two months some large individuals of Madrepora prolifei-a^ 
which he broke away, were restored to their original size. 
More definite and valuable is the observation of M. L. F. 
de Pourtales, that a specimen of Mceaiidi'ina labyrinthica, 
measuring a foot in diameter, and four inches thick in the 
most convex part, w^as taken from a block of concrete at 
Fort Jefferson, Tortugas, which had been in the water only 
twenty years. Again, Major E. B. Hunt mentions, in the 
Ameriam Journal of Science for 1863, the fact of the growth 
of a Moeandrina 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 de- 
posited specimens 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 i8t)o, or in fourteen years. Two 
are specimens of Oculiiia diffusa; one is a clump four inches 
high and qight 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 Mcea?idrina clivosa V. ; it has a height of 
tvvo-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 about 
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 



KATE OF GROWTH OF CORALS. gq 

frigate Sever/i, lost in 1793 near ''Silver Bay," off Turk's 
Islands, is covered with growing corals. It lies (according 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 Orbicella annularis, 
shaped somewhat like a hat ; it is attached to the top of a bell 
and spread outward on all sides. The thickness of the coral 
at the centre is about eight inches, and the breadth fifteen. 
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 vessel, 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 2 1, 1857. — Moored our boat over the remains of a 
large wreck, . . its depth being from three to ten fathoms. 
I made the first descent in the armour. I found the bottom 
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 pro- 
jected out of the coral rock. 

'''■ April 22. — Made a second descent and commenced exa- 
mining in six fathoms of water on what appeared to be midships. 
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 wdth hammer and 
chisel. . . . Near these cannon, which must have been near 
the forward part of the ship, I commenced to work on a clear 

H 2 



lod CORALS AND CORAL LSLANDS. 

space between the cannon. After 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 at- 
tained in sLxty-fou?' 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 
Astrsea 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 inclose an 
larea, and the number of polyps counted, the numerical in- 
crease of polyps resulting from budding might be ascertained. 
If specimens are selected, as done by Mr. Allan, it is import- 
ant that they should be placed where other corals are growing 
in luxuriance, so as to be sure that there are no deleterious 
influences to retard growth. It is to be hoped that some of 
the foreign residents at the Sandwich, Society, Samoan, or 
Feejee Islands will take this subject in hand. There are also 
many parts of the West Indies where these investigations 
might be conveniently made. 



CHAPTER 11. 

STRUCTURE OF CORAL REEFS AND ISLANDS. 

'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, however, 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 vege- 
tation ; 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. CORAL REEFS. 
GENERAL FEATURES. 

Coral reefs are banks of coral rock built upon the sea- 
bottom 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 



I02 . CORALS AND CORAL LSLANDS. 

tide ; but, at the ebb, they commonly present to view a broad, 
flat, bare surface of rock, just above the water level, strongly 
contrasting with the steep slopes of the incircled island. 

Nearing in a vessel a coral-bound coast, the first sign of the 
reef, when the tide is well in, is a Ime 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 
in 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 
look-out aloft, favourable 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 
f?'ingi7ig and a barrier reef, as these two parts are called. At 
a single place the sea is faced by a cliff; and here, owing to 
the boldness of the shores and depth of waters, the reef is 
wanting. The barrier reef at one point has a passage through 
it, which is an opening to a harbour ; and many such harbours 
exist about coral-girt islands. 



STRUCTURE OF CORAL REEFS. 103 

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 incloses 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. 




HIGH ISLAND WITH BAKRIER AND FRINGING REEFS. 

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 cauiion 
necessary. Patches of growing corals, from a few square feet 
to many square miles in extent, are met with over the broad 
area inclosed 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 x^rchipelago at the close of this 
volume. 

Near the middle of the chart is the island Goro ; its shores, 
excepting the western, are bordered by a fringing reef 1 he 
island Angatc^ south of Goro, is incircled by a coral break- 
water, which on the southern and western sides runs far from 
the shores, and is a proper barrier reef, while on the eastern 



104 COKALS AND CORAL ISLANDS. 

side, the safe 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 incircling, 
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, C/iic/iia, and Naiau, other examples of islands fiinged 
around with narrow reefs. Lakemba^ a little more to the south- 
ward, is also incircled 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 incloses. 
The Argo Reef., east of Lakemba, is a still larger barrier, in- 
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 greater 
or less distance of the reef from the shores and the extent of 
the inclosed land. 

Passing to the large islands Vanua Levii and Viti Levu, we 
observe the same peculiarities illustrated on a much grander 
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 incircling reefs depend evidently to a great 
extent on that of the land they inclose. That this is the case 



STRUCTURE OF CORAL REEFS. 105 

even in the Argo reef, and such other examples as offer now 
but a single rock above the surface of the inclosed lagoon, we 
shall endeavour 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 (i) entirely incircling ; or they may be (2) confined to a 
larger or a smaller portion of the coast, either continuous or 
interrupted ; they may (3) constitute throughout a distant 
barrier ; or (4) the reef may be fringing in one part and a bar- 
rier 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 between 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. 
Between them, and also outside of all, there are the submerged 
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 inclosing 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 
along its wliole 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. 



io6 



CORALS AND CORAL LSLAXDS. 



KEAV 
CALEDONIA 

'ont. inch to 00 miles. 




i^\ \i^ 



STRUCTURE OF CORAL REEFS. 107 

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 un- 
fathomable within a short distance of the line of breakers. 

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

1. Outer reefs ^ or reefs formed from the growth 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 barriers, wliich may receive 
detritus either from the reefs, or from the shores, or from both 
of these sources combined. 

4. Beaches and beach formations, produced by coral accumu- 
lations 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 
i.-.lr.nds. 

II. OUTER RERFS. 

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 work 
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, 
especially toward its outer limits, where corals of various kinds 
are growing luxuriantly, with 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 



io8 CORALS AND CORAL LSLANDS. 

• 
along the outer margin of the reef, and in the adjoining 
shallow sea«;. Here they grow in profusion ; but yet the eager 
lover of coral landscapes will be often disappointed by finding 
among the crowded 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 
entrance 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 
fathoms, and then falls away more gradually for many rods, or 
it may be some hundreds of yards ; over the bottom in these 
shallow waters are spread out the coral plantations, down to 
a depth of 80 or 100 feet. Finally there is a rather abrupt 
descent to depths beyond the reach of an ordinary sounding- 
lead. The great difference in the rapidity with which the 
water deepens depends chiefly on the varied character of sub- 
marine 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 
various shades of pink and purple. These colours and the 
smoothness, as observed by Chamisso, are due to incrusting 
Nullipores; 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 



STRUCTURE OF CORAL REEFS. 109 

coral, for it is without a pore ; and layer is added to layer until 
it has considerable thickness. It is thus an important pro- 
tection 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 
outer reef, and are not always present ; the outer margin is 
higher than the rest of the reef when they are absent. 

The NuUipores are not alone on this outer edge, for there 
are always sprigs of Madrepores, small Astraeas, and some 
other corals, lodged in the cavities, with many echini, star- 
fishes and sea-anemones, besides barnacles and serpulas ; 
and fish of many colours 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 waters 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 
processare more particularly described further on, where treat- 
ing of atolls. 

The rock of the outer reef, wherever broken, exhibits 
usually 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 conglo- 
merate. Still others, more common, are solid v/hite limestones, 



no CORALS A XI) CORAL ISLANDS. 

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 debris oi the coral fields, 
consolidated by a calcareous cement ; and the great abundance 
of the finer variety of rock indicates that much of it has ori- 
ginated from 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 
sometmies contains them as fossils, along with bones of fishes, 
exuvia of crabs, spines and fragments of echini, orbitolites 
(disc-shaped foraminifers), and other remains of organic life 
inhabiting reef-grounds. 

III. 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 loo 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 99, figures 
and describes one of these " coral heads " standmg in water 
fifty feet deep, near Turk's Island. Its trunk, which made up 



STRUCTURE OF CORAL REEFS. in 

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 favourable 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- 
region such united coral-heads cover acres in extent, being 
joined together above and supported by their pillars. A case is 
reported of a whale having gone through one of these under 




THE LIXO CORAL REEF, ABROLHOS. 



passages after being struck with a harpoon. Mr. Whipple 
also states that there are cavernous recesses in some of these 
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." 

Professor C. F. Hartt, in his " Geology, &c., 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 



112 CORALS AND CORAL LS LANDS. 

speaks of it as giving simply a general view of the region with- 
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 repre- 
sented 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 
chapeh'oes (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 
metres 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 chapeiroes like a weather-cock on the top of a tower." 

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



STRUCTURE OF CORAL REEFS. 113 

The rock of the submerged coral-heads is but a loose aggre- 
gation 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 together. 

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 
material for impalpable compact limestones. The waters out- 
side 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 Reefs 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 Australian 
reef region, and others in that vicinity, in H.M.S. F/y, states 
that in the deeper waters outside of the great barrier, " and in 
all the neighbouring East India seas, from Torres Straits, north 
of Australia, to the Straits of Malacca, wherever 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 essentially carbonate of lime. 
The substance, when dried, looked much like chalk, excepting 
in its greener tinge. How far this calcareous matter may be 
due to foraminifers, rather than corals, 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 oceanic 
currents, like that of the Gulf Stream, might bear away the 
lighter material for long distances, if it swept with full strength 
over the shore reefs ; but it is generally true that such currents 
are little felt close in shore. Notwithstanding the proximity of 

I 



114 CORALS AND CORAL LSLANDS. 

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 fathoms ; 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, 
Globigeriiia j?md, as it is called from the species characterising 
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. 

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 incloses 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 gene- 
rally much resemble the outer reefs. They are nearly flat, and 
though mostly bare of life, and much covered with coral sand, 



STRUCTURE OF CORAL REEFS. 115 

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 w^de 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 in 
such a ramble ; for, besides living corals, there are myriads of 
other beings which science alone has named, of various beau- 
tiful forms and colours, 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 extent, 
there are other patches, still submerged, that are covered 
with growing corals throughout. They are of different eleva- 
tions under the water's surface ; and though at times but 
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 Vmcemtes 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 



ii6 CORALS AND CORAL LSLANDS. 

an instance diving is found to be the only resource left for 
freeing the foul anchor. 

The margins of the reefs in and about the inner channels are 
often luxuriant with magnificent corals quite to the edge 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 
finally cemented and so made solid. At Tongatabu and 
among the Feejee Islands, reefs thus formed of corals standing 
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 
Astrseas and Maeandrinas, both there and in the Feejees, mea- 
sure 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 
branchi7ig 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 miany parts is still cavernous, or but imper- 
fectly cemented. 



STRUCTURE OF CORAL REEFS. 



117 



There is al?o to be found about inner reefs, over large 
areas, the soHd 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 
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 distinction 
between the inner and outer reefs consists in the less frag- 
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 water, and there are species peculiar to the different 
regions. 



ii8 CORALS AND CORAL LS LANDS. 

V. CHANNELS AMONG REEFS. 

To complete this review of the general appearance and 
constitution of reef formations, it remains to add some par- 
ticulars 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 from 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 good 
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 inclosed by dotted 
lines. Tiie 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 
twenty fathoms in depth. Occasionally it enlarges into har- 



STRUCTURE OF CORAL REEFS. 



119 



bours ; 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, tlie reef is rather a fringing than a barrier reef. Within 
the green belt that mcircles Bolabola (p. 109) 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 







CORAL REEFS OFF THE NORTH SHORE OF TAHITI. 

upper portions constitute the so-called barrier and fringing 
reefs. The rock w^ould 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 off from the higher reefs by the currents. 

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. 



I20 CORALS AND CORAL LS LANDS. 

At Upolu the white coral sands of the reefs (or in more 
general terms the reef debris) form 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 
greyish blue calcareous mud, appearing as plastic as commcm 
clay ; it consisted solely of comminuted corals and shells, with 
colouring 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 frequently brought up with our dredges. On the north 
side of Vanua Lebu, a stream had so filled with its detritus 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, the reefs 
have probably added somewhat to these accumulations ; 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 anchored, 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 within 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. 



STRUCTURE OF CORAL REEFS. 121 

These tidal currents often have great strength, and are 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 dis- 
tribute only the shore detritus. It is thus seen that the same 
region may differ widely in its adjacent parts, and seemingly 
afford 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 effect 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 in- 
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- 
tralian barrier, according to Jukes, as brought up by the 
dredge from depths of fifteen to twenty fathoms, often resem- 
bled 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 neighbouring 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. 



CORALS AND CORAL LSLANDS. 



VI. BEACH SAND-ROCK. 

Besides the ordinary coral rock, there are also beach for- 
mations made of coral sands, worn shells, &c., 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 
tineness, 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 j 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 
include 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 
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 
produce 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 
consolidated up to a line a little above high-tide mark. In all 



STRUCTURE OF CORAL REEFS. 123 

instances observed, the layers dip at an angle of six to eight 
degrees 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 
sloping surface. Tutuila and Upolu, in the Navigator group, 
and Oahu in the Hawaiian, afford many examples of these 
beach formations. At certain localities the beach sand-rock has 
been washed away after it was formed ; and occasionally large 
masses 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 
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 
Islands, some of which are cited further on. 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 water 
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." 



t24 CORALS AND CORAL LSLANDS. 



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 drifdng of the 
sand into hillocks or ridges by the winds. 

The drifts resemble ordinary sand-drifts, and are often 
quite extensive. On Oahu, they occur at intervals around the 
eastern shores, from the northern cape to Diamond Point, 
which 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 westward, as well as to the regular trades. They 
also occur on Kauai, another of the Hawaiian 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 waters, 
fresh or salt, become cemented into a sand-rock, more or less 
friable, which is frequently oolite. The rock consists of thin 
layers or laminas, which are very distinct, and indicate, gene- 
rally, every successive drift of sand which pufTs 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 displayed in 
the rock. Several catastrophes of this kind may be made out 
from the character of the lamination in the sand-bluffs 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 de- 
gradation), in which the lamination is finely exposed to view. 
The layers are but a fraction of an inch ; at one of the 
hills large slate-like slabs may be obtained ; they have a sanded 
surface, but are so hard within as to clink under the hammer. 



STRUCTURE OF CORAL REEFS. 125 

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 Ume from the waters often 
occupying them ; but this is an exceptional variety of the 
rock. A particular description of these bluffs is given in the 
author's report on the geology of the Hawaiian Islands. 

One of the most interesting facts observed in connection 
with these drift hills, is the absence of shells, and even of fra^-- 
ments of shells or corals sufficiently large to be referred to 
either of these sources. The material is sand, without organic 
remains, although situated on shores off which, within a hun- 
dred yards, there are shells and corals innumerable. The grind- 
ing 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. 



VITI. THICKNESS OF REEFS. 

We have considered in the preceding pages the peculiari- 
ties of form and structure characterising the reef formations 
bordering islands and continents, and their influence upon the 
inclosed 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 



126 CORALS AND CORAL LSLANDS. 

the land, and others incircling it Uke 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. Darwin has thus estimated the thick- 
ness of the reefs of the Gambler group (p. 227) and some other 
Pacific islands, and he arrives at the conclusion, as his figures 
indicate, that some coral reefs, at their outer limits, are at least 
two thousa?id 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 Mauna Loa, on the 
island 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, except- 
ing 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 Jii'e degrees, 460 feet. Adopting the 
first estimate, the Gambler group would give for the outer 
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 ; Upolu, by the same esti- 
mate. 440 feet. The deduction for Upolu may be too large : 



STRUCTURE OF CORAL REEFS. 127 

taking three degrees as the inclination, it gives 260 for the 
thickness at the outer margin. The results are sufficiently- 
accurate 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. 



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 inclosed channels greatly enlarge the limits tributary 
to the lands they incircle. 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 



128 CORALS AND CORAL LSLANDS. 

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 
encroaches upon the unprotected shores of small islands, but 
carries off much of whatever the streams empty into it. The 
delta of Rewa, on Viti Lebu, resultmg 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 consequendy rivers of such magnitude are not common. 
But there is rarely a coral-girt island which has not at least 
some narrow plains from this source; and upon them the vil- 
lao-esof 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 
natives, 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 characterises the islanders ; for 
these circumstances have favoured the construction of large sail- 
canoes in which they venture beyond their own land, and often 
undertake voyages hundreds of miles m length. Communica- 
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, harbourless and thinly 
habitable, like St. Helena, in the tropics, and nearly all extra- 
tropical islands, the shores of these reef-bound lands are 
blooming to the very edge, and wide plains are spread out 
with bread-fruit and other tropical productions. Harbours, 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 afforded a single good anchorage. Jukes 
remarks that the sea within the great Australian barrier is 
" one great natural harbour ; " and this harbour is as long as 
from the extremity of Florida to Newfoundland. 



STRUCTURE OF CORAL REEFS. , 129 

Coral-reefs are sometimes viewed as only traps to surprise 
and wreck the unwary mariner ; but whoever has visited the 
dreary prison-house, St. Helena, will have some appreciation 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 biche de mat 
(called also bkhe de nier, sca-ginse;ig, and in China, tripang), 
thousands of hundredweight 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 favourite material for Chinese dishes, either stews 
or soups, &c., is dried holothicria — large slug-like animals, 
called often sea slugs, and also sea cucumbers, from their form 
in tlie 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 
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 Hke 
that in taste when stewed." They are brought to China by the 
Malays from Macassar and elsev/here. 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 biche de mar, 
and also the French form of it, beche de 7ner, are corruptions 
of the Portuguese bicho do mar, which means sea-wjrm, or 
sea-sbis:. 



[30 CORALS AND CORAL ISLANDS. 



II. STRUCTURE OF CORAL ISLANDS. 
I. FORMS AND GENERAL FEATURES. 

Coral islands resemble the reefs just described, except that 
a lake or lagoon is incircled instead of a mountainous islands. 
A narrow rim of coral reef, generally but a few hundred yards 
wide, stretches around the inclosed 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 fohage 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 after 
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 its belt 
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 colour 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. 

The 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 
intervals 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 lagoon islands are called atolls^ a word of Maldive 
origin. The king of the Maldives bears the high-sounding 



STRUCTURE OF CORAL ISLANDS. 



131 



title of " Ihraliim Sultan, King of the thirteen Atollons and 
twelve thousand Isles" (see page 153); 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 siaiilarly roughened by the wind, though not to the 
same extent. Standing on the north shore of the Raraka 
lagoon and looking south-west, 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. 





CORAL ISLAND, OR ATOLL. 



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 
continous line of foliage. Traces may perhaps be still detected 
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 

K 2 



132 ' CORALS AND CORAL ISLANDS. 

most finished state ; the lake rests quietly within its circle of 
palms, hardly ruffled by the storms that madden the surround- 
ing ocean. 

From the islands with small lagoons, there is every variety 
in gradation down to those in which there is no trace of a 
lagoon. 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 throughout 
when the leeward reef is bare. The entrances to the lagoons 
are accordingly on the leeward side. 

A single group of islands, the Gilbert or Kingsmill, affords 
good examples of the principal varieties. It is at once seen 
from these examples that atolls are not annular. In the 
southernmost, Tapateuea, the form is very narrow, the length 
being thirty-three miles, with the width of the southern pordou 
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 patches 
of verdure, thus strung together, seem to rise out of a long 
white litie of breakers, the sea surging violently against the 
unseen 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 north-east. The reef of the opposite side, though bare 
of vegetation, stands near low-tide level, and the whole incloses 
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 pre- 
ceding in having two narrow ship entrances to the lagoon, one 
through the north-western reef, and another through the 
south-western. 



4 



\[araki 



tl >| Apia 



Tarawa 



^ 



7 



\.^/f' Mai: 



Apj 



I 



orFitts 



Maldn. 



Tari 
Island 



l^s° 



Kuriav5*j 



X:" 



i^««. 



^^:^~Jil!^aTiould 



GILBERT 



OR 



klNGSMlLL ISLANDS 






TaputeoneaX ""- 



^i 

••>i-.i>> 



irb' 



jzi-^ 



134 CORALS AND CORAL LSLANDS. 

Kuria is a remarkable double island, witlioiit a proper lagoon. 
It consists of two neighbouring groves, each about a square 
mile in extent, on adjacent patches of reef. 

Maiana is quite regularly quadrangular, with an uninterrupted 
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 
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 
correspond 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 south-western reef. 

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

Tari-tari, lying to the south of Apia, is a large triangular 
atoll. It is wooded almost continuously on the side facing 
south-east, and has a few spots of verdure on the south-west, 
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 map of the Wilkes Expedition to a 
scale of four-tenths of an inch to a mile. 

Taiara and Henuake (Figs, i and 2) are two small belts of 
foliage, somewhat similar to Maraki. Henuake possessed an 
additional charm in being tenanted only by birds ; and they 



STRUCTURE OF CORAL ISLANDS. 



^35 



were so tame that we took them from the trees as if they had 
been their flowers. 



jM^ 




'■^\<,^ 



^^^^^^^# 



HENUAKE, OR HONUEN. 



Jarvis's and Swain's Islands (Figs. 3 and 4) are of still 
smaller size, and have no lagoon. The surface of the former 



JAkVISS ISLANI 



c/ .-J 




:• 






'^> 






,i~^ 


-^^ 


s 


w 


-.-^ 


'■'-v--' 


s\\ 


IK 


n's 


ISLAND. 



/'a^ 






'-v.ferj 



\;> 



I 



FAKAAFO, OR BOWDITCH S ISLAND. 



is sandy, while the latter is densely covered with foliage. 
Both islands are a little depressed about the centre, a fact 
indicating that there was formerly a lagoon. 



136 CORALS AND CORAL LS LANDS. 

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 emerg;ed from the 
waves and become verdant; in other portions the reef is ot 
the usual height, — that is, near low-tide level, — excepting a 
few spots elevated a little by the accumulation of sand. 

The Paumotu Archipelago, the crowded cluster of coral 
islands east and north-east 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 Expedition, 
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 will 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. 





LENGTH. 


(JRFATE.ST 
IJI^EADTH. 


AREA IN 
SQ. MILES. 


HABITABLE 
I'AKTS IN 
SQ. MILKS. 


Cailshoff, Pauniotiis 


.. 27 . 


13 - 




200 .. 


.... 10 


Wolchonsky ,, 


.. 15 .. 


3 ••• 




40 .. 


.... 3 


Raraka ,, 


.. 15 . 


10 ... 




90 .. 


.... 8 


Manhii , , 


.. 14 .. 
50 • 


6i . . 




50 •• 
,000 .. 


... 9 
.... 16 


Nairsa or Deans, Paumotus 


19 •■■ 


... I 


Fakaafo, Union group .... 


.. 75 ■ 


44 - 




20 .. 


.... 21 


Duke of Clarence ,, 


.. 8^ ., 


5i - 




27 .. 


.... 2 


Tapateuea, Kini^smills 


■:>i 


6 .. 




60 .. 


.... 6 


Tarawa , , 


.. 20 
.. 22 . 


10 . 




130 •; 
125 .. 


.... 8 


Nonouti ,, 


9 ••• 




.... 7 


Tari-tari ,, 


.. 18 


II ... 




HO .. 


.... 4 



The ten islands here enumerated have an aggregate area of 
,852 square miles, while the amount of actual dry habitable 



STRUCTURE OF CORAL ISLANDS. 



137 



land is but seventy-six miles, or less than one twenty-fourth. 
In the Caroline Archipelago the proportion of land is still 
smaller. Menchikoff atoll covers an area of 500 square miles, 
and includes hardly six square miles of wooded land. In the 
Marshall Islands the dry land is not over one-hundredth ot 
the whole surface ; while in the Pescadores the proportion ot 
land to the whole area is about as i to 200. 

The distribution of the land upon the reef is obvious from 
the sketches already given. It is seen, as long since remarked, 
that the windward side is, in general, the highest. It is also 




MENCHIKOKF ATOLL {^^ OK AN INCH TO A MILE). 

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 onl) 
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 Carohnes, 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 
current, especially during the ebbing tide. At Depeyster 



138 CORALS AND CORAL ISLANDS. 

Island, il 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 
results. 

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 south-east 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. 

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. 



STRUCTURE OF CORAL ISLANDS. 



139 



In general, for one to five hundred yards from the margin 
of the shore reef, the water slowly 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 surt 
line, 5 fathoms; 80 yards, 13 fathoms; 120 yards, 18 
fathoms ; 200 yards, 24 fathoms ; and immediately beyond, 
no bottom with 35 fathoms. At Henderson's Island, sound- 
ings 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 moudi 
of the lagoon of Diego Garcia, Captain Moresby found no 
bottom with 150 fathoms. At Egmont Island, 50 fathoms 
from the reef, soundings were struck in 150 fathoms. At 
Cardoo Atoll, only 60 yards from the reef, no bottom was 
obtained 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 five and 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 north- 
east of Cuba have very great depth close alongside. 

There are examples also of less abrupt slopes. North-west 
of the Hawaiian 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 



HO CORAL AND CORAL LSLANDS. 

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-fathoms. Christmas Island affords on its western 
side another example 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 generally 
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, soundings 
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 abrupt than 
that to windward, 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 already 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 



STRUCl'URE OF CORAL ISLANDS. 141 

apparent by a review of their characters. The description will 
be found to be a simple 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 jagged 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 
NuUipores 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 
fragments. Generally the barren areas much exceed those 
flourishing with zoophytes, and not unfrequently the clusters 
are scattered like tufts of vegetation in a sandy plain. The 
growing corals extend up the sloping edge of the reef, nearly 
to 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 re- 
treat for the Echini, asterias, sea-anemones and inullusks ; and 
over this portion of the platform, the gigantic Tridacna, some 
times 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 coloured mantle. Further in are occasional pools 
and basins, ahve 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. 



142 



CORALS AND CORAL LSLAMIXS. 



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

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 pre- 
sented that is novel after the excellent 
descriptions of these authors. Sketches of 
several of these islands, showing the gene- 
ral relation of the rim of land to the reef 
and the lagoon within, are given in the 
^ maps of islands on pages 133, 135. The 

< accompanying sketch represents a section o 

< the rim of land from the sea on one side 
° (the left) to the lagoon on the other. In 
i the view, the part ?n a represents the shallow 
I sea bordering an island, and abruptly deep- 
ir enin^ one to six hundred feet from the 
§ line of breakers. In these shallow waters 
t 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. 

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



STRUCTURE OF CORAL ISLANDS. 143 

In the Paiimotus, 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 platfonii 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 ofif. The 
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 generally 
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. More- 
over, 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 from a fourth 



144 CORALS AXD CORAL ISLANDS. 

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 prob- 
ably a result of a subterranean movement or shaking. 

The beach consists of coral pebbles or sand, with some worn 
shells, and occasionally the exuvi^ 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 artificial 
wall or embankment running parallel with the shores. On 
""lermont Tonnerre, the first of these islands visited by us, t))e 
natives seen from shipboard, standing spear in hand along the 
top of the beach, were believed by some to be keeping patrol 
on the ramparts of a kind of fortification. This deception 
arose from the dazzling whiteness of the coral sand, in conse- 
quence of which, the slope of the beach was not distinguished 
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 colour 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 de 
tected 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. 



STRUCTURE OF CORAL ISLANDS. 



145 



Both of these stages are ilhistrated 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- 
coloured by vegetable or animal decomposition. Scattered 
among the trees stand, still uncovered, many of the larger 
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 anything but coral sand. It is 
seldom discoloured 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 





BLOCKS OF CORAL ROCK ON THE SHORE PLATFORM. 

two it is usually cemented together into a more or less com- 
pact coral sand-rock. 

One singular feature of the shore platform, occasionally ob- 
served, 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 plat- 
form rock. Sketches of two of these masses are given above. 

Figure i represents a mass on the island of Waterland 
(one of the Paumotus), six feet high and about five in dia- 
meter; 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- 

i, 



146 CORALS AND CORAL LSLANDS. 

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 jdiameter. 
Below, it had been worn like the one just described, though 
to a less extent. Another similar mass was eight feet high. 
Figure 2 represents a block six feet high and ten feet in its 
longest diameter, seen on Water] and ; 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 at 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 Astreeas and Madrepores, and contained some imbedded 
shells, among which an Ostrasa 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 tlie 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 
described were found isolated, and only at considerable inter- 
vals. In no instance were they observed clustered. The loose 



STRUCTURE OF CORAL /SLA .YDS. 



147 



l)Iocks and those cemented below had the same general cliarac- 
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° 44' on a continuous mass of Porites whicJi 
was at least twenty feet across, and it seemed to ])ass down 
wards into the mass of the reef below water without any 
disconnection. 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 attracted our attention for a distance of three miles." 

The shore of the lagoon is generally low and gently inclined, 
yet in the larger islands, in which the waters of the lagoon are 
much disturbed by the winds, there is usually a beach resem- 
bling 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 out- 
ward in an abrupt descent, of a few yards or fathoms, to a 
lower area of growing corals, or a bottom 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, charac- 
terizing 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 tliere 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 quite extensive, and of a white colour. 
At Enderbury's Island, another having a shallow lagoon, the mud 
was so deep and thick that there was some difficulty in reaching 
tlie waters of the lagoon; the foot sank in eight or ten inches, 

L 2 



148 CORALS AND CORAL LSLANDS. 

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 lagoojis 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, 
become, in some instances, very salt by evaporation, and con- 
tain 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 
obstructed by them. At Henuake, the sea is shut out ex- 
cept at high water, and there were consequently but few 
species of corals, and those of small size. At Ahii (Pea- 
cock's Island), there was a small entrance to the lagoon, 
and though com.paratively 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 
sea, with deep waters and a sandy or muddy bottom. There 
are instances, as at the sourthern Maldives, of a depth of fifty 
and sixty fathoms. From twenty to thirty-five fathoms is the 
usual depth in the Paumotus. This was the result of Captain 
Beechey's investigations ; and those of the Expedition, though 
few, correspond. It is however probable that deeper soundings 
would be found in the large island of Nairsa (Dean's). In 
Gilbert's Group, south-east of the Carolines, the depth, where 
examined by the Expedition, varied from two to thirty-five 
fathoms. Mr. Darwin found the latter depth at Keeling's 
Island. Chamisso found twenty-five to thirty-five fathoms at 
the Marshall Islands. 



STRUCTURE OF CORAL ISLAXDS. 149 

The bottom of these large lagoons is very nearly uniform, 
varying but little except from the occasional abrupt shallovvings 
l)roduced by growing patches of reef. Soundings bring up 
sand, pebbles, shells, and coral mud ; and the last mentioned 
material appears to be quite common, even in lagoons of 
considerable size. ' It has the same character as above 
described. The bluish clay-like mud of the harbour of 
Tongatabu may be classed with these deposits. Darwin de- 
scribes this mud as occurring at the Maldives, and at Reeling'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 
ijuier 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 (Kingsmilfs 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. 

Beach formations of coral sand-rock are common on the coral 
islands, and they present the same features in every respect as 
those described. They were observed among the Paumotus, 
on Raraka, Honden, Rawehe, and other islands. The strati- 
fied character is ahvays distinct, and the layers slope toward 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 seaward slope 
of similar deposits at Rey West. The rock is largely a fine 
oolite. They often occupy a breadth of thirty to fifiy yards, 
appearing hke a series of outcrops ; yet they are frequently 
covered by the sands of the steep part of the beach. It is 
jjrobable 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 lime- 



ISO ■ COA'ALS AiVD COITAL ISLAiVDS. 

stone, excepting in its whiter colour ; but generally 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 Exploring 
Expedition, on Aratica or Carlshoff's Island, in the Paumotus, 
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 d?ift 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 north-eastern and south-western, are 
commonly a little higher than other parts ; and it is altogether 
probable that some of the sand-heaps there formed will prove 
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. R. H Schomburgh, 
in an article in the Journal of the Royal Geographical 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, aiid 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 pecuharities of structure apart from such as necessarily 
arise from the absence of high rocky lands. The incircling 
atoll reef corresponds with the outer reefs that inclose 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 position 
to the inner channels* within barrier reefs ; they receive coral 
material only from the action of degrading agents, because no 
other source of detritus but the reefs is at hand. The 



STRUCTURE OF CORAL ISLANDS. 



151 



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 
under 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 
Group, the shore platform is seldom as extensive as at the 
Paumotus. 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 con- 
glomerate 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 
Madrepora ; 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 
palniata ; 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 observed, 
it maybe remarked that the tides in the Paumotus are two to 
three feet, and about Enderbury's Island five to six feet, in height. 



:52 



CORALS AND CORAL LSLANDS. 






s TiUeu dou, MaU^ 



MMcL dow J teuton 






Ma/ilos Mahdoo ■. 



\i: • ■ - ■ :■■:■. 



Pl^oo^*'cb 
JloLohio ^ 






■■v.-;?y 






i 












w 

m 






■ \ ~r.! 

r.i /f/MoTxiqiie- 






'"I 



-•■■■KS....y 



MALDIVE ARCHIPELAGO (ONE INCH TO 6o MlLEs). 



STRUCTURE OF CORAL LSLANDS. 153 

Maldne Archipdai:;o. — 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 
Maldives, by Captain Moresby, is contained in the Journal of 




'■■sf 



S'^f gl 




^^QHorsburdi Atoll 

MAHLOS MAHDOO ATOLL, WITH HOKSBURGH ATOLL (.'j, OF AN INCH TO A MILE) 

the Royal Geographical Society, vol. v. p. 398 ; and another on 
this group by J. J. Horsburgh, and W. F. W. Owen, in 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 fifty 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 eighty-eight miles, while Suadiva, one of the southern- 



154 



CORALS AND CORAL LSLANDS. 



most, is forty-four miles long from north to south, and thirty- 
four miles across. 

The point of special interest in their structure is the occur- 
rence of atolls or annular reefs within the larger atolls. The 
islets of the lagoon and those of the incircling reef are in 
many instances annular reefs, each with its own little lake. 
Gems within gems are here clustered together. 

This feature is well exhibited in the Mahlos Mahdoo atoll, 
an enlarged map of which, from Darwin's work, is inserted on 
the preceding page. 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 hve 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 
iheir 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 illustrate 
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 



STRUCTURK OF CORAL ISLANDS. 



155 



that the ring-forined reefs are based on a shallow foundation 
instead of on the floor of the open sea, and that instead of being 
scattered irregularly, they are grouped closely together." — " It 



:Si^O^ 



r\ ^ 



.-'>^ 



■■^ 



^•■^. 



.4 



.^v 



av 



1'. 





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- 



1^6 



CORALS AND CORAL fSLAXDS. 




4<» 10 ratJivnjs. 



to 20 r"} 



atoll being freely exposed to the waters of the 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 margmal portions 
of reef, and especially those 
close 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. 
Although their presence is thus 
contingent on the openness of 
the marginal channels, the theory 
of their formation, as we shall 
hereafter see, is included in that 
of the parent atolls, of which 
they form the separate portions."' 
The G?'€at 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 opi- 
nion 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 become a coral island, vrith a lagoon 




STRUCTURE OF CORAL ISLANDS. 157 

forty fathoms deep. He says that, in the words of Captain 
Moresby,, it is in truth *' nothing more than a half-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 ]). 155, from Darwin, 
and for which, as well as for other information about the bank, 
he gives credit to Captain Moresby. The cross section is still 
further illustrated in the cut on p. 156. 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 then to the 
bottom of what was once the lagoon, now for the most part 
forty to fifty fathoms under water, though having its shoals that 
are five to ten flithoms 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. The bottom over the interior is 
muddy ; on the flat bordering it, fifteen to tw^enty fathoms deep, 
there is coral sand with " a very little live coral ; the outer rim 
is coral rock with scarcely any live coral ; " while the shoals or 
knolls of the interior are "covered with luxuriantly-growing 
corals." Darwin states also that the rim is steep on both sides, 
and outward slopes abrupdy 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 elenated Coral Islajids. — Metia, or Aurora 
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 of coral 
limestone. Approached from the north-east, its high vertical 
cliffs looked as if basaltic, resembling somewhat the Palisades 
on the Hudson. This appearance of a vertical structure was 
afterwards traced to vertical furrowings by the waters dripping 
down its front, and the consequent formation of stalagmitic 
incrustations. Deep caverns were also seen. 



158 CORALS A AW CORAL LS LANDS. 

The cliff, though vertical in some parts, is roughly sloping 
in others, and on the west side the surface of the island 
gradually 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. Occa- 
sionally 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 




METIA, OR Al I C)J A. ISIAND 



containing recent land shells that had been inclosed by a 
calcareous film while hibernating. 

It is probable that more extensive caverns would have been 
found had there been more than a few hours for the examina- 
tion 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, with- 
out 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), 



STRUCTURE OF CORAL ISLANDS. 159 

appear to be solid masses of compact limestone, in wJiidi nothing 
liize a cell can be detected T 

Beechey, in his description of Henderson Island, another 
of this character, speaks of the rock as compact, and hai'ing the 
fracture of a secondary limestone. 

The surface of the island is singularly rough, owing to 
erosion by rains. The paths that cross it wind through narrow 
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 of 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 standing 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 : — 

farvis's Island. — (Fig. 3, page 135.) Lat. o°2 2'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 are 
distinguishable in it. Its surface is a low sandy flat, eighteen 
or twenty feet high, without trees, and partly covered with 



i6o CORALS AMD CORAL LS LANDS. " 

small shrubs. A high sloping beach continuous around. Has 
a shore platform about 300 feet wide. 

Birnies. — Lat. 3° 35' S. ; Long. 171° 30' W. Four-fifths 
of a mile by one-third, trending north-west. No lagoon. A 
sandy flat about ten feet high, except near the north-north-east 
extremity, where it is about twelve feet. To the south-south- 
west the submerged reef extends out nearly a mile, over which 
the sea breaks. In passing it, distinguished no vegetation 
except the low purslane and some trailing plants. 

Siuain's.—i^xg. 4, page 135.) Lat. 11° 10' S. ; Long. 170'' 
52' W. I J miles by |; 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 cocoa-nuts ; 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 were 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 Nullipores. The outer margin of this platform was 
very uneven, and much intersected by channels, though less so 
than at Enderbury's Island. Great numbers of Birgi (large 
Crustacea) were burrowing over the island, some of which 
were six inches in breadth. 

Otiihu^ Paumotu Archipelago. — 14° 5'" S. ; 141° 30' W. 
i-| 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 



STRUCTURE OF CORAL ISLANDS. i6i 

with no entrance. North-east side alone wooded, and in two 
patches. 

Tcku Or Four Crowns, Paumotu Archipelago. — 20° 28' S. 
143^ 18' W. Diameter i| miles, nearly circular. A small 
lagoon with no entrance. South-western reef bare ; five patches 
of forest on the other part. 

Washington Island. — Lat. 4° 41' N. Long. 160° 15' W. 
3 miles by i^, trending east and Avest. It is a dense cocoa-nut 
grove with luxuriant shrubbery. No lagoon. The shore plat- 
form 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. 

Enderbiu-ys.— -^ 8' S. 171"^ 15' W. 2| miles by i mile 
nearly, trending N. N. W. and S. S. E. ; form trapezoidal or 
nearly rectangular. Little vegetatiori on any part, and but few 
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 saline incrusta- 
tions. 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 
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 
latter 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 inclose fragments of different sizes to a foot or 
more in diameter. 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. 



1 62 CORALS AND CORAL LSLANDS. 

Captain Hudson obtained soundings half a mile off in two 
hundred fathoms 3 the lead struck upon a sandy bottom, but 
was indented by coral. 

Honden or Henimke, Paumotu Archipelago. — Size 3I- miles 
by 2 miles. Oblong, five-sided ; trending west-north-west. A 
small shallow lagoon, communicating 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 con- 
sisting of large forest trees, with the Pandanus and other 
species, but no cocoa-nuts ; its breadth half 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 nearly flat. On one 
side there was a large area of extremely fine coral sand and 
mud, which extended a long distance into the lagoon. Else- 
where about the centre of the island, the reef-rock was bare, 
and contained numerous shells of Tridacnae. A few small 
Madrepores still growing in the lagoon. Beach on the sea- 
shore side eight feet high. In lower part of beach, several 
layers of white limestone (the beach sand-rock), formed of 
coral fragments or sand, shells, &c., 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 
archipelago. 

The facts above stated are evidence of a slight elevation, 
probably not exceeding three feet. 

Taiara, or Kings, Paumotu Archipelago. — 15° 42' S. ; 144° 
46' W. 2 1 miles by i j, trending north-west. Has a small 
lagoon with no entrance. Reef almost continuously wooded 
around, somewhat broken into patches. 

Sydney Island. — Lat. 4° 20 S. Long. 171° 15' W. Trends 
north-east and south-west. Well wooded nearly all round ; but 
on leeward side the forest in patches, with breaks of bare coral. 



STRUCTURE OF CORAL ISLANDS. 163 

Lagoon narrow, without entrance. Width of island 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 platform fifty to 
eighty feet wide ; five or six feet of water 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 covered with 
growing corals ; the corals rather tender species of Madrepores. 
In the interior of the lagoon many knolls and large patches 
of coral. 

Duke of York's.— %^ 38^ S., 172° 27' W. Form irregularly 
oblong, trending north-west. Length, 3I miles ; breadth, 2 
miles. Circuit, 9J miles, and about one-half wooded in 
patches. South-west reef mostly bare. A lagoon, but without 
entrance except for canoes at high tide, on leeward side. 
Island 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. 

Fakaafo or Bowditch's. — 9° 20' S., 171° 5' W. 6| 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 hundred 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 elevated three or 
four feet, indicating an elevation of the island. Lagoon 
shallow, with some growing coral, but none near the shore. 
Some corals growing on the platform, near its margin, mostly 
small Madrepores, Astraeas, Nullipores. Fragments of pumice 
were found among the natives, which had floated to the island 

M 2 



1 64 CORALS AND CORAL ISLANDS. 

Ahii, 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 colour. 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 Nullipore 
incrustations, which give it a variety of delicate shades of 
colour, mostly reddish, of peach-blossom red, rose, scarlet. 
For thirty to fifty feet from the margin, very cavernous, and 
containing many Tridacnge, lying half imbedded, with the 
variously tinted mantle expanded when the surface is covered 
with water. Rock of the platform either a compact white 
limestone or a solid conglomerate ; dead over its surface, ex- 
cepting a few Madrepore tufts or Astrseas 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 commonly 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 decom- 
position intermingled. On the bottom, exterior to the shore 
platform, observed the same corals growing as occurred in frag- 
ments upon the island ; but the larger part of the bottom was 
without coral, or consisted only of sand. 

Rai^aka, Paumotu Archipelago. — 16° 10' S., 145° W. 14 
miles by 8, trending east and west. Shape somewhat tri- 
angular. North side nearly continuously wooded ; south angle 
and south-west 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 



STRUCTURE OF CORAL ISLANDS. 165 

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 projecting 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. Growing coral in 
the entrance to the lagoon, within two feet of the surface, 
mostly a species of Millepora (J/, squari'osa). Interior 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 Vincennes 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 prevail), 
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 m^asses of coral on the shore platform, 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 three feet under water at low tide. As elsewhere, this 
platform is nothing but a compact coral conglomerate or lime- 
stone, 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. 

Maiihii, Wilson's or Waterlandt, Paumotu Archipelago, 14° 



1 66 CORALS AND CORAL ISLANDS. 

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. 146. 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 conglomerate. Beach, regular as usual, six to ten feet 
high, consisting of coral sand, and fragments of worn shells, 
with occasional exuvioe of crabs, remains of Echini, fish, &c. The 
entrance to the lagoon, is deep and narrow, with vertical sides. 

Aratica 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 north-west 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 with blocks of coral, one to thirty cubic feet and 
larger, 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- 
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 v/hole. 



STRUCTURE OF CORAL ISLANDS. 167 

Florida Reefs and Keys. — This region of coral formations 
has been described by Prof M. Tuomey [A?nej'tcan Journal 
of Science, vol. xi., 185 1), Professor Agassiz (Coast Survey 
Reports for 185 1 and 1866, and Bull. Mus. Comp. ZooL, i., 363), 
and Captain E. B. Hunt {A?n. J. Scl.^ 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 illustra- 
ting this Florida reef-region is from the Report on Deep-Sea 
Corals of L. F. de Pourtales, published in the Illustrated Cata- 
logue of the Museum of Comparative Zoology in 187 1. First, 
from Professor Tuomey : — 

" Key West is about six miles in length and two m.iles 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 suHiciently 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, consists in the distinctly oolitic 
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, re- 
semble those on the shores of the island. Except in degree of 
hardness, the rock does not differ from the calcareous sands 
thrown up by the waves on the shore in the vicinity; and 
the conditions presented by the loose moving sands are not 
favourable to the habits of molluscous animals, nor are fossil 
shells very abundant in the limestone of the island. Oblique 



i68 CORALS AND CORAL ISLANDS. 

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, (S:c. 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 be- 
comes a source of annoyance to the collectors of Algae. 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 
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 
proceeding 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 



STRUCTURE OF CORAL ISLANDS. 169 

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 entangled 
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, and present not the 
slightest evidence of disturbance, beyond the upward move- 
ment 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 away. 

"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 mangrove-tree is seen striding 
about in the soft mud. This 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 Algae, 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 navigation amongst 
these Keys dangerous. On lower Matacumba 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." 



I70 CORALS AND CORAL ISLANDS. 

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 south-westerly direction, gradually receding 
from the mainland until, opposite Cape Sable, they have so 
far retreated as to be separated from it by a shallow sheet of 
water forty miles wide. Further to the west they project in a 
more westerly course, with occasional interruptions, as far as 
the Tortugas [in longitude Z^^ 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, they all agree in one respect — 
that their steepest shore is turned toward the Gulf Stream, 
while their more gradual slope inclines toward the mud flats 
which they incircle. 

" 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 mainland, 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 mainland, or, in case of 
circular reefs inclosing basins (atolls), than that which borders 
the lagoon. 



STRUCTURE OF CORAL ISLANDS. 171 

" The reef proper extends parallel to the main range of 
Keys, for a few miles south or south-west of it, following the 
same curve and never receding many miles from it. The 
distance between the reef and the main range of Keys varies 
usually from six to two or three miles, the widest separation 
being south of Key West, and east of the Ragged Keys, where 
the space is about seven miles. Between this reef, upon which 
a i^w 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. 
" Further 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 mainland. Protected 
by the outer reef, this channel affords 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 
baiTier. . . . 

" The reef proper, as we have remarked above, runs almost 
parellel to the main range of Keys from Cape Florida to the 
western extremity of the Marquesas, where it is lost in the 
deep. It follows, in its whole extent, the same curve as the 



172 CORALS AXD CORAL LSLAXDS. 

Keys incircling, 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 surface 
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 Car}-sfort, Alligator Reef, Tennessee Reef, 
and a few other shoils 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 
south-west to north-east, but more frequently in the opposite 
direction, the prevailing winds blowing from the north-east. 
Such are Sombrero Key, Love Key, the Sambos and Sand 
Key. Here and there are isolated coral boulders, which 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 wnthin 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 
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 labours 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 



STRUCTURE OF CORAL ISLANDS. 173 

Florida reefs and the opposite shores or reefs along the 
Bahamas and Cuba, called the Straits of Florida. A few para- 
graphs on these straits by Mr. de Pourtales are cited from 
his memoir referred to on page 167. 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 Sak 
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 five 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 
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 colour of the water after passing 
the reef seems to indicate a very abrupt slope, there is in no 
part of it anything to compare with the sudden deepening on 
the edge of the coral reefs of the Pacific Ocean, or even of 
the Baham.as or the coast of Cuba. The distance from the 
reef to the loo-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 



174 CORALS AND CORAL ISLANDS. 

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- 
tales Plateau is a true coral-rag — in other words, ordinary coral 
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 south-west in a double 
series, 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 loo-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 



STRUCTURE OF CORAL ISLANDS. 175 

the eastern and western ranges of land in this Great Bank is 
really analogous to that of the opposite sides of the great Mal- 
dive 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. 

The following are notes from an abstract of a paper pre- 
sented to the Geological Society in 1852, by Major-General 
R. J. Nelson, R.E., and published in the Quarterly Journal of 
the Society for 1853, p. 200 : — 

" The loftiest land in the Bahamas, according to the maps of 
the Hydrographical 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-water level, and have a rough and cavernous surface. 
Water, more or less brackish, rises and falls everywhere 
throughout the lower parts of these flats, though not contem- 
poraneously 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 arched over with sub-stalagmitic substance. 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, &c., grow luxuriantly. 
Besides these ' rock-marshes ' there are also ordinary marshes 
and mangrove swamps, of no great extent or depth, which 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 

* At Nassau, Bahamas, the tide rises from 4 to 3 feet (spring to neap) ; 
but at Bermuda it rises from 6 to 42. 



176 CORALS AND CORAL LSLANDS. 

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 
number, 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 fre- 
quently 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 appears 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 the Bahama Islands 
as in the Bermudas ; but so few extensive excavations have 

been made, that this cannot be positively aflEirmed 

One of the most striking objects in the topography of the 
Bahamas is the very deep submarine valley forming the gulf 
known as ' the Tongue of the Ocean,' which runs into the 
Great Bahama Bank from its northern end. The colour of the 
water around the islands is usually that of the aqita-viariiie 
variety of beryl ; but the water of the Tongue of the Ocean 
has the deep blue colour of oceanic depths. 

" The author describes a coral-reef as consisting of masses of 
numerous species of Madrcpora, Astrcea, Dcedalea, Oculina, 
bases and axes of Gorgonia, Millepora, Nullipora^ CoralUnce, 
&c. &c., growing confusedly together without any other apparent 
order than that of accidental succession and accretion, both 
laterally and vertically. These are at times aided or even super- 
seded by Serpulce^ &c., as seen in the serpuline reefs. . . . 

" Captain Nelson points out a few of the localities that exhibit 
most clearly the character, source, and mode of aggregation of 
the materials of the ordinary Bahama rock, such as is formed 
above the sea-level ; at the same time referring to the illustra- 
tive specimens in the Bahama collection. For instance : the 
south side of Silver Cay and the beach extending westward 
from Nassau aftbrd rolled blocks, pebbles, and sand derived 
from the massive corals, mixed with remains of turtles, fish, 



THE BAHAMA ISLANDS. 



177 



crustaceans, echinoderms, and moUusks. On the beach be- 
tween Clifton Point and West Bay (specimen No. i) the shells 
of Strombiis gigas more especially accompany the rolled corals. 
At East Point (specimens Nos. 2 and 3) the sand is derived 
from corallines and nuUipores ; the finer sand being often in 
approximately spherical grains, though not so perfectly as at 
the White Cay (specimen No. 4) and between Exuma and 
Long Cay. The beach near Charlotteville Point (specimen 
No. 5) consists principally of Luciiia Pemisylvaiiica in various 
stages of comminution. At Six Hills (Caicos Group) the mass 
of Conch shells {Strombiis gigas) is so great and sufficiently 
cemented together as to form not only rock, but an island 
several hundred feet in length. Along the N.W. beach at 
Gun Cay (specimen 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 deposited in 
irregularly laminated beds, which, being consolidated in various 
degrees, are converted into rock of different quahties. . . . 
The ordinary Bahama rock everywhere consists of the above- 
mentioned calcareous sandstone. It is somewhat similar to Port- 
land 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- 
grey colour 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 95 to 145 pounds per cubic 
foot. Its inferior value as a building material arises from the 
numerous sand-flaws (specimen No. 7;, and consequent 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 homogeneous, and may be raised in good blocks for build- 
ing purposes. The looser and softer kinds of rock are found 
usually on the hill tops. A variety offering a singular counter- 
feit of true oolitic structure is found at or near White Cay, 



178 CORALS AND CORAL LS LANDS. 

Exuma, 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 bottoms in every principal group, though 
nowhere so extensively as along the western coast of Andros 
Island, where it may almost be termed a young chalk forma- 
tion. . 

" The ' red earth ' previously mentioned as forming, generally 
speaking, the scanty soil of the Bahamas, is at times interstra- 
tified with the rock, and sometim.es it is incorporated with it. 
It is identical with the ' red earth ' of the Bermudas (specimen 
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 con- 
tradicted by the presence of the characteristic Jle/ix 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 a, b). 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 part 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 Royal 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 inhabiting once-existing caverns ; at the same 
time, he considers it probable that birds, their droppings supply- 
ing a sort of guano^ have also assisted in the formation of 
this deposit. 

" The occurrence of pumice floated ashore at Wading Island, 
and elsewhere in the Bahamas, is briefly noticed." 



SA L T KE Y BA NK. 1 79 

Prof. Agassiz gives the following account of a part of these 
reefs in the first volume of the *' Bulletin of the Museum of 
Comparative Zoology:" — 

"The Bahamas and the reefs to the north-east of Cuba 
exhibit very abrupt slopes, and a great depth is reached close 
to the shores of the Banks, so that the Bahamas resemble the 
coral 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 Strouibiis gigas is the most common 
besides that, Astraie {Orbicella) aimularis, SiderasircBa siderea 
and McBandriiia mammosa prevail. The shells of Strombus are 
so common that they give great solidity and hardness to the rock. 

N 2 



i8o CORALS AND CORAL LSLANDS. 

The stratification is somewhat irregular, 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 formation, namely, that while the 
foundation rock is slightly inclined, and never rises above the 
level of high water, the accumulation 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 high waves, rise to about twelve and 
fifteen feet. This is evidently the foundation for the accumu- 
lation 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 tlieir 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 
thirty degrees, and steeper to the seaward than on the land- 
ward side. 

" In the interior of Salt Key there is a pool of intensely salt 
water, the tint of which is pinkish or flesh-coloured, owing to 
the accumulation of a small alga. When agitated by the wind, 
this pool is edged all around by foam of the purest white, 
arising from the frothing of the viscous water. Along the edge 
the accumulation of this microscopic plant forms large cakes, 
not unlike decaying meat, and of a very offensive odour. The 
foundation rock of this Key is exactly like what Gressly de- 
scribed as the 'fades corallien ' of the Jurassic 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 moutoimees' at intervals 
interrupted by breaks, so that the whole looks like a dismanded 



SAL T KE Y BA NK. 1 8 1 

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 deposits ; the strati- 
fication is more distinctly visible where 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 Doubled-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 creeping 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 under- 
going 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 Key. 
" 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 
cavities of ancient pot-holes, which have been gradually filled 
with materials identical with those of the older deposits. The 
pot-holes themselves show nothing very peculiar ; there are 
many such upon these Keys — some large ones many yards in 
diameter, and others quite small — evidently formed by the 
wearing action 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 



1 82 CORALS AND CORAL LSL.ANDS. 

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 coat- 
ings of solid, compact, and hard limestone, 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 coat- 
ings are a sub-aerial formation, increasing by 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 limestone, 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 
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, alter- 
nating with the oolitic beds, which have no doubt been formed 
in the same manner as the coating of the pot-holes.'' 

The oolitic limestones, referred to by Prof. Agassiz as the 
description states, are not the true coral reef-rock, the basement 
rock of the reefs, but the superficial beach sand-rock and drift 
sand-rock of the preceding pages, which are very generally 
oolitic in structure. 

The Bei-muda or So7?iers' Islands. — The Bermudas are the 
parts of a single atoll, as first announced by Major-General (then 



BERMUDA ISLANDS. 183 

Lieut.) Nelson, R.E., in his paper in the Transactions 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 //zvV/^ coral reef ; the principal species of 
corals are mentioned on page %'^. 






b-^l 







THE BERMUDA ISLANDS. 



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 north-east-by-east, and is about 
twenty-five miles in length, while the transverse diameter is 
about fifteen miles. 

Although an elevated atoll, die emerged land — about fifteen 
miles in length — is confined to the side facing south-east, 
excepting a single isolated rock on the north (between c and d 



iS4 CORALS AND CORAL LS LANDS. 

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 position of Hamilton, the seat of Government, and G of 
St. George's, the other principal town. A (Castle Harbour), B 
(Harrington Sound), and C (Great Sound), are three encircled 
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. 

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 Mseandrina (Diploria) 
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 
l)rought 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), b (Blue cut, 
shallow), c (N. W. Channel), d (N. £. Channel), e (Mills' 



BERMUDA ISLANDS. 185 

Breaker Channel), / (the Channels affording the nearest 
routes to Murray Anchorage and St. George's Harbour), g 
(Channel by St. David's Head, shallow), and // (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 discoloured 
water above them. The bottom, over large areas, is a 
calcareous clay or mud ; that of Murray Anchorage, a fine 
chalky clay. 

The wind for three-fourths of the year is from the south-east 
or south-west, 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 nan-ow, not over a fourth of a mile wide, and 
the waters abruptly deep ; and consequently we may conclude 
that this south-eastern side of the original iskmd was bold and 
high, while off to the no-rth the surface was relatively low 
and flat. 

Twenty miles south-west-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 3,3 to 47 fathoms. Dredging on these banks 
might make some interesting disclosures. 

The following observations bearing on the question as to the 
former extent of the Bermudas group are from a paper by 
Mr. S. Matthew Jones, in Nature^ August 1872 : — 

" As my late visit to the Bermudas has placed me in 
possession of facts relating to their original aspect of a some- 
what conclusive nature, I deem it advisable to communicate 
such in a brief form, instead of awaiting the time requisite for 
the preparation of a more elaborate paper on the subject. On 
previous occasions I have always regretted my inability, from 
lack of time, to look more closely into their geological char- 



i86 CORALS AND CORAL LSLANDS. 

acter in the hope of discovering some satisfactory clue to their 
primitive condition. I was aware 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 consistence 
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 formed 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 compact sand- 
stone. 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 afforded no evidence of a contrary nature— viz. 
the submergence 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 
investigations, 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 Serpulae, 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 Harbour, 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 



BERMUDA ISLANDS. 187 

Kindness of his Excellency Major-General Lefroy, C.B., F.R.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 harbour 
situated at the western extremity of the islands, for the purpose 
of forming a bed of sufficient depth for the reception of the 
' Great Bermuda 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 of forty-eight feet below the present low-water 
level,- which consequently grants an equal elevation above it 
in former times. Now, on carefully surveying the Bermuda 
chart, we find that an elevation of forty-eight feet will bring 
the whole 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 submer- 
gence to the present barrier reef? But having clearly ascer- 
tained beyond doubt that the Bermudas were once forty-eight 
feet higher than at present, will any one be bold enough to 
deny them a greater elevation ? 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 suppose that a low-lying 
group of islets did actually exist here in former times ? Again, 
in Smith's ' History of Virginia,' which gives an excellent 
account of the islands in the early part of the seventeenth 



i88 CORALS A.YD CORAL LSLANDS. 

century, it is stated, among other notes upon their natural 
history, that flocks of crows, no doubt the same species {Corvus 
Amcricaniis) 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 simplicity I should 
the more readily believe to be a true statement, would clearly 
prove the existence of land in that direction at no great dis- 
tance ; 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 Burmudas once presented 
a much more extensive aspect than they do at present ; and 
certain additional evidences which I hope to bring forward 
shortly in a collected form will, I conceive, tend to confirm 
my impression that the restricted ten-aqueous area lying within 
the limits of the outer barrier reef is merely 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 dep-th only to be correctly ascer- 
tained by borings, which might be successfully accomplished 
under the auspices of the Government at a trifling expense." 



CHAPTER III. 

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

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 uniformly over 
its upper surface, and as gradually enlarging upward through 
this living growth ; and such preconceived views, when ascer- 
tained to be erroneous by observation, have sometimes 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 wdiich follow. 

Coral plantation and coral field are more appropriate appel- 
lations 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 shrubbery, 
in other parts bearing only occasional tufts of vegetation in 
barren plains of sand, here a clump of saplings, and there a 
carpet of variously-coloured flowers in these barren fields — 
such is the coral plantation. Numerous kinds of zoophytes 



190 CORALS AND CORAL LSLANDS. 

grow scattered over the surface, like vegetation 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 fragments 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 their habits require, just as vegetation ex- 
tends 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 the 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 flourishing 
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 history of the coral mead. Accumu- 
lations of fragments and sand from the coral zoophytes grow- 
ing over the reef-grounds, and of shells and other refics of 
organic life, are constantly making ; and thus a bed of coral 
debris is formed and compacted. There is this difference, 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 coaal debris and 
shells fill up the intervals between the coral patches and the 
cavities among the living tufts, and in this manner produce the 
reef deposit ; and the bed is finally consolidated while still 
beneath the water. 



FORMATION OF CORAL REEFS AND ISLAND'S. 191 

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 below 
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 
extent 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 uptorn 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 
fathoms, the water is very evidently discoloured by the action 
of the waves on the sand and mud of the bottom. M. Siau 
mentions {Comptes Re?idus t. xii. 744) that ripple-marks are 
formed on the bottom by the motion of the water, which may 
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 north-west of the St. Paul's Roads. 

In an article on the Force of Waves, by Thomas Stevenson, 
of Edinburgh, pubhshed in the Transactions of the Royal 
Society of Edinburgh (vol. xvi., 1845), it is stated as a deduc- 



192 CORALS AND CORAL LSLANDS. 

tion from two hundred and sixty-seven experiments, extending 
over twenty-three successive months, that the average force for 
Skerryvore, for five of the summer months, during the years 
1843, 1^44? was six hundred and eleven pounds per square 
foot ; and for six of the winter months of the same years 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, ^ pressure 
of six thousand and eighty-three pounds was registered by 
Mr. Stevenson's dynamometer (the name of the instrument 
used). He mentions several remarkable instances of trans- 
ported 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 m.oved. 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 run extended up to the grass-Hne 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 vi^ith a jerk, leaving it with very little water about it, when 
the next incoming wave made it recline again." 

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 
pressure of nearly three ions per sqtiarefoot. 

With such facts, any incredulity respecting the power of 
waves should be laid aside. Moreover, it may be remarked 
that the Pacific is a mucli wider ocean than the Atlantic, with 
far heavier waves in its ordinary state. 



FORMATION OF CORAL REEFS AND ISLANDS. 193 

We must, therefore, allow that some effect will be produced 
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 planta- 
tion, which will destroy and grind down everything 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 tena- 
cious of life, and ready to sprout anew on any rock where 
they may find quiet long enough to give themselves again a 
firm attachment. 

But it should be observed, that the sea would have far 
lesy 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 
breakers w^hich plunge against the shores. Yet owing to the 
many nooks and recesses deep among the corals, the rapidly 
moving waters, during the heavier swells, must produce whirl- 
ing eddies 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, 
somewhat 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 lamellae worn 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. 

o 



194 CORALS AND CORAL LS LANDS. 

In the Alcyonia family, which inckides semi-fleshy corals, 
and in the Gorgoni^e, the lime is often scattered through the 
polyps in granules \ and the process of death sets these cal- 
careous 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 Astrseas, 
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 iimd-Uke deposits about coral reefs (pp. 113, 149, 167) 
have been attributed to the causes just mentioned, but with- 
out due consideration. There is an unfailing and abundant 
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 lagoons, 
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 material 
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, acaunulates only in the more quiet waters some distance 
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. 



FORMATION OF CORAL REEFS AND ISLANDS. 195 

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 Hving zoophytes ; 
and from Mr. Allan, of Forres, he learned also that Holothu- 
rians subsisted on them. With regard to the facts here stated, 
no positive asertion can be made. Small fish swarm about the 
branching clumps, and when disturbed, seek shelter at once 
among the branches, where they are safe from pursuit. The 
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. Darwm, that frag- 
ments of coral and sand may be found in the stomachs of these 
animals, but this is not sufficient 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. 16), 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 Holothurians, though numerous, are 
quite inadequate for the supply ; and, moreover, we have, as 
explained above, an abundant source of the finest coral ma- 
terial without such aid. Motion of particle over particle will 
necessarily wear to dust, even though the particles be diamonds; 
and this incessant grinding acdon about reefs accounts satis- 
factorily 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 ele- 
ments and natural decay are producing gradual accumulations 
of material, like those of vegetation. The history of the 
growing reef has consequently its counterpart among the 
ordinary 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 already 
presented. The production of debris will necessarily continue 



196 CORALS AND CORAL ISLANDS. 

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 surface. The layer 
of dead coral rock which makes the body of the reef, has its 
border of growing corals, and is thus undergoing 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 dryland. 
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 eighteen feet with a tide of 
six or seven. 

The Ocean is thus the architect, while the coral polyps 
afford the material for the structure ; and, when all is ready, 
it sows the land with seed brought from distant shores, cove- 
ring 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 breakers, 
which are formed by the gradual growth of layer upon layer of 
incrusting NuUipores ; 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 sho7'e platform 
appears to be one of the most singular, and its origin has not 



FORMATION OF CORAL REEFS AND ISLANDS. 197 

been rightly understood. It will be remembered that it lies 
but little above low-tide level, and it is often over three hun- 
dred feet in width, with a nearly flat surface throughout. 

Though apparently so peculiar, the existence of this platform 
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 sandsto?ie 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 hundred 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 
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. 




THE OLD HAT. 



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 favour the production of a horizontal surface ; it 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 
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 



198 CORALS AND CORAL ISLANDS. 

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 
velocity, and drive violently upon whatever obstacle is presented. 
The lower 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 mechani- 
cal advantage ; moreover, they gradually swell over the shores, 
and receive, in part, the force of the upper waters. The wave, 
after breaking, sweeps up the shore till it gradually dies away. 
Degradation from this source is consequently 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 v/ould plunge obliquely 
downward against the rock, or any obstacle before it. It is 
obvious that, under such circumstances, the greatest force 
would be felt not far from the line of high tide, 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 regions where the 
tide is higher than just supposed, as six feet for example, 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. 



FORMATION OF CORAL REEFS AND ISLANDS. 199 

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 surge, 
instead of causing degradation, are accumulative in their ordin- 
ary 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 waters 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 accompanying 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 cUffs of rock, of great extent; yet below a certain 
level, the e has had Httle or no effect. This height, on the 
eastern shores of Australia, is three feet above ordinary low 
tide, and at New Zealand, above 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 propor- 
tionally less than at Australia 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 effect of the comparatively quiet 
surges of the middle Pacific, 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-action, remains to be determined more accurately by 



20O CORALS AND CORAL ISLANDS. 

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 platform, as 
the rock scarcely undergoes any degradation, except from the 
most violent seas ; such coasts are consequently often covered 
with large fragments of the basaltic rocks. But on sandstone 
shores, this gradual action keeps the platform of nearly uniform 
breadth. Moreover, any uptorn masses thrown upon it, are soon 
destroyed by the same action, and carried off; and thus the plat- 
form is kept nearly clean of debris, even to the base of the cliff. 

It is apparent that one single principle meets all the various 
cases. The rocky platform of some sea-shores, the low tide 
sand-spits 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 
through the infiltrating waters. These surges, advancing 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 ordinary 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. 
Tlie 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 



FORMATION OF CORAL REEFS AND ISLANDS. 201 

rocks from the edge of the platform, and throw them on the 
reef From the observations of Mr. Stevenson, cited on a pre- 
ceding page (p. 191), it appears that the force of the waves 
during the summer and winter months differs at Skerryvore 
more than 1,200 pounds to the square foot, — in the former it 
averaging but d^^d 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 Pacific. 
Still there must be a marked difference between the ordinary 
seas and those during stormy weather. We have, therefore, no 
difficulty in comprehending how the ordinary wave-action 
should build up and keep entire the shore platform, 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 of^er 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 h;i(les will go on together, though at different rates 
of progress. We may often find no very great difference in 
the width of the leeward and windward reefs, especially 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 weak- 
ened for the transportation of uptorn 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 133). 
All the islands of this group are well wooded to windward — 



202 CORALS AND CORAL LSLANDS. 

the side fronting east. But the north and north-east sides of 
lari-tari are only a bare reef, through a distance of twenty 
miles, although the south-east reef is a continuous line of ver- 
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 calcareous 
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 continual 
progress. Moreover, the structure built amid the waves will 
necessarily have the form and condition best fitted for with- 
standing 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-waves which overleap 
the whole land, may occasion 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 distribution 
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 {Aih.Jouj: Sci., 
II., xxxiv: 237), that the shifting sands change their place twice 
a year. " The western shore of the island trends nearly north- 
east and south-west ; the southern shore, east-by-north. At 
their junction there is a spit of sand extending out toward the 
south-west. During the summer, the ocean swell, like the wind, 
comes from the south-east, 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 accu- 



FORMATION OF CORAL REEFS AND ISLANDS. 203 

mulating during the summer on the south side, are all washed 
around the south-west point and are heaped up on the western 
side, forming a plateau along the beach two or three hundred 
feet wide, nearly covering the shore platform, and eight or ten 
feet deep. With October and November comes the winter 
swell from the north- north-east, 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 southern 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 
hundred feet. This lasts until February or March, when the 
operation is repeated," 



IT. CAUSES MODIFYING THE FORMS AND GROWTH OF 

REEFS. 

Coral reefs, although (i) dcpciident oiithe coniiguration of the 
snbuiai'ine lands for ma7iy of their features, undergo various 
modifications of form, or condition, through the influence of 
extraneous causes, such as (2) unequal exposure to the ivaves ; 
(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 afterwards, 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. 

I. BARRIER AND FRINGING REEFS. 

The existence of harbours 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 



204 CORALS AND CORAL LS LANDS. 

presented may be taken as those of an independent witness, 
as they were written out before the publication of his work. 

There are usually strong tidal currents through the reel 
channels and openings. These currents are modified in 
character by the outline of the coast, and are strongest wher- 
ever there are coves or bays to receive the advancing tides. 
The harbour of Apia, on the north side of Upolu, affords a 
striking illustration of this general principle. The coast at this 
place 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 harbour averages ten feet in depth, and at the entrance is 
fifteen feet. In this harbour there is 
a remarkable out-current along the 
»"' ^ ^ bottom, which, during gales, is so 

n strong at certain states 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 wea- 
ther 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 rigging and 
hull. The cause of such a current is obvious. The sea 
is constantly pouring water over the reefs into the harbour, 
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 harbour-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. 




HARBOUR OF APIA, UPOLU. 



FORMA TION OF CORAL REEFS AND ISLANDS. 205 

" Through the channels and among the inner reefs of the 
Austrahan 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 destroyed 
by depositions of earth or sand, and require, for most species, 
a firm basement. Or if the flow is very strong, it will scour 
out the channels and so keep them open. The existence of 
an opening through a reef may require, therefore, no other 
explanation ; and it is obvious that harbours 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 harbours 
are most likely to be found, are also the embouchures of valleys 
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 mentioned. 
These waters from the land bring down also much detri:us, 
especially during freshets, and the depositions aid those from 



206 



CORALS AND CORAL LSL.ANDS. 



marine currents in keeping the bottom dear of growing coral. 
These are the principal means by which fresh-water streams 
contribute toward determining the existence of harbours ; 
for little is due to their freshening the salt waters of the 
sea. 

The small influence of the last-mentioned cause — the one 
most commonly appealed to — will be obvious, when we 
consider the size of the streams of the Pacific islands, and the 
fact that fresh water is lighter than salt, and therefore, instead 
of sinking, flows on over its surface. The deepest rivers 
are seldom over six feet, even at their mouths ; and three or 




PART OF THE NOK'IH SHORE OF lAHITl. 



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 harbour-making about the 
islands of the Pacific. The harbours, with scarcely an excep- 
tion, would have existed without them. They tend, however, 



FORMA TIOiV OF CORAL REEFS AND ISLANDS. 207 

by the detritus which they deposit, to keep the bottom more 
free from growing patches'of coral and consequently produce 
better anchorage ground ; moreover, within the harbours 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 the 
left, and the west cape of Matavai harbour, on the right, 
here reproduced, affords illustrations of this subject. 

a. The harbour of Papieti is inclosed 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 harbour receives an unimportant streamlet, while a 
much larger stream empties itself just to the east of the east 
cape, opposite lu/iick the reef is close at hand and imbroken. 

b. Toanoa is the harbour 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, harbour-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 interrupted 
for about two miles. The harbour is formed by an extension 
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 waters find 
theii 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 



2c8 CORALS AND CORAL LSLANDS. 

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 harbour of Falifa, Upolu, 
represents another coral harbour, 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- 
jects some distance in front of it. Its surface is dead, but 
corals are growing upon its outer slope. 

/. The harbour of Rewa, in the Feejees, may be again 
alluded to. The waters received by the bay amount to at least 
500,000 cubic feet a minute. Yet there is an extensive reef 
inclosing the bay, lying but three miles from the shores, and 
with only two narrow openings for ships. 
^.^ The case is so remarkable that we can 

hardly account for the facts without 
supposing the river's mouth to have 
neared the reef by depositions of de- 
tritus since the inner parts of the reef 
were formed ; and there is some evi- 
dence that this was the case, though 
HARBOUR OF FALIFA. ^o what distancc wc cannot definitely 

state. With this admission, the facts 
may still surprise us ; yet they are explained on the principle 
that fresh water does not sink in the ocean, but is super- 
ficial, and runs on in a distinct channel ; its effect is almost 
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 harbour, with- 
out a stream of fresh water ; — so also Vakea and Direction 
Island. 

The instances brought forward are a fair example of what is 
to be found throughout coral seas ; and they establish, beyond 
dispute, that while much in harbour-making should be attri- 
buted to the transported sand or earth of marine and fresh- 




FORMATION OF CORAL REEFS AND ISLANDS. 209 

witer 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 harbours, we should remember 
another prevalent cause already remarked upon, which is 
perhaps more wide in its effects than those just considered. I 
refer to the features of the supporting land, or the character of 
soundings 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 widening of the inner channel at Papieti, forming a space 
for a harbour, may be another example of it ; for the reef here 
extends to a greater distance from the 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 harbours. 
A remarkable instance of the latter is exemplified in the 
annexed chart of Whippey harbour, Viti Levu, reduced from 
the chart of the Wilkes Expedition to the scale of half an 
inch to the mile. 

The existence of harbours 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 harbours follows directly from the 
facts above presented. They are secure against any immediate 
obstruction from reefs. Any growing patches within them 
may still grow, and the margins of the inclosing reef may 
gradually extend and contract their limits ; yet only at an 
extremely slow rate. Notwithstanding such changes, the chan 
nels will remain open, and large anchorage grounds clear, as 
long as the currents continue in action. Coral harbours are 
therefore nearly as secure from any new obstructions as those 

p 



CORALS AND CORAL ISLANDS. 



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 changes 
in the harbour ; but such effects need seldom be feared, and 
results from them would be appreciable only after long periods, 
since, even in the most favourable 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 

,\ "'-Vx no cause sufficient to prevent its 

i ; >., growth, the reef will continue to 

• •■ '\ rise slowly toward the surface. 

\ Again, when the channels are 

\\ \ more than twenty fathoms in depth, 

,\ ij they have an additional security 

'• '■ beyond that from currents, in the 

\\ \\ fact that corals will not grow at 

// ;•; such a depth. The only possible 

i \ li 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 belov/. 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 har- 
bours, 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 plan.tation. 

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- 




WHIPPEY HARBOUR, VITI LKVU 



FORMATION OF CORAL RFEFS AND ISLANDS. 211 

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. Harbours 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 streams 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 further on. 

II. ATOLL REEFS. 

The remarks in 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 
supply, which is greatly increased in times of storms ; and this 
action 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 
strongest 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 lee- 
ward 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 

p 2 



212 CORALS AND CORAL ISLANDS. 

coves of land to give force to the waters of currents, and to 
direct their course, and the absence also of fresh-water streams, 
are the only modifying causes not present. It is readily under- 
stood, therefore, why lagoon entrances are more likely to become 
filled up by growing coral, than the passages through barrier 
reefs. 

HI. RATE OF GROWTH OF REEFS. 

The formation of a reef has been shown to be a very 
different 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. 

/;. The character of the coral plantation under consideration 
should be carefully studied ; for it is of the greatest conse- 
quence to know whether the clusters of zoophytes are scattered 
tufts over a barren plain, or whether in crowded profusion. 
Compare the debris of vegetation on the semi-deserts of 
California with that of regions buried in foliage ; equally 
various 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 given 
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 neighbouring 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 



RATE OF GROWTH OF CORAL REEFS. 



213 



patches, so that one will enlarge at the expense of others. Or 
currents may carry the detritus into the channels or deeper 
waters around a coral patch, and leave little to aid the planta- 
tion 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 v/hich may afl"ect the latter. 

No results with reference to this question of the rate of 
])rogress 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, mentioned 
on page 99, 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 M. cervicortiis 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 
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 



214 CORALS AND CORAL ISLANDS. 

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 Mosandrina clivosa, stated on page 
98, 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. 75) — 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 j'<?(2/'/)' 
increase would be about i-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 i-iooth of an 
nch. But supposing that shells add one-fourth as much as 
the corals to the reef material, the rate of increase would be- 
come about i-8oth of an inch per year. 

The specimen of Oculifia diffusa, referred to on page 98, 
weighs 44 ounces, which is five-sixths more than that of the 
Mgeandrina, while the average diameter of the clump is the 
same. The average annual increase would consequently cover 
a circular area of seven inches diameter i-i8th of an inch 
deep. And making the same allowances as above, the rate 
for the year for the whole reef-grounds would be i-44th of an 
inch. The specimen of Maeandrina mentioned by Major 



RATE OF GROWTH OF CORAL REEFS. 215 

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 Mceandrina clivosa and Ocuhfia 
diffusa have this great source of uncertainty, that the growth 
of the 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 favourably 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 uncertainues, it is evident that a reef increases 
its height or extent with extreme slowness. If the rate of 
upward progress is one-sixteenth of an inch a year, it would 
take for the addition of a single foot to its height, one hundred 
and ninety years, and iox five feet a tJiousaiid years. 

It is here to be considered, that the thickness of a growing 
reef could not exceed twenty fathoms (except by the 'iQw fee 
added through beach and wind-drift accumulations), even it 
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 increase 
of reefs, a slab of rock was planted, by the order of Captain 
Wilkes, on Point A^enus, Tahiti, and by soundings, the depth 



2i6 CORALS AND CORAL LS LANDS. 

of Dolphin shoal, below the level of this slab, was carefully 
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 towards 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 growing 
upon it be identified, and the influence of the currents investi- 
gated 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 afiford some data for estimat- 
ing 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 

^ Since the above was written, a memoir, by MM. Le Clere and de 
Benaze, has appeared in Paris (1872), on their attempts to make use of the 
stone planted by Captain Wilkes in determining 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 of a head of coral or 
from a solid bank on which the corals were growing, and further, that the 
use of an "excellent spirit level,'' from a stone of so little length is not 
sufficiently exact for correct results ; and hence, were not able to draw any 
satisfactory conclusion from their results. Before leaving the region, they 
made the following arrangements with reference to future measurements. 
They planted two blocks of coral, cementing them below and nearly burying 
them in the soil, placing them 0'2I 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 40 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 
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' E. A horizontal line passing from the 
mark on the new stone is 7 "460'" above the madreporic heads. This obser- 
vation they leave for comparison with future measurements. They farther 
made observ tions that satisfied them that Tahiti was not at present under- 
going any general elevation. Two maps accompany the pamphlet ; one is 
copied from Wilkes; the other (see opposite page) is from a chart by MM. Le 
Clerc and Minier, lieutenants of the vessel, and contains hnes showing the 
position of the points refeired to above. 



RA TE OF GRO WTH OF CORAL REEFS. 



217 



occur in the dead rock — generally where there are no growing 
corals, except rarely some small tufts. If they indicate any- 



Scale of 5oo*meters 




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 



21 8 CORALS AND CORAL LS LANDS. 

being determined, as has been shown, by wave action (page 
197). They resemble, in fact, other saxicavous mollusks, 
several 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 inclose 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 made by some the sub- 
ject of special admiration ; for the " helpless animalcules " 
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 lea, " where," 
as Flinders observes, " their infant colonies might be safely 
sent forth." 



ORIGIN OF THE BARRIER REEF. 



219 



It has been a more popular theory that the coral structures 
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 since a more satisfactory expla- 
nation has been offered by Mr, Darwin, numerous objections 
to this hypothesis have become apparent, such as the follow- 
ing : — 

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 crater would 
have been destroyed, wdth rare exceptions, during the subsi- 
dence; and in the latter there is reason to beUeve that a distinct 
crater would seldom, if ever, be formed- 

b. 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 nearl\^ 
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. Mount 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 differ 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 



220 CORALS AND CORAL LSLANDS. 

miles in diameter, and that twenty and thirty miles should be 
a common size. Facts give no support to such an assump- 
tion. 

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, so far as is known, in the Marquesas, 
Gambier, or Society Group, the three which lie nearest to the 
Paumotus. Even this supposition fails, therefore, of giving 
plausibility to the crater hypothesis. 

Thus at variance with facts, the theory has lost favour, and it 
is no longer sustained even by those who were once its strongest 
advocates. 

The question still recurs with regard to the basement 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 con- 
tinents widi elevations so uniform in height ; and submerged 
banks of this kind are of extremely 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 flourish 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 beheve, at the 
true theory of barrier reefs and coral islands. It is satisfactory, 
because it is a simple generalization of facts. The explora- 



ORIGIN OF THE BARRIER REEF. 221 

tions 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 Reef, 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 island 
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 difference in position, but none in 
mode of formation. In the last of the islands enumerated, the 
barrier reef includes a large sea, and the island it incloses is 
but a rocky peak within this sea. 

Can we account for this diversity in the position of barrier 
reefs, and in their extent as compared with the inclosed land ? 
There is evidently one way, in accordance with Mr. Darwin's 
theory, in which these features might have been* produced. 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 explained, 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 Exploring Isles ? On 
such a supposition, reefs of large size encircling a mere point 
of rock might be explained even to every feature. The sub- 
sidence 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 level 
over vast areas of the earth's surface have taken place is fully 



222 CORALS AND CORAL ISLANDS. 

proved, and accounts of some of them which are now in pro- 
gress, as ihat of Sweden and that of Greenland, are to be 
found in any geological treatise. 

But it admits of direct demonstration that such a subsidence 
has actually taken place. It has been stated that the depth ot 
the reef at different distances from the shore it encircles may 
generally be estimated from the slope of the shore. On this 
principle it has been shown on a former page (p. 125) that the 
thickness of the distant barrier reef cannot be less in some 
instances than a thousand feet ; and in many cases it is prob- 
ably much greater. Now as reef corals do not grow below 
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 remove 
any doubt 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 progressing 
subsidence, like that which is now going on in Greenland. 

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 
water line, the island, like Goro, has a simple fringing reef,//.- 



ORIGIN OF THE BARRIER REEF. 223 

— it is a narrow platform of rock at the surface, dropping off 
at its edge to shallow depths, and then some distance out, 
declining more abruptly. Let the same island become sub- 
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 b' f b' /'. There is here a fringing 
reef and also a barrier reef, with a narrow channel between, 
such as we have described as existmg on the shores of Tahiti 
(see p. 206) ; b' is a section of the barrier, c of the channel, 
and /' of the fringing reef. Suppose a farther submergence, 
till III is the water line : then the channel {c" c") within the 
barrier becomes quite broad, as in the island of Nairai or 
Angau ; on one side (/'") the fringing reef remains, but on tlie 
other it has disappeared, owing perhaps, to some change of 



SECTION ILLUSTRATING THE ORIGIN OF THE BARRIER REEFS. 

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 dis- 
appeared. 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 
exemplified, for the view is a good transverse section of either 
of them. //" b"' are sections of the distant inclosing barrier, 
and c" c"\ 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. There are two peaks in the lagoon, precisely as above; 



224 CORALS AND CORAL LSLANDS. 

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 bb, U b\ of the map. It is unnecessary 
to add other illustrations. They may be made out from any of 
the eastern groups of the Feejees, the Gambler Group of the 
Paumotus, or Hogoleu in the Carolines. Wallis's Island is 
another example of islets of rock in a large lagoon inclosed 
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 




MAP, AND IDEAL SECTION, OF AIVA ISLAND. 

result, instead of a narrow belt ; and this has been urged against 
the theory. But it is a sufficient reply to such an argument to 
state the fact that the subsidence admits of no doubt, and that 
the islands referred to as exemplifications of it, present this 
very peculiarity. It should be received therefore, as a conse- 
quence 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 subsidence 
during the growth of the reefs. Broad channels, and 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. 



ORIGIN OF THE BARRIER REEF. 225 

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 currents within, while 
the inner reefs contribute a large proportion 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 accumulations 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 increases one foot in height in a century, the 
inner reef, according to this supposition, would increase but 
half a foot ; and any rate of subsidence between the two men- 
tioned would sink the inner reefs more rapidly than they could 
grow, and cause them to disappear. There is therefore not 
only no objection \o the theory from the existence of wide 
channels and open seas ; 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, destroying growing 

corals over its interior parts. 

Q 

V 



226 CORALS AND CORAL ISLANDS. 

From these considerations it is evident that a barrier reef 
indicates approximately the former limits of the land inclosed. 
The Exploring Isles (Feejee chart), instead of an area of six 
square miles, the whole extent of the existing land, once 
covered three hundred square miles ; and the outline of the 
former land is indicated by the course of the inclosing reef. 
A still greater extent may be justly inferred. For a barrier, as 
subsidence goes on, gradually contracts its area, owing 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 incUnation. 

In the same manner it follows that the island Nanuku, in- 
stead of one square mile, extended once over two hu?idred sqyi?LYt 
miles, or had two hundred times the present area of high land. 
Bacon's Isles once formed a large triangular island of equal ex- 
tent, though now but two points of rock remain above the water. 

The two large islands in the western part of the group, 
Vanua Levu and Viti Levu, have distant barriers on the western 
side. Off the north point of the former island, the reef begins 
to diverge from the coast, and stretches off from the shores till 
it is twenty and twenty-five miles distant ; then, 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, tracing 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 harbour, page 210, 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. 



ORIGIN OF THE A TOLL. 



227 



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 facis 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 




GAMBIEK ISLANDS. 



the distant barrier, if continued a step farther, would produce 
the lagoon island. Nanuku 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 
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 
Gambier Group, near the Paumotus, appears to have afforded 

Q 2 



228 CORALS AND CORAL ISLANDS. 

the philosophical mind of Mr. Darwin the first hint with regard 
to the origin of the atoll ; the contrast, and, at the same time, 
the resemblance, were striking ; the conclusion was natural 
and most happy. Captain Beechey, in his Voyage in the 
Pacific, implies this resemblance, when he says of the Gambier 
Group, which he surveyed, *' It consists of five large islands 
and several small ones, all situated in a lagooji fo?'med by a reef 
of coral'' 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 Gambier Group. The very features 
of the coast of the included islands, — the deep indentations, — 
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, b"'\ b"", then incloses a broad area of 
waters, or a lagoon, with a few island patches of reef over the 
peaks of the mountains. A cpntinuation of the subsidence 
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 following figure, VL, 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 increasing 
in height, would go on to widen, and the accumulations pro- 
duced by the sea would commence the formation of dry land, 
as exhibited in figure 2. Verdure may soon after appear, and 
the coral island will finally be completed. It is not impossible 
that dry land might form in certain favourable spots on the reef 



ORIGIN OF THE A TOLL 



229 



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 they are as various and irregular as 
the outlines of barrier reefs. Compare Angau of the Feejees, 
with Tari-tari of the Gilbert Group (p. 133) ; Nairai or Moala 
with Tarawa ; Nanuku with Maiana or Apam.ama. The resem- 
blance is close. In the same manner we might find the many 
forms of lagoon reefs represented among barrier reefs. 



SECTION ILLUSTRATING THE ORIGIN OF ATOLLS. 

AVe 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 



230 CORALS AND CORAL ISLANDS. 

tliese 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 extend a long 
distance to sea, with slight inclination compared with the slopes 
or declivities bounding the ridge on either side. 

Goral islands or reefs often lie in chains like the peaks of 
a single mountain range : — for example, the sickle-shaped line 
of islets north of Nanuku. Tari-tari and Makin (Gilbert 
Group, see map, page 133) 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 




MENCHICOFF ATOLL {^^TU »F AN INCH TO A MILE). 

by their extremities, and further subsidence might reduce it to 
three islands, 

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 inclosing 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 



ORIGIN OF THE ATOLL. 231 

broken as to admit the influence of waves and winds. Some 
of the large atolls of the Maldives are properly atoll archi- 
pelagos. 

The sizes of atolls offer no objection to these views, as they 
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 
subordinate craters. No hypothesis of such extravagance is 
necessary. The facts all fall in with known principles, and are 
illustrated by known and established truths, without hypotheses 
of any kind. 

Reefs surrounded by shallow seas, gradually deepening out- 
ward, require no different principle for their explanation from 
reefs with abrupt depths around. The explanation of the 
peculiarities of the Bermudas, on page 188, can now be fully 
understood. If the original island had a high, bold mountain 
ridge along its south-eastern 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 ot 
250 feet, indicated by the height of the hills, the shallow region 
on the north and west of the high land (the existing reef region), 
must have been mostly bare of living 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. 183), 
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 size 
of the atoll, owing to the fact already noted, that the detritus 



232 CORALS AND CORAL LSLANDS. 

is mostly thrown inward by the sea. The lagoon will con- 
sequently 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, with only traces of a 
former 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 doubt been generally 
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 
atoll-formed reefs of the Chagos Group, in the Indian Ocean 
(p. 156), as stated by Darwin; a third had only "two or 
three very small pieces of living reef rising to the surface," 
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 orce 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 
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 inclosed 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 



THE COMPLETED ATOLL. 233 

island cemetery, where each atoll marks the site of a buried 
island. The whole Pacific is scattered over with these simple 
memorials, 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 
grandeur 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-born, 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 Httle 
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 
seen gliding over the waters. 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 
clumsy outrigger to keep them right-side up, as well as their 
thatched huts, are as little in harmony as themselves with 
nature's grace and loveliness. 

Where the islets of a coral reef are heaped up blocks of 
coral rock, blackened with lichens, and covered with barely 
enough of trailing plants and shrubs to make the surface green 



234 CORALS AND CORAL ISLANDS. 

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 enjoyment 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 effected 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-going wave and ride upon it over the line of breakers 
to a stopping-place somewhere on the reef or shore-platform. 

Less easy is the return through the breakers, especially it 
the sea has risen during the ramble ashore. The boat, in 
order 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 
being dashed against the reefs to its destruction, or thrown 
broadside to the sea and swamped under a cataract of waters. 
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 
distance outside of the breakers, a kedge or anchor, for aid 
both in landing on and leaving the reef. But the bottom of a 
coral 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 . 

Bowditch or Fakaafo island is the easternmost of three small 
atolls, situated to the north of the Samoan or Navigator Group, 
near the parallels of 8^°, 9°, and 9^° S., and between the meri- 
dians of 171° and 172^° VV., and has already been described 



THE COMPLETED ATOLL. 235 

(p. 135). The grove of cocoanut-trees contains the sacred 
or public house ot the island — a well-made structure measuring 
fifty feet by thirty-five in length 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- 
crown tree. 




F/.KAAFO,. OR BOWDITGH LSI ANOv 

This island and the two others near it were among the few, 
perhaps the last, examples that remained until 1840, ot 
Pacific lands never before visited, by the white man. The 
people therefore were in that 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. 



236 CORALS AND CORAL LSLANDS. 

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 
navigation or discovery without harbours. 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 
repeated the rubbing of noses and the howhng ; and the 
moment 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 a while quite familiar, and took advantage 
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 
required to recover it — a most undignified run on the part of 
the celestial. 

While the men wore the maro, the equivalent of tight- 
fitting breeches six inches or less in length, the women were 
attired in a simple bloomer costume, consisting solely of a 
petticoat or apron, twelve to eighteen inches long, made of a 
large number of slit cocoanut leaves, and kept well oiled. 
Besides this they had on, as ornaments, necklaces of shell or 
bone. The girls and boys were dressed au 7iatiirel^ after the 



THE COMPLETED ATOLL. 237 

Style in the garden of Eden. These primitive fashions, 
however, are 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 
Bowditch Island until he discovered it ; and from him comes 
the name it bears, given in honour of the celebrated author of 
" Bowditch's Navigator " as well as of the translation of 
Laplace's " Mecanique Celeste. " 

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. The public house of 
the island is even larger than that on Bowditch Island, 
measuring one hundred and twenty feet in length, forty-five feet 
in width, and forty in height to the ridge-pole. This island, 
unhke 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 circumstances 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 w^as actually too large to have reached the deck except 
by the use of a tackle. It was evident that infanticide — a 
necessity according to 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 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 productive 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 



238 CORALS AND CORAL ISLANDS. 

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 
another, 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 des- 
perate 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 un- 
civihzed people ; that the men do the hard out-door work, while 
the women clear and weed the ground, and attend to the 
domestic 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 always 
hold in practice. He adds : " The word nianda signifies 
among the Gilbert Islanders a man thoroughly accomplished 
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 excitements 
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 luxuriance 
that characterizes more favoured tropical lands, the number of 
species of land plants is small. When Gray's " Botany of the 
Paumotus " shall appear, it will contain descriptions of only 
twenty-eight or thirty species. The most common kinds are 
the following : — 

Portulacca oleracea Z. (lutea Lepidium piscidium Forst. 

of Solander). Pemphis acidula Forst. 

Triumfetta procumbens Forst. Pandanus odoratissimus L. J. 

Tournefortia argentea L. Pisonia grandis Parkinson. 

Scgevola Konigii Vahl. Morinda citrifolia L. 

Ipomsea longiflora t'v. Br. Guettarda speciosaZ. 



THE COMPLETED ATOLL. 239 

Cassytha filiformis Z. Heliotropium prostratum R. Br. 

Gouldia Romanzoffiensis A. Cr. Nesogenes euphrasioides, A. DC. 

Euphorbia Chamissonis Boiss. Asplenium Nidus Z. 

Hoerhavia diffusa Z. A Polypodium, and a species of 
Boerhavia hirsuta IVild. Grass. 

Achyranthes canescens R. Br- 

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 ornamental 
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 petticoats of the 
women, above alluded to. The fruit, besides its delicately- 
flavoured hollow kernel, affords, by the grating of this kernel, 
a milky juice, that is richer than cream for purposes of native 
cookery, and which we explorers often used with satisfaction in 
coffee, cows being unknown in those regions ; also, from each 
nut, a pint of the thinner " cocoanut milk," a more agreeable 
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 visitor whom they would 
honour 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 corresponding products of the ripe fruit. 
The husk is excellent for cordage, twine, thread, fishing-lines ; 
and the smaller cord serves in place of nails for securing together 
the beams of their domestic and public buildings, and also for 
ornamenting the structure 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, 



240 CORALS AND CORAL LSLANDS. 

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 plant- 
ing 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 
evidence that any island never inhabited has been found sup- 
plied 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 Cocos ?iucifera of the botanists — is not included in the 
list of native coral island species on page 238. 

Another tree, peculiarly fitted for the region, is the Pan- 
danus or Screw-pine — well named as far as the syllable screiv 
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 
another grows out from the trunk and plants itself in the 
ground ; and by this means its base is widened, and the grow- 
ing tree supported. The fruit, a large ovoidal mass made up 
of oblong 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 girth. 

Among the species that are earliest in taking root in the 



THE COMPLETED ATOLL. 241 

emerging coral de'bris over the reef, there are the Portulacc^e 
(species of purslane) ; the Triumphetta procumbens, a creeping 
yellow-flowering plant of the Tilia family; the Tourjiefortia 
scricca, 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 vege- 
tation is more varied, and the islands have probably undergone 
some elevation since they were made, Chamisso observed fifty- 
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. 157), 250 feet above the sea, 
sugar-cane and breadfruit, 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 (Carlshoff) 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 water, 
which is esteemed by them a great luxury. On Tari-tari (of 
the Gilbert Group, p. 133), as Mr. ELoratio 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 several miles long, and two feet deep. They 
have tai'o plantations (wliich 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 

R 



242 CORALS AND CORAL LSLANDS. 

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 
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, Lon- 
don, 1821, iii. 145. 

The island of Quiros, or Gente-Hermosa, has, according 
to S. J. Whitnell, a fresh-water lagoon, only slightly brackish, 
about three miles in diameter. He states that the connec- 
tion between the lagoon and the sea must have been closed 
at a comparatively recent date ; its level is unaffected by the 
tides. There is a fresh-water lagoon also, according to the 
same authority, in the neighbouring island of Lakena. 

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 Httle 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 keeping 
with the beautiful scenery about them than the savage inha- 
bitants. On one atoll— Honden Island, of the Paumotus, where 
no natives had ever dwelt — the birds were so innocent of fear, 
that we took them from the trees as we would fruit, and many 
a songster lost a tail-feather, as it sat perched on a branch, 



THE COMPLETED ATOLL. 243 

apparently unconscious that the world contained an enemy. 
J. D. Hague gives an account of the birds of Jarvis's and 
some other uninhabited islands in the equatorial Pacific, 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 
])rincipal are the 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 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, 
generally inhabiting that part of the deposit which is shallowest 
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 attempt 
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 groups on the ground, where they lay 
their eggs and raise their young. One variety, not very 

R 2 



244 CORALS AND CORAL LSLANDS. 

numerous, has the habit of building up a pile of twigs and sticks, 
twenty or thirty inches in height, particularly on Howlands, 
where more material of that sort is at hand, on which they 
make their nest. When frightened, these birds disgorge the 
contents of their stomachs, the capacity of which 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 {Tachypetcs aquiius) 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 frigate 
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 consi- 
derable numbers on Rowland's Island, but seldom on Jervis'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 was 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, 245 

in the fall and winter, but I never found any evidence of their 
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 ot 
remark. 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 collects 
in its accustomed roosting place, but all in peace and harmony. 
The feud between the fishing birds and their oppressors, 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 fish, 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 Enderbury's Island, and many 
other coral islands in the Pacific. The stones at the Gilbert 
Islands, as far as could be learned, are 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 Enderbury's Island, were forty feet or more long. 
Several large masses of compact cellular lava occur on Rose 



246 CORALS AND CORAL LSLANDS. 

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 waves 
to many of the islands in the Central Pacific. We were in- 
formed at the Gilbert Islands that the pumice was gathered 
from the shores by women and pounded up to fertilize 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 volcanic 
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 received a red- 
dish colour. This group has its own active volcano to supply 
the ashes, and the volcanic group of the new Hebrides is not 
far distant to the south-west. 

Notwithstanding all the products and all the attractions of a 
coral island, even in its best condition it is but a miserable 
place for human development, physical, mental or moral. There 
is poetry in every feature, but the natives find this a poor 
substitute for the bread-fruit and yams of more favoured lands. 
The cocoanut and pandanus are, in general, the only products 
of the vegetable kingdom afforded for their sustenance, and 
fish, shell-fish, 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 natives 
indicates their poverty as well as the limited productions and 
unvarying features of the land. All words like those for 



THE COMPLETED ATOLL. 247 

mountain, hill, river, and many of the implements of their 
ancestors, as well as the trees and other vegetation of the land 
from which they are derived, ^re 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 by 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 twenty- 
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 
tends to cultivate the extremest selfishness ? Assuredly, there 
is not a more unfavourable spot for moral or intellectual pro- 
gress 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 bathing, 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 dryland of an atoll is so limited, its features 
so tame, its supply of fresh water so small, and of salt water 
so large, that whoever should build his cottage on one of them 



248 CORALS AND CORAL LSLANDS. 

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 moun- 
tains and precipices ; its gorges and open valleys ; leaping 
torrents not less than surging billows; and forests spreading up 
the dechvities, 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 
basins ; and also large deposits of guano from the multitudes 
of sea birds that occupy them. Such are Jarvis's, Baker's, 
Rowland's, Maiden's, McKean's, Birnie's, Phoenix's, Ender- 
bury'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 destitute land, a few facts are here cited from an article in 
the American Journal of Science, volume xxxiv. (1862), by 
J. D. Hague, who resided for several months on the islands he 
describes. 

Baker's Island is situated in lat. 0° 13' north, and long. 
176° 22' west from Greenwich, and excepting Rowland's Is- 
land, forty miles distant, is very remote from any other land. 
It is about one mile long and two-thirds of a mile wide. The 
surface is nearly level ; the highest point is twenty-two feet 
above the level of the sea, showing some evidence of ele- 
vation. 

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 



I 



THE COMPLETED ATOLL. 249 

composed of fine sand and small fragments of corals and shells 
mixed with considerable guano ; on the eastern or windward 
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 north-west to south-east, giving the guano a variable depth 
from six inches at the edges to several feet at the deepest 
part. 

Howland's Island is situated in lat. 0° 51' 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 
sev^eral 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 composed 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 



250 CORALS AND CORAL ISLANDS. 

island, and stretches, with some interruptions of intervening 
sand, nearly from the north to the south end. Its surface is 
even, and in many places covered by a thick growth of purslane, 
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 observed at 
Baker's, that vegetation flourishes most where the guano is 
shallow, is also quite apparent here, and the consequent charac- 
teristic 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 
partial, and, on breaking some of these, in the centre was 
usually found a nucleus or co7X 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. g° 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 cietritus, while the whole island has undergone 
some elevation. It therefore presents 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 
crown 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 sur- 
face of the island is gently depressed. 



THE COMPLETED ATOLL. 25 1 

Within this depression there are other ridges, parallel to the 
outer one, and old beach-lines and water-marks, the remaining 
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 Rowland'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 undergone 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 compact and crystal- 
line, sometimes soft and amorphous), frequently 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 pene- 
trated 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 eva- 
porated in the basin. By this means deposits would be formed 
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 



252 CORALS AND' CORAL LSLANDS. 

different parts of the surface, which, though nearly flat, show 
some sHght 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 evaporated, 
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 incrus- 
tations of crystallized gypsum and common salt, ripple-marks, 
and similar evidences of the gradually disappearing lake. The 
whole is composed of a crystalline deposit of sulphate of lime, 
which, around the borders, as already observed, is mixed with 
some common salt, while near the centre, 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 generally be found. 

These facts help us to understand the varying conditions in 
which we now find the guano beds. The most important part, 
and that from which the importations have thus far come, rests 
on a bed of sulphate of lime, of an earlier but 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 be 1, 
has a peculiar character. It is covered by, or consists of, a 
hard crust, that is froni 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 Hes immediately 
on the sulphate. This crust, when pure, is snow-white, with an 



THE COMPLETED ATOLL, 



253 



a]ipearance somewhat resembling porcelain, but is usually 
coloured 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 phos- 
phoric acid and lime, but, owing to the variable amount of 
sulphate of lime, wnth which it is mechanically mixed, there is 
a lack of uniformity in different samples. Hence the per- 
centage 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 snuff colour, and, where it underHes 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 contains a large deposit of gyp- 
sum. Its supposed guano I have found to consist of the 
hydrated sulphate of lime, containing about twelve percent. 
of phosphate of lime, and coloured by a little organic matter. 
So far as my observation extends, all elevated lagoons have 
similar deposits of gypsum. 

As regards the distribution of these phosphatic guano de- 
posits, I believe them, in this region of the Pacific, to be con- 
fined to lati;:udes 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 unfavourable 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. 
Julien, gives an account of. the various phosphatic minerals 



^54 CORALS AND CORAL ISLANDS. 

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 
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 
violent 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 neighbouring islands, under 
the equator, near i8o° in longitude from Greenwicli, 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." 



GEOGRAPHICAL DISTRIBUTION: 255 



CHAPTER IV. 

GEOGRAPHICAL DISTRIBUTION OF CORAL REEFS AND 
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, — (fi) the nature of the shores, — {c) the presence of 
streams. 

3. Liability to exposure to destructive agents, such as 
volcanic heat. 

It has been stated (p. 255) that reef-growmg corals will 
flourish in the hottest seas of the equator, and over the ocean, 
wherever 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. 255), 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 



256 CORALS AND CORAL LSLANDS. 

observations of various voyages with those of the Expedition, the 
author has been enabled to draw these boundary lines with a 
considerable degree of accuracy, and they are laid down upon 
the chartof the world published in his Report (Wilkes's Explor- 
ing Expedition) on Geology, and, with other isocrymal lines, 
on a full isocrymal chart of the globe, in his Report on Crus- 
tacea, from which it was reproduced in volume xv. (1853) of 
the second series of the Ame?'ican 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 sea-s, 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, yoi", 714° F. 
While, under the equator, about the middle of the Pacific, the 
range of surface temperature of the sea through the year is 
81° to 88° 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 eastward. 
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 dow^nward to 
the latitude of the Cape Verds, and the southern upward 
nearly to the equator. The following table gives the positions 
of the coral boundary lines where they meet the coasts of the 
continents : — 

Pacific Ocean. Atlantic Ocean. 

East side of ocean — Northern, Lat. 21" N Lat. 10° N. 

Southern. 4° S 5° S. 

West side of ocean— Northern. 15° N. 26° N. 

Somhern. S 3°° S., N Holland. j ^^„ g, 
( 29° S., Africa ) 



GEOGRAPHICAL DISTRIBUTION. 257 

It follows from the above, that while the coral-reef seas are 
about fifty-six degrees wide in mid-ocean, they are 

/// the Pacific twenty-five degrees wide on the west coast of 
America, and forty-five degrees on the Asiatic side. 

/// 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 oif 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 seeming 
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 effect of a 
deep abrupt coast on the distribution of reefs has been pointed 
out (p. 89). The unfavourable character of sandy or muddy 
shores, and the action of detritus, marine currents, and fresh 
waters have also been stated (p. 93), 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 influence 
are numerous throughout the Pacific. The existence of narrow 
reefs, or their entire absence, may often be thus accounted 
for. For example, in the Hawaian Group, the island of Hawaii, 
still active with volcanic fires, has but few traces of corals about 
it, while the westernmost islands, which have been longest 
free from such action, have reefs of considerable extent. The 
island of Maui exemplifies well the same general 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 having become ex- 
tinct 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 

s 



258 CORALS AND CORAL LSLANDS. 

Streams, and much resembles Hawaii in character ; it bears 
proof in every part of being the last seat of the volcanic 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 destruction 
of the zoophytes by heat, consequent on volcanic action. 
Submarine eruptions, which are frequent as long as a volcano 
near the sea is in action, heat the waters and destroy what- 
ever of life they may contain. After the eruption of Kilauea, 
in 1840, there were numerous dead fish thrown on the beach; 
and many such instances in different regions are on record. 

The agencies affecting the growth of coral reefs being before 
the mind, we may proceed to notice the actual distribution 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 dis- 
tribution of reefs is treated of at length. The facts here 
detailed have been obtained from independent sources, except 
where otherwise acknowledged. In accounting for the cha- 
racter and distribution of reefs, Mr. Darwin appears to attribute 
too much weight to a supposed difference in the change of 
level in different regions, neglecting to allow the requisite 
limiting influence to volcanic agency, and to the other causes 
mentioned. His conclusion that the areas of active volcanoes 
in general are areas of elevation, and not of subsidence, 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 probable 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 



GEOGRAPHICAL DISTRIBUTION. 259 

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. 86). 

In Captain Colnett's voyage, allusion is made to a beach of 
coral sand on one of the Revillagigedo Islands, in latitude 18°; 
besides this statement we have met with no allusion 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. 

Captain Beechey mentions, however, that at forty-one 
fathoms, 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 former 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 Httle 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 
extent 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 the base. The 
Marquesas may, therefore, have once had barrier reefs, which 
were sunk from too rapid subsidence ; and afterward, on the 
cessation of the subsidence, others failed to form again on 
account of the deep waters. 

The Society Islands have extensive coral reefs with distant 

s 2 



26o CORALS AND CORAL LSLANDS. 

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 v/ithout coral 
shores. The Rurutu and Hervey Islands, ju§t north-west of 
Rapa, 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, Rurutu. Okatutaia 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 some- 
what less extensive than around Upolu, 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 harbour 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 Ilapai 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. 



GEOGRAPHICAL DISTRIBUTION: 261 

The many islands afford a peculiarly favourable region for the 
growth of zoophytes, and the displays of reefs 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 fring- 
ing or barrier reefs. The reefs of Wallis's Island are very 
extensive. 

The Gilbert or Kingsmill Islands, the Marshall Islands, and 
the Carolines, about eighty in number, are all atolls, excepting 
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 
sixty 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 north-west of Kauai are represented as coral reefs, ex- 
cepting the rQcks Necker and Bird Island ; the line stretches on 
to 28° 30' N., the northern limit of the coral seas. Lisiansky's 
Voyage, i8o3-'6 in the Nrua, 4to., London, 1814, pp. 254, 
256, contains an account of some of these islands ; also the 
Hawataji Spectator, vol. i. ; and also a " Report to the U. S. 
Bureau of Navigation," December, 1867, by Captain William 
Reynolds, U.S.N., partially reproduced in the Ame^-icaJi Journal 
of Science for 187 1, 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 smoking 
cones. The appearances of recent igneous action increase 
therefore as we go northward, and the extent of the coral reefs 
increase as we go southward ; no reefs occur about the northern- 
most islands, while they are quite extensive on the shores of 



262 CORALS AND CORAL ISLANDS. 

Guam. This group, consequently, like the Hawaian and 
Navigator, illustrates the influence of volcanic action on the 
distribution of reefs. 

A short distance south-west 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. 

Soidh of the 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 com- 
paratively recent igneous action, in which respect they differ 
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 south-east 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, 
north-east of Tinakoro, according to Kruesenstern, as stated 
by Darwin, is low, with large rdefs ; Duff's Islands have bold 
summits with wide reefs. 

New Caledonia, and the north-east coast of New Holland, 
with the intermediate seas, constitute one of the grandest reef- 
regions in the world. On the New Caledonia shores (p. io6), 
the reefs are of great width, and occur not only along the 
whole length of the western coast, a distance of 200 miles, but 



GEOGRAPHICAL DISTRIBUTION. 263 

extend to the south beyond the mainland 50 miles, and north 
150 miles, making in all a line of reef full 400 miles in length. 
Towards the north extremity, however, it is interrupted or 
broken into detached reefs. This surprising extent is partly 
explained by the fact that New Caledonia is not a land of 
volcanoes ; 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 several 
high islands, one of which, Lafu, has been described {Quart. 
Jour. Geol. Soc, 1847, p. 61) 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. 

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 



264 CORALS AND CORAL ISLANDS. 

cape. South of this cape there are only a few scattered coral 
zoophytes. 

The 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 Ire- 
land, according to D'Urville, has distant reefs on part of its 
shores. 

The Admiralty Islands, farther west, are inclosed 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 
volcanic summits, and one of them, near New Britain, and 
another, 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 
assigned as limiting or promoting their growth, is obvious. 
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 volcanic character of the land. At whatever time the ex- 
isting reefs in the Pacific commenced their growth, they began 
about those of the igneous islands whose fires had become 
nearly or quite extinct; and as others in succession were 
extinguished, 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 
favoured spots. Zo5phytes and volcanoes are the land-making 






GEOGRAPHICAL DISTRIBUTIOM. 265 

agents of the Pacific. The latter prepare the way by pour- 
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 from other parts of the 
coral-reef seas. 

Along the north and north-west coasts 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 north-west cape in latitude 23° S. 

In the East Indies, there are large, scattered reef-islands 
south of Borneo and Celebes, about some of the Moluccas, 
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. 

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-men- 
tioned 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 Calaminianes. There are fringing reefs at Singapore. The 
islands of Borneo, Celebes, Java, and Sumatra, according to 
all the authorities seen by the writer, have but few coral 



266 CORALS AND CORAL LSLANDS. 

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 between it and 
Formosa. But the whole eastern coast of China appears to be 
without coral. Quelpaert's Island, south of Corea, in 34° N., is 
described as having coral about it ; and this has been con- 
firmed 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 favourable region for tropical productions ? We 
are not prepared for a full answer to this inquiry ; for it would 
demand a thorough knowledge of the shores, as well as of the 
currents, and of the former and present condition of volcanic 
fires. From personal observation we may reply satisfactorily 
as far as regards part of the southern half of the east coast of 
vSumatra. This coast is low and sandy, or muddy, and thus 
affords the most unfavourable 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 



GEOGRAPHICAL DISTRIBUTION. 267 

volcanic action had become comparatively quiet and deluges 
of hot water ceased. There appears, therefore^ to be some 
reason for the fact that the reefs are small, and have seldom 
reached the surface. The Sooloo Group is but one of the vol- 
canic 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 doubted that the frequent eruptions prevented the growth of 
anything more than isolated corals, for a long period, over 
each of these areas. For other causes we must look to the 
nature 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 the 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 the open seas, 
between 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 the scenes of igneous action, and from the 
detritus and fresh water of island streams, remains to be deter- 
mined. A sinking island becomes a more and more favourable 
spot for the growth of coral as it descends ; for as its extent 
diminishes, its streams of fresh water and detritus also decrease. 
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 undergone. 
Still the fact of a greater subsidence is not impossible or 
improbable. 

In the India7i Ocean^ the Asiatic coast is mostly free from 
growing coral. The great rivers of the continent are probably 



268 CORALS AND CORAL LSLANDS. 

the most efficient cause of their absence, both directly, 
through their fresh waters, and through the detritus they 
transport and 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 fring- 
ing reefs. 

The islands of the Indian Ocean are, to a great extent, 
purely of coral. Of this character are the Laccadives, Mal- 
dives, Keehng's, Saya-de-Malha, Almirante, and Cosmoledo. 
The Chagos Group is of the same character, and the shoal 
Cargados is probably similar. The Seychelles are small islands 
with extensive reefs. 

Madagascar has a fringing reef upon its south-western point, 
according to Mr. Darwin, and on some parts of the coast 
above : also on the north and eastern shores far down as 
latitude i8° S. The Comoro Islands, between Madagascar 
and the continent, have large barrier reefs. 

The eastern coast of Africa has narrow reefs extending north 
with some interruptions from Mozambique, in latitude i6° 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 
under 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. 

On the African coast there are coral reefs at Port Natal, in 
latitude 30° S. ; and here, owing to the warm currents from the 



GEOGRAPHICAL DISTRIBUTION. 269 

tropical regions, tlie 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 described as 
coral by Captain Owen, R.N., in the Journal of the Geographi- 
cal 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 western African coast are the cause of the 
absence of corals from it, to within six or seven degrees of the 
equator ; and these cold waters may at times extend still farther 
north. The same obstacle to the diffusion of species east- 
ward, 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. 1 67), Cuba, the 
Bahamas (p. 174), 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 the west 
shores of the Gulf of Mexico, as well as the northern, hke 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. 87). 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, 



270 CORALS AND CORAL ISLANDS. 

there are reefs at intervals, from the vicinity of Cape St. Roque 
to the Abrolhos shoals in latitude i8°, as described by Prof. C. 
F. Hartt, while reef corals extend south to Cape Frio. De- 
scriptions of part of the Abrolhos reefs are given on page in. 
North of the Abrolhos reefs, there are others of coral stretch- 
ing on to Point Carumba ; again, off the Bay of Porto Seguro, 
and across the Bay of Santa Cruz ; in the vicinity of Camamd, 
around Quieppe Island ; along the shores of Itaparica Island ; 
and at Bahia and Periperi ; then, after an interruption, oft 
Maceio, in the vicinity of Pernambuco. Moreover the Roccas, 
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 equator, 
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 
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 fresh 
water and detritus into the sea. Thus the influence of con- 
tinental 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 effect, 
seldom doing more than modifying somewhat the shores and 



GEOGRAPHICAL DISTRIBUTION. 271 

bottom of a harbour. It has been further demonstrated that 
in difterent 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 action 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 where the 
neighbouring lands are mostly destitute of coral reefs, har- 
monizes with the conclusions announced, since such islands are 
in general removed from the deleterious influences just men- 
tioned ; 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 on either side. 

The modifications of form and interruptions of reefs, arising 
from abrupt or sloping shores, and tidal or local currents, have 
also been exemplified. 



2 72 COKA LS AND CORA L ISLANDS. . 



CHAPTER V. 

ON CHANGES OF LEVEL IN THE PACIFIC OCEAN. 

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. 

I. 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 grow 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. 



When the tide is three feet, beach accumulations of large 
masses seldom exceed ei^ht 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 accumulations 
may be fifteen to t7venty feet in height, and occasionally thirty 
\o forty feet. These latter are drift deposits, finely laminated, 
generally with a sandy texture, and commonly without a dis- 
tinguishable 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 deposits, 
or layers of rolled stones, intersiratified among the layers of 
igneous or other rocks constituting the hills. 

B. Evidence of subsidence. 

1. The existence of 7i'ide and deep channels between an Island 
and any of its coral reefs; or in other words, the existence of 
harrier reefs. 

2. The existence of lagoon islands or atolls. 

3. The existence of submerged atolls. 

4. Deep bay-ijidentations 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 inclosing ridges 
stand 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 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. 

T 



274 CORALS AND CORAL LSLANDS. 

C. Probable evidence of subsidence now in progress. 

I. An atoll reef without green islets, or loith but 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 wholly 
ceased. 

From the above review of evidences of change of level, it 
appears that where there are 7io barrier reefs, and only fringing 
reefs, the corals may afford 7io evidence of subsidence. 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 we 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, as is done by Darwin, 
from the fact that the reefs are small or wholly wanting, until 
the possible operation of the several causes limiting their dis- 
tribution 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. 

There are two epochs of changes in elevation which may be 
here distinguished and separately considered, i. The subsi- 
dence indicated by atolls and barrier reefs. 2. Elevations 
during more recent periods. 

II. SUBSIDENCE INDICATED BY ATOLLS AND BARRIER REEFS. 

Looking at atolls as covering buried islands, we observe, 
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 



SUBSIDENCE IN PACIFIC CORAL REGIONS. 275 

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 Kingsmill or 
Gilbert Group, the Marshall Group, and the Carolines, com- 
prise seventy-five or eighty atolls. 

If a line be drawn from Pitcairn's Island, the southernmost 
of the Pauniotus, by the Gambler Group, the north of the 
Society Group, the Navigators, and the Salomon Islands to the 
Pelews, 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 long, 
there are two hundred and four islands, of which ojily three are 
high, 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 occasional 
atoll ; but beyond this distance there are none, excepting the 
few in the Friendly Group and one or two in the Feejees. 

If each coral island scattered over this wide area indicates 
the 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, T^r J-/, that the barrier reefs are, in general, 
evidence of less subsidence than atoll reefs (p. 229). 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 

T 2 



276 CORALS AND CORAL LSLANDS. 

universally north of this line, are evidence of some depression 
just below the line ; of less farther south ; and of the greatest 
■amount noTth of the line or over the coral area. 

b. 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 sub- 
sidence. 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 fifty miles iu length, and rarely one less than three miles. " 
It is probable, therefore, that the subsidence indicated was 
greater at some distance north of the boundary line, over the 
region of small equatorial islands, between' the meridians 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 finally 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 north-west. 

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 ? 



SUBSIDENCE IN PACIFIC CORAL REGIONS. 277 

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 north-east portion (see chart), consists of immense 
barriers, with barely a single point of rock remaining of the 
submerged land ; while in the west and south-west there are 
mountain islands of great magnitude. Again, along the north 
side of the A^anikoro Group, Salomon Islands, and New 
Ireland, there are coral atolls, but scarcely one to the south. 

In view of this combination of evidence, we cannot doubt 
that the subsidence increased from the south to the north- 
Avard or north-eastward, and was greatest between the Navigator 
and Hawaian Islands, near the centre of the area destitute 
of islands, about longitude 170^ to 175° W., and 8° to 10° N. 

But we may derive some additional knowledge respecting 
this area of subsidence from other facts. 

Haiuaian 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 
eastward 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 subsidence, 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 ^rea, 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.y eighteen miles in circumference, has on its 



278 CORALS AND CORAL LSLANDS. 

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 wall, thus described by Capt. Wm. Reynolds, U.S.N. , 
appears 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 
ox five feet. 

Ocea?i Island^ in 28^ 25' N., 178° 25° W., another of this 
range, is very similar to Brooks's in its wall of coral rock on 
the east; and so also is Pearl and He7'mes'' 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 abrupt 
shores, often inaccessible cliffs, and deep bays. The absence 
of gentle slopes along the shores, their angular features, 
abrupt soundings close alongside the island, and deep indenta- 
tions, all bear evidence of subsidence to some extent ; for 
their features are very similar to those which Kauai or Tahiti 
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 tlie 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 
extent. They are nearly destitute of coral, and apparently 
because of the depth of water about the islands. 

Gambler Group.-^ln 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, Fit- 
calnls and Gambler s. There is evidence, however, in the 
extensive barrier about the Gambler^ s (see cut on page 227), 
that this subsidence, although less than farther north, was by 
no means of small amount. On page 126, we have estimated 
it at 1,150 feet — possibly 1,750. These highlands therefore, 
although toward the limits of the subsiding area, were still 



SUBSIDENCE IN PACIFIC CORAL REGIONS. 279 

far within it. The valley-bays of the islets of the lagoon 
are of great depth, and afford additional evidence of the 
subsidence. 

Tahitian Islands. — The Tahitian Islands, along with Samoa 
and the Feejees, are near the southern limits of the area 
pointed out. Twenty-five miles to the north of Tahiti, within 
sight of its peaks, lies the coral island Tetuaroa, a register 
of subsidence. Tahiti itself, by its barrier reefs, gives evidence 
oi 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 north-western islands of the group 
iie more within the coral area, and correspondingly, they have 
\Wder reefs and channels, and deep bays, indicating a greater 
amount of subsidence. 

Sainoan 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 126, at one or two hundred feet. The volcanic land 
west of Apia declines with an unbroken gradual slope oi 
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 western 
extremities of Upolu, or accompanied this change of leveL 
The large island of Savaii, \Ne^?it of Upolu, has small reefs, 
small because probably of volcanic action ; for it bears, every^ 
where, evidence of comparatively recent eruption ; from it, 
therefore, we gather no certain facts bearing on this subject. 
East of Tutuila is the ^ora/ island^ Rose. It may be, there- 
fore, that the greatest subsidence in the group was at its 
eastern extremity. 

Feejee Islands. — We have already remarked upon this group 



28o CORALS AND CORAL ISLANDS. 

(p. 127). A large amount of siihsidence is indicated by the 
extensive reefs in every portion of the group, but it was 
greatest beyond doubt in the north-eastern 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 disappeared 
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 south-west, in the 
line of the Ladrones. 

We have thus followed around the borders t'f 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 tlie Hawaian Group would pass along the northern 
boundary line of the area ; and taking the soutl:iern boundary 
as given on page 273, the oblong area narrows eastward. An 
axis nearly bisecting this space, drawn from the eastern Pau- 
motus 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. 

It is worthy of special note, that this axial line., or line oj 
greatest depression., coincides in direction with the mea7i 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 boundajy 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 south-eastward in 
some places beyond the boundary line. One of the regions 
of this prolongation lies between the Samoan or Navigator 
Group and the Feejees and Tonga Group ; another is east of 



SUBSWE^fCE IN PACIFIC CORAL REGIONS. 281 

Samoa, along by the Hervey Group. Each of these exten- 
sions trends parallel wit Ji the gi'oups of islands. It would seem, 
therefore, that the Society and Samoan islands were regions of 
less change of level than the deep seas on 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 may mark the course of a great central 
anticlinal in the oceanic basin. 

The Hawaian range has experienced its greatest subsidence 
to the north-west, where the islands are all atolls, and show 
some evidences of recent sinking; and this north-western 
extremity of the range is nearer to the axis of the area of 
subsidence, above laid down, than is the south-western. 

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 
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 feet, could not have buried the 
many peaks of these islands. Even the 1,200 feet of depres- 
sion at the Gambler Group is shown to be at a distance 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 estimate, 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 



282 CORALS AND CORAL LSLANDS. 

show that they have undergone ; 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 Hedrides 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 without 
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. 

HI. 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 en- 
during 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 proceeded ; 
since many lands, owing to their abrupt shores, or to volcanic 
agency, must have had no reefs about them, and have dis- 
appeared without a mark ; and since others may have subsided 
too rapidly 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 



SUBSIDENCE IN PACIFIC CORAL REGIONS. 283 

about the heights of a single subsiding land of large size. 
Such facts show additional error in the above estimate, evin- 
cing that the scattered atolls and reefs tell but a small part of 
the story. Why is it, also, that the Pacific Islands are confined 
to the tropics, if not that beyond thirty degrees the zoophyte 
could not plant its growing registers ? 

The island of Ponape, in the Caroline Archipelago, affords 
evidence of a subsidence in progress, as Mr. Horatio Hale, the 
Philologist of the Wilkes Expedition, gathered from a foreigner 
who had been for a while a resident on this island. Mn Hale 
remarks, after explaining the character of certain sacred struc- 
tures of stone : " It seems evident that the constructions 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 present 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 inclosures.' '' Mr. Hale hence 
infers "that the land, or the whole group of Ponape, and 
perhaps all the neighbouring groups, have undergone a slight 
depression." He also states respecting 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 Paum.otus, there is no reason 
whatever for supposing that a general subsidence is still in 
progress ; the changes indicated are of a contrary character. 



284 CORAL'S AND CORAL ISLANDS. 



IV, PERIOD OF THE SUBSIDENCE. 

The period during which these changes were in progress 
extends back to the Tertiary era, and perhaps still farther. 
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 inner margin 
of shore reefs there is the same identity with existing genera. 
AVe do not claim to have examined the basement of the coral 
islands, and offer these facts as the only evidence 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 flourished, 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 comparatively 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. ELEVATIONS OF MODERN ERAS IN THE PACIFIC. 

Since the period of subsidence discussed in the preceding 
pages, there has been no equally general elevation. Yet 
various 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. 



RLE J 'A TIONS IN PA CIFIC CORA L REGIONS. 2S5 

The most convenient mode of reviewing the subject is to 
state in order the facts relating to each group. 

a. Paumotu Archipelago. — The islands of this archipelago ap- 
pear in general to have that height which the ocean may give 
to the materials. Nothing was detected indicating any geuei-al 
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 ob- 
servations 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 Expe- 
dition 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 relating 
to Ducie's Island and Osnaburgh, which afford some suspicions 
of a rise. 

Hondcji Island or Henuake. — This island is wooded on its 
different sides, and has a shallow lagoon. The beach is eight 
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 these 
Tridacnas evidently 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 Paumotu s, was coasted along by the Feacock, 
one of the Sloops of War of the Wilkes Exploring Expedition, 
and from the vessel we observed that the rim of land consisted 
for miles of an even wall of coral rock, apparently 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 hundred rods, and then 



286 CORALS AND CORAL LSLANDS. 

there followed again a line of columns, and walls, with occa- 
sional arches as before. The reef, formerly 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 certain parts to the masses 
seen here and there on the shore platforms of other islands ; 
but the latter are only distantly scattered masses, while on this 
island, for the greater part of the course, there were long walls 
of reef-rock. The height, moreover, 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 wooded 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 
elevation stated at two himdred and fifty feet. (See page 157.) 

Clermo7it Toniwre shows the same evidence of elevation 
from Tridacnas as Honden Island. Clermont Tonnerre and 
Honden are on the north-eastern limits of the Paumotus. 

Elizabeth 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 
is eighty feet. It is one of the south-eastern Paumotus, near 
Ducie's. 

Ducie's Island is described by Beechey as twelve feet high, 
which would indicate a probable elevation of 07ie or two feet. 

Os7iaburgh Island., according to the same author, affords 
evidence of having increased its height since the wreck of the 
Matilda, 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, ironworks, and a large gun (4-pounder) of this 



ELEVATIONS IN PACIFIC CORAL REGIONS. 287 

vessel were two hundred yards inside of the hne of breakers. 
Captain Beechey suggests that the coral had grown, and tlius 
increased 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 certain), 
it must have arisen from an upheaval. 

b. TaJiitian Group. — The island of Tahiti presents no con- 
clusive evidence of elevation. The shore plains are said to rest 
on coral, which the mountain de'bris 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 confidendy believing 
that any of them have been elevated. The change, however, 
of the barrier reef around Bolabola into a verdant belt encir- 
cling 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 fur- 
thered by at least a small amount of elevation. The obser- 
vation by the Rev. 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 
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 Ruriitu Groups. — These groups lie to the 
south-west and south of Tahiti. 

Afangaia is girted by an elevated coral reef three hundred 
feet in height. Mr. Williams, in his Missionary 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. 



2SS CORALS AND CORAL ISLANDS. 

Aim (Wateoo of Cook) is a raised coral island. Cook 
{Voy., i. i8o, 197) observes 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 
covered with verdant hills and plains, with no streams. It is 
described by Williams in his Missionary Enterprises, Mauke 
is a low elevated coral island according to Williams, and Mitiaro 
resembles Mauke. Okatiitaia 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. 

Rurutu has an elevated coral reef one Jiundred and fifty feet 
in height, as stated by Stutchbury, and also Williams. Tyerman 
and Bennet describe the island as having a high central peak 
with lower eminences, and speak of the coral rock as two 
hundred feet high on one side of the bay and three hundred 
on the other (ii. 102). — EUis says that the rocks of the interior 
are in part basaltic, and in part vesicular lava (iii. 393). 

With regard to the other islands of these groups, Manuai^ 
Aitutaki, Rarotonga, Rimetara, Tubiiai., and Raivavai, the 
descriptions by Williams and EUis appear to show that they 
have undergone no recent elevation. 

d. Tonga or Friendly Islands, and others in their vicinity. 

AH' 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 thi'ee himdred feet. From the appearance of the land, we 
judged that the interior was basaltic ; but nothing positive was 
ascertained with regard to it. 

Tongatabu (an island visited by us) lies near Eua, and is in 
some parts fifty or sixty feet high, though in general but 



ELEVATIONS IN PACIFIC CORAL REGIONS. 289 

twenty feet. It has a shallow lagoon, into which there are two 
entrances ; 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). 

Vavan, the northern ot 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 many excavations along the coast. 

Fylstaaj'fs ■ Island, south of Tongatabu, is a small rocky 
islet without coral. Tafiia and Proby are volcanic cones, and 
the former is still active. 

Savage Island, a little to the east of the Tonga Group, 
resembles Vavau in its coral constitution and cavernous cliffs 
It is elevated, according to Williams (pp. 275, 276), one 
hufidred feet. 

Beveridge Reef, a hundred miles south-east of Savage, is low 
coral. 

e. Sainoan or Navigator' Islands. — No satisfactory evidences 
of elevation were detected about these islands. 

f. Atolls, no7'th of Samoa. 

On account of the high tides (four to six feet), the sea may 
give a height of twelve to sixteen feet to the land. 

Swain's, 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. 

Fakaafo, 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 

u 



290 CORALS AND CORAL LSLANDS. 

high. Whether elevated or not is uncertain ; probably as 
much so as Fakaafo. 

g. Scattered islands farther norths near the equator, east of 
the Gilbert Group. 

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 
cocoanut and other trees. The height of the land is ten or 
twelve feet. The unusual size of the island for one without a 
lagoon, and the luxuriance of the forest vegetation, are probable 
evidence of some elevation, but not beyond three feet. 

Palmyra Island, north-east of Washington, is described by 
Fanning as naving two lagoons, the westernmost with twenty 
fathoms water. 

Fanning' s Island, south-east of Washington, according to the 
same voyager, is lower than that island. The accounts give no 
evidence of elevation in either Fanning's or Palmyra. 

Christmas Island, 'vi\\2X. 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 sea-coast, 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. Jonrn., 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 248.) 

Maiden's, in 4° 15' S., 155° W\, two hundred and fifty 
miles south-east of Jarvis, visited by Lord Byron, is described 
by him as not gw^x forty feet high. It is ten miles long. 

Starbucks 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.) 



ELEVATIONS IN PACIFIC CORAL REGIONS. 291 

Penrhyn's Isla/id, near 9° S. and 157' W., has a length 
of nine miles, and an extensive lagoon with a boat entrance 
into it. According to Captain Ringgold of the Wilkes Ex- 
pedition, it has a height of fifty feet, which, if correct, would 
indicate an elevation of full thirty-five feet. The north-west 
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 
Captain Ringgold, which is unusual for so small an island 

Staver's Island^ in 10° 5' S., and 152° 22^' W., is only 
half a mile across, and yet is well wooded. Both of these 
islands were passed by Captain Ringgold, but he does not 
state the height. — (Wilkes's Narr., iv. 277.) 

Baker'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 twenty-two feet, " showing some evidences 
of elevation." (See further, p. 247.) It has probably been 
elevated at least six feet. 

Howlands Island, 0° 51' N., and 176° 32' W., is about 
forty miles north of Baker's. It is about one and half 
miles long, and half a mile wide. The highest point, ac- 
cording 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. 

McKeafis Island, of the Phoenix 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's Island. It has 
a lagoon depression, in which there is a gypsum and guano 
deposit ; 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. 

Enderbury's, in 3° 8' S., 174° 14' W., is eighteen feet high. 
It has probably experienced some elevation. But the height 
of the tides is such in the seas as to give the beach and drift 

u 2 



292 CORALS AND CORAL LSLANDS. 

sands much greater height than they have in the Paumotus. 
Birjiie's Isla?id is a small bank of coral, only six feet above the 
sea, according to Wilkes (Narr. v. 4). 

Gard?iers, HiilVs^ Sydney, and Newmarket were visited by 
the Wilkes Expedition. No satisfactory evidences of elevation 
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. Sandwich or Hawaian 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 harbour, that the island is slowly 
rising. Upon this point we have nothing satisfactory. The 
present height of the reef is not sufficiently 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 
began ; or, at the most, no elevation is indicated beyond 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. 
Andrews, 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 tlie eastern or 
highest part of the island, over a surface of more than twenty 
or thirty acres, and extends almost to tlie sea. We had no 
means of accurately measuring the height ; but the specimens 
were obtained at least thre heundred 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." 



ELEVA riONS IN PACIFIC CORAL REGIONS. 293 

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 effer- 
vesce with acids, and therefore is not calcareous. 

There are large masses of coral rock, according to Mr, 
Andrews, along the shores of Maui, from two to tvelve 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 twelve feet. 

On page 277, 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 broken 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. 

/. 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 
barrier 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, WalHs, EUice, 
Depeyster, and four islands on the track toward the Kingsmills, 
were passed by the sloop of war Peacock of the Wilkes Ex- 
pedition ; but from the vessel no evidences of elevation could 
be distinguished. The first two are high islands, with barriers, 
and the others are low coral. S. J. VVhitnell. Esq., has recently 
stated that at Ellice Island (or Funafuti), " on the windward 
side of the largest island of the atoll, there is a small lagoon 
(dry at low water), 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 



294 CORALS AND CORAL LSLAMDS. 

in situ rising four feet above low-water mark." Rotuma (177° 
15' E., and 12° 30' N.) is another high island, to the west of 
Wallis's. It has encircling reefs, but we know nothing as to 
its changes of level. 

k. Kings mill ox Gilbert Group. (Map, p. 133.) 

Tapateuea or Drummond. — 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 Astraeas 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 Astraeas 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. 

Apaia?ig or Charlotte's Island, one of the northernmost of 
the group, has the i'eef-7'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. 

Nononti, Kuria, Maiajia, and Tai'awa^ 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 north-east 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 Apaniama was elevated, precisely like that of Apaiang, 
to a height oi Jive feet ; and this was confirmed by Lieutenant 



ELEVATIONS IN PACIFIC CORAL REGIONS. 295 

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 north- 
ward. 

Alarakei, 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. Makw, 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. 241). 

/. The Marshall diud Carolme 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 inclines 
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 261, is an elevated coral island, 
having a height of 100 feet. 

;;/. Ladroties. — The seventeen islands which constitute this 
group may all have undergone elevations within a recent period, 
but owing to the absence of cora! from the northern, we have 
evidence only with regard to the more southern. 

Guam, 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. 

n. Pelews and neighbouring Islands. — The island Feis, three 
hundred miles south-west of Guam, is stated by Darwin, on the 
authority of Lutke, to be of coral, and ninety feet high. 
Mackenzie Island, seventy-five miles south of Feis, is a low 
atoll, as ascertained by the Expedition. No evidences of ele- 
vation are known to occur at the Pelews. 



296 



CORALS AND CORAL ISLANDS. 



0. Melanesian Isla?ids. — 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 presented 
in a tabular form. 



Paumotu Archipelago, 



2 or 3 

2 or 3 

6 

80 

250 



Tahitian Group, .... 
Hervey and^Rurutu Groups, 



Tongan Group, 



Savage Island, .... 
Samoan or Navigator Islands, 
North of Samoa, .... 



Scattered Equatorial Islands, 



Honden, 

Clermont Tonnerre , . 
Nairsa or Dean's, . . 

Elizabeth, 

Metia or Aurora, . . 

Ducie's, I or 2 

Tahiti, o? 

Bolabola, ? 

Atiu, ' 12? 

Mauke, . . . somewhat elevated. 
Mitiaro, ... ,, „ 

Mangaia, , 300 

Rurutu 150 

Remaining Islands, .... o ? 

Eua, . 300? 

Tongatabu, 50 to 60 

Namuka and the Hapaii,. . 25 

Vavau, ....... 100 

100 

o 

Swain's, 2 or 3 

Fakaafo, or Bowditch, .... 3 
Oatafu, or Duke of York's, . 2 or 3 

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, ? 

Phoenix and McKean's, . . . o 

Enderbury's, 2 or 3 ? 

Newmarket, 6 or 8 ? 

Gardner's, Hull's, Sydney, Birnie's, o? 



ELEVATIONS IN PACIFIC CORAL REGIONS. 297 

FEET. 

Feejee Islands, Viti Levu and Vanua Levu, 

Ovalau, 5 or 6 

Eastern Islands, ...... o? 

North of Feejees, .... Home, Wallis, Depeyster, ... o ? 

Ellice 5 or 6 

Sandwich Islands, .... Kauai, i or 2 

Oahu, 25 or 30 

,, ,, Molokai 300 

,, ,, Maui, 12 

Gilbert Islands, Taputeuea, 2 or 3 

,, ,, Nononti, 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, o? 

New Hebrides, New Caledonia, Salomon Islands, . none ascertained. 

Several deductions are at once obvious : — 

1. That the elevations have taken place in aJl parts of the 
ocean. 

2. That they have in some instances affected single islands, 
and not those adjoining. Metia is 250 feet high, and yet the 
other Paumotus 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 extended 



298 CORALS AND CORAL ISLANDS. 

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 general 
rise is, or has been, in progress ; yet some large areas appear 
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 
gradual action. 



GEOLOGICAL CONCLUSIONS. 299 



CHAPTER YI. 

' GEOLOGICAL CONCLUSIONS. 

The geological bearing of the facts that have been detailed 
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 
subject. 

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 hmestone. 

The reefs illustrate two different modes of origin of such 
beds: (i), by undisturbed growth, with only additions of fine 
material to fill up the intervals; (2), by the grinding of the 
corals, &c., 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 movement of the waves, — unless 
Rhizopods, or minute shells of some kinds, multiplied so 
rapidly over the same sea-bottom as to fill up the interstices. 



300 CORALS AND CORAL ISLANDS. 

There is no reason to believe that such aid from shells or 
Rhizopods is consistent with the grouping of living corals 
thickly enough to form reefs. 

The other kind of Umestone beds referred to, where unmixed 
with the former, grow up in compact layers to the surface, as a 
necessary consequence of wave-action ; and limestones 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 degradation 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 persistent 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 moUusk ; and 
neither fish, nor holothurian, nor alcyonoid 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 very finest and most compact unfossiliferous 
limestones ; that fine compact limestone, as flint-like in fracture 
as any of Silurian time, is one of the most common of coral- 
reef rocks, and is nothing but consolidated mud, or fine sand, 
of coral origin. 

The elevated portion of the island of Matea, which consists 
largely of this kind of white, compact, coral-made limestone, 
appears to correspond to the interior of the original lagoon ol 
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 channels are very 
broad, there is an opportunity for the formation 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-rocks, which are accumulated 



GEOLOGICAL CONCLUSIONS. 301 

and consolidated above low-tide level. These formations 
illustrate 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 
respectively with those of beach and drift-sand deposits in 
other regions. 

II. BEDS OF 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 furnishes 
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 shown to have in some cases 
a thickness of at least 2,000 feet (page 126). The reefs are, 
therefore, examples of great limestone strata, nearly as remark- 
able 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. 221). This 
is the only method by which any thick stratum of limestone 
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. 



302 CORALS AND CORAL LSL.ANDS. 

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 hereafter 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 i [4, 173. 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 bearing, for they teach that lands 
separated by a range of deep ocean cannot supply one another 
with material for rocks. The existence of an Atlantic 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 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. 

VL 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 oohte (pp. 122, 158). The rocks 
are formed at the sea-level, and in the midst of abundant life, 



GEOLOGICAL CONCLUSIONS. 303 

and yet trituration by the action of the waves and winds has 
in many places reduced all to the finest material, so that an 
embedded 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 appears 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 secofid, 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 WIDE RANGE OF THE OLDER LIMESTONES NOT EXEMPLI- 
FIED 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 great width. The substratum, however, is, in general, continu- 
ous coral-rock ; and if these more elevated parts were removed 
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. 132), 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 difierences 



304 CORALS AND CORAL ISLANDS. 

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 gradually formed over the broad surface 
of a continent as it lay slightly submerged. 

The Abrolhos reefs of the Brazilian coast, described on page 
I IT, illustrate one of the methods by which the coral banks 
extend 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 
unavoidable 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 is possible that such barriers may often have existed in 
ancient time, and have disappeared through subsequent denu- 
dation 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 narrow 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 
ancient unfossiliferous limestones were made. The narrt)w 
limits of the former make the comparison unsatisfactory ; for, 
in the coral island, coarsely fossiliferous beds are all the while 
forming about the exterior of the island, but a few miles at 
the most from the lagoon-marsh ; while the ancient limestones 
retain their unfossiliferous character often through many thou- 
sands of square miles. Still, the above-mentioned difference 



GEOLOGICAL CONCLUSIONS. 305 

between the continental sea and the existing deep oceans may 
perhaps account for the diversity of resuUs. 



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, the last with mud or sands intermixed 
— by (i), an under-water process ; (2), at the ordinary tempera- 
ture; 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 (i), the rains which wash it down from 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 mud. 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 consolidation. 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 structure is produced. Facts are men- 
tioned on page 122 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 Hme being added until all 

X 



3o6 CORALS AND CORAL LS LANDS. 

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 south-west, the rocks which are situated at the end 
of the long beach become coated by a white, thick, and very 
hard cal'Careous layer. I saw portions of this remarkable 
deposit, which had been protected by an accumulation 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 cal- 
careous 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 arrangement of 
the sea-beach, and this again the quantity of calcareous matter 
held in solution by the waters of the neighbouring 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 building-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 
already explained. 



GEOLOGICAL CONCLLSIONS. 307 



IX. FORMATION OF DOLOMITE, OR MAGNESIAN CARBONATE 
OF LIME. 

Analyses of the coral limestone of the elevated coral island 
Matea, by Prof 13. Silliman, junr., have determined the singular 
fact that, although the corals themselves contain very little 
carbonate of magnesia, magnesia is largely present in some 
specimens of the rock. The rock is hard (H. .— 4), and 
splintery 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 
magnesia. 

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 75 show, contain very little or no 
magnesia. The coral sand from the Straits of Balabac, 
afforded Prof Silliman carbonate of lime 98*26, carbonate 
of magnesia 1-38, alumina 0*24, phosphoric acid and silica 
a trace. 

This introduction of magnesia into the consolidating 
under-water coral sand or mud has apparently taken place 
(i) m sea-waters at the ordinary temperature; and (2) with- 
out the agency of any mineral waters except the ocean. 
But the sand or mud may have been that of a contracting and 
evaporating lagoon, in which the magnesian and other salts of 
the ocean were in a concentrated state. It has been already 
observed (p. 300), that this was probably the actual condition 
of the elevated portion of the island of Matea, everything 
about it looking as if it corresponded to the lagoon part of the 
old atoll ; and also that the idea of the existence of mineral 
springs there has no support in known facts. 

X 2 



3o8 CORALS AND CORAL ISLANDS. 



X. FORMATION OF CHALK. 

The formation of chalk from coral is known to be exem- 
plified at only one spot among the reefs of the Pacific. 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 Nelson 
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 only 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 ex- 
tent, and eight or ten feet deep. The rock could not be dis- 
tinguished from much of the chalk of England ; it is equally 
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 
contained, according to Professor Silliman, 92-80 per cent, of 
carbonate of lime, 2*38 of carbonate of magnesia, besides 
some alumina, oxide of iron, silica, &c. 

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 Oahu, 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 



GEOLOGICAL CONCLUSIOA'S. 309 

afforded no certain proof of any connection between the fires 
of the mountain and the formation of the chalk. 

The fine earthy texture of the material is evidence that the 
deposit was not a siibaerial 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 \vere some peculiar 
circumstances 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 forammifers, the shells of 
Rhizopods. Professor Bailey found under his microscope no 
traces of foraminifers, or of anything distinctly organic, in the 
Oahu chalk. 

XI. RATE OF INCREASE OF LIMESTONE FORMATIONS. 

On page 212 it is shown that coral-reef limestones are of 
slow formation, the rate of increase in thickness, where all is 
most favourable, not exceeding perhaps a sixteenth of an inch 
a year, or five feet in a thousand years. And yet such lime- 
stones probably form at a more rapid rate than those made of 
shells, because the animals are to a larger extent calcareous, or 



3IO CORALS AND CORAL LSLANDS. 

make proportionally larger calcareous secretions ; and in addi- 
tion they have the property of rapid multiplication by bud- 
ding. The mollusks that grow and multiply most rapidly, 
and have proportionally the largest shells, are the Lamelli- 
branchs, or bivalves, among which the oyster is a famous ex- 
ample ; 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 Gas- 
teropods (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 those bivalves that grow in large banks live in beds 
of ordinary sand or mud, such as reef-regions do not gene- 
rally 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 cur- 
rents 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, as 
stated on page 157. 

In the raised coral rock of Oahu (p. 290) 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 157, 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. 



GEOL OGICA L CONCL USIONS. 



311 



The Rev. John WilHams 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 neighbouring 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 beautiful 
— one of them "a perfect bijou." 

These are examples of the comparatively rapid formation 
of caverns. The waters which run or perx;olate through them 
must be charged with carbonic acid to accomplish such work, 
and yet they have no source for this ingredient except. the atmo- 
sphere, 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. 

XIII. OCEANIC TEMPERATURE. 

Facts seem to indicate — though perhaps not sufficient to 
demonstrate — that the Gulf Stream has had, from the Jurassic 



312 CORALS AND CORAL LSLANDS. 

period in Geological history onward, the same kind of influence 
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- 
trsea 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 Astrsea tribe are now confined to coral-reef seas (p. 84). 
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., through the middle of the two oceans, the Pacific and 
Atlantic, 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 north-eastward 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 6.8° more 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 globe) to bear the heat required for corals as 
far north as northern England. 

The present isocryme of 44° F., as drawn on the chart of 



% 



GEOLOGICAL CONCLUSIONS. 313 

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 ; a,nd 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. 

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 favourable 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 Cretaceous, 
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 present extension and oceanic cha- 
racter; 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. 

' The influence of oceanic currents on the isothermal lines of the ocean 
is Liijfly stated on pages 255, 256. 



314 CORALS AND CORAL ISLANDS. 



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 
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 Hnear ranges.; and they have, along with the equally 
linear ranges of high islands just south, a nearly uniform 
trend, curving into north-west and north-north-west at the 
western extremity. The coral islands consequently cap the 
summits 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 280, 
has a length of more than six thousand miles— equal to one 
quarter of the circumference of the globe ; and the breadth, 



OCEANIC CORAL ISLAND SUBSIDENCE. 315 

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 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 tropical 
Pacific, and perhaps for the warmer latitudes of all the oceanic 
areas, while 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. 281) 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 elevation 
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 northern continental upward movements which intro- 
duced the Glacial era, carrying the Arctic far toward the 
Tropics, may have been a balance to the downward oceanic 
movements that resulted in the formation of the Padfic 
atolls. While the crust was arching upward over the former 
(not rising into mountains, but simply arching upward) it may 

^ The arguments which have seemed to favour the view that the por- 
tions of North America in the higher latitudes, and probably also in the 
corresponding parts of the other continents, were above I heir present 
level, are briefly presenttd by the author in his " Manual of Geology," 
and also, recently, in the Amerkan Journal of Science, third series, 
volume V. 



3i6 CORALS AND CORAL LS LANDS. 

have been bending downward over the vast 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 tliey cover a submerged 
land of large area stretching over six hundred miles from 
north-vvest to south-east. The long line of reefs and the 
Florida Keys, trending far away from the land of southern 
Florida, are evidence that this Florida region participated in 
the downward movement, though to a less extent than the 
Bahamas. Again, the islands of the West Indies diminish in 
size to the eastward, being quite small, in a long line that looks 
out upon the blank 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 south-eastern prolongation of the continent. The north- 
western and south-western 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 north-west, existing in Florida 
and the Bahamas, 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 south-east), in the high lands of 
north-western and south-eastern Cuba, and in the Florida Hne 
of reefs, and even farther, 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 



OCEANIC CORAL ISLAND SUBSIDENCE. 317 

participated in it equally with the intermediate or adjoining 
seas ; for the facts in the Pacific have shown that the sub- 
siding oceanic area had its nearly parallel bands of greater 
and less subsidence, that areas of greatest sinking alternated 
with others of less, as explained on page 279; and that the 
groups of high islands are along the bands of least sinking. 
So in the Atlantic, the subsidence was probably much greater 
between Florida and Cuba than in the peninsula of Florida 
itself; 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 natural 
for islands to be alone. The tongue of warm water due to the 
Gulf Stream, in which the Bermudas lie, is narrow, and an 
island a hundred miles or more distant to the northeast-by- 
east, or in the line of its trend (p. 183), if experiencing the 
same subsidence that made the Bermuda land an atoll, would 
have disappeared without a coral monument 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. This suggestion as to the former extent 
of the Bermuda Group has been recently sustained by the 
observations of Mr. J. Matthew Jones, cited on page 185. 

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. 152). 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 south-west of the Chagos Group ; while 



3i8 CORALS AND CORAL ISLANDS. 

Keeling's is another outlying atoll south-west 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 
part of their interiors may be a consequence of it. A rate of 
sinking exceeding five feet in a thousand years (if the esti- 
mate on page 215 is right) would have buried islands and 
reefs together 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 move- 
ment 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 pro- 
bability 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 valleys that prevails over the continents ; and, through 
this observation (and also by the discovery that some ancient 
tj^es 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 



OCEAVIC CORAiL ISLAND SUBSIDENCE. 319 

in the ocean of nnany granitic mountain chains, they do teach 
that there are long ranges, or Hnes, 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 suface in the 
dredge. 

We may also accept, with some confidence, the conclusion 
that atolls and barrier reefs originated in the same great 
balance-like movement of the earth's cruse 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 
balance the beauty and repose of the tropics, through all 
the progressing changes, against the prolonged scenes of 
glacial desolation 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 A?'cheozoic, from 
the Greek for bcgiiuiing 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, In- 
sects, Fishes and Reptiles existed. It includes three Ages : (i), the 
Silurian; (2), the Devonian, or Age of Fishes ; and (3), the 
Ca7'boniferoiis, or Age of Coal-plants, when the most extensive 
beds of mineral coal of the world were originated. 

2 Mesozoic time, or ih^t oi medieval life. It corresponds to 
the Age of Reptiles— being the era, not of the earliest reptiles, but 
that of their chmax 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. 

Cenozoic time is divided into two Ages, the Tertiary and the 
Quaternary. The Quaternary age, the last in the geological 
series, commences with the Glacial period, when, over Northern 
North America, vast quantities of stones, gravel and sand, were 

Y 



322 



APPENDIX. 



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, extending 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 
continental 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 moderating of the climate, and 
a melting of the glacier. Next came the 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. 

II. RADIATES. 

Polyps have been described as constituting one of the grand 
divisions of Radiates. 

Radiates are characterized by a radiate system of structure, 
apparent both externally and internally : in other words, they 
consist of different 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 five, as follows : 

1. Sub-kingdom of Vertebrates. — This designation refers to a 
fundamental feature of the species, — the backbone or spinal column, 
consisting of a series of bones (sometimes cartilaginous only), 
articulated together, called, in the Latin language, vertebrcB. 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 i)ivertebralcs, that is, have no vertebral 
column. 

2. Sub-kingdom of AUTICULATES — 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 



APPENDIX. 



;23 



cavity containing both the viscera and the principal nervous cord, 
the latter situated below the alimentary canal. The species 
included arc Insects, Spiders, Centipedes, Crustaceans (or Crabs, 
Lobsters, Shrimps and the like), and Worms. 

3. Sub-kingdom of IMOLLUSKS — or, as the name implies, species 
having soft fleshy bodies, which are characterized also by a simple 
bag-like structure, 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 succession of segments in the body, 
or of corresponding ganglia (nervous masses) in the nervous 
system ; and, consequently, Mollusks have not that composite 
feature that characterizes and distinguishes Articulates. Examples 
are the Oyster, Clam, Snail, Cuttle-fish, and Bryozoans (mentioned 
on page 81). 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. 

I St. Polyps., whose characters have already been stated (p. 3 and 
beyond). 

2d. Acalephs, or Telly-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 furnished 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 cavity instead of radiating 
compartments. Acalephs, or jelly-fishes, float in the ocean, usually 
with the mouth downward, moving ordinarily by the contraction 
and expansion of the sides of the body. Hydroids (p. 76) are 
sexless forms under one division of Acalephs ; they are usually 
attached, and look like polyps. 

3d. Echinodervis. Examples of this class 2Lre,Jirsf, the star-fishes., 
oxjivc-fingcrs, whose bodies, although containing calcareous plates, 
are somewhat flexible, and ordinarily either five-rayed (fingered) or 
five-angled (but sometimes more than five) : — seco)id\}[^Q Echinus or 

Y 2 



t 



324 



APPENDIX. 



sea-hcdoeJwo-^ so called from the spines that stand out in all direc- 
tions over the thin, but firm, hollow shell ; third, the Holoihurians, 
or -f-^vr-i-Z/z^i-, alluded to on page 129, 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 
typically a multiple either of six or oi foiij-j in Acalephs, oi four j 
in Echinoderms, oi five. Some variations occur under each of these 
divisions ; but they may probably be regarded as modifications of 
the type by suppression in development, or the reverse. 

The Echinoderms are the highest of Radiates. They show their 
superiority 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 stingmg apparatus 
in the skin being a special attribute 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 animal ; 
and the tentacular (or ambulacral) compartments alternate with 
others non-tentacular (inter-ambulacral). When the body is long, 
as in the Holothurians, the five 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 structure ; 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 Acalephs, the isolated parts existing in these 
species are manifestly rudiments of the nervous ring of the 
Echinoderms ; in the system of water-circulation, which in Polyps 
differs 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 systematists Ccclenterates. 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 is something fund- 
amental 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 



APPENDIX. 325 

fact of the nutritive system having one or two open extremities, or 
by the perfection of the nervous or branchial systems, or by the 
condition of the general visceral cavity. Moreover some Kchino- 
derms have only one opening to the alimentary cavity, while so)nc 
Acali'pJis 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 nervous 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 Holothurians, in the sand, have sometimes a 
similar branchial rosette, the crimped or finely divided appendages 
among the tentacles of such Actiniae being true branchiae, as Verrill 
has observed ; and, further, such appendages have no compartment 
of their own, but grow out from one that bears its normal tentacle 
(page 19J. 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 confirmatory 
evidence that Polyps and Echinoderms are one in system of 
structure and alike Radiates. 



III. PROTOZOANS. 

Foraminifers, which include the Orbitolites (mentioned on page 
121), the Globigerinfe (page 174), 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, fii'st. their minuteness, the animals being mostly 
between a looth and a 1 0,000th of an inch in length ; secondly, in 
having no external organs or parts, excepting (i) a mouth, and (2) 
minute cilia or thread like processes ; thirdly, in having no dis- 
tinguishable digestive apparatus excepting a stomach ; fourtlily, \\\ 
the fact that the stomach and movith are sometimes wanting, or 
exist only when extemporized fo)- 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 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, 



326 APPENDIX. 

signifying Toot-likc 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 foi'aniinifers. 

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 Globigerime, and various 
other kinds, cominon 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 Orbitolites, referred to, ^n page 121, as 
contributing largely to the coral reefs of the Austi. iian seas, while 
common throughout the reef regions of the Pacific. 

In one division of Rhizopods — that including the Globigerinae 
and Orbitolites — the foraminifers are calcareous ; in another, they 
consist of agglutinated sand ; in another (that of the Polycystines^ 
they are siliceous. 

In another section of Protozoans called the Flagellate Infusoria., 
and including the Monad, there is a permanent mouth, and often a 
slender process {^flagelliuji) which appears to serve the mouth by 
pushing in food. The animals are much more minute than the 
Rhizopods, To this section, as Prof. H. James Clark has shown, 
belong the sponges — a sponge being a compound group of these 
living infinitebimals 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 — occasionally large enough to be visible to the 
-naked eye — often grow in clusters resembling somewhat those of 
the Hydroids and Bryozoans. 



IV. NAMES OF SPECIES IN THE AUTHOR'S 
REPORT ON ZOOPHYTES. 



The following catalogue contains the names that are now accepted for the 
<^pecies 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 prepared for this place by Prof. Verrill, and the 
explanatory Notes have been added by him. 





NAMES IN THE AUTHOr's REPORT. 


NAMES NOW ACCEPTED, WHEN DIFFER 


PAGE 






ING FROM THOSE OF THE REPORT. 


159- 


Euphyll 


la pavonina 


Flabellum pavoninum Lesson. 






anthophyllum 


,, anthophyllum^. &= II. 






spheniscus 


,, spheniscus £. &= //. 






rubra 


,, rubrum E. or' II. 






spinulosa 


Desmophyllum spinulosum Vcrrill. 






glabrescens 


unchanged. 






gracihs 


,, 






aspera 


Eusmilia aspera E. d^ //. 






aperta 


,, fastigiata L. 6^ H. (?) 






costata (p. 720) 


,, costata Verrill. 






rugosa 


unchanged. 






turgida 


j> 






meandrina 


Euphyllia fimbriata E. ^ II. 






sinuosa 


Pterogyra sinuosa E. &= H. 






cultrifera 


cultrifera E. &- H. 




170. 


Ctenophyllia pectinata 








(not of Lani.) 


Pectinia Danoe E. ^ H. 






quadrata 


,, quadrata E. &= II. 






pachyphylla 


,, pachyphylla E. e^ //. 






profunda 


, , profunda E. er= //. 


174 


Mussa ' 


fastigiata 






jj 


carduus 


unchanged. 




j> 


angulosa 


>> 




>» 


corymbosa 


>} 



328 




NAMES OF SPECIES. 




NAMES IN THE AUTHOR's REPORT. 


NAMES NOW ACCEPTED, WHEN DIFFER- 


PAGE 






ING FROM THOSE OF THE REPORT. 


174. 


Mussa 


cactus 


unchanged. 




^j 


costata 


5 J 






sinuosa (not of Ellis) 


Mussa tenuidentata E. &= II. 




»5 


cytherea 


unchanged. 






multilobata 


>> 




^^ 


cerebriformis 


5J 




^^ 


regalis 


5 ) 




5> 


crispa (not of Lam. ) 


Mussa Indica Verrill, and Mussa radian 
Verrill. 




J » 


clipsacea 


Isophyllia dipsacea Verj-ill. 






fragilis 


,, fragilis Verrill. 




'> 


gyros 


Colpophyllia gyrosa E. <^ II. 






recta 


unchanged. 




j^ 


nobilis 


5) 


189. 


Manicin 


a amarantum 


Tracyphyllia amarantum E. &= //. 




5> 


fissa 


Colpophyllia. 






arealata 2 


Manicina areolata E/ir. 




J) 


meandrites 








hispida 

pra^rupta 

dilatata 




195- 


Tridacophyllia lactuca 


unchanged. 


196. 


5) 


paeonia 


j> 




J, 


manicina 


j> 


198. 


Caulast 


rcea furcata 


5 J 


199. 


}> 


distorta 


J > 






undulata 


_j> 


205. 


Orbicella^ radiata 


Orbicella radiata Dana. 




,, 


argus 


,, cavernosa Verrill. 




?> 


glaucopis 


,, glaucopis Dana. 




>j 


patula 


Acanthastrcea patula E. &> II. 




;> 


ciirta 


Plesiastrrea curta E. &= H. 




)> 


rotulosa 


Astrtea rotulosa Lam. 




>) 


coronata 


Plesiastraea coronata E. &" H. 




J> 


hyades 


Solenastraea hyades Verrill. 




9 ; 


excelsa 


,, excelsa Pour talcs. 




?» 


pleiades 


,, pleiades Ve7'rill. 




5> 


annularis 


Orbicella annularis Dana. 






stellulata 


,, stellulata Dana. 




,, 


stelligera 


Plesiastraea stelligera E. &^ H. 




,, 


crispata 


Ulastrcea crispata E. 6^ //. 




>» 


microphthalma (not 








of Lam.) 


Cyphastrsea Dan?e E. 6- //. 




J> 


ocellina 


,, ocellina E. &= H. 


720. 




orion 


Orbicella orion Dana. 


205. 


Siderina galaxea 


Siderastrsea radians Verrill. 


205. 


Astraea 


(Fissicella) speciosa 


Astrcea'* speciosa Dana. 




>> 


•,, 11 va 


Dichocoenia uva E. ^ II. 




)> 


, , ananas 


Astra;a ananas Lam. 




»> 


, , pandanus 


,, pandanus Dana. 




>> 


,, puteoliaa 


,, puteolina Dana. 



NAMES OF SPECIES. 



329 



NAMES IN THE AUTHOk's KKI'OKT. 
PACE 

205. Astrrea (Fissicella) pallida 
dinsacea 

,, ,, porcata (not 

of B.sper) 
,, ,, flexuosa 

,, ,, fusco-viridis 

,, ,, virens 

,, ,, echinata 

,, ,, fragilis 

,. ,, tenella 

,, ,, magnifica 

(not oiBv.) 
,, ,, filicosa 

,, ,, versipora 

., ., ,, (var.) 

,, ,, denticulata 

{not of Lam.) 
,, ,, pectinata 

,, ,, deform is 

, , , , var. dedalina 

,, ,, varia 

rigid a 
,, ,, reticularis 

[notof Lc7m.) 
,, ., petrosa 

,, ,, purpurea 

,, ,, pulchra 

,, ,, pentagona 

,, ,, favistella 

,, ,, van, from 

Wakes I. 
,, >> eximia 

,, ,, sinuosa 

,, ,, melicerum 

,, ,, , parvistella 

, , , , favulus 

,, ,, cerium 

,, ,, intersepta 

(not of Lam.) 
,, ,, abdita 

,, ,, tesserifera 

,, ,, robusta 

,, 5, complanata ( 

,, ,, heliopora 

,, figured 
,, ,, Hemprichii 

,, ,, halicora 

,, ,, cyclastra 

, , , , favosa 

254. Meandrina dedalea (not oi Ellis) 
,, spongiosa 



NAMF.S NOW ACCKl'TED, WHEN DJFFEK 
ING FROM THOSE OF THE KEl'ORT. 

Astrxa pallida Dana. 
Acanthastra.»a dipsacea VcrrilL 

Astnva Dana; Verrill. 
Prionastra^a flexuosa Verrill. 

,, fusco-viridis EJ. <^ If. 

,, virens E. &^ II. 

AcanthastrKa echinata E. cr^ L. 
Astr^a fragilis Dana. 
Acanthastreea tenella Verrill. 

Prionastraea spectabilis l^crrill. 
Orbicella filicosa Verrill. 
Astra^a versipora Lain. 
,, Putnami Verrill. 

,, cellulosa Verrill. 

,, pectinata Dana. 
Aphrastrrea deformis E. 6^ //. 
Coeloria daedal ina Verrill. 

,, spongiosa, var. E. cr^ //. 
Isophyllia rigida Verrill. 

Prionastrsea Agassizii E. &^ II. 
Dichocoenia petrosa Verrill. 
Leptastrrea purpurea Verrill. 

,, pulchra Ve^-rill. 

Goniastraea pentagona Verrill. 

,, favistella Verrill. 

Astr^a Pacifica Verrill. 
Goniastraea eximia E. &^ II. 
Prionastriea sinuosa Verrill. 

,, melicerum E. &^ II. 

Goniastraea pai-vistella E. &^ II. 
Prionastraea favulus Verrill. 
Goniastraea cerium E. &^ H. 

Plesiastraea armata Verrill. 
Prionastrcea abdita E. &= H. 

,, tesserifera E. &^ II. 

,, robusta E. &> II. 

?) ,, complanata E. &^ II. 

Orbicella heliopora Verrill. 
Prionastraea valida Verrill. 
Prionastraea Plemprichii E. 0-= //. 

,, halicora E. &= II. 

Astraea cyclastraea Dana. 
Prionastraea favosa E. er^ //. 
Cceloria dcedalina, var. Vei'rill. 
,, spongiosa E. &= H. 



330 



NAMES OF SPECIES. 



NAMES IN THE AUTHORS REPORT. 
TAGE 

205. Meandrina labyrinthica 

,, strigosa 

, , inteiTupta 

,, rustica 

,, valid a 

, , phrygia (not of Ellis) 
gracilis 

,, tenuis 

,, filograna 

,, cerebriformis 

,, truncata 

, , mammosa 

,, cylindrus 

, , caudex 
266. Monticularia microcona 

,, lobata 

,, polygonata 

270. Phyllastraea tubifex 

271. Merulina ampliata 

, , regalis 

,, speciosa 

,, crispa 

, , folium 

, , scabricula 

,, laxa 

, , rigida 
278, Echinopora undulata 

,, vosularia 

,, ringens 

,^ reflexa 

, , aspera 

,, horrida 
289. Fungia cyclolites 

,, tenuis 

,, glans 

,, discus 

, , agariciformis 

,, var. tenuifolia 

,, dentata 

,, echinata (not of /'rt'//(7.y) 

,, var. from Feejees 

,, repanda 

, , integra 

,, confertifolia 

,, horrida 

,, actiniformis 

,, crassitentaculata 

,, Paumotensis 

,, dentigera 

,, scutaria 

,, pectinata 



NAMES NOW ACCEPTED, WHEN DIFFER- 
ING FROM THOSE OF THE REPORT. 

Mreandrina labyrinthiformis Verrill. 
unchanged. 



INlDsandrina rudis I crrill. 
Leptoria gracilis E. ^ H. 
, , tenuis E. dr^ H. 
Mceandrina clivosa (young) Verrill. 
Diploria cerebriformis E. &= H. 

,, truncata E. &= H. 
Mseandrina clivosa Verrill. 
Dendrogyra cylindrus EJir. 

,, caudex E/ir. 

Hydnophora microconos E. &= H. 
,, exesa E. ^ H. 

'» polygonata E. &^ //. 

unchanged. 



Hydnophora Demidoffi Fischer. 

Clavarina scabricula Verrill. 

unchanged. 

Hydnophoro rigida E. &^ H. 

unchanged. 



Trachypora aspera Verrill. 
Acanthopora horrida Verrill. 
Cycloseris cyclolites E. c2r=. //, 

„ tenuis Verrill. 

,, glans Verrill. 
unchanged. 
Fungia patella E. &^ H. 

,, tenuifolia Dana (not E. ^ H. 
unchanged. 
Fungia Dance E. &f H. 

,, lacera Verrill. 
unchanged. 



Lobactis Paumotensis Verrill. ^ 

,, Dance Verrill. 

Pleuractis scutaria (Ag. MSS.) Verrill. 

Ctenactis echinata (Ag. MSS.) Verrill. 



NAMES OF SPECIES. 



33* 



NAMES IN THE Al'THOR S KEl'OKT. 
■.\(,V. 

289. Fungia Ehrenbergii 
,, var. gigantca 
,, asperala 
,, Ruppellii 
,, crassa 
107. Hcrpetolithus limacinus 
,, interniptus 

,, foliosus 

., stcllaris 

,, strictus 

,, crassus 

\ I. Ilalomitra pileus (not of Linn. ) 
13. PolyphylHa talpa 

,, leptophylla 

„ sigmoides 

,. pelvis 

,, fungia 

,, pileiformis 

,, galeriformis 

,19, Zoopilus echinatus 
,21. Pavonia explanulata 
,, crispa 
, , papyracea 
,, elephantotus (not of 
Pallas) 
,, cactus 
,, pvsetorta 
,, formosa 
., venusta 
,, divaricata 
,, boletiformis (not of 
Lnin.) 
„ frondifera 
,, decussata 
,, lata 
,j crassa 
,, var. loculata 
,, siderea 
,, latistella 
,y clavus 
;35, Agaricia (Undaria) iindato 

,, „ rugosa (not 

of Lam.) 
,, ,, speciosa 

,, ,, levicollis 

,, ,, planulata 

,, (Mycedia) cucullata 
)» ,, purpurea 

fragilis 
, , , , gibbosa 

,, ,, agaricites 



NAIMKS NOW ACCEPXrcn, WHEN niFFRK- 
INr, KKOM THOSR OK TIIK KKl'OKT. 

Ctenactis Ehrenbergii VerrilL 

,, gigantea Verrill. 

,, asperata Ferfi'll. 

,, echinata Verj-ill. 

,, crassa Verrill. 
Herpetolitha limax Esch. 



unchanged, 

Ilalomitra clypeus Verrill. 
Cryptabacia talpina E. e7= IL 

,, leptophylla E. &^ II. 

,, sigmoides Verrill. 
unchanged. 

Lithactinia pileiformis E. ^ II. 

,, galeriformis E. &^ II. 
unchanged. 

Podabacia Crustacea E. &= LI. 
Haloseris crispa E. &^ H. 
Leptoseris papyracea Verrill. 

IVlycediiim elegans E. <^ II. 
unchanged. 



Pavonia Danoe Verrill. 
unchanged. 



Pavonia loculata Verrill. 

Siderastrcea siderea Blainz'. 

unchanged. 

Siderastra^a clavus Verrill. 

Undaria^ undata Dana. 

,, monticulosa VerrilL 

,, speciosa Dana. 

,, levicollis Dana. 

Asteroseris planulata Verrill. 
Mycedium elephantotus E. ^11. 
Agaricia purpurea Les. 
Mycedium fragile Verrill. 
Agaricia gibbosa Dana. 

, , agaricites E. cr= //. 



332 



NAMES OF SPECIES. 



PAGE 

335- 
345- 



NAMES IN THE AUTHORS KEl'OKT. 

Agaricia (Mycedia) cristata (not 

of Lam,) 
Psammocora obtusangula 

,, plicata (act of 

Lam.) 
,, fossata 

column a 



NAMES NOW ACCEPTED, WHEN DIFFER- 
ING FROM THOSE OF THE REPORT. 

Agaricia Dance E. *>= H. 
unchanged. 

Psammocora frondosa Vcrrill. 
unchanged. 





,, exesa 


5 J 


349- 


Monomyces anthophyUum 


Flabellum anthophyUum E. of IL 




, , eburneus 


Cai-yophyllia cyathus Lam. 


370' 


Cyathina cyathus 
,, pezita 


»> j> 




,. Smithii 


,, Smithii Stokes. 




, , turbinata 


,, clavus Scacchi. 


375- 


Desmophyllum dianthus 


Desmophyllum crista-galli E. &-' H. (? 




,, stellaria 


unchanged. 


376. 


Culicia stellata 


,, 




,, tenella 


>i 




, , truncata 




379- 


Caryophyllia cespitosa 


Cladocora cespitosa Forbes. 




,, conferta 


,, conferta^. ^ II. 




,, flexuosa 


steUaria E. ^ H. (?) 




,, arbuscula 


,, arbuscula Edia. 




,, cornigera 


Dendrophyllia cornigera. 




,, anthophyUum 


Lophohelia anthophyllites E. ^^ IL 




,, sohtaria 


Astrangia solitaria Verr'Ul. 




, , pocilkim 


Phyllangia pocillum Verrill. 




,, dilatata 




385. 


Dendrophyllia ^ ramea 

,, micrantha 
,, nigrescens 
. , aurantiaca 


unchanged. 




,, coccinea 


Dendrophyllia DauEe Verrill. 




,, diaphana 


unchanged. 




,, rubeola 






,, scabrosa 


Balanophyllia scabrosa Verrill. 


391 


Oculina hirtella 


Sclerohelia hirtella E. &> IL 




,, horrescens 


Acrohelia horrescens E. &= H. 




,, prolifera 


Lophohelia prolifera E. &^ H. 




, , axillaris 


Cyathohelia axillaris E. er= H. 




, , varicosa 


unchanged. 




,, oculata 






,, pallens 


unchanged. 




,, virginea 


Lophohelia oculata Pourt. 




,, diffusa 


unchanged. 


399 


AnthophyUum musicale 


Galaxea musicalis Oken. 




,, fasciculatum 


,, fascicularis Oken (in part). 




,, astreatum 


,, astrceata E. &^ H. 




, , cespitosum 


,, cespitosa Verrill. 




,, hystrix 


,, hystrix Verrill. 




,, cuspidatum 


,, cuspidata Oken. 



NAMES OF SPECIES. 



333 



r.MiE 

399- 
404. 
406. 

409. 



414. 



418. 



420, 



423. 



435- 



491 



NAMES IN THE AITHOK S REl'OKT. 

Anthophyllum clavus 
Stylina echinulata 
Astroitis caliculaiis 

,, viridis 

Gcniniipora palifera 
,, peltata 

,, patula 

,, crater 

,, cinerascens 

,, frondens 

, , brassica 

Astra:opora pulvinaria (not of 
Lam. ) 
,, punctifera 

,, fungiformis 

,, stellulata 

Isaura Hemprichii 
,, Saviguii 
,,. aster 
,, speciosa 
Zoantha Ellisii 
,, sociata 
,, Solandri 

,, dubia 
,, Bertholetii 
Palythoa denudata 
,, auricula 
,, nymyhaea 
,, fuliginosa 
,, mammillosa 
,, ocellata 
,, glareola 
,, flavo-viridis 

,, argus 
,, caesia 
Madrepora 

Names of species unchanged ex- 
cept the following : 
No. 23, corymbosa(not ofZa;//. ) 
,, 26, plantaginea (notofZaw.) 
,, 28, acervata 
,, 56, secunda 

,, 90, deformis (not of Mich.) 
Manopora 

Names of species unchanged, ex- 
cept the following : 
No. i,gemmulata 
,, 6, crista-galli (not of Z/zr. ) 
,, 7, spumosa (not of Lam.) 
,, 8, circumvallata 
,, 9, foliosa (not of Pallas) 



NAMES NOW ACCEPTED, WIIEX DIFFKN 
ING IROM THOSE OF THE REPOKT. 

Calaxea clavus E. 6^ //. 
unchanged. 

Goniopora viridis E. &= IL 
Turbinaria palifera LI. ^ LL. 
peltata E. &- LL 

,, patula E. &= IL 

,, crater Oken. 

,, cinerascens Oh'f/. 

,, frondens Verrill. 

„ brassica E. ^^ II. 

Astroeopora profunda Vcnill. 
unchanged. 

Turbinaria fungiformis Verrill. 
stellulata E. 6^ //. 
unchanged. 



Zoanthus Ellisii Lmih. 
,, sociatus Lc's. 
,, Solandri Les. 
,, dubius L6's. 
,, Rertholetti Z'//r. 
Mammillifera denudata E/ir. 
,, auricula Les. 

,, nymphrea Les 

,, fuliginosa E/zr. 

unchanged. 



Madrepora. 



Madrepora convexa (young) Da ft a. 

,, appressa (var.) Dana. 

,, plantaginea Lam. 

,, nobilis (var.) Dana. 

,, Dame Verrill. 

Montipora. 



Turbinaria gemmulata Vtrrill. 
Montipora aspera Verrill. 
M. hispida (var.) Dana. 
M. monasteriata E. o^ H. 
M. Ehrenbergii Verrill. 



334 



NAMES OF SPECIES. 



NAMES IN THE AUTHOR S REl'ORT. 



NAMES NOW ACCEPTED, WHEN DIFFER- 
ING FROM THOSE OF THE REPORT. 





No. 21, 


nudiceps 




M. crista-galli E. &= H. 




,, 25, 


tuberculosa (not of Lam.) 


M. Danc« E. d^ H. 


5"- 


Alveopora retepora 




unchanged. 




jj 


dedalea (from 


Red 


5 > 




>i 


Sea) ( 


speci- 








men figured) Alveopora Verrilliana Dana. 




,, 


spongiosa 




unchanged. 




»5 


rubra 

fenestrata 

viridis 




Montipora rubra E. &= H. 
unchanged. 


515- 


Sideropora digitata 




Stylophora digitata E. 6^ H. 




5> 


elongata 

pistillata 

subdigitata 

palmata 

mordax 




,, YL'i'ixW.dXz. Schwei^ger. 

,',' Dan.x E. ^ H. 
,, mordax Verrill. 


519- 


Seriatopora subulata 




ttnchanged. 




11 


lineata 
hystrix 
octoptera 




?» 




) > 


caliendrum 




,j 




»» 


var. gracilis 




Seriatopora gracilis Dana. 




J J 


vaiida 




unchanged. 


523- 


Pocillopora 




Pocillipora. 




Names of species unchanged, 






excepting : 








No. 3 


brevicornis (var. 


from 








Sandwich Islands). 


Pocillipora cespitosa Dana. 




„ 6, 


favosa (var. from Feejees) 


,, Dante Verrill. 




9) 


,, (var. from 


Sand 








wich Islands) 


,, aspera Verrill. 




„ 7, 


verrucosa (var. from 
wich Islands) 


Sand 


,, nobilis Verrill. 




„ 15, 


plicata (var. from 
wich Islands) 


Sand- 


,, aspera (var. lata) Vernll 


540 


Helio 


Dora coerulea 




unchanged. 


543 


Millepora alcicornis 




j» 




,, 


moniliformis 




Millepora alcicornis (var.) Linn. 




,, 


ramosa 




unchanged. 




,, 


pumila 




,, 




,, 


tortuosa 




>> 




,, 


plicata 








,, 


complanata 




A variety of plicata. (?) 




,, 


squarrosa 




unchanged. 




,, 


platyphylla 




>> 




,, 


■ mordax 




,, 




5) 


compressa 
clavaria 




>> 




5 J 


flexuosa 






551 


. Ponies fuvcata 




5 J 




J) 


recta k 




Porites furcata (var. ) Lam. 



NAMES OF SPECIES. 



335 





NAMES 


IN THE AUTHOR S KEl'OKT. 


NAMES NOW ACCEPTEIJ, WHICN 


UH-I-K 


I'AGE 






ING FKOM THOSE Ol' THE KErOKl 


551. 


Pontes divaricata 


unchanged. 






,j 


conferta 


>> 






5» 


nigrescens 

var. mucronata 

lalmata 

evis 

cylindrica 

contigua (not of Esper) 
astra^oides 

conglomerata (not 
Lam. 
lobata 
fragosa 
limosa 


Porites mucronata Dana. 
unchanged. 

SynariTca Dana Vcrrill. 
unchanged. 

1 Porites lutea E. &^ 11. 
unchanged. 






>> 


favosa 


J5 






>> 


cribripora 

informis 

erosa 

monticulosa 

lichen 


Synarrea informis IWrilL 
,, erosa Verrill. 
,, monticulosa Verrill. 

unchanged. 






59 


reticulosa 
arenacea 


5> 

Porites arenosa E. &= H. 




569. 


Goniopora pedunculata 


unchanged. 






j> 


columna 


>» 






_?j 


Savignyi 


»> 




571. 


EiTina 


aspera 


>> 




575. 


Antipathes "^ spiralis 


»> 








anguma 


>> 






^, 


larix 


>> 






>> 


eupteridea 








5» 


pectinata 


Hyalopathes pectinata E. d- 


//. 






myriophylla 


unchanged. 








subpinnata 


•>■> 








reticulata 


j> 








flabellum 


j> 






,, 


ericoides 


>» 






>> 


mimosella 


>> 








pinnatifida 


j> 






M 


cupressus 


>) 






5> 


paniculata 
pennacea 
scoparia 
foeniculum 


>> 








corticata 


Hyalopathes corticata E. d^ 


H. 






lacerata 


unchanged. 






" 


pyramidata 
Boscii 


Hyalopathes pyramidata E. 
unchanged. 


or H. 




J) 


alopecuroides 
arborea 
dichotoma 


5J 






,, 


glaberrima 


Leiopathes glaberrima E. &= H. 




,, 


compressa 


,, compressa E, (^ 


H. 



336 NAME OF SPECIES 

^ The genus, 3fussa, as here restricted, inckides both Miissa and Sym- 
phyllia of JNIihie-Edwards and Haime, — different specimens of the same 
species sometimes dififei-in<^ in the same way, and to the same extent, as do 
these two so-called genera. The only difference given, is dependent upon 
the mode of growth. 

2 It is probable that this, and some of those following it, are only varie- 
ties of one species. 

2 The name Orbicella is now restricted to the genus of which O. annu- 
laris and 0. cavernosa are types. This group is equivalent to Heliastrcca 
ot Edwards and Haime, of more recent date. 

"* The genus, Aslrcra, is here restricted to the group of which A. rotulosa 
is the type. This was the original type named by Lamarck, in i8oi, when 
the genus Astrcea was first established. The genus, thus limited, is equiva- 
lent to Favia of Oken, 1 815. 

^ The genus, Undaria, is equivalent to Pachyseris Edwards and Haime, 
of later date. 

^ Ca:nopsa7nmia is recombined with Dendrophyllia, 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 farmer genus has a smaller number of lamellae, — a charac- 
ter that is by itself seldom of generic value. 

■^ The genus, Antipathes, as here adopted, includes Cirrhipathes, AracJi- 
ttopaihes, and Rhipidopathes of Edwards and Haime. Those divisions were 
based only upon the modes of growth and branching, which are quite 
insufficient for establishing genera among Polyps. 



V. LIST OF WORKS AND MEMOIRS REFERRED TO, 
AND OF ABBREVIATIONS. 



A. Ag. Alexander Agassiz, and Mrs. L. Agassiz. Seaside Studies in 

Natural History, 158 pp. 8vo., Boston, 1871. {]. R. Osgood 

& Co). 
Ag. L. Agassiz. Contributions to the Natural History of the United 

States. 4to., vols. iii. and iv., on Acalephs. 
Report on i)eep-Sea Dredgings in the Gulf Stream, during the 

third cruise of the U. S. Steamer Bibb. Bulletin of Mus. Comp. 

Zool, No. 13. 
Am. T- Sci. American Journal of Science and Arts, New Haven, Ct. ist 

series of 50 vols., 1818-1845 inch ; 2nd series of 50 vols., 

1 846- 1 870, inch ; 3rd series from 1 87 1. 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; 2nd 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, ou Polypes proprement dits. 3 vols. 8vo., Paris, 
1 85 7- 1 860. Parts of the work published earlier in the Annales 
des Sci. Nat., and Archives du Mus., since 1847. H. Milne 
Edwards also published I vol. on Zoophytes, in 2nd 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 Curiou 
and Uncommon Zoophytes. I vol. 4to., London, 1786. 

EsPER. E. T. C. Esper. Die Pflanzenthiere, etc. 4 vols. 4to. Nurem- 
berg, 1 79 1 eis^q. 

Z 



338 



LTST OF WORKS REFERRED TO. 



GosSE. Philip Henry Gosse, F. R. S. Actinologia Britannica ; a History 
of the British Sea- Anemones and Corals, with Coloured Figures 
of the species and principal varieties. 362 pp. 8vo., London, 
i860. (Van Voorst.) 

Hartt. Ch. Fred. Hartt. Geology and Physical Geography of Brazil ; 
620 pp. Svo. 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. 

Leidy. Joseph Leidy, M. D. Contributions toward a Knowledge of the 
Marine Invertebrate 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. 

.I>ES. C. A. Lesueur. Description de plusieurs animaux appartenant aux 
Polypiers lameUiferes 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, I vol. 8vo. Histoire Naturelle des Animaux sans 
Vertebres. Paris, 1815-1822, 7 vols. 8vo. 

I^AMX. J. V. Lamouroux. Histoire des Polypiers tlexibles. I vol. 8vo., 
with many Plates. Caen, 1816. 

Exposition Methodique des genres de I'Ordre des Polypiers. 
Quarto, with 84 Plates, 63 of which are from Ellis and Solan- 
der. Paris, 1821. 

MoBius. Dr. Karl Mobius. Ueber den bau, den Mechanismus und die 
Entwicklung der Nesselkapseln einiger Polypen und Quallen. 
24 pp. 4to., with 2 Plates ; Abh. Nat. Vereins zu Hamburg, 
erstes Heft des fiinften Bandes. Hamburg, 1866. (G. E. 
Nolte.) 

PouRT. C. F. de Pourtales. Deep-Sea Corals, 94 pp. 4to., with 8 
Lithographic Plates. Cambridge, 1 87 1. No. 4 of the Illus- 
trated Catalogue of the Museum of Comparative Zoology. 

St. Stimpson, in papers, by A. E. Verrill. 

V. A. E. Verrill. Revision of Polyps of the Eastern Coast of the 
United States, 46 pp. 4to., with a Lithographic Plate. Cam- 
bridge, 1864. Mem. Bost. Soc. Nat. Hist., vol. i. 

List of Polyps and Corals sent by the Museum of Compara- 
tive Zoology to other institutions, in exchange, with Annotations. 
Bulletin Mus. Comp. Zool., vol. i , No. 3. 1864. 

Corals and Polyps of the North Pacific Exploring Expedition, 
under Commodore C. Ringgold, and Capt. John Rodgers, 
U.S.N., from 1850 to 1856, collected by 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 Corals and Echinoderms collected by Prof. C. F. 
Hartt, at the Abrolhos Reefs ; No. 6, Review of the Corals 
and Polyps of the West Coast of America ; No. 7, Memoir on 
the Geographical Distribution of the Polyps and Corals of the 
West Coast of America. Trans. Connecticut Academy of Arts 
and Sciences, vol. i,. 1868 to 1870, pp. 351-570 ; 8vo., with 7 
Plates. New Haven. 



LIST OF WORKS REFERRED TO. 339 

V. A. K. Vkrrill. On the Parasitic habits of Crustacea. American 
Naturalist, vol. iii. p. 239, July, 1869. Salem, Mass. 

Also several other Papers on Corals, in the Proceed ngs of 
the Boston Society of Natural History, and Amcr. Journal 
of Science. 

Wilkes. Charles Wilkes, U.S.N. Narrative of the United States 
Exploring Expedition, during the years 1838, 1839, 140, 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 1837. 



) 



\ 



Z 2 



INDEX. 



ACALKPHS, characters of, 323 

Acontia, 15 

Aiou, 262 

Actinacea, 40 

Actinaria, 40 

Actinoid Polyps, 5 

Aciamsia pall lata, 16 

Admiralty Islands, 264 

Africa, reefs of eastern, 268 

Agassiz, L., on Astrangia, 46 

,, depth of reef corals, 90 

,, coral borers, 95 

,, on Florida reefs, 169 

,, on Bahamas and Salt 

Key Bank, 1 74 et seq. 

Agassiz, A., on Arachnactis, 11, 
,, Seaside Studies, 46, 

80 

Ahii, 138 143, 148, 164 

Aitutaki, 288 

Aiva, 224 

Alcyonacea, 58 

Alcyonium, derivation of term, 57 

Alcyonoid, polyps, 57 

Almirante, 268 

Aveopora, 54 

,, spongiosa, 54 
,, Verilliana, 54 

Andrews, on Molokai and Maui, 
292 

Anguilla Key, 179 

Antipathacea, 42 

Antipathes arborea, 41 

Anthea cereus, 19, 36 
,, flagellifera, 19 

Anthelia lineata, 59 

Apaiang, elevation of, 134, 294 

Apamama, 132, 294 

Apatite on Mauke, 254. 

Apia on Upolu, harbour of, 204 

Aratica, 143, 146, 166 

Ami Group, 265 

Ascension Island, 306 

Asia, temperature of ocean along 
the east coast of, 256 

Asia, 262 



Astrrca pallida, 36, 43 
Astra;acea, 43 

„ distribution of, 84 

Astrangia Dance, 46 
Atiu, 158, 260, 288, 310 
Atlantic Ocean, subsidence in, 316, 

317 
Atolls, structure of, 130, 131, 141 
Atoll reefs, origin of, 211 

,, origin of lagoons of, 

218, 227 
,, completed, 233 
Aurora Island, 158 
Australian reefs, 107, 113, 118, 264, 

265, 282 
Bahamas, 174, et seq. 
Bahama region, subsidence in, 316 
Bailey, J. W., on absence of fora- 
minifers from chalk of Oahu, 

309 
Baker's Island, 248, 291 
Balbi, remarks on encircling reefs, 

228 
Barrier reefs, origin of, 218, 219 
Beach formations, 149 
Beechey, on Henderson Island, 159 

,, soundings by, 139 

,, remarks on Gambler 
Islands, 227 

„ on Elizabeth Island, 286 

,, on Ducie's and Osnaburgh 

,, Islands, 286, 287 

Benaze, rate of growth of reef at 

Tahiti, 2i6« 
Bermudas, corals of, 88 ; structure 

of islands, 149, 182, 185 

,, geological character of 
the, 185 et seq. 

,, the result of an upheaval 
of the ocean bed, 186 

,, former height and extent 
of, 185, 187, 317 

,, caverns of, 310 
Beveridge reef, 289 
Biche-de-Mar, 129 
Birds of Coral Islands, 242 



342 



INDEX. 



Bimie's Island, i6o, 248, 292 
Bischof, composition of sea-water, 

75 
Bolabola, 287 
Borneo, 265 
Bowditch's Island, 135, 136, 163, 

235 
Branchiae in Actiniae, 19 
Brazil, corals of, 88 

,, reefs, iii, 269, 270 
Brooks's Island, 217, 293 
Bryozoans, 81 
Budding in Actiniae, 20 
Budding in Coral Polyps, 27 
Bunodes gemma, 5 
Byron, of the Blonde, apatite on 

Mauke, 254 
Calaminianes, 265 
Calicle, 23, 24, 28 
California Gulf, corals of, Zd 
Cancrisocia expansa, 7 
Cape St. Ann, 269 
Carlshoff, 136, 143, 146, 166 
Caroline Archipelago, 137 

,, ,, elevations in, 295 

Caryophyllia cyathus, 22 

,, Smithii, lasso cell, 13 

,, ,, animal of, 46 

Carysfort Island, 139 
Caulastraea furcata, 37, 42, 71 
Caverns in coral limestone, 158, 310 
Celebes, 265 
Ceylon, reefs of, 268 
Chaetetes, 81 

Chagos Bank, 155, 156, 268 
Chalk, origin of, 308 
,, of Oahu, 309 
Channels among reefs, 118 
Charlotte's Island, 294 
China, coast of, free from corals, 267 
Christmas Island, 140, 290 
Cladocora arbuscula, 34, 48, 71 
Clarke, H. J., on budding in 

Actiniae, ii 
Classification of Actinoid Polyps, 40 
Clermont Tonnerre, 138, 286 
Cnidae, 13 
Cocoanut Grove, on Bowditch 

Island, 235 

,, ■ tree, 239 
Coenenchyma, 39 
Columella, 24 

Commensalism in polyps, 7, 42 
Cook, Capt,, on Christmas Island, 

290 



Cophobelemnon clavatum, 68 
Corals changed to a phosphate by 

guano, 249 
Corals, rate of growth of, 96 
,, temperature limiting, 83 
,, influence of impure and fresh 

waters on distribution, 93 
,, injured by boring animals, 

95 
Coral, precious, 67 
Coral Heads, no, in, 114 

,, islands, forms and features, 

130 
,, ,, birds of the Pacific, 

242 
, , , , poor place for human 

development, 246 , 
Coral-makers, 3 
Coral mud and sand of bottom, 113, 

119, 147-150, 197 
Coral reefs, rate of growth of, 212. 
,, benefits from, 127 

»j geographical distribution 

of, 258, et seq. 
Coral Reef Harbours, 128 

,, seas, extent of, 257 

Coral rocks, consolidation of, 122, 

305 
Coral sands, formation of, 113, 191, 

299 
Coral sand-rocks, 122, 124, 125, 299 
Corallet, 28, 39 
Corallidae, 67 
Corallines, 83 
Corallium from the Sandwich Islands, 

67 
Corallium rubrum, 66 
Corallulum, 39 
Corallum, 23, 28, 39 

,, composition of, 74, 81 

,, hardness of, 74 
Comora Islands, 268 
Corynactisviridis, lasso-cells, 13 — 15 
Coryne, 77 
Cosmoledo, 268 
Couthouy, J. P., on Anthea flagel- 

lifera, 17 
Ctenactis echinata, 25, 44. 
Currents in Atoll channels, 137, 138 

,, among reefs, 204, 205 
Cyathophyllia cyathus, 22, 46 

,, clavus, 46 

Cyathophylloids, 55 
Dana's Report on Zoophytes, names 
of species, of 327 



INDEX. 



343 



Dana's Report on zoophytes, size ot 
edition of, 70 

Darwin on depth of reef corals, 89 
,, rate of growth of corals, 96 
,, origin of coral mud, 194, 195 
,, thickness of reefs, 126 
,, on sountiings, 139 
,, on the Maldives, 148 — 153 
,, on the Great Chagos Bank, 

135 

,, on the Oambier Islands, 
227, 228 

,, on the Maldives, 232 

,, geographical distribution of 
coral reefs, 258 

,, on consolidation of coral 
sands, and change of posi- 
tion with the seasons, 306 
Dead-men's fingers, 60 
Dean's Island. 136, 166, 285 
Depth of reef-corals, 89 
Dendrophyllia arborea, 52 
,, cornigera, 52 

,, nigrescens, 31, 51 

Depeyster Island, 137, 293 
Diego Garcia, 139 
Diploria cerebriformis, 44 
Disappointment Islands, 138 
Dissepiments, 39 
Distribution of corals, 83, 89 
Dolomite, formation of, 307 
Dolomitic nature of coral rock of 

Matea, 308 
Dorippe facchino, 7 
Drift sand-rock, 150 
Drummond's Island, 294 
Ducie's Island, 286 
Duke of Clarence's Islands, 136,289 
Duke of York's Island, 163, 289 
Duffs Islands, 262 
Eap, 262 

Easter Island, 259 
Echinoderms, characters of, 323 
Echinopora reflexa, 23 
Echthoraea, 16 
Edwards & Haime, Phyllangia 

Americana, 47 
Edwardsia callimorpha, 8, 21 
Egmont Island, 139 
Elevations in the Pacific, 286 
Elizabeth Island, an elevated coral 

island, 286 
EUice's Island, 293. 
Enderbury's Island, 147, 151, 161, 

248, 291 



Endotheca, 39 

Eoa, 260, 288 

Epiactis prolifera, 21 

F^pitheca, 39 

P^scharella variabilis, 82 

Eugorgia aurantiaca, 64 

Eunicclla, 64 

Eupagurus pubescens, 40 

Evans, Lieut., consolidation of coral 

sands of Ascension Island, 306 
Exotheca, 39 
Fanning Group, 290 
Fakaafo, 135, 136, 163, 234 
Favosites, 80 

„ relation to Alveopora, 

54, 55 
Peejees, corals of, 85 

„ delta of Rewa, 208 
„ reefs of, 221, 227, 279, 280 
„ elevations among, 293 
Feis, 295 

Fission, fissiparity, 36 
Fissures in reef-rock, 143 
P'itzroy, Capt., soundings by, 139 

„ temperature about 

the Galapagos, 256 
Flint's Island, 291 
Florida Reefs, soundings, etc., 140, 

167, et seq 
Florida Region, subsidences in, 316 
Flustra, 80 

Foraminifers of reefs, 122, 377 
Forchammer, magnesia in some 

corals, 75 
Four Crowns, 161 
Fresh-water lagoon at the island of 

Quiros, 242 
Fungacea or Fungia tribe, 44 

„ distribution of, 84 
Fungia echinata, 25 

„ lacera, 25, 26 

„ DcJnae, 45 
Galapagos, temperature about, 

Fitzroy, 256 
Gambler Group, 126, 227, 259, 281, 

282 
Gardner's Island, 292 
Gemmipora, 52 
Geographical distribution of coral 

reefs, 255 
Geological time, subdivisions of, 321 
Gilbert Islands, 132, 137, 149, 237, 

261 

,, elevations in, 295 

Glacial era synchronous with the era 



344 



INDEX. 



of the coral island subsidence, 

315 

Globigerinos, nature of, 325 
Globigerina mud, 1 14 
Goniopora columna, 32, 71, 73 
Gorgonacea, 61 
Gorgonia flabellum, 62 
,, flexuosa, 62 
,, quercifolia, 63 
Gorgonise, spicules of, 63 
Crosse, P. H., species of Peachia, 
Edwardsia, etc,, 
from his British 
Sea- Anemones, 8 
,, on lasso-cells, 15 

,, on spontaneous fis- 

sion in Anthea, 36 
,, mention of his work, 

British Sea-Ane- 
mones, 70 
Guam, 262 

,, elevation of, 295 
Guano, birds contributing to, 242, 

245 
Guano islands of Pacific, 248 
Gulf Stream, influence of, in the 
Oolitic and Cretaceous eras, on 
the temperature of the Atlantic 
Ocean, 311, 312 
Gypsum on coral islands, 251 
Hague, J. D., sands shifted in posi- 
tion with the season, 
202 
,, on guano islands of 

Pacific, 248, 254 
,, on birds of Pacific 

coral islands, 242 
Hale, H., on Gilbert Islanders, 238 
,, on subsidence at Ponape, 
283 
Halocampa chrysanthellum, 9 
Hapaii Group, 260, 289 
Haplophyllia paradoxa, 57 
Harbours and channels, conditions 
determining the formation and 
condition of, 201, 210 
Hartt, C. F., corals of Brazilian 
coast, 88 

,, Brazil reefs, in 

Hawaian chain, length of, 365 

,, ,, western coral atolls 

of, 261, 277, 281 

,, ,, northwestern part, 

soundings in, 139 

Hawaian Islands, corals of, 86 



Hawaian Islands, elevations at, 292 

Hawaii, reefs of, 261 

Heliopora, 80 

Henuake, 134, 148, 162, 284 

Henderson's Island, 139, 159 

Hero Island, 253, 290 

Hervey Group, elevations in, 287 

Hogoleu, 261 

Holothurians, characters of, 324 

Holothuria dried, 129 

Honden, See Henuake 

Home Island, 261, 293 

Horsburgh, J. J., on the Maldives, 

153 
Howland's Island, 251, 291 
Huahine, shells of, at elevations, 287 
Hull's Island, 292 
Hunt, E. B., rate of growth of 

corals, 98 
,, ,, -on Florida Reefs, 

reference to paper 
by, \6-i et seq. 
Hunter's Island, 262 
Hydra, 77 

Hydrallmania falcata, 78 
Hydroids, 76, 80 
Indian Ocean, reefs of, 267 

,, subsidence in, 317 

Isis hippuris, 65 
Isothermal or isocrymal chart, 83, 

256 
Jarvis's Island, 135, 159, 250, 290 
Jones, J, M., on the Bermudas, 

185—188 
Jukes, Australian reefs, 113, 147 
Julien, on guano minerals, 253 
Kao, 260 
Kawehe, 146, 165 
Kauai, 261, 277, 292 
Reeling's Island, 139, 268 
Kent, W. S., on Vertillum cyno- 

morium, 69 
Key West, 167 tt seq. 
Kingsmills. See Gilbert Group 
King's Island, 162 
Kophobelemnon. See Cophobele- 

mon. 
Kotzebue, on water of coral islands, 

242 
Kuria, 134, 140, 294 
Kusaie, 261 
Lacaze Duthiers, on Corallium 

rubrum, 67 
Laccadives, 268 
Ladrones, 261, 280 



hVDEX. 



345 



Ladrones, elevations in, 294 

Lafu, 263 

Lagoon, a freshwater, at the island 

of Quiros, 242 
Lagoons of atolls, 147, 148 
Lasso-cells, 13, 14 
Leptogorgia, 63 

Level, changes of, in the Pacific, 272 
Life and death in concurrent pro- 
gress, 70 
Lime in sea-water, 75 
Limestones, formation of, 299 

,, beds of, with living 

margins, 301 
,, thick strata of, 301 
,, subsidence essential to 
the makinij of thick 
strata of, 301 
,, deep sea, from coral 
reef debris, rarely 
made, 302 
., rate of increase of, 309 
,, unfossiliferous, 302 
, , difference of continental 
and modern oceanic, 
302 
,, consolidation of, 305 
Lisiansky, soundings by, 139 

,, on islands northwest of 
Kauai, 261 
Lixo coral reef. 1 1 1 
Logs on coral islands, 245 
Los Guedes, 262 
Los Matelotas, 262 
Ldochoo, 266 
Louisiade Group, 264 
Loyalty Group, 263 
Lucina Pennsylvanica, 177 
McAsKiLL Islands, 261 
Mackenzie Island, 262, 295 
Madagascar reefs, 268 
McKean's Island, 248, 253, 2 
Madrepora aspera, 29, 50 
,, formosa, 51 

,, cribripora, 50, 94 

,, of wreck, amount of con- 

tribution from, to reef, 
213 
Madreporacea, distribution of, 85 
Madreporaria, 42 
Mseandrina cerebriformis. See 

Diploria 
Mseandrina clivosa, rate of growth 

of, 98, 215 
Maeandrina labyrinthica, 43, 98 



Magnesia in corals, 75 

Mahlos Mahdoo Atoll, 154 

Maitea, 260 

Maiana, 134, 294 

Makin, 134 

Maiden's Island, 248, 290 

Maldives, 130, 131, 139, 153, 268 

,, map of, 152 
Mangaia, elevation of, 287 
Marakei, 134, 295 
Mangaia, 260 
Manhii, 165 
Manopora, 52 
Manual, 288 
Margaret, 160 
Marquesas, 259, 278 
Marshall Islands, 137, 148, 295 
Matea, dolomitic nature of coral 

rock of, 307 
Maui, elevation of, 293 
Mauke, 260, 288 
Melitsea, 66 

Menchicoff Island, 137, 230 
Mendana, 262 
Metia, 131, 158, 286 
Metridhim marginatum, lasso-cell, 13 
Millepora alcicornis, 79, 80 
Mitiaro, 260, 296 
Minerals of coral islands, 248 
Mobius, K., on lasso-cells, 13 
Molluccas, 265 
Molokai, elevation of, 292 
Montipora, 52 
Moresby, Capt. on the Maldives and 

Chagos Bank, 139, 153, 157 
Mountain chains buried in the ocean, 

314 
Mud of channels and lagoons, 113 

120, 147—149, 197 
Muricaea, 64 
Mussa, 43 

Nairsa, 136, 166, 285 
Namuka, 289 

Navigator Group, 260, 279, 289 
Necker Island, 261 
Nelson, on Bermudas, 183 

,, on the Bahamas, 176 — 178 
Nettling Cells, 13 
New Britain, 264 
New Caledonia reefs, 105, 106, ii8, 

263 
New Guinea, 264 
New Hebrides, 262 
New Ireland, 264 
Newmarket, 292 



346 



INDEX. 



New Zealand Old Hat, 197 
Nonouti, 132, 136, 291 
Norfolk Island, 263 
Nukunono, 289 
Nullipores, 82, 141 
Oahu, 261, 277 

f,, caverns in elevated coral 

reef of, 310 
,, chalk of, 308 
Oatafu, 289 
Oceanic currents carry away little 

detritus from islands, 113, 114 
Oceanic subsidence, proofs of, 314 
Ocean Island, 278, 293 
Ocean, the Tongue of the, 176 
Oculinacea, 45, 85 
Oculina diffusa, growth of, 98, 215 

,, varicosa, 48 
Okatutaia, 288 
Old Hat, 197 
Oolite, 122, 125 
OoHtic rocks of Florida Keys, 167, 

181 
Orbicella cavernosa, 35 
Orbicellid^e, 45 

Orbit olites about Australian reefs, 121 
Orbitolites, relations of, 325 
Organ-pipe Coral, 61 
Otuhu, 160 
Pacific, elevations in, 284 

,, axis of subsidence in, 273, 
280 

,, subsidence in by broad 
anticlinals and syncli- 
nals, 280 

,, chain, central length of, 

365 
Pali, 24 

Palao. See Pelews. 
Palmyra Island, 290 
Panama, corals of, 86 
Pandanus, 240 
Paractis rapiformis, 6 
Paumotus, 86, 136, 238, 259 
,, elevations in, 285 
Pavonaridse, 70 
Peachia hastata, 8 

Peacock's Island, 138, 143, 148, 164 
Pearl and Hermes Reef, 278 
Penrliyn's Island, 291 
Pelews, 262, 295 
Pennatulacea, 68 
Pennatulidse, 69 
Peritheca, 39, 73 
Persian Gulf, reefs in, 268 



Pescadores, 137, 283 
Phoenix's Island, 248, 291 
Philippine Islands, 267 
Phosphate of lime collected on a 
coral island by Lord Byron of 
the Blonde, 254 
Phymactis clematis, 5 

,, florida, 5 
Pitcairn's Island, 259, 278 
Plants of Paumotus, list of, 238, 239 
Plexaurella, 64 
Pliobothrus, 80 
Pocillipora, 49 
Pocillipora grandis, 49 

,, elongata, cell of, 49 

,, plicata, cell of, 49 

Polyps, classification of, 3, 21, 57 
Ponape, 256, 283 
Porites family, Poritidae, 52 
,, size of some, 116 
„ levis, 55, 56 
„ mordax, 33, 55 
Port Natal, 268 
Pourtales, L. F. de, on Thecocyathus, 

24 
,, ,, on Haplophyllia, 

57 
,, ,, on rate of growth 

of corals, 98 
,, ,, bottom of Florida 

reefs, 114 
., ,, depth of reef 

corals, 90 
,, ,, on Florida region, 

172—174 
Pouynipete, 261 

Powell, Lieut., on the Maldives, 153 
Protozoans, characters of 377 
Pumice on coral islands, 246 
Pylstaarts, 260, 289 
Quelpaert's Island, 266 
Quiros Islamp, 242 
Quoy and Gaymard, depth of reef 

corals, 90 
Radiates, characters of, 322 
Raivavai, 288 
Rapa, 259 

Raraka, 136, 138, 164 
Rarotonga, 288 

Redearth of the Bahamas, and its 
uses, 175, 178 ; of the Bermu- 
das, 186 
Red Sea corals, 90, 268 
Reefs, formation of, 189 

„ causes modifying forms of, 203 



INDEX. 



347 



Reefs, rate of growth of, 212 

„ of windward side highest, 201 
Renillidx. 70 

Reproduction in Actinia?, 19 
Revillagigedo Islands, 259 
Rimetara, 288 
Ringgold, Capt., on Penrhyn's and 

other islands, 291 
Rivers, effects of, 205 
Rock, appearance and composition 

of Bahama, 177 
Rocks, consolidation of coral, 121 

—123, 305 
Rose Island, 282 
Rota, elevation of, 297 
Rotuma, 261, 294 
Rurutu, 260, 261 
Rurutu, an elevated island, 288 
Sagartia parasitica, 17 
St. Augustine shell rock, 310 
Sala-y-Gomez, 259 
Salomon Islands, 264 
Salt Key Bank, 174 
Samoa. See Navigator Group 
Sandwich Islands, elevations at, 

292 ; see further Hawaian 
Savage Island, 289 
Savaii, 279 
Saya-de-Malha, 268 
Schomburgh, R. H., drift sands of 

Anegada, 150 
Sea-cucumbers, 129 
Sea, depths of disturbance by waves, 

291 
Sea-ginseng, 129 
Sea-slugs, 129 

Sea-water, composition of, 75 
Seriatopora, 49 
Senses in Actinice, 19 
Septa, 23, 39 
Serle's Island, 138 
Seychelles, 268 

Sharpies, S. P., analyses of corals, 75 
Sherboro Island, 269 
Shore-platform, origin of, 196 
Siau, M., on ripple marks at the 

bottom of the sea, 191 
Silliman, B., analysis of dolomitic 

coral rock of Matea, 307 
Silliman, B., anyalysis of coral sand 
of Straits of Balabac, 

307 
Society Islands, 260, 274, 281 
Somers' Islands, 182 



Sooloo Sea, 265 
Soundings about atolls, i 
Sponges, nature of, 321 
Spontaneous fission, 36 
Starbuck's Island, 253, 290 
Starve Island, 253 
Staver's Island, 291 
Stevenson, force of waves, 191 
Stimpson, \Vm., observations by, 8, 

59, 60, 68 
Stones of basalt or other rocks on 

coral islands, 246 
Strombas gigas, 177 
Stutchbury, on Rurutu, 288 
Stylaster erubescens, 48 
Stylo phora Danae, 49 
Subsidence in the Pacific, 272, 281 
,, amount of land lost by, 

280 
,, period and extent of, 

and accompanying 
changes over the 
globe, 314 
Sunday Island, 261 
Swain's Island, 135, 160, 289, 
Sydney Island, 162, 292 
Synapticulae, 39 
Tafua, 261, 289 
Tahiti, north shore of, 206 
,, thickness of reef, 127 
,, no elevation at, 287 
Taiara, 135, 162 
Tanna, 263 
Tapateuea, 132, 136, 149 

„ elevation of, 294, 297 

Tarawa, 132, 134 

Tarawan Archipelago. See Gilbert 
Tari-tari, 134, 136 
Tealia crassicornis. See Urticina 
Teku, 161 

Telesto ramiculosa, 60 
Temperature limiting distribution of 
corals, ZT) 
„ of Atlantic Ocean in 

past time, 312, 313 
„ chart, 256 

Tetuaroa, 260, 279 
Thecocyathus cylindraceus, 23 
Tikopia, 263 
Timor, 265 
Timorlaut, 265 
Tinakora, 263 
Tonga Islands, 288 
Tongatabu, 261, 288 



INDEX. 



Tongue of the Ocean, the, 176 

Tripang, 129 

Tmk, 261 

Tubipora fimbriata, 61 
„ syringa, 61 

Tubuai, 260, 288 

Tubularia, 77 

Tuomey, M., on Florida reefs, 167 

Tutuila, 261, 279 

Tyerman on Huahine, 287 
„ on Rurutu, 288 

Ualan, 262, 283 

Umbenularid?e, 70 

Upolu, 261, 279 

„ thickness of reef, 126 
„ harbour of, at Apia, 205 ; 
at Falifa, 208 

Urticina crassicor. lasso-cells, 13-17 

Vanikoro Group, 262 

Vavau, 260, 289 

Veretillum Stimpsoni, 68, 69 

, , cynomorium, phosphor- 

escence of, 69 

Verrill, A. E., on Cancrisocia ex- 
pansa, 7 ; on Epi- 
actis prolifera, 21 ; 
on coral secretion, 
22 ; classification of 
Actinoid corals, 40 ; 
compartments in 
Alcyonia all ambu- 
lacral, 58 ; Anthelia 
and Telesto, 60 ; 
spicules of Gor- 
gonise, 63 ; on a 
species of Veretil- 
lum and Cophobe- 
lemnon, 68 ; on 
corals of Panama, 

86 ; corals of La 
Paz, JS6 ; corals of 
the West Indies, 

87 ; corals of the 
Brazilian coast, 87 ; 
corals of the Bermu- 
das, 87 ; Whipple's 
observations on co- 
rals of a wreck, 
99, 100; accepted 
names for species in 
Dana's Zoophytes, 
327—336 J 



Vincennes Island, 146, 165 

Virgularidae, 70 

Volcanic action, effect of, in limit- 
ing the distribution of corals, 
257, 264, 273 

Vorticella, nature of, 374 

Vulcano, 264 

Waihu, 259 

Wallis's Island, 261, 293 

Washington Island, 140, 161, 290 

Wateoo or Atiu, 288 

Water on coral islands, 241 

Waterlandt, 165 

Waves, action of on coasts, 196 — 
199 
,, force of, Stevenson, 191 

West Indies, corals of, 87 

Weinland, L). F., rate of growth of 
corals, 97 

Whippey Harbour, 209 

Whipple, J. A., corals from a wreck, 
99, 100 

,, ,, coral heads of Turk's 
Island, 1 10, III 

Whitnell, S. J., on ElUce Island, 

293 
,, ,, freshwater lagoon on 
Quiros Island, 242 
Whitsunday Island, 139 
Williams's Missionary Enterprises, 
260 
,, rock and caverns of 

Atiu, 158, 310 
,, on Mangaia, Atiu, and 

Rurutu, 287, 288 
Williams, S. W., on Biche-de-mar, 

129 
Wilson's Island, 165 
Winds about coral islands, 254 

„ effects of, 200 — 203 
Wolchonsky, 136 
Xenia Uan^, 58 
,, elongata, 59 
,, florida, 58 
Yap or Eap, 262 
Zoanthacea, 40 
Zoanthus Americana, 40 
Zoophyte, 27. 28 

Zoophytes, names now used for 
species in Dana's Report on, 
Verrill, 379 
Zoothome, 28, 39 



34 

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