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OBSERVATIONS OF A NATURALIST IN THE
PACIFIC BETWEEN 1896 AND 1899

NA RARO (2,420 feet) from the south-west, a peak of acid andesite.

NDRANDRAMEA (1,800 feet) from the south-east, a peak of acid andesite rising about a thousand feet from its base.

[Frontispiece.

OBSERVATIONS OF

A NATURALIST IN

THE PACIFIC BETWEEN

1896 AND 1899

BY

H. B. GUPPY, M.B., F.R.S.E.

VOLUME I

VANUA LEVU, FIJI

A description of its leading Physical and Geological characters

London

MACMILLAN AND CO., Limited

NEW YORK; THE MACMILLAN COMPANY

1903

All rights reserved

Richard Clay and Sons, Limited.

BREAD STREET HILL, E.C., AND

BUNGAY, SUFFOLK.

Dedication

TO THE FIJIAN PEOPLE

PREFACE

During a sojourn in the Pacific, which covered a period of rather over a year in Hawaii (1896-97), and of two years and three months in Fiji (1897-99), my attention was mainly confined to the study of plant-distribution and to the examination of the geological structure of Vanua Levu.

With Hillebrand’s “Flora of Hawaii” always in my hands I roamed over the large island of Hawaii, ascending the three principal mountains of Mauna Kea, Mauna Loa, and Hualalai, and in the case of my second ascent of Mauna Loa spending twenty-three days alone on its summit. Similarly in Fiji, Seemann’s “Flora Vitiensis” was my counsellor and guide in the matter of plants.

In Hawaii I was in a land of active sub-aerial volcanoes, and I paid my devotions at all the altars of “Pele,” their presiding deity. In Fiji I trod upon the surface of submarine volcanoes that emerged ages since from the ocean and still retain their coverings of sea-deposits. Both in Hawaii and Fiji I lived much among the people; and though my chief interest lay in the comparison of these two types of volcanic islands, I could not but be drawn to the kindly natives whose hospitality I so long enjoyed.

Destiny led me to Vanua Levu in the following fashion. With the relief party to take me down from Mauna Loa there arrived a well-known German naturalist who, like myself, had been interested in coral-reef investigations. We discussed this warm topic at an elevation of nearly 14,000 feet above the sea, with the thermometer at 20° F. As we sipped our hot coffee and listened to the occasional “boom” from the bottom of the great crater, at the edge of which we were camped, I remarked to my friend that I was thinking of spending some months in Samoa. To this he good-humouredly replied that I might leave Samoa to his countrymen and describe one of the large islands of Fiji. International rivalry over that group of islands was then rather keen. However, Dr. K. went to Samoa, and I have now completed this volume on the geology of Vanua Levu, Fiji.

It will not be necessary to lay stress here on the difficulties and hardships connected with the exploration of little known tropical regions. Many will be familiar with all that these imply, where the rainfall ranges from 100 to 250 inches, where the forests are dense, where tracks are few and swollen rivers are numerous, and where the torrent’s bed presents often the only road.

The only extensive geological collections made in Fiji previous to my visit were those of Kleinschmidt in 1876-78, which together with a small collection previously made by Dr. Gräffe were examined by Dr. A. Wichmann. These rocks were obtained from Viti Levu, Kandavu, Ovalau, etc., but not from Vanua Levu. Dr. Wichmann’s paper of 1882, descriptive of these collections, presents us with the results of one of the earliest studies by modern methods of research of the volcanic rocks of the Pacific Islands. It is to this investigator that we are indebted for the establishment of the occurrence of plutonic rocks, such as granites, gabbros, diorites, in Viti Levu.

Although, as far as I can ascertain, few, if any, rocks have been specially described from Vanua Levu, this island was visited by Dana in 1840 when attached to the United States Exploring Expedition under Wilkes. His observations on its geology were published in his volume on the geology of the expedition. Although not extensive they are valuable from their reference to his discovery of trachytic and rhyolitic rocks as well as acid pumice-tuffs in the island. It is singular that his observations have apparently been overlooked by all his successors. Wichmann with this discovery unknown to him remarked on the seeming absence of quartz-bearing recent eruptive rocks from the South Seas.

When the “Challenger” Expedition visited the group in 1875 some geological collections were made which were described by Prof. Renard in the second volume on the “Physics and Chemistry” of the expedition. No collections, however, were made in Vanua Levu. In 1878 Mr. John Horne, Director of the Botanic Gardens at Mauritius, made some important observations on the geological structure of this island and of other parts of the group, which he published in his account of the islands given in “A Year in Fiji.” No collections were obtained by him; but prominence is given to his observations by Dr. Wichmann and others. Like Dana in the case of the acid volcanic rocks, Mr. Horne has forestalled me in his conclusion that Vanua Levu amongst the other larger islands has been formed mainly of the products of submarine eruptions.

The visit of Prof. A. Agassiz to Fiji in 1897-98 gave a fresh impetus to its geological investigation. We are indebted to him not only for his own extensive memoir on the islands and coral reefs of this group, but also for the subsequent important explorations of Mr. E. C. Andrews and Mr. B. Sawyer in Viti Levu and the Lau Islands. These two gentlemen have since published a short paper on the caves of these islands. Mr. Eakle has described the volcanic rocks collected during the visit of Prof. Agassiz. It is, however, noteworthy that, although the collections were made in Viti Levu, Kandavu and in many other of the smaller islands, Vanua Levu is not represented. Mr. Eakle’s conclusion that basic andesites and basalts are the characteristic rocks of the region, the augite-andesites predominating, would apply to Vanua Levu in great part. This island possesses also in fair amount hypersthene-andesites and dacitic or felsitic andesites, which are very scantily represented in the collections examined by Mr. Eakle. In connection with the quartz-porphyries and trachytic rocks which also occur in Vanua Levu, it should be observed that Mr. Andrews describes a rhyolite from Suva in Viti Levu. Unlike Viti Levu, Vanua Levu displays but a small development of plutonic rocks.

In conclusion it should be pointed out that much remains to be done in the geological exploration of this island, and that I would have spent a third year in this task much to my profit. Still I hope that a period of two years devoted to its investigation will be regarded as some excuse for a certain over-confidence in the expression of my opinions.

To enumerate all those from whom I received much kindness in these islands would be a lengthy task. My indebtedness is very great to Bishop Vidal, Father Rougier, and to various other members of the Roman Catholic Mission, and I experienced similar favours at the hands of Mr. Williams and other Wesleyan Missionaries in Vanua Levu. Mr. F. Spence and Mrs. Spence showed me great kindness, and from Dr. Corney I received valuable assistance on my arrival in the group. To the planters my debt is equally great, more especially to Mr. Barratt, Mr. Dods, and Mr. Mills.

In conclusion I would suggest the foundation of a “Fijian Society” for the investigation of the islands, for the gathering together of all that has been written about the group and its people, and for the advancement of science.

Henry Brougham Guppy.

June, 1903.

Note.—A type set of my geological collections representing the massive rocks from this island has been kindly accepted by the Curator of the Geological Museum, Jermyn Street.

LIST OF SOME OF THE PRINCIPAL AUTHORITIES QUOTED IN THIS BOOK

Dana, J. D., on the Geology of Fiji in vol. x, Geology, United States Exploring Expedition Reports, Philadelphia, 1849.

Kleinschmidt, T., “Reisen auf den Viti-Inseln,” Journal des Museum Godeffroy, heft 14, Hamburg, 1879.

Horne, J., “A Year in Fiji,” London, 1881.

Wichmann, A., “Ein Beitrag zur Petrographie des Viti-Archipels, Mineralogische und Petrographische, Mittheilungen,” band v, heft 1, Wien, 1882.

Renard, A., on andesites from Kandavu, “Report on the Petrology of Oceanic Islands,” vol. ii of “Physics and Chemistry,” Challenger Expedition, 1889.

Agassiz, A., “The Islands and Coral Reefs of Fiji,” Bulletin, Museum of Comparative Zoology, Harvard College, vol. xxxiii, 1899, Cambridge, Mass.

Eakle, A. S., “Petrographical Notes on some rocks from the Fiji Islands,” Proceedings, American Academy of Arts and Sciences, vol. xxxiv, no. 21, May, 1899.

Andrews, E. C., Notes on the limestones and general geology of the Fiji Islands, with special reference to the Lau Group. Based upon surveys made for Alexander Agassiz. With a Preface by T. W. Edgeworth David. Bulletin, Museum of Comparative Zoology, Harvard College; vol. xxxviii, Cambridge, Mass. 1900.

CONTENTS

CHAPTER I

GENERAL INTRODUCTORY REMARKS ON SOME OF THE LEADING PHYSICAL

FEATURES OF THE ISLAND

Its remarkable shape, [1].—Its building up, [2].—Study of its profile, [3].—Mount Seatura.—Regions of acid andesites.—Basaltic tablelands.—Great ridge-mountains, [5].—Boundary of the regions of basic and acid rocks, [6].—Its primary features, the dacitic peak, the basaltic plateau, and the ridge-mountain

Pages [1-6]

CHAPTER II

ON THE EVIDENCE OF EMERGENCE OR OF UPHEAVAL AT THE SEA-BORDERS

Elevated coral reefs scantily represented, [7].—Apparent absence of coral reefs in the early stages of the emergence, [8].—Elevated reefs confined to the coast and its vicinity.—Detailed examination of the sea-borders, [9].—Silicified corals and siliceous concretions the only evidence in many localities of the upraised reefs, [13].—The relations of the mangrove-belt to the reef-flat, [14].—Indications of a very gradual movement of emergence in our own time, [15].—The rate of advance of the mangroves, [16].—Conclusions, [19]

Pages [7-20]

CHAPTER III

THE HOT SPRINGS OF VANUA LEVU

The thermal springs of other parts of the group, [21].—The hot springs of the Wainunu valley, [22].—The boiling springs of Savu-savu, [25].—Analyses of the water, [28].—The hot springs of other localities, [31].—Distribution of the springs, [35].—The algæ and siliceous deposits, [37].—The cold and thermal springs of Hawaii and Etna, [38].—Infiltration, the source of the springs, [39].—A view negatived by Prof. Suess.—List of the hot springs of Vanua Levu, [40].—Summary of the chapter, [42]

Pages [21-42]

CHAPTER IV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES OF

VANUA LEVU

Naivaka, [43].—Korolevu Hill, [45].—Bomb formation of Navingiri, [46].—Remarkable section near Korolevu, [48].—Wailea Bay to Lekutu, [50].—Mount Koroma, 51.—Mount Sesaleka, [53].—The Mbua-Lekutu Divide, [55].—The Mbua and Ndama plains, [55].—The shell-bed of the Mbua river, [58].—Lekumbi Point, [60]

Pages [43-60]

CHAPTER V

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

Mount Seatura, [61].—Its eastern slopes, [63].—Its western slopes, 64.—Its northern slopes, [65].—Ascents to the summit, [66].—The Ndriti Basin, [67].—A huge crateral cavity, [68].—Its dykes of propylite, [69].—Seatura a basaltic mountain of the Hawaiian order, [72].—The Seatovo Range, [73].—Solevu Bay, 75.—Koro-i-rea, [77].—Nandi Bay, [78].—Na Savu Tableland, [79]

Pages [61-81]

CHAPTER VI

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The basaltic plateau of Wainunu, [82].—Its margins covered by pteropod and foraminiferous ooze-rocks, [86].—The hill of Ulu-i-ndali, [87].—Kumbulau Peninsula, [90].—The basaltic flow of Kiombo Point, [92].—Soni-soni Island, [93].—Yanawai coast, [95]

Pages [82-97]

CHAPTER VII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Ndrandramea district, [98].—Its mountains and hills of acid andesites, [100].—Ngaingai, 101.—Ndrandramea, [102].—Soloa Levu, [103].—The underlying altered acid andesites, [106].—Section of the district, [107].—The magnetic peak of Navuningumu, [108].—The Mbenutha Cliffs and their pteropod and foraminiferous beds, [109]

Pages [98-112]

CHAPTER VIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

Mount Vatu Kaisia and district, [113].—The Nandronandranu district, [117].—Nganga-turuturu cliffs, [119].—Ndrawa district, [120].—Tavia ranges, [121].—Na Raro, [123].—Its Ascent, [125].—Na Raro Gap, [127]

Pages [113-127]

CHAPTER IX

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The basaltic plains of Sarawanga, [129].—Tembe-ni-ndio and its foraminiferal limestones, [131].—The basaltic plains of Ndreketi, [132].—The Nawavi Range, [135].—Nanduri, [136].—Tambia district, [137].—The basaltic plains of Lambasa, [138]

Pages [128-139]

CHAPTER X

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Va Lili Range, [140].—Its Nambuni spur, [144].—Originally submerged and covered with palagonite-tuffs and agglomerates, [145].—The Waisali Saddle, [146].—Narengali district, [147].—Nakambuta, [148].—The valleys of the Ndreke-ni-wai, [150].—Their origin, [151]

Pages [140-152]

CHAPTER XI

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Korotini Range, [153].—Traverse from Waisali to Sealevu, [154].—Traverse from Mbale-mbale to Vandrani, [156].—Traverse from Vatu-kawa to Vandrani, [160].—Traverse from Nukumbolo to Sueni, [161].—The Sueni valley, [163].—General inference concerning the range, [164]

Pages [153-165]

CHAPTER XII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Koro-mbasanga Range, [166].—The Sokena Ridge, [169].—Lovo valley, [169].—Mount Mbatini, [172].—The Vuinandi Gap, [175].—The Thambeyu or Mount Thurston Ranges, [176].—Structure of Thambeyu, [177].—The Avuka Range, [179]

Pages [166-180]

CHAPTER XIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Valanga Range, [181].—Its western flank, [183].—Ngone Hill, [183].—Valley of Na Kula, [184].—The Mariko Range, [185].—Savu-savu Peninsula, [189].—Naindi Bay, [192].—The Salt Lake, [194]

Pages [181-196]

CHAPTER XIV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Natewa Peninsula, [197].—Viene district, [198].—Lea district, 199.—Waikawa Mountains, [201].—Ndreke-ni-wai coast, [203].—Waikatakata, [203].—Mount Freeland or the Ngala Range, [204].—Traverse from Tunuloa to Ndevo, [205].—Coast from Ndevo to Mbutha Bay, [205]

Pages [197-206]

CHAPTER XV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The north-east portion of the island from Mount Thurston to Undu Point, [207].—Coast between Vuinandi and Tawaki, [208].—The corresponding inland region, [209].—The gabbro of Nawi, [211].—Uthulanga Ridge, [211].—Ascent of Mount Vungalei or Ndrukau, [213].—Nailotha, [214].—Exposure of altered trachytes and quartz-porphyries at its base, [215].—From Nandongo to Vanuavou, [216].—From Ngelemumu to Wainikoro, [217].—Sea border between Lambasa and Mbuthai-sau, [218].—Coast between Mbuthai-sau and the Wainikoro and Langa-langa Rivers, [219].—Coast between the Langa-langa River and Thawaro Bay, [221].—The Globigerina clay of Visongo, [221].—Vui-na-Savu River, [222].—Some General inferences, [223]

Pages [207-223]

CHAPTER XVI

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

(continued)

The Wainikoro and Kalikoso Plains, [224].—Vaka-lalatha Lake, [225].—Its floating islands, [226].—A region of acid rocks, [227].—Silicified corals and limonite, [228].—Tawaki district, [229].—Thawaro district, [230].—Mount Thuku, [231].—Undu Point, [232].—General characters of the Undu Promontory, [233]

Pages [224-234]

CHAPTER XVII

THE VOLCANIC ROCKS OF VANUA LEVU

Their varied character, [235].—Their classification, [236].—Descriptive formula, [237].—Synopsis, [239].—Orders of the Olivine-Basalts, [241].—Orders of the Augite-Andesites, [245].—Orders of the Hypersthene-Augite-Andesites, [247].—Description of the Plutonic Rocks, [249]

Pages [235-251]

CHAPTER XVIII

THE VOLCANIC ROCKS OF VANUA LEVU (continued)

The Olivine Basalts

Pages [252-265]

CHAPTER XIX

THE VOLCANIC ROCKS OF VANUA LEVU (continued)

The Augite-Andesites

Pages [266-284]

CHAPTER XX

THE VOLCANIC ROCKS OF VANUA LEVU (continued)

The Hypersthene-Augite-Andesites

Pages [285-292]

CHAPTER XXI

THE VOLCANIC ROCKS OF VANUA LEVU (continued)

THE ACID ANDESITES, TRACHYTES, QUARTZ-PORPHYRIES.

The Hornblende-Andesites of Fiji, [293].—Occurrence of Dacites in Fiji, [294].—Suggestion of “felsitic andesite” as a rock-name, [295].—The Acid Andesites of Vanua Levu, [295].—The Hypersthene-Andesites, [296].—The Hornblende-Hypersthene-Andesites, [298].—The Quartz-Andesites or Dacites, [302].—Tabular comparison of the Acid Andesites, [304].—The characters of the Rhombic Pyroxene, [306].—Magmatic Paramorphism, [306].—The Oligoclase Trachytes, [308].—Quartz-Porphyries and Rhyolitic rocks, [309]

Pages [293-311]

CHAPTER XXII

THE VOLCANIC ROCKS OF VANUA LEVU (continued)

Basic pitchstones and basic glasses, [312].—Volcanic Agglomerates, [314]

Pages [312-316]

CHAPTER XXIII

CALCAREOUS FORMATIONS, VOLCANIC MUDS, PALAGONITE-TUFFS

General Character, [317].—Coral Limestones, [318].—Foraminiferal Limestones, [319].—Pteropod-oozes, [320].—Foraminiferous Volcanic Muds, [321].—Samples, [322].—Altered kinds, [324].—Submarine Palagonite-tuffs of mixed composition, [326].—Samples, [330].—Altered Basic Tuffs, [332].—Submarine Basic Pumice Tuffs, [333].—“Crush-tuffs” formed of basic glass and palagonite, [334].—Zeolitic Palagonite-Tuffs, [334].—Palagonite-marls, [335].—Acid Pumice Tuffs, [336]

Pages [317-336]

CHAPTER XXIV

PALAGONITE

Its abundance in a fragmental condition in Vanua Levu, [337].—Its occurrence in deep-sea deposits, [338].—Modes of formation in situ, [338].—In the upper portion of a basaltic flow, [339].—In the groundmass of hemi-crystalline basaltic rocks, [339].—In veins in a basic tuff-agglomerate, [340].—In the fissures of a basaltic dyke, [341].—In the matrix of pitch-stone agglomerates, [349].—In “crush-tuffs,” [341].—Regarded as a solidified magma-residuum of low fusibility, [342].—Its connection with crushing, [342].—Bunsen’s experiment, [343].—Rosenbusch and Renard, [344].—The Nandua series of beds, [345].—Suggested explanation of the origin of palagonite, [346].—Type of basalt associated with palagonite, [347].—Hydration and disintegration of palagonite, [348]

Pages [337-349]

CHAPTER XXV

SILICIFIED CORALS, FLINTS, LIMONITE

Mode of occurrence of the silicified corals, [351].—Their character and structure, [352].—Flints, nodules of Chalcedony, Agates, etc., [353].—Other siliceous concretions, [354].—Jasper, [355].—Deposits of Limonite, [356].—Magnetic Iron-sand, [357].—Suggested explanation of the silicification of the corals, [358].—Note on a silicified Tree-fern, [360]

Pages [350-360]

CHAPTER XXVI

MAGNETIC ROCKS

Previous observations, [361].—Magnetic Polarity usually caused by atmospheric electricity, [362].—Displayed by both acid and basic rocks, [364].—Very frequent in Vanua Levu, [365].—Its relation to specific weight, [366].—The influence of locality, [367].—Frequently observed in mountain peaks, [367].—Description of the peaks, [368].—Measurement of the polarity of rocks, [370]

Pages [361-371]

CHAPTER XXVII

SOME CONCLUSIONS AND THEIR BEARINGS

Vanua Levu, a composite island formed during a long period of emergence, [372].—The submarine plateau probably produced by basaltic flows, [373].—The distribution of the volcanic rocks, [374].—Comparison with Iceland, [374].—The mountain-ridges, [375].—The emergence of the Fiji Islands, [376].—Wichmann’s view of the early continental condition not supported, [376].—Age and character of the emergence, [377].—The evidence of the Lau Group and of the Tongan Islands, [378].—Two principal stages of the emergence, [379].—Relative antiquity of the Hawaiian, Fijian, and Tongan Islands as indicated by their floras, [379].—Islands have always been islands, [380].—The hypothesis of a Pacific continent not yet needed, [381].—The great dilemma, [381].—Much remains to be learned of the possibilities of means of dispersal in the past and in the present, [382]

Pages [372-382]

APPENDIX.

(1) Note on microscopical examination of stone-axes.

(2) Note on the ascent of the tide in the Ndreketi River.

(3) Note on the “talasinga” districts.

INDEX [385]

LIST OF ILLUSTRATIONS

VANUA LEVU,
FIJI ISLANDS.
Drawn on a scale of 25 miles to 3 inches by H. B. Guppy, M.B.
Based on the Admiralty Surveys, but most of the topographical
details of the interior have been supplied from the author’s observations
with the aneroid and prismatic compass in 1897-99. It is
merely intended to illustrate his general account of the physical
and geological characters of the island and is very far from
complete. (see introduction.)

OBSERVATIONS OF A NATURALIST IN THE PACIFIC

CHAPTER I
GENERAL INTRODUCTORY REMARKS ON SOME OF THE LEADING
PHYSICAL FEATURES OF THE ISLAND

The remarkable shape of this island at once attracts the attention: and indeed it is in its irregular outline and in the occurrence over a large portion of its surface of submarine tuffs and agglomerates that will be found a key to the study of its history. With an extreme length of 98 miles, an average breadth of 15 to 20 miles, and a maximum elevation of nearly 3,500 feet, it has an area, estimated at 2,400 square miles, comparable with that of the county of Devon.

Whilst its peculiarly long and narrow dimensions are to be associated with the narrowing of the submarine basaltic platform, from which it rises together with the other large island of Viti Levu, its extremely irregular shape is closely connected with the composite mode of its origin. We have here exemplified the process of the building up of a continental island in the great area of emergence of the Western Pacific, that region which displays at various heights above the sea the ancient reefs and the underlying deposits of the Solomon Islands, New Hebrides, Fiji, Tonga, &c. But this process of construction has never been completed, and is at present suspended; yet it is in its incomplete condition that Vanua Levu possesses its importance for the investigation of this subject.

This island has in fact been formed by the union of a number of smaller volcanic islands during a long protracted period of emergence. These original islands are indicated approximately by the 1,800-feet contour-level in the accompanying map. There is, however, no reason for supposing that the movement of emergence has altogether ceased. In the course of ages the extensive submarine plateau, from which it rises, will be laid bare; and the small surrounding islands that are situated upon it, such as Yanganga, Kia, Mali, Rambi, Kioa, &c., will be included in the area of Vanua Levu.[^[1]]

Excluding for the moment the effects of denudation, which have been very great, we shall be able to discern some of the stages of the building-up of the island during the emergence or upheaval by looking at the map and reversing the process in imagination. A subsidence of only 50 feet would cause the Natewa Peninsula to be isolated by a sea-passage along the line of the Salt Lake; whilst several islands would be formed along the northern and southern coasts, and the Naivaka Peninsula would become detached. If the subsidence extended to 300 feet, the sea would flow over a large portion of the island, where it would regain what was not many ages since its own, an area of basaltic plains, which by their prolongation under the sea form the great submarine plateau. A subsidence of 1,000 feet would break up the remaining elevated axis of the island into a number of lesser portions; and after a total lowering of 1,800 feet there would exist only a few scattered islands, the arrangement of which would show but little relation to the present form of Vanua Levu. At either end of the area there would arise from the sea the isolated volcanic peaks of Seatura and Ngala (Mount Freeland); and between them would be situated four or five long narrow islands, together with a group of small islands and islets where Na Raro and the other acid andesite mountains of the Ndrandramea district now lie.

As might be partly expected, there is in the surface-configuration of the interior of Vanua Levu an absence of that simplicity of contour which exists in a volcanic island of supra-marine formation, as for instance in the large island of Hawaii where the three great volcanic mountains of Mauna Kea, Mauna Loa and Hualalai together with the older Kohala range, determine the form of the whole island’s surface.[^[2]] Here in Vanua Levu there is, on the contrary, but little order amongst its physical features. The rivers often run obliquely with the sea-border, whilst mountains frequently rise at the coast and plains lie far inland, and the view of the elevated interior, as obtained from one of the peaks, presents in many parts a series of mountain-ridges running athwart the island’s axis.

A study of the profile of the island is an important preliminary step to its more detailed examination. One may ramble over a particular region of it for weeks, as I have done, without getting any satisfactory idea of the true configuration of the surface. In a locality densely wooded and occupied by steep mountain ridges and deep gorges, the field of view is often very limited; but seen from the deck of a passing ship the main features of the island assume their true proportions and relations, and much that was uncertain is in this manner made plain. The profile here given has been constructed from a number of others, and represents in a graphic fashion Vanua Levu as viewed from the southward. I have here sacrificed smaller details and occasionally some degree of accuracy in small matters in order to bring out the principal features of the island.

At and near the extreme western extremity rise the conspicuous hills of Sesaleka (1,370 feet), Naivaka (1,651 feet) and Koroma (1,384 feet), all of them formed of basic volcanic materials.[^[3]] Naivaka, which is connected with the main island by a narrow isthmus, only about 30 feet in height, is probably one of the most recent additions to the island’s area; and it is at the same time one of the most recent of the numerous volcanic vents that once existed. The leading feature, however, of this end of Vanua Levu is the great mountain of Seatura (2,812 feet), which occupies a large part of the Mbua province and monopolises most of the landscape whilst largely determining the form of the western extremity of the island. It is a basaltic mountain of the Mauna Loa type, its long eastern slope descending gently at an angle of three or four degrees for about ten miles to the mouth of the Wainunu River. In its deeply eroded radial valleys and gorges, and in other respects, it is not unlike the island of Tahiti, as described by Dana.

The Ndrandramea region to the eastward, which I have named after one of its best known peaks, has a profile of a very different character. Its broken outline indicates the existence of numerous mountains and hills of acid andesites, occasionally dacitic. Although some of them attain a height of 2,000 feet and over their tops alone are seen from seaward. Between the foot of these mountains and the south coast extends a great plateau of columnar basalt, incrusted at its borders with submarine deposits, which descends coastward with a very gentle slope, the fall in about five miles being only about 300 feet (1,100 to 800 feet). It terminates abruptly opposite the elevated headland of Ulu-i-ndali, a range, composed mainly of grey olivine-basalts, which is not indicated in the profile.

Profiles of Vanua Levu as Viewed from the South. Graphically

Represented on a Horizontal Scale of about 16 miles to the inch.

From Naithombothombo Point to Undu Point, representing the length of the island (98 miles).

The Natewa Peninsula from the Salt Lake to Kumbalau Point.

The two conical peaks of Vatu Kaisia (1,880 feet) and Na Raro (2,420 feet), which rise up so unexpectedly in the region immediately east of the Ndrandramea district, are also of acid andesitic rocks, in the last case approaching the dacitic type. They lie within the borders of the area of basic tuffs, basic agglomerates, and basic massive rocks, that here begins and extends eastward to Mount Thurston and a little beyond. East of Na Raro there is a gap or break in the profile, where the greatest elevation is probably not over 800 feet; and on its farther side rises up the mountain of Va Lili (2,930 feet), a lofty inland ridge that lies towards the southern coast. Palagonite-tuffs and agglomerates are the prevailing surface-formations in this district.

Eastwards from Va Lili extends for eight or nine miles a lofty, level-topped, and almost peakless range, which I have called the Korotini Table-land, after the towns once situated on its southern slopes. Its outline is shown in the background of the view facing page [153]. It is, however, not so level-topped as it appears to be; but the gradual variations in elevation between 2,000 and 3,000 feet, when spread over a length of some miles, are more or less lost in the general outline of the range as viewed from the coast. Basic agglomerates are principally exposed on the lower slopes; whilst higher up, reaching often to the summit of the table-land, occur palagonite-tuffs containing tests of foraminifera and molluscan shells, massive basic rocks being exposed in places.

The level profile of the Korotini tableland gives place, as one proceeds eastward, to the broken outline of the several lofty peaks of Mariko (2,890 feet), Mbatini (3,437 feet), Thambeyu (3,124 feet) and others.[^[4]] Each of these peaks marks one of the bold mountain-ridges that form such a striking feature in the surface-configuration of this part of the island. On the slopes of these ridges, and often also on their summits, appear basic agglomerates and palagonitic tuffs and clays often inclosing tests of foraminifera; whilst exposed in the gorges and protruding at times through the tuffs and agglomerates on the crests of the ridges are displayed massive basic rocks of the type of the hypersthene-augite andesites.

East of Thambeyu the level sinks to about 1,000 feet above the sea, and beyond rises an irregular group of hills and mountains which attain their greatest height in Nailotha,[^[5]] 2,481 feet above the sea. We are now near the limit of the area of basic rocks. Following the profile as it slopes away, marked by occasional peaks and breaks, towards Undu Point, we pass at first over a district where basic rocks are mixed with those of more acid type; but before we reach Mount Thuku we enter the district of oligoclase-trachytes, quartz-porphyries, and rhyolitic tuffs, that extends to the extremity of the Undu promontory.

There remains to be noticed the profile of the Natewa Peninsula. As shown in the diagram, this level begins at a few feet above the sea in the vicinity of the Salt Lake; and as it proceeds eastward it attains a level of 1,960 feet in Ngalau-levu and of 1,540 feet in the Waikawa promontory, finally culminating, as it nears Kumbulau Point, in a mountainous district which attains its greatest elevation of 2,740 feet above the sea in the lofty ridge of Ngala, the Mount Freeland of the chart. Altered basic rocks prevail in this peninsula; but more acid andesites also occur, and foraminiferous tuffs and clays are exposed on the slopes, reaching to over 1,000 feet above the sea.

I will conclude this reference to the profile of the island with the remark that if I had neglected to indicate here the close connection that exists between the nature of the surface-configuration and the character of the prevailing rocks I should have ignored a means of investigation which has proved of the greatest value. The rock and surface characters go together. The inland plateau now upheaved 1,000 feet above the sea, was built up by submarine flows of basaltic lava. The isolated conical peak that so unexpectedly intrudes itself into the view is the dacitic core of some submarine volcano long since stripped of most of its fragmental coverings. The lofty mountain-ridges that run athwart the island’s breadth, with their summits usually in the rain-clouds received their coverings of tuffs and agglomerates ages ago when they were submerged; and now they rise to heights of over 3,000 feet above the sea. Bound up with the mysterious origin of these great ridges is the history of the island of Vanua Levu.

These preliminary remarks are only intended to serve as a general introduction to the detailed description of the island and its formations. The closing chapter is devoted to a summary of the principal results of my investigations.

CHAPTER II.
ON THE EVIDENCE OF EMERGENCE OR OF UPHEAVAL AT THE SEA-BORDERS.

One would have expected that in an island where submarine muds and tuffs are of such common occurrence at the surface, extending from the sea-border to elevations of 2,000 feet and over, upraised coral reefs would be also frequent and extensive. But it is remarkable that the uplifted masses of reef-limestone, so characteristic of the islands of the Lau Group, are here very scantily represented. It is certainly true that the fossiliferous volcanic muds that form the foundations of coral reefs are often exposed at and near the coast; but the elevated reefs that ought to be found reposing on them are rarely to be observed.

It is not to be inferred, however, that in a region so remarkable for the great development of reef-formations coral reefs did not then thrive in these localities, but rather that such a long period has elapsed since the emergence of the present sea-border that the upraised coral reefs at and near the coast have long since been in a great part stripped off by the denuding agencies. Notwithstanding this, it is evident that coral reefs could never have been very extensive at the sea-border during the last stages of the emergence; whilst they do not appear to have existed at all during the early periods of the history of the island.

In this connection it may be observed that hard compact limestones of any kind are rarely to be found, and only in a scanty fashion. The extensive development of dolomites and hard limestones, described by Mr. Andrews and others in the valley of the Singatoka in Viti Levu, is not a character of Vanua Levu. The foraminiferous and pteropod clays, which exist in the interior and often in the heart of the island, are not overlaid by ancient reef-limestones, but by great masses of volcanic agglomerate and coarse fossiliferous tuffs, the foraminiferous muds in their turn covering the core of massive volcanic rocks. There were no signs of coral-reef fragments in the volcanic agglomerates in any locality examined, notwithstanding that these agglomerates are so intimately associated with the fossiliferous tuffs and clays that their submarine origin could not be doubted.

The conditions for reef-formation evidently did not exist in that early stage of the island’s history, when the foraminiferous tuffs and clays, now occurring at elevations of 2,000 feet and over, were being deposited on the sea-bottom. At some time or other, however, these high mountain-slopes, previous to their emergence from the sea, must have been within the limits of the zone of reef-building corals. If reefs had been formed along those ancient coasts, or on the original shoals, they would have been in some cases preserved, as in the case of the foraminiferous tuffs and clays, by a covering of volcanic agglomerate. These soft submarine deposits have been in this manner saved from the destructive effects of denudation over a large part of the island whether on the higher slopes or at the lower levels; but no trace of reef-formation ever came under my notice in the higher regions of the interior. This is a puzzling point that will have to be considered in connection with the origin of the great mountain ridges, one of the most difficult problems in the history of the building-up of Vanua Levu.

I will now refer to the evidence of the latest stage of the upheaval of the island as indicated at and near the sea-border by the scantily occurring upraised reefs. The elevated reefs are mostly to be found on the south coast between Fawn Harbour and Na Viavia Islet off Harman’s or Savu-savu Point. Na Viavia Islet itself is 300 or 400 yards in length and is formed of much honeycombed reef-limestone, which is raised 10 or 12 feet above the high-water line. Proceeding eastward along the south coast of the Savu-savu promontory we next come upon uplifted reefs in a curiously isolated hill that rises on the coast between Naithekoro and Naindi Bay. This hill is about 250 feet in height and is composed in the mass of coral limestone. About 100 feet above the sea-level it exhibits an erosion-line, above which it rises precipitously to the summit. The west point of Naindi Bay is formed of reef-limestone reaching to a height of 40 to 50 feet and displaying in position massive corals, “Fungiæ,” and “Tridacna” shells. Near its base, four to five feet above the present high-water level, it shows an erosion line. This limestone overlies a rock in which blocks of volcanic rocks, five to six inches across, are imbedded in a calcareous matrix.

Raised coral limestone occurs at intervals on the coast between Naindi Bay and the mouth of the Salt Lake Passage, usually forming low islets, of which the smaller about 12 feet in height often assume, through the erosion of the sea at their base, that peculiar mushroom-shape, so characteristic of upheaval on reef-bound coasts. The passage into the Salt Lake lies in a slightly elevated reef-mass; and the islet which rises up in its centre to about a foot above the water-level is mainly formed of coral blocks, although I did not find any remains of coral on the low neck of land intervening between the Salt Lake and Natewa Bay. Eastward from the Salt Lake Passage to Nanutha in the vicinity of Fawn Harbour low cliffs of coral limestone, six to eight feet high and occasionally displaying massive corals in position, most frequently constitute the sea-border, rarely, however, extending more than a few paces inland or attaining there a greater elevation than 12 or 15 feet.

This limitation of the upraised reef-belt to the immediate vicinity of the coast is true of all this district. It is only when the sea-border is low and swampy that it is found 100 or 200 yards inland; and in any case as one follows it inland it soon gives place to the fossiliferous mud-rocks and tuffs of the interior. It should be noted that the upraised reefs of this region were rarely observed at greater heights than 20 feet above the sea, in fact usually at a much lower level. The exceptional occurrence in mass of reef-limestone at a height of 250 feet in a coast hill between Naithekoro and Naindi therefore lends colour to the idea that the elevated reefs formerly extended farther inland and that they have been stripped off by denudation.

On the north coast of the Natewa Peninsula elevated reefs are of very rare occurrence. I walked along the whole of that coast from the head of Natewa Bay to within four miles of Kumbulau Point and only found them in the locality, one to one and a half miles west of the mouth of the river Ndreke-ni-wai. Here there were two islets, 20 to 25 feet high and lying close to the shore, which were formed entirely of coral-rock, massive corals occurring in position in their lower part. Although, however, upraised reefs are so scantily to be found on this coast, other proofs of upheaval are to be observed in the fossiliferous tuffs exposed occasionally by the beach. On the east coast of this peninsula, between Ndevo and Loa, submarine tuffs and sandstones, at times fossiliferous, were alone noticed.

Upraised reefs are also very rare on the north coast of Natewa Bay. Here again I traversed the whole coast from the head of the bay to Undu Point, a distance as the crow flies of about 50 miles; but I find no record in my notes of any elevated reef-formations. However the calcareous nature of the volcanic tuffs exposed in places at the coast indicate emergence. The extreme rarity, if not the absence, of upraised reefs on this long stretch of coast, which is usually bordered by shore-reefs, is very remarkable, more especially since there is extensive evidence of upheaval in the plains of Kalikoso in the interior, as indicated in the succeeding paragraph.

On the other side of Undu Point, between that headland and Lambasa, elevated reefs did not come under my observation, although in the low-lying inland district of the Kalikoso lake silicified corals are scattered about in quantity at an elevation of 20 or 30 feet above the sea. But the emergence of the sea-border is shown in the occurrence of a “Globigerina” sedimentary tuff near Visongo at a height of 200 feet (see page [221]), and by the occasionally calcareous character of the pumice-tuffs that mainly compose the coast cliffs. Near Nukundamu these tuffs of the shore cliffs inclose subangular fragments of massive corals of the size of a walnut; whilst in a cutting between Mbuthai-sau and Lambasa, about 50 feet above the sea, I observed bits of coral limestone in a basic tuff. Mr. Horne refers to seams or layers of coral limestone occurring in the volcanic agglomerate of the coast cliffs between Lambasa and Tutu Island.[^[6]] Since his experience of this coast was mostly confined to a passage in a canoe along the shore, it is very probable that he only saw the beds of white pumice-tuffs that prevail in places on this coast. I found no beds of coral limestone in the shore-agglomerates of this coast, nor does Dana in his description of the pumiceous formation of the cliffs of Mali Point make any reference to them.[^[7]]

Along the stretch of 50 miles of coast between Lambasa and Naivaka upraised reefs are of infrequent occurrence. However between Lambasa and Wailevu, coral limestone is extensively exposed in a low range of hills a mile or two inland but not over 100 feet above the sea. No elevated reefs came under my notice between the mouth of the Wailevu river and Nanduri Bay. That a small upheaval has been recently in progress in this part of the coast is indicated by two circumstances. In the first place an erosion-line about a couple of feet[^[8]] above the high-water line, and a few paces removed from it, is displayed in the volcanic tuff of the point bordering the reef-flat on the east side of Nanduri Bay. In the next place there exist at different places in the midst of the mangrove-belt extensive bare mud-flats, sometimes several hundred yards across, which are only covered by the higher tides. These flats are quite bare of mangrove or any other vegetation and are often cracked on the surface and sun-dried and firm to walk upon.[^[9]] These naked mud-flats in the midst of the mangrove tracts are peculiar to this part of the coast. Their general level must be between one and two feet above that of the mangrove belt in other parts of the island; and I infer that a slight upheaval or emergence has led to the death of the mangroves in these situations.

I know little of the coast between Nanduri Bay and the mouth of the Ndreketi River. At two localities where I landed no elevated reef-formation was observed. Dana referring to the coast opposite Mathuata Island alludes only to the volcanic agglomerates. The low mangrove-bordered coast between the mouths of the Ndreketi and Lekutu rivers was not actually visited by me; but I traversed the region behind the broad mangrove-belt, and found occasionally in the tuffs and muds exposed in the river-banks marine-shells and foraminiferous tests, indicating an elevation of a few feet. I examined much of the coast between Lekutu and the extremity of the Naivaka peninsula, but came upon no upraised reef-rocks. In the low isthmus, 20 to 30 feet high, which connects this peninsula with the main island only volcanic rocks came under my notice. A palagonitic tufaceous sandstone exposed in the cliffs on the north coast of Naivaka contains a little carbonate of lime, and being probably a submarine deposit it implies an emergence of the sea-border.

Although I have been able to produce but scanty evidence of uplifted reefs on the north coast of Vanua Levu, it is probable, judging from the heights given in the Admiralty Sailing Directions, that such formations exist in a few of the numerous low islands and islets that front this coast. Some of these islands and islets, which are often not much more than reef-patches largely reclaimed by the mangroves, will be noticed below when considering the question of the extension of the mangrove belts since the survey of Commodore Wilkes in 1840.

Neither on the south coast of the peninsula of Naivaka nor on the west coast of the Sesaleka promontory did upraised reefs come under my observation; but my acquaintance with the last locality is very scanty. The emergence of the Sesaleka promontory is however indicated by the occurrence inland at heights of at least 700 feet of palagonitic tuffs, occasionally containing foraminifera.

With the long tract of coast between Naithombothombo Point and Solevu Bay, I am fairly well acquainted. However, with the doubtful exception of Lekumbi Point, no elevated reef-formations were observed. Evidence of an emergence of a few feet, and of a very extensive seaward advance of the land-surface in recent times, is afforded by a curious bed of marine shells exposed in the banks of the Mbua River, nearly two miles inland and in the vicinity of the Wesleyan Mission station. This is described on page [58]. The submergence at some period of the watershed between the Mbua and Lekutu districts is indicated by the presence of microscopic foraminifera in the hyalomelan tuffs that are exposed in the dividing ridge.

Along the whole coast between the mouth of the Mbua River and Solevu Bay, there are but few if any traces of upheaval. Even volcanic tuffs are of rare occurrence, and there is only the case of the formation of Lekumbi Point to be here referred to. This singular low cape is described on page [60]. Here it is sufficient to remark that it is monopolised by the mangroves except at the outer part where the swampy ground passes into the dry sandy soil of a reef-islet, occupied by the usual littoral vegetation, and raised only a foot or two above the high-water level. It exhibits on the beach the bedded sand-rock so often found on coral islets, but this in itself is no evidence of emergence.

Neither on the shores of Wainunu Bay nor in the Kumbulau peninsula were upraised reefs observed, although the presence in places of submarine tuffs inland and near the coast affords evidence of elevation. The same remark applies to the coasts of Savu-savu Bay.

I have little doubt that the absence of elevated reefs on the coasts of by far the greater part of the island is the result largely of denudation. In this case we have to explain why an island in a region of coral reefs exhibits on the surface of its interior submarine tuffs and clays in most localities, whilst uplifted reefs are very rarely to be found at the coast or in fact anywhere. This view receives support from the existence of traces of old elevated reefs in different parts of the island. These traces are afforded by the occurrence on the surface in different localities of silicified fragments of coral associated with concretions of chalcedony, bits of flints and hornstones, jasper, impure siliceous nodules, &c. The localities may be at the coast or a mile or two inland, and are not usually more than 100 or 200 feet above the sea. This subject is treated with some detail in [Chapter XXV]. Here I may say that such localities are confined mostly to the open, low, undulating districts on the north side of the island. Silicified corals are not always present with the fragments of chalcedony and other siliceous concretions that are found so frequently in these situations; but from their association in the plains of Kalikoso, where the silicification of corals may almost be observed in operation, the previous existence of corals may be more than suspected in localities where only the other siliceous materials are observed.

I pass on now to some general considerations regarding the relations of the mangrove-belt to the sea-border and the character of the slope of the land-surface as compared with that of the submarine platform. An accurate conception respecting these matters will help one to avoid some pitfalls in forming an estimate of the character of the movement of emergence which this region has experienced.

Beginning with the mangrove-belt, some curious preliminary reflections arise, when we endeavour to look back into the past stages of the history of a mangrove tract in an area of emergence. We might perhaps expect to find the remains of such a belt in the upraised sea-borders; or if no traces existed, we ought to find in some places an extension inland of the reef-flat on which the mangroves at one time flourished. If a rapid movement of emergence is now in progress, the mangroves ought to cover the whole or greater part of the reef-flat; and in the mangrove tract of an emerging area we might look for signs of central decay and marginal growth, the mangroves dying in the middle of the tract and flourishing at the advancing margins.

When, however, we look at the mangrove-belt, as it at present exists around much of the coast of this island, we find that, except in the vicinity of the mouths of rivers, there extends beyond it a considerable extent of bare reef-flat, varying usually between 200 and 1,000 yards in width, and covered by the rising tide. There is no evidence of recent emergence in this condition of things. This relation between the mangrove-belt and the reef-flat indicates a state of equilibrium which might have been established long ago. It is the normal relation that exists between reef and mangrove growth; and it excludes all but very gradual movements of upheaval or emergence of the sea-border. It is not always easy to see why there should be this fine adjustment between the rapidly-growing mangrove and the slowly-growing reef. Under normal conditions, however, that is to say, when the land is stationary or when the change of level is of a very gradual nature, the reclaiming agency of the mangrove receives a check, and this relation between the mangrove-belt and the outer reef-flat is maintained.

Actual acquaintance with such localities soon forced me to the conclusion that whilst a gradual emergence or upheaval of 3 or 4 feet in a century would not materially affect the relation between the mangrove-belt and the reef-flat, a sudden or rapid change of level of that amount would destroy the mangroves around the whole island. There is some evidence, however, of there having been a rapid upheaval of this kind in different parts of the coast: and it follows, therefore, if this movement was general, that the present mangrove-belts date only from the last upheaval. But this elevation may have occurred ages ago; and the equilibrium between mangrove-belt and reef-flat may have been long since established. Accordingly, the breadth of the mangrove-belt can afford no indication of the period that has since elapsed. From data referred to below, it is evident that the mangrove-belt, taking its average width, away from the estuaries, at about 500 yards, might have been formed in two or three centuries, whilst a thousand years or more may have passed since it assumed its present relation to the reef-flat. If, therefore, upheaval is in progress, it must be of a very gradual character, since the normal relation of mangrove-belt to reef-flat now prevails.

There are indeed signs of such a gradual movement of emergence or of elevation being in operation on the north coast of Vanua Levu at the present time. I have before referred (page [11]) to the extensive bare mud-flats in the midst of the mangrove-belt between Nanduri and Lambasa, which are well represented on the Tambia coast and in Nanduri Bay. They are only covered by the higher tides, and in the intervals their surfaces are dried and cracked by exposure to the sun. Here we have the central decay and the marginal growth which would be expected in a mangrove tract situated in a gradually rising area.

An indirect indication of such a slow upheaval on the north coast is to be found in the circumstance that the great submarine platform, which reaches seaward to the line of barrier-reefs, 15 to 20 miles away, passes gradually, as it extends landward, into the low-lying plains that constitute the sea-border between Lekutu and Ravi-ravi Point. As shown in the profile-section on p. [62], these low coast districts are prolonged inland, with an average rise of between 20 and 30 feet in a mile, to the heart of the island; and we have here an extension inland of the slope of the submarine platform. These broad inland plains, and I may here include those behind Lambasa, are covered over much of their surface with submarine tuffs and clays in such a manner that we may almost trace their continuity at the coast with similar deposits now in actual formation beyond the low-water level on the surface of the submarine platform.

A glance at the map of the island, where these inland plains are indicated by the 300 feet of the contour-line, will make this point more clear. These plains are traversed by the Sarawanga, Ndreketi, Wailevu, and Lambasa rivers; and so slight is the fall that cutters usually ascend the rivers for several miles, whilst the tide extends for a considerable distance up their courses. That the emergence of the inland plains of Kalikoso in the eastern part of the island is comparatively recent there can be but little doubt. In that locality as described on page [224], the low marshy land, surrounding the fresh-water lake of Vakalalatha, although five miles inland, is only elevated 20 to 30 feet or less above the sea, and silicified corals are scattered over its surface.

There is one other method of ascertaining the character and amount of elevation that may be still in progress in this island namely the comparison of the results of surveys of the coasts at different periods. In this manner data may be obtained as regards the growth of the mangrove belt, changes in size of the low reef-islets and islands, and alterations in depth. For this purpose I have employed the charts of the north and west coasts of the island made by Commodore Wilkes in 1840[^[10]] and the Admiralty charts 379 and 382 as completed from the survey of these coasts by Commander Combe in 1895-96.

It was not easy to make many good comparisons in the case of the advance of the mangrove-belt of the main coast. There certainly has been no great advance seaward of the margin of the mangroves in this half century. The average amount probably lies between the estimate obtained for the coast opposite Mathuata Island, where there has either been no change or an advance of only 100 yards or so, and that for the advance seaward of the mangrove promontory of Lekutu which amounts to 500 or 600 yards. In this last case, however, much of the extension may be due to the advance of the mangroves on the mud brought down by the Lekutu river, so that, as far as these data show, the average advance of the belt of mangroves on this coast between 1840 and 1895 would appear to be slight.[^[11]]

On the other hand, the mangrove-borders of the several low islands and islets, mainly formed of reef-débris, that lie off the coast, have often extended themselves during this period in a marked degree. The results of my comparisons are given below, the rate of advance being obtained by halving the increase in length or breadth as measured between the mangrove-borders, the breadth being used in the long islands.

Advance of the Mangrove-Borders of Low Islands on the North Coast of

Vanua Levu between 1840 and 1895.

It will be noticed that the islands of the Talailau Reef are not marked in the chart of 1840; they are both low mangrove islands, the largest being slightly under a mile long and the smallest a little under half a mile. In Nukuira Island, the Vatou of Wilkes, there has been a decrease of about two-thirds of a mile during this period. The difference between Thukini in 1840 and in 1895 is very noticeable. In the time of Wilkes the mangroves only occupied about one-third of the reef-patch. Now they occupy about two-thirds, the area of the reef-patch remaining much about the same. Taking the minus and plus values of all the islands here measured, the average rate of the advance of the mangrove-margins during this half-century may be placed at about 250 yards in the case of these reef-islands, which would amount to a mile in 400 years.

It is probable that a long island like Ndongo, which is about four miles in length, has been formed by the union of smaller mangrove islands. Therefore, taking half its maximum breadth of a mile as a guide, it would at this average rate of growth require two centuries for its formation. But since the extension of the mangroves depends on the growth of the reef-patch, which takes place on the average at a much slower rate, it follows that this can only be a minimum limit for the age of this island. We can only assume that if the reef-patch had suddenly appeared 200 years ago, Ndongo Island could by this time have acquired its present dimensions. It does not follow that the mangrove border has been continuously advancing. A hundred years ago there may have been a state of equilibrium between the growth of the mangrove and the reef-patch, which does not now exist. All we can say of some of these low islands is that the mangroves have been rapidly extending their margins during the last half century, and that the normal adjustment between reef-growth and mangrove-growth, which must have once existed, does not now prevail.

There is evidence of the shoaling of the ship channel amongst these islands to the extent of about a fathom during this period.[^[12]] The usual depth immediately around the patches, on which the islands have been formed, is 8 to 10 fathoms. If, therefore, the shoaling is a general process, it is to be inferred that although the outward growth of the reef-patches would be usually very slow, probably not over fifty yards in a century, there must be times when, in shallowing depths, the growth of the reef-patch would be comparatively rapid; and it is at such times that the adjustment between the relations of mangrove and reef-patch would be upset so that the advance of the mangroves would be for a time unrestricted.

It is, therefore, apparent that the rate of growth of one of these low islands is not to be determined by the rate of growth of the mangrove-tract occupying the surface. The subject is a complicated one; but I think enough has been said to show that the destructive agencies do not prevail on this great submarine platform on the north coast of Vanua Levu.

If the data here adduced of the increase of the low islands, of the shoaling of the channels, and of the advance of the delta of the Lekutu river,[^[13]] are well founded, all the islands, islets, and reef-patches that lie along this north coast will be united to each other and to the main island within a thousand years.

The facts here produced do not directly indicate a movement of upheaval but they are quite consistent with the conclusion that the great movement of elevation which has built up Vanua Levu by the union of several smaller islands is still in operation at its coasts. To assume that there is now in progress at the sea-border the same process of island-building which has produced Vanua Levu, as we now see it, is to assume a uniformity in nature’s methods which is disregarded by the hypothesis that the great submarine platform, from which the large islands of Viti Levu and Vanua Levu now arise, represents the work of marine erosion into the flanks of the upheaved islands since the last elevation. The origin of this submarine platform is dealt with in [Chapter XXVII]. Here it may be remarked that I regard it as older than the islands that rise from it.

However, this movement of upheaval is so gradual that the utmost one can expect to do by the comparison of surveys made half a century apart is to show the lack of evidence of the destructive agency of erosion. As far as the comparison admits of judging, there seems to have been no important change on the coasts of the western end of the island during this period. The low neck of land connecting Naivaka with the main island, if we take the low-water line in the Admiralty chart as the limit, had much the same breadth at the time of both surveys. The depths in Mbua Bay remain about the same, with perhaps a shoaling of less than a fathom in places. There are two cays awash in the Admiralty plan of this bay which were described as sand-spits in the time of Wilkes. The promontory of Lekumbi could scarcely have been expected to show any extension during this time, since there are depths of 10 to 16 fathoms close to its extremity; and there is in fact no difference of critical importance indicated in the charts.

Some of the principal points of this chapter may be thus summed up:—

(1) Upraised reef-limestones are of very limited occurrence. They occur at and near the coast and do not extend higher than 300 feet. Their scarcity at the sea-border is to be attributed to the denuding agencies.

(2) Since foraminiferous muds and sedimentary tuffs with marine organic remains occur at all elevations up to over 2000 feet, it is assumed that the absence of reef-limestones in the elevated interior indicates the paucity or absence of reef-growths in the early stages of the history of the island. The overlying agglomerates have often preserved from destruction the soft sedimentary deposits beneath; but they seem to have never covered over a coral reef.

(3) The relation between the mangrove-belt and the reef-flat indicates a state of equilibrium which might have been established long ago. If the movement of emergence is still in progress, it must therefore be of a very gradual nature, since the normal relation between the mangrove-belt and reef-flat now prevails.

(4) From the circumstance that the submarine platform passes with a uniform slope into the low-lying plains, covered with submarine deposits, it may be inferred that a very gradual emergence is now in operation.

(5) A comparison of the charts of Wilkes and of the British Admiralty shows that on the north coast of the island during the last half century the destructive agencies of marine erosion have not prevailed.

(6) The results of the comparison of the charts, whilst they do not directly imply a change of level, are quite consistent with the conclusion that the movement of emergence, which has been in operation probably since the later Tertiary period, is not suspended.

Note.—The extensive evidence of emergence presented by this island is treated in [Chapter XXVII.] in connection with the whole group. It is not always possible to avoid in such a discussion the use of terms such as “upheaval” and “subsidence,” although there is much to be said for the terms “negative” and “positive” employed by Suess. In the present chapter, however, I have avoided committing myself definitely to any view relating to the stability either of the land or of the sea, reserving the consideration of the subject for [Chapter XXVII.]

CHAPTER III
THE HOT SPRINGS OF VANUA LEVU

The abundance of hot springs in Vanua Levu, and in fact in the group generally, is not commonly known. In the earlier accounts of these islands those of Savu-savu are often alone referred to, not only for this island but for the whole archipelago. The United States Exploring Expedition under Wilkes spent six months in 1840 in making a survey of the whole group. Yet Dana, who was attached to the expedition, remarks that “the only trace of actual volcanic heat which the islands appear to contain is found at Savu-savu Bay.”[^[14]] Horne in his excellent account of the group, which he visited in 1878, was among the first to direct attention to the abundance of hot springs there; but he does not enumerate many. Although he travelled extensively over Vanua Levu, he refers to only three in that island, namely, at Savu-savu, Wainunu, and Vunisawana.[^[15]] It will be shown below that most of the thermal springs discovered by me might easily have been overlooked.

Before dealing with those of Vanua Levu I will mention the other localities in the group in which thermal springs are from various sources known to me. They probably form but a small proportion of those that actually exist; but the list can be readily extended by those acquainted with special parts of the archipelago. In Viti Levu they occur amongst other places at Wai Mbasanga, on the Singatoka river (Horne) and at Na Seivau on the Wai Ndina, where Macdonald in 1856 found temperatures of 106° and 140° Fahr. in two different springs.[^[16]] Mr. Thiele in more recent years referred by hearsay to some hot springs on the Wai Ndina.[^[17]] Kleinschmidt in 1876 visited a hot spring near the village of Nambualu in the island of Ono which rose up in the midst of a brook and had a temperature of about 100° Fahr.[^[18]] The same naturalist in July of that year, when accompanied by Dr. Max Büchner, came upon a hot spring issuing among the mangroves at the coast about a mile from the village of Ndavingele in Kandavu. He did not take the temperature; but he says that Colonel Smythe (about 1860) observed the temperature to be 144° Fahr.[^[19]] Different writers refer to extensive hot springs on the island of Ngau. They are placed near the beach, and close to an ordinary cool spring. Miss Gordon Cumming in At Home in Fiji gives an illustration of them. Horne mentions a hot spring on the island of Rambi. Andrews describes two others that bubble up through the limestone near the tidal zone in the southern part of Vanua Mbalavu. Both these springs are in close proximity to the junction line between the intruded andesite and the old reef rock. One of them, though not boiling, was hot enough to scald the skin.[^[20]] This list is no doubt capable of being much extended, especially for Viti Levu and the Lau Group.

A description of the several systems of thermal springs of Vanua Levu will now be given.

1. The Hot Springs of the Lower Valley of the Wainunu River.—This is one of the most extensive systems of the kind in the island. The temperature of the various springs during my sojourn in this district in 1898 ranged from 100° to 130° Fahr. Those known to me are mostly situated in the lower part and at the mouth of the Ndavutu Creek, one of the tributaries of the Wainunu. They open usually on the river-bank, either close to the water or a few feet above it, but some of them find an exit under water at the bottom of the river. Natives allege that hot springs occur at intervals on the left bank and at the river-bottom along the whole length of the river below Ndavutu Creek. There is certainly a hot spring on the right side of the river’s mouth near Mr. Dyer’s house. It issues from the reef-flat and can only be observed at exceptionally low tides. There is also a hot spring which rises up at the edge of the stream at Thongea (Cogea) nearly a mile above Ndavutu. If the above statement of the natives is correct, as I believe it is, then these thermal springs issue along a line quite four geographical miles in length extending inland from the mouth of the Wainunu.

All the springs are situated in the tidal part of the river-valley, with the exception of that of Thongea, which is just above this limit. They are but little elevated above the sea-level, those exposed being usually not more than ten feet above the river and often much less. This is a region of basalt, the valley of the Wainunu lying, as described on page [82], in the fold between two great basaltic flows, and probably representing a line of weakness, along which the hot springs issue either from among loose blocks, or from the soil, or from a tufaceous sandstone. They deposit little if any of the siliceous sinter which is often found in the thermal waters of this island. This is due probably to their scanty exposure and to their low temperature. The density of the water is near that of fresh water, being not over 1001. The following temperatures may be useful for comparison with future observations:

2. The Hot Springs of Natoarau and its Vicinity.—This thermal system lies in the lower valley of the Mbale-mbale branch of the river Ndreke-ni-wai. The principal springs are situated at Natoarau, a village about half a mile in a direct line from Mbale-mbale, about three miles from the coast, and only about fifty feet above the sea. They bubble up in pools near brooks, and extend at intervals over an area probably several hundred yards across. Five springs came under my notice; but there are doubtless several others in the low-lying and often swampy land of this district. No deposits were noticed, but the mode of occurrence and low temperature of the springs serve to explain this fact. The following temperature observations were made by me in March, 1899:—

The natives and others often state that the thermal springs here and in other localities are much hotter in dry than in rainy weather. This is correct in a sense, because in wet weather the surface water would usually find access to the pools; but there is no reason to believe that the temperature of the water at the hole of exit varies at all from this cause. The temperature of pool A was taken at the bottom where the water bubbled up; and probably it represents the true degree of heat of these springs, since in the other cases observation of this point was not so easy. The weather was dry during this visit; but, three months before, I tested the temperature of this pool after heavy rain, when the district was flooded, and then I got a reading of 127° at the exit-hole of the spring.

Another thermal spring, which is distant about a mile from Natoarau, is known as Waitunutunu, that is, Warm Water. It lies about a third of a mile from the village of Nambuniseseri, between Mbale-mbale and Waisali, and is quite four miles inland and about 100 feet above the sea. The springs bubble up into a pool, about 12 feet across, which is close to a brook and had a temperature in March, 1899, of 109-112° F.

3. The Hot Springs of Nukumbolo.—The village of Nukumbolo, where the springs are situated, lies on the banks of a tributary of the Vatu-kawa branch of the river Ndreke-ni-wai, and is distant as the crow flies about six miles inland from the river’s mouth. The springs issue on a hill-slope from several places a few steps apart, and are removed about a hundred yards from the river, and from 20 to 30 feet above it. Their elevation above the sea would be about 130 feet. The temperature taken in the two hottest places was 157° F, in November 1898, and 158° in the following February. As in the case of the springs of Savu-savu and a few other localities, the rocks are coated with siliceous sinter mixed with carbonate of lime, and a gelatinous incrusting alga grows on the borders of tiny hollows bathed often in water of a temperature 137-140°, but thriving most where the temperature is 115-120°. The water runs down the slope into a series of pools made by the natives for bathing, the temperature of the lowest pool being 103-105° and of the highest 120°. This is one of the best localities I have seen in the island for the erection of thermal baths. The rock pierced by the springs is apparently a basic agglomerate-tuff. Large blocks of a hard and somewhat altered palagonitic tuff lie around the bathing pools.

4. The Boiling Springs of Savu-savu.—These springs figure in all the descriptions of the group, and they are also famous amongst the natives. Since they were described by Wilkes, who visited them in 1840, in his narrative of the United States Exploring Expedition, many accounts of them have been written by subsequent visitors; not infrequently they have been sketched as well as described; and several analyses of their waters have been made.[^[21]] The accounts of these springs that lie before me extend at intervals over a period of nearly sixty years; but I shall allude to them only so far as they throw light on the history of the springs during this period.

The principal springs are situated in a slight hollow in a more or less level tract extending in from the beach, and are distant about 150 yards from the shore and about ten feet above the sea-level. They are five or six in number, and at the time of my visits in July and November, 1898, they were boiling briskly, the thermometer readings being 208-210° F., but the mercury probably fell two or three degrees in withdrawing the thermometer. When, as was the case when Wilkes visited this locality in 1840, there is but a slight appearance of boiling, brisk ebullition is produced by covering them over with leaves. The natives call this locality Na Kama, which signifies “the burning place,” and employed the springs extensively for cooking their food. Just as Wilkes describes, a freshwater brook runs past the springs and receives their outflow. The temperature of the brook immediately above the springs is that of an ordinary freshwater stream 75-76° F.; but below it is scalding. The account given by Wilkes of the spring and of the brook in 1840 applies to them in our own time. The small stones lying in the effluent channels of the springs are incrusted with siliceous sinter, and a green alga lines the sides, bathed generally in the steam but sometimes partially immersed in water only a few degrees below the boiling point. It is noteworthy that this alga which was flourishing in July was all dead in November.

The scalding water also oozes through the sand of the adjacent beach in abundance for a distance of at least some hundreds of yards. It is even stated that as far as Ndaku, a mile to the westward, the hot springs issue at intervals through the beach.[^[22]] There are evidently also extensive submarine springs close to the beach; and probably Wilkes was not far from the truth when he remarked that the “whole area of half-a-mile square seems to be covered with hot springs.”

Off the beach, a few hundred yards to the westward of the springs, is a batch of dead reef formed of massive corals and only approachable from the shore at extreme low-tide when it is a little exposed. From numerous small holes and cracks in the dead-coral hot water issues almost at the boiling point (210° F). It is apparent that these springs have appeared at this particular spot since the corals grew. But it is remarkable that this has been apparently going on since the visit of Wilkes in 1840. He refers to a coral rock, distant one-third of a mile from the springs and 150 feet from the beach, through which boiling water was issuing in several places. This rock which was then 10 feet wide and 20 feet long, was at his visit exposed for three feet at low-tide and covered at high-tide.[^[23]]

The geological characters of this locality are described on page [191]. I may here remark that if these thermal springs occupy the position of an old crater, it would require much imaginative power to restore it now. The off-lying small island of Nawi might by its situation appear to countenance this idea, but I found no special indication, when I examined it, in support of this view. From the geological character of the district, I would infer that if a crater once existed here it was submarine and that it has been long since obliterated by marine and aërial denudation. The boiling springs come up through apparently a rotten volcanic agglomerate. The slight hollow of three or four feet deep, in which they lie, was considered by Kleinschmidt to be an old crater cavity; but it is only 40 or 50 feet across, and in the earlier descriptions the hollow is described as surrounded by a mound of earth. As shown below, the natives themselves may be held responsible for many changes in the surface around the springs. There is, in fact, no trace of a crateral cavity in this district now.

I will now briefly notice the history of the boiling springs since 1840, when they were visited by Commodore Wilkes. At that time there were five springs, situated in a basin 40 feet across, and possessing a temperature of 200-210° F. Although there was scarcely any appearance of boiling, rapid ebullition could be excited by covering the springs with leaves and grass. The natives alleged that the springs had always been in the same condition. In 1863, when the Chief of Wainunu (Tui Wainunu) came to fight the Savu-savu people, he endeavoured but without success to choke up the springs by heaping earth over them. I was informed of this circumstance by Mr. A. H. Barrack, the owner of the springs. Miss Gordon Cumming also refers to it in her book At Home in Fiji. When this lady visited the springs in August, 1876, they were intermittent in their action, the highest making a fountain two to three feet high. According to the description of Kleinschmidt they were in the same intermittent condition in May of the same year. There were then four springs situated in a bowl-shaped hollow. The two larger springs were not constantly bubbling up, but displayed periodic ebullitions of about twenty minutes’ duration, the waters disappearing in the intervals. The other two springs were not then active. Horne, who visited this locality in 1878, refers to three or four principal springs situated in the centre of a hollow, which was surrounded by a mound of earth, the water boiling up to the height of about a foot.

About this time the springs entered for a while into a new phase of action and assumed the form of geysers. According to information received from Mr. A. H. Barrack and other old residents in Savu-savu, the waters spouted up to a height of from 40 to 60 feet, not vertically but at an angle. Each outburst, which lasted for ten or twenty minutes, was followed by a similar interval of repose, during which the springs dried up. This continued for a month or two, after which the springs gradually resumed their normal level. When I visited the springs in July and November, 1898, they were boiling briskly, attaining a height of a few inches, and showed no signs of intermittent action.

I come now to the different analyses that have been made of the water of these thermal springs of Savu-savu. Specimens have been analysed at different times by chemists in various parts of the world, in America, in Germany, in Australia, etc., and the results as far as known to me are now appended.

A. Analysis by Dr. C. T. Jackson of Boston, U.S., of the water

obtained in 1840 by the Wilkes Exploring Expedition.[^[24]]

Specific Gravity 1·0097. Temperature 57° F.

The evaporation of a quantity equal to 1000 grains of distilled water gave 7·2 grains of salt, thus composed:—

B. Analysis by Dr. Oscar Pieper of Hamburg of the water

obtained by Mr. Kleinschmidt in May, 1876.[^[25]]

The report stated that the water was clear, neutral in reaction and salt-bitter in taste, brown flakes of hydrated iron oxide occurring in it after long standing. The dissolved salts amounted to “8·48 g. per litre,” and the remark is made that “the concentration is therefore not so great as in sea-water.” The solid constituents consisted in by far the greatest part of Natrium and Calcium chlorides. A quantitative determination, which on account of the small quantity of the water was confined to “eine Chlor und Kalkbestimmung,” gave this result:—

Reckoned as Chlornatrium (Kocksalz) and Chlorcalcium, these results were obtained:—

Amongst other constituents found in small quantities were Sulphuric acid, Silicic acid (Kieselsäure), Potash, and Iron oxide. Iodine, Bromine, Nitrates, and Borates were completely wanting. “If this water,” says Dr. Pieper, “has healing properties, it does not owe them to its chemical composition.”

C. Analysis by Mr. H. Rocholl of sample obtained by Mr. H.

Stonehewer Cooper probably in 1877 or 1878.[^[26]]

D. Analysis by Prof. Liversidge of the Sydney University of a sample of the water collected by Dr. Bromlow, R.N., about 1879.[^[27]]

The specific gravity was 1·0064 at 60° F. The total solids in solution were 582·4 grains per gallon; but when heated to a dull red heat, the residue was 546·9 grains per gallon, the combined water having been driven off. Iodine and bromine were carefully sought for, but in vain. Four pints of the water were examined.

Composition.

Looking at the general character of these thermal springs of Savu-savu we may quote the remarks of Prof. Liversidge and Dr. Pieper that the salts in solution consist for the most part of chlorides, the chlorides of calcium and sodium largely prevailing.

Comparison of the analyses of the water of the Savu-savu thermal

springs, stated in grains per thousand of water.[^[28]]