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OBSERVATIONS OF A NATURALIST IN THE
PACIFIC BETWEEN 1896 and 1899

NA KARO (2,420 feet) from the south-west, a peak ot 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
J description of its leading Physical and Geological characters

Hontion
MAC MILL AN AND CO., Limited

NEW YORK : THE MACMILLAN COMPANY
1903

All rights reserved

Richard Clay and Sons, Limited.

bkead street hill, e.cl and

bungay, suffolk.

ZC 2 1 1965
'fVyy of TO^^
1154749

V. )

2)eMcation
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), ^Y 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

viii PREFACE

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 icx) 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. Graffe 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.

PREFACE ix

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 Home, 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. Home 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 explora-
tions 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

X PREFACE

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
Godeflfroy, heft 14, Hamburg, 1879.

HORNE, J., "A Year in Fiji," London, 1881.

WiCHMANN, A., " Ein Beitrag zur Petrographie des Viti-Archipels," Mineralo-
gische und Petrographische, Mittheilungen," band v, heft i, 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, I.— 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 Pagt^ 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, — Silici-
fied 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 algae 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

xiv CONTENTS

CHAPTER IV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES OF

VANUA LEVU

Naivaka, 43. — Korolevu Hill, 45. — Bomb formation of Navingiri, 46. — Remark-
able 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 — 6c

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 moun-
tain of the Hawaiian order, 72. — The Seatovo Range, 73. — Solevu Bay, 75^
— Koro-i-rea, 77. — Nandi Bay, ^Z. — 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, loi. — 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

CONTENTS XV

CHAPTER VIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

{continued)

Mount Vatu Kaisia and district, 113.— The Nandronandranu district, ii?-—
Nganga-turuturu cliffs, 1x9.— 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

xvi CONTENTS

CHAPTER XIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES

{continued)

The Valanga Range, i8i. — 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, 2ir. —
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 float-
ing islands, 226. — A region of acid rocks, 227. — Silicified corals and linion-
ite, 228. — Tawaki district, 229.— Thawaro district, 230. — Mount Thuku,
231. — Undu Point, 232. — General characters of the Undu Promontory, 233. —

Pages 224 — 234

CONTENTS xvii

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 Pa^^j 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 Horn blende- 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 Hom-
blende-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 Oligo-
clase 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
b

xviii CONTENTS

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-tufifs of mixed composi-
tion, 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 2,^7— ZZ(>

CHAPTER XXIV

PALAGONITE

Its abundance in afragmental 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-crystal-
line 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 experi-
ment, 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 sihcified 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

CONTENTS xix

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.
(i) 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 38s

LIST OF ILLUSTRATIONS

Plates

TO PACK
TAGR

INa Raro (2,420 feet) from the south-west, a peak of acid andesitel Frontis-
Ndrandramea (1,800 feet) from the south-east, a peak of acid }- j,igrg'
andesite rising about a thousand feet from its base .... J

The Ndrandramea District from the westward 98

Mount Tavia (2,210 feet) from Vatu Kaisia \ „

The magnetic peak of Navuningumu (1,931 feet) from the south ] ^

Mbenutha Cliffs, showing volcanic agglomerates overlying tuffs and clays,
containing shells of pteropods and foraminifera, which are raised

I, lOo feet above the sea rii

Duniua Lagoon, representing an old mouth of the Ndreke-ni-wai .... 153

Lithographs

Vanua Levu, Fiji Islands i

Fiji Islands 373

Figures

PAGE

Profiles of Vanua Levu as Viewed from the South. Graphically Repre-
sented on a Horizontal Scale of about 16 miles to the inch 4

Korolevu Hill (800 feet) from Wailea Bay 46

Profile and Geological Section of the western end of Vanua Levu from the
Wainunu estuary across the summit of the basaltic mountain of
Seatura to the edge of the submarine platform off the Ndama coast

as limited by the loo-fathom line 62

Profile, looking north from off the mouth of the Wainunu River .... 83
Rough plan of the Ndrandramea district in Vanua Levu ; made with

prismatic compass and aneroid by H. B. Guppy 99

Profiles of Ngaingai and Wawa Levu from Nambuna to the south-west.

Both are dacitic mountains loi

Profile and Geological Section of Vanua Levu, across the island from the

Sarawanga (north) coast to the Yanawai (south) coast 107

Profile-sketch of the Vatu Kaisia district from S.S.E 113

Section of the Vatu Kaisia district 115

Profiles of Na Raro .... 124

Profile-sketches of the Va-Lili Range 141

Profile-sketch of the mountainous axis of Vanua Levu 167

Koro-mbasanga from the north-north-east 167

Mount Mbatini from the top of Koro-mbasanga 173

View from Muanaira on the south coast of Natewa Bay 173

Ideal Section of Thambeyu 177

Diagram illustrating the two sets of felspar-lathes in a dyke 238

Magma-lakelet, •25mm. in size, magnified 290 diameters, from a basalt at

Navingiri . . 339

Showing fragments of glass with eroded borders and of plagioclase with

more even edges in a matrix of palagonite traversed by cracks . . . 342

Diagram showing the succession of deposits below the Nandua tea-estate 345

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 atten-
tion : and indeed it is in its irregular outline and in the occurrence
over a large portion of its surface of submarine tuffs and agglome-
rates 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 ofViti
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 pre-
sent 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

B

2 A NATURALIST IN THE PACIFIC chap.

plateau, from which it rises, will be laid bare ; and the small surround-
ing islands that are situated upon it, such as Yanganga, Kia, Mali,
Rambi, Kioa, &c., will be included in the area of Vanua Levu.^

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 pro-
longation 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 con-
tour 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.^ Here in Vanua Levu there is, on the con-
trary, 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.

^ In the case of the island of Faro in the Solomon Group, I have described
a similar process of island-building. {Geology of the Solomon Islands^ p. 37.)

2 In 1897 I spent several months in travelling over this island and ascended,
sometimes more than once, the three great volcanic mountains. Perhaps at
some future time I may renew my examination of this interesting region.

LEADING PHYSICAL FEATURES 3

A study of the profile of the island is an important preliminary
step to its more detailed examination. One may ramble over a
oarticular region of it for weeks, as I have done, without getting
iny satisfactory idea of the true configuration of the surface. In a
ocality densely wooded and occupied by steep mountain ridges
md deep gorges, the field of view is often very limited ; but seen
"rom the deck of a ^.passing ship the main features of the island
issume their true proportions and relations, and much that was
uncertain is in this manner made plain. The profile here given
]ias been constructed from a number of others, and represents in a
graphic fashion Vanua Levu as viewed from the southward. I
liave here sacrificed smaller details and occasionally some degree
of accuracy in small matters in order to bring out the principal
leatures 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
,384 feet), all of them formed of basic volcanic materials.^ Naivaka,
^v^hich is connected with the main island by a narrow isthmus, only
j.bout 30 feet in height, is probably one of the most recent addi-
1 ions 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
J Teat mountain of Seatura (2,812 feet), which occupies a large part
(if the Mbua province and monopolises most of the landscape
A/hilst largely determining the form of the western extremity of
the island. It is a basaltic mountain of the Mauna Loa type, its
1 3ng eastern slope descending gently at an angle of three or four
degrees for about ten miles to the mouth of the Wainunu River.
)n its deeply eroded radial valleys and gorges, and in other
1 espects, it is not unlike the island of Tahiti, as described by Dana.

The Ndrandramea region to the eastward, which I have named
i. fter one of its best known peaks, has a profile of a very different
character. Its broken outline indicates the existence of numer-
( us mountains and hills of acid andesites, occasionally dacitic.
Although some of them attain a height of 2,000 feet and over
t leir tops alone are seen from seaward. Between the foot of these
r lountains and the south coast extends a great plateau of columnar
\ asalt, incrusted at its borders with submarine deposits, which
c escends coastward with a very gentle slope, the fall in about
f ve miles being only about 300 feet (1,100 to 800 feet). It termi-
I ates abruptly opposite the elevated headland of Ulu-i-ndali, a

1 Strictly speaking Korolevu indicated in the profile would not be visible.

B 2 .

o

10 ^i

PM

cH. I LEADING PHYSICAL FEATURES 5

range, composed mainly of grey olivine-basalts, which is not
indicated in the profile.

The two conical peaks of Vatu Kaisia (i, 880 feet) and Na Raro
(2,420 feet), which rise up so unexpectedly in the region imme-
diately east of the Ndrandramea district, are also of acid andesitic
locks, in the last case approaching the dacitic type. They lie
^vithin the borders of the area of basic tuffs, basic agglomerates,
and basic massive rocks, that here begins and extends eastward
10 Mount Thurston and a little beyond. East of Na Raro there
is a gap or break in the profile, where the greatest elevation is
] )robably 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-tufifs 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

;^orotini Table-land, after the towns once situated on its southern

; lopes. Its outline is shown in the background of the view facing

)age 153. It is, however, not so level-topped as it appears to be;

)ut the gradual variations in elevation between 2,000 and 3,000 feet,

vhen spread over a length of some miles, are more or less lost in

he general outline of the range as viewed from the coast. Basic

agglomerates are principally exposed on the lower slopes; whilst

liigher up, reaching often to the summit of the table-land, occur

j)alagonite-tuffs containing tests of foraminifera and molluscan

! hells, massive basic rocks being exposed in places.

The level profile of the Korotini tableland gives place, as one

)roceeds eastward, to the broken outline of the several lofty peaks

of Mariko (2,890 feet), Mbatini (3,437 feet), Thambeyu (3,124 feet)

■ md others.^ Each of these peaks marks one of the bold

nountain-ridges that form such a striking feature in the surface-

I onfiguration of this part of the island. On the slopes of these

: idges, and often also on their summits, appear basic agglomerates

; .nd palagonitic tuffs and clays often inclosing tests of foraminifera ;

' i^hilst exposed in the gorges and protruding at times through the tuffs

; .nd agglomerates on the crests of the ridges are displayed massive

)asic rocks of the type of the hypersthene-augite andesites.

East of Thambeyu the level sinks to about 1,000 feet above

1 Mariko is the native name ot the Drayton Peak of the chart. Mbatini
i i the correct name for the Koro Mbasanga of the chart, the true Koro
: Ibasanga lying three miles to the north. Thambeyu is a native name for the
; lount Thurston Range.

6 A NATURALIST IN THE PACIFIC ch. i

the sea, and beyond rises an irregular group of hills and mountains
which attain their greatest height in Nailotha, ^ 2,48 1 feet above the
sea. We are now near the limit of the area of basic rocks. Follow-
ing 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 east-
ward 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-configura-
tion 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 frag-
mental 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.

^ There has been some confusion in the native names of the peaks in this
part of the island, which I have not been able to remove.

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 lime-
stones of any kind are rarely to be found, and only in a scanty
fashion. The extensive development of dolomites and hard lime-
stones, 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

8 A NATURALIST IN THE PACIFIC chap

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 up-
heaval 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 honey-
combed 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 com-
posed 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, " Fungiae," 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

II EVIDENCE OF RECENT EMERGENCE 9

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. East-
ward 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

lo A NATURALIST IN THE PACIFIC chap.

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. Home refers to seams or layers of coral limestone
occurring in the volcanic agglomerate of the coast cliffs beween
Lambasa and Tutu Island.^ 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.^

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^ above the high-water line, and

1 A Year in Fiji, 1881, pp. 22, 167.

2 Geology of the United States Exploring Expedition, 1849.

' This height has been suppUed from memory, as I omitted to refer to the
exact level of the erosion line in my notes.

II EVIDENCE OF RECENT EMERGENCE ii

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.^
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

^ They were described to me as dry for a fortnight at a time. I was pre
vented from making more than an occasional visit to them.

12 A NATURALIST IN THE PACIFIC chap.

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 sub-
marine 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

II EVIDENCE OF RECENT EMERGENCE 13

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 silicifica-
tion 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 sub-
marine 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 emer-
gence 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 mar-
ginal 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

14 A NATURALIST IN THE PACIFIC chap.

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 afiect 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 ot emergence
or of elevation being in operation on the north coast of Vanua
Levu at the present time. I have before referred (page 1 1 ) 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

II EVIDENCE OF RECENT EMERGENCE 15

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^ 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 icxD yards or so, and that for the advance seaward of the

^ A^ias 0^ the United States Exploring Expedition, vol. i., Philadelphia,
1850,

1 6 A NATURALIST IN THE PACIFIC chap.

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.^

On the other hand, the mangrove-borders of the several low
islands and islets, mainly formed of r&Qi-dSris, 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.

Thukini, or Gibson Island of Wilkes . . . 700 to 800 yards
Nangano, or Piner's Island of Wilkes . . 300 to 400 „

Nandongo, or Nuvera of Wilkes 500 „

Talailau (two new islands) 400 to 900 „

Nukunuku or Clark's Island of Wilkes . ) Not much change.
Thakavi, or Day's Island of Wilkes . . S

It will be noticed that the islands of the Talailau Reef are not
marked in the chart of 1 840 ; 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, however, is not the case with the recent changes at the mouth ot the
Rewa River in Viti Levu, where the bare sandy point of Lauthala has extended
itseh seaward betv/een 500 and 600 yards since 1840, whilst Port Nukulau has
shoaled a fathom in the same period. But I can find no evidence of any marked
advance in the mangrove margins either towards Nukulau or on the Kamba
side, the only change recognisable being in the bare sandy point of Lauthala,
the rapid extension of which has been such as to attract the attention of resi-
dents, both whites and natives. Dana, who was in this locality in 1840, remarks
in the Geology of the U.S. Exploring Expedition, that he had learned from a
person who had resided there for forty years that during this period the deposits
had lengthened the river half a mile. When I was on the Rewa in 1897 I
heard that the natives in old time could see Suva Point from Rewa. This is
probably a native legend connected with the modern extension of Lauthala
Point. (The charts compared in making the above measurement of the recent
advance of this point were the plan of the Rewa Roads by Wilkes, in 1840,
and the Admiralty charts 1757 and 905, the former of which was based on
Lieut. Dawson's survey in 1875, the last being corrected to 1897.)

II EVIDENCE OF RECENT EMERGENCE 17

ihis period. The difference between Thukini in 1840 and in 1895
s very noticeable. In the time of Wilkes the mangroves only
occupied about one-third of the reef-patch. Now they occupy
ibout two-thirds, the area of the reef-patch remaining much about
'he same. Taking the minus and plus values of all the islands
liere 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
^.CXD 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 man-
grove islands. Therefore, taking half its maximum breadth of a
nile as a guide, it would at this average rate of growth require
t wo centuries for its formation. But since the extension of the
riangroves depends on the growth of the reef-patch, which takes
place on the average at a much slower rate, it follows that this
c m 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 mangtove border
his been continuously advancing. A hundred years ago there
n ay have been a state of equilibrium between the growth of the
n angrove and the reef-patch, which does not now exist. All we
c.n say of some of these low islands is that the mangroves have
b ;en rapidly extending their margins during the last half century,
aid that the normal adjustment between reef-growth and
rr angrove-growth, which must have once existed, does not now
p evail.

There is evidence of the shoaling of the ship channel amongst
tl- ese islands to the extent of about a fathom during this period.^
T le usual depth immediately around the patches, on which the
is ands have been formed, is 8 to 10 fathoms. If, therefore, the
si oaling is a general process, it is to be inferred that although the
01 tward growth of the reef-patches would be usually very slow,
pi Dbably not over fifty yards in a century, there must be times
w len, in shallowing depths, the growth of the reef-patch would be
cc Tiparatively rapid ; and it is at such times that the adjustment
be tween the relations of mangrove and reef- patch would be upset

Between Mathuata Island and the coast a change is indicated from 9 — 10
fat 10ms to 8 — 9 fathoms, north of Motua Island 12 — 13 to 11 — 12, and between
N mgano and Thakavi 16 to 14 fathoms.

C

i8 A NATURALIST IN THE PACIFIC chap.

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 com-
plicated 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,^ 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 1 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

* By referring to the chart it will be seen that extensive mud-flats occur at
the mouths of the Sarawanga and Ndreketi rivers, where the land-margin is
slowly advancing.

II EVIDENCE OF RECENT EMERGENCE 19

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 : —

(i) 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
3ver a coral reef

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

(4) From the circumstance that the submarine platform passes
vith a uniform slope into the low-lying plains, covered with sub-
marine 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
1 1st half century the destructive agencies of marine erosion have
I ot prevailed.

(6) The results of the comparison of the charts, whilst they do
I ot directly imply a change of level, are quite consistent with the
c Dnclusion that the movement of. emergence, which has been
i 1 operation probably since the later Tertiary period, is not sus-
f ended.

Note. — The extensive evidence of emergence presented by this
if land is treated in Chapter XXVII. in connection with the whole

C 2

20 A NATURALIST IN THE PACIFIC ch. ii

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
n 1840 in making a survey of the whole group. Yet Dana, who was
ittached to the expedition, remarks that " the only trace of actual
/olcanic heat which the islands appear to contain is found at Savu-
;avu Bay."^ Home 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.^ It will be shown below that most of the thermal
! prings discovered by me might easily have been overlooked.

Before dealing with those of Vanua Levu I will mention the
(ther localities in the group in which thermal springs are from
> arious sources known to me. They probably form but a small
J 'roportion of those that actually exist ; but the list can be readily
< xtended by those acquainted with special parts of the archipelago.
1 n Viti Levu they occur amongst other places at Wai Mbasanga,
c n the Singatoka river (Home) and at Na Seivau on the Wai
Ndina, where Macdonald in 1856 found temperatures of 106° and
1 4.0° Fahr. in two different springs.^ Mr. Thiele in more recent
y 3ars referred by hearsay to some hot springs on the Wai Ndina.*

^ Unitea States Exploring Expedition^ vol. x. ; Geology, by J. D. Dana,
P 343-

2 A Year in Fiji, by John Home, London, 1881, p. 163.
^ Journal, Royal Geographical Society, 1857, vol. 27.
* Scottish Geographical Magazine, August, 1891.

2 2 A NATURALIST IN THE PACIFIC chap.

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.^ The same
naturalist in July of that year, when accompanied by Dr. Max
Biichner, 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 i860) observed the temperature to be i44°Fahr.2 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. Home mentions a hot spring on the island of Rambi.
Andrews describes two others that bubble up through the lime-
stone near the tidal zone in the southern part of Vanua Mbalavu.
Both these springs are in close proximity to the junction line be-
tween the intruded andesite and the old reef rock. One of them,
though not boiling, was hot enough to scald the skin.^ 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.

I. 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

^ Journal des Museum Godeffroy, heft 14, Hamburg, 1879.

2 Dr. Max Biichner also refers to this spring in his Reise durch den Stillen
Ozean, 1878.

^ Bulletin Museum Comparative Zoology, Harvard, vol. 38 ; Geolog.
Series V., No i, Nov. 1900.

HI THE HOT SPRINGS 23

;. mile above Ndavutu. If the above statement of the natives is
correct, as I believe it is, then these thermal springs issue along a
1 ne 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,
\'ith the exception of that of Thongea, which is just above this
1 mit. They are but little elevated above the sea-level, those ex-
josed being usually not more than ten feet above the river and
cften much less. This is a region of basalt, the valley of the
\Vainunu 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,
cr from the soil, or from a tufaceous sandstone. They deposit
li ttle if any of the siliceous sinter which is often found in the ther-
mal waters of this island. This is due probably to their scanty
exposure and to their low temperature. The density of the water
15 near that of fresh water, being not over icxDi. The following
ti ;mperatures may be useful for comparison with future observations :

T hongea, when not covered by the stream July, 1898, 127° F^

> davutu, bath-spring at Mr. Barratt's house Usually 100° „,

„ on left bank of the creek near the landing place . June, 1898, 126° „.

„ on left bank of creek near mouth Dec. „ 127° ,„

„ pool in foot-path on left bank J i , ' " „ '*

' ^ I July 27, „ 111° „

at bottom of main river in depth of 3 feet, close

to the left bank and just above the mouth xj , ^^^c

^ , -KT 1 , ,,- • • ^- /July „ 122

of the Ndavutu creek, self-registenng Six '

thermometer used

}'

2. The Hot Springs of Natoarau and its Vicinity. — This
tl ermal system lies in the lower valley of the Mbale-mbale branch
o: the river Ndreke-ni-wai. The principal springs are situated at
N atoarau, a village about half a mile in a direct line from Mbale-
n: bale, about three miles from the coast, and only about fifty feet
al >ove the sea. They bubble up in pools near brooks, and extend
a1 intervals over an area probably several hundred yards across.
F ve springs came under my notice ; but there are doubtless several
0I hers in the low-lying and often swampy land of this district. No
d« posits were noticed, but the mode of occurrence and low temper-
at ire of the springs serve to explain this fact. The following
te nperature observations were made by me in March, 1899 : —

A. Pool 4 feet across, with sides of stone, close to village . . 126° F.

B. Pool 10 feet wide, a few paces from pool A 114°))

24 A NATURALIST IN THE PACIFIC chap.

C. Pool 12 feet wide, loo yards from village, near the river . 103° F.

D . Pool on the road to Mbale-mbale, mixed with surface water 100° „

The natives and others often state that the thermal springs here
and in other locahties 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 tempera-
ture in March, 1899, of 109 — 112° F.

3. The Hot Springs of Nukumbolo.— The village of Nukum-
bolo, 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 1 20°. 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.

Ill THE HOT SPRINGS 25

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 Explor-
ing 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.^ 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 1 50 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, 1 898, they were boiling briskly, the thermo-
meter 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 note-
worthy 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

Amongst the other descriptions of these springs I may refer to that or
Kleinschmidt in the work quoted on p. 22, to that of Miss Gordon Gumming
in At Home in Fiji, to that of Home in his Year in Fiji, &c. They are
sketched in the descriptions of Kleinschmidt, Miss Gumming, and Gommodore
Wilkes. The analyses are given on a later page together with the references.

26 A NATURALIST IN THE PACIFIC chap.

yards. It is even stated that as far as Ndaku, a mile to the west-
ward, the hot springs issue at intervals through the beach.^ 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 (2 io°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.2

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 aerial 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

^ Pacific Islands^ Sailing Directions, vol. ii.. Central Groups, 1900, p. 185.

2 From what I remember the usual exposure at low- water in 1898 was less
than a foot. I have little doubt as to the identity of the locality. This rock is
one of the " sights " of the place at the present time. It would be interesting
for a resident to compare carefully its present condition with that as described
by Wilkes. Dana in the work quoted on p. 10, refers to this rock as a knoll
of basalt ; but he never visited the locality and only obtained his account from
the officers of Wilkes.

Ill THE HOT SPRINGS 27

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 — 2io°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 circum-
stance by Mr. A. H. Barrack, the owner of the springs. Miss
Gordon Gumming 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 dis-
played periodic ebullitions of about twenty minutes' duration, the
waters disappearing in the intervals. The other two springs were
not then active. Home, 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 infor-
mation 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.

28 A NATURALIST IN THE PACIFIC chap.

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

obtained in 1 840 by the Wilkes Exploring Expedition}

Specific Gravity I '0097. Temperature 57° F.

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

Chlorine 3'577

Sodium 1-665 or Soda 2-238.

Magnesia 0-440

Lime 0-366

Silica and iron with a trace of phosphate

of lime 0-200

Carbonic acid 0-493

6-741
Organic matter and loss 0-459

7*2oo

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

obtained by Mr. Kleinschmidt in May, i Z'jG?

The report stated that the water was clear, neutral in reaction
and salt-bitter in taste, brown flakes of hydrated iron oxide occur-
ring 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 Kalk-
bestimmung," gave this result : —

Chlor (Chlorine) 4-79 g. per litre.

Kalk (Lime) 2-31 „ „

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

Chlorcalcium (Calcium chloride) 4-55 g. per litre.

Chlornatrium (Sodium chloride) 3-09 „ „

Amongst other constituents found in small quantities were
Sulphuric acid, Silicic acid (Kieselsaure), 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."

^ Narrative of the United States Exploring Expedition, III., 199, by
Commodore Wilkes. See also Dana's Geology of the same expedition.
2 foumal des Museum Gode^roy, heft 14, Hamburg, 1879.

Ill THE HOT SPRINGS 29

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

Stonehewer Cooper probably in 1877 or 1878.^

Total solids at 212° F -8796 per cent.

„ „ ignited 7726 „ „

The residue consisted of —

Free Sulphuric Acid (SO3) "0049 „ „

Calcium sulphate '0260 „ „

Calcium chloride '4355 » »

Magnesium chloride •0021 „ „

Potassium chloride "0415 „ ,,

Water '1070 „ „

Sodium chloride "2641 „ „

•881 1

D. Analysis by Prof. Liver sidge of the Sydney University of a

sample of the water collected by Dr. Bromlow^ R.N., about
1879.2

The specific gravity was 1-0064 at 60° F. The total solids in
solution were 5824 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.

Silica, insoluble

Silica, soluble

Alumina and traces of Iron sesquioxide

Aluminium chloride

Phosphoric acid

Calcium chloride

Calcium sulphate

Magnesium chloride

Sodium chloride

Potassium chloride

Carbonic acid

Loss

Per cent, in
residue.

I -681
•074

•534
I "646
traces

46754
4770

•154

42-171

1-756

traces

•460

100 "ooo

Parts per
million of water.

I33'3

5-8

417

1 28 6

traces

3.6529

3727

I2-0

3,294'8
137-2
traces
34 'o

7,8i3"0

Grains per
gallon.

9-20

-40

2-92

9-00

traces

25570

26-09

-84

230-64

9-60

traces

2-52

546-91

Looking at the general character of these thermal springs of
i Javu-savu we may quote the remarks of Prof Liversidge and Dr.

* Islands of the Pacific, by H. Stonehewer Cooper, 1888 edition.
2 Journal Royal Society, New South Wales, 1880, vol. 14. Miss Gordon
( umming in At Home in Fiji gives the same analysis but differently stated.

30

A NATURALIST IN THE PACIFIC

CHAP

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. ^

Date
col-
lected.

Chlo-
rine.

Sodium.

Calcium.

Calcium
chloride.

Natrium
chloride.

Total
salts.

Density.

Dr. Jackson ....

Dr. Pieper

Mr. Rocholl ....
Prof. Liversidge . .

1840
1876
1878
1879

3-57
479

{4-50)

1-66

(1-29)

0-36
2-31

(1-42)

4-55
4-35
3-65

3-09
2-64
3-29

7 "20

8-48

8-8i
7-8i

1-009
1-006

Sea-water, tropics

19-46

ii-o8

0-46

—

35-00

1-02

It is to be inferred from the above that the quantity of salts in
solution remains about the same, the proportion varying only in the
four analyses, which extended over a period of forty years,
between 7*2 and 8'8 grains per thousand grains of water. This is
considerably less than the salts in solution in sea-water, namely
35 grains per thousand. The relative proportions of the salts,
excepting those of calcium, do not vary more than we should
expect in the case of analyses made by varying methods and
probably with a varying degree of exactness.

Dana^ considered from Dr. Jackson's analysis that the water
of the Savu-savu springs is probably of marine origin ; but the
absence of bromine and iodine, as especially remarked by Dr.
Pieper and Prof Liversidge does not support this view. We
might also expect the proportion of the salts to each other to show
a greater similarity to that in sea-water than they do. On the
other hand the total volume of water discharged, not only by the
springs proper but for several hundred yards along the beach, and
also between the tide-marks and beyond, must be far greater than
could be supplied by the rainfall of this portion of the Savu-savu
peninsula, which is only one and a half to two miles across and 800
feet high. We must look, I think, for the source of these waters
in deep subterranean streams or artesian basins that would be
fed by the rains precipitated in the mountainous districts where
the rainfall amounts to at least 200 — 300 inches in the year.

^ To avoid error, I have given the results of each without converting them
to a common standard. The numbers in brackets are taken from the form of
Prof. Liversidge's analysis given in Miss Gordon Cumming's book.

2 United States Exploring Expedition, vol. 10^ QgoIo^y-

Ill

THE HOT SPRINGS 31

This matter is further discussed in my general remarks on the hot-
springs of this island (page 38).

5. The Hot Springs near Ravuka. — These springs rise
up in the centre of the breadth of the island about nine miles
direct from the coast. They are about 200 feet above the sea
and are situated on the Ndrawa branch of the Ndreketi River
some two miles below the hamlet of Ravuka. They are on a
small scale and ooze through a bed of rounded blocks and pebbles
close to the water on the left bank. Their temperature in August,
1898, was 148° F. They are covered by the river when it is
swollen by the rains, and very probably other hot-springs issue
along the river-bottom. The conditions are not suitable for the
formation of deposits.

6. The Hot Springs of Vuinasanga. — These thermal
springs are also situated in the heart of the island on a tributary
of the Ndreketi some three or four miles westward from Va Lili
and about 150 feet above the sea. On each bank of the river
four or five paces from the water and three or four feet above it,
there is a small pool two to four feet wide. In June, 1899, the
pool on the right bank had a temperature of 131° F., and that on
the left bank of 134°. There were no deposits.

7. The Hot Springs on the South Side of the Nawavi
Range. — These springs also lie within the borders of the valley
of the Ndreketi. They may be " located " by describing them as
lying a few miles inland from the north coast fronted by Mathuata
Island. I did not visit them and have only learned of them from
Mr. Thomson's Mathuata paper.^ That gentleman refers to them
as two in number and situated at the back of the coast range about
four miles inland from the village of Nangumu ; but no particulars
are given.

8. The Hot Springs of Vatuloaloa. — These springs lie
on the Mathuata Coast in the neighbourhood of Mathuata Island.
I have not seen them, but am indebted to Mr. Thomson for the
particulars here given, which are taken from his paper above quoted.
Mr. Thomson, who discovered them in 1880, named them the
" Gragie " springs. They issue below high-water mark at Vatu-
loaloa, and had a temperature in 1880 of about 140° F. They are
said to possess many valuable healing qualities.

^ Proceedings, Queensland Branch, Geographical Society, Australia, vol. 1.
r886.

32 A NATURALIST IN THE PACIFIC chap.

9. The Hot Springs of Nambuonu. — These springs are
situated on the same part of the Mathuata coast as those of
Vatuloaloa above referred to. I learned from Mr. Bulling of Undu
Point that they issue from swampy ground half a mile inland.
They were discovered accidentally by a Japanese who put his foot
into them, the temperature being sufficiently high to scald the feet,
but not at the boiling-point, probably about 140° F.

10. The Hot Springs near Tambia. — These extensive
springs, situate i| to 2 miles inland, and rather under 100 feet
above the sea, lie near the Mathuata or north coast of the island,
some four miles west of the Wailevu river. They rise up in the
midst of level country about a mile from the town of Tambia,
and near the village of Ngovungovu. Although situated in the
valley of the Tambia river, these springs are not adjacent to
the river, and in this respect they differ from nearly all the
inland hot springs. The hottest spring bubbles up into a pool
5 or 6 feet across, which had a temperature of 180° F., in March,
1899. Near by is a large deep pool, some 20 feet or more across,
with a temperature of i(X)°. It receives the overflow from the
smaller pool, and apparently hot water also bubbles up at the bottom.
Around the smaller hottest pool there is a considerable deposit of
what is mainly siliceous sinter. It incrusts the stones and also the
oyster-shells lying about the pool in quantities, where they have been
left by the natives after their contents had been cooked and eaten.
Some of the shells are almost decayed away, the sinter for the
most part alone remaining.

11. The Hot Springs of Vandrani. — These springs occur
in the heart of the island, about 8 miles from the coast in a straight
line, and about 270 feet above the sea. This is the greatest
elevation, as far as I know, at which a hot spring exists in this
island. Here they rise up near the base of the central mountain
range, close to the head-waters of the Wailevu river which opens
into Lambasa bay. The springs bubble up into a pool, a foot deep,
on the left side of the river, four or five paces away from the water's
edge, and scarcely raised above it. They are covered over when the
river is in flood. In February, 1899, the temperature recorded by
my thermometer was 100° F. ; but probably it was a few degrees
higher at the bottom of the pool. I noticed no deposits.

12. The Hot Springs of Na Kama on the Wailevu
River. — These boiling springs, which are of an extensive character,

HI THE HOT SPRINGS

33

come up in half-a-dozen places on either bank of the river, and are
from 5 to 6 miles inland, and about 90 feet above the sea. They
<'.re close to the water, and from i to 10 feet above it. The
temperature of one small pool, where the water bubbled up briskly,
\/as 204° F. in February, 1899. In another it was 194°. The
\/ater was probably at the boiling-point in some cases as it entered
thie pools, and in the others it could have been only a few degrees
I elow it The rocks of the district are agglomerates and tuffs. I
\ ave no recollection of deposits of any extent around the springs.

13. The Hot Springs of Vunimoli on the Lambasa
ILIVER. — A few minutes' walk from Vunimoli, and about 100 yards
fiom the left bank of the river, these hot springs issue in a place
named Vunimbele from the foraminiferous clay rock (soapstone) of
the district. They are on the side of a ditch which communicates
vith the river. The natives have cut out of the soft rock small
square basins which receive the waters. The temperature of the
hDttest spring in August, 1899, was 155° F. That of others
was 140°. The conditions are not favourable for the formation of
d ;posits. These springs lie about 8 miles inland and are rather
o/er 100 feet above the sea. They are, however, small and un-
iriportant, and the locality in which they occur is now overgrown
with vegetation and not easy to discover.

14. The Hot Springs of Mbati-ni-kama on the Ngawa
River.— These springs are situated in the Lambasa district about
7. miles from the coast, and rather over 100 feet above the sea.
T ley issue copiously from the volcanic agglomerate at a tempera-
tire of 161° F. (August, 1899), and are only removed a few paces
fr )m the river, and a foot or so above it. Algse flourish in the
w Iter, and siliceous sinter incrusts the rocks.

15. The Hot Spring of Nandongo on the Head- Waters
or THE Wai-ni-koro River.— a few hundred yards from the
vi lage and elevated about 180 feet above the sea there is a small
pc ol in the clay of the river bank, 2 or 3 feet above and close to
th ; water, which in September, 1899, had a temperature of 97° F.

16. The Hot Springs of Natuvo on the North Coast
op Natewa Bay.— About a mile east of Mbiagunu and near the
vil age of Natuvo, there are two hot springs of small size which I
visited in August, 1899. One that issued on the reef-flat from the
CO al-rock at a temperature of 136° F. was covered over towards

D

34 A NATURALIST IN THE PACIFIC chap

high-tide. The other issued near by at a temperature of 131° from
swampy ground a few paces among the trees.

17. The Hot Springs of Ndaku-ndaku on the North
Coast of Natewa Bay. — At this place about 2 miles north of
Vuinandi some hot springs rise through the reef-flat, which are
only exposed at low tide. At the time of my visit they were
covered over by the rising tide. The natives described them as
not very hot and like the neighbouring hot springs of Natuvo.

18. The Hot Spring of Navakaravi, Natewa Bay. — The
coast village thus named lies about one and a half miles north of
Were-kamba. The hot spring is about a mile inland and not over
30 to 40 feet above the sea. It is reached after traversing a low
and often swampy tract The spring in August, 1899, issued from
a little rise at a temperature of 133° Fahr., and formed a rivulet 18
inches across.

19. The Hot Springs of Vunisawana at the head of
Natewa Bay. — Mr. Home, who was in this locality in 1878, refers
to these springs in his book A Year in Fiji. They had at one
time, he remarks, a wide reputation for their curative qualities ; but
the people around became so poor on account of the hospitality that
custom compelled them to extend to the numerous visitors that
they buried up the springs. Mr. Home was shown the site at the
bottom of a muddy creek. I saw it in 1898. It lies 300 or 400
yards in from the beach and only a few feet above the sea. There
were no signs of heat then ; but I was told that when the stream
close by is very low it sometimes is a little warm.

20. The Hot Spring of Ndreke-ni-wai on the South
Coast of Natewa Bay. — This small spring issues between the
tide-marks from an old reef-patch close to the shore and is only to
be seen at low-water. Its temperature in May, 1898, was
130—135° Fahr.

21. The Hot Spring of Waikatakata on the South
Coast of Natewa Bay. — This important spring lies about four
miles east of the town of Natewa. It issues on a hill-slope about 400
yards from the beach and is some 25 or 30 feet above the sea ; but it
is so beset by undergrowth that the source is not easy to reach.
Boulders and blocks of a basaltic rock lie about on the slope ; and
it is from under a huge boulder of five or six tons in weight that the
spring emerges at a temperature of 148° Fahr. (April, 1898).
There is a good volume of water, and a series of bathing pools of

HI THE HOT SPRINGS

35

varying temperature could be readily made. Unlike most of the
inland hot springs, it is not in connection with a stream or river.

22. The Hot Spring of Ndevo on the Coast opposite to
IUmbi, — I did not hear of any spring when in the locality ; but I
learned afterwards that near a stream on the beach there is a hot
s pring which is covered at high tide.

23. The Hot Spring of Navuni near Fawn Harbour.
— This small spring is situated in a hilly district in a region where
oiivine-basalts prevail. I was indebted to Mr. Pickering for show-
h >.g me its locality. It lies about three-quarters of a mile inland
aid about 100 feet above the sea. It issues from the volcanic
a; ^glomerate a few paces from the right bank of the Navuni stream
and five or six feet above its level. In May, 1898, it had a tem-
piirature of 112 — 113° Fahr.

GENERAL REMARKS ON THE HOT SPRINGS

This island is therefore remarkable for the number of its hot
springs. In the list given on page 40 I have enumerated 23
lo :alities where they occur ; but, as shown below, their number will
probably in time be extensively increased.

On referring to the map it will be observed that the distribution
Df these springs is fairly general over two-thirds or three-fourths of
thi island. Taking this area at about 1,500 square miles and
di-iding it into squares with sides of eight miles, we should, if the
5p ings were quite evenly dispersed, find a thermal system in every
3q lare. Even amongst the Fijians and among the white residents
hi number of hot springs will cause surprise. Only those of
5a/u-savu, Wainunu, Nukumbolo, Mbatini-kama, and Na Kama
)n the Wailevu river have been up to this time generally known,
rh 2 reason of this is that most of them are insignificant, and with a
:er iperature far below the boiling-point, and ooze up in unlikely
ind out-of-the way places, as by the water-side in little visited
■iv. :r-valleys, on the reef-flats of not much frequented coasts, and in
'W< mpy situations where they are likely to be overlooked. The
lat ves only recognise as " Na Kama " the boiling or very hot
pr ngs ; and it was only after much questioning that I could get
he n to tell me of some unimportant " wai katakata " (hot water)
^hi :h they deemed to be far beneath my notice. The natives were
:ee ily interested in my botanical and geological investigations ;
ut they considered it to be beneath the dignity of a man who had
3ei the wonders of Na Savu-savu to spend some time looking for

D 2

36 A NATURALIST IN THE PACIFIC cha

a half-forgotten thermal spring in a swamp. From this cause alon
I no doubt failed to find several springs. All the boiling spring
and those of very high temperature are probably known ; but as i
pointed out below it is more than likely that a large number c
unimportant springs remain to be discovered in many a deserte
inland valley and between the tide-marks along the very extensiv
reef-bound coasts.

As above remarked the hot springs did not come under m
notice in all parts of the island. They are to all appearance wani
ing in the western or Mbua portion, and also in the Undu portio
north of Natewa Bay. Taking the first-named region, it will b
noticed that no hot springs are indicated in the map west of th
Ndreketi and Wainunu rivers. I made inquiries wherever I wen
but with no result. On my writing to Mr. Wittstock, of Mbai
lailai, who is well acquainted with the Mbua peninsula, he informe
me that if hot springs existed in that part of the island he woul
probably have known of them. In that portion of the island whic
ends in Undu Point I could neither discover nor hear of an
thermal springs east of Lambasa on the north side, and of Lakemb
on the south or Natewa Bay side ; nor could Mr. Bulling, who ha
resided at Undu Point for many years, tell me of any springs i
his neighbourhood.

On looking at the general map it will be observed that th
hot springs are confined to the area of basic rocks, although the
do not occur all over that area, not being indicated in the map t
the west of the Ndreketi and Wainunu rivers. They are not know
to occur in the region of dacites and acid andesites, as in the cas
of the Drandramea district ; and they have not been found in th
area of rhyolitic and trachytic rocks that extends from Undu Poir
to Mbuthai-sau on the north coast and to near Tawaki on th
Natewa Bay side. The region of hot springs would be limited o
the east by a line joining the Mbati-ni-kama springs with those (
Nandongo on the Wainikoro river and Natuvo on the north shoi
of Natewa Bay. Such a line, though lying within it, roughl
indicates the limit between the regions of basic and acid rocks.

The situation of the hot springs in the lower levels, and the
non-discovery at elevations exceeding 300 feet above the sea, ai
facts of importance. In more than half the cases they arise clos
to and often on the banks of streams and rivers, occasionally indee
at the river-bottom ; and no doubt numerous unknown thermi
springs issue under water from the river beds. In about a thir
of the known cases the springs come up on the coast between th

HI THE HOT SPRINGS 37

tide-marks, usually rising through the reef-flat. At times even they
i.re to be observed below the low tide level ; and one can scarcely
(!oubt that there are a large number of undiscovered springs that
ere never exposed at the lowest tides. It is also very likely that
a number of hot springs issuing between the tide-marks are still to
be discovered without much difficulty.

The same may be said of inland hot springs. Looking at the
iisignificant character of many of them and noting their occurrence
iii places where they might easily be overlooked, it is highly prob-
able, as before remarked, that a number of springs exist inland,
V hich, though once known to the natives, are now forgotten. The
interior of the island is very sparsely inhabited now; but there is
e /idence of a much more populous condition in old times. The
p'esent natives are fast losing the knowledge of the interior of the
island which their forefathers possessed ; and many tracts in the
n ountain districts are far removed from existing paths. From the
h iphazard manner in which I lighted upon thermal springs beside
tl e head-waters of the Ndreketi, Wailevu, and Wai-ni-koro rivers,
I cannot doubt that many more exist in similar localities not
visited by me.

With regard to the distribution of the springs as respecting
t€ mperature, I cannot find any marked arrangement either in their
gi ouping or in the amount of elevation. It is noticeable, however, that
the three systems of hottest springs, that of Savu-savu (210°), that
of Na Kama on the Wailevu river (204°), and that of Tambia (180°)
are all less than 100 feet above the sea. Although the springs of
hi ^hest temperature are confined generally, with the exception of
th Dse of Savu-savu, to the main mass of the island, it would seem
th it adjacent systems of springs may differ much in temperature.
T-\e springs of Vunimoli, for instance, have a maximum tem-
perature of 155°, which is nearly 50° lower than that of Na Kama,
th ee miles to the westward. Hot springs are more numerous in
th ; region around Lambasa than in most other districts. Lastly,
I 1 aay add that earthquakes are apparently more frequent in the
M )ua district, where no thermal springs are known, than in any
ot] ler part of the island.

With regard to the deposits formed around the springs, it may
be observed that the circumstances are not usually suitable for their
foi nation, as for instance when they rise through the reef-flat or in
sw impy localities. In those springs, however, where the tem-
pe ature is over 1 50° F., and where the water spreads over a surface
so is to facilitate evaporation, deposits of white sinter associated

38 A NATURALIST IN THE PACIFIC chap^

with algae occur, as at Savu-savu, Tambia, and Nukumbolo. Its
composition varies a little in different localities. At Savu-savu it
is compact and laminated and formed almost entirely of hydrated
amorphous or colloid silica. At Mbati-ni-kama the siliceous sinter
is more friable, with a tendency to form opal. The sinter of the
Nukumbolo springs resembles that of Savu-savu ; but it also con-
tains a good proportion of carbonate of lime (20 per cent.) in a
granular form, and that of Tambia has the same characters. It
is not unlikely that this lime is derived from the decayed shells,

such as I have referred to in the case of the Tambia springs

It may be here observed that Mr. Weed and others, who have
studied the origin of siliceous sinter in the Yellowstone region
and elsewhere, regard it as the secretion of algae, mosses, &c., that
grow in hot waters {American Journal of Science, vol. 37, 1889).

I come now to some general considerations respecting the hot
springs of Vanua Levu. In the first place there is the singular fact
that the inland hot springs nearly always make their appearance
along the present lines of surface-drainage. But I do not gather
that the hot springs are of more recent origin than the rivers and
streams, by the side of which they rise. On the contrary the hot
springs are probably far older. The conditions of subterranean
drainage that favour the formation of springs at the surface, whether
cold or thermal, would no doubt often determine the direction of
surface drainage in a newly-formed land. Those familiar with
modern volcanoes will recall the absence or rarity of streams and
rivers, and the frequency often of cold and thermal springs at and
near the coast, which are sometimes of such bulk at the exits that
the expression " subterranean river " would be nearly appropriate.
The presence of artesian reservoirs may also in some localities be
safely assumed. I will here draw a little on my own experience of
volcanic regions.

On the lava-bound coasts of the riverless southern portion of
the large volcanic island of Hawaii, the subterranean waters issue
as cold and thermal springs at numerous localities. At Punaluu,
and at Ninoli, a mile to the westward, there are extensive fresh-
water springs at and near the beach which have a temperature of
64° F. all through the year,^ those at Ninoli issuing as a large
subterranean stream. East of Punaluu and at intervals along the
Puna coast, springs of water, sometimes fresh and cold with a

1 I took the temperature at monthly intervals between October, 1896, and
September, 1897. The mean annual temperature of the air in the shade would
be about 64° at an elevation of between 3,000 and 4,000 feet.

Ill THE HOT SPRINGS 39

temperature occasionally as low as 64°, at other times mineral and
thermal, but with a temperature not usually above 95°, issue at the

surface or at the bottom of deep fissures in the old lava flows

[n Oahu, another island of the Hawaiian group, where the volcanic
brces have been long extinct, artesian wells have been in extensive
Lse for some years in the irrigation of the sugar-cane plantations.
The last water-bearing strata are reached at depths of 400 to
;oo feet.^ The subterranean or artesian reservoirs are evidently
1 herefore on a large scale ; yet Oahu is scarcely one-third the size

of Vanua Levu in Fiji Lastly, I will refer to the numerous

subterranean streams that issue forth, as cold and thermal springs,
from beneath the lavas near and at the Etna coast, as for instance
ii the vicinity of Acireale. The Etna slopes are in great part
ceforested, and in consequence soakage is relatively small, and
sfterheavy rains much of the water runs off in the torrents. Whilst
i 1 this locality I was impressed with these facts, and I formed the
opinion that in ancient times when Etna was well wooded the
discharge of subterranean streams at the coast was far greater
t lan at present.

For these reasons and on other grounds, amongst them notably
tie absence of recent crateral cavities, I infer that the numerous
hDt springs are the outflows of subterranean streams, fed originally
b / the " soakage " arising from a rainfall of at least 200 to 300
h ches in the mountainous portions of the island. Such subter-
r; nean streams run probably at considerable depths, emerging, it is
li <ely, as often under the sea as they do on the land.

Since writing the above I have read in the Journal of the Royal
Geographical Society (November 1902), an abstract of a lecture by
Prof Suess on the subject of hot springs and volcanic phenomena.
T hermal springs, he holds, are supplied by hypogene waters and do
m )t receive their salts from the sea. Such springs, according to
t\ is view, being the survivals of volcanic activity, originate in the
d< pths of the earth's crust and bring water to the surface for the
fi; st time, not deriving it from infiltration. It seems almost im-
p ;rtinent to suggest a view opposed to that of such a high authority ;
bi t it appears to me that the frequent situation of the Vanua Levu
th 2rmal springs along the lines of surface-drainage requires an
e? planation that does not altogether exclude the agency of
in iltration.

^ At Ewa there are pumping plants capable of supplying 75 million gallons
ay, the water being drawn entirely from artesian wells. {Report on Hawaii^
by Dr. Stubbs, bulletin 95, 1901 ; U.S. Department of Agriculture.)

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Summary of the previous remarks on the hot springs of Vanua
Levu.

(i) Hot springs have been recorded from 23 localities, but there
are probably many undiscovered or forgotten.

(2) They are distributed over much of the island ; but have not
been observed in the Mbua or Western end and in the Undu ex-
tremity east of Lambasa and Lakemba.

(3) They are confined to the areas of basic rocks and are not
known in the districts of dacites and other acid andesites or in those
of quartz-porphyry and trachyte.

(4) They are always found at low elevations, never exceeding
300 feet.

(5) Whilst more than half are situated along river and stream
courses, nearly all the remainder lie between the tide-marks.

(6) In only two localities is the temperature at or near the
boiling-point. In one place it is 180° F., and in most of the other
springs it ranges between 100° and 150°.

(7) Siliceous sinter is formed where the temperature is over 150°.

(8) As exemplified by the water of the Savu-savu springs the
proportion of salts in solution (8 per 1000) is constant over many
years ; whilst in this fact and in the relative amounts of each salt
there is a sharp distinction from the composition of sea-water.

(9) The hot springs are older than the streams and rivers, along
which they are so frequently found.

It would appear that they are largely supplied from the
" soakage " of the heavy rainfall in the mountains.

CHAPTER IV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES OF VANUA LEVU.

In this chapter the detailed description of the island is
commenced, beginning with the western extremity and proceeding
eastward. Most of the petrol ogical details are dealt with under
their respective sections ; but it has been found necessary also to
frequently refer to them in this connection.

The Naivaka Peninsula. — This mountainous peninsula
forms the conspicuous feature of the western extremity of Vanua
Levu. Amongst all the mountains of the island its appearance
from a distance gave most promise of displaying the products of
recent volcanic eruptions ; but as shown below it affords evidence
of an antiquity nearly as great as that of the rest of the island,
although there are reasons for believing that its eruptions took
place during the last stage of the emergence.

Naivaka is connected with the adjacent relatively little elevated
part of the main island by a low and narrow neck a little less
than a mile in breadth. In its highest part, where it is only
raised between 20 and 30 feet above the sea, this isthmus is formed
of the basic volcanic rocks of the district ; but about three fourths
of its width are occupied by mangrove-swamps which are especially
extensive on the south side.

Viewed from some miles to the eastward the mountain has a
regular conical outline ; but from the south, when seen from Ruku-
ruku Bay, it has an elongated and a much more irregular profile,
descending rapidly on the east side, but displaying a gradual and
a fairly regular slope of about 10 degrees on the west side. The
upper part of the mountain is in the form of a curve with the
concavity facing south, the crest being more or less broken up into
five or six peaks showing often precipitous and at times vertical

44 A NATURALIST IN THE PACIFIC chap.

rocky faces having a drop of from lOO to 300 feet, the highest
peaks ranging from 1500 to 1658 feet above the sea.

All around the mountain, except on the upper steep portion
on the south side where it is well-wooded, the slopes have the
usual character of the " talasinga " districts, being occupied only
by grass, ferns, cycads, and the ordinary scanty vegetation of such
regions. Whilst on most sides the surface configuration is fairly
regular and the ascent to the summit is more or less regular, on
the south side bold spurs with valleys between them descend to
the coast, and the central mass rises abruptly in the middle of the
peninsula from a height between 300 and 500 feet above the sea.
It is on this side that Naivaka has the appearance of having been
originally a crateral mountain, of which, however, only the north
segment in a much degraded condition now remains, whilst the
other two-thirds have disappeared.

The prevailing rocks are a blackish compact olivine-basalt,
having as a rule much smoky glass in the ground-mass and
possessing a specific gravity of 2*92 — 2 '94. They are referred to
in the description of genus 25 of the olivine-basalts given on
page 259.

These rocks compose the agglomerate and the agglomerate-
tuffs that form the eastern portion of the summit and probably
most of the elevated part of the mountain. Similar agglomerates
occur along most of the north coast, the rock being in a few
places scoriaceous or amygdaloidal ; and they occur in huge fallen
masses on the south side near the foot of the precipitous portion.
The blocks in the agglomerate of the summit are usually six to
eight inches across.

On the south-west side the massive rocks exposed are less
basic with a specific gravity of 276 to 279. They are also more
altered, the olivine being infrequent and the interstitial glass
scanty. They differ besides in the parallel arrangement and in
the length of the felspar-lathes ('iS mm.), which are on the average
half as long again as those of the prevailing olivine basalts
(•12 mm.). They are placed in a different order of these rocks
and belong to genus 37 described on page 262.

Tuffs did not come frequently under my notice. At one part
of the north coast the cliffs are formed of a palagonitic tuff-sand-
stone, effervescing with an acid, which is described on page 330.
Although no organic remains are to be noticed, it is probably a
submarine deposit.

On a spur on the south-west side, at an elevation of 600 feet.

IV NAIVAKA 45

there is exposed a hard red palagonitic tuff dipping away from
the summit at an angle of 40°. It is mainly composed of the
palagonitised debris of a vacuolar basic glass and incloses broken
and entire crystals of plagioclase, augite, and olivine.

The augite crystals, which attain a length of five or six mm.,
project from the weathered surface and are easily detached, lying
about in quantities on the ground in places. Although they are
now imbedded in evidently a submarine tuff, these pyroxene
crystals could only have been ejected as such from a subaerial
vent ; and it would therefore appear that they fell into the sea
around the shores of a volcanic island in a state of activity. These
crystals are often cracked and are as a rule not so perfect as
those I have gathered from the slopes of Vesuvius, Stromboli, and
Etna. They exhibit an unusual tabular form arising from the
great development of the clinopinakoid at the expense of the
orthopinakoid faces.

On the whole it may be inferred that the Naivaka volcano was
submerged at the time of its origin, but that the eruptions continued
after it began to show itself above the sea. In many of its features,
especially in the character of the agglomerate that forms its upper
portion, and in the palagonitic nature of the tuffs, Naivaka differs
only from other elevated districts of the island, where organic
remains occur, in the absence of such remains. Its form bears
testimony to the extreme degradation we find in other districts, and
the occurrence of foraminiferous tuffs high up the neighbouring
slopes of Mount Sesaleka affords additional evidence of the original
submergence of this district.

The Hill of Korolevu.^ — About three miles east of Mount
Naivaka there rises to a height of 800 feet, about a mile inland
from the shores of Wailea Bay, the singular flat-topped hill of
Korolevu. It displays vertical cliff-faces, with a drop often of 200
or 300 feet, which have become so deeply furrowed or fluted by the
eroding atmospheric agencies that they appear at a distance to be
made of columnar basalt. The hill is, however, formed in mass of
a compacted tuff or agglomerate tuff built up of materials of a
hyalomelan basic glass that has undergone partial conversion
into palagonite. In the upper thirds these rocks show no bedding,
but in the lower slopes on the seaward side they are bedded and
dip to the north away from the summit at an angle of 15° or 20°.

1 This hill is figured in Wilkes' narrative under the name of Dillon's Rock
(vol. 3, p. 235). This, however, is not the Dillon's Rock of his chart, where
the name is given to a rock on the west side of the entrance to Wailea Bay.

46

A NATURALIST IN THE PACIFIC

CHAP.

The form of this hill is well shown in the sketch attached, and
there is little doubt that we have here an old volcanic " neck," the
remains of a submarine vent.

A specimen of the tuff from the summit is made up of com-
pacted fragments, in size ranging up to one third of an inch, of a
bottle-green vacuolar glass, which fuses readily in a lamp-flame
and is not dissolved by hydrochloric acid. This glass is usually
isotropic, but much of it is also palagonitic and feebly refractive,
the vacuoles or steam-holes, which are often elongated, being in the
last case filled with the same palagonitic material. Plagioclase
crystals occur macroscopically in the glass ; they are much eroded
and contain numerous large inclusions both of the clear isotropic
glass and of its palagonitised form.

About a third of a mile west of the Korolevu hill rises the hill of
Ngangaturuturu, 450 feet high, which presents a precipitous cliff-

faced summit in which are exposed basic tuffs showing pyroxene
crystals projecting from the weathered surface.

The Bomb Formation of Navingiri. — A mile north-west of
Korolevu Hill, where the coast road crosses a spur at the back of
Navingiri, a very curious formation is exposed at an elevation
somewhat under 200 feet above the sea. Here there are to appear-
ance a number of large more or less spherical volcanic bombs, two
to three feet across and formed of a semi-vitreous scoriaceous basalt,
imbedded in a hyalomelan-tuff displaying the same microscopical
characters as in the case of the tuff forming the adjacent hill of
Korolevu.

The ash is light grey in colour and rather friable ; but where
in contact with the bombs it becomes darker and is hardened.
The steam pores of the bombs are round and not elongated ; and
as is usual with these bodies they increase in size from the outside,
where they are very small (i millimetre and less), to the centre,

IV BOMB-FORMATION 47

where they vary from two to five millimetres across, A vitreous
border, about an inch in breadth, forms the outer shell of the bomb
where it is in contact with the tuff. Some of the bombs are only
two or three inches apart ; and one of them shows evidence of
fracture, fragments of the outer vitreous shell lying imbedded in
disorder in the surrounding tuff.

Before entering into more detail it may be at once observed
that the contiguity of some of the bombs to each other makes it at
first difficult to view them as having been formed in the manner
volcanic bombs are supposed to originate. Those who have seen
the huge bombs lying scattered about on the summit of Vulcano in
the Lipari Islands will appreciate the difficulty of imagining how
these bombs can occur in such a close arrangement without having
often shattered each other to fragments. However, Mr. Wittstock of
Mbaulailai in a letter to me describes even larger bombs that came
under his notice exposed on the surface in the Mbua district, their
outer crust when broken looking " like the slag of a blast-furnace."
The bomb-rock is a semi-vitreous basaltic andesite. It displays
microporphyritic plagioclase in a ground-mass formed mainly of a
smoky, almost isotropic glass, in which numbers of felspar micro-
liths (•! mm.) are developed, the augite being but slightly differen-
tiated. Scattered about in the glass are little irregular patches,
or " lakelets," of residual magma composed of a yellowish feebly
refractive material that I cannot distinguish from palagonite.

The ash, in which the bombs are imbedded, is a somewhat
friable hyalomelan-tuff composed of fragments of basic glass often
partially palagonitised, and usually 2 or 3 mm. in size. In it
occur pumiceous lapilli of the same material up to 2 centimetres
in diameter. The glass is markedly vacuolar, the cavities being
either filled with gas or with alteration-products. The vacuoles
are often drawn out into tubes, giving the glass a fibrillar appear-
ance. The numerous plagioclase phenocrysts inclosed in the glass
are much honeycombed and contain large inclosures of the glass,
both altered and unchanged.

Although the line of contact is well defined in a hand-specimen,
;he two rocks cannot be separated along the junction. In a thin
lection, in which the union of the vitreous shell of the bomb with
he ash is well shown, there is no defined line of demarcation, the
lon-vacuolar isotropic glass of the bomb being there broken up
nto fragments, with the interspaces filled with the partially
)alagonitised pumiceous ash. In the vitreous shell the felspar
: tiicroliths are much less developed both in size and number than

48 A NATURALIST IN THE PACIFIC chap.

in the central portion of the bomb. Numerous cracks commu-
nicating with the round steam-pores, which are much larger than
the vacuoles of the ash-glass, are filled with the same yellowish
magma-exudation referred to in the case of the rock forming the
centre of the bomb. Through the cracks this palagonite-material
has found its way into the steam-pores.

It would appear from the above that the bombs were but
partially consolidated when they fell into the bed of ash. The
tuff is somewhat " baked " where it is in contact with the bombs ;
and there is evidence of a collision between the bombs in the
fragments of the vitreous shell imbedded in the ash. Although
the ash itself contains no organic remains, there occur, not many
hundred yards away and at an elevation lOO feet higher above
the sea, foraminiferous tuffs of basic glass which are described
below. There is no indication of a crateral cavity in this locality ;
whilst the ancient " neck " represented by Korolevu Hill is a mile
away. These bombs most probably after being ejected from some
sub-aerial vent fell into the sea around, on the floor of which much
basic pumice-ash had been previously deposited. Such masses as
they sank would lose most of their original momentum.

Remarkable Section near Korolevu Hill. — Between
the hills of Korolevu and Nganga-turuturu, at an elevation of
about 300 feet above the sea, there is a singular exposure of tuffs
horizontally stratified and forming a low escarpment or line of cliff
about 15 feet high on the hill-side. These beds display the passage
from basic tuffs below to relatively acid tuffs above, and they
establish that in this locality the period of acid andesites followed
that marked by the eruption of basalts and basaltic andesites.
From their horizontal and undisturbed position, it may be inferred
that these deposits began to be formed under the sea when the
activity of the submarine basic vents was on the wane. In their
composition and in the various degrees of coarseness of their
materials, we can plainly discern the history of volcanic action in
this locality.

A hard compacted palagonite-tuff makes up the lower half of
the thickness of beds exposed, 1 5 feet in all. The greater portion
of it has the uniform texture of a sedimentary rock, fine-grained
below where the fragments are "i to "3 mm. in size, and becoming
coarser above where the larger measure i to 2 mm. It is composed
of more or less angular fragments of a basic vacuolar isotropic glass,
and of plagioclase and augite with much fine palagonitic debris.
There is no effervescence with an acid ; but in the upper part there

IV KOROLEVU SECTION

49

are a few casts of foraminifera of the " globigerina " type, as indicated
in the thin sections. Above this Hes a bed of a similar basic tuff,
laving however a banded appearance from the arrangement of
naterials of different degrees of coarseness, the finer being •1-2 mm.
in size, the coarser •4--8 mm. There is little or no carbonate of
lime; but occasional tests of foraminifera of the type above
mentioned occur in the slide. The basic tuffs here abruptly
terminate. They represent the quiet deposition in water com-
paratively deep of the products of marine erosion, and of the finer
ejectamenta of some distant subaerial vent.

Above the basic tuffs lie a series of tuffs, about 5 feet in
t lickness, and composed mainly of the debris of acid andesitic
rocks of the hornblende-andesite type, such as occur in the
^'drandramea district. They mark a period of active eruption on
tlie part of some neighbouring acid andesitic vent in this neighbour-
fa Dod, which the subsequent explorer may be able to identify with
some volcanic "neck."

These tuffs are composed partly of fragments of a hemi-
ciystalHne hornblende-andesite and partly of crystals, broken and
ei tire, of plagioclase, hornblende, rhombic pyroxene, and augite.
T le plagioclase is tabular, zoned, and glassy, and gives extinctions
of oligoclase-andesine (6 to 12°). The hornblende is bottle green,
m irkedly pleochroic, and gives extinctions up to 14°. The rhombic
P) roxene has the characters described on page 301, in the case of
th i Ndrandramea rocks. The augite is less frequent, but the two
p>roxenes are sometimes associated as intergrowths.
I These acid tuffs do not effervesce with an acid, nor can any
Ite.' ts of foraminifera be observed in them ; but since these organisms
ian represented in the basic tuffs below, it is highly probable that
th( whole series of these horizontal beds is submarine. The first
or lowest bed of the acid tuffs indicates a somewhat violent
vo. canic outbreak in this neighbourhood, following the deposition
of ;he basic tuffs. It is composed of loosely compacted subangular
Fra jments, i to 3 millimetres in size, in which the macroscopic
3ri ;ms of the rhombic pyroxene are especially frequent. It passes
apvard without interruption into a regularly grained sandstone
j:or ned of rounded and subangular fragments measuring -3 to
\7 1 im. across. Above this lies a quite distinct bed, a few inches
hi( k, of a fine compact clay rock, where the mineral fragments
ne. .sure only -05 to -12 mm. in diameter, hornblende being well
ep esented, although the rhombic pyroxene is very scanty. Up
O; t !iis time these beds of acid tuffs indicate a gradual defervescence

E

50 A NATURALIST IN THE PACIFIC chap.

of the volcanic activity that began with some violence, as shown by
the characters of the lowest bed. Now another outbreak occurred,
and overlying the clay-like bed we find a coarse tuff made up of
fragments 2 to 5 millimetres across, and approaching in texture and
appearance a subaerial tuff, but in other respects similar to those
below it. It is the last and uppermost of this series of acid tuffs,
and with it terminates an interesting record of the past in this
region, the chief features of which may thus be summarised.

A prolonged period of quiet deposition of submarine basic tuffs,
the products partly of marine erosion and partly of distant
eruptions, was abruptly followed by the outbreak of a neighbouring
vent during which tuffs formed of the debris of acid andesites were
deposited. The gradual decrease in the degree of activity is
plainly shown in the gradual diminution in size of these tuffs, until
they acquire the fineness of a clay. Then another burst of activity
from the same vent or vents occurred, and the record ends. Since
that time there has been apparently an upheaval to an elevation of
300 feet above the sea. As, however, the beds are quite un-
disturbed, the emergence may have been due to the lowering of
the sea-level, a subject which is discussed in Chapter XXVII.

Coast between Wailea Bay and Lekutu. — The hills
here often approach the coast, their spurs running down to the
beach. In the low range, 250 to 300 feet high, east of Wailea Bay,
are exposed palagonite-tuffs dipping gently north-east and com-
posed of fragments of a vacuolar basic glass, more or less palagoni-
tised, and of minerals (plagioclase, etc.) not exceeding 2 mm. in
size. These deposits are apparently non-calcareous and show no
organic remains.

Farther along the coast towards Nativi basic tuffs and agglo-
merates appear at the surface ; but the underlying rock, exposed
in position in the stream-courses and prevailing along much of the
sea-border to Nativi and a mile or so beyond, is a vesicular semi-
ophitic basaltic andesite with coarse doleritic texture and containing
much interstitial smoky glass. (It belongs to the non-porphyritic
group of genus 9 of the augite-andesites described on page 273.)
Such rocks evidently represent ancient flows. They give place as
one proceeds east to porphyritic semi-ophitic doleritic rocks of the
same genus and to semi-vitreous basic rocks. About half a mile west
of Nukunase a vesicular doleritic basaltic andesite forms a spur
protruding at the coast. It is semi-ophitic and contains in the
smoky glass of the groundmass little irregular cavities filled with
a yellowish residual magma like palagonite in character. (It is

[V MOUNT KOROMA 51

referable to genus 12 of the augite-andesites, described on page 275.)

\ few paces west of this spur a vertical dyke, 20 feet wide and

Tending N.W. and S.E., appears on the beach. It is formed of a

)luish scoriaceous basaltic andesite containing much glass in the

;jroundmass and showing imperfectly developed felspar lathes. It

is included in genus 4 of the augite-andesites described on page 270.

A little east of the spur there is another dyke apparently vertical

i nd formed of a vesicular rather than a scoriaceous basaltic andesite

referred to genus i of the augite-andesites (page 267). It differs from

tie rock of the previous dyke in the presence of small plagioclase

f henocrysts which contain abundant magma-inclusions ; but it

resembles it in the characters of the groundmass. This dyke is

about 40 feet in thickness and trends N.E. and S.W.

It may be inferred from the foregoing remarks that there was at
oie time a volcanic vent in the district west of Nukunase. The
liaes representing the trend of the two dykes above noticed would
if extended meet at a common focus a little way inland. The
r( )cks of the dykes differ conspicuously from the prevailing doleritic
n )cks that form, as before remarked, the ancient flows, the average
k ngth of the felspar-lathes in the former being •i-'2 mm., in the latter
•3 -4 mm. Both, however, belong probably to the same vent of which
n( )w the exact situation would not be easy to discover, on account
01 the re-shaping of the surface through the denuding agencies.

Mount Koroma. — The highest peak of the hills lying inland
be tween Wailea Bay and Lekutu is named Koroma and attains a
height of 1,384 feet. I did not ascend its slopes higher than 900
fei t, and approached it from the Mbua or south side. Extensive
pi; lins, covered with the usual " talasinga " vegetation, reach inland
frcm the shores of Mbua Bay to the foot of this range without
attaining a greater elevation than 100 feet. This low district is
dn.ined by the Mbua river and its tributaries, the rock usually
ex Dosed at its surface being a decomposing porphyritic basaltic
an lesite. It is again referred to on page 56 in connection with the
lo\ -lying level region of this portion of the island of which it in
fac : forms a part.

A basic non-calcareous fine-grained tuff-sandstone is exposed
in 1 stream at the foot of the south slope of Mount Koroma.
W] ilst crossing some low wooded outlying hills in this locality,
[ ( ame suddenly upon what seemed like a desert in miniature,
:jui e bare of vegetation and occupying an area of some acres,
fie e a porphyritic basic rock, from some cause unknown to me,
las decomposed in the mass to a depth of 20 feet and more ; and

E 2

52 A NATURALIST IN THE PACIFIC chap,

the result is a surface of white crumbling rock scored deeply by
the rains and carved out by the denuding forces into miniature
hills and dales. It is not improbable that a small crater in its last
solfatara-stage once existed here ; but the whitened disintegrated
rocks alone remain, and we can now only hazard a conjecture as to.
the cause. 1

I found a variety of basic rocks exposed on the hill slopes up
to 900 feet. The most frequent of the deeper-seated rocks which
occurred in mass at this elevation, and as large blocks on the
lower levels, is a dark grey rather altered hypersthene-augite-
andesite, referred to genus i of that sub-class as described on page
286. The specific gravity is 273, whilst the groundmass displays
a little greenish altered glass. Another of the deeper rocks^
exposed 500 feet up the slopes, is placed in the same sub-class,
augite and rhombic pyroxene being porphyritically developed,
separately and as intergrowths. The groundmass displays short
stout felspars, augite, and a little altered glass. The rock is
therefore referred to the orthophyric order described on page 290.
Spec. grav. 278.

Evidence of more recent surface lava-flows here exists. In
one place I came upon such a bed 1 2 feet thick, compact in its
upper half and slaggy or scoriaceous in its lower half. The rock
is an aphanitic augite-andesite (spec. grav. 277) and belongs to
species B, genus 16, of the augite-andesites, as described on page
281. Its groundmass displays felspar-lathes in flow-arrangement
with a little interstitial glass. Slaggy lava is not uncommon on
these slopes. One specimen beside me is a semi-vitreous form of
the deeper hypersthene-augite-andesites of this range.

There appears to be better evidence of sub-aerial lava-flows on
the lower slopes of Mount Koroma than I found in any other part
of the island. It should have been before remarked that one of
these flows lies upon a bed of a hard reddish compact tuff", which
appears in the thin section as an altered palagonite-tuff", containing
fragments of minerals including both rhombic and monoclinic
pyroxene, but showing neither lime nor organic remains. The
larger fragments are 2 mm. in size. It seems likely that this flow
ran into the sea during the emergence of this part of the island.

The prevalence of rocks of the hypersthene-augite-andesite
type in Mount Koroma distinguishes this range from the surround-
ing regions of olivine-basalts and basaltic andesites. This district
is well worth a detailed examination, and perhaps the remains of
a crateral cavity may yet be found.

IV MOUNT SESALEKA 53

The Coast between Naivaka and Koro-ni-solo at the

FOOT OF THE NORTH SLOPE OF THE SESALEKA RaNGE. —
Basaltic andesites, and olivine-basalts of the Naivaka type occur
on this coast. A rock of more acid character, Hght grey and much
altered, is exposed at the surface where the track crosses the head-
land projecting into Ruku-ruku Bay. It is one of the propylites
referred to in my description of the second genus of the augite-
andesites (p. 269). The felspars of the groundmass give the small
extinctions of oligoclase ; and in this respect it differs from the
other augite-andesites. Besides the altered plagioclase phenocrysts
there is much microporphyritic augite but slightly changed.
Calcitic and other alteration products occur in the interstitial
glass.

Mount Sesaleka. — This is the name of the highest peak,
1,370 feet, of a remarkable ridge-shaped range, which is very
precipitous on the east and north-east sides, where there is a sheer
•drop apparently of 500 or 600 feet, whilst on the other sides the
slope is more gradual, especially on the north where there is a
gentle descent to the sea. The actual summit is bare, rocky, and
narrow. There is a curious native legend relating to a pond on
the top of this hill. From what Mr. Wittstock tells me, it seems
probable that there is a spring near the summit. Close to the top
are the remains of an old " koro-ni-valu " or war-town ; whilst
numbers of shells of species of Cardium, Cyprasa, and Strombus,
such as would be used for food, lie about. Many years ago there
was a prolonged siege of this stronghold, which is referred to here
as indicating that the defenders had some independent water-
supply.

In ascending from Koro-vatu on the west side basic agglomer-
ates and agglomerate-tuffs were found exposed as far as half-way
up. In the upper half occurred at first fine-grained calcareous
tuffs, bedded and dipping gently down the slope, composed of
palagonite-debris, mineral fragments and calcitic material and
displaying a few macroscopic tests of foraminifera. These tuffs
became non-calcareous and coarser as one approached the summit.
A specimen obtained from the top is coarse-grained, being composed
of fragments of basic glass, usually palagonitised, much augite, a
little plagioclase and fresh olivine, but no tests of foraminifera, the
size of the fragments being usually *5-i*5 mm. Massive rocks
were rarely exposed on this side ; but half-way up in a stream
course I came upon an exposure of a porphyritic olivine-basalt
containing a fair amount of devitrified interstitial glass. Its

54 A NATURALIST IN THE PACIFIC chap.

specific gravity is 2*85 and it is referred to genus 25 of the olivine
basalts (page 259). I descended by a gentle slope to the north,
coarse basic tuffs and agglomerates containing amygdaloidal
fragments being displayed on the surface. In a stream at the
foot, close to Koro-ni-solo, were blocks of a heavy compact olivine-
basalt with specific gravity 2*96.

District between Mount Sesaleka, Thombo-thombo
Point, and Vatu-karokaro Hill. — This is a broken country
with several abruptly rising lesser hills. Starting from Koro-vatu
and crossing the Thombo-thombo promontory, I reached the coast of
Mbua Bay near Navunievu. Basic tuffs and agglomerates pre-
vailed on the way, the last containing blocks of a scoriaceous
basaltic lava bearing olivine. The massive rocks exposed belong
in some cases to genus 13 of the olivine-basalts as described on
page 256, being dark grey and having a specific gravity of 2'88,
and in other cases to genus 16, species B, of the augite-andesites
when they are lighter in colour and have a specific gravity of 277.
In both cases the interstitial glass is scanty.

I ascended Vatui, one of the numerous small hills of the
district. It is 450 feet high and is capped by a bare mass of tuff-
agglomerate, 40 to 50 feet high and containing fragments of
vesicular basic lava. This mass is pierced by a dyke, 18 inches
thick, which is inclined to the N.NE. at a high angle of 60 or 65
degrees with the horizon. This dyke is composed of a compact
olivine-basalt which is remarkable for the prevalence of small
augite prisms in the groundmass. It is described on page 265
under genus 44 of the olivine-basalts. Hand-specimens are
magnetic and display polarity, which is due, as pointed out in
Chapter XXVI., to the exposed situation of the peak.

Vatui in its characters is evidently typical of the other lesser
hills around, which, as viewed from below, possess bare tops and
precipitous declivities of the same formation. All the hills in the
district including Sesaleka are capped by these basic tuffs and tuff-
agglomerates ; and doubtless as in the case of Sesaleka these
deposits are all submarine. This is true also of Vatu-karokaro, a
hill 600 feet high, overlooking Mbua Bay and about two miles
east of Sesaleka. In the lower part of this hill is exposed a dark
compact basaltic andesite, referred to genus 13, species B, of the
augite-andesites (sp. gr. 2"83), whilst blocks of a black olivine-basalt
(sp. gr. 2"9i) occur in the agglomerate of the summit. These hills
may all be regarded as " volcanic necks " or the stumps of volcanic
cones, probably submarine.

IV MBUA AND NDAMA PLAINS 55

The Dividing Ridge between the Mbua and Lekutu
Plains. — A level rolling " talasinga " district intervenes between
Mbua Bay and the dividing ridge. The upper part of this ridge,
which attains a height of about 500 feet above the sea, is composed
of a hard grey sandstone-like tuff, effervescing feebly with an acid,
which on examination proves to be formed in great part of frag-
ments, 'oy-'i mm. in size, of a dark basic glass occasionally
vacuolar. The rest of the deposit consists of similar-sized frag-
ments of plagioclase and other minerals, and includes also a few
tests of foraminifera of the " Globigerina " type.

The mass of the ridge, however, is composed of coarse tuffs and
agglomerates of a different kind which have been covered over by the
foraminiferous deposit just described. Thus there are exposed on the
lower slopes, tuffs and agglomerates of a basic pitchstone formed of
a brown glass containing a few felspar and pyroxene microliths.
In the tuff the fragments are three to six mm. in size and show
evidence of crushing in situ, the interstices being filled with
debris of the same material more or less palagonitised,i but there
is no carbonate of lime. Large masses of an agglomerate made
up of blocks of an acid andesite occur higher up the slopes. The
component rock belongs to an unusual type of hypersthene-andesite,
specially noticed on page 297.

The interesting feature in this ridge lies in the testimony it
affords that the extensive Mbua and Ndama basaltic plains, on
which I was unable to discover any submarine deposits, were at one
time submerged.

The Mbua and Ndama Plains. — These rolling plains are a
striking feature in the western end of Vanua Levu. They have an
arid barren look, are clothed with a scanty and peculiar vegetation,
possess a dry crumbling soil often deeply stained by iron oxide, are
traversed by rivers without tributaries descending from the wooded
uplands of the interior, and in fact have well earned the name given
to them by the natives of "talasinga" or sun-burnt land. Both
Seemann and Home have remarked on the South Australian aspect
of these regions, which are characteristic of the lee and drier sides
of the larger islands of the group. Covered for the most part with
grass, ferns and reeds, these low-lying districts are dotted here and
there with Casuarinas, Pandanus trees and Cycads, whilst such
other trees and shrubs as Acacia Richii and Dodonaea viscosa, add
to the variety and peculiarity of the vegetation. The origin of
these " talasinga " districts is discussed in the last chapter.
^ See remarks on " crush-tuffs " on p. 334.

56 A NATURALIST IN THE PACIFIC chap.

The Mbua and Ndama plains form a continuous region extend-
ing three to five miles inland to the foot of the great mountain of
Seatura, to the watershed between Mbua and Lekutu, and to the
base of Mount Koroma ; whilst it reaches along the sea border
from the vicinity of Navunievu about four miles west of the Mbua
River to beyond Seatovo a few miles south of the Ndama River.
Their extent is defined in a general sense by the 300 feet contour
line in the map. Their elevation, however, above the sea does not
generally exceed 200 feet and is usually only 50 or 100 feet ; but
at the foot of Seatura they rise to between 300 and 400 feet.
Whilst on the one side these plains form a continuation of the
lower slopes of the great Seatura mountain, on the other side they
are extended under the sea as the broad submarine platform, the
edge of which, as defined by the lOO-fathom line, lies eight to ten
miles off the coast. It is pointed out on page 372 that this continuity
of surface, both supra-marine and submarine, extends probably to
the geological structure and that the submarine platform represents
the extension under the sea of the basaltic flows of the plains.

The whole region of the plains is occupied by olivine -basalts
and basaltic andesites, such as are found on the neighbouring lower
slopes of the Seatura mountain. They are as a rule much de-
composed, even at a depth of several feet below the surface.
Typically, they are neither vesicular nor scoriaceous, and in this
respect they possess the character of submarine lava-flows. The
rolling surface of the plain is varied occasionally by small " rises "
or hillocks marking apparently some secondary cone, of which the
much degraded " wreck " alone remains. Here and there fragments
of limonite, approaching haematite in its compact texture, lie in
profusion on the soil, representing doubtless small swamps long
since dried up, some of which still occur in the hollows of the
plain. Mingled with these fragments are often pieces of siliceous
rocks and concretions, such as are found in the other " talasinga "
districts of the island, the description of which is given on
pages 128, 132, &c.

I will now refer more in detail to some of the points alluded to
in this short description of these plains. With reference first to the
compact limonite, it should be remarked that it occurs on the sur-
face either as fragments of hollow nodules two or three inches
across, or as portions of flat " cakes " half to one inch thick. It
is especially abundant in the district lying a mile or two on either
side of the Navutua stream-course between Ndama and Mbua.
Here the subsoil is charged with ferruginous matter, and the water

IV MBUA AND NDAMA PLAINS 57

of the series of stagnant pools in the bed of the stream is stained
blood-red by iron-oxide, a circumstance that has naturally given
rise to native legends of a corresponding hue. These fragments of
iron ore, which lie between 100 and 150 feet above the sea,
represent the final stage of a process which is now no doubt in
operation on the bottom of the neighbouring pools and small
swamps. Their presence on the surface goes to indicate that this
open country has been for ages a land-surface free from forest, as it
is in our own time.

In a similar manner, the extensive disintegration of the basaltic
rocks that form these plains affords evidence of the great antiquity
of these "talasinga" plains in their present unforested condition.
The extent to which these rocks have weathered downwards is very
remarkable. Between Ndama and Mbua they are decomposed to
a depth often of eight or ten feet below the surface. This is well
exhibited in the sides of deep channels excavated by the torrents
during the rains. Here the spheroidal structure is well brought out
in the disintegrating mass, all stages being displayed in the form-
ation of the boulders that are scattered all over these plains.

In one locality, near the lower course of the Ndama river, a
thickness of 25 feet of decomposed rock was exposed in a cliff-face.
In this case the rock was a porphyritic basaltic andesite, the
disintegrating process having affected the whole thickness of the
large spheroidal masses with the exception of a hard central
nucleus of the size of the fist. In one of these nuclei by my side it
is apparent that during the extension of the weathering process the
phenocrysts of glassy plagioclase become opaque long before the
groundmass is affected. In this specimen the stage of disintegra-
tion as affecting the felspar phenocrysts is at least one and a half
inches in advance of that affecting the groundmass.

This great disintegration of the basaltic rocks, which as pointed
out on page 64 is also in progress on the slopes of the adjacent
spurs of Mount Seatura, is more characteristic of the porphyritic
basaltic andesites than of the olivine-basalts. It is to the spheroidal
weathering that we must look for an explanation of the rounded
boulders so frequent in these districts. It may also be inferred
that the soil produced from this extensive decomposition of the
rocks is often very deep. At the Wesleyan Mission Station at
Mbua, on level ground nearly a hundred feet above the river, a well
has been sunk to a depth of 20 feet in soil of this description ; and
iway to the westward a similar thickness of soil produced by the
>ame cause is in places to be observed.

58 A NATURALIST IN THE PACIFIC chap.

Coming to the characters of the basaltic rocks of the Mbua and
Ndama plains, it may be remarked that the prevailing rocks are the
porphyritic basaltic andesites, having a specific gravity of 277 to
2*8 1, which are in most cases to be referred to genus 13 (porphyritic
sub-genus) of the augite-andesites described on page 278. They
possess large phenocrysts of plagioclase and but little interstitial
glass. The other rocks are olivine-basalts with specific gravity
2*88 to 2*90 and showing only a few small plagioclase-phenocrysts.
They display a little residual glass and belong for the most part to
genus 37 of the olivine basalts described on page 262. In both
these basaltic rocks the felspar-lathes are in flow-arrangement ; but
in the basaltic andesites they average • 1 1 mm. in length, whilst in
the olivine-basalts they average "iS mm.

The low mound-like " rises " in these plains, to which previous
reference has been made, are not usually elevated more than 50
feet above the general surface. One of these hillocks that lies near
the track from Mbua to Navunievu, about two miles from the
Wesleyan Station, is composed of a remarkable semi-vitreous
pyroxene-andesite passing upward into a rubbly rock of the same
nature. The rock of this old volcanic neck is of an unusual type
and is referred to the prismatic order of the hypersthene-augite
andesites described on page 289. Both the felspar and pyroxene
prisms of the groundmass are in flow-arrangement. One of these
mounds near the Mbua Wesleyan Station is apparently formed of
the decomposing basaltic andesite of the district. On its surface
are fragments of earthy limonite and siliceous rocks.

The rarity of submarine tuffs and clays on these plains is some-
what singular ; but in the occurrence of foraminiferous tuffs high up
the slopes of Sesaleka and on the crest of the Mbua-Lekutu divid-
ing ridge we have evidence of the original submergence of all these
lower regions. It is probable enough that the ages of exposure
that have since witnessed the reduction of the solid basaltic rock to
a crumbling mass several feet in depth were more than sufficient
for the stripping off" of most of the overlying submarine deposits.
Such deposits are, however, common on the surface of the extensive
" talasinga " plains that constitute much of the north side of the
island.

The Shell-bed of the Mbua River. — Rather curious
evidence of an emergence of a few feet and of a considerable
advance of the delta of the Mbua river in comparatively recent
times is afforded by a bed of marine shells exposed in the right
bank of this river, about 200 yards below the boat-shed of the

IV MBUA SHELL-BED 59

Wesleyan Mission Station and about two miles in a straight line
from the sea. This bed, which is about a foot in thickness, is ex-
posed for a distance of 70 or 80 yards. It slopes gradually sea-
ward as one descends the river, being raised two or two and a half feet
at its upper end above the river level at low tide, whilst at its lower
end it is at about the water-level. The river-bank is here 15 or 16
feet high, and is composed in its upper half of a fine gravel of
volcanic rocks mixed with earth, which below passes abruptly into
a friable non-calcareous black mud-rock (not bedded and looking
like consolidated swamp mud), in which the layer of shells is con-
tained. These shells are, therefore, covered by deposits, 13 or 14
feet in thickness, of which the upper eight feet are formed of gravel
and earth, and the rest of mud-rock. They are evidently gathered
together on the slope of an old mud-flat.

The shells are all large marine bivalves, belonging to the genera
Ostrsea, Meleagrina, Cardium, Area, &c,, no freshwater shells
occurring. They are often much decayed and have lost the liga-
ments. The valves are generally separate ; but in some cases they
are still in apposition, the cavity being then filled with the same
black mud in which the shells are embedded. They lie about in
all positions, some vertical, some horizontal, and are often piled on
each other. In some cases large borers have perforated one or
both of the valves ; and here and there valves may be noticed with
smaller oyster-shells attached to the inner surface. No vegetable
remains were discovered with the exception of a single " stone " of the
fruit of the Sea tree,^ which is common in these islands, its empty
almost indestructible stones occurring frequently in the drift stranded
at the mouths of rivers.

At first sight one would look to human agency for the explana-
tion of this shell-bed ; but many of its features are inconsistent
with such a view. If the shells had been originally collected by
the aborigines for food, the absence of those of marine univalves of
the genera Turbo, Strombus, Cypraea, &c., such as are much
appreciated as food by natives, is inexplicable. The extent of the
bed and its uniform thickness are characters that give no support
to such an explanation. It represents, as I apprehend, an ancient
shell-bank formed on a muddy bottom in comparatively shallow
water near the mouth of a river. Since that time the Mbua River
has cut through its old deposits, and the margin of its delta is now
two miles to seaward, the intervening new land being formed
of extensive mangrove-swamps in its lower part, whilst nearer the
^ Species not identified.

6o A NATURALIST IN THE PACIFIC ch. iv

shell-bed there is much level land raised a few feet above the sea,
on which the native town and different villages now stand. The
amount of emergence here indicated since the time when this bank
of shells was forming under the sea does not probably exceed a
couple of fathoms.

Lekumbi Point. — This singular long and low promontory is
between three and three-and-a-half miles in length and rather less
than a mile in average width. It is monopolised by mangroves,
except at the extremity where the swampy ground passes into the
dry sandy soil occupied by the characteristic vegetation of coral
beaches. This terminal portion, which is about a third of a mile in
length and raised a couple of feet above high-water mark, was
originally a reef-islet. The outer third of the cape, however, is cut
off from the remainder by a narrow winding passage in the man-
groves, which being 25 or 30 feet wide can be traversed by boats
at and near high-water, and is often used to shorten the journey
down the coast. The flowing tide rushes in at both entrances, and
when the tide is ebbing it finds its way out at both exits, the
passage presenting the readiest way of the filling and emptying
of the interior swamps with the flow and ebb of the tide.

Before explaining the origin of this low tongue-shaped promon-
tory of Lekumbi, it should be observed that it lies on a long
projecting patch of coral reef which is continuous with the neigh-
bouring shore-reefs. Depths of seven and eight fathoms are found
off the sides and of 1 1 and 1 2 fathoms off the end of the reef-patch.
This reef in its turn must have been built up on a submarine bank
protruding from the coast. Such a bank may have originally been
produced by the deposits brought down by the Ndama River which
finds an exit through the mangroves near the base of the cape.
With the exception, however, of the Lekutu River, none of the
other Vanua Levu rivers have given rise to such tongues of land at
their mouths. I am more inclined to hold that the submarine
shoal, which underlies the present low cape of Lekumbi, indicates
an old lava-flow from the great crateral valley of Seatura, opposite
the mouth of which it lies. Traces of such flows are still to be found
in that locality.

CHAPTER V

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Seatura Mountain. — In my description of the profile of
this part of Vanua Levu, reference has already been made (p. 3)
to the great mass of this mountain which occupies five-sixths of
the breadth of the island. Viewed from seaward it looks like a
huge table-topped mountain-ridge, and as such it is represented in
the Admiralty charts ; but when its true contours are distinguished
it appears, when defined by the 300-feet level in the map, as a
somewhat rounded mass, measuring 12 miles in length and 10 miles
in breadth and attaining a maximum height of 2,812 feet Seen
from the deck of a passing ship it displays more or less regular
volcanic slopes, especially on the east, where there is a gradual
descent at an angle of 3 or 4 degrees for some 10 miles, and on
the north towards the Lekutu lowlands. It also shows a fairly
regular descent towards Mbua Bay on the west. (See profile,
p. 62.)

On the west side, however, there is a great gap in the mountain-
mass (the Ndriti Gap), marking, as I hold, an old crateral cavity of
large dimensions, and now occupied by the Ndama River and its
tributaries.

The adjacent Seatovo Range to the southward obscures the
profile of the mountain on the south ; and it is in fact not at all
2asy for this reason to get a view with all the slopes displayed.
It is only at times, when viewed in its complete mass with uninter-
rupted outlines, as from off the mouth of the Ndreketi River to the
north-east, or when the symmetry of its long eastern slope is
observed from Wainunu Bay that Seatura displays itself as a gentle-
sloped mountain-mass of the Mauna Loa type. Dense forest

62

A NATURALIST IN THE PACIFIC

CHAP.

o S

^ o

S2 >,

CI] V

s o
c o

S-5

s a,
o H

S-5

o

s

§■

N ^

IS

clothes the greater part of it, ex-
cept on the north and north-west,
where it lies within the limits of
the scantily vegetated " talasinga "
region.

The slopes of this mountain
are deeply furrowed by river- valleys
which radiate like the spokes of a
wheel from its central elevated
mass. Down its northern slopes
flow the Lekutu River and its tri-
biitaries and the principal tribu-
taries of the Sarawanga River.
The large western affluents of the
Wainunu River descend ^from its
eastern side, whilst the Korolevu,
Tongalevu, and other small rivers
flow south into Wainunu Bay, and
the Ndama River drains its western
slopes. In all these cases, except-
ing that of the Ndama River, the
rivers have worn deep valleys into
the mountain-mass, valleys of de-
nudation that represent the work
of ages. That of the Lekutu is a
deep cut almost into the heart of
the mountain ; at Nandroro in this
valley, which lies 6 to 7 miles inland
and 800 feet above the sea, the hills
rise steeply on either side of the
river to an elevation of 1,100 and
1,200 feet and more. Some of the
large tributaries of the Sarawanga
and the Wainunu flow through
gorge-like valleys 200 to 300 feet in
depth. On the western slopes north
of the Ndama river, the mountain-
side presents an alternating series of
lofty spurs and deep broad valleys.
In fact, all around Seatura its slopes
are deeply furrowed through the
denudation and erosion of ages.

V MOUNT SEATURA 63

The rocks of this ancient volcanic mountain are almost all of
the massive basic type, and except at the mouth of the Ndriti Gap
hardly ever display a scoriaceous character. It is also noteworthy
that no detrital rock, whether agglomerate, tuff, or tuff-clay came
under my observation. The rocks exposed on the surface are
mostly blackish brown olivine-basalts and porphyritic basaltic
andesites, the former much prevailing. In the northern portion,
however, grey olivine basalts of a different type occur. In the great
crateral hollow, which I have named the Ndriti Gap, are displayed
numerous dykes formed of highly altered basaltic rocks that may
be classed among the propylites.

The dense forest that clothes the greater part of this mountain
offers many serious hindrances to geological exploration. Except
in the northern portion, views of the surroundings are very limited,
and one has often to rely mainly on the aneroid and the compass
to obtain correct ideas of the contours and general configuration.
During most of the time spent in the southern part of the mountain,
my work was greatly impeded byheavy rains, and from this cause and
from the frequent necessity of following up the stream-courses and
of crossing rivers in flood, I was usually wet through all the day.

(«) The Eastern Slopes of Seatura. — The basaltic flows, of

which this mountain is principally composed, are best observed on

the eastern side where the original volcanic slopes are preserved.

Although the rivers have worn such deep valleys into the mountain

sides, it is however not often that any great exposure of rock

occurs, on account of the dense forest-growth over much of this

region. It is only occasionally that the columnar structure of these

old basaltic flows is displayed. It is especially well exhibited in

the face of a waterfall, distant about two miles in a straight line

from Tembenindio and elevated about 700 feet above the sea.

Here there is an exposure to the extent of 25 feet of huge basaltic

vertical columns, four to five feet across, and pentagonal in form.

The rock is a blackish basalt with scanty olivine and a specific

gravity of 2-87. It is referred to genus 25 of the olivine-basalts

vvhich is described on page 259. Micro-phenocrysts of plagioclase

ind a few of augite occur, the olivine being mostly replaced by

3seudomorphs. The felspar-lathes of the ground mass average

18 mm. in length, and there is a little brown opaque interstitial

jlass. Boulders and fragments of a closely similar basalt, with a

ipecific gravity of 2'9, lie about on the surface in this region. The

ieatura slopes here abut on the plateau of Na Savu, formed largely

)f volcanic agglomerates, to be subsequently described.

64 A NATURALIST IN THE PACIFIC chap.

On the south-eastern slopes of the mountain between Ndawa-
thumi (inland) and Korolevu (at the coast), somewhat similar
basalts with scanty olivine are exposed (sp. gr. 2'86 — 2"9i). Some
of them show the felspar-lathes of the groundmass arranged in a
plexus (genus 25), whilst others exhibit flow-structure (genus 37),
the average length of the lathes varying in different localities be-
tween '15 and '21 mm. All display scanty residual glass. On the
shores of Wainunu Bay between the Wainunu and Korolevu
rivers occur porphyritic basaltic andesites with a considerable
amount of glass in the groundmass. There is exposed on the right
side of the mouth of the last-named river a highly basic variety of
olivine-basalt with a specific gravity of 3 07. It is referred to
genus 15 (described on page 258), which includes the most basic
rocks in my collection. There are in this rock no plagioclase
phenocrysts and the felspar-lathes of the groundmass are relatively
infrequent, whilst olivine and augite occur in abundance. There is
little or no residual glass. In the district of Tongalevu blackish
oHvine-basalts and basaltic andesites of the usual character are
found. In the Na Suva range, which lies two miles inland from
the shores of Nasawana Bay and forms the southerly extension of
the mountain, a somewhat compact variety of olivine-basalt (sp. gr.
2*92) prevails up to the summit, 1,550 feet above the sea. It is in-
cluded in genus 37 of the olivine-basalts. In the length of the
felspar-lathes (-15 mm.) it belongs to the Seatura type of these
dark basalts.

{b) The Western Slopes of Seatura. — Here overlooking the
plains north of the Ndama River the same olivine-basalts and
porphyritic basaltic andesites occur. The vegetation is of the
scanty " talasinga " character, and since there is little or no soil-cap
the disintegration of the rocks has been very great, often extending
to a depth of 10 or 12 feet. It is remarkable that this disin-
tegration is most marked in the "talasinga" and similar scantily
wooded districts of the mountain. On the densely wooded eastern
and southern sides where there is a thick soil-cap, it is by no means
so evident. Here on the western slopes have been carved out deep
broad valleys and lofty spurs, the last in their turn furrowed on
their flanks, without any apparent sufficient cause. The shallow
streams at the bottom of the valleys appear quite incompetent to
produce such great erosion ; and doubtless these results are partly
due to the action on the crumbling rock-surface of temporary
torrents formed during the rains.

{c) The Northern Slopes of Seatura. — Here within the scantily

V MOUNT SEATURA g-

vegetated "talasinga" region the conformation of the land is well
displayed. Broad, deep and nearly parallel valleys, separated by
level-topped spurs and occupied by the Lekutu and its tributaries
score the mountain's slopes. The prevailing rocks are blackish-
brown ohvme-basalts and porphyritic basaltic andesites. such as
occur around the other parts of Seatura ; but grey olivine-basalts
also occur, possessmg opaque plagioclase-phenocrysts and lookine
like porphyrites. They are essentially holocrystalline and are pro-
bably more deeply situated than the other basaltic rocks Thev
are referred to genera 26 and 38 described on pages 261, 263 and
have a specific gravity of 275-2-83. Dark doleritic basalts distinct
trom all the others are exposed in places.

A good idea of this region may be obtained by following the

road westward from Tavua on the head-waters of the Sarawanga

River to Wailevu on the westernmost tributary of the Lekutu

River, a distance of about 6 miles. Leaving Tavua one at once

begins to ascend and cross the long spur that descends from

Seatura and divides the valleys of these two river-systems On its

slopes are exposed much decomposed blackish basalts possessing

scanty olivine and showing large porphyritic crystals of plagioclase

rhey have a specific gravity of 2-84 and are assigned to the

Dorphyritic sub-genus of genus 25 (page 259). At the summit, 800

eet above the sea, occur blocks of a grey holocrystalline bLalt

vith scanty olivine and semi-opaque plagioclase-phenocrysts

referred to genus 26 and having a specific gravity of 276 It

appears to form the axis of the spur. Descending to the main

^.ekutu River, just below Kavula. where the elevation is about too

.i.^et above the sea, one observes exposed in mass in the river-bed

' dark semi-ophitic doleritic basalt similar to the doleritic rocks

vithout olivine prevailing on the coast between Wailea Bay and

Lekutu (see page 50), but differing in the absence of felspar-

henocrysts. It displays a considerable amount of opaque in^ter-

a4 t:^ Th " "T'^ '° ^'""' '^ "^ '^^ augite-andesites
( >age 275). The specific gravity is 278, but there are a i^v^
n inute irregular cavities in its substance.

On leaving Kavula one crosses another of the Seatura spurs at a
k vel of 650 feet, descending then into a smaller river-valley occupied
b .a tributary of the Lekutu, on the banks of which lies the village
o Nawai, 350 feet above the sea. Then another spur is crossed It
a: . ebvation of 450 feet and the descent is made into the valley of
t e Wailevu tributary of the Lekutu. Crossing the valley which
ai the town of Wailevu is elevated 300 feet, one rises to a he^ht

F

66 A NATURALIST IN THE PACIFIC chap.

of 700 feet and then descends into the Mbua plains. These three
almost parallel valleys of the Lekutu and its two tributaries are
worthy of a detailed examination.

The rocks on the surface between Kavula and Wailevu vary in
character. Nearer Kavula there appears a blackish compact olivine-
basalt (spec. grav. 2-88), showing a little microporphyritic plagioclase
and belonging to genus 37 of the olivine rocks. Further on is
exposed one of the holocrystalline grey olivine-basalts with
porphyritic plagioclase-phenocrysts and specific gravity 2*83. It
belongs to the type described in genus 38 of the rocks on page 263.
Nearer Wailevu there occurs a blackish porphyritic basalt with
scanty olivine and specific gravity 2*8 1. It contains but little
residual glass and is referred to the porphyritic sub-genus of genus
25. In some cliffs at the river-side close to Wailevu, there is
displayed a semi-vitreous basaltic andesite, showing large porphy-
ritic plagioclase crystals, 3 to 8 mm. Its low specific gravity
(2-68) is to be attributed to the large amount of glass in the
groundmass. There is a loose mesh-work of felspar-lathes, but
the augite is not differentiated. Westward of Wailevu com-
mence the decomposing basaltic rocks of the Mbua plains.

{d) Traverse of the Northern Part of the Summit of Seaturafrom
Kavula South- West to Narawai. — The track first lay up the
picturesque valley of the Lekutu River to Nandroro, 2 J miles distant
and 800 feet above the sea. On the way blackish basaltic rocks of
the prevailing Seatura type, with or without scanty olivine, were
displayed often in a decomposing condition. At one place a
characteristic grey olivine-basalt, showing opaque porphyritic
plagioclase (sp. gr. 2-87), and looking like a porphyrite, was exposed.
On account of the abundance of the olivine, it is placed in genus
2 of the olivine-rocks. After Nandroro the path lay up the steep
mountain-side to a height of 1,500 feet : and afterwards across the
summit of the northern part of Seatura, which is here about two
miles in breadth. This elevated region is well wooded with here
and there a patch of " talasinga " land ; but it is by no means level,
its elevation varying between 1,400 and 1,800 feet, and it soon
became evident that we were crossing the heads of valleys, some-
times 200 or 300 feet in depth, that could only have been excavated
by the torrential rains. These streamless valleys afford another
indication of the denudation to which this ancient mountain has
been subjected.

The rocks prevailing in this elevated northern portion of Seatura,
at heights of 1,500 to 1,800 feet above the sea, are : {a) blackish

MOUNT SEATURA

67

basalts with scanty olivine, a little interstitial glass, and belonging
to the porphyritic and non-porphyritic sub-genera of genus 25 of
the olivine-rocks : {b) grey olivine-basalts with porphyritic opaque
plagioclase, containing but little residual glass, but varying greatly
in the amount of olivine and belonging to the genera 2 and 26 of
the olivine-basalts ; they would be classed, as far as appearance
goes, as porphyrites ; their specific gravity ranges 2-85 to 2-90.
The rock exposures were, however, scanty ; and but little infor-
mation could be obtained of the mode of occurrence. No
scoriaceous rocks were found except in the instance of a compact
dark basalt without plagioclase phenocrysts, apparently a dyke
rock, and belonging to genus 40 of the olivine-basalts.

{e) Ascent to the Summit of Seatura from Ndriti. — The town of
Ndriti lies in the great gap in the south-west side of the mountain
which has been previously mentioned as probably an old crateral
cavity. After traversing a district of highly altered basic rocks
Dr propylites, to be subsequently described, and reaching an
ilevation of about 4CX) feet above the sea, I came to the long
;lope that leads up to the summit. A dense forest hid every-
thing from view, so that the compass and aneroid had alone
o be relied on.

At first one traversed a series of step-like alternations of level
j.TOund and steep " rises," until the old site of the village of Seatura,
<bout 1,200 feet above the sea, was reached. There are some
f trange legends connected with this old mountain-village, which is
1 ow only indicated by little piles of stones and the debris of a wall,
c-nd was evidently abandoned long ago. We finally reached the
^jmmit by following up a spur or ridge in a northerly direction
f om Seatura. There was a precipitous descent on either side of the
r dge with evidently a broad, deep valley to the eastward. The
s immit was rounded ; but on account of the forest no view could
b; obtained. There was never any extensive exposure of rock
noticed during the ascent; but all the way up occasional small
b ocks of a blackish olivine-basalt were observed on the surface, of
tl e same general type as that found all around the mountain and
rt ferred to genus 37 in the synopsis.

(/) The Ndriti Basin or C^/-.— This great hollow in the side of
S iatura, which I have named after the town in its midst, is appar-
ei tly a crateral cavity now drained by the Ndama river, and its
tr butaries, and covered with dense forest to such a degree that a
?( neral view of the whole is impracticable. The glimpses, however,
th It one obtains of the mountain scenery are very grand, the town

F 2

68 A NATURALIST IN THE PACIFIC char

of Ndriti lying in the midst of mountains that rise almost on all
sides of it except on the west. This great cavity is contracted at
its mouth a little below the town and expands in its interior, where
it must be two or three miles in width. Its floor is fairly level and
is elevated only about 200 feet above the sea ; ^ whilst its mountain-
ous sides rise to 2,000 feet and over.

As shown in the map there are two breaks in the outline of this
ancient crater, the one on the west through which the Ndama
river flows, the other on the south where the dividing ridge,
separating it from the Nandi Valley is under 700 feet in elevation.
The Nandi Gorge, as I will term the last-named, is a narrow
picturesque ravine leading through the mountains from Nandi
to Ndriti. One follows up a rocky stream-course hemmed
in by precipitous sides until the top of the gorge is reached,
when the watershed is crossed, and the descent is then made
to Ndriti by one of the tributary stream-courses of the Ndama
river.

Two or three large rapid streams, after draining its mountainous
slopes, unite within the basin to form the Ndama river, which, as it
issues from its mouth, becomes a comparatively placid stream
rolling sluggishly along to the sea, some five or six miles away,
with an average drop of about thirty feet in a mile. In the course
of ages the original configuration of this great hollow has doubtless
been extensively modified by the denuding agencies. The rainfall
on the mountain-slopes must be very great, probably not under
250 inches in the year 2; and Ndriti, though only 200 feet above
the sea, is in all probability on account of its situation one of the
wettest places in the island. The rivers have evidently been
important factors in reshaping the original cavity.

Nearly all the rocks exposed in situ in the beds of the rivers
and streams in the floor of the great Ndriti basin, and for 300 or
400 feet up its sides are more or less highly altered basic rocks, to
which the old and the new names of greenstone and propylite may
be fitly applied. They often sparkle with pyrites, and not un-
commonly effervesce with an acid, so that one is apt to imagine

^ In one of my traverses I crossed a level district extending a mile N.E. of
Ndriti without changing my elevation.

2 At Delanasau, on the north or dry coast of the island, the average rainfall,
according to many years' observations by Mr. Holmes, is about 115 inches. At
Wainunu, near the wet or south coast, the observations of Mr. Barratt and others
extending over 16 years give an average of 160 inches. In the mountains this
would be nearly doubled.

V MOUNT SEATURA 69

one's self in a region of limestone. The degree of alteration varies
considerably, those most altered being light-coloured and greenish,
whilst the others are darker, the specific gravity ranging from 2*69
to 279. In spite of these differences almost all of them appear to
belong to the same eruptive series, being as a rule sharply dis-
tinguished from the prevailing unaltered surface basaltic rocks of
the slopes of Seatura by the size of the felspars of the groundmass,
which average about '3 mm. in length, whilst those of the basaltic
rocks just alluded to average only' 17 or "iS mm. long. These
rocks are also well displayed in the sides of the Nandi Gorge ; and
from their mode of exposure by river-erosion, as well as from their
relatively coarse crystalline texture, and from their alteration, it
may be inferred that they are older and more deeply situated than
any of the Seatura rocks before referred to. Whether these rocks,
which extend over an area of some square miles, have been altered
by solfataric action or contact-metamorphism,^ I will not now say.
The fact remains, however, that they are best exposed wherever
the streams have worn deeply into the floor, and lower slopes of
the great basin, or have cut down into the mountain-mass as in the
case of the Nandi Gorge. The rocks that lie in loose blocks on the
surface either at the bottom of the basin or on its slopes extending
even to the very summit of the mountain (see page 6^^, are
characteristic blackish olivine-basalts of the type prevailing around
the mountain's slopes. These propylites are most frequently
exposed as dykes in the beds of the rivers at the bottom of the
basin. Such dykes vary from 4 to 6 feet in thickness, and they
are very conspicuous when they stretch across the river's breadth
projecting more or less above the water. From their frequency it
may be inferred that in many other small exposures, ill suited for
displaying the mode of occurrence of the rock, we have also to deal
with dykes. Judging from four dykes that were particularly
examined, they are all vertical or nearly so, and all run in much the
same direction, namely, N.N.W. — S.S.E. or N.W. — S.E,, whether on
the north or south side of the great basin. In one instance, a rudely
columnar structure across the thickness of the dyke was observed.
From their exposure in river-beds it was rarely possible to ascertain
much more than is given above. However, in the bed of a river, a
mile above Ndriti, there was an extensive exposure of a highly

^ This question, which has so often been raised with respect to the propylites,
will probably receive a different answer from different localities. The matter is
further discussed on later pages.

70 A NATURALIST IN THE PACIFIC chap.

altered greenish rock which was crossed by a vertical dyke, 4 feet
thick, formed of a dark grey less altered rock. I have referred
these two propylites to two different genera of the augite-andesites,
the dyke-rock to genus 2, and the other to genus 4. In the case
of the dyke the rock is a little vesicular ; whilst in the other it is
densely charged with pyrites. Both have been subjected to the
same alteration ; but in a different degree ; and it would thus seem
that solfataric influences were here in operation before and after the
intrusion of the dyke.

With reference to the characters of the alteration of these rocks
of the Ndriti basin, it may be remarked that where the change is
greatest the felspars of the groundmass are alone recognisable.
The plagioclase phenocrysts are quite disguised by alteration
products, and chlorite, viridite, epidote, calcite, pyrites, &c, occupy
much of the groundmass. Other rocks are less affected and in a
few the change is only slight.

With regard to the prevailing types of the propylites of the
Ndriti Basin, it has already been observed that in most of them
the felspar-lathes of the groundmass are unusually large, the
average length being "3 mm. From the rare occurrence of olivine
in some of the rocks that are but slightly changed, it is to
be inferred that most of them belong to the augite-andesites,
and might be termed doleritic basaltic andesites. But in other
respects they differ considerably, both as regards the presence
or absence of flow-arrangement of the felspar-lathes, and in
the occurrence and size of the plagioclase-phenocrysts, some
having large porphyritic crystals, others small phenocrysts, and
others none at all. Many of them contained a little interstitial
glass. In my classification of the augite-andesites they are
assigned to genera 2, 4, 16, &c., and additional particulars con-
cerning their characters are given in the description of those
genera. Judging from the average large size of the felspar-lathes
it may be held that, although in other features they often differ,
some of the general conditions under which they were produced
were the same.

On the right bank of the Ndama river, opposite Ndriti, there is
a singular association of a vertical dyke of a bluish-grey basic
andesite with a reddish scoriaceous lava, apparently a flow. The
dyke is about 4 feet thick and runs N.W. and S£., like the other
dykes of the basin, exhibiting also a rudely columnar structure
across its breadth. Where the two rocks are in contact, the dyke
has a vitreous border half an inch thick, and an offshoot of the

V MOUNT SEATURA 71

dyke, four inches wide, has penetrated the lava, acquiring at the
same time a more glassy texture. The small size of the felspar-
lathes of both rocks distinguishes them from the dyke rocks of the
basin, where the felspars are twice as long. Both rocks show some
degree of alteration.^

In following the valley of the Ndama River from Ndriti to
Telana, about three miles farther down, one traverses a picturesque
region. Emerging from the great basin the river flows through
the rolling plains of the "talasinga" district. Near Ndriti, and
occasionally on the way to Telana, is exposed a scoriaceous grey
basaltic rock ; and between two and three miles below Ndriti
there is to be observed in the river-bed evidence of a comparatively
recent flow of a highly basic scoriaceous lava from the ancient
crater of the Ndriti basin. The rock, which is dark and fresh-
looking, shows large porphyritic crystals of augite and olivine but
no plagioclase, whilst the ground mass contains a little brown inter-
stitial glass. Its characters will be found described under genus 3
of the olivine-basalts (p. 255). Its specific gravity, notwithstanding
its large empty steam-pores, is 2-91. It differs markedly from
the basaltic rocks of the Seatura slopes and the Mbua and Ndama
plains, in the great porphyritic development of augite and olivine*
in the large size of the felspars and augite of the groundmass, and
in its numerous steam-holes. But in the coarseness of its small
felspars it belongs to the same type as the altered or propylitic
basic rocks of the Ndriti basin. It is probably by some such lava

^ The dyke-rock has a specific gravity of 27 ; but is slightly vesicular. It
shows a few small plagioclase phenocrysts in a groundmass of felspar-lathes,
augite grains and prisms, magnetite, and a little brown interstitial glass. The
felspar-lathes average "14 mm. in length and are for the most part not parallel.
Secondary calcite occurs in the groundmass, and the powdered rock effervesces
a little in an acid.

The rock forming the offshoot of the dyke differs only from the parent rock
in its more vitreous character. Although the felspars and augites of the
groundmass are fairly developed, the residual glass is much more copious, and
in places where it has segregated, forming " lakelets," it has been subjected to
an alteration often observed in palagonite when there are concentric alternating
zones of a tan-coloured fairly refractive material and calcite.

The reddish scoriaceous lava in contact with the dyke shows no pheno-
:rysts. The groundmass displays more or less parallel felspar-lathes, "i mm.

ong, augite grains, and much magnetite. The residual glass is fair in quantity ;

Dut is mostly gathered into " lakelets " of brown altered glass with sometimes

:alcite in the centre.

The vitreous border of the dyke is composed of a dark glass quite opaque

n the outer portion, but clearer and showing incipient crystallisation in the

nner portion.

72 A NATURALIST IN THE PACIFIC chap.

flow from the old Ndriti crater that the submarine bank was
formed off the adjacent coast on which the low Lekumbi promontory
has been built up.

In the numerous dykes of the Ndriti basin and in the great
alteration which their rocks have frequently undergone, we have
evidence in support of the view that this is an old crateral cavity,
an opinion that is supported by the indications of lava-flows that
have issued, apparently in later times, from the mouth of the
basin. Reference has already been made to the locality where
a dyke-rock and the rock-mass, into which it has been intruded,
are both propylitic ; and from this and other facts, such as the
varying degrees of alteration in different parts of the basin, it is to
be inferred that in the last stage of the activity of this vent its
bottom and sides were extensively affected bysolfataric influences.
Since that period, the configuration of the crater-basin has been
greatly modified through the denuding agencies.

The absence, or at least the great rarity, of tuff's and agglo-
merates in the case of Seatura is remarkable. The mountain has
evidently been built up in the mass by flows of basic lava ; and
from this source have no doubt in an important degree been
derived the basaltic flows of the Ndama, Mbua, and Sarawanga
plains, great streams of basalt that further seaward have helped
to form the submarine platform extending several miles from the
coast. The submarine tuffs and agglomerates that occur at
various elevations, reaching as high as 1,200 feet above the sea, in
the Sesaleka, Lekutu, Sarawanga, and Ndrandramea districts lying
to the north-west, north, and east, did not come under my notice
on the Seatura slopes. On the other hand, except in the few
localities, where scoriaceous rocks occur, the general type of the
basalts is such as we would expect to find in submarine flows.
In no part of the island, however, is the antiquity of the land-
surface so well attested by the disintegration of the basaltic flows>
which extends here to depths of ten and even twenty feet. This
is in favour not only of the sufficiency of time, but also of
the ability of the denuding agencies to strip off" the surface-
deposits.

However this may be, it is evident that the mountain of
Seatura possesses a history quite independent of that of the rest
of the island. I have pointed out in Chapter I. that it represents
a mountain of the Tahitian type. In its radiating valleys and in
its basaltic character it much resembles the mountainous island of
Tahiti, which Dana describes as a gently sloping cone of the

V SEATOVO RANGE 73

Hawaiian order that through the erosion of ages has become a
dissected mountain.^

The Seatovo Range. — This remarkably situated mountain-
range, which I have named after a town at the foot of its western
slope, extends from the valley of the Ndama River to Solevu
Bay. It attains a maximum height of about 1,800 feet, and varies
between this elevation and 1,500 feet until in theVicinity of Solevu,
where it descends as a mountainous headland to the coast. Its
summit is narrow and ridge-shaped, and although the whole range
is not interrupted by gaps it has a composite origin. At its north
end, where it is cut off from the Seatura Range by the Nandi Gorge
it helps to close in the large Ndriti basin. Towards the south an
offshoot proceeds eastward and shuts in Solevu Bay. But,
although apparently all the rocks are basic, considerable variety
prevails, and there are many puzzling points in the geological
structure of this region.

At the place where this range abuts on the Ndama valley,
below Ndriti, the grey scoriaceous basalt, before referred to, is
exposed at its foot. However, the usual blackish basaltic rocks,
often carrying a little olivine, form in mass the mountainous
southern headland that culminates in Solevu Peak (Ulu-i-matua) ;
and the same rocks prevail in the lower regions on the west side
of the range from Vuia Point to the valley of the Ndama River.
The southern portion will be described in the account of Solevu
Bay ; and I will now give the results of my journey across the
summit of the range about half a mile south of the Leading Peak
of the chart.

The eastern slopes are steep and often precipitous, whilst on
the western side there is a more or less gentle descent to the lower
levels, suggestive of a volcanic slope ; and it is remarkable that
whilst the rocks exposed on the precipitous eastern side for the
lower two-thirds are sometimes markedly altered, on the western
side they are comparatively unchanged. These facts at once
suggest that we have here the western rim of a large crateral
cavity, though the topography of this district is not sufficiently
well shown in the chart to enable one to define its original limits.
This inference is also supported by the occasional scoriaceous
character of the rocks below referred to.

The most frequent rocks in the upper two-thirds of the range
are grey porphyritic olivine-basalts, displaying opaque plagioclase
phenocrysts and more or less hematised olivine, the specific gravity
^ Characteristics of Volcanoes, 1 890.

74 A NATURALIST IN THE PACIFIC chap,

being about 2-9. They approach in characters the grey porphyritic
olivine-basalts of the northern part of Seatura (pages 65, 66) ; but
differ amongst other features in the greater abundance of the
olivine and in exhibiting flow-structure. They are usually almost
holocrystalline, and are assigned for the most part to genus 14 of
the olivine-basalts. They are extensively exposed in the stream-
courses on the west side between 500 and 900 feet ; and huge
masses of the same rocks, but containing less olivine and more glass^
and displaying much calcite, viridite, and other alteration products,
are found near the base of the eastern slopes. The semi-vitreous
condition of these rocks is represented in the large masses of a
dark very scoriaceous porphyritic lava, possessing quite a cindery
appearance, that occur on the narrow ridge-shaped summit. The
groundmass shows a few scattered felspar microliths ; but it is in
the main composed of a dark opaque glass. Small cube-like
crystals of chabazite line some of the cavities.

Other basic rocks are not infrequent and apparently represent
dykes. Thus on the eastern side at 800 feet is exposed a dark-
grey semi-ophitic doleritic rock (sp. gr. 277) assigned to genus 12
of the augite-andesites (page 275). The felspar-lathes average -3
mm. in length, and there is a little interstitial glass containing^
viriditic and calcitic alteration products, the same materials filling^
small rounded vesicular cavities. On the same slope between 1,000
and 1,200 feet, there are displayed fresh-looking compact non-
porphyritic basaltic andesites (sp. gr. 2-84), where the felspar-lathes
average '2 mm. and the interstitial glass is scanty. They are
referred to genus 16, species C, of the augite-andesites. On this
side also between 600 and 800 feet occur blocks of a highly altered
slightly vesicular augite-andesite showing a little microporphyritic
plagioclase. It is assigned to genus 13, species B, of the augite-
andesites. In one place where it is in position it is scoriaceous, the
steam-holes being round, empty and one to five mm. in size. In the
less glassy rock it displays numerous small irregular cavities either
filled with fibrous viridite or calcite or showing concentric zones of
the two minerals. The felspar-lathes are '1^-2 mm. in length. In
blocks near the foot of the eastern slope occur a blackish olivine-
basalt (sp. gr. 2-88) of the prevailing Seatura type, possessing a
little interstitial glass and felspar-lathes with an average length of
•2 mm. It belongs to genus 25 of the olivine-rocks. . . . On the
western slopes at a height of 500 feet occurs a dark compact rock
(sp. gr. 2*89) with abundant olivine which is referred to genus i of
the olivine basalts. There is a little residual glass, the felspar-lathes

V SOLEVU BAY 75

averaging only "oS mm, in length. A similar-looking rock is
exposed at 1,400 feet, which displays felspar-lathes averaging '2 mm.
long (sp. gr. 2"9). It belongs to genus 37 of the same olivine
class. Here also is assigned an aphanitic basalt, with a few
scattered large plagioclase phenocrysts and felspar-lathes averaging
•15 m. long, which is displayed near the base of the slope.

I could not satisfy myself as to the presence of tuffs on the
slopes of this range. Some fine argillaceous rocks exposed half-
way up on either side show no lime and contain no organic
remains. One specimen beside me is certainly a disintegrated
basic rock. No agglomerates came under my notice. In the
absence or rarity of detrital rocks this part of the range resembles
the adjacent mountain of Seatura.

Although olivine-basalts prevail in this part of the Seatova
Range there is great variety in their characters ; and it does not
appear possible to explain such a diversity except to assume that
we have here an old crateral ridge which has again and again been
penetrated by dykes and has since been greatly denuded. We
have here one of those singular mountain-ridges that characterise
the central portion of the island, but differing in this respect that
the submarine tuffs and agglomerates, which there occur on the
surface, even in the higher levels, are here absent.

SOLEVU Bay. — There are few localities in the island where so
many kinds of basic rocks are displayed as around Solevu Bay.
In addition to the prevailing blackish porphyritic basalts and
basaltic andesites, there are grey porphyritic basalts, grey non-
porphyritic basalts, black basalts with abundant large crystals of
Dlivine, &c., all of which have their distinctive characters.

This picturesque bay is surrounded by hills. On the west side
t is inclosed by the promontory forming the southern extension
)f the Seatovo range which, culminating in Ulu-i-matua, or the
' Head-of-the-Strong " peak, descends at first steeply and then
: gradually to the coast, where it projects as Vulavulandre Point.
On the east side is a broken line of hills, of which Koro-i-rea, the
hill known to the natives as the "Town of the Albinos," is the
; nost conspicuous. Beyond it stretches the eastern point of the
hay, which the Fijians call " Ua-nguru," that is, "the noise of the
^ /aves." On the shores lie the village of Nawaindo, " the running-
! tream," and the once populous town of Solevu, which has given
i s name to the bay. Solevu, as its name indicates, is the place
( f the " great assembly." In the background rises the three-
I eaked mountain of Koro-tolutolu, " the three towns," which forms

76 A NATURALIST IN THE PACIFIC chap.

a continuation inland of the eastern arm of the bay, and joins the
Seatovo Range at the head of it. Between these two ranges in-
closing the bay lies the valley of Solevu, down which descends the
Solevu River to the sea. In ascending this valley from the shore,
one rises only about lOO feet above the sea for the first mile or two.

The promontory, which in the even-topped Ulu-i-matua or
Solevu Peak, attains a height of i,ioo feet above the sea, displays
on its summit and on its eastern slopes descending to the Solevu
river, and on its western slopes reaching down to the coast at
Vuia, more or less porphyritic blackish olivine-basalts of the usual
type with specific gravity 2"88 — 2'go. These basaltic rocks
contain scanty olivine and only a little interstitial glass. The
felspars of the groundmass vary in different localities from "ii
to •15 mm. in average length. The rocks belong to genus 37 of
the olivine class which is described on page 262.

They are in the lower regions often decomposed to a consider-
able depth, the spheroidal structure being well displayed during
the weathering process. Where this promontory terminates in the
low Vulavulandre point, these rocks give place in part to grey
porphyritic olivine-basalts, with specific gravity 279 — 2*83, which
from the abundance of the macroscopic opaque felspar look like
porphyrites. They come near to the rocks exposed on the north
slopes of Seatura and in the Seatovo Range. At the end of the
point they become scoriaceous and more vitreous ; but with this
exception they contain but little glass. They vary somewhat in
character and are referred to genera 2 and 38 of the olivine-class.

The prevailing rock in the interior of the Ua-nguru pro-
montory to the south of Koro-i-rea is the blackish porphyritic
basalt, containing a little olivine, and often much decomposed ; but
at the point and on the east shores of Solevu Bay, there is a con-
siderable variation in the character of the basic rocks, of which the
two following are the most conspicuous. Near the village of
Nawaindo, there is an apparent intrusion of a black lava-like basalt
of high basicity (specific gravity 3*01) showing abundant large
olivine crystals, five or six mm. across, with some porphyritic
augite, but no macroscopic felspar. At the point the rock is
somewhat scoriaceous, with calcite occasionally filling the cavities,
whilst the olivine is so thoroughly haematised that it glistens like
brown mica. The compact rock contains a little devitrified inter-
stitial glass, the felspar-lathes being unusually small, their average
length being only "07 mm. It belongs to genus 15, the most basic
of the genera of the olivine class represented in the island. The

/ SOLEVU BAY 77

iecond rock to be noticed is a slightly altered compact basalt
without olivine forming apparently a dyke near the coast about
lalf way between the village of Solevu and Ua-nguru Point. It
;ias a specific gravity of 2*84, the felspar lathes ("15 mm.) presenting
.1 marked flow-arrangement, whilst there is a fair amount of altered
•esidual glass in irregular spaces, a millimetre in size. The rock, on
account of its joint-structure, could be easily worked as a building-
stone. It is referred to genus 16, species B, of the augite andesites.
The hill of Koro-i-rea, which rises on the east side of the bay
I0 a height of 850 feet, has a ridge-shaped summit. Its upper
half is composed of a bluish-grey rock looking like a phonolite and
usually compact, except at the top of the hill, where it is a little
i coriaceous. It has, however, a specific gravity of 2'gi or 2*92,
f.nd is in fact a pretty grey olivine- basalt studded with small
C'livine crystals about a millimetre in size and showing no other
phenocrysts. This type of olivine-basalt occurs also at Ulu-i-
iidali on the east side of Wainunu Bay, but is rare in the island.
It differs amongst other features from the porphyritic olivine-
l asalts of the northern part of Seatura and of the Seatovo range
i 1 the absence of plagioclase phenocrysts. There is apparently no
iiterstitial glass, whilst the average length of the more or less
( arallel felspar-lathes is '13 mm.^ On the lower slopes of the hill
tie common blackish porphyritic basalt or basaltic andesite is
exposed. In the grey-basaltic upper portion of this hill we have
I robably an old volcanic " neck."

Following the line of hills inland from Koro-i-rea, we cross the
i itervening saddle 450 feet above the sea, and ascend the slopes of
1 loro-tolutolu, a ridge-shaped mountain backing Solevu Bay, and
h aving, as its name indicates, three peaks, of which the highest is
1 ,280 feet above the sea. My observations indicate that this moun-
t lin is formed in mass of the common blackish-basalts described
t nder genus 37, their specific gravity being 2*88 to 2*94. But Koro-
t )lutolu has also the peculiarity that it appears to be in mass
r lagnetic. The rocks obtained from its summit, half-way up its
V estern slopes, and near its foot on the same side, all display
f Dlarity, a character also of the rocks of the neighbouring hills of
I lu-i-matua and Koro-i-rea, but in their cases seemingly confined
h > the higher levels.^

Neither tuffs nor agglomerates came under my notice at Solevu
I: ay. This appears to be an ancient corner of the island, from

* Referred to genus 16 of the olivine-basalts.
' This subject is discussed in Chapter XXVI.

78 A NATURALIST IN THE PACIFIC chap.

which denudation has stripped off nearly everything that could
guide us in speculating as to its past. Although the hills of Koro-
i-rea and Koro-tolutolu doubtless represent old volcanic necks, the
relation of Ulu-i-matua to the very differently composed northern
part of the same range, as described on page 73, is extremely
puzzling. Then again in the opposite sides of Solevu Bay we see
exposed the remains of lava-flows that bear no relation to the
present configuration of the surface. We may suspect, however,
that most of the volcanic energy was displayed under the sea.

Nandi Bay. — Lying north of Solevu Bay, this bay is situated
between spurs, descending to the coast from the mountainous
interior. The valley extends a long distance inland without
much change of level, the elevation i| miles from the coast being
not over 100 feet above the sea. At its head is the Nandi Gorge,
which leads into the Ndriti Basin, the great crateral cavity of
Seatura. There are some remarkable lofty, isolated hills in this
valley that would be well worth examining.

That the bay represents the site of an old volcanic centre is indi-
cated by the occurrence on the shore of two basaltic dykes, one on
either side of the village of Na Savu and 300 to 400 yards apart. The
eastern dyke is perhaps 30 feet thick, whilst that to the west is
scarcely half this thickness. They exhibit an imperfect columnar
structure, the columns, which are 6 to 12 inches across, being inclined
at an angle of 1 5° or 20° from the vertical in such a way that it may be
inferred that the molten material was ejected from some subter-
ranean focus lying to the northward (or inland) at an angle of 15°
or 20° above the horizon. The basalt is a compact bluish-black
rock with specific gravity TgS-2'gg. It contains abundant olivine
but no other phenocrysts and very scanty interstitial glass, whilst
the felspar-lathes average 'i mm. in length. It is referred to genus
16 of the olivine basalts, and is remarkable for the flow arrange-
ment not only of the felspar-lathes but also of the smaller olivine
crystals.

Blackish basaltic rocks of the prevailing type are exposed on
the surface of the broad spur, not over 500 feet in height, that
divides the Nandi and Nasawana valleys and descends to the coast
between the two bays thus named. They belong to genus 37 of
the olivine-basalts and display a few small plagioclase phenocrysts.
The felspar-lathes average '2 mm in length, and there is a little
interstitial glass. Entering Nasawana Bay we find ourselves on
the southern slopes of Seatura, of which the high Na Suva range
that backs the bay is the southern extension.

V NA SAVU TABLE-LAND 79

The Table-land of Na Savu. — This remarkable plateau
has an elevation varying usually between 700 and 800 feet above
the sea and a maximum breadth of four or five miles. It is an area
)f basic agglomerates and basic tuffs and lies in the hollow between
:he basaltic mountain of Seatura and the acid andesitic hilly region
of Ndrandramea. For the convenience of description I have named
it after the picturesque falls of Na Savu^ at its southern edge.
These falls are celebrated in Fijian tradition ; and from the brink
in old time the native desirous of ending his life leapt into the
|;orge below.

After flowing sluggishly along on the surface of the table-land,
the Mbutu-mbutu River arrives suddenly at the edge of a line of
cliffs of volcanic agglomerate, that here form the southern border
c f the plateau, and with a volume 30 to 40 feet across, it plunges
cown into the ravine 150 feet below. As shown in the view from
t le gorge below, there is a break in the middle of the descent.
These falls, however, are not easily accessible. They are best
approached by proceeding from Wainunu to Ndawathumi and
tience up the gorge of the Mbutu-mbutu River.

The surface of the plateau of Na Savu is densely wooded. In
places it is marshy, and here thrives the Giant Sedge (Scirpoden-
d'on costatum). The Makita tree (Parinarium laurinum) also
fl Durishes in the wet districts ; and in the drier localities occur the
^dakua (Dammara vitiensis) and the Ndamanu (Calophyllum-
b irmanni) together with a palm of the genus Veitchia. Here on
tl is level watershed between the basins of the Wainunu and
S irawanga rivers, the sluggish streams flow aimlessly along in but
si ghtly eroded channels ; and it is not always possible to determine
tV e side of the island to which they ultimately direct their course.
Ii their beds are pebbles and irregularly formed concretions of an
impure reddish flint which I have described on page 354. On the
n< rth and south sides the table-land is much excavated by the
tr butaries of. the Sarawanga and Wainunu rivers. On the west
w lere it meets the foot of the Seatura slope portions of columns of
be saltic rocks appear on the surface, and deep gorges are worn by
th I large streams descending from the mountain. On the east
to vards Nuku-ni-tambua and Tambu-lotu, the surface is also much
CL t up. The preservation of this table-land in a region, where the
de luding agencies are very active in their operations all around it,
is 0 be attributed to its being a level watershed, where the head-

^ "Na Savu" is the Fijian for waterfall. The complete name of this fall is
"fa Savu ni nuku."

/

ii

8o A NATURALIST IN THE PACIFIC chap.

waters of the Wainunu and Sarawanga rivers in part take their rise
but have little or no eroding power.

It is not easy to obtain a good general view of the district of
the falls on account of the dense forest-growth. When making the
traverse from Tambu-lotu to Ndawa-thumi, it is observed that
there is here a singular hollow, about half a mile in length, which
receives the falls at the western end. The river crosses this hollow
and is at once received into the gorge below, but there is no stream
to explain the origin of the cavity. On its north side the cliffs of
agglomerate rise to a height of 150 to 200 feet from their base, but
on the south the sides are much lower. Here there seem to be the
remains of the crater of the ancient vent from which all the tuffs and
agglomerates of the district were derived. We must look for their
origin in the vicinity, and the only evidence of a crateral cavity is
this streamless hollow extending east from the falls of Na Savu.

With reference to the basic tuffs and agglomerates of this
plateau it may be observed that they cover the massive basic rocks
and are probably not over 100 or 150 feet in maximum thickness.
They are well exposed where the streams cut into the borders of
the plateau. The tuffs are sometimes bedded and slightly inclined,
and they may be fine or coarse grained. They are more or less
palagonitised hyalomelane-tuffs, being composed mainly of frag-
ments of a basic glass, often finely vesicular and even fibrillar, the
vacuoles being filled with different materials, whilst the palagoniti-
sation is well advanced. Sometimes they have a brecciated
appearance, and in that case when the alteration of the basic glass
is very extensive we find angular fragments, i to 2 inches across,
of a greenish palagonite imbedded in a pale matrix of palagonitic
debris, the whole rock having a soapy feel and a steatitic appear-
ance. This is well shown on the sides of the stream-course at
Ndawathumi which lies at the border of the table-land. These
tuffs effervesce but slightly with an acid.

The basic agglomerate is displayed in the face of the falls and
in the gorges. The blocks are as a rule composed of semi-vitreous
basaltic andesites of varying type, showing no olivine and con-
taining a fair amount of smoky glass in the groundmass. At times
they are scoriaceous and display amygdules of calcite or a zeolite.
In places the rock shows large phenocrysts of plagioclase and
a semi-ophitic groundmass, when it is referred to the porphyritic
group of genus 9 of the augite-class. In a few of the scoriaceous
blocks the augite of the groundmass is for the most part prismatic
and rarely granular (genus 5).

V NA SAVU TABLE-LAND 8i

The massive rocks underlying the agglomerates in the vicinity
of Na Savu are aphanitic augite-andesites, differing in important
characters from the rocks of the agglomerates. They probably
represent ancient lava flows of the Na Savu vent. They are
compact (sp. gr. 272 — 276), and display a groundmass formed of
a felt of felspar-lathes, averaging -05 or -06 mm. only in length, and
in flow-arrangement. That occurring just below the falls is almost
aphanitic, but is referred to genus 13, species A, sub-species a,
Df the augite-andesites. The rock from the gorge below is of
:he same character, but on account of its opaque plagioclase
Dhenocrysts it is referred to genus 14, and is described on p. 279.
In one place on the plateau a tuff-agglomerate is penetrated
l)y veins, a few inches thick, formed apparently of a finely brec-
ciated tuff of basic glass fragments in a palagonitic matrix. It is,
however, pointed out on p. 340 that they were originally veins of
basaltic glass which have been subjected to crushing, and that the
palagonite has since been produced.

In concluding this description of the table-land of Na Savu, it
nay be inferred that the source of its basic tuffs and agglomerates
is to be found in the same locality ; and probably the original
vant is now represented by the hollow extending eastward from
tlie falls. With the exception of a large block of silicified coral
found in the vicinity of Ndawathumi and of the impure flints of
the surface of the plateau, which are described on pages 354, &c,, no
d rect testimony of its submarine origin offered itself to me. The
pilagonitic characters of the tuffs afford, however, indirect evidence
ir this connection ; and indeed the occurrence of submarine tuffs
,,ai d limestones in the vicinity of Tembenindio on its lower northern
. sbpes (see page 131), and the existence at elevations of several
hi ndred feet above the sea of fossiliferous tuffs and clays in the
W ainunu and Ndrandramea districts to the eastward, afford strong
pr isumptive evidence that the tuffs and agglomerates of the table-
land were deposited under the sea, and I may add in a period
su Dsequent to that of the formation of the great basaltic flows of
Sc atura and Wainunu.

CHAPTER VI

:(

I

1

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES (continued)

The Basaltic Plateau of Wainunu.— This table-land
extends for a distance of seven miles from the base of the Ndrand-
ramea mountains in the heart of the island, where it is elevated
i,ioo to 1,200 feet above the sea, to the valley immediately north
of the hill of Ulu-i-ndali, where within a short distance of its termi-
nation it still retains a height of 700 to 800 feet. Limited on the
west by the valley of the Wainunu River and on the east by that
of the Yanawai River, its breadth varies usually between four or
five miles. It is best seen in profile when viewed from the south-
west on the western shores of Wainunu Bay, between Korolevu
and Nasawana, when it presents itself to the eye as a table-land,
descending with a very gradual slope from the interior towards
the coast. From such a point of view the two great basaltic
slopes of Seatura and Wainunu may be seen together, the former
descending eastward to the Wainunu valley at an angle of 3 or 4
degrees, the latter descending at right angles to it to the southward
with a similar small gradient of 2 or 3 degrees.

In the profile of- the island attached to this work the Seatura
slope is well shown ; but that of the Wainunu table-land being
seen from the south is represented only by a level contour-line
at the base of the Ndrandramea mountains. The two great series
of basaltic flows, though closely approaching in a direction at right
angles to each other, do not come into actual contact, and the
intervening space is now occupied by the valley of the Wainunu
River. In the accompanying rude outline-sketch of this region,
as seen from off the mouth of the Wainunu estuary, the relation
of this valley to the two great series of basaltic flows is clearly

CH. VI WAINUNU TABLE-LAND 83

shown. On the left is the foot of the Seatura basaltic slope ; on
the right is the Wainunu basaltic table-land ; and between them lie
the estuary and valley of the Wainunu, at the back of which appears
the " Na Savu " table-land, formed of basic tuffs and agglomerates.
Behind all there rise up suddenly the Ndrandramea mountains
formed of acid andesites ; whilst in the foreground to the right
is the hill of Ulu-i-ndali, which is composed in the mass of a grey
basalt of a type quite different from the blackish basaltic rocks
of the Seatura slope and of the Wainunu table-land. It was from
this view off the mouth of the estuary that I received my first
lesson in studying the structural formation of the island. I kept

Profile, looking north from ofiF the mouth of the Wainunu River.

T Inland Fdran'draniea MotmLains

Seatura Slope 'Wainuna Wainunu Ulu-i-ndjli

Estuary- Tabldand.

it always in my mind's eye, and for months in an almost unmapped
region it was my only guide.

The gradual slope of the Wainunu table-land from an eleva-
:ion of 1,100 or 1,200 feet in the interior to 700 or 800 feet near
:he coast has already been referred to. Beyond this lower limit
t descends much more rapidly and within less than a mile it
erminates at Masusu in a steep-sided declivity 300 feet high
')pposite Ulu-i-ndali, and in a gentler slope on the eastern side in
ihe Ndranimako district. Its somewhat undulating surface is well
^ v^ooded ; but on account of the small gradient the small streams
< in the table-land do not excavate deep channels, but flow slowly
c long in shallow courses and often stagnate in swampy land where
1 lie interesting "Scirpodendron costatum," the giant-sedge, flourishes.
] n their beds occur reddish flinty concretions, up to 3 inches across
i 1 size, and magnetic iron sand in great abundance. A sample of
tiis sand roughly washed on the spot contains JJ per cent, of
r lagnetic iron.^

Basaltic rocks, often exhibiting a columnar structure, are ex-
\ Dsed at intervals on the surface and slopes of this table-land all
c/er its area. Now and then when traversing this region one

1 The flinty concretions are described on page 354, and the iron sand on
P 356. ^

G 2

84 A NATURALIST IN THE PACIFIC chap,

comes upon a tract strewn with large blocks, amongst which occur
fragments of huge columns 3 to 4 feet in diameter ; but it is on the
steep southern slopes of the plateau in the vicinity of Ndavutu and
Masusu that the most extensive exposures of columnar basalt are
to be found. Here there have been large clearings made for the
tea-plantations, and portions of columns 2 to 3 feet in thickness
are scattered all over the slopes and surface of Masusu.

A very interesting exposure occurs on the southern edge of
the Masusu flat facing Ulu-i-ndali. Here there is displayed in the
face of a waterfall a mass of basalt about 40 feet deep, formed of
regular cross-jointed columns, 3 to 4 feet in diameter and often
pentagonal in shape, which are almost perpendicular, being inclined
about five degrees from the vertical. But in the upper portion of
the fall the columns are smaller (2 to 3 feet across) and become
arched and nearly horizontal. This was the only section of the
inner mass of the basaltic flows that I found, and here the columns
are almost vertical. In this locality several other exposures of
the columnar basalt occur ; but they are all at the surface and the
columns are nearly horizontal or very much inclined from the
vertical, being often pentagonal in form, 2 to 3 feet across, and
sometimes curved with joints 10 to 20 feet in length.

Neither vesicular nor scoriaceous rocks came under my notice
in this region, and the presence of pteropod-ooze deposits and of
foraminiferous clays and tuffs on the slopes of the basaltic table-
land indicates that the flows were submarine. The common
character of a sub-aerial basaltic flow, where there are large
vertical columns below and smaller radiating columns above, did
not present itself ; and it is probable that the singular arrangement
of the columns in the upper portion of these flows may be con-
nected with the conditions of depth under which the flows took
place.

It is apparent from the description given by Dana of the
columnar basalt of Tahiti^ that it was formed under different
conditions from those under which the basaltic flows of Wainunu
and Seatura were formed. The columns composing a cliff 500
feet high in the Matavai valley were 10 to 20 inches across. A
bluff, 200 to 300 feet high, in another part of the valley, was made
up of columns 5 to 8 inches in width. The tallest cliff displayed
in places converging and curved columns, which is attributed to
the unequal cooling of the interior of the mass ; but it is evident
from a diagram given by the author that the columns were not
^ Geology of the United States Exploring Expedition.

VI WAINUNU TABLE-LAND 85

inclined at a large angle from the perpendicular.^ He also refers
to some prisms of a grey basalt exposed just below the Wailuku
Falls near Hilo in the large island of Hawaii which were 8 feet
in diameter and were surmounted by others only i to 4 feet across.
The basalts of the Wainunu table-land are blackish and non-
vesicular, with a density of 2-87 to 2-90. They all carry olivine
and microporphyritic plagioclase, and display a little interstitial
glass, and the felspar-lathes are usually in plexus-arrangement,
being stout and often showing twin lamellae. But the rocks
exhibit important variations in different localities as regards the
amount of olivine, the length of the felspar-lathes, the presence or
absence of the ophitic character, &c., and they are grouped in
different genera of the olivine class (i, 13, 25, 33). Probably the
type of genus 25, with scanty olivine and granular augite, would
prevail.

From the varying size of the felspars of the groundmass it is
apparent that the flows are not all of the same character. At
Masusu, where the rock is doleritic in texture, they average from
•25 to '3 mm. in length. A mile further north, they are about
♦17 mm. long, and two miles more to the north they average only
•I mm. in length. It is probable that a semi-vitreous basaltic
andesite (spec. grav. 273), that shows no olivine and is referred to
the porphyritic sub-genus of genus 9 of the augite-andesites, which
is exposed in the stream-courses near the base of the dacitic
mountains of the interior, is the product of a later eruption.
Occasionally one finds, as at Thongea in the Wainunu valley, a
Dasalt rich in olivine (spec. grav. 2-95), the felspars of the base
iveraging -i mm. in length. It may be remarked here that one
':annot draw a sharp distinction between the basalts of this region
i nd those of the adjacent eastern slope of Seatura. Their specific
i;ravity is about the same (2-87 to 2-90) ; but the coarse texture of
lhe Masusu basalts did not come under my notice in the last
bcality, where the felspars of the groundmass average -18 mm. in
Imgth or about two- thirds the length of those of the Masusu
I Dcks.

By referring to the section across this part of the island, it will
1: 3 observed that the basaltic lavas of this table-land must have
i: sued from some fissure near the south side of the base of the
^ drandramea mountains. In crossing the head of this plateau

^ A similar arrangement was observed in the columnar basalt of Kauai
ir the Hawaiian Islands. It is presumed that these Hawaiian flows are sub-
a< rial.

86 A NATURALIST IN THE PACIFIC chap.

on the way from Nambuna to Ndrawa one passes from the region
of the acid andesites into that of the basalts. The track first
skirts the base of Mount Wawa-Levu, where the prevailing altered
dacitic rocks are exposed in a much decomposed condition in the
stream-courses. Then there is a gradual ascent through somewhat
broken country to reach the western slope of the table-land, and
here are at first displayed the semi-vitreous basaltic andesites just
referred to.

The Wainunu table-land is bisected in a singular fashion by
the Ndavutu River. Since, however, the deep and often gorge-like
channel of the river displays submarine deposits incrusting the ba-
saltic slopes on its sides, it is evident that the break in the basaltic
table-land existed in part at least before the emergence.

With regard to the total thickness of the basaltic flows of this
plateau I have only a few data. In the bed of the Ndavutu River
opposite Vunivuvundi, and about 400 feet above the sea, there is
exposed a greyish porphyritic rock showing pyrites, apparently an
altered andesite. If this is the bed-rock, the basaltic plateau in
that locality would be 300 to 400 feet in thickness. This is rather
over the thickness of the end of the table-land at Masusu.

I pass on now to consider briefly the submarine deposits that
overlie the marginal slopes of this basaltic table-land in places.
They are for the most part pteropod and foraminiferous ooze-rocks
and are extensively represented on the surface and slopes of the
Nandua flat to the north of Ndavutu, where they occur at all
elevations up to 500 feet above the sea. They are also displayed
on the eastern slopes overlooking the Yanawai but at rather lower
heights ; and little patches of them occur here and there in differ-
ent places but not exceeding 500 feet in elevation. These friable
clayey rocks, which contain from 30 to 40 per cent of carbonate of
lime, are described in detail on page 320. It may however be re-
marked here that these deposits are but partly derived from the
degradation of the submerged basaltic table-land or from the wash-
ings of a basaltic coast. They were formed in a clear sea-way, but
probably at no great depth, at a time when the basaltic plateau
was submerged below the level of breaker-action.

It is remarkable that these deposits do not repose directly on
the basaltic rock. In one place below the Nandua tea-plantation,
where there is a steep descent to the river of about 250 feet, the
pteropod ooze-rock, which is exposed in the upper half, passes
down into a chocolate-coloured marl that contains 5 per cent of
carbonate of lime and is horizontally bedded. It is composed in

VI NANDUA 87

the main of fine palagonitic debris, with some fragments of min-
erals, &c, and contains a few microscopic tests of foraminifera.
This deposit passes down into apparently a rock of pure palagonite.
The succession of these beds and their characters are described
more in detail on page 344 ; and as indicated in the diagram there
given it is to be inferred that a very extensive formation of pala-
gonite has taken place on the surface of a submarine basaltic flow.

On a similar slope of the Nandua district, and about half a
mile nearer Ndavutu, the pteropod ooze-rock overlies a coarse
zeolitic palagonite-tuff composed in great part of fragments of a
highly altered vacuolar basic glass, but without organic remains.
These tuffs are horizontally stratified. Tuffs precisely similar
occur on the northern slopes of Ulu-i-ndali three miles to the
south. They are all described in detail on page.335.

Some miles up the valley of the Ndavutu River on the steep
slope descending from Vunivuvundi to the river, and on the sides
of the river lower down, are exposed dark palagonitic and some-
times calcareous clays and tuffs. I traced them as high as 450 feet
above the sea where they were bedded and dipped gently to the
west. In the river-channel they were mostly confined to the right
bank, the slope on the other side being strewn with large fragments
of columnar basalt. At the mouth of the Ndavutu River, there are
exposed tufaceous sandstones and a tuff"-conglomerate, probably
in great part formed of palagonitic materials, but I have kept no
specimens.

There is much that is puzzling about the tuffs of the region
between Ndavutu and Vunivuvundi. The surface pteropod and
foraminiferous ooze-rocks, that are found here and on the Yanawai
or eastern border of the basaltic plateau and in other localities,
offer no difficulties ; but the origin of the palagonitic tuffs that in
places lie beneath them is not so easy to explain. At Mr.
Simpson's old estate on the Nandua flat one finds numbers of huge
blocks of columnar basalt scattered about on the slope descending
to the river ; and in places there is exposed in a small stream, up
to a height of 500 feet, a fossiliferous ooze-rock containing marine
shells. The ooze-rock is evidently an incrusting deposit ; but
when one goes down to the river-side, which is there about 200 feet
ibove the sea, one finds displayed in situ in the river-bed an
imygdaloidal basic lava with coarse tuffs and agglomerates a little
ower down.

The Hill of Ulu-i-Ndall — The meaning of the name of
;his hill is " Head of the rope." It is noted on account of the dense

88 A NATURALIST IN THE PACIFIC chap.

growth of tall forest trees that clothes its surface, such as the Vesi
(Afzelia bijuga), the Ndamanu (Calophyllum burmanni), the
Ndakua (Dammara vitiensis), the Wathi-wathi (StercuHa sp.) &c. ;
and it may be that its name is connected with the launching of the
large canoes that were at one time constructed on its slopes.

Ulu-i-ndali, which has a broad level summit i,ioo to 1,150 feet
in height, rises on the left side of the mouth of the Wainunu estuary.
Its relation to the surrounding region is partly shown in the rough
sketch given on page 83. It is separated from the basaltic table-
land to the north by a deep and wide valley, the bottom of which
is raised only a few feet above the sea ; the small stream known as
Ndawa-ndingo, that apparently flows through it, is merely a branch
of the Wainunu estuary, the tide ascending it for some distance.
This singular valley, like the main valley of the Wainunu, dates
back in great part to the period preceding the emergence of this
region. The steep basaltic slopes of Masusu, strewn with fragments
of large columns, bound it on the north. On its south side are the
lower slopes of Ulu-i-ndali which are composed of volcanic tuffs.

A long spur descends to the south from Ulu-i-ndali to form
the rocky promontory of Vatu Vono or " Stone turtle," so-named
from the fanciful resemblance of the large rounded blocks of basalt
on the shore to the backs of turtles. To the south-east extend the
low tuff-formed Ravi-ravi plains which are but slightly elevated
above the sea. The Ulu-i-ndali range is apparently connected by
a " col " with a range of similar height to the eastward, the highest
peak of which is about 3 miles distant.

A more or less coarse doleritic grey olivine-basalt forms the mass
of this hill and is chiefly exposed in its upper portion. Around its
slopes, extending from the coast usually half way up the hill, are
blackish-brown olivine-basalts ; they differ amongst other points
from the grey basalts — which are practically holocrystalline, in
their greater amount of interstitial glass, to which, doubtless, is due
their dark colour. These dark basalts also occur scantily on the
summit ; but from their greater prevalence on the lower slopes and
from some other of their characters, it may be inferred that they
are in the main formed at the surface. Outside all, on the north
and south sides of the hill, are exposed coarse tuffs composed of
fragments of palagonitised vacuolar basic glass and containing
much secondary zeolitic and calcitic materials. They are purely of
■eruptive origin, and although containing no organic remains were
doubtless, as in the case of the precisely similar tuffs of the
neighbouring district of Nandua, deposited under the sea. A

VI ULU-I-NDALI 89

description of their characters is given on page 335. Such tuffs
extend as high as 300 feet above the sea on the north-west slopes,
where there are exposures, 10 to 12 feet in thickness, in the dry
stream courses ; and here they may be seen overlying the basalt
and rudely bedded, dipping away from the summit at an angle
of 15 degrees.

The grey olivine-basalts of Ulu-i-ndali, which often look like
clinkstone, range generally in specific gravity from 2*9 to 2'95.
They contain microporphyritic olivine in abundance, which is
usually more or less haematised and in extreme cases of the change
looks like brown mica. Most of them are referred to genus 16 of
the olivine class and their characters will be found described on
page 258. The felspar-lathes are stout and show sometimes
lamellar twinning, and on account of their large size ("2 to "5 mm
in average length) the rock acquires a doleritic texture. They
display as a rule a flow arrangement around the olivine crystals.
Augite granules occur in great abundance, and there is rarely any
interstitial glass.

These grey olivine-basalts are as a rule non-vesicular, but rocks
with minute irregular cavities, though without glass, occur scantily
on the upper slopes. They come near to the grey olivine-basalts
of the hill of Koro-i-rea in the Solevu district, as described on
page yy ; but they differ in their doleritic or coarser texture, the
felspar-lathes in the last-named locality being much smaller, their
average length being '12 mm.

The blackish basalts, mostly characteristic of the lower slopes
Df Ulu-i-ndali, vary somewhat in character ; but they may on the
whole be regarded as surface forms of the more deeply situated
jrey basalts which are practically holocrystalline. The rock of
:his kind that prevails on the south and west sides has a specific
gravity of 2*96. It is referred to the same genus (16) as the grey
jasalts, but differs from them in the circumstance that the
nicroporphyritic olivine is serpentinised and not haematised, and
n the occurrence of a fair amount of devitrified interstitial glass, to
\^hich probably the dark colour of the rock is due. . . . The dark
i.phanitic basalt, with flinty fracture and a specific gravity of 3*00,
1 hat is displayed in Vatu Vono Point, is merely a compact surface
"" ariety of the more coarse-textured grey basalts, being referred to
the same genus. Here there is a great abundance of micro-
] orphyritic olivine in a groundmass of parallel felspar-lathes and
< ugite grains ; but the felspars are unusually small, averaging
• mm. in length ; and there is a much larger amount of fine

90 A NATURALIST IN THE PACIFIC chap,

magnetite than in the grey basalts. There seems to be no inter-
stitial glass ; and the olivine when not fresh is usually serpent-
inised but occasionally haematised.

The dark basalts of Ulu-i-ndali when they occur on its upper
slopes become ophitic. A specimen lying beside me has a specific
gravity of 2*9 1. Allowing for the structural differences, it appears
as an ophitic surface variety of the deeper seated grey basalts. A
description of it is given under genus 12 on page 256, of which it
forms the type.

From the data above given, the hill of Ulu-i-ndali is to be
regarded as the basal portion of a submarine volcano still retaining
part of its ash-coverings. The grey doleritic basalts probably
represent the core and the dark fine-grained basalts represent the
flows of this ancient vent.

The Kumbulau Peninsula. — South-east of Ulu-i-ndali
stretches a remarkable " talasinga " district which for convenience
I will call the peninsula of Kumbulau. Its south or seaward
border is broken and hilly, and presents an irregular line of hills
300 to 470 feet in height, extending from Kumbulau Point to
Soni-soni Island, which is almost connected with the coast. The
rest of the peninsula is a low-lying and often marshy plain, which,
though elevated in some places 20 to 25 feet above the sea, is
usually much lower. On the north-east side of the isthmus is the
narrow Nandi inlet, bordered by low mangrove-belts, which repre-
sents the broad channel that in a very recent: period of the island's
history cut through the present neck of the peninsula between the
head of the Nandi inlet and Ravi-ravi.

Stratified and often steeply inclined tuff-sandstones and clays,
more or less basic and palagonitic in character, form together
with basaltic agglomerates the prevailing rocks of the peninsula,
whether in the hilly portion or in the plains. They belong to the
basic tuffs of mixed composition described on page 330 ; and though
the agency of eruptions can be recognised in their components
they are also the products of marine erosion.

Some of the hills represent volcanic " necks " ; whilst the low
narrow promontory between Kiombo and Soni-soni Island has
been formed by an old basaltic flow.

I will begin the description of this peninsula with the eastern
extremity north of Kumbulau Point, the interior of which is cut
up into ridgy hills 300 to 350 feet in height. On its eastern coast
are exposed volcanic agglomerates, composed of large blocks,
which from their dimensions given below would weigh between

VI KUMBULAU PENINSULA gi

one-third and two-thirds of a ton, a size indicating the immediate
vicinity of the vent, now obliterated, from which they were origin-
ally ejected. Near Kumbulau Point the blocks, which are made
of basaltic andesite, measure five or six cubic feet. Further north
in the vicinity of Vatu-Ndamu, the precipitous coast cliffs are
composed of agglomerates, the large blocks of which, often ten
cubic feet in dimension, are formed, not of the prevailing basaltic
andesites, as in other parts of the peninsula, but of a grey horn-
blende-andesite. This singular appearance of an acid andesite in
a region of basic rocks has no doubt given rise to the native name
of Vatu-Ndamu, "the red or brown stone." It belongs to the
second order of the hornblende-hypersthene-andesites, and is
described on page 298.

Proceeding along the south coast westward from Kumbulau
Point, before arriving at the village of Na Tokalau we pass from
the district of agglomerates into that of the bedded tufaceous
sandstones and clays which are exposed all along the coast to
Kiombo about three miles away. The transition is indicated by
the agglomerates becoming interstratified with the tuff-beds.
These sedimentary tuffs are as a rule steeply inclined at angles of
20 to 40 degrees, the prevailing direction of the dip being to the
north-east, its uniformity for such a length of coast being note-
worthy. These beds however are occasionally " crumpled " ; and
here arid there a globular structure is developed.

The hills of this region of sedimentary tuffs between Na
Tokalau and Kiombo are the highest of the peninsula. They
usually attain a height of 400 feet, but do not reach 500 feet.
From each of them descends to the coast a spur terminating in a
rocky point ; whilst between these points lie low sandy flats, where
the native villages of Levuka, Kiombo, &c., are situated. The
tuff-rocks extend to the top of the hills behind Na Tokalau, and
probably this will be found true of most of the other hills.
Agglomerates are not common in the district. In the point west
of Na Tokalau, however, they are overlaid by basaltic agglo-
merates, some of the blocks being scoriaceous. In the point east
of Levuka, a chocolate-coloured somewhat calcareous tuff-clay
occurs interstratified in thin beds with the coarser deposits.

The general characters of these tuff-sandstones and tuff-clays
have already been briefly referred to. The former are much
more prevalent and non-calcareous ; the latter are sometimes a
little calcareous and look like marl, and may perhaps contain a
few tests of foraminifera. Both are formed of the debris of basic

92 A NATURALIST IN THE PACIFIC chap.

rocks and are more or less palagonitic. The coarser deposits are
described as sample A on page 330. At times these tuffs are com-
posed of much coarser fragments of the same materials, some of
them a centimetre in size. A type of tuff intermediate in character
is not uncommon.

The promontory that lies between Kiombo and Soni-soni
Island has been formed by a remarkable basaltic flow. The low
tongue, about 50 feet high and 2CX) to 300 yards across, in which
it terminates, was originally severed by a passage worn by the sea
from the main portion ; but it is now joined by a low tract only
2 or 3 feet above the beach and partly occupied by mangroves.

The structure of the flow is well exhibited in the shore-flat and
coast-cliffs west of Kiombo, and extending to the end of the point.
The waves have here cut into its mass and exposed its structure.
Its lower part, as exposed in the shore-flat, is made of a compact
hemicrystalline basalt ; whilst its upper portion, as displayed in
the cliffs, 30 or 35 feet in height, is composed of vitreous and semi-
vitreous forms of the same rock looking like pitchstone. The
upper vitreous part is sometimes massive ; but usually it is rubbly,
with a tendency to form spheroidal masses. All transitions can
there be traced between the hemicrystalline rock of the shore-flat
and the vitreous rock of the cliffs.

The rock of the shore-flat, which has a specific gravity of 2"83,
is a blackish porphyritic basalt with scanty olivine, and on account
of the semi-ophitic character of the augites of the groundmass it
is placed in genus 33 of the olivine class. The plagioclase pheno-
crysts are 3 to 5 mm. in size. About half of the groundmass
is made up of felspar-lathes (*I7 mm. long) and large augites ('ii
mm.), the rest consisting of a smoky devitrified glass containing a
few irregular " lacunae " filled with the residual magma in the form
of a reddish-brown opaque palagonite-like material. The rock
intermediate between the lower and upper portions of the flow is
also intermediate in character, having a specific gravity of 277,
whilst quite three-fourths of the groundmass are of smoky glass.

The vitreous rocks of the cliffs, though usually rubbly in
appearance, have also the aspect in places of brecciated pitchstone
tuffs with the interstices filled with waxy palagonite ; but the
microscopical examination shows that we have not to deal with a
rock of detrital origin. We have here the effects of the breaking
up and crushing in situ of a dark-brown isotropic basic glass ^

^ The unaltered glass, which incloses a few plagioclase phenocrysts, has a
specific gravity of 27, and is readily fusible.

VI KIOMBO 95

carrying porphyritic plagioclase. The interspaces then became
partially filled with the finer fragments of the glass and of the
crushed felspar ; but they were in the main occupied by a still
liquid magma which penetrated into the cracks of the glass-
fragments and into those of the felspars, where the fractured
portions in some cases remained in position. There it has become
devitrified and often palagonitised. Whether this liquid magma
was produced by a partial remelting resulting from the heat de-
veloped during the crushing of the glassy upper portion of the
flow during the contracting process, or whether it was squeezed
upwards from the less consolidated lower portion, I cannot deter-
mine, although the last supposition seems more probable. At all
events the edges of the glass-fragments are peculiarly eroded as if
by the magma. (The bearing of these facts on the origin of
palagonite is discussed in Chapter XXIV.)

I infer that this flow has descended from the hills west of
Kiombo. Huge masses of agglomerate are exposed in the lower
third of the hill marked " 470 feet " in the chart, and immediately
north of the town. Fine clayey tufis are exposed in the hill at the
back and to the westward of this place ; but the locality requires
a more detailed examination. The absence to all appearance of
vesicular and scoriaceous rocks in the case of this basaltic flow is
remarkable. This would not have been expected in the case of a
supra-marine flow ; and indeed the testimony of the tuffs of this
peninsula sufficiently indicates that during their deposition the
whole district was submerged.

The future inquirer will doubtless discover some old volcanic
" necks " in the hills of this peninsula. One such hill overlooks
the Soni-soni inlet about a mile west of Kiombo. It is a singular
isolated hill which I have named Bare-poll Peak for descriptive
purposes. In my notes its height is stated as 120 feet, but it
appeared to me to be rather higher than this. It is capped by two
luge masses, 14 or 15 feet high, of a dark grey slightly scoriaceous-
lugite-andesite with a cryptocrystalline groundmass, which ap-
Darently form the uppermost portion of a volcanic " neck " or pipe.
'\ccording to the size of these rock-masses the " neck " would have
I circumference of 80 or 90 feet. These masses are in part incrusted
vith agglomerate.

The adjacent island of Soni-soni, which is almost joined by the

nangrove-belt to the adjoining coast, probably represents one of

he numerous small vents that were once active in this region. Its

; ingle peak is 460 feet in height. As there did not seem much

94 A NATURALIST IN THE PACIFIC chap.

prospect of finding rocks exposed on its upper part, its slopes
being densely covered with tall reeds, my examination was con-
fined to the lower portion during a walk around the island. On
its east and north sides occur rocks of much the same character as
those exposed in the neighbouring low promontory to the east of
it. In addition to agglomerates and basaltic andesites occurred a
rubbly pitchstone composed of fragments, up to a centimetre in
size, of an opaque brown glass displaying a few phenocrysts of
plagioclase and pyroxene, the interstices being filled with crushed
fragments of the phenocrysts and finer glass debris. This rock is
allied to the " crush-tuffs " described on page 334. It may be added
that the basic tuffs are more frequent on the west and south sides
of the island.

The low island of Na Vatu in the midst of the Soni-soni inlet
is about 250 feet across and only 3 or 4 feet above the ordinary
high-tide level. In 1898, when I visited it, this tiny island pos-
sessed about 20 houses and a population of 60 or 70 persons, and
I gather from Hazlewood's account of these islands that Na Vatu
was crowded with houses more than half a century ago. It was
apparently in the first place a sand-key, and is protected against
the wash of the waves by a low sea-wall formed of large blocks of
stone.

An interesting exposure of bedded tuffs and clays is displayed
at Ravi-ravi on the west side of the peninsula. A broad shore-
flat has been formed by the marine erosion of a line of coast
composed of these deposits. The strike is well exhibited, the dip
being about 30 degrees N. by W. Here there are alternating beds,
a few inches thick, of coarse and fine tufaceous sandstones, some-
times calcareous, with marls or calcareous clays. The mineral
fragments of the coarser rocks are composed of plagioclase, augite
and rhombic pyroxene, the last being abundant and giving a more
acid character to these deposits. The calcareous fragments appear
to be principally shell debris. The marl is in part composed of
much finer detritus of the same minerals. The other materials of
these deposits are derived from the degradation of basic andesitic
rocks, and include also a little palagonite. To the westward of
Ravi-ravi these beds show signs of disturbance, being steeply
tilted to the N.W. Agglomerates also occur in the disturbed
area.

The history of the Kumbulau peninsula is evidently the history
of the eruptive phases of a number of more or less submerged
small vents and of the periods of great marine erosion that

VI YANAWAI COAST 95

followed during the emergence of this part of the island. The
absence or rarity of dykes is remarkable ; but most of the hills
would represent volcanic "necks" whether of massive rock,
tuff, or agglomerate.

The District Between the Kumbulau Peninsula and
THE Yanawai River. — Between Nandi Inlet and the village of
Rewa the sea-border is low and often swampy, whilst occasional
spurs descend from the inland range into the swamps without
reaching the coast. Pebbles of "soapstone " (foraminiferous mud-
rock) occur in streams and are no doubt derived from the incrusting
deposits of the neighbouring hill slopes. In one stream-bed in the
swamps is exposed in situ a remarkable chocolate-coloured rock
that looks like a greasy pitchstone or a palagonite-rock. It is
however of detrital origin, and is composed in mass of minute
fragments of a basic, sometimes vacuolar, glass in great part
converted into palagonite ; whilst there are a number of broken
crystals of olivine and plagioclase. Through the palagonitic
alteration the fragmental character is somewhat obscured, zeolites
being extensively developed in the interstices. A little lime occurs
and there is a suspicion of foraminifera. The deposit belongs to
the group of palagonite marls described on page 335. The deeper
rocks of the district are represented in a spur by an altered augite-
andesite, originally hemicrystalline and containing much granular
^pidote.

Proceeding northward from the village of Rewa, one crosses
mother spur descending from the inland range. It is formed in
nass of a dark doleritic olivine-basalt (spec. grav. 2 '91) charac-
:erised by the length of the felspar-lathes ('28 mm), possessing a
Jttle interstitial glass, and referred to genus 25 of the olivine class,
t probably represents an ancient flow. Its surface is incrusted, as
J ligh as the road ascends, nearly 200 feet above the sea, by fine and
( oarse palagonite-tuffs ; whilst the pebbles of foraminiferous mud-
jock in the stream indicate the existence of incrusting marine
( leposits further up the slopes. The road then leads down into a
] Dw-lying undulating district that forms the sea border as far as the
1 louth of the Yanawai, and reaches about two miles inland without
< xceeding an elevation of 100 feet, although low hills occur here
I nd there. This region is fronted by mangrove swamps and is
t -aversed by the Matasawalevu and Ndranimako streams. It is a
c istrict of basic tuffs and foraminiferous clays, which, as shown
I elow, extend up the slopes of the basaltic Wainunu table-land that
1 3S behind. The soil in all the low country between Rewa and the

96 A NATURALIST IN THE PACIFIC chap,

Yanawai is red, heavy, wet, and clayey ; and affords a contrast to
the dry friable soil of the Kumbulau and Kiombo region to the
southward. ]

The Navakavura plain lying north of Rewa deserves especial
mention. It is a low, swampy district which a mile inland is raised
only 20 or 30 feet above the sea, and is mostly occupied by
casuarina and pandanus trees. Red argillaceous rocks, repre-
senting more or less decomposed palagonite coarse and fine tuffs,
are exposed in the banks of the streams. Some of them were
originally made up of fragments of basic glass which after being
palagonitised became much disintegrated. A typical specimen
by my side has a soapy feel and looks like a lump of red
clay. Microscopical examination shows that it is composed in
mass of palagonite, but in an extreme stage of the alteration
process.

After traversing the Navakavura plain, one crosses a low hill
rather over 100 feet above the sea before descending to Ndrani-
mako. On the hill are exposed reddish clay-rocks, much weathered^
but showing vegetable remains and a few univalve and bivalve
shells. Extensive submarine deposits occur in the inland district
west of Ndranimako. They are the usual foraminiferous clay-
rocks or " soapstones," and in places they contain pteropod shells.
They are well displayed in river-banks, and in the hill-slopes on
either side ; but they are probably of no great thickness since in
one locality named Na Savu, nearly two miles west of Ndrani-
mako, the underlying basaltic rock is exposed in the bed of a
gully, the sides being of " soapstone." These deposits were formed
in comparatively deep water.^ The greatest elevation at which
they were observed was about 100 feet ; but this was as high as I
reached in the ascent of the river. According to the natives, who
are very observant in such matters, these submarine deposits ex-
tend up the slopes of the adjacent Wainunu plateau. On page 86
reference is made to their occurrence on the slopes of this basaltic
table-land, i| or 2 miles farther north.

In the district between the Ndranimako and the Yanawai rivers
basic tuffs and "soapstone" prevail. In this locality, and espe-
cially in the vicinity of Ndranimako, siliceous concretions 2 to
3 inches across, occur in places on the surface. Their nature is
described in Chapter XXV.

From the foregoing remarks it may be inferred that the sea-

1 They are described on p. 322.

VI YANAWAI COAST ^^

border between the Kumbulau Peninsula and the Yanawai River
IS formed of submarine deposits overlying basic rocks which
probably represent ancient flows. Some of the deposits are
largely formed of glassy erupted materials, which have been
converted mto palagonite. Others again are more characteristic
sedimentary formations accumulated in relatively deep water

H

CHAPTER VII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Ndrandramea District

This hilly region of acid andesites is a continuation of the
mountainous backbone of the island, being separated from the
basaltic mountain of Seatura by the saddle formed by the Na
Savu table-land. These acid andesites exhibit in nearly all cases
a felsitic groundmass and phenocrysts of plagioclase and rhombic
pyroxene ; whilst many of them are characterised by brown horn-
blende more or less pseudomorphosed in the manner described on
page 306, and a few display porphyritic quartz. Although these
rocks have a common facies, they vary considerably among them-
selves ; and it is difficult to find a term that would strictly include
them all. A general description of their characters is given in the
chapter on the Acid Andesites.

In this interesting region a number of hills or mountains formed
in mass of acid andesites rise up abruptly without any regular
arrangement within an area measuring 5 by 6 miles, and elevated
600 to 1,000 feet above the sea. Of these hills, thirteen in all,
nine range in height between 1,600 and 2,500 feet above the sea,
none of the others rising less than 1,000 feet above that level. But
the actual height of each hill above the country at its base is much
less than this. The height of the hill-mass, in five or six of the
largest, ranges between 900 and 1,200 feet, whilst in the smaller
hills it varies between 400 and 800 feet. (See accompanying plan.)

These hills have sometimes a rounded profile, when their summits
are usually wooded. Others again terminate in conical bare rocky
peaks, either pointed or truncated. They have often precipitous
slopes and display vertical cliff-faces high up their sides. Their

CH, VII

NDRANDRAMEA DISTRICT

99

arrangement is rather singular. To the south and apart from the
others lies Soloa Levu (i,6oo feet). Navuningumu (1,930 feet) is simi-
larly isolated on the north. On the east rises Ngaingai (2,430 feet),

lough plan of the Ndrandramea district in Vanua Levu ; made with prismatic compass
and aneroid by H. B. Guppy.

° T 2

Scale of miles I I I

1 he highest of the peaks, with Wawa Levu (2,000 feet), Vatu Keri-
iiasi (1,900 feet), Vatu Vanaya (1,600 feet), and Mbona Lailai
(j,ioo feet) closely clustered by its side. On the west there is

H 2

lOO

A NATURALIST IN THE PACIFIC chap.

another group of hills, of which Ndrandramea (i,8oo feet) is the
highest and best known. Associated with it are Kala-Kala (i,6oo
feet), Mako-mako, Thoka-singa (1,300 feet), Vatu Mata (1,050 feet),
and another unnamed peak (1,400 feet) lying west of Ndrandramea.

The districts between and among the hills are much cut up into
lesser hills and ridges, the result of the very extensive denudation
to which this region has been subjected. The greater part of this
area is drained by the Tambu-lotu tributary of the Wainunu ; but
in the northern part we cross the watershed between the Wainunu
and Ndreketi basins, and to reach Navuningumu we cross the
valley of one of the tributaries of the Ndreketi. To the east ot
the Ndrandramea region extends a broken country, elevated rather
more than 1,000 feet above the sea, and from it there rise one or
two hills with bare cliff-faces, which are probably composed of
similar acid andesites.

Although for the most part composed of these acid andesites,
each hill, as far as my observations show, has as a rule its own
type of the rock, differing from the others in specific weight, in the
texture of the groundmass, and in the relative proportion of the
porphyritic constituents. The petrological characters will be found
more fully discussed in Chapter XXI. ; and only some of the more
distinctive features will be noticed here in the following description

of the district.

The Ngaingai Group of Hills.— Within a space less
than a mile square rise Ngaingai, Wawa Levu, and the other three
hills above named, so closely clustered together that the collective
name of " Hen and Chickens " might be aptly applied to the

group.

The peculiar form of Ngaingai is shown in the accompanymg
profile-sketch. It is the Nangorongoro of the Admiralty chart.
The height of the mountain from its base is 1,100 to 1,200 feet.
Its ascent, which is not difficult, may be made from the west side.
Above its wooded slopes rises its bare rocky peak, from which
a magnificent panoramic view of the western half of Vanua Levu
can be obtained. Characteristic dacites with porphyritic quartz
came under my notice all the way up from the foot to the summit,
being occasionally exposed in perpendicular cliff-faces. Specimens
taken from the upper and lower portions are uniform in character,
and have a specific gravity of 2-57. No other rocks were observed
on its slopes. The whole hill-mass is in great part if not entirely
formed of these acid andesites. _ ^

The contrast between the narrow crested peak of Ngaingai and

VII NGAINGAI loi

the dome-shaped summit of Wawa Levu is seen in the sketch ;
and this is the more remarkable because it is not associated, as far
as I could ascertain, with any important difference in geological
character. Wawa Levu rises precipitously to a height of 900 or
i,cxx> feet above its base, and displays often perpendicular cliff-
faces on its sides. Its broad level soil-covered summit is mostly
covered with young wood, few of the trees having trunks more
than 4 inches in diameter, whilst they are usually clothed with
damp moss, and are often decayed and rotten.^ True dacites,

Nqainqai (2428 f^ Wawa Leva (2000 n)

Profiles of Ngaingai and Wawa Levu from Nambuna to the south-west. Both are dacitic

mountains.

closely similar to those of the neighbouring Ngaingai and having
a specific gravity of 2"6i, were displayed often in slab-like blocks
from the base to near the top. The rudely columnar structure to
be observed in some of the other hills is rarely exhibited. No other
rocks came under my notice. The remains of the stone walls of
two old " war-towns," one of them named " Ndaku-i-tonga," occur
on its south and south-east slopes.

The other three hills of the Ngaingai group were not ascended
by me. They show the same bare cliff-faces and have to all ap-
pearance the same geological character. Mbona Lailai and Vatu
Kerimasi are two blunt-topped conical hills with precipitous slopes
that rise respectively about 900 and 700 feet above the country at
their base. Vatu Vanaya, about 500 feet in height, has a rounded
summit.

The Ndrandramea Group of Hills. — A view of these hills
from the westward is given in the accompanying illustration.
They have a lower elevation than the hills of the Ngaingai group,
none of them rising to over 1,800 feet above the sea, whilst their •

^ This absence of a healthy forest-growth, such as occurs on the level
summit of the neighbouring Soloa Levu and in all like situations, has probably
some geological significance.

102 A NATURALIST IN THE PACIFIC chap.

height from the base is also less, ranging between 400 and 900 feet.
They rise, as the illustration shows, in the midst of a densely-
wooded broken country.

Ndrandramea, which is 1,800 feet above the sea, has an indi-
vidual height of about 900 feet. Fijians in distant parts of the
island are familiar with the name of this remarkable peak. It has
a legendary fame ; and like Wawa Levu in the old time it served
as a mountain stronghold in times of war. The remains of a stone-
wall of a " koro-ni-valu " or " town of war," known as Mata-mei-
ndami-ndami, occur on its side, 300 or 350 feet below its summit ;
whilst among the wild lemon trees that cover the slopes below large
ovoid sling-stones 4 or 5 inches in length may still be found.
Viewed from the south-east, as shown in the frontispiece, Ndran-
dramea has the shape of a woman's breast ; and evidently the
origin of its name is connected with this resemblance. But seen
from the west and south-west, as in the other general view of the
district (page 98), it has a broadly truncated conical outline, its
form being indeed somewhat elongated or elliptical.

This hill presents precipitous slopes, and on the south side it
shows bare rocky faces. As seen in the illustration, it might
appear inaccessible ; but the ascent is not difficult on the west side.
It is composed in mass of an acid andesite allied to the dacites of
Ngaingai and Wawa Levu, but differing in the hemicrystalline
character of the groundmass (except at the base), in the porphyritic
development of rhombic pyroxene, and in the absence of porphyritic
quartz. As remarked on page 301, the rock becomes more basic as
one descends the hill. At the top its specific weight is 2-44, about
300 feet below it is 2*58, at 700 feet from the top it is 2"68, and at
the base of the hill where it is holocrystalline and has a dioritic
appearance it is 271. That it possesses a rudely columnar
structure is shown by the occurrence here and there on the slopes
and at the base of the hill of portions of prostrate columns, 3 to 4
feet broad and sometimes 20 to 25 feet long, which have a rounded
surface and look like fossil tree-trunks. Masses of agglomerate of
the same andesitic rocks lie about in places on the lower slopes, the
included blocks, which are a few inches across, being sometimes
rounded.

The neighbouring hills lying south and west of Ndrandramea
are, as far as my observations show, of the same acid type of
andesite. It is connected with those nearest by a saddle, 1,100
feet above the sea, where the same holocrystalline form of the rock
occurs, having a specific gravity of 27 and being often rudely

VII THOKA-SINGA 103

columnar in structure. Kala-kala, about 1,600 feet above the sea,
is an imposing-looking hill with perpendicular cliff-faces on some
of its sides. I did not ascend it, but found at its base a rock of the
same andesitic type, differing from that of Ndrandramea in the
more crystalline character of the groundmass, and having a specific
gravity of 2"6i. West of Kala-kala is the outlying hill of Vatu
Mata with a flat top and rising only about 400 feet from its base.
It has all the appearance of being composed of the same andesitic
rocks. It is shown on the left-hand in the illustration.

Lying south of Kala-kala are the two peaks of Mako-mako and
Thoka-singa, rising respectively 1,400 and 1,300 feet above the sea.
I ascended the last-named, which has a rounded summit covered
with trees. Approaching it from Nambuna on the east, I found at
its foot a large mass of pitchstone-agglomerate, formed of fragments
of vitreous basic rocks, such as occurs around the lower part of
Soloa Levu on the other side of the valley. The slopes of Thoka-
singa, between 200 and 450 feet below the summit, are strewn with
masses of another kind of agglomerate made up of blocks 3 to 8
inches across, occasionally rounded, and composed of the same
felsitic andesite, of which the mass of the hill is formed. This last-
named rock is exposed in bulk in the upper part, but on the summit
the agglomerate reappears. It has a granitoid appearance, and is
distinguished from the acid andesites of the other hills of the
Ndrandramea district by its greater specific gravity (272 to 274), by
its holocrystalline texture, and by the coarse grain of the mosaic
of its felsitic groundmass, which is probably quartz-bearing but is
relatively scanty. It is, however, referable to the same group of
felsitic andesites, but is to be placed at the basic end of the series.
(Its description is given on page 302.) In Thoka-singa we have
therefore a hill which is evidently formed in mass of these holo-
crystalline felsitic andesites but covered in places with an agglomer-
ate of the same materials. I have already referred to this feature
in the structure of Ndrandramea. Since the blocks are sometimes
rounded, such agglomerates may represent the result of marine
erosion during the emergence of this part of the island. In the
case of Navuningumu, where they lie abruptly on calcareous clays
containing tests of foraminifera and shells of pteropods, a different
explanation appears to be needed.

The Hill of Soloa Levu. — This isolated hill, which
presents another type of these acid andesites, has a broad rounded
summit ; and though elevated about 1,600 feet above the sea, the
hill itself rises only 800 or 900 feet above the country at its base,

104 A NATURALIST IN THE PACIFIC chap.

It is not easy to obtain a view of the profile of this hill and to
ascertain its relation to its surroundings ; and it was only when I
viewed it from near the top of Vatu Kaisia six miles to the eastward
that I was able to understand its position. Looking from that
standpoint across the basaltic table-land of Wainunu one observed
Soloa Levu rising as a dome-shaped hill at the western margin of
the table-land and apparently not separated from it. The examin-
ation of the district shows that on the east and south-east sides this
hill was in part surrounded by the great basaltic flows by which the
table-land was built up. Basic tuffs and agglomerates,lhowever, occur
on the lower slopes on the north-west, west, and south-west sides,
so that Soloa Levu in fact lies in the midst of an area of basic rocks.
The type of acid andesite which is displayed in the upper two-
thirds of the hill is distinguished from those of the other hills of
the Ndrandramea district by its orthophyric groundmass. Instead
of a fine mosaic, the matrix displays as a rule an arrangement of
short stout plagioclase prisms ; but in one of my slides the two
forms of groundmass are associated. In their general characters
as described on page 296, they cannot be separated from the acid
andesites of the Ndrandramea district. Their specific weight
ranges between 2*54 and 2'62, and like most of the other acid
andesites they contain little, if any, interstitial glass. Huge'blocks
of these rocks lie about on the slopes, often assuming a columnar
form, the fragments of such columns being sometimes 5 or 6 feet
in diameter, and 12 to 15 feet in length. I found one such block
standing erect like a solitary obelisk.

The best way to observe the basic rocks that invest the lower
slopes of Soloa Levu is to follow the track that skirts it on the
south side on the way from Tambu-lotu to Vunivuvundi. Palagon-
itic tuffs containing in places a little lime ^ and composed of frag-
ments of basic glass of varying size and more or less palagonitised
extend from Tambu-lotu and Nuku-ni-tambua (two villages lying
about a mile to the westward) to the west and south-west slopes
of Soloa Levu. A pitchstone-agglomerate, formed of fragments of
a basic glass inclosing large crystals of plagioclase felspar one-
third of an inch in length, is associated with these tuffs on the
lower north-west, west, and south-west slopes of the hill. The tuffs
are formed of the same materials as the pitchstone-agglomerates,
but differ in their character of being more or less palagonitised.
However, on the north-west side the latter have also undergone

^ These tuffs are probably submarine. They will be found described with
tuffs of the same character on p. 333.

VII SOLOA LEVU 105

this change. On page 312 will be found a description of the basic
glass of these agglomerates in its fresh and in its altered condition.
Huge blocks of these rocks strew the surface on the south-west
slopes of Soloa Levu, and in one place the underlying acid andesite
that forms the mass of the hill is exposed in a stream-course.

These pitchstone-agglomerates and palagonitic pitchstone-tuffs
are elevated between 600 and 750 feet above the sea. As one
proceeds on the road to Vunivuvundi and skirts the south-east side
of the hill one ascends the western border of the basaltic Wainunu
table-land which, however, is much cut up by rivers in this locality.
Here the tuffs and agglomerates give place to a basaltic andesite,
and on reaching an elevation of 1,000 feet we arrive at the top of
the table-land from which an ascent of Soloa Levu is easily made.
The road then lies on, but parallel to, the border of this plateau for
some distance until it descends into a deep valley worn by one of
the tributaries of the Wainunu River.

This hill of Soloa Levu is in fact a mass of acid andesite
situated in the midst of an area of basic rocks. I found basaltic
rocks exposed in the stream courses to the north and similar rocks
prevail on the north-west on the way between Nambuna and
Tambu-lotu. It has been above remarked that on the east and
south it has been in part surrounded by the basaltic flows of the
Wainunu table-land, and that pitchstone-tuffs and agglomerates
cover its lower slopes on the west and south-west, yet it is not easy
to find any trace of the vent from which they flowed or were
ejected.

It may be here remarked that the occurrence here and there
of basic rocks in the midst of this region suggests the vicinity of
dykes. For instance, in a deep gulley about half a mile south-west
of Kalakala, where a dacitic rock was exposed in sitUy I came
upon a single large mass of an aphaniticaugite-andesiteof the type
described under genus 16, species A, of the augite-andesites.

The Altered Acid Andesites of the Ndrandramea
District. — One of the most important features of the geological
structure of this district lies in the fact that the bed-rock exposed
in the lower region between the hills is a highly altered acid
andesite of the type found in the hills around. By referring to the
map of this locality, it will be observed that between the Ndrand-
ramea hills on the west and the Ngaingai hills on the east is the
valley of the Tambu-lotu river and its tributaries, an open broken
country deeply eroded by the streams, and elevated 600 to 700 feet
above the sea. These altered rocks are well exposed in the deep

io6 A NATURALIST IN THE PACIFIC chap.

gorge-like channel of the river between the village of Nambuna
and the foot of Ndrandramea, and in fact in all places in this
district where the streams have worn deeply into the surface.

They have a coarse felsitic groundmass, and are described under
the felsitic order of the hypersthene-andesites on page 297, They
present all degrees of change from the hard dark grey mottled
rocks, in which the phenocrysts of plagioclase and rhombic
pyroxene are in part replaced by calcitic, viriditic, and chloritic
materials, to those where the pseudomorphism and alteration is
complete, when the decomposition products give their character
to a pale yellowish rock, which sparkles with pyrites and often
effervesces briskly with an acid. After this comes the final stage
of disintegration, and we get a whitish rotten stone, often full of
pyrites, the last condition of which is shown in a kaolin-like
material exposed in the river-side.

The extensive alteration of these rocks is also indicated by the
occurrence amongst the gravel of the river-bed and small stream
courses near Nambuna of fragments of clear quartz prisms, half an
inch across, and of nodules, three inches in size and sometimes
hollow in the centre, formed of radiating quartz crystals that once
filled cavities in the altered rock. Small masses of vein-quartz also
occur in these streams, formed in a fissure by the growth of the
crystals from the sides towards the centre. I was unable to find
the source of the quartz ; but it is probable that it was produced
near the line of contact between the basaltic flows to the eastward
and the older felsitic rocks of the district. The great alteration of
the acid andesitic rocks exposed as the bed-rocks in this region
may in all probability be attributed to the vicinity of these basaltic
rocks. The two formations apparently come into contact about a
mile east of Nambuna. In traversing this district on the road to
Ndrawa one first observes in situ in the streams the decomposed
felsitic bed-rock with occasional loose blocks of a quartzitic rock that
displays in the thin section a mosaic of irregular grains of quartz.
Afterwards, as one rises gradually to the top of the basaltic plateau,
basaltic rocks are alone exposed in position.

In the character of the fine river sand a clue may be found to
the exact locality of the contact. In the midst of the andesitic
area between Nambuna and Ndrandramea, the sand, besides
containing much magnetic iron, is also composed to a large extent
of rhombic pyroxene prisms, clear quartz grains, and fragments of
plagioclase, all derived from the porphyritic crystals of the dacites,
&c. Near the basaltic district we find that the quartz and rhombic

VII

NDRANDRAMEA DISTRICT

107

pyroxene have disappeared, the sand
being largely made up of magnetic-iron
grains mixed with fragments of plagio-
clase.

The Extent of the Area of
Acid Andesite Rocks in the
NDRANDRAMEA DISTRICT, — By refer-
ring to the map of this locality it will
be observed that this region of andesites
extends northward to the Navuningumu
Range, and that on the south it would
be separated from the district of tuffs
and agglomerates, named the table-land
of Na Savu, by a line joining the hills
of Soloa Levu and Thokasinga. On the
east it is bounded by the basaltic area
of the Wainunu table-land. On the west
it extends at the surface, with an occa-
sional overlying patch of submarine
tuffs and clays, for a distance of at least
two or three miles from the base of the
hills, and sometimes, as in the direction
of Sarawanga, more than half way to the
coast. I have endeavoured to show the
relation of these acid rocks to the basalts
and to the sedimentary deposits in the
geological section.

When taking the track from Sara-
wanga to Nambuna by way of Ndran-
dramea one soon enters the region of
these acid andesites. The prevailing
rock exposed on the surface, where it
is usually much decomposed, is a bluish-
grey hypersthene-andesite with a specific
gravity of 2*54, and displaying in a
cryptocrystalline groundmass, where the
felsitic texture can be recognised, abund-
ant phenocrysts of plagioclase and rhom-
bic pyroxene. As high as 500 feet above
the sea it is occasionally capped by
patches of palagonitised clays and tuffs
scantily foraminiferous, and at one place

o

•s O » I

II 'i^

ill I

y-^

ptlisr

io8 A NATURALIST IN THE PACIFIC chap.

I noticed a patch of agglomerate, the subangular blocks six to eight
inches across being formed of the same acid andesite. In the same
way by taking the road from Tembe-ni-ndio to Nambuna, passing
the hill of Kala-kala on the way, we leave behind the foraminifer-
ous tuffs and limestones of the lower coast regions ; and when about
4CX) feet above the sea we enter the inland district of felsitic
andesites which begin about two miles from Tembe-ni-ndio.

The Navuningumu Range. — By following the track from
Nambuna to Navuningumu one skirts the bases of Wawa Levu and
Ngaingai, where dacitic rocks are exposed. After passing the water-
shed ^ between the Wainunu and Ndreketi rivers, the track descends
into the deep valley of one of the western tributaries of the
Ndreketi, where a characteristic holocrystalline type of these felsitic
andesites is exposed. Approaching Navuningumu one finds
exposed at its base agglomerates, composed of scoriaceous and
amygdaloidal semi-vitreous basic rocks, overlying a' dark tufaceous
sandstone which on examination proves to be a basic pumiceous
tuff of the type described on page 333, and scantily foraminiferous.

We stand now in a region of basic rocks on the south-east side
of the range, and before us rises abruptly the weird-looking
magnetic peak of Navuningumu, which is well represented in the
accompanying illustration. In the wet season its summit is usually
enveloped in the thunder-clouds. Its elevation above the sea is
1,930 feet, but estimated from its base its height is 1,000 to 1,100
feet. The natives also name this peak Na Seyanga, after a town
that once existed in this locality. It is the summit of a range that
extends a mile or more to the north where it terminates in a lesser
peak known as Mumu.

Ascending the peak of Navuningumu from the south-east one
finds exposed in its lower part, up to 1,200 feet above the sea,
pitchstone-agglomerates (composed of fragments of a vitreous
basic rock) and white tufaceous sandstones (containing a few tests
of foraminifera), such as are described below in the case of the
neighbouring Mbenutha Cliffs. Between 1,300 and 1,500 feet there
is displayed in position a typical dacite of the type described on
page 303.

The peak itself is formed of a dark-brown slightly vesicular
semi- vitreous basaltic andesite, of which, in fact, for the upper 200
feet, the summit is composed. The rock is somewhat rubbly ; and
where it is exposed on the bare peak it is powerfully magnetic,

* The track attains an elevation of about 1,300 feet, but the top of the
watershed is two or three hundred feet lower.

Mr. TAVIA (2,210 feet) irom VATU KAISIA. It
probably formed of an acid andesite.

The magnetic peak of NAVUNINGUMU (1,931 feet) from the south.
Tile summit represents a basaltic neck.

VII MBENUTHA CLIFFS

109

displaying polarity in a marked degree, and rendering the compass
useless (see page 368). A specimen of the magnetic rock, which is
a little vesicular, has a specific gravity of 2-82. It is referred to
genus I of the augite-andesites described on page 267. It displays
in the slide porphyritic plagioclase, with a little augite, in a
groundmass formed of a plexus of minute felspar-lathes (-06 mm.
in length), and exhibiting a large amount of a brown opaque glass
in which grains and rods of magnetite with a few pyroxene granules
are developed. The magnetite in the groundmass, although
abundant, is not in greater quantity than is usually found in semi-
vitreous basaltic rocks without polarity. . , . This terminal mass of
basic lava-rock evidently forms the " plug " of a volcanic pipe that
pierces the acid andesitic rocks of the district ; and from this
ancient vent were doubtless ejected the basic tuffs and agglomerates
that now cover the lower slopes of the mountain.

The conditions under which this volcano displayed its activity
are further illustrated in a remarkable section exhibited on the
east side of the mountain half a mile or more north of the summit.
Here there is a line of bold cliffs, in which, as shown in the
illustration, a bed of agglomerate, 60 or 70 feet thick, overlies a
series of foraminiferous clays and tufaceous sandstones, which are
elevated about 1,100 feet above the sea. The locality is named
" Mbenu-tha " or " Rubbish-heap." It is well known to the natives
on account of its caves, which serve as a half-way resting-place on
the road from Nambuna to Ndreketi. These caves have been
produced by the more rapid weathering of the underlying clays
and sandstones. The line of cliff extends northward to Mumu, the
peak at that end of the range, and preserves there the same
structure. The clays and tuff-sandstones are more or less stratified,
and dip generally to the west or south-west at an angle perhaps of
20 degrees ; but in more than one place they show signs of great
disturbance, being contorted and steeply tilted.

The foraminiferous clays form a more or less compact rock and
:ontain 15 or 16 per cent of lime. They inclose pteropod shells in
places and show many minute foraminiferous tests of the pelagic
:ype. Their composition is given on page 323 ; but it may be
lere remarked that the residue is made up mainly of palagonitic
iebris, fine clayey material and minerals. The mineral fragments
brm about 20 per cent of the mass, and consist principally of
jlassy plagioclase, with some rhombic pyroxene, and magnetite,
;heir size averaging -i mm. The tuff-sandstones interstratified with
he clays contain only 2 or 3 per cent of lime, and show only a few

no A NATURALIST IN THE PACIFIC chap.

scattered microscopic tests of foraminifera. About two-thirds of
the rock consist of fragments of a bottle green basic glass, vacuolar
and but little altered, the rest being composed chiefly of glass
debris, plagioclase, and a little pyroxene, the larger mineral and
glass fragments averaging "3 to "5 mm in size. They are in
fact submarine hyalomelane tuffs very similar to those first met
with at the foot of the mountain, which are referred to on page io8.
(They are described on page 333.)

These interbedded clays and tufaceous sandstones of the
Mbenu-tha cliffs were deposited under somewhat different con-
ditions. The clays represent the quiet deposition in fairly deep
water of fine materials derived from the degradation of acid ande-
sites as well as of basic rocks. The hyalomelane tuff"-sandstones
were formed more rapidly by the accumulation of fine volcanic
ash consisting of fragments of a basic glass ejected from some
neighbouring volcano that rose above the sea-surface.

Submarine hyalomelane-tuffs with basic agglomerates appear
to be of common occurrence around the base of the Navuningumu
mountain. As we leave the range behind and begin to descend
the long spur that slopes northward to Ndreketi, we find for the
first mile or two these agglomerates. But where the deeper rocks
are exposed at an elevation of 600 feet, near the village of Singa-
singa, there are displayed fine basic pumiceous tuffs and compact
palagonitised clays containing little if any lime, the last, however,
containing a few casts of microscopic foraminifera. The tuff" is
made up of minute fragments, the largest less than 'i mm. in size,
of a basic hyalomelane glass, which is vacuolar, and often fibrillar
like ordinary pumice, and in places shows the early stage of altera-
tion into palagonite. The clay principally consists of more or less
palagonitised debris of the same basic glass, together with minute
fragments of plagioclase and rhombic pyroxene. These tuffs and
clays represent the two conditions of deposition above referred to,
the last indicating a period of quiescence when the fine materials
resulting from the degradation of both acid and basic andesites
were slowly accumulating in deep water, the first denoting the
activity of a neighbouring supra-marine vent from which fine dust
and ash formed of basic pumice were ejected.

The bed of agglomerate, 60 to 70 feet thick, which overlies the
foraminiferous tuffs and clays exposed in the line of cliff" extending
from Mbenu-tha to Mumu, is made up of subangular blocks, not
usually over 6 inches in diameter, of an acid andesite of the general
type found in the Ndrandramea region, but possessing a semi-

VII MBENUTHA CLIFFS iii

vitreous groundmass.^ By clambering up the steep slope on the
south side of these cliffs, it will be observed that this thick bed of
agglomerate is covered by bedded foraminiferous clays and tuffs
similar to those that underlie it. It is therefore without doubt
submarine, and presents the result of the more violent outbursts
of some neighbouring vent. That this vent is now represented by
the " plug " of basic lava forming the peak of Navuningumu is
highly probable. It is, however, noteworthy that these beds of
agglomerates, tuffs, and clays, as shown in the photograph of the
cliffs, are all inclined at an angle of 20° towards the axis of eruption
or to the westward. The tuffs and clays underlying the agglome-
rates are, as already remarked, much disturbed in places. It would
seem that all the beds here exposed were originally horizontal, and
were tilted up during the disturbances accompanying the outbursts
of volcanic activity.

The natural section, which the Mbenu-tha cliffs present, is
doubtless due to landslips. Similar exposures, displayed by cliffs
of basic agglomerate with submarine tuffs and clays at their base,
are common on the mountain-slopes of other parts of the island.
Water oozes through the underlying soft deposits, and the result
is seen in the occurrence of huge masses of agglomerate on the
slopes below.

From the details here given respecting Navuningumu and its
surroundings, it is apparent that there have been two stages in the
listory of this volcanic mountain. The first was submarine and
vas characterised by the discharge of acid lavas which consolidated
iround the vent and were afterwards covered over with deposits of
braminiferous clays. The second was in the last part supra-
narine. With the renewal of activity, the overlying acid andesites
• vere broken through and basic materials were discharged from the
new vent. The bed of acid agglomerates exposed in the Mbenu-tha
< liff belongs to that period of the second stage when the explosive
; gencies were most violent. It represents the extensive destruction
<'f the overlying rocks. The foraminiferous tuff-sandstones are
submarine accumulations of the finely comminuted fragments of
1 asic pumice that constituted the dust and fine ash discharged
1 'om a supra-marine vent. The scoriaceous and amygdaloidal
I locks of the basic agglomerates overlying these tuffs around the
I ase of the mountain have had a similar origin. The original ash-
c Dne that at one time rose above the surface of the sea has long

^ It belongs to the 3rd order of the hornblende-hypersthene-andesites
c jscribed on p. 299.

112 A NATURALIST IN THE PACIFIC ch. vii

since been destroyed by the denuding agencies ; and its situation
is alone indicated by the " neck " of basic lava-rock that forms the
peak of Navuningumu.

A very long period must have elapsed since this last stage in
the activity of the vent The clays containing pteropod-shells and
tests of foraminifera, with which the basic pumice tuffs and the
acid agglomerates were interstratified, are now about i,ioo feet
above the sea, and are situated in the centre of the island. During
the emergence the denudation of the new land-surface was no
doubt very great ; and these submarine clays and tuffs, as displayed
in the cliffs, owe their preservation in great part to the protection
of the overlying mass of agglomerate.

Much light is thrown on the history of the whole Ndrandramea
region of acid andesites by the examination of this old volcano of
Navuningumu. Some of the hills, as in the case of Ngaingai and
Wawa Levu, seem to have been stripped of everything that could
give information to the geologist. Others again, like those of
Thoka-singa and Ndrandramea, display here and there on their
slopes agglomerates of the same materials, the rounded forms of
some of the blocks being in part indicative of marine erosion
during the emergence of this region from the sea. In Soloa Levu,
however, we have one of these hills partially surrounded by
later basaltic . flows and covered in places on its lower slopes by
basic tuffs and agglomerates, probably submarine. In Navu-
ningumu the original mass of acid andesite is only scantily ex-
posed. It is for the most part buried beneath submarine clays
which are in their turn covered by the tuffs and agglomerates of
later basic eruptions.

CHAPTER VIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

Mount Vatu Kaisia and District

This peak, i,88o feet in height, starts up suddenly in the
1 lountainous interior of the island. Being situated in the valley
( f the Yanawai river, which opens to the south, it forms a con-
spicuous landmark for vessels off the south coast ; but from most
ether points of view, on account of its peculiar situation, it is
t sually difficult and often impossible to obtain even a glimpse of
ii.^ From its remarkable blunt-topped conical shape it has

Profile-sketch of the Vatu Kaisia district from S.S.E.
tian dronaadranu
Ndrandramea Pange \ Vatu Kaisia

Yanawai Valley

r€ ceived the not very appropriate name of Marling Spike in the
Admiralty charts. The natives name it Vatu Kaisia, the first
w )rd signifying " rock," whilst the second is the name of a demon.
Some idea may be formed of its situation and of the character
ol the neighbouring country from the profile-sketch and photograph
ht re produced. I was unable for reasons given below to take a
pi otograph of the mountain itself, as it was either too near or too
fa away. Vatu Kaisia is approached either from Ndrawa on the
nc 'th or from Ndawara on the south, the ascent being best made

1 Occasional views of its summit only are "obtained from the eastward, as
fro n the Ndrandramea mountains and their vicinity,

I

114 A NATURALIST IN THE PACIFIC -chap.

from the west side. The regions traversed on the way are so
densely wooded that the mountain does not become visible until
the traveller is right upon it. He becomes suddenly aware that
there is some huge mass close to him looming above his head
through the trees ; and it is with a feeling of awe that he first
looks upon a mountain that although only a few hundred yards
away nearly escaped his search. He is startled by its proximity,
and wonders what strange forces have been at work to place it
there ; but his view is transitory, and whether proceeding north or
south he sees it no more, unless he essays to climb its slopes.

Vatu Kaisia lies not in the centre but towards the west side of
the Yanawai valley the river flowing as an impetuous stream
around the foot of ts eastern slope. In the profile-sketch the
mountain itself conceals the peculiar feature of its position, which
is, however, shown in an exaggerated form in the geological section
below. On its west side rises a broad ridge running south which
in places is not much higher than the basaltic plateau of Wainunu
to the west of it. This ridge is only separated from Vatu Kaisia
by a dark narrow gorge not many hundred yards in width, across
which my natives were able to make themselves heard when near
the summit. The mountain rises i,ioo or 1,200 feet above the
gorge on its west side, which is 700 feet above the sea, and some
1,400 or 1,500 feet above the Yanawai river on the east, which is
300 or 400 feet above the sea. It possesses two peaks, of which
the western one is smaller and lateral and has a height of 1,600 or
1,650 feet, whilst the eastern is the main peak and rises to 1,880
feet. The saddle between the peaks has an elevation of about
1,500 feet. It is very difficult to obtain a distant view of the two
peaks, which lie about N.W. and S.E. with each other. They are
either merged into one as in the view from the south, or else the
highest portion of the main peak is alone visible.

On the lower slopes of the mountain as high as 1,100 or 1,200
feet is exposed a porphyritic doleritic basalt showing semi-ophitic
augite and abundant interstitial glass. Its specific gravity is 2'8,
but there is no olivine. It belongs to a type of basalt described
under genus 9, sub-genus A, of the augite-andesites. The upper
double-peaked portion rises precipitously, displaying bare rocky
cliff-faces with a drop of 100 or 150 feet, and formed in mass of a
grey andesitic rock with a specific gravity of 271 and showing
abundant small porphyritic crystals of hornblende and rhombic
pyroxene. It represents a type of the hornblende-hypersthene-
andesites described on page 301. I was unable, through want of

vin

VATU KAISIA

^15

a rope-ladder, to accomplish the last hundred feet of the summit ;
but the general uniformity of structure was evident. No detrital
rocks came under my observation.

That the porphyritic basalt represents a later flow around this
old andesitic mountain is indicated amongst other things by this
absence of tuffs and agglomerates. Vatu Kaisia is undoubtedly
the core of an ancient cone of hornblende-andesite, and as in the
case of Mount Soloa Levu, which is formed of somewhat similar
andesites (see page 103), it has been more or less completely sur-
rounded by later basaltic flows. Vatu Kaisia and Soloa Levu
occupy similar positions with respect to the great basaltic table-land
of Wainunu, the first lying just within its eastern border, the second
lying partly within its western margin.

The structure of the ridge immediately west of Vatu Kaisia
lends support to this view of the formation of this region. The
ridge is here, it is true, elevated a hundred feet or so above the
table-land which is about 1,000 feet above the sea ; but whilst on
its slopes facing the mountain the same porphyritic basalt prevails,
there is a limited exposure on its top of the same rock (sp. gr. 2 "68),
differing only in the larger size of its porphyritic crystals of
hornblende and rhombic pyroxene.

The narrow gorge isolating the mountain on the west is occu-
lied by a tributary of the Yanawai River. It has a depth of 400
eet below the ridge ; and as illustrated in the section below it has

Vatu Kaisia

1880

W

Basaltic Ba tern of
'WainanxL .

il basaltic Pocks.
EZl Dacittc Rocks.

Heights in Feet above se^
Length of section 3 miles.

e /idently been largely formed by the eroding agency of the stream.
I 'owever, at the bottom of the gorge there is exposed a heavy
a )hanitic basalt showing no olivine and having a specific gravity
o " 2"85. Though of much finer texture, the felspar microliths only
n easuring '05 mm. in length, it differs conspicuously from the
o erlying porphyritic basalt in possessing little or no interstitial

I 2

ii6 A NATURALIST IN THE PACrFIC chap.

glass. It is referred to genus 16, species A, sub-species i, of the
augite-andesites (page 280).

The probable structure of this district is shown in the geological
section here given. It is assumed from the limited exposure ot
the same rock on the top of the ridge that the basaltic flows which
surrounded the lower portion of Vatu Kaisia at the same time
covered over another similar peak lying immediately west of it.
Through stream-erosion Vatu Kaisia has now been isolated on its
west side ; and since the basaltic rocks rise to about the same
height on both sides of the gorge thus produced, the original
surface was probably as indicated by the dotted line in the
diagram.

By following the summit of the ridge, as it runs south on the
right side of the Yanawai valley towards Ndawara, some interesting
rocks are observed. For the first mile from the camping-place
opposite Vatu Kaisia the elevation increased from' 1,100 to 1,300
feet, and blocks of a blackish basaltic andesite (sp, gr. 276) lay on
the ground. About a mile further on fragments of white quartz-
rock appeared on the surface having been thrown out of a shaft
close to the track which had been sunk to a depth of 15 or 20 feet
by a gold miner ^ a few years before. I could not descend the
shaft to examine it : but the specimens picked up are evidently a
white vein-quartz, some of them having a striated " slickenside "
surface on one side.^ There is evidently a "contact" in this
locality, probably of a basaltic rock with an acid andesite.

Leaving the shaft, the track proceeds southward and eastward
and one descends gradually from a height of 1,100 feet down to the
Yanawai river where the elevation is only about 1 50 feet above the
sea. Occasional blocks of basaltic rocks lie on the surface of the
ridge, and in one locality there is exposed a curious-looking
agglomerate formed of fragments of a greenish altered augite-
andesite, somewhat scoriaceous, the cavities being filled with a
zeolite. At the crossing of the river a black basalt (sp. gr. 2"82)
occurs in situ ; whilst loose blocks of basalt and of an acid
andesite occur in the river-bed. Continuing the journey from the
Yanawai crossing to Ndawara near the mouth of the river, one
follows the track across a range of hills, 500 to 600 feet in height,
basaltic rocks prevailing on the surface.

^ Alluvial gold has long been known to occur in the bed of the Yanawai
below Vatu Kaisia ; but it has never been found in paying quantity.

2 Under the microscope it is shown to be granular in structure, exhibiting a
mosaic of irregular quartz grains.

VIII NANDRONANDRANU ^t^

The NANDRONANDRANU DISTRICT.

Lying north-west of Vatu Kaisia is an elevated district which
I have named after its highest summit, a square-topped peak rather
higher than Vatu Kaisia and probably about 2,100 feet above the sea.
Koro-ni-yalewa, which signifies " town of the women," is another
name of this peak. It is shown in the sketch given on page 113,
and is situated about two miles north-west of Vatu Kaisia. I did
not ascend this mountain, which from its form would seem to be
made of an acid andesite like the Ndrandramea peaks. Much of
this elevated region varies between 1,000 and 1,500 feet in elevation.
It is connected with the Ndrandramea district by somewhat broken
country not much over 1,000 feet in height, which is the "divide"
between the river systems of the Ndreketi and Wainunu. A long
;ongue-like extension of similar elevation projects to the north-
A^est between the Ndrawa and Navuningumu branches of the
Vdreketi. This elevated region is continuous to the eastward with
■ he Tavia Range which is described below. For convenience the
valleys of the upper course of the Ndrawa river have been included
in this district as their geological features can in this connection be
best explained.

This region is well distinguished from most of the other districts
of the island by the prevalence of aphanitic augite-andesites.
' These rocks have also supplied the agglomerates of the locality,
nd the palagonite-tuffs which are in places extensively represented
re evidently in great part derived from vitreous forms of the same
r Dcks. We seem to get nearer to supra-marine eruptions in this
rigion than in most others. The palagonitic-tuffs and agglo-
r lerates appear to have rapidly accumulated in shallow water, and
t lere is reason for regarding one exposure of the aphanitic augite-
a idesites as at all events a shallow-water lava-flow. The aphanitic
c laracter of the massive rocks, however it may have arisen, is here,
a ; I take it, associated with the shallow-water habit of the tuffs
a id agglomerates.

(i) East Side of the Nandronandranu District.— By
f( llowing the track leading from the ridge on the west side of Vatu
J aisia northward to Ndrawa one rises gradually to a more elevated
n gion. The rocks exposed on the surface for the first mile are for
tl e most part altered hypersthene-augite-andesites possessing a
ir icro-felsitic groundmass. When a height of about 1,400 feet was
attained, the track could not have been far from the peak of

ii8 A NATURALIST IN THE PACIFIC chap.

Nandronandranu, but on account of the wood no view was ob-
tainable. In this locality between 1,300 and 1,400 feet soapy
palagonitic clay-rocks and coarser palagonite-tufifs are displayed
on the surface. No organic remains are to be noticed in the
specimens collected here, but they are much affected by hydration.
Judging from the fossiliferous character of similar deposits over a
large part of the island, it is highly probable that these tuffs and
clays are also submarine.

Afterwards a descent was made to an undulating region about
I J miles across and elevated between 750 and 850 feet. The
blocks there displayed on the surface are composed of a dark
rather compact augite-andesite with a specific gravity of 275 (see
genus 13) and of an altered greenish aphanitic augite-andesite
with a specific gravity of 2*59 in which calcite occurs as an
alteration product (genus 16). Aphanitic rocks of this character
as shown below, are very prevalent in the north-west and north
parts of the Nandronandranu district, but are not usually
altered.

(2) The North-west Part of the Nandronandranu
District. — The best route to follow here is to take the track from
Nambuna to Ndrawa. After crossing the upper portion of the
Wainunu table-land one reaches the headwaters of the Ndavutu
River and then ascends the watershed between the Ndreketi and
Wainunu river-systems, reaching Savulu, about 1,050 feet above the
sea, where a solitary house marks the site of an old mountain town.
This region is much cut up in deep valleys usually 200 to 300 feet
deep, which are occupied by affluents of the Ndrawa branch of the
Ndreketi, flowing north. The valley of the main affluents is from
400 to 500 feet in depth ; and this constant ascent and descent of
steep and often slippery valley sides makes the journey very
tedious.

At Savulu one stands within the Nandronandranu district.
Behind lies the Wainunu table-land with its olivine basalts ; but
here aphanitic augite-andesites prevail and extend to Ndrawa and
beyond. They are exposed in position in the stream-courses and
furnish most of the blocks and pebbles found in the bed of the
main Ndrawa River for miles down its course towards the sea.
They are dark, compact, and non-porphyritic rocks and are all re-
ferred to genus 16 of the augite-andesites as described on page 279.
They vary, however, in certain features, as in the specific gravity,
the amount of glass, &c. The residual glass is, however, usually
small ; but in a stream-course east of Savulu I found in position at

VIII NGANGA-TURUTURU CLIFFS 119

an elevation of 750 feet a semi-vitreous scoriaceous variety of
these rocks, in which the steam-pores had been drawn out into
long tubular cavities half an inch and more in length. The scori-
aceous character is infrequent ; but reference should here be made
to another exposure of a slaggy semi-vitreous rock showing
abundant steam-pores in the tuff-district of the river valley above
Ravuka. It differs in some respects from the prevailing rock, since
it displays prismatic augite as well as felspar microliths in its
glassy groundmass, and is for this reason referred to genus 20 of
the augite-andesites. In the elevated region east of Savulu the
aphanitic augite-andesites are in places overlain by tuffs and
agglomerates formed of the same materials. There is a very good
exposure of the tuffs in the Nganga-turuturu cliffs about 2 miles
west of Savulu.

(3) The Nganga-turuturu Cliffs. — These picturesque
cliffs, 50 to 70 feet in height, rise up at the head of the Liwa-liwa
valley between Savulu and Ndrawa. They are elevated about i,2CX)
feet above the sea ; and probably derive their name from a small
waterfall which, after descending over their face, drops into the
valley below. At its bottom is situated the hamlet of Liwa-liwa,
which is about 600 feet above the sea. This is the Fijian word for
" cold," and doubtless it has allusion to the coolness of the valley.
On account of the more rapid weathering of the tuffs in the lower
part of the cliffs, there is a rude shelter afforded by the overhanging
portion which is the main feature of interest that the cliffs present
from a native's point of view.

The tuffs composing the cliffs are horizontally bedded and over-
lie the prevailing aphanitic augite-andesite exposed on the valley-
slopes below. Originally grey in colour, they have been largely
affected by the hydration accompanying the weathering process.
They are fine in texture and somewhat friable, but contain no lime,
and are chiefly made up of the palagonitised fine detritus of
vitreous varieties of the aphanitic augite-andesites of the district.
No organic remains came under my notice. Some of the beds
contain a number of lapilli of basic pumice, i to 3 centimetres in
size, which are often in the last stage of the disintegration pro-
duced during palagonitisation. It would seem probable that these
lapilli, after having been ejected from some supra-marine vent,
were deposited with the tuffs in the sea around. It should, how-
ever, be not forgotten that vesicular and pumiceous materials may
be discharged during a submarine eruption. When I visited the
museum at Catania, Prof Platania showed me portions of a bomb,

120 A NATURALIST IN THE PACIFIC chap.

highly vesicular, that had been thrown up in a submarine eruption
off Vulcano in the Lipari Islands.

(4) The Upper Valleys of the Ndrawa River. — The
two valleys of Liwa-liwa and Ndrawa meet at Ravuka, where their
two streams unite to form the main Ndrawa River. The former is
the largest ; and its large impetuous stream, during its descent of
about two miles from Liwa-liwa past Lutu-kina to Ravuka, which
is between 200 and 250 feet above the sea, has a drop of 300 or 350
feet. The main stream flows with a gentle gradient to the coast
about ten miles away. I did not descend its course for more than
two miles below Ravuka, where some hot springs well up through
the gravel on the left bank (see page 31.)

This is a region of palagonite-tuffs which like those of the
Nganga-turuturu cliffs are mainly derived from vitreous and semi-
vitreous aphanitic augite-andesites. They do not effervesce with
an acid, and neither foraminiferous tests nor other organic remains
occur. The palagonitic material is usually vacuolar, the vacuoles
being filled with palagonitic glass or with a zeolite as in the more
altered rocks. Where bedding is shown, the beds are generally
horizontal. These tuffs are extensively displayed in the sides and
beds of the rivers from Liwa-liwa and Ndrawa to Ravuka and as
far as I went down the main river, namely to the hot springs.
They are associated with agglomerates, formed of the aphanitic
augite-andesites, below Ravuka and in the Ndrawa valley.

(5) The Vicinity of Ndrawa. — The village of Ndrawa,
which is not elevated more than 300 feet above the sea, is situated
in the heart of the island in a deep valley more or less hemmed in
by the mountains. This is one of the wettest localities in Vanua
Levu, and probably, as in the case of that of Ndriti in the Seatura
basin, the rainfall is not far under 300 inches in the year. In the
river-gorge descending westward to Ravuka are displayed horizon-
tally bedded palagonite-tuffs and agglomerates above referred to in
the description of the Ravuka district, and the same rocks are
exposed on the mountain-slopes to the south of the village.^

Immediately to the north lies a broken hilly country, about 800
feet above the sea, which has to be crossed on the way to Mbatiri
and is much cut up by streams descending from the vicinity of Na
Raro to join the Ndrawa River below Ravuka. The prevailing
rocks are tuff-breccias and agglomerates. The first are made up
chiefly of angular fragments, less than an inch in size, of aphanitic

^ The blocks of the agglomerate in this last locality are from one to three
feet across.

VIII TAVIA RANGES 121

augite-andesites, some of them being more or less vitreous and in
different stages of palagonitisation, whilst the finer material derived
from the same rocks contains some carbonate of lime. The
agglomerates are composed of the same type of these augite-
andesites, with however but little interstitial glass. It should be
added that pebbles of a kind of jasper or iron-flint occur in the
stream-beds in this locality. (The microscopical characters are
described on page 355.)

By following up the valley that extends to the east from
Ndrawa, one enters after about a mile into the region of Na Raro,
which is described on page 123.

The Tavia Ranges.

North of Vatu Kaisia the elevated Nandronadranu district
divides into two ranges, one of which stretches eastward to the
south of Na Raro as far as the gap of that name, whilst the other
extends southward on the east side of the Yanawai valley. Near
the angle of bifurcation is situated Mount Tavia, a remarkable
pyramidal peak marked 2,210 feet in the Admiralty chart and lying
l^ miles north-east (N33''E) of Vatu Kaisia. It is shown in the
view facing page 108. All this region is densely wooded, and I had
chiefly to rely on " course-and-distance," and on my aneroid, to
determine the surface-configuration.

(i) Range on the East Side of the Yanavs^ai Valley. —
No ascent of these hills was made. They vary from 1,500 to 1,800
feet in height, and judging from the loose blocks and gravel in the
bed of the Yanawai River below Vatu Kaisia they would seem to
be mainly formed of basaltic rocks, acid andesites being also
represented. However, I crossed the southern end of the range,
Adhere it is 500 to 600 feet in height, to the north of Ndawara, and
bund basaltic andesites prevailing at the surface.

(2) Range Extending Eastward from Mount Tavia on
the South Side of Na Raro.— Mount Tavia, which has the
ippearance of a dacitic peak, was not ascended ; but the range was
' Tossed in two places in going from Ndrawa to Vatu-vono and
:rom Valeni to Nareilangi, its usual height varying between 1,200
; nd 1,500 feet, the extreme height being about 1,700 feet.

In making the traverse from Ndrawa to Vatu-vono, one first
] asses through a part of the hornblende-andesite region of Na
] Laro, which is described in a later page. Afterwards while ascend-

122 A NATURALIST IN THE PACIFIC chap.

ing the north slopes of the range, basaltic andesites, often doleritic
in texture and referred to genus i of the augite-andesites, are usually-
found as far as the summit 1,200 to 1,300 feet above the sea. On
descending the south slopes one finds coarse and fine palagonite-
tufifs and clays at 900 to 1,100 feet up, similar to those prevailing near
the sea-border. They are probably submarine, but my specimens
are weathered and give no effervescence with an acid. In the bed of
the river above Vatu-vono, about 400 feet above the sea, there
occurs in position an aphanitic augite-andesite (spec. grav. 277),
referred to genus 16, species A ; whilst blocks of a coarser grained
basaltic andesite lie loose in the stream.

In my traverse across the range from Valeni to Nareilangi I
noticed about a mile from Valeni and not much over 100 feet
above the sea an agglomerate formed of blocks of an altered acid
andesite possessing a micro-felsitic groundmass and showing micro-
porphyritic rhombic pyroxene with dark alteration borders (spec.
grav. 2'5). It is distinct from the Na Raro rocks ; and its presence
in an agglomerate seems to indicate the vicinity of some old acid
andesite peak buried beneath later basic eruptive products.
Ascending the south slopes of the range, I found decomposing
basaltic andesites and basic tuffs, the prevailing rocks up to an
elevation of 1,300 feet ; but in one locality (800 feet) occurred large
masses of what seemed to be a disintegrating dacitic rock penetrated
by quartz veins less than an inch thick. An aphanitic augite-andesite,
of a somewhat exceptional character (spec, grav, 2-63), was displayed
at the top of the ridge, 1,500 feet above the sea.^ Basic rocks were
exposed in the spur running northward on the east side of Na
Raro.

The Sea-border Extending East from the Yanawai
River to the Lango-lango River. — In this district is in-
cluded the area between the foot of the slopes of the Tavia Ranges
and the shores of Savu-savu Bay. This undulating country, two
to three miles in breadth, does not attain a greater elevation inland
than 300 or 400 feet. . Fine and coarse palagonite-tuffs, some of
them with the texture of sandstone, are the characteristic rocks.
They at times contain a little lime and probably a few tests of
foraminifera. The palagonitised glass is often vacuolar, the vacuoles
being filled with the same material. In places where they are well
displayed these tuffs generally show bedding, as in a hill-slope just
east of Vuni-evu-evu, where there are fine and coarse tuffs inter-

^ It displays in the groundmass augite prisms in flow-arrangement, and is
referred to genus 20 of the augite-andesites.

viii NA RARO 123

stratified and dipping 'gently W, by S. Basic agglomerates also
occur in this district.

In the promontory named Yanutha Point in the map there is
displayed an old flow of basaltic lava, showing a columnar structure
at the end of the point. The columns are 20 inches in diameter,
and are inclined about 20 degrees from the vertical in such a direction
that it may be inferred that the original flow, doubtless submarine,
descended at that angle from N.N.W. The dark grey rock of the
columns (spec. grav. 276) has a fair amount of interstitial glass, whilst
a blackish compact rock (spec. grav. 278) that represents apparently
a more superficial part of the flow has an abundance of smoky
glass in the groundmass. These rocks are basaltic andesites and are
neither vesicular nor scoriaceous, and come near the basalts of the
Kiombo flow which, however, contain some olivine (see] page 92).
They are semi-ophitic and are referred to genus 2 1 of the augite-
andesites which is described on page 283.

Na Raro.

In Na Raro we have one of the most interesting of the isolated
hornblende-andesite mountains of Vanua Levu. Unlike Vatu
Kaisia, which often eludes the observation, Na Raro is visible from
most points of view. It is double-peaked, the two peaks lying in a
north and south line and rising precipitously. It is this feature that
gives the mountain such a variety in its profile. From the north
and south it appears as shown in the accompanying sketch as a
sharp conical peak. From the north-east and south-east, as illus-
trated in the two other sketches, it has the form of a blunt or
square-topped mountain ; and its true shape is only shown when it
is seen from the east or west. In the photograph here reproduced
which was taken about i| miles to the south-west, the two peaks
are with difficulty distinguished. (See frontispiece.)

Not many ascents have been made of these precipitous peaks.
Mr. A. Barrack, who kindly supplied me with some information
about it, made the ascent some years ago ; and Mr. Blyth (?), a
magistrate, also reached the top. There are stories of some big
officials being hauled up in baskets ; and the natives told me of a
white man who was seized with a shivering-fit when he arrived at
the summit. It is certainly a rather hazardous climb ; but the
safest plan is to resign oneself into the hands of the natives, who
" bundle " one up in an expeditious, if not in a very ceremonious,
fashion. Nareilangi, near the foot of the mountain on the north

124

A NATURALIST IN THE PACIFIC

CHAP.

side, is a convenient starting-point, and half a dozen stout Fijians will
not prove too many to assist the climber in the difficult parts of
the ascent. Since the top usually becomes clouded as the day
progresses, it is best to spend a night in a cave about 1,400 feet

Profiles of Na Raro.

}faR3ro(24Z0)

A. Tavia Range (1200 -1500)

From the south off Kumbulau Point.

From the north in the Ndreketi Plains.

From the North-east.

From the East-south-east.

above the sea from which the ascent can be made in the early
morning. The view from Na Raro is panoramic and extends over
a large part of the island from Naivaka to Savu-savu.

Na Raro rises up to a height of 2,420 feet in the midst of a
region of basic rocks. Agglomerates and coarse tuffs formed of
aphanitic augite-andesites prevail in the broken country on the
north and west sides towards Nareilangi and Ndrawa. Immedi-
ately south rises the Tavia Range with its basaltic andesites and
overlying palagonite-tuffs ; whilst on the east lies a spur of this
range.

Nareilangi, the village from which the start is made, is about

VIII NA RARO 125

2| miles distant from Na Raro, and though situated in the
heart of the island it is only about ICX) feet above the sea. The
track first passes through a district of foraminiferous tuffs and clays
reaching up to 200 or 250 feet. Afterwards a broken country
extending up to 800 feet is traversed. Here prevail agglomerates
and tuff-agglomerates derived from aphanitic augite-andesites.^
One then descends into a valley about 600 feet above the sea,
and from this place the ascent of the mountain proper begins.

The ascent at first is fairly steep, dacitic tuffs prevailing up to
1,000 or 1,100 feet above the sea and forming in places precipitous
cliff-faces. Large masses of hornblende-andesite lie on the slopes.
The dacitic tuffs distinguish Na Raro from all the other peaks of
hornblende-hypersthene-andesite rocks that I examined. They
seem generally to have been stripped off by the denuding
agencies ; and only at times, as around the slopes of Ndrandramea
and Thokasinga, are to be found the remains of agglomerates of
the same formation. In the case of Na Raro, however, the tuffs
differ somewhat in their components from the rocks forming the
mountain mass. The tuffs are derived from a hornblende-
andesite of dacitic type ; whilst the massive rocks of the mountain
are of hornblende-hypersthene-andesites, without porphyritic
quartz, but approaching the dacitic habit.

The tuffs of Na Raro, which are sometimes compacted and at
other times rather friable, do not display bedding. They contain
a little lime ; but I found no tests of foraminifera. They are
composed of fragments, up to a centimetre in size, of a dacite
displaying brown hornblende, plagioclase, and quartz in a
microfelsitic groundmass, together with a few fragments of a
semi-vitreous basic andesite.

Above 1,100 feet the tuffs give place to the massive hornblende-
lypersthene-andesite. At an elevation of 1,450 feet, a shoulder of
:he mountain is reached, near the top of which is the cave above
nentioned. Crossing the shoulder one descends for 100 or 150
"eet into a gap, thus reaching the foot of the precipitous northern
)eak, which rises up like a wall for a height of from 900 to 1000
eet overhead. It is in mass of the andesite just mentioned, many

< >f its faces presenting inaccessible cliffs displaying seemingly no
; tructure. This peak is somewhat lower than the southern peak.
. placed its height at 2,270 feet, which, taking the total elevation

< f the mountain at 2,420 feet, as given in the chart, makes the

< ifference 150 feet. A deep and broad cleft, that goes half-way

^ Referred to genera 16 and 20 of the augite-andesites.

126 A NATURALIST IN THE PACIFIC chap.

down the mountain, separates the two peaks. The southern one,
which appears to be inaccessible, is evidently formed of the same
acid andesite.

These hornblende-andesites, with or without porphyritic
quartz, appear to be for the most part restricted to the immediate
vicinity of Na Raro, except to the south-west, where at a distance
of about a mile and a half from the mountain at an elevation of
500 feet occur a rubbly hornblende-andesite and agglomerates of
the same materials. Though the rock is of the Na Raro type, its
presence here is suggestive of a distinct vent of small size, of
which most of the traces have been swept away during the
emergence of the island. About half a mile south-east of this
locality at an elevation of 450 feet occur some singular banded
palagonite-tuffs which, although they do not show foraminifera in
the section examined, contain a little calcite and are probably of

submarine origin In this locality I found a large white

mass, measuring 4x4x5 feet, formed of a siliceous rock appear-
ing in thin sections as granular chalcedonic quartz (see page 355).

The hornblende-andesite of Na Raro, as in the case of the rocks
of most of the other peaks of acid andesites, has its peculiar
characters. It differs, for instance, from that of Vatu Kaisia in
the larger grain of the felsitic groundmass (N. R. -021 mm. ; V. K.
■013 mm.), in the absence or rarity of phenocrysts of rhombic
pyroxene, in its lower specific gravity (2'6 N. R. : 27 V. K.), in the
presence of a little interstitial glass, and in other particulars.
Both, however, belong to the sub-class of hornblende-hypersthene-
andesites, and are described on page 301. In the Na Raro rock the
rhombic pyroxene is represented in the groundmass.

With regard to the relative age of Na Raro I am inclined to
think that it is the most recent of the acid andesite peaks of the
island. Neither vitreous nor vesicular rocks came under my notice
in its vicinity ; whilst the tuffs that clothe its lower slopes are
non-pumiceous, though of dacitic origin, but containing also a few
fragments of a semivitreous basic andesite showing tiny felspar
lathes and augite-granules. Since the everywhere prevailing sub-
marine palagonite-tuffs and foraminiferous clays do not extend
over its area, we may assign to it a later date. It is evidently
also posterior in time to the basaltic andesites and aphanitic
augite-andesites around, which are covered by these submarine
deposits. Relatively recent as it apparently is, this mountain
bears the impress of a high antiquity. There is nothing to
indicate that this " core " of a volcanic mountain belonged to a

VIII NA RARO 127

subaerial vent. Na Raro has shared in all the later stages of the
submergence and emergence of the island. Though it presents
the final page in the history of the hornblende-andesite volcanoes,
that chapter has been for unknown ages closed.

The Na Raro Gap. — Between the Tavia and Va-lili Ranges
there is a break in the mountainous backbone of the island, to
which I have given this name. The greatest elevation is probably
not over 800 feet. It is from the south side of this watershed that
the Lango-lango river takes its rise.

CHAPTER IX

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Basaltic Lowlands of Sarawanga and Ndreketl

One of the most striking features of the north side of the
island is the extensive undulating plain that stretches from the
Lekutu river to near Sealevu on the head-waters of the Ndreketi,
a distance of almost 30 miles. In its western half this plain slopes
gradually to the sea-coast, where it is bordered by a broad belt of
mangroves. In its eastern half, from the mouth of the Ndreketi
eastward, the lofty Nawavi coast range intervenes between it and
the sea-shore. Its breadth varies usually between 4 and 6 miles,
and its elevation, though it reaches a maximum of about 300 feet,
is as a rule between 100 and 200 feet above the sea.

Over nearly all its area it presents the dried-up and scantily
vegetated appearance of the " talasinga " regions. It is an open
country mostly clear of forest ; and it is to this character as well as
to its peculiar vegetation that it in some measure owes its barren
look. Amongst the bracken, grass, and tall reeds (Eulalia
japonica) that clothe much of its surface flourish the Pandanus, the
Casuarina, and the Cycad, which give a special physiognomy to the
whole area ; whilst several sea-side plants, as Ipomea pes caprae,
Morinda citrifolia, Cerbera odollam, &c., have spread themselves far
and wide over its extent. It is traversed by the rivers Ndreketi,
Sarawanga, and Lekutu, the two first named being navigable for
several miles, as the tide ascends a long way from the coast.

In its essential characters this region corresponds with the
Mbua and Ndama plains at the west end of the island, which
have been previously described. Wherever the rivers have worn
channels of any depth, basaltic rocks, sometimes columnar in
structure, are exposed ; and over most of its surface the same rocks

CH. IX THE SARAWANGA PLAINS 129

are displayed, often much decomposed and developing a spheroidal
character, or lying in large blocks all around. Overlying the
basaltic rocks in various localities occur foraminiferous clays and
other submarine deposits. This great region of plains is partially
divided into two by the projecting mass of the dacitic district of
Ndrandramea, the slopes of which descend to within 3 or 4 miles
of the coast between the Sarawanga and Ndreketi rivers. For
convenience of description I will deal with these two sub-regions
separately under the names of the Sarawanga and Ndreketi plains.

The Basaltic Plains of Sarawanga.— These plains extend
about 6 miles inland to the village of Tembe-ni-ndio on the head-
waters of the Sarawanga river. The prevailing type of basalt in
this region is a porphyritic olivine-basalt showing a few large
crystals of glassy plagioclase and having a specific gravity of 2-84
to 2-9. They are neither vesicular nor scoriaceous and are referred
to genera 25 and 37 of the olivine class. The felspar-lathes of the
jroundmass average 2 mm. in length, and there is a little
nterstitial glass. They cannot often be distinguished in their
:haracters from the olivine-basalt displayed in vertical columns, 4
':o 5 feet in diameter, on the lower slopes of Seatura at the back of
Tembe-ni-ndio (page 63). It is highly probable that most of the
basalts of these plains belong to lava-flows that descended from
Ihe great Seatura vent. In the lowlands it is much decomposed,
j.nd a spheroidal structure is frequently developed during the
ciisintegrating process, just as has been noticed in the case of the
llbua and Ndama plains on the west side of Seatura. The
iDunded blocks that commonly occur on the surface may be
r-garded in each instance as the nucleus of a weathering spheroidal
nass. When this rock is exposed unaltered in the streams it is
lisually massive or non-columnar.

There is a less common type of basalt in this region which
perhaps may represent the upper portion of these basaltic flows.
I found it exposed in the bed of the Selesele river about half-way
b Jtween Lekutu and Sarawanga and about 2 miles inland, where it
f( rmed vertical columns \\ feet across. It differs principally in the
p esence of a few small amygdules and in the greater amount of
ir terstitial glass. The columnar basalt that Dana in the " Geology
o; the United States Exploring Expedition " describes as occurring
al the mouth of the same river probably belongs to the same flow.
H e remarks that a few hundred yards back from the " Watering-
pi ice " there is an exposure of columnar basalt, the columns being
V( rtical, i to 2\ feet in diameter, and usually six-sided.

K

130 A NATURALIST IN THE PACIFIC chap.

The incrusting submarine deposits found in patches over these
plains are generally calcareous clay-rocks containing tests of forma-
minifera and often also univalve, bivalve, and pteropod shells. They
are referred to the foraminiferous mud-rocks described on page 321.
Such deposits are properly dark-coloured ; but as exposed at and
near the surface they have often lost by hydration most of their
lime, and have acquired by the removal of the iron oxides a
whitish or pale-yellow appearance, whilst they have a peculiar
soapy " feel," on account of which they are generally known as
" soapstone " amongst the whites. Streams flowing through such
districts have a somewhat milky colour. These deposits are ex-
tensively represented on the slopes of the Sarawanga valley, and
especially to the east of the town of that name. They are well
displayed on the way from Sarawanga to Tembe-ni-ndio, and are
also to be seen on the surface of the plains between Lekutu and
the Mbua-Lekutu watershed to the southward.

In the vicinity of Sarawanga they attain an elevation of 200 feet
above the sea ; but they may be traced in patches up to 500 feet
on the adjacent slopes of the acid andesite region of Ndrandramea.
Near the river, and less than 100 feet above the sea, these deposits
are in one place overlain by an agglomerate formed of large blocks,
I to 2 feet across, of these Ndrandramea andesites and dacites. In
another place, near the town of Sarawanga, I found them exposed
in the river-bank, where they were covered over by a coarse pala-
gonitic bedded tuff, dipping gently eastward and somewhat cal-
careous. From the character of the shells of marine univalves
inclosed in this tuff, it appears to have been formed in shallow

water.

A very interesting display of these surface marine deposits
occurs in the upper part of the Sarawanga valley in the vicinity ot
Tembe-ni-ndio. Here we have fine and coarse calcareous pala-
gonitic tuffs, containing tests of foraminifera, associated with im-
pure foraminiferal limestones. They occur up to elevations of
300 feet above the sea on either side of the Sarawanga valley
above this town, incrusting on the north side the lower dacitic
slopes of the Ndrandramea district, and on the south side the
lower basaltic slopes of Seatura. At the bottom of the valley, as in
the rising ground between Tavua and Tembe-ni-ndio, they conceal
in part the basaltic rocks of the district.

Near the last-named place, on the right bank of the Tembe-ni-
ndio branch of the Sarawanga river, the foraminiferal limestones
are displayed in low cliffs 15 to 20 feet in height. They are some-

IX TEMBE-NI-NDIO 131

times earthy when they contain about 25 per cent, of lime, and at
other times more compact with about 45 per cent, of lime, the
residue being composed of palagonitic materials, tiny fragments of
minerals and of a basic rock, &c.i Large shells of Ostraea and
Cardium are also contained in these limestones, the valves being
detached from each other. The oyster shells project from the
weathered surface ; and it is probable that the name of Tembe-ni-
ndio, which signifies " the shell of the oyster," may be thus ex-
plained. Underneath the foraminiferal limestones in this locality
occur bedded coarse tufaceous sandstones, slightly inclined E.N.E.,
arid inclosing waterworn gravel and pebbles. These low limestone
cliffs, although about six miles inland, are not more than 120 or
130 feet above the sea. In their face there is evidence of an old
erosion-line of the river 10 or 1 1 feet above its present level.

By following up this branch of the river for a little distance I
came upon an exposure of neariy horizontal bedded palagonitic
tuffs on its floor and sides. Here a coarse tuff, of which the larger
fragments composing it range between 3 and 5 mm. in size, passes
upward into a chocolate-coloured compact tuff-clay formed of the
same materials, the larger averaging -2 or -3 mm. in size. These
tuffs are made up chiefly of a palagonitised vacuolar basic glass,
the vacuoles being filled with the alteration products. The lower
coarse tuffs contain very little lime, probably not over i per cent,
md exhibit no organic remains in the slide. The upper fine tuffs
lave 3 or 4 per cent, of lime, and inclose numerous minute tests of
oraminifera of the globigerina type, their cavities being generally
illed with palagonitic material.

Further up the valley about a mile above Tembe-ni-ndio, and
j.bout 250 feet above the sea, the impure foraminiferal limestones
k gam appear ; but they here exhibit an important difference in
texture. In the groundmass of those of the lower locality, the
calcite is granular and loosely arranged, or displays in an obscurely
1 idicated mosaic the commencement of recrystallization. In the
c ise of those of the upper locality the calcitic material of the
g roundmass has more completely recrystallized, and shows a fairiy
c ear mosaic ; whilst in one place the rock was overlain or rather
ii crusted above by a layer, 3 inches thick, of a white crystalline
h nestone, looking like statuary marble, and inclosing portions of
a material like that of the rock beneath it. This last, when ex-
a: amed in the slide, exhibits itself as formed in mass of crystalline
CJ Icite, displaying a regular mosaic, and inclosing small fragments
* These foraminiferal limestones are described on p. 319.

K 2

132 A NATURALIST IN THE PACIFIC chap.

of palagonitised materials and of minerals (pyroxene) such as are
abundant in the rock below. In places the grains of the mosaic
are bordered by brown and black iron oxide. It would, therefore,
appear that a metamorphism has been in operation here, and that
the process which began with the recrystallization of the matrix in
the lower rock is almost completed in the overlying thin layer
where even most of the non-calcareous materials have disappeared.
No evidence suggestive of contact-metamorphism came under my
notice in this locality. These foraminiferal limestones are surface
formations, and it was in the uppermost portion that the metamor-
phism was most complete. We here witness in operation the trans-
formation of a rock containing 46 per cent, of carbonate of lime
(the residue of minerals, palagonite, &c.), into a marble or crystal-
line limestone. I gather that as in the instance of several of our old
British limestones the change is a purely interstitial one, and is not
connected with thermal metamorphism.

These remarks on the basaltic plains of Sarawanga and on
their incrusting submarine deposits may be concluded with a brief
reference to the siliceous concretions, 2 or 3 inches across, the
silicified portions of corals, and the fragments of clay iron-stone and
limonite resembling haematite, that occur frequently on the surface.
They are common on the plains south of Lekutu and between Lekutu
and Sarawanga, and up to elevations of 200 feet in the foraminiferous
clay district east of Sarawanga, where fragments looking like por-
tions of the silicified branches of Madrepores are to be found ; but
they are not limited to such localities, and may occur also where
the surface is formed of decomposed basaltic rock. (These matters
are generally discussed in Chapter XXV.)

The Basaltic Plains of the Ndreketi. — This low-lying
region of rolling " talasinga " country now serves as the basin
of the Ndreketi river, the largest of the rivers of Vanua Levu. It is
usually elevated between 100 and 300 feet above the sea, and its
limits are well defined by the 300 feet contour line in the map of
the island. On the east it is separated from the basin common to
the Wailevu and Lambasa rivers by the Sealevu Divide, which
is described on p. 136. On the west, as before observed, it is only
in part distinguished from the basin of the Sarawanga by the spur
descending from the dacitic mountains of Ndrandramea. It meets
the coast in the vicinity of the mouth of the Ndreketi ; but for
two-thirds of its length it is cut off from the sea by the great
Nawavi range. It supports the characteristic vegetation of the
" talasinga " or sun-burnt land. Whilst the Pandanus and the

IX THE NDREKETI PLAINS 133

Casuarina are most conspicuous amongst the trees, bushes, herbs,
grasses and ferns predominate. Here the native Ginger and the
native Turmeric with species of Tacca are frequently to be recog-
nised, and the waste-land bushes of Dodonaea viscosa and Mus-
saenda frondosa are abundantly to be found.

As in the Sarawanga plains, the basaltic rocks are here often
overlain or incrusted by submarine deposits, the former exposed in
all the deeper river-beds, the latter frequently displayed in the
sides of their tributaries.

I will deal first with the basaltic rocks. In the places where
the surface deposits have been stripped off, these rocks are
generally exposed as decomposing boulders, the spheroidal
structure being well developed in the weathering process. Not
infrequently, however, a rudely columnar structure is exhibited
where the rivers have cut deeply into the basalt. The columns
that I observed were usually vertical. In the river-bed at the
landing-place at Mbatiri, for instance, the columns are from 2^ to
3 feet across and vertical. As exposed in the river-crossing about
a mile above this town they are 12 to 15 inches in diameter and
also vertical. However, at Na Kalou, a coast village about i^ miles
east of the mouth of the Ndreketi, where there is an unexpected
exposure of basalt, the columns, about a foot in diameter, are
inclined at an angle of about 20° from the vertical and face to the
north.

These rocks are, as a rule, compact, only showing a typical
scoriaceous structure in the case of specimens obtained near the
foot of Nakambuta, an isolated hill about three miles to the
southward of Natua, which probably represents a vent of more
recent times. Often, however, they have a pseudo-vesicular
appearance, from the occurrence in the midst of the patches of
interstitial glass of minute irregular cavities that seem to have been
formed during the last stage of consolidation of the magma.

The prevailing type of basalts is a blackish, doleritic, semi-
ophitic rock without olivine, with specific gravity 278 to 2"8o.
They are characterised by the length of the felspars of the ground-
mass ("22 — "35 mm.), by the large size of the augite granules
(•I — '3 mm.), and by the quantity of dark interstitial glass. They
present two forms, one with and the other without plagioclase
phenocrysts. The first kind is referred to genus 9 of the augite-
andesites (page 272), some of the specimens being referred to the
porphyritic sub-genus, and others to the non-porphyritic sub-
genus, according to the size of the plagioclase phenocrysts. The

134 A NATURALIST IN THE PACIFIC chap.

second kind, without felspar phenocrysts, belongs to genus 12 of
the same class (page 275). A good example of the porphyritic
rocks is afforded in the large blocks lying in the stream-beds
during the first half of the way from Ndreketi to Sarawanga.

It may be pointed out here that these doleritic, semi-ophitic
basaltic andesites of the Ndreketi plains differ conspicuously from
the prevailing type found on the slopes of Seatura, on the
Sarawanga and Mbua plains, and on the Wainunu table-land.
There we have, as a rule, olivine-basalts, having a specific gravity
of 2*86 to 2*90, and showing but scanty interstitial glass, the
felspars of the groundmass being on the average not over "2 mm.
in length, whilst the augite granules are, as a rule, only
'02 — '03 mm. in diameter, and the ophitic structure is infrequent.

The submarine deposits, consisting of foraminiferous clays and
coarser tuff-sandstones, the former being usually beneath, are
found at intervals all over this area. They occur inland as far as
Vuinasanga and Nareilangi, near the base of the mountains of
Va Lili and Na Raro, reaching as high as 300 feet, their place
being taken on the mountain slopes by coarser tuffs and
agglomerates. When not weathered they are more or less
calcareous, and contain occasionally marine molluscan shells,
whilst palagonitic debris enter largely into their composition.
The foraminiferous clays, often much bleached by hydration, are
well represented around Mbatiri and in the districts between that
town and Natua and Nareilangi. They are relatively deep-water
deposits, and belong to the type described on page 323. Others,
again, as exposed in the banks of the river at Natua, are chocolate
coloured and of the kind referred to in detail on page 335. These
foraminiferous clays in the region between Natua and Mbatiri are
overlain in places by coarse, almost brecciated, tuffs, formed in
part of the debris of acid andesites, such as compose the not far
distant mountain of Na Raro.

Since the massive basaltic rocks are exposed in all the deeper
rock channels of these plains, it is apparent that the overlying
submarine deposits can possess no great thickness. Probably they
are never 100 feet thick, and usually far less. In many places,
through their denudation, the underlying basaltic rocks are
exposed, and in a decomposing condition largely form the surface.
These deposits as a rule display bedding, the beds being horizontal
or at least only inclined 2 or 3 degrees. This horizontality is a
nearly constant feature of these submarine beds, as they overlie
the basaltic rocks of the plains ; and it is a feature we should

IX THE NAWAVI RANGE 135

expect to find where there has been emergence rather than
upheaval.

Siliceous concretions and silicified coral fragments, so character-
istic of the surface of some of these plains of Vanua Levu, did not
frequently come under my notice here. They, however, occur
occasionally, as in the district between Nanduri and Natua.

The Nawavi Range.

With this remarkable coast range, which fronts the Mathuata
sea-border for a distance of 12 or 13 miles between Ravi-ravi
Point and Nanduri, I have unfortunately but scant acquaintance.
It attains its maximum elevation in Mount Nawavi of 2,238 feet,
and is described by Mr. J. P. Thomson,^ who surveyed this coast,
as broken in two nearly opposite Niurua, the pyramidal mountain
of Koro Navuta rising in the gap Various other peaks, besides
that of Nawavi, are marked in the latest Admiralty chart ; they
vary in height from 1,000 to 1,700 feet. As this range lies only a
mile or less back from the beach, it gives to the sea-border a bold
and often precipitous appearance, which is well shown in an
illustration in Wilkes' Narrative of the United States Exploring
Expedition (iii. 226).

Basic rocks probably prevail in this range. When I ascended
its eastern spurs from Nanduri, and reached a height of 800 feet,
only basic tuffs and agglomerates came under my notice. From
Dana's remarks ^ it is to be inferred that the " frowning bluffs "
opposite Mathuata Island are of similar formation ; and it would
seem that the rugged black stones, described in the Admiralty
Sailing Directions ^ as topping the hills behind Ravi-ravi Point,
are of the same basic character. From its contour and profile I
would gather that, as in the great mountainous ridges that
constitute the backbone of the island between Va Lili and Mount
Thurston, palagonitic tuffs and clays of submarine origin will,
together with volcanic agglomerates, be found far up the slopes of
this range, and that the axis will prove to be largely composed of
massive basic rocks.

The hot springs referred to by Thomson and others as
occurring at the foot of the north and south slopes, namely at

^ Proceedings^ Queensland Branch, Geographical Society of Australasia,
Brisbane, 1886, vol. i.

^ Geology of the United States Exploring Expedition.

^ Pacific Islands, vol. ii. 1900. '

136 A NATURALIST IN THE PACIFIC chap.

Vatuloaloa, Nambuonu, and in another unnamed inland locality,
are briefly mentioned on page 31.

The Sealevu Divide.— This broad range which separates
the Ndreketi and Lambasa basins is an offshoot from the central
mountains at Sealevu and reaches the coast just east of Nanduri.
Its highest part according to the elevation given in the Admiralty
chart is 1,437 feet. The road from Sealevu to Nanduri, which
crosses its broad level summit for a distance of about three miles,
does not rise over 1,100 feet. Between 800 and 1,100 feet are
exposed calcareous tuffs and clays all largely made up of pala-
gonitic materials. The coarser might be described as sandstones.
The clays have 12 per cent, of lime and are foraminiferous and
are of the type described on page 321. The rocks displayed on
the lower northern slopes on the way to Nanduri are at first the
same submarine deposits, and afterwards decomposing basaltic
andesites. It is apparent that in the central elevated part of this
range there are hills of volcanic formation more or less completely
buried beneath these deposits.

The District between Nanduri Bay and Wailevu

River

The sea-border between Nanduri Bay and Middle Point, nearly
four miles to the east, consists of a fringe of lowland margined by
the mangrove-belts and banked by a line of hills between a quarter
and two-thirds of a mile inland. These hills form a continuation
of the Nawavi coast range of mountains extending from Ravi-
ravi Point to Nanduri. They attain their greatest height in the
case of Ulu-i-sori, a cockscomb-like peak 1,141 feet above the sea.
Another of these hills, Vatu-tangiri, is capped by a remarkable
obelisk-like rock. Behind this coast range lies a hill with an eleva-
tion of nearly 1,400 feet.

The rocks exposed for the first mile or two along the coast
east of Nanduri are agglomerates and basic tuffs. The blocks of
the agglomerates, however, are made of an altered grey porphyritic
rock which has the characters of a porphyrite of a rather acid
type.i This composition of the agglomerate is quite exceptional

1 It is referred to the 5th sub-order (genus 18) of the hypersthene-augite-
andesites characterised by prismatic pyroxene and more or less parallel felspar
lathes in the groundmass, as described on p. 289. It displays abundant opaque
porphyritic plagioclase giving extinctions of oligoclase-andesine. The pyroxene
phenocrysts have dark alteration-borders. There is a little altered interstitial
glass. Spec. grav. 2-55.

IX TAMBIA 137

and indicates the antiquity of the volcanic rocks in this locality.
Farther along the coast the typical agglomerates occur, where the
blocks, 3 to 10 inches across, are composed of the usual semi-
vitreous black basaltic rock showing plagioclase phenocrysts.
Nearer Middle Point a decaying doleritic basalt is displayed at
the surface. It is similar to the prevailing rock of the Ndreketi
plains, and is referred to the ophitic rocks forming genus 9 of the
augite-andesites.

The elevated promontory of Middle Point is a prolongation
■of a spur of Ulu-i-sori. Where it is crossed by the road it is
about 350 feet above the sea. On its west slopes are exposed
yellowish-white tuff-like rocks, evidently the prevailing basic clay-
tuffs which have become bleached through the hydration accom-
panying the weathering process. Beneath these deposits lies an
amygdaloidal augite-andesite which is bai*ed in places. The rock
is semi-vitreous and the amygdules it contains are often a centi-
metre long. They are composed of a white mineral with fibro-
radiate structure and made up of needle-like prisms. It gives off
water, but it is not easily fused, and does not gelatinise in HCl.

From the top of the promontory the road strikes inland in an
•east-south-east direction for Tambia, passing inside the coast
range, which is here 600 feet in height, and descending gradually
through a region of basaltic andesite into the valley of the Tambia
river. (This rock, which has a specific gravity of 2*84, displays
more or less parallel stout felspar-lathes, '23 mm. in length, and
has a little interstitial glass. It belongs to genus 13 of the augite-
andesites.) Low hills shut in the little valley on all sides except
where the river breaks through the coast range. The town of
Tambia is not over 100 feet above the sea. About a mile to the
north exist hot springs of considerable extent which are described
on page 32.

The road from Tambia to the Wailevu River traverses an
undulating district varying from 100 to 300 feet above the sea.
A basalt containing a little olivine, with a specific gravity of 2*91,
is commonly exposed at the surface in a disintegrating condition.
Here and there occur basic tuffs. In one locality, there is displayed
a dyke-like mass in a small stream course, 200 feet above the sea,
of an altered grey and compact andesite marked with parallel red
streaks or bands. It is an aphanitic augite-andesite ; and is to be
referred to genus 13 of the augite sub-class. It displays closely
crowded felspar-lathes, 'O/ mm. in length, in flow-arrangement.
The bands are due to the gathering of the residual glass in streaks

138 A NATURALIST IN THE PACIFIC chap,

parallel to the flow. Chalcedonic flints, some of them showing
the agate-structure, together with fragments of silicified corals, are
found occasionally on the surface in this district.

The Lambasa Plains

These remarkable inland plains, about ten miles long and three
to five miles broad, are well described in the Admiralty chart as
a low undulating country covered with grass, screw-pines, and
Casuarina trees. They are backed by the mountains forming the
central axis of the island, whilst broken groups of hills, not usually
more than 500 or 600 feet in height and attaining in Ulu-i-Mbau
an elevation of 1,160 feet, intervene between them and the sea-
border. They are traversed by the Wailevu, Lambasa, and Ngawa
rivers which after breaking through the seaward hill-ranges pass
through broad mangrove-belts to reach the coast. The tide
ascends these river-courses for several miles ; and in the case of
the Lambasa river boats can follow its winding course for ten
miles penetrating into the heart of the plains. Much of this level
inland region is less than 100 feet above the sea ; whilst the contour
line of 300 feet by which the region is defined in the map attached
to this book fairly well indicates the higher levels.

The features which we have described in the instances of the
Sarawanga and Ndreketi plains are in the main reproduced in the
Lambasa region ; but in the last-named each of the three rivers
has a system of hot springs along its course, namely (as described
in Chapter III.), at Na Kama on the Wailevu River, at Vuni-moli
on the Lambasa River, and at Mbati-ni-kama on the Ngawa River.
Basaltic andesites, often exposed at the surface in a decomposing
condition, form the foundation of the plains. They are overlain
by submarine clays containing pteropod shells and tests of fora-
minifera ; and over these in their turn coarse palagonitic tuffs and
agglomerate-tuffs are found in places. Formations still more recent
are represented by elevated reef-rock on the seaward side of the
hills that bound the plains. Nodules of chalcedony, silicified
corals, and other siliceous rocks, together with fragments of impure
limonite, lie on the surface over much of this region.

The basaltic rocks of this region rarely show olivine, and belong
as a rule to the basaltic andesites, being referred to genera 13 and
21 of the augite-andesites, the specific gravity being about 2*8.
The felspar-lathes, '12 to •14 mm. in length, are in flow-arrange-
ment, and the augite is at times semi-ophitic ; whilst there is a little

IX THE LAMB ASA PLAINS 139

interstitial glass. The basic rocks prevailing between Vatu-levoni
and Vandrani belong to genus 13 of the augite-hypersthene-
andesites and have a groundmass of much finer texture, the
felspars only measuring "05 mm. Their specific gravity ranges
between 27 and 275.

The overlying foraminiferous and pteropod clay rocks, the
so-called " soapstone," are exposed over large areas of the surface.
A good idea of the important part they take in the formation of the
lower plains may be formed by visiting the hot springs of Vuni-
mbele, close to Vuni-moli, which issue from the side of a deep
trench cut into these deposits. As generally displayed at the
surface, they have been subjected to so much hydration in the
weathering process that they appear as yellowish- white clay-rocks
deprived of their lime ; and it is only now and then that the
remains of foraminifera and pteropods can be detected. They are,
however, fairly well preserved around the base of Ulu-i-mbau in
the vicinity of Koro-wiri, where they contain, besides the shells of
pteropods and foraminifera, portions of decaying coral, and extend
to 200 feet and over above the sea. Here they are overlain by
rather coarser basic tuffs of mixed character, containing 5 or 6 per
cent, of carbonate of lime and some palagonite, which I followed
as high as the track lay, rather over 500 feet above the sea.^ The
reef-limestones, already noticed as exposed in the low hills between
Wailevu and Lambasa, lie a mile or two inland and reach to 100
feet above the sea.

The fragments of siliceous rocks, which with occasional bits of
impure limonite, occur at intervals all over the surface of these
plains and largely form the gravel and pebbles in the river-beds,
include nodules of chalcedony, fragments of jasper or iron-flint,
white quartz-rock formed of chalcedonic silica, silicified corals, &c.
They are especially frequent in the vicinity of Nasawana and
Koro-utari, and include fine specimens of agates and of onyx.

^ I did not ascend to the top of Ulu-i-mbau. It is, however, evidently
composed of basic andesitic rocks, occasionally amygdaloidal. On its slopes
ap to at least 600 feet above the sea occur agglomerate-tuffs and finer submarine
:uffs, as above described, overlying foraminiferous clays, a submergence of
juite 500 feet being indicated by the investing deposits.

CHAPTER X

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHVSICAL
FEATURES {continued)

The Va-lili Range

This range extends from the Na Raro Gap before mentioned
to the Ndreke-ni-wai river. It is partly isolated on the north-
east from the Korotini Range, the extension eastward of the
mountainous axis of the island, by a depression or saddle which
at its lowest part is not more than 1,200 or 1,300 feet above the
sea ; but there is no real break in the line of mountains. It is,
however, convenient to make this distinction, and I have named
the dip between the two ranges, the Waisali Saddle. The range
now to be described attains its greatest elevation in the summit of
Va-lili, which is 2,930 feet above the sea. There are two or three
other peaks that exceed 2,000 feet, and much of the range is not
under 1,700 feet. My acquaintance with this range is not extensive ;
but it will serve to illustrate its general geological structure.

The summit of Va-lili is very conspicuous from most points of
view. From the north, east, and south-east, it has a remarkable
broad and square-topped profile with a little conical elevation in
the centre. From the south-west, it displays a different outline
with a solitary squarish block on the top, and this is the form most
familiar to the navigator. Unfortunately, for reasons given below,
I did not quite reach the summit, and although I was able to
obtain sufficient data for forming a general idea of the structure of
this part of the range, the structure of the actual summit has yet
to be ascertained.

(i) Ascent of Va-lili from Narengali. — This village,
which is elevated 400 feet above the sea, lies about two miles in a
direct line, N.N.E. from the peak. In traversing the intervening

CH. X

VA-LILI

141

country, one crosses the Loma-loma ridge, elevated 1,000 feet, on
the top of which was once situated the village of Loma-loma
visited by Home in 1878. The rocks exposed on the surface are
scanty, a hard palagonite-tuff, which owes its induration to a
calcitic cement, occurring on the upper part of the ridge, the
original site of the village being marked by a large block of this
stone.^ The track then descends into the valley of the Loma-loma
river, about 400 feet above the sea, in the bed of which occur
blocks of an amygdaloidal basaltic andesite, containing phenocrysts
of both rhombic and monoclinic pyroxene, and referred to genus i

Profile-sketches of the Va-Lili Range.
Va-Uh (2930)

i2200)

(1900) KorotiniTableldnd

(2400)

NambunlSpar.

View from the south-east near Savarekareka.

View from the south-west.

of the rhombic pyroxene andesites. The amygdules are formed of
calcite.

Beyond the river the ascent of the northern slope of Va-lili
begins. As high as 1,100 feet occur basic agglomerates overlying
fine and coarse palagonite-tufifs, which are at times horizontally
bedded, the finer kinds being sometimes calcareous, and like that
of the Loma-loma ridge above mentioned. At 1,300 feet is a line
of tall cliffs which extend for some distance at intervals along
the mountain-slope, and are indicated by some fine waterfalls.
My track struck these cliffs at a place named " Nangara-ravi " (the
leaning cave-rock) where they have a height of 1 50 feet or more.
The tall cliff leans slightly forward, so that it forms a shelter at its
foot, and hence the name. It is composed of a tuff-agglomerate,

^ I did not find any foraminiferal shells or other organic remains either in
this tuff or in the similar tuffs occurring on the adjacent slope of Va-lili up to
1,100 feet. My specimens, however, are very small. /

142 A NATURALIST IN THE PACIFIC chap.

the blocks, which are formed of a semi-vitreous basaltic andesite
of the augite class, being not generally more than 3 or 4 inches
across. These blocks, which are rounded on the outer exposed
side and angular on the imbedded side, are inclosed in a hard,
probably calcareous matrix. The whole face of the cliff has the
appearance of having been worn smooth by attrition, and there are
not to be observed the projecting blocks from its surface which are
so characteristic of other agglomerate-cliffs. It shows no strati-
fication ; but at its base flush with the cliff-face are large masses of
a basic massive rock. But few portions of rock have been detached
from the cliff. However, I found in the midst of a huge fallen
fragment of the agglomerate a dyke-like mass of a basaltic andesite,
which differs chiefly from the rock forming the blocks of the
agglomerate in being more crystalline. This dyke must have been
about 15 feet thick.

Having regard to these various features, I am inclined to
consider that this leaning cliff represents one side of a large fissure
in the agglomerates which was occupied by a dyke. Reference
has been above made to the fact that the agglomerates may be
seen overlying the tuffs farther down the slope, so that the
conditions favourable for landslips exist. I have shown on page
III that the origin of the Mbenutha cliffs where agglomerates He
on clayey tuffs may be thus attributed to a landslip. In the case
of the Nangara-ravi cliffs, the occurrence of this fragment of a
large basaltic dyke is of some importance in connection with the
origin of the basic agglomerates of this locality.

The top of the mountain-ridge is about 700 feet above Nangara
ravi, or 2,000 feet above the sea. The tuffs and agglomerates that
once existed here have been stripped off to a great extent and the
deeper rocks of the range are in part exposed. The upper part of
this ridge (1,700 to 2,000 feet) is formed of a rubbly pitchstone
where a basic glass has been broken up and then consolidated, the
interstices being filled up with palagonite as described in other
cases on page 313. Though non-vesicular, it is just such a rock as
one would expect to find on the surface of a lava-flow or on the
sides of a dyke.

The crest of the range is here only a narrow ridge. I followed
it along in a north-west direction, gradually ascending on the way,
and in time the rubbly pitchstone gave place to a hardened
palagonitic clay rock, which was observed as high as 2,300 feet. It
apparently contains a little lime, and probably was at one time
foraminiferous ; but it is now much affected by hydration. Soon

X VA-LILI ■ 143

after this, we arrived at the foot of the steep ascent leading to the
summit of Va-lili. We were now rather over 2,400 feet above the
sea ; but my natives refused to go on, the heavy rain having made
the slope too slippery for a safe ascent. With much reluctance I
retraced my steps ; and as the bad weather continued for several
days after, I did not make another attempt. There would, how-
ever, be no difficulty in dry weather.

(2) Traverse of the Va-lili Range from the old

SITE OF LOMA-LOMA TO WaIWAI ON THE COAST OF SAVU-
SAVU Bay. — This route, which was taken by Mr, Home, the
botanist, in the reverse direction in 1878, is thus described in his
book, A Year in Fiji (p. 19) : " The path, rough and apparently
not much used, ran along streams, up steep ascents and down
awkward descents, over slippery boulders and fallen trees, up the
sides and along the crests of densely wooded mountains."

Ascending the north slope of the range I found at the Tangi-
nandreli cave, which is 1,050 feet above the sea, a palagonite-tuff-
sandstone underlying the basic agglomerate. This tuff, which is
of the type described just below, does not effervesce with an acid,
and shows no tests of foraminifera when examined with a lens.
Further up the slopes large masses of agglomerate occur. At
1,350 feet I came upon a large mass of a fine-grained compacted
palagonite-tuff made up chiefly of fragments of palagonitized
vacuolar basic glass. Among the mineral fragments occur plagio-
clase, augite, and rhombic pyroxene, and a little fresh olivine,
which is of very rare occurrence in these palagonite-tuffs. It
contains little or no lime, and shows no tests of foraminifera in the
slide. The summit of the range is here about half a mile broad,
and is relatively level. I placed its elevation at 1,760 feet, which
is not far from Home's estimate of 1,800 feet. The southern slope,
which is the rainy side of the range, is much cut up into gorges.
In the upper 200 feet palagonite-tuffs, similar to those above
referred to, are displayed, and basic agglomerates occur lower

down This part of the range is remarkable through being

completely covered over by palagonite-tuffs and agglomerates.
It has been pointed out above that this is not the case with the
range close to the highest peak, where the underlying rocks are
n part exposed at the crest of the range.

(3) The Eastern Peak of the Va-lili Range. — This
lill, about 1,100 feet in height, overlooks the Mbale-mbale branch
)f the Ndreke-ni-wai river. At its foot near the river there is
exposed at the roadside a rubbly pitchstone formed of a basic glass,

144 A NATURALIST IN THE PACIFIC chap.

inclosing porphyritic crystals of plagioclase, augite, and olivine,,
which is described on page 313. Here also occurs an agglomerate
made up of blocks of a semi-vitreous basaltic andesite (sp. gr. 278),
showing prismatic pyroxene in the groundmass, and referred to
genus 20 of the augite-andesites.

The upper part of the hill displays the same agglomerate, and
a tuff-agglomerate in which small fragments of the basaltic andesite
are inclosed in a matrix largely made up of fine debris of basic
glass. There protrudes through these detrital rocks at the top of
the hill a broad dyke-like mass of the same basaltic andesite that
forms the agglomerate around ; and the structure of the hill is
thus displayed as that of an old volcanic neck. It has evidently
an axis of massive basaltic rocks, more or less covered over with
agglomerates and tuffs.

(4) The Nambuni Spur. — This singular spur runs down to
the coast between Waiwai and Wailevu ; but it is partly separated
by a deep gap from the main range. It attains a height of 550 to
600 feet, and has two little peaks which the natives call Vatu-
tolutolu and Vatu-tangitangiri. Its position is shown in one of
the profile-sketches of Va-lili, given on page 141. The crest of the
spur is formed by a dyke-like mass, 25 to 30 feet thick, which is
composed of a basic agglomerate passing down into a palagonite-
tuff. The blocks of the agglomerate are composed of a semi-
vitreous basaltic andesite, showing minute felspar-lathes in flow-
arrangement in an abundant smoky glass, the fine pyroxene being
not differentiated. The tuff, into which the agglomerate passes
down is non-calcareous, and displays no organic remains. It is,
however, composed of fragments, which do not generally exceed a
millimetre in size, of palagonitised vacuolar glass, basic andesites,
plagioclase, monoclinic and rhombic pyroxene, &c.

This dyke-like mass forms the axis of the ridge and protrudes
vertically about icxD feet, the bulk of the spur being composed of a
compacted brecciated palagonite-tufT made up mainly of fragments
a centimetre in size, of a basic vacuolar glass, sometimes fibrillar,
which is extensively palagonitised.

The filling up of a fissure in a mass of tuff-breccia by palagonite-
tuffs and agglomerates probably occurred during the submergence,
the original dyke-rock having been removed by marine erosion.
After the emergence the subaerial denuding agencies reshaped the
surface, and as a result of the less yielding character of the materials
filling the fissure, they protrude as a dyke-like mass from the
crest.

X VA-LILI 145

In a cliff-face of the adjacent main range there are displayed
an agglomerate of basaltic andesite and a pitchstone-breccia, com-
posed of fragments of but little altered basic glass, the interstices
being filled up with palagonite. In the case of the Kiombo flow
I have endeavoured to explain the origin of a closely similar pitch-
stone-breccia (page 92).

(5) The Sea-border and the Low-lying Districts at
THE Base of the Va-lili Range. — It may be generally re-
marked that palagonite-tuffs and clays, often foraminiferous, prevail
in these localities. Thus in the sea-border between Waiwai and
the mouth of the Ndreke-ni-wai basic agglomerates are displayed
where the mountains approach the coast ; but further west a broad
tract of undulating land, elevated usually 100 to 300 feet, inter-
venes between the range and the sea-border, and here coarse and fine
palagonite-tuffs predominate On the north-west the forami-
niferous tuffs and clays of the Ndreketi plains approach the Va-lili
range in the vicinity of Vuinasanga, and extend for at least 200 or

300 feet up its sides At the east end of the range, where the

slopes descend to the plains of the Waisali valley, a little west of
Mbale-mbale, there are exposed bedded palagonite-tuffs, tilted up
at an angle of about 20° to the south-west. They contain a little
[ime and display microscopic tests of foraminifera, the palagonite
Deing minutely vacuolar, the cavities also being filled with the
iltered glass. I noticed those submarine deposits at an elevation
Df 100 feet, but probably they reach much higher.

The inference to be drawn from the data above given concerning
he Va-lili range seems clearly to be this. We have here indicated
■ he emergence of a submarine mountain-ridge covered over with
;)alagonite-tuffsand agglomerates, the last being uppermost. These
coverings have been in places stripped off by the denuding agencies
;.nd the underlying massive basic rocks exposed. These rocks,
liowever, vary much in texture, some being vitreous, as in the case
(f the pitchstones, others hemi-crystalline as in the case of the
1 'asaltic andesites ; and it is to be gathered from this and other
similar indications that different submarine vents were formed
c long a fissure or fissures at the sea-bottom. No evidence of sub-
i erial eruptions came under my notice. After the vents became
e xtinct they were buried beneath the palagonite-tuffs and agglo-
r lerates. During and after the emergence the denuding agencies
r ishaped the surface of the range and left but little of its original
f )rm.

Since it is my object to build up a theory of the origin of the

L

146 A NATURALIST IN THE PACIFIC chap.

ridge-mountains as I proceed with the systematic description of
the island, it will be here convenient to follow up the preceding
remarks on the Va-lili Range by a preliminary reference to the
great ridge district lying east of it.

When a panoramic view of this region is obtained, one observes
a series of lofty ridges more or less parallel and running about
N.W. and S.E. There are the Va-lili, Narengali, and Sealevu ridge-
mountains with lesser ridges between. The intervening valleys
are elevated about 400 feet above the sea, whilst the mountains
rise up to over 2,000 feet. In many localities this configuration of
the surface would be attributed mainly to subaerial denudation.
In this island I will endeavour to show that these mountain-ridges
existed before the emergence. They do not owe their form to
the rivers that flow through the valleys, though no doubt river-
erosion has brought these features into greater relief.

In Vanua Levu, as there will be frequent occasion of showing,
rivers often flow in valleys that they have not made. This is
especially pointed out on page 151; and it is necessary to empha-
sise it here, before proceeding farther with the description of the
geological structure of the mountain-ridges.

The Waisali Saddle

This saddle, which connects the Va-lili and the Koro-tini
ranges, has probably a minimum elevation of not over 1,200 or
1,300 feet. To understand this district thoroughly a regular survey
is, however, necessary. It is only at times in this densely wooded
range that a view of the surrounding country is obtained ; but in
spite of this drawback I was able by a diligent use of watch,
aneroid, and prismatic compass, to obtain a fair general notion of
the surface-configuration.

The track that proceeds westward from Waisali to Narengali
leads also to the villages of Na Sinu and Sealevu. About ii^ or 2
miles from Waisali, the track branches off to the westward for
Narengali and to the northward for Na Sinu and Sealevu. After
half an hour's walk along this last-named path, one comes to a
place where at an elevation of about 900 feet it branches off to the
left for Na Sinu, crossing the lowest part of the saddle, and to the
right for Sealevu across the Koro-tini Range. It may here be
remarked that since the natives are gradually abandoning their
mountain-villages and are settling at the coast, many of the
mountain-tracks used by me will before long be overgrown and
forgotten.

X THE WAISALI SADDLE 147

In taking the path from Waisali to Narengali one soon enters
the hilly country where large masses of basic tuffs and basic
agglomerates, the last formed of blocks of a compact basaltic
andesite, occur on the surface up to 700 or 750 feet above the sea.
The rock just named has a specific gravity of 2-84, and since it
displays rhombic pyroxene amongst its phenocrysts, it is placed in
genus I of the hypersthene-augite andesites. Above this elevation,
and as far as the top of the range, 1,800 — 1,900 feet above the sea,
porphyritic basaltic andesites, having a specific gravity of 2*8,
prevail at the surface. They display small porphyritic crystals of
plagioclase, augite, and rhombic pyroxene in a groundmass com-
posed of small felspar-lathes, prismatic pyroxene, and much
smoky glass, and are referred to genus 5 of the same pyroxene
andesites. It is probable, judging from one of these exposures,
that such rocks are dyke-like masses : but on account of the thick
soil-cap it is not possible to obtain a good view of them.

In the stream-courses occur large blocks of altered basaltic
andesites of the propylitic type, having a specific gravity of 264 to
270, and exhibiting abundant alteration products, such as calcite,
viridite, &c. These propylites, I presume, constitute the deeper
portion of the range. It will often be necessary to distinguish
between the altered basaltic andesites, such as are above referred
:o, and the relatively fresh rocks of the same type. The former
ire light coloured (sp. gr. 2*6 to 275), and are only exposed in
; gorges and stream-courses that deeply score the mountain-slopes.
The latter are blackish (sp. gr. about 2-8), and at times penetrate
' he covering of tuffs and agglomerates.

Descending the opposite or north-west side of the saddle-range,
< ne finds the same basic andesites, both fresh and altered, down to
i. bout 1,100 feet above the sea. Then the track leads one down a
I recipitous slope into the picturesque gorge traversed by the head-
\ 'aters of the Narengali River. At its lower end the gorge opens
c ut into the broad Narengali valley, and here the dense forest of
tie higher districts gives place to the scanty vegetation of the
" talasinga " region.

The rocks exposed in the sides of the gorge are basic agglome-
r. Ltes overlying palagonitic tuffs of mixed composition and evidently
S( dimentary. On the bottom lie huge masses, some of them 70 or
8) tons in weight, of altered grey aphanitic or non-porphyritic
a igite-andesites, penetrated in some cases by thin veins of white
q lartz, and at times displaying a rudely columnar structure, the
C( lumns being 12 to 14 inches across. Sometimes the alteration is

L 2

148 A NATURALIST IN THE PACIFIC chap.

mainly confined to the filling of the fissures with chalcedonic
quartz, minute nests of the same material occurring in the ground-
mass. At other times the small augite granules are also decom-
posing. The specific gravity varies from 2*64 to 273 ; the rocks
being referred to genus 16, species A, of the augite-andesites.
Occasional detached masses of a propylitic basic andesite,
displaying porphyritic plagioclase and pyroxene, also occur in this
gorge, the felspar phenocrysts being largely occupied by calcitic
and other alteration products, whilst much viridite occurs in the
groundmass. It exhibits both monoclinic and rhombic pyroxene ;
and on account of the prism form of the groundmass pyroxene it
is placed in the 2nd sub-order of the hypersthene-augite andesites.
These altered rocks are deep-seated intrusive masses that were
originally covered over by the basic agglomerates and palagonite-
tuffs exposed in the sides of the gorge.

Below the gorge there is an extensive exposure in the sides
and bed of the river of light-coloured calcareous tuffs which were
originally composed of palagonitic materials ; but owing partly to
hydration, and partly to other secondary changes, the original
structure is much disguised.

Crossing the river in the midst of these tuffs there is a dyke, 1 5
feet thick, formed of a propylitic basaltic andesite, a semi-vitreous
rock in which calcitic and zeolitic materials have been developed in
quantity. The dyke, which is not columnar, is steeply inclined at
an angle of 45° to the north-east. . . . Further down the river-valley
as far as Narengali, occur basic tuff-agglomerates.

The Tract of Nakambuta

This is a tract of broken country that projects from the
mountainous backbone of the island (between the Va-lili and Koro-
tini ranges) into the heart of the Ndreketi plains in the vicinity of
Natua. As limited by the 300-feet contour line, it is indicated in
the map attached to this work. Its general level varies between
300 and 600 feet in elevation ; but a number of isolated peaks are
included within this area. More than one of these hills attain a
height of 1,000 feet, Nakambuta a very conspicuous hill being as
much as 1,500 feet. Basaltic andesites with basic agglomerates
and palagonite-tuffs prevail.

Towards Natua the basaltic andesites, which are often much
decomposed, are of the doleritic type referred to in the account of
the Ndreketi Plains on page 133. Inland, towards Narengali and

X NAKAMBUTA 149

Va-Hli, these rocks are often more or less glassy and take the form
of pitchstones ; whilst the agglomerates have the same character.
The first probably represent submarine flows of basaltic lava which
have spread far and wide over the Ndreketi plains. The inland
rocks are, as is pointed out below, the products of vents that, as in
the case no doubt of Mount Nakambuta, rose out of a shallow sea.
The palagonite-tuffs and clays, often foraminiferous, which cover
the Ndreketi plains, are extensively represented in the lower levels
up to 4(X) feet or more.

Between one and two miles to the westward of the Narengali
valley, and immediately north of Va-lili, the agglomerates, over-
lying palagonite-tuffs, form lofty precipices. The agglomerates
are composed of blocks of more or less vitreous basaltic-andesites,
some of them semi-vitreous and amygdaloidal, some in the form of
pitchstone, and others again as tachylyte that fuses in the lamp-
flame. The underlying palagonite-tuffs are bedded, and are
composed of fragments of basic glass that originally inclosed
porphyritic crystals of plagioclase. In the slide it is observed that
the glass and mineral fragments have often been re-fractured as
they lie in the tuff and that the former have rounded angles and
eroded edges. The interstices are filled with a more or less
palagonitised magma. Similar rocks occur in other localities, and
they will all be found described on page 334. It may, however, be
remarked here that in all cases these rocks would seem to have
undergone some crushing, the heat developed in the process being
sufficient to partially remelt the glass. A high temperature was
not required to effect this fusion, since splinters of the tachylyte
occurring in the overlying agglomerate fuse in an ordinary lamp-
flame. It is pointed out on page 341 that tuffs of this character
differ in origin and in characters from the prevailing foraminiferous
palagonite-tuffs.

The road from Narengali to Natua traverses the length of this
district. At and near the mouth of the Narengali valley there are
exposed basic tuffs and agglomerates, the blocks in the last case
being formed of a semi-vitreous, vesicular or almost scoriaceous
basaltic andesite. In this neighbourhood the track passes across
the top of a waterfall which is the result of the existence of a huge
dyke-like mass of a compact basaltic andesite showing a little
interstitial glass and referred to genus 13 of the augite-andesites.
It lies in a district of tuffs and agglomerates. Farther on, about
two miles north-west of Narengali, the track crosses some rounded
hills, elevated about 600 feet, on the top of which is displayed a

ISO A NATURALIST IN THE PACIFIC chap.

concretionary pitchstone, showing little nodular concretions of the
size of filberts, and having the microscopical characters of " vario-
lite," as described on page 313. This is the only locality of this
rock that is known to me.

My acquaintance with the tract of Nakambuta is, however,
very imperfect. But it is apparent that in the pitchstones and in
the semi-vitreous basic rocks, sometimes vesicular and amygda-
loidal, we get a nearer approach to the products of subaerial
eruptions than is to be observed in most other portions of the
island. The examination of the Nakambuta peak by some future
investigator will bring to light some interesting facts concerning
this region. It is not unlikely that during a late stage of the
emergence of this region Nakambuta and the other peaks around
protruded as active vents above the surface of a shallow sea, at the
bottom of which the products of their eruptions accumulated.

The Valley of the Ndreke-ni-wai and its
Tributaries

Ndreke-ni-wai, which signifies " the hollow of the water," is the
name of a broad tidal estuary, opening into Savu-savu Bay, which
is formed by the union, about half a mile above its mouth, of two
rivers, the Mbale-mbale River flowing from the north-west past a
village of that name, and the Vatu-kawa River, the largest, flowing
from the eastward, which I have also named after a village on its
banks. The valleys of these two rivers are separated by a moun-
tainous dividing-ridge connected by a saddle with the main range.
Its highest peaks rise to 2,100 feet above the sea, the elevation of
this " divide " rapidly decreasing as it approaches the coast, where,
within a mile of the beach, it terminates in some low hills 200 or
300 feet in height.

It may be observed here that a mouth of the river was
originally situated 700 or 800 yards to the west of its present
site. This old mouth is now represented by a lagoon communi-
cating with the Mbale-mbale River above, but closed by the sand-
mound of the beach at its lower end, which, however, is occa-
sionally broken through when the rivers are in flood. This lagoon
is shown in the view facing page 153.

The valley of the Mbale-mbale River, which is much the
smaller of the two rivers, is bounded on the north by the pre-
cipitous slopes of the Koro-tini Range, which rise to over 2,000
feet, and on the south and west by the lofty Va-lili Range, The

X NDREKE-NI-WAI VALLEY 151

valley, above the village of Mbale-mbale, is broad and low-lying ;
and one can ascend it to the vicinity of Waisali, three to four miles
from the river's mouth, without attaining an elevation of 100 feet
above the sea. The main stream, which flows down from Waisali,
is joined near Mbale-mbale by a more impetuous stream that
descends the steep mountain-sides just to the east of the Koro-
tini Bluff.

The valley of the Vatu-kawa River is bounded by lofty moun-
tain-ranges that rise to elevations varying from 2,000 to 3,500 feet.
On the south side lies the Mariko Range, on the east lies Mount
Mbatini, the most elevated peak of the island, whilst on the north
rise up the steep slopes of the Koro-tini Range and of the moun-
tainous " divide." The valley has such a gentle gradient that one
can follow it inland for five or six miles from the estuary to the
vicinity of Nukumbolo without exceeding an elevation of 100 feet
above the sea. Below Na Salia the valley is confined between the
hills that approach the river ; but above that village it is very
broad ; and on account of its slight fall the river here often
changes its course, so that the floor of the valley is strewn with
water-worn blocks and pebbles marking the old channels.

The Vatu-kawa River, which rises on the west slopes of
Mbatini, flows with a placid current past Nukumbolo and Na
Salia, until it reaches the village of Vatu-kawa, where it is joined
by its impetuous tributary, the Wai-ni-ngio, "the river of the
shark." This affluent, after descending the steep slopes of the
Koro-tini mountains, bursts through the dividing range that
separates the Mbale-mbale and the Vatu-kawa valleys. It would
seem that the Wai-ni-ngio without any great effort on its part
might become a tributary of the Mbale-mbale River.

The great character of these two valleys, as shown above, is
their little elevation above the sea. For miles inland the level
does not attain 100 feet, and high ranges rise steeply in each case
on either side to 2,000 feet and over. Here, as in the instance of
most of the large valleys of the island, the original configuration
of the surface was not dependent on river-erosion. Rivers no
doubt have done much to carve out the lesser and to deepen and
widen the greater valleys ; but, as is often remarked in this work,
the main features of the surface were in existence before the
emergence of the island from the sea.

The geological formation of the slopes of these two valleys is
described in the accounts of the various ascents of the mountains
bounding them. Since foraminiferous tuffs occur high up their

152 A NATURALIST IN THE PACIFIC ch. x

sides, up to elevations of 2,000 feet and over, the valleys them-
selves were at one time no doubt also covered with these submarine
deposits, which, however, have been in great part stripped off by
the denuding agencies. They are still to be found, containing
large tests of foraminifera, between Mbale-mbale and Waisali ;
but the basaltic andesites, originally underlying them, are more
frequently exposed. One of these rocks found a little east of
Waisali, which has an aphanitic appearance and a specific gravity
of 2*82, is merely a basic glass in its early stage of crystallisation,
being made up of very minute crystallites ^x^Vo- of an inch in
length. On the surface in this locality there also occur basic
agglomerates containing scoriaceous rocks, the products of some
of the last stages of volcanic action in this part of the island. . . .
In the case of the broad part of the Vatu-kawa valley above
Na Salia blocks of basic rocks derived from the mountains around
strew the bottom in great abundance. Lower down, where the
valley is confined between the hills, basic agglomerates and coarse
tuffs are displayed in the hill-sides.

Mention should be made here of the various hot springs
existing in these valleys in the low levels near the rivers and
stream-courses. In the Vatu-kawa valley they exist at Nukum
bolo, and in the Mbale-mbale valley at Natoarau, Waitunutunu
and other localities. These springs are described in Chapter III.

CHAPTER XI

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Koro-tini Range or Table-land

The level-topped range that forms the mountainous backbone

of the island for a distance of nearly lo miles is one of the

remarkable features of Vanua Levu.^ In the general profile of the

island it is named the Koro-tini Table-land on account of the level

profile which it presents whether viewed from the north or from

the south. But this is merely its appearance en masse. When it

is examined in detail it is found that although much of the range

has an elevation between 2,000 and 2,400 feet above the sea, it

attains an elevation of about 3,000 feet in the case of two gently

sloping peaks. With regard also to its table-top, it is necessary to

remark that whilst in some portions of the range the summit is

Droad and level, in others it is much cut up into ridges, and in

Dthers again it presents a single narrow crest. Nor can we realise

)n looking at the profile the extent to which its slopes have been

:arved out by river-erosion, and we get no indication of the several

ofty spurs that descend north and south far into the plains, as in

he case of the spur west of Sueni and in that terminating in the

<^oro-tini Bluff. In the profile the eye ignores the details with

vhich the investigator during many toilsome ascents has filled the

)ages of his note-books. To this extent it is useful in that it

I enables him to rise a little above the level of his facts, and permits

] dm (to employ a figure-of-speech) to regard the style and general

I haracter of the edifice without being exclusively absorbed in the

: tudy of the bricks.

This range, which extends from a mile or two west of Sealevu
1 D a couple of miles east of Sueni, is connected on the west with
1 he Va-lili Range by the Waisali Saddle before described, and on
^ It rises in the background of the view.

^'

154 A NATURALIST IN THE PACIFIC chap,

the east with the Thambeyu or Mount Thurston Range by a
broken chain of mountains, of which Koro-mbasanga is the most
conspicuous. It is connected by an elevated col with Mount
Mbatini and the Mariko Range to the southward. The name of
Koro-tini has been appHed to this range because it is familiar to
the natives. It signifies " ten towns," and was given to a once
populous district on the slopes of the lofty bluff overlooking on
the north the mouth of the Ndreke-ni-wai. I crossed the range in
foHr places, namely, between Waisali and Sealevu, between Mbale-
mbale and Vandrani, between Vatu-kawa and Vandrani, and
between Nukumbolo and Sueni.

(i) Traverse of the Koro-tini Range from Waisali
TO Sealevu. — Starting from Waisali by the Narengali track, I
ascended the east slope of the Waisali Saddle, as described on
page 146, until an elevation of about 750 feet was reached, when
my way lay to the northward across the Koro-tini Range to
Sealevu. At 850 feet a singular altered tuff was displayed in
position in a stream-course. It shows calcite and pyrites, and is
interesting from the fact that although it is made up largely of
basic glass the tuff does not seem to have undergone the pala-
gonitic change.

Afterwards, there was a fairly steep ascent to the summit of
the range, 2,400 feet above the sea, which has merely a ridge-like
crest. Between an elevation of 1,400 feet and the top there are
exposed at the surface compacted coarse and fine palagonite-tuffs
and agglomerate-tuffs formed of the same materials. They contain
often abundant organic remains, such as valves of " Cardium " and
" Pecten " shells, macroscopic tests of Foraminifera, and some
curious scale-like bodies, showing a concentric structure and about
an inch across, which look like fish-scales. It is probable that these
interesting rocks extend to a greater elevation than 2,400 feet,
which was merely the highest level reached in the traverse, but is
not the highest point of the range.

These deposits are made up in mass of a more or less
palagonitised basic glass originally containing phenocrysts of
plagioclase and pyroxene. The palagonitic process is nearly
always far advanced ; but it is seen in all its stages, the least
altered materials fusing under the blow-pipe into a black glass.
The fragments are usually sub-angular in the case of the coarse
tuffs ; but small rounded pebbles up to half an inch in size and
fine water-worn gravel are not infrequent. The matrix is composed
of palagonitic debris, portions of crystals of plagioclase and

XI THE KOROTINI RANGE 155

pyroxene, fine gravel, occasional tests of foraminifera ; and it often
contains a fair amount of carbonate of lime, in one specimen
tested as much as 13 per cent. The amount of lime, however,
varies, being in some places scanty.

The term " conglomerate " could not be applied to the coarser
deposits, since the sub-angular and angular fragments always
predominate. They could scarcely be deemed "breccias" on
account of the mixture with pebbles and gravel. Their character
is therefore intermediate between the two. I have used the ex-
pression " agglomerate-tuff" because it best describes their ap-
pearance. A specimen of such a rock presents a curious mixture,
in the well-compacted mass, of angular and sub-rounded fragments
of palagonite up to an inch in size, small pebbles and fine gravel
of the same material, and detached valves of " Cardium," entire
and broken. One is forced to draw the inference that these
materials accumulated in shallow water. They are such as might
have been produced by the marine erosion of an emerging volcanic
island endeavouring to hold its own above the waves. But from
the occasional occurrence of blocks of a scoriaceous basaltic rock
it would appear that during the formation of the deposits there
were periods of eruption.

At times massive and comparatively fresh-looking basaltic
rocks are exposed in situ on the mountain sides in the midst of
these submarine deposits. A specimen obtained at 1,800 feet is a
semi-ophitic porphyritic olivine-basalt with a specific gravity of
2"86 and showing a little interstitial glass. The mode of exposure
did not admit of my ascertaining the exact relation of these rocks
to the deposits. They are no doubt dyke- like masses representing
the original fissures of eruption of a submarine vent ; and during
the emergence they were covered up with tuffs and deposits, the
work of the marine erosion of the emerging land. These, however,
are points on which light will be thrown when we come to examine
other localities.

Descending the northern slopes of the range from the summit
to Sealevu the general course was N.N.E. Several valleys were
crossed, of which that occupied by the Na Sinu river was 600 feet
in depth, the rivers and streams all flowing to the north-west into
the Ndreketi basin. Basic tuffs and agglomerates were exposed
at the surface all the way down to Sealevu, 400 feet above the sea.

At the head of the Sealevu valley, about a mile or rather more
above the village, and a little east of the track followed in the
descent above described, the mountain-range terminates abruptly

156 A NATURALIST IN THE PACIFIC chap.

in lofty cliffs 400 or 500 feet in height. At their base, which is
about 1,000 feet above the sea, once stood the village of Lovutu.
These cliffs are formed of basic agglomerate-tuffs which display a
horizontal arrangement, but there is no distinct bedding. They
have the castellated appearance that often characterises horizontally
bedded sedimentary formations. The inclosed rock-fragments
vary in size from 18 inches to half an inch and smaller. The
larger are angular or sub-angular, and are composed of hemi-
crystalline basaltic andesites, scoriaceous and vesicular and some-
times amygdaloidal. The smaller fragments are more or less
rounded and of the same material. The matrix is made up of fine
detritus of the large fragments and of lapilli of a vacuolar palagonitic
basic glass, whilst small crystals of calcite fill the cavities and line
the fissures. The phenocrysts of plagioclase and augite inclosed
in the altered glass also display extensive alteration, and in the
first case are largely replaced by calcite, secondary quartz, and
other products. No organic remains came under my notice ; but
on account of the alteration of the tuff-matrix their preservation
could hardly be expected. Bearing in mind, however, the fossili-
ferous character of the tuffs and agglomerates in the higher part
of the range, it can scarcely be doubted that the agglomerate-tuffs
of the Sealevu cliffs are also submarine.

Each traverse of the great Koro-tini Range will provide us with
new facts to aid us in framing an explanation of the origin of this
long mountain-ridge. The principal lesson to be learned from the
journey across the range from Waisali to Sealevu, and from the
visit to the cliffs, is concerned with the great extent and thickness of
these submarine basic tuffs and agglomerates. From 1,000 feet
above the sea up to the summit, 2,400 feet in height, they are
almost the only rocks exposed, excepting the occasional masses of
basaltic rocks, which probably represent dykes. Their maximum
thickness must amount to some hundreds of feet.

(2) Traverse of the Koro-tini Range from Mbale-
MBALE TO Vandrani. — In this traverse the track before as-
cending to the summit crosses a spur of the Koro-tini Bluff, and
then descends into the valley of the Natoarau river on the east
side of it. It will therefore be convenient to describe the bluff
before giving my description of the journey across the range.

The Koro-tini Bluff is a lofty headland (if I may so term it),
lying about four miles inland from the mouth of the Ndreke-ni-wai.
It attains an elevation of about 2,000 feet, and terminates above
in a line of precipices 300 or 400 feet in height. It represents the

XI THE KOROTINI RANGE 157

southern edge of the level-topped mountain range behind, and like
the Sealevu cliffs on the north side it affords a natural section of
its mass. It is shown in the plate facing page 153, where it rises at
the back of the lagoon.

Approaching the bluff from Mbale-mbale, one crosses a low-lying
district less than 100 feet above the sea before striking the spur.
Here and in the lower few hundred feet of the spur are exposed
basic agglomerates, and occasionally in the mass a semi-vitreous
vesicular olivine-basalt, almost like a pitchstone, and displaying
large porphyritic crystals of plagioclase, 5 or 6 millimetres long, the
agglomerates being made up of the same material. Higher up, at
elevations between 1,000 and 1,500 feet, are exposed coarse pala-
gonite-tuffs made up of fragments, usually i to 3 mm. in size^
of extensively palagonitised basic vitreous rocks, such as occur in
the cliffs above. These tuffs become coarser as one approaches
the precipitous bluff, the base of which lies about 1,650 feet above
the sea. Here the cliffs present a bare rocky face, some 200 feet
high. The lower portion is composed of an agglomerate-tuff, and
the upper portion mainly of agglomerates. These deposits dis-
play no bedding excepting a single plane of division inclined
steeply to the north at an angle of perhaps 40°.

The blocks in the agglomerate-tuff are either angular or sub-
angular, and are less than a foot across. They are all composed
of more or less vitreous porphyritic olivine-basalts, showing large
crystals of plagioclase a fifth of an inch (5 or 6 mm.) in length. But
they vary somewhat in character. Some of them, that are vesicular
and almost scoriaceous, may be termed from their glassy nature
porphyritic pitchstones. Others again, where the groundmass is
hemi-crystalline, may be designated porphyritic compact basalts,
and are referred to genus 37 of the olivine-basalts.

The matrix of the agglomerate-tuff is made up of angular frag-
ments, up to 5 mm. in size, of singular vitreous and semi-vitreous
olivine-basalts, in part palagonitised. There is evidence of crushing
in situ of some of the porphyritic felspar crystals ; but it is not sc^
marked as elsewhere noticed. The palagonite is also in part inter-
stitial, a character that goes to support the view advanced on
page 342, that the palagonite may be connected in its origin with
the heat developed during crushing, only a moderate temperature
being required for the partial fusion of the glass.

In crossing the range by this route from Mbale-mbale one first
ascends, as above observed, the spur of the Koro-tini Bluff up ta
a height of 1,200 feet. The track then descends into the valley-

158 A NATURALIST IN THE PACIFIC chap.

gorge of the Natoarau river on the east, the bottom of which is
750 feet above the sea, and from here the climb begins. One
ascends the bed of the stream course, clambering over slippery
rock surfaces up to 1,2c D or 1,300 feet, where the stream is left,
and the mountain-slopes, often steep and precipitous, are then
followed to the summit, 2,000 feet in height. Coarse and fine
palagonite-tuffs and agglomerate-tuffs of the same character are
exposed on the surface from the commencement of the ascent up
to 1,850 feet ; but they are displayed much more extensively in the
stream-course than in the soil-covered upper slopes.

The tuffs are grey except when hydrated, when they turn yel-
lowish-brown. Some of them contain lime, as much at times as
10 or 12 percent; whilst others possess little or none. Tests of
foraminifera are not infrequently inclosed, even as high as 1,850 feet.
A description of one of these tuffs containing a few tests of Globi-
gerina, which was obtained at 1,200 feet, is given on page 331, under
sample D. It will be there seen that they are derived from different
basic rocks, some containing but little glass, others mainly vitreous,
only the more glassy constituents being palagonitised. The palago-
nite-tuff sandstones exposed in large blocks on a bare spur at 1,850
feet contain 12 per cent, of lime, the largest tests of foraminifera being
not over half a millimetre.-^ These tuffs occasionally show bedding.
At 1,000 feet they dip gently to the S.S.W., and at 750 feet
they are inclined about 15° in the same direction. In this last
locality they consist of alternating layers, i to 4 inches in thickness,

of fine and coarse tuffs, the coarser looking like sandstone

The blocks in the agglomerate-tuff are sub-angular, and of an
olivine-basalt with hemi-crystalline groundmass,^ their size ranging
from 2 feet to an inch. I noticed one large block of this rock,
measuring 2x1^ X i feet, imbedded alone in the tuffs at 1,200 feet.
At one place a tuff containing small fragments of basalt displayed
a concretionary structure, indicating probably the proximity of a
dyke, the globular masses being 4 feet across. A little lime occurs
in the matrix of the agglomerate-tuff

The summit of the range, 2,000 feet in height, is " ridgy," about
half a mile in width, and cannot therefore be described as table-
topped. The rocks exposed in blocks on the surface are composed
of a semi-ophitic olivine-basalt containing a large amount of inter-
stitial glass which shows the fibrous crystallites of the early stage
devitrification. It is referred to genus 33 of the olivine-basalts.

^ They are described under sample E on p. 332.
^ Referred to genus 37 of the olivine-basalts.

XI THE KOROTINI RANGE 159

Descending the northern side of the range I followed the steep
slopes down to 1,000 feet above the sea. A rubbly doleritic olivine-
basalt, semi-ophitic, and assigned to the same genus (33), prevailed
■on the way ; and it is probable that a waterfall with a drop of
50 feet or more that is situated on these slopes indicates a large
intrusive mass of this rock. During the rest of the descent to
Vandrani, which lies in a valley at the foot of the range, and is
elevated about 300 feet above the sea, basic agglomerates and
palagonite-tuffs, together with deposits intermediate in character,
were exposed at the surface. At times a semi-ophitic doleritic
basalt similar to those displayed above, but without olivine, oc-
curred in position. The blocks in the agglomerates are formed of
a compact semi-vitreous basaltic rock, and are sometimes vesicular.
At one place the palagonite-tuffs exhibited signs of alteration, being
traversed by small fissures not over a third of an inch broad (5 to
8 mm.), and filled with a zeolite behaving like natrolite.

In some cliffs by the river at Vandrani are displayed fine and
coarse non-calcareous palagonite-tuffs, bedded and dipping about
15° N. by W. They are penetrated by cracks, 5 mm. in breadth,
which are filled with chalcedony. These tuffs are evidently in part
derived from acid as well as from basic rocks, though mainly from
the latter ; and they show other alteration-characters. At the
Tiouth of the Vandrani valley there are exposed in the river-bed
:oarse palagonite-tuff sandstones containing a little lime, and
probably a few tests of foraminifera.

Reference may here be made to the mountain of Ravi-koro
vhich, when seen from the north-east, rises up as a partially inde-
)endent peak, with a broad base and a conical truncated summit,
immediately west of the track followed in the descent from the
; ummit of the range to Vandrani. It is probably not much under
: !,ooo feet in height, and exhibits bare precipitous cliff-faces on the
north side. It would be worthy of the attention of the future
i nvestigator.

Recurring to the principal features of the range between Mbale-
j ibale and Vandrani, one may remark the extensive occurrence of
basic agglomerates and tuffs on both slopes, the prevalence of

< livine-basalts, the frequency of the semi-vitreous and vitreous or
3 ather pitchstone condition of these rocks, and their semi-ophitic

< haracter, especially on the summit and north slopes. From the
\ esicular structure of the rocks of the Koro-tini Bluff and from the

< haracter of its tuffs and agglomerates, it is to be inferred that
t ley are the direct products of eruptions, probably in shallow seas.

i6o A NATURALIST IN THE PACIFIC chap.

On the other hand, the tuffs (often foraminiferous) as well as the
agglomerate-tuffs of the north and south slopes of the range are in
part suggestive of marine erosion. Intrusive masses of basalt are
to be observed occasionally, and doubtless to this cause may be
attributed the concretionary structure of the tuffs in places, and
the alteration of these deposits in one or two localities, where they
are penetrated by cracks filled with chalcedony.

(3) Traverse of the Koro-tini Range from Vatu-kawa
TO Vandrani. — On leaving Vatu-kawa\ which is not more than
50 feet above the sea, the ascent for the first 600 feet up the steep
mountain-side lies along the rocky bed of the Wai-ni-ngio River,
which from its rapid fall has more the character of a torrent. On
its sides are exposed basic agglomerates and agglomerate-tuffs ;
whilst the large boulders in its bed are composed of a somewhat
altered olivine-basalt. At 600 feet the track abandons the stream-
course for the steep mountain slopes, and thence up to 1,100 feet
similar agglomerates and tuffs prevail. At this last-named elevation
there are displayed fine and coarse indurated palagonite-tuffs, a
little altered in character and with little or no lime. A specimen
of the former, of which the materials composing it do not exceed
'2 mm. in size, shows in the slide an occasional " Globigerina " test
filled with palagonitic debris. Such a marine deposit is evidently
not of shallow-water origin. The coarser tuff is made up of com-
pacted sub-angular fragments, not over 2 mm. in size ; but contains
no organic remains. The prevailing rocks exposed between 1,100
and 1,900 feet, a little below the summit of the range, are somewhat
altered compacted non-calcareous breccia-tuffs, composed of
sub-angular fragments 5 or 6 mm, in size, of a more or less glassy
and often vacuolar basic or basaltic andesite, only in part pala-
gonitised, the vacuoles as well as the interstices between the
fragments being sometimes filled with a zeolite.^

^ On the right side of the river close to Vatu-kawa there are some cliffs
displaying a section of the mountainous spur, referred to on p. 1 51, that separates
the valleys of the Mbale-mbale and Vatu-kawa rivers, an exposure quite apart
from the rocks exhibited on the adjacent southern slopes of the main range.
These cliffs are formed of bedded grey tuffs marked by single layers of blocks
6 to 8 inches across and dipping about 30" S.S.W. The tuffs in their texture
are not unlike sub-aerial tuff-deposits. They contain no lime and are composed
of basic materials with a little palagonite. They seem to indicate some sub-
sidiary vent, close to the present village of Vatu-kawa, which may have been
active shortly before or during the emergence of this district.

2 These altered tuffs on the southern slope of this range are described
on p. 332.

XI • THE KOROTINI RANGE

i6i

The summit of the range may be described as a " ridgy " table-
land. Though about 2 miles in breadth, its level only varies
between 2,000 and 2,200 feet, the inequalities being probably the
effect of denudation. Here, as in many other similar localities, on
account of the dense forest it was only possible to determine the
surface-configuration by the use of compass, watch and aneroid
The prevaihng rocks displayed in this region are grey non-calcareous
basic tuffs, somewhat altered in character, and composed of frag-
ments usually not exceeding i mm. in size of a basic glass the
palagonitic process being masked by other changes. These tuffs
often become brownish-yellow through hydration. Tests of foramin-
ifera are enclosed, but they are very scanty.

On the north slopes basic agglomerates and palagonite-tuffs are
the predommant rocks down to the foot of the range. A specimen
of the tuffs taken at 1,300 feet is calcareous in patches and probably
contams tests of foraminifera ; but it is too much weathered to
enable one to speak with certainty on this point. The interestino-
eature of this slope is the exposure at 1,600 to 1,700 feet of largS
Dlocks of a dark grey hypersthene-augite andesite referred to the
orthophyric order of those rocks described on page 290 Lower
<Iown (1,000-1,300 feet) occasional solitary blocks of the same rock
l)ut somewhat altered, occur imbedded in the palagonite-tuff This
type of rock which is characterised by the orthophyric structure of
the groundmass and by other features is rarely represented in
^'anua Levu.

Summing up the general results of this traverse we observe that

!f'/^'\''^i^'Pf^' °^^^^ range, basic agglomerates, breccias,
and tuffs, the last however scantily foraminiferous, occupy a great
extent of the slopes and summit. The alteration of these deposits
01 the southern slopes is noteworthy. The only deeper seated
n lassive rocks observed were the pyroxene-andesites above alluded to
(4) Traverse of the Koro-tini Range from Nukumbolo
TDSUENL— The hot springs at Nukumbolo, which are described
01 page 24, rise up through agglomerate-tuffs. Around the
bathing pools he large masses of altered palagonite-tuffs which give
te first indication of the region of altered rocks that extends from
Nukumbolo to the lower slopes of the range, a distance of about
tr ree miles.

For about a mile and a half or two miles from this place the
tr.xk lies through a broken country and does not rise to a height
m )re than 300 feet above the sea. A variety of altered rocks are
he re exposed in position in the stream courses. Some of them are

M

1 62 A NATURALIST IN THE PACIFIC chap.

fine and coarse basic tuffs showing secondary calcite, quartz and
opal, as alteration products. Others are palagonite-breccias with
the vacuoles of the altered glass filled with opal. Others again are
massive basic rocks, such as fine-textured augite-andesites, or
doleritic basaltic andesites, semi-ophitic in character, the plagioclase
phenocrysts being more or less occupied by calcitic and other
products. The alteration is not always far advanced, but it is
sufficiently marked to give a common character to the rocks of the
district.

Ascending the lower slopes of the range up to 800 feet one finds
the altered rocks still exposed in the stream-courses ; but the
changes exhibited are not always the same. A specimen from 500
feet looks like a tuff, but in the slide it appears as a semi-vitreous
augite-andesite, its substance being penetrated by fine veins of
chalcedonic quartz and opal, whilst the same material is developed
within the larger plagioclase crystals. Another specimen from 800
feet, which is apparently a tuff, contains so much lime that it effer-
vesces freely with an acid. It was composed originally of fragments
of a hemi-crystalline basic rock, of which the plagioclase pheno-
crysts have been replaced by calcite ; whilst the augite and inter-
stitial glass is now represented by viridite and a chloritic mineral.
It is to be inferred that at some time hot springs were very
numerous in the district between Nukumbolo and the lower slopes
of the range, those at Nukumbolo, as far as I know, alone existing
in our time.

From a height of 1,100 or 1,200 feet the mountain slopes rise
steeply to the summit rather over 2,000 feet in elevation. At the
foot are exposed in situ aphanitic augite-andesites,^ which in some
specimens show a little alteration in the chalcedonic quartz filling
minute cracks, and in one case there is an irregular cavity, f inch
across, filled with milk-white opal. Another rock exposed at the
foot of the steep ascent is a semi-vitreous basaltic-andesite, doleritic
in texture and ophiticin structure, but apparently not muchchanged.^
At 1,700 feet is displayed a vesicular basic andesite, semi-vitreous
in character, and above this I found a porphyritic basaltic andesite.

The summit of the range is i^ ox 2 miles in breadth and is
relatively level, its undulating surface varying in elevation between
1,900 and 2,200 feet. The prevailing rocks exposed on this elevated
plateau are vitreous pitchstone-like rocks finely vesicular and
scoriaceous, the cavities being filled either with aragonite or with

1 Referred to genus 16, species A, sub-species i, of the augite-andesites.

2 Referred to genus 9, sub-genus A, of the augite-andesites.

XI THE KOROTINI RANGE 163

opal. The basic glass, of which they are formed, shows incipient
crystals, and begins to fuse in an ordinary flame. One specimen
obtained here is a doleritic basaltic andesite, slightly ophitic and
containing a fair amount of residual glass.^ However, the vitreous
and scoriaceous character of most of the rocks on the summit is
very remarkable. (Similar rocks occur on the top of Mount
Thambeyu where the slopes of the mountain are covered with
submarine tuffs and agglomerates.) There is a precipitous descent
on the north side of the range to Sueni at its foot, massive basaltic
andesites being exposed at first, whilst basic tuffs and agglomerates
are displayed lower down.

The special features of this traverse of the range are the
alteration of the tuffs and massive rocks between Nukumbolo
and the lower southern slopes, the variation in character of the
basic rocks in the upper southern slopes, the occurrence of vitreous
vesicular and scoriaceous rocks on the summit, and the restriction
of the ordinary basic agglomerates and tuffs to the northern
slopes. Any attempt on my part to explain the structure of this
part of the range from the data here given would be futile without
comparing them with those obtained from other parts of the range.
It will be subsequently pointed out that the difficulties will be in
part removed if it is assumed that the submarine palagonite-tuffs
and agglomerates, that so often cover the flanks of the mountains
to their summits, have been in this case largely stripped off by
the denuding agencies.

(5) The Sueni Valley.— My acquaintance with the extreme
eastern part of the Koro-tini Range is restricted to the descent of
the picturesque valley from Sueni to Koro-utari. It is occupied
by a tributary of the Lambasa River, and is bounded on the east
side by the lofty slopes of the main range, and to the westward by
a mountainous spur that projects far into the Lambasa plains
Sueni lies by the river-side in the midst of mountains which rise
steeply on most sides to heights of 2,000 feet and over, and often
display precipitous bare faces apparently of volcanic agglomerates
Numerous waterfalls may be observed on their flanks, which as in
Dther localities, doubtless indicate the occurrence of large intrusive
Jykes. Sueni is situated about 300 feet above the sea, the descent
:o Koro-utari at the mouth of the valley, a distance of 3 to 4 miles
n a direct line, being about 150 feet.

The river as it flows down the valley from Sueni to Koro-utari
raverses a region of basic agglomerates and agglomerate-tuffs,
1 Referred to genus 9, sub-genus B, of the augite-andesites.

M 2

1 64 A NATURALIST IN THE PACIFIC chap.

These deposits, as they are displayed in the hill-slopes lying
W.S.W. and at the back of Sueni, are composed of blocks of the
size of the fist of a vesicular basaltic andesite ; whilst the large
masses on the surface are made of the same, but non-vesicular,
rock. The blocks in the agglomerates between Sueni and Koro-
utari range usually from a few inches to a foot in diameter. A
specimen obtained from one of them is made of a partly vitreous
basaltic andesite ; whilst in another case the rock is an altered
basic andesite, the glassy groundmass being largely impregnated
with colloid silica looking like opal under the lens.^

Nearly a mile below Sueni, within a space of less than 60 yards,
there are exposed at the river-side in the agglomerates three
vertical or nearly vertical dykes, 4 to 6 feet in thickness. They
trend roughly N.E. and S.W., and are non-columnar, except in the
case of the one farthest up the river, which has rude, transverse
joints.^ The rocks composing these dykes are somewhat doleritic
basaltic andesites, olivine being very rare or absent. The two
highest, which are only 15 to 20 feet apart, are made of similar
rocks characterised by abundant interstitial glass, and having a
sp. gr. of 278. The rock of the third dyke, about 50 yards farther
down the river, has but scanty glass in the groundmass, the sp. gr.
being 2'Sg. The differences between the two types represented in
the three dykes are mainly concerned with the degree of crystal-
lisation, and it is probable that though not contemporaneous they
were derived from the same fluid magma which, as we may infer
from the proximity and lie of the dykes, was situated at no great
depth.s

General Inference Respecting the Koro-tini Range.
— If we can imagine a line of vents, protruding in some cases

* Both these rocks belong to the hypersthene-augite andesites, showing
phenocrysts of both monodinic and rhombic pyroxene. The first belongs to
the orthophyric order described on p. 290 ; whilst the second belongs to the
second order (genus 13, p. 287) where the felspars of the groundmass are lathe-
like and in flow arrangement.

2 The highest dyke trends N. 48^ E. and is inclined from the vertical about
15° N.W. The dyke, 5 or 6 yards below it, trends N. 30° E. and is vertical.
The dyke, 50 yards farther down, trends N. 35° E. and is inclined from the
vertical about 5° N.W. The inclination was only estimated. The bearings
are true.

3 Both the types are referred to genus i of the augite-andesites, the olivine,
when present, being quite insufficient to give a character to the rock. They
however belong to different species according to the length of the felspar-
lathes, which in the doleritic rocks averages '2 mm. and in the other type
'08 mm.

XI THE KOROTINI RANGE 165

above the surface of the sea, that were ultimately worn down to a
common level through marine-erosion, and were then largely
covered over with submarine tuffs and agglomerates, we should
have in our mind's eye the first and most important stage in the
formation of this range. If we then assume that there followed
a period of emergence characterised by a renewal on a very
extensive scale of marine-erosion, during which the agglomerates
were mainly formed, and that since that period the sub-aerial
denuding agencies have been for ages in operation, we shall, I
think, obtain some idea of the history of the Koro-tini Range.

CHAPTER XII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Koro-mbasanga Range

As is illustrated in the accompanying profile-sketch, the
relatively level-topped range of Koro-tini gives place at its eastern
end to a broken line of mountains, of which the round-topped Koro-
tambu, 2,753 ^^^^ ^^ height, and the pinnacled Koro-mbasanga,^
2,537 feet, are the highest peaks. Further east lies the broad
Vuinandi Gap which separates the Koro-mbasanga and Mount
Thurston, or Thambeyu, ranges. The twin-peaks of Mount
Mbatini, the highest mountain of the island, appear in the back-
ground in the sketch, and to the left rises Thambeyu, the second
highest summit.

We enter here another complex region of mountains ; and if
the character of the rocks are sometimes different we shall yet
have to bear in mind in our interpretation of its geological features
the lesson derived from the examination of the Koro-tini Range.
Before and behind all our facts of observation lie the two
great periods of marine-erosion and the later ages of sub-aerial
denudation.

When approached from the north, the western part of the
range has a rude crescentic form, and looks like the remnant of a
gigantic crater-cavity about two miles across. At the back rise^
as shown in the second of the profile-sketches, the precipitous
slopes of Koro-mbasanga proper ; whilst the two spurs descending
from it, one on the west, the Sokena spur, towards Koro-utari, the
other on the east, at the back of Nasawana, give the crescentic

^ It is pointed out on p. 5 that this name is wrongly applied in the
Admiralty charts to Mount Mbatini, a mountain about three miles south of it.

CH. XII

KORO-MBASANGA

167

figure open to the north. The last-named village lies nestled in
this great hollow, the floor of which, though not in its lowest part
below the level of the Lambasa plains, is not over 200 feet above
the sea. However, the facts adduced in the following description
of this region do not give much support to this view of its surface-
configuration.

For the convenience of description, I will first describe the
peak of Koro-mbasanga, and then the Sokena ridge and, lastly, the
Lovo valley that cuts through the range to the eastward.

Thamleyu fMf Thurston) 3124 ft •

These three sections form a continuous profile-sketch of the mountainous axis of Vanua
Levu for a length of 15 or 16 miles and include the Thambeyu, Koro-mbasanga, and
Koro-tini ranges as viewed from the northward near Na Kama. The eastern section
is at the top and the western section at the bottom. The summit of Thambeyu was
covered with clouds.

Karo -Mbasanffa. 2637 F*

Sokena. moft

Koro-mbasanga from the north-north-east.

(i) Koro-mbasanga. — The ascent of Koro-mbasanga is best
made from Nasawana, a village at its base, elevated rather over
200 feet above the sea, and distant about a mile and a half north-
east from the peak. On the way to the foot of the mountain we
traverse an undulating region of basaltic andesite,^ which is merely
the extension to the base of the mountains of the basaltic Lambasa
plains. After commencing the ascent of the steep slopes, we find
exposed in a stream-course, 'JQO to 800 feet above the sea, a

^ Referred to genus 13 of the aiigite-andesites.

1 68 A NATURALIST IN THE PACIFIC chap.

sedimentary basic tuff, presenting layers of coarse and fine
materials, and partly palagonitic in composition. It is a little
calcareous, and apparently incloses tests of foraminifera. These
submarine deposits have evidently been stripped off the basaltic
low-lands beneath. It thus becomes evident that the structural
features of the Lambasa plains (basaltic rocks overlain by
submarine deposits) are preserved to the base of the range.

These submarine deposits, as exposed in the stream-course, lie
beneath agglomerates which repose horizontally upon them ; and
from this level up to the bare rocky peak of the mountain,
agglomerates and agglomerate-tuffs are alone displayed either as
large detached masses or in cliff-faces.

In the lower part of the mountain the blocks, usually sub-
angular, are about a foot across ; but they become smaller as one
ascends towards the summit, where they are 3 or 4 inches in
diameter. At the top there are extensive exposures in cliff-faces
of the agglomerate-tuffs ; and here the finer materials of the matrix
include a few rounded pebbles not exceeding half an inch in size.
This is a fact of importance in connection with the submarine
origin of these formations.

As regards their composition, the blocks of the agglomerates
have not the uniform character we would expect to find in the case
of materials directly ejected from a volcanic vent. The most
frequent type of rock represented is a grey hypersthene-augite-
andesite, having a specific gravity of 272 — 278. It displays small
phenocrysts of plagioclase and of rhombic and monoclinic
pyroxene, but in other respects it exhibits much variety, not only
in the arrangement and average length of the felspar-lathes ('oS
to "iS mm.) but in the form of the pyroxene of the groundmass
(either granular or prismatic) and in the amount of residual glass,
sometimes abundant, sometimes scanty. Two distinct genera
(i and 5) of the sub-class are therefore represented.

Other rocks found in these agglomerates contain no rhombic
pyroxene, and are referred to genera 13 and 16 of the augite-
andesites according to the presence or absence of plagioclase
phenocrysts. In the last case we have a dark aphanitic rock
(sp. gr. 274), sometimes scoriaceous, where the average length of
the felspar-lathes may be as little as '04 mm. One of the blocks
was composed of a highly scoriaceous semi-vitreous rock, the
cavities being filled with a zeolite. Another was composed of a
black porphyritic augite-andesite, showing large crystals of plagio-
clase. . . . The matrix of the agglomerate-tuff is formed of sub-

XII THE SOKENA RIDGE 169

angular and rounded fragments, up to a centimetre in size, of the
same andesites, the interstitial material being formed of fine
detritus and palagonitic debris.

Though the agglomerates of the peak of Koro-mbasanga are
composed of a variety of rocks, all the rocks are to be referred to
the pyroxene-andesites with specific gravity below 2*8 but above
27. They are therefore less basic than the olivine-basalts and
basaltic andesites of the Koro-tini range, where the density is
usually 2*8 and over. Their variation, however, is more consistent
with the characters of an agglomerate formed by marine erosion.
The same may be said of the sorting of the blocks according to
their size and of the occasional occurrence in the matrix of small
rounded pebbles. That these deposits of agglomerates were
formed under the sea is indicated also by their overlying submarine
sedimentary tuffs near the base of the mountain.

(2) The Sokena Ridge. — To the west of Koro-mbasanga,
and forming a spur of the same range, is the flat-topped hill of
Sokena, which rises about 1,100 feet above the country at its base
and about 1,600 feet above the sea. From a distance it has the
appearance of being formed in its higher portion of nearly hori-
zontal strata dipping gently northward. In its upper part it
terminates in a line of cliffs about 200 feet in height, and there is a
similar line of cliffs lower down the slopes. These cliffs are com-
posed of bedded fine and coarse non-calcareous tuffs, dipping about
10° N.N.W., in which are imbedded without any arrangement
blocks, ranging in size from 2 or 3 inches to 3 or 4 feet, of a
remarkable blackish pitchstone-like rock displaying opaque plagio-
clase phenocrysts. It is referred to genus 18 (see page 289) of
the hypersthene-augite andesites, both rhombic and monoclinic
pyroxene being represented in the phenocrysts and in the ground-
mass where they take the form of minute prisms ('03 mm.). There
is a considerable amount of pale brown glass. A rock very similar
occurs in the Thambeyu agglomerates (see page 178). The tuffs
are formed largely of palagonitic materials, the angular fragments
in the coarser beds being | to 2 centimetres in size, the palagonite
being often vacuolar but much affected by hydration.

These tuffs and agglomerates of the Sokena cliffs apparently
:ontain no organic remains. They appear to have accumulated
jnder water as the result of the eruptions of a neighbouring vent
A^ithout the intermediate agency of marine erosion.

(3) The Ascent of the Lovo Valley. — About two miles
:o the east of the peak of Koro-mbasanga the picturesque Lovo

lyo A NATURALIST IN THE PACIFIC chap,

valley cuts deeply in a southerly direction into the mountainous
backbone of the island. The site of the old town of Lovo lies
within the valley about two miles from its mouth. " Lovo " is the
Fijian word for a cannibal-oven ; and I gathered from my natives
that in the old times this vale was noted for its cannibal orgies.
It is occupied by the Nasawana tributary of the Lambasa River,
and often becomes so narrow that it may be described as a gorge..
I followed the valley from its mouth, where it is elevated about
300 feet above the sea, for some miles in a southerly direction up
to a height of 1,000 feet, where the northern slope of the great
mountain-mass of Mbatini commences.

On either side of the Lovo valley rise precipitous mountain-
slopes, displaying in their cliff-faces and in the large detached rock-
masses basic agglomerates. The same formation is also usually
displayed in the sides of the river. The blocks composing the
agglomerates are formed of the usual type of hemi-crystalline or
semi-vitreous blackish basaltic andesite so characteristic of these
deposits. It is generally compact, but is at times amygdaloidal.
Some distance below the old site of Lovo, and at an elevation of
about 500 feet above the sea, there is an interesting exposure in the
river-side, where the agglomerates overlie bedded coarse calcareous
basic tuffs containing large flat tests of foraminifera with pieces of
molluscan shells, and dipping about 15° S.W. These tuffs can be
traced up the valley towards Lovo.

Displayed in mass in the bed of the river in the same locality,,
and beneath the submarine tuff just referred to, is a porphyritic
basaltic andesite (sp. gr. 279) containing but scanty interstitial
glass, the felspar-lathes being '15 mm. in average length. It is
referred to genus i of the augite-andesites. The same rock is
exposed at intervals in the river-bed as far as Lovo, which is about
850 feet above the sea. At one place it exhibits a rudely columnar
structure, the columns being horizontal and 2 to 2i^ feet in diameter,,
the trend of the dyke-like mass being W. by S. and E. by N.
Near Lovo a small dyke, 6 feet thick and trending N.N.W. and
S.S.E., pierces the agglomerate. It is composed of a somewhat
aphanitic augite-andesite closely resembling the rocks exposed in
the river-course for a mile or so above Lovo up to an elevation of
1,000 feet. In this upper part of the valley whilst agglomerates are
exposed in the cliffs and precipitous mountain-slopes on either side,
pyroxene-andesites, somewhat aphanitic in texture and with a
specific gravity of 2'68 to 27, are displayed in mass in the river
bed. These last-named rocks, which are closely similar to those

XII THE LOVO VALLEY lyr

found on the lower slopes of Mount Mbatini (see page 173) are, as
I should have also remarked in the case of the basaltic andesite
above mentioned, a little altered, as is indicated by the existence of
calcite and viridite in the groundmass.^

From this instructive ascent of the Lovo valley we may learn
that whilst the mountain mass is formed, to a considerable depth,
of agglomerates with underlying submarine tuffs, the deeper seated
rocks exposed in the river-beds are massive intrusive rocks. The
overlying agglomerates have preserved the submarine tuffs from
destruction, and there is no difficulty in assuming that they also
were accumulated under the sea, but in shallow water, as evidenced
by the character of the tuffs. I found no signs of alteration in
these tuffs, and except in the case of the small dyke above noticed
there is no sign of the dykes penetrating the agglomerates. We
have here a section into the heart of the mountain-range ; and
assuming that the large intrusive masses of basic andesites had
penetrated these deposits, there would certainly have been some
evidence of this in the extensive exposures of agglomerates far up
the mountain-sides. As it is, however, we find such rocks only in
the deeply excavated river-bed. If we imagine a submarine
volcanic mountain, or one but slightly raised above the surface of
the sea, to be subjected during a long period of emergence to
marine erosion, the " basal wreck " of the mountain would ultimately
be covered over by submarine tuffs and agglomerates. This is the
condition that seems to be presented here.

I did not make the ascent of Koro-tambu, the other principal
peak of the Koro-mbasanga Range. This round-topped mountain
is well seen from the summit of Mbatini from which it bears N. 30°
W. by compass. It is probably the peak marked 2,753 ^^^^ i" ^he
Admiralty chart, and is connected with Mbatini by a saddle not
under 1,500 feet in elevation.

Some of the most important features in the above account of
this district may here be emphasised. We have seen that in the
peak of Koro-mbasanga and in the Lovo valley agglomerates and
agglomerate-tuffs, several hundred feet thick, overlie sedimen-
tary submarine tuffs. In the last-named locality the deeper
massive basic rocks are also exposed ; and we may infer in both
instances that the agglomerate-formation is a submarine deposit.

1 They are blackish and somewhat compact (sp. gr. 2*67 — 271) and have
very small felspar-lathes less than 'i mm. long. They contain both rhombic
and monoclinic pyroxene, and are referred to genera i and 13 of the hypersthene-
augite-andesites.

172 A NATURALIST IN THE PACIFIC chap.

On the other hand, in the Sokena Ridge, which is a spur of the
main range, we have apparently the accumulation of materials on
a sea-bottom, directly ejected from a vent without the intervention
of the agency of marine-erosion. In regard to this and other
districts in this part of the island it should be remembered that
east and west occur undoubted evidences of extensive submergence.
It has already been shown that submarine tuffs containing tests of
foraminifera and other organic remains occur at heights of 2,000
feet and over on the summit of the Koro-tini Range, and it will be
subsequently shown that similar deposits are to be found on the
neighbouring slopes of Thambeyu as high as 2,100 feet.

Mount Mbatini

According to the Admiralty chart this is the highest mountain in
Vanua Levu, its elevation being 3,437 feet. It has twin peaks which
lie either N.W. and S.E. or W.N.W. and E.S.E. with each other.
The northerly or westerly peak is pointed and tooth-like. Hence
probably arises its name of Mbatini (mbati-tooth). The southerly
or easterly peak is known as Soro-levu. It has a broadly conical
outline with a truncated summit. The mountain is named Koro-
mbasanga in the Admiralty chart, a name that really belongs to a
peak lying about 3 miles nearly due north (N. 5° W.). The natives
are very clear in this matter ; but it must be remarked in this
connection that Koro-mbasanga, which signifies " a forked emi-
nence," would be a very suitable appellation for the double-peaked
summit of Mbatini.^ By the natives of the surrounding district
the whole mountain is known as Mbatini ; but by the natives of
the eastern shores of Natewa Bay, it is usually known as Soro-levu,
since the western peak is often more or less hidden from view or is
less conspicuous. The profile of this mountain and of the neigh-
bouring region is shown in the accompanying profile-sketches and
also in one of those illustrating the Koro-mbasanga range on page
167.

As viewed from the top of Mariko to the southward, Mbatini
presents itself as a long mountain-ridge, trending W.N.W. and
E.S.E., which is connected on the north with Koro-tambu, the
liighest peak of the Koro-mbasanga Range, by a saddle probably

^ I discovered this error in a rather practical fashion by ascending the wrong
mountain. The natives were engaged to take me to Koro-mbasanga and they
performed their task, my aneroid and compass soon indicating that I was not
on the highest peak of the island, but on a lesser peak three miles north of it.

XII

MOUNT MBATINI 173

not over 1,500 feet above the sea, and on the south with the
mountain-ridge of Mariko by a col which appears not to be
under 1,000 feet in elevation.

My ascent of this mountain was made from the north by the
way of the Lovo valley. In ascending the Lovo valley one
reaches, at an elevation of about 1,000 feet, the foot of the north

Som-Lom,. Mbatini 3437^

Mount Mbatini from the top of Koro-mbasanga. The distant peak on the right is one ot
the summits of the Mariko ridge.

Marine [Drayton- Peak.) ZS90fl Mbaiini.3437ff Thambeyu (Mf Thurston/) 3J2^fi

View from Muanaira on the south coast of Natewa Bay.

slope of Mbatini. The slope is somewhat steep up to 2,000 feet,
the rocks exposed on the surface being closely similar in the
groundmass to those displayed in the upper part of the Lovo
valley. They are compact-looking blackish augite-andesites
(sp. gr. 27), the very small felspar-lathes of the groundmass,
which are in flow arrangement, averaging only '05 mm. in length.
Like the rocks below, they are a little altered ; and here the inter-
stitial glass is also scanty. But they differ in the absence of
rhombic pyroxene and are therefore referred to the augite-andesites
(genus 13).

■i At 2,000 feet, where one crosses the foot-track from Nukumbolo
to Korolau, the ascent of the true Mbatini ridge begins, the summit
lying nearly two miles to the south-east. Whilst following along
this lofty mountain-ridge we were for the greater part of the time
in the rain-clouds, so that very little was seen of our surroundings.
The crest is densely wooded so that our progress was very slow.
The rocks are but sparingly exposed. At the commencement of
the ridge (2,100 feet) is displayed an altered hypersthene-augite
andesite, rudely columnar blocks of which, up to 2 feet in dia-
meter, were lying about. It belongs to genus i of this sub-class
(see page 286) which also includes the rocks exposed farther along
the ridge. In these rocks the felspar-lathes are small ("05 — '07
mm. long) and are not in flow arrangement. The interstitial glass
varies in amount, and the specific gravity is about 27.

174 A NATURALIST IN THE PACIFIC chap.

The ascent is very gradual for the first one and a half miles,
when an elevation of 2,600 feet is attained. From here one ascends
the steep-sided peak of Mbatini, which rises some 700 or 800 feet
from the ridge. As one nears the highest point the crest becomes
very narrow, between 1 5 and 20 feet across ; and on either side
there is apparently a drop of several hundred feet. The actual
peak, which is bare and rocky, is yet narrower ; and when it is
enveloped in dense mist as it was in my instance, it is not a very
secure situation for a geologist. It is highly magnetic, as is the
case with most of the other bare peaks of the island. The rocks
exposed in the upper 500 feet, that is, in the peak proper, are
highly altered semi-vitreous, but extensively weathered, hypers-
thene-augite-andesites which are referred to genus i of that sub-
class. Much of the glassy groundmass is replaced by viridite,
silica, calcite, &c. Less altered specimens display in a brown
opaque glass small felspar-lathes averaging less than "i mm. in
length. They exhibit phenocrysts of rhombic pyroxene and augite,
the first prevailing.

I did not climb Soro-levu, the other of the twin-peaks. Its
ascent should be made either from Nukumbolo or from one of the
villages on the neighbouring shore of Natewa Bay. My acquaint-
ance with Mbatini, although very incomplete, enables me however
to point out a few of its general features. As remarked before,
there is a general uniformity in the type of its rocks. The olivine-
basalts and basaltic andesites, prevailing in the Koro-tini Range,
are not here represented, nor are the dacites or acid andesites to
be found. The characteristic rocks are more or less altered
hypersthene-augite-andesites having a specific gravity in the least
altered and least vitreous condition of about 27 ; whilst the average
length of the felspar-lathes is always less than "i mm. The same
type prevails from the upper part of the Lovo valley to the summit
of Mbatini ; but it is only in the actual peak that these rocks
show much glass in the groundmass, though extensively affected
by alteration. Neither tuffs nor agglomerates came under my
notice ; but they might be expected to occur on the other slopes.
I am inclined to regard this mountain-ridge as a huge dyke-like
mass or sill, representing the remains of a volcanic vent that has
been subjected at different periods to marine-erosion and in later
ages to sub-aerial denudation.

XII VUINANDI GAP 175

The Vuinandi Gap

I have given this name to the break between the Thambeyu
(Mount Thurston) and Koro-mbasanga ranges, where the level of
the mountainous backbone of the island descends to about 1,200
feet above the sea. This is the route taken by the track from
Vuinandi on the shores of Natewa Bay across the island to
Lambasa.

At Vuinandi the mountains recede from the coast leaving a
broad level plain extending about two miles inland to the village
of Tarawau without rising over 60 feet above the sea. Basaltic
rocks are exposed in the spurs that descend from the mountains
to the coast on each side of the plain. After traversing the low-
lying region that lies between Vuinandi and the main range, one
finds on ascending the eastern slopes, en route to Lambasa,
basaltic andesites of the usual type prevailing up to 1,000 feet.
The upper portion of the dividing range, 1,000 to 1,200 feet, is
composed of a more compact basaltic andesite which is often
rubbly and in this condition is penetrated by fine cracks, ^ of an
inch broad, filled with chalcedony. This rock, which has a specific
gravity of 2*85, has a very fresh-looking appearance in the slide,
and the segregation of silica does not therefore appear to arise
from an alterative change. The felspar-lathes, which are in flow-
arrangement, average 'ii mm. in length, and there is a little
residual glass.

The mountains rise on either side of the Vuinandi Gap to
about 2,000 feet. Descending on the west side of the range one
follows a stream-course down to a level of 400 feet above the sea,
agglomerates and coarse basic tuffs being exposed on the way.
The rocks forming the agglomerates are for the most part to be
referred to genus i of the hypersthene-augite andesites. They
are sometimes compact and sometimes amygdaloidal, the amyg-
dules being formed of chalcedony and other minerals, whilst the
glass of the groundmass is often altered.

The track then lay across a spur, 800 feet ' in height, princi-
pally composed of a greyish porphyrite, exhibiting large opaque
crystals of plagioclase, 4 to 7 mm. long, in an almost holo-crystal-
line groundmass formed of stout lamellar felspars with large augite
granules. It is described on page 268 under the porphyritic sub-
genus of genus 2 of the augite-andesites, and is an unusual type
of rock for this island. After this I descended into the picturesque

176 A NATURALIST IN THE PACIFIC chap,

gorge of the Satulaki River, which is only elevated about 200 feet
above the sea, agglomerates prevailing. In the vicinity of Satu-
laki a rather compact basaltic andesite (sp. gr. 2'82) is commonly
exposed in position. It is referred to genus 13 of the augite
andesites and belongs to the species with felspar-lathes less than
•I mm. in average length. It occurs both north and south of this
place and in the hill-spurs on either side. This is the bed-rock of
the Lambasa plains which here begin and extend to the north
coast, being usually covered with submarine tuffs and clays.

The Thambeyu or Mount Thurston Range

Mount Thurston is the name given in the Admiralty charts
to the highest peak (3,124 feet) of this range. There does not
appear to be any general native name. The highest peak visible
from the Lambasa side is known as "Thambeyu." The lofty
mountain-mass, as it is viewed from Vuinandi, is known as Ulu-i-
ndiri-ndiri.^ The whole mountain-range has yet to be properly
explored. It is a much more complicated system of mountain-
ridges than is indicated in the chart, my acquaintance with it
being restricted to the Thambeyu ridge, the elevation of which is
2,600 feet above the sea. It trends N.N.W. and S.S.E. ; but its
relation to the highest peak of the range could not be ascertained,
as we were in the rain-clouds during the two days we were on the
mountain.

I made the ascent from the village of Numbu-ni-a-vula about
three miles to the westward, which is only 200 feet above the sea.
In the intervening low district a basaltic andesite is exposed in the
stream-courses. The structure of the ridge, as indicated by the
ascent of its western slope, is shown in the accompanying dia-
gram. The core or central axis is formed of massive basic rocks
which protrude at the summit and in one or two of the crests
of the spurs. The flanks are composed of submarine tuffs and
clays overlaid by agglomerates of considerable thickness. The
tuffs reach to within 50 feet of the top, whilst the agglomerates
extend to within 400 feet of the summit. The results obtained
from this ascent are specially interesting, since it afforded me the
opportunity of studying in a satisfactory manner the junction of
the agglomerates with the tuffs.

There are two caves on the mountain-side which can be used

^ Vula Votu is the name of a peak lying to the east. Ngoinangai is a forked
mountain still further east.

xn THE THAMBEYU RANGE 177

for night-shelter by those exploring the range. The lowest, 1,500
feet above the sea, is the Taloko Cave (na-ngara-taloko). The
highest is the Ndromo Cave,^ 2,100 feet, known to the natives as
" na-ngara-vatu-ni-ndromo." Like most of the caves all over the
island they occur at the junction of the agglomerates and tuffs,
and are to be attributed to the more rapid weathering of the
underlying tuffs. ... In describing the results of my examination
of this mountain-ridge, I will deal in succession with the tuffs, the

Ideal Section ofThmbevu..

2600 ft. ..a^fetv"*^^^'-

^; ■§ Pyroxene -andesites

% S ForaminiferovLS Tu/Fs and Clays

^ Volcanic agglomerates.

agglomerates, the junction between these two deposits, and the
axis or core of basic rocks.

(i) The submarine tuffs and tuff -clays. — As exposed in the
stream-courses near and at the foot of the mountain and as high
as the Taloko Cave, these deposits are bedded horizontally. At
higher levels, owing to insufficient exposure the bedding is not so
clear. Up to 700 or 800 feet coarse palagonite-tuffs prevail ; but
they do not effervesce with an acid, and apparently contain but
scanty organic remains. At 950 feet coarse and fine sedimentary
tuffs alternate, the last being greenish foraminiferous tuff-clay
rocks, somewhat compacted and containing 10 per cent, of car-
bonate of lime. The tests of the foraminifera, which are abundant
and of the Globigerina type, are filled with calcite. Several frag-
ments, of a semi-vitreous basic rock, not however exceeding '2 mm.
in size, are inclosed in the deposit ; but the mass of it is made up
of yet finer materials of the same rock, palagonitic detritus, plagio-
clase fragments, fine calcitic debris, tests of foraminifera, &c.
These fine tuff-clays were evidently formed in relatively deep-
water.

At the Taloko Cave (1,500 feet), where there are exposed rather
coarse tuffs containing bands about a centimetre thick of a fine
clay-tuff, the last-named effervesce freely with an acid, whilst

^ A kind of " edible " bird's-nest is found in this cave.

N

178 A NATURALIST IN THE PACIFIC chap.

the first contain only a little carbonate of lime. No sections have
been made of these deposits ; but when powdered and examined
under the microscope they appear to have the same general
composition as the deposit described above from an elevation
of 950 feet. They are probably foraminiferous though scantily.
The tuffs found at the Ndromo Cave (2,100 feet) contain 4 per
cent, of carbonate of lime and small tests of foraminifera are
visible with a lens. The mineral fragments include plagioclase
and rhombic pyroxene, and there are inclosed rounded gravel-
fragments, 5 mm. in size, of a semi-vitreous rock. Palagonitic
debris make up the mass of these tuffs. A coarse deposit from
2,500 feet is non-calcareous, but has the same general composition.

(2) The agglomerates. — These deposits are best represented
in the upper part of the mountain, between 1,500 and 2,200 feet
above the sea. Here they often present vertical precipices having
a drop varying between 100 and 400 feet, with the submarine tuffs
exposed at their base. Such cliffs, however, display no structure.
Their vertical faces are to be attributed to joints and to the
extensive " slips " that frequently occur on these slopes, when
large masses of agglomerate, undermined by the percolation of
springs through the tuffs beneath them, roll far down the moun-
tain-sides. The blocks of the agglomerates are fairly uniform in
size, being usually 4 or 5 inches across. They are composed of a
semi-vitreous hypersthene-augite andesite, containing both augite
and rhombic pyroxene, but of an unusual type. It is a blackish
rock carrying opaque phenocrysts of plagioclase, and is charac-
terised by the prismatic form of the pyroxene (monoclinic) of the
groundmass, A very similar rock from the Sokena agglomerates
has been before described. It is referred to genus 18 of the class,
and the prismatic sub-order to which that genus belongs is
described on page 289.

(3) The junction of the agglomerates and submarine tuffs. — This
is well displayed at the Taloko Cave. Here the agglomerates lie
conformably on the sedimentary tuffs ; but the line of junction
is sharply defined and the only evidence of transition is afforded
by the great diminution in the size of the blocks of the agglo-
merates, which are i to 2 inches across. Immediately beneath the
agglomerate is a layer 2\ centimetres thick of a rather coarse
sedimentary palagonite-tuff having the composition of the deposits
above described, but not effervescing with an acid, and showing
no foraminiferous tests. The size of its " grain " is about a milli-
metre. This passes downward rather abruptly into a chocolate-

XII THE AVUKA RANGE 179

coloured marl-like rock, a centimetre thick, which is formed of
the same materials but in a clayey condition. Beneath this is the
calcareous foraminiferous palagonite-tufif referred to in the first
paragraph.

It is apparent that for some time before the agglomerates
began to accumulate on the sea-bottom there had been a fairly
uniform deposit of submarine tuffs, evidently in rather deep water.
Then followed a period during which the finest mud was deposited
which is represented by the thin layer of chocolate-coloured clay.
This was succeeded by the deposition of coarser sedimentary tuffs
forming a layer about an inch in thickness. Then commenced
the accumulation of the agglomerates, of which the materials
were at first small and afterwards larger in size.

(4) The core or axis of volcanic rocks. — This is represented on
the summit by masses, 2 to 5 feet across, of two kinds of hypers-
thene-augite andesite, which are referred to genus i of that sub-
class. One is a compact grey rock (sp. gr. 272) carrying pheno-
crysts both of rhombic and monoclinic pyroxene, the former
prevailing, and displaying a small amount of interstitial glass.
It is magnetic and exhibits marked polarity, as noticed in Chapter
XXVI. The other is a scoriaceous rock containing numerous
round steam-pores, ranging up to 5 millimetres in diameter and
generally filled with clear quartz-crystals and lined by chalcedony.
It contains semi-opaque glass in abundance, and is apparently a
semi-vitreous form of the rock just described. Both rocks are to
some extent altered. . . . On the crest of a spur, 500 feet below
the summit, is exposed in position an augite-andesite, assigned to
genus 13, sub-genus i, species B, of that sub-class. It is non-
scoriaceous and exhibits a considerable amount of greenish altera-
tion products. (Sp. gr. 279.)

The Avuka Range

This high range, which lies immediately to the east of Lambasa,
attains its greatest elevation in Mount Avuka, which is 1,976 feet
above the sea. It represents the extension northward to the coast
of the inland Thambeyu mountains that culminate in Mount
Thurston. In its upper portion Mount Avuka presents bare
precipitous faces apparently of agglomerates and some hundreds
of feet in height. My acquaintance with this range is scanty. In
a traverse from Lambasa to Ngele-mumu I crossed it a mile or
more south of Mount Avuka, where it is only 700 feet in elevation.

N 2

i8o A NATURALIST IN THE PACIFIC ch. xii

I also rounded the end of the range where it reaches the coast
between Lambasa and the valley of Mbuthai-sau. This last
locality, which is described on page 218, derives especial interest
from the circumstance that here the regions of basic and acid
rocks meet. The basic rocks that occupy nearly all the sea-
border from Naivaka to Lambasa here become mingled with, and
finally give place to, the acid rocks which prevail in all the region
eastward as far as Undu Point.

In crossing the range on the way from Lambasa to Ngele-
mumu, I noticed as high as 450 feet basic non-calcareous tuffs
displaying a concretionary arrangement suggestive of the prox-
imity of an intrusive igneous rock. Further up the western slope
occur basic agglomerates, whilst at and near the top (700 feet)
there lie on the surface large boulders of a dark grey hypersthene-
gabbro having a specific gravity of 27 and belonging to the type
of plutonic rocks described on page 249. It is very probable
that this gabbro forms the axis of the range ; and we have
here no doubt one of the oldest of the mountain-ridges in the
island.

CHAPTER XIII

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Valanga Range

This range, which trends N.W. and S.E. between the Mariko
mountain-ridge and the head of the valley of Na Kula, attains a
height of 1, 8 80 feet at its N.W. and of 1,710 feet at its S.E.
2nd. The average elevation, however, is probably not over 1,300
Dr 1,400 feet. My acquaintance with the range is only partial,
but it is sufficient to bring to light some of its leading structural
'eatures. Those who follow me will find in these mountains a
/ery interesting region for their geological explorations.

(i) Traverse of the Valanga Range. — In making the

ourney from Valanga to Vunimbua, I crossed the range where

ts elevation was about 1,300 feet. Basic agglomerates, containing

iometimes amygdaloidal blocks, are displayed in the low district

)etween Valanga and the foot of the range. In the stream-course

at the base of the slope the deeper seated rocks of the range are

; it once exposed. Large masses, 5 or 6 feet across, of altered grey

■ )yroxene andesites lie in the bed of the stream. Some of them

; how opaque porphyritic felspar and have the appearance of

])orphyrites (sp. gr. 2*67). They belong to the type described

on page 271 under genus 6 of the augite-andesites. Others are

} rey propylitic varieties of a basic semi-doleritic andesite pene-

1 rated by cracks containing calcite, and displaying in a ground-

1 lass, exhibiting much viridite and a little pyrites, calcitic pseudo-

1 lorphs of the felspar phenocrysts and more or less parallel felspar-

;1 ithes, '15 mm. long and somewhat altered. Another of the

< eeper-seated rocks commonly exposed on the upper west

J opes of the range is a dark grey rock showing much porphyritic

1 82 A NATURALIST IN THE PACIFIC chap.

pyroxene (sp. gr. 272). It has a micro-felsitic groundmass
and is referred to the fourth order of the hypersthene-augite-
andesites described on page 291.

About two-thirds of the way up the western slope of the range,
there is exposed a coarse palagonite-tuff, evidently an incrusting
deposit. Stout crystals of augite can be picked out of it, and it
contains also lapilli up to an inch in size of a basic vesicular semi-
vitreous basalt.

Descending the eastern slopes one observes between i,2CX) and
1,000 feet large blocks of the same grey hypersthene-augite-
andesite above mentioned and of a grey granitoid rock of the
gabbro type. This last is a hypersthene-gabbro with specific
gravity of 275, and belongs to the group of plutonic rocks
described on page 250. Its pyroxene phenocrysts are often
represented by fibrous bastite. One can scarcely doubt that this
gabbro is the plutonic equivalent of the prevailing grey pyroxene-
andesites.

Lower down the slope only small fragments of rocks were
exposed, probably derived from an agglomerate. One of the
specimens here obtained is a doleritic basaltic andesite (sp. gr.
277). Another is a very interesting rock displaying large por-
phyritic crystals of a mineral like bronzite in a groundmass
originally to a large degree vitreous ; but the glass is now replaced
by viridite and secondary crystalline silica. The " bronzite " is the
result of the conversion of associated rhombic and monoclinic
pyroxene into fibrous bastite.

From the results of the traverse across this part of the Valanga
Range it may be inferred that more or less altered grey basic
andesites passing into gabbros chiefly compose it. No doubt at
one time it was largely covered with basic tuff's and agglomerates,
but these deposits have been almost completely stripped off by the
denuding agencies, and were only noticed in one place on the
western flank.

That the northern part of the range towards the Mariko ridge
has a similar structure is shown by the character of the loose
blocks in the upper course of the Vunimbua River, which takes its
rise on these slopes. Amongst those in the river above the village
I noticed a solitary block of a coarsely crystalline diorite con-
taining prisms of brown hornblende a centimetre in length.^ But
the rocks most frequently represented were propylitic grey hypers-
thene-andesites, in which the pyroxene is mostly changed into
' This rock is described on p. 251.

XIII THE VALANGA RANGE 183

bastite, whilst the surface often sparkles with pyrites (see page
297).

(2) Ngone Hill. — This is a curious conical hill, about 700 feet
in height, that rises up on the right side of the Vunimbua River
about i^ miles above the village of that name and near the foot of
the range. It evidently represents a " volcanic neck," and doubt-
less this vent was the source of the large blocks forming the basic
agglomerate that occurs in huge masses in the river-course in the
vicinity of this hill. On its lower flanks is exposed a hard com-
pacted tuff, showing pyroxene crystals, which is composed prin-
cipally of fragments of a palagonitised vacuolar basic glass, the
minute cavities being often filled with opal. In the upper part of
the hill is displayed a massive altered augite-andesite penetrated
by fine veins of chalcedony. Numerous irregular cavities filled
with the same material occur in its dark opaque glassy groundmass.

The blocks of the agglomerates found in the vicinity of the hill
vary in size from 4 to 18 inches. They are composed of a compact
blackish semi-vitreous basic andesite (sp. gr. 273) of the type
characteristic of the basic agglomerates over most of the island.
The matrix of the agglomerate is hard and somewhat altered, and
is chiefly made up of fragments, ranging up to 5 mm. in size, of
a vacuolar basic glass, sometimes but slightly changed, though
usually converted into palagonite, the vacuoles being filled with
chalcedonic opal. The large masses of coarse tuffs displayed in
the bed of a stream-course close to Ngone Hill are non-calcareous
and composed of palagonitic materials. Palagonite-tufif clays are
also exposed in the river-course a little above Vunimbua. About
half-way between the village and the hill there occurs in posi-
tion at the river-side an amygdaloidal basic rock, the amygdules
being formed of chalcedonic opal.

It is apparent that this hill represents a lesser vent which
probably dates back to the period before the emergence. All the
products of its eruption are, however, more or less altered. From
the absence of sorting in the blocks of the agglomerates, and from
the character of the matrix, it may be inferred that these deposits
have been accumulated directly from the ejected materials without
the intervention of the agency of marine erosion.

(3) The Western Flank of the Valanga Range. —
One of the boldest pieces of coast in the island lies on the eastern
side of Savu-savu Bay, between the mouth of the Ndreke-ni-wai
River and Valanga Harbour. Here a number of lofty headlands
separated by broad valleys descend with precipitous fronts to the

1 84 A NATURALIST IN THE PACIFIC chap.

shore, some of them, as in the case of the Nambathi promontory
on the north side of Valanga Harbour, retaining an elevation of
i,ooo feet within a few hundred yards of the coast.

By following the coast-track from the Ndreke-ni-wai River to
Valanga one crosses some of these headlands. As far as Vatu-lele
altered red tuffs, basic agglomerates, and massive basaltic andesites
are the prevailing rocks. The red tuffs exhibit a double alteration.
They were originally composed of finely pulverised basic vacuolar
glass, which subsequently became palagonitised, and afterwards
there was an extensive deposition of chalcedonic silica and of red
iron oxide. No organic remains appear to exist ; whilst the scanty
calcite present is evidently an alteration product. Where the road
"* tops " the headland on the north side of Vatu-lele Bay, there is
exposed a dyke-like mass of a rubbly semi-vitreous basaltic rock
penetrated in all directions by veins, i to 3 inches thick, of a
tachylytic glass, splinters of which fuse readily in the ordinary
spirit-lamp flame. The numerous fissures were doubtless pro-
duced during the consolidation of the rock ; and subsequently
they were filled with the still fluid residual portion of the magma,
which would be composed of the most fusible constituents. This
subject, which bears on the origin of palagonite, is discussed in
Chapter XXIV.

Between Vatu-lele and Urata, palagonite-tuffs and basic ag-
glomerates are chiefly displayed. On the north slope descending
to Urata there is exposed in the foot-path a dyke-like mass of a
-dark-grey hornblende-pyroxene-andesite, an unusual type of rock
which is described on page 298. Just south of Urata I observed
an agglomerate containing large blocks, 3 or 4 feet across, of the
deeper-seated altered grey pyroxene-andesites that with the
gabbros and diorites form the axis of the range.

(4) The Valley of Na Kula.— In crossing from Sava-reka-
reka to Natewa Bay, one ascends the remarkable valley of the
Kula and traverses the ridge at its head. This ridge, which is
about 700 feet in height and forms the termination of the Valanga
Range, is composed of altered grey hornblende-pyroxene-andesites
and of similar holo-crystalline rocks representing the gabbro or
plutonic type of the same. One of these rocks is described on
page 250, under the head of hornblende-gabbro. Another is
referred provisionally to the hypersthene-gabbros (page 249) ; but
it is extensively occupied by chlorite, viridite, and other alteration
products. Here, as with the other rocks of the Na Kula Ridge,
the plagioclase phenocrysts are opaque, the result of the numerous

XIII THE MARIKO RANGE 185

fine cracks with decomposition products in the interior of the
crystals. ... It is thus seen that in general structure the Na Kula
Ridge represents the main axis of the Valanga Range to the north.

The valley of Na Kula is occupied by a river which does not
empty itself, as one would expect, into Savu-savu Bay, but turns
off sharply to the south at right-angles to its previous course, and
after breaking through the coast range, opens into Naindi Bay.
This peculiarity has attracted the attention of the natives. The
village of Sawa-Ndrondro, which lies about i| miles up this valley,
is not elevated more than 50 feet above the sea. The gradient is
evidently not only very slight but is also irregular, so that in their
upper course about 3 miles inland, where the elevation is only 130
feet, the waters of the river are partially checked in their flow and
form extensive swamps where the "vitho" or wild sugar-cane
flourishes.

(5) Concluding Remarks on the Valanga Range. — It
may be inferred from the geological structure of the range that it
is one of the oldest in the island. The agglomerates and tuffs
that enter so largely into the formation of most of the other
mountain-ridges are here to a great extent absent, except in the
lower flanks; and we have exposed the axis of the range composed
of more or less altered grey pyroxene and hornblende-pyroxene
andesites passing, as appears to be the case, into gabbros and
diorites. It is true that the exposure of the gabbros is limited and
that only a single block of diorite came under my notice ; but
this might be looked for where the plutonic rocks are deeply
seated. Although far overtopped by the neighbouring agglomerate
mountain-ridge of Mariko, the Valanga Range would seem to date
back to a much earlier stage in the history of the island.

The Mountain-Ridge of Mariko

This mountain-ridge, which trends nearly east and west and
joins the Valanga Range, rises in mass to a height of rather over
2,000 feet. Above this elevation it terminates in several short
conical peaks, of which the highest, 2,890 feet, is named Mariko, the
Drayton Peak of the chart. One of the peaks, lying a little to the
east of the summit, and apparently between 100 and 200 feet
lower, is called the Vatu-mbutho or White Rock. In the profile
of the range, as seen nearly " end-on " from the distant south shore
of Natewa Bay, it would appear to be rounded in its upper part.
Its true outline, however, when viewed in length, is, as described
above, namely, a massive ridge with various peaks.

1 86 A NATURALIST IN THE PACIFIC chap.

When viewed from the top of the hills behind Valanga, this
mountainous range has a very imposing appearance. On the
south side it rises precipitously to the summit, but the northern
slopes below an elevation of i,8oo or 1,900 feet descend with a very
easy gradient for i^ or 2 miles into the valley of the river Ndreke-
ni-wai. In the first case the average angle of the slope would be
from 15 to 20 degrees and in places often more ; whilst in the
second case the average inclination would be about 7 degrees.
The contrast between the two sides of the range is very striking"
and one ought, I think, to find a parallel in the broken-down rim
of a large crater with a gentle outer slope and a precipitous inner
face. When descending recently the outer slope of Monte Somma,
the ancient Vesuvian vent, I found reproduced some of the features.
of the northern slope of Mariko. The tuffs and agglomerate-tuffs
that cover their outer flanks are in both mountains deeply scored
by the gorges and ravines worn by the torrents. After the de-
scription of the geological structure of the Mariko Range, we shall
perhaps be in a better position to consider this question ; but until
a proper survey of the region has been made it will not be possible
to give a final answer. There are also many other uncertainties
which would be removed by the accurate mapping of the district,
such for instance as the mode of connection between the Mariko
and Valanga Ranges.

The highest peak of the Mariko Range is irregularly square-
topped and is only a few paces across. It has a soil-cap and
supports small trees and shrubs, whilst there is a precipitous rocky
face on the east and south. Like most of the other lofty peaks of
the island it is magnetic, and as remarked on page 368, it markedly
deflects the compass-needle.

I made two ascents of this mountain from Vunimbua, one to
the highest peak (2,890 feet), and the other across the range to
Nukumbolo at a point half a mile or more to the west of the
summit, where its elevation is 2,200 feet. Basic agglomerates and
agglomerate-tuffs prevail on both the slopes up to 1,800 or 2,000
feet, the blocks being composed of a dark semi-vitreous basic
andesite referred to the hypersthene-augite sub-class with specific
gravity 275. It contains much glass in the groundmass, and since
the pyroxene of the groundmass is prismatic, this rock belongs to
the prismatic sub-order described on page 289. Ordinary basic
tuffs are also well represented on the north flank. On the south or
precipitous side they are usually more or less altered. Here, for
instance, they may take the form of a hard breccia-tuff containing

XIII THE MARIKO RANGE 187

vesicular lapilli, up to half-an-inch in size, of a semi-vitreous basic
rock, the small steam-holes being either empty or filled with opal
or chalcedony. The matrix of the rock is made up of finer
fragments of a banic vacuolar glass, showing a few felspar micro-
liths, but often more or less palagonitised. Evidence of further
alteration is afforded by the small cracks and crevices filled with
chalcedony.

Other altered tuff-rocks are exposed on the south slope. At an
elevation of 400-450 feet above the sea, and underlying the
agglomerates and breccia-tuffs, I found exposed in a stream-course
a hard dark rock looking like a compact andesite. Under the
microscope, however, it is shown to be an altered palagonite-tufiT
composed in part of angular fragments of plagioclase and of
rhombic and monoclinic pyroxene, not exceeding '15 mm. in size,
and containing also similar-sized fragments of a basic hemicrystal-
line rock. The base is made up of palagonitic material and
contains a few " Globigerina " tests sometimes displaying calcite
in their interior. Fine cracks filled with chalcedonic silica testify to
a subsequent alteration of the deposit. At 1,500 feet occurs a hard
red altered palagonite-tuff, having a similar composition and being
altered in like fashion, but not displaying tests of foraminifera in the
slide.

The foregoing remarks refer to the main undivided mass of the
range, that is, up to 2,000 feet. The highest peak of Mariko
probably represents in structure the other peaks rising to various
heights on either side of it. Here, at elevations between 2,000 feet
and the summit, a rubbly agglomerate prevails of a somewhat
different character from that occurring at lower levels. It is well
exposed in some cave-clififs at a height of 2,500 feet and also in the
rocky face of the peak. The rock composing the blocks is a
dark -grey aphanitic augite-andesite (sp. gr. 2'65), referred to genus
20 of that sub-class and displaying prismatic pyroxene in the ground-
mass. Smoky residual glass exists usually in fair amount ; whilst
in the blocks of the cave-cliffs it is so abundant that the rock may
be termed semi-vitreous. In the locality just named the blocks are
scoriaceous, the steam-pores, which are drawn out to a length of
5 or 6 mm. and more, being partially or completely filled with
calcite and occasionally with opal. At times the steam cavities are
much larger. In one of my specimens there is an elongated cavity
5 cm. (2 inches) in length, which has a thin lining of chalcedony,
from the surface of which pyramidal crystals of calcite project into
the interior. (I found the same grey andesite exposed in situ lower

i88 A NATURALIST IN THE PACIFIC chap

•down the south slope at an elevation of 1,800 feet, but non-scoria-
ceous.) The matrix of the agglomerate principally consists of fine
palagonitic material with small fragments of plagioclase and
pyroxene but apparently no lime.

At heights of about 2,800 feet on the south side of the peak, and
of 1,600 feet on the north flank of the range, are exposed non-
calcareous greyish tuffs remarkable for the quantity of crystals of
rhombic pyroxene, entire and in fragments, that they contain.
This is a characteristic feature of the more acid andesitic tuffs of the
island, and it is to these deposits that the Mariko tuffs in question
make a near approach. They contain at times subangular
fragments of more basic rocks ; and are true tuffs in the sense that
although perhaps deposited on a sea-bottom they represent the
ejected materials of a subaerial vent.

The crest of the range, where it is crossed by the road from
Vunimbua to Nukumbolo and for 200 feet below, is formed of a
decomposed rock, perhaps a breccia. A fragment of the rock ob-
tained from the crest is a grey somewhat altered hypersthene-augite
andesite(sp. gr. 275) with an orthophyric groundmass, and referred to
the order described on page 290. This rock may be connected with
the tuffs above alluded to ... . Reference may here be made to a
black basaltic rock (sp. gr. 2*88) of which, at an elevation of 2,500 feet
at the foot of the peak, I found a portion of a columnar block about
18 inches across. It may prove to be an olivine-basalt ; but no
section has been made of it.

It is apparent from the foregoing description of the Mariko Range
that in general structure it does not differ materially from the other
mountain-ridges of the island, although in the types of the rocks it
presents some variety. Here also we have agglomerates prevailing
on the flanks and forming the summit. As far as the characters of
the rocks can guide us, we cannot determine whether the range has
been built up by a number of vents on a great fissure, or whether
it represents the remains of a huge crater. In this uncertainty we can
only appeal to the contrast between the gentle gradient of the north
slopes and the precipitous descent of the south slopes as favouring the
last supposition. We cannot, however, doubt that the agglomerates
of the upper portion of the range are the products of an eruptive vent
or of vents that rose above the surface of the sea, since the blocks
are all of one kind of andesite and are often scoriaceous. We can
be fairly certain that at such a time the lower slopes were in part
submerged, seeing that foraminiferous tuffs underlying the agglo-
merates are now exposed. But we have to distinguish between these

XIII SAVU-SAVU PENINSULA 189

submarine basic tuffs of the lower slopes which may in part be the
result of marine-erosion and the grey rhombic-pyroxene-tuffs of the-
upper levels which are probably derived from subaerial eruptions.

The Savu-savu Peninsula

I include in this district the promontory west of Naindi Bay
and Sava-reka-reka Bay. Although its surface is much cut up, it
has, when viewed from a distance, a fairly even profile and attains
a maximum height of rather over 800 feet. From the region east
of it, it is separated by the Naindi Gap. Here one can cross the
peninsula between the two bays above named without rising more
than 50 feet above the sea. The elevated interior is divided into
two parts, which are divided by a col, about 250 feet in elevation,
which is ascended in crossing from Naithekoro on the south coast
to Na Kama on the north coast. Much of the surface is clothed
with the usual " talasinga " vegetation. Close to the north shore,
with which it is connected by the reef-flat, rises the small island of
Na-Wi, and off the extremity of the peninsula, which is known as
Harman's Point, is the islet of Naviavia, formed of raised reef-
limestone as described on p. 8. The celebrated boiling springs
known as Na Kama are situated on the north coast opposite
Na-Wi. It may be remarked in passing that besides finding an
exit in the springs, the hot water oozes through the beach and
below the tide-marks for several hundred yards along the shore^
These springs are described in detail on p. 25.

This is one of the few districts of the island in which elevated
reef-masses occur at the sea-border. These old reefs, which attain
a maximum elevation of 250 feet above the sea, are principall)r
restricted to the neighbourhood of Naindi Bay. (They are referred
to in detail in Chapter II.) But they indicate only a part of the
submergence which this region has experienced. There is an
exposure of a very interesting rock in a stream-course that is
crossed on the road from Yaroi to Naindi, less than a mile from
the first-named place, and about 30 feet above the sea. Here we
find a dark, impure " Globigerina " limestone, or, as it might be-
also designated, an altered calcareous palagonitic clay-tuff.i The
larger fragments in it average only "2 mm,, and it affords evidence
of a period of submergence during which the hill-tops of the
Savu-savu Peninsula were below the sea-level.

We get the same indication, but in a more pronounced degree^
* It is described under Sample C on p. 325.

^9o A NATURALIST IN THE PACIFIC chap.

in the stratified sedimentary clay-tuffs which are exposed on the
shore-flat of the south side of the neighbouring Sava-reka-reka
Bay. These beds, which within a distance of fifty paces are
inclined lo — 15° to the south-west and the same amount to the
north-west, have apparently a quiquiversal dip. In places they
•exhibit a spheroidal and concentric structure, and are penetrated
by cracks containing some calcite, but mostly filled with a white
zeolitic mineral.^ One of these rocks is a bright green, hard and
<:ompact deposit, containing but little lime, and evidently an altered
palagonitic clay-tuff. It contains a few minute tests of the
" Globigerina " type ; and on account of the small size of its
fragments of minerals, which range from •01 to '04 mm., it may be
regarded as a relatively deep-water sediment.^ It is interstratified
with a coarser, somewhat altered palagonite-tuff, which shows but
little lime and only a suspicion of tests of foraminifera. The size
of the larger included fragments does not exceed half a millimetre.
...... The low hill, near Yaroi, on which the magistrate's house

is built, is composed of fine and coarse tuffs, probably submarine.
It is doubtful whether any but sedimentary tuffs occur in this
peninsula.

In the hills of the western part of the peninsula, that is, west
of Na Kama and Naithekoro, a particular type of basaltic andesite
prevails, characterised by rhombic pyroxene as well as augite
phenocrysts, and referred for the most part to genus 13 of the
hypersthene-augite andesites. Their specific gravity ranges from
276 to 2*83, and the interstitial glass may be fair or scanty in
amount. The average length of the felspar-lathes is unusually
small, "04 — '06 mm. In these respects the basaltic andesites of
the Savu-savu Peninsula differ from the basaltic andesites found in
most other parts of the island, where, as exemplified by those of
the Wainunu, Solevu, and Seatura regions, the felspar-lathes
average between -i and '2 mm. in length, and there is practically
no rhombic pyroxene. A somewhat scoriaceous semi-vitreous
form of pyroxene andesite is exposed on the south slopes above
Nukumbalavu, where it is covered by basic agglomerates. The
pyroxene in the groundmass is here prismatic, and not granular,
and for the most part rhombic ; and the rock is referred to the
prismatic sub-order of the hypersthene-augite andesites described
on p. 287.

^ It is granular, but fuses in the blowpipe flame into a clear glass and
gelatinises in HCl. Probably a form of natrolite.
2 It is described under Sample D on p. 326.

XIII SAVU-SAVU PENINSULA 191

The basaltic andesites of the peninsula are often extensively
■decomposed through the weathering process, a spheroidal structure
being then displayed. It rarely happens that the basaltic rocks of
this locality assume a propylitic character. Yet, if this change is
due to hydrothermal metamorphism, we ought to find altered rocks
■of this kind in the vicinity of the boiling-springs. Such rocks did
not come under my notice at the surface ; but this only indicates
that if this alteration has taken place here, it has been effected at
•some depth ; and, indeed, it would seem probable that the alter-
ation known as " propylitic " is a change produced generally in
deep-seated rocks.

A semi-ophitic basaltic andesite that is exposed in the small
stream-course at the back of the springs, and not 100 yards distant,
displays no propylitic change, and is only affected by hydration.
The basaltic andesites found on the hill-slopes further inland from
the springs exhibit no change of such a nature. However, rocks
of this description occur at and near the coast about a mile
to the westward. One of them, which is light green in colour,
inight be taken for a limestone, since it effervesces with an acid.
When examined in the slide it is shown to be the prevailing basaltic
andesite greatly altered. The porphyritic rhombic pyroxene is
replaced by viriditic material ; the plagioclase phenocrysts are
replaced by calcite, secondary silica, and other alteration products ;
and the structure of the groundmass is disguised by chalcedony,
calcite, viridite, &c. Another rock from this locality displays great
alteration. The structure of the groundmass is obscured by
secondary silica, and is traversed by fine cracks passing through
the felspar phenocrysts and filled with blood-red films of hematite.

On the hill-slopes behind Harman's Point, at an elevation of
300 to 400 feet, blocks of a reddish, volcanic rock, greatly altered
by the deposition of silica, were displayed on the surface. The
ground was here strewn in places with beautiful pyramidal prisms
of clear quartz, ranging up to an inch in length. They contain
numerous inclusions, their faces being sometimes deeply etched or
eroded. These crystals appear to have been formed rather rapidly
in some highly siliceous thermal underground waters.

I did not ascend the hills of the portion of the peninsula
lying east of Na Kama and Naithekoro. But whilst crossing the
saddle between these two places, I perceived that the prevailing
basaltic andesites extended up the slopes to the east. The
neighbourhood of Naindi Bay offers several features of interest.
The bay, which is circular in shape, is closed in on the east and

192 A NATURALIST IN THE PACIFIC chap,

west by projecting points, where we find elevated reef-limestone^
40 or 50 feet above the sea, displaying massive corals and large
" Tridacna " shells in their natural position, and overlaying a
cement-stone composed of blocks of volcanic rocks in a calcareous
matrix. On the beach on the west side of the bay there is
exposed a reddish-grey altered pyroxene-andesite, which, as
regards the size of the felspars of the groundmass and other
characters, appears to be an altered form of the prevailing
basaltic andesites of the peninsula. In the midst of the low
passage that isolates the peninsula, which I have termed the
Naindi Gap, there is displayed a highly altered basic andesite
which contains a white, zeolitic mineral in its numerous cracks.

The small island of Na-Wi consists of two low hills, the highest
130 feet in height, connected by a mangrove swamp and a sandy
beach. There is no trace of a crateral cavity. The prevailing
rock is a porphyritic, compact, basic andesite, differing from the
other rocks of the neighbourhood in the greater amount of glass
it contains. Though it is not easy to find a good, unweathered
specimen of the rock, it would appear that Na-Wi represents an
old volcanic neck.

We may infer from the above description of this peninsula that
it has a history similar to that of most other parts of the island.
There is evidence in the upraised reefs and in the " Globigerina "
clays and limestones of considerable submergence at one period ;
and it is highly probable that the prevailing basaltic andesites are
the products of submarine eruptions. In my account of the hot
springs given on page 26, reference is made to the absence of any
trace of a crateral cavity in that locality. The same is true, as far
as my observation goes, of the whole peninsula. Altered rocks do
not occur in the vicinity of the springs, but they are to be found
at distances a mile and more away. It does not seem possible to
restore in imagination the original form of this part of the island.
The present contours are the results of more than one reshaping
of the surface through the agencies of marine erosion and sub-
aerial denudation.

The District Between Naindi Bay and the Salt Lake

Three or four of the peaks of this hilly district rise to about
1,000 feet or rather over, the highest being that of Na Suva-suva,
which attains a height of 1,110 feet. Since my acquaintance with
this region is incomplete, I will confine my remarks to the localities
actually examined.

XIII NA SUVA-SUVA 193

Through the kindness of Mr. F. Spence, I was able to make
use of a track cleared to the top of Na Suva-suva. This eminence,
which forms a conspicuous landmark for many miles, both land-
ward and seaward, has a rounded summit and is to all appearance
an old volcanic neck. It is composed in mass in its upper half of
a heavy dark olivine-basalt (sp. gr. 3"Oi), seemingly non-columnar,
and referred to the highly basic rocks forming genus 16 of the
olivine-basalts. There is such a thick soil-cap on the lower slopes
that I was unable to ascertain the character of the rocks there.
It is, however, noteworthy that a very similar olivine-basalt (sp. gr.
2*99) crops out on the coast south of this hill and to the east of
Naindi Bay. They both contain abundant small olivine-pheno-
crysts and a little residual glass, the felspar-lathes averaging
'I — "14 mm. in length. Since their localities are rather more than
a mile apart, it is not possible to say without a further examination
of the locality whether or not we have here the same intrusion.

On the coast between Naindi Bay and Salt Lake Passage,
calcareous tuffs, probably fossiliferous, are occasionally exposed in
the low spurs descending to the sea, whilst islets of elevated reef-
rock front the beach.

The coast immediately west of the Salt Lake Passage is of
exceptional interest. Here the sea-cliffs and the shore-flat are
formed of an agglomerate tuff penetrated in all directions by veins
of calcite, an inch and under in thickness. The matrix of this
deposit, which is a little calcareous, is principally made up of frag-
nents, ranging up to 3 or 4 millimetres in size, of vacuolar pala-
jonite, the minute vesicles being filled with some alteration pro-
'luct. It also contains large macled augite crystals 5 or 6 mm. in
;iize, which can be picked out in numbers by the fingers. The
blocks vary from a few inches to two feet across, and are usually

< omposed of an augite-andesite, containing large porphyritic

< rystals of augite, and are often amygdaloidal, the amygdules, 3 or
i. mm. in size, being formed of a zeolite. But blocks of very
different rocks also occur in this agglomerate tuff. One, about
Iwo feet across, was composed of a coarsely crystalline diorite
1 lade up, as described on page 25 1, of large crystals of hornblende,
: to 2*5 centimetres long, and of large opaque crystals of acid
1 ibradorite. Another was made of hornblende-hypersthene ande-
£ te belonging to the ortho-phyric order of that sub-class (see
( age 299). There is a little altered glass in the groundmass, and
1; rge secretions of brown hornblende, more than an inch in size,
a 'e to be observed in the rock.

O

194 A NATURALIST IN THE PACIFIC chap.

It is probable that this singular deposit represents a submarine
accumulation of materials ejected from some neighbouring vent.
Organic remains did not come under my notice ; but apart from
the palagonitic character of the matrix and the abundance of veins
of calcite, the submarine origin is indicated by the existence of
upraised reefs in the coast districts east and west of this locality.
The block of diorite affords an important clue as to the character
of the deep-seated plutonic rocks in this part of the island. A
similar diorite was found by me amongst the blocks in the bed of
the Vunimbua River ; and on page 185, reference is made to the
probability of such rocks forming the nucleus of the Valanga
Range.

The hills on the west side of the Salt Lake are worth further
examination. On the coast of the Natewa Bay side of this
district, in the vicinity of Vuni-tangaloa and between that place
and Vuni-sawana, there are displayed agglomerates formed of
blocks of hornblende-andesite, some of the specimens being very
similar to that obtained from the block of hornblende-andesite
noticed in the agglomerate-tuff on the neighbouring south coast.

The Salt Lake

The low isthmus, about 2^ miles in breadth, which connects the
Natewa Peninsula with the rest of the island, can be crossed without
rising more than 40 or 50 feet above the sea. From the occur-
rence of upraised reefs in the islets and in the low sea-cliffs of the
south coast it may be inferred that at no distant period in the history
of Vanua Levu this isthmus was submerged.

The lake, which is oblong in form, is about four-fifths of a
mile long and about two-fifths broad. Its maximum depth
according to the Admiralty chart is 3 fathoms ; but the usual
depth in the centre varies, as I found, between 2 and 2i fathoms.
It communicates with the sea on the south coast by a long narrow
passage, rather over a mile in length, which for the greater part of
its course, excepting near its seaward mouth, is only between 25
and 30 feet broad. Mangroves flourish around the lake and also
line the passage ; whilst elevated reef-rock is to be observed on
the sides of the passage. Mr. Home was informed that corals
abound in the lake-waters ; but I find no reference to this point in
my notes. Judging from the density of the effluent water, the
specific gravity of the lake-water is that of the sea. The " rise
and fall," as noticed below, is considerably less than in the case of
the tides at the coast.

XIII THE SALT LAKE 195

Near the centre of the lake there is a low islet, some 40 paces
across, and only raised about a foot above the level of the lake at
the time of high-water. It is chiefly made up of coral blocks ; but
there are a few fragments of basaltic andesite lying about, which
were probably brought there by natives. This islet is mentioned
in Mrs. Smythe's account ^ of the visit made by Colonel Smythe to
the lake in i860 ; and by reason of its little elevation it may be
accepted as a rude datum-mark of the relative level of land and
sea in this region. From this it would appear that there has been
no appreciable change of level in this region for the last forty
years.

Except on the north and north-west sides, the lake is more or
less surrounded by hills reaching up to 400 or 500 feet, the passage
representing a break in the range. On the Natewa Bay side the
level of the surface is much lower. The low strip of land that
intervenes between the north-west corner of the lake and Natewa
Bay is about a mile across, and does not attain a greater elevation
than 40 or 50 feet above the sea. On its surface, fragments of
basic volcanic rocks are displayed ; but no reef debris came under
my notice. At its north-east side the lake is only separated from
"Natewa Bay by a neck of land 300 to 400 yards in breadth and
-ibout 100 feet high. It was across this neck that the natives in
( )ld times used to drag their large canoes.

Mr. Home 2 who visited this neighbourhood in 1878, suggested
1 hat the Salt Lake occupies a crater-cavity. The hills around are
( .f volcanic formation, and I am rather inclined to support this
> iew ; but certainty is scarcely possible now, on account of the
ireat degradation which the surface has evidently, experienced
curing and since the emergence; whilst subsequent reef-growth

I as also to some extent masked the original form of the district.

I I is noteworthy that a somewhat parallel condition of things is
p resented a few miles to the west by the circular Naindi Bay and
tie low passage, not more than 50 feet above the sea, that partly
i; olate the Savu-savu Peninsula.

The peculiar behaviour of the tides in connection with the
S lit Lake and its passage attracted my attention during two visits
t( this locality. On the first occasion I noticed that between two
a id three hours after the tide at the coast had commenced to rise
tl ere was still a strong flow through the passage from the lake,
ai d that the current was only reversed in the latter half of the

1 Ten Months in Fiji, London, 1864.

2 ^ Year in Fiji, pp. 154, 169 ; London, 1881.

O 2

196 A NATURALIST IN THE PACIFIC ch. xiii

rising tide. During my second visit at the end of May, 1899,
when I was accompanied by Mr. Smallwood, I spent a night in
observing the behaviour of the spring tides at a spot below the
narrow portion of the passage 600 or 700 yards from the opening
on the coast. Here the breadth was about 100 feet, the depth at
low-water 5 feet, and the rise of the tide 4 feet. The current ran
seaward at a velocity varying from 1,500 to 2,500 yards per hour ;
and it continued to flow in this direction for 2^ hours after the tide
had begun to rise on the coast. (In the narrow part of the
passage the rate of the current would probably be not over 3
knots.) It is curious that at the place of measurement the bottom
was formed of mud into which the pole sank six feet without
striking a hard substratum. The observations on the current were
made with a vertical float immersed about 3 feet.

The point of difficulty in the behaviour of the tides is
this. The water is running rapidly out of the lake for nine hours ;
whilst during the remaining three hours there is a sluggish return-
flow up the passage into the lake. A far greater quantity of water
finds an exit by the passage than is returned by the same channel ;
and I can only explain this by assuming that there is an extensive
percolation of water from Natewa Bay into the lake. It is easy to
show that with such a narrow effluent, which cannot have a sec-
tional area exceeding 180 square feet, the level of the lake would
be only lowered 2 or 3 feet, if the average velocity during the nine
hours was two nautical miles. The great bulk of the water would
thus remain unchanged. The ultimate result of such conditions
would be a lake of brine. Since, however, the sea-water of the
lake possesses the ordinary density, it is apparent for this reason
only that there is some other means of supply than by the present
narrow passage leading to the sea. The mean level of the Salt
Lake is evidently rather above that of the sea, perhaps a foot
or two ; and the " rise-and-fall " is probably very small.

CHAPTER XIV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The Natewa Peninsula

This remarkable peninsula is connected with' the rest of the
island by the low-lying Salt Lake district, a narrow isthmus, de-
scribed in the preceding chapter, which one can cross without
rising 50 feet above the sea. My acquaintance with this region
is far from complete ; but from the following notes a fair general
idea of its geological characters may be gathered.

By referring to the map it will be seen that there are three

groups of mountains. The north-eastern culminates in Mount

Freeland or Ngala, 2,740 feet ; the southern is formed by the

rugged Waikawa Range, 1,540 feet ; whilst the Lea Range to the

west attains in Ngalau-levu a height of 1,960 feet. They are much

cut up by the denuding agencies, and all bear the stamp of an

ancient land-surface. Though hot springs are not infrequent, as

at Ndreke-ni-wai, Waikatakata, Ndevo, and Navuni, no evidence

Df recent volcanic action came under my notice. Submarine

deposits occur at intervals on the surface up to elevations of

[,000 feet and over ; but with the exception of the comparatively

•ecent upheaval or emergence of some 20 or 30 feet, indicated by

he raised reef-masses and foraminiferous tuffs and clays in dif-

erent parts of the coast, there is nothing to suggest that these

':hanges did not occur ages since. In the frequent alteration of

;ts andesitic rocks, and in the occasional occurrence of porphyrites,

' /e have sufficient indication of the antiquity of this part of the

island as far as its volcanic history is concerned.

I will commence the description of this peninsula at its
^ '^estern end.

198 A NATURALIST IN THE PACIFIC chap.

The broken elevated district that extends eastward from the
Salt Lake to Fawn Harbour on the south coast, and to the
mouth of the Ndreke-ni-wai River on the north coast, is divided
into two principal masses, which are connected by a ridge or col
about 400 feet above the sea, which is situated a little east of Viene.
The western portion, which may be named the Viene sub- district,
attains a maximum height of 1,000 feet. The eastern portion
reaches in the peak of Ngalau-levu, a height of 1,960 feet, and may
be termed the Lea sub-district.

The Viene Sub-District.— The cliffs on the north coast
between Muanaira and a little east of Viene are mainly formed of
basic tuffs, often calcareous. At a place about \\ miles east of
Viene, these tuffs as exposed in a coast spur display large flat
spiral tests of shallow-water foraminifera 4 or 5 millimetres across.
They may be described in this locality as palagonitic calcareous
tuff-sandstones, more or less compacted, and containing fragments
of palagonitised basic rocks. When crossing the col above referred
to one finds similar palagonitic calcareous sandstones and clays
exposed on its slopes up to its summit (400 feet).

On the south side, in the vicinity of Vunilangi Inlet, foramini-
ferous clays and reef-limestones are displayed at the foot of the
slopes ; and the coast between this place and Tathelevu to the
westward is bordered by low cliffs of reef-limestone raised 6 to
8 feet above the high-water mark and displaying massive corals
in their position of growth. Near Tathelevu there occur raised
reefs 10 to 15 feet above the sea ; whilst the hills, 250 to 300 feet
in height, at the back of this place are composed of fine and coarse
tuffs and tuff-sandstones containing little or no lime, and apparently
no organic remains. They are sedimentary tuffs of mixed com-
position, made up of fragments of plagioclase, rhombic and mono-
clinic pyroxene, brown hornblende, portions of semi-vitreous basic
andesite, and palagonitic debris. In the lower levels they are fine
textured with a grain of '2 to *3 mm. In the higher part their grain
is '5 to I mm., and they are more basic in character and come near
to the palagonite-tuffs. At an elevation of 200 feet they form
inland cliffs, 50 feet high, in which are imbedded blocks, 2 feet
across, of a blackish pyroxene-andesite with a specific gravity of
273, and belonging to the prismatic sub-order of the orthophyric
order of the hypersthene-augite andesites. It is remarkable for the
pyroxene prisms of the groundmass, and shows a little interstitial
glass. These cliffs are well displayed behind Navelatha, about
half a mile from Tathelevu. Between this locality and the Salt Lake

XIV LEA BAY 199

Passage, elevated reef-limestones, forming low cliffs 6 to 8 feet
high, together with occasional tuff-agglomerates, occur at the coast.

The Lea Sub-District. — This region, which includes the
mountain-range of Ngalau-levu at the back of Lea, is limited
by Fawn Harbour and Vunilangi Inlet on the south coast, and by
the Ndreke-ni-Wai River and a point between Viene and Lea on
the north coast. Its structure, as is shown below, is very compli-
cated, acid and basic rocks being associated in a remarkable
manner ; whilst over all lie the submarine tuffs. Marine and sub-
aerial denuding agencies have shaped and re-shaped the surface
to such a degree that it is now impossible to restore it in
imagination.

On the north coast of this sub-district, about two miles east of
Viene, is exposed an altered darkish porphyrite displaying large
opaque crystals of plagioclase, 5 to 7 mm. long, the rock-mass
being penetrated by fine veins of chalcedonic quartz, which also
traverse the phenocrysts. Its specific gravity is 2*6 ; but on account
of the imperfect development of the felspar-lathes and the amount
of altered glass in the groundmass, which also contains a little
calcite, it can be only generally referred to the augite-andesites.
A greenish altered foraminiferous tuff showing fine cracks filled
with chalcedony composes a spur in this locality. A propylitic
or highly altered dolerite is exposed half-way between Viene
and Lea.

As one nears Lea from the west the lofty spurs of the mountain
of Ngalau-levu reach the coast, and basic tuffs and agglomerates
prevail. The blocks in the agglomerate are composed of a vesi-
cular semi-vitreous hypersthene-augite andesite, which is assigned
to the second prismatic sub-order, since it carries prismatic
pyroxene in the groundmass. The town of Lea is picturesquely
situated on the coast at the foot of the steep mountain-slopes, being
closed in on the east and west by elevated spurs descending to the
sea. Fragments of jasper and chalcedony occur in the beds of the
streams that here drain the precipitous sides of the range. Two
dykes of dark basic rocks protrude through the beach in Lea Bay.
They are composed of augite-andesites referred to genus 1 3 of the
augite-class ; but the two rocks belong to different species of that
genus. In the one the felspar-lathes are only "04 mm. in length,
and there is a little altered glass in the groundmass, the specific
gravity being 2-63. In the other the felspar-lathes average '2 mm.
in length, and the rock has a coarser texture, whilst the specific
gravity is 27. The augite granules are large (-03 mm.), and there

200 A NATURALIST IN THE PACIFIC chap.

are irregular lacunar spaces filled with calcite and lined by a
brown palagonite-like material.

I ascended the second highest peak of the Ngalau-levu moun-
tain, which rises to a height of i,68o feet behind the town of Lea,
the highest summit lying to the eastward. Ngalau-lailai, which I
also ascended, is a lesser peak, 1,400 feet in height, situated yet
nearer to the town. Basic tuffs and agglomerates similar to these
exposed in the western spur of the bay occurred all the way up to
the bare rocky pinnacles forming the summits. The blocks in the
agglomerates are made up of a semi-vitreous augite-andesite, whch
is sometimes scoriaceous or amygdaloidal, and at other times
pseudo-vesicular. Augite crystals, 5 or 6 millimetres in length,
are inclosed in the tuffs which contain palagonitised materials, but
apparently no organic remains.

In the spur on the east side of Lea Bay occurs a Hght-colour2d
altered hornblende andesite. The brown hornblende is mostly repre-
sented by black pseudomorphs. Such a rock appears in strange con-
trast with its basic surroundings. This is followed, as one proceeds
eastward along the coast, by basic tuffs and agglomerates. It
should have been before observed that blocks of a blackish-brown
olivine basalt (sp. gr. 2"89), referred to genus 1 3 of the olivine class,
occur at intervals on the coast between Viene and Ndreke ; but the
rock never presented itself in position. The tiny felspar-lathes
(•03 mm. long) are in flow arrangement ; but there is little or no
residual glass, and the augite granules ('Oi mm.) occur in great
abundance.

About two-thirds of the way between Lea and Ndreke-ni-wai
there lie close to the shore two islets, 20 to 25 feet high, of reef-
limestone, in which massive corals may be observed in their
position of growth. Further east, about half a mile west of Ndreke-
ni-wai, there is exposed at the coast a bedded light-coloured non-
calcareous compacted tuff-rock, dipping 12° to 15° to the southward.
It contains pebbles and blocks of acid and basic andesitic rocks,
and may be described as an altered hornblende-andesite tuff.
Basic agglomerates occur as one approaches Ndreke-ni-wai. This
town lies at the mouth of the river of that name, the first river that
one meets on the north side of this peninsula. There exist here
between the tide-marks some hot springs, to which reference is
made on page 34.

When crossing the Natewa peninsula from Ndreke-ni-wai to
the head of Fawn Harbour, one reaches a height of 660 feet
above the sea. This ridge represents the " divide " between the

XIV THE WAIKAWA MOUNTAINS 201

Lea and Waikawa mountain-ranges. In the lower part of the
northern slopes of this ridge occur basic tuffs and agglomerates ;
but between 200 and 400 feet a light-coloured acid rock of the
hornblende-andesite type prevails, both in the form of agglomerate
and of loose blocks. This rock is described under the second
order of the hornblende-hypersthene andesites on page 299.

Descending the south slope, I found at an elevation of 500
feet a single large mass, about 4 feet across, of quite another type
of volcanic rock, which is referred to the orthophyric order of the
hypersthene-augite andesites (page 290). It is a dark grey almost
holo-crystalline rock (sp. gr. 2*69) showing porphyritic pyroxene to
the eye and displaying in its relatively scanty ground mass short
stout felspars, '05 mm. in length. On the surface of the lower
two-thirds of this southern slope occur basic tuffs and agglo-
merates, basaltic blocks being found in the streams. The tuffs
are palagonitic and contain a few calcareous particles. They
apparently contain some foraminiferous shells and are doubtless of
submarine origin.

It would seem that the axis or deeper portion of this ridge is
composed of the hornblende and hypersthene-augite andesites,
whilst the basic tuffs and agglomerates form the slopes.

With reference to the south side of the Lea sub-district, it
may be observed that whilst on the north side the mountains rise
up close to the sea-border, here they are separated from the coast
by a broad tract of lowland, where bedded pteropod and foramini-
ferous clay-rocks are exposed, dipping gently to the south-east.
Usually between Fawn Harbour and Vunilangi Inlet the coast
is margined by low cliffs of coral-limestone, showing the massive
corals in position ; but sometimes the deposits above noticed
compose the low cliffs and even the islets close by.

The Waikawa Mountains. — This range occupies nearly the
whole area of the broad and elevated promontory that is only
separated from Taviuni by the narrow straits of Somo-somo,
which, however, have a minimum depth of 120 fathoms. These
mountains extend to the vicinity of Mbutha Bay on one side and
to near Fawn Harbour on the other. Several of the peaks reach
to over 1,000 feet, the greatest height given in the Admiralty
chart being 1,540 feet. The whole region has a very rugged
aspect, the mountains rising up near the coast, whilst the surface is
much cut up into ridges and valleys.

A single traverse across the range was alone made, but the
results obtained are very suggestive and may doubtless be applied

202 A NATURALIST IN THE PACIFIC chap.

to much of this rugged promontory. I crossed the mountains
from Loa to Waikawa. The summit was about a mile broad and
undulating, the level varying between 900 and 1,150 feet. At one
place on the top there was a deep hollow, some 300 or 400 yards
across, perhaps the remains of an old crater-cavity ; but the higher
slopes were so densely wooded that it was not possible to get a
clear view of my surroundings. Basic tuffs and agglomerates
prevailed on either side from the foot to the top of the range.
Specimens obtained from between 800 and 900 feet above the sea
are characteristic palagonitic tuffs of varying degrees of coarseness
containing 5 to 10 per cent, of carbonate of lime and a few tests
of foraminifera. At 1,100 feet I obtained a specimen which on
account of the large proportion of carbonate of lime (35 per cent.)
and the abundance of foraminiferal tests may be termed an impure
foraminiferal limestone belonging to the group of these rocks
described on page 319. The tests range up to a millimetre in
size, and there are also inclosed a few large fragments, i to 2
centimetres in size, of shells and crystalline limestone. The
residue is made of the detritus of semi-vitreous basic rocks, pala-
gonitic debris, fine clayey material and minerals (15 per cent), the
last including beside plagioclase abundant more or less perfect
pyroxene prisms, mostly of the rhombic type.

Near the summit there occurred in one place blocks of a highly
basic blackish olivine-basalt (sp. gr. 2*99), marking evidently the
situation of a dyke. This rock is referred to genus 13 of the
olivine-class. It displays abundant phenocrysts of olivine and
augite with but little plagioclase. Interstitial glass is scanty, the
groundmass consisting of stoutish felspar-lathes (•06 mm. long),
abundant augite granules and prisms, and magnetite.

The Waikawa mountains would thus seem to possess the same
general structure that characterises many of the ranges of the
island. Submarine basic tuffs and agglomerates cover their sides
and their summits, the deeper rocks forming the axis of the range
being in this case not so frequently exposed.

On the coast between Waikawa and Navuni, rather over a
mile east of Fawn Harbour, basic agglomerates, palagonitic tuff-
sandstones, and calcareous clay-rocks containing pteropod and
foraminiferous tests, prevail. The tuff-sandstones and clay-rocks
are bedded, the stratification being often well shown in the
horizontal sections displayed in the shore-flat. In one locality
within an area a few hundred yards across, a quaquaversal dip
was exhibited. At Navuni, where the hills reach the coast, the

XIV WAIKATAKATA

203.

same formations occur. I ascended the stream-course there for
about a mile, basic tuffs and agglomerates being exposed in its
sides, whilst blocks of a heavy dark olivine-basalt ^ lay in the bed.
The hot springs which issue inland at the side of this stream are
described on page 35.

The Basin of the Ndreke-ni-wai River. — With the
region, which is bounded on the north by the Mount Freeland
Range or the Ngala mountains and on the south by the Waikawa
Range, I have but slight acquaintance, except in the case of the
coast fronting Natewa Bay. A little way up the course of the
river Ndreke-ni-wai, which drains this area, lies the town of Koro-
ni-yasatha, where Mr. Home, the botanist, spent some days in
1878. Probably much of this area is not over 200 feet above the
sea, and apparently there is a good deal of talasinga country.

The Coast between the Mouth of the Ndreke-ni-
wai River and the Foot of the Ngala or Mount
Freeland Range. — Between this estuary and Valavala, two
miles to the eastward, occurs a bedded calcareous palagonitic tuff
of sedimentary origin, dipping steeply to the north. In one
locality there is a rudely columnar dyke of a porphyritic augite-
andesite. Coarse basic tuffs exposed in the cliffs and shore-flat
of Ko-nandi-nandi Point on the side of Valavala Bay display a
spheroidal structure, due probably to the vicinity of some igneous
intrusion. The sea-border extending from this bay to Natewa,
and farther on to Waikatakata, near the foot of the Ngala moun-
tains, is in most parts a broad low strip of coast- land, where rock-
exposures are infrequent. A dark grey andesite forms the blocks
of the agglomerate in this locality. It is noticeable on account of
the prismatic pyroxene of the groundmass ; and it is assigned to
genus 5 of the second (prismatic) sub-order of the hypersthene-
augite andesites. A blackish semi-vitreous pyroxene-andesite
occurs in the vicinity of Natewa.

At Waikatakata (the Fijian word for " hot water "), where an
outlying spur of the Mount Freeland or Ngala Range reaches the
coast, hot springs issue on the hill-side, as described on page 34,
On the slopes around the springs lie huge masses of an aphanitic

^ It displays an abundance of small phenocrysts of plagioclase, augite, and
olivine partly serpentinised, in a groundmass composed in the main of coarse
augite grains (-025 mm. in size) and of felspar microliths ("07 mm. in length)
in smaller proportion, with little if any residual glass. Specific gravity 2-98.
It is near the Waikawa basalt, referred to on p. 202, and is placed in the same
genus (13) of the olivine class.

204 A NATURALIST IN THE PACIFIC chap.

basaltic andesite having a specific gravity of 2*8 1 and referred to
genus 1 6 of the augite sub-class. It displays a characteristic
andesitic groundmass, showing crowded felspar-lathes in flow-
arrangement with average length of •!/ mm., and containing
scarcely any residual glass.

Proceeding along the coast east of Waikatakata, one enters
the region of altered pyroxene-andesites, for which Mount Free-
land, or the Ngala Range, is remarkable. There are first to be
observed on the shore blocks of a grey altered ophitic dolerite,
which belongs to the non-porphyritic division of genus lo of the
augite-andesites and is described in detail on page 275. After-
wards the characteristic rocks of the district occur. The lofty
spurs of the Ngala Range here reach the shore ; and between
them lies the coast village of Ngara-vutu, from which the ascent
to the summit is best made.

Mount Freeland or the Ngala Range

This high range forms a conspicuous object in the profile of
this part of the island. It derives its Fijian name from the old war-
town of Ngala that was situated at an elevation of 1,500 or 1,600 feet
overlooking Ngara-vutu on the west. The main mass of the range
takes a crescentic sweep, 3 or 4 miles in extent and facing Natewa
Bay. It incloses the coast district of Tunuloa. The steep
mountain-slopes here rise to 2,000 feet and over, the greatest
elevation being 2,740 feet. The densely wooded spurs of the range
occupy most of the area between the town of Natewa, Kumbulau
Point, and Mbutha Bay.

The summit is a long narrow ridge covered with a dense
entangled mass of Freycinetia stems which render progress very
difficult. The rocks exposed all the way up from the stream-
courses in the vicinity of Ngara-vutu to the top, are almost all of
the same type, namely altered augite-andesites. They are dark
grey in colour and effervesce slightly with an acid, whilst occasionally
they show a little pyrites.^ Agglomerates were not observed and
tuffs only in one locality, 1,200 feet above the sea, where a highly
altered tuff composed of debris of the prevailing rocks was exposed.
At an elevation of 500 feet there occurred a grey doleritic porphy-
ritic rock, displaying large opaque crystals of plagioclase, and
looking like a porphyrite. It exhibits a semi-ophitic groundmass,

^ They are described on p. 269 under the non-porphyritic sub-genus of genus
2 of the augite-andesites.

XIV MOUNT FREELAND 205

and is probably an intrusive mass. A description of it will be
found under genus 10 of the augite-andesites (page 274).

The general petrological characters of the principal summit of
Mount Ngala point to its high antiquity as a volcanic mountain.
It probably ranks among the oldest extinct volcanic vents in the
island.

Proceeding along the coast from Ngara-vutu to Navetau, the
Bull's town of the Tunuloa district, one observes blocks of basic
rocks. Farther to the eastward for a distance of two or three miles
basic agglomerates and basic tuff-agglomerates prevail along the
sea-border, being often extensively exposed in the cliff-faces of the
hills. The rock composing the blocks is a hemi-crystalline pyroxene-
andesite remarkable for the prismatic pyroxene in the ground-
mass, and referred to genus 17 of the hypersthene-augite sub-class.

I crossed the range to Ndevo on the other side of the peninsula
from a place three or four miles west of Kumbulau Point, rising on
the way to a height of 930 feet. For the lower 300 feet on the
north slope basic agglomerates and basic tuff-agglomerates are
exposed. They are made up of the same materials as those above
described on the coast. Near and at the summit occur compacted
brecciated tuffs made up of palagonitised basic materials but con-
taining no lime, and these are associated with light greenish
fine-textured hard tuffs of an acid character, but without lime or
organic remains. In this last case the deposit is formed of mineral
fragments (oligoclase, rhonibic and monoclinic pyroxene, &c.), the
debris of a hemi-crystalline volcanic rock, and a quantity of greenish
alteration products.

On the south side in the vicinity of Ndevo the sea-border is
composed of calcareous palagonitic clays and tuffs containing
pteropod shells and large tests of foraminifera in abundance.
These deposits, which are horizontally bedded, extend a mile inland
and reach to between 250 and 300 feet up the slopes. A hot spring
is stated to occur between the tide-marks near Ndevo.

At intervals all along the coast between Ndevo and Nuku-
ndamu, passing on the way the villages of Koro-i-vonu,Tuvumila and
Kanakana, fine and coarse basic tuffs, often calcareous, are to be seen
exposed in the sea-cliffs and in the low hills behind. They are
bedded and dip 5° to 10° W.S.W. near Ndevo and 15° to 20° S. b W.
south of Kanakana. The lower slopes of the Ngala mountains here
approach the coast, and it is highly probable that the submarine
tuffs which form the sea-border extend a considerable distance
inland and to some height above the sea. Between Nuku-ndamu

2o6 A NATURALIST IN THE PACIFIC ch. xiv

and Tukavesi, where the mountains rise close to the beach, occur
basic agglomerates and agglomerate-tuffs, derived from basaltic
andesites. A specimen of the last named represents an uncommon
type of basaltic rock (sp, gr. 2"85), which on account of the character
of the felspars and of the pyroxene of the groundmass is referred
to the prismatic sub-order of the orthophyric order of the
hypersthene-augite andesites (page 290).

It may be inferred from the foregoing remarks that whilst the
main elevated mass of the Ngala Range is composed of altered
basic andesites, the product of ancient eruptions, the basic agglomer-
ates, tuffs, and clays, which occur on the lower slopes and in the
outlying spurs, are of later date. These tuffs and clays are evidently
of submarine origin, at least in the lower levels ; but although
fossiliferous deposits were not observed at greater elevations than
300 feet above the sea, it is probable that future investigators will
find them at much higher levels. Their discovery, as before
noticed, at an elevation of 1,100 feet in the adjacent Waikawa
mountains, renders it likely that as in the case of the rnountainous
districts of the main portion of the island the whole of the Natewa
peninsula was at one time submerged, or at least all the region
excepting the summit of Mount Ngala.

CHAPTER XV

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued)

The North-east Portion of the Island

This large area, which extends for a distance of nearly forty
miles from the eastern slopes of the Mount Thurston Range to
Undu Point, forms the region closing in Natewa Bay on the north.
It would be difficult to imagine an area of this size with a greater
variety of surface or showing such a lack of arrangement of its
principal features. The hills and mountains on the north side
gather at the coast, and extensive inland plains, raised but a few
feet above the sea and strewn with silicified corals, occupy a portion
of its interior. A long valley with a very small gradient extends
nearly across its breadth ; and the rivers are for the most part
tidal estuaries fed, except in one or two cases, by insignificant
streams. There is, however, a lofty range of ridge-mountains in
its broadest part attaining a height of 2,500 feet ; whilst away to
the east stretches the great Undu Promontory singular for the
straightness of its form.

Volcanic rocks of acid types, such as oligoclase-trachytes,
quartz-porphyries, and white pumice-tuffs prevail in the northern
part between Undu Point and the promontory opposite Mali
Island. In the southern part, from the foot of Mount Thurston
and Vuinandi to the vicinity of Tawaki, massive rocks and tuffs and
agglomerates of basic characters predominate. Although my
acquaintance with this area is incomplete, the data below given will
be sufficient to enable a general idea to be formed of its structure.
The more conspicuous features in its geology will gradually come
into prominence as the various localities visited are described.

2o8 A NATURALIST IN THE PACIFIC chap.

The Southern Sea-border between Vuinandi and
THE Vicinity of Tawaki

The basic rocks, which characterise this long extent of coast,
give place about two miles west of Tawaki to the acid rocks. I
will proceed methodically with the description from Vuinandi
eastward.

(a) The coast between Vuinandi and Nakarambo, — Along this
coast, spurs from the Mount Thurston Range reach the borders of
Natewa Bay, forming a succession of small bays a mile or so across,
on the shores of which are situated the villages and towns of
Vuinandi, Ndaku-ndaku, Korotasere, and Nakarambo. The basaltic
rocks characteristic of the "vicinity of Vuinandi are predominant here ;
but agglomerates and tuffs are of rare occurrence, the prevailing
rocks exposed in the spurs being fine textured basaltic andesites
(sp. gr. 2'82). A calcareous tuff-clay is, however, to be observed in
the east point of Vuinandi Bay, where it is apparently penetrated
by a dyke of the above mentioned rock. In Ndaku-ndaku Bay
there issue from the shore-flat between the tide-marks some hot
springs which are referred to on page 34.

ib) The coast between Nakarambo aud Waimotu. — In this tract
we meet with rocks of a somewhat different character, though still
basic in their type. Through the agglomerates and agglomerate-
tuffs of the spurs protrude coarsely crystalline grey pyroxene-
andesites.^ They are to some degree altered, and are characterised
by their abundant phenocrysts of plagioclase and of rhombic and
monoclinic pyroxene, the groundmass being relatively scanty.
The agglomerates are formed of similar materials. There is an
interesting exposure in the point east of Nakarambo. My
specimens from this locality were unfortunately lost ; but in my
notes reference is made to the coarsely crystalline grey andesite
above noticed, to the later intrusion of a dark amygdaloidal rock,
and to an altered calcareous tuff.

{c) The coast between Waimotu and Natasa Bay. — A low belt
of land often forms the sea-border. Between these two localities
there is a broad estuary, the village of Vanuavou being situated on
the right side and Malati on the left side. Tuffs usually calcareous

^ These rocks are in most cases referred to the orthophyric and felsitic
orders of the hypersthene-augite andesites. The rocks of the last-named order
prevail, and form the type of the group, as described on p. 291.

XV NATASA BAY 209

and probably submarine are here displayed together with basaltic
andesites.

{d) The coast between Natasa Bay and the vicinity of Tawaki. —
This extensive stretch of sea-border, nearly 15 miles in length, is
characterised by hilly spurs and long intervening low-lying tracts.
The prevailing rocks exposed are tuff-clays, somewhat hard and
altered, and coarser basic tuffs sometimes calcareous and overlying
the former. These sedimentary deposits, which are evidently
submarine, are often bedded and have a fairly constant dip over
most of this region of 10 to 15 degrees to N.W. or W.N.W. They
are frequently pierced by dykes, 6 to 10 feet thick, of compact
basic rocks. A specimen of one of these dyke-rocks from between
Natasa and Vatu-karoa is a doleritic basalt with scanty olivine
(sp. gr. 2-8i) 1 ; but the rock of the dykes east of Vatu-karoa is less
basic (sp. gr. 272), and may be described as an augite-andesite ^
with a doleritic structure in part disguised by alteration. Between
Natasa and Sangani there is a remarkable exposure of an intrusive
opaque white rhyolitic rock associated with altered tuffs. This
rock, which has undergone some degree of alteration, is described
on page 311. It is the only indication of the vicinity of a region
of acid rocks that I came upon on this tract of coast. It probably,
if traced inland, would be found connected with the district of acid
rocks. In following along the coast, however, towards Undu Point,
the region of acid rocks is not reached until within 2 or 3 miles
west of Tawaki. Reference should be made here to two hot springs
that, as described on page 33, rise up on the coast at Natuvu, a
little east of Lakemba.

The Inland Mountainous Region between the Eastern
Foot of the Mount Thurston Range and the Vicinity

OF Tawaki

This inland region corresponds for the most part to the tract
of coast before described between Vuinandi and the vicinity of
Tawaki. We have here a very much broken area traversed in a
northerly and southerly direction by mountain-ridges and penetrated
in places on the north side by prolongations of the Wainikoro and
Kalikoso plains. The two loftiest summits, the Ndoendamu and

1 It belongs to genus 37 of the olivine class. The felspar-lathes average
0*2 mm. in length, and there is a little altered interstitial glass.

2 It is referred to genus 16, species D, of the augite-andesites. The felspar-
lathes have an average length of -3 mm.

2IO A NATURALIST IN THE PACIFIC chap

Savu-riti peaks of the chart, rise respectively to heights of 2,481
and 2,238 feet. The former is the Hale Peak of the Wilkes"
Expedition ; but as regards the native names there is some
confusion and I have not been able to clear it up. Several of the
lesser peaks rise to over a 1,000 feet, and four or five of them to
rather over 1,500 feet.

With the exception of the fixing of the positions of the more
conspicuous peaks, the interior of this part of the island is un-
surveyed. I was able to lay down my positions approximately ;
but before a systematic examination can be made of the geology
of this region a survey is necessary. Several traverses and ascents
were made by me ; but much more in the way of exploration
remains to be done. I venture, however, to think that from the
data below given a fairly accurate notion of some of the leading
geological features of this region may be formed. The districts
visited will be described in their order from east to west.

(a) The mountainous district east of the mountains of Vungalei
and Nailotha^ extending to the vicinity of Tawaki. — Mr. Thomson ^
in his map of the sea-border of this district shows a continuous
coast range from near Tawaki to Natasa lying about two miles
inland. This is the appearance when the region is seen in profile
from a distance ; but when viewed from an elevation in its interior
its surface is seen to be for the most part traversed by a series of
mountainous and hilly ridges trending roughly north and south,
the greatest height not exceeding 1,500 or 1,600 feet.

The geological character of the sea-border of this district has
already been described on page 208. It is there shown that fine
and coarse sedimentary tuffs, sometimes calcareous, and often
penetrated by basic dykes, here prevail. Their general story is
one of great denudation, and we have the same testimony
impressed on us when examining one of the inland mountain-
ridges.

I followed the crest of one of these ridges from the hamlet of
Nawi, on the headwaters of the Vui-na-savu River, in a south-
easterly direction for about 4 miles to the peak of Uthulanga,
which overlooks Lakemba on the shore of Natewa Bay. During
the walk my level rose fairly gradually from that of Nawi, less than
100 feet above the sea, until near Lakemba, where a height of
1,400 feet was attained. Here the ridge abruptly terminates in
the round-topped peak of Uthulanga, which rises steeply from

^ Proceedings, Queensland Branch, Geographical Society of Australia,
vol. i. ; 1886.

XV NAWI TO UTHULANGA 211

its crest for another 1 50 feet or rather more, and has a precipitous
face on the southern side descending far down the mountain-slope.
This peak, which is about 1,550 feet above the sea, when seen from
the opposite shores of Natewa Bay is very conspicuous and looks
like a thumb or a nose. The first part of the Fijian name of this
peak signifies a nose.

The hamlet of Nawi, from whence the ridge begins, is built on
a low mound-like "rise," which is composed of a dark-grey
hypersthene-gabbro. Since plutonic rocks are of very rare oc-
currence in this island, the Nawi gabbro has a particular interest.
It belongs to the group of plutonic rocks described on page 250 ;
and is to be referred to the more basic kinds, its specific
gravity being 2*84. In appearance it is like a diallage-gabbro, and
in the slide displays monoclinic and rhombic pyroxene filling the
interspaces between the large plagioclase crystals and undergoing
respectively the diallage and bronzite stages of schillerisation. This
rock forms the type of the group and need not be referred to in
more detail here. It should be added that in the bed of the
neighbouring river occur blocks of a basaltic andesite (sp. gr. 2*86)
referred to genus i of the hypersthene-augite andesites. It is a
less crystalline form of the gabbro just mentioned.

The prevailing rock exposed for the first 2 miles on the crest of
the ridge (by starting from Nawi) was a greenish porphyrite
displaying large opaque crystals of oligoclase, but showing much
alteration of the propylitic kind, its specific gravity being 2*5, but
the structure of the groundmass is much disguised. During the
next mile, basic agglomerates and a massive hypersthene-augite
andesite were exposed. The last-named is semi-vitreous, and on
account of the prismatic pyroxene of the groundmass is placed in
genus 5 of its sub-class. Its specific gravity is 27. In the last
and fourth mile of the ridge was exposed a dark grey doleritic
basalt (sp. gr. 2*85), which rings like clinkstone under the hammer,
and weathers in a honeycombed fashion. The felspar-lathes
average '3 mm. in length, the residual glass being scanty. The
oyroxene phenocrysts include some of rhombic pyroxene ; and the
*ock is therefore referred to genus 4 of the hypersthene-augite
mdesites. The actual peak of Uthulanga, as it rises abruptly
ibout 150 feet from the end of the ridge, is of agglomerate, the
)locks being composed of a compact grey andesite.

The peculiar succession of rocks displayed in this mountain-
idge along its length of four miles is worthy of notice. Neither
esicular nor scoriaceous rocks came under observation ; and it is

P' 2

212 A NATURALIST IN THE PACIFIC chap.

to be assumed that there existed originally a line of submarine
vents, some of them ejecting acid and others basic materials.
Mainly on account of the great marine erosion during the period
of emergence, but partly also on account of the subsequent sub-
aerial denudation, a plain ridge now represents this line of vents.
Probably the peak of Uthulanga, which is evidently an old
volcanic neck, represents the last of the stages in the volcanic
history of this ridge ; but a very long period must have since
elapsed. When, however, we look at the exposed gabbro at the
other end of the ridge, we have to carry the period much farther
back, since here the superjacent surface volcanic rocks have been
stripped off completely. On page 2 I have referred to an island
in the Solomon Group where we have such a chain of ancient
vents of acid and basic rocks. In that case the forms of the
separate hills indicating the original vents are still to be recog-
nised. In this old mountain-ridge of Vanua Levu no such outlines
remain except in the instance of the terminal peak.

(3) The Nailotha and Vungalei Range. — This lofty range,
which towers above all around it, attains a height of 2,481 feet
in the peak of Nailotha and of 2,238 feet in that of Ndrukau
or Vungalei. The first is, as I infer, the Ndoendamu or Hale
Peak of the charts ; but it is uncertain whether the name Savu-riti
should be applied to the northern peak of the range as it is in
the charts, or whether it belongs to an independent peak farther
to the east. By the natives in the vicinity the northern peak is
known as Ndrukau, and I have added the name of Vungalei
from the village at its foot. The southern peak is that of
Nailotha. The range runs roughly north and south. It is, how-
ever, obvious that the internal topography of this part of the island
is but scantily known.

Brief reference will first be made to the country bordering the
range on the north-west and west sides in the vicinity of the
villages of Vungalei and Tembe. In proceeding south from
Kalikoso, which lies in the midst of the low-lying Wainikoro
plains, to Vungale one traverses this level district, of which the
elevation is never more than 150 feet above the sea and often
much less. About a mile south-east of Kalikoso the limit of the
region of quartz-porphyries and of acid tuffs is passed and the
area of basic rocks is entered, a dark semi-vitreous pyroxene-
andesite with a flinty fracture prevailing at the surface as far
as Vungalei. This rock displays a few small phenocrysts of oligo-
clase and pyroxenes in a blurred glassy groundmass exhibiting

XV MOUNT VUNGALEI 213

the felspar and pyroxene microliths in process of development
(sp. gr. 2-46).

Vungalei itself is only elevated about 130 feet above the sea.
In proceeding from this village to Tembe, lying about two miles
S.S.W., one crosses a line of hills, about 600 feet in height, which
form a spur of the main range. Basic agglomerates similar to
those found on the slopes of Mount Vungalei, as described below,
prevail in the district between these two villages up to the top of
the intervening hills. In places one notices that they overlie the
ordinary sedimentary deposit, known as " soapstone," a slightly
calcareous clay-tuff but showing no organic remains to the eye.
The rock exposed in the stream-courses is a semi-ophitic basaltic
andesite (sp. gr. 274) which contains a considerable amount of
interstitial glass.^ When proceeding S.S.W. from Tembe on the
way to Nandongo one passes on either hand, as described on
page 216, hills about 700 feet high displaying vertical cliffs formed
of agglomerates over-lying finer sedimentary beds apparently of
the " soapstone " character.

I made the ascent of Mount Vungalei from the village of that
name. The peak is also known as Ndrukau. Basic agglomerates
were exposed all the way up to an elevation of about 2,000 feet,
where a bed of a somewhat scoriaceous basaltic andesite was dis-
played, the upper 200 feet being inaccessible but of the same
agglomerate. At a height of 300 feet was observed another layer
of the same basaltic rock. These intercalated beds appeared to
be lava-flows rather than horizontal dykes. The agglomerates
become less coarse in the upper part of the mountain where they
take the character of agglomerate-tuffs. The blocks are composed,
like those in many other parts of the island, of a dark semi-
vitreous basaltic andesite, but often scoriaceous. But the most
remarkable features of these agglomerates are the indications of
two distinct pauses in their deposition afforded by the occurrence
at elevations of 900 and 1,700 feet of a single horizontal bed, two
to three feet thick, of coarse palagonite-tuffs. Each bed is exposed
at the foot of a tall cliff of agglomerate forming a line of escarp-
ment along the mountain-side. The larger fragments making up
these tuffs are usually from 2 to 3 millimetres in size ; but
the process of palagonitisation is not complete ; and we find
inclosed abundant angular pieces of a dark fresh tachylyte-glass,
finely vesicular, and fusing readily in the ordinary spirit-lamp
flame. The tuffs contain little or no lime and seemingly no
^ Referred to genus 9 of the augite-andesites.

214 A NATURALIST IN THE PACIFIC chap.

organic remains. In the lowest bed I noticed a little water-worn
gravel. Both beds pass gradually into the underlying agglomer-
ate ; but their upper limits are well defined and the agglomerate
commences abruptly.

It is thus seen that in the formation of the agglomerates there
were two pauses when they gradually gave place to deposits of
fine detritus made up of a vesicular basic glass that has since been
largely converted into palagonite. Then followed a sudden renewal
of the agglomerate-producing process. We can scarcely doubt
that the agglomerates, with their scoriaceous blocks, and the
palagonite-tuffs are in the main the direct products of volcanic
eruptions. The rival claim of marine denudation as the agency
concerned can be mostly but not altogether excluded. The
agglomerates and tuffs of Mount Vungalei cannot be distinguished
from those so often described in the case of the great inland
ranges of the other parts of the island, the submarine origin of
which is frequently demonstrated by the inclosed organic remains.
It would seem that in the instance of Vungalei these deposits
took place around the shores of a volcanic mountain that rose
above the sea. On page 315 it is pointed out that in Stromboli
with its dribbling eruptions we have a good illustration of the
manner in which such deposits could be formed.

My examination of the mountain of Nailotha was restricted
to the lower slopes up to an elevation of 600 feet ; but the results
obtained are very suggestive. When following up the stream-
course on the way from Tembe to the mountain one notices in
its bed blocks of a light-coloured rock like a compact quartzite.
It is, however, a highly altered oligoclase-trachyte (sp. gr. 2"53)
with its structure much disguised by secondary quartz. This is
the first intimation one gets, on leaving behind the district of
basic agglomerates about Tembe, of the otherwise unexpected
character of the acid rocks displayed in the lower part of
Nailotha.^

A torrent here cuts deeply into the mountain-side. At the
base, between 200 and 300 feet above the sea, a bluish-grey rather
scoriaceous rock with the steam-pores drawn out to a length of
from I to 2 centimetres, is first exposed. Its specific gravity
after allowing for the cavities is less than 2'6. It shows a
groundmass partly disguised by secondary quartz and containing
numerous small vesicles lined by quartz and filled with viridite
and epidote. Where the alteration is less advanced small parallel
^ The general characters of these rocks are described on p. 308.

XV NAILOTHA 215

felspar-lathes with fine decomposing pyroxenes are shown. The
lathes give extinctions of two or three degrees and average '04 mm.
in length. In its somewhat scoriaceous nature, in the absence of
phenocrysts, and in its less altered condition, this rock differs from
those exposed higher up the ravine ; but it is evidently to be
referred to the same acid type. At a height of 300 feet a light
grey highly altered oligoclase-trachyte (sp, gr. 2*43) is exhibited.
It contained originally some phenocrysts of felspar and pyroxene,
which, however, have been more or less replaced by calcite, quartz,
and other materials ; whilst the groundmass, originally hemi-
crystalline but now blurred by the deposition of silica, shows
felspar-lathes in process of development.

A little farther up the gorge there is displayed another highly
altered rock with a siliceous appearance, such as has been noticed
above as forming blocks in the stream near the foot of the moun-
tain. It is an oligoclase-trachyte impregnated with crystalline
silica and exhibiting a singular prismatic structure, the small
columns or prisms being only 3 or 4 inches in diameter. Between
400 and 500 feet occurs a light-coloured compact rock sparkling
with pyrites and also displaying a columnar structure, the columns
being between 4 and 6 inches across. It looks like a limestone
and effervesces freely with an acid ; but it is in fact a highly altered
oligoclase-trachyte (sp. gr. 2-5) of the propylite type. It seems
originally to have inclosed a few phenocrysts of oligoclase, sanidine,
and pyroxene, and here and there a stout felspar-lathe is to be
noticed in the groundmass giving straight extinction. The whole
texture of the rock, however, is more or less impregnated with
secondary quartz, calcite, chlorite, viridite, pyrites, &c. Farther up
the ravine, between 500 and 600 feet in elevation, is displayed a
remarkable quartz-porphyry which exhibits opaque porphyritic
crystals of felspar as well as rounded crystals of quartz in a grey
compact base. It has been subjected to considerable alteration
and will be found described on page 310.

At 600 feet large slabs of the ordinary sedimentary clay-tuffs,
containing but little lime and showing no organic remains to the
eye, lay about on the more level slopes, and evidently formed a
surface deposit incrusting the altered massive rocks. If my ascent
had lain up the mountain-side away from the stream-courses, these
sedimentary rocks would alone have been observed. In the gorge,
however, is exposed to view the deeper-seated rocks that make up
the mountain's mass. We have here a thickness of about 400 feet
of altered acid rocks. All are doubtless intrusive, and were sub-

2i6 A NATURALIST IN THE PACIFIC chap.

Jected to alteration after the development of the columnar structure
and before the deposition of the overlying clay-tuffs or "soap-
stones," which are no doubt of submarine origin. These sedi-
mentary tuffs belong probably to the period when the submarine
agglomerates and palagonite-tuffs of the neighbouring peak of
Vungalei were formed.

(c) Traverse of the coast range from Nandongo to Vanuavou on
the shore of Natewa Bay. — This route was taken by Mr Home,
the botanist, in 1878. I approached Nandongo from Tembe to
the northward. The road at first lay between hills about 700 feet
in height displaying in their precipitous faces agglomerates
overlying fine sedimentary tuffs. These deposits in the form of
slightly calcareous basic tuff-clays, the so-called " soapstones," are
exposed in the bed of the Wainikoro River as one nears Nandongo.
This village, which is situated on the headwaters of the Wainikoro
at an elevation of about 180 feet above the sea, lies near the foot of
the range. In its vicinity there is a small thermal spring which is
referred to on page 33.

Proceeding south from Nandongo one notices in the stream-
course at the foot of the slopes the sedimentary tuff deposits above
mentioned, bedding and dipping gently to the west. Farther up
the slopes, higher than 250 feet above the sea, there are exposed
the deeper-seated rocks of the range in the shape of compact red-
dish rocks (sp. gr. 2*48), which appear under the microscope to be
highly altered acid andesites or oligoclase-trachytes originally
displaying flow-structure and a fair amount of glass, but now much
disguised by the formation of secondary quartz. On this north
slope of the range I also found an amygdaloidal variety of the same
altered rocks containing irregular amygdules, 5 or 6 millimetres
long, of fibrous quartz or chalcedony. Blocks of basaltic andesite
were observed on the summit, which has an elevation of 950 to
1,000 feet. On the southern slopes descending towards Natewa
Bay coarse basic tuffs together with blocks of basaltic andesite are
chiefly exposed. The last-named probably represent dykes both
on the south slope and on the summit. The rocks exhibited on the
portion of the coast of Natewa Bay corresponding to this range
are dark and light-coloured sedimentary tuffs usually calcareous,
with occasional basaltic andesites indicating dykes. . . . From this
traverse it would appear that the range has an axis of altered acid
rocks overlain by basic sedimentary tuffs and pierced by basaltic
dykes.

{d) The mountainous district lying between the head waters

XV COAST RANGES 217

of the Wainikoro River and the Mount Thurston Range. —
Of this region I know very little. The highest peak according
to the chart has an elevation of about i,6cxD feet. Some
indication of the character of the inland rocks may be obtained
from that of those exposed on the coast between Nakarambo
and Waimotu where, as observed on page 208, grey pyroxene-
andesites, coarse in texture and almost holo-crystalline in structure,
protrude through agglomerates of the same materials. When on
the way from Ngelemumu to Wainikoro I crossed the extreme
northern prolongation of this range where the elevation above the
sea is only 700 feet. Non-calcareous basic tuff-clays occur on the
slopes ; but the deeper-seated rocks, judging from an exposure on
the east side, are dark grey altered pyroxene-andesites penetrated
by fine cracks filled with a mosaic of quartz and having a specific
gravity of 27. On the summit I found a gritty sandstone-like rock,
of which my specimen has been lost. In a stream at the foot of
the east slope occur small blocks of basaltic andesite probably
derived from a dyke. The region of acid rocks, such as quartz-
porphyries, oligoclase-trachytes, &c., is not entered until about two
miles south-west of Wainikoro.

The Coast Ranges and Sea-border between Mbuthai-

SAU AND THAWARO OR MbEKANA BAY

We have in this region the mountains and hills at the coast and
the low-lying plains inland. This feature of the north side of
Vanua Levu is very remarkable. For some sixty miles, that is to
say, for more than half the length of the island, between the
mouth of the river Ndreketi and Thawaro or Mbekana Bay, Vanua
Levu possesses this character. The coast ranges west of Lam-
basa, where basic rocks evidently prevail, have been referred to on
pages 135, 136. Those east of the Lambasa mountains as far as
Thawaro Bay will be dealt with here ; and instead of basic we
find acid rocks, such as quartz-porphyries akin to the rhyolites,
oligoclase-trachytes, pumice-tuffs, &c.

The sea-border is here characterised not by a continuous range
running parallel to the coast, as in the case of the district between
Nanduri and the Ndreketi River, but by a number of separate
groups of hills and lesser mountains, separated by deep gaps or
valleys which are occupied by tidal rivers and extensive mangrove
swamps. The tide ascends these rivers into the plains behind the
coast ranges, so that a depression of only 30 feet would convert

2i8 A NATURALIST IN THE PACIFIC chap.

these groups of hills into separate islands and would cover much
of the inland plains with the sea. The hills attain an elevation
of 1,200 or 1,300 feet a mile or two inland and descend often as
bold promontories to the coast. I will refer in order to the differ-
ent parts of this sea-border.

(i) The Sea-border between Lambasa and Mbuthai-sau

In the sea-border between Lambasa and Mbuthai-sau we have
the junction of the regions of basic and acid rocks, the former
extending westward to Naivaka, the latter reaching to Undu Point.
In such a locality the two types of rocks might be expected to be
associated, and this is what occurs. Acid pumice-tuffs and basic
agglomerates, sometimes associated, are here displayed. In the
low hills between Lambasa and Vuni-ika Bay, which lies west
of Mbuthai-sau, I found basic agglomerates prevailing, together
with some acid pumice-tuffs. The blocks in the agglomerates are
composed of a blackish semi-vitreous pyroxene-andesite (sp.gr. 2*68),
which is characterised by prismatic pyroxene in the groundmass,
and is referred to genus 6 of the second sub-order of the hypers-
thene-augite andesites described on page 287.

East of Vuni-ika on the way to Mbuthai-sau, at an elevation of
about 50 feet above the sea, dark tuffs containing small fragments
of reef-limestone are exposed in a cutting. A little farther on
there is a considerable deposit of a pale grey rhyolitic pumice-
tuff, a soft stone easily worked, and indeed now quarried by the
plantation authorities. It contains no lime and in microscopical
characters is scarcely distinguishable from a sample of fine pumice
debris collected by me in the Chirica district of Lipari Island. It
is made of fragments up to a centimetre in size, of ordinary
fibrillar pumice in a matrix of much finer material of the same
nature. Portions of crystals of glassy felspar (oligoclase and
sanidine) also occur in it, together with some quartz and rhombic
pyroxene.

The association in this locality of acid and basic eruptive pro-
ducts was observed by Dana in 1840 in the cliffs of" Mali Point." ^
It is not quite clear whether Mali Island, which lies immediately
adjacent to the coast, is here alluded to, or whether it is a head-
land opposite to it. Dana describes the deposits displayed in
these clififs as coarse aggregates of fragments of pumice and
decomposing trachyte, which pass on the one side into fine
^ Geology of the United States Exploring Expedition.

XV MBUTHAI-SAU VALLEY 219

clayey material, and on the other into an agglomerate formed
of angular blocks of vesicular and compact basalt with the
interstices filled with pale yellow tufaceous material.

East of the Avuka Range that limits the Lambasa plains on
this side is the picturesque valley of Mbuthai-sau. This broad
valley runs in a south-east direction into the heart of the island.
So small is the gradient that the river flowing down it can be
ascended in boats for some miles ; whilst Ngele-mumu, a village
situated between 5 and 6 miles up the valley, is not much over
50 feet above the sea. This valley in its lower part roughly
divides the regions of acid and basic rocks that lie east and west
of it respectively. It has, however, been above pointed out that
the two regions overlap in the coast region on the west side of the
valley. The two types of rocks are also associated in the coast
hills immediately east of the valley, since when striking inland
from Lloyd Point to the Mbuthai-sau sugar-cane district, one
leaves behind the acid rocks at the coast and traverses a region of
basic agglomerates. With these qualifications, therefore, the above
line of demarcation holds good.

(2) The Sea-border between the Mbuthai-sau and the
Langa-langa Rivers

The rocks predominating in this district are white and pale-
yellow pumice-tuffs and pumice agglomerates, with quartz-por-
phyries and oligoclase-trachytes as intrusive masses. The light
colour of the sea-cliffs, thus composed, makes them conspicuous
from seaward. Their appearance evidently led Mr. Home into an
error in 1878 when he viewed this coast from his canoe during his sea-
passage from Lambasa to Tutu. " The coast from Lambasa " — he
says — " is a series of bold projecting bluffs of agglomerate inter-
spersed with seams of coralline sandstone." ^ The principal feature
of this coast, however, is the prevalence of light-coloured pumice-
tuffs, though it is not improbable that elevated reef-formations may
occur in some localities.

I particularly examined the coast districts in the vicinity of the
Wainikoro and Langa-Langa rivers. In a spur that descends to
the right bank of the river, a little above the mouth of the Waini-
koro, is exposed an open-textured rhyolite or quartz-porphyry
containing, as described on page 310, phenocrysts of glassy felspar
(oligoclase and sanidine), quartz, and a little hornblende. Some
^ A Year in Fiji, p. 22.

220 A NATURALIST IN THE PACIFIC chap..

interesting exposures occur on the coasts between Narikosa Point
(Nari-Roso Point of the chart) and the mouth of the Wainikoro..
Here the pumice-tuffs and agglomerates are pierced by dykes,
some of them vertical and 6 feet across and composed of a light-
grey rhyolitic rock, similar except in its compact texture to the
rock above mentioned.^ The small quartz crystals, which are i to
2 millimetres in size, are sometimes bipyramidal. Many of them
are rounded and have a fused-like surface. The pumice-tuff,
which displays no effervescence with an acid, is composed mainly
of finely pulverised vacuolar and fibrillar istropic colourless glass,.
and contains also small fragments of glassy felspar and small
rounded quartz crystals, such as occur in the rock forming the
dykes in these deposits. Imbedded in the tuffs in places are small
masses, up to 4 inches in size, of a pretty grey vesicular rhyolite-
glass exhibiting the intermediate condition between compact
obsidian and pumice which is so characteristic of the rocks of
Vulcano in the Lipari Islands. A more detailed account of this
rock is given on page 311. In the pumice-agglomerates of this
locality occur pale-yellow decayed and altered pumice blocks.

The headland, known as Narikosa Point, which lies between
the mouths of the Wainikoro and Langa-langa rivers, terminates
in a rocky spur formed by a large intrusive mass or dyke of a
reddish oligoclase-trachyte altered in character and displaying in
places a rudely columnar structure,^ The pumice-tuffs and
agglomerates are well exposed at the coast between Narikosa
Point and the Langa-langa River, In the vicinity of Songom-
biau, a village here situated, the tuffs are penetrated by dykes.
One dyke at the back of the village is 4 or 5 feet thick and has
vitreous margins. It is composed of a darkish pyroxene-andesite
which in the interior of the intrusion in hemi-crystalline and a little
vesicular, but in the margins it is more glassy and rather scoriace-
ous.^ Though not a basic rock in itself, its specific gravity in the
compact state being only about 2*55, it is relatively basic when
contrasted with the rhyolitic and trachytic rocks of the district,
which have v/hen compact a specific gravity of not over 2*3.

Pumice-tuffs and agglomerates appear in the cliff-faces of the
hills on either side of the lower course of the Langa-langa River

^ Described on p. 310.

2 These rocks are described on p. 308.

^ It contains small phenocrysts of plagioclase (medium andesine), and or
augite and rhombic pyroxene, and is referred to genus i of the hypersthene-
augite andesites.

XV VISONGO 221

from the vicinity of Kalikoso to the sea. At one place about 3
miles up the river a dyke of trachyte, much altered and showing
■columns 12 to 18 inches across, was exposed at the bank.

<3) Sea-border between the Langa-langa River and

Thawaro Bay

The next part of the coast which I visited was that opposite
Tutu Island. Here a range of high hills, 1,100 or 1,200 feet in
height, sends a lofty spur to the sea, in the precipitous faces of
which are exposed breccia-tuffs and agglomerates derived from
acid rocks, A specimen of the tuffs shows, besides fragments of
altered rhyolitic or trachytic rocks, portions of decomposing
pumice, the vacuoles and tubular cavities of which are filled with
alteration products. The blocks in the agglomerates are altered
oligoclase-trachytes, both compact and vesicular. These deposits
are non-calcareous and rarely display bedding ; but in one place
there was a rude arrangement of the materials, the dip being to the
north-west. I crossed this coast range where it is only 600 feet
above the sea, and descended into the Kalikoso plains in the
vicinity of Numbu.

In the coast district between Tutu Island and the village of
Naua, 3|- miles to the east, the same altered coarse pumiceous and
trachytic tuffs, occasionally bedded and dipping W.N.W., form the
low hills near the sea. In one place, where the elevation was less
than 200 feet, I noticed on the surface small fragments of branch-
ing corals. They had perhaps weathered out of the tuffs, and
though in part silicified still effervesced freely in an acid.

Between Naua and the town of Visongo occur low hills formed
■of acid tuffs. At an elevation of 200 feet the tuffs display a remark-
able character. When examined with the lens they are seen to be
crowded with the minute tests offoraminifera of the " Globigerina"
type. The deposit forms a fairly hard light-grey clay-rock which
according to the usual acid-test has no lime. Under the micro-
scope it is seen to be composed nearly in equal proportion of the
tests of foraminifera and of very fine detritus apparently derived
from acid rocks, the materials being generally not over 'Oi mm. in
diameter, though some of the felspar fragments measure "05 mm.
across. A secondary process of silicification, as exhibited in the
occurrence of minutely granular quartz, has affected the matrix of
the clay as well as the tests of the foraminifera. The deposit is of

222 A NATURALIST IN THE PACIFIC chap.

deep-water origin and appears to have been formed from the fine
washings of a coast some distance away.

It is noteworthy that the surface in this locality is in places
strewn with quantities of angular fragments and round pebbles of
chalcedonic flint, together with large nodules which when broken
across are found to be occupied by radiating crystals of quartz and
were doubtless formed in the cavities of some rock. Reference
has already been made to the partially silicified coral fragments
lying on the surface of the low coast hills a few miles to the west
of this locality. They indicate a relatively recent emergence and
we get the same indication from the flints on the surface of this
district. These evidences, however, relate only to the last stage of
the emergence. The testimony of the silicified " Globigerina " clay
carries us back to the earlier periods of these changes of level, and
probably dates back to a time when the greater part of this portion
of the island was submerged, with the exception of the mountain
peaks. Not the least interesting feature of the emergence is the
silicifying proces~ that accompanied it. This is illustrated on a
much greater scale in the neighbouring inland plains of Kalikoso
and Wainikoro which are described in Chapter XXV.

Proceeding eastward from Visongo to Namukalau one traverses
a coast district not elevated more than 3CK) feet above the sea.
Here there are displayed whitish and pale yellow compacted tuffs
differing in aspect from those prevailing to the westward and often
bedded, the dip being about 20° N.W. or N.N.W. They show no
lime and apparently inclose no organic remains. Where the upper
surface of a bed is bared, it shows regular shrinkage-lines inclosing
hexagonal spaces 2 to 3 inches across ; but there is no correspond-
ing columnar structure in the bed-mass. The rock is very light in
weight and homogeneous in texture and looks a little like China-
clay. In a section its structure appears obscure ; but it seems to
be formed of the finest detritus, derived from some acid partly
devitrified glass, the pumiceous structure being in places faintly
mdicated ; but the whole mass appears to have been subjected to a
process of alteration perhaps similar to the ultimate palagonitic
change in basic rocks. In the slide a few small felspar fragments^
about 'I mm. in size, are displayed.

Just east of Namukalau is the mouth of the Vui-na-savu River,
the Na Savu River of the chart. This is a tidal river, and is
navigable for boats for several miles. In the lower part of its
course agglomerates and tuffs prevail, probably in part at least
derived from acid rocks. Near Rauriko, which lies about 5 miles

XV VUI-NA-SAVU RIVER 225

up the river, a bare bluff, overlooking the valley on the east, is
formed of a decomposed trachytic rock remarkable for the fact that it
displays, as described on page 370, faint magnetic polarity. Above
Vitina, a mile or two farther up, I found a similar rock but amyg-
daloidal in character. On the head-waters of the river is situated
the hamlet of Nawi, where, as mentioned on page 211, a plutonic
rock of the gabbro type occurs. Tuffs and agglomerates appear to
prevail in the low coast tract between the Vui-na-Savu river and
Thawaro Bay.

In drawing some general inferences respecting the acid for-
mations, mostly fragmental in character, that are displayed in the
sea-border between Lambasa and Thawaro Bay, it is necessary to
distinguish between the deposits west and east of the Langa-langa
River. Between Lambasa and the river just named the tuffs may
usually be regarded as the products of sub-aerial eruptions. Some
of the specimens might have been obtained, as far as their characters
go, from the pumice-districts in the island of Lipari. Their lime-
less condition and the apparent absence of organic remains are
noteworthy features, though of course the products of sub-aerial
eruptions may be deposited under the sea. It is, however, remark-
able that no compact obsidian came under my notice. The frag-
ments of rhyolitic glass, intermediate in structure between compact
obsidian and pumice, that were imbedded in the pumice-tuffs in one
locality, were probably ejected from some sub-aerial vent.

In the region between the Langa-langa River and Thawaro
Bay acid tuffs and agglomerates prevail ; but they have all been
subjected to alteration by the deposition of secondary silica, and
the pumice-structure when present is largely disguised. They have
evidently, in part at least, been derived from compact rhyolitic and
trachytic rocks, and are probably in some measure the products of
marine erosion. Although neither lime nor organic remains were
detected, the presence of the altered " Globigerina " clay near
Visongo is very suggestive and indicates a considerable submer-
gence of this region at some distant period.

Much, however, remains to be done in the examination of the
peaks of the coast ranges of this part of Vanua Levu ; and it is
likely that some interesting results will be obtained from such an
exploration.

/

CHAPTER XVI

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL
FEATURES {continued^

THE NORTH-EAST PORTION OF THE ISLAND {continued)

The Wainikoro and Kalikoso Plains

These extensive inland plains occupy a considerable area in this
part of the island. I estimate that there is an area of about 20
square miles that does not exceed an elevation of 100 feet above
the sea and is often much less. Of the two villages situated in the
midst of these plains, about 5 miles inland, Kalikoso is about 30
feet and Wainikoro is scarcely 20 feet above the sea ; whilst much
of the surrounding district is similarly low. Taking the 300-feet
contour-line as a guide, this low-lying region, as shown in the map,
would be much larger. The plains are backed on the sou*:h by the
high mountain-range of Vungalei and Nailotha. On the north the
coast-ranges, which attain a height of 1,100 or 1,200 feet, separate
them from the sea-border ; whilst on the west they are shut off
from the Mbuthai-sau valley by a line of hills, of which the minimum
elevation is about 700 feet. This region is occupied by the scanty
open vegetation characteristic of the " talasinga " or " sun-burnt "
districts. The tall " Ngasau " reed is common ; the Pandanus trees
are frequent ; and amongst the bushes and small trees are re-
presented " Dodonaea viscosa," " Morinda citrifolia," and a species
of " Hibbertia."

Different rivers and streams, rising in the mountains on the
south side of the plains, traverse this area; and after breaking
through the coast-ranges reach the sea. They acquire an ex-
aggerated size from the circumstance that they are in great part
tidal estuaries. The tide ascends them for several miles reaching

CH. XVI THE KALIKOSO PLAINS 225

behind the coast-ranges into the plains ; whilst the dense man-
groves, which line their lower courses amongst the hills, extend be-
yond into the low-lying level districts farther inland. Boats can
follow up the winding course of the Wainikoro River until they
reach the village of that name, which lies about five and a half miles
in a direct line from the coast and nearly in the centre of this part
of the island. The mangroves extend up to the village. The
Langa-langa River, which is of much smaller size, is similarly
navigable for three or four miles. The mangroves that line its
banks spread out in broad tracts when in ascending the river we
emerge from the hills into the plains. Above the influence of the
tide it dwindles into a stream ridiculously small. The same
remarks apply to the river two miles to the eastward. The Vui-
na-savu River near the eastern margin of this low-lying region can
be ascended by boats into the heart of the island.

From the foregoing remarks it will be expected that some por-
tion of this low-lying inland region will be occupied by swamps.
This is in truth the case. About one and a half miles north-east
from the village of Kalikoso is a small fresh-water lake, about 100
yards across, which lies in a slight depression in the plains and is
surrounded by a wide margin of swampy ground, occupied by reeds
and sedges, in which one sinks knee-deep when approaching the
banks. The level of the surface of the lake is not over 25 feet
above the sea, and only a foot or so below that of the plains around.
Since the depth, as I ascertained it, is 1 5 to 18 feet, it follows that the
bottom of the lake is only a few feet above the high-tide level.
The mangroves extend to within a mile of its border ; and it is
possible that though lying about five miles inland, it may be
indirectly affected by unusually high tides. It would be interesting
to determine whether the water is ever brackish.

This small lake is, or was, regarded with superstitious awe by
the natives on account of the floating islands that it contains.
Different legends are connected with it, and the Fijians have
given it the name of " Vaka-lalatha," in allusion to the drifting of
the islands from one side of the lake to the other, the small trees
Trowing upon them acting " in the manner of sails." Mr. Home,
ivho was in this locality in 1878, refers to the lake in his book, A
Year in Fiji (p. 24) ; but does not appear to have seen it. Mr.
Thomson^ visited it in 1880, and describes it as containing a single
loating island, a quarter to a half an acre in extent. The

^ See paper quoted on p. 31. It is noteworthy that Mr. Home refers only
o a single floating island.

Q

226 A NATURALIST IN THE PACIFIC chap.

island was in existence, the natives said, in the days of their great-
grandfathers, a statement indicating that the people of the district
had no reason to doubt its antiquity. A chief, who formed one of
the party, dived under the island.

When I visited this lake in 1899 there were three floating
islands, named by the natives " Wanga levu " and " Wanga lailai,"
that is, " Large canoe " and " Small canoe." The largest was 90 or
100 feet long, whilst the two smaller were about 50 feet long, the
breadth being less than half the length. They are composed of a
dense growth of reeds and sedges supporting small living trees 10
to 17 feet in height, swamp ferns, and other smaller vegetation, the
whole forming fairly solid standing-ground, and doubtless possess-
ing considerable thickness.

The origin of these floating islands is probably to be found in the
circumstance that the dense mass of swamp-vegetation lies on a
rocky substratum, and that during some unusually heavy flood
large portions of the swampy soil-cap became detached and floated
up. A floating island occurs near the sea in the Lauthala district
on the Lower Rewa in Viti Levu. The floating island in Derwent-
water in the north of England is said to be " a blister of sub-
lacustrine turf." Those in Russia and Hungary, according to Mr.
Hanusz, appear to be felted masses of tree-trunks, branches, and
marsh-plants thinly covered with soil.^

I will preface my remarks on the geology of the Wainikoro and
Kalikoso plains by observing that this region displays three con-
spicuous features. In the first place, it is a region of acid rocks,
mostly altered tufis, derived from quartz-porphyries, the alteration
consisting in the deposition of quartz often of the chalcedonic type.
In the second place, a silicifying process has been in operation here
on an extensive scale, as evidenced by the abundance of silicified
corals lying on the surface, especially in the district around the lake
and by the abundance of concretions of chalcedony, of fragments
of chalcedonic flints, and of portions of white chalcedonic quartz-
rock that in places strew the ground. In the third place, earthy
limonite, or bog iron ore, has been produced in quantity, par-
ticularly around the lake ; and in places small round concretions
of impure carbonate of iron cover the soil. Before referring more
in detail to the different parts of this region, it may be remarked
that the silicified corals, flints, iron-ore deposits, &c., of this and
other parts of the island are dealt with in Chapter XXV.

This region of acid rocks extends about two miles to the west
^ Journal^ Royal Geographical Society, June, 1894.

XVI THE WAINIKORO PLAINS 227

and south-west of the village of Wainikoro. Here prevail white
acid tuffs often decomposing and altered by the formation of
secondary quartz. They are derived from the degradation of
quartz-porphyries or rhyolitic rocks. The surface is irregular but
the elevation is small, the 100- feet level lying about one mile and
the 200-feet level about two miles west of Wainikoro.

The villages of Wainikoro and Kalikoso are from two to three
miles apart, the intervening district not attaining a greater elevation
than 70 feet above the sea. Decomposing altered white acid tuffs
here occur with occasional large blocks, a couple of tons in weight,
of apparently a quartz-porphyry or trachyte with its structure
disguised by silicification. Fragments of siliceous concretions, as
chalcedony, chalcedonic flints, &c., lie on the surface, the soil being
friable and of a deep ochreous red ; whilst in places the ground is
covered with round marble-sized concretions composed of a mix-
ture of carbonate of iron and limonite which I have described on
page 356. A few hundred yards to the north-west of Kalikoso,
where there is a little rise, a decomposed quartz-porphyry is ex-
posed displaying rounded crystals of quartz fractured in position,
the matrix of the rock being impregnated with chalcedony. In one
part of this mound there is a friable white rock, composed of a
crumbling mass of small irregular quartz-grains, rarely showing
crystal-faces. It appears to be disintegrated quartz-felsite.

In taking the track from Kalikoso to the village of Vungalei,
which is distant about 2| miles to the south-east, one traverses
after the first mile, where the acid rocks terminate, a rather
more elevated region which rises to a maximum height of
180 feet above the sea. Though the acid rocks give place to a
semi-vitreous pyroxene-andesite as described on page 212, small
fragments of chalcedonic flints are frequent on the surface over
both areas. The district that intervenes between Kalikoso and
the landing-place on the Langa-langa River, about two miles in
length, is not more than 30 feet above the sea, and is crossed by
small sluggish streams, in the beds of which occur numerous frag-
ments of silicified corals, up to 3 or 4 inches in size, belonging to
the Porites and Astraean type. In these stream-beds also occur
bits of mamillated chalcedony and of onyx, flattish agates, 3 or
4 inches across, and pebbles of the compact pyroxene-andesite
above alluded to, the last probably derived from the south side of
the plains.

The plains extend in a north-east direction as far as Numbu,
which lies between 2| and 3 miles north-east of Kalikoso. The

Q 2

2 28 A NATURALIST IN THE PACIFIC chap.

country between these two places is usually elevated between
60 and 100 feet and is nevermore than 130 feet above the sea.
It is known as the Kuru-kuru district. The surface is strewn with
the fragments of. flints and of a white chalcedonic quartz-rock ;
whilst the soil is friable and deep-red in colour, limonite in
abundant fragments occurring on the ground. Here and there one
passes slabs of a hard white silicified tuff, small portions of which
are frequent on the surface.

Silicified corals and earthy limonite are to be found in abund-
ance scattered over the surface of the plains immediately surround-
ing the small lake , of Vakalalatha. We also find lying on the
ground in this district bits of chalcedony and onyx, portions of
chalcedonic flints, and nodules of the size of the fist, which when
fractured either disclose the regular layers of the agate or radiating
crystals of quartz. The silicified corals occur usually in fragments
not over 4 inches across, and include portions of branching corals
of the Madrepore habit, bits of massive corals of the Astraean
type, small rounded nobs of " Porites " just as one commonly
observes on a reef-flat, &c. They have an ancient weathered look,
and in some cases it is evident from the existence of boring-shells
in the fractured end of a branching coral that it once lay as a dead
fragment on the surface of a reef-flat.

In Chapter XXV. the characters of the silicified corals of the
island are discussed in detail ; and I have there advanced the view
that the extensive silicification of the Kalikoso and Wainikoro
plains took place during the consolidation of the calcareous muds
of a reef-flat whilst the land was emerging. I have already alluded
on page 222 to an area of silicification on the neighbouring sea-
border between Visongo and Tutu. There can be no doubt that
during the last stage of the emergence the present situation of the
fresh-water lake near Kalikoso was occupied by the sea, which
also extended far over the surrounding plains. The process of
silicification would of necessity be restricted to the period that
has since elapsed ; and the discussion is therefore confined to the
nature of the conditions under which this change was induced.
As a factor in the process we cannot disregard the acid character
of the rocks of the district.

The Undu Promontory -
The north-east portion of the island terminates in a long
narrow promontory which I have named after Undu Point at its
extremity. Commencing at Thawaro Bay and near Tawaki it runs

XVI TAWAKI 229

in a straight line for a distance of between 13 and 14 miles, its
breadth varying between i| and 2^ miles. Its greatest elevation
of nearly 1,600 feet is attained at its western end ; and it diminishes
irregularly in height as one proceeds towards Undu Point, where
a height of 400 feet is maintained about a mile from the cape.
It is bordered by reefs sometimes a mile in breadth, and the reefs
prolong the promontory for another three miles beyond Undu
Point. As indicated by the lOO-fathom line, the submarine
contour corresponds to that of the land, and the extent of marine
erosion during the existing relations of land and sea is evidently
displayed in the breadth of the reefs. I found no sign of upraised
reefs ; and although diligent inquiries were made nothing could be
learned of any hot springs.

It will be seen from the following remarks that pumice-tuffs,
quartz-porphyries, and oligoclase-trachytes, are the prevailing
rocks. On the north side they may be regarded as continuous
with the acid rocks of the region extending from near Lambasa
to Thawaro Bay. On the south side they commence in the
vicinity of Tawaki.

(i) The District Extending two and a half miles
West of Tawaki

When proceeding eastward along the north coast of Natewa
Bay one enters the region of acid rocks between 2 and 2^ miles
west of Tawaki. Here the country is much broken, picturesque
hills with bare precipitous faces rising up near the coast, one of
which named Natoto has a rudely conical and truncated form.
Grey oligoclase-trachytes having a specific gravity of 2*4 and
possessing the characters described on page 308, prevail in the
district extending west of Tawaki. Sometimes they occur in
mass ; but they often form agglomerates. A singular pitchstone-
agglomerate occurs at the coast at the foot of Natoto. The
pitchstone, which has a specific gravity of 2*48, is a semi-vitreous
form of a hypersthene-augite andesite. It shows abundant small
pyroxene prisms in its glassy groundmass and is referred to the
prismatic sub-order (5) described on page 289.

(2) Naithombothombo Range

A high range of hills, forming the backbone of this part of
the island, extends eastward for about five miles from Thawaro
and Tawaki. It is named " Naithombothombo " in the Admiralty

230 A NATURALIST IN THE PACIFIC chap.

j
chart. From it rise two conspicuous peaks, Thawaro Peak (i,S73

feet) at its western end, where it overlooks the village of that

name, and Mount Thuku (1,288 feet) near its eastern end. West

of Thawaro Peak this range is connected with the hills beyond by

a saddle 600 feet in height, which is ascended when crossing the

promontory from Thawaro Bay to Tawaki. i

(a) Thawaro Peak. — This represents an old " volcanic neck " '
of agglomerate rising out of the tuffs that are exposed on its
slopes to an elevation of about 600 feet. As viewed from the
saddle above mentioned, the upper part of the hill presents bare
precipitous sides, several hundred feet in height, of agglomerate,
the blocks of which are composed of a compact hypersthene-augite
andesite (sp. gr. 2'\Z\ It displays a few small phenocrysts of
medium andesine and of rhombic and monoclinic pyroxene ; and
is referred to the prismatic sub-order (5) described on page 289,
characterised by prismatic pyroxene in the groundmass.

{U) South coast between Tawaki and the foot of Mount Thuku. —
The tall cliffs that rise to a height of from 2(X) to 300 feet behind
Tawaki are composed of white tuffs and agglomerate-tuffs derived
from the acid rocks of the district. Eastward from Tawaki to
the base of Mount Thuku the coast scenery is particularly fine.
A little inland a line of hills, named " Na Kula," rises precipitously
to a height of 700 or 8cx) feet, and in the vertical sides are displayed
tuffs and agglomerates probably of the character of those above
noticed. Light-coloured tuffs are sometimes exposed at the coast
in which are inclosed fragments varying in size of a pitchstone ^
(sp. gr. 2'36) approaching in structure a trachytic glass. At one
place the tuffs were evidently sedimentary and bedded, the dip
being about 15° N.W.

The massive rock most frequently exposed at the coast
and on the hill-slopes between Tawaki and Mount Thuku is a
quartz porphyry ^ displaying abundant porphyritic crystals of
quartz and felspar in a groundmass originally semi-vitreous but
now obscurely felsitic in character. The shore-flat for more
than half a mile west of Mount Thuku is strewn with great
numbers of detached columnar blocks, 12 to 15 inches across,
of a slightly vesicular oligoclase-trachyte of the type described
on page 308.

ic) North coast between Thawaro Bay and the foot of Mount
Thuku. — Coarse and fine tuffs prevail at the coast and on the
neighbouring hill-slopes ; and in the bare rocky faces of the hills
^ Described on p. 309. ^ Described on p. 310.

XVI MOUNT THUKU 231

inland they are also to be observed. T he streams have worn deep
gorges into their mass. Towards Thuku they are acid and pumice-
ous, and are evidently the products of eruption. Towards Thawaro,
they are more basic and darker, and are in part at least to be
attributed to marine degradation.

{d) Mount Thuku. — My ascent of this hill, which is 1,288 feet
in height, was made from the north coast. I found it to be com-
posed from the foot to the summit of white pumiceous tuffs without
any evident arrangement. It has a narrow top and shows no sign
of a crateral cavity. The hills east and west, as viewed from its
summit, are ridge-shaped and display nothing in their configur-
ation at all suggestive of craters. The pumice-tuffs of Mount
Thuku are non-calcareous, and exhibit greyish pumiceous lapilli in
an abundant white matrix formed of fine pumice-debris. Under
the microscope it shows the characteristic vacuolar and fibrillar
structure ; but the material has not the fresh appearance of ordin-
ary pumice and the minute cavities are often filled with alteration
products. The two rocky points on the north coast opposite the
hill are formed in one case of a somewhat altered oligoclase-
trachyte and in the other of a quartz-porphyry. Both no doubt
represent intrusive masses, the almost horizontal columns, 12 to
1 5 inches in diameter, of the former indicating a nearly vertical
dyke.

(3) The Undu Promontory East of Mount Thuku

East of Mount Thuku the hilly backbone of the promontory
is of much less elevation. About three miles to the eastward the
highest hill is 630 feet, and thence to within a mile or two of
Undu Point the hills retain a height of 400 to 500 feet.

(a) The north coast between Mount Thuku and the coast village
of Nuku-ndamu. — On this stretch of coast, about five miles in
length, the shore-cliffs are composed of white and pale-yellow,
coarse and fine stratified pumice-tuffs, the beds being either hori-
zontal or with a gentle dip northward. They are as a rule non-
calcareous, and contain some quartz grains and small bits, i to 3
millimetres in size, of bottle green compact obsidian, much as one
finds in Lipari pumice-tuffs. In general character, both naked-eye
and microscopic, they correspond to the Mount Thuku pumice-
tuffs above described. Large blocks of basic rocks are occasion-
ally to be observed on this coast, sometimes probably indicating
dykes, but in one place near Mount Thuku forming an agglomerate.

232 A NATURALIST IN THE PACIFIC chap.

The rock is a dark-grey augite-andesite with a specific gravity of
277. It is compact and has a hemi-crystalline groundmass.^

{b) The south coast between Mount Thuku and Moala, a distance
of about five miles. — Pumice-tuffs and agglomerates are displayed
at the coast, the former often bedded and in one place having a
dip of 35 or 40 degrees to the north, A quartz-porphyry, some-
what banded and a little altered, and displaying rounded quartz
crystals 3 or 4 millimetres in size, is the prevailing massive rock
exposed on the hill-slopes and occasionally at the coast. It is
well exhibited about a mile east of Mount Thuku. Blocks of a
grey oligoclase-trachyte also occur. These rocks are described on
pages 308, 309.

{c) The terminal portion of the promontory from Nuku-ndamu
and Moala to Undu Point. — The same pumiceous tuffs, usually
non-calcareous, form the shore-cliffs on the south coast from Moala
to Mr. Bulling's station at Ndothiu, which lies about 2 miles from the
point. On the corresponding part of the north coast between Nuku-
ndamu and Ndothiu these tuffs are often calcareous ; and near the
first-named place they contain sub-angular bits of coral of the size
of a walnut. On the beach at Vunikondi in this locality they are
overlain by nearly horizontal beds of .basic lava, the upper sur-
face of which when exposed displays the smooth, " ropy " crust
of a lava flow. The rock is a dark slightly vesicular augite-
andesite, hemi-crystalline in structure, and containing a fair amount
of residual glass.^ Since the underlying tuffs were evidently
deposited on a sea-bottom, it follows that this is a submarine
flow. I intended to revisit this locality, but was prevented. A
detailed examination of it would be worth undertaking.

From Ndothiu to Undu Point, about 2 miles distant, the
interior of the promontory has an undulating surface, the elevation
being usually 200 or 300 feet and rising to 400 feet. On the
coasts are exposed bedded pumiceous tuffs, steeply inclined and
usually calcareous. As displayed in the hill-slopes of the interior
they are horizontally stratified and as a rule non-calcareous.
These deposits sometimes exhibit a spheroidal arrangement indi-
cative of the proximity of a dyke. In one or two places at the
coasts occur basic agglomerates, formed of the same augite-andesite

^ Referred to genus 13 of the augite-andesites. The felspar-lathes average
"I mm. in length, and there is a Httle interstitial glass.

2 Referred to genus 16 of the augite-andesites. There are two sets of felspar-
lathes in the groundmass ; the larger, '23 mm. long, are more or less parallel ;
the smaller, "04 mm, long, form a plexus.

XVI UNDU PROMONTORY 233

lava-rock of which the Vunikondi beds are composed, but scori-
aceous and containing more glass in the groundmass. In the
hand-specimen beside me, the steam cavities are of all sizes,
from that of a pin-prick to a third of an inch (8 mm.) and are
generally elongated.

A careful search of the tuff-deposits in this part of the Undu
promontory ought to result in the discovery of remains, both ot
plants and of marine mollusks, Mr. Chalmers informed me that
fossilised tree-trunks occur on the coast near Vunikondi ; but I was
unfortunately not able to discover them.

Brief Summary of the General Characters of the
Undu Promontory from Thawaro and Tawaki to Undu
Point. — One suggestive negative feature of this region is to be
found in the absence, as far as I could ascertain, of any trace of a
crater. Here also, as in the area of acid rocks extending westward
along the north side of the island to near Lambasa, hot springs are
not to be found. The prevailing rocks are in the first place the
pumice-tuffs, which not only as a rule form the coast-cliffs, but
occur inland as high as the summit of Mount Thuku almost 1,300
feet above the sea. They were probably in great part ejected
from sub-aerial vents, though no doubt, as in the vicinity of Undu
Point, they were often deposited under the sea. The acid and
basic tuffs in the vicinity of Tawaki and Thawaro are, as I imagine,
largely derived from marine degradation. Next to the pumice-
tuffs, massive quartz-porphyries and oligoclase-trachytes are the
characteristic rocks. They are probably in most cases intrusive,
and present themselves sometimes as vertical columnar dykes,
evidently of considerable dimensions.

The basic rocks, however, are not unrepresented. They occur
in one or two places as agglomerates, as in the vicinity of Mount
Thuku on the north coast and near Undu Point ; whilst they form
" flows " overlying the pumiceous tuffs at Vunikondi. Occasional
blocks lying on the surface on the north coast are indications of
dykes. The basic rocks, nevertheless, take a very secondary part
in the composition of the Undu Promontory. They are in most
cases to be referred to the augite-andesites with a specific gravity
2'6 to 277 ; but some, as in the case of those forming the agglom-
erates of Thawaro Peak, are hypersthene-augite andesites with
specific gravity of about 2"5. Olivine-basalts are not represented.

234 A NATURALIST IN THE PACIFIC ch. xvi

The vents, from which the materials forming this promontory
were ejected, were arranged in a single straight line for a length of
14 miles. Along this linear fissure, which was probably submarine,
vents were at different times formed ; and though owing to sub-
aerial and marine degradation the present surface has been since
shaped and reshaped, their situation may still be recognised in the
" necks " of tuff and agglomerate that form the peaks, and in
the large dykes or sills of quartz-porphyry and oligoclase-trachyte.

CHAPTER XVII

THE VOLCANIC ROCKS OF VANUA LEVU

The varied character of the volcanic rocks in my collection is
brought out in the following Table, where I have grouped about
400 rock-sections, excluding those of the tuffs and finer detrital
deposits. The small proportion of plutonic rocks should be noted.

Olivine-basalts 23 per cent.

Augite-andesites 40 ,, >,

Hypersthene-augite-andesites 17 ., ,,

Acid andesites, including hornblende and quartz-

andesites, &c 12 „ „

Oligoclase-trachytes, quartz-porphyries or rhyohtes . 6 ,, ,,

Hypersthene-gabbros and diorites 2 „ „

100

In order to avoid the necessity of frequently describing rocks
of the same type it has been found requisite to devise a method of
classification. In carrying out this somewhat laborious task I have
often been surprised at the readiness with which rocks, the relations
of which had been previously very difficult to ascertain, fell into
their place in the scheme. Although many of my uncertainties
have been thus removed, a large number of doubtful points remain.
I venture to think, however, that others may be able to employ and
also to extend the method of classification here employed.

The general plan followed has been worked out in detail for the
olivine-basalts and the pyroxene-andesites of the more basic type ;
whilst lack of materials has prevented its further elaboration in the
case of the acid andesites, oligoclase-trachytes, quartz-porphyries,
&c. The treatment of all the classes has been uniform, the scheme
being the same whether applied to a basalt or to a dacite.

In describing the general method I will take the Augite class.
As will be seen in the Synopsis that follows, this class is first

236 A NATURALIST IN THE PACIFIC chap.

divided according to the absence or presence of a groundmass into
two sub-classes, the first referring to the plutonic rocks, which,
however, are not represented in my collection, the second com-
prising the augite-andesites which make up 40 per cent, of the
total. These andesites are again divided into four orders, according
as the groundmass presents parallel or non-parallel felspar-lathes, or
short and stout felspars (orthophyric), or displays a felsitic character.
The last two orders are practically unrepresented here, though many
examples of them are found amongst the more acid andesites.
Each order is then split up into three sub-orders depending on the
nature of the pyroxene of the groundmass, whether granular,
prismatic, or ophitic.

Each sub-order is broken up into two sections, one displaying
plagioclase-phenocrysts, the other without them, or possessing very
few of them. The first section is divided into two genera, according
to the character of the plagioclase-phenocrysts, whether glassy or
opaque, the second genus often comprising rocks allied to the
porphyrites. The second or aphanitic section is subdivided into
two genera according to the character of the pyroxene-phenocrysts ;
in the one case they are macroporphyritic ; in the other they are
either small or absent. The genera are split into four species
according to the length of the felspar-lathes, a method which
readily separates out the doleritic rocks. In cases where the
materials are abundant, the genera have been first divided into
porphyritic and non-porphyritic sub-genera, based on the macro-
porphyritic or the micro-porphyritic character of the plagioclase-
phenocrysts, when present. The species can be also split into sub-
species, according to the degree of basicity of the rocks, as indicated
by the specific gravity.

This method is fully worked out in the later pages and need
not be further described here. With abundant material from
different regions it appears to me that a ready mode is here afforded
of assigning to a rock its place in the scheme. In this way it would
be possible to follow the systematist in his method of comparing
plants and animals from different localities. To facilitate this end,
I have suggested in the synopsis the employment of abbreviations,
so that the description of the critical characters of a rock can be
condensed into a formula capable of easy interpretation.

As an example of the use of these abbreviations I will take the
instance of a common form of augite-andesite which is represented
by the^ formula : — " Plag^ aug, matr, Jiu, gran, non-phen, parv, 'l-^
mm." This is the formula for an aphanitic augite-andesite, and it

xvn CLASSIFICATION OF VOLCANIC ROCKS 237

signifies that it is a rock of the plagioclase-augite class possessing
a groundmass showing parallel felspar-lathes (between -i and
•2 mm, in average length) and granular pyroxene, and displaying
no phenocrysts of plagioclase or only a very few of small size,
whilst pyroxene phenocrysts if present are micro-porphyritic.

As another example the following formula for a type of
porphyrite found in this island may be given : — Plag^ hypersth-augy
matr, orth, prism, phen, opac. This is an andesite in which rhombic
and monoclinic pyroxene are associated both in the phenocrysts
and in the groundmass where the pyroxene is prismatic and not
granular. The plagioclase phenocrysts are opaque and the felspars
of the groundmass are of the orthophyric type.

There are one or two points that require further reference. In
the first place the early employment in the scheme of the characters
of the felspars of the groundmass for distinguishing the orders
scarcely seems needed in the cases where they take the lathe-form ;
but the importance of its early use is shown in the acid andesites
where it is certainly of prime importance in an early stage of the
classification to distinguish the rocks by the character of the
felspars of the groundmass, whether lathe-like, orthophyric, or
felsitic. It may also be objected that the two orders obtained by
dividing the lathe group into *' parallel " and " non-parallel "
divisions are not equivalents of the two other orders, the ortho-
phyric and the felsitic. The distinction, however, between the flow
or non-flow arrangement, though in practice not always readily
established, is a far-reaching one. On d. priori grounds the first
division might be expected to have no plutonic equivalent ; whilst
in the second division, it is easy to trace the gradations through the
doleritic stage, where the felspar-lathes are very large, to the
granitoid condition. Then, again, the ophitic habit is as a general
rule confined to rocks with a doleritic or semi-doleritic groundmass,
where the felspar-lathes are coarse and form a mesh-work. Two
quite distinct lines of development unite in the felspar-lathes and
begin to diverge with the difference in their arrangement in the
groundmass.

The nature of the difference between the flow and non-flow
arrangement of the felspar-lathes is well brought out in some dykes
of basalt and augite-andesite that I examined in this island and
also in the Valle del Bove on the Etna slopes. In the outer vitreous
portion the felspar-lathes, which are fairly well represented, are all
about the same length and are more or less parallel with the sides
of the dyke. In the central more crystalline portion two sets of

238 A NATURALIST IN THE PACIFIC chap.

lathes can be distinguished, one (A) corresponding in the average
length and in the flow-arrangement with the lathes of the borders,
the other (B) being about half the length and forming a plexus
between the larger parallel lathes. Those of the A set, which are
those that usually catch the eye in a section, are contemporaneous
in their origin with those in the margins of the dyke ; whilst those
of the B set have been subsequently formed. In the preliminary
" stiffening " of the first stage of consolidation, the whole mass of
the dyke would be affected. To this stage the lathes of the A set
belong ; whilst to the later stage of con-
solidation which would proceed much more
slowly in the interior than at the margins of
the dyke, the lathes of the B set are to be
referred. This distinction so plainly illus-
trated in a dyke must be postulated for all
intrusive masses ; but I have not yet found it
Centre possible to make much use of it. Much ground

Diagram illustrating the will have first to be cleared before it can be
kthesTn a^dykeT^' safely employed, since it is apparent, for in-
A, long and parallel, Stance, that there are often all gradations in
dispersed through the ^ gij^jg between a lathe and a phenocryst,
£, short and non- and that the term "phenocryst" is applied
parallel and found ^q crystals having very different histories.

only in the centre. / ^ / ,..,,.

With regard to the ophitic habit of some
of the basaltic rocks the following conclusions may be drawn :

(a) Typical ophitic " plates " are not very common in the slides.
More frequently the habit of the pyroxene is semi-ophitic.

(d) This character is as a general rule associated with the
plexus or non-fluidal arrangement of the felspar lathes.

(c) The felspar-lathes are nearly always large, frequently
averaging more than '2 mm. in length. This coarse doleritic
groundmass is almost diagnostic of an ophitic rock.

It is not always possible to allow for the influence of locality in
drawing up such a classification as this, since it is well known that
in each volcanic region the rocks have a particular facies recognis-
able in hand-specimens as well as in the slide, though it is not easy
to express such a distinction in a definition. Perhaps this is
represented in " adaptation " as we find it in the organic world, and
the question arises as to the value of such characters for critical
purposes. Regional variation plays such an important part that it
cannot be ignored in rock-classification.

XVII

CLASSIFICATION OF VOLCANIC ROCKS

239

SYNOPSIS
I. Class. — Olivine Rocks {Flag., oHv.).

Sub-class.

Division.

Order.i

I.
No groundmass

{non-matr.)

LlMBURGITES,

(Not represented in collection.)

Peridotites,

Olivine Gabbros,

etc.

I.

Felspar lathes not in flow-arrange-

r ^•

ment (non-flu.).

Olivine abundant

-

(cop.)

2.

Felspar lathes in flow-arrange-

2.

^ ment (flu.).

Groundmass (matr.)

Olivine-basalts.

Felspar lathes not in flow-arrange-

2.

ment (nan flu.).

Olivine relatively

I, scanty (pauc. ).

4-
Felspar lathes in flow-arrange-
ment (flu.).

* Each division would theoretically also possess an orthophyric and a felsitic
order ; but these orders are not represented in my collection and need only be
mentioned.

IL Class.— AuGiTE Rocks {Flag., aug.).

Sub-class.

Order.

I.

No groundmass (non-matr. )

Gabbros, in part.

2.

Groundmass (mair.)

Basaltic Andesites ;

Augite-andesites ;

Pvroxene-andesites

in part.

Not represented in collection.

I.
Felspar lathes not in flow-arrangement (nonflu. ).

2.

Felspar lathes in flow-arrangement (flu. ).

3.

Felspars short and broad (orthophyric, ofih.).^

4-
. Groundmass felsitic (fels.).^

^ Not represented in the collection.

240

A NATURALIST IN THE PACIFIC

CHAP.

III. Class. — Hypersthene-Augite Rocks {Flag.,
hypersth.-aug.).

Sub-class.

Order.

I.

No groundmass {non-ma/r.)
Gabbros, in part. j

i

2.

Groundmass (matr.)
Pyroxene- AN DEsiTES, in part.

Represented by the Hypersthene-gabbros in
collection.

I.

Felspar lathes not in flow-arrangement (non-flu. ).

2.

Felspar lathes in flow-arrangement {flu. ).

3-

Felspars of the groundmass short and broad
(orthophyric, orth.).

4-
Groundmass granular or presenting a mosaic

(felsitic, fels. ).

fIV. Class. — Hypersthene Rocks.

V. Class. — Hornblende-Hypersthene Rocks.
I VI. Class. — Quartz-Hornblende-Hypersthene Rocks or
Dacites.

These last three classes are merely provisional. They include
the Acid Andesites of Vanua Levu, which are all characterised by
the prevalence of rhombic pyroxene amongst the phenocrysts and
by its predominance or rather by its usually exclusive occurrence
in the groundmass. All the classes are capable of being split up
into two sub-classes and four orders as in the case of the third class.
The characters of these rocks are given in Chapter XXI.

VII. Class. — Hornblende Rocks.

In this class are included those rocks where hornblende is the
only ferro-magnesian mineral. It is only represented by two
diorites described on page 251.

VI 1 1. Class. — Oligoclase-Trachytes.
IX. Class. — Quartz-porphyries and
Rhyolites

Described in
Chapter XXI.

XVII

SYNOPSIS

241

First Order of the Olivine Basalts.

Characters. — Olivine in abundance. Felspars of the groundmass
not in flow-arrangement.

Formula. — Oliv., matr., cop., non-flu.

Sub-order.

Pyroxene

of the

groundmass.

I.

Granular
(gran. )

Prismatic
{prism.)

3-. .
Ophitic
{oph.)

Section.

Presence or
absence of plagio-
clase phenocrysts.

Plagioclase

phenocrysts

{phen.)

No plagioclase
phenocrysts
(non-phen. )

5. Phen. .

6. Non-phen.

Genus.

Character

of the

phenocrysts.

Glassy plagioclase

phenocrysts

{vitr. )

Opaque plagioclase

phenocrysts

[opac. )

Large phenocrysts
of olivine and
pyroxene, over
2 mm. {magn.)

4-

Small phenocrysts

of olivine and

pyroxene under

2 mm. Pyroxene

scanty and often

absent (parv. )

5. Vilr. .

6. Opac.
7 Magn.
8. Parv.

9. Vitr. .

10. Opac.

11. Magn.

12. Parv.

Species

•I — '2 mm.

Number of
specimens.

Not repre-
sented.

{Not repre-
sented.

/ Not repre-
\ sented.

242

A NATURALIST IN THE PACIFIC

CHAP»

Second Order of the Olivine-Basalts.

Characters. — Olivine in abundance. Felspars of the groundmass
in flow-arrangement

Formula. — Oliv.^ matr., cop., flu.

Sub-order.

Pyroxene

of the

groundmass.

4-

Granular

(gran. )

Prismatic
{prism.)

6.

Ophitic
{oph.)

Section.

Presence or
absence of plagio-
clase phenocrysts.

7-

Plagioclase

phenocrysts

(phen.)

No plagioclase
phenocrysts
(non-phen. )

9. Phen. . .
ID. Non-phen. .

11. Phen. . .

12. Non-phen. .

Genus.

Character

of the

phenocrysts.

13-

Glassy plagioclase

phenocrysts

{vih'. )

14.

Opaque plagioclase

phenocrysts

{opac. )

15-

Large phenocrysts

of olivine and

pyroxene, over

2 mm. [magn.)

16.

Small phenocrysts

of olivine and

pyroxene, under

2 mm. Pyroxene

scanty and often

absent (parv.)

17. Vitr.

18. Opac

19. Magn. . . .

20. Parv

21. Vitr

22. Opac

23. Magn

24. Parv

Species.

Length

of felspar

lathes.

Number of
specimens.

Not repre-
sented.

Not repre-
sented.

XVII

SYNOPSIS

243

Third Order of the Olivine-Basalts.

Characters. — Olivine scanty. Felspars of the groundmass not
in flow-arrangement.

Formula. — Oliv., matr., pauc, non-flu.

Sub-order.

Pyroxene

of the

groundmass.

7-
Granular
{gran.)

Prismatic
{prism.)

9-. .
Ophitic

{opk.)

Section.

Presence or
absence of plagio-
clase phenocrysts.

?3-

Plagioclase

phenocrysts

{phen.)

14.

No plagioclase

phenocrysts

{non-phen.)

' 15. Phen. .

16. Nonphen.

17. Phen.

^ 18. Nonphen.

Genus.

Character

of the

phenocrysts.

c 25.

Glassy plagioclase

phenocrysts

{vitr. )

26.

Opaque plagioclase

phenocrysts

{opac. )

27.

Large phenocrysts

of olivine and

pyroxene, over

2 mm. {magn.)

Species.

Length of
felspar lathes
and prisms.

28.

Small phenocrysts
of olivine and some-
times pyroxene,
\. under 2 mm. {parv. )

29. Vitr. .

30. Opac.

31. Magn.

32. Parv.

33. Vitr.

34. Opac. .

35. Magn.

36. Parv.

Number of
specimens.

I

5

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

3
I
2

Not repre-
sented.

Not repre-
sented.

R 2

244

A NATURALIST IN THE PACIFIC

CHAP.

Fourth Order of the Olivine-Basalts.

Characters. — Olivine scanty. Felspar-lathes of the groundmass
in flow-arrangement.

Formula. — OHv.^ matr., pauc.^flu.

Sub-order.

Pyroxyene

of the

groundmass.

Section.

lO.

Granular
(gran. )

II.
Prismatic
( prism. )

12.

Ophitic
{oph.)

Presence or
absence of plagio-
clase phenocrysts.

Genus.

Character

of the

phenocrysts.

19.

Plagioclase

phenocrysts

{phen.)

20.

No plagioclase

phenocrysts

( tioji-phen. )

'21. Fhen.

22. Non-phen.

37- .

Glassy plagioclase

phenocrysts
( vitr. )

38. .
Opaque plagioclase
phenocrysts
{opac. )

39-

Large phenocrysts

of olivine and

pyroxene, over

2 mm. {inagn.)

40.
Small phenocrysts
of olivine and some-
times pyroxene,
^ under 2 mm. {pai'V.)

41. Vitr. .

42. Opac.

43. Magn.

44. Parv.

Species.

Length

of felspar

lathes.

Number of
specimens.

•02 — "I mm.

12
6

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

XVII

SYNOPSIS

245

First Order of the Augite-Andesites.

Characters. — Felspar lathes or prisms of the groundmass not in

flow-arrangement.

Formula. — Aug., matr., non-flu.

Sub-order.

Section.

Genus.

Species.

Number of

Pyroxene

Presence or

Character

Length of

specimens.

of the

absence of plagio-

of the

felspar lathes

groundmass.

clase phenocrysts.

phenocrysts.

and prisms.

i ^'

f '02 — •! mm.

9

Glassy plagioclase

•I--2 „

5

Plagioclase

phenocrysts

1 •2--3 .,

4

{^vitr. )

I •3--5 ..

phenocrysts
{phen.)

2.

[ '02 — •! mm.

6

Opaque plagioclase

•I — -2 ,,

4

phenocrysts

i •2--Z „

3

I.

V. [ppac. )

[ •3--5 M

3

Granular

f^gran.)

/ 3-

2.

Large phenocrysts
of augite, over
2 mm. (magn.)

)

/ Not repre-
\ sented.

No plagioclase

\ 4.

phenocrysts

\non-phen. )

Small phenocrysts

f -02 — "I mm.

of augite, under

J -i-'z „

3

2 mm., or none

1 2— 3 ..

I

\ {parv.)

I '3— 5 »

2

'3. Phen. . . .

i 5. Vitr. ...

/ '02 — 'I mm.
\ •I--2 „

I
2

2.

[ 6. Opac

•I— -2 „

2

Prismatic

^ prism. )

4. Noii-phen. .

J 7. Magn. . . .
[ 8. Pa>-v

1

f '02 — "1 mm.

/ Not repre-
\ sented.

I

/• 9. Fiir

J -I — '2 ,,
1 -2- -3 „

3

4

' 5. Phen. . . .

■

I '3— -5 M

7

3. .

Ophitic

.

V 10. Opac

/ '2 — '3 mm.
I •3-'5 „

I

I

i^oph.)

, 6. Non-phen. .

fix. Magn.

\ 12. Parv

f -2— -3 mm.
I -3— "5 „

3
3

246

A NATURALIST IN THE PACIFIC

CHAP.

Second Order of the Augite-Andesites.

Characters. — Felspar-lathes of the groundmass in flow-
arrangement.

Formula. — Au^;:, matr.^flu.

Sub-order.

Pyroxene

of the

groundmass.

Section.

Presence or
absence of plagio-
clase phenocrysts.

Genus.

Character

of the

phenocrysts.

Speoes,

Length of
felspar lathes
and prisms.

Number of
Specimens.

4-
Granular
{gran. )

Prismatic
{prism.)

Plagioclase

phenocrysts

{phen.)

No (or very few
and small)
plagioclase
phenocrysts
(non-phen. )

g. Fhen.

ID. Non-phen.

^3-
Glassy plagioclase
phenocrysts
{vitr, )

14.
Opaque phenocrysts
of plagioclase
{opac. )

15-

Large phenocrysts

of augite, over

2 mm. (magn.)

16.
Small augite pheno-
crysts, under 2 mm.
or none {parv.)

17. Vitr.

•I mm.
•2 „
•3 »

•5 »

•I — "2 mm.

f II. Phen. . .

6.

Ophitic
{oph.)

12. Non-phen. .

18. opac. .

19. Magn.

20. Parv.

21. Vitr. .

22. Opac.

23. Mapt.

24. Parv.

•02-
•I-

•I mm.
•2 ,,

10

ID

4
I

Not repre-
sented.

12

14

4

3

/ Not repre-
\ sented.
/ Not repre-
\ sented.

4

4

Not repre-
sented.

Not repre-
sented.

XVII

SYNOPSIS

247

First Order of the Hypersthene-Augite Andesites.
Characters. — Felspar-lathes not in flow-arrangement.

Formula. — Hypersth.-aug.^ matr., non-flu.

Sub-order.

Pyroxene

of the

groundmass.

Granular
(gran.)

2.

Prismatic
{prism. )

3-

Ophitic

(oph.)

Section.

Presence or
absence of plagio-
clase phenocrysts.

Plagioclase

phenocrysts

{phen.)

No plagioclase
phenocrysts
(non-phen.)

'3. Phen.

4. Non-phen.

Genus.

Character

of the

phenocrysts.

Glassy plagioclase

phenocrysts

(vitr. )

Opaque phenocrysts

of plagioclase

[opac. )

f 3-

Large phenocrysts

of pyroxene, over

2 mm. (magn.)

Small pyroxene

phenocrysts, under

2 mm. , or none

(parv.)

Species.

Length

of felspar

lathes.

•02 — 'I mm.
•I— -2 „

•3— -5 mm.

Number of
specimens.

12
4

/ Not repre-
\. sented.

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

248

A NATURALIST IN THE PACIFIC

CHAP.

Second Order of the Hypersthene-Augite Andesites.

Characters. — Felspar-lathes in flow-arrangement.

Formula. — Hypersth.-aug., matr., flu.

Sub-order.

Pyroxene

of the

groundmass.

4-

Granular

(gran.)

. 5-
Prismatic
(prism. )

6.

Ophitic

(oph.)

Section.

Presence or
absence of plagio-
clase phenocrysts.

Plj^oclase

phenocrysts

(phen.)

No plagioclase
phenocrysts
{non-phen.)

9. Phen.

10. Non-phen.

Genus.

Character

of the

phenocrysts.

^3- .
Glassy plagioclase
phenocrysts
{vitr. )

14.
Opaque phenocrysts
of plagioclase
^{opac.)

{ ^5-

Large phenocrysts

of pyroxene,
over 2 mm. {i/iagn.)

16.

Small pyroxene
, phenocrysts, under
2 mm., or none
(parv.)

Species.

Length

of felspar

lathes.

•02-
•I-

•I mm.
•2 „

Number of
specimens.

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

Not repre-
sented.

4
2

Not repre-
sented.

Third Order of the Hypersthene-Augite Andesites.

Characters. — Felspars of the groundmass short and stout

(orthophyric).

Formula. — Hypersth.-aug., matr., orth.
Remarks. — The same classification is to be employed here as in
the case of the two previous orders, but as the rocks in my collec-
tion that belong to this order are not numerous (nine sections), it
will be sufficient to refer to the general remarks on the order
on p. 290.

XVII

PLUTONIC ROCKS

249

Fourth Order of the Hypersthene-Augite Andesites.

Characters. — Groundmass presenting a rudely granular
appearance or blurred mosaic (microfelsitic).

Formula. — Hypersth.-aug.^ matr.yfels.

Remarks. — My sliced specimens (five) are too few for the
elaboration of this order to which the classification employed for
the other orders is scarcely applicable. This is due to the partial
decomposition or imperfect development of the pyroxene of the
groundmass. The general characters of the order are given
on p. 291.

The Plutonic Rocks.

These rocks are very infrequent and are for the most part
hypersthene-gabbros or norites, with a few representatives of
diorites^ without pyroxene. True plutonic rocks did not come
under my observation in the western half of the island (west of
Lambasa and Savu-savu), those of Mount Thoka-singa in the
Ndrandramea district making the nearest approach (see p. 302).
The localities in which they were found are below enumerated : —

No.

Nature of rock.

Locality.

Mode of occurrence.

Page.

I

Hyperslhene-gabbro

Avuka Range between Lam-
basa and Mbuthai-sau

Probably forms the
axis of the range.

180

2

Ditto

Nawi, at the head of the
Vui-na-savu River

Deep-seated.

211

3

Ditto

Valanga Range between
Savu-savu and Natewa
Bays

Probably forms the
axis of the range.

182

4

Ditto

Ridge at the head of Na
Kula valley between Savu-
savu and Natewa Bays.

Ditto.

184

5

Hornblende-gabbro.

Ditto

Ditto.

184

6

Diorite

Vunimbua River, oa south
side of the Mariko Range

Loose blocks in
river-bed.

182

7

Ditto

Coast cliffs west of the Salt
Lake Passage

Large block in ag-
glomerate-tuff.

193

* I apply the term " diorite " to granitoid rocks formed entirely of plagioclase
and hornblende.

2SO A NATURALIST IN THE PACIFIC chap.

The Hypersthene-GABBROS. — These rocks also contain
monoclinic pyroxene, and are the plutonic equivalents of the
hypersthene-augite-andesites which as a rule prevail in the locali-
ties where these rocks occur. They are usually dark grey or steel-
grey in colour with a specific gravity ranging from 27 to 2'84 and
have a granitoid aspect. The following characters are common to
all the specimens.

. They display a mixture of plagioclase and pyroxene, the last
filling up the spaces between the felspars and apparently of later
formation. The plagioclase crystals, which are i to 2 mm. in
size, are opaque ; and since they are traversed by numerous fine
fissures filled with dust-like decomposition products, their appear-
ance is often semi-saussuritic. They are much cross-macled, are
at times zoned, and give lamellar extinctions of andesine-labrado-
rite (20° — 30°). . . . The pyroxene includes both the rhombic and
monoclinic forms, the last with extinction angles of over 30°. They
may be associated or may occur as separate crystals, the rhombic
prevailing in the less basic and the monoclinic in the more basic
rocks. The rhombic pyroxene is usually more or less converted
into bastite which by further change passes into a chloritic
material ; whilst the augite sometimes undergoes the diallagic
change resulting from schillerisation.

Some special features are presented by rocks from different
localities. That from Nawi is most basic and looks like a diallage-
gabbro. That from the Valanga Range (sp. gr. 275) contains
some quartz, apparently secondary and filling up the interspaces.
The rock from the Na Kula Ridge shows traces of a groundmass ;
but it comes near the plutonic type.

A HORNBLENDE-GABBRO. — This granitoid rock, which is from
the Na Kula Ridge, has a specific gravity of 272. Hand-speci-
mens display large porphyritic crystals of hornblende (7 mm. long)
in a base of opaque felspar and smaller hornblende. In the slide
we observe besides the large crystals of plagioclase and hornblende
a little pyroxene ; but the mass of the rock consists of greenish-
brown hornblende, plagioclase, and some secondary quartz, form-
ing a coarse mosaic with a " grain " of about a millimetre. The
hornblende is displayed in regular hexagonal sections, markedly
pleochroic, and gives extinctions up to 12°. It shows no dark
resorption borders ; and the larger porphyritic crystals have the
same characters. Almost all the plagioclase of the rock is
traversed by numerous fine fissures, and often acquires a semi-
saussuritic appearance from the presence of dust-like decom-

XVII PLUTONIC ROCKS 251

position products. The lamellar extinctions indicate andesine-
labradorite. The quartz occurs mostly in nests. The pyroxene
is formed of large grains of both the monoclinic and rhombic
types.

The Diorites. — The rock forming blocks in the Vunimbua
River has a specific gravity of 278 to 2*8. It is a pretty rock
showing long black blades of hornblende, 10 mm. in length, in an
opaque felspar base. In the slide the hornblende, which is dark
brown and markedly pleochroic, shows six-sided sections with
characteristic prismatic cleavage lines, the longitudinal sections
giving extinctions up to 15°. The borders in some cases display
traces of resorption. The felspar (plagioclase) is in the form
usually of broad regular crystals, 3 to 4 mm. in size, and giving
■extinctions of andesine-labradorite (28°) ; they are " clouded "
through the presence of fine alteration products associated with
numerous fissures. The relation between the hornblende and
the plagioclase is not constant. This appears to be partially due
to the occurrence of traces of a groundmass.

The diorite forming blocks in the agglomerate of the coast
cliffs, west of the Salt Lake Passage, is a remarkable rock showing
large blackish hornblende crystals, in the shape of blades 25 mm.
long and 3 or 4 mm. broad, set in a base of opaque plagioclase
felspar which surrounds the hornblende. The last-named is deep-
brown, very pleochroic, yields extinctions up to 22°, and displays
but little evidence of resorption. The plagioclase is irregular
in shape and exhibits broad lamellae giving extinctions of acid
labradorite (28° — 30°). It is traversed by numerous fine fissures
filled with decomposition products and contains abundant dust-like
materials. (Spec. grav. 2-8),

CHAPTER XVIII

THE VOLCANIC ROCKS OF VANUA LEVU {continued)

Olivine Class
Sub-Class II

The Olivine Basalts {Flag, oliv, matr.)

This sub-class includes the plagioclase-olivine-basalts.
Although these rocks are not the most numerous of the basic
rocks, they are well represented in the island, being in great part
confined to the western half, and being especially characteristic of
the districts of Wainunu and Solevu and of the mountains of
Seatura and Naivaka. It will be seen from the Synopsis that
this sub-class is split up into two divisions, according to the
relative abundance of the olivine. Many of the rocks are grey
basalts with the olivine more or less hematised ; but the majority
are blackish with the olivine usually more or less serpentinised.
In the typical blackish rocks there is a little dark opaque inter-
stitial glass. In the grey basalts the groundmass is as a rule
holo-crystalline. The specific gravity ranges generally from
2-8 to 3.

It will be noticed in the scheme that the " prismatic " sub-
orders, where the pyroxene of the groundmass is for the most part
in prisms, are scarcely represented. The " ophitic " sub-orders are
poorly represented, since they only include about 10 per cent, of
the total. The ophitic oHvine-basalts are indeed mostly confined
to the division where the olivine is scanty, and the felspars of the
groundmass are for the most part not parallel, the plexus arrange-
ment, as will be often pointed out, being almost essential for the
development of the ophitic structure. With the basaltic andesites,
which cannot always be sharply separated from the basalts with

CH. XVIII OLIVINE-BASALTS 253

scanty olivine, the proportion of ophitic rocks is much higher,
probably about 20 per cent. The pyroxene in the olivine-basalts
is nearly always augite, intergrowths with rhombic pyroxene being
only occasionally observed.

I. Division of the Olivine-Basalts
Characters. — Abundant olivine.
Formula. — Oliv, matr, cop.

These rocks are characterised by abundant olivine usually as
phenocrysts but sometimes represented in the groundmass. When
a basalt presents much of this mineral in an ordinary hand-speci-
men and displays at least five or six phenocrysts in a slide, it is
placed in this division. Olivine-basalts of this character are well
exhibited in the hills around Solevu Bay and in the neighbouring
Seatovo Range. They are also fairly represented on the northern
slopes of Mount Seatura, on the coast between the Wainunu River
and Nandi Bay, and on the Wainunu basaltic tableland. In the
Ulu-i-ndali Range, which lies east of the Wainunu estuary, they
are especially frequent. Whilst confined mostly to the portion of
the island west of Savu-savu Bay, they occur sporadically in other
localities to the eastward, as in Na Suva-suva Hill and in some
parts of the Natewa Peninsula. The grey basalts, which form one-
third of the total, are chiefly characteristic of the hill of Ulu-i-
ndali, of the Solevu district, and of the northern slopes of Seatura.
Whilst the blackish basalts usually compose the flows, the grey
basalts form dykes and volcanic necks.

Two-thirds of these olivine-basalts belong to the order present-
ing flow-structure and almost all (28 out of 29) are included in the
sub-order exhibiting granular augite in the groundmass. The
ophitic structure is displayed in only one case ; and the prismatic
form of the augites is never a predominant feature.

I. Genus of the Olivine-Basalts
Formula. — OHv, matr, cop, non-flu, gran, phen, vitr.

Characters. — Abundant olivine. Felspar-lathes of the
groundmass not in flow arrangement. Pyroxene of the ground-
mass granular. Phenocrysts of glassy plagioclase.

Description. — Dark-brown or blackish rocks. Sp. gr. 2-88
to 2*93. Phenocrysts of pyroxene occur in fair quantity in addition

254 A NATURALIST IN THE PACIFIC chap.

to those of the olivine and plagioclase. The groundmass displays
a plexus of felspars and augite-granules with much magnetite in
grains and irregular patches. The interstitial glass is scanty or
almost absent The olivine phenocrysts, of which the larger are
3 to 4 mm. in size, are as a rule hematised at the borders and
in the fissures, and are sometimes partially serpentinised. In
some cases small crystals of olivine are enclosed in the pyroxene-
phenocrysts. The plagioclase phenocrysts do not usually exceed
2 mm. in size. They give lamellar extinctions of 1 5° — 28°, and are
often cross-macled. They generally contain magma-inclusions,
which may be arranged in zones, and they sometimes inclose small
pyroxene crystals. Their borders are often eroded. The pyroxene-
phenocrysts, which frequently are 3 to 4 mm. in size, give
extinctions of 30° and over, and may be described as composed of
brown augite. It is only at times that intergrowths of rhombic
pyroxene occur. They are often twinned and are sometimes eroded
and may contain magma and other inclusions. The felspars of the
groundmass, which for the most part form a plexus, are small and
stout, their average length varying from "oS to '13 mm., whilst they
frequently display lamellar twinning and give extinctions of about
15° (oligoclase-andesine). The pyroxene-granules of the ground-
mass, which are of brown augite, vary in average size from '02
to -04 mm.

Two of the four species, where the felspar-lathes are less than
•I mm. and between "i and '2 mm. in length, are represented in this
collection.

2. Genus of the Olivine-Basalts
Formula. — O/iv, matr, cop, non-flu, gran, phen, opac.

Characters. — Abundant olivine. Felspar-lathes of the
groundmass not in flow-arrangement. Pyroxene of the ground-
mass granular. Phenocrysts of plagioclase opaque white.

Description. — Grey compact-looking rocks ; sp. gr. 2*83 to
2*9. Interstitial glass scanty. The olivine phenocrysts, which
range up to 5 mm. in size, are more or less hematised ; and in
extreme cases of this alteration, where schiller-planes are formed,
the hand-specimen appears to carry brown mica. There are some-
times small grains of olivine ('i mm.) in the groundmass. The
plagioclase-phenocrysts, varying in size from 2 to 4 mm., owe
their opacity partly to their composite character, when they present
an aggregate of smaller clear crystals, and partly to multiple

XVIII OLIVINE-BASALTS 255

macHng. They give extinctions of acid labradorite (25° — 32°),
Pyroxene-phenocrysts, when present, are scanty, pale brown, not
over 2 mm. in size, and give the large extinctions ( + 30°) of augite.
In their absence small augites ("2 mm.) are frequent. Fine
granules ('Oi — "03 mm.) of similar augite, together with magnetite,
abound in the groundmass. The felspars of the groundmass are
fairly stout and lathe-like and show at times a few twin-lamellae
which give extinctions of 13° to 20° (medium andesine).
Species represented :

(a) felspar lathes "i — '2 mm.
W » » '2— '3 „

3. Genus of the Olivine-Basalts
Formula. — Oh'v, matr, cop, non-Jlii, gj-an, non-phen, magn.
Characters. — Abundant olivine. Felspar-lathes of the

groundmass not in flow-arrangement. Pyroxene of the ground-
mass granular. No plagioclase phenocrysts. Large phenocrysts
of olivine and pyroxene over 2 mm. in size.

Description. — A remarkable blackish-grey rock. Although
somewhat scoriaceous, it has a sp. gr. of 2*9 1. It displays large
phenocrysts of olivine and pyroxene, 4 to 8 mm. in size, in a
coarse-textured groundmass of stout felspars, augite granules,
magnetite and a little glass. The olivine is extensively hematised.
The pyroxene phenocrysts are of brownish-yellow augite with
regular outlines and giving angles of extinction up to 40°. The
broad lamellar felspars of the groundmass, which are on the average
•3 to '4 mm. long, give extinctions indicating both acid labradorite
(23° to 28°) and medium andesine (16° or 17°). The abundant
augite-grains average '05 mm. in size ; but the prism form occurs
at times.

The species with felspar-lathes '3 to *5 mm. long is alone
represented.

4. Genus of the Olivine-Basalts
Formula. — Oliv^ matr, cop, non- flu, gran, non-phen, parv.

Characters. — Abundant olivine. In the groundmass the
felspar-lathes are not in flow-arrangement and the pyroxene is
granular. No plagioclase phenocrysts. Small phenocrysts of
olivine and occasionally pyroxene under 2 mm.

Description. — A grey coarse-grained rock. Sp. gr. 29. It
displays abundant small phenocrysts of olivine, all less than a

256 A NATURALIST IN THE PACIFIC chap.

millimetre in size ('2 — "8 mm.), which are hematised in the fissures
and at the borders. The felspar-lathes, which display a few twin-
lamellae giving extinctions of 16° — 18° (medium andesine), vary
greatly in size. The smaller are 'i to '3 mm. and the larger '3 to
•5 mm. long ; but the two are connected by felspars of intermediate
length. The abundant augite granules average '037 mm. in
breadth. Pyroxene phenocrysts are not represented in the slide.
From its coarsely crystalline texture this rock merits the field-name
of a grey doleritic basalt ; and except in the arrangement of the
felspar-lathes it does not differ from the grey doleritic basalts of
genus 16.

12. Genus of the Olivine-Basalts
Formula. — 0/w, matr, cop, non-flu, oph, non-phen, parv.

Characters. — Olivine abundant. Felspars of the ground-
mass not in flow-arrangement. Pyroxene of the groundmass
ophitic or semi-ophitic. No plagioclase phenocrysts. Small
phenocrysts (under 2 mm.) of olivine and occasionally a few of
pyroxene.

Description. — A dark greenish-brown rock, with sp. gr. 2"9i,
showing abundant micro-porphyritic olivine in a groundmass con-
sisting of ophitic pale-brown augite inclosing the felspar-lathes,
together with small olivines, patches of magnetite, and a little
altered interstitial glass. The olivine-phenocrysts are about '5 mm.
in average size and are more or less hematised. The felspar-lathes,
which average '15 mm. in length, often show twin-lamellse that give
extinctions of 23° — 30° (andesine-labradorite).

The species with felspar-lathes "i — '2 mm. long is alone
represented.

13. Genus of the Olivine-Basalts
Formula. — Oliv, matr, cop, flu, gran,phen, vitr.

Characters. — Olivine abundant. Felspars of the groundmass
in flow-arrangement. Pyroxene of the groundmass granular.
Phenocrysts of glassy plagioclase.

Description. — Dark grey or dark brown rocks with sp. gr.
2*88 to 2-99. Phenocrysts of olivine, pyroxene, and plagioclase
occur in a groundmass showing partially parallel felspar-lathes
abundant pyroxene grains, and fine magnetite, residual glass being
scanty or absent. The olivine-phenocrysts do not exceed 3 or

XVIII OLIVINE-BASALTS

257

4 mm. in size and in some rocks are less than i mm. They
are usually more or less serpentinised and hematised at the borders
and in the cracks ; but sometimes they are almost fresh and
present regular outlines. In some rocks the olivine also occurs as
grains ("3 mm.) in the groundmass. When the phenocrysts of
olivine have blackish borders they are surrounded by a halo, as
though the crystal had attracted the magnetite from the groundmass
immediately around. The plagioclase phenocrysts vary from i
to 3 mm. in size. They often contain abundant magma-
inclusions and give lamellar extinctions of 15° to 25° (basic ande-
sine). In some rocks they are rudely parallel. The pyroxene
phenocrysts, which are of pale brownish-yellow augite giving ex-
tinctions of over 30°, do not usually exceed 3 mm. They
present regular octagonal cross-sections and sometimes display
lamellar twinning. Occasionally there is a suspicion of intergrowth
with rhombic pyroxene. The felspar-lathes, which according to
the species' vary much in length, at times show a few lamellae. The
augite grains of the groundmass are abundant and are as a rule
about "02 mm. in size ; but in some rocks they are larger and in
others smaller.

This genus may be divided into two sub-genera, the porphyritic
sub-genus where the felspar phenocrysts are larger than 3 mm., and
the non-porphyritic where they are smaller. All four species, as
indicated by the length of the felspar-lathes, are represented.

14. Genus of the Olivine-Basalts
Formula. — OHv, matr, cop, flu, gran, phen, opac.

Characters. — Olivine abundant. Felspars of the groundmass
n flow-arrangement. Pyroxene of the groundmass granular.
Opaque plagioclase phenocrysts.

Description. — Dark grey rocks, with sp. gr. 2-9 to 2-93,

ihowing phenocrysts of olivine and pyroxene with opaque whitish

)henocrysts of plagioclase in a groundmass of felspar lathes,

)yroxene grains, and magnetite, with occasional fine olivine. The

• ilivine phenocrysts, which are sometimes 5 or 6 mm. in size, are

< -ften deeply eroded. They are at times so extensively hematised
; long the schiller-planes that they appear like brown mica. The
] 'lagioclase phenocrysts owe their opacity in part to their consisting

< f an aggregate of lesser crystals which are clear and glassy and
{ ive lamellar extinctions of 20° to 30° (andesine labradorite).
' 'hey do not usually exceed 3 mm. and are sometimes scanty.

\ S

258 A NATURALIST IN THE PACIFIC chap.

The pyroxene phenocrysts, which are at times infrequent, may be
5 mm. in size. They are of pale yellowish-brown augite, giving
extinctions of 40°. The felspar-lathes are rarely lamellar ; but in
one such case the angle of extinction was 17° (medium andesine).
The grains of augite in the groundmass average "02 mm. in
diameter.

The only species represented is that with the felspar-lathes i
to '2 mm. long.

15. Genus of the Olivine-Basalts

Formula. — Oh'v, matr, cop, flu, g^an, non-phen, magn.

Characters. — Abundant olivine. In the groundmass the
felspars are in flow-arrangement and the pyroxene is granular. No
plagioclase phenocrysts, but large phenocrysts, over 2 mm., of
olivine and pyroxene.

Description. — This genus includes the most basic rocks
represented in my collection. They are compact heavy blackish
rocks with sp. gr. 3 to 3"i, and display large porphyritic crystals of
olivine and pyroxene often 3 or 4 mm. in size. The olivine
phenocrysts may be fairly fresh with clean outlines, or they may be
deeply eroded and stained by iron oxide, or they may be passing into
serpentine. The pyroxene phenocrysts may be either eroded or
possess regular outlines. They are of pale brown augite and give
extinctions over 30°. The pyroxene granules, which average "02
mm. and are very abundant, are of the same augite. The felspar-
lathes are relatively scanty. In the two rocks here included they
average in length '06 mm. and 'oS mm. When lamellae can be
recognised they give extinctions of 30° — 40° (labradorite). The
untwinned lathes give extinctions of 20° — 28° (labradorite).

The only species represented is that with felspar-lathes less
than •: mm. in length.

16. Genus of the Olivine-Basalts
Formula. — OHv, matr, cop, flu, gran, non-phen, parv.
Characters. — Abundant olivine. In the groundmass the

felspar-lathes are in flow arrangement and the pyroxene is granular.

There are no plagioclase phenocrysts ; but there are numerous

small phenocrysts, under 2 mm. in size, of olivine and occasionally

a few of pyroxene.

Description. — As a highly basic genus this ranks next to

the preceding one, the specific gravity of the rocks ranging from

XVIII OLIVINE-BASALTS 259

2"9i to 3 •or. All the four species indicated by the varying length
of the felspar-lathes are represented in my collection. The rocks
of the first two, with the felspars averaging less than 'i mm. and
between 'i and '2 mm., are compact aphanitic basalts, only
displaying an occasional small phenocryst of augite and blackish-
grey or bluish-black in colour. Those of the last two species, with
the average length of the felspar-lathes "2 — "3 mm. and '3 — "5 mm.
respectively, are lightish-grey coarse-textured rocks of the doleritic
type. In all the rocks no pyroxene phenocrysts are displayed
in the slide ; and the olivine phenocrysts, which are very numerous,
do not usually exceed i mm., though occasionally the average
size is i'3 mm., and not infrequently it is only '5 mm. In some
cases where the larger olivine phenocrysts lie athwart the current of
the felspar-lathes, the smaller ('$ mm.) lie with their long axes parallel
to the flow. The olivine is either fresh, or it may be beginning to
serpentinise in the cracks, or it may be in part hematised. The
crystals may have regular outlines, or they may be rounded and
sometimes deeply eroded. The pyroxene granules of the ground-
mass are of pale-brown augite, and average 'Oi to '03 mm. in size.
Occasionally a few prism forms occur, giving extinctions of 30° to
40°. In the case of the more compact rocks, with the felspar-lathes
averaging less than '2 mm. in length, lamellar twinning is but
scantily to be noticed in the lathes, which give extinctions measured
from the long axis of 20° to 25° and by the twin lamellae of 30° to 35°,
indicative of acid labradorite in both instances. With the coarser
doleritic grey basalts, where the felspar-lathes are stouter and have
an average length exceeding "2 mm., lamellar twinning is more
frequent ; the extinctions afforded by the lamellae range between
15° and 25° (medium andesine). Residual glass is scanty in these
rocks, and in the grey dolerites it is often difficult to recognise
any.

2, Division of the Olivine-Basalts
Characters. — Scanty olivine.
Fo RM u LA. — 0/tv, matr, pane,

25. Genus of the Olivine-Basalts

Formula. — Oliv, matr, pauc, non-flu, gran, phen, vitr.

Characters. — Olivine scanty. Felspars (lathes and prisms)
Df the groundmass not in flow-arrangement. Pyroxene of the
jroundmass granular. Glassy plagioclase phenocrysts.

S 2

26o A NATURALIST IN THE PACIFIC chap.

Description. — About two-thirds of these rocks have a common
facies, being closely similar in appearance, brownish-black in colour,
and with spec. grav. usually between 2*84 and 2*92. They belong
to the species with the felspar-lathes 'i to "2 mm. in length. They
are essentially the rocks of the old submarine basaltic flows ; and
they are often columnar, the columns being 2 to 4 feet across.
My remarks will mainly apply to this predominant group.

To the eye they are somewhat compact and show scattered
porphyritic crystals of plagioclase. Intheslide they display numerous
phenocrysts of plagioclase, with a few of olivine and pyroxene, in a
groundmass formed of stout lamellar felspar-lathes and small prisms
forming a plexus with granular augite in the meshes. There is a
good deal of magnetite and generally scanty residual glass. The
plagioclase phenocrysts are usually 2 to 3 mm. in size, but they
may be smaller (i to 2 mm.) or larger (3 to 5 mm. or more) when
the rock has a porphyritic appearance.^ They are often cross-
macled and at times show zoning. In many slides two kinds are
distinguished by the extinctions which indicate in one case medium
andesine(i5° to 22°) and in the other acid labradorite (27° to 32°).
They contain inclusions of the magma and are often eroded. The
pyroxene phenocrysts are of pale brown augite, scanty and small,
and give extinctions of 30° to 40°. They are sometimes twinned
and may be eroded and contain inclusions of the magma. The
olivine phenocrysts, which do not usually exceed 2 or 3 mm., are
mostly rounded, but sometimes have the regular outlines, and are
in various stages of serpentinisation. The felspars of the ground-
mass, which average 'ij mm. in length, are mostly stout and
lamellar ; but they exhibit all transitions from the lathe-shape with
one or two lamellae to broad multi-lamellar prisms where the
breadth is half the length. They give lamellar extinctions averag-
ing 15° to 18° (andesine). The augite granules of the groundmass
are pale brown and average '02 to "03 mm. in size. In a few cases
they are larger ('05 mm.) which is an indication of an approach to
the ophitic type. In most slides occur a few small augites of
prism-form, two or three times the size of the granules, which give
extinctions of over 30°. Where the phenocrysts of augite are very
scanty or absent, there exist large grains ('i mm.) of an inter-
mediate size. The magnetite is often abundant, occurring in
crystals, rods, and irregular masses, the last associated often with

* According to the size of the plagioclase phenocrysts, whether averaging
less than or more than 3 mm. in size, these rocks may be divided into a non-
porphyritic and a porphyritic sub-genus.

XVIII OLIVINE-BASALTS 261

the interstitial glass which is present in small quantities in most
rocks, being greenish or brownish and showing fibrous devitrifi-
cation.

In some localities semi-vitreous rocks referable to this genus are
frequent. This is especially the case in the Naivaka peninsula,
where the rocks show a fair amount of glass in the groundmass,
the porphyritic augite being well developed, whilst the pyroxene of
the groundmass is only in part differentiated. Three of the four
species are here represented. Those with large felspar-lathes
("2 — '3 mm. long) and coarse augite granules ("OS) approach the
semi-ophitic rocks included in genus 33.

26. Genus of the Olivine-Basalts
Formula, — Oliv, matr, pane, non-flu, gran, phen, opac.

Characters. — Olivine scanty. In the groundmass the fel-
spar-lathes and prisms are not in flow-arrangement and the
pyroxene is granular. The plagioclase phenocrysts are opaque.

Description. — Dark grey porphyritic rocks, which, from the
Dpacity of the felspar phenocrysts, look like porphyrites. They
ire not very frequent and occur mostly on the northern slopes of
Mount Seatura. Two different types occur in my collection
A^hich may be regarded as sub-genera. In the most basic kind,
vhere the sp. gr. is 2'86 to 2'89, the plagioclase phenocrysts, 2 to
5 mm. in size, owe their opacity chiefly to their aggregate struc-
ure. They give lamellar extinctions (15° — 30°) of andesine labra-
lorite. Porphyritic olivine is scanty and more or less hematised ;
)ut a fair amount of olivine grains, less than 'i mm., occur in the
; jroundmass. Pyroxene phenocrysts are scanty, but micro-
])Orphyritic pale brown augite ("i mm.) is frequent. In the
iToundmass are found stoutish felspar-lathes, averaging '2 mm.
long, together with an abundance of fine augite granules ('Oi — "02
I im.) and fine magnetite, the residual glass being scanty. ... In
1 tie other type the sp. gr. is 275 ; and the plagioclase phenocrysts
i to 6 mm. in size give extinctions of andesine and acid labra-
( orite (10° — 30°). There is an approach to the orthophyric struc-
t are in the groundmass, as is indicated by the number of short
\ road felspars, averaging '2 mm. in length and giving lamellar
e xtinctions of acid and basic andesine. The granular augite of
t le groundmass is coarse ('04 mm.), and occasional prism-forms
% ive extinctions of 40°.

262 A NATURALIST IN THE PACIFIC chap.

33. Genus of the Olivine-Basalts
Formula. — Oliv, matVy pauc^ non-flu, oph,phen, vitr.

Characters. — Olivine scanty. In the groundmass the fel-
spar-lathes are not in flow-arrangement and the pyroxene is
ophitic or semi-ophitic. Plagioclase phenocrysts glassy.

Description. — These brownish-black rocks are all of the
semi-ophitic type. Although no ophitic " plates " occur in the
slide, the augites of the groundmass have no longer the granular
form, but are large, '08 — "i mm. in size, and tend to invest the
felspar-lathes. The specific gravity ranges from 278 to 2*86. As
in other of the ophitic and semi-ophitic rocks of this collection
(genera 9, 10, 12, of the augite-andesites), the large size of the
felspar-lathes (-2 — -3 mm. long) of the groundmass gives a doleritic
texture in the slide. In most of the other characters these rocks
approach those of genus 25 which possess felspar-lathes more than
•2 mm. in length. But they are more often semi-vitreous, and
display a considerable amount of dark smoky glass showing
numerous magnetite rods and skeletal crystals with fibrous devitri-
fication. The plagioclase phenocrysts, which vary much in size
in different rocks (in some 2 or 3 mm., in others 4 or 5 mm.), give
extinctions of andesine labradorite (20° — 35°). They are often
eroded and contain numerous large black inclusions of the magma.
The pyroxene phenocrysts, which are of pale-brown augite, often
have an aggregate-structure, having been formed in situ.
Others again consist of single crystals and have been much
affected by the magma. The olivine phenocrysts, which are at
times deeply eroded, are generally small and in part serpenti-
nised.

37. Genus of the Olivine-Basalts
Formula. — OHv, matr, pauc, flu, gran, phen, vitr.

Characters. — Olivine scanty. In the groundmass the fel-
spar-lathes are in flow-arrangement and the pyroxene is granular.
Glassy plagioclase phenocrysts.

Description. — Brownish-black rocks which cannot be dis-
tinguished, except in the flow-arrangement of the felspars of the
groundmass, from those described under genus 25. Like them
they enter into the formation of the basaltic plains of Sarawanga
and Mbua and elsewhere. Most of the rocks of this genus group
themselves into one type where the felspar-lathes average in

XVIII OLIVINE-BASALTS 263

length '15 — •21 mm. The sp. gr. is usually between 2'8y and 2*9 1.
Though rarely porphyritic, such rocks display to the eye a few
small scattered glassy phenocrysts of plagioclase and an occasional
grain of olivine. It is to this type of the genus that the following
description applies.

In the thin sections they display small plagioclase phenocrysts,
with a few of olivine and occasionally of pyroxene, in a ground-
mass where the flow-arrangement of the felspar-lathes is well
marked, the rest of the groundmass being made up of granular
augite with magnetite and generally a little residual glass. . . . The
plagioclase phenocrysts do not usually exceed 2 mm. in size and
contain magma inclusions. Two kinds are often indicated in the
same slide by the extinctions, namely, one of medium andesine
(17° — 22°), and the other of acid labradorite (28° — 33°). . . . The
pyroxene phenocrysts are of pale brown augite ; but they are small
(less than 2 mm.), scanty, and often absent when their place is
taken by microporphyritic augite, '2 mm. in size. . . . The olivine
phenocrysts are generally small. Though sometimes showing the
long hexagonal sections, they are often rounded and more or less
serpentinised. . . . The felspars of the groundmass present more
typical lathes than are to be observed in the non-parallel felspars of
the rocks of genus 25. The twin-lamellae, when present, are fewer ;
but give similar extinctions (15° — 21°) of medium andesine. . . . The
augite granules are, as a rule, "02 or '03 mm. in diameter ; but
occasional more prismatic forms occur, two or three times the
length, which give extinctions of over 30°. The magnetite is
abundant, and the scanty interstitial glass is green or brown and
displays fibrous devitrification.

The following three species, as indicated by the length of the
felspar-lathes, are represented in my collection :

(fl) -02 — -I mm. (d) -I — -2 mm.

(c) '2 — "3 mm.

38. Genus of the Olivine-Basalts
Formula. — OHv, matr, pauc, Jlu, gran, phen, opac.

Characters. — Olivine scanty. In the groundmass the fel-
spar-lathes are in flow-arrangement and the pyroxene is granular.
Opaque plagioclase phenocrysts.

Description. — Grey rocks, sp. gr. 278 to 2-83, showing small
opaque porphyritic crystals of plagioclase with a few phenocrysts

264 A NATURALIST IN THE PACIFIC chap.

of olivine and pyroxene in a groundmass of parallel felspar-lathes,
augite granules, and magnetite, with very scanty, if any, inter-
stitial glass. . . . The plagioclase phenocrysts, 2 to 3 mm. in size, are
often aggregates of smaller crystals. They contain colourless
granular inclusions and are sometimes zoned, giving extinctions of
medium andesite(i5° — 18°), and of andesine labradorite (25° — 29°).
. . The pyroxene phenocrysts are pale-brown, scanty, 2 to 3 mm. in
size, often twinned and give the large extinctions of augite. . . . The
olivine phenocrysts, which do not exceed 2 or 3 mm., are deeply
eroded by the magma and are hematised and schillerised. Small
grains also occur in the groundmass. . . . The felspar-lathes, which
in the species here represented average "15 mm. in length, are stout
and give lamellar extinctions of andesine (18° — 22°). . . . The augite
granules are pale-brown and usually "02 — "03 mm. in diameter.

The only species represented in my collection is that with the
felspar-lathes "i — '2 mm. long.

40. Genus of the Olivine-Basalts
Formula. — Oliv, matrypauc,flu, gran, non-phen, parv.

Characters. — Olivine scanty. In the groundmass the
felspar-lathes are in flow-arrangement and the pyroxene is granular.
No plagioclase phenocrysts ; but there are a few small phenocrysts
of olivine and sometimes of pyroxene under 2 mm. in size.

Description. — Compact-looking non-porphyritic blackish-
brown rocks, sp. gr. about 2*9. Occasionally a little vesicular. For
the most part dyke-rocks.

In the slide are displayed a few small phenocrysts of olivine
and pyroxene in a groundmass formed of more or less parallel
felspar-lathes, augite granules, magnetite, sometimes in rods, and a
little greenish devitrified residual glass. . . . The pyroxene pheno-
crysts are of pale-brown augite and are generally less than a milli-
metre in size. They may be single crystals or they may be formed
of an aggregate of a few smaller crystals. . . . The olivine pheno-
crysts rarely exceed 2 mm. in size and are in part serpentinised. . . .
The augite granules vary usually from 'Oi to '03 mm. in
diameter. . . . The felspar-lathes of the rocks in this collection are
large, often exceeding "2 mm. in length, giving the rock a doleritic
texture in the slide. In a single slide they may range from "i to '6
mm. When lamellar they give extinctions of 15° to 25° (basic
andesine).

XVIII OLIVINE-BASALTS 265

Two species are represented in this collection : —
{a) with felspar-lathes '2 — "3 mm.

(^) „ » » '3— "5 ,.

44. Genus of the Olivine-Basalts

Formula. — Oliv, matr, pauc, flu, prismy non-phen,parv.

Characters. — Olivine scanty. In the groundmass the
felspar-lathes are in flow-arrangement and the pyroxene is in great
part prismatic. There are no phenocrysts of plagioclase ; but there
are a few small phenocrysts of olivine and sometimes of pyroxene,
less than 2 mm. in size.

Description. — A dark grey compactish rock ; sp. gr. 2*9 ;
showing a little macroscopic olivine ; forming a dyke in the tuffs
on the summit of the hill of Vatui (p. 54).

In the section it exhibits a few phenocrysts of olivine (more or
less serpentinised) and of augite in a groundmass formed of stout
augite prisms and small augite granules with felspar-lathes, mag-
netite, and a little devitrified yellowish interstitial glass. The
augite prisms and the felspar-lathes are in flow-arrangement. . . .
The pyroxene phenocrysts, which are pale brown and give ex-
tinctions of over 30° from the single cleavage-lines, may be aggre-
gates of five or six smaller crystals or single crystals presenting
sometimes lamellar twinning. The first are doubtless formed in
situ. The second though showing regular outlines may have a
nucleus giving a different extinction and possessing eroded margins.
The stout augite prisms of the groundmass, which are occasionally
twinned, have an average length of '2 to "3 mm. and give angles of
extinction with the long axis of 30° to 40°. The felspar-lathes
average only 'oy mm. in length and afford extinctions, when
untwinned, of 18° to 24° (acid labradorite).

The only species represented is that where the average length
of the felspar-lathes is between -02 and "i mm.

CHAPTER XIX

THE VOLCANIC ROCKS OF VANUA LEVU {continued^)

AuGiTE Class

StJB-CLASS II

Augite-Andesites including the Basaltic Andesites
(JPlag, augy matr.)

This sub-class, which comprises 40 per cent, of the volcanic
rocks, is characterised by the absence of olivine on the one hand,
and by the rarity or absence of rhombic pyroxene on the other.
On the basic side it shades into the olivine-basalts through the
basaltic andesites, and on the acid side by intermediate stages into
the hypersthene augite andesites ; and for these reasons it is not
always possible to draw a sharp line of distinction. In cases
where a hand-specimen displays no macroscopic olivine and where
a solitary small phenocryst of olivine is alone observed in the slide,
it should be referred to this sub-class ; and here also all doubtful
specimens as regards the occurrence of olivine should be placed.
When the question of the occurrence of rhombic pyroxene arises,
it should be remembered that the great prevalence of monoclinic
pyroxene amongst the phenocrysts and the practical absence of
rhombic pyroxene from the groundmass are essential characteristics
of this sub-class. Rhombic pyroxene is only indicated at times by
intergrowths in the phenocrysts.

The basaltic andesites enter into the formation of old " flows,"
as in the Mbua and Ndama plains. The other rocks enter princi-
pally into the composition of dykes, necks, and agglomerates.

I. Granular Sub-order (Augite-Andesites)
Formula. — Aug, matr, non-fiu, gran.

CHAP. XIX AUGITE-ANDESITES 267

I. Genus of the Augite-Andesites
Formula. — Ati^, matr^ noti-Jlu, gran, phen^vitr.

Characters. — In the groundmass the felspar-lathes and
prisms are not in flow-arrangement and the augite is granular.
Phenocrysts of glassy plagioclase.

Description. — These rocks frequently form dykes ; and it is
probable that most of the instances where the nature of the
exposure could not be ascertained also fall into this category.
They are dark-brown or blackish, and their sp. gr. ranges, except
in the semi-vitreous rocks, from 27 to 2"83. They are sometimes
vesicular, and rocks with abundant interstitial glass are common.
They admit of grouping into two sub-genera according to the size
of the plagioclase phenocrysts :

{a) Porphyritic, where the average size is 3 mm. or over.
{b) Non-porphyritic „ „ „ „ „ less than 3 mm.

Nearly all the rocks in my collection belong to the second group.

In the sections they display phenocrysts of plagioclase and
occasionally of pyroxene in a groundmass formed of a plexus of
felspar-lathes, augite granules, magnetite, and usually a fair amount
of smoky more or less opaque interstitial glass. . . . The felspar
phenocrysts, which are sometimes abundant, give lamellar extinc-
tions of andesine labradorite (15° to 30°). They are frequently
small (i to 2 mm.) and contain often many magma-inclusions.
Whilst the corroded aspect of some indicate that they belong to an
earlier period, the aggregate character and regular outlines of
others suggest that they have been produced in position. . . .
Pyroxene phenocrysts are absent in half the rocks. When present
they are generally small and of a pale augite which gives extinctions
of 30°. Their size does not usually exceed 2 mm. ; and they may
consist of single crystals (sometimes twinned) or of an aggregate of
smaller crystals. At times there is a suspicion of intergrowth with
rhombic pyroxene ; but no phenocrysts formed alone of that
mineral occur. . . . The augite granules of the groundmass as a rule
vary from "02 to '04 mm. in diameter. Occasional prism-forms
giving large extinctions occur. . . . The felspar-lathes vary much
in length in different rocks. In some they average as little as "05
mm., and in others as much as '2 mm. ; but the doleritic type with
yet longer lathes is not represented in the collection except among

268 A NATURALIST IN THE PACIFIC chap.

the altered rocks. Most of the lathes show a single median twin-
line, and when broader they display twin-lamellae. The angles of
extinction indicate acid and basic andesine.

Three out of the eight species distinguished by the length of the
felspar-lathes occur in my collection, that with the longest lathes
('3 — *5 mm.) being not represented.

2. Genus of the Augite-Andesites
Formula. — Au^, matr, non-flu, gran, phen, opac.

Characters. — In the groundmass the felspar-lathes and
prisms are not in flow-arrangement and the augite is granular.
Opaque plagioclase phenocrysts.

Description. — This genus may be divided into two groups
according to the size of the plagioclase phenocrysts, the first
" porphyritic," where they average 3 mm. and over, the second
" non-porphyritic," where they are smaller than 3 mm., usually not
over 2 mm. The former would include some of the " porphyrites,"
and to this only one of the rocks sliced is to be referred. All the
rest belong to the non-porphyritic type ; and several of them are
rocks that have undergone the propylitic change, as indicated by
the formation of pyrites, chlorite, calcite, and other alteration-
products.

{a) Porphyritic Sub-genus. — A greyish rock, with sp. gr.
278, showing abundant porphyritic opaque plagioclase (4 to 7 mm.),
from the vicinity of Satulaki. These phenocrysts are often
aggregates of lesser crystals, or they may be extensively cross-
macled. They are traversed by numerous fine cracks and show
much dust-like included material. They are in part corroded by
the magma and give evidence of fracture in their present position,
the re-union being sometimes effected by the growth of new
substance. Their lamellar extinctions (10° to 20°) are those of
andesine. The groundmass displays a plexus of stout felspar-
lathes, averaging 'i mm. long, with the meshes occupied by coarse
augite granules, '03 to -05 mm., with little, if any, interstitial glass.
The felspars are often lamellar and give extinctions like those of the
phenocrysts.

{b) Non-porphyritic Sub-genus. — Reference will first be
made to some of the propylitic rocks of the dykes of the Ndriti
Basin which belong to this group (see p. 70). They are greenish
or greyish, with sp. gr. 276 to 2-8, and often sparkle with pyrites

XIX AUGITE-ANDESITES 269

and contain secondary calcite, sometimes to such an extent that
they might be taken at first sight for impure Hmestones.

The small opaque plagioclase phenocrysts (under 2 mm.), that
they contain, are more evident in the slide than in the hand-
specimen, and scarcely give a macroscopic character to the rock.
They give extinctions (10° to 30°) ranging from those of acid
andesine to acid labradorite, and are traversed by numerous cracks
occupied by calcitic and other alteration products. The few
pyroxene phenocrysts that once existed are now entirely represented
by chloritic pseudomorphs. The groundmass displays a doleritic
texture, exhibiting a plexus of Jong felspar-lathes, "2 to '4 mm. in
average length, which often present a false resemblance to a flow-
arrangement from their aggregation into bundles. They are often
clouded by secondary products, but occasionally give lamellar
extinctions (20° to 30°) indicating andesine labradorite. The rest
of the groundmass is greatly altered, the granular augite and the
interstitial glass, which originally existed in fair amount, being
replaced by calcite, chlorite, pyrites, and occasionally epidote, so
that the rock mass appears largely impregnated with alteration
products. In addition there is much secondary magnetite, and
in some cases there are a few minute cavities filled with chalcedonic
silica and zeolites.

Reference may here be made to a singular rock from Ruku-ruku
Bay, which resembles the Ndriti rocks in its propylitic alteration,
but the felspar-lathes of the groundmass, '21 mm. in length, give
the small extinctions of oligoclase. Spec. grav. 2'6i.

Most of the prevailing rocks of Mount Freeland belong to this
sub-genus. They are dark grey and show small opaque plagioclase
phenocrysts i or 2 mm. in size. They usually, however, are more
or less altered, the change being often of the propylitic type, calcite,
chloritic material, viridite, and occasionally pyrites occurring as
alteration products. The specific gravity of the altered rocks is
2*6i — 2'69 ; that of the least affected is about 276. They all,
however, belong to the same genus, displaying small phenocrysts of
plagioclase and augite in a groundmass composed of minute stoutish
felspar-lathes ("03 — "06 mm.), augite granules, magnetite, and a
little residual glass. The plagioclase phenocrysts owe their opacity
partly to the numerous fine cracks traversing them and partly to the
alteration products. The pyroxene phenocrysts, which are mostly
of pale yellow augite, display at times intergrowths of rhombic
pyroxene.

2 70 A NATURALIST IN THE PACIFIC chap.

4. Genus of the Augite-Andesites

Formula. — An^-, matr, non-flu^ gran, non-phen, parv.

Characters. — In the groundmass the felspar-lathes and prisms
are not in flow-arrangement and the augite is granular. There are
no plagioclase phenocrysts, and those of augite when present are
small (under 2 mm.).

Description. — Two groups of these rocks occur in my
collection. In the one there are vesicular and scoriaceous rocks
forming dykes near Nukunase and near the village of Ndriti. They
display a plexus of felspar-lathes with abundant smoky more or
less devitrified glass, the augite granules not being always differ-
entiated. The felspar-lathes vary from •: to '2 mm. in average
length, and when lamellar give extinctions of basic andesine (25°).
There are no pyroxene phenocrysts, and the augite granules when
present average "02 mm. in size.

In the other group are included some propylites from the dykes
of the Ndriti Basin. They are greyish or greenish rocks, have a
sp. gr. of 272 to 276, sparkle often with pyrites, and contain so
much secondary calcite that they effervesce freely with an acid.
Except in the rarity or absence of plagioclase phenocrysts, they
come near to the propylitic rocks described under genus 2. They
usually display a doleritic groundmass exhibiting long felspar-lathes^
•2 to "33 mm. in length, which present the same pseudo-flow
arrangement from their being gathered into bundles. The alteration
corresponds precisely to that previously described, chlorite,
epidote, pyrites, &c., occurring in quantity as secondary products.

II Prismatic Sub-Order of the Augite-Andesites where
the Felspar-lathes are not in Flow-arrangement

Formula. — Aug, matr, non-flu, prism.

The augite-andesites, which display in the groundmass a plexus
of felspar-lathes and much prismatic pyroxene, are not frequent in
my collection. About half of the specimens belong to agglomerates,
whilst the rest are of the massive type, none apparently being
obtained from dykes. They admit of the same classification as
that generally adoped for the " granular " sub-orders ; and it must
be not forgotten that granular pyroxene also occurs but is not pre-
dominant.

XIX AUGITE-ANDESITES 271

5. Genus of the Augite-Andesites
Formula. — Aug; mair, non-flu^ prism, phen, vitr.

Characters. — In the groundmass the felspar-lathes and
prisms are not in flow-arrangement and the augite is for the most
part prismatic. Plagioclase phenocrysts glassy.

Description. — Except as regards the prismatic pyroxene
these rocks do not differ much from the " granular " augite-andesites.
Those before me show phenocrysts of plagioclase and sometimes
of augite in a groundmass displaying a mesh-work of felspar-lathes,
prismatic pyroxene, and much interstitial glass. . . . The plagioclase
phenocrysts, i to 3 mm. in size, show abundant magma-inclusions
arranged either zone-wise or parallel to the twinning-planes.
They are often eroded. . . . The phenocrysts of augite, which give
extinctions of over 30°, are often rounded and display glass and
other inclusions. . . . The prismatic pyroxenes of the groundmass
vary in average length from '03 to "oS mm. They have the peculiar
pale muddy brown hue characteristic of the prismatic augite in
these rocks, and give oblique extinctions up to 30° and over. They
may be short and broad or long and slender, and when there is
much glass in the rock they resemble the felspar-lathes in their
forked and imperfect extremities. Granular pyroxene occurs, but
is subordinate. . . .The felspar-lathes, t mm. long, are rarely
lamellar, and give extinctions measured from their long axis of 20°
(basic andesine).

6. Genus of the Augite-Andesites
Formula. — Aug, matr, non-flu, prism, phen, opac.

Characters. — In the groundmass the felspar-lathes are not in
flow-arrangement and the augite is for the most part prismatic.
The plagioclase phenocrysts are opaque.

Description. — Light and dark grey rocks displaying abundant
opaque plagioclase phenocrysts not exceeding 2*5 mm. They
are somewhat altered, one of the specimens having a sp. gr.
of 2-68.

In the section they exhibit phenocrysts of plagioclase, and
occasionally of augite in a groundmass of felspar-lathes, pyroxene
prisms and granules (the former predominating), with a fair amount of
altered interstitial glass. . . . The plagioclase phenocrysts owe their
opacity to the great number of fine and sometimes parallel cracks

272 A NATURALIST IN THE PACIFIC chap.

filled with alteration products, that traverse them. Although much
of their original material has often disappeared, they still display
the lamellar twinning of medium andesine (15° to 20°) .... The
phenocrysts of pale yellowish augite, which give the large extinc-
tions of that mineral, exhibit but little alteration, although lying in
the same slide with those of the plagioclase, . . . The pyroxene
prisms of the groundmass are of the same yellowish augite. They
are broad with rounded extremities and are arranged in a loose
plexus. . . . The felspars of the groundmass, which average "i mm.
in length and give extinctions of medium andesine, are either lathe-
shaped or short and broad when they display lamellae. The last-
named approach the orthophyric type, and such rocks come near
the porphyrites ; but I do not feel justified in placing them in a
separate orthophyric order.

Ill Ophitic Sub-order of the Augite- Andesites with the
Felspars of the Groundmass not in Flow-arrange-
ment.

Formula. — Ati^, matr, non-flu, oph.

These rocks form generally ancient flows. They are for the
most part semi-ophitic, large ophitic " plates " being uncommon.

9. Genus of the Augite-Andesites
Formula. — Aug, matr, non-flu, oph, phen, vitr.

Characters. — The felspar-lathes and prisms of the ground-
mass are not in flow-arrangement. The augite of the groundmass
is ophitic or semi-ophitic. Glassy plagioclase phenocrysts.

This genus may be divided into two sub-genera,

{a) Porphyritic, where the average size of the plagioclase pheno-
crysts is 3 mm. and over.

{b) Non-porphyritic, where the size is less than 3 mm.

A. Porphyritic Sub-genus

Description. — Coarse-looking brownish-black porphyritic
rocks displaying large plagioclase crystals that often show a play
of colours. Their sp. gr. is about 2 '8. None of the rocks in my
collection are vesicular. On account of the considerable porphy-
ritic development of the plagioclase, the groundmass is relatively
diminished, the large phenocrysts occupying about a third of the
mass. They form ancient basaltic flows more especially in the

XIX AUGITE-ANDESITES 273

vicinity of the isolated hills and mountains of acid andesite, as
around Vatu Kaisia ; whilst they may enter into the formation of
the low basaltic plains as in the region west and south of the
Ndreketi River. They are, however, limited in their extent and
occurrence. From the large amount of glass in the groundmass,
they may be inferred to belong to flows formed under different
conditions from those under which the great basaltic plateaux were
formed, where the rock contains but scanty interstitial glass.

In the slide they show the large plagioclase phenocrysts
together with a few small plates of ophitic augite in a groundmass
displaying in an abundant smoky glass a loose plexus of long
stout lathe-like plagioclase prisms partly wrapped around by lesset
augites. . . . The plagioclase phenocrysts, which attain a size of
4 to 6 mm., give lamellar extinctions of basic andesine (20° — 27°)
and show concentric zone-lines with transmitted light. They often
polarise in brilliant colours and are extensively cross-macled.
They contain usually abundant inclusions of the magma some-
times arranged zone-wise, and are frequently eroded. . . Non-
ophitic pyroxene phenocrysts are uncommon. In the slide occur
one or two small " plates," i to 2 mm. in size, of ophitic pale-
brown augite, and a number of lesser augites.. "2 to '3 mm. in size,
which in part wrap around the felspar-lathes and by their aggrega-
tion form imperfect ophitic " plates." . . . The long stout felspar-
lathes, which are on the average "3 to '45 mm. in length, give
lamellar extinctions of 15° to 20° (medium andesine) .... The
copious smoky glass is rendered partially opaque by the abundant
development of rods and skeletal crystals of magnetite, and shows
the fibrous devitrification arising from the formation of incipient
microliths. In some rocks there appear in the smoky glass brown-
ish-yellow patches of the residual magma which under the micro-
scope cannot be distinguished from palagonite.

All but one of the specimens belong to the species where the
felspar-lathes average over "3 mm. in length.

B. NON-PORPHYRITIC SUB-GENUS

Description. — Blackish-brown semi-ophitic rocks, sp. gr.
274 — 277, frequently of doleritic texture and showing a few small
Tfiacroscopic plagioclase phenocrysts. They are sometimes vesi-
:ular, and form old flows in a few localities, as in the vicinity of
Vatua in the eastern part of the Ndreketi plains and in the coast
listrict between Lekutu and Wailea Bay.

T

274 A NATURALIST IN THE PACIFIC chap.

They display in the slide small plagioclase phenocrysts, often
abundant, in a groundmass exhibiting a loose plexus of large lathe-
shaped felspar prisms, together with occasional small ophitic
" plates " of augite and numerous smaller semi-ophitic augites,
whilst there is much interstitial smoky glass. . . . The plagioclase
phenocrysts are as a rule i to 2 mm. in size and do not exceed
3 mm. They often contain abundant inclusions of the magma
sometimes arranged schiller-fashion, and are frequently eroded.
Theirlamellar extinctions (i5°-30°)indicateandesine labradorite. . .
The stout plagioclase lathes, which in most of my specimens range
between '2 and '3 mm., and contain at times magma-inclusions,
give the rocks their doleritic texture. . . . The occasional small
ophitic " plates " of pale augite are not over i mm. in size and give
extinctions of +30° from the single cleavage-lines. The lesser
augites, '2 mm. in size, are several times larger than typical granular
pyroxenes (•02-'03 mm.), and adapt their form to the interspaces
of the felspar-lathes which they in part invest. . . . The copious
interstitial glass is generally smoky and sometimes quite opaque
through the deposition of magnetite. It is never clear and
isotropic, but displays fibrous devitrification and is usually a little
altered.

These rocks come near to those of the previous sub-genus in
several respects, but they differ conspicuously in their non-por-
phyritic character, in being sometimes vesicular, and in their
general appearance. All the four species indicated by the length
of the felspar-lathes are here represented ; but the doleritic types
with the lathes exceeding '2 mm. are the most frequent.

10. Genus of the Augite-Andesites
Formula. — Au^, matr, 7ion-flu, oph^phen^ opac.

Characters. — In the groundmass the felspar-lathes and
prisms are not in flow-arrangement and the augite is ophitic or
semi-ophitic. The plagioclase phenocrysts are opaque.

This genus may be divided into two sub-genera, porphyritic
and non-porphyritic, according to the average size of the plagio-
clase phenocrysts, whether above or below 3 mm.

A. Porphyritic Sub-genus. — This is represented by a
light grey porphyritic rock, with sp. gr. 275, from the lower part
of Mount Freeland. It comes near to the porphyrites, and
displays large opaque white phenocrysts of plagioclase 5 or 6 mm.
long. It is a somewhat altered rock.

XIX AUGITE-ANDESITES 275

In the thin section it displays the plagioclase phenocrysts in a
ground mass of doleritic and semi-ophitic texture showing a plexus
of long felspar-lathes partly invested by small augites with a fair
amount of altered greenish opaque interstitial glass. . , . The
plagioclase phenocrysts, which give extinctions of 11° to 15° (acid
andesine), are traversed by a network of fine cracks and contain a
quantity of colourless dust-like inclusions and alteration-products.
They are long and rectilinear in outline and are not much affected
by the magma. . . . The felspar-lathes, which average '26 mm. in
length, are occasionally lamellar when the angle of extinction
indicates acid andesine. Like the phenocrysts they contain many
dust-like inclusions. . . . The augite may at times form an aggre-
gate phenocryst of small size ; but usually it occurs as semi-ophitic
masses 'i mm. in diameter.

B. NON-PORPHYRITIC SUB-GENUS. — The Specimen represent-
ing this group is a coarse-grained greyish altered rock, sp. gr. 2*81,
found in blocks near Waikatakata (p. 204), showing small some-
what opaque plagioclase phenocrysts. In the section these
phenocrysts are displayed in numbers together with a few of augite.
The groundmass, doleritic in texture in this species, displays a
plexus of long stout felspar-lathes with numerous semi-ophitic
lesser augites, chloritic pseudomorphs after pyroxene, and scanty
interstitial altered glass. . . . The plagioclase phenocrysts, 2 to 3 mm.
in size, give extinctions (22° to 28°) of basic andesine. They are
traversed by many fine cracks and contain an abundance of colour-
less dust-like inclusions, apparently altered magma products. . . .
The small pyroxene phenocrysts consist of aggregates of smaller
crystals of pale augite. The lesser augites, 'i mm. in size, partly
invest the felspars. . . . The broad felspar-lathes, which average
•25 mm. in length and give lamellar extinctions of medium andesine
(15°), contain inclusions similar to those of the phenocrysts. . . .
The scanty interstitial glass is converted into viriditic and chloritic
materials. Secondary calcite also occurs here and in the chloritic
pseudomorphs.

The only species represented is that with felspar-lathes '2 to
■3 mm. in length.

12, Genus of the Augite-Andesites

Formula. — Aug^ matr, non-flu, oph, non-phen,parv.

Characters. — In the groundmass the felspar lathes and
prisms are not in flow-arrangement and the augite is ophitic or

T 2

2 76 A NATURALIST IN THE PACIFIC chap.

semi-ophitic. No plagioclase phenocrysts. Augite phenocrysts
when present less than 2 mm. in size.

Description. — These rocks come near to the non-porphyritic
group of genus 9 ; but differ in the absence or rarity of plagioclase
phenocrysts, in their more frequently vesicular and scoriaceous char-
acter, and in the fresher condition of the rock. Their sp. gr, is about
277. They present themselves usually as blackish-brown doleritic
rocks and form ancient flows in the coast-plains, sometimes
exhibiting a columnar structure as in the crossing of the Ndreketi
above Mbatiri. They are, however, of limited occurrence and are
mostly represented in the Ndreketi plains and in the district
between the Lekutu River and Wailea Bay.

Typically they display in thin sections no phenocrysts either of
plagioclase or of pyroxene, and exhibit a plexus of usually long
stout felspar-lathes partly invested by the lesser augites in a
copious smoky glass. . . . The felspar-lathes, "25 to -4 mm. in
length, give lamellar extinctions of 10° to 20° (andesine) and contain
a few magma-inclusions. . . . The semi-ophitic augites, 'i to '2 mm.
in size, are sometimes twinned. . . . The smoky glass polarises
feebly and displays dark feathery aggregates of microliths. Within
it are brownish-yellow semi-opaque patches of residual glass, which
polarise faintly and behave like palagonite.

The two species with felspar-lathes '2 to "3 mm. and "3 to '5 mm.
are represented in my collection.

4. Granular Sub-order of the Augite-Andesites
Formula. — Aug, matr, flu, gran.

13. Genus

Formula. — Aug, matr, flu, gran, pken, vitr.

Characters. — In the groundmass the felspar-lathes or prisms
are in flow-arrangement and the augite is granular. The plagioclase
phenocrysts are glassy.

Description. — This genus readily splits up into two sub-genera,
the non-porphyritic, where the plagioclase phenocrysts are less than
3 mm. in size, and the porphyritic where they are larger.

I. NON-PORPHYRITIC SUB-GENUS. — Dark-brown or blackish
rocks displaying small plagioclase phenocrysts, usually only i or 2
mm. in size. Three of the four species defined by the length of
the felspar-lathes are represented in my collection.

XIX AUGITE-ANDESITES 277

Species A. — Felspar-lathes •02-1 mm. in average length. This
may again be sub-divided according to the degree of basicity of
the rocks : —

(a) Sub-species of greater basicity. — Sp. gr. 276 to 2*82. . . ■
Such rocks are represented in dykes and in the prevailing basic
agglomerates. They are at times scoriaceous. The small plagio-
clase phenocrysts, which are fairly numerous, give lamellar
extinctions of andesine labradorite (20 to 30°). Two kinds occur
which may or may not be represented in the same slide. In the
one the crystal is much corroded and contains abundant magma-
inclusions. It belongs in such a case to an earlier period. In the
other the outlines are clean and regular, and the crystal is often
cross-macled to such an extent that it may be inferred from its
unbroken condition to have been formed in situ. Augite
phenocrysts when present are small and scanty, pale-yellow, idio-
morphic, and giving extinctions of -f- 30°. The felspar-lathes,
which average '06 — "08 mm. in length, give extinctions indicating
andesine labradorite. The augite granules are small ("Oi — '02 mm.).
Interstitial glass, generally scanty, is sometimes abundant when it
is smoky, showing fibrous devitrification, with irregular " lacunae "
filled with a brownish yellow opaque glass like palagonite.

{b) Sub-species of lesser basicity. — Sp. gr. 2'65 — 270. . . . The
remarks on the plagioclase phenocrysts of the more basic sub-
species here apply, except that the lamellar extinctions indicate
medium andesine (12° — 20°). The characters of the augite pheno-
crysts and granules are in both groups the same ; but in this case
there is more frequently a suspicion of intergrowth with rhombic
pyroxene. The felspar-lathes are very small, "04 or "OS mm, and
]five simple extinctions of acid andesine (5 — 10°). Interstitial glass
ixists in moderate amount.

Species B. — Felspar-lathes 'i — *2 mm. in average length.

Blackish or dark -grey rather compact rocks, sp. gr. 275 — 279,
' hat cannot be readily divided into groups according to their
1 )asicity. They form dykes and volcanic " necks " and are some-
limes scoriaceous. The small plagioclase phenocrysts, which are
1 tiost evident in the slide, present the two kinds above described
1 nder Species A. They give lamellar extinctions varying from those
(f medium andesine to acid labradorite (15 — 30°). The augite
I henocrysts, which are small and scanty, occasionally show inter-
\ rowths of rhombic pyroxene. The augite granules are generally
•< )2 to "03 mm. in size, and here and there a prism form gives
extinctions of -f 25°. The felspar-lathes which average 'ii to

2 78 A NATURALIST IN THE PACIFIC chap.

•15 mm. long, are often rather stout, showing a few lamellae that
give extinctions of medium and basic andesine. Interstitial glass
occurs in fair amount.

Species C. — Felspar-lathes '2 — '3 mm. in average length.

Blackish rocks with sp. gr. 275 — 284. The description of
Species B applies here. The plagioclase phenocrysts are for the
most part microporphyritic. The size of the augite granules is as
above given.

2. PORPHYRITIC Sub-genus. — This group of rocks is mostly
confined to the slopes and vicinity of Mount Seatura in the western
part of the island, being prevalent in the Mbua and Ndama plains,
and occurring also as dyke-rocks in the Nandi Gorge leading into
the Ndriti Basin, and at and near the coasts of Wainunu Bay
between the Tongalevu and Wainunu rivers. They come near in
appearance to the porphyritic forms of the blackish olivine-basalts
belonging to genera 13, 25, and 37 of the olivine rocks; but they
differ in the absence of that mineral, in their lower density, and in
other characters. They are the type to which the term " porphy-
ritic basaltic andesite " is most frequently applied in the text when
the ophitic structure is not displayed.

They are blackish rocks having a specific gravity of 271 to 2*8 1
and exhibiting large porphyritic crystals of plagioclase, but they
vary in their minute structure on account of the different size of
the felspars of the groundmass. Those forming dykes in the
Nandi Gorge are often more or less propylitic in character. The
felspar-lathes, which have an average length of '2 to -3 mm., some-
times show a few lamellae giving extinctions of medium andesine
(12° — 20°). The plagioclase phenocrysts of the same andesine are
3 to 5 mm. in size. They are eroded and contain abundant
magma inclusions. There are a few small phenocrysts of pale
brown augite. The augite granules are "03 or '04 mm. in diameter,
and there is a little dark opaque residual glass.

The rocks of the Mbua and Ndama plains have a specific
gravity of 2'8i. The plagioclase phenocrysts, which yield extinct-
ions of basic andesine (21 — 27°), are sometimes a centimetre in
length. They are traversed by cracks filled with dark altered glass or
occupied by brownish films. The felspar-lathes, which average "ii
mm. in length, are often stout and lamellar and give extinctions like
the phenocrysts. Augite phenocrysts are either absent or scanty ;
whilst the granules average '02 — '03 mm. in size. There is usually
a little interstitial glass.

XIX AUGITE-ANDESITES 279

A rock, almost holocrystalHne and 274 in density, which was
obtained from the Tongalevu district in Wainunu Bay, approaches
the orthophyric type in the character of the ground mass. The
felspars are short ("06 mm.) and stout, and yield lamellar extinc-
tions of oligoclase (5° — 10°). The plagioclase phenocrysts are of
basic andesine. Amongst the granules ("025 mm.) of pale brown
augite occur prismatic forms giving oblique extinctions of + 30°.

14. Genus of the Augite-Andesites
Formula. — Aug, matr, flu, gran, phen, opac.

Characters. — In the groundmass the felspar-lathes are in
flow-arrangement and the augite is granular. The plagioclase
phenocrysts are opaque.

Description. — Only two rocks are referred to this genus.
One which is dark grey with a specific gravity of 272 is exposed
in the gorge of the Mbutu-mbutu River below the falls of Na
Savu. Flow-arrangement is displayed both by the felspar pheno-
crysts and lathes. The phenocrysts, 2 to 3 mm. in size, owe their
opacity to the abundance of inclusions of brown glass. They are
corroded and give extinctions of acid labradorite {26 — 32°).
Pyroxene phenocrysts are scanty and small. The groundmass
has a characteristic " pilotaxitic " appearance, the densely packed
felspar-lathes averaging only "05 mm. in length, whilst the pyroxene
granules are "Oi mm. in size. Residual glass scanty.

The other rock is from the range behind Sueni. It shows large
porphyritic crystals (5 or 6 mm.) of medium andesine which
contain magma-inclusions in abundance. The average length of
the felspar-lathe is "oS mm. and the size of the augite granules is
•02 mm. There is but little glass. The rock is somewhat altered.

16. Genus of the Augite-Andesites

Formula. — Aug, matr, flu, gran, non-phen, parv.

Characters. — In the groundmass the felspar-lathes are in
flow-arrangement and the augite is granular. Plagioclase
phenocrysts are absent, or if present very scanty and not usually
over I mm. in size. When present the augite phenocrysts are
under 2 mm.

Description. — This is a very extensive genus, admitting
considerable variation and including most of the aphanitic augite-

28o A NATURALIST IN THE PACIFIC chap.

andesites, where the felspar-lathes are as a rule very small (under
•I mm. in length), as well as some of the doleritic types where
they are very large ("2 to '4 mm. long). In assigning a rock a
place in this genus some regard must be paid to its macroscopic
aspect as well as to the presence or absence of plagioclase
phenocrysts. In many cases two or three small phenocrysts may
be observed in a slide, under a millimetre in size ; but they do not
give a character to the naked-eye appearance of the rock, and
such rocks cannot be distinguished from others that do not display
them.

These rocks range in specific gravity from 2*55 to 2'S$. This
large range is in the main concerned with different degrees of
basicity depending on the character of the plagioclase, the
relative abundance of the augite granules, &c. ; but it is also
connected with the amount of interstitial glass. The variety of
plagioclase ranges between oligoclase and andesine labradorite.
The fluidal structure is nearly always well-marked, and the closely
packed felspar-lathes have often the peculiar " felted " appearance
of many andesites. A little interstitial glass is present in most
rocks.

Many, perhaps nearly all, of the rocks belong either to dykes
or to larger intrusive masses. All the four species indicated by the
length of the felspar-lathes are represented in my collection, especially
the two with smallest felspars. They may again be split up into
two sub-species according to the degree of basicity of the rocks.

Species A. — Felspar-lathes between '02 mm. and "i mm. in
average length.

(i) Mosi basic sub-species . . . Sp. gr. 275-2*85. Dark-brown
and dark-grey compact aphanitic rocks showing no plagioclase
phenocrysts to the eye. When a few of these phenocrysts
are present in a slide they are not usually much over i mm. in size,
and give extinctions of andesine labradorite (20° to 30°). Augite
phenocrysts are often absent, and when present are not over i mm.
in size and are as a rule scanty, occasionally affording a suspicion
of inter-growths with rhombic pyroxene. The felspar-lathes
which display marked flow-structure, vary in average length in
different rocks from "05 — '08 mm. Lamellar twinning is rare, the
extinctions being those of oligoclase andesine (10° to 20°). The
usual extinction, as measured from the long axis of the lathe, is
10° to 15° (medium andesine). The augite granules are small
(•01 — *02 mm.) and abundant. There is generally a little interstitial
glass with small magnetite.

XIX AUGITE-ANDESITES 281

(2) Least basic sub-species . . . Sp. gn 2*55 — 275. Dark com-
pact aphanitic rocks especially characteristic of the Ndrawa.-
district. When plagioclase phenocrysts are present, they are very
scanty and not generally over a millimetre in size, possessing
rectangular clean outlines and showing but few inclusions. They
may display carlsbad twinning and zoning, or albite twinning,
when they give extinctions of oligoclase andesine (10° — 15°).
Pyroxene phenocrysts are either absent, or scanty and small, being
usually of pale yellow augite with occasional indications of inter-
growth with rhombic pyroxene. The felspar-lathes as a rule
average "O/ or '08 mm. and present a dense fluidal arrangement.
They rarely display lamellar twinning and give extinctions
measured from the long axis of oligoclase and oligoclase andesine
(2° — 8°). The pyroxene granules are very small, averaging "Oi mm.
and less. There is also fine magnetite. A little interstitial glass is
usually present. When abundant it is not generally smoky but
shows clear fibrous devitrification. . . . One of the specimens,
which is semi-vitreous, exhibits tube-like steam-pores drawn out to a
length of I — 1 1 centimetres. The felspar microliths are only "02 mm.
in length. The copious glass has the character above described.

Species B. — Felspar-lathes 'i — '2 mm. in average length.

This species may also be sub-divided into two sub-species
(more basic and less basic). Since, however, all but one of the
fifteen rocks belonging to the species are of the more basic kind
my remarks will mainly apply to them. They are dark-brown or
dark-grey compact aphanitic rocks, occasionally banded or streaky,
in appearance, and ranging in specific gravity from 275 to 2'84.
They occur in several districts, but are especially characteristic of
the Ndrawa district. The plagioclase phenocrysts, if present, are
very scanty and small (i or i| mm.). They contain inclusions of
the magma and give lamellar extinctions of andesine labradorite
(20° — 30°). Pyroxene phenocrysts do not generally occur. When
present, they are small and of pale yellow augite yielding large
extinctions . Occasionally micro-porphyritic augite is well repre-
sented. The felspar-lathes, which exhibit a well-marked flow-
arrangement, are generally '13 to '15 mm. long. Lamellar twinning
is uncommon, the extinctions measured from the long axis indicat-
ing basic andesine (10° — 20''). The augite granules are abundant
and small ("Oi — "02 mm.). Occasional prism-forms yield large
extinctions. Magnetite is abundant, its grains corresponding in
size to the augite granules. There is as a rule a little residual
glass, which shows fibrous devitrification and is not smoky. The

282 A NATURALIST IN THE PACIFIC chap.

banded appearance of some of the rocks arises from the glass
collecting in streaks rudely parallel and running in the direction of
the " flow " of the felspar-lathes.

The only specimen in my collection of " sliced " rocks belonging
to the less basic sub-species is an altered bluish-grey rock (sp. gr.
27) from the range between the Mbuthai-sau valley and the
Wainikoro plains. Its long parallel untwinned felspar-lathes give
the nearly straight extinctions of oligoclase. Fine cracks in the
rock are filled with crystalline silica.

Species C, felspar-lathes -2 — -3 mm. long.

Species D, „ „ -3— -5 „
The rocks of these species in the collection are for the most part
dyke-rocks of the more basic kind. They are blackish or dark-
brown, almost doleritic in texture, and range in specific gravity
from 277 to 2*87. At times they are vesicular or scoriaceous, as in
the specimens from an agglomerate at Undu Point and from a flow
or dyke at Vunikondi. The most typical of these rocks are those
of some of the dykes of the Ndriti basin, which, however, display
propylitic alteration in a varying degree. They would be
described as semi-doleritic basalts without olivine or as non-porphy-
ritic basaltic andesites. Plagioclase phenocrysts are typically
absent, or they are scanty and not over i mm. in size. Augite
phenocrysts are usually scanty and small. The felspar-lathes,
which are more or less in flow-arrangement, are rather stout, and
range in average length in different rocks from '23 to "35 mm.
They often show a few twin-lamellae which yield extinctions of
medium and basic andesine (15 — 28°). The augite granules are
large ("03 mm.) in the Ndriti rocks. Magnetites, usually corres-
ponding in size to the augite granules, are abundant. Interstitial
glass occurs often in fair quantity and is dark and semi-opaque.

At times there can be recognised a later generation of minute
felspar microliths between the much larger lathes. They display
a plexus rather than a flow-arrangement Whilst the larger
parallel lathes of the Vunikondi rock, above referred to, average
•23 mm. long, the felspar microliths of the interspaces average only
•03 mm. The significance of these two crops of felspars in the
groundmass is discussed on page 237.

The only rock of the less basic sub-species in my collection is
from a dyke near Vatua-karoa. It shows secondary calcite and
viridite and other evidences of the propylitic change. The
felspar-lathes, which average '3 mm. in length, give extinctions of
oligoclase (o — 5°) The specific gravity is 272.

XIX AUGITE-ANDESITES 283

5. Sub-order, Prismatic, of the Augite-Andesites
(Felspar-lathes in flow-arrangement. Ati^; matr,^u, prism.)

This sub-order includes dark-brown or blackish semi-vitreous
rocks, all but one of which belong to the genus below described.
Since the exception (which belongs to genus 17 of the synopsis)
differs only in the presence of plagioclase phenocrysts, its separate
description is not needed,

20. Genus of the Augite-Andesites
Formula. — Aug, matr, flu, prism, non-phen, parv.
Characters. — In the groundmass the felspar-lathes are in
flow-arrangement, and the augite is prismatic. Plagioclase pheno-
crysts are absent or are very small and scanty, and pyroxene
phenocrysts when present do not exceed 2 mm. in size.

Description. — These dark semi-vitreous rocks occur in
agglomerates and as " necks " and dykes, and are at times scoria-
ceous. They are usually compact and aphanitic, showing few if
any plagioclase phenocrysts and having a semi-conchoidal fracture.
The specific gravity varies, being generally 2*6 — 2-6$, but according
to the degree of basicity and amount of glass it may be as low as
2'5 or as high as 277. In the less glassy condition, as in the case
of a rock from the ridge east of Na Raro, the felspar-lathes are
relatively scanty and the groundmass is mainly formed of augite
prisms in flow-arrangement. The lathes are generally small, less
than 'I mm., and rarely over '2 mm. Their extinctions are those of
oligoclase and acid andesine. The pyroxene prisms, which give
the large extinctions of augite, have a pale muddy-brown hue and
are as a rule '03 — 'oy mm. long. Granular pyroxene, if present, is
subordinate in amount. The glass, which is always in good
quantity and is sometimes abundant, displays fibrous devitrification.
In a rock from the vicinity of Narengali a variolitic structure is
exhibited in the form of sheaf-like aggregates of fibre-like felspars
and skeleton prisms of pyroxene.

6. Sub-order, Ophitic, of the Augite-Andesites
(Felspar-lathes in flow-arrangement. Aug, matr,flu, oph.)

21. Genus of the Augite-Andesites
Formula. — Aug, matr,flu, oph, phen, vitr.
Characters. — In the groundmass the felspar-lathes are in

284 A NATURALIST IN THE PACIFIC ch. xix

flow-arrangement and the augite is ophitic or semi-ophitic. Glassy
plagioclase phenocrysts.

Description. — Dark rocks, sp. gr. 276 — 2"8, forming ancient
flows and displaying at times a columnar structure as at Yanutha
Point (page 123). The ophitic character is only in part developed,
which may be connected with the flow-arrangement of the felspars.
These rocks come near to the blackish ophitic basalts with scanty
olivine (genus 33 of the olivine sub-class).

They all belong to the non-porphyritic sub-genus where the
plagioclase phenocrysts are less than 3 mm. in size. These
phenocrysts, which often contain abundant magma-inclusions, give
extinctions of andesine labradorite (20° — 30°). The augite pheno-
crysts are small and composite in character as often happens with
these ophitic rocks. They sometimes invest the smallest felspar
phenocrysts, and occasionally display intergrowths of rhombic
pyroxene. The felspar lathes are 'i to "14 mm. in length, and give
extinctions of medium and basic andesine. The augite granules
are large ("02 — •06 mm.), and tend to wrap around the lathes.
Interstitial glass exists in fair amount.

CHAPTER XX

THE VOLCANIC ROCKS OF VANUA LEVU {continued)

Hypersthene-Augite Class
II. Sub-Class. Hypersthene-Augite-Andesites
Formula. — Flag, hypersth-aug, inatr.

Characters. — The pyroxene phenocrysts usually are re-
presented by separate crystals of the monocHnic as well as the
rhombic type, and the two forms are often associated in the same
crystal. The monoclinic form prevails in the groundmass in most
cases.

Remarks. — It is not possible to draw a sharp line between
the augite and the hypersthene-augite-andesites ; but where two or
three phenocrysts of the rhombic type occur in a slide the rock may
be placed in this division. Between this variety and that where
rhombic pyroxene prevails, both among the phenocrysts and in the
groundmass, numerous intermediate kinds exist. These rocks
mostly occur in agglomerates and form small and large dykes or
sills, but rarely are found in flows. They are distributed over most
of the island except in the western portion (the basaltic districts of
Wainunu, Seatura, and Solevu), but reappear again in the Mbua
peninsula in places, as at Mount Koroma.

The pale yellow rhombic pyroxene is uniform in its optical
behaviour. The prisms are noticeably pleochroic, being nearly
colourless when lying across the long axis of the lower nicol and
pale yellow when parallel with it. The intergrowths with mono-
clinic pyroxene often take the form of lamellar bands, whilst in
some cases a nucleus of the one (usually rhombic) is invested by a
growth of the other.

286 A NATURALIST IN THE PACIFIC chap.

I. Sub-Order, Granular, of the Hypersthene-Augite-

Andesites

{Felspar-lathes not in flow-arrangement^
Formula. — Hypersth-aug, matr, non-flu, gran.

1 genus . . . (Vtfr.) )

2 „ . . . . (Opac.) I „ ^

3 „ . . . . (,i/^^.) See Synopsis, p. 247.

4 „ . . . . (Parv.) J

-^ Nearly all of the rocks of this sub-order that are represented in
my collection belong to the genus (r) with phenocrysts of glassy
plagioclase. They vary considerably in appearance and in colour
(black to grey), and occur under very different conditions, as in
"necks," old flows, large intrusive masses, dykes, agglomerates,
&c. Their specific gravity has rather a wide range according to the
degree of basicity. In the heavier rocks where the rhombic
pyroxene is scanty, it is usually 27 to 2*8. In the others, where
rhombic pyroxene is more predominant and where the felspar is
less basic, it is 26 to 27.

In the slide small phenocrysts of plagioclase and pyroxene
occiir in a groundmass of felspar-lathes and pyroxene granules,
whilst there is as a rule a fair amount of residual glass. The
plagioclase phenocrysts, which give extinctions in different rocks of
acid and basic andesine and contain abundant magma-inclusions,
are generally one to two mm. in size. The pyroxene phenocrysts
are small, and may be represented by separate crystals of the mono-
clinic and rhombic kinds, or by crystals displaying intergrowths of
the two sorts. The pyroxene granules vary much in size and are
evidently in great part of augite. In most of the rocks the felspar-
lathes are less than 'i mm. in length. In those where the length is
•I to "2 mm. they are sometimes stout and display a few lamellae,
yielding extinctions corresponding to those of the phenocrysts.

A singular dark grey almost holocrystalline doleritic rock (sp.
gr. 2-85) is exposed in the Thulanga Ridge (p. 211). It shows no
plagioclase phenocrysts, but those of pyroxene are numerous, which,
however, do not exceed 2 mm. in size, so that the rock would be
referred to genus 4 of this sub-order. It appears to be a doleritic
form of the plutonic rock found at Nawi in this neighbourhood
(p. 211). The pyroxene phenocrysts are mostly of brownish-yellow
augite, but rhombic pyroxene, either as separate crystals or as
intergrowths, is not uncommon. The plagioclase lathes are long

XX HYPERSTHENE-AUGITE-ANDESITES 287

and fairly stout, giving at times lamellar extinctions of 20°. Their
average length is -3 mm., and it is to their large size that the
doleritic texture is due. The pyroxenes of the groundmass are
similarly coarse (-2 mm.), and include both monoclinic and rhombic
forms, the latter infrequent. There is a slight tendency to semi-
ophitic behaviour in places ; but generally these pyroxenes are
irregular in shape or rudely prismatic.

2. Sub-order, Prismatic, of the Hypersthene-Augite-

Andesites

{Felspar-lathes not in flow-arrangement^

Formula. — Hypersth-aug, matr, non-flu, prism.
5 genus . . . ( Vitr.)

6 „ ... {Opac.)

7 „ ... {Magti.)

8 „ ... {Parv,)_

See Synopsis.

This sub-order includes rocks varying much in appearance, but
all alike in the presence of prismatic pyroxene in the groundmass
and in the absence of flow-arrangement of the felspar-lathes. They
belong to the two genera, with glassy and opaque plagioclase
phenocrysts. These crystals are not usually over 2 mm. in size
and are of medium andesine (15° — 20°). The pyroxene pheno-
crysts are small and may be entirely of monoclinic or of rhombic
pyroxene, or the two may be associated either as lamellar inter-
growths, or by displaying an eroded nucleus (generally rhombic)
around which a regular crystal of monoclinic pyroxene has grown.
The felspar-lathes are in some cases less than 'i mm. long, and in
others "i — -2 mm. The pyroxene prisms of the groundmass
average "Oi — "04 mm. in length, and give both straight and oblique
extinctions, the last prevailing. The specific gravity ranges from
2*55 to 275 according to the degree of basicity and amount of
interstitial glass, which is usually in fair quantity.

' 4. Sub-order, Granular, of the Hypersthene-Augite-

Andesites

{Felspar-lathes in flow-arrangement^
13. Genus
Formula. — Hypersth-aug, matr, flu, gran, phen, vitr.
Characters. — Glassy plagioclase phenocrysts.

288 A NATURALIST IN THE PACIFIC chap.

Description. — This is a group of rocks that comes near the
basaltic andesites represented in genera i and 13 of the augite
sub-class ; and to the more basic kinds the terms of basaltic
andesite is equally applicable. These rocks, however, differ in the
prevalence of rhombic pyroxene, which occurs as phenocrysts, but
always accompanied by monoclinic pyroxene, whether as separate
crystals or as inter-growths. Such rocks are intermediate between
those of the augite and rhombic pyroxene classes. They are
particularly characteristic of the Savu-savu peninsula, but they are
also found in other scattered localities. Sometimes they appear to
form ancient flows, and at other times intrusive masses and dykes ;
but they are rarely scoriaceous.

Almost all the rocks in my collection referred to this genus be-
long to the species where the felspar-lathes of the groundmass are
•02 — -I mm. long. They are generally blackish or dark-brown, and
the specific gravity ranges usually from 272 to 2-83. They display
in the slide a fair number of plagioclase and pyroxene phenocrysts
in a groundmass of felspar-lathes, pyroxene granules, and mag-
netite, the interstitial glass being scanty or moderate in amount. . .
The plagioclase phenocrysts are rarely as large as 3 mm., so that
most of the rocks belong to the non-porphyritic group of the
genus. These phenocrysts, which are often zoned, give extinctions
of basic andesine (15° — 25°). They contain magma-inclusions,
sometimes in abundance, which are arranged in zone-lines. , . The
pyroxene phenocrysts are small, the two kinds being always
represented in the same slide. In some cases separate crystals
occur, and in others the two are associated as intergrowths, but in
most cases separate and compound crystals occur in the same
section. Not infrequently the phenocryst is an aggregate of lesser
crystals of the two pyroxenes. The monoclinic form is a brownish
yellow augite with large extinctions and often twinned. The
felspar-lathes of the groundmass, which usually average "05 or '06
mm. in length, are either narrow and untwinned, or they may be
stouter and display simple and at times lamellar twinning, giving
extinctions of medium andesine. . . The granules of pyroxene are
generally 'Oi — -02 mm. in size ; but occasional prism-forms occur
which give sometimes the straight extinction of rhombic pyroxene
and at other times the large oblique extinctions of the augite type.

XX HYPERSTHENE-AUGITE-ANDESITES 289

5. Sub-order, Prismatic, of the Hypersthene-Augjte-

Andesites
{Felspar-lathes in flow-arrangemenf)

Formula. — Hypersth-aug^ matr, fiu, prism.

17 genus . . . {Vitr.)

18 „ ... {Opac.)

19 „ . • . {Magn.)

20 „ ... {Parv.)

See Synopsis.

The rocks of this sub-order that are represented in my col-
lection admit easily of a general description, and since the diag-
noses of the genera are given in the Synopsis, there will be no
need to separately describe each genus.

Almost without exception these rocks form a constituent of
agglomerates in various parts of the island ; and they occur in
this condition in some of the highest mountains, as Mariko,
Thambeyu, and Koro-mbasanga. The exception refers to a low
mound-like hill, apparently a " volcanic neck," that rises from the
basaltic plains west of Mbua (see page 58).

In about half of the specimens the rocks are referred to section
10, where the plagioclase phenocrysts are either small and very
scanty or are absent altogether. In a fair number these pheno-
orysts are opaque (genus 18); whilst in a few they are glassy
I genus 17). The rocks are typically blackish or dark grey, and
often have a pitchstone-like appearance, the groundmass being
Irequently semi-vitreous in character. Vesicular and scoriaceous

1 ocks occur at times.

In all cases the felspar-lathes and pyroxene prisms are more
( r less in flow-arrangement ; whilst pyroxene granules, if present,
J re subordinate. The felspar-lathes, which are either simple or
c nce-twinned and give extinctions of acid and medium andesine,
e re usually small, and average in different sections -05 — -08 mm.
i I length. The pyroxene prisms are pale brown and are -03 or
•('4 mm. long. Most of them give oblique extinctions of over

2 5* ; but in the same slide some give straight extinctions ; the
proportion varies in different rocks. The pyroxene phenocrysts
ii all the specimens are small (not over 2 mm.), and are rhombic
a id monoclinic. In most sections the two forms are represented
b T separate crystals and are also associated in the same phenocryst.
1 hose of rhombic pyroxene have often dark borders. There is a
o nsiderable amount of a pale brown glass in the groundmass,

U

290 A NATURALIST IN THE PACIFIC chaf.

more or less devitrified. The specific gravity varies considerably,
but is as a rule between 2*55 and 275, the more basic rocks con-
taining augite in preponderance and basic andesine, whilst the
less basic possess a large proportion of rhombic pyroxene and dis-
play oligoclase-andesine. Sometimes, as in the case of a rock
composing an agglomerate east of Nanduri, where the porphyritic
plagioclase is opaque and there is some degree of alteration, the
rock looks very like a porphyrite.

.Third Order, Orthophyric, of the Hypersthene-Augite-

Andesites

Formula. — Hypersth-aug, matr, orth.

Characters. — Felspars of the groundmass short and broad.

Since the material is insufficient for the separate description
of each genus, a general account of the order is alone given.
These rocks are often represented in agglomerates or they occur
as large blocks, either lying on the surface or imbedded in luffs.
Many of them are somewhat altered.

They are for the most part dark grey dull-looking rocks, with
a specific gravity of 27 to 2*8, showing macroscopic plagioclase
together with conspicuous pyroxene phenocrysts. The plagio-
clase phenocrysts are usually small (i to 3 mm.), and give extinc-
tions of medium andesine (15° — 20°) and in some rocks of acid
labradorite (30°). They are as a rule corroded and are penetrated
by numerous fissures, whilst they contain a considerable amount
of altered magma-inclusions with sometimes other alteration pro-
ducts. The pyroxene phenocrysts are from 2 to 4 mm. in size.
Brownish-yellow augite, giving extinctions of over 30°, and pale-
yellow rhombic pyroxene of the type before described occur
generally in the same slide, and are frequently associated as inter-
growths in the same crystal. They may have regular outlines
or dark eroded borders, and at times they exhibit abundant dark
opaque inclusions. The broad felspars of the groundmass are
sometimes rectangular and give lamellar extinctions of medium
and acid andesine (12° — 17°). They vary in length in different
rocks from "05 to '2 mm. and more. The pyroxene of the ground-
mass is generally granular and coarse ('02 — '05 mm.). As indi-
cated by the extinctions of occasional prism-forms it is composed
of both augite and rhombic pyroxene, the former prevailing. The
prismatic sub-order is also represented, and here the pyroxene of
the groundmass is in great part prismatic, the length of the prisms

XX HYPERSTHENE-AUGITE-ANDESITES 291

not often exceeding "05 mm., whilst both the monoclinic and
rhombic kinds occur. Interstitial glass varies in amount, some-
times absent, sometimes scanty and viriditic, at other times
abundant and opaque. Magnetite abounds in the groundmass
much of it often being of secondary origin.

Fourth Order, Felsitic, of the Hypersthene-Augite

Andesites

Formula. — Hypersth-aug, matr, fels.

Characters. — The groundmass presents a rudely granular
appearance or a blurred mosaic.

This order is capable of subdivision, as in the other orders of the
hypersthene-augite-andesites (see Synopsis, page 247) ; but since
it is only represented by six of my rock-sections, I will confine the
description to the general characters.

These rocks are dark-grey, sometimes granitoid in appearance,
with specific gravity 2'65 to 275. They usually show some
alteration, arising from secondary changes within the rock-mass ;
and probably the felsitic or semi-mosaic appearance of the scanty
groundmass is the result of such a secondary change. Such rocks
in some respects approach the type of the gabbros. They are
frequent on the north coast of Natewa Bay in the vicinity of
Waimotu and also occur in the Valanga Ridge. They generally
present themselves as deeper-seated massive rocks exposed by the
stripping off of the superficial deposits.

There are as a rule more or less conspicuous phenocrysts, up
to 3 mm. in size, of plagioclase and pyroxene, in a relatively
scanty micro-felsitic groundmass, displaying a blurred mosaic, in
which a few stout felspar-lathes can still be recognised, and com-
posed apparently of felspar and crystalline silica. The " grain "
Df the mosaic may range in different rocks from '005 mm. to
02 mm. The pyroxene of the groundmass is largely decom-
posed, and the scanty residual glass is represented by viriditic
naterials.

The plagioclase phenocrysts, which give extinctions of medium
md basic andesine (15° — 25°), are often semi-opaque and. cor-
oded. They are traversed by numerous cracks and often contain
nany whitish alteration products, though the lamellar structure is
isually well preserved. The pyroxene phenocrysts are composed
< 'f brownish-yellow augite (ext. -|- 30°) and pale rhombic pyroxene

U 2

292 A NATURALIST IN THE PACIFIC ch. xx!

of the type described before, either as separate crystals or
associated as intergrowths. The rhombic pyroxene crystals are
often sub-rounded with dark borders ; and as a rule the pyroxene
phenocrysts are much fresher than the plagioclase phenocrysts.
As far as can be ascertained, most of the original pyroxene of the
sroundmass was monoclinic with a little rhombic.

CHAPTER XXI

THE VOLCANIC ROCKS OF VANUA LEVU {continued)

Acid Andesites
Previous observations on the Hornblende- Andesites of Fiji

These rocks were first described by Wichmann ^ from specimens
obtained by Kleinschmidt from the mountain of Mbuke Levu in
Kandavu. These Kandavu rocks had a microfelsitic base, the
porphyritic brown hornblende having usually black borders in
which a change into epidote was observed. Rhombic pyroxene
was only noted as an occasional constituent of a rock from Ono.
Renard ^ described these rocks from the vicinity of Ngaloa
Harbour in Kandavu and remarked that bronzite was of more
common occurrence than the monoclinic pyroxene. In the ground-
tnass were numerous felspar and augite microliths, whilst there was
1 porphyritic development of plagioclase, hornblende, biotite, and
pyroxene. The hornblende phenocrysts played an important part
n the rock-composition, being surrounded by a black zone of
nagnetite or bordered by a bacillary aggregate of small pyroxene
)risms, parallel and colourless or greenish, with extinction-angles of
. xf. There was often also a development of biotite in the heart of
1 he mineral, the whole hornblende section being sometimes thus
1 ransformed.

Mr. Eakle ^ has more recently described the hornblende-andesites
1 fom Mbuke Levu in Kandavu. As the result of his examination
( f a collection of volcanic rocks made by the Agassiz expedition in

1 Petrographie des Viti Archipels ; Miner, und Petrogr. Mittheil ; band v,
left I, Wien, 1882.

2 Physics and Chemistry, II. Report Scient. Results; H.M.S. Chat/enger ;
1 ondon, 1889.

3 Petrographical Notes on the Fiji Islands; Proceed. Amer. Acad. Arts and
5 :iences ; vol. 34 ; no. 21 ; May, 1899.

294 A NATURALIST IN THE PACIFIC chap.

Viti Levu, Kandavu, Mbenga, Totoya, Malolo, Yasawa group, and
in several other small islands, he inferred that the hornblende-
andesites are much more limited in their occurrence in Fiji than the
augite-andesites ; whilst hypersthene-andesite was only represented
in the collection from Vomo-lailai near Waia in the Yasawas. The
specimens from Waia had a microfelsitic base with pseudomorphs
of hornblende and some augite. Mr. E. C. Andrews ^ in his account
of his collection of volcanic rocks, made mostly in the Lau Group
and Taviuni, makes no special reference to hornblende-andesites,
the andesites being mainly augitic, rhombic pyroxene also occurring
as a common porphyritic constituent.

It may be inferred from the above and from my own observa-
tions in Vanua Levu below given that hornblende-andesites have a
relatively limited distribution in Fiji. They are not generally
distributed as in the case of the augitic and basaltic andesites ; but
are confined to certain localities in Viti Levu,^ Vanua Levu, Ovalau,
Kandavu, Ono, Malolo, Yasawa Islands, etc.

The occurrence of qtiartz-andesites or dacites in Fiji. — In con-
nection with the existence of these rocks in Vanua Levu, it is note-
worthy that except in Mr. Eakle's paper there is no reference in any
of these writings to the occurrence of quartz-andesites in Fiji.
Wichmann expressly states that the rocks he examined were free
from quartz, and that up to his time (1882) no quartz-bearing
younger eruptive rocks were known from the South Seas. Mr.
Eakle in 1899 described a holo-crystalline andesite with a felsitic
aspect from Malolo and another similar looking rock from Vatu
Mbulo, in the same sub-group of the Fijian Islands, showing quartz
both in the phenocrysts and in the microcrystalline groundmass,
concerning which he observed that it was perhaps more of a dacite
than an andesite. Dacites were found by me in 1884 in the island
of Fauro in the Solomon group,^ and it is probable that they are of
more frequent occurrence in the Pacific than has been generally
supposed. As shown immediately below, they are represented in
Vanua Levu ; and the extent of their distribution in the island
depends on the limits we assign to the definition of the term
" dacite."

^ Notes on the Limestones and General Geology of the Fiji Islands^ Bull.
Mus. Comp. Zool, vol. 5. Geolog. Ser. vol 5, no. i, Cambridge, Mass., U.S.A.
Nov. 1900.

^ Wichmann describes rocks from the cliffs of the Singatoka river and from
Ovalau.

^ Geology of the Solomon Islands, by H. B. Guppy, 1887, pp. 6, 36.

XXI ACID ANDESITES 295

If we restrict the term to a hornblende-andesite carrying por-
phyritic quartz and displaying a microfelsitic groundmass, such
rocks, though they form some of the highest peaks in the
Ndrandramea district, namely Ngaingai and Wawa-levu, would not
be very frequent in Vanua Levu. If, however, a microfelsitic
groundmass is alone necessary to constitute a " dacite," the great
majority of the acid andesites of the island would fall under this
designation.! This has long been a controverted point in petrology.
If I adopted the last procedure, my general classification for the
andesites would fall into confusion and many rocks without any
<3uartz would be included in the dacites.

In the Synopsis it will be seen that my classification of the
andesites is as far as concerns the great groups based on the
mineral and not on the structural characters. There are three
sub-classes closely allied to each other, the hypersthene-andesites,
the hornblende-hypersthene-andesites, and the quartz-hornblende-
hypersthene-andesites or dacites, which cannot be distinguished at
their boundaries by their petrological characters or by their different
modes of occurrence. These groups of rocks which include all the
acid andesites of the island will now be dealt with.

The Acid-Andesites of Vanua Levu

{Comprising the hypersthene-andesites ; hornhlende-hypersthene-ande-
sites ; and quartz-hornblende-hyperstJiene-andesites or dacites)

These rocks compose in mass numerous isolated hills that rise
up abruptly in the interior of the central portion of the island.
Such hills, or mountains, as they might be often termed, usually
attain a height of from 700 to 1200 feet above the surrounding
country, and possess precipitous slopes and frequently perpendicular
<:liff-faces. In the geological description of the island, I have re-
ferred in detail to these mountains, when speaking of Na Raro,
Vatu Kaisia, Ndrandramea, Ngaingai, etc. ; and illustrations of
some of them are included in this work. It may, however, be here
remarked that they are as a rule rudely conical with rounded or
peaked summits. The ground-plan is generally elliptical in outline ;
and in consequence the profile often varies from different points
of view, so that as in the case of Na Raro, it is that of a sharp conical
peak when the mountain is viewed " end-on," or of a broad trun-

^ The term " felsitic andesite " is suitable for this microfelsitic type.

296 A NATURALIST IN THE PACIFIC chap.

cated mass when seen from the side. A similar change of form is
to be noticed in the illustrations of Ndrandramea. No traces of
crateral cavities came under my notice. The rocks are neither
vesicular nor scoriaceous, and are usually massive ; but exhibit at
times a rudely columnar structure.

Each hill or mountain has its peculiar variety of these rocks^
This is well shown in the Ndrandramea district. Thus the rocks
of Ngaingai and of Wawa-levu in carrying porphyritic quartz
differ from those of all the other hills around. Those of Soloa
Levu are distinguished by the orthophyric groundmass and by the
absence of hornblende. Those of Mount Ndrandramea again have
no porphyritic quartz, but little hornblende, and possess a micro-
felsitic groundmass. The rocks of Na Raro and Vatu Kaisia differ
as regards specific gravity, the " grain " of the felsitic groundmass,
the presence of phenocrysts of rhombic pyroxene, etc. The
characters of these rocks from various localities are contrasted in
the table given on a later page, whilst the different sub-classes to
which they belong are described in detail below.

Sub-Class Hypersthene-Andesites

These are dark and light grey rocks, sometimes granitoid in
appearance. They pass on the one hand into the hypersthene-^
augite-andesites before described and on the other into the horn-
blende hypersthene-andesites to be subsequently dealt with.
From the former they are distinguished by the great predominance
of rhombic pyroxene both as phenocrysts and in the groundmass ;
whilst from the latter they are separated by the absence of brown
hornblende or its pseudomorphs. These rocks are found in the
Ndrandramea, Valanga, and Vunimbua districts. They may form
isolated dome-shaped hills as in that of Soloa Levu, or they may
constitute the deeper-seated rocks of the region from which these
hills arise, as in the Ndrandramea district. In their general mode
of occurrence, however, they cannot be treated apart from the
allied hornblende-hypersthene-andesites and the dacites.

This sub-class may be divided like the hypersthene-augite-ande-
sites into four orders according to the character of the groundmass ;
and these are enumerated in the Synopsis. Only the orthophyric
and felsitic orders are represented in my collection. Of the former
the most typical rocks are those composing the hill of Soloa Levu
which is described on page 103.

These Soloa Lev^u rocks are lightish grey and granitoid in aspect,,

XXI ACID ANDESITES 297

with specific gravity of 2*54 — 2-62, and displaying abundant por-
phyritic crystals of pyroxene, 2 — 3 mm. in size. In the slides they
show a large number of plagioclase phenocrysts together with those
of pyroxene in a relatively scanty groundmass, for the most part
orthophyric in texture and without residual glass. . . . The plagio-
clase phenocrysts, which are not usually over 2 or 3 mm. in size, are
often tabular and show distinct zone-lines. Though they are
traversed by minute cracks and have frequently a semi-saussuritic
appearance arising partly from change-products and partly from
the abundance of colourless inclusions, they yield clear lamellar
extinctions of medium and basic andesine (15° — 25°). . . . The
pyroxene phenocrysts, which are not much altered, are in most
cases long pale-yellow rhombic prisms with rounded ends, behaving
optically as described on page 285 ; but intergrowths with mono-
clinic pyroxene may occur and even separate crystals of augite. . . .
The scanty groundmass, though in the main formed of short and
broad felspars, '12 mm. long, of the orthophyric type, displays in
places a rude mosaic, apparently of quartz and felspar. It also
shows abundant small pyroxenes in the form of small prisms
(•05 mm. in length), giving extinctions nearly always straight but
occasionally oblique (30° — 35°).

As examples of the felsitic order of these rocks, most of which
are altered like the propylites, I will first take the case of those
deep-seated rocks that are exposed in the river-bed above Nam-
buna in the Ndrandramea district. In the least altered state they
are dark grey and mottled, and have a specific gravity of 2*66 — 2*69.
In section they display tabular zoned plagioclase phenocrysts,
usually more or less occupied by alteration products, but at times
giving lamellar extinctions of basic andesine (20' — 25°). The
rhombic pyroxene is more or less replaced by chloritoid pseudo-
morphs ; whilst the " grain " of the mosaic is often coarse ('03 mm.),
and much of it is evidently quartz. The more advanced stages of
alteration of these rocks are described in the account of the
district given on page 106. . . . Similar rocks, showing pyrites,
occur amongst the blocks of Vunimbua River ; but here the
rhombic pyroxene is mostly converted into bastite, and the
groundmass is in part trachytic as well as felsitic in texture. The
specific gravity is 27.

(In the last survey of my collection I have found a solitary
specimen from an agglomerate in the Mbua-Lekutu "divide,"
which must be referred to the order with felspar-lathes in flow-
arrangement. It is a pale grey rock showing abundant macro-

298 A NATURALIST IN THE PACIFIC chap.

scopic pyroxene prisms, 2 mm. long, mostly rhombic but showing
also intergrowths with monoclinic pyroxene. The felspar-
lathes do not average more than t mm., and there is a quantity cf
small prisms of rhombic pyroxene in the groundmass, which also
contains a little residual glass.)

Sub-Class Hornblende-Hypersthene-Andesites

This is an extensive group which includes the rocks forming
several of the hills in the Ndrandramea district as well as the
isolated peaks of Na Raro, Vatu Kaisia, etc. It passes on the one
side into the Hypersthene-Andesites before described and on the
other into the Hornblende-Hypersthene-Quartz-Andesites, the
Dacites of this island.

Of the four orders established in the Synopsis (page 236)
according to the general method there adopted, the first, where the
groundmass exhibits felspar-lathes not in flow-arrangement, is
not represented in my collection.

Second Order of the Hornblende-Hypersthene-Ande-

SITES
{Felspar-lathes in flow-arrangement)

This order is only represented by three rocks, all of which belong
to the prismatic sub-order where the pyroxene of the groundmass
is prismatic and not granular.

Two of these rocks are very similar in appearance and char-
acter, though coming from different localities on the opposite sides
of Savu-savu Bay, one from the agglomerate of Vatu-ndamu in the
Kumbulau peninsula (page 91), the other from an intrusive mass
in the vicinity of Urata (page 184). They are dark grey, with
specific gravity 2*6 to 27, and display macroscopic crystals of
hornblende and pyroxene. In the slide they exhibit in addition
numerous phenocrysts of plagioclase, i to 2 mm. in size, in a
groundmass showing small felspar-lathes (less than "i mm. in
length) in partial flow-arrangement and numerous pyroxene
prisms ("05 mm. long) giving straight extinctions, together with a
little residual glass. . . . The plagioclase phenocrysts, which
give extinctions of medium and basic andesine, are often tabular
and display zone-lines. They contain abundant pale inclusions
arranged zone-wise. . . . The hornblende phenocrysts are dark
brown, markedly pleochroic, and give extinctions up to 12 degrees.

XXI ACID ANDESITES 299

•

They have dark resorption borders and are sometimes deeply
corroded. They show in various stages the remarkable conversion
at the borders into fine pyroxene, which is described on page 306 ....
The pyroxene phenocrysts are more numerous in the Urata rock.
They are for the most part of the pale yellow feebly pleochroic
rhombic type that prevails in the island. A few phenocrysts of
pale augite (ext. 35°) may occur in the same slide ; whilst the two
pyroxenes may be associated as intergrowths.

A crypto-crystalHne variety of these rocks, where the felspar -
lathes and rhombic pyroxene prisms of the groundmass are only
in part differentiated, is found on the hills of Ndreke-ni-wai on the
shores of Natewa Bay (page 201). It is a pale-grey open-textured
rock, displaying numerous small macroscopic crystals of horn-
blende.

Third Order of the Hornblende-Hypersthene-

Andesites

{Felspars of the groundmass, short and broad, of the orthophyric

type)

These rocks occur generally as agglomerates and are more
particularly characteristic of the district between the Mariko Range
and the Salt Lake. They belong for the most part to the prism-
atic sub-order of the group and to the section with plagioclase
phenocrysts, and fall naturally into two divisions corresponding to
the two genera with glassy and opaque phenocrysts. The last
named would be regarded by some as porphyrites. The specific
gravity of the specimens ranges from 2*52 to 27.

The plagioclase phenocrysts, i to 2 mm. in size, give extinc-
tions indicating in some rocks oligoclase-andesine (10° — 15°) and
in others basic andesine (15° — 25°). Their opacity in the porphy-
rites is sometimes due to multiple macling, but more usually it
arises from the numerous fine cracks filled with decomposition
products that traverse them. The phenocrysts of dark brown
hornblende are generally abundant and give extinctions of 1 5 degrees.
They as a rule have dark resorption borders in which the process
of conversion into fine pyroxene is in active operation. The
pyroxene phenocrysts are scanty and in most cases rhombic ; but
intergrowths with augite and separate crystals of the last-named
may occur. In the altered rocks or porphyrites they are largely
replaced by bastite and viridite. The felspars of the groundmass

300 A NATURALIST IN THE PACIFIC chap.

are broad and often rectangular and may give lamellar extinctions
of oligoclase-andesine. The pyroxene in the groundmass of the
porphyrites is often partly decomposed. It is as a rule prismatic.
A little interstitial glass, altered in the porphyrites, is generally
present.

Fourth Order of the Hornblende-Hypersthene-

Andesites

{Groundmass felsitic, displaying a granular mosaic structure)

These are light and dark grey rocks showing usually macro-
scopic pyroxene and hornblende. They vary considerably in
appearance from the open-textured rock to that with a granitoid
coarsely crystalline aspect. They generally carry brown horn-
blende phenocrysts, but frequently these are represented by
pseudomorphs ; and they all have a felsitic groundmass. They
are only separated by the absence of porphyritic quartz from the
dacites of Vanua Levu, which are treated in the next sub-class.
They present all stages from the crypto-crystalline to the holo-
crystalline condition, but all show a groundmass which may be
scanty in the more coarsely crystalline rocks.

These rocks are characteristic of some of the hills of the
Ndrandramea district and of the isolated peaks of Vatu Kaisia
and Na Raro. They include a large proportion of the acid
andesites of the island, and all belong to the prismatic sub-order
with prismatic pyroxene in the groundmass, and to the section
with plagioclase phenocrysts. Their specific gravity ranges usually
from 2-55 in the more acid and less crystalline types to 274 in the
most crystalline and basic kinds.

In the typical slides they display phenocrysts of plagioclase,
pyroxene, and brown hornblende in a microfelsitic groundmass
formed evidently of felspar and quartz together with much prism-
atic pyroxene. They may be conveniently divided into three
species according to the size of the "grain " of the groundmass.

Of the first species, where the "grain" is less than 'Oi mm.,
the rocks of Mount Ndrandramea are typical. They have a
crypto-crystalline groundmass where the felsitic structure is in
process of development and where the pyroxene prisms or micro-
liths are very minute. The plagioclase phenocrysts (i mm. in size)
give extinctions of acid and medium andesine (10° — 20°), and are
tabular, zoned, and contain abundant pale inclusions. The horn-
blende phenocrysts, except in the case of the rocks at the foot of

XXI ACID ANDESITES 301

the hill, are represented by pseudomorphs in various stages of
dispersion, so that this character is likely to be overlooked. The
pyroxene phenocrysts are in most cases of the pale yellow feebly
pleochroic rhombic type, but they may present intergrowths of
both the monoclinic and rhombic forms. These are light grey
rocks with a specific gravity increasing as one descends from the
summit, where it is about 2*5, to the base where it is 27, a change
corresponding with increase of the ferro-magnesian minerals and
with the more crystalline structure of the groundmass.

The second species, where the " grain " of the mosaic is between
•01 and "02 mm., is represented by the Vatu Kaisia rock and by
that exposed in the opposite side of the gorge. They are granitoid
in appearance and have a specific gravity of 2'68 to 271. Large
porphyritic crystals of pyroxene and hornblende, the last some-
times 7 mm. in length, occur in a dark grey base. In the slide
these phenocrysts together with those of plagioclase are displayed
in a somewhat scanty holo-crystalline groundmass, where the
" grain " of the mosaic averages "012 mm. The plagioclase pheno-
crysts are zoned, and give in different crystals extinctions in some
cases of oligoclase-andesine (10° — 12°) and in others of andesine-
labradorite (25° — 30°). The hornblende phenocrysts in their
pseudomorphism illustrate the various stages of the process of
conversion into fine granular and prismatic pyroxene. The least
altered crystals have dark resorption borders and are at times
deeply corroded. The pyroxene phenocrysts are for the most
part rhombic ; but intergrowths with the monoclinic form occur.
The pyroxene of the groundmass consists for the most part of
small rhombic prisms averaging '05 mm. in length.

The third species, where the groundmass may be described as a
coarse mosaic with a " grain " between 02 and '03 mm., is repre-
sented by the rocks of the peak of Na Raro and of Mount Thoka-
singa in the Ndrandramea district.

The Na Raro rocks are light grey with a specific gravity in the
un weathered state of about 2*6, and display macroscopic crystals
of glassy plagioclase and hornblende. In the slide they exhibit
tabular phenocrysts of the plagioclase, together with dark pseudo-
morphs after hornblende, in a coarsely felsitic groundmass (grain
•022 mm.) where a little very fine prismatic pyroxene, apparently
rhombic, occurs. There is also a little altered interstitial glass.
The plagioclase phenocrysts are zoned and give extinctions of 15°
to 25° (acid and basic andesine), whilst they often show magma
inclusions. An interesting feature of these rocks is concerned

302 A NATURALIST IN THE PACIFIC chap.

with the rarity or absence of phenocrysts of pyroxene. They are
to be seen, however, in the process of being built up within the
substance of the hornblende pseudomorphs, which consist entirely
of minute prisms and granules of pyroxene and of fine magnetite.
The process seems to consist in the formation of parallel layers of
rhombic and monoclinic pyroxene.

The Thoka-singa rocks are more basic (spec. grav. 272 to 274),
and in the scanty holo-crystalline groundmass approach the plutonic
type. They are dark grey granitoid rocks displaying abundant
macroscopic pyroxene crystals 2 to 3 mm. long. The original
hornblende phenocrysts are only represented by traces of pseudo-
morphs of fine pyroxene and magnetite, the process of dispersion,
described on page 307, being almost completed. The pyroxene
phenocrysts are mostly rhombic ; but intergrowths with the mono-
clinic form occur. The " grain " of the mosaic of the groundmass is
coarse ('023 mm.), and there is a fair amount of prismatic with a
little granular pyroxene, the prisms, '04 mm. long, giving usually
straight extinctions, whilst the granules are apparently monoclinic.

Sub-Class Quartz-Hornblende-Hypersthene-Andesites

OR Dacites

These rocks are infrequent. They compose in mass the
adjacent mountains of Ngaingai and Wavva Levu in the Ndran-
dramea district, and appear also on the lower slopes of the neigh-
bouring mountain of Navuningumu. They differ chiefly from the
hornblende-hypersthene-andesites in the presence of porphyritic
quartz, which, however, is not as a rule abundant. In their general
origin and affinities and in their mode of occurrence they cannot
be separated from the two sub-classes of hypersthene-andesites
and hornblende-hypersthene-andesites before described. They
all belong to the felsitic order of the sub-class, and all are referred
to the sub-order with prismatic pyroxene and to the section with
plagioclase phenocrysts.

They are light grey rocks, with a specific gravity of 2*57 to
2*6 1, showing usually dark pseudomorphs after hornblende and a
little porphyritic quartz. In the slide they display these pseudo-
morphs and quartz crystals, associated with abundant plagioclase
phenocrysts, in a felsitic groundmass, evidently a mixture of felspar
and quartz, with fine pyroxene, mostly prismatic and rhombic.
Pyroxene phenocr>'sts are absent or rare ; but they may be seen
in process of formation in the substance of the hornblende-pseudo-

XXI ACID ANDESITES 305

morphs. It is only at times, as in the instance of the Navuningumu
rock, that the brown hornblende phenocrysts are in part unchanged
and that complete pyroxene phenocrysts occur. In such cases the
last may be entirely rhombic, or may exhibit at times intergrowths
with the monoclinic form.

The plagioclase phenocrysts, 2 mm. in size, are often tabular
and zoned and give two sets of extinctions, indicating acid and
basic andesine. Their abundant inclusions are arranged in zones.
The quartz-crystals, i to 2 mm. in size, present hexagonal sections
with rounded angles. They are sometimes traversed by cracks
occupied by iron oxide films. The pseudomorphs after hornblende,
which consist of fine pyroxene mixed with magnetite, exhibit often
the building up in their interior of pyroxene phenocrysts, apparently
rhombic, by long parallel rows of stout prisms. In other cases
the pseudomorphs display the different stages of dispersion. The
fine pyroxene of the groundmass consists mostly of rhombic
prisms ('02 — '06 mm. long) with some granules. The " grain " of
the groundmass is usually between 'Oi and '02 mm. There is little
or no residual glass.

The rocks of Wawa Levu and Ngaingai are closely similar,
but they differ in the size of the prismatic pyroxene of the ground-
mass, which is coarser in the first-named mountain ("055 mm. long)
than it is in the second (-025 mm. long). In both the " grain " of
the mosaic is about the same ("014 mm.).

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3o6 A NATURALIST IN THE PACIFIC chap.

Note on the Rhombic Pyroxene of the three foregoing sub-classes
of the Acid Andesites. — The term " hypersthene " has been here
used as a convenient expression equivalent to " rhombic pyroxene."
The mineral is always a little pleochroic and is never colourless,
and it is only in very rare cases that the term " enstatite " could be
used. As a matter of fact there is practically only one form of
rhombic pyroxene represented in my collections whether in acid
or basic andesites or in hemi-crystalline and plutonic rocks. In
the acid andesites it occurs not only as phenocrysts but also as
minute prisms forming a constituent of the groundmass.

This mineral, when composing the phenocrysts, presents itself
usually as single untwinned prisms which exhibit the typical octa-
gonal cross-sections with much reduced prism-faces. The prismatic
sections give straight extinctions ; whilst with the cross-sections
we obtain straight extinctions parallel with the pinakoid faces.
The colour in transmitted light is pale brownish yellow. The
pleochroism, though usually feeble, is quite distinct, the colour
being pale yellow, when the prism lies parallel with the long
axis of the lower nicol, and almost white when it lies across.
Not infrequently these phenocrysts behave abnormally and give
small oblique extinctions. This is often the case when monoclinic
pyroxene occurs in the same section. The association of the
two pyroxenes in one crystal can in some cases be clearly
recognised. At one time a plate of pyroxene exhibits itself as a
coarse aggregate of the two pyroxenes. At other times the two
occur as parallel intergrowths, as in the accompanying figure.
But it is rarely that such intergrowths are so typically displayed,
the reason of which has been supplied by Zirkel in his Lehrbiich
der Petrographie ; 2nd edit. : I. 271.

l^ote on the " magmatic paramorphism " ^ of the hornblende
phenocrysts. — Reference has before been made in the general
description of these rocks to the dark alteration margins
of the hornblende phenocrysts. The dark borders display the
"bacillary" structure noticed by Renard in the case of some
hornblende andesites from Kandavu in the same group of islands,^
being composed of minute granules and parallel prisms of
pyroxene and also of magnetite grains. With the Kandavu
rocks Renard observed that the tiny pyroxenes were colourless or

1 I have borrowed this term from Rosenbusch's Microscopical Physiography
of the Rock-making Minerals, translated by Iddin^s.
' Challenger Reports y Physics and Chemistry II.

XXI MAGMATIC PARAMORPHISM 307

greenish and had an extinction angle of 40°. In the Vanua Levu
rocks, however, there is a mixture in these dark margins of both
monoclinic and rhombic pyroxene ; and the process may be
observed in all stages as it advances into the interior of the crystal,
until a dark pseudomorph or paramorph of pyroxene and
magnetite results. When the magnetite prevails, the pseudomorph
may ultimately form a black patch in which the process is
obscured. But when, as is generally the case, the pyroxenes
are more frequent, it occurs as a dark grey mass.

Finally follows the dispersion of the pseudomorph, which
first becomes a loosely arranged aggregate of the two pyroxenes
and magnetite, and then breaks down, and at length is only
represented by small pale patches of its original constituents.
These patches are easily recognisable, and in not a few rock-
sections offer the only indication of the previously existing
hornblende phenocryst. There can be little doubt that this is
the source of much at least of the often abundant pyroxenes of
the groundmass, which are usually most frequent in the vicinity of
the patches.

In the earliest stage when the dark border alone exists, it is
not easy to distinguish the one pyroxene from the other, the
granules and prisms being colourless and very minute, less than
•01 in size. But in a far advanced stage of the paramorphism the
granules and prisms become sometimes much larger, the first
attaining a breadth of '04 and -05 mm. and the last a length of '15
mm. Finally the interior of the paramorph is seen to be more or
less completely composed of very pale brown augite and pale
yellow rhombic pyroxene in coarse grains and prisms, the first
distinguished by its oblique extinction of 30° to 35°, the last
recognised by its straight extinction and feeble though distinct
pleochroism.

Although as a rule the paramorph becomes dispersed and its
pyroxene constituents are added to the groundmass, it sometimes
exhibits a change of another character. In this case the outer
Dortion is alone dispersed, whilst the growth of a single large
:rystal of pyroxene proceeds within the mass. In a later stage,
A^hen the dispersion of the outer part is complete, we have a fresh-
ooking pyroxene phenocryst with unformed edges, on the borders
)f which little granules and prisms of pyroxene may be seen
irranging themselves, as if the crystal-building was still in progress,
)r rather as if it had been interrupted and left unfinished by the
00 rapid dispersion of the outer portions of the paramorph.

X 2

3o8 A NATURALIST IN THE PACIFIC chap.

It will be gathered from the above that the source of the
pyroxene of the groundmass is to be found in the magmatic
paramorphism of the porphyritic hornblende. The hornblende is
dark-brown, markedly pleochroic, and extinctions up to 1$" are
given in prismatic sections. It is well known that the conversion
of a hornblende crystal into an aggregate of pyroxene prisms and
magnetite was long since experimentally effected by Doelter and
Hussak by immersing the hornblende in molten basalt, andesite,
&c.^ I would imagine that the transformation of the hornblende
and the dispersion of the paramorph occurred under two con-
ditions ; in the first case whilst the " flow " was still in motion
when the resulting pyroxene would be mixed up in the
magma ; in the second case after movement had ceased, but before
consolidation of the groundmass, when a paramorph or pseudo-
morph would be formed.

Oligoclase-Trachytes

The term " trachyte " is here applied in a general sense to a
group of light-grey intrusive acid rocks, having a specific gravity
when compact of 2*4 to 2 '45 and showing phenocrysts of glassy
felspar, but not of quartz. These rocks, which are especially
characteristic of the districts around Tawaki and Mount Thuku
and of the Wainikoro sea-border, are often open-textured and
sometimes a little vesicular, whilst several of them exhibit some
degree of alteration in the groundmass. In all cases they appear
to be intrusions rather than surface-flows ; and at times they
display a columnar structure.^

The difference between the oligoclase-trachytes in various
localities appears to be mainly concerned with the varying degrees
of crystallisation. There are two principal varieties. In the most
crystalline type there are small phenocrysts of glassy felspar and
a few of pale augite, the angle of extinction of the last being
over 30 degrees. The felspar phenocrysts, which contain but few
inclusions and have sharp rectilinear outlines, in most cases show
zoning and give lamellar extinction of 5° to 12° indicating oligo-
clase ; but some of them have the tabular untwinned or simple
twinned form of sanidine. The groundmass is in the main
composed of minute felspar-lathes, less than 'i mm. in length,
arranged in a dense plexus, and giving nearly straight extinctions.

* Neues Jahrb.fur Mineralogie, 1884.

^ For their mode of occurrence, see pp. 215, 220, 230-233.

XXI QUARTZ PORPHYRIES 309

But it also contains a number of scattered larger felspar-lathes
averaging '2 mm. in length and giving extinctions of 5° when
simple, and of 8° to 10° when lamellar. There is also some small
prismatic augite in the groundmass but often decomposing. The
original interstitial glass is represented by numerous reddish-brown
patches of devitrified glass.

In the second type of these trachytes, the rock is more open in
texture and is at times vesicular, the specific gravity being usually
less than 2*4. The general characters are much the same, but
sanidine is better represented among the phenocrysts, and the
groundmass is more blurred ; but when the felspar-lathes are
distinct they give an extinction either nearly straight or from 4° to
8°, according as they are simple or display lamellae. The augite of
the groundmass is scanty and more or less decomposed ; whilst
the interstitial glass when unaltered is in fair quantity and nearly
isotropic.

The alteration observed in several of these oligoclase-trachytes
is restricted chiefly to the interstitial glass in which secondary
quartz and at times calcite and viridite are developed. Scarcely
any of them are quite free from these changes.^

The pitchstone or vitreous form of these trachytes is displayed
in the blocks of an agglomerate-tuff between Tawaki and Mount
Thuku. It has a specific gravity of 2"36, is dark-brown, and has
a conchoidal fracture. Phenocrysts of felspar, mostly oligoclase,
with extinction-angles of 5° to 11°, and often penetrated by the
magma, are inclosed in a semi-isotropic groundmass showing
incipient development of felspar and other darker microliths.
There are also a few small phenocrysts of pale augite.

Quartz Porphyries and Rhyolitic Rocks

Wichmann when he wrote in 1882 that no quartz-bearing
younger eruptive rocks had hitherto been observed either in Fiji or
in the South Sea Islands generally, had apparently overlooked
Dana's observations in the Fijian group. The American geologist ^
refers to a rock found on the north-east shores of Vanua Levu
which exhibited in a greenish base thickly disseminated crystals of
quartz (bipyramidal dodecahedrons, | of an inch in diameter) and
glassy felspar, together with a few sphene crystals.

^ Highly altered rocks of this class are exposed at the base of Mount
Nailotha as described on p. 215.
2 See work quoted on p. 218.

3IO A NATURALIST IN THE PACIFIC chap.

Quartz porphyries, akin to the rhyolites, are especially charac-
teristic of the north-east part of the island, to which in fact they
are entirely confined. They perhaps are best represented in the
vicinity of Mount Thuku and in the neighbourhood of the mouth
of the Wainikoro River. None of my specimens have the fresh
appearance of the Lipari rhyolites and all are more or less altered.
Their specific gravity does not exceed 2*4, and they are for the
most part intrusive in character.

A rock frequently exposed between Tawaki and Mount Thuku ^
contains abundant phenocrysts of glassy felspar (oligoclase and
sanidine) and quartz in a greenish opaque groundmass having a
blurred microfelsitic structure. There appears to have been a
secondary devitrification of the groundmass since consolidation.
The porphyritic quartz crystals are rounded and about 2 mm. in
diameter.

Another rock displayed in the coast-cliffs on the north side of
Natewa Bay, a mile east of Mount Thuku, has a somewhat banded
appearance. It shows crystals of quartz, more or less rounded and
3 to 4 mm. in diameter, together with phenocrysts of glassy felspar
(oligoclase with lamellar extinction of 5° and sanidine). The
groundmass displays traces of spheruHtes and is in places semi-
isotropic ; but for the most part it is microfelsitic.

The type of rock found in the Wainikoro district and in the
adjacent sea-border, where it may be observed forming dykes in
the pumice-tuffs, is light-grey and loose-textured with a specific
gravity of 2*i. It exhibits small phenocrysts of quartz and of
glassy felspar (oligoclase 5° to 12°, and sanidine), with, in one
locality only, a scanty amount of dark green hornblende yielding
extinctions up to 20°. The quartz crystals, which are i to 2 mm.
in size, are sometimes bipyramidal ; but are often rounded and
have fused-like outer surfaces. The groundmass is semi-isotropic
with a blurred aspect, and shows traces of spherulites and numerous
crystallites, with occasional felspar-lathes giving a nearly straight
extinction.

An extensively altered quartz porphyry of a different type is
associated with other altered rocks at the base of Mount Nailotha.
It has a specific gravity of 2*54, and displays large opaque
crystals of plagioclase, 2 to 5 mm. in size with small quartz crystals
I to 2 mm. across, in a grey compact matrix. The first-named
shows the felspar to be mostly replaced by alteration products ;
but occasionally a lamellar extinction of 6° or f can be observed.

^ See p. 230.

XXI QUARTZ PORPHYRIES 311

The quartz crystals are rounded and penetrated by the magma,
and contain numerous strings of fluid-cavities. The groundmass
was originally spherulitic ; but this structure is more or less
disguised by the development of a mosaic of chalcedonic quartz.
It shows some micro-porphyritic patches of viridite and calcite.
A singular altered white rhyolitic rock is exposed on the north
coast of Natewa Bay between Natasa and Sangani, where it is
associated with altered tuffs. It is compact with a conchoidal
fracture and has a specific gravity of 2'48. The hand-specimen
has a banded appearance. Under the microscope it appears as a
rhyolitic glass for the most part devitrified and rendered opaque
by the formation of secondary silica. Much of it presents a micro-
felsitic structure, the bands appearing as semi-opaque streaks.

Glassy forms of the quartz porphyries or intrusive rhyolitic
rocks are extensively represented in the pumice tuffs of the Undu
Promontory and of the coasts between the Langa-langa river and
Lambasa, These tuffs will be found described on page 336.
Fragments of a grey rhyolitic glass looking like perlite are inclosed
in the pumice-tuffs near the mouth of the Wainikoro River. Under
the microscope it is displayed as a colourless glass inclosing
phenocrysts of sanidine, oligoclase (ext. 4°), and quartz, the last
with rounded outlines and a fused-like outer surface. The glass
shows in places perlitic cracks ; but it is mainly characterised by a
vacuolar structure, the minute cavities being lengthened out in the
direction of the flow and displaying eddy-currents around the
phenocrysts. The elongated steam-cavities sometimes contain
water, but are usually more or less filled with granular materials.

CHAPTER XXII

basic glasses and volcanic agglomerates

Basic Pitchstone and Basic Glass

1
It is not possible to draw a sharp distinction between the |

pitchstone and the purely vitreous condition of these glasses. The 1
following remarks will therefore apply to both.

Regarded as components of the pitchstone-tuffs and palagonite-
tufifs these rocks have a very extensive distribution in the island ;
but in the massive state they are hardly ever to be found, whilst in
the form of agglomerates they are only frequent in certain localities,
as in the cliffs of the Korotini Bluff, in the vicinity of Mbale-mbale,
on the slopes of Soloa Levu, and in the dividing ridge between the
Mbua and Lekutu plains. On rare occasions they are to be found
in a rubbly condition, as in the upper part of a basaltic flow
described on p. 92, or they may form veins in a more crystalline
basaltic rock as at Vatulele Bay. Their specific gravity ranges
from 2'6i to 277, and they fuse readily before the blow-pipe, the
melting beginning in the ordinary flame. Since they are not
dissolved under any condition in HCl, they would be referred to
the old hyalomelane group of basic glasses.

One of the most interesting of these rocks occurs on the slopes
of Soloa Levu. As displayed on the south-west slope, it presents
itself as a brownish-black rock with a specific gravity of 2'6i and
exhibiting large porphyritic crystals (6 to 8 mm.) of plagio-
clase. It is generally compact, but it is in places a little vesicular,
the minute cavities being often filled with a zeolite. The mode of
occurrence of this pitchstone-porphyry is described on p. 104. In
the slide the plagioclase phenocrysts give lamellar extinctions
(21° — 27°) of andesine labradorite, and have regular outlines, with
but few inclusions of the glassy magma. There are also a few

CH. XXII BASIC GLASSES 313.

small phenocrysts of augite with dark rounded borders and showing
in some cases lamellar twinning. The groundmass is a brown
rather turbid glass in which dark points of devitrification occur»
It is traversed by cracks that also penetrate the felspar phenocrysts.
These cracks are filled with a feebly refractive material like
palagonite ; and there are traces of the early stage of the
palagonitic change in one or two places. This is of importance,
because on the north-west side of the hill occurs the same rock, in
which the basic glass has been converted into a reddish-brown
almost opaque palagonite ; but in this case the porphyritic crystals
of plagioclase are more affected by the magma, being rounded and
extensively penetrated schiller-fashion by this material ; whilst the
augite phenocrysts are somewhat similarly affected. The altered
glass is also vacuolar, the cavities being filled with a zeolite. There
is an indication of some degree of crushing in the fracture of some
of the felspar phenocrysts in situ. There appears to be a con-
nection, as shown on p. 342, between the crushing of a basic glass
and the formation of palagonite. It is noteworthy that with this
change the specific gravity drops from 2*6 1 in the comparatively
fresh rock to 2-14 in the palagonitised hydrated condition.

As another example of these basic pitchstones I will take that
forming an agglomerate near Mbale-mbale. It has a specific
gravity of 277 and displays phenocrysts of plagioclase, olivine, and
augite. The first-named, which give the lamellar extinction of acid
labradorite, (22° — 28°), are fresh-looking and only affected to a small
extent by the magma. Those of olivine and augite are in much the
same condition. The glass of the groundmass is rather turbid and
displays numerous dark patches of incipient crystallisation, which
in some cases prove to be composed of brush-like crystallites
around a clear H-shaped nucleus, and in other cases have a more
prismatic form.

A vitreous rock having some of the characters of a variolite is
found near Narengali (see page 150). It, however, has the low
specific gravity of 2'43 and is not readily fusible with the blow-pipe.
It displays an imperfect spheroidal structure on a small scale, being
made up of nodules, the largest having the size of a filbert. In the
slide it appears as a grey glass made up of sheaf-like aggregates of
fibre-like crystallites, apparently of felspar, with minute skeleton
prisms of pyroxene in parallel arrangement, and is traversed by
perlitic cracks.

314 A NATURALIST IN THE PACIFIC chap.

The Volcanic Agglomerates

In this place my remarks will be chiefly confined to a summary
of some of the leading features of these formations. The
agglomerates, which pass by all gradations through the tuff-
agglomerates into the submarine tuffs, rank amongst the most
prevalent and the most conspicuous of the rocks exposed at the
surface in this island. Their lithological characters vary according
to the type of the massive rocks of the district. Thus in the
Ndrandramea district the blocks are composed of the prevailing
acid andesites. In the Koro-mbasanga district they are formed of
hypersthene-augite-andesites. In the Korotini and Va-lili ranges
they are composed of olivine basalts and basaltic andesites. The
agglomerates derived from basaltic rocks and basic andesites are by
far the most frequent, and it is to them that the following general
observations apply.

The basic agglomerates and tuff-agglomerates are found almost
everywhere and at all elevations up to 2,5CX) feet above the sea and
over. They compose the inland cliffs and the long lines of
precipitous declivities that give character to the valleys and gorges
of the mountainous interior. The blocks are often scoriaceous
and semi-vitreous, but the characters of the rocks will be found
described on page 316. They are generally sub-angular and vary in
size from a few inches to one or two feet ; and, though sometimes
heaped together in confusion, they will generally be found in the
case of any extensive exposure to be ruddy sorted according to
size, or to present a rude horizontal arrangement.

The matrix varies much in amount, being sometimes barely
appreciable and at other times so abundant that the deposit may
be termed a tuff-agglomerate. Typically it has the character of the
palagonite-tuffs of mixed composition described on page 326, being
made up of fragments of palagonitised vacuolar basic glass, por-
tions of crystals of plagioclase and augite, with the debris of the
basic semi-vitreous and hemi-crystalline rocks forming the blocks.
When it is scanty it contains neither carbonate of lime nor organic
remains ; but in the tuff-agglomerates it may be calcareous and
may inclose tests of foraminifera and molluscan shells.

From the circumstance that the basic agglomerates overlie
submarine sedimentary tuffs and clays almost everywhere, their
submarine origin could alone be safely postulated. There are one
or two localities that throw especial light on the conditions under

XXII VOLCANIC AGGLOMERATES 315

which these accumulations occurred. They are dealt with at some
length in the general description of each district and only a brief
reference can be made to some of their indications here.

The testimony supplied by the interesting exposures on the
slopes of Mount Thambeyu (page 178) goes to show that after the
deposition of the foraminiferous tufifs and clays the stage of the
agglomerates was ushered in gradually. The tuffs increased in
coarseness, and afterwards they were covered up with an
agglomerate formed of blocks at first only one or two inches in size,
but afterwards of larger dimensions. . . . Curious evidence is
afforded by the agglomerates of Mount Vungalei (page 213), where
two beds of palagonite-tufif, at elevations of 900 and 1,700 feet, mark
two pauses in the accumulation of the agglomerates. In each case
the pause was introduced by the gradual decrease of the agglomer-
ates which gave place by gradation to the tufifs. In each case also
the pause was followed by a sudden renewal of the deposition of
agglomerates.

With reference to the maximum thickness of these deposits, it
would appear that on the slopes of the Korotini Range this amounts
to some hundreds of feet, if we also include the tuff-agglomerates.
Their origin is to be attributed partly to eruptions and partly to
marine erosion. The two agencies although often associated were
in their turns predominant in their different phases, and it is not too
much to suppose that the agglomerates without arrangement, with
scanty matrix, and composed of scoriaceous blocks, belong more to
an eruptive period, and that those with abundant tufaceous matrix
and sorted blocks are mainly the product of marine erosion. In
either case the deposition was submarine.

But the history of these agglomerates and of their associated
foraminiferous tuffs and clays must of necessity be a complicated
one, since they indicate a minimum emergence of 2,500 feet. Their
accumulation first began when a number of vents, in linear arrange-
ment, were striving to raise their heads above the surface of the sea.
It was continued after the waves had ultimately worn the volcanic
islets down to below the sea-level, and the shoals became covered
over with submarine deposits. Again and again no doubt this
struggle between the eruptive agencies and the waves was renewed,
until at length the great emergence began, and probably from that
date the agency of marine erosion was predominant.

When on the island of Stromboli I had presented for my
observation at least two modes of agglomerate-building under the
sea. There was the ordinary work of the marine erosion of the

3i6 A NATURALIST IN THE PACIFIC ch. xxii

lava-cliffs, of which the beach represents but a small part of the
result ; and there were the dribbling eruptions of the crater, from
which at intervals of only a few minutes masses of semi-molten lava
bounded down the steep slopes into the sea.

Note on the general characters oj the rocks of the basic
agglomerates. — In appearance the basic rocks forming the blocks
are often very similar. They are usually compact blackish with a
semi-vitreous aspect and display some plagioclase phenocrysts.
But to enumerate the types to which they belong would be to go
over much of the ground traversed in the classification of the
basic rocks, whether olivine basalts, basaltic andesites, ordinary
augite-andesites, or hypersthene-augite-andesites. The ground-
mass as a rule contains much smoky glass, but the hemi-crystalline
portions of it vary considerably in character. Whilst fine granular
augite prevails, semi-ophitic coarser augites are not uncommon, and
prismatic pyroxene, sometimes of the rhombic form, is represented
in the groundmass of the rocks composing the agglomerates of
Mount Thambeyu and of the Sokena Cliffs. In some localities, as
on the south-west slopes of the Korotini Range, rocks of the basic
pitchstone kind are predominant.

CHAPTER XXIII

CALCAREOUS FORMATIONS, VOLCANIC MUDS, PALAGONITE-TUFFS

The classification that is adopted in my work on the geology of
the Solomon group with respect to the calcareous formations and
volcanic muds of those islands is only in part applicable to the
calcareous rocks and volcanic deposits of Vanua Levu. Deposits
strictly comparable with those of the Solomon Islands here exist,
and have in some places an extensive distribution ; but many
others cannot be referred to that classification. In addition to the
calcareous oozes and volcanic muds, such as are now forming off
these reef-bound coasts, the result partly of marine erosion and
partly of sub-aerial denudation, there are many kinds of submarine
deposits in Vanua Levu that have been largely formed from the
materials ejected by volcanic vents. Basic glasses, for instance,
often finely vesicular and usually converted into palagonite, enter
largely into the composition of submarine deposits that frequently
form the surface from the sea-borders to the summits of the
mountain-ranges ; and it is by the degradation of a land-surface
formed of such materials that the volcanic muds comparable to
those of the Solomon Islands are mainly produced. It is therefore
apparent that we have to distinguish here between the deposits of
sedimentary and eruptive origin, a distinction, however, which is
not always easy to make, since they are in both cases submarine,
and doubtless were often in process of forming together. The
deposits most prevalent in the island are the submarine tuffs partly
sedimentary and partly eruptive in their origin and the overlying
volcanic agglomerates. The first are usually palagonitic and
calcareous and often contain organic remains, being usually
associated with volcanic muds and clays mainly the product of
marine erosion.

3i8 A NATURALIST IN THE PACIFIC. chap.

In connection with the employment of the terms " upraised "
and " elevated " in the case of the Vanua Levu deposits I will take
this opportunity to remark that I do not thereby commit myself to
the view that there has been an actual upheaval of this region.
This is a matter, however, that will be found discussed in Chapter
XXVII.

The Upraised Coral Limestones

These reef-limestones are scantily represented in the island,
though one can scarcely doubt that they were once far more
extensive, having been largely stripped off by the denuding
agencies. They are mostly found on the south coast between
Naindi Bay and Fawn Harbour, and rarely extend to heights
greater than 20 or 30 feet above the sea, usually composing the sea
cliffs and not occurring as a rule inland. Massive corals are often
to be seen imbedded in their position of growth, as described in
Chapter II. ; and as far as the absence of signs of disturbance is
concerned, these ancient reefs might owe their present situation,
either to the withdrawal of the sea or to the upheaval of the land.
Such reef-limestones exist over much of the Pacific, and they
belong to the usual type of these rocks.

Shelly and Foraminiferal Limestones

These rocks are composed partly of reef-debris, partly of
volcanic detritus, and partly of the tests of foraminifera (usually
bottom forms), fragments of lamellibranchiate and gasteropod
shells, together with those of pteropods, and other organic remains.
Occasionally separate valves of the genera " Cardium " and
" Ostraea " are inclosed in the limestone. These rocks have been
evidently formed in rather shallow water. In places they overlie
palagonite-tuffs and clays, also foraminiferal. Similar limestones
are doubtless forming at the present time off the coast.

They are usually hard in texture and greyish or pale yellow in
colour. They contain between 25 and 45 per cent, of carbonate of
lime ; whilst the residue consists of fragments of minerals (10 to 15
per cent), including plagioclase, monoclinic and rhombic pyroxene,
and occasionally brown hornblende, with siliceous casts of foramini-
fera (4 to 20 per cent), mostly formed of chalcedonic silica but some-
times black and glauconitic ; the remainder (30 to 40 per cent)
being composed of rounded and sub-angular portions of palagonite
and semi-vitreous basic rocks, of which the larger vary from 5^ to i
millimetre in diameter. In some cases the carbonate of lime of the

XXIII FORAMINIFERAL LIMESTONES 31^

inclosed organic remains has been mainly replaced by more or less
crystalline silica. In others a recrystallisation of the calcitic
material is in progress, as described on page 131 ; and the matrix
presents in places a mosaic of calcite.

These rocks have therefore been subject to some degree of
alteration, the causes probably lying within the mass. They are,
however, far from frequent. They are best represented in the upper
valley of the Sarawanga River in the vicinity of Tembe-ni-ndio,
where they reach to a height of about 250 feet above the sea. The
greatest elevation at which I found them was in the mountainous
interior of the Waikawa Promontory, where they occur at a height
of 1,100 feet above the sea.

As samples, the results of the examination of two rocks froni.
the Tembe-ni-ndio district are here appended : —

A.

Carbonate of lime 46 per cent.

'Fragments of palagonite and of semi-vitreous

basic rocks 30 » ?>

Residue -{ Minerals 12 „ „

Secondary silica replacing the carbonate of
lime in the organic remains 12 , „

It displays to the naked eye fragments of shells including
pteropods, and numerous tests of foraminifera 2 or 3 millimetres in
diameter. In the section it displays in addition coral debris and a
considerable quantity of rounded and sub-angular pieces of pala-
gonite and semi-vitreous basic rocks, usually less than a millimetre
across, with smaller fragments of minerals (pyroxene and plagio-
clase), and much calcitic material in the matrix.

B.

Carbonate of lime 25 per cent.

Debris of palagonite and of basic volcanic rocks . 45 „ „

Minerals 10 » )>

Siliceous casts of foraminifera 20 „ „

The organic remains mainly consist of tests of foraminifera,
many of which occur in the residue as colourless siliceous casts,.
The fragments, whether of minerals or of volcanic rocks, are
usually less than half a millimetre across. The foraminifera are
mostly small and of the " Globigerina " type ; but there is a cast
of a tube of some boring-mollusc, and fragments of shells also-
occur.

32 o A NATURALIST IN THE PACIFIC chap.

Pteropod-ooze Rocks

These rocks are bluish-grey when not exposed ; but through the
hydration accompanying exposure they become much lighter in
colour. They are crowded with pteropod shells, and contain also
small gasteropod and lamellibranchiate shells together with tests
of foraminifera both microscopic and macroscopic. They yield
between 30 and 40 per cent, of carbonate of lime, the residue being
made up of disintegrated palagonitic debris and fine clayey
material derived from the same source, together with a fair amount
of mineral fragments (10 per cent.) which include plagioclase,
pyroxene, and brown hornblende, and measure in the case of the
larger fragments between t and "4 mm. in diameter. Such rocks
are somewhat friable and correspond with the pteropod-ooze rocks
of the Solomon Islands ; but they are not very frequent, being best
represented on the flanks of the basaltic table-land between the
Wainunu and Yanawai rivers, as in the vicinity of the Nandua tea-
plantation where they extend up to 500 feet above the sea. In
this particular locality (see page 345) they overlie horizontally-
stratified tuffs and clays, composed of the debris of a basic glass
usually vacuolar but now for the most part converted into pala-
gonite, and showing a few small tests of foraminifera.

These deposits are always either surface or incrusting formations.
The circumstance of their passing down into characteristic
palagonite-formations is repeated in the case of the Tembe-ni-ndio
limestones, as observed on page 131 ; and there is no doubt that
much of their non-calcareous material is derived from the disinte-
gration of palagonite.

Sample of pteropod-ooze rock from below the Nandua tea-
plantation.

Carbonate of lime 38 per cent.

/• Palagonitic debris and clayey material . . 51 ,, ,>

Residue -! Minerals 8 ,, „

I Casts of foraminifera 3 „ „

100

Fine clayey material makes up the greater part (72 per cent.)
of the residue. It presents the microscopic characters of material
•derived from the degradation of palagonite. Amongst the mineral
fragments, of which the larger are '2 to '3 mm. in size, occur brown
hornblende, pyroxene, felspar, magnetite, &c. The casts of foramin-
ifera are usually glauconitic, but a few are of crystalline silica. A

XXIII VOLCANIC MUD-ROCKS 321

number of curious little pellets of palagonite, oblong or oval in
form, occur in the residue. Their size is ^ to '6 mm., and they
apparently represent the minute amygdules of palagonite that
occupy the vacuoles in an altered basic glass.

FORAMINIFEROUS VOLCANIC MUD-ROCKS

These deposits, which represent the " volcanic muds " forming
around the coasts of volcanic islands, are more or less consolidated
clay-rocks. They contain in varying numbers the tests of foram-
inifera with occasionally pteropod-shells. The former are usually
minute and of the " Globigerina " type ; but in some rocks larger
bottom-forms prevail. The original colour of these deposits is
bluish-grey, but as generally displayed they are pale-brown and
considerably affected by hydration and are known as " soapstones "
in the group. The ultimate effect of exposure is the production of
a whitish or yellowish soapy rock that has lost all the carbonate of
lime and all the organic remains and breaks down easily in the
fingers. Such a crumbling material, when examined with a high
power, cannot be distinguished from the products of the final
disintegration of palagonite as described on page 348.

These deposits are frequently displayed in the lower regions up
to elevations of 300 feet above the sea, incrusting the basaltic plains
of Lekutu, Sarawanga, Ndreketi, and Lambasa, that occupy
such a large area of the north side of the island, and exhibiting
there in the prevailing horizontality of their beds the same indica-
tion that is presented by the vertical position of the columns of the
under-lying basalt, namely, the comparative absence of disturbance
during the emergence. At the foot of the mountains these
deposits are interstratified with and finally overlaid by coarse
palagonite-tuffs, also containing marine remains ; and these are in
their turn covered over by the agglomerates that often enter so
largely into the composition of the mountainous backbone of the
island. Such beds form apparently the lowest of a series which
begins with the foraminiferous clay and ends with the agglomerate.
But in some places, as has been noticed in the cases of the
pteropod-ooze rock of Nandua, and of the shelly and foraminiferous
limestone of Tembe-ni-ndio, beds composed largely of characteristic
palagonite lie beneath.

In the elevated interior of the island these volcanic mud-rocks
ire usually concealed by the tuffs and agglomerates. Occasionally,
lowever, they are to be seen exposed by landslips high up the

Y

322 A NATURALIST IN THE PACIFIC chap.

flanks of the mountains, as on the slopes of Thambeyu 1,000 feet
above the sea. An interesting exposure of them is displayed in
the heart of the island in the face of the Mbenutha cliffs where the
elevation is about 1,100 feet. Here they are overlaid by a thick
bed of agglomerate ; and tuff-beds largely made up of vacuolar
basic glass debris and showing a few foraminifera are interstratified
with them ; but they exhibit signs of considerable disturbance (see
page 109).

These deposits contain between 5 and 25 per cent, of carbonate
of lime, and as a rule about 90 per cent, of the residue consists of
fine clayey material derived from the final degradation of palagonite
and of basic rocks. The mineral fragments (plagioclase, augite,
rhombic pyroxene, and occasionally hornblende) vary much in
amount, their average proportion being 13 or 14 per cent, of the
mass. Their size is usually less than '2 mm. and does not exceed
■4 mm. Casts of foraminifera are nearly always present in the
residue and form generally 3 or 4 per cent, of the whole deposit.
Sometimes they are black and glauconitic ; but more frequently
they are white and composed of chalcedonic silica. Such casts
represent on a small scale the results of the same silicifying opera-
tion to which the flints and silicified corals that occur so frequently
on the surface in some localities owe their origin (see Chapter
XXV.).

With regard to the age of these volcanic mud-rocks of Vanua
Levu, it is most likely that as in the case of similar deposits
in Viti Levu, which were examined by Mr. H. B. Brady, they are
of post-tertiary origin. Samples of the Suva " soapstone " contain-
ing 5 or 6 per cent, of lime and displaying shells of foraminifera,
pteropods, and other molluscs, were obtained from different heights
up to 100 feet above the sea. Since 87 out of the 92 species of
foraminifera represented in the deposits are known to be living
now in the Pacific, Mr. Brady had no hesitation in assigning the
beds to the post-tertiary epoch.^

Samples of the Volcanic Mud-rocks ^

A. From districts west of Ndranimako^ 100 ^eet above the sea.
Carbonate of lime 20 per cent.

{Fine debris of palagonite and semi-vitreous
basic rocks 62 „ „
Mmerals 14 >, »
Casts of foraminifera 4 „ „

100
1 Quart. Journ. Geolog. Soc. xliv. 1888.

XXIII VOLCANIC MUD-ROCKS 323

The organic remains consist mainly of tests of minute foramini-
fera of the " Globigerina " type, casts of which, both glauconitic
and chalcedonic, occur in the residue. About 88 per cent, of the
residue consist of fine clayey materials less than "25 mm. in size.
The mineral fragments, which average about "i mm. in diameter, are
mostly of felspar with a little pyroxene and brown hornblende.

B. From the Mbenutha Cliffs, 1,100 feet above the sea.

Carbonate of lime 15 per cent.

/Fine material mainly derived from the degra-

„ . , I dation of palagonite 60 „ „

R^^^due-^ Minerals 23 ,, ,"

leasts of foraminifera 2 „ „

100

This rock is somewhat hard, so that the proportion of
fine clayey material, which is however large, cannot be ac-
curately determined. It shows in places dark streaks composed
of an abundance of minute and often perfect tabular crystals of
zoned plagioclase and prisms of rhombic pyroxene, the size in
neither case exceeding half a millimetre, both of them being
derived from the acid andesites of the neighbourhood. In the
slide it displays minute tests of foraminifera of the " Globigerina ""
type in a matrix formed mainly of palagonitic debris, fragments;
of minerals and semi-vitreous basic rocks. The larger fragments
of the minerals and of the volcanic rocks do not exceed '15 mm. ;
but most of the material is very fine. The tests of the foramini-
fera are sometimes filled with the matrix, but often they are
entirely of calcite and exhibit in polarised light a dark cross.

C. From between Natua and Mbatiri, about 290 feet above the
sea.

Carbonate of lime 25 per cent.

[■Fine material derived from the degradation of

palagonite and of semi-vitreous basic rocks 62 „ „

Residue

Minerals 2

^ Casts of foraminifera 11

» )>

100

This is a relatively deep-water deposit, the foraminifera being
ninute and of the *' Globigerina " type. About 90 per cent, of the
•esidue consists of fine clayey material, with which the calcite is
;o intimately mixed that each particle is highly refractive and
effervesces freely in an acid. The mineral fragments (pyroxene

Y 2

324 A NATURALIST IN THE PACIFIC chap.

and felspar) are very scanty, the largest being less than -25 mm.
The white casts of foraminifera, composed of chalcedonic silica,
form a conspicuous elements in the residue.

D. From the vicinity of Mbatiri, 100 feet above the sea.

Carbonate of lime 4 per cent.

Fine material derived from the degradation of palagonite 90 „ „

Minerals 2 „ „

Casts of foraminifera 4 » 51

ICX3

About 94 per cent, of the residue consists of fine clayey
material. The fragments of minerals are very scanty and are all
less than '2 mm. in size. The casts of foraminifera are white and
of chalcedonic silica. From the fineness of the materials and the
small size and pelagic character of the foraminifera, this deposit
may be regarded as formed in relatively deep water.

E. From the eastern flank of the Wainunu table-land, 200 feet
above the sea. — This is a shallow-water deposit and contains,
besides small gasteropod shells, large flat tests of foraminifera
5 or 6 mm. in diameter. It possesses 24 per cent, of carbonate
of lime, 62 per cent, of palagonitic debris, &c., and 14 per cent, of
minerals.

Altered Volcanic Mud-rocks
This group includes compact hard foraminiferous usually dark-
brown rocks, which exhibit evidence of alteration in their indura-
tion, in the presence of pyrites, and in the chalcedonic quartz
filling fine cracks in the rock-mass. Occasionally special types of
alteration occur, one of which will be referred to in the description
of some of the rocks given below. The proportion of carbonate
of lime is generally small ; but sometimes it amounts to 10 per

cent, or more. , |

They admit of being examined in thin sections ; and their true
nature is at times so much disguised that I have taken them at
first for aphanitic basic andesites. In the slide they display a few
scattered tests of foraminifera of pelagic habit in a matrix
composed of the fine debris of palagonite and of basic rocks,
together with fragments of plagioclase and pyroxene. Most of
the material is very fine, and the size of the largest mineral
fragments does not exceed '2 mm.

Such rocks, however, are not very frequent. They may be

XXIII ALTERED VOLCANIC MUD-ROCKS 325

displayed on the flanks of mountain-ranges buried beneath basic
tuffs and agglomerates, as in the case of Mount Mariko (page 187)
and of the mountain-slope behind Mbale-mbale (page 158); or
they may be found at much lower levels as at Savarekareka Bay
(page 190), where, however, they assume sometimes a peculiar
character. Though in the last-named locality the alteration is
possibly connected with thermal metamorphism, it is probable
that in most instances it is a normal interstitial change occurring
in beds of some antiquity which are covered over by a considerable
thickness of later deposits. In places, where these rocks have
been subjected to much hydration in the weathering process, they
become red in colour, as is found on the flanks of Mount Mariko.

Samples of the Altered Volcanic Mud-rocks

A. From between 400 and 500 feet above the sea on the south
slope of the Mariko Range. . . . The characters and mode of
occurrence of this rock are described on page 187.

B. From an elevation of 1,100 feet on the south slope of the
Korotini Range. . . . The description of the locality will be found
on page 160.

This rock is hard and compact and looks like an altered basic
rock showing a few minute specks of pyrites. It is composed of
fine palagonitic debris, and small fragments of semi-vitreous basic
rocks and of crystals of pyroxene and felspar, none of the
fragments exceeding "2 mm. in diameter. Tests of minute
foraminifera, filled with matrix and of the " Globigerina "
type, occur very scantily. There is little or no carbonate of lime ;
but secondary silica, both colloid and crystalline, is present as an
iteration product.

C. From the vicinity of Yaroi, 30 feet above the sea. . . . The
ocality is described on page 189.

This is a dark grey hard compact rock, containing probably
between 10 and 15 per cent, of carbonate of lime, and looking like
m' altered limestone. In the section it displays minute tests of
braminifera of the " Globigerina " type in a matrix composed of
ine disintegrated palagonitic material, impregnated with calcite
md containing also fragments of minerals (augite and felspar),
lone of which exceed '2 mm. in diameter. There are also a few
: imilar-sized fragments of semi-vitreous basic rocks. Some fine

326 A NATURALIST IN THE PACIFIC chap.

cracks in the rock-mass are filled with a quartz mosaic. The tests
of the foraminifera remain calcitic ; but their cavities are filled
either with the matrix or with calcite or with a colourless fibro-
radiate mineral polarising in blackish-blue hues.

D. From the south shore of Savarekareka Bay. . . . The
locality is described on page 190.

This is a bright green hard compact rock with flinty fracture
and not effervescing with an acid. In the slide it shows a few
casts of foraminifera of the " Globigerina " type in a matrix com-
posed mainly of fine debris (•01-04 mm.) of felspar and pyroxene
with much greenish opaque amorphous alteration products. The
abundance of pyroxene is remarkable. The material of the tests
of the foraminifera is altogether replaced by a greenish yellow
mineral, occurring in grains and radiating prisms, apparently
epidote.

E. From an elevation of 950 feet on Mount Thambeyu. . . .
The locality is described on page 177.

A hard dark grey rock containing 10 or 15 per cent, of
carbonate of lime and showing fine specks of pyrites. In the
slide are displayed numerous tests of foraminifera of varying size
up to '5 mm. ; scattered patches of pyrites ; fragments of a semi-
vitreous basic rock, not exceeding "15 mm. in diameter, and of
plagioclase and pyroxene ; in a matrix of the finest debris of the
same materials impregnated with granules of calcite. The tests of
the foraminifera are filled either with calcite, showing a black cross
in polarised light, or with a zeolite, or with pyrites, or with the
matrix.

Submarine Basic Tuffs of Mixed Composition

These tuffs, which are composed not only of palagonitic
materials but also of the fine detritus of usually semi-vitreous
basic rocks, rank first in frequency amongst the volcanic sedimen-
tary deposits of the island. In their character they pass on the
one hand into the foraminiferous volcanic mud-rocks or clay rocks
and on the other into the tuff-breccias and tuff-agglomerates. We
have here a series beginning with the agglomerate and ending
with the clay that represents in a general sense the successive
stages of the degradation of the same materials.

These tuffs occur at all elevations from the sea-border, where
they may form the shore-cliffs, to the upper slopes and summits of
the mountain-ranges, where they are found at elevations between

XXIII SUBMARINE PALAGONITE TUFFS 327

2,CKDO and 2,500 feet above the sea. In the interior of the island
they are generally to be observed underlying the basic agglomer-
ates. Wherever an extensive exposure of the agglomerates exists
in the mountainous districts, these tuffs are as a rule to be found at
the base of the cliffs. The precipitous bluff of agglomerate, that
so often gives a character to the mountainous interior, and the line
of cliff of the same formation that runs along the slopes, represent the
work of landslips, as is shown by the huge masses of agglomerate
lying on the ground below. These " slips " are not uncommon, and
are due to the undermining influence of the springs that percolate
through the tuffs and clays underlying the agglomerates.

When the tuffs are well displayed they as a rule show stratifi-
cation. The bedding may be indicated either by distinct parting-
lines or by alternating bands of varying degrees of coarseness.
That these deposits, when occurring in mass in the upland regions,
are often horizontal or but slightly inclined, is evidenced by the
Nganga-turuturu Cliffs, 1,200 feet above the sea, which are described
in Chapter VIII., in the line of cliffs behind Sealevu (Chapter XL),
and high up the slopes of Mount Thambeyu (Chapter XII.) as high
as 1,500 feet. This is also shown in the circumstance that the line of
junction with the overlying agglomerate, except in rare cases, as in
that of the Mbenutha Cliffs, is generally horizontal. It is, however,
not uncommon to find the beds exposed on the mountain-flanks
dipping away from the axis of the range at a small angle, as on the
slopes behind Mbale-mbale and in the Sokena Cliffs. In the
lower regions, where these deposits are associated with the volcanic
mud-rocks on the basaltic plains, they are but slightly inclined-
On the other hand, as in the Kumbulau district, the sea-cliffs for
some miles may be composed of tuffs more or less steeply tilted.

These tuffs are generally more or less compacted and have a
greyish colour ; but as usually exposed in a weathered condition
they are often pale brown or yellowish and are more friable. They
may be uniform in structure, or they may display thin seams of a
marl-like clay, or they may contain numerous lapilli of vesicular
basic glass extensively palagonitised. Not uncommonly they
contain larger fragments of basic rocks, and when these are at all
frequent the terms " agglomerate-tuff" or " tuff-agglomerate " have
been employed according to the preponderance of either material.

Many of these tuffs show no effervescence with an acid ; and
this is especially the case with specimens at all weathered. On the
other hand there are just as many that contain a little carbonate of
lime, not usually more than 3 or 4 per cent, but sometimes

328 A NATURALIST IN THE PACIFIC chap.

amounting to 1 2 or 13 per cent. It often happens in the case of a
series of tuffs, apparently non-calcareous, that an occasional thin
band of a fine clay-like rock contains a good percentage of lime.
It is pointed out below, however, that the absence of effervescence
does not necessarily imply the absence of foraminiferous tests.

Tests of foraminifera, often macroscopic bottom forms, together
with shells of small gasteropods, are displayed at times ; but they
are as a rule in such cases not frequent. I found foraminiferous
tuffs at considerable heights in some localities, as for instance
between 2,cxx) and 2,500 feet on the slopes of Mount Thambeyu
(page 178), at an elevation of 1,850 feet on the south slope of the
Korotini Range above Vatu-kawa (page 158), and between 2,000
and 2,400 feet on the summit of the range between Waisali and
Sealevu (page 154). In the last-named locality, where the tuffs are
coarse and often of the nature of agglomerate-tuffs, they are
highly fossiliferous ; but such a character is exceptional.

The submarine origin of the tuffs can often be demonstrated in
the absence of evidence of organic remains, as by their inter-
stratification with foraminiferous clay rocks, such as we find at an
elevation of 1,000 to 1,100 feet on the top of the "divide" between
the Ndreketi and Lambasa basins. A single seam of marl-like
rock displaying only a solitary test of a foraminifer in the slide
may throw light on the origin of the coarser tuffs with which it is
associated. The use of the microscope is essential in the case of
some of the harder tuffs, where there has been a little alteration.
Here casts of foraminifera may be observed, although no carbonate
of lime is indicated by an acid. In some localities where no
organic remains are evident in the tuff, fine waterworn gravel is to
be noticed.

These deposits are composed as a rule of sub-angular fragments
of semi-vitreous basic or basaltic rocks and of palagonite, together
with fragments of plagioclase and pyroxene, the interspaces being
filled with fine debris of the same materials. The relative propor-
tion, however, of the three principal constituents varies considerably^
the palagonite, for instance, being sometimes scanty and sometimes
abundant. The size of the larger fragments in a tuff of the most
common kind is about a millimetre ; but deposits rather finer and
rather coarser are also frequent. In the very coarse tuffs and in
the breccia-tuffs, where the larger materials are mostly of pala-
gonite, the larger fragments may be a centimetre in size and even
more, the interspaces being filled with fine debris of the same
character cemented together often by carbonate of lime.

jxxiii SUBMARINE PALAGONITE TUFFS 329

^ The fragments of semi-vitreous basic rocks forming a regular
constituent of these tuffs are usually dark and opaque and display
a few plagioclase lathes. They correspond with the type of the
semi-vitreous basalt or basaltic andesite, of which the blocks of the
overlying agglomerates are as a rule composed and are doubtless
derived from the same source. Fragments of unaltered basic
glass are rarely to be observed in these tuffs. It is as a rule all
converted into palagonite. This material presents itself in various
stages of secondary alteration, from the compact greenish or
yellowish waxy mass to a white friable pulverulent substance,
which represents the last stage of degradation. These changes
will be found described on page 348. It can, however, be stated
here that they are mainly concerned with hydration. In the case
of the lapilli of finely vesicular basic glass, that is, of basic
pumice, which are inclosed in some of the tuffs, all stages of the
secondary alteration of palagonite are often exhibited, and the
last stage of the change is merely indicated by a white powdery
patch containing a few minute siliceous amygdules. The puzzling
little white patches so common in basic tuffs merely represent
lapilli of basic pumice that have been palagonitised, and then
bleached and disintegrated by hydration.

The minerals are more or less abundant and may constitute a
third of the whole mass. They include plagioclase, augite, rhombic
pyroxene, and magnetite, olivine being rare and scanty. Entire
crystals of any size are infrequent. However, crystals of augite,
5 or 6 mm. in length, are found in the tuffs at Naivaka and of the
coast cliffs near the Salt Lake Passage. ... It may be observed
that zeolitic minerals which are frequently developed in the tuffs
consisting almost entirely of palagonite are not typical of the tuffs
of mixed composition.

There is nothing suggestive of recent eruptions in any of these
formations. They were formed ages since on the sea-floor at vary-
ing depths around volcanic vents. Sometimes a cone was able to
rear itself above the level of the sea ; but in most cases it rapidly
succumbed to breaker-action. Three agencies, concerned with
sub-aerial eruptions, submarine eruptions, and marine denudation,
have co-operated in the production of these deposits, but their
parts in the process have varied greatly. The last is indicated
when the tuff is formed of a variety of basic rocks with but little
palagonite. The tuffs containing much palagonite representing an
original vacuolar basic glass are regarded as mainly the products
of submarine-eruptions. In those cases where lapilli of altered

330 A NATURALIST IN THE PACIFIC chap.

basic pumice occur in the deposit, sub-aerial eruptions are directly
indicated. When an extensive exposure of these tuffs occurs, as
in the case of the Nganga-turuturu Cliffs and in that of the section
displayed near the hill of Korolevu (page 48), all three agencies
are often illustrated.

Samples of the Submarine Basic Tuffs of Mixed
Composition

A. As examples of the non-fossiliferous tuffs where the palagonite
constituents do not predominate, I will take those exposed in beds
in the coast cliffs and in the low hills in the vicinity of Na Tokalau
in the Kumbulau peninsula (page 90). They are grey in colour
and have the texture of a sandstone, being more or less compacted
and showing no effervescence with an acid. They are composed
of fragments of basic rocks and of minerals, varying in size from
•5 to I mm., in a scanty matrix made up of fine detritus of the
same materials and of palagonitic debris. The fragments of
volcanic rocks are rounded and sub-angular, and formed mainly of
a basaltic rock, with a black opaque groundmass showing some
small plagioclase crystals and in places more or less palagonitised.
There are also portions of a hemi-crystalline basic rock showing
small augite crystals. The minerals entire and in fragments,
which make up quite a third of the mass, are mostly of plagio-
clase, but monoclinic and rhombic pyroxene are also well repre-
sented. It is evident that through the alteration of the palagonitic
constituents, which were probably more frequent when the tuffs
were deposited, the structure of the matrix is somewhat disguised.

B. A yellowish grey tuff composing the cliffs on the north coast
of Naivaka affords a good example of a tuff where the palagonitic
materials predominate. It is somewhat fine-textured and displays
a tendency to lamination. The powdered material effervesces
slightly with an acid. In the slide it is exhibited as composed
mainly of palagonite and of fragments of minerals, the latter
making up about one-third of the whole and ranging in size
usually between '2 and '5 mm. A number of more or less parallel
fine cracks, filled with calcite and traversing also the inclosed
crystals of plagioclase, together with small fragments of basic
rocks are displayed in the section. There are a few fragments of
semi-vitreous basic rocks, as just indicated, but the palagonite is
the principal constituent. It shows numerous minute amygdules
occupying the original vacuoles of the basic glass ; and in its

XXIII SUBMARINE PALAGONITE TUFFS 331

substance occur irregular patches formed of a colourless semi-
isotropic mineral which is either zeolitic or a form of opal.
Plagioclase and augite compose the mineral fragments, the former
prevailing. Although these tuffs are derived from a vent that was
probably the last in eruption in this island, they display con-
siderable alteration which is mainly connected with the secondary
changes affecting the palagonite since the deposition of these
materials.

C. As an example of the banded tuffs composed of coarse and fine
materials I will take a compact grey rock forming one of the
horizontal beds in the natural section exposed near the hill of
Korolevu (p. 49). It is also an example of those tuffs which
whilst not effervescing with an acid display a few casts of fora-
minifera in the slide. The alternating bands which are about a
centimetre in thickness pass gradually into each other. The bands
of finer materials are made up of sub-angular fragments, 'i to
"2 mm. in size, of the dark opaque groundmass of a semi-vitreous
basic rock and of a grey hemi-crystalline groundmass of an augite-
andesite, together with palagonite more or less decomposed, and
fragments of plagioclase and augite, whilst the interspaces are
filled with the finer debris. The layers of coarse materials have
much the same composition, the fragments varying usually between
•5 and I mm. in diameter, with occasional larger pieces of pala-
gonite 2 to 5 mm. in size representing original lapilli of a vacuolar
basic glass. The tests of the foraminifera, which occur scantily in
the layers of fine material, are all minute. They are filled with
palagonitic material.

D. The tuffs prevailing on the higher flanks of the mountainous
backbone of the island are well represented by those exposed at
an elevation of 1,200 feet above the sea on the south slope of the
Korotini Range behind Mbale-mbale. It is a somewhat coarse-
grained rather hard grey rock effervescing feebly with an acid. It
is composed of sub-angular or partly rounded fragments, i to 4 mm.
in size, of various basic rocks, and of rather smaller fragments of
plagioclase and augite, the interstices being filled up with fine
debris of the same materials, in which a few minute tests of fora-
minifera of the " Globigerina " type may be observed. The basic
rocks of which the fragments are formed comprise the following :
(a) a grey aphanitic augite-andesite, with but little interstitial glass,
presenting a parallel arrangement of the minute felspar-lathes
which have an average length of -05 mm. ; (d) a grey augite-ande-

332 A NATURALIST IN THE PACIFIC chap.

site of coarser texture but in other respects similar, the felspar-
lathes being about 'i mm. in length, whilst there is a little micro-
porphyritic plagioclase ; (c) a semi-vitreous basaltic rock showing
small porphyritic crystals of plagioclase, and augite in a ground-
mass usually black and opaque, but sometimes smoky and displaying
felspar microliths ; (d) a vacuolar basic glass more or less pala-
gonitised.

E. As a specimen of the calcareous tuffs those exposed on the
south slope of the Korotini Range at an elevation of 1,850 feet
may be given. They contain about 1 1 per cent, of carbonate of
lime and inclose a few tests of foraminifera i to 2 mm. in diameter.
The other constituents are fragments of semi-vitreous basic rocks
and of palagonite, together with fragments of plagioclase and
pyroxene crystals and of an amorphous siliceous mineral which
behaves optically like chalcedonic silica. When the rock is gently
rubbed down, minute fragments of this white mineral can be
picked out. They have a wrinkled surface and an irregular form
and are not affected by acids. In polarised light they display a
rude mosaic or an imperfect radiate structure.

F. As specimens of the fossiliferous agglomerate-tuffs composed
mainly of palagonite, those exposed on the high mountain slopes
of the Korotini Range at heights of 2,000 feet may be here cited.
They are described on p. 1 54.

NoU. — The examples of mixed tuffs above given represent
only some of the principal types of these deposits. Short descrip-
tions of others will be found in the detailed account of the geology
of the island.

Altered Basic Tuffs of Mixed Composition

These form a group of hard compact rocks, the fragmental
character of which is not always apparent in hand-specimens,
microscopical examination of thin sections being usually required
for the determination of their true nature. They are commonly
exposed on the southern flanks of the Korotini Range at the back
of Vatu-kawa and Nukumbolo. They are composed of compacted
fragments, varying in different localities from i to 5 or 6 mm. in
size, of a variety of semi-vitreous basic rocks, the matrix being
scanty but often containing zeolites and secondary silica, whilst
occasionally secondary calcite is developed. They contain no

XXIII SUBMARINE BASIC PUMICE TUFFS 333

organic remains, and palagonite when present is usually scanty,
whilst viridite and similar materials represent the decomposition of
the pyroxene. ... A hard breccia-tuff found on the flanks of Mariko
and in one or two other localities contains vesicular fragments,
where the steam-holes are filled with opal or chalcedony, and the
cracks traversing the matrix are also filled with this mineral.

The alteration of these tuffs has evidently arisen from a variety
of causes. In some cases the change appears to be purely inter-
stitial. In other times it has arisen from contact-metamorphism,
or from hydro-thermal agencies, as in the case of the altered tuffs
near the hot springs at Nukumbolo (p. 161).

Submarine Basic Pumice Tuffs

These deposits, which, however, are not of frequent occurrence,
are interstratified with volcanic mud -rocks in certain localities, as
at the Mbenutha Cliffs (p. no), and in the vicinity of the hill of
Korolevu (p. 47). They indicate periods of volcanic activity
during the deposition of the foraminiferous muds, with which they
are associated, when the fine materials ejected from sub-aerial vents
fell into the seas around.

Such tuffs are more or less compact and usually fine in texture.
When the glass fragments are but slightly altered, the tuff-rock is
dark grey ; but when the palagonitic change is well advanced, it
becomes pale and yellowish. They are made up chiefly of small
fragments of a bottle-green basic glass, which are as a rule vacuolar
and sometimes fibrillar ; but it never happens that the pumiceous
character is as pronounced as in acid pumice ; and in some cases
the vacuoles or steam-pores are to be observed only in the minority
of the fragments displayed in a slide. The size of the glass
fragments is as a rule small, in some tuffs averaging only 'i mm.
and in others "5 mm. ; but occasionally they may be i or 2 mm.
in diameter.

Fragments of minerals (plagioclase and pyroxene) correspond-
ing in size to the glass fragments are as a rule well represented,
forming a fourth or a third of the mass. A little fine detritus of
a semi-vitreous basic rock also occurs. Tested in an acid several of
the tuffs either do not effervesce or give an indication of a small
percentage of carbonate of lime ; whilst others effervesce freely.
They usually display a few minute tests of foraminifera of the
" Globigerina " type, the cavities of which are filled with fine
palagonitic debris.

334 A NATURALIST IN THE PACIFIC chap.

The palagonitic alteration is to be noticed in all cases ; but it
varies considerably in its extent. In the dark grey tuffs it affects
the margins only of a few of the glass-fragments. In the paler
tuffs it has extended more into their substance, although the
alteration is never more than partial. The pale greyish material
filling up the interspaces is composed of disintegrated palagonite.
The steam-pores or vacuoles are sometimes empty ; and at other
times, especially where the palagonitic change has begun, they are
filled with a granular alteration product. The glass fuses readily ;
but is not affected by acids. It is clear and isotropic, showing
however a few scattered microliths. These tuffs correspond with
the hyalomelan-tuflf from the island of Munia in this group as
described by Wichmann ; but in that instance no mention is made
of inclosed tests of foraminifera.

"Crush-Tuffs" formed of Basic Glass

This is a remarkable group of compacted tuff-like rocks which
as hand-specimens would be generally regarded as pitchstone-tuffs.
Their detrital origin is, however, often very doubtful. They are
composed of fragments of basic glass, carrying plagioclase pheno-
crysts, with the interspaces occupied by palagonite and by the
finer debris of the glass and felspar. The larger glass fragments,
which vary in different rocks from i or 2 to 4 or 5 mm. in size^
have been crushed in situ, the broken portions often remaining
more or less in position. These fragments are invested by pala-
gonite and have eroded borders, as shown in the figure on page 342.
The glass is bottle-green, non-vacuolar, fuses readily, and only at
times displays incipient crystallisation. The explanation of the
origin of these rocks is attempted in Chapter XXIV. They
contain neither carbonate of lime nor organic remains. The most
typical example is present in a bed underlying a pitchstone-
agglomerate near Narengali (see page 149). It is not uncommon
to find evidence of crushing in the glassy matrix of a pitchstone-
agglomerate or of rubbly pitchstone, as in the Va Lili Ridge (142),
the Korotini Bluff (157), and Mount Soloa Levu (313) ; and here
also palagonite has been produced around the crushed fragments.

Coarse Zeolitic Palagonite-tuffs

These deposits represent coarse kinds of the submarine tuffs of
basic glass, in which the palagonitic change is far advanced, and

xxiii PALAGONITE-MARLS 335

where zeolites and at times secondary calcite have been produced
in abundance as a result of the alteration. They present themselves
in the mass as mottled grey rocks which when examined in thin
sections are seen to be composed in great part of fragments of more
or less palagonitised vacuolar basic glass, whilst zeolites are
extensively developed in numerous irregular cavities and in the
interspaces. Although displaying no organic remains, their sub-
marine character is indicated as at Nandua by the circumstance of
their occurring as horizontal beds overlaid by pteropod-ooze
deposits, or as at Tembe-ni-ndio by their forming part of a series
of horizontal beds with a shelly limestone and a foraminiferous
palagonite clay overlying them.

The fragments of bottle green basic glass vary usually between

I and 4 millimetres. They were originally vacuolar and at times

fibrillar from the lengthening out of the minute steam-pores ; but

through the palagonitic change these characters have been often

disguised, and it is only at times that the unaltered glass is

observed. Plagioclase and sometimes augite and occasionally

olivine formed phenocrysts in the original glass. The zeolites,

which include chabazite and natrolite, may be so extensively

devel6ped that they make up a fourth or a fifth of the rock mass.

One may observe them in cavities where the walls are lined by

ibrous natrolite with the cube-like crystals of chabazite occupying

:he interior. The calcite is usually subordinate to the zeolites, but

sometimes the tuff contains as much as 10 per cent of this mineral,

vhich is evidently of secondary origin. . . . The history of these

ufifs in the district of Nandua and Ulu-i-ndali is no doubt applic-

ible to these deposits in other localities. They are the products of

: ubmarine eruptions which shattered into fragments the extensive

)alagonite crusts of flows of basaltic lava. In Chapter XXIV.

have attempted to show how palagonite is formed on a large

: cale in the case of such submarine displays of volcanic activity.

( '.HOCOLATE-COLOURED FORAMINIFEROUS PaLAGONITE-MARLS

We have here hard, somewhat calcareous, clay-rocks which con-
i ist in great part (nine-tenths) of fine palagonite debris with some
i -agments of minerals and a little fine detritus of semi-vitreous basic
1 Dcks. Some hand-specimens would be taken for pure palagonite ;
I ut the fragmental nature appears at once in the slide. This is
i specially the case with a rock exposed in a stream-course near
iLewa on the shores of Savu-savu Bay (see page 95). The

1

336 A NATURALIST IN THE PACIFIC ch. xxiii

materials composing them are exceedingly fine, the largest frag-
ments not usually exceeding '2 mm. As a rule they contain a
little carbonate of lime and sometimes as much as lo per cent.,
whilst a few tests of minute foraminifera are to be noticed in the
slide. These deposits are horizontally bedded, and underlie a
pteropod-ooze rock at Nandua and a shelly impure limestone at
Tembe-ni-ndio. They are not very frequent, and sometimes
approach in characters the volcanic-mud rocks, which, however, are
much more mixed in composition. I regard them in the main as
sedimentary deposits derived from the disintegration of the pala-
gonitised vitreous surface of a submarine basaltic flow. They pass
downward at Nandua, as described on page 345, into a rock of
pure palagonite ; and they are only to be found in localities where
basaltic plains or plateaux are covered over with submarine deposits.

Acid Pumice Tuffs

The general characters of these deposits are described on
pages 10, 218, 220, 222, 223, 231, 233, &c. Such tuffs are restricted
to the north-east part of the island east of Lambasa and Tawaki,
and are well displayed in the coast cliffs. They are pale yellow or
whitish, and are usually non-calcareous. They are composed of
the debris of a vacuolar and fibrillar isotropic glass, nearly colour-
less and in some localities altered. Small crystals of quartz and
of glassy felspar with bits of obsidian (up to 3 mm.) and lapilli of
rhyolitic glass are inclosed in them. In places inclosed pieces of
coral and coral rock indicate submarine deposition.

CHAPTER XXIV

PALAGONITE

From the sea-border to the mountain-top in almost every part
of the island, palagonite occurs in a fragmental condition. It is
only where tuffs are not found, as in the mountainous mass of
Seatura, or where these deposits are formed of acid rocks as in the
north-east portion of the island, that palagonite has not been
observed. Perhaps, it is not too much to say that the later if not
ill the stages in the history of Vanua Levu are bound up with the
listory of this material. In this place I will only deal with certain
eatures in the problem connected with the origin of palagonite
■ vhich seem to receive further elucidation from my observations in
this island. The literature is already extensive, and those inter-
( sted in the matter will find in Zirkel's Petrographie and in the
Challenger Report on Deep-Sea Deposits by Murray and Renard
£ good introduction to the subject.

In Vanua Levu we are confronted with the same difficulty that
tas perplexed geologists in various parts of the world. If we
expected to find in this island the source of the enormous quantities
' the basic glass that are represented by the palagonite of the tuffs,
V e should look in vain. Basic or basaltic glass usually occurs in
a jglomerates in the form of tachylytic pitchstones, as described on
pige 312, and is also found at times in basic pumiceous tuffs, as
d:scribedon page 333; but it is far from frequent. Palagonite-
rc ck, that is to say, a basaltic glass converted in mass into this
SI bstance, never came under my notice.

In order to clear the ground for the discussion of my own observa-
tit ns, I will quote from the report on deep-sea deposits above named.
F; agments of basic glass undergoing the palagonite change are
fo md everywhere in these deposits and especially in the red-clay

z

338 A NATURALIST IN THE PACIFIC chap.

areas The hydro-chemical modifications determining the decom-
position of these fragments into palagonite, and at the same time
the formation of zeolites, have likewise resulted in the complete
transformation of these lapilli into ferruginous argillaceous matter
(p. 309). The authors, however, of this report do not attribute the
frequent occurrence of fragments of basic glass on the bottom of
the ocean to the buoyant powers of basic pumice. Unfortunately,
the problem does not permit of such a simple solution. Basic
volcanic glass, writes Prof Renard, though known only from a few
geological formations and from a few eruptions of recent volcanoes
at the surface of the continents, appears in abundance and in most
typical form among the products of submarine eruptions, as if the
deep oceans had been in some way specially favourable to the
development of this lithological type (p. 299).

The palagonite-tuffs of this island are described in detail in
Chapter XXIIL, and a few general remarks are alone needed here.
This altered glass enters into the composition, to a greater or less
extent and in varying stages of disintegration, of nearly all the
submarine basic tuffs and clays. In the volcanic muds, however,
and in the tuffs of mixed character, which are the prevailing
deposits, it is associated with other components. Here the question
of the origin of palagonite within the deposit does not as a rule
arise, since there is nothing to indicate that this material was not
derived from rocks previously palagonitised, and the point of main
interest is connected with the last stages in the degradation of this
substance. There are not a few cases, however, where, unless we
assume that the lapilli of vesicular basic glass were ejected in the
palagonitic condition from a volcanic vent, we must apparently
regard the alteration as having occurred in the tuff But even this
will prove to be by no means a necessary consequence if it can be
shown, as I have attempted to do below, that the palagonitic
condition exists potentially in a particular type of basic glass and
that the effect of hydration is not so much to produce but to make
evident a condition that was previously latent.

It will be therefore of interest to determine whether palagonite
occurs in this island independently of the tuff-deposits, and under
such circumstances that it may be regarded as having been
produced within the rock- mass. An example is afforded in the
case of a basaltic flow near Soni-soni Island, which is fully described
on page 92. Whilst the lower part of this flow is composed of a
hemicrystalline basalt with scanty olivine, the upper portion is
made of a basaltic glass which has been broken up or crushed " ir

XXIV PALAGONITE

339

situ," the spaces between the fragments being filled with pala-
gonite. It would seem from the peculiar erosion of the glass
fragments that after the crushing a liquid magma occupied the
nterspaces, and afterwards solidified and underwent the pal agon itic
:hange.

In this connection it is noteworthy that in the sections of the
,ower hemicrystalline portion of the flow there are shown in the

J [agma-lakelet, '25 mm, in size, magnified 290 diameters, from a basalt at Navingiri.
The groundmass, which is a smoky devitrified glass containing abundant felspar-
lathes, is coloured black. The magma-lakelet is pale yellow in the slide and
displays concentric lines of congelation. It behaves like palagonite.

groundmass collections of a palagonitic material forming, as I
l ave termed them, " magma lakelets " of microscopic dimensions
( 25 mm. in average size). These " lakelets " are irregular in form,
a id are not uncommon amongst a certain type of basaltic rocks.
( ine of them is figured above ; and it may be added that they are
h 2st examined when displayed in a groundmass containing much

z 2

340 A NATURALIST IN THE PACIFIC chap.

smoky, partly devitrified, glass. They are usually more or less opaque
and reddish-brown or yellowish in colour, whilst they have often
a marked zoned structure, the concentric bands conforming to the
irregular contours of the lakelet. In the least affected stage the
zones show fibrous devitrification across their breadth, but as the
palagonitic change progresses the material becomes opaque. In
the secondary changes, such as those associated with the early
alteration of the propylites, these " magma lakelets " are the first
affected. They then present alternating layers of calcite and
viridite and are often bordered by magnetite.

If these "lakelets" were to be described as collections of
residual glass, the description would be insufficient, since they
may occur in the midst of a smoky, partially devitrified, glass.
During the last stage in the consolidation of the basaltic mass,
the magma-residuum that still retains its fluidity collects here and
there in the crevices of the groundmass, and forms little pools of
usually microscopic dimensions into which the felspar-lathes often
protrude from the sides. These little pools or lakelets represent
that portion of the yet fluid magma that during the last stage of
consolidation is imprisoned in the stiffening mass — like the whey
in a cheese — whilst the greater part of it has been squeezed into
the cracks of the cooling mass, as occurs in a dyke-like intrusion
below described, or has been extruded on its surface, as in the case
of the basaltic flow above referred to.

As a suggestive instance of the formation of palagonite "in
situ," I will now refer to a basic tuff-agglomerate on the plateau
of Na Savu (see p. 8i) which is penetrated by veins, a few inches
thick, apparently composed of a finely brecciated pitchstone-tuff.
In the section the material forming the veins is seen to be
composed of fragments of basic glass (carrying porphyritic
plagioclase and augite) which have been crushed in position, the
interspaces being filled up with the finer debris of the glass and
of the minerals together with palagonitic material. The glass
fragments, which have lost their sharp edges and angles, are often
palagonitised at the borders, and we thus get a patch of isotropic
brown glass with a yellowish margin formed of a feebly refractive
turbid substance. Where this border is not so evident, it is noticed
that the edge of the glass is peculiarly eroded. The indication
appears to be that the fissures in this agglomerate were filled with
a basic magma that after its solidification into a glass was
subjected to a crushing process, and that during this process a
partial remelting of the glass took place which resulted in the

XXIV PALAGONITE

341

molecular change characteristic of palagonite. Since the unaltered
glass-fragments fuse in the ordinary flame, it would seem that the
heat developed during the crushing might be sufficient to partially
remelt the glass without affecting the rock penetrated by the
veins ... It is of importance to note that in the palagonite-tuffs
of the Canary Islands the change is often most complete along
fissures, which thus present the appearance of being occupied by
veins of pitchstone.^

In this connection allusion may be made to a dyke-like mass of
a rubbly semi-vitreous basaltic rock exposed at Vatu-lele Bay,
described on page 184. It is penetrated in all directions by veins,
I to 3 inches thick, of a tachylytic glass which begins to fuse
in the ordinary flame. The glass is traversed by cracks which
sometimes contain palagonite. The basalt, penetrated by the
veins, has a smoky groundmass displaying imperfect felspar-lathes
in a feebly refractive glassy base and containing a few small
■" magma-lakelets " that cannot be distinguished from palagonite.^

Near the mouth of the Narengali valley (see page 149) I found
what appears to be a palagonite-tuff overlain by agglomerates
formed of tachylytic pitchstone and of semi-vitreous amygdaloidal
basalts. The tuff consists of fragments of a brown basic glass, the
larger i to 2 millimetres in size, carrying porphyritic plagioclase,
and fractured in position, the interspaces being filled with
palagonite. The glass fragments possess the eroded margins
indicated in the accompanying figure. It may be remarked that
this type of tuff differs from that of the prevailing palagonite-tuffs
in being rarely vacuolar, in the absence of marine organic remains,
and in its homogeneous composition. It is described on page 334
under the head of " crush-tuffs." Whether it is derived from the
destruction of a mass of basic glass that had previously undergone
crushing and partial palagonisation I cannot say ; but its
characters point in the direction of this conclusion.^

In the foregoing pages it has been attempted to show that
palagonitisation has taken place in the veins of basaltic glass
traversing in one case a basic tuff agglomerate and in another case
an intrusive basaltic mass, and that it has also occurred in the
upper vitreous portion of a basaltic flow and in the materials now
composing a so-called "crush-tuff." In order to explain this
group of facts I venture to propose this theory.

^ Zirkel's Petrographie, iii., 694.

2 This basalt is not fusible in the ordinary blow-pipe flame.

^ In this connection see the description of the Soloa-levu pitchstone on p.312.

342 A NATURALIST IN THE PACIFIC chap.

In certain types of basaltic lava,^ when cooling and consolidation
take place under peculiar conditions, such as we would expect to
find in submarine eruptions, there is a residuum of the magma
with relatively low fusibility that remains fluid after general
solidification of the mass is well advanced. As the rock continues
to consolidate, portions of this magma residuum become imprisoned
in the mass, like whey in a cheese, giving rise to the " magma
lakelets " above described ; whilst other portions, during the
contraction and fissuring accompanying the cooling process, are
squeezed out into the cracks thus formed, or are intruded on the
surface of the consolidating mass, as in the case of a submarine lava-
flow. This solidified magma-residuum differs from the ordinary

Showing fragments of glass with eroded borders and of plagioclase with more even edges
in a matrix of palagonite traversed by cracks. The length of the largest fragment
is half a millimetre. The glass has been evidently fractured in position and this is
true of one of the felspar fragments. It is also apparent that whatever its cause the
erosion of the margins of the glass has been produced since the fracture.

basic glass not only in its lower degree of fusibility but in its
mineral composition and in its molecular condition. It probably
in the first place does not differ much in appearance from the
typical glass, but it is an unstable substance and is capable under
certain hydro-chemical conditions of developing the characters of
palagonite.

In those cases where the occurrence of palagonite is associated
with evidence of crushing, the process appears to be in a sense
reversed, since partial palagonitisation of an ordinary basic glass
takes place as a result of the elevation of temperature due to the

^ See the note at the end of this chapter.

XXIV PALAGONITE

343

crushing. The heat thus developed is sufficient to partly fuse the
glass ; but since it is not great, it only affects the most fusible
constituents, and the remelted material corresponds therefore to
the magma-residuum of the consolidating mass, which is referred
to in the previous paragraph. It has the same unstable characters
and the same tendency to assume the palagonitic condition.

This theory centres around the relatively low fusibility of the
magma-residuum that gives rise to palagonite. This degree of
fusibility has yet to be ascertained, since according to the views
here advanced it may even be much lower than that of tachylyte.
It is, however, noteworthy that the melting-point of tachylyte is
far below that of the more crystalline basaltic rocks, since it can
be readily determined, as I have done in the instance of a dyke-
like mass penetrated by tachylyte- veins before referred to, that the
veins are composed of a much more fusible material than the
rock-mass. From a very crude experiment I would infer that the
melting-point of ordinary tachylyte is not much above that of lead
(335° C). The fusion-point of an ordinary hemicrystalline basalt,
according to the well-known experiments on the lavas of Vesuvius
and Etna, would probably be over 1,000 degrees C.

Two interesting experiments, the one artificial, the other
natural, may be here cited in connection with this view. Bunsen ^
more than half a century ago, as a result of some experiments in
which he produced palagonite, arrived at the conclusion that the
tuffs formed of this material are submarine deposits derived from
the breaking up of previously formed palagonite-masses. Having
obtained this substance by placing powdered basalt in an excess of
melted potash-hydrate (Kalihydrat) and then adding water to the
silicate of potash thus formed, he concluded that palagonite results
from the reaction between glowing augitic-lavas and rocks rich in
lime and other alkalies. Although Zirkel quotes in this connection
the example where this material has been produced in the Cape de
Verde Islands by basic lava flowing over limestone, he rejects
Bunsen's explanation as inapplicable to extensive palagonite
districts, such as occur in Iceland, though allowing that it would
account for the local production of this substance.

I venture to think, however, that in these two experiments the
general principles involved in the production of palagonite are
partly illustrated. We may accept the results of an experiment
without acquiescing in its interpretation. As I take it, it is in the
partial wet fusion of the powdered basalt that the secret of this

1 Quoted in Zirkel's Petrographie, iii., 689.

344 A NATURALIST IN THE PACIFIC chap.

successful production of palagonite lies. In both these experiments
some of the conditions of a submarine flow have been reproduced.

Whilst Rosenbusch established the true character of palagonite
as the product of a peculiar alteration of a basic glass, Renard
pointed out the conditions under which it was most typically and
in greatest abundance formed. But Bunsen was happy in his
suggestion that palagonite-tuffs are submarine deposits derived
from the breaking up of previously formed palagonite masses.
The question thus resolves itself into one concerning the conditions
of submarine eruptions and the behaviour during consolidation of
a submarine basaltic flow. In the nature of things the field of
investigation is mainly restricted to the examination of ancient
submarine basaltic flows that have been raised above the sea.

A remarkable series of beds exposed in a stream-course below
the Nandua tea-estate may be here described in connection with
the question of the origin of palagonite formations. As observed
on page 86, this locality lies on the flanks of a basaltic plateau,
which are incrusted with recent submarine deposits. A pteropod-
ooze, containing also the tests of large and small foraminifera and
the shells of small bivalves, is displayed on the sides of the
stream-course for the first 150 feet of the descent. Below this, as
shown in the diagram, is a declivity with a drop of 60 or 70 feet
where there is a waterfall. Horizontal beds of the pteropod-ooze
rock are exposed in the upper-third of this declivity ; but below,
they pass into a chocolate-coloured marl-like deposit also horizon-
tally bedded, and sometimes having a banded appearance from the
alternation of layers of different degrees of fineness. This rock
contains 5 or 6 per cent, of carbonate of lime and incloses a few
scattered tests of minute foraminifera of the " Globigerina " and
•" Nodosaria " types. In the slide the rock appears to be of massive
palagonite inclosing a few felspar-lathes 'i to "3 mm. in length, and
exhibiting a zeolite and calcite in the crevices and cracks. But it
was not until I had discovered the tests of the foraminifera and
had observed some fragments of larger crystals of plagioclase and
a little detritus of a semi-vitreous basaltic rock that its clastic
character was disclosed. The palagonite change has here to a
great extent disguised the character of the deposit.

This palagonite-marl formation is 20 or 30 feet in thickness.
It passed downward into a reddish-brown rubbly unstratified rock
which falls to pieces in one's hands, breaking up into little cube-
like masses an inch or two across. These masses display in
their interior a radiate prismatic structure ; but after drying they

XXIV

PALAGONITE

345

crumble into small fragments exhibiting the same minute prismatic
structure, the miniature prisms being about a millimetre in dia-
meter. Fine cracks, filled with calcite and a zeolite, traverse this
rock in all directions, and no doubt this peculiar structure arises
from shrinkage.

My idea that I was dealing with a clay-rock affected by the
proximity of an igneous intrusion was dispelled when the
powdered material presented itself as pure palagonite with scarcely
any mineral fragments. Unlike the marl above, it does not effer-
vesce with an acid ; and appears as a mass of compacted minute
fragments of basic glass converted into palagonite, which is
seemingly non-vacuolar, and containing about 15 per cent, of
water.

In connection with the diagram it should be remarked that I
did not find the palagonite-rock actually passing down into the

} Ptenpod -ooze Rock (Wfxc)

)

\ Palagonite -marl containing

j a few-foramimfera .(90p.c)

\ PaLsgonitQ • rock . {98 p. c.)
basalt.

Diagram showing the succession of deposits below the Nandua tea-estat The total
thickness is about 250 feet. The figures refer to the proportion of palagonite.

basalt which, however, is exposed in the river-bed below. The
whole district is characterised by columnar basalt, and the series
of deposits here described have been formed on the flank of the
great basaltic table-land of Wainunu. It is noteworthy that in
the uppermost deposits of the pteropod-ooze palagonite forms a
noticeable proportion (10 — 20 per cent.) of the residue ; and per-
haps most of the fine clayey material is thus derived. As noted
on page 321, minute pellets of pure palagonite are not infrequent
in the residue. Probably about 90 per cent, of the underlying
marl consists of palagonite. In the lowest palagonite-rock the
proportion would be quite 98 per cent.

Whilst it is apparent that we have represented in this series
the covering of a submarine basaltic flow with submarine deposits,

346 A NATURALIST IN THE PACIFIC chap.

it is also evident that the mode of junction between the flow and
the overlying deposits is of an unexpected nature. Before drawing
any inferences, it is necessary to point out that when we begin on
d priori grounds to frame our notions as to the course of events
on the surface of a submarine basaltic flow, we are entering a little
known region of inquiry. I would, however, suggest in the light
of the theory before advanced, the following explanation of the
appearances presented by this series.

During the consolidation of the flow much of the magma-
residuum that still retained its fluidity was extruded on the sur-
face, where after solidification it became palagonitised. Accord-
ing to my view this would be the typical behaviour of submarine
basaltic flows ; but, owing to the unstable and perishable nature of
the palagonitic crust of the flow, it would be rarely preserved in
upheaved volcanic regions. There would probably be, as in the
case of the Nandua series, no sharp line to be drawn between the
palagonite-crust and the deposits subsequently covering it, deposits
indeed that would derive no inconsiderable proportion of their
materials from the disintegration of the crust itself. During and
after the emergence of such a district of submarine eruptions the
unstable palagonitic crust would be further subjected to the
hydration resulting from weathering and similar agencies ; and as
a result of its final degradation there would often alone remain a
bed of reddish argillaceous material.

In concluding these remarks on palagonite the following
summary of the principal points here dwelt upon may be
added :

{a) The basic glass, that undergoes the palagonitic change, is
the vitreous form of the magma-residuum that in a particular
type of basalt and under certain conditions remains fluid after the
mass of the rock has solidified. During the last stage of the con-
solidation it is in part imprisoned in the " magma-lakelets " of the
groundmass ; whilst the rest of it is squeezed into cracks and
fissures, or extruded on the surface of the flow.

{b) This glass differs from ordinary basic glass in its molecular
condition, its mineral composition, its low degree of fusibility, and
in its unstable character.

if) The formation of palagonite in connection with the crush-
ing of a basic glass is to be explained by the hypothesis that the
heat developed during the crushing is sufficient to partially re-fuse
the glass, the material thus produced corresponding to the magma-
residuum of low degree of fusibility, which is above referred to.

XXIV PALAGONITE 347

(d) In submarine eruptions are to be found the conditions
favouring the production of palagonite on a large scale. In the
case of such basaltic flows it is probable that their upper portions
are formed entirely of palagonite arising from the alteration of a
vitreous magma-residuum extruded on the surface in the manner
above described. Such a crust, as a result of shrinkage and other
processes, would probably present itself to the geologist as a some-
what friable material, passing gradually into the overlying sub-
marine deposits.

Note on the type of basalt found associated with palagonite.

The type is characterised, it would appear, rather by its
structural features than by its mineral composition. It is the
basalt of ophitic or semi-ophitic habit that would seem to be
usually associated with palagonite ; and since this habit is as a
rule to be found where the groundmass displays large felspar-lathes
in plexus arrangement, coarse augites, and at least a fair amount
of smoky glass, it follows that a hemi-crystalline, ophitic or
semi-ophitic, doleritic basalt is the type to be associated with
palagonite.

This is the type of rock that forms the lower part of the
basaltic flow near Kiombo, the upper part of which is largely
palagonitic. To this structural type also belong most of the
basalts in my collection where palagonite exists in the form of
" magma-lakelets " in the groundmass. These " lakelets " are
almost diagnostic of this type of basalt. Here also belongs the
famous globular basalt of Acicastello on the coast of Sicily.^ In
such rocks the felspar-lathes form a mesh-work and vary usually
in average length between *! and *3 mm. The augites of the
groundmass, typically semi-ophitic, range up to 'i mm. in size.
They are always large, that is, over '03 mm., and this coarseness
is another important indication.

* I have visited this locality on several occasions with the special object of
studying the relation of the basalt to the associated palagonite-tuffs and clays.
A general discussion of this question would be out of place here ; but I may
remark that the conclusion arrived at by me is that these deposits are not sedi-
mentary but are entirely the result of the disintegration of palagonite in situ.
This is quite opposed to the view of their sedimentary origin held by Dr.
Johnston-Lavis, Prof. Platania, and other Italian geologists. . . . The basalt
is scoriaceous, semi-vitreous, and semi-ophitic, and closely approaches the type
of basalt above defined.

348 A NATURALIST IN THE PACIFIC chap.

Note on the changes produced through the hydration

OF palagonite.

Most of that which is detailed below is not according to my
views palagonitisation, but the effect of hydration in the disinte-
gration of this material. The initial molecular condition and
the other characters which represent potentially the palagonitic
change are not connected with hydration ; but are concerned with
the causes before explained that led to the formation of a basic
glass of such an unstable constitution. Indeed, there is good
reason to believe that the changes to be now described may be
observed under the ordinary influences of weathering in a wet
region.

The early stages of alteration are well displayed in some of
the tuffs formed mainly of basic vacuolar glass, the submarine
character of which is often indicated by a few tests of foramini-
fera. Whilst the glass retains its original bottle-green colour, it
loses the clean sharp conchoidal edges and displays rough and
uneven or granular borders. With a high power the surface of
the fragment is seen to be minutely pitted or pock-marked in
places, the shallow circular pits, less than 'Oi mm. in diameter,
being sometimes arranged in a row like a number of overlapping
rain-prints. This process proceeds until all the surface is affected,
and from this cause there is often an appearance of polygonal
markings. The pock-marking, however, continues ; and as the
pits encroach more and more on each other an irregularly wrinkled
rough surface results. Up to this time the glass has retained
much of its original colour ; but its clearness is replaced by
turbidity, and collections of very minute rounded, rod-shaped, and
irregular granules, composed of a colourless feebly polarising
material, are displayed here and there in its substance, whilst
some of the previously empty vacuoles are now filled with water.

In the next stage the hydration of the iron-oxides begins,
and the glass becomes opaque and yellowish or reddish-brown,
and has a more granular appearance, polarising feebly. Cracks
now traverse the substance, and penetrate into the vacuoles, which,
as they become filled with the alteration products, whether pala-
gonitic, zeolitic, or siliceous, become ruptured and curiously dis-
torted. The hydration and consequent disintegration continue
until the deep stain of the iron-oxide is removed, and a semi-
pulverulent whitish material remains. This is the history of the

XXIV PALAGONITE 349

little bleached powdery patches so common in basic tuffs, each
representing originally a lapillus of basic pumice. This powder
when examined with the microscope is shown to be made up of
fine granular and tubercular materials which lose much of their
distinctness when mounted in Canada balsam. It is not affected
by boiling in HCl, and contains usually an abundance of minute
siliceous oval amygdules that have been freed in the last stage of
the disintegration of the palagonite.

Such is the story of the degradation of the palagonite daily in
operation in the basic tuffs of this island. From this source is
doubtless derived much of the finest constituents of the submarine
clays so common over Vanua Levu.

Stipplementary note on the occurrence of palagonite in the glassy
matrix of pitchstone-agglomerates and in rubbly pitchstones. — In my
last revision of the proofs I find that I have not laid sufficient stress
on the production of palagonite under these conditions. The evi-
dence of crushing is often very evident, and especial references to-
this point will be found in the index under " Pitchstone," and on
P^gG 334 under " Crush-tuffs."

CHAPTER XXV

SILICIFIED CORALS AND FLINTS
f

SiLICIFIED corals, together with siliceous minerals (quartz, chal-
cedony, jasper, &c.) and siliceous concretions are evidently widely
distributed in these islands. Kleinschmidt in his journal refers to
large blocks of flint on the island of Ono, from which the natives
used to obtain their musket-flints,^ and he collected from this
island as well as from Viti Levu, Ovalau, &c., numerous specimens
of these and other siliceous minerals and rocks, such as hornstone,
chalcedony and jasper, which were examined by Vv^ichmann and
described in his paper.^ Mr. Andrews observed silicified corals on
the summits and higher slopes of Vanua Mbalavu.^ The Fijian
name for flints, " ngiwa " (thunderbolt) or " vatu-ngiwa " (stone-
thunderbolt), affords a good instance of that 'curious superstition
connected with the origin of these stones, which came also under
my notice in the Solomon Islands,* and in fact is widely spread.

In Vanua Levu these siliceous rocks and minerals are in places
abundant. They are especially frequent on the surface of the
extensive low plains on the north side of the island which consti-
tute the basins of the Sarawanga, Ndreketi, Wailevu, and Lam-
basa rivers ; but it is in the low-lying district of Kalikoso, in the
north-eastern part, that they exist in the greatest quantity. They
do not occur usually at greater elevations than 300 feet, and are
found as a rule at much lower levels.

It must be understood that reference is not here made to quartz-
veins, such as are found in certain localities and of which mention
is made on pages 106, 116. It is not with the ordinary products

* Reisen aufden Viti-Inseln, as quoted on p. 22.

2 Petro graphic des Viti-Archipels^ quoted on p. 293.
^ See work quoted on p. 378.

* Solomon Islands and their Natives^ by H. B. Guppy, p. 78.

CH. XXV SILICIFIED CORALS AND FLINTS 351

of contact or general metamorphism that we have here to deal ;
but with the remarkable surface-collections of silicified corals,
nodules and flints of chalcedony, fragments of white quartz-rock,
bits of jasper, and certain curious siliceous concretions, that occur
often in association with fragments of limonite in these low-lying
regions. All the siliceous materials above named have, as the
microscope indicates, a common character, chalcedonic silica in a
greater or less degree being the basis of all of them, whether
coral, flint, white quartz-rock, or jasper. It soon became apparent
whilst examining these districts that one general condition pre-
vailed whilst this extensive deposition of silica and the formation
of the beds of limonite were in progress. It cannot, however, be
pretended that these processes are actually in operation on the
plains now. Except in the case of the limonite in a few localities
the processes have been suspended ; but they were in active
operation not long ago : and an examination of the general char-
acters of the districts will probably disclose some of the conditions
under which these products have been formed.

On the surface of the Kalikoso plains, where these materials
are most abundant, we find silicified corals associated with frag-
ments and nodules of chalcedony, flints, white quartz-rock, limonite,
concretions of carbonate of iron, &c., in the low-lying and often
swampy district around the fresh-water lake, the whole region
being only elevated between 20 and 60 feet above the sea. This
is an area of decomposing acid rocks (quartz-porphyries, trachytes).^
On the other hand in most of the regions where these materials
occur on the surface we have areas of basic rocks (basalts and
basaltic andesites) incrusted in places with submarine tuffs and
foraminiferous clays, the volcanic rocks undergoing extensive
disintegration. Such for instance are the Lekutu, Sarawanga,
Ndreketi, and Lambasa plains. In the Lambasa plains, which
are described in this connection on page 139, we find besides the
corals and flints and nodules of chalcedony, fragments of jasper. In
the Sarawanga and Lekutu lowlands, we find silicified corals and
limonite ; but here the crystallised silica of the corals contains a
large quantity of water, whilst in its lesser degree of hardness and
in its low specific gravity it comes near to semi-opal. In these
and other localities, as in the level country around Ndranimako on
the right side of the Yanawai estuary, we find curious concretions
of the same kind of hydrous silica more or less crystalline. These
concretions are described below.

^ The region is described on pp. 224-228.

352 A NATURALIST IN THE PACIFIC chap.

It may be remarked that nearly all the districts in which the
silicified corals and concretions, siliceous minerals, and Hmonite
occur, are scantily vegetated " talasinga " lands ^ with reddish soil.
Except in the instance of the Kalikoso plains, the swamps and
lakes have as a rule long since disappeared, their sites being alone
indicated by the limonite on the surface. In the Mbua plains,
however, there are occasional small ponds and swamps, and there
is no doubt that the limonite so bountifully represented on the dry
districts is still in process of formation.

Before drawing some general inferences as to the conditions
under which this deposition of silica and iron took place, I will refer
to the characters of the materials thus produced.

The silicified corals include massive corals of the Astraean and
" Pontes " kinds and branching specimens of the Madrepore type
or habit. The former are rarely larger than 7 or 8 inches across
and are merely fragments. The latter are always portions of
branches, never exceeding 3 or 4 inches in length. In the last case
it is sometimes possible to show, as in the case of a specimen found
on the Kalikoso plains, that before silicification occurred the dead
fragment of branching coral had been extensively eroded by solvent
agencies and had been penetrated by burrowing molluscs. The
larger blocks of massive corals have usually been extensively
chipped by the natives in obtaining flints. In past times they
were carried from one place to another, the result being that
occasionally they were brought to me in the mountain-villages, all
showing evidence of their having supplied flints to a past genera-
tion.

These corals are as a rule completely silicified. When a
massive specimen is broken across it is not infrequently found
that whilst the coral structure is preserved in its outer part, the
inner portion is composed of a compact seemingly structureless
mass of bluish-white or pale-grey flint, which has the characteristic
microscopical appearance of chalcedony and a specific gravity of
2"59.2 It is from the more compact parts of the silicified massive
corals that the " worked " flints found on the surface were obtained,
though in some of them, as in the case of a " scraper " in my
collection, the traces of coral structure are still apparent to the eye.
Wichmann observed in the case of the silicified corals from Fiji
that the whole petrifying process appears to consist in the satura-
tion of the coral with silica, the coral structure being usually

^ For the meaning of "talasinga" see p. 55.

'^ The portion exhibiting the coral structure has a specific gravity of 2'54.

XXV SILICIFIED CORALS 353

distinct, whilst the septa, often still calcitic, show the points of the
calcite crystals projecting into the chalcedony which forms the
mass. Lime however rarely occurs in the silicified corals of Vanua
Levu. It was only in the case of one or two localities that the
corals displayed any effervescence with an acid. In the microscope
slide the massive specimens appear to be entirely of chalcedonic
silica, the outlines of the cells and of the septa being indicated by
ferruginous material. In a specimen of Porites by my side the
crystallization of the silica has advanced beyond the chalcedonic
stage and the coral is composed entirely of minute quartz-crystals,
•2 to "4 mm. in size, often irregular, but sometimes forming doubly-
terminated prisms. This has produced a somewhat crumbling
rock, which is easily powdered by the finger ; and in this case,
therefore, the complete crystallization of the silica is resulting in
the disintegration of the silicified coral.

The ordinary silicified massive corals of Vanua Levu, where the
replacement by chalcedonic silica is complete, though the structure
is preserved, have a hardness of about 6 and a specific gravity of
2*54, and yield but little water in the closed tube. Occasionally,,
however, as in the Sarawanga plains and in the Lekutu lowlands
we find silicified fragments of branching corals which are easily
scratched with a knife and have a hardness of 3 to 4 and a specific
gravity of 2*3. The fractured surface is milk-white or reddish, and
looks like semi-opal. When powdered and heated in a closed
tube, the material loses one fourth or one fifth of its weight of
water, the finest dust (passing away in the steam) being deposited
on the sides of the glass. In the slide there is displayed a finely
granular crypto -crystalline structure with in places a somewhat
coarser quartz-mosaic, whilst chalcedonic quartz fills minute cracks
in the mass. No coral structure is preserved. Numerous points
coloured by iron oxide occur in the section, and minute dust-like
inclusions abound, which are doubtless water-pores. I have des-
cribed on a later page certain concretions found associated with
these silicified corals which though formed of the same crypto-
crystalline hydrous silica, are apparently silicified portions of
nullipore-rocks.

The fragments of flint that occur commonly on the surface in
these districts are, as above remarked, derived from the hard
silicified coral-masses. Nodules of chalcedony, having all the
appearance of having originated in cavities, are also very frequent.
They may take the mamillary, agate, or onyx form, some of the
agates when polished making beautiful specimens. These nodules

A A

354 A NATURALIST IN THE PACIFIC chap.

are of all sizes up to 3 or 4 inches across. Some of them are
hollow and lined with clear quartz-crystals, whilst with others the
cavity may be completely filled by interlocking quartz-crystals.
The outer surface of one of the agates displays markings showing
in relief casts of the " cups" of a minute-celled coral.

Mingled with the other siliceous materials on the surface of the
Kalikoso and Lambasa plains are found fragments of a whitish
quartz-rock, having a specific gravity of 2-53 — 2-57, being therefore
markedly lighter than quartzite (2'63 — 2-67) which it somewhat
resembles. It usually occurs as small hand-specimens ; but in the
vicinity of Mbati-ni-kama I found blocks, 12 to 15 inches across,
lying in the river-bed. Under the microscope it displays a fine
radio-globular aggregate of chalcedonic quartz.

Mention has already been made of the siliceous concretions,
composed mainly of hydrous crypto-crystalline silica, which are
associated with the silicified coral fragments formed of the same
kind of silica on the surface of the plains of Mbua, Lekutu, and
Sarawanga. They also occur in the Ndranimako lowlands on the
right side of the Yanawai estuary, and in the more elevated inland
districts of the Wainunu and Na Savu table-lands at elevations of
650 to 770 feet above the sea. They take the form of irregular
nodules, or of flat uneven " cakes," usually two or three inches in
size. They are as a rule reddish, but sometimes pink and white.
Their hardness is only 3 to 4, and they are easily scratched with a
knife ; and when powdered and heated in a closed tube, they lose
about one fourth of their weight of water. Under the microscope
they exhibit a grey crypto-crystalline ground mass showing very
finely granular crystalline silica with the cracks and small cavities
filled with more brightly polarising chalcedonic quartz. But they
differ as regards their other components and also in their mode of
occurrence ; and it is highly probable that the history of their
origin is not always the same.

Those associated with the silicified corals on the Sarawanga
and Lekutu lowlands show no structure in the slide that gives me
a clue as to their origin ; but they may perhaps represent old
Nullipore nodules. Those around Ndranimako are coloured deep
red ; and whilst some give no indication as to their source, others
are transitional in character, and display in the sections traces of
the vacuolar semi-vitreous basic rock of which the original frag-
ment was composed. The same red siliceous concretions form the
pebbles and gravel in the stream-beds on the surface of the Na
Savu table-land, 700 feet above the sea. These red flint- like

XXV JASPER AND CHALCEDONY 355

nodules of Ndranimako and Na Savu somewhat resemble the
jasper of the island ; but they are sharply distinguished by their
microscopic characters, by being easily scratched with a knife, and
by the large amount of water which they contain. Rolled stones,
which were found in the shallow stream-courses on the surface of
the Wainunu table-land 750 to Soo feet above the sea, exhibit in
the sections, in spite of the general silicification of the ground-
mass, the outlines of the original phenocrysts of felspar, and
abundant skeletal magnetite rods, such as would characterise a
semi-vitreous basic rock. It is evident that in the basaltic districts
of the Na Savu and Wainunu table-lands these concretions have
been formed under certain conditions by the decomposition of the
silicates of basic rocks. But these conditions do not exist now ;
and I infer that the silicified rocks, which occur only in fragments
on the surface, represent the silicification that occurred during .the
emergence of the land ages since.

Occasionally one comes upon in the mountain districts, as in
the vicinity of Ndrawa, large solitary blocks 2 to 4 feet across of
a whitish chert-like rock which has a hardness of 5 or 6, the harder
variety having a specific gravity of about 2*58 and the softer,
which yields a fair amount of water, a specific gravity of about
2*46. I noticed such solitary masses also on the Mbua plains.
The first-named locality is dacitic and the last basaltic. They
exhibit in the slides a patchy appearance, showing in some places
finely granular crypto-crystalline silica and in others a coarser
mosaic of chalcedonic quartz. Apart from the absence of any
definite coral structure, I can only surmise that they were originally
masses of reef-limestone. Their elevation even in the mountainous
districts was not over 400 or 500 feet above the sea.

Fragments of jasper, which are associated with nodules of
chalcedony and silicified corals in the Lambasa plains, are also to
be found as pebbles and small blocks in the mountain streams of
the Ndrawa, Ndrandramea, and Lea districts, together with bits of
chalcedony and quartz-crystals. They do not occur, or are of rare
occurrence, in the recently emerged Kalikoso district and probably
belong to an earlier stage in the history of the island's emergence
from the sea. They have a hardness of 6 to 7, not being scratched
by a knife, and a specific gravity of 2"65 to 270 ; whilst but little
water is given off in the closed tube. They are a variety of
chalcedony, rendered opaque by the large quantity of red oxide of
iron that it contains, and are really, therefore, iron-flints. The
microscopical section in one case displays in the clear spaces a

A A 2

356 A NATURALIST IN THE PACIFIC chap.

beautiful globular aggregate, each globule having a nucleus of the
iron oxide and giving a black cross in polarised light. In another case
the globular structure is less perfect, and the chalcedonic groundmass
is penetrated by a multitude of fine cracks filled with iron oxide.

The deposits of limonite vary in character in different localities,
and evidently they have not all the same history. The soil of the
low-lying plains around Wai-ni-koro and Kalikoso, and especially
in the vicinity of the fresh-water lake, is often coloured a deep
ochreous red. Small fragments of an earthy yellowish-brown
limonite occur on the surface in quantity and are particularly
abundant near the lake. They yield much water when heated.
In some places in this district, as in the country traversed between
Wai-ni-koro and Kalikoso, the surface is strewn with a number of
small round concretions of the size of small marbles (6 to 12 mm.)
which are composed of a mixture of carbonate of iron and limonite,
but show no recognisable structures. They are somewhat friable
and give off much water when heated, whilst they effervesce freely
in hot hydrochloric acid. It is probable that some of the earthy
limonite of the Kalikoso district contained originally iron carbonate
and has been produced from concretions such as I have just
described.

The variety of limonite found in fragments on the surface of
the plains of Mbua, Lekutu, and Sarawanga, at elevations usually
of 100 or 200 feet above the sea, is a heavy compact kind with a
specific gravity of 3 to 3*5, and closely resembling red hematite.
Since, however, it is lighter in weight and still contains a little water,
it may be regarded as in the transition stage. It occurs as portions
of cake-like masses varying usually from a third of an inch to
rather over an inch in thickness. As a rule it is found in localities
where no lakes or swamps now exist and may be associated, as in
the Sarawanga and Lekutu plains, with silicified corals and silice-
ous concretions ; but in some cases, as in that of the Mbua plains,
ponds and swamps are still scantily represented in the vicinity,
and the water of the stagnant streams is deeply coloured with iron
(see page 56).

Ironstone gravel occurs in great quantity strewn over the
surface of the basaltic table-lands, especially in the case of that
between the Wainunu and the Yanawai rivers. The smaller
gravel varies usually between one eighth and one third of an
inch in size, the larger fragments being about an inch. The
specific gravity is 3*1 to 3'2. The material forming the finer gravel
dissolves with but little effervescence and scanty residue in hot

XXV LIMONITE AND IRON-SAND 357

hydrochloric acid ; it gives off water and is evidently impure
limonite. The larger fragments, i to 2 inches in size, represent
the partial conversion into limonite of a basic volcanic rock with
much glass in the groundmass which formed probably the surface
of the basaltic flows of the plateaux. There must be an enormous
amount of this iron-stone in the island. The finer gravel has a
concretionary character, some of the pieces appearing like bits of
stick that have been converted into limonite. It seems to have
been formed during the disintegration of the rock on the moist
surface of these densely wooded basaltic plateaux ; the process was
not accomplished in ponds or swamps, but was carried out on
ordinary damp ground.

It must be observed in the above connection that the soil in
the areas of basalt and basaltic andesites, which occupy a large
portion of the surface of the island, contains a large amount of fine
magnetic iron-sand. After heavy rains the foot paths glisten with
this fine material which has been washed out on the ground.
This is especially the case in the extensive scantily vegetated
" talasinga " regions where the basaltic rocks are disintegrating for
a considerable depth. The river-sand of these areas, after a little
washing, yields about 75 per cent, of magnetic iron grains which give
in some cases a slight titanium reaction. The amount of magnetic
iron-sand in these rivers, as for instance in the Yanawai and the
Wainunu, must be very great. In the beds of the small sluggish
streams on the surface of the Wainunu table-land the amount is also
very large.

Any explanation of the origin of the extensive silicification
evidenced by the occurrence of silicified corals and siliceous con-
cretions on the surface in various parts of the lower regions of the
island will -have to include that of the formation of the limonite
fragments so often accompanying them. The necessary conditions
would, I think, be afforded by an emerging land-surface during
the consolidation of the exposed calcareous muds and the subse-
quent draining of the new surface. On parts of the newly formed
land, there would follow the successive stages of sea-water, brack-
ish, and fresh-water swamps, such as are clearly indicated by the
abundance of silicified coral fragments that strew the surface of the
low-lying and often swampy districts around the fresh water lake
of Kalikoso,

In such a locality as that of Kalikoso, there were no doubt at
the time of the emergence large tracts covered with chalky cal-
careous mud derived from reef-debris ; and it was during the con-

358 A NATURALIST IN THE PACIFIC chap.

solidation of this mud in the recently reclaimed area that the frag-
ments of coral imbedded in it became silicified. In these cases
where the imbedded corals were already much decayed, it is proba-
ble that the empty cavities thus produced were filled with silica,
and that in this manner the nodules of chalcedony were produced.
Here and there a pebble or a larger block of a volcanic rock would
have been inclosed in the mud ; and in this case also silica largely
replaced the original material of the stone. I imagine that with
the evaporation of the water in the mud during the drying and
consolidating processes the proportion of silica in solution would
attain a degree of super-saturation and that the silicification would
hence be brought about.

With the consolidation of the mud the deposition of silica
ceased ; and in the case of any coral fragments, where the trans-
formation was not completed, decay would often commence. In
the instance of some bits of coral found imbedded in foraminiferous
mud- rock in the Lambasa plains the process of the change had
been suspended, and the fragments were in a state of decay, and
coloured red by iron oxide. If silicification occurred in a sub-
marine deposit only after it became a portion of an old land-surface
we ought not to find incompletely silicified corals inclosed in it.
For these reasons I do not consider that silicification would occur
in the case of submarine deposits long after they have been raised
above the sea.

On the other hand it would seem that the deposition of silica
in the hard parts of dead organisms does not proceed in the
shallow-water calcareous mud of coral reef coasts previous to
emergence. Silicified corals have never as far as I know been
found under such conditions. Nor could the coral fragments now
lying on the Kalikoso plains, often only elevated some 20 or 30
feet above the sea, have undergone this change whilst exposed on
the land-surface as they now lie. They must have been inclosed
in some material containing abundant free silica ; and it is reason-
able to suppose that this material was the chalky mud of the reef-
flats on which they once lived. If this is admitted, then it follows
that since, as above assumed, silicification does not occur in such a
mud either before upheaval or long after it has been raised above
the sea, it must take place in the intermediate period, or in other
words whilst the recently exposed submarine deposits are con-
solidating and drying.

Several objections at once occur with reference to this explan-
ation of the silicification of corals in this island ; but much more

XXV CONDITIONS OF SILICIFICATION 359

investigation is needed to establish any view on the subject. In
the Kalikoso plains, however, we have a critical locality for the
pursuit of this inquiry. Concretions of carbonate of iron and
deposits of earthy limonite are here associated with silicified corals
on the surface of a level and often swampy district around a fresh-
water lake in a region which is only elevated 20 to 60 feet above
the sea. We are dealing here with an area of land that has
emerged in comparatively recent times as far as the history of the
island is concerned. The element of time is limited, and the
problem is not complicated, as it would be in the case of an old
land-surface, raised some hundreds of feet above the sea, by the
intrusion of many other disturbing agencies. Nature has simplified
matters here for the inquirer.

The evidence of recent emergence with regard to the whole
island is discussed in Chapter II., and need not be again referred to
here ; whilst the general description of the Kalikoso district is
given in Chapter XVI. In this connection it maybe remarked that
before their emergence the Kalikoso plains were covered by the
waters of a large irregular sea-water lagoon or lake, which though
more or less surrounded by hills had free communication with the
sea on the north along the line of the passages now occupied by
the Wai-ni-koro and Langa-langa rivers. Both massive and
branching corals then thrived in the waters of the lagoon. There
is no ground for supposing that during the emergence there was an
intermediate stage characterised by brine-ponds and salt-swamps.
The drainage from the slopes of the mountains to the southward
would have prevented it. Whilst this change of level was in
operation, brackish water collected in the deeper part of the
original lagoon, forming a lake which as evidenced by the present
distribution of limonite on the surface of the plains was then far
larger than it is now. As the plains became exposed large flats
covered with chalky mud in which dead corals were more or less
imbedded were bared ; and there and then as the drying and con-
solidation proceeded silicification took place in the manner before
surmised. This deposit was of no great thickness, and has been
since removed by the denuding agencies, whilst the silicified corals
remain behind.

When in the Solomon Islands I was unable to find the source
of the chalcedonic worked flints of such frequent occurrence in that
region. In my general work on those islands (pp. 77 to 80) refer-
ence is made to this subject. It will probably be shown that there
as in Fiji most of the flints are silicified corals.

36o A NATURALIST IN THE PACIFIC ch. xxv

In conclusion it may be remarked that those who object to the
explanation of the origin of silicified corals advanced in this chapter
will be able to find support for their alternative hypothesis in many
facts detailed in these pages. Vanua Levu, for instance, abounds
in hot springs ; and Mr. Andrews might regard this fact as giving
strength to his view that the silicified corals of Vanua Mbalavu in
this group owe their condition to the agency of superheated water
derived from volcanic rocks, more especially since hot springs are
found on the island. Such an explanation could not, I think, apply
to the extensive area of the Kalikoso plains where the silicified
corals are associated with limonite on the surface of a recently
emerged area. If these changes had been induced by hydro-
thermal action, one ought to find evidence of this in those localities
in Vanua Levu where the hot springs issue from foraminiferous
clay deposits, as in the vicinity of Vuni-moli ; but no traces of such
a transformation came under my notice. Wichmann does not ad-
vance any explanation of the silicification of the corals ; but he
considers that the " hornstones," which he obtained from Fiji, rocks
corresponding to the chert-like rocks described by me on page 355,
are the products of disintegration of the basic andesites. I have
already pointed out that certain siliceous nodules have probably this
origin. It is also likely that some of the jasper of Vanua Levu has
been thus formed.

Note on a silicified Fern Rhizome. — This is a specimen, about
three inches long, picked up by a native in a stream near Sueni in the
centre of the island. It has the appearance of being a portion of
the stem or rhizome of a tree-fern, and is permeated in its entirety
by chalcedonic quartz, the fibro-cellular structure being still pre-
served. No other specimen of the kind came under my notice.
The probability of the occurrence of silicified plant-remains in the
pumice-tuffs of the Undu Promontory is pointed out on page 233.

CHAPTER XXVI

• MAGNETIC ROCKS

The literature on the subject of the magnetism of rocks is very
extensive/ and even if I was capable of doing so, any attempt to
deal generally with this complicated phenomenon would be out of
place here. Zirkel in his characteristically thorough fashion has
reviewed the subject in his general work on petrography, but since
the date of the last publication of that book, 1893-94, the literature
has been much increased and the subject has from time to time
been opened up in scientific periodicals, occasionally in ignorance
of the labours of those that have gone before. Here, the local
magnetisation of rocks is alone considered, the general question of
earth magnetism not being entered into.

According to Zirkel one of the earliest known observations of
this phenomenon was made by Bouguer, the French geographer,
whilst he was engaged in the measurement of a degree of the
meridian in the vicinity of Quito in 1742. Alexander von Hum-
boldt, however, was one of the first to attract general attention to
this subject by the announcement of his discovery in 1796 of a

^ A good list of references to the early German authorities on the subject is
given in the American Journal of Science and Arts for 1831, vol. 20. . . . Zirkel
in his Lehrbuch der Petrographie (1893, vol. i. p. 565) gives most of these and
many more recent. . . . Harker in his paper below named refers to a review of
the earlier literature in Verh. naturh. Vereins. Bonn, 1851, vol. 8, and to a more

complete bibliography by Meli in Boll. Soc. Geol.Ital. 1881, vol. 9 British

Association Report in 1889 by Professors Riicker and Thorpe on the Magnetic
State of the British Isles. . . . Nature for August and September, 1894, &c. . . .
Harker on magnetic disturbances in the Isle of Skye, Proc. Cafubr. Philos. Soc.
vol. 10, part 5. . . , Skinner in Proc. Cambr. Philos. Soc. May, 1894. . . . Clark in
Journ. Roy. Instit. Cornwall, 1890-93. . . . Folgheraiter in Frammenti con-
cernanti la geo_fisica, Rome : referred to in Nature, July 27, 1899, and Nov. 8,
1900.

362 A NATURALIST IN THE PACIFIC chap.

" great magnetic mountain " in the heart of Germany. He was then
director-general of the mines in two Franconian principalities ; and
in order to awaken the interest of German physicists and
mineralogists in this matter, he announced his discovery with an
air of mystery, and did not disclose the locality for many months.
He then placed his specimens in the mining-office at Bayreuth to
be sold at so much by weight for the relief of poor miners. His
plan succeeded, and this young savant who had yet before him his
great career, had soon enlisted the interests of several of the noted
scientific men in Germany, including Werner the mineralogist,
Voigt the mathematician, Blumenbach the naturalist, Charpentier,
and others. The amount of attention that this subject then excited
can be inferred from the pages of the " Intelligenzblatt der
Allgemeine Literatur-zeitung " for 1796- 1797 and from the con-
temporary publications. It has been almost forgotten now, and
the matter is indeed often approached " de novo."

However, although by these means the data became largely
increased, no generally accepted explanation resulted. Opposing
views continued at various times to be advanced ; and it has only
in recent years come to be recognised that the magnetic polarity ^
of rocks in exposed situations, as in the mountain-peak or in the
crested spur, often arises from atmospheric electricity inde-
pendently of the inductive action of terrestrial magnetism. This is
the conclusion to which the later evidence given by Zirkel is
directed and was that which Oddone and Sella formed from their
study of the magnetic rocks of the Central Alps. It is not, how-
ever, always necessary to suppose that the affected rocks have been
struck by lightning, although Sella and Folgheraiter have shown
that this is the result of such a contact. They may be found, as
indicated by Mr. Harker, in mountainous localities where thunder-
storms are remarkably rare, and where the peaks act, it is suggested,
as natural conductors. It is easy to show, remarks the same
author, that no lapse of time is required for rocks in exposed
situations to become magnetised. The stones of cairns erected a
few years before on the mountain-tops of the Isle of Skye become
invariably highly magnetic ; whilst the loose stones lying on the
ground display this property to a much less degree. Nor is it
requisite that the rocks affected should be basic volcanic rocks. It

^ Nearly all volcanic rocks at all basic are magnetic, owing to the constant
presence of magnetite ; but magnetic polarity, when the rock-fragment has a
negative and a positive pole, is not directly concerned in volcanic rocks with
the mineral composition.

XXVI MAGNETIC ROCKS 363

has long been known that granites, trachytes, &c., can possess
magnetic polarity ^ ; and the existence of this quality among acid
volcanic rocks is well shown in the case of the dacites in Vanua
Levu, rocks which compose some of the isolated mountain-peaks.

One finds occasional reference to the highly magnetic character
of the rocks in oceanic islands of volcanic origin, but the nature of
the property is not always described ; and it is sometimes not
possible to gather from the data given whether the magnetism
affects the whole mountain mass, when it would be of the regional
kind, due probably to induction, or whether it is the simple
magnetic quality that almost all basic volcanic rocks possess on
account of the fine magnetite disseminated through the rock, or
whether there is evidence of a deposit of magnetite in the vicinity,
or whether it is a mere surface phenomenon confined to the bare
rocks of peaks and ridges, when such rocks, whether gabbro,
granite, basalt, trachyte, or dacite, display magnetic polarity.
Dana, with regard to the basaltic mountain of Tahiti, remarks that
the compass was often rendered useless by the local attraction of
the rocks, bearings taken being found to vary two to three points
on changing the position of the instrument.^ Major Haig says that
the compass becomes perfectly useless anywhere in the neighbour-
hood of one of the mountain-masses or extinct craters in Mauritius,
and attributes this effect to the magnetite in the basalt.^

On the summit .of Mauna Loa in Hawaii, at the edge of the
great crater and in the vicinity of the site where Commodore
Wilkes carried out his pendulum observations in 1840, I found my
compass-needle greatly affected by local attraction, but I neglected
to inquire further into the matter. Judging from my sojourn of
twenty-three days on this mountain-top, thunder-storms are of very
rare occurrence there ; but the electric condition of the air is at times
very evident, and its physiological effects are somewhat distressing.
My blanket at night crackled in my hands and emitted sparks, so
that I could trace with my finger the letter A in phosphorescent
hues on its surface.

That lightning is directly responsible in some instances for the
magnetic polarity of rocks in mountain-peaks is also well estab-
lished. It has been illustrated in an indirect fashion only last
year in the disaster on the Wetterhorn, Rocks partially fused by
thunderbolts and displaying polarity occur on the summit of the

* Some of the earliest observations were made on granite? and trachytes.
^ Geology of the United States Exploring Expedition^ 1849, p. 294.
' Quarterly Journal Geological Society, vol. li., p. 469.

364 A NATURALIST IN THE PACIFIC chap.

Riffelhorn and on one of the peaks of Monte Rosa, and fulgurites
have been also obtained from Mont Blanc. . . It is not always easy
to explain, however, isolated cases of polaric rocks where no signs
of fusion occur. Whilst descending into the Valle del Bove from
the Etna Observatory, I picked up four small volcanic bombs of
basic lava, of which one displayed polarity, the poles being situated
at the sides of the bomb. Zirkel quotes the observation of
Naumann on the summit of the volcano of Moryoshi in Japan.
Here out of a number of lava-blocks lying about only one ex-
hibited marked polarity, whilst the rest showed no signs of it.

Before dealing with the polaric rocks of Vanua Levu, I will
refer to two localities in other parts of the group where magnetic
rocks have been observed. During the Wilkes' expedition in 1840,^
Lieutenant Underwood observed great local attraction at Naikovu,
a rock 90 feet high of volcanic formation lying off the south end
of Nairai Island. He found a "deviation" of 13I points (149
degrees) at the top of the rock, whilst at the foot near the water
the needle gave correct bearings. In the Sailing Directions for the
Pacific Islands, published in 1900, the "deflection " at the summit
is said to be 87 degrees. It is stated by Mr. Eakle in his paper
(quoted on p. 293) on the rocks collected by the recent Agassiz
expedition that this rock is composed of an augite-andesite. ... I
have learned from Mr. Alex. Barrack that there are some highly
magnetic rocks on the west coast of Viti Levu in the vicinity of
Likuri Harbour in the Nandronga district. It is said that speci-
mens sent down to the colonies were found to contain 95 per cent,
of magnetite.

It is very probable that the results obtained by me for Vanua
Levu can be generally applied to the other large islands of the
group. The observations were made during my various geological
journeys and deal only with certain aspects of this interesting
subject.

The first feature in this connection is the frequency with which
simple magnetism is displayed by the acid as well as basic volcanic
rocks of this island. About 95 per cent, of the volcanic rocks
collected attract both ends of the needle.^ This property of
volcanic rocks is well known, and is to be attributed to the mag-

^ Wilkes' Narrative of the U.S. Exploring Expedition, iii., 185.

2 Of the tuffs and clays, almost all submarine and often containing tests of
foraminifera and sometimes molluscan shells, about 90 per cent, exhibit simple
magnetism in a slight degree, but out of nearly 100 specimens tested none show
polarity.

XXVI MAGNETIC ROCKS 365

netite in the groundmass> On examining the character of the
non-magnetic rocks it appears that almost all belong to two groups
where magnetite might be expected to be scanty. The first in-
cludes the pitchstones or basic glasses, sometimes fresh, at other
times more or less palagonitised. The second comprises the highly-
altered basic rocks, where the ferro-magnesian silicates have been
replaced by viridite, calcite, and pyrites. It is not, however, to be
implied that rocks of these two kinds will not sometimes attract
the needle. Many do not, and those in my collection that do so
act feebly.

Coming to the magnetic polarity displayed by some of these
rocks, when the ordinary hand-specimen behaves like a magnet in
attracting one pole of the needle and repelling the other, it is to be
at first observed that a rock can become polaric without being pre-
viously magnetic. Dr. Folgheraiter has observed polarity in the
case of fragments of ancient bricks and pottery ; and he has
described the same effect in the masonry of a house struck by
lightning. In one or two of the Vanua Levu acid rocks showing
polarity this can be also premised since magnetite is present in
very slight degree.

Polarity is very frequent among the volcanic rocks of this
island. Out of 520 specimens in my collection, which was made
without any reference to this matter, 80, or 1 5 per cent, are polaric.
Of these seven-eighths are basic and the rest are acid rocks ; but
this proportion is partly accounted for by the far greater prevalence
of basic rocks in the island. The basic rocks showing polarity
include some of the heaviest olivine-basalts with a specific weight
of 3'0, as well as some of the lighter augite-andesites with specific
weight of 27. They comprise the coarse textured dolerite as
well as the vitreous pitchstone and include both scoriaceous and
amygdaloidal rocks. The polaric acid rocks are mostly referable
to the dacites, with a specific gravity of 2*5 to 2"6.

Humboldt remarked long ago that there is no direct relation
between the degree of polarity and the specific weight. This is
well brought out in the table subjoined ; but it should be at once
observed that there is an indirect relation. Although when we
arrange the rocks in a series according to their specific weight we
find no corresponding relation in the amounts of the polarity, we
observe that the extent to which polarity can be developed is
markedly greater in basic than in acid rocks. From this it may be

^ On p. 357 will be found some notes on the magnetic iron sand that occurs
in great abundance in river and stream beds.

366 A NATURALIST IN THE PACIFIC chap.

inferred that the degree of intensity of the exciting cause required
to give polaric powers of a certain value to an acid rock, like a
dacite, would be much greater than that necessary to endow a
basalt with equal powers. We should not expect to find the
same amount of polarity in the bare rocky peaks of two adjacent
mountains, where one was of dacite and the other of basalt ; and,
other things being equal, if two mountains had been exposed for
ages to the same conditions, we should regard the polaric powers
of the two as nature's equivalent values for the work of atmo-
spheric electricity, on the two rocks in question. We have two
such mountains in Vanua Levu in the case of the adjacent peaks
of Ngaingai (2,448 feet) and Navuningumu (1,931 feet) which are
about 2j miles apart and possess similar bare rocky pointed
summits. I take it that the polaric power of 25° of the dacite
(sp. gr, 2"57) in the first case is equal to the power of 90° of the
basaltic andesite (sp. gr. 2*82) in the other. In the dacitic peak
of Ngaingai and in the basaltic peak of Navuningumu we can
measure what work atmospheric electricity can accomplish in the
course of ages in the magnetisation of rocks. The other conditions
being taken as about the same, the main determining difference is
to be found in the rock-characters.

In the table on the opposite page we have a series of volcanic
rocks placed according to their specific weights, which range from
2*5 to 3*o, and in the second column are shown their relative
polaric powers as indicated by the number of degrees the north
end of the magnetic needle is repelled by the corresponding pole
in the hand-specimen. For this purpose a magnetic needle
2^ inches in length (strictly speaking &$ centimetres) was em-
ployed, a card marked in degrees being placed beneath. The
north pole of the stone was placed in contact with the north end
of the needle, and after the needle had become stationary in its
new position a reading was taken.

These polaric rocks came under my notice over most of the
island. They are infrequent in the district between Undu Point
and the Wai-ni-koro River, where, however, acid tuffs are largely
exposed ; and I did not find them in the Natewa Peninsula east of
Lea, their absence from my collections made in the Mount Freeland
range being remarkable. But it is probable that this is due to the
surface conditions, since dense wood covers the slopes, and bare
rocky peaks are rarely to be seen.

With regard to the influence of locality on the occurrence of
polaric rocks, the results may thus be classified. About one-third

XXVI

MAGNETIC ROCKS

367

are found in the exposed rocky peaks of hills and mountains.
Another third are found where the rocks are bared in headlands,
coast cliffs, inland-bluffs, ridge-tops, and in the open basaltic plains
where trees are scanty. On the other hand, a third occur in
situations, as in wooded districts where the rock exposure is scanty,
when it is not easy to explain the polarity, unless it was developed
in clear districts that have since become covered with forest.

Table showing the Relation between the Specific Gravity and the
Polarity of Volcanic Rocks.

Character of rock.

Specific gravity.

Amount of polarity.^

Dark olivine-basalt

3-00
2-94
2-92
2-90
2-87
2-82
277
272
2-6i
2-59
2-57
2*50

10°
29°
7°
10°
30°
QO

'5°
38"
17°

5°
25°
14

Grey ,, ,,

Dark ,,

Basaltic andesite

Pyroxene-andesite

Dacite

"

"

In no place did any evidence of the direct action of lightning
come under my notice. Mr. S. Skinner who kindly looked at a
few of these rocks says that he found no trace of fulgurites in them.
It is probable that here as in the mountains of Skye, as described
by Mr. Harker, these effects are the result of the general influence
of atmospheric electricity independently of the direct agency
of lightning. The frequency of polaric rocks in the highest peaks
of the island is very remarkable. Generally speaking, all the bare
summits of the mountains are polaric. In my experience there is
no exception. All the rocks obtained from the actual summits
show polarity. The variety of rocks thus affected is suggestive ;
and this chapter may be concluded with a brief reference to their
mode of occurrence on some of the mountain-peaks.

In Mbatini, 3,437 feet in height, which is the highest mountain
of Vanua Levu, the pyroxene-andesite of which the bare rocky
peak is composed is somewhat weathered and has a polaric or

1 These values represent the number of degrees that the magnetic needle is
repelled. The method is described above. A note on the average amount of
polarity found in all my polaric rocks is given at the end of the chapter. The
term " dacite " is here an equivalent of " felsitic andesite."

368 A NATURALIST IN THE PACIFIC chap.

repellent power of 28°. Specimens of rock obtained below the top
show no polarity, the mountain being well wooded except at the
summit. In the adjacent mountain of Koro-mbasanga/ the
polaric rocks are limited to those exposed in the peak which is
bared of vegetation. The rocks in question are tuff-agglomerates,
the small blocks of pyroxene-andesite standing out from the tuff
having a polaric force of 14° or 15°. This effect has been produced
in greatest intensity in the isolated peak of Navuningumu (1,931
feet) in the Ndrandramea region. Here the bare summit is formed
of a semi-vitreous, slightly vesicular, basaltic andesite with a
specific gravity of 2*82 in its present condition.^ This rock is
powerfully polaric, and rendered the compass useless, the deviation
generally to the westward varying from 20° to 50°. I place its
repellent force at about 90°, hand specimens affecting the magnetic
needle at a distance of 13 or 14 inches. None of the various rocks
obtained from the wooded slopes below displayed polarity.

The neighbouring mountain of Ngaingai is composed entirely
of dacite having a specific weight of 2*57. The highest point of
the summit, 2,448 feet above the sea, is bare and rocky, and the
stone here is markedly polaric, the repellent force being about 25°.
Specimens from the lower wooded slopes show no polarity. Near
by rises the hill of Ndrandramea, which is composed in mass of
acid andesites or dacitic rocks. The summit (1,800 feet) is scantily
vegetated, and here the somewhat weathered rock which has a
specific weight of 2'44 (probably near 2*5 in the fresh condition)
has a polaric force of 14°. Specimens of a more compact rock
taken from the wooded slopes 300 feet below the summit
(sp. gr. 2*58) and from 700 feet below the top (sp. gr. 2*68) showed
no such effect ; but a specimen taken from a mass of agglomerate
in the last locality repels the needle 12°. Its specific gravity is
2'6i, and no doubt the mass had been originally a portion of an
exposed cliff-face.^

The summit of Mariko (2,890 feet), the Drayton Peak of the
chart, is formed of a rubbly agglomerate of a compact basic andesite.

^ This name has been wrongly applied in the Admiralty chart to the
mountain of Mbatini. Koro-mbasanga, 2,500 feet, lies three miles to the
north.

2 This rock is described on p. 109. There is no exceptional development
of magnetite for a basic rock in the groundmass.

^ Unfortunately, I have no data for the peaks of Na Raro and Vatu Kaisia,
except that specimens obtained below the summits are non-polaric. In the
case of Na Raro I did not retain the specimen obtained at the top ; whilst in
my ascent of Vatu Kaisia I did not quite reach the summit.

XXVI MAGNETIC ROCKS 369

Though it displays bare rock-faces, the actual peak has a soil-cap
at least 18 inches deep and supports small trees and shrubs.
Notwithstanding this, I found when standing on the peak that
my compass was very noticeably affected, the pull being to the
eastward, whilst the amount of deviation increased from 11° to 16"
when changing from the sitting to the standing position. Specimens
of blocks from the agglomerate forming a rock-face 10 feet below
the summit possessed polaric powers of 12° and 5°. Others of the
same rock exposed in a cliff-face 450 feet below had a weak
repellent power of only 4°. . . As in the case of Mariko, the top of
Thambeyu (2,700 feet) is vegetated ; and beneath the smaller trees
blocks of polaric rocks lie on the surface. One of these, a
pyroxene-andesite (sp. gr. 272), from which I obtained a specimen,
has a polaric power of 38°. In another case, that of an amyg-
daloidal rock of the same character, the repellent power is 14°.

I might mention seveial other polaric peaks, but it will be
sufficient to refer to one or two other localities. In the mountainous
basaltic district around Solevu Bay the peaks are usually polaric.
Specimens from the top of Uli-i-matua, 1,100 feet, have a repellent
power of 15°. The three-peaked hill of Koro-tolu-tolu appears to
be in the mass of polaric basalt from the foot to the summit, having
a repellent power varying from 4° to 30°, the most active specimens
being obtained from the lower slopes, which, however, are scantily
covered with trees. Samples of the grey basalt from Koro-i-rea
show polaric powers of 3° to 7°.

As examples of the numerous lesser hills with bare rocky
polaric summits I will first take Bare-poll Hill facing Soni-soni
Island. This hill is only about 150 feet above the sea, its top
being formed by two large masses of a basic andesite lava with
a glassy groundmass, incrusted with agglomerate, the whole
representing a volcanic " neck." A specimen of the rock masses
has a repellent force of 22°. Another instance is afforded by
Vatui, a hill 450 feet in height situated south of Mount Sesaleka.
Its summit is capped by a naked mass of tuff-agglomerate
pierced by a dyke 18 inches thick of an olivine-basalt, with a
specific gravity of 2*90 and a polaric power of 10°.

A somewhat suggestive example is afforded by the hill of Na

5uva-suva, 1,110 feet high, which overlooks Naindi Harbour to the

:ast of Savu-savu Bay. It is only occupied by trees in its upper

)art, and a specimen of the olivine-basalt, of which the hill is

' omposed, that was obtained from the wooded summit, shows no

1 lolarity ; whilst another from the slopes, two thirds of the way up,

B B

A NATURALIST IN THE PACIFIC

CHAP.

which had been cleared of trees, has a repellent force of 10°. The
polarity of the olivine-basalt from the well-wooded slopes of
Ulu-i-ndali, a range 1,100 feet in height on the east side of the
Wainunu estuary, is not so easily explained ; the intensity varies
from 8° to 28°. Ngalau-levu, a hill 1,650 feet in height, rising
behind Lea on the south coast of Natewa Bay, is polaric in its
upper portion. Specimens of a hemicrystalline basic andesite,
somewhat scoriaceous, which form the agglomerate of the rocky
summit, have a repellent force of 18°, whilst a similar rock from the
agglomerate of an exposed spur two-thirds of the way up the hill has
a force of as much as 38°. A curious case of polarity is exhibited
in a bare tuff overlooking the Vui-na-Savu River between Rauriko
and Vitina. It is composed of a much weathered whitish trachytic
rock, which in appearance affords no promise of polarity, but has
the power of repelling the magnetic needle 2° to 3°. ^

Note on the Average Polarity {Repellent Power) of the Volcanic
Rocks of Vanua Levu.

It would appear from the table given below that the difference
in the average polarity of acid and basic rocks is not very great.
The average for rocks with a specific gravity below 27 is about
10° ; and that for heavier rocks is about 14°- The difference
mainly lies at the maximum end of each series, the capacity for
extreme polarity being, as before remarked, markedly greater in
the basic rocks.

Specific
gravity.

2-SO-2-59
2 '60-2 "69
270-279
2 -80-2 -89
2'9o-3"oo

Character of rocks.

Dacites

Dacites and augite-andesites

Augite-andesites

Basaltic andesites and oli-

vine-basalts
Olivine-basalts

Number of
specimens.

6

5

5

18

14

Polarity.^

Range.

2°-25
3°-i6°

3°-90°
3°-29°

J The mode of measurement is described on p. 366.

Average.

11-6°
8-6°
13-2°
15-0°
127°

XXVI MAGNETIC ROCKS 371

It is, however, noteworthy, as indicated by the value of the
average in each series that not one of them is a good series. They
form curves which in each case present an extreme maximum
variant which is suggestive of quite another degree of magnetising
agency. This is also illustrated in the combined curve of all the
results given above. The acid as well as the basic series are thus
characterised, and the extreme maximum variants are in each
instance afforded by the highest mountain peaks. It is probable
that there is an accelerating ratio of magnetisation with increased
elevation. However that may be, it appears evident from my obser-
vations on the two adjacent peaks of Ngaingai and Navuningumu
that the limits of polarity acquired through atmospheric electricity
without the direct action of lightning would be, as measured by
the scale here employed, four times as great for a dacite (25°) as
for a basaltic andesite (90°).

B B 2

CHAPTER XXVII

SOME CONCLUSIONS AND THEIR BEARINGS

Vanua Levu is a composite island built up during a long period
of emergence, that began probably in the later Tertiary period, by
the union of a number of large and small islands of volcanic
formation representing the products of submarine eruptions. It
differs in this respect from Viti Levu which is much more massive
in its profile and possesses a greater proportion of plutonic rocks.
When, however, Viti Levu comes to be systematically examined,
it is likely that traces of its composite origin will be found. The
evidence seems to show that it is older than Vanua Levu ; but they
are both situated on the same submarine platform, the area of which
is nearly equal to the combined areas of the two large islands that
rise from it.

This platform, as indicated in the small plan of the group, is
limited by the lOO- fathom line in the charts ; but since the reefs
on their seaward slopes plunge down precipitously, such a line
practically serves to delineate the margin of the plateau. It has
been my object to show on previous pages ^ that this submarine
platform is a basaltic plateau built up by submarine lava-flows and
incrusted with coral reefs and their deposits. It has been pointed
out that this platform passes gradually, as it proceeds landward,
into the low-lying basaltic plains that constitute the sea-border in
the western part of the island, where the breadth of the submerged
plateau is greatest. The basaltic flows of the plains often display
the almost vertical columns of slightly inclined flows. Their
apparent termination at the sea-border, where they are in places
covered over with submarine deposits, cannot, however, be accepted
as their real limits. According to my view they extend several

1 See pp. 2, 15, 18, 56, 62, 72, &c. il

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CH. XXVII THE SUBMARINE PLATEAU 373

miles seaward and form the platform, as is shown in the sections
on pages 62 and 107.

We have in the great basaltic mountain of Seatura, which
forms the bulk of the western end of the island, a probable source
of many of these basaltic flows ; and the occurrence inland in
the western half of Vanua Levu of elevated table-lands of basalt
like that of Wainunu, which extend from the centre of the island
to near the coast, afford testimony that the formation of these
flows extends over a considerable period of the island's history.

It is held by Professor Agassiz that these submarine platforms
are the work of erosion into the flanks of the up-heaved islands.^
In Chapter II. it has been pointed out that the eroding agencies
are not actively in operation in our own day, and that there is
good reason for the belief that the process of amalgamation by
which Vanua Levu has been built up during a prolonged period
of emergence, is not suspended at the present time. It is assumed
that the uniformity in Nature's methods has not been broken. If,
however, we have here platforms of erosion, the coasts of Vanua
Levu, as far as my interpretation goes, supply no evidence of it ;
and we have to imagine that a period of emergence extending over
a geological age has been followed by a similarly vast period of
erosion without much change in level.

Whatever agencies have been at work, the production of sub-
marine platforms 10 to 20 miles in width must have been a
stupendous operation ; and we shall be obliged to inquire whether
plateaux, either submarine or upheaved, occur in association with
volcanic islands in other parts of the world, and under what con-
ditions they have been formed. At least four hypotheses have
be^n framed with regard to the submarine platforms of Fiji.
There is first the original theory of subsidence of Darwin ; but
Vanua Levu, which presents one long story of emergence, offers
nothing to support this view. There is the growth of a reef sea-
ward on its own talus, as advanced by Murray. There is the theory
of erosion of Agassiz. There is lastly my own idea of basaltic
plateaux incrusted by reefs. We may therefore inquire as to the
evidence afforded by Vanua Levu in favour of these views. Basaltic
flows, in places covered by submarine deposits, form the low plains
at its sea-border, where the platforms are broadest ; and there
rises a basaltic mountain of the Mauna Loa type, occupying most
Df the western end of the island. No one would be bold enough

^ The Islands and Coral Reefs of Fiji, Bull. Mus. Comp. Zool. Harv. Coll,
'ol. 33, 1899.

374 A NATURALIST IN THE PACIFIC chap.

to place the limit of these basaltic flows at the water's edge ; and
as is indicated in the sections, they probably extend for miles under
the sea.

If we look for an island which in its extensive palagonite-
formations, in its basaltic table-lands and later basaltic flows, in its
huge mountain-ridges, and in its evidence of submergence, most
resembles Vanua Levu, we seem to find it in Iceland. It is in
Iceland, I think, that we must expect an explanation of many of.
the puzzling features in the structure of Vanua Levu. |

I pass on now to refer to some of the general points in the
geology of this island, which have been dealt with in detail in the
earlier chapters of this work. With regard first to the distribution
of the volcanic rocks, it may be remarked that my materials do not
lend themselves to making a geological map. The most compre-
hensive idea of the principal points in the geological structure
will be obtained by reading the description of the profile given in
Chapter I. There is, however, a method in the distribution of the
rocks that may be again noticed here. The plutonic rocks are
very scantily exposed, as is shown on page 249 ; and they are not
displayed at all in the western half of the island. The more basic
eruptive rocks, the olivine-basalts and basaltic andesites, are mainly
confined to the western half, that is, west of Nanduri on the
north and of the Ndreke-ni-wai River on the south. Ordinary
augite-andesites occur also in the western half ; and together with
the hypersthene-augite-andesites they are found over most of the
rest of the island, excluding the north-east portion, east of Lambasa
and Tawaki, where quartz-porphyries, oligoclase-trachytes, and
acid pumice tuffs prevail. The acid andesites, including the horn-
blende-andesites and the dacites or felsitic andesites, are best repre-
sented in the Ndrandramea district in the midst of the basic rocks.
They occur in the isolated peaks of Na Raro and Vatu Kaisia and
in one or two other localities, as in the Valanga Range and on the
shores of Natewa Bay in the vicinity of the Salt Lake. These
peaks of acid andesites, as in the instances of Vatu Kaisia and
Soloa Levu, are at times in part overwhelmed or surrounded by
the basaltic flows. This singular feature of bosses of acid rocks in
the midst of basaltic fields offers another point of resemblance
between Iceland and Vanua Levu.

The mountain-types vary considerably, the ridge-mountains,
however, being most characteristic of the island. The basaltic
mountain of Seatura, though its lava-flows were evidently in the
main submarine, belongs as before observed to the Mauna Loa

XXVII THE RIDGE-MOUNTAINS 375

type. In its radiating valleys and gorges and in other characters
it recalls the description given by Dana of the island of Tahiti.
The peaks of acid andesites, represented in the isolated hills and
mountains of the Ndrandramea district, and in the solitary
mountains of Vatu Kaisia and Na Raro, are the necks and stumps
of submarine volcanoes dating back to the pre-basaltic period of
the island. It is, however, in the great mountain-ridges of the
central portion of the island, those of Va Lili, Korotini, Nawavi,
Thambeyu, Mbatini, Mariko, &c., that we find, as just remarked,
the most typical features of the internal topography of Vanua
Levu.

Agglomerates overlying palagonite-tuffs and clays, that are
usually foraminiferous and sometimes inclose molluscan shells, clothe
the slopes of these mountain-ridges up to elevations of 2,500 feet and
over above the sea. Most of these great ridges, now more or less
covered over by these submarine deposits, represent lines of sub-
merged vents, of which only a few raised their summits above the
sea in the earliest stages in the history of the island. At this early
period there were no coral reefs. Some of the ridges present a
marked parallel arrangement, recalling the arrangement of the
mountain-ridges and lesser chains of hills as described by Dr.
Johnston-Lavis in the account of his visit to Iceland.^ The
description of Hekla (as given by Thoroddsen) as "an oblong
ridge which has been fissured in the direction of its length and
bears a row of craters along the fissure," ^ comes very near to my
conception of the original condition of these great mountain-ridges
before the emergence. Dr. Johnston-Lavis sees in Hekla a type of
volcanic mountain very different from that of Vesuvius and Etna.
He regards it as a ridge marked by a number of parallel ridges and
furrows, and built up along a main fissure with a number of
subsidiary parallel fissures.

The part taken by palagonite in the composition of the finer
deposits over the greater portion of Vanua Levu is another
prominent characteristic of the island. Palagonite, as I have
suggested in Chapter XXIV., is formed probably on the surface of
submarine flows of an ophitic basaltic rock.

The age of the more recent of the deposits of this island, the
fossiliferous tuffs, the pteropod-ooze rocks, and the foraminiferous
muds, cannot be far different from that of the same deposits in
other parts of the group, since it is apparent that the same general

1 Scott. Geogr. Mag. 1895.

2 Ancient Volcanoes of Great Britain^ by Sir A. Geikie, 1897, ii. 260.

376 A NATURALIST IN THE PACIFIC chap.

movement of emergence has affected both of the two larger islands.
Professor Martin of Leyden informed Dr. Wichmann that the
fossil shells found in the tuffs of Viti Levu, Ovalau, and other
islands were Tertiary but not older than the Miocene.^ Dr. Dall,
after examining the fossil mollusks collected by Professor Agassiz
from the elevated limestones of Fiji, confirmed the impression
formed by the latter as to their late Tertiary age. None of the
genera were extinct, and the fossils were in his opinion younger
than Eocene and either Miocene or Pliocene.^ The Rev. J. E.
Tenison- Woods described as extinct Tertiary fossils, some corals
and mollusks from the interior of Ovalau.^ Mr. H. B. Brady,
basing his conclusions on the character of the foraminifera, assigned
a Post-Tertiary date to the Suva " soapstone " taken at elevations
up to 100 feet in that neighbourhood.* Professor David referring
to some fossil teeth of Carcharodon and to a fossil Tridacna found
at Walu Bay infers that the deposits are at least as old as Pliocene
but not as old eis the earlier Tertiaries.^ Since, as pointed out by
Professor David, the latest movements of emergence have taken
place in recent geological time, these various observations go to
show that whilst the latest exposure of deposits has occurred in
recent time the mass of the fossiliferous deposits date back to the
Pliocene and the Miocene periods.

According to Wichmann these islands were in a continental
condition during the Palaeozoic and Mesozoic periods, and it was
only in the later Tertiary age that the movement of subsidence
began that prepared the way for the formation of the more recent
deposits. The submergence during the Tertiary period and the
subsequent emergence are facts that cannot be gainsaid ; but we
may ask where is the evidence of the continental condition during
the earlier periods. There is little in the results obtained from
Vanua Levu that directly supports such an hypothesis. Under
such circumstances one ought to have discovered in the deposits of
this island some evidence of this early condition, and there should
be found in the fauna and flora some traces of the original
•organisms. According to Hedley there is some indication of a
continental condition in the molluscan fauna, and he quotes

* See Wichmann in Min. und Petrog. Mitth. band v. heft i.

* Amer. Journ. Sd.Yl. 165, 1898. See also Agassiz on the Islands and
<Coral Reefs of Fiji, before quoted.

3 Proc. Linn. Soc. N.S.W. 1879-80, p. 358.

* Quart, fourn. Geolog. Soc. vol. 44, 1888.

' See Preface to the report of Mr. Andrews quoted on a later page.

xxvii EMERGENCE OF THE FIJIS 377

Fairmaire as regarding the Coleoptera as of a continental character ;
but no one, that I am aware of, has found any direct evidence of
the Pre-Tertiary periods in this group. It is in harmony with the
geological characters to assume that these islands made their first
appearance during the Tertiary epoch.

Coming to the subject of the movements whether of land or
sea that led to the appearance of these islands, we shall not be
begging the question if we speak of their " emergence." There is
po doubt as to there having been during and since the Tertiary
epoch an emergence of some thousands of feet, allowing for the
original depth of the foraminiferous deposits now found at
elevations of over 2,000 feet above the sea. In Chapter II. it is
shown that there is good ground for the belief that these changes
of level have not altogether ceased. Of what nature, we may ask,
is this movement. We have before us the grand conception of
Suess that the emergence of the land in the different phases of
geological time has been produced by the general lowering of the
level of the ocean arising from local subsidences of the earth's
crust. This view in the case of the recent calcareous formations of
the Pacific is applied to the terraces of the Loyalty Islands ;i and
it follows that it is also applicable to the elevated calcareous
deposits of the islands of the Western Pacific as a whole, as in the
case of the Tongan Islands, the New Hebrides, the Solomon Group,
&c. Such a general change of level ought to be represented in the
large island of Hawaii in the North Pacific, since it could not be
confined to one locality in this ocean. There is no evidence of
emergence, as far as I know, presented by this island. During my
sojourn there, I examined much of its coasts. Now the antiquity
of the flora of this group is sufficiently attested by the cir-
cumstance that it ranks first among the oceanic groups of the
Pacific for the number of endemic plants that it possesses ; and
the same conclusions may be drawn from the insects and the birds.
There is no evidence in this group, one of the most ancient of the
Pacific archipelagoes, of that great movement of emergence, which
is abundantly demonstrated over the Western Pacific.

The standpoint is therefore taken that the movement of
emergence which began in the Tertiary period and is probably
still in operation is confined to the southern portion of the tropical
Pacific. Speaking of the time of the Fijian emergence. Professor
Agassiz observes that " it is not unnatural to assume that it was
coincident with the elevation of Northern Queensland, and that the
^ Das Antlitz der Erde, French edition by E, de Margerie, ii. 534,

378 A NATURALIST IN THE PACIFIC chap.

area of elevation included New Guinea, the islands to the east of
it as far as New Caledonia, and as far east as the most distant of
the Paumotus, and extended northward of that line to include the
Gilbert, Ellice, Marshall, and Caroline Islands." ^

From the report of Mr. Andrews ^ it is evident that in the
Lau Islands of the Fiji Group volcanic outbreaks have taken
place since the last upheaval. He describes in the case of Mango
and other islands the manner in which cliffs of limestone form
inliers in flows of andesitic lava. In the history of these islands
he first distinguishes the period of calcareous deposits, when the
-bedded limestones forming the submarine plateau were laid down.
Then followed a period of volcanism during which masses of
volcanic materials were erupted along the axis of elevation. Alter-
nating epochs of upheaval and stable equilibrium ensued, during
the last of which the reefs grew outwards and formed the terraces
now so characteristic of the profiles of the islands. After the last
upheaval the volcanic forces became again active. There is much
of special interest in the account given by Mr. Andrews of the
Lau Group. The blocks of limestone included in the volcanic
agglomerates distinguish the Lau detrital rocks from those of
Vanua Levu. There is no evidence that coral reefs existed
during the early stages of the emergence of Vanua Levu to be
obtained from the submarine formations found on the higher levels,
i,ooo to 2,500 feet above the sea.

The period of emergence for this island may be divided into
an earlier and into a later stage, the last corresponding to the age
of emergence of the Lau Islands. The earlier stage, which may
be termed the " Pre-Lau " stage, is represented by the deposits of
the higher slopes of Vanua Levu, that is above 1,000 or 1,200 feet.
This is really the critical epoch in the history of this group, and
assuming that the movement of emergence has been fairly uni-
form over the archipelago we cannot but be astonished at the
absence of all traces of ancient reefs in the earlier stage.

We may infer from the observations of Mr, Lister ^ that the
islands of the Tonga Group represent the Lau stage of the
emergence. They are similar in height and in general geological

* See the paper before quoted on the coral reefs of Fiji.

2 Bull. Mus. Comp. Zool. Harv. Coll. vol. 38. Geolog. Ser. vol. 5, no. i,
1900. On the Limestones and General Geology of the Fiji Islands^ by E. C.
Andrews.

^ Quart. Journ. Geolog. Soc. vol. 47, p. 590, 1891. See also Mr. Marker's
paper below quoted.

XXVII STAGES OF THE EMERGENCE 379

structure to the islands of Lau, that of Eua, for instance, which
has an elevation of 1,100 feet, being formed of reef-limestones
overlying volcanic tuffs. Dykes penetrate the tuffs but do not
enter the incrusting calcareous strata. Mr. Harker,^ after examin-
ing the collections of Mr. Lister, remarks that all the rocks
excepting those from Falcon Island appear to be of submarine
formation. The volcanic material, he adds, seems to have been
almost exclusively of fragmental character. It would be rash, it
is remarked, to refer all the rocks to a Recent age, and some of
them may be found to go back far into Tertiary times.

My division of the long period occupied by the emergence of
the Fiji Islands into two stages, the Lau stage corresponding to
elevations of less than 1,000 or 1,200 feet, and the Pre- Lau stage
which includes the earlier evidence of emergence found at heights
exceeding these elevations and ranging up to 2,000 or 3,000 feet,
may perhaps be applicable to other regions of emergence.

As bearing on the question of the isolation and antiquity of
the Pacific Islands the following approximate results for the
Hawaiian, Fijian, and Tongan floras may be here quoted.^ These
data are liable to correction ; but they are near enough to the
truth to be very suggestive. Of peculiar genera of flowering plants
and ferns the Hawaiian Islands possess about 40, the Fiji Group
about 16, and the Tongan Islands none. Of endemic species of
flowering plants there are about 80 per cent, in Hawaii, about 50
per cent, in Fiji, and 3 or 4 per cent, in Tonga. Granting that
there is much to be done yet in the investigation of these floras,
it would be underrating the brilliant results of the labours of
Hillebrand and Seemann to characterise their work as sampling.
Let us suppose, however, that the floras of Hawaii, Fiji, and
Tonga have been only sampled, the data above given would be
still reliable. It is quite possible to obtain a botanical equivalent
corresponding to the geological estimates of the relative ages of
these islands ; and taking the proportion of endemic plants as our
guide, the Lau stage, as represented by the Tongan Islands, would
have a value of 3 or 4, the Pre-Lau stage now exhibited in the
earliest stage of emergence of Vanua Levu would have a value of
50, and the Hawaiian stage older than all would have a value of
80. These results are intended as suggestive and I hope to work

* Geolog. Mag. June, 1891.

2 Seemann's Flora Vitiensis, Home's Year in Fiji., Hillebrand's Flora of
the Hawaiian Islands., Hemsley's "Flora of the Tonga Islands" va Journal
Linnean Society, Botany, vol. 30.

38o A NATURALIST IN THE PACIFIC chap.

out this subject in the second volume. They make the problem
of the relative antiquity of these islands more mysterious than it
even appeared before.

With regard to the vexed question of the light thrown on the
past condition of these islands by the present state of their floras
and faunas, it may be at once observed that my belief in the
general principle that islands have always been islands has not
been shaken by the results of the examination of the geological
structure of Vanua Levu. In a correspondence in Nature about
fifteen years ago it was suggested by me that this is the position
we ought to take with regard to the stocking with plants of the
islands of the Southern Ocean, such as Kerguelen ; and I take the
same standpoint for the islands of the Pacific. If the distribution
of a particular group of plants or animals does not seem to accord
with the present arrangement of the land, it is by far the safest
plan, even after exhausting all likely modes of explanation, not
to invoke the intervention of geographical changes. New possi-
bilities of inter-communication, new ways of looking at old facts,
and new discoveries of an unexpected nature come monthly before
us in the progress of scientific research ; and I scarcely think that
our knowledge of any one group of organisms is ever sufficiently
precise to justify a recourse to hypothetical alterations in the
present relations of land and sea.

The hypothesis of a Pacific continent,^ whether it takes a
trans-oceanic form, as advocated by Von Ihering, Hutton, Baur
and others, or whether it is represented by an island-continent
isolated in mesozoic times, as suggested by Pilsbry, receives no
support from the geological characters of Vanua Levu. Nor can
I accept as regards Fiji Mr. Hedley's theory of the Melanesian
Plateau. There is no evidence that the various islands of the
Fiji Group were ever amalgamated and no indication of a geological
nature that they were ever joined to the Solomon Group. The
Fijis, as we see them, have had an independent history, and the
process at work is not one of disruption but of amalgamation,
lesser islands being united to larger islands during the prolonged
period of emergence. Mr. Hedley, however, has some weighty
data on his side more especially zoological ; but even here it would
be wise to suspend one's judgment. Though the great mass of
botanical evidence is as respects Fiji opposed to such connections,

^ See Hutton Proc. Linn. Soc. N.S.W. 1896, Baur, Amer. Nat. 1897,
Pilsbry, Proc. Nat. Set. Philad. 1900, Hedley, Proc. Linn. Soc. N.S.W. 1892,
1899, &c.

XXVII PERMANENT INSULAR CONDITIONS 381

the distribution of Dammara may, however, be fairly claimed on
their behalf.

The dilemma into which such discussions lead us is aptly
stated by Dr. Pilsbry. If we do not accept the hypothesis of a
Pacific continent, we have to explain the cessation of the means
of transportal in later geological times, since this is implied in the
isolation necessary for the development of peculiar characters in a
fauna or a flora. This was the dilemma that presented itself to
me in studying the origin of the Fijian plants. Assuming on
geological grounds that the insular condition had been always
maintained I had to explain the differentiation in the inland
plants, or in other words to account for the failure of the means of
transportal that once existed. Since this subject bears directly on
the past condition of the Fiji Islands, I may be pardoned for
referring to it here. It belongs properly to the second volume
which it is proposed to devote to the dispersal and distribution of
Pacific plants ; but as I contest the pre-existence of a Pacific
continent, it is fitting though not necessary that this difficulty
should be faced at once.

If we in imagination combine in a typical island the characters
of the flora presented by islands of different elevation in the
Pacific we get a result of this kind in an island of the height of
Hawaii, nearly 14,000 feet. The littoral plants of such an island
are found all over the coasts of the tropical Pacific, and for the
explanation of this fact we look mainly to the agency of the
ocean-currents. The plants of the mountain summit, belonging to
the temperate genera of Geranium, Rubus, Ranunculus, Vaccinium,
&c., are represented at least generically on the tops of the lofty
ranges of the Pacific coasts and in the interior of the continents ;
and we find the explanation of the wide diffusion of such plants
in the agency of the migrant birds that at no distant time, if not
actually in our own time, were regular visitors to these mountain
regions. The plants of the marsh, of the stream, and of the pond,
belong often to species that occur in similar stations over a great
portion of the world, such as species of Drosera, Ruppia, Pota-
mogeton, &c. ; and here the agency of wild duck and other water-
fowl may be observed in active operation.

But when in such an island we regard the intermediate region
between the uplands and the coast, usually the forest-zone, we
find an area of change not only for the plants but also for the
birds. It is here that the new genera of plants have been developed
that distinguish the floras of the Pacific groups each from the

382 A NATURALIST IN THE PACIFIC ch. xxvii

others ; and here also the migrant bird, having from some cause
changed its ways, has given rise to new varieties and to new
species. It is with this loss of the migratory powers of the birds
of the forest-zone that I connect many of the important differences
between the forest-floras of the different groups of the Pacific.
At one time, it would seem, birds were far more active agents in
dispersing seeds and fruits over these archipelagoes than they are
at present ; but it is not held that this is concerned with the
extermination and extinction of the birds of these islands in the
present day. The change dates far back and is far-reaching in its
effects. It is assumed in this argument that the alpine plant and
the plant of the pond and of the sea-shore preserve their characters
by reason of the means of free dispersal that they still enjoy ; and
it is inferred that the plant of the forest-zone has varied more
because opportunities of transportal of its kind no longer are
afforded. Many a line of ancient migration is now broken.

It is suggested that in the past when birds were more gene-
ralised in type they were much more migratory in habits and that
limitation of range has been associated with specialisation. The
plants dispersed by the birds have undergone "a parallel series of
changes. At first widely distributed, as in the more generalised
types of birds, they became localised in proportion as the birds to
which they owed their means of dispersal lost their migratory
ways ; and both plant and bird began to vary. There is, I am
convinced, a profound connection between birds and plants, of
which we now perceive only the last of a long series of changes.
This subject will be dealt with at length in the volume on plant-
dispersal ; and it is only referred to here to illustrate my contention
that we have yet much to learn before it would be safe to look to
hypothetical changes of sea and land to explain difficulties in
distribution.

APPENDIX

Note on the Stone- Axes. — Two of these polished stone-axes from a
collection made in Vanua Levu were selected for sections. One is light-
green and smooth. The other has a very different appearance, being
blackish and rather rough, its smooth surface having been apparently
lost by lying in a stream-course or in wet ground for a long period. Both,
however, are made of the same type of basaltic rock, the specific gravity
in one case being 2*93, in the other 2*97. It is an aphanitic basalt with
scanty olivine containing little or no residual glass and referred to genus
40 of the olivine-basalts. It is by no means a common type of basalt
in Vanua Levu, and I cannot refer it to any particular locality on account
of the peculiarities it presents when contrasted with rocks of the same
genus. The olivine is very scanty and small, and in one of the specimens
is represented only by pseudomorphs. The felspar-lathes vary usually
from "05 to '2 mm. in length, and the augite granules which are very
abundant are •01 or '02 mm. in diameter. There is an occasional small
phenocryst of augite. The rock shows little or no alteration and cannot
be characterised as a greenstone. The greenish hue of one axe is due
to weathering; but its extension into the internal black portion of the
tool is not appreciable.

Note on the ascent of the tide up the Ndreketi River. — On July 20th
and 2ist, 1899, by observing the surface density it was ascertained that
at high- water the sea- water reached Navundi a mile or two below
Mbatiri. At low-tide it reached about half-way between Kanathangi
and Navundi.- The moon was in her quarters.

Note on the " talasinga " districts. — This subject will be discussed in
the second volume.

INDEX

Note. — It has been deemed best to follow the example of the Admiralty surveys in
the spelling of native names. In this book, therefore —

Mb = the Fijian B
Th = ,, ,, C
ND = „ „ D
NG= „ ,, GandQ

Abbreviations, for rock descriptions,

236
Acicastello, Sicily, basalt and pala-

gonite, 347
Acid and basic rocks, regions of, 219,

374
Agassiz, Prof. A., 294, 373, 376, 377
Agates, 138, 139, 227, 353, 354
Agglomerates ; see Volcanic agglomer-
ates
Algae in hot springs, 24, 25, 33, 38
Alps, magnetic rocks of the, 362, 363
Altered rocks ; see Propylites, etc.
Andesites, acid, 98-108, 112, 123-127,
193, 194 ; relative frequency of,
235 ; classification of, 293-306 ;
distribution of, 374 ; peaks in ba-
saltic flows, 104, 115, 116, 374;
altered, 105, 297 ; columnar, 102,
104 ; pre-basaltic, 375
Andrews, Mr. E. C., 7, 22, 294, 350,

378
Artesian reservoirs, 39
Augite, crystals of, in tuffs, 45, 182,

193

Augite-andesites, 51, 162, 199, 204,
209, 232, 235, 294, etc. ; classifica-
tion of, 239, 245, 246, 266-284 ;
distribution of, 374 ; aphanitic, 117-
120, 125, 162, 168, 279 ; relative
frequency of, 235 ; see Basaltic an-
desites

Avuka, range, 179

Axes, stone, structure of, 383

Bare-poll, peak, near Soni-soni, 93

Barrack, Mr. A. H., 27, 123

Barrack, Mr. Alex., 364

Barratt, Mr., 68

Barrier-reef, great, of Fiji ; see under
Submarine plateau

1 Basaltic andesites, 47, 56, 64, 75,
108, 123, 137, 147, 148, 160, 164,
190, 204, 206, 208, 288 ; classification
of, 239, 266, 278 ; distribution of,

374

Basaltic rocks, extensive disintegration
of, 57,64,72, 129

Basaltic flows surrounding hills of
acid andesite, 104, 115, 116, 374

Basaltic plains and plateaux, 6, 55, 62,
82, 107, 128-135, 373

Basaltic submarine flows, 338, 342,
344, 346, 347, 372, 375 ; ^ee under
Submarine plateau and Basaltic
plains

Basalts, columnar, 3, 63, 78, ^3, 84,
85, 123, 129, 133, 147, 170, 173, 203,
260, 284

Basalts, ophitic, 50, 74, 1x4, 133, 137,
138, 155. 159, 162, 191, 204, 213,
252, 256, 347 ; the ophitic habit,
237, 238 ; ophitic sub-orders, 236,
241-245 ; ophitic genera, 256, 262,
272-276, 283

Basalts, olivine, relation of black and
grey, 89, 90 ; classification of, 239,
241-244, 252-265 ; relative frequency
of, 235 ; distribution of, 374

^ The term "basalt" is here used in a general sense to include olivine-basalts,
basaltic andesites, and other basic types of the augite-andesites and hypersthene-augice
andesites.

C C

386

INDEX

Basalts, grey olivine, 65-67, 73-7 S, 77,

89, 253-255, 257, 261, 263
Basalts, highly basic, 258
Basalts, of Acicastello, 347 ; of Mbua

and Ndama plains, 58, 134, 262,

278; of Ndreketi plains, 133, 134;

of Sarawanga plains, 129, 134, 262 ;

of Savu-savu peninsula, 190, 288 ;

of Seatura, 63-72, 85 ; of Solevu

Bay, 75-77 ; of Wainunu, 85 ; of

Ulu-i-ndali, 89
Basalts associated with palagonite,

347
Basic glass, 312, 338 ; see Pitchstone,

Crush- tuffs, Hyalomelan-tuffs
Bastite, 182, 297
Baur, Mr., 380
Blyth, Mr., 123
Brady, Mr. H. B., 322, 376
Breccias ; see Volcanic agglomerates
Bronzite, 182
Bromlow, Dr., 29
Biichner, Dr. Max, 22
Bulling, Mr., 32, 36, 232
Bunsen, on palagonite, 343, 344

Carbonate of iron, concretions of,
227,351,356

Carcharodon, 376

Chalcedony, 13, 138, 162, 183, 199,
226-228, 350-355 ; see Agate, Onyx,
Flints

Chalmers, Mr., 233

Charts, old and new compared, 18, 19

Chert, 355

Classification of volcanic rocks, 235

Coleoptera of Fiji, 377

Columnar structure ; see Basalt, Acid
andesite, Dacite, Oligoclase- trachyte

Combe, Commander, 15

Cooper, Mr. H. S., 29

Coral reefs, upheaved, 7-12, 189, 200,
201, 318 ; their absence in the higher
levels, 7, 8, 12, 19, 375

Craters, traces of, 44, 52, 67, 80, 166,
186, 192, 195, 202

Crush-tuffs, 55, 94, 149, 157, 341 ;
general description, 334 ; see below

Crushing of basic glass ; in veins, 340,
341 ; on surface of a submarine
flow, 93, 338 ; in matrix of pitch-
stone-agglomerate and in rubbly
pitchstone, 94, 142, 145, 157, 313;
its connection with palagonite, 93,
339, 340-342, 346

Cumming, Miss Gordon, 22, 25, 29

Dacites, 3, 5, 100, 108, 235, 294, 304 ;
columnar, loi, 102 ; definition of

the term, 295 ; classification and

characters, 240, 302 ; see Acid ande-

sites
Dall, Dr., 376
Dana, Prof, 3, 10, 11, 16, 21, 26, 72,

84, 129, 135, 218, 309, 363
Darwin, Mr., on barrier-reefs, 373
Datum-mark, 195
David, Prof., 376
Deep-sea deposits, 337
Delanasau, 68
Dillon's Rock, 45 -
Diorite, 182, 193, 235, 249, 251
Doelter, on hornblende paramorphism,

308
Doleritic, use and definition of the

term, 236, 238, 259, 274
Dolomite, 7

Drayton, peak ; see Mariko
Dykes, 51,54,63,68-72, 78, 81, 142,
144, 148, 155, 156, 163, 164, 170, 171,
184, 199, 202, 209, 216, 220, 233, 234,
267, 268, 270, 277, 280, 282 ; their
two sets of felspar-lathes, 238

Eakle, Mr., 293, 294

Earthquakes, 37

Emergence of Vanua Levu, i, 7-20,
321, 376-379 ; age of, 376

Etna, mount, coast springs of, 39 ;
dykes in Valle del Bove, 237 ; mag-
netic bomb, 364

Fairmaire, M., 377

Faro, island, Solomon Group, 2

Fawn, harbour, 9, 200, 3 1 8

Felsitic andesites, 106, 108, 295, 300 ;
see Acid andesites and Dacites

Felsitic groundmass, as employed in
classification, 236, 239, 240, 249

Felsitic orders, 249, 291, 297, 300, 302

Felspar-lathes in classification, 236,
241

Fern, tree, silicified caudex of, 360

Fish-scales, fossil, 1 54

Flints, 13, 81, 83, 138, 139, 222, 226,
350-360

Floating islands, 225

Floras of Fiji, Hawaii, and Tonga, 379

Flow-arrangement in classification,
236-238

Folgheraiter, Dr., 362, 365

Foraminiferal limestones, 130-132,
202, 318

Foraminiferous deposits (tuffs, muds,
clays), 96, 109, 130, 134, 136, 139,
149, 154, 161, 170, 198, 205; de-
scription of, 321-333 ; altered, 324-

INDEX

387

326; thickness of, 156; see Globi-
gerina deposits and Palaeonite-
tuffs

Fossilised trees, 233

Freeland, Mount, 2, 6, 203-206,269,274

Gabbros, 180, 182, 184, 211, 235;
classification of, 239, 240 ; charac-
ters, 249, 250 ; see Plutonic rocks
Geikie, Sir A., 375
Giant sedge ; see Scirpodendron
Globigerina deposits, 10, 55, 131, 158,
177, 187, 189, 190, 221, 321-326, 344 ;
see Foraminiferous deposits
Globigerina limestone, 319
Gold, alluvial, in Vanua Levu, 116
Granular pyroxene, the sub-orders

characterised by, 236, 241, &c.
Greenstones ; see Propylites
Groundmass, characters of, used in
classification, 236-238

Haig, Major, on magnetic rocks, 363

Hale Peak, 210, 212

Hanusz, on floating islands, 226

Harker, Mr., 362, 367, 379

Harman's Point, 191

Hawaii, 2, 38, 85, 363 ; flora of, 379 ;
coast springs of, 38

Hedley, Mr., 376, 380

Hekla, Mount, 375

Holmes, Mr., 68

Hornblende, magmatic paramorphism
of, 293, 299, 301, 303 ; process de-
scribed, 306

Hornblende andesites, 91, 184, 193,
194, 201, 235, 294; see Acid ande-
sites and hornblende-hypersthene
andesites

Homblende-gabbro, 184,249,250

Hornblende - hypersthene - andesites,
240, 298-302

Home, Mr., 10, 21, 22, 25, 34, 55, 141,
143, 194, 195, 203, 225 ; see the
preface

Hornstone, 350

Hot springs, general description of,
21-42 ; hst of, 40 ; analysis, 28 ;
distribution in Vanua Levu, 36, 138,
233

Humboldt, A. von, on magnetic rocks,
361, 36s

Hussak, on magmatic paramorphism,
308

Hutton, 380

Hyalomelan tuff"s, 47, 80, no, 333, 334

Hydrothermal metamorphism ; see
Solfataric

Hypersthene ; see Pyroxene, rhombic
Hypersthene-andesites, 29.'}, 296
Hypersthene-augite-andesites, 5, 52
147, 161, 164, 168,171, 173-175. 178,
179, 182, 186,190, 199,201,203,208,
211, 230; classification, 240, 247
248 ; characters of the orders and
sub-orders, 285-292 ; relative fre-
quency, 235 ; distribution, 374

Iceland, Vanua Levu compared to,

374, 375
Iddings, Mr., 306
Iron ore ; see Limonite
Iron sand, magnetic, 83, 106, 357
Ironstone gravel, 356
Islands, permanence of, 380, 381

Jackson, Dr. C, T., 28

Jasper, 13, 121, 139, 199, 350, 351, 355

Johnston-Lavis, Dr., 347, 375

Kalakala, Mount, 103, 305
Kalikoso District, 10, 15, 224-228, 350,

356, 358
Kandavu, 293, 306 ; hot springs of,

22
Kavula, 65, 66
Kia Island, 2
Kioa Island, 2
Kiombo Coast, 92
Kleinschmidt, 22, 25, 293, 350
Koro, significance as a prefix ; see

Place-Names
Koro-i-rea Hill, 75, 77
Korolevu Hill, 45 ; natural section near

48
Korolevu River, 62, 64
Koroma, Mount, 3, 51, 285
Koro-mbasanga Mountain, 166-169,

289 ; name wrongly applied in Ad-
miralty charts, 5, 172
Koro-navuta, 135
Koro-ni-valu ; see under Towns
Koro- ni-yalewa Mountain, 117
Koro-tambu Mountain, 167, 171
Koro-tasere, 208
Korotini Bluff, 156
Korotini Range or Tableland, 5, 153-

165, 167, 325
Koro-utari, 163
Koro-wiri, 139
Kumbulau Peninsula, 90-95
Kurukuru District, 228

Lambasa coast, 2i8
Lambasa Plains, 138, 351

388

INDEX

Lambasa River, 15, 138

Landslips, effects of, iii, 178, 327

Langa-langa River, 220, 225

Lango-lango River, 122

Lau Group, 7, 294, 378

Lava-flows, indications of sub-aerial,
52,71, 119, 133, 152, 187, 190, 213,
232

Lea District, 199

Lekumbi Point, 12, 19, 60

Lekutu District, coast of, 11, 50, 273 ;
plains, 128, 351, 353, 356 ; promon-
tory, 16, 18 ; river, 18, 62, 65

Limestones, recrystallisation of, 131 ;
coral, 318; see Foraminiferal lime-
stones

Limonite, deposits of, 56, 132, 138,
226,228,351,352,356,359

Lister, Mr., 378

Liversidge, Prof,, 29

Liwa-liwa, 119

Loma-loma Ridge, 141

Lovo Valley, 169-173

Lovutu, 156

Macdonald, Dr., 21
Magma lakelets, 47, 71, 92, 273, 276,
277 ; description of, 339-342, 346,

347

Magmatic paramorphism ; see Horn-
blende

Magnetic iron sand, 83, 106, 357

Magnetic peaks and rocks, jj, 108,
174, 186, 361-371

Mako-mako Hill, 103

Mali Island, 2, 218

Mali Point, 218

Malolo Island, 294

Mangrove belt, bare tracts in, 11, 14 ;
relation to reef-flat, 13 ; rate of
growth, 15, 19

Mangrove islands, growth of, 16,

17
Mariko, range and peak of, 5, 173,

185-189, 289, 368
Martin, Prof., of Leyden, 376
Masusu District, 84
Mauna Kea, 2
Mauna Loa, 2, 3, 363
Mauritius, magnetic rocks of, 363
Mbale-mbale District, 143, 313 ; river,

150
Mbatini Mountain, 5, 166, 172-174,

367
Mbati-ni-kama, hot springs of, 33
Mbatiri, 134, 324
Mbenutha Cliffs, 109-111, 323
Mbona-lailai Mountain, 101

Mbua District, 3, 36, 37, 47 : bay, 18 ;

coast, 12
Mbua and Ndama Plains, 55-58, 356
Mbua-Lekutu Divide, 55, 297
Mbua shell- bed, 12, 58
Mbuthai-sau Valley, 218, 219
Mbutu-mbutu River, 79, 279
Middle Point, 137
Mountain ridges and their structure ;

see under Ridge-mountains
Mountain-towns, see Towns
Muanaira, 198
Mumu Peak, 108-110
Murray, Sir J., 337, 373

Naikovu Rock, 364

Nailotha Mountain, 6, 214-216, 310

Naindi Bay, 8, 189, 191, 195, 318

Naindi Gap, 189, 192

Naithekoro, 190

Naithombothombo, point, 54 ; range,

229
Naivaka, 2, 3, 11, 18, 43-45> 261
Na-kalou, 133

Na Kama, Savu-savu, 25 ; Lambasa, 32
Nakambuta District, 148-150
Nakarambo, 208
Na Kula, valley, 184 ; range, 230
Nambuna District, 106
Nambuni Spur, 144
Nambuonu, hot springs, 32
Nandi Bay, 78
Nandi Gorge, 69, 78, 278
Nandongo, island, 16, 17 ; town, 216 ;

hot springs, 33
Nandronandranu district, 117-121
Nandroro District, 66
Nandua District, 86, 320, 344
Nanduri District, 11, 14, 135, 136
Nangara-ravi Cave, 141
Nangara-vutu, 205 ,

Nangorongoro Peak ; see Ngaingai
Na Raro Gap, 127
Na Raro Mountain, 2, 5, 123-127, 296,

301, 305
Narawai District, 66
Nareilangi, 124

Narengali District, 140, 147, 149
Narikosa Point, 220
Na Salia, 151
Na Savu, tableland, 79-81 ; falls, 79,

279
Na Seyanga, 108
Na Sinu, 146
Na Suva Range, 64
Na Suva-suva Hill, 192, 369
Natasa Bay, 209
Natewa Bay, north-coast, 9, 208, 209,,

291

INDEX

389

Natewa Peninsula, 6, 9, 197-206

Nativi, 50

Natoarau, hot springs, 23 ; river, 158

Na Tokalau, 91

Natoto Hill, 229

Natua District, 134, 149, 323

Natuvo or Natuvu, hot springs, 33, 209

Naumann on polaric lavas, 364

Navakaravi Hot Springs, 34

Navakavura, 96

Na Vatu Islet, 94

Navetau, 205

Naviavia Islet, 8

Navingiri, 46

Navuni, 202 ; hot springs, 35

Navuningumu, 108-112, 303, 368

Nawavi, range, 135 ; hot springs near,

31
Nawi or Na Wi, island, 26, 192 ; ham-
let, 211
Ndaku-ndaku,bay,2o8 ; hot springs,34
Ndama, river and valley, 62, 67, 68,

71 ; plaiHS, 55-58
Ndavutu, district and river, 87 ; for

hot springs ; see Wainunu
Ndawathumi, 64, 80
Ndevo district, 205 ; hot springs, 35
Ndoendamu Mountain, 209 212
Ndrandramea, district, 2, 3, 83, 296 ;

map, 99 ; description, 98-112
Ndrandramea Mount, 102, 296, 300,

304, 368
Ndranimako, 96, 322, 351
Ndrawa, district, 120, 281 ; river, 118,

120
Ndreke-ni-wai, Natewa Bay, 200, 203 ;

hot springs, 34
Ndreke-ni-wai, Savu-savu Bay, 150,152
Ndreketi, river, 15, 128, 132, 383;

plains, 132, 273, 351
Ndriti Basin, 67-72, 268, 270, 282
Ndrukau Mountain, 213
New Hebrides, i
Ngaingai Mountain, 100, 296, 302, 304,

368
Ngala Mountain, see Freeland.
Ngalau-levu Range, 6, 199, 200, 370
Ngangaturuturu Cliffs, 119
Ngau Island, hot springs of, 22
Ngawa River, 138
Ngelemumu, 180, 219
Ngone Hill, 183
Nukumbolo, district, 151, 161, 162 ; hot

springs, 24
Nukunase or Nuku-ngase, 50, 270
Nuku-mbalavu, 190

Nuku-ndamu, 232

Numbu, 227
Numbu-ni-avula, 176

Oddone on magnetic rocks, 362

Oligoclase-trachytes, 6, 207, 219, 229 ;
description of, 308 ; distribution, 374 ;
altered, 214-216; columnar, 215, 220,
230, 231, 233.

Olivine rocks, classification of, 239

Olivine-basalts ; see Basalts, olivine.

Ono Island, hot springs, 22 ; acid
andesite, 293 ; flints, 350

Onyx, 139, 227, 228, 353

Opal, 162, 163, 183, 351, 353

Ophitic basalts, their relation to pala-
gonite, 347

Ophitic structure, as used in classifica-
tion, 236, 237, 238

Ophitic sub-orders and genera, synop-
sis, of, 241-248 ; description of, 256,
272-276, 283

Orthophyric groundmass, as used in
classification, 236, 237, 239, 240

Orthophyric orders and genera, 248,
290, 296, 297, 299.

Ovalau, 294, 350

Palagonite, chapter on, 337-349; see
also Palagonite-tuffs, Crush-tuffs,
Crushing of basic glass, Pitchstone
&c.

Palagonite of Acicastello, 347

Palagonite tuffs, classification and
characters, 317-336; zeolitic, 334;
marls, 335, 344 ; modes of occur-
rence, 5, 48, 53, 80, 81, 95, 96, 117,
1 18-122, 130, 131, 141, 143, 145, 148,
1 56-161, 169, 177, 193, 198, 202, 213

Palagonite, hydration and degrada-
tion of, 329, 348

Phenocrysts, their use in classifica-
tion, 236

Pickering, Mr., 35

Pieper, Dr. O., 28

Pilsbry, Dr., 380

Pitchstone agglomerates and rubbly
pitchstones, petrological characters,
312, 313 ; evidence of crushing and
its connection with palagonite, 92-
94, 142, 145, 157, 312, 313, 334, 340-
342, 346 {see Palagonite, Crush-
tuffs, Crushing of basic glass) ; mode
of occurrence, 105, 108, 142, 157,
169, 229, 230, 309

* Place-names, meaning of Fijian, 75,
79, 102, 119, 151,172

■* The usual signification of " koro " as a prefix or part of names of hills and mountains
is a "prominence " or " projection." It is a mistake on my part to assume that in such
cases it is as a rule equivalent to a town or village.

39°

INDEX

Platania, Prof., 119, 347

Plutonic rocks, general description,

249-251 ; relative frequency, 235 ;

distribution, 249, 374 ; mode of

occurrence, 180, 182, 184, 185, 193,

211
Polarity of magnetic rocks, 366-370
Porphyrites, 136, 175, 181, 197, 199,

204, 211, 261, 268, 274, 299 ; belong

to many orders, 236
Prismatic pyroxene of groundmass,

its use in classification, 236, 241-

248 ; sub-orders and genera, 265,

270-272, 283, 287, 289, 298, 300, 302
Profiles of Vanua Levu, 3-6, 62, 83,

107, "3. 153, 167, 173
Propylites, 68-72, 106, 147, 162, 181,

191, 199,204, 214, 215,268-270, 282,

297 ; origin of, 69, 72, 191.
Pteropod-ooze deposits, description of,

320 ; mode of occurrence, 84, 86,

109, 139, 201, 205, 344
Pumice-tuffs, acid, 6, 207, 218-223,

229-233 ; general description, 336 ;

special descriptions, 218, 220, 231
Pumice-tuffs, basic, 119, 333; see

H yalomelan-tuffs
Pyroxene of groundmass, as a basis of

classification, 236 ; see Granular

pyroxene, Prismatic pyroxene,

Ophitic structure, and Synopsis
Pyroxene, rhombic, characters of, 285,

306 ; intergrowths with monoclinic,

266, 306
Pyroxene, derivation from hornblende,

306

Quartz, crystals of, 106, 191, 354,
veins of, 106, 116

Quartz-andesites ; see Dacites

Quartz-porphyries, mode of occur-
rence, 215, 219, 220, 226, 227, 229-
233 ; relative frequency, 235 ;
general description, 309-311 ; dis-
tribution. 6, 207, 374

Quartz-rock, I39> 35i> 354

RAlNFAti-, 30, 68, 120

Rambi, island, 2 ; hot springs, 22

Ravi-koro mountain, 1 59

Raviravi, 94

Ravuka, 120; hot spring, 31

Renard, Prof, 293, 306, 338, 344

Rewa District in Vanua Levu, 95, 96

Rewa River, Viti Levu, changes at

mouth, 16
Rhyolites, 209 ; see Quartz-porphyries
RhyoUte-glass, 220,311

Rhyolitic-tuffs ; see Pumice-tuffs, acid

Ridge-mountains, their general ap-
pearance, 2, 6, 146, 153, 185, 210,
374 ; their structure and mode of
origin, 75, 145, 156, 165, 166, 171,
172, 177-180, 182, 188, 202, 210-212
216, 234 ; final conclusion, 375

Rivers ; see under Ndreketi, Lambasa
Sarawanga, Wainikoro, &c.

Rivers, eroding power of, 62

Rocholl, Mr. H., 29

Rosenbusch, Prof., 306, 344

Rukuruku Bay, 53, 269

Salt Lake District, 2, 6, 9, 192-196
Sarawanga Plains, 15, 129-132, 351,

356
Sarawanga River, 15, 62, 129-131
Satulaki, 176, 268
Savarekareka Bay, 190, 326
Savulu, 118

Savu riti Mountain, 210, 212
Savu-savu Hot Springs, 21, 25-30,

189
Savu-savu Peninsula, 189-192, 288
Sawa-ndrondro, 185
Scirpodendroncostatum (Giant Sedge),

79,83
Scoriaceous lava ; see Lava flows
Sealevu District, 146, 155, 156
Sealevu Divide, 136
Seatovo Range, 73-75
Seatura, mountain, 2, 3, 56, 253, 261,

374 ; general description of, 61-72 ;

old town of, 67
Sections across Vanua Levu, 62, 107 ;

see also Profiles
Seemann, Dr., 55
Sella, on magnetic rocks, 362
Semi-opal, 351, 353
Sesaleka Mountain, 3, 12, 53
Sihceous concretions, 81, 83,96, 132,

135,351-355
Siliceous rock, blocks of, 126, 355
Siliceous sinter, 24, 25, 32, 33, 37, 42
Silicification, conditions of, 358
Silicified corals, 10, 13, 81, 132, 135,

138, 139, 207, 221, 226-228 ; theory

of their origin, 228, 357 ; general

account of, 350-360
Silicified fern rhizome, 360
Silicified nullipores, 353, 354
Singa-singa, no
Singatoka River, Viti Levu, 7
Skinner, Mr. S., 367
Skye, Isle of, magnetic rocks, 362
Smallwood, Mr., 196
Smythe, Colonel, 22, 195

INDEX

391

Soapstones, see Foraminiferous de-
posits

Sokena Ridge, 167, 169, 172

Solevu Bay, 75-7^, 253

Solfataric action on rocks, 52, 69, 72,
191

Soloa-levu Mountain, 103-105, 115,
296, 305, 312, 374

Solomon Islands, i, 2, 294, 359

Songo-mbiau, 220

Soni-soni Island, 93, 94

Soro-levu Mountain, 172-174

Spence, Mr. F., 193

Spheroidal weathering in basalts, 57,
129

Stromboli, 214, 315

Submarine basaltic flows and erup-
tions, see Basaltic submarine flows

Submarine plateau or platform of Fiji,
15, 18, 19, 56, 62, 72, 107, 372;
different explanations of, 373

Submarine tuffs, 326-336

Sueni District, 163

Suess, Prof., on thermal springs, 39 ;
on changes in the sea-level, 20, 377

Suva soapstone, 322, 376

Synopsis of classification of volcanic
rocks, 239-249

Tachylyte or basic glass, 312, 337,
341, 343 ; see Basic glass. Pitch-
stone, Hyalomelan, &c.

Tahiti, 3, 72, 84, 363

Talasinga Districts, 55, 57, 64, 128,
132, 133, 224, 352, 383

Tambia, district, 137 ; hot springs, 32

Tambu-lotu District, 104, 105

Tathelevu, 198

Tavia, mountain, 121 ; ranges, 121-
123

Tavua, 65

Tawaki District, 209, 229, 230

Tembe, 213, 214

Tembe-ni-ndio District, 130, 131, 319

Tenison-Woods, Rev., 376

Thambeyu, mountain, 5, 167,289, 315,
326 ; description of, 176-179

Thawaro Peak. 230

Thermal springs ; see Hot springs

Thiele, Mr., 21

Thoka-singa Mountain, 103, 249, 302,

305
Thombo-thombo ; see Naithomboth-

ombo
Thomson, Mr. J. P., 31, 135, 210, 225
Thongea, hot springs, 22 ; basalt, 85
Thoroddsen, on Hekla, 375
Thuku, Mount, 6, 231, 308-310

Thulanga ; see Uthulanga

Thurston Range, 5, 167, 176 ; see

Thambeyu
Tonga Group, i, 378, 379
Tongalevu District, 62, 64, 279
Towns, old sites of mountain, 53, 67,

loi, 102, 108, 156, 170
Trachytes ; see Oligoclase-trachytes
Tuffs, chapter on, 317-336 : foramini-
ferous, 326-333 ; altered, 184, 187^
190, 332; dacitic, 125, 126; see
Pumice tuffs, acid and basic ;
Hyalomelan tuffs ; Palagonite tuffs ;
Crush tuffs ; mode of occurrence,
48, 90, 109, 119, 130, 156, 160, 177,
190, 205, 209, 215
Tunuloa District, 205
Tutu Island, 221

Ulu-i-matua, 75, 76

Ulu-i-mbau, 138, 139

Ulu-i-ndali, 3, 83, 87-90, 253, 370

Ulu-i-sori, 136

Underwood, Lieut., 364

Undu, district and promontory, 6, 10,,
36, 228-234, 311, 360

Upheaval ; see Emergence

Urata, 184, 298

Uthulanga Ridge, 211, 286 (also-
named Thulanga)

Vakalalatha lake, 15, 225

Valanga Range, 1 81-18 5

Valavala Bay, 203

Valeni, 122

Va Lili, 5, 140-146

Valleys, origin of, 2, 146, 151, 219

Vandrani, district, 139, 159 ; hot

springs, 32
Vanua Mbalavu. hot springs, 22
Variolite, 150, 283, 313
Vatui, 54, 369
Vatu Kaisia, 5, 1 1 3-1 16, 296, 301, 305,

374, 375
Vatu-karoa, 209, 282
Vatu-karokaro, 54
Vatu-kawa, river, 151 ; district, 160
Vatu-kerimasi, loi
Vatu-lele Bay, 184
Vatu-levoni, 139
Vatu-loaloa Hot Springs, 31
Vatu Mata, 103
Vatu-ndamu, 91
Vatu-tangiri, 136, 144
Vatu Vanaya, loi
Vatu Vono Point, 88, 89
Vatu-vono District, 121, 122

392

INDEX

Viene District, 198

Visongo District, 221

Viti Levu, 7, 18, 350, 364, 372

Vitina, 223

Volcanic agglomerates, general de-
scription of, 314-316; their thick-
ness, no, 156, 171, 178,315 ; mode
of occurrence, 5, 79, 91, no, 112,
117, 141, 143, H4, 149, 155, 156,
161, 169-172, 176-179, 188, 193, 213,
214 ; lying above submarine de-
posits usually palagonitic and often
foraminiferous, no, 141, 143, 149,
168, 169-171, 176-179, 188, 213,
214 ; see Pitchstone-agglomerates
and Landslips

Volcanic bomb-formation, 46-48

Volcanic mud deposits ; see Foramin-
iferous deposits

Volcanic necks, 54, 58, 90, 93, 95, n2,
183, 192, 230, 234, 253, 277, 283,
286, 375

Volcanic rocks, classification of, 235 ;
distribution of, 374

Vuinandi Bay, 208

Vuinandi Gap, 175

Vuinatanga, district, 145 ; hot springs,

31

Vui-na-savu, river and district, 222,

223, 225
Vula Votu Peak, 176
Vungalei Mountain, 212, 213, 315
Vuni-ika Bay, 218
Vunikondi, 232, 233, 282
Vunimbele, 139 ; hot springs, 33
Vunimbua, district and river, 182, 183
Vunimoli, hot springs and district, 33,

138, 139
Vunisawana, district, 194 ; hot springs,

34
Vunitangaloa, 194
Vunivuvundi District, 87

Waikatakata, Natewa Bay, hot

spring and district, 34, 203, 275
Waikawa Mountains, 201, 319
"Wailea, bay and district, 46, 50

Wailevu River, i?, 138

Wai Mbasanga, Viti Levu, hot springs,

21
Waimotu District, 208

Wai Ndina, Viti Levu, hot springs, 21

Wainikoro, district, 217, 224-228, 356 ;
coast, 219, 308, 310 ; river, 225

Wai-ni-ngio River, 151, 160

Wainunu, hot springs, 22 ; rainfall
68 ; river and valley, 62, 82, 83

Wainunu, plateau or tableland, 3,
82-87, 373 ; see figures on pages 83,
107

Waisali District, 146, 151

Waisali Saddle, 146-148

Waiwai, 143-145

Waterfalls, 79, 141, 163

Wawa Levu Mountain, loi, 302, 304

Weed, Mr., on the origin of siHceous
sinter, 38

Wichmann, Dr. A., on a continental
condition of the Fiji Islands, 376 ;
on hyalomelan tuff, 334 ; on flints
and silicified corals, 350, 352, 360 ;
on Kandavu andesites, 293 ; on the
absence of quartz-andesites in the
South Seas, 294, 309 ; see the pre-
face

Wilkes, Commodore, n, 15, 19, 25,
363, etc.

Wittstock, Mr., 36, 47, 53

Yanawai coast, 95-97, 122
Yanavvai, river and valley, n3-n6,

121
Yanganga Islands, 2
Yanutha Point, 123, 284
Yaroi, 189, 325
Yasawa Group, 294

Zeolites, formation of, in palagonit'

338
Zeolitic palagonite-tuffs, 334
Zirkel, on intergrowths of rhombic

pyroxene, 306 ; on palagonite, 343 ;

on magnetic rocks, 361

THE END

R. CLAY AND SONS, LTD., BREAD ST. HILL E.G., AND BUNGAY, SUFFOLK.

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