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Full text of "Observations of a naturalist in the Pacific between 1896 and 1899"

8ERKEIEY 

LIBRARY 

; "NIVERSITY OF 
CALIFORNIA 



EARTH 

SCIENCES 

LIBRARY 




OBSERVATIONS OF A NATURALIST IN THE 
PACIFIC BETWEEN 1896 AND 1899 




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




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



{Frontispiece. 



OBSERVATIONS OF 
A NATURALIST IN 
THE PACIFIC BETWEEN 

1896 AND 1899 



BY 

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



VOLUME I 

VANUA LEVU, FIJI 
A description of Its leading Physical and Geological characters 



ILontJon 
MACMILLAN AND CO, LIMITED 

NEW YORK : THE MACMILLAN COMPANY 



All rights reserved 



QE 



: 



5 



EARTH 

SCIENCES 

LIBRARY 



RICHARD CLAY AND SONS, LIMITED, 

ZiKEAD STREET WILL, B.C., AND 
JJUNGAY, SUFFOLK. 



H>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), my attention was mainly confined to the 
study of plant-distribution and to the examination of the geological 
structure of Vanua Levu. 

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

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

Destiny led me to Vanua Levu in the following fashion. With 
the relief party to take me down from Mauna Loa there arrived a 
well-known German naturalist who, like myself, had been interested 
in coral-reef investigations. We discussed this warm topic at an 
elevation of nearly 14,000 feet above the sea, with the thermometer 
at 20 F. As we sipped our hot coffee and listened to the 



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 100 to 250 inches, where the forests are 
dense, where tracks are few and swollen rivers are numerous, and 
where the torrent's bed presents often the only road. 

The only extensive geological collections made in Fiji previous 
to my visit were those of Kleinschmidt in 1876-78, which together 
with a small collection previously made by Dr. GrafTe 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. Agasciz 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 
Godeffroy, heft 14, Hamburg, 1879. 

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

WlCHMANN, 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 Pages i 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 60 



CHAPTER V 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued) 

Mount Seatura, 61. Its eastern slopes, 63. Its western slopes, 64. Its northern 
slopes, 65. Ascents to the summit, 66. The Ndriti Basin, 67. A huge 
crateral cavity, 68. Its dykes of propylite, 69. Seatura a basaltic moun- 
tain of the Hawaiian order, 72. The Seatovo Range, 73. Solevu Bay, 75. 
Koro-i-rea, 77. Nandi Bay, 78. Na Savu Tableland, 79. Pages 61 81. 



CHAPTER VI 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued} 

The basaltic plateau of Wainunu, 82. Its margins covered by pteropod and 
foraminiferous ooze-rocks, 86. The hill of Ulu-i-ndali, 87. Kumbulau 
Peninsula, 90. The basaltic flow of Kiombo Point, 92. Soni-soni Island. 
93. Yanawai coast, 95 \ . Pages 82 97 



CHAPTER VII 
DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued) 

The Ndrandramea district, 98. Its mountains and hills of acid andesites, 100. 
Ngaingai, 101. Ndrandramea, 102. Soloa Levu, 103. The underlying 
altered acid andesites, 106. Section of the district, 107. -The magnetic 
peak of Navuningumu, 108. The Mbenutha Cliffs and their pteropod and 
foraminiferous beds, 109 Pages 98 112 



CONTENTS xv 



CHAPTER VIII 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued) 

Mount Vatu Kaisia and district, 113. The Nandronandranu district, 117. 
Nganga-turuturu cliffs, 119. Ndrawa district, 120. Tavia ranges, 121. 
Na Raro, 123. Its Ascent, 125. Na Raro Gap, 127 . Pages 113127 



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 128139 



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 166180 



xvi CONTENTS 



CHAPTER XIII 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued] 

The Valanga Range, 181. Its western flank, 183. Ngone Hill, 183. Valley 
of Na Kula, 184. The Mariko Range, 185. Savu-savu Peninsula, 189. 
Naindi Bay, 192. The Salt Lake, 194 Pages 181 196. 



CHAPTER XIV 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued) 

The Natewa Peninsula, 197. Viene district, 198. Lea district, 199. Waikawa 
Mountains, 201. Ndreke-ni-wai coast, 203. Waikatakata, 203. Mount 
Freeland or the Ngala Range, 204. Traverse from Tunuloa to Ndevo, 
205. Coast from Ndevo to Mbutha Bay, 205 Pages 197 206. 



CHAPTER XV 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued] 

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

Pages 207 223 



CHAPTER XVI 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL FEATURES 

(continued) 

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

Pages 224234 



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 Pages 235 251 

CHAPTER XVIII 

THE VOLCANIC ROCKS OF VANUA LEVU (continued) 

The Olivine Basalts Pages 252 265 

CHAPTER XIX 

THE VOLCANIC ROCKS OF VANUA LEVU (continued) 

The Augite-Andesites Pages 266 284 

CHAPTER XX 

THE VOLCANIC ROCKS OF VANUA LEVU (continued) 

The Hypersthene-Augite-Andesites Pages 285 292 

CHAPTER XXI 

THE VOLCANIC ROCKS OF VANUA LEVU (continued} 
THE ACID ANDESITES, TRACHYTES, QUARTZ-PORPHYRIES. 

The Hornblende-Andesites of Fiji, 293. Occurrence of Dacites in Fiji, 294. 
Suggestion of " felsitic andesite " as a rock-name, 295. The Acid Andesites 
of Vanua Levu, 295. The Hypersthene-Andesites, 296. The Horn- 
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 312316 
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-tuffs 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 /^J 317 336 

CHAPTER XXIV 

PALAGONITE 

Its abundance in a fragmental condition in Vanua Levu, 337. Its occurrence in 
deep-sea deposits, 338. Modes of formation in situ^ 338. In the 
upper portion of a basaltic flow, 339. In the groundmass of hemi-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 337349 

CHAPTER XXV 

SILICIF1ED CORALS, FLINTS, LIMONITE 

Mode of occurrence of the silicified corals, 351. Their character and structure, 
352. Flints, nodules of Chalcedony, Agates, etc., 353. Other siliceous 
concretions, 354. Jasper, 355. Deposits of Limonite, 356. Magnetic 
Iron-sand, 357. Suggested explanation of the silicification of the corals, 
358. Note on a silicified Tree-fern, 360 Pages 35036 

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. 

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

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

(3) Note on the " talasinga " districts. 

INDEX 385 



LIST OF ILLUSTRATIONS 

PLATES 

Na Raro (2,420 feet) from the south-west, a peak of acid andesite^j 

Ndrandramea (i, 800 feet) from the south-east, a peak of acid |- 

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 \io8 

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

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

1,100 feet above the sea in 

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 101 

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 11.3 

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 



VANUA 

FIJI 



y, 



DRAWN OH A SCALE OF 25 MILES TO 3 INCHES BY HB.GUPPY, MB 

3456 7 8 3 10 II li 13 14 15 !6 17 18 l 20 21 22 ; 



21 22 23 2* 2$ HUES 



Based on the Admiralty Surveys, but most of the topographical 
details of the interior have been supplied from the author's obser- 
vations with the aneroid and prismatic compass in 1891-99. It is 
merely intended to illustrate his general account of the physical 
and geological characters of the island and is very far from 
complete, (see introduction.) 





Kumbalau PP / 

/RAMBI 

( 1550 

6-- 



EXPLANATION OF THE CONTOURS. 
| | Sea level to 300 feet 

E;:ixffi:::| 300 to 1000 feet above the sea 
liiii'iiiiiiiiiil 1000 to 1 800 , . . . 
[ | 1800 to 3500 . . . . 

//o< Springs 

. //? /?e co^ of t/?e Wainunu Tableland 



the lower limit is 800 feet. 



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 ofVjiL 
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 
is process of construction has never been completed, and is at pre- 

t suspended ; yet it is in its incomplete condition that Vanua 

vu possesses its importance for the investigation of this subject. 

This island has in fact been formed by the union of a number 
f smaller volcanic islands during a long protracted period of 
emergence. These original islands are indicated approximately by 
the i,8oo-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 




t: si';l:V^ ; 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. 1 

Excluding for the moment the effects of denudation, which have 
been very great, we shall be able to discern some of the stages of 
the building-up of the island during the emergence or upheaval by 
looking at the map and reversing the process in imagination. A 
subsidence of only 50 feet would cause the Natewa Peninsula to be 
isolated by a sea-passage along the line of the Salt Lake ; whilst 
several islands would be formed along the northern and southern 
coasts, and the Naivaka Peninsula would become detached. If the 
subsidence extended to 300 feet, the sea would flow over a large 
portion of the island, where it would regain what was not many 
ages since its own, an area of basaltic plains, which by their 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. 2 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. 

1 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 
particular region of it for weeks, as I have done, without getting 
any satisfactory idea of the true configuration of the surface. In a 
locality densely wooded and occupied by steep mountain ridges 
and deep gorges, the field of view is often very limited ; but seen 
from the deck of a passing ship the main features of the island 
assume their true proportions and relations, and much that was 
uncertain is in this manner made plain. The profile here given 
has been constructed from a number of others, and represents in a 
graphic fashion Vanua Levu as viewed from the southward. I 
have here sacrificed smaller details and occasionally some degree 
of accuracy in small matters in order to bring out the principal 
features of the island. 

At and near the extreme western extremity rise the conspicuous 
hills of Sesaleka (1,370 feet), Naivaka (1,651 feet) and Koroma 
1,384 feet), all of them formed of basic volcanic materials. 1 Naivaka,. 
which is connected with the main island by a narrow isthmus, only 
about 30 feet in height, is probably one of the most recent addi- 
tions to the island's area ; and it is at the same time one of the 
most recent of the numerous volcanic vents that once existed. 
The leading feature, however, of this end of Vanua Levu is the 
great mountain of Seatura (2,812 feet), which occupies a large part 
of the Mbua province and monopolises most of the landscape 
whilst largely determining the form of the western extremity of 
the island. It is a basaltic mountain of the Mauna Loa type, its 

ong eastern slope descending gently at an angle of three or four 

egrees for about ten miles to the mouth of the Wainunu River. 

n its deeply eroded radial valleys and gorges, and in other 
spects, it is not unlike the island of Tahiti, as described by Dana. 
The Ndrandramea region to the eastward, which I have named 
after one of its best known peaks, has a profile of a very different 
character. Its broken outline indicates the existence of numer- 

us mountains and hills of acid andesites, occasionally dacitic. 
Although some of them attain a height of 2,000 feet and over 
their tops alone are seen from seaward. Between the foot of these- 
mountains and the south coast extends a great plateau of columnar 
basalt, incrusted at its borders with submarine deposits, which 
descends coastward with a very gentle slope, the fall in about 
five miles being only about 300 feet (1,100 to 800 feet). It termi- 
nates abruptly opposite the elevated headland of Ulu-i-ndali, a 
1 Strictly speaking Korolevu indicated in the profile would not be visible. 

B 2 



lUJ 



a 
* 



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

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

The level profile of the Korotini tableland gives place, as one 
proceeds eastward, to the broken outline of the several lofty peaks 
of Mariko (2,890 feet), Mbatini (3,437 feet), Thambeyu (3,124 feet) 
and others. 1 Each of these peaks marks one of the bold 
mountain-ridges that form such a striking feature in the surface- 
configuration of this part of the island. On the slopes of these 
ridges, and often also on their summits, appear basic agglomerates 
and palagonitic tuffs and clays often inclosing tests of foraminifera ; 
whilst exposed in the gorges and protruding at times through the tuffs 
and agglomerates on the crests of the ridges are displayed massive 
basic rocks of the type of the hypersthene-augite andesites. 

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

1 Mariko is the native name ot the Drayton Peak of the chart. Mbatini 
is the correct name for the Koro Mbasanga of the chart, the true Koro 
Mbasanga lying three miles to the north. Thambeyu is a native name for the 
Mount 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, l 2,481 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. 

1 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 Ndeva 
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 



io 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. 1 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. 2 

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 3 above the high^water line, and 

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

2 Geology of the United States Exploring Expedition, 1849. 

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



ii EVIDENCE OF RECENT EMERGENCE n 

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. 1 
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 

1 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 affect the relation between 
the mangrove-belt and the reef-flat, a sudden or rapid change of 
level of that amount would destroy the mangroves around the 
whole island. There is some evidence, however, of there having 
been a rapid upheaval of this kind in different parts of the coast : 
and it follows, therefore, if this movement was general, that the 
present mangrove-belts date only from the last upheaval. But this 
elevation may have occurred ages ago ; and the equilibrium 
between mangrove-belt and reef-flat may have been long since 
established. Accordingly, the breadth of the mangrove-belt can 
afford no indication of the period that has since elapsed. From 
data referred to below, it is evident that the mangrove-belt, taking 
its average width, away from the estuaries, at about 500 yards, 
might have been formed in two or three centuries, whilst a thousand 
years or more may have passed since it assumed its present 
relation to the reef-flat. If, therefore, upheaval is in progress, it 
must be of a very gradual character, since the normal relation 
of mangrove-belt to reef-flat now prevails. 

There are indeed signs of such a gradual movement 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 I84O 1 and the Admiralty 
charts 379 and 382 as completed from the survey of these coasts 
by Commander Combe in 1895-96. 

It was not easy to make many good comparisons in the case of 
the advance of the mangrove-belt of the main coast. There 
certainly has been no great advance seaward of the margin of the 
mangroves in this half century. The average amount probably 
lies between the estimate obtained for the coast opposite Mathuata 
Island, where there has either been no change or an advance of 
only 100 yards or so, and that for the advance seaward of the 

1 Atlas of 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. 1 

On the other hand, the mangrove-borders of the several low 
islands and islets, mainly formed of reef-#%rz>, 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 . i Not much ch 
Thakavi, or Day's Island of Wilkes . . J 

It will be noticed that the islands of the Talailau Reef are not 
marked in the chart of 1840 ; they are both low mangrove islands, 
the largest being slightly under a mile long and the smallest a 
little under half a mile. In Nukuira Island, the Vatou of Wilkes, 
there has been a decrease of about two-thirds of a mile during 

1 This, however, is not the case with the recent changes at the mouth 01 the 
Rewa River in Viti Levu, where the bare sandy point of Lauthala has extended 
itsell seaward between 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 

this period. The difference between Thukini in 1840 and in 1895 
is very noticeable. In the time of Wilkes the mangroves only 
occupied about one-third of the reef-patch. Now they occupy 
about two-thirds, the area of the reef-patch remaining much about 
the same. Taking the minus and plus values of all the islands 
here measured, the average rate of the advance of the mangrove- 
margins during this half-century may be placed at about 250 yards 
in the case of these reef-islands, which would amount to a mile in 
400 years. 

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

There is evidence of the shoaling of the ship channel amongst 
these islands to the extent of about a fathom during this period. 1 
TEe"usual depth immediately around the patches, on which the 
islands have been formed, is 8 to 10 fathoms. If, therefore, the 
shoaling is a general process, it is to be inferred that although the 
outward growth of the reef-patches would be usually very slow, 
probably not over fifty yards in a century, there must be times 
when, in shallowing depths, the growth of the reef-patch would be 
comparatively rapid ; and it is at such times that the adjustment 
between the relations of mangrove and reef-patch would be upset 

1 Between Mathuata Island and the coast a change is indicated from 9 10 
fathoms to 8 9 fathoms, north of Motua Island 12 13 to n 12, and between 
Nangano 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, 1 are well founded, all the islands, islets, and reef- 
patches that lie along this north coast will be united to each other 
and to the main island within a thousand years. 

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

However, this movement of upheaval is so gradual that the 
utmost one can expect to do by the comparison of surveys made 
half a century apart is to show the lack of evidence of the 
destructive agency of erosion. As far as the comparison admits 
of judging, there seems to have been no important change on the 
coasts of the western end of the island during this period. The 
low neck of land connecting Naivaka with the main island, if we 
take the low-water line in the Admiralty chart as the limit, had 
much the same breadth at the time of both surveys. The depths 
in Mbua Bay remain about the same, with perhaps a shoaling of 
less than a fathom in places. There are two cays awash in the 

1 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 : 

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

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

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

(4) From the circumstance that the submarine platform passes 
with a uniform slope into the low-lying plains, covered with 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 
last half century the destructive agencies of marine erosion have 
not prevailed. 

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

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

C 2 



20 A NATURALIST IN THE PACIFIC CH. 11 

group. It is not always possible to avoid in such a discussion the 
use of terms such as " upheaval " and " subsidence," although 
there is much to be said for the terms "negative" and "positive" 
employed by Suess. In the present chapter, however, I have 
avoided committing myself definitely to any view relating to the 
stability either of the land or of the sea, reserving the consideration 
of the subject for Chapter XXVII. 



CHAPTER III 

THE HOT SPRINGS OF VANUA LEVU 

THE abundance of hot springs in Vanua Levu, and in fact in 
the group generally, is not commonly known. In the earlier 
accounts of these islands those of Savu-savu are often alone referred 
to, not only for this island but for the whole archipelago. The 
United States Exploring Expedition under Wilkes spent six months 
in 1 840 in making a survey of the whole group. Yet Dana, who was 
attached to the expedition, remarks that " the only trace of actual 
volcanic heat which the islands appear to contain is found at Savu- 
savu Bay." 1 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. 2 It will be shown below that most of the thermal 
springs discovered by me might easily have been overlooked. 

Before dealing with those of Vanua Levu I will mention the 
other localities in the group in which thermal springs are from 
various sources known to me. They probably form but a small 
proportion of those that actually exist ; but the list can be readily 
extended by those acquainted with special parts of the archipelago. 
In Viti Levu they occur amongst other places at Wai Mbasanga, 
on the Singatoka river (Home) and at Na Seivau on the Wai 
Ndina, where Macdonald in 1856 found temperatures of 106 and 
140 Fahr. in two different springs. 3 Mr. Thiele in more recent 
years referred by hearsay to some hot springs on the Wai Ndina. 4 

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

1 A Year in Fiji, by John Home, London, 1881, p. 163. 

3 Journal, Royal Geographical Society, 1857, vol. 27. 

4 Scottish Geographical Magazine, August, 1891. 



22 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. 1 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 1860) observed the temperature to be 144 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. 3 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 

1 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. 

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



Ill 



THE HOT SPRINGS 23 



a mile above Ndavutu. If the above statement of the natives is 
correct, as I believe it is, then these thermal springs issue along a 
line quite four geographical miles in length extending inland from 
the mouth of the Wainunu. 

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

Thongea, when not covered by the stream July, 1898, I27F, 

Ndavutu, 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 J une 2 ' II2 

/July 27, in 

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

to the left bank and just above the mouth I j , 

of the Ndavutu creek, self-registering Six j 
thermometer used ^ 

2. THE HOT SPRINGS OF NATOARAU AND ITS VICINITY. This 
thermal system lies in the lower valley of the Mbale-mbale branch 
of the river Ndreke-ni-wai. The principal springs are situated at 
Natoarau, a village about half a mile in a direct line from Mbale- 
mbale, about three miles from the coast, and only about fifty feet 
above the sea. They bubble up in pools near brooks, and extend 
at intervals over an area probably several hundred yards across. 
Five springs came under my notice ; but there are doubtless several 
others in the low-lying and often swampy land of this district. No 
deposits were noticed, but the mode of occurrence and low temper- 
ature of the springs serve to explain this fact. The following 
temperature observations were made by me in March, 1 899 : 

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

Another thermal spring, which is distant about a mile from 
Natoarau, is known as Waitunutunu, that is, Warm Water. It lies 
about a third of a mile from the village of Nambuniseseri, between 
Mbale-mbale and Waisali, and is quite four miles inland' and 
about 100 feet above the sea. The springs bubble up into a pool, 
about 12 feet across, which is close to a brook and had a 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 1 30 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. 



in 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. 1 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, 1898, 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 Commodore 
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. 1 There 
are evidently also extensive submarine springs close to the beach ; 
and probably Wilkes was not far from the truth when he remarked 
that the " whole area of half-a-mile square seems to be covered with 
hot springs." 

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

1 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. 



in 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 2ioF. 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 Cumming also refers to it in her book At Home in Fiji. 
When this lady visited the springs in August, 1876, they were 
intermittent in their action, the highest making a fountain two to 
three feet high. According to the description of Kleinschmidt they 
were in the same intermittent condition in May of the same year. 
There were then four springs situated in a bowl-shaped hollow. 
The two larger springs were not constantly bubbling up, but 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 situat^J 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 1840 by the Wilkes Exploring Expedition^ 

Specific Gravity 1*0097. Temperature 57 F. 

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

Chlorine 3'577 

Sodium r665 or Soda 2-238. 

Magnesia 0-440 

Lime 0*366 

Silica and iron with a trace of phosphate 

of lime o"2oo 

Carbonic acid o'493 

6741 
Organic matter and loss 0-459 

7*200 

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

obtained by Mr. Kleinschmidt in May, 1 8/6. 2 

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 g^atest part of Natrium and Calcium 
chlorides. A quantitative oetermination, which on account of the 
small quantity of the water was confined to " eine Chlor und Kalk- 
bestimmung," gave this result : 

Chlor (Chlorine) 479 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." 

1 Narrative of the United States Exploring Expedition, III., 199, by 
Commodore Wilkes. See also Dana's Geology of the same expedition. 

2 Journal des Museum Godejfroy, 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 I878. 1 

Total solids at 212 F ........... '8796 per cent. 

ignited ........... 7726 

The residue consisted of 

Free Sulphuric Acid (SO 3 ) ........ '0049 

Calcium sulphate ............ '0260 

Calcium chloride ............ '4355 

Magnesium chloride ........... '0021 

Potassium chloride ........... '0415 

Water .......... . ...... -1070 

Sodium chloride ............. '2641 

88 1 1 

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

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



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



COMPOSITION. 





Per cent, in 
residue. 


Parts per 
million of water. 


Grains per 
gallon. 


Silica, insoluble 


I '68 1 


iv 


Q/2O 


Silica, soluble . . . 


*O74 


5 '8 


*4O 


Alumina and traces of Iron sesquioxide . 
Aluminium chloride 


'534 
1*646 


&l 


2*92 
9*OO 


Phosphoric acid 


traces 


traces 


traces 


Calcium chloride . 


46 '7 54 


3,6**,2*Q 


2*;T7O 


Calcium sulphate 


4'77O 


372*7 


26*09 


Magnesium chloride . ... 


*I 1:4 


I2'O 


84 


Sodium chloride 


42 ' 1 7 1 


3,294*8 


230*64 


Potassium chloride ... 


i"7**i6 


137*2 


9*60 


Carbonic acid 


traces 


traces 


traces 


Loss 


460 


^4*0 


2*t;2 












lOO'OOO 


7,813-0 


546-9I 



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

1 Islands of ike Pacific, by H. Stonehewer Cooper, 1888 edition. 

2 Journal Royal Society, New South Wales, 1880, vol. 14. Miss Gordon 
dimming in At Home in Fiji gives the same analysis but differently stated. 



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. 1 





Date 
col- 
lected. 


Chlo- 
rine. 


Sodium. 


Calcium. 


Calcium 
chloride. 


Natrium 
chloride. 


Total 
salts. 


Density. 


Dr. Jackson .... 
Dr. Pieper . 


1840 
1876 


3*57 

4 '70 


1-66 


0-36 
2"3I 


4.-CC 


VOQ 


7-20 

8-48 


1-009 


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


1878 
1879 


(4-50) 


(1-29) 


(l- 4 2) 


4'35 
3-65 


J "Sf 

2-64 
3-29 


8-81 
7-81 


1-006 


Sea-water, tropics . . 




19-46 


11-08 


0*46 








35 'oo 


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 2 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. 

1 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, Geology. 



in 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 LiH 
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 1 34. 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. 1 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. 

1 Proceedings, Queensland Branch, Geographical Society, Australia, vol. i. 
1886. 



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 ij 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 R, in March, 
1899. Near by is a large deep pool, some 20 feet or more across, 
with a temperature of 100. 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, 



m 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 
are close to the water, and from I to 10 feet above it. The 
temperature of one small pool, where the water bubbled up briskly, 
was 204 F. in February, 1899. In another it was 194. The 
water was probably at the boiling-point in some cases as it entered 
the pools, and in the others it could have been only a few degrees 
below it. The rocks of the district are agglomerates and tuffs. L 
have no recollection of deposits of any extent around the springs. 

13. THE HOT SPRINGS OF VUNIMOLI ON THE LAMBASA 
RIVER. A few minutes' walk from Vunimoli, and about 100 yards, 
from 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 
with the river. The natives have cut out of the soft rock small 
square basins which receive the waters. The temperature of the 
hottest spring in August, 1899, was 155 F. That of others 
was 140. The conditions are not favourable for the formation of 
deposits. These springs lie about 8 miles inland and are rather 
over 100 feet above the sea. They are, however, small and un- 
important, 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 
7j miles from the coast, and rather over 100 feet above the sea. 
They issue copiously from the volcanic agglomerate at a tempera- 
ture of 161 F. (August, 1899), and are only removed a few paces 
from the river, and a foot or so above it. Algae flourish in the 
water, and siliceous sinter incrusts the rocks. 

15. THE HOT SPRING OF NANDONGO ON THE HEAD- WATERS 
OF THE WAI-NI-KORO RIVER. A few hundred yards from the 
village and elevated about 180 feet above the sea there is a small 
pool in the clay of the river bank, 2 or 3 feet above and close to 
the water, which in September, 1899, had a temperature of 97 F. 

1 6. THE HOT SPRINGS OF NATUVO ON THE NORTH COAST 
OF NATEWA BAY. About a mile east of Mbiagunu and near the 
village 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 
coral-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. 

1 8. 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 i 3 5 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 



in 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 
RAMBI. 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 
spring 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 

olivine-basalts prevail. I was indebted to Mr. Pickering for show- 
ing me its locality. It lies about three-quarters of a mile inland 
and about 100 feet above the sea. It issues from the volcanic 
agglomerate 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- 
perature 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 
localities 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 
of these springs is fairly general over two-thirds or three-fourths of 
the island. Taking this area at about 1,500 square miles and 
dividing it into squares with sides of eight miles, we should, if the 
springs were quite evenly dispersed, find a thermal system in every 
square. Even amongst the Fijians and among the white residents 
the number of hot springs will cause surprise. Only those of 
Savu-savu, Wainunu, Nukumbolo, Mbatini-kama, and Na Kama 
on the Wailevu river have been up to this time generally known. 
The reason of this is that most of them are insignificant, and with a 
temperature far below the boiling-point, and ooze up in unlikely 
and out-of-the way places, as by the water-side in little visited 
river-valleys, on the reef-flats of not much frequented coasts, and in 
swampy situations where they are likely to be overlooked. The 
natives only recognise as " Na Kama " the boiling or very hot 
springs ; and it was only after much questioning that I could get 
them to tell me of some unimportant " wai katakata " (hot water) 
which they deemed to be far beneath my notice. The natives were 
keenly interested in my botanical and geological investigations ; 
but they considered it to be beneath the dignity of a man who had 
seen the wonders of Na Savu-savu to spend some time looking for 

D 2 






36 A NATURALIST IN THE PACIFIC CHAP. 

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

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

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

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



in THE HOT SPRINGS 37 

tide-marks, usually rising through the reef-flat. At times even they 
are to be observed below the low tide level ; and one can scarcely 
doubt that there are a large number of undiscovered springs that 
are 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 
insignificant character of many of them and noting their occurrence 
in places where they might easily be overlooked, it is highly prob- 
able, as before remarked, that a number of springs exist inland, 
which, though once known to the natives, are now forgotten. The 
interior of the island is very sparsely inhabited now ; but there is 
evidence of a much more populous condition in old times. The 
present natives are fast losing the knowledge of the interior of the 
island which their forefathers possessed ; and many tracts in the 
mountain districts are far removed from existing paths. From the 
haphazard manner in which I lighted upon thermal springs beside 
the 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 
temperature, I cannot find any marked arrangement either in their 
grouping 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 
highest temperature are confined generally, with the exception of 
those of Savu-savu, to the main mass of the island, it would seem 
that adjacent systems of springs may differ much in temperature. 
The springs of Vunimoli, for instance, have a maximum tem- 
perature of 155, which is nearly 50 lower than that of Na Kama, 
three miles to the westward. Hot springs are more numerous in 
the region around Lambasa than in most other districts. Lastly, 
I may add that earthquakes are apparently more frequent in the 
Mbua district, where no thermal springs are known, than in any 
other 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 
formation, as for instance when they rise through the reef-flat or in 
swampy localities. In those springs, however, where the tem- 
perature is over 150 F., and where the water spreads over a surface 
so as 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 algse, 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, 1 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. 



in 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 

In Oahu, another island of the Hawaiian group, where the volcanic 
forces have been long extinct, artesian wells have been in extensive 
use for some years in the irrigation of the sugar-cane plantations. 
The last water-bearing strata are reached at depths of 400 to 
500 feet. 1 The subterranean or artesian reservoirs are evidently 
therefore 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 
in the vicinity of Acireale. The Etna slopes are in great part 
deforested, and in consequence soakage is relatively small, and 
after heavy rains much of the water runs off in the torrents. Whilst 
in 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 
than at present. 

For these reasons and on other grounds, amongst them notably 
the absence of recent crateral cavities, I infer that the numerous 
hot springs are the outflows of subterranean streams, fed originally 
by the " soakage " arising from a rainfall of at least 200 to 300 
inches in the mountainous portions of the island. Such subter- 
ranean streams run probably at considerable depths, emerging, it is 
likely, 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. 
Thermal springs, he holds, are supplied by hypogene waters and do 
not receive their salts from the sea. Such springs, according to 
this view, being the survivals of volcanic activity, originate in the 
depths of the earth's crust and bring water to the surface for the 
first time, not deriving it from infiltration. It seems almost im- 
pertinent to suggest a view opposed to that of such a high authority ; 
but it appears to me that the frequent situation of the Vanua Levu 
thermal springs along the lines of surface-drainage requires an 
explanation that does not altogether exclude the agency of 
infiltration. 

1 At Ewa there are pumping plants capable of supplying 75 million gallons 
a day, 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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42 A NATURALIST IN THE PACIFIC CH. m 

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

(1) 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 R, 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 100 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 ('18 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. 1 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. 



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- 



KorolevuHill (800m from WaiksiBav, 




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 (*i 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, 
the two rocks cannot be separated along the junction. In a thin 
section, in which the union of the vitreous shell of the bomb with 
the ash is well shown, there is no defined line of demarcation, the 
non-vacuolar isotropic glass of the bomb being there broken up 
into fragments, with the interspaces filled with the partially 
palagonitised pumiceous ash. In the vitreous shell the felspar 
microliths 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 rilled 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 100 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 1 5 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 lies a bed of a similar basic tuff, 
having however a banded appearance from the arrangement of 
materials 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 
thickness, and composed mainly of the debris of acid andesitic 
rocks of the hornblende-andesite type, such as occur in the 
Ndrandramea district. They mark a period of active eruption on 
the part of some neighbouring acid andesitic vent in this neighbour- 
hood, which the subsequent explorer may be able to identify with 
some volcanic " neck." 

These tuffs are composed partly of fragments of a hemi- 
crystalline hornblende-andesite and partly of crystals, broken and 
entire, of plagioclase, hornblende, rhombic pyroxene, and augite. 
The plagioclase is tabular, zoned, and glassy, and gives extinctions 
of oligoclase-andesine (6 to 12). The hornblende is bottle green, 
markedly pleochroic, and gives extinctions up to 14. The rhombic 
pyroxene has the characters described on page 301, in the case of 
the Ndrandramea rocks. The augite is less frequent, but the two 
pyroxenes are sometimes associated as intergrowths. 

These acid tuffs do not effervesce with an acid, nor can any 
tests of foraminifera be observed in them ; but since these organisms 
are represented in the basic tuffs below, it is highly probable that 
the whole series of these horizontal beds is submarine. The first 
or lowest bed of the acid tuffs indicates a somewhat violent 
volcanic outbreak in this neighbourhood, following the deposition 
of the basic tuffs. It is composed of loosely compacted subangular 
fragments, i to 3 millimetres in size, in which the macroscopic 
prisms of the rhombic pyroxene are especially frequent. It passes 
upward without interruption into a regularly grained sandstone 
formed of rounded and subangular fragments measuring -3 to 
7 mm. across. Above this lies a quite distinct bed, a few inches 
thick, of a fine compact clay rock, where the mineral fragments 
measure only -05 to '12 mm. in diameter, hornblende being well 
represented, although the rhombic pyroxene is very scanty. Up 
to this time these beds of acid tuffs indicate a gradual defervescence 

E 



5o 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 



Ill 

r 

qu 



iv MOUNT KOROMA 51 

referable to genus 12 of the augite-andesites, described on page 275.) 
A few paces west of this spur a vertical dyke, 20 feet wide and 
trending N.W. and S.E., appears on the beach. It is formed of a 
bluish scoriaceous basaltic andesite containing much glass in the 
groundmass 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 
and formed of a vesicular rather than a scoriaceous basaltic andesite 
referred to genus I of the augite-andesites (page 267). It differs from 
the rock of the previous dyke in the presence of small plagioclase 
phenocrysts 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 
one time a volcanic vent in the district west of Nukunase. The 
lines representing the trend of the two dykes above noticed would 
if extended meet at a common focus a little way inland. The 
rocks of the dykes differ conspicuously from the prevailing doleritic 
rocks that form, as before remarked, the ancient flows, the average 
length of the felspar-lathes in the former being '1-2 mm., in the latter 
'3-'4 mm. Both, however, belong probably to the same vent of which 
now the exact situation would not be easy to discover, on account 
of the re-shaping of the surface through the denuding agencies. 

MOUNT KOROMA. The highest peak of the hills lying inland 
between Wailea Bay and Lekutu is named Koroma and attains a 
height of 1,384 feet. I did not ascend its slopes higher than 900 
feet, and approached it from the Mbua or south side. Extensive 
plains, covered with the usual " talasinga " vegetation, reach inland 
from the shores of Mbua Bay to the foot of this range without 
attaining a greater elevation than 100 feet. This low district is 
drained by the Mbua river and its tributaries, the rock usually 
exposed at its surface being a decomposing porphyritic basaltic 
andesite. It is again referred to on page 56 in connection with the 
low-lying level region of this portion of the island of which it in 
fact forms a part. 

A basic non-calcareous fine-grained tuff-sandstone is exposed 
in a stream at the foot of the south slope of Mount Koroma. 

Uhilst crossing some low wooded outlying hills in this locality, 
came suddenly upon what seemed like a desert in miniature, 
ite bare of vegetation and occupying an area of some acres. 
Here a porphyritic basic rock, from some cause unknown to me, 
has 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. 

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 12 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, light 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, Cypraea, 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 '$-!'$ 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*91) 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, "07 * 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, 1 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. 
1 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 
away to the westward a similar thickness of soil produced by the 
same 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 2'9O 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 *n mm. in length, whilst in 
the olivine-basalts they average *i8 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 
Ostraea, 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, 1 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 
1 Species not identified. 



60 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 3<DO-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 
easy 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 



A NATURALIST IN THE PACIFIC 




CHAP. 



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- 
butaries 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 by heavy 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. 

(a) 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 
which is described on page 259. Micro-phenocrysts of plagioclase 
and a few of augite occur, the olivine being mostly replaced by 
pseudomorphs. The felspar-lathes of the groundmass average 
i 8 mm. in length, and there is a little brown opaque interstitial 
glass. Boulders and fragments of a closely similar basalt, with a 
specific gravity of 2-9, lie about on the surface in this region. The 
Seatura slopes here abut on the plateau of Na Savu, formed largely 
of 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*91). 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 
olivine-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. 

(fr) 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 65 

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 olivine-basalts and porphyritic basaltic andesites, such as 
occur around the other parts of Seatura ; but grey olivine-basalts 
also occur, possessing opaque plagioclase-phenocrysts and looking 
like porphyrites. They are essentially holocrystalline and are pro- 
bably more deeply situated than the other basaltic rocks. They 
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 
from 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. 
They have a specific gravity of 2*84 and are assigned to the 
porphyritic sub-genus of genus 25 (page 259). At the summit, 800 
feet above the sea, occur blocks of a grey holocrystalline basalt 
with 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 
Lekutu River, just below Kavula, where the elevation is about 300 
feet above the sea, one observes exposed in mass in the river-bed 
a dark semi-ophitic doleritic basalt similar to the doleritic rocks 
without olivine prevailing on the coast between Wailea Bay and 
Lekutu (see page 50), but differing in the absence of felspar- 
phenocrysts. It displays a considerable amount of opaque inter- 
stitial glass and is assigned to genus 12 of the augite-andesites 
(page 275). The specific gravity is 278, but there are a few 
minute irregular cavities in its substance. 

On leaving Kavula one crosses another of the Seatura spurs at a 
level of 650 feet, descending then into a smaller river-valley occupied 
by a tributary of the Lekutu, on the banks of which lies the village 
of Nawai, 350 feet above the sea. Then another spur is crossed at 
an elevation of 450 feet and the descent is made into the valley of 
the Wailevu tributary of the Lekutu. Crossing the valley, which 
at the town of Wailevu is elevated 300 feet, one rises to a height 

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 \ 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 



v 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 
or propylites, to be subsequently described, and reaching an 
elevation of about 400 feet above the sea, I came to the long 
slope that leads up to the summit. A dense forest hid every- 
thing from view, so that the compass and aneroid had alone 
to be relied on. 

At first one traversed a series of step-like alternations of level 
ground and steep " rises," until the old site of the village of Seatura, 
about 1,200 feet above the sea, was reached. There are some 
strange legends connected with this old mountain-village, which is 
now only indicated by little piles of stones and the debris of a wall, 
and was evidently abandoned long ago. We finally reached the 
summit by following up a spur or ridge in a northerly direction 
from Seatura. There was a precipitous descent on either side of the 
ridge with evidently a broad, deep valley to the eastward. The 
summit was rounded ; but on account of the forest no view could 
be obtained. There was never any extensive exposure of rock 
noticed during the ascent ; but all the way up occasional small 
blocks of a blackish olivine-basalt were observed on the surface, of 
the same general type as that found all around the mountain and 
referred to genus 37 in the synopsis. 

(/) The Ndriti Basin or Gap. This great hollow in the side of 
Seatura, which I have named after the town in its midst, is appar- 
ently a crateral cavity now drained by the Ndama river, and its 
tributaries, and covered with dense forest to such a degree that a 
general view of the whole is impracticable. The glimpses, however, 
that one obtains of the mountain scenery are very grand, the town 

F 2 



68 A NATURALIST IN THE PACIFIC CHAP. 

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 ; 1 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 

1 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 'i8 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, 1 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 67), 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 

1 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. 



yo 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.E., 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. 1 

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 groundmass 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 

1 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- 
crysts. The groundmass displays more or less parallel felspar-lathes, "I mm. 
long, augite grains, and much magnetite, The residual glass is fair in quantity ; 
but is mostly gathered into " lakelets " of brown altered glass with sometimes 
calcite in the centre. 

The vitreous border of the dyke is composed of a dark glass quite opaque 
in 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 v/as 
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 by solfataric 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 tuffs 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. 1 

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 the Vicinity 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 
1 Characteristics of Volcanoes, 1890. 



74 A NATURALIST IN THE PACIFIC CHAP. 

being about 2*9. They approach in characters the grey porphyritic 
divine-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 -i5-'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 -08 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 Seatovo 
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 
olivine, &c., all of which have their distinctive characters. 

This picturesque bay is surrounded by hills. On the west side 
it is inclosed by the promontory forming the southern extension 
of 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 
most conspicuous. Beyond it stretches the eastern point of the 
bay, which the Fijians call " Ua-nguru," that is, " the noise of the 
waves." On the shores lie the village of Nawaindo, " the running- 
stream," and the once populous town of Solevu, which has given 
its name to the bay. Solevu, as its name indicates, is the place 
of the "great assembly." In the background rises the three- 
peaked 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 100 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 1,100 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*90. These basaltic rocks 
contain scanty olivine and only a little interstitial glass. The 
felspars of the groundmass vary in different localities from *n 
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 hsematised 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 



v SOLEVU BAY 77 

second rock to be noticed is a slightly altered compact basalt 
without olivine forming apparently a dyke near the coast about 
half way between the village of Solevu and Ua-nguru Point. It 
has a specific gravity of 2-84, the felspar lathes (-15 mm.) presenting 
a marked flow-arrangement, whilst there is a fair amount of altered 
residual 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 
to 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 
scoriaceous. It has, however, a specific gravity of 2*91 or 2*92, 
and is in fact a pretty grey oli vine-basalt studded with small 
olivine crystals about a millimetre in size and showing no other 
phenocrysts. This type of olivine-basalt occurs also at Ulu-i- 
ndali on the east side of Wainunu Bay, but is rare in the island. 
It differs amongst other features from the porphyritic olivine- 
basalts of the northern part of Seatura and of the Seatovo range 
in the absence of plagioclase phenocrysts. There is apparently no 
interstitial glass, whilst the average length of the more or less 
parallel felspar-lathes is '13 mm. 1 On the lower slopes of the hill 
the common blackish porphyritic basalt or basaltic andesite is 
exposed. In the grey-basaltic upper portion of this hill we have 
probably an old volcanic " neck." 

Following the line of hills inland from Koro-i-rea, we cross the 
intervening saddle 450 feet above the sea, and ascend the slopes of 
Koro-tolutolu, a ridge-shaped mountain backing Solevu Bay, and 
having, as its name indicates, three peaks, of which the highest is 
1,280 feet above the sea. My observations indicate that this moun- 
tain is formed in mass of the common blackish-basalts described 
under genus 37, their specific gravity being 2'88 to 2*94. But Koro- 
tolutolu has also the peculiarity that it appears to be in mass 
magnetic. The rocks obtained from its summit, half-way up its 
western slopes, and near its foot on the same side, all display 
polarity, a character also of the rocks of the neighbouring hills of 
Ulu-i-matua and Koro-i-rea, but in their cases seemingly confined 
to the higher levels. 2 

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

1 Referred to genus 16 of the oli vine-basalts. 

2 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 J 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 1 5 
or 20 above the horizon. The basalt is a compact bluish-black 
rock with specific gravity 2'95~2'99. 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 
1 6 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 
of basic agglomerates and basic tuffs and lies in the hollow between 
the 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 l 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 
gorge 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 
of the plateau, and with a volume 30 to 40 feet across, it plunges 
down into the ravine 150 feet below. As shown in the view from 
the 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 
thence 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- 
dron costatum). The Makita tree (Parinarium laurinum) also 
flourishes in the wet districts ; and in the drier localities occur the 
Ndakua (Dammara vitiensis) and the Ndamanu (Calophyllum- 
burmanni) together with a palm of the genus Veitchia. Here on 
this level watershed between the basins of the Wainunu and 
Sarawanga rivers, the sluggish streams flow aimlessly along in but 
slightly eroded channels ; and it is not always possible to determine 
the side of the island to which they ultimately direct their course. 
In their beds are pebbles and irregularly formed concretions of an 
impure reddish flint which I have described on page 354. On the 
north and south sides the table-land is much excavated by the 
tributaries of the Sarawanga and Wainunu rivers. On the west 
where it meets the foot of the Seatura slope portions of columns of 
basaltic rocks appear on the surface, and deep gorges are worn by 
the large streams descending from the mountain. On the east 
towards Nuku-ni-tambua and Tambu-lotu, the surface is also much 
cut up. The preservation of this table-land in a region, where the 
denuding agencies are very active in their operations all around it, 
is to be attributed to its being a level watershed, where the head- 

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



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 81 

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 #, 
of the augite-andesites. The rock from the gorge below is of 
the same character, but on account of its opaque plagioclase 
phenocrysts it is referred to genus 14, and is described on p. 279. 

In one place on the plateau a tuff-agglomerate is penetrated 
by 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 
may be inferred that the source of its basic tuffs and agglomerates 
is to be found in the same locality ; and probably the original 
vent is now represented by the hollow extending eastward from 
the 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 
direct testimony of its submarine origin offered itself to me. The 
palagonitic characters of the tuffs afford, however, indirect evidence 
in this connection ; and indeed the occurrence of submarine tuffs 
and limestones in the vicinity of Tembenindio on its lower northern 
slopes (see page 131), and the existence at elevations of several 
hundred feet above the sea of fossiliferous tuffs and clays in the 
Wainunu and Ndrandramea districts to the eastward, afford strong 
presumptive evidence that the tuffs and agglomerates of the table- 
land were deposited under the sea, and I may add in a period 
subsequent to that of the formation of the great basaltic flows of 
Seatura and Wainunu. 



CHAPTER VI 

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 
1,100 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 off the mouth of the Wainunu River. 

TabMand Ndran'dramea Mountains 




Seat ura Slope 'Wdinunu, WamiLnu VLu-i-ndali 

Estuary. Tableland. 

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- 
tion of 1,100 or 1,200 feet in the interior to 700 or 800 feet near 
the coast has already been referred to. Beyond this lower limit 
it descends much more rapidly and within less than a mile it 
terminates at Masusu in a steep-sided declivity 300 feet high 
opposite Ulu-i-ndali, and in a gentler slope on the eastern side in 
the Ndranimako district. Its somewhat undulating surface is well 
wooded ; but on account of the small gradient the small streams 
on the table-land do not excavate deep channels, but flow slowly 
along in shallow courses and often stagnate in swampy land where 
the interesting "Scirpodendron costatum," the giant-sedge, flourishes. 
In their beds occur reddish flinty concretions, up to 3 inches across 
in size, and magnetic iron sand in great abundance. A sample of 
this sand roughly washed on the spot contains 77 per cent, of 
magnetic iron. 1 

Basaltic rocks, often exhibiting a columnar structure, are ex- 
posed at intervals on the surface and slopes of this table-land all 
over 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 1 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 
1 Geology of the United States Exploring Expedition. 



VI 



WAINUNU TABLE-LAND 85 



inclined at a large angle from the perpendicular. 1 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'go. 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 
basalt rich in olivine (spec. grav. 2*95), the felspars of the base 
averaging 'i mm. in length. It may be remarked here that one 
cannot draw a sharp distinction between the basalts of this region 
and those of the adjacent eastern slope of Seatura. Their specific 
gravity is about the same (2-87 to 2*90) ; but the coarse texture of 
the Masusu basalts did not come under my notice in the last 
locality, where the felspars of the groundmass average *i8 mm. in 
length or about two- thirds the length of those of the Masusu 
rocks. 

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

1 A similar arrangement was observed in the columnar basalt of Kauai 
in the Hawaiian Islands. It is presumed that these Hawaiian flows are sub- 
aerial. 



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 50x3 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 
above the sea, one finds displayed in situ in the river-bed an 
amygdaloidal basic lava with coarse tuffs and agglomerates a little 
lower down. 

THE HILL OF ULU-I-NDALI. The meaning of the name of 
this 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 (Sterculia 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 1,100 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 halfway 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 hsematised 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 77 ; but they differ in their doleritic or coarser texture, the 
felspar-lathes in the last-named locality being much smaller, their 
average length being *I2 mm. 

The blackish basalts, mostly characteristic of the lower slopes 
of Ulu-i-ndali, vary somewhat in character ; but they may on the 
whole be regarded as surface forms of the more deeply situated 
grey basalts which are practically holocrystalline. The rock of 
this 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 
basalts, but differs from them in the circumstance that the 
microporphyritic olivine is serpentinised and not haematised, and 
in the occurrence of a fair amount of devitrified interstitial glass, to 
which probably the dark colour of the rock is due. . . . The dark 
aphanitic basalt, with flinty fracture and a specific gravity of 3*00, 
that is displayed* in Vatu Vono Point, is merely a compact surface 
variety of the more coarse-textured grey basalts, being referred to 
the same genus. Here there is a great abundance of micro- 
porphyritic olivine in a groundmass of parallel felspar-lathes and 
augite grains ; but the felspars are unusually small, averaging 
'I mm. in length ; and there is a much larger amount of fine 



9 o 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*91. 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. 2 5 6, 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 91 

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 basaliic 
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 and 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 200 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 ('17 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 x 

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



vi KIOMBO 93 

carrying porphyritic plagloclase. 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 tufTs 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 
huge masses, 14 or 15 feet high, of a dark grey slightly scoriaceous 
augite-andesite with a cryptocrystalline groundmass, which ap- 
parently form the uppermost portion of a volcanic " neck " or pipe. 
According to the size of these rock-masses the " neck " would have 
a circumference of 80 or 90 feet. These masses are in part incrusted 
with agglomerate. 

The adjacent island of Soni-soni, which is almost joined by the 
mangrove-belt to the adjoining coast, probably represents one of 
the numerous small vents that were once active in this region. Its 
single 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 
epidote. 

Proceeding northward from the village of Rewa, one crosses 
another spur descending from the inland range. It is formed in 
mass of a dark doleritic olivine-basalt (spec. grav. 2*91) charac- 
terised by the length of the felspar-lathes ('28 mm), possessing a 
little interstitial glass, and referred to genus 25 of the olivine class. 
It probably represents an ancient flow. Its surface is incrusted, as 
high as the road ascends, nearly 200 feet above the sea, by fine and 
coarse palagonite-tuffs ; whilst the pebbles of foraminiferous mud- 
rock in the stream indicate the existence of incrusting marine 
deposits further up the slopes. The road then leads down into a 
low-lying undulating district that forms the sea border as far as the 
mouth of the Yanawai, and reaches about two miles inland without 
exceeding an elevation of 100 feet, although low hills occur here 
and there. This region is fronted by mangrove swamps and is 
traversed by the Matasawalevu and Ndranimako streams. It is a 
district of basic tuffs and foraminiferous clays, which, as shown 
below, extend up the slopes of the basaltic Wainunu table-land that 
lies 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. 1 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 



97 



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 into 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 
00 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 (1,600 feet). Navuningumu (1,930 feet) is simi- 
larly isolated on the north. On the east rises Ngaingai (2,430 feet), 




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

012 

Scale of miles I 



the highest of the peaks, with Wawa Levu (2,000 feet), Vatu Keri- 
masi (1,900 feet), Vatu Vanaya (1,600 feet), and Mbona Lailai 
(2,100 feet) closely clustered by its side. On the west there is 

H 2 



ioo A NATURALIST IN THE PACIFIC CHAP. 

another group of hills, of which Ndrandramea (i,Soo feet) is the 
highest and best known. Associated with it are Kala-Kala (1,600 
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 accompanying 
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 



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 
1,000 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. 1 True dacites, 




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*61, 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 

1 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. 



!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, 



io 4 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 x 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 

1 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 situ, I came 
upon a single large mass of an aphanitic augite-andesite of 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 5 

NDRANDRAMEA DISTRICT. By refer- f 

ring to the map of this locality it will '| 
be observed that this region of andesites 

extends northward to the Navuningumu >* 

<u 

Range, and that on the south it would 

be separated from the district of tuffs ~ 

and agglomerates, named the table-land o 

of Na Savu, by a line joining the hills 

of Soloa Levu and Thokasinga. On the | 

east it is bounded by the basaltic area T 

J tJD 

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 ,2 

hills, and sometimes, as in the direction *g 

of Sarawanga, more than half way to the J 

coast. I have endeavoured to show the . 

relation of these acid rocks to the basalts 

and to the sedimentary deposits in the 

geological section. zf 

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- w 

grey hypersthene-andesite with a specific . 

gravity of 2*54, and displaying in a J? 

cryptocrystalline groundmass, where the o 

felsitic texture can be recognised, abund- 1* 

ant phenocrysts of plagioclase and rhom- ^ 

bic pyroxene. As high as 500 feet above 2 
the sea it is occasionally capped by 
patches of palagonitised clays and tuffs 
scantily foraminiferous, and at one place 



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 
400 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 l 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, 

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




MT. TAVIA (2,210 feet) irom VATU KAISIA. 

probably formed of an acid andesite. 




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

[Face p. i 



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, m "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 
contain 15 or 16 per cent of lime. They inclose pteropod shells in 
places and show many minute foraminiferous tests of the pelagic 
type. Their composition is given on page 323 ; but it may be 
here remarked that the residue is made up mainly of palagonitic 
debris, fine clayey material and minerals. The mineral fragments 
form about 20 per cent of the mass, and consist principally of 
glassy plagioclase, with some rhombic pyroxene, and magnetite, 
their size averaging 'I mm. The tuff-sandstones interstratified with 
the 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 108. 
(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 in 



vitreous groundmass. 1 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 
history of this volcanic mountain. The first was submarine and 
was characterised by the discharge of acid lavas which consolidated 
around the vent and were afterwards covered over with deposits of 
foraminiferous clays. The second was in the last part supra- 
marine. With the renewal of activity, the overlying acid andesites 
were broken through and basic materials were discharged from the 
new vent. The bed of acid agglomerates exposed in the Mbenu-tha 
cliff belongs to that period of the second stage when the explosive 
agencies were most violent It represents the extensive destruction 
of the overlying rocks. The foraminiferous tuff-sandstones are 
submarine accumulations of the finely comminuted fragments of 
basic pumice that constituted the dust and fine ash discharged 
from a supra-marine vent. The scoriaceous and amygdaloidal 
blocks of the basic agglomerates overlying these tuffs around the 
base of the mountain have had a similar origin. The original ash- 
cone that at one time rose above the surface of the sea has long 

1 It belongs to the 3rd order of the hornblende-hypersthene-andesites 
described on p. 299. 



ii2 A NATURALIST IN THE PACIFIC CH. vn 

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 1,100 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, 1,880 feet in height, starts up suddenly in the 
mountainous interior of the island. Being situated in the valley 
of the Yanawai river, which opens to the south, it forms a con- 
spicuous landmark for vessels off the south coast ; but from most 
other points of view, on account of its peculiar situation, it is 
usually difficult and often impossible to obtain even a glimpse of 
it. 1 From its remarkable blunt-topped conical shape it has 

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

Nan dronan.dran.ii 
Ndrandramea Range } Vatu Xaisia 




Yanawai Valley 

received the not very appropriate name of Marling Spike in the 
Admiralty charts. The natives name it Vatu Kaisia, the first 
word signifying " rock," whilst the second is the name of a demon. 
Some idea may be formed of its situation and of the character 
of the neighbouring country from the profile-sketch and photograph 
here produced. I was unable for reasons given below to take a 
photograph of the mountain itself, as it was either too near or too 
far away. Vatu Kaisia is approached either from Ndrawa on the 
north or from Ndawara on the south, the ascent being best made 

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

I 



ii 4 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 1,100 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 



viii VATU KAISIA 115 

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- 
pied by a tributary of the Yanawai River. It has a depth of 400 
feet below the ridge ; and as illustrated in the section below it has 



Vatu Kaisia 

1380. 




Basaltic'Plateaii of 
W 



11 Basaltic 'Rocks . Heights in Feet above, sea 
EE3 Dacitic Rocks. Length of section 3 miles. 



evidently been largely formed by the eroding agency of the stream. 
However, at the bottom of the gorge there is exposed a heavy 
aphanitic basalt showing no olivine and having a specific gravity 
of 2*85. Though of much finer texture, the felspar microliths only 
measuring '05 mm. in length, it differs conspicuously from the 
overlying porphyritic basalt in possessing little or no interstitial 

I 2 



n6 A NATURALIST IN THE PACIFIC CHAP. 

glass. It is referred to genus 1 6, 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 01 
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 1 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. 2 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 150 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. 

1 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. 



vin NANDRONANDRANU nj 



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 
tongue-like extension of similar elevation projects to the north- 
west between the Ndrawa and Navuningumu branches of the 
Ndreketi. This elevated region is continuous to the eastward with 
the 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, 
and the palagonite-tuffs which are in places extensively represented 
are evidently in great part derived from vitreous forms of the same 
rocks. We seem to get nearer to supra-marine eruptions in this 
region than in most others. The palagonitic-tuffs and agglo- 
merates appear to have rapidly accumulated in shallow water, and 
there is reason for regarding one exposure of the aphanitic augite- 
andesites as at all events a shallow-water lava-flow. The aphanitic 
character of the massive rocks, however it may have arisen, is here, 
as I take it, associated with the shallow-water habit of the tuffs 
and agglomerates. 

(i) EAST SIDE OF THE NANDRONANDRANU DISTRICT. By 
following the track leading from the ridge on the west side of Vatu 
Kaisia northward to Ndrawa one rises gradually to a more elevated 
region. The rocks exposed on the surface for the first mile are for 
the most part altered hypersthene-augite-andesites possessing a 
micro-felsitic groundmass. When a height of about 1,400 feet was 
attained, the track could not have been far from the peak of 






u8 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-tuffs 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 
ij 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" 1 6 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 



vin 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 1,200 
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. 1 

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 

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



vni 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 
ij miles north-east (N33E) 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. 

(1) RANGE ON THE EAST SIDE OF THE YANAWAI 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, 
where it is 500 to 600 feet in height, to the north of Ndawara, and 
found 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 
appearance of a dacitic peak, was not ascended ; but the range was 
crossed in two places in going from Ndrawa to Vatu-vono and 
from Valeni to Nareilangi, its usual height varying between 1,200 
and 1,500 feet, the extreme height being about 1,700 feet. 

In making the traverse from Ndrawa to Vatu-vono, one first 
passes through a part of the hornblende-andesite region of Na 
Raro, 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- 
tuffs 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. 1 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- 

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



vin 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 J 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 



I2 4 



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. 

NaRaro (2420) 

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 

2j miles distant from Na Raro, and though situated in the 
heart of the island it is only about 100 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. 1 
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 
i, coo 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- 
hypersthene-andesite. At an elevation of 1,450 feet, a shoulder of 
the mountain is reached, near the top of which is the cave above 
mentioned. Crossing the shoulder one descends for 100 or 150 
feet into a gap, thus reaching the foot of the precipitous northern 
peak, which rises up like a wall for a height of from 900 to 1000 
feet overhead. It is in mass of the andesite just mentioned, many 
of its faces presenting inaccessible cliffs displaying seemingly no 
structure. This peak is somewhat lower than the southern peak. 
I placed its height at 2,270 feet, which, taking the total elevation 
of the mountain at 2,420 feet, as given in the chart, makes the 
difference 150 feet. A deep and broad cleft, that goes half-way 
1 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-tufTs 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 



vin 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 NDREKETI. 

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 divine-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 
groundmass average '2 mm. in length, and there is a little 
interstitial glass. They cannot often be distinguished in their 
characters from the olivine-basalt displayed in vertical columns, 4 
to 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 
the great Seatura vent. In the lowlands it is much decomposed, 
and a spheroidal structure is frequently developed during the 
disintegrating process, just as has been noticed in the case of the 
Mbua and Ndama plains on the west side of Seatura. The 
rounded blocks that commonly occur on the surface may be 
regarded in each instance as the nucleus of a weathering spheroidal 
mass. When this rock is exposed unaltered in the streams it is 
usually 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 
between Lekutu and Sarawanga and about 2 miles inland, where it 
formed vertical columns I \ feet across. It differs principally in the 
presence of a few small amygdules and in the greater amount of 
interstitial glass. The columnar basalt that Dana in the " Geology 
of the United States Exploring Expedition " describes as occurring 
at the mouth of the same river probably belongs to the same flow. 
He remarks that a few hundred yards back from the " Watering- 
place " there is an exposure of columnar basalt, the columns being 
vertical, i to 2\ feet in diameter, and usually six-sided. 

K 



1 30 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 hyd ration 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 of 
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. 1 Large shells , of Ostrsea 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., 
and 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 nearly 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, 
and exhibit no organic remains in the slide. The upper fine tuffs 
have 3 or 4 per cent, of lime, and inclose numerous minute tests of 
foraminifera of the globigerina type, their cavities being generally 
filled with palagonitic material. 

Further up the valley about a mile above Tembe-ni-ndio, and 
about 250 feet above the sea, the impure foraminiferal limestones 
again 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 
indicated mosaic the commencement of recrystallization. In the 
case of those of the upper locality the calcitic material of the 
groundmass has more completely recrystallized, and shows a fairly 
clear mosaic ; whilst in one place the rock was overlain or rather 
incrusted above by a layer, 3 inches thick, of a white crystalline 
limestone, looking like statuary marble, and inclosing portions of 
a material like that of the rock beneath it. This last, when ex- 
amined in the slide, exhibits itself as formed in mass of crystalline 
calcite, displaying a regular mosaic, and inclosing small fragments 

1 These foraminiferal limestones are described on p. 319. 

K 2 



i 3 2 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*80. 
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 2'9O, 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 
O2 '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, 1 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 z 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 3 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 

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

2 Geology of the United States Exploring Expedition. 

3 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 f eet - 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. 1 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. 



sx 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 bared 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 HC1. 

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, '07 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, *I2 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 AS A 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. 1 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. 

1 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 
up to at least 600 feet above the sea occur agglomerate-tuffs and finer submarine 
tuffs, as above described, overlying foraminiferous clays, a submergence of 
quite 500 feet being indicated by the investing deposits. 



CHAPTER X 

DESCRIPTION OF THE GEOLOGICAL AND GENERAL PHYSICAL 
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. 1 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-lih (2930) 




NambuiiiSpur. 

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-tuffs, 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, 

1 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 
ill that the origin of the Mbenutha cliffs where agglomerates lie 
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-turTs. 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 
in part exposed at the crest of the range. 

(3) THE EASTERN PEAK OF THE VA-LILI RANGE. This 
hill, about 1,100 feet in height, overlooks the Mbale-mbale branch 
of 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 y 
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 100 feet, the bulk of the spur being composed of a 
compacted brecciated palagonite-tuff 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 
lime and display microscopic tests of foraminifera, the palagonite 
being minutely vacuolar, the cavities also being filled with the 
altered glass. I noticed those submarine deposits at an elevation 
of 100 feet, but probably they reach much higher. 

The inference to be drawn from the data above given concerning 
the Va-lili range seems clearly to be this. We have here indicated 
the emergence of a submarine mountain-ridge covered over with 
palagonite-tuffs and agglomerates, the last being uppermost. These 
coverings have been in places stripped off by the denuding agencies 
and the underlying massive basic rocks exposed. These rocks, 
however, vary much in texture, some being vitreous, as in the case 
of the pitchstones, others hemi-crystalline as in the case of the 
basaltic andesites ; and it is to be gathered from this and other 
similar indications that different submarine vents were formed 
along a fissure or fissures at the sea-bottom. No evidence of sub- 
aerial eruptions came under my notice. After the vents became 
extinct they were buried beneath the palagonite-tuffs and agglo- 
merates. During and after the emergence the denuding agencies 
reshaped the surface of the range and left but little of its original 
form. 

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 i 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 sinee-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 2-64 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 
to, and the relatively fresh rocks of the same type. The former 
are 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 
the covering of tuffs and agglomerates. 

Descending the opposite or north-west side of the saddle-range, 
one finds the same basic andesites, both fresh and altered, down to 
about 1,100 feet above the sea. Then the track leads one down a 
precipitous slope into the picturesque gorge traversed by the head- 
waters of the Narengali River. At its lower end the gorge opens 
out into the broad Narengali valley, and here the dense forest of 
the higher districts gives place to the scanty vegetation of the 
" talasinga " region. 

The rocks exposed in the sides of the gorge are basic agglome- 
rates overlying palagonitic tuffs of mixed composition and evidently 
sedimentary. On the bottom lie huge masses, some of them 70 or 
80 tons in weight, of altered grey aphanitic or non-porphyritic 
augite-andesites, penetrated in some cases by thin veins of white 
quartz, and at times displaying a rudely columnar structure, the 
columns 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, 15 
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 3OO-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 i, OCX) 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-lili, 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 400 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 




150 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 TT n7 f an i ncn m 
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 10 miles is one of the 
remarkable features of Vanua Levu. 1 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 
broad and level, in others it is much cut up into ridges, and in 
others again it presents a single narrow crest. Nor can we realise 
on looking at the profile the extent to which its slopes have been 
carved out by river-erosion, and we get no indication of the several 
lofty spurs that descend north and south far into the plains, as in 
the case of the spur west of Sueni and in that terminating in the 
Koro-tini Bluff. In the profile the eye ignores the details with 
which the investigator during many toilsome ascents has filled the 
pages of his note-books. To this extent it is useful in that it 
enables him to rise a little above the level of his facts, and permits 
him (to employ a figure-of-speech) to regard the style and general 
character of the edifice without being exclusively absorbed in the 
study of the bricks. 

This range, which extends from a mile or two west of Sealevu 
to a couple of miles east of Sueni, is connected on the west with 
the Va-lili Range by the Waisali Saddle before described, and on 
1 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 applied 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 
four 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 15 3, 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 so- 
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 to 
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 i,2CD 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- 
Jowish-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. 1 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, 2 their size ranging 
from 2 feet to an inch. I noticed one large block of this rock, 
measuring 2 x i| 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. 

1 They are described under sample E on p. 332. 

2 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 
mouth of the Vandrani valley there are exposed in the river-bed 
coarse 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 
which, when seen from the north-east, rises up as a partially inde- 
pendent peak, with a broad base and a conical truncated summit, 
immediately west of the track followed in the descent from the 
summit of the range to Vandrani. It is probably not much under 
2,000 feet in height, and exhibits bare precipitous cliff-faces on the 
north side. It would be worthy of the attention of the future 
investigator. 

Recurring to the principal features of the range between Mbale- 
mbale and Vandrani, one may remark the extensive occurrence of 
basic agglomerates and tuffs on both slopes, the prevalence of 
olivine-basalts, the frequency of the semi-vitreous and vitreous or 
rather pitchstone condition of these rocks, and their semi-ophitic 
character, especially on the summit and north slopes. From the 
vesicular structure of the rocks of the Koro-tini Bluff and from the 
character of its tuffs and agglomerates, it is to be inferred that 
they are the direct products of eruptions, probably in shallow seas. 



160 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 KOROTINI RANGE FROM VATU-KAWA 
TO VANDRANI. On leaving Vatu-kawa 1 , 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. 2 

1 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. 151, 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 161 

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 prevailing 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 predominant rocks down to the foot of the range. A specimen 
of the tuffs taken at 1, 300 feet is calcareous in patches and probably 
contains tests of foraminifera ; but it is too much weathered to 
enable one to speak with certainty on this point. The interesting 
feature of this slope is the exposure at 1,600 to 1,700 feet of large 
blocks of a dark grey hypersthene-augite andesite referred to the 
orthophyric order of those rocks described on page 290. Lower 
down (1,000 1,300 feet) occasional solitary blocks of the same rock, 
but 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 
Vanua Levu. 

Summing up the general results of this traverse we observe that 
here, as in other parts of the 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 
on the southern slopes is noteworthy. The only deeper seated 
massive rocks observed were the pyroxene-andesites above alluded to. 
(4) TRAVERSE OF THE KORO-TINI RANGE FROM NUKUMBOLO 
TO SUENI. The hot springs at Nukumbolo, which are described 
on page 24, rise up through agglomerate-tuffs. Around the 
bathing pools lie large masses of altered palagonite-tuffs which give 
the first indication of the region of altered rocks that extends from 
Nukumbolo to the lower slopes of the range, a distance of about 
three miles. 

For about a mile and a half or two miles from this place the 
track lies through a broken country and does not rise to a height 
more than 300 feet above the sea. A variety of altered rocks are 
here 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, 1 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 much changed. 2 
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 ij or 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. 1 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 :he 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 
other localities, doubtless indicate the occurrence of large intrusive 
dykes. Sueni is situated about 300 feet above the sea, the descent 
to Koro-utari at the mouth of the valley, a distance of 3 to 4 miles 
in a direct line, being about 1 50 feet. 

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

" 



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. 1 

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. 2 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. 3 

GENERAL INFERENCE RESPECTING THE KORO-TINI RANGE. 
If we can imagine a line of vents, protruding in some cases 

1 Both these rocks belong to the hypersthene-augite andesites, showing 
phenocrysts of both monoclinic 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 
*o8 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 f eet m height, and the pinnacled Koro-mbasanga, 1 
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 

1 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. 



Thambeyu (M* Thurston) 3J24 ft 
cSv2\> 




W 

Kiinandt Cap 



Koro -Mbftsanga 



Koro -Ts.mbu, 
Z753ff 




W 



Koro -Uni Range. 2200 -sooof!" 



r: 



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. 



Xoro -Mbasanga. 2637 ft 




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, 1 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, 700 to 800 feet above the sea, a 



Referred to genus 13 of the augite-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 (-08 
to *i8 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 divine-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 J to 2 centimetres in size, the palagonite 
being often vacuolar but much affected by hydration. 

These tuffs and agglomerates of the Sokena cliffs apparently 
contain no organic remains. They appear to have accumulated 
under water as the result of the eruptions of a neighbouring vent 
without the intermediate agency of marine erosion. 

(3) THE ASCENT OF THE Lovo VALLEY. About two miles 
to 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 2 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 



171 



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. 1 

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 f eet m tne 
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*67271) 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. 1 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 



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 
highest peak of the Koro-mbasanga Range, by a saddle probably 

1 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 

Soro-levti. Mbatini. 3437* 



Mount Mbatini from the top of Koro-mbasanga. The distant peak on the right is one of 
the summits of the Mariko ridge. 




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). 

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 x>7 
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-tin ; 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, -J- 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 *n 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 



1 76 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. 1 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 

1 Vula Votu is the name of a peak lying to the east. Ngoinangai is a forked 
mountain still further east. 



xii 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, 1 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 



2600ft. 




R9 Pyroxene -andesites 

^ Foraminiferous Tuffs and Clays 

E23 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 

toarse tuffs containing bands about a centimetre thick of a fine 
lay-tuff, the last-named effervesce freely with an acid, whilst 
1 A kind of " edible " bird's-nest is found in this cave. 
" 



i y8 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-tuff 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. xn 

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 1,880 feet at its N.W. and of 1,710 feet at its S.E. 
end. The average elevation, however, is probably not over 1,300 
or 1,400 feet. My acquaintance with the range is only partial, 
but it is sufficient to bring to light some of its leading structural 
features. Those who follow me will find in these mountains a 
very interesting region for their geological explorations. 

(i) TRAVERSE OF THE VALANGA RANGE. In making the 
journey from Valanga to Vunimbua, I crossed the range where 
its elevation was about 1,300 feet. Basic agglomerates, containing 
sometimes amygdaloidal blocks, are displayed in the low district 
between 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 
at once exposed. Large masses, 5 or 6 feet across, of altered grey 
pyroxene andesites lie in the bed of the stream. Some of them 
show opaque porphyritic felspar and have the appearance of 
porphyrites (sp. gr. 2*67). They belong to the type described 
on page 271 under genus 6 of the augite-andesites. Others are 
grey propylitic varieties of a basic semi-doleritic andesite pene- 
trated by cracks containing calcite, and displaying in a ground- 
mass, exhibiting much viridite and a little pyrites, calcitic pseudo- 
morphs of the felspar phenocrysts and more or less parallel felspar- 
lathes, '15 mm. long and somewhat altered. Another of the 
deeper-seated rocks commonly exposed on the upper west 
slopes of the range is a dark grey rock showing much porphyritic 



i8 2 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 1,200 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 tuffs 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. 1 But 
the rocks most frequently represented were propylitic grey hypers- 
thene-andesites, in which the pyroxene is mostly changed into 
1 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 rilled 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 1 8 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-tuff 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 
1,000 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 
41 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 



xni 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 tttms 
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 ij 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-RlDGE 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 1,800 or 1,900 feet descend with a very 
easy gradient for I J 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 M-ariko 
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 basic 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-tufF 
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-cliffs 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 



1 88 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 
1 8 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 principally 
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. 1 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^ 
1 It is described under Sample C on p. 325. 



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 10 15 to the south-west and the same amount to the 
north-west, have apparently a quaquaversal 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. 1 One of these rocks is a bright green, hard and 
compact 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 *oi to "04 mm., it may be 
regarded as a relatively deep-water sediment. 2 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 *o6 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. 

1 It is granular, but fuses in the blowpipe flame into a clear glass and 
gelatinises in HC1. 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, 
might 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 



1 92 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 olivme-basalt (sp. gr. 3*01), 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- 
ments, ranging up to 3 or 4 millimetres in size, of vacuolar pala- 
gonite, the minute vesicles being filled with some alteration pro- 
duct. It also contains large macled augite crystals 5 or 6 mm. in 
size, which can be picked out in numbers by the fingers. The 
blocks vary from a few inches to two feet across, and are usually 
composed of an augite-andesite, containing large porphyritic 
crystals of augite, and are often amygdaloidal, the amygdules, 3 or 
4 mm. in size, being formed of a zeolite. But blocks of very 
different rocks also occur in this agglomerate tuff. One, about 
two feet across, was composed of a coarsely crystalline diorite 
made up, as described on page 251, of large crystals of hornblende, 
2 to 2*5 centimetres long, and of large opaque crystals of acid 
labradorite. Another was made of hornblende-hypersthene ande- 
site belonging to the ortho-phyric order of that sub- class (see 
page 299). There is a little altered glass in the groundmass, and 
large secretions of brown hornblende, more than an inch in size, 
are 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 2\ 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 1 of the visit made by Colonel Smythe to 
the lake in 1860 ; 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 
about 100 feet high. It was across this neck that the natives in 
old times used to drag their large canoes. 

Mr. Home 2 who visited this neighbourhood in 1878, suggested 
that the Salt Lake occupies a crater-cavity. The hills around are 
of volcanic formation, and I am rather inclined to support this 
view ; but certainty is scarcely possible now, on account of the 
great degradation which the surface has evidently experienced 
during and since the emergence ; whilst subsequent reef-growth 
has also to some extent masked the original form of the district. 
It is noteworthy that a somewhat parallel condition of things is 
presented a few miles to the west by the circular Naindi Bay and 
the low passage, not more than 50 feet above the sea, that partly 
isolate the Savu-savu Peninsula. 

The peculiar behaviour of the tides in connection with the 
Salt Lake and its passage attracted my attention during two visits 
to this locality. On the first occasion I noticed that between two 
and three hours after the tide at the coast had commenced to rise 
there was still a strong flow through the passage from the lake, 
and that the current was only reversed in the latter half of the 

1 Ten Months in Fiji, London, 1864. 

2 A Year in Fiji, pp. 154, 169 ; London, 1881. 

O 2 



196 A NATURALIST IN THE PACIFIC CH. xin 

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 
of recent volcanic action came under my notice. Submarine 
deposits occur at intervals on the surface up to elevations of 
1,000 feet and over ; but with the exception of the comparatively 
recent upheaval or emergence of some 20 or 30 feet, indicated by 
the raised reef-masses and foraminiferous tuffs and clays in dif- 
ferent parts of the coast, there is nothing to suggest that these 
:hanges did not occur ages since. In the frequent alteration of 
its andesitic rocks, and in the occasional occurrence of porphyrites, 
we have sufficient indication of the antiquity of this part of the 

>land as far as its volcanic history is concerned. 

I will commence the description of this peninsula at its 

astern 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 13 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 1,680 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 those 
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, which 
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 light-coloured 
altered hornblende andesite. The brown hornblende is mos.tly 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 13 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 groundmass 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 (*o6 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 205 

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 1 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 r 
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 

1 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*81 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 "17 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 10 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. 1 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, 

1 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 
Buli'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, rhombic 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 



206 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 mountainous 
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. 



208 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. 

(b) The coast between Nakarambo and 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. 1 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 

1 These rocks are in most cases referred to the orthophyric ancTfelsitic 
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 NAT AS A 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'Si) 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 2 
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. 

P 



210 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 x 
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 

1 Proceedings, Queensland Branch, Geographical Society of Australia, 
vol. i. ; 1886. 



xv NAWI TO UTHULANGA 211 

its crest for another 150 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 
pyroxene phenocrysts include some of rhombic pyroxene ; and the 
rock is therefore referred to genus 4 of the hypersthene-augite 
andesites. The actual peak of Uthulanga, as it rises abruptly 
about 150 feet from the end of the ridge, is of agglomerate, the 
blocks being composed of a compact grey andesite. 

The peculiar succession of rocks displayed in this mountain- 
ridge along its length of four miles is worthy of notice. Neither 
vesicular 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. 

(b) 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, whkh 
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. 1 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 
1 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. 1 

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 
1 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 ta. 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- 



216 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 1 80 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 1,600 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 



218 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 seconcl 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." 1 
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 cliffs as coarse aggregates of fragments of pumice and 
decomposing trachyte, which pass on the one side into fine 
1 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." 1 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 
1 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. 1 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. 2 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. 3 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 when 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 

1 Described on p. 310. 

2 These rocks are described on p. 308. 

3 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 of foraminifera 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 process 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 300 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 
indicated ; 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 223 

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 3<DO-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 south 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 15 to 1 8 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 
growing upon them acting " in the manner of sails." Mr. Home, 
who 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 1 visited it in 1880, and describes it as containing a single 
floating island, a quarter to a half an acre in extent. The 

1 See paper quoted on p. 31. It is noteworthy that Mr. Home refers only 
to 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. 1 

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 tuffs, 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 
1 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 loo-feet level lying about one mile and 
the 2OO-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 
1 80 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 Astrsean 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 



228 A NATURALIST IN THE PACIFIC CHAP. 

country between these two places is usually elevated between 
60 and 100 feet and is never more 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 ij 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 rape. 
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 



2 3 o A NATURALIST IN THE PACIFIC CHAP. 

chart. From it rise two conspicuous peaks, Thawaro Peak (1,573 
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. 

(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*48). 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. 

(b) South coast between Tawaki and the foot of Mount Thuku. 
The tall cliffs that rise to a height of from 200 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 800 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 l 
(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 2 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. 

(c) 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 

1 Described on p. 309. 2 Described on p. 310. 



xvi MOUNT THUKU 231 

inland they are also to be observed. The 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 1,2 88 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 
2*77. It is compact and has a hemi-crystalline groundmass. 1 

() 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. 2 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 



1 Referred to genus 13 of the augite-andesites. The felspar-lathes average 
'i mm. in length, and there is a little 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 2*77 ; 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 rhyolites . 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 : " Flag, aug, matr, flu, gran, non-phen, parv, '1-2 
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-aug + 
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 a 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 
SLrd5*?r safely employed, since it is apparent, for in- 

A, long and parallel, stance, that there are often all gradations in 
dispersed through the a s nfe between a lathe and a phenocryst, 

B, short and non- and that the term "phenocryst" is applied 

parallel and found t crysta i s having very different histories. 
only in the centre. J 

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. 

(#) 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 



2 39 



SYNOPSIS 
I. CLASS. OLIVINE ROCKS (Flag., oliv.}. 



SUB-CLASS. 



DIVISION. 



ORDER. 1 



No groundmass 
(non-matr.} 

LlMBURGITES, 

PERIDOTITES, 

OLIVINE GABBROS, 

etc. 



Groundmass (matr.} 
OLIVINE-BASALTS. 



Olivine abundant 
(cop.) 



Olivine relatively 
scanty (pauc.}. 



(Not represented in collection.) 



Felspar lathes not in flow-arrange- 
ment (non-flu.}. 

2. 

Felspar lathes in flow-arrange- 
ment (flu.}. 

3- 

Felspar lathes not in flow-arrange- 
ment (non-flu. }. 



Felspar lathes in flow-arrange- 
ment (flu. }. 



1 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. 



II. CLASS. AUGITE ROCKS (Flag., aug.\ 



SUB-CLASS. 



ORDER. 



No groundmass (non-matr. } 
GABBROS, in part. 



Groundmass (matr.} 

BASALTIC ANDESITES ; 

AUGITE-ANDESITES ; 

PYROXENE-ANDESITES 

in part. 



Not represented in collection. 



Felspar lathes not in flow-arrangement (non-flu. }. 



Felspar lathes in flow-arrangement (flu. }. 



Felspars short and broad (orthophyric, orth.}.- 



k Groundmass felsitic 



1 Not represented in the collection. 



2 4 



A NATURALIST IN THE PACIFIC 



CHAP. 



III. CLASS. HYPERSTHENE-AUGITE ROCKS (Plag., 
hypersth.-aug^. 



SUB-CLASS. 



ORDER. 



No groundmass (non-mafr.) Represented by the Hypersthene-gabbros in 

GABBROS, in part. collection. 



Felspar lathes not in flow-arrangement (non-flu. ). 



2. 

Groundmass (matr.) 
PYROXENE-ANDESITES, in part. 



Felspar lathes in flow-arrangement (flu.}. 



Felspars of the groundmass short and broad 
(orthophyric, ortk.}. 



Groundmass granular or presenting a mosaic 
I (felsitic, fels. ). 



'IV. CLASS. HYPERSTHENE ROCKS. 
V. CLASS. HORNBLENDE-HYPERSTHENE ROCKS. 

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. 



VIII. CLASS. OLIGOCLASE-TRACHYTES. 
IX. CLASS. QUARTZ-PORPHYRIES AND 
RHYOLITES 



Described in 
Chapter XXL 



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. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 


Presence or 
absence of plagio- 


Character 
of the 


Length 
of felspar 


Number of 
specimens. 


groundmass. 


clase phenocrysts. 


phenocrysts. 


lathes. 








j 


( 'O2 *i mm. 


x 






Glassy plagioclase 


1 -1-2 


2 






phenocrysts 


1 '2--3 






Plagioclase 


(vitr.) 


I '3--S 






phenocrysts 
(phen.) 


2. 

Opaque plagioclase 


{02 'i mm. 


I 






phenocrysts 


2--3 ;; 


2 






I (opac.) 


3 '5 




I. 










Granular 




3- 






(gran.) 




Large phenocrysts 
of olivine and 


C 'O2 'I mm. 

1 -I--2 








pyroxene, over 


1 '2--3 






2. 


2 mm. (magn.) 


1 -3--S 


I 




No plagioclase 


J A 








phenocrysts 
V (non-phen.) 


\ *** 

Small phenocrysts 
of olivine and 


C 'Q2 I mm. 








pyroxene under 


1 'i "2 








2 mm. Pyroxene 
scanty and often 


1 -3 -5 ',! 


I 






absent (parv. ) 










(5. Vitr. . 


V 






13. Phen. . . . 








2. 

Prismatic 




6. Opac 




/ Not repre- 


(prism. ) 


4. Non-phen. . 


{7 Magn 
8. Parv 


4 


\ sented. 


3- 


15. Phen. . . . 


| 9- Vitr 
( 10. Opac 


} 


f Not repre- 
V sented. 


Ophitic 
(o-bh ) 




{I I . Magn. . . 




/ Not repre- 


\upn. ) 


6. Non-phen. . 






\ sented. 






12. Parv 


i '2 mm. 


i 



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. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length 
of felspar 
lathes. 


Number of 
specimens. 






f I3 ' 


{02 'I mm. 


3 






Glassy plagioclase 


i -2 


2 






phenocrysts 


2 '3 


I 





Plagioclase 


(vitr. ) 


3 '5 






phenocrysts 
(phen.) 


14. 
Opaque plagioclase 


{02 'i mm. 
i -2 


3 






phenocrysts 


2 '3 








V (opac. ) 


'3 '5 




4- 










Granular 




f I5 ' 






(gran. ) 




Large phenocrysts 
of olivine and 


f -02 ! mm. 

I 'I '2 


2 






pyroxene, over 


1 '2 '3 






8. 


2 mm. (magn.) 


1 '3--5 






No plagioclase 


< tf\ 








phenocrysts 
(non-phen. ) 


10. 

Small phenocrysts 
of olivine and 


'02 'i mm. 


I 






pyroxene, under 


. '! '2 


5 






2 mm. Pyroxene 


2 '3 


2 






scanty and often 


'3 '5 


I 






absent (parv.) 










( 17. Vitr. . 


\ 




Prismatic 
(prism.} 


f 9. Phen. . . 
[ 10. Non-phen. . 


1 

\ 18. Opac 

T 19. Magn. .... 
\ 




/ Not repre- 
\ sented. 






{ 20. Parv 










f 21. FzVr. . 








f 11. Phen. . . 


J 






6. 

Ophitic 




[ 22. Opac 




/ Not repre- 


(oph.] 




f 23. Magn 




\ sented. 


* * / 


[ 12. Non-phen. . 


I 










^ 24. Parv 




. 



XVII 



SYNOPSIS 



243 



THIRD ORDER OF THE OLIVINE-BASALTS. 

CHARACTERS. Olivine scanty. Felspars of the groundmass not 
in flow-arrangement. 

FORMULA. Oliv. t matr.^ pauc.^ non-flu. 



SUB-ORDER. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length of 
felspar lathes 
and prisms. 


Number of 
specimens. 






25 


C *O2 'i mm. 


i 






Glassy plagioclase 


1 'I-* 


13 




, 


phenocrysts 


~\ .~ .., 

* 6 


5 




Plagioclase 


(vitr.} 


1 '3 '5 






phenocrysts 
(phen.} 


26. 
Opaque plagioclase 


/ *O2 'I mm. 
I 'I '2 


4 






phenocrysts 


I -2 '3 




7. 




V (opac. } 


1 -3-'5 




Granular 










(gran.} 




( 27. 










Large phenocrysts 


f *O2 *i mm. 


) 






of olivine and 


1 -12 


1 Not repre- 




14. 

No plagioclase 


pyroxene, over 
2 mm. (magn.} 


1 '2--3 
I '3- '5 


j sented. 




phenocrysts 


~Q 








(non-phen.} 


zo. 

Small phenocrysts 


f -02 -i mm. 


| 






of olivine and some- 
times pyroxene, 


1 -i '2 

1 "2 '3 ,, 


1 Not repre- 
f sented. 






. under 2 mm. (parv.} 


1 '3- '5 


| 






(29. Vitr. . . . 






8. 
Prismatic 


( 15. Phen. . . 


<. 30. Ofac 




r Not repre- 


(prism.} 




{31 Masn 




sented. 




[ 1 6. Non-phen.. 












32. Parv 












02 'i mm. 








C 33- Vitr. 


'I "2 ,, 


3 






' 


2 '3 


i 




r 17. Phen. . . 




I '3--*5 


2 


9- 




1 34. Opac. . . . 




' Not repre- 


Ophitic 








sented. 


(oph.} 


. 1 8. Non-phen. . 


' 35. Magn 




Not repre- 






36. Parv 




, 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. Oliv., matr., pauc., flu. 



SUB-ORDER. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxyene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length 
of felspar 
lathes. 


Number of 
specimens. 






37- 


C -02 *i mm. 


2 






Glassy plagioclase 


I -2 


12 




f T C\ 


phenocrysts 


! '2 '3 


6 




iy. 

Plagioclase 


(ritr.) 


I -3--S M 






phenocrysts 
(phen.) 


3& 
Opaque plagioclase 
phenocrysts 


( '02 'I mm. 

1 'I '2 

1 '2-- 3 


2 


10. 




I (opac. ) 


I '3- '5 




Granular 










(gran.) 




( 39- 










Large phenocrysts 
of olivine and 


C '02 'I mm. 

I 'I '2 ,, 


1 Not repre- 




20. 


pyroxene, over 


1 '2- '3 


j sented. 




No plagioclase 


2 mm. (magn.) 


\ '3'S 


J 




phenocrysts 
( non-phen. ) 


40. 
i Small phenocrysts 


{02 'i mm. 








of olivine and some- 


I -2 ,, 








times pyroxene, 


2 "3 ,, 


2 






1^ under 2 mm. (parv.} 


3-'5 


I 






( 41. Vitr. . 


\ 






(21. Phen. 




1 


/ Not repre- 


11. 




\ 42. Opac 


/ ' 


\ sented. 


Prismatic 










( prism. ) 




{4.3. M&gn. 




{Not repre- 




22. Non-phen. . 






sented. 






44. Parv 


02 *i mm. 


i 


13. 
Ophitic 








/ Not repre- 


(oph.) 








\ 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. 




Pyroxene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length of 
felspar lathes 
and prisms. 


Number of 
specimens. 






j 


{02 'I mm. 


9 






Glassy plagioclase 


'I *2 


5 




j 


phenocrysts 


2- '3 


4 




Plagioclase 


(vitr.) 


3-'S 






phenocrysts 
(phen.) 


2. 

Opaque plagioclase 


{*O2 "I mm. 
I -2 ,, 


6 
4 






phenocrysts 


'2 "3 j) 


3 


I. 




, (opac. ) 


3--5 


3 


Granular 










(gran. ) 




(3- 










Large phenocrysts 
of augite, over 


1 


/ Not repre- 




2. 


2 mm. (magn.) 


J 


\ sented. 




No plagioclase 










phenocrysts 
(non-phen.) 


4- 
Small phenocrysts 
of augite, under 


f '02 'I mm. 

J "I '2 


3 






2 mm., or none 


2 "3 s 


i 






(parv.) 


1 '3 '5 


2 


2. 


(3. Phen. . . . 


j 5- Vitr. 
\ 6. Opac 


f '02 -i mm. 

I 'I '2 
'I '2 


I 
2 

2 


Prismatic 










(prism.) 


A Non-phen. 


J 7. Magn. ... 


I 


/ Not repre- 






( 8. Parv 


J 


\ sented. 








{02 *i mm. 


i 






{Q Vitr. 


I--2 


3 








2- '3 


4 




(5. Phen. . . . 




3-'S 


7 


3. 




10. Opac. 


/ *2 '3 mm. 


i 


Ophitic 






I -3-'5 M 


i 


(oph.) 


6. Non-phen. . 


f II. Magn. 
\ 12. Parv 


/ *2 '3 mm. 


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. Aug., matr.,flu. 



SUB-ORDER. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 


Presence or 
absence of plagio- 


Character 
of the 


Length of 
felspar lathes 


Number of 
Specimens. 


groundmass. 


clase phenocrysts. 


phenocrysts. 


and prisms. 








( I3 ' 


{'O2 'I mm. 


10 






Glassy plagioclase 


I -2 


10 




7 


phenocrysts 


2 '3 


4 




/ 

Plagioclase 


(vitr.) 


'3 '5 >, 


I 




phenocrysts 


} 


\ 






(phen.) 


14. 

Opaque phenocrysts 
of plagioclase 


V 'O2 *i mm. 


2 


4- 




(opac.) 


J 




Granular 










(gran. ) 




15- 


^j 






8. 
No (or very few 
and small) 


Large phenocrysts 
of augite, over 
2 mm. (magn.) 


} 


f Not repre- 
\ sented. 




plagioclase 
phenocrysts 
(non-phen. ) 


1 6. 
Small augite pheno- 
crysts, under 2 mm. 


( -02 * i mm. 

I "2 
I '2 '3 


12 

H 

4 






or none ( parv. ) 


I -3-'5 


3 






f 17. Vitr. . 


'I '2 mm. 


j 


5. 


(9. Phen. . . 


\ 

[ 1 8 Opac. 




f Not repre- 


Prismatic 








\ sented. 


(prism.) 




{IQ M (isn't 




/ Not repre- 




10. Non-phen. . 


20. Parv 


/ '02 'I mm. 

X 'I '2 


\ sented. 
4 
4 






( 21. Vitr. ... 


'i '2 mm. 


2 


6. 


(II. Phen. . . 


22. Oi>ac. 




J 

/ Not repre- 


Ophitic 








\ sented. 


(oph. ) 




{23. Magn. 


^1 




\ v jf"" 1 


12. Non-phen. . 




I . 


/ Not repre- 






24. Parv 


) 


\ sented. 



XVII 



SYNOPSIS 



247 



FIRST ORDER OF THE HYPERSTHENE-AUGITE ANDESITES. 
CHARACTERS. Felspar-lathes not in flow-arrangement. 

FORMULA. Hypersth.-aiig.^ matr.> non-flu. 



SUB-ORDER. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length 
of felspar 
lathes. 


Number of 
specimens. 






I. 


^| 








Glassy plagioclase 


I *O2 *i mm. 


12 




f ! 


phenocrysts 


I 'I '2 


4 




Plagioclase 


(vitr.) 


J 






phenocrysts 




% 






(phen.) 




Opaque phenocrysts 


I 


/ Not repre- 






of plagioclase 


I 


t sented. 


i. 




(opac.) 


J 




Granular 










(gran.} 




( 3 ' 


} 








Large phenocrysts 




f Not repre- 






of pyroxene, over 





\ sented. 




2. 


2 mm. (magn. ) 


} 






No plagioclase 










phenocrysts 


4- 








, (non-phen.} 


Small pyroxene 










phenocrysts, under 


3 '5 mm. 


I 






2 mm. , or none 










(parv.} 










( 5. Vitr. . 


{02 'I mm. 


2 


2. 

Prismatic 


3. Phen. . . . 


\ 6. Opac 


i -2 
f 'O2 "I mm. 
I -I '2 


2 

I 
I 


(prism.} 


4. Non-phen. . 


{7. Magn 
8. Parv 


} 


/ Not repre- 
\ sented. 


Ophitic 




r 9] 

\ I0 h - 




/ Not repre- 


(oph.) 




1 | 

liij 




X sented. 



2 4 8 



A NATURALIST IN THE PACIFIC 



CHAP. 



SECOND ORDER OF THE HYPERSTHENE-AUGITE ANDESITES. 

CHARACTERS. Felspar-lathes in flow-arrangement. 

FORMULA. Hypersth-aug., rnatr., flu. 



SUB-ORDER. 


SECTION. 


GENUS. 


SPECIES. 




Pyroxene 
of the 
groundmass. 


Presence or 
absence of plagio- 
clase phenocrysts. 


Character 
of the 
phenocrysts. 


Length 
of felspar 
lathes. 


Number of 
specimens. 




Plagioclase 
phenocrysts 
(phen.) 


13- 
Glassy plagioclase 
phenocrysts 
(vitr.) 

Opaque phenocrysts 


1 *O2 *i mm. 

J ' l ~' 2 " 
\ 


9 

2 

/ Not repre- 


4- 
Granular 
(gran. ) 




of plagioclase 
(opac. ) 

Large phenocrysts 


1 


\ sented. 
/ Not repre- 




8. 
No plagioclase 
phenocrysts 
v (non-phen.) 


of pyroxene, 
over 2 mm. (tnagn. } 

1 6. 

Small pyroxene 
phenocrysts, under 
2 mm., or none 
(parv.} 

{17. Vitr. . 


/ 

*O2 'i mm 


\ sented. 

/ Not repre- 
\ sented. 

2 


5- 

Prismatic 
(prism ) 


(9. Phen. . . 


18. Opac 
f 19 Magn. 


02 'i mm. 


4 
/ Not repre- 


6. 
Ophitic 


10. Non-phen. . 


{ 20. Parv 

m 


/ *O2 'i mm. 
\ -I--2 


\ sented. 
4 

2 

f Not repre- 


(oph.) 




r 3 
124; 




\ 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.,fels. 

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 1 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 


Hypersthene-gabbro 


Avuka Range between Lam- 
basa and Mbuthai-sau 


Probably forms the 
axis of the range. 


1 80 


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 
6 


Hornblende-gabbro. 
Diorite 


Ditto 
Vunimbua River on south 


Ditto. 


I8 4 


7 


Ditto 


side of the Mariko Range 
Coast cliffs west of the Salt 


river-bed. 
Lar"e block in ag- 


182 






Lake Passage 


glomerate-tuff. 


193 



1 I apply the term " diorite" to granitoid rocks formed entirely of plagioclase 
and hornblende. 



250 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 DlORlTES. 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 olivine-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. xvni 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. Oliv, matr, cop, non-flu, gr an, p hen, 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 15 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 '08 to '13 mm., whilst they 
frequently display lamellar twinning and give extinctions of about 
I 5 (oligoclase-andesine). The pyroxene-granules of the ground- 
mass, which are of brown augite, vary in average size from *O2 
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. Oliv, 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 



xvm OLI VINE-BASALTS 255 

macling. 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. 

(*) '2 '3 

3. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr, cop, non-flu, gran , 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*91. 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. 2-9. 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 1 6. 

12. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr y cop, non-flu^ oph^tion-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. 2^91, 
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-lamellae 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 



xvin 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 'O2 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. Oliv, matr, cop) flu, gran, phen, opac. 

CHARACTERS. Olivine abundant. Felspars of the groundmass 
in flow-arrangement. Pyroxene of the groundmass granular. 
Opaque plagioclase phenocrysts. 

DESCRIPTION. Dark grey rocks, with sp. gr. 2-9 to 2-93, 
showing phenocrysts of olivine and pyroxene with opaque whitish 
phenocrysts of plagioclase in a groundmass of felspar lathes, 
pyroxene grains, and magnetite, with occasional fine olivine. The 
olivine phenocrysts, which are sometimes 5 or 6 mm. in size, are 
often deeply eroded. They are at times so extensively hematised 
along the schiller-planes that they appear like brown mica. The 
plagioclase phenocrysts owe their opacity in part to their consisting 
of an aggregate of lesser crystals which are clear and glassy and 
give lamellar extinctions of 20 to 30 (andesine labradorite). 
They 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 *O2 mm. in 
diameter. 

The only species represented is that with the felspar-lathes T 
to '2 mm. long. 

15. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr, cop) flu, gran^ non-pJien, 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*1, 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 *O2 
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 *o6 mm. and *o8 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 'i mm. in length. 

16. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, 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 



xvin OLIVINE-BASALTS 259 

2-91 to 3 -oi. 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 (*5 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 4 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. 
FORMULA. Oliv, matr,pauc, 

25. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr, pane, non-flu^ gran> plien, vitr. 

CHARACTERS. Olivine scanty. Felspars (lathes and prisms) 
of the groundmass not in flow-arrangement. Pyroxene of the 
groundmass granular. Glassy plagioclase phenocrysts. 

S 2 



260 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. In the slide 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. 1 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 "17 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 1 8 (andesine). The augite granules of the groundmass 
are pale brown and average 'O2 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 

1 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. 



xvin OLI VINE-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 ('05) approach the 
semi-ophitic rocks included in genus 33. 

26. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv y matr^pauc^ non-flu >gr an ^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 
opacity of the felspar phenocrysts, look like porphyrites. They 
are not very frequent and occur mostly on the northern slopes of 
Mount Seatura. Two different types occur in my collection 
which may be regarded as sub-genera. In the most basic kind, 
where the sp. gr. is 2*86 to 2*89, the plagioclase phenocrysts, 2 to 

3 mm. in size, owe their opacity chiefly to their aggregate struc- 
ture. They give lamellar extinctions (15 30) of andesine labra- 
dorite. Porphyritic olivine is scanty and more or less hematised ; 
but a fair amount of olivine grains, less than *i mm., occur in the 
groundmass. Pyroxene phenocrysts are scanty, but micro- 
porphyritic pale brown augite ("I mm.) is frequent. In the 
groundmass are found stoutish felspar-lathes, averaging *2 mm. 
long, together with an abundance of fine augite granules ( g oi '02 
mm.) and fine magnetite, the residual glass being scanty. ... In 
the other type the sp. gr. is 275 ; and the plagioclase phenocrysts 

4 to 6 mm. in size give extinctions of andesine and acid labra- 
dorite (10 30). There is an approach to the orthophyric struc- 
ture in the groundmass, as is indicated by the number of short 
broad felspars, averaging '2 mm. in length and giving lamellar 
extinctions of acid and basic andesine. The granular augite of 
the groundmass is coarse ('04 mm.), and occasional prism-forms 
give extinctions of 40. 



262 A NATURALIST IN THE PACIFIC CHAP. 

33. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr,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, *o8 '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. Oliv, matr, pane, flu, gran, p hen, 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 



xvin OLIVINE-BASALTS 263 

length '15 '21 mm. The sp. gr. is usually between 2*87 and 2*91. 
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, 'O2 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 : 

(a) 'O2 -i mm. () 'i '2 mm. 

(V) -2 -3 mm. 

38. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr, pauc,flu, gran y p hen, 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. 

ofolivine 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 ( 1 8 22). . . . Theaugite 
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, matr,pauc,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 T to '6 
mm. When lamellar they give extinctions of 15 to 25 (basic 
andesine). 



xvin OLIVINE-BASALTS 265 

Two species are represented in this collection : 
(a) with felspar-lathes *2 '3 mm. 

(J) ,, "3 '5 

44. GENUS OF THE OLIVINE-BASALTS 
FORMULA. Oliv, matr, pane, flu, prism, 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 -07 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 
SUB-CLASS II 

AUGITE-ANDESITES INCLUDING THE BASALTIC ANDESITES 
(Flag, aug, 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-flu , gran. 



CHAP, xix AUGITE-ANDESITES 267 

i. GENUS OF THE AUGITE-ANDESITES 
FORMULA. Aug> matr, non-flu, 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 *O2 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. Aug, 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 limestones. 

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 , long 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 
2-6 1 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 *o6 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 7 o A NATURALIST IN THE PACIFIC CHAP. 

4. GENUS OF THE AUGITE-ANDESITES 
FORMULA. Aug, 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 "i 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 *O2 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, matr, non-flu, prism y 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 '08 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, *i 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. Aug, 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 lesser 
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 
macroscopic plagioclase phenocrysts. They are sometimes vesi- 
cular, and form old flows in a few localities, as in the vicinity of 
Natua in the eastern part of the Ndreketi plains and in the coast 
district 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 (i5-3O)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 (*O2-*O3 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. Aug, matr^non-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 



276 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, phen, 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- i 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 + 30. The felspar-lathes, 
which average *o6 '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. 

(U] 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 -05 mm, and 
give simple extinctions of acid andesine (5 10). Interstitial glass 
exists in moderate amount. 

SPECIES B. Felspar-lathes 'I '2 mm. in average length. 

Blackish or dark-grey rather compact rocks, sp. gr. 275 279, 
that cannot be readily divided into groups according to their 
basicity. They form dykes and volcanic " necks " and are some- 
times scoriaceous. The small plagioclase phenocrysts, which are 
most evident in the slide, present the two kinds above described 
under Species A. They give lamellar extinctions varying from those 
of medium andesine to acid labradorite (15 30). The augite 
phenocrysts, which are small and scanty, occasionally show inter- 
growths of rhombic pyroxene. The augite granules are generally 
*O2 to '03 mm. in size, and here and there a prism form gives 
extinctions of -f 25. The felspar-lathes which average 'II to 



278 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 2'84. 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*81 
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*81. 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 *O2 '03 mm. in size. There is usually 
a little interstitial glass. 



xix AUGITE-ANDESITES 279 

A rock, almost holocrystalline 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 (*o6 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 y flu^gran y 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 *o8 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 y 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- 



2 8o 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*85. 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 *O2 mm. and *i mm. in 
average length. 

(i) Most 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 
("Oi 'O2 mm.) and abundant. There is generally a little interstitial 
glass with small magnetite. 



xix AUGITE-ANDESITES 281 

(2) Least basic sub-species . . . Sp. gr. 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 '07 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 I \ 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 \\ 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 'O2 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'S/. 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 
23mm. 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. Aug, matr^flu^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*65, 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 "07 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, rnatr^flu, oph.) 

21. GENUS OF THE AUGITE-ANDESITES 
FORMULA. Aug, matr.fiu, 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-AUGJTE CLASS 

II. SUB-CLASS. HYPERSTHENE-AUGITE- ANDESITES 
FORMULA. Flag, hypersth-aug, matr. 

CHARACTERS. The pyroxene phenocrysts usually are re- 
presented by separate crystals of the monoclinic 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. Hyperstk-aug, matr, non-flu, gran. 

i genus . . . (Vitr.) \ 
ic.} ( 



' see 



3 . \ 

4 . . . . (Pan/.) J 

Nearly all of the rocks of this sub-order that are represented in 
my collection belong to the genus (i) 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 2*6 to 27. 

In the slide small phenocrysts of plagioclase and pyroxene 
occur 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. 21 1). 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. Hyperstk-aug^ rnatr^ non-flu, prism. 
5 genus . . . ( Vitr.} \ 

7 " ! .' .' (M P agn\ See Synopsis. 

8 . . . (Pan,.}) 

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 f oi '04 mm. in length, and give both straight and oblique 
extinctions, the last prevailing. The specific gravity ran'ges 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. 



^88 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 
'O2 '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-AUGITE- 
ANDESITES 
(Felspar-lathes in flow-arrangemenf) 

FORMULA. Hypersth-ang, matr, flu, prism. 



17 genus . . . (Vttr.) 

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- 
crysts are opaque (genus 18) ; whilst in a few they are glassy 
(genus 17). The rocks are typically blackish or dark grey, and 
often have a pitchstone-like appearance, the groundmass being 
frequently semi-vitreous in character. Vesicular and scoriaceous 
rocks occur at times. 

In all cases the felspar-lathes and pyroxene prisms are more 
or less in flow-arrangement ; whilst pyroxene granules, if present, 
are subordinate. The felspar-lathes, which are either simple or 
once-twinned and give extinctions of acid and medium andesine, 
are usually small, and average in different sections "05 *o8 mm. 
in length. The pyroxene prisms are pale brown and are '03 or 
04 mm. long. Most of them give oblique extinctions of over 
25" ; but in the same slide some give straight extinctions ; the 
proportion varies in different rocks. The pyroxene phenocrysts 
in all the specimens are small (not over 2 mm.), and are rhombic 
and monoclinic. In most sections the two forms are represented 
by separate crystals and are also associated in the same phenocryst. 
Those of rhombic pyroxene have often dark borders. There is a 
considerable amount of a pale brown glass in the groundmass, 

u 



290 A NATURALIST IN THE PACIFIC CHAP, 

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, ortJi. 

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 tuffs. 
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 (*O2 '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 " 
of 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 
materials. 

The plagioclase phenocrysts, which give extinctions of medium 
and basic andesine (15 25), are often semi-opaque and cor- 
roded. They are traversed by numerous cracks and often contain 
many whitish alteration products, though the lamellar structure is 
usually well preserved. The pyroxene phenocrysts are composed 
of 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 
groundmass 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 x 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 2 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- 
mass were numerous felspar and augite microliths, whilst there was 
a porphyritic development of plagioclase, hornblende, biotite, and 
pyroxene. The hornblende phenocrysts played an important part 
in the rock-composition, being surrounded by a black zone of 
magnetite or bordered by a bacillary aggregate of small pyroxene 
prisms, parallel and colourless or greenish, with extinction-angles of 
40. There was often also a development of biotite in the heart of 
the mineral, the whole hornblende section being sometimes thus 
transformed. 

Mr. Eakle 3 has more recently described the hornblende-andesites 
from Mbuke Levu in Kandavu. As the result of his examination 
of a collection of volcanic rocks made by the Agassiz expedition in 

1 Petrographie des Viti Archipelsj Miner, und Petrogr. Mittheil ; band v, 
heft i,Wien, 1882. 

2 Physics and Chemistry, II. Report Scient. Results; H.M.S. Challenger \ 
London, 1889. 

3 Petro graphical Notes on the Fiji Islands; Proceed. Amer. Acad. Arts and 
Sciences ; 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 1 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, 2 Vanua Levu, Ovalau, 
Kandavu, Ono, Malolo, Yasawa Islands, etc. 

The occurrence of quartz-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, 3 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." 



1 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. 

2 Wichmann describes rocks from the cliffs of the Singatoka river and from 
Ovalau. 

3 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. 1 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 
quartz 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 ; hornblende-hypersthene-ande- 
sites ; and quartz-hornblende-hypersthene-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 
cliff- 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- 

1 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 b^ 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 maybe 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 Levu 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, *I2 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- 



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 'I mm., and there is a quantity of 
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-crystalline 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 15 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 
*oi and *O2 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 
unweathered 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 



3 o2 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 Wawa 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 phenocrysts 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 (*O2 '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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3 o6 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 Lehrbuch 
der Petrographie ; 2nd edit. : I. 271. 

Note on the " magmatic paramorphism " 1 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, 2 
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 Iddings. 
* Challenger Reports^ 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 
QI 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 
portion is alone dispersed, whilst the growth of a single large 
crystal of pyroxene proceeds within the mass. In a later stage, 
when the dispersion of the outer part is complete, we have a fresh- 
looking pyroxene phenocryst with unformed edges, on the borders 
of which little granules and prisms of pyroxene may be seen 
arranging themselves, as if the crystal-building was still in progress, 
or rather as if it had been interrupted and left unfinished by the 
too rapid dispersion of the outer portions of the paramorph. 

X 2 



3 o8 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 15 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. 1 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. 2 

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 1 2 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. 

1 Neues Jahrb. fur Mineralogie, 1884. 

2 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. 1 

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 n, 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 2 ' 
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, J of an inch in diameter) and 
glassy felspar, together with a few sphene crystals. 

1 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. 



3 io 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 l 
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 spherulites 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*1. 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 7 can be observed. 

1 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 PlTCHSTONE AND BASIC GLASS 

IT is not possible to draw a sharp distinction between the 
pitchstone and the purely vitreous condition of these glasses. The 
following remarks will therefore apply to both. 

Regarded as components of the pitchstone-tuffs and palagonite- 
tuffs 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 HC1, 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*61 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 

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*61 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 2,500 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 rudely 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 tuffs 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-tuff, 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 tuffs. 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 



316 A NATURALIST IN THE PACIFIC CH. xxn 

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 of 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. 



318 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 arid 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 J to i 
millimetre in diameter. In some cases the carbonate of lime of the 



xxm FORAMINIFERAL LIMESTONES 319 

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 from 
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 
Minerals 12 
Secondary silica replacing the carbonate of 
lime in the organic remains 12 , 

100 

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 

100 

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. 



320 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 'I 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 ,, 

Minerals 8 ,, 

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 '3 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 
are usually concealed by the tuffs and agglomerates. Occasionally, 
however, 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. 1 

SAMPLES OF THE VOLCANIC MUD-ROCKS 

A. From districts west of Ndranimako, 100 f eet above the sea. 
Carbonate of lime 20 per cent. 

(Fine debris of palagonite and semi-vitreous 
basic rocks 62 
Minerals 14 
Casts of foraminifera 4 

ICO 

1 Quart. Journ. Geolog. Soc. xliv. 1888. 



xxm 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, i,ioofeet above the sea. 

Carbonate of lime 15 per cent. 

(Fine material mainly derived from the degra- 
dation of palagonite . . . 60 
Minerals 23 
Casts of foraminifera 2 

IOO 

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 
Res,due | Minerals 2 ^ ;> 

Casts of foraminifera 11 

IOO 

This is a relatively deep-water deposit, the foraminifera being 
minute and of the " Globigerina " type. About 90 per cent of the 
residue consists of fine clayey material, with which the calcite is 
so 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, loofeet above the sea. 

Carbonate of lime 4 per cent. 

Fine material derived from the degradation of palagonite 90 

Minerals 2 ,, 

Casts of foraminifera 4 

100 

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 



xxni 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 
alteration product. 

C. From the vicinity of Yaroi, 30 feet above the sea. . . . The 
locality 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 
an altered limestone. In the section it displays minute tests of 
foraminifera of the " Globigerina " type in a matrix composed of 
fine disintegrated palagonitic material, impregnated with calcite 
and containing also fragments of minerals (augite and felspar), 
none of which exceed *2 mm. in diameter. There are also a few 
similar-sized fragments of semi-vitreous basic rocks. Some fine 



326 A NATURALIST IN THE PACIFIC CHAP. 

cracks in the rock-mass are rilled 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 ('Oi-'O4 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 



xxin SUBMARINE PALAGONITE TUFFS 327 

2,000 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, arid 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 XI.), 
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 12 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 2,000 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. 



xxiii 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 



xxin 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. ; () 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. 

Note. 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 



xxni 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 
rilling 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 
rilled 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 hyalom elan-tuff 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 y 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 



xxin 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 
developed 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 
fibrous natrolite with the cube-like crystals of chabazite occupying 
the interior. The calcite is usually subordinate to the zeolites, but 
sometimes the tuff contains as much as 10 per cent of this mineral, 
which is evidently of secondary origin. . . . The history of these 
tuffs in the district of Nandua and Ulu-i-ndali is no doubt applic- 
able to these deposits in other localities. They are the products of 
submarine eruptions which shattered into fragments the extensive 
palagonite crusts of flows of basaltic lava. In Chapter XXIV. 
I have attempted to show how palagonite is formed on a large 
scale in the case of such submarine displays of volcanic activity. 

CHOCOLATE-COLOURED FORAMINIFEROUS PALAGONITE-MARLS 

We have here hard, somewhat calcareous, clay-rocks which con- 
sist in great part (nine-tenths) of fine palagonite debris with some 
fragments of minerals and a little fine detritus of semi-vitreous basic 
rocks. Some hand-specimens would be taken for pure palagonite ; 
but the fragmental nature appears at once in the slide. This is 
especially the case with a rock exposed in a stream-course near 
Rewa on the shores of Savu-savu Bay (see page 95). The 



336 A NATURALIST IN THE PACIFIC CH. xxin 

materials composing them are exceedingly fine, the largest frag- 
ments not usually exceeding "Z mm. As a rule they contain a 
little carbonate of lime and sometimes as much as 10 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 
all the stages in the history of Vanua Levu are bound up with the 
history of this material. In this place I will only deal with certain 
features in the problem connected with the origin of palagonite 
which seem to receive further elucidation from my observations in 
this island. The literature is already extensive, and those inter- 
ested in the matter will find in Zirkel's Petrographie and in the 
Challenger Report on Deep-Sea Deposits by Murray and Renard 
a good introduction to the subject. 

In Vanua Levu we are confronted with the same difficulty that 
has perplexed geologists in various parts of the world. If we 
expected to find in this island the source of the enormous quantities 
of the basic glass that are represented by the palagonite of the tuffs, 
we should look in vain. Basic or basaltic glass usually occurs in 
agglomerates in the form of tachylytic pitchstones, as described on 
page 312, and is also found at times in basic pumiceous tuffs, as 
described on page 333; but it is far from frequent. Palagonite- 
rock, that is to say, a basaltic glass converted in mass into this 
substance, never came under my notice. 

In order to clear the ground for the discussion of my own observa- 
tions, I will quote from the report on deep-sea deposits above named. 
Fragments of basic glass undergoing the palagonite change are 
found 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 XXIII., 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 " in 



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 
interspaces, and afterwards solidified and underwent the palagonitic 
change. 

In this connection it is noteworthy that in the sections of the 
lower hemicrystalline portion of the flow there are shown in the 




MAGMA-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 
have termed them, " magma lakelets " of microscopic dimensions 
(25 mm. in average size). These " lakelets " are irregular in form, 
and are not uncommon amongst a certain type of basaltic rocks. 
One of them is figured above ; and it may be added that they are 
best 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. 81) 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. 1 

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. 2 

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. 3 

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. 

1 Zirkel's Petrograpkie^ in., 694. 

2 This basalt is not fusible in the ordinary blow-pipe flame. 

3 In this connection see the description of the Soloa-levu pitchstone on p.3i2. 



342 



A NATURALIST IN THE PACIFIC CHAP. 



In certain types of basaltic lava, 1 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 

1 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 Q. 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 l 
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 1 50 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 f 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 




> Pfefopod -ooze Rock (J0p.c.) 



} Palagonile-msrl containing 
\ a few-foraminifera .(90p.c) 



' HP'lffl } Palagonite -rock.(98p.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 
a 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 Hght 
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 paiagonitic 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 paiagonitic 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 paiagonitic 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. 

(c) 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. 1 In 
such rocks the felspar-lathes form a mesh-work and vary usually 
in average length between T 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. 

1 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 HC1, 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. 

Supplementary 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 a g e 334 under " Crush-tuffs." 



CHAPTER XXV 

SILICIFIED CORALS AND FLINTS 

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, 1 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 Wichmann and 
described in his paper. 2 Mr. Andrews observed silicified corals on 
the summits and higher slopes of Vanua Mbalavu. 3 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, 4 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 

1 Reisen auf den Viti-Inseln, as quoted on p. 22. 

2 Petrographie des Viti-Archipels^ quoted on p. 293. 

3 See work quoted on p. 378. 

4 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). 1 
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. 

1 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 limonite 
occur, are scantily vegetated "talasinga" lands 1 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 
" Porites " 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 

1 For the meaning of " talasinga" see p. 55. 

2 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 groundmass 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 800 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. 



360 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, 1 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 

1 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 Lehrbtich der Petrographie (1893, vol. i. p. 565) gives most of these and 
many more recent. . . . Marker 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. GeoLItal. 1881, vol. 9 British 

Association Report in 1889 by Professors Rticker and Thorpe on the Magnetic 
State of the British Isles. . . . Nature for August and September, 1894, &c. . . . 
Marker on magnetic disturbances in the Isle of Skye, Proc. Cambr. Philos. Soc. 
vol. 10, part 5. ... Skinner in Proc. Cambr. Philos. Soc. May, 1894. . . . Clark in 
fourn. Roy. Instit. Cornwall, 1890-93. . . . Folgheraiter in Frammenti con- 
cernanti la geofisica, 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 l 
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 

1 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 l ; 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. 2 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 3 

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 

1 Some of the earliest observations were made on granites and trachytes. 

2 Geology of the United States Exploring Expedition, 1849, P- 2 94- 

3 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 I84O, 1 
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 13 J 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. 2 This property of 
volcanic rocks is well known, and is to be attributed to the mag- 

1 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. 1 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 

1 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 2\ 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 6*5 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. 1 


Dark olivir 
Grey 

)) 
Dark 

J> 5 J 

Basaltic an 


Pyroxene-a 


ic-basalt 


3-00 
2-94 
2-92 
2-90 
2-87 
2-82 
277 
272 

2'6l 

2*59 
2'57 
2-50 


IO 

29 

, 

30 

t" 
38 

'? 
% 




5J 




desite 




ndesite .... . . . 








" 













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, 1 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. 2 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. 3 

The summit of Mariko (2,890 feet), the Drayton Peak of the 
chart, is formed of a rubbly agglomerate of a compact basic andesite. 

1 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. 

3 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 
Suva-suva, 1,110 feet high, which overlooks Naindi Harbour to the 
east of Savu-savu Bay. It is only occupied by trees in its upper 
part, and a specimen of the olivine-basalt, of which the hill is 
composed, that was obtained from the wooded summit, shows no 
polarity ; whilst another from the slopes, two -thirds of the way up, 

B B 



37 



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. 


Character of rocks. 


Number of 
specimens. 


Polarity. 1 


Range. 


Average. 


2-60-2-69 


Dacites 


6 

5 


3-i6 


11-6 
8-6 


Dacites and augite-andesites 


270-279 


Augite-andesites 


5 


5-38 


132 


2-80-2-89 
2-90-3-00 


Basaltic andesites and oli- 
vine-basalts 
Olivine-basalts 


18 


3-9o 


15-0 
127 





1 The mode of measurement is described on p. 366. 



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 zoo-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 1 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, 1 8, 56, 62, 72, &c. 



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CH. xxvn 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. 1 
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 
been 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 
of the western end of the island. No one would be bold enough 

1 The Islands and Coral Reefs of Fiji, Bull. Mus. Comp. Zool. Harv. Coll. 
vol. 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 



xxvn 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. 1 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," 2 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. 1 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. 2 The Rev. J. E. 
Tenison- Woods described as extinct Tertiary fossils, some corals 
and mollusks from the interior of Ovalau. 3 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. 4 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 as the earlier Tertiaries. 5 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 

1 See Wichmann in Min. und Petrog. Mitth. band v. heft i. 

2 Amer.Journ. Sri. VI. 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. 

4 Quart. Journ. Geolog. Soc. vol. 44, 1888. 

6 See Preface to the report of Mr. Andrews quoted on a later page. 



xxvn 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 
no 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 ; l 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 
1 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." l 

From the report of Mr. Andrews 2 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, 
1,000 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 3 that the 
islands of the Tonga Group represent the Lau stage of the 
emergence. They are similar in height and in general geological 

1 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. 

3 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, 1 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. 2 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 1 6, 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 

1 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" in Journal 
lAnnean Society, Botany, vol. 30. 



3 8o 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, 1 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, 

1 See Hutton Proc. Linn. Soc. N.S.W. 1896, Baur, Amer. Nat. 1897, 
Pilsbry, Proc. Nat. Sci. Philad. 1900, Hedley, Proc. Linn. Soc. N.S.W. 1892, 
1899, &c. 



xxvn 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. xxvn 

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 2oth 
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 

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 ; see under 
Submarine plateau and Basaltic 
plains 

Basalts, columnar, 3, 63, 78, 83, 84, 
85, 123, 129, 133, 147, 170, 173, 203, 
260, 284 

Basalts, ophitic, 50, 74, 114, 133, 137, 
138, 155, 159, 162, 191, 204, 213, 
252, 256, 347 ; the ophitic habit, 
2 37, 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 



1 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-augite 
andesites. 

C C 



3 86 



INDEX 



Basalts, grey olivine, 65-67, 73-75, 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 
Kav , 75-77 5 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 
Bromlovv, 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, 
1 86, 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, 101, 102 ; definition of 



the term, 295 ; classification and 

characters, 240, 302 ; see Acid ande- 

sites 

Dall, Dr., 376 
Dana, Prof, 3, 10, II, 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 

Dray ton, 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 5 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 5 altered, 324- 



INDEX 



387 



326 ; thickness of, 1 56 ; see Globi- 
gerina deposits and Palagonite- 
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, 1 16 
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 

Marker, 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 

Hornblende-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; list of, 40; analysis, 28; 

distribution in Vanua Levu, 36, 138, 

233 
Humboldt, A. von, on magnetic rocks, 

361, 365 
Hussak, on magmatic paramorphism, 

308 

Hutton, 380 

Hyalomelan tuffs, 47, 80, no, 333, 334 
Hydrothermal metamorphism ; see 

Solfataric 



Hypersthene ; see Pyroxene, rhombic 
Hypersthene-andesites, 294, 296 
Hypersthene-augite-andesites, 5, 52 
147, 161, 164, 168,171, 173-175, 178, 
179, 182, 1 86, 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, 218 
Lambasa Plains, 138, 351 



3 88 



INDEX 



Lambasa River, 15, 138 

Landslips, effects of, in, 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, 1 6, 1 8 ; 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-lorna 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, 77, 108, 
174, 1 86, 361-371 

Mako-mako Hill, [03 

Mali Island, 2, 218 

Mali Point, 218 

Malolo Island, 294 

Mangrove belt, bare tracts in, n, 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, n, 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, 

3oi, 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, 

3 1 

Nawi or Na Wi, island, 26, 192 ; ham- 
let, 211 

Ndaku-ndaku,bay, 208 ; hot springs,34 
Ndama, river and valley, 62, 67, 68, 

71 ; plams, 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, 2 14-2 1 6 ; columnar, 2 1 5, 220, 
230, 231, 233. 

Olivine rocks, classification of, 239 

Oli vine-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, 
118-122, 130, 131, 141,143,145,148, 
156-161, 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 

1 Place-names, meaning of Fijian, 75, 
79, 102, 119, 151,172 



1 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. 



390 



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, 113, 153, 167, 173 
Propylites, 68-72, 106, 147, 162, 1 8 1, 

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 

Hyalomelan-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, 139, 351, 354 

RAINFALL, 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, 1 6 

Rhyolites, 209 ; see Quartz-porphyries 
Rhyolite-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, l82, 1 88, 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 
Siliceous 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 
Small wood, Mr., 196 
Smythe, Colonel, 22, 195 



INDEX 



Soapstones, see Foraminiferous de- 
posits 

Sokena Ridge, 167, 169, 172 

Solevu Bay, 75~78 3 253 

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, 

101, 102, 108, 156, 170 
Trachytes ; see Oligoclase-trachytes 
Tuffs, chapter on, 317-336 : foramini- 

ferous, 326-333; altered, 184, 187,. 

I 9> 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, 181-185 

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, 113-116,296,301, 305, 

374, 375 

Vatu-karoa, 209, 282 
Vatu-karokaro, 54 

Vatu-kawa, river, 151 ; district, 160 
Vatu-kerimasi, 101 
Vatu-lele Bay, 184 
Vatu-levoni, 139 
Vatu-loaloa Hot Springs, 31 
Vatu Mata, 103 
Vatu-ndamu, 91 
Vatu-tangiri, 136, 144 
Vatu Vanaya, 101 
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, 144, 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, 1 88, 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, 112, 
183, 192, 230, 234, 253, 277, 283, 
286, 375 

Volcanic rocks, classification of, 235 ; 
distribution of, 374 

Vuinandi Bay, 208 

Vuinandi Gap, 175 

Vuinasanga, district, 145 ; hot springs, 

3. 1 

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 
Vumsawana, distrrct, 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, 15, 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 5 see figures on pages 83, 
107 

Waisali District, 146, 151 

Waisali Saddle, 146-148 

Waiwai, 143-145 

Waterfalls, 79, 141, 163 

Wawa Levu Mountain, 101, 302, 304 

Weed, Mr., on the origin of siliceous 
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, II, 15, 19, 25, 
363, etc. 

Wittstock, Mr., 36, 47, 53 



YANAWAI COAST, 95-97, 122 
Yanawai, river and valley, 113-116, 

121 

Yanganga Islands, 2 
Yanutha Point, 123, 284 
Yaroi, 189, 325 
Yasawa Group, 294 



ZEOLITES, formation of, in palagonite, 

338 

Zeolitic palagonite-tuffs, 334 
Zirkel, on intergrowths of rhombic 

pyroxene, 306 ; on palagonite, 343 ; 

on magnetic rocks, 361 



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