REPORT OX THE PETROLOGY OF OCEANIC ISLANDS. 149 



XL— ROCKS OF KANDAVU, FIJI ISLANDS. 



A paper by Professor Wiclimann * has already made known a good many rocks 

 collected in the Fiji archipelago by the naturalists of the Godeffroy Museum in 

 Hamburg. He has shown that the whole series of paleo-volcanic rocks are present 

 in these islands. 2 The more recent are especially represented by basalts and andesites. 

 The latter, associated with fossiliferous volcanic tufas of tertiary age, compose by them- 

 selves almost all the small islands of the archipelago. According to the same author, 

 the volcanic products of Kandavu are andesites. Professor Wichmann described some 

 specimens taken from Mount Washington or Buke-Levu, which rises at the western 

 extremity of Kandavu. Those about to be described came from a point to the north 

 of the port of the island, where they were collected in August 1874 by the staff of 

 the Challenger. All that is known about the geological nature of Kandavu is that the 

 greater part of the island is a volcanic conglomerate of coarse structure, in which large 

 blocks of lava are embedded. The island is covered with rounded hillocks, rising tier 

 above tier. Mr. Moseley explains the regularity in form to the action of denudation. 

 We may add that in Ovalau, the nearest island to Kandavu, the appearance is similar, 

 and the rocks seem to be of the same nature. 3 According to Mr. Buchanan, all the 

 rocks we are about to describe crop out near the port of Kandavu, and show a 

 columnar structure. 



We shall first describe those belonging to the amphibolic andesites. The naked 

 eye distinguishes in a greyish ground-mass rather large, whitish, vitreous sections 

 of plagioclase, and black specks of hornblende or biotite. The rock is rough to the 



1 Beitrag zur Petrographie des Viti Archipels, Min. pet. Mitth., Bd. v. pp. 1-60. 



2 It seems advisable to poiut out here, in connection with Professor Wichmann's paper, such geological details of the 

 archipelago as we are acquainted with. Meinicke (Die Inseln des Stillen Oceans, p. 2, Leipzig, 1876) has summarised 

 the mineralogical observations made on the Fiji Islands by Graffe, Macdonald, Seemann, &c, and we may refer also 

 to Home (A Year in Fiji, pp. 163-170, London, 1881). According to these authors, the most abundant rocks are 

 argillaceous and calcareous, also breccias and conglomerates, and in some places sandstone and clay slates, while 

 basalts and trachytes form the highest summits, and more recent sedimentary rocks are deposited on the slopes. The 

 island of Taviuni is the only one in the group which is exclusively volcanic, and this, according to Home, is the only one 

 of subaerial formation. But Professor Wichmann observes that the absence of tufas or of other rocks on the declivities 

 of Buke-Levu in Kandavu seem to show that this island is not altogether of submarine origin. The rocks collected in 

 Fiji by Graffe (1862 and 1865), and by Kleinschmidt (1876-1878), showed that crystalline and schisto-crystalline 

 rocks of the ancient series played a considerable part in Buke-Levu. The fossiliferous rocks there are of tertiary 

 age. All the other islands visited by the explorers were found to be composed of andesites and basalts, and of tufas 

 of these two lithological types. In some of them coral limestone, sometimes silicified, has been found. All these 

 observations lead to the opinion that in the palaeozoic and mesozoic epochs this archipelago formed a continent which 

 became submerged about the middle of the tertiary period. Professor Wichmann made it evident that the data furnished 

 by the study of the rocks of the Fiji archipelago present a great analogy from this point of view with those resulting 

 from the examination of other Pacific islands. Contrary to the general opinion, held until very recently, that all 

 the Pacific islands were of volcanic formation, it is now proved that several of them are built up of ancient crystalline 

 and sedimentary rock3. In his paper on the rocks of the Fiji archipelago, Professor Wichmann has established very 

 clearly the facts on which he founds this interpretation (see he. cit., pp. 1-8). 



3 Moseley, Notes of a Naturalist on board the Challenger, p. 301. 



