ANDREWS: LIMESTONES OF THE FIJI ISLANDS. 37 



dolomitization at the bases of the old terraces, appear to make up the 

 sum of the more conspicuous metamorphic phenomena at work in the 

 limestones of Lau. 



The Volcanism of Fiji with reference to Lau and the 

 Smaller Islands- 



The erupted material of Viti Levu appears to consist of andesites, 

 porphyrites, and andesite tuffs. At Suva great beds of volcanic boul- 

 ders occur beneath the i*eef limestone, intercalated in the " soapstone " 

 at Walu Bay. Some of the rounded blocks are upwards of 15 inches in 

 diameter, and are surrounded, in individual cases, by a thick layer of 

 soft-brown earthy crust, the result of the rock decomposition. They 

 consist of porphyrite, quartz, and felspar porphyry, andesite dolerites, 

 and andesites. As the base of the quartz and felspar porphyry is 

 minutely sphenelitic, the rock probably represents an old rhyolite flow. 



In the smaller islands the prevailing rock-types are andesites, occur- 

 ring as lava and agglomerate and basalts, the latter occupying a much 

 smaller area than the former. The influence of the volcanism on island- 

 making will be appreciated when it is stated that Taviuni, Kandavu, 

 Ovalau, Ngau, Nairai, Totoya, Moala, and Matuku are wholly volcanic, 

 while islands which to a casual observer seem wholly limestone, such as 

 Mango, Thithia, Vanua Mbalavu, and Naitamba, are two thirds volcanic, 

 only the remaining third being limestone. Vanua Mbalavu affords 

 splendid examples of andesite agglomerates and conglomerates covered 

 with andesite lava, and exhibits numerous small outlying islands formed 

 of audesite tuff's covered with lava and pierced with dykes of the same 

 material. 



Ovalau, Munia, and Vanua Mbalavu are, in great part, composed of 

 huge, uniformly dipping strata of andesite blocks (Plate 6). These 

 blocks are angular, and present stages of coarseness varying from the 

 finest grained rock with a few scattered pyroxene and plagioclase crys- 

 tals to blocks consisting of huge idiomorphic crystals of augite and 

 felspar crowded in a fine base. 



Insular masses, such as Ovalau and Munia, composed of andesite 

 agglomerates, present very high angles of slope to the sea. In fact, the 

 coastal scarps can hardly be described as slopes. They are very steep 

 ascents broken by precipices 400 or 500 feet, sheer in places. The soft 

 ash beds throughout the mass allow weathering into gorges and cliffs to 

 take place very rapidly. The slopes of andesite flows of Lau (Plates 



