EAKLE. — ROCKS FROM THE FIJI ISLANDS. 585 



Olivine is present in large and small irregular grains, but is not 

 abundant. A slight serpentiuization has taken place along some of the 

 fissures. 



Small grains of magnetite occur. 



Besides these eruptive rocks just described from Viti Levu, a few 

 specimens of sedimentary formation were collected from along the south- 

 ern shore of the island. One of them is a coarse conglomerate, which 

 forms a bluff near Suva. It consists of large rounded pebbles and frag- 

 ments of rock, apparently decomposed andesite, cemented by a very 

 impure calcareous cement. A specimen of a compact white limestone, 

 somewhat siliceous and stained slightly yellowish by iron oxide was col- 

 lected from a locality twenty-five miles up the Singatoka River. 



Specimens were also brought from the two very small islands, Viwa 

 and Mbau, which are close to the eastern coast of Viti Levu. From 

 Viwa is a dark gray compact fossiliferous limestone, and from Mbau a 

 brown decomposed mass termed " soapstone," apparently a sedimentary 

 de|)osit from an altered eruptive rock. 



AUGITE-BIOTITK AnDESITE FROM Na SoLO. 



The Solo rock on which the lighthouse stands rises just above the 

 water in the centre of the lagoon formed by the North Astrolabe coral 

 reef. Several specimens of this rock were collected, but no differences 

 are seen in any of them. 



The rock has a very fine liolocrystalline structure with no porphyritic 

 tendency apparent in the hand specimen. It is light ash gray in color, 

 sprinkled with small dark augite crystals. 



Microscopically, however, the rock, while not possessing a prominent 

 porpliyritic structure, does show many small idiomorphic phenocrysts in 

 a distinctly finer feldspathic base. The feldspars are characterized by 

 isometric forms and zonal structure. Extinctions on the successive 

 zonal layers show a passage from an acid rim to a very basic centre, 

 the maximum extinction in the centres being 35°. The extinction 

 angles of the laths vary from 0° to 20°, the majority being low and indi- 

 cating oligoclase as the chief feldspar. The Carlsbad and albite twinning 

 are common. 



Augite or diopside is well disseminated in the rock as very pale green 

 rounded crystals and fragments. They have all lost their original boun- 

 daries, and some have altered to calcite. 



Biotite occurs in small brown plates, but is not abundant. It is only 



