EAKLB. — ROCKS FROM THE FIJI ISLANDS. 587 



Basalt from Mbengha. 



Mbengha is a small islaud lying near tlie southern coast of Viti Levu. 



The structure of the biisalt is somewliaL hitersertal, cousisting of stout 

 laths of feldspar with the interspaces hlled with a mixture of glass and 

 mascnetite grains and some au<rite niicrolites. 



The feldspar phenocrysts show labradoritic extinctions, and are gener- 

 ally cloudy from numberless brownish glass inclusions and dust particles 

 zonally arranged. The centres of the sections are mostly ([uite dark with 

 these inclusions, vvliile the rims are pure and colorless. 



Augite occurs abundantly as the largest phenocrysts. It is of the 

 common pale green color, non-pleochroic, and occurs in very perfect 

 idiomorphic crystals. Tliey show a well developed cleavage, and often 

 a zonal and also a beautiful hourglass structure. The orthopinacoidal 

 twinning is seen on some of the plates. Large well formed crystals of 

 apatite are present. Yellowish brown stains of iron oxides traverse' the 

 groundmass and line the cavities with banded layers. 



Specimens were collected from a few of the small islands lying directly 

 west of Viti Levu which appear to belong to the more acidic end of the 

 andesitic group of rocks. 



Andesite from Malolo. 



Malolo is a small low island lying near the west coast of Viti Levu. 



The rock from this island is compact, holocrystalline, and of a lead 

 gray color. It has a feebly polarizing feldspathic base in which frayed 

 out rods of feldspar occur, giving the rock a trachytic appearance. The 

 small laths of feldspar show less than 5° extinction angles. A few 

 small patches of chlorite in bright grenu plates occur. The specimen is 

 from the surface, and appears as if it had been exposed to the action of 

 the waves, by which its original condition has been changed into a felsitic 

 appearing rock. Magnetite is present in grains. 



Andesite from Vatu Mbulo. 



Vatu Mbulo is a mere projecting rock above the water, belonging to 

 the Malolo group. In appearance the specimen from this island is very 

 much the same as the preceding. It has the same compact felsitic 

 a[)pearance, with a lead gray color, and seems also to have been altered 

 by the constant exposure to the waves. Under the microscope, however, 

 it shows a few phenocrysts in the base. The groundmass is a mixture of 



