GKOLOCICAL ()HSK1{\ Al IONS IN 11.11. I I I 



2. Ba.'ioll.f composed cliic/li/ of Aiigitr (Uid IrUl.sjxir with Olivine. 

 The basalts characterized hy ohvine were collected Iroiii the south- 

 eastern or deeply dissected side of IMI)eii}i,ha, at Ndakuni and 

 Ndakuinibengha. 



They are Aery similar in general appearance to the types just de- 

 scribed; though a glassy ground-mass appears in only one s])eciinen. 

 The typical rock is greenish l)lack in color, compact and porphyritic 

 in structure. The euhedral olivine phenocrysts are 8 to 10 mm. in 

 diameter. The angite phenocrysts, in cases corroded, are about the 

 same size or smaller. Zoned labradorite, (Ab^DAn.-is to Al)3oAn7o) is 

 present but is often indistinct in tlu> hand specimen. The ground- 

 mass is usually ophitic. 



3. Basalt composed of Augite and Feldspar with Ilornhlende. Some- 

 what east of the center of the southern coast of ]\Ibengha, a consider- 

 able bay indents the island. The town of Natheva lies at the head 

 of the bay. Near its center and around its sides there outcrops a 

 porphyritic hornblende basalt. The hornblende phenocrysts are 

 largest (8 to 12 mm. long) at the east side of the bay and decrease in 

 size to the west. The other phenocrysts are euhedral angite and 

 labradorite, Ab4oAn6o. The augite occurs in sharply euhedral crystals, 

 showing the forms (001), (010), (100) and (Oil).' The crystals are 

 elongated parallel to c. The hornblende is a basaltic variety, pleo- 

 chroic, chestnut-brown to yellow. The crystals are surrounded bq 

 an opaque rim of magnetite with some augite.^ 



III. Rocks from the Yasawa Group. 



Very few of the Yasawa Islands were A'isited. Volcanic rocks were 

 collected from but two islands, Nathula and Arawa, a small island 

 just west of Yasawa-i-lau. 



Nathula yields only basalts of quite imiform composition. Arawa 

 is composed of agglomerates. All the regular boulders from the 

 agglomerate appear to be very similar. The specimen collected was a 

 hornblende andesite. 



1. Basalt. The specimen was collected from a flow interbedded 

 with agglomerates near sea-level at the southwestern corner of 

 Nathula. 



The rock is greenish black in color, holocrystalline and porphyritic. 



2 Cp. Guppy, 1903, p. 306. 



