118 FOYE. 



3. Rocks from the Savu Savu Bay District. 



a. Hypersthene Basalt. Along the seaward side of the peninsula 

 forming the southeastern boundary of Savu Savu Bay, there are 

 several masses of elevated limestone. The largest mass is cut by a 

 river-valley broadening toward the sea. The western remnant, near 

 the village of Nandi, is underlain by a basalt flow and calcareous 

 agglomerate, passing upward into conglomerate and the coralliferous 

 limestone mentioned. The change from volcanic activity to the de- 

 position of coralliferous limestone was accomplished in a comparatively 

 short time. Specimens were collected from the underlying flow and 

 from a boulder enclosed in the limestone. They were found to be 

 identical. The specimen from the flow will be described. 



The rock is iron-black in color and shows needles of feldspar (5 

 to 8 mm. in length) abundant in an aphanitic ground-mass. Occa- 

 sional phenocrysts of augite are found and an inclusion of silicified 

 limestone. 



All the phenocrysts are euhedral or subeuhedral. An older gener- 

 ation of feldspar phenocrysts is much clouded by inclusions of glass. 

 They show renewed growth. The augite phenocrysts are on the 

 contrary resorbed. One augite crystal has a core of hypersthene. 



The zoned feldspars show the following composition: — 



Outer zone andesine, AbesAusy 



Central zone labradorite, Ab47Ano3 



Inner zone basic labradorite, AbasAnea 



The average feldspar is medium labradorite. 

 The structure of the ground-mass is hyalopilitic. 



b. Basalt. The ridge between Savu Savu and Xatewa Bays near 

 Valanga is composed largely of agglomerates interbedded with flows. 

 The agglomerates are olive-gray in color and are composed of ash 

 with angular bits of olivine basalt. On the other hand, the specimens 

 of flow rock lack olivine. 



The flow rock is slate-gray in color and consists of abundant, 

 small, augite phenocrysts, 2 to 3 mm. in length, set in an aphanitic 

 groundmass. Feldspar (Ab45 Anss) laths of the same size are so like 

 the ground-mass in color that they are indistinct in the hand 

 specimen. 



