586 1>E0CEEDINGS OP THE AMERICAN ACADEMY. 



seen in the more acid varieties of the andesites, and therefore ajjpears in 

 but two or three of the rocks from this region. Magnetite is common as 

 fine dust particles and occai^ionally as anhedrons. A few apatite prisms 

 occur in the feldspars. 



HORNBLENDE-ANDESITE FROM KaNUAVD. 



Kandavu is an irregularly shaped island, stretching northeast to south- 

 west about thirty-two miles long and quite variable in width, lying south 

 of Viti Levu. It is of volcanic origin and has several elevated peaks, 

 that of Mbuke Levu or Mt. Washington, 2,750 feet, being the highest. 



Specimens from this mountain are light gray in color, and have plieno- 

 crysts of feldspar and hornblende distinctly visible in a glassy base. 



Under the microscope the grouiidrnass is seen to be a thick filz of 

 feldspar rods with much magnetite in grains, in a colorless glass, the 

 structure being hyalopilitic. The phenoci-ysts are miiinly plagioclase and 

 hornblende. 



The feldspar pheuocrysts occur in automorphic plates with a zonal 

 structure. The extinctions of these zonal layers show also a passage 

 from acid rims to basic centres. The small rods of feldspar in the 

 groundmass usually extinguish under 5°, making oligoclase the main 

 feldspar. A lew of the large plates contain glass and gas inclusions. 



Hornblende is present in yellowish green to deep green pleochroic 

 basal and prismatic sections, having perfect boundaries. Some of the 

 plates are twinned on the orthopinacoid and some show resorption borders. 

 Stout apatites are included. A little calcite has been formed from the 

 alteration of the hornblende. 



Biotite is seen in one or two flakes only, showing that it is a rare 

 accessory. A few grains of very pale green, almost colorless pyroxene 

 also occur, probably a diopside ; a few anhedrons of magnetite and some 

 basal and prismatic sections of apatite constitute a part of the accessories. 



A specimen collected from the John Wesley bluff, which is on the 

 north shore of the southern half of the island, near Tavukie, is an ande- 

 sitic tuff, showing remains of hornblende crystals whose contents have 

 been altered to chlorite and calcite with a separation of magnetite, em- 

 bedded in a dusty amorphous base. Considerable tridymite has formed 

 along the fractures in the rock and in cavities. 



Kandavu is the only island of the group besides Viti Levu from 

 which specimens were collected, which have been previously described by 

 Wichman. A description of the hornblende andesite from Mt. Wash- 

 ington is given by him. 



