BY D. MAWSON. 423 



oldest rocks encountered being volcanic agglomerates underlying 

 the fossiliferous Miocene series. 



AoBA occupies a position midway between the eastern and 

 western wings of the Group. It is oval-shaped with the following 

 appi-oximate dimensions : — Length, 25 miles; breadth, 8 miles; 

 area, 105 sq. miles. 



There is a little low-lying land, undulating in character, at 

 either extremity of the island; for the rest it rises steeply 

 to a height of 4000 ft., at which elevation the natives report the 

 existence of a shallow lake, no doubt occupying the position of a 

 former crater. 



The island, so far as ascertained in our short visit, is 

 entirely volcanic, and cannot long have been extinct. Specimens 

 collected of the volcanic rocks were tuffs, agglomerates, and 

 vesicular and porphyritic basic lavas, conspicuous amongst which 

 were olivine basalts bearing olivines one-third of an inch in 

 diameter, and porphyritic pyroxene olivine basalts. 



The fragmentary types of rocks proved to be much more 

 abundant than solid lavas; the former being specially abundant 

 at the eastern and western extremities of the island. 



A very fine example of bedded tuffaceous ash-beds is to be 

 noted at the north end of Bice Roads, where they appear well 

 bedded, dipping 12° S., 45° W., and overlie solid lava. The finer 

 material constituting these beds is of the nature of pulverised 

 volcanic rock; distributed through this base, in roughly parallel 

 bands, are pebbles and boulders, up to 2 ft. in diameter, of 

 various types of basalt. No raised coral was observed on the 

 island, though growing reefs fringe the south-east shore. 



Aragh Aragh or Pentecost Island extends northward of 

 Ambrym, forming part of the eastern wing of the Group, which 

 continues through the Island of Aurora to the Banks Group. 



The island is long and narrow, with a greatest length of 35 

 miles, breadth 6 miles, and approximate area of 125 sq.miles. 

 A high ridge attaining a maximum elevation of 2500 ft. runs in 

 a north and south direction, forming a backbone to the island. 

 Its rugged aspect bears the semblance of a volcanic island. 



