4C8 THE GEOLOGV OF THE NEW HEBRIDES, 



The island is roughly 18 miles long by 10 miles broad, with 

 an area approximately 150 sq. miles. The general direction of 

 the land-surface agrees with that of the central range of hills, 

 and trends to the KN.W. and S.S.E. The Admiralty chart 

 indicates the maximum height attained as about 3500 ft. 



As we were not able to land on this interesting island we 

 quote from reports by the Rev. W. Gray and others, who state 

 that it is composed mainly of volcanic material such as scoria 

 and agglomerate, but that at the north end the soil seems to be 

 derived from sedimentary rocks. Raised coral reefs are stated 

 to occur along part of the east coast, round the north end, and 

 down the west coast, attaining a maximum elevation in the 

 latter locality where they appear at heights of over 100 ft. 



Professor A. Liversidge has recorded the analyses of three 

 samples of Tanna lava.* These specimens appear to have been 

 chocolate-coloured to black glassy lavas, for the most part highly 

 vesicular to a degree approaching that of pumice, carrying 

 porphyritic glassy crystals of felspar. 



A specimen of a similar lava from Tanna, preserved in the 

 Sydney University Geological Museum, contains porphyritic 

 albite crystals (R.I. 1-535); the lava is therefore an andesite. 



Aniwa is a small island about 4 miles long by 2 miles wide, 

 situated 12 miles E.N.E. of Tanna. 



The Rev. W. Gray has reported raised coral limestone from 

 this island, and as it attains a height of only 140 ft., it is 

 probable that the whole of the land above sea-level is built up of 

 raised reef-material. 



The same author has reported native traditions to the effect 

 that a volcano previously existed on the island, and that it was 

 once connected up to the south end of Tanna by a land-bridge. 

 If such be true it would partially reconstruct what might once 

 have been a huge crater ring, the island of Tanna representing 

 the western side only. To settle this point it would be interesting 

 to run a line of soundings to the eastward of Tanna over this 

 submerged bank, if such exists at all. 



* Journ. Proc. R. Soc. N. S. Wales, xx. 1886, 236-237 [1887]. 



