BY D. MAWSON. 427 



smaller olivines 5 %, much decomposed and stained red by iron 

 oxide; large magnetite grains 3 %. The base is largely glassy, 

 but contains particles of plagioclase, augite, olivine, with abundant 

 magnetite dust. 



Torres or Vava Islands. — The approximate dimensions of 

 the four main islands are : Toga or South Island — 3 miles long, 

 area 5 sq.miles, height 896 ft. Lo or Saddle Island — 2>\ miles 

 long, area 4 sq.miles, height 390 ft. Tegua or Middle Island — 

 4 miles long, area (with Ovale I.) 7 sq.miles, height 640 ft. Hiu 

 or North Island — 7 miles long, area 14 sq.miles, height 1230 ft. 



The islands of this chain preserve a W.N.W. trend, and are 

 separated b}'- narrow channels about 2 miles wide; they appear 

 to be a continuation of the western arm of the New Hebrides. 



Time did not allow of a detailed examination, and general 

 impressions only can be- given. 



They appear to be wholly composed of a coralliferous limestone 

 formation rising up in terraces to a maximum elevation of 1230ft. 

 All the rocks examined were coral limestones, but, no doubt, 

 these are underlaid shortly below by tuffaceous foundation-beds. 



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Fig.3. General outline of Hiu, Torres Group; looking from the south. 



The woodcut (text-fig. 3) was sketched from the deck of H.M.S. 

 'Archer' while steaming along the south coast of Hiu, and affords 

 a general idea of the topography of the Torres Islands. 



Sec. 2. VULCANOLOGY AND SEISMOLOGY. 



Active Volcanoes. — The volcanoes of the New 

 Hebrides have attracted more attention from visitors than have 

 any of the other physical features, and as a result numerous 

 descriptions are on record. 



Included within the region of our explorations are the two 

 permanently active volcanoes of Yasowa and Ambrym. Further 



