406 THE GEOLOGY OF THE NEW HEBRIDES, 



When making a call on the northern coast of the island a very 

 strongly developed volcanic agglomerate could be seen forming 

 some low cliffs close by the shore. What, in the distance, 

 appeared to be a similar agglomerate forms a small knob"^ just 

 to the south of the Mission Station at Anelgauhat. 



From what we have been able to ascertain, therefore, Aneityum 

 represents the remains of an ancient volcano of the same age 

 probably as Mau and others further to the north. The northern 

 boundary of the old crater ring appears to be represented by the 

 existing chain of hills; the southern portions do not appear, due 

 to denudation and other causes. 



The absence of raised coral reefs demonstrates the fact that 

 regular upheaval, such as is strongly evidenced in the more 

 northerly islands, has not visited this region to the same extent; 

 the conditions being probably that of stable equilibrium or very 

 slow subsidence allowing of the silting up of old lagoons and tha 

 formation of a comparatively wide 100 fathom belt. 



1. Olivine Basalt Porphyrite outcrops a few hundred yards 

 behind Wilson's store. 



Macroscopic Character s. — A compact dark greenish- 

 grey-coloured rock, with porphyritic individuals of pyroxene and 

 olivine standing out conspicuously in a dark base of finer texture. 

 Steam holes are developed to a slight extent only. 



Microscopic Character s. — A holocrystalline porphy- 

 ritic rock. The porphyritic felspar individuals are even-sized 

 and rectangular, about O'GxO'-imm.; they contain numerous 

 regularly included fragments of magnetite and black glass, and 

 exhibit very perfect polysynthetic twinning after the albite law 

 with an extinction angle referring them to the more basic labra- 

 dorites. Large porphyritic 'pyroxenes 0*5 cm. diameter represent 

 about 10 % of the rock, and another 5 % is represented by idio- 

 morphic crystals of a pinkish olivine 0'8 mm. diameter. The 

 hase^ which is present to the extent of abont 15 % of the rock, is 



* Since returning we have heard that M. Pelatan had described the rocks 

 of this hill as being similar to New Caledonian serpentines. The source of 

 the information, however, cannot be located. 



