436 THE GEOLOGY OF THE NEW HEBRIDES, 



and general dip of the rough bedding planes of the agglomerates 

 at the north-east corner of the island, we were early led to con- 

 sider Undine Ba}" as the remnant of an old crater whose lip 

 ringed in the islands of Nguna and Mau, which, on this hypothesis, 

 would be daughter-cones standing in the old crater, as do Mts. 

 Benbow and Marum in the crater of Ambrym. 



Although the evidence supporting this view seemed at first 

 sight conclusive enough, yet, when further attention was paid to 

 the character of the rocks, it was at once evident that the 

 Undine Bay agglomerates are, for the most part, to be referred 

 to the later basic eruptions, and could not be reconciled with the 

 andesitic pumice tuffs of Havannah Harbour and elsewhere. 



It seems probable, therefore, that several smaller vents now 

 largely obliterated by later extravasations of more basic lavas and 

 agglomerates, contributed to the earlier series of andesitic 

 eruptions. One of these craters must have been situated in the 

 vicinity of Havannah Harbour. 



ii. Coarse Pumice Tuffs. — A coarse tuff composed of 

 fragments of an ashy-grey pumice with occasional pieces of a 

 dark-coloured glass forms the base of the series At Havannah 

 Harbour (see Section, Plate xxiv.) where these beds are so well 

 developed, they are coarsest at sea-level, containing fragments 

 up to 4: inches diameter; above, at an elevation of several hundred 

 feet, they pass into a finer-grained rock which has all the essential 

 characters of the Fiji soapstone; this succession is repeated 

 several times at higher levels. Examination has shown that 

 these tuffs are referable to an andesite lava; the fragments are 

 in every respect similar to the light grey pumice found at the 

 present day drifting in the Pacific, derived from submarine 

 volcanoes distributed along the great fold-area further to the 

 east. Analysis of some of the perlitic glass (Sec. 3, §5) contained 

 in these tuffs shows that it is similar in composition to the 

 pumice, though slightly more acid. 



iii. The Soapstone Series. — The fine-grained beds noted 

 in the last paragraph as being similar to the .soapstones of 



