214 A NATURALIST IN THE PACIFIC chap. 



organic remains. In the lowest bed I noticed a little water-worn 

 gravel. Both beds pass gradually into the underlying agglomer- 

 ate ; but their upper limits are well defined and the agglomerate 

 commences abruptly. 



It is thus seen that in the formation of the agglomerates there 

 were two pauses when they gradually gave place to deposits of 

 fine detritus made up of a vesicular basic glass that has since been 

 largely converted into palagonite. Then followed a sudden renewal 

 of the agglomerate-producing process. We can scarcely doubt 

 that the agglomerates, with their scoriaceous blocks, and the 

 palagonite-tuffs are in the main the direct products of volcanic 

 eruptions. The rival claim of marine denudation as the agency 

 concerned can be mostly but not altogether excluded. The 

 agglomerates and tuffs of Mount Vungalei cannot be distinguished 

 from those so often described in the case of the great inland 

 ranges of the other parts of the island, the submarine origin of 

 which is frequently demonstrated by the inclosed organic remains. 

 It would seem that in the instance of Vungalei these deposits 

 took place around the shores of a volcanic mountain that rose 

 above the sea. On page 315 it is pointed out that in Stromboli 

 with its dribbling eruptions we have a good illustration of the 

 manner in which such deposits could be formed. 



My examination of the mountain of Nailotha was restricted 

 to the lower slopes up to an elevation of 600 feet ; but the results 

 obtained are very suggestive. When following up the stream- 

 course on the way from Tembe to the mountain one notices in 

 its bed blocks of a light-coloured rock like a compact quartzite. 

 It is, however, a highly altered oligoclase-trachyte (sp. gr. 2"53) 

 with its structure much disguised by secondary quartz. This is 

 the first intimation one gets, on leaving behind the district of 

 basic agglomerates about Tembe, of the otherwise unexpected 

 character of the acid rocks displayed in the lower part of 

 Nailotha.^ 



A torrent here cuts deeply into the mountain-side. At the 

 base, between 200 and 300 feet above the sea, a bluish-grey rather 

 scoriaceous rock with the steam-pores drawn out to a length of 

 from I to 2 centimetres, is first exposed. Its specific gravity 

 after allowing for the cavities is less than 2'6. It shows a 

 groundmass partly disguised by secondary quartz and containing 

 numerous small vesicles lined by quartz and filled with viridite 

 and epidote. Where the alteration is less advanced small parallel 

 ^ The general characters of these rocks are described on p. 308. 



