48 A NATURALIST IN THE PACIFIC chap. 



in the central portion of the bomb. Numerous cracks commu- 

 nicating with the round steam-pores, which are much larger than 

 the vacuoles of the ash-glass, are filled with the same yellowish 

 magma-exudation referred to in the case of the rock forming the 

 centre of the bomb. Through the cracks this palagonite-material 

 has found its way into the steam-pores. 



It would appear from the above that the bombs were but 

 partially consolidated when they fell into the bed of ash. The 

 tuff is somewhat " baked " where it is in contact with the bombs ; 

 and there is evidence of a collision between the bombs in the 

 fragments of the vitreous shell imbedded in the ash. Although 

 the ash itself contains no organic remains, there occur, not many 

 hundred yards away and at an elevation lOO feet higher above 

 the sea, foraminiferous tuffs of basic glass which are described 

 below. There is no indication of a crateral cavity in this locality ; 

 whilst the ancient " neck " represented by Korolevu Hill is a mile 

 away. These bombs most probably after being ejected from some 

 sub-aerial vent fell into the sea around, on the floor of which much 

 basic pumice-ash had been previously deposited. Such masses as 

 they sank would lose most of their original momentum. 



Remarkable Section near Korolevu Hill. — Between 

 the hills of Korolevu and Nganga-turuturu, at an elevation of 

 about 300 feet above the sea, there is a singular exposure of tuffs 

 horizontally stratified and forming a low escarpment or line of cliff 

 about 15 feet high on the hill-side. These beds display the passage 

 from basic tuffs below to relatively acid tuffs above, and they 

 establish that in this locality the period of acid andesites followed 

 that marked by the eruption of basalts and basaltic andesites. 

 From their horizontal and undisturbed position, it may be inferred 

 that these deposits began to be formed under the sea when the 

 activity of the submarine basic vents was on the wane. In their 

 composition and in the various degrees of coarseness of their 

 materials, we can plainly discern the history of volcanic action in 

 this locality. 



A hard compacted palagonite-tuff makes up the lower half of 

 the thickness of beds exposed, 1 5 feet in all. The greater portion 

 of it has the uniform texture of a sedimentary rock, fine-grained 

 below where the fragments are "i to "3 mm. in size, and becoming 

 coarser above where the larger measure i to 2 mm. It is composed 

 of more or less angular fragments of a basic vacuolar isotropic glass, 

 and of plagioclase and augite with much fine palagonitic debris. 

 There is no effervescence with an acid ; but in the upper part there 



