46 



A NATURALIST IN THE PACIFIC 



CHAP. 



The form of this hill is well shown in the sketch attached, and 

 there is little doubt that we have here an old volcanic " neck," the 

 remains of a submarine vent. 



A specimen of the tuff from the summit is made up of com- 

 pacted fragments, in size ranging up to one third of an inch, of a 

 bottle-green vacuolar glass, which fuses readily in a lamp-flame 

 and is not dissolved by hydrochloric acid. This glass is usually 

 isotropic, but much of it is also palagonitic and feebly refractive, 

 the vacuoles or steam-holes, which are often elongated, being in the 

 last case filled with the same palagonitic material. Plagioclase 

 crystals occur macroscopically in the glass ; they are much eroded 

 and contain numerous large inclusions both of the clear isotropic 

 glass and of its palagonitised form. 



About a third of a mile west of the Korolevu hill rises the hill of 

 Ngangaturuturu, 450 feet high, which presents a precipitous cliff- 



faced summit in which are exposed basic tuffs showing pyroxene 

 crystals projecting from the weathered surface. 



The Bomb Formation of Navingiri. — A mile north-west of 

 Korolevu Hill, where the coast road crosses a spur at the back of 

 Navingiri, a very curious formation is exposed at an elevation 

 somewhat under 200 feet above the sea. Here there are to appear- 

 ance a number of large more or less spherical volcanic bombs, two 

 to three feet across and formed of a semi-vitreous scoriaceous basalt, 

 imbedded in a hyalomelan-tuff displaying the same microscopical 

 characters as in the case of the tuff forming the adjacent hill of 

 Korolevu. 



The ash is light grey in colour and rather friable ; but where 

 in contact with the bombs it becomes darker and is hardened. 

 The steam pores of the bombs are round and not elongated ; and 

 as is usual with these bodies they increase in size from the outside, 

 where they are very small (i millimetre and less), to the centre. 



