184 A NATURALIST IN THE PACIFIC chap. 



shore, some of them, as in the case of the Nambathi promontory 

 on the north side of Valanga Harbour, retaining an elevation of 

 1,000 feet within a few hundred yards of the coast. 



By following the coast-track from the Ndreke-ni-wai River to 

 Valanga one crosses some of these headlands. As far as Vatu-lele 

 altered red tuffs, basic agglomerates, and massive basaltic andesites 

 are the prevailing rocks. The red tuffs exhibit a double alteration. 

 They were originally composed of finely pulverised basic vacuolar 

 glass, which subsequently became palagonitised, and afterwards 

 there was an extensive deposition of chalcedonic silica and of red 

 iron oxide. No organic remains appear to exist ; whilst the scanty 

 calcite present is evidently an alteration product. Where the road 

 " tops " the headland on the north side of Vatu-lele Bay, there is 

 exposed a dyke-like mass of a rubbly semi-vitreous basaltic rock 

 penetrated in all directions by veins, 1 to 3 inches thick, of a 

 tachylytic glass, splinters of which fuse readily in the ordinary 

 spirit-lamp flame. The numerous fissures were doubtless pro- 

 duced during the consolidation of the rock ; and subsequently 

 they were filled with the still fluid residual portion of the magma, 

 which would be composed of the most fusible constituents. This 

 subject, which bears on the origin of palagonite, is discussed in 

 Chapter XXIV. 



Between Vatu-lele and Urata, palagonite-tuffs and basic ag- 

 glomerates are chiefly displayed. On the north slope descending 

 to Urata there is exposed in the foot-path a dyke-like mass of a 

 dark-grey hornblende-pyroxene-andesite, an unusual type of rock 

 which is described on page 298. Just south of Urata I observed 

 an agglomerate containing large blocks, 3 or 4 feet across, of the 

 deeper-seated altered grey pyroxene-andesites that with the 

 gabbros and diorites form the axis of the range. 



(4) The Valley of Na Kula. — In crossing from Sava-reka- 

 reka to Natewa Bay, one ascends the remarkable valley of the 

 Kula and traverses the ridge at its head. This ridge, which is 

 about 700 feet in height and forms the termination of the Valanga 

 Range, is composed of altered grey hornblende-pyroxene-andesites 

 and of similar holo-crystalline rocks representing the gabbro or 

 plutonic type of the same. One of these rocks is described on 

 page 250, under the head of hornblende-gabbro. Another is 

 referred provisionally to the hypersthene-gabbros (page 249) ; but 

 it is extensively occupied by chlorite, viridite, and other alteration 

 products. Here, as with the other rocks of the Na Kula Ridge, 

 the plagioclase phenocrysts are opaque, the result of the numerous 



