XVI THE WAINIKORO PLAINS 227 



and south-west of the village of Wainikoro. Here prevail white 

 acid tuffs often decomposing and altered by the formation of 

 secondary quartz. They are derived from the degradation of 

 quartz-porphyries or rhyolitic rocks. The surface is irregular but 

 the elevation is small, the 100- feet level lying about one mile and 

 the 200-feet level about two miles west of Wainikoro. 



The villages of Wainikoro and Kalikoso are from two to three 

 miles apart, the intervening district not attaining a greater elevation 

 than 70 feet above the sea. Decomposing altered white acid tuffs 

 here occur with occasional large blocks, a couple of tons in weight, 

 of apparently a quartz-porphyry or trachyte with its structure 

 disguised by silicification. Fragments of siliceous concretions, as 

 chalcedony, chalcedonic flints, &c., lie on the surface, the soil being 

 friable and of a deep ochreous red ; whilst in places the ground is 

 covered with round marble-sized concretions composed of a mix- 

 ture of carbonate of iron and limonite which I have described on 

 page 356. A few hundred yards to the north-west of Kalikoso, 

 where there is a little rise, a decomposed quartz-porphyry is ex- 

 posed displaying rounded crystals of quartz fractured in position, 

 the matrix of the rock being impregnated with chalcedony. In one 

 part of this mound there is a friable white rock, composed of a 

 crumbling mass of small irregular quartz-grains, rarely showing 

 crystal-faces. It appears to be disintegrated quartz-felsite. 



In taking the track from Kalikoso to the village of Vungalei, 

 which is distant about 2| miles to the south-east, one traverses 

 after the first mile, where the acid rocks terminate, a rather 

 more elevated region which rises to a maximum height of 

 180 feet above the sea. Though the acid rocks give place to a 

 semi-vitreous pyroxene-andesite as described on page 212, small 

 fragments of chalcedonic flints are frequent on the surface over 

 both areas. The district that intervenes between Kalikoso and 

 the landing-place on the Langa-langa River, about two miles in 

 length, is not more than 30 feet above the sea, and is crossed by 

 small sluggish streams, in the beds of which occur numerous frag- 

 ments of silicified corals, up to 3 or 4 inches in size, belonging to 

 the Porites and Astraean type. In these stream-beds also occur 

 bits of mamillated chalcedony and of onyx, flattish agates, 3 or 

 4 inches across, and pebbles of the compact pyroxene-andesite 

 above alluded to, the last probably derived from the south side of 

 the plains. 



The plains extend in a north-east direction as far as Numbu, 

 which lies between 2| and 3 miles north-east of Kalikoso. The 



Q 2 



