232 A NATURALIST IN THE PACIFIC chap. 



The rock is a dark-grey augite-andesite with a specific gravity of 

 277. It is compact and has a hemi-crystalline groundmass. 1 



(b) The south coast between Mount Thuku and Moala, a distance 

 of about Jive miles. — Pumice-tuffs and agglomerates are displayed 

 at the coast, the former often bedded and in one place having a 

 dip of 35 or 40 degrees to the north. A quartz-porphyry, some- 

 what banded and a little altered, and displaying rounded quartz 

 crystals 3 or 4 millimetres in size, is the prevailing massive rock 

 exposed on the hill-slopes and occasionally at the coast. It is 

 well exhibited about a mile east of Mount Thuku. Blocks of a 

 grey oligoclase-trachyte also occur. These rocks are described on 

 pages 308, 309. 



(c) The terminal portion of the promontory from Nuku-ndamu 

 and Moala to Undu Point. — The same pumiceous tuffs, usually 

 non-calcareous, form the shore-cliffs on the south coast from Moala 

 to Mr. Bulling's station at Ndothiu, which lies about 2 miles from the 

 point. On the corresponding part of the north coast between Nuku- 

 ndamu and Ndothiu these tuffs are often calcareous ; and near the 

 first-named place they contain sub-angular bits of coral of the size 

 of a walnut. On the beach at Vunikondi in this locality they are 

 overlain by nearly horizontal beds of basic lava, the upper sur- 

 face of which when exposed displays the smooth, " ropy " crust 

 of a lava flow. The rock is a dark slightly vesicular augite- 

 andesite, hemi-crystalline in structure, and containing a fair amount 

 of residual glass. 2 Since the underlying tuffs were evidently 

 deposited on a sea-bottom, it follows that this is a submarine 

 flow. I intended to revisit this locality, but was prevented. A 

 detailed examination of it would be worth undertaking. 



From Ndothiu to Undu Point, about 2 miles distant, the 

 interior of the promontory has an undulating surface, the elevation 

 being usually 200 or 300 feet and rising to 400 feet. On the 

 coasts are exposed bedded pumiceous tuffs, steeply inclined and 

 usually calcareous. As displayed in the hill-slopes of the interior 

 they are horizontally stratified and as a rule non-calcareous. 

 These deposits sometimes exhibit a spheroidal arrangement indi- 

 cative of the proximity of a dyke. In one or two places at the 

 coasts occur basic agglomerates, formed of the same augite-andesite 



1 Referred to genus 13 of the augite-andesites. The felspar-lathes average 

 'I mm. in length, and there is a little interstitial glass. 



2 Referred to genus 16 of the augite-andesites. There are two sets of felspar- 

 lathes in the groundmass ; the larger, "23 mm. long, are more or less parallel ; 

 the smaller, "04 mm. long, form a plexus. 



