CH. VI WAINUNU TABLE-LAND 83 



shown. On the left is the foot of the Seatura basaltic slope ; on 

 the right is the Wainunu basaltic table-land ; and between them lie 

 the estuary and valley of the Wainunu, at the back of which appears 

 the " Na Savu " table-land, formed of basic tuffs and agglomerates. 

 Behind all there rise up suddenly the Ndrandramea mountains 

 formed of acid andesites ; whilst in the foreground to the right 

 is the hill of Ulu-i-ndali, which is composed in the mass of a grey 

 basalt of a type quite different from the blackish basaltic rocks 

 of the Seatura slope and of the Wainunu table-land. It was from 

 this view off the mouth of the estuary that I received my first 

 lesson in studying the structural formation of the island. I kept 



Profile, looking north from ofiF the mouth of the Wainunu River. 



T Inland Fdran'draniea MotmLains 



Seatura Slope 'Wainuna Wainunu Ulu-i-ndjli 



Estuary- Tabldand. 



it always in my mind's eye, and for months in an almost unmapped 

 region it was my only guide. 



The gradual slope of the Wainunu table-land from an eleva- 

 :ion of 1,100 or 1,200 feet in the interior to 700 or 800 feet near 

 :he coast has already been referred to. Beyond this lower limit 

 t descends much more rapidly and within less than a mile it 

 erminates at Masusu in a steep-sided declivity 300 feet high 

 ')pposite Ulu-i-ndali, and in a gentler slope on the eastern side in 

 ihe Ndranimako district. Its somewhat undulating surface is well 

 ^ v^ooded ; but on account of the small gradient the small streams 

 < in the table-land do not excavate deep channels, but flow slowly 

 c long in shallow courses and often stagnate in swampy land where 

 1 lie interesting "Scirpodendron costatum," the giant-sedge, flourishes. 

 ] n their beds occur reddish flinty concretions, up to 3 inches across 

 i 1 size, and magnetic iron sand in great abundance. A sample of 

 tiis sand roughly washed on the spot contains JJ per cent, of 

 r lagnetic iron.^ 



Basaltic rocks, often exhibiting a columnar structure, are ex- 

 \ Dsed at intervals on the surface and slopes of this table-land all 

 c/er its area. Now and then when traversing this region one 



1 The flinty concretions are described on page 354, and the iron sand on 

 P 356. ^ 



G 2 



