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 off the mouth of the Wainunu River. 



£bieSnd Ndrait'dTamea Mountains 



1.^^ 



m 



Seatura Slope 'Wainunu. Wainunu Ulu.-i-ndali 



Estuary. Tableland. 



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- 

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

 the coast has already been referred to. Beyond this lower limit 

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

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

 opposite Ulu-i-ndali, and in a gentler slope on the eastern side in 

 the Ndranimako district. Its somewhat undulating surface is well 

 wooded ; but on account of the small gradient the small streams 

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

 along in shallow courses and often stagnate in swampy land where 

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

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

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

 this sand roughly washed on the spot contains yy per cent, of 

 magnetic iron.^ 



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

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

 over 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 



