5 6 A NATURALIST IN THE PACIFIC chap. 



The Mbua and Ndama plains form a continuous region extend- 

 ing three to five miles inland to the foot of the great mountain of 

 Seatura, to the watershed between Mbua and Lekutu, and to the 

 base of Mount Koroma ; whilst it reaches along the sea border 

 from the vicinity of Navunievu about four miles west of the Mbua 

 River to beyond Seatovo a few miles south of the Ndama River. 

 Their extent is defined in a general sense by the 300 feet contour 

 line in the map. Their elevation, however, above the sea does not 

 generally exceed 200 feet and is usually only 50 or 100 feet ; but 

 at the foot of Seatura they rise to between 300 and 400 feet. 

 Whilst on the one side these plains form a continuation of the 

 lower slopes of the great Seatura mountain, on the other side they 

 are extended under the sea as the broad submarine platform, the 

 edge of which, as defined by the 100-fathom line, lies eight to ten 

 miles off the coast. It is pointed out on page 372 that this continuity 

 of surface, both supra-marine and submarine, extends probably to 

 the geological structure and that the submarine platform represents 

 the extension under the sea of the basaltic flows of the plains. 



The whole region of the plains is occupied by olivine-basalts 

 and basaltic andesites, such as are found on the neighbouring lower 

 slopes of the Seatura mountain. They are as a rule much de- 

 composed, even at a depth of several feet below the surface. 

 Typically, they are neither vesicular nor scoriaceous, and in this 

 respect they possess the character of submarine lava-flows. The 

 rolling surface of the plain is varied occasionally by small " rises " 

 or hillocks marking apparently some secondary cone, of which the 

 much degraded " wreck " alone remains. Here and there fragments 

 of limonite, approaching haematite in its compact texture, lie in 

 profusion on the soil, representing doubtless small swamps long 

 since dried up, some of which still occur in the hollows of the 

 plain. Mingled with these fragments are often pieces of siliceous 

 rocks and concretions, such as are found in the other " talasinga " 

 districts of the island, the description of which is given on 

 pages 128, 132, &c. 



I will now refer more in detail to some of the points alluded to 

 in this short description of these plains. With reference first to the 

 compact limonite, it should be remarked that it occurs on the sur- 

 face either as fragments of hollow nodules two or three inches 

 across, or as portions of flat " cakes " half to one inch thick. It 

 is especially abundant in the district lying a mile or two on either 

 side of the Navutua stream-course between Ndama and Mbua. 

 Here the subsoil is charged with ferruginous matter, and the water 



