130 A NATURALIST IN THE PACIFIC chap. 



The incrusting submarine deposits found in patches over these 

 plains are generally calcareous clay-rocks containing tests of forma- 

 minifera and often also univalve, bivalve, and pteropod shells. They 

 are referred to the foraminiferous mud-rocks described on page 321. 

 Such deposits are properly dark-coloured ; but as exposed at and 

 near the surface they have often lost by hydration most of their 

 lime, and have acquired by the removal of the iron oxides a 

 whitish or pale-yellow appearance, whilst they have a peculiar 

 soapy " feel," on account of which they are generally known as 

 " soapstone " amongst the whites. Streams flowing through such 

 districts have a somewhat milky colour. These deposits are ex- 

 tensively represented on the slopes of the Sarawanga valley, and 

 especially to the east of the town of that name. They are well 

 displayed on the way from Sarawanga to Tembe-ni-ndio, and are 

 also to be seen on the surface of the plains between Lekutu and 

 the Mbua-Lekutu watershed to the southward. 



In the vicinity of Sarawanga they attain an elevation of 200 feet 

 above the sea ; but they may be traced in patches up to 500 feet 

 on the adjacent slopes of the acid andesite region of Ndrandramea. 

 Near the river, and less than 100 feet above the sea, these deposits 

 are in one place overlain by an agglomerate formed of large blocks, 

 I to 2 feet across, of these Ndrandramea andesites and dacites. In 

 another place, near the town of Sarawanga, I found them exposed 

 in the river-bank, where they were covered over by a coarse pala- 

 gonitic bedded tuff, dipping gently eastward and somewhat cal- 

 careous. From the character of the shells of marine univalves 

 inclosed in this tuff, it appears to have been formed in shallow 



water. 



A very interesting display of these surface marine deposits 

 occurs in the upper part of the Sarawanga valley in the vicinity ot 

 Tembe-ni-ndio. Here we have fine and coarse calcareous pala- 

 gonitic tuffs, containing tests of foraminifera, associated with im- 

 pure foraminiferal limestones. They occur up to elevations of 

 300 feet above the sea on either side of the Sarawanga valley 

 above this town, incrusting on the north side the lower dacitic 

 slopes of the Ndrandramea district, and on the south side the 

 lower basaltic slopes of Seatura. At the bottom of the valley, as in 

 the rising ground between Tavua and Tembe-ni-ndio, they conceal 

 in part the basaltic rocks of the district. 



Near the last-named place, on the right bank of the Tembe-ni- 

 ndio branch of the Sarawanga river, the foraminiferal limestones 

 are displayed in low cliffs 15 to 20 feet in height. They are some- 



