194 A NATURALIST IN THE PACIFIC chap. 



It is probable that this singular deposit represents a submarine 

 accumulation of materials ejected from some neighbouring vent. 

 Organic remains did not come under my notice ; but apart from 

 the palagonitic character of the matrix and the abundance of veins 

 of calcite, the submarine origin is indicated by the existence of 

 upraised reefs in the coast districts east and west of this locality. 

 The block of diorite affords an important clue as to the character 

 of the deep-seated plutonic rocks in this part of the island. A 

 similar diorite was found by me amongst the blocks in the bed of 

 the Vunimbua River ; and on page 185, reference is made to the 

 probability of such rocks forming the nucleus of the Valanga 

 Range. 



The hills on the west side of the Salt Lake are worth further 

 examination. On the coast of the Natewa Bay side of this 

 district, in the vicinity of Vuni-tangaloa and between that place 

 and Vuni-sawana, there are displayed agglomerates formed of 

 blocks of hornblende-andesite, some of the specimens being very 

 similar to that obtained from the block of hornblende-andesite 

 noticed in the agglomerate-tuff on the neighbouring south coast. 



The Salt Lake 



The low isthmus, about 2^ miles in breadth, which connects the 

 Natewa Peninsula with the rest of the island, can be crossed without 

 rising more than 40 or 50 feet above the sea. From the occur- 

 rence of upraised reefs in the islets and in the low sea-cliffs of the 

 south coast it may be inferred that at no distant period in the history 

 of Vanua Levu this isthmus was submerged. 



The lake, which is oblong in form, is about four-fifths of a 

 mile long and about two-fifths broad. Its maximum depth 

 according to the Admiralty chart is 3 fathoms ; but the usual 

 depth in the centre varies, as I found, between 2 and 2i fathoms. 

 It communicates with the sea on the south coast by a long narrow 

 passage, rather over a mile in length, which for the greater part of 

 its course, excepting near its seaward mouth, is only between 25 

 and 30 feet broad. Mangroves flourish around the lake and also 

 line the passage ; whilst elevated reef-rock is to be observed on 

 the sides of the passage. Mr. Home was informed that corals 

 abound in the lake-waters ; but I find no reference to this point in 

 my notes. Judging from the density of the effluent water, the 

 specific gravity of the lake-water is that of the sea. The " rise 

 and fall," as noticed below, is considerably less than in the case of 

 the tides at the coast. 



