38 A NATURALIST IN THE PACIFIC chap. 



with algae occur, as at Savu-savu, Tambia, and Nukumbolo. Its 

 composition varies a little in different localities. At Savu-savu it 

 is compact and laminated and formed almost entirely of hydrated 

 amorphous or colloid silica. At Mbati-ni-kama the siliceous sinter 

 is more friable, with a tendency to form opal. The sinter of the 

 Nukumbolo springs resembles that of Savu-savu ; but it also con- 

 tains a good proportion of carbonate of lime (20 per cent.) in a 

 granular form, and that of Tambia has the same characters. It 

 is not unlikely that this lime is derived from the decayed shells, 



such as I have referred to in the case of the Tambia springs 



It may be here observed that Mr. Weed and others, who have 

 studied the origin of siliceous sinter in the Yellowstone region 

 and elsewhere, regard it as the secretion of algae, mosses, &c., that 

 grow in hot waters {American Journal of Science, vol. 37, 1889). 



I come now to some general considerations respecting the hot 

 springs of Vanua Levu. In the first place there is the singular fact 

 that the inland hot springs nearly always make their appearance 

 along the present lines of surface-drainage. But I do not gather 

 that the hot springs are of more recent origin than the rivers and 

 streams, by the side of which they rise. On the contrary the hot 

 springs are probably far older. The conditions of subterranean 

 drainage that favour the formation of springs at the surface, whether 

 cold or thermal, would no doubt often determine the direction of 

 surface drainage in a newly-formed land. Those familiar with 

 modern volcanoes will recall the absence or rarity of streams and 

 rivers, and the frequency often of cold and thermal springs at and 

 near the coast, which are sometimes of such bulk at the exits that 

 the expression " subterranean river " would be nearly appropriate. 

 The presence of artesian reservoirs may also in some localities be 

 safely assumed. I will here draw a little on my own experience of 

 volcanic regions. 



On the lava-bound coasts of the riverless southern portion of 

 the large volcanic island of Hawaii, the subterranean waters issue 

 as cold and thermal springs at numerous localities. At Punaluu, 

 and at Ninoli, a mile to the westward, there are extensive fresh- 

 water springs at and near the beach which have a temperature of 

 64" F. all through the year,i those at Ninoli issuing as a large 

 subterranean stream. East of Punaluu and at intervals along the 

 Puna coast, springs of water, sometimes fresh and cold with a 



1 I took the temperature at monthly intervals between October, 1896, and 

 September, 1897. The mean annual temperature of the air in the shade would 

 be about 64° at an elevation of between 3,000 and 4,000 feet. 



