112 A NATURALIST IN THE PACIFIC ch. vii 



since been destroyed by the denuding agencies ; and its situation 

 is alone indicated by the " neck " of basic lava-rock that forms the 

 peak of Navuningumu. 



A very long period must have elapsed since this last stage in 

 the activity of the vent. The clays containing pteropod-shells and 

 tests of foraminifera, with which the basic pumice tuffs and the 

 acid agglomerates were interstratified, are now about i,ioo feet 

 above the sea, and are situated in the centre of the island. During 

 the emergence the denudation of the new land-surface was no 

 doubt very great ; and these submarine clays and tuffs, as displayed 

 in the cliffs, owe their preservation in great part to the protection 

 of the overlying mass of agglomerate. 



Much light is thrown on the history of the whole Ndrandramea 

 region of acid andesites by the examination of this old volcano of 

 Navuningumu. Some of the hills, as in the case of Ngaingai and 

 Wawa Levu, seem to have been stripped of everything that could 

 give information to the geologist. Others again, like those of 

 Thoka-singa and Ndrandramea, display here and there on their 

 slopes agglomerates of the same materials, the rounded forms of 

 some of the blocks being in part indicative of marine erosion 

 during the emergence of this region from the sea. In Soloa Levu, 

 however, we have one of these hills partially surrounded by 

 later basaltic flows and covered in places on its lower slopes by 

 basic tuffs and agglomerates, probably submarine. In Navu- 

 ningumu the original mass of acid andesite is only scantily ex- 

 posed. It is for the most part buried beneath submarine clays 

 which are in their turn covered by the tuffs and agglomerates of 

 later basic eruptions. 



