228 A NATURALIST IN THE PACIFIC CHAP. 



country between these two places is usually elevated between 

 60 and 100 feet and is never more than 130 feet above the sea. 

 It is known as the Kuru-kuru district. The surface is strewn with 

 the fragments of flints and of a white chalcedonic quartz-rock ; 

 whilst the soil is friable and deep-red in colour, limonite in 

 abundant fragments occurring on the ground. Here and there one 

 passes slabs of a hard white silicified tuff, small portions of which 

 are frequent on the surface. 



Silicified corals and earthy limonite are to be found in abund- 

 ance scattered over the surface of the plains immediately surround- 

 ing the small lake of Vakalalatha. We also find lying on the 

 ground in this district bits of chalcedony and onyx, portions of 

 chalcedonic flints, and nodules of the size of the fist, which when 

 fractured either disclose the regular layers of the agate or radiating 

 crystals of quartz. The silicified corals occur usually in fragments 

 not over 4 inches across, and include portions of branching corals 

 of the Madrepore habit, bits of massive corals of the Astraean 

 type, small rounded nobs of " Porites " just as one commonly 

 observes on a reef-flat, &c. They have an ancient weathered look, 

 and in some cases it is evident from the existence of boring-shells 

 in the fractured end of a branching coral that it once lay as a dead 

 fragment on the surface of a reef-flat. 



In Chapter XXV. the characters of the silicified corals of the 

 island are discussed in detail ; and I have there advanced the view 

 that the extensive silicification of the Kalikoso and Wainikoro 

 plains took place during the consolidation of the calcareous muds 

 of a reef-flat whilst the land was emerging. I have already alluded 

 on page 222 to an area of silicification on the neighbouring sea- 

 border between Visongo and Tutu. There can be no doubt that 

 during the last stage of the emergence the present situation of the 

 fresh-water lake near Kalikoso was occupied by the sea, which 

 also extended far over the surrounding plains. The process of 

 silicification would of necessity be restricted to the period that 

 has since elapsed ; and the discussion is therefore confined to the 

 nature of the conditions under which this change was induced. 

 As a factor in the process we cannot disregard the acid character 

 of the rocks of the district. 



THE UNDU PROMONTORY 



The north-east portion of the island terminates in a long 

 narrow promontory which I have named after Undu Point at its 

 extremity. Commencing at Thawaro Bay and near Tawaki it runs 



