360 A NATURALIST IN THE PACIFIC ch. xxv 



In conclusion it may be remarked that those who object to the 

 explanation of the origin of silicified corals advanced in this chapter 

 will be able to find support for their alternative hypothesis in many 

 facts detailed in these pages. Vanua Levu, for instance, abounds 

 in hot springs ; and Mr. Andrews might regard this fact as giving 

 strength to his view that the silicified corals of Vanua Mbalavu in 

 this group owe their condition to the agency of superheated water 

 derived from volcanic rocks, more especially since hot springs are 

 found on the island. Such an explanation could not, I think, apply 

 to the extensive area of the Kalikoso plains where the silicified 

 corals are associated with limonite on the surface of a recently 

 emerged area. If these changes had been induced by hydro- 

 thermal action, one ought to find evidence of this in those localities 

 in Vanua Levu where the hot springs issue from foraminiferous 

 clay deposits, as in the vicinity of Vuni-moli ; but no traces of such 

 a transformation came under my notice. Wichmann does not ad- 

 vance any explanation of the silicification of the corals ; but he 

 considers that the " hornstones," which he obtained from Fiji, rocks 

 corresponding to the chert-like rocks described by me on page 355, 

 are the products of disintegration of the basic andesites. I have 

 already pointed out that certain siliceous nodules have probably this 

 origin. It is also likely that some of the jasper of Vanua Levu has 

 been thus formed. 



Note on a silicified Fern Rhizome. — This is a specimen, about 

 three inches long, picked up by a native in a stream near Sueni in the 

 centre of the island. It has the appearance of being a portion of 

 the stem or rhizome of a tree-fern, and is permeated in its entirety 

 by chalcedonic quartz, the fibro-cellular structure being still pre- 

 served. No other specimen of the kind came under my notice. 

 The probability of the occurrence of silicified plant-remains in the 

 pumice-tuffs of the Undu Promontory is pointed out on page 233. 



