REPORT ON MATERIALS FROM THE BORINGS AT FUNAFUTI ATOLL. 333 



Halimeda and Lithothamnion. With these are commingled, mostly in a fragmentary 

 condition, the spines and test plates of echinids, annelid tubes,, crustacean tests, 

 polyzoa, ascidian spicules, sponge spicules and the shells or casts of lamellibranchs 

 and gastropods. These fragmentary remains are embedded in a calcareous sediment 

 of minute organic particles and amorphous material, which fills up the interspaces of 

 the corals and other organisms, and the whole mass is cemented by either crystalline 

 carbonate of lime or ddlomite. In places the crystalline cement is only slightly 

 developed, and the organic debris then readily breaks up into its constituent 

 elements. After consolidation many of the smaller organic particles have been 

 dissolved, leaving the rock porous, and larger cavities have been produced by the 

 removal of corals by solution. The corals, unfortunately, have suffered greater 

 alteration in the fossilisation than any of the other organisms in the rock. From 

 the surface to the depth of about 180 feet, the structural change has not beeu 

 great, but they are often obscured by the infilling of their interstices with fibrous 

 crystalline material ; at greater depths the coral walls and other structures have 

 been dissolved and removed, and only casts in sedimentary or crystalline materials 

 remain. 



The construction of the rock is best shown in the solid cores from the upper part 

 of the boring to the depth of 150 feet, and in the lower third, from 750 feet to the 

 bottom. The solid cores, in the upper portion, to a large extent consist of masses of 

 coral — Millepora, Heliopora, Pocillopora, and Madrepora — in their positions of 

 growth and often overgrown by Lithothamnion, but not much changed, otherwise 

 than by the infiltration referred to above. The interspaces between the corals are 

 filled with foraminifera, fragmentary organisms and sediment, and these materials 

 also compose the softer, incoherent portions of the rock, which in this part of the 

 boring comprise five-sixths of the whole. Allowing for coral fragments amongst 

 the debris, the proportion of strictly coral rock would not be more than one-fifth. 



In the 350 feet of the lower part of the boring, where the rock cores are nearl}' 

 continuous, and the corals, now in the condition of casts, are more numerous and 

 varied than nearer the surface, there is a similar disposition of layers mainly of 

 coral, alternating with layers mainly of foraminifera and fragmentary organic 

 materials. There is no sharp boundary between these alternating layers, they 

 gradually merge into each other. In contrast to the incoherent foraminiferal and 

 fragmental layers of the higher part of the boring, these layers are here cemented 

 by crystalline dolomite, and they are harder and more compact than the coral layers. 

 These latter form a larger proportion of the whole rock than in the higher beds, 

 but even here thfey appear to be considerably exceeded by the foraminiferal and 

 fragmentary rocks. 



In that portion of the Main Boring between 150 feet and 748 feet, the greater 

 part of the rock has broken up into granular particles, and only about 8 per cent, of 

 it has reached the surface as solid cores of limestone. Both the cores and the 



