GENERAL REPORT ON THE MATERIALS SENT FROM FUNAFUTI. 173 



Mr. Chapman have been subsequently studied with regard to the mineral chauges 

 which have gone on in them by Dr. Cullis, and he has been further supplied with 

 special thin sections and slices for staining, where tliis has been found necessary. 

 From these materials he has been able to prepare a series of drawings which 

 illustrate fully the numerous and very interesting mineralogical changes which have 

 taken place in the rocks of Funafuti, as they are traced from the surface to the lowest 

 point reached in the boring. 



The cores as they reached London were all stained of a light brown tint, but on 

 cutting them across, the rock was found in every case to be of a pure white colour, 

 the ferruginous stain being quite superficial, and evidently due to rust from the 

 boring apparatus. The examination of the cut surfaces revealed a number of facts of 

 considerable interest. The parts played by corals in the building-up of the rock was 

 by no means so great as might have been anticipated. The corals which occur are 

 sometimes upright, and in the position of growth, but very frequently broken and 

 fragmentary — this being true of all parts of the core from the top to the bottom. So 

 far as could be made out, the corals were as often in situ in the lower as they were in 

 the upper parts of the core. The spaces around the entire and broken corals are 

 filled in with a detritus composed of foraminifera, Halimeda fronds and other 

 organisms, and in many parts of the core the foraminifera are present in much larger 

 quantities than the corals, and constitute the bulk of the rock. 



Very striking, indeed, is the quantity of calcareous algse that go to make up the 

 rock. Fragments of Halimeda, and of the different forms of Lithothamnion, are 

 everywhere abundant. Corals are found which have evidently been killed and 

 enveloped in gro\^i:hs of the encrusting Litliothamnion. Much of the cementing 

 calcareous matter is clearly not of purely chemical origin, but consists of Lithothamnion 

 which has encrusted and bound together the various fragments, to a greater or less 

 extent filling up their interstices. With the encrusting Lithothamnion, and often 

 intergrown with it, is found the foraminifer referred to below as Polytrema 'planum. 



In the whole of the core no trace could be found of oolitic structure, a circumstance 

 the more remarkable when these Funafuti rocks are compared with those of the 

 Bahamas, which have been so well described by Captain Nelson* and others. On the 

 other hand, we find, everywhere scattered through the rocks, organisms, and 

 fragments of organisms, encrusted with successive layers of a foliaceous Lithothamnion, 

 till irregular nodules from 1 to 2 inches, or even more, in diameter, have been built up. 

 The researches of Mr. Chapman have proved that similar nodules are formed by 

 successive growths of the encrusting foraminifer Polytrema planum, and in some 

 cases, as Dr. Hinde has shown, nodules appear to be built of alternating plant 

 [Lithothamnion) and foraminiferal [Polytrema) growths. These nodular masses, 

 composed of fragments of coral enveloped in successive layers of foraminiferal and 



* ' Quarterly Journal of the Geological Society,' vol. 9 (1853), p. 200. 



