GENEEAL REPORT ON THE MATERIALS SENT FROM FUNAFUTI. 171 



At the depth of G-37 feet the white chalky-looking rock gave such indications of 

 having undergone great chemical change, that I tested for magnesia and found it to 

 he present in large quantities. In view of the important observations made by the 

 late Professor J. D. Dana in 1843 and subsequently in many of his writings* on the 

 dolomitisation of coral reefs, I determined to make a complete examination of the 

 chemical composition of the whole ot the materials from the borings at Funafuti. 

 Two of my assistants. Dr. C. G. Cullis and Dr. E. W. Skeats, could fortunately be 

 spared for a time to undertake portions of the work, while the remainder of the 

 chemical work was done in the Chemical Laboratory of the Royal College of Science 

 by Mr. J. PI art Smith under the superintendence of Professor Tilden, the expenses 

 of this part of the work being defrayed by a grant from the Royal Society. The 

 results of this chemical work and a discussion of them are given in a separate 

 report, t 



In order to determine the nature of the organisms in the solid cores it was proposed, 

 in the first instance, to make a thin slice of the whole size of each core, cut out of 

 its middle. It was found, however, to be very difficult to make such large slices 

 sufficiently thin for the jDurpose of exact study, while it would have been necessary 

 to submit each of these sections in succession to specialists who would study every 

 group of organisms that might be represented in them. This method was, therefore, 

 abandoned for another when a depth of about 200 feet was reached. It v/as found 

 that the slice cut from the middle of the core afforded a good indication of the 

 general composition of the core, and that doubtful or difficult points could be settled 

 by having very thin sections made from that portion of the slice in which the difficulty 

 presented itself When a depth of 800 feet was reached it was found that the 

 surfaces presented by the hard cores, when slit by the lapidary's wheel, were 

 sufficiently well polished to indicate the general nature of the organisms, and in 

 consequence the labour of making the double cut through the core was avoided ; 

 small thin sections were, however, prepared whenever the study of the polished core 

 surfaces showed such to be desirable. 



The examination of the cores from the depth of 637 feet to the bottom indicated 

 that the materials had undergone the most extensive chemical and mineralogical 

 changes. It was evident that not only portions of or the whole substance of 

 organisms had been removed in solution, after their interstices had been filled with 

 calcareous mud, but that recrystallisation and dolomitisation had gone on to a 

 considerable extent. In the lower and more crystalline portions of the core, the 

 corals, with some of the mollusca and other organisms, only existed in the form of 

 casts, while secondary crystalline deposits had evidently been formed in the cavernous 



* See 'Amer. Journ. Sci.,' vol. 45 (1843), p. 120; ibid, vol. 47 (1844), p. 135. "United States 

 Exploring Expedition (Zoophytes)," 1846, p. 712 Compare also the successive editions of 'Dana's 

 Manual of Geology.' 



t Section XIV. 



Z 2 



