172 PROFESSOR J. W. JUDD. 



mass, rendering it more or less solid and compact. Although no trace could be found 

 of anything but existing organisms, it was evident that the remains of these had 

 undergone such great chemical and mineralogical changes that they would have to 

 be studied like fossils, especially by the aid of thin sections, and that the ordinary 

 methods of diagnosis of the zoologist were of little avail. 



Under these circumstances it was very fortunate that I was able to induce Dr. G. J. 

 HiNDE to give his invaluable aid in determining the organisms contained in the core. 

 With the exception of the foraminifera, which were determined by my assistant 

 Mr, F, Chapman, all the other organisms were diagnosed by Dr. G. J. Hinde, with 

 the advice, where necessary, of the zoologists and botanists of the British Museum. 



As a preparation for the work, specimens of the various genera of corals represented 

 in the core (generally obtained from Funafuti) were selected as types, and from these 

 longitudinal and transverse sections, with occasional oblique sections, were cut. As 

 casts were of such frequent occurrence in the lower cores, wax-impressions of all the 

 forms were also taken, wherever found necessary. In this way a good series of types 

 for comparison were obtained for the corals, while the numerous collections made on 

 and around the islets of the atoll supplied the means for equally exact comparison in 

 the case of other classes of organisms. 



The cut faces of the cores and the slices taken from them offered sufficiently 

 polished surfaces for a general determination of the organisms present in them, all 

 difficult cases being met by preparing thin transparent sections from selected portions. 

 In the course of the work over 500 thin microscopic sections were cut and studied, 

 and these are preserved together with the half-cores in the British Museum, 



In his notes on the cores, Dr, Hinde lias remarked upon the general mode of 

 preservation of the organisms and the more or less crystalline character of the 

 material in whicli they are embedded. A selection from the series of thin sections 

 was submitted to Dr, H. C. Sorby, who lias kindly furnished a general report on 

 the subject of the chemical and mineralogical changes which coral-reef rocks 

 undergo.* 



The more detailed study of the mineralogical changes taking place in the cores 

 has been carried on by Dr, C, G. CuLLlS, following the lines laid down by Dr. 

 Sorby in his Presidential Address to the Geological Society in 1879. The work 

 has, however, been greatly facilitated by the employment of more recently discovered 

 micro-chemical methods — namely, Meigen's test for discriminating between calcite 

 and aragonite, and Lemberg's test for distinguishing calcite from dolomite. In 

 arranging for the best methods of applying these valuable tests, we have received 

 much assistance from the oflScers of the Geological Survey and of the Mineralogical 

 Department of the Natural History Museum, our special thanks being due to 

 Mr. Teall and Dr. Pollard, and to Mr, L. J. Spencer. 



The whole of the thin sections examined in the first instance by Dr. Hinde and 



* Section XIII. 



