REPORT ON iMATERIALS V\um THE r>ORIN&S AT EITNAEITTI ATOEE. f^ll 



Samples of the vock iiiaterials, taken at varions depths in tlie horings, as well 

 as some from the floor of the laffoon, were forwarded to London. The rock from the 



CD 



borings appears to be entirely of carbonate of lime, withont any admixtnre ot 

 dolomite. From the surface, to a depth of about 70 feet, the materials consist 

 of calcareous organisms, entire and fragmentary — principally calcareous algse — quite 

 loose and apparently not cemented in any way. Below 70 feet the rock is a Mdiite, 

 porous, rubbly limestone, partially consolidated by calcite, which, in the process 

 of l)oring, has been broken up, so that the samples now consist of small angular 

 fragments and much fine, powdery material. In the lower part of the boring the 

 rock seems to have been more compact, and the fragments in the samples coarser, 

 and there are in it many pieces of corals, which seem to have been broken off from 

 colonies in position. 



Dej^th from Floor of Lagoon, 0-62 feet ; Distance Bored, 62 feet ; Numhers of 



Samples, L. 2-L. 5. 



The materials from the first part of the boring, to the depth of 62 feet, consist, to 

 a very large extent, estimated between 80 and 95 per cent., of the detached fan- 

 like joints or segments of the calcareous alga, TIalimeda. According to Miss E. S. 

 Barton (Mrs. Gepp),* they all belong to Halimeda opuntia, Lamouroux, var. 

 macropus, Askenasy. 



The individual joints are about 10 millims. in length, ...13 millims. wide, and 

 1 millim. in thickness ; some are entire, but a large number are now broken up into 

 fragments, probably in the boring operations. They retain their minute structures 

 perfectly, and Miss Barton states that the specimens, from the depth of 3 5i feet 

 below the lagoon floor, were still sufliciently preserved to show the peripheral cells on 

 decalcification, and at 50 feet the large central tubes were still to be recognised, but 

 below that depth, though the form of the joint was retained, and the cells and tubes 

 were distinctly shown, there was no cell-substance after treatment. The Halimeda 

 remains from the borings are distinguished from those dredged up from the floor of 

 the lagoon by their bleached appearance, and those from the depth of 22|- feet, 

 when dry, are, if anything, lighter and more fragile than the recent surface specimens, 

 but lower down in the boring, the cells and tubes of the joints become infiltrated to 

 a varying extent with crystalline calcite, and are thus rendered heavier, more stony 

 and resistant, so that they do not break readily between the fingers. 



The segments are now quite free ; not infrequently foraminifera, Spirorhis, &c., are 

 attached to their smooth surfaces, and separate joints are sometimes completely 

 encased by concentric layers of the encrusting foraminifer, Polytrema planum,. 



The foraminifera, from this part of the boring, are represented by a number of 

 species and varieties, but they do not contribute to any extent to the mass of 



* 'Eiiuiean Soc. Jouni.,' Botany, vol. 34, 1900, p. iSL 



