REPOET ON MATERIALS FROM THE BORINGS AT FUNAFUTI ATOLL. 193 



Crystalline dolomite largely replaces calcite as the cementing material. Together 

 with these changes, is an increase in the proportion of the solid core, the length of 

 which altogether is 1 9 feet or about one-sixth of the distance passed through. The 

 rock cores are mainly composed of foraminifera, and in some portions the detached 

 joints of Halimeda, with a few casts of small corals. Nodules formed by the enciust- 

 ing layers of Polytrema planum round corals and other organisms form a prominent 

 feature of the cores. Examples of Cycloclypeus are numerous and of very general 

 occurrence in the rock between 643-698 feet. Alveolina first appears at the depth 

 of 725 feet and continues down to 740 feet. Amphistegina a,nd Heterostegina are very 

 abundant. 



In addition to the coral genera noted in the core above, the following are present 

 as casts : Hydnophora, Cyphastrcea, Cycloseris, Astrceopora and Turbmm'ia. 

 Encrusting foi-ms of Lithothamnion occur, but as a rock former it has here less 

 importance than Halimeda. 



Depth from. Surface in feet 748-11 14|-. Distance Bored in feet 8665. 

 Numbers of Cores 32a-709a. 



The lower third of the boring, from the level of 748 feet to the bottom at 1114| feet, 

 a distance of 366|- feet, is, with one exceptional interval, of the same general character, 

 and it markedly differs from the middle and upper portions. The rock is a hard, greyish 

 to greyish -brown, dolomitic limestone, porous to compact, according to the measure in 

 which the interspaces have been filled with the crystalline dolomitic matrix ; frequently 

 with hollows and cavities where corals and other organisms have been dissolved out, 

 though oftentimes these cavities have been again filled with the crystalline matrix. 

 It is sufficiently consolidated to yield a practically continuous, solid, cylindrical core 

 of the length of311|- feet. Though the organic remains in this dolomitic rock are 

 often less favourably preserved than those in the limestone rock above, the con- 

 tinuity of the core is better suited for determining the nature and arrangement of 

 the constituent organisms than where the larger part of the rock has been broken 

 up into fine granular material, as is the case in the higher part of the boring. 



The rock-forming organisms in this dolomitic rock consist apparently of the same 

 kinds of foraminifera, corals, calcareous algse, &c., as in the beds above. They show 

 a general disposition in layers or zones in which one or the other of the groups of 

 corals or foraminifera predominate.* The various layers are not distinctly marked off 

 individually, but they gradually merge into each other. Thus for a distance varying 

 from a few inches to several feet the solid cores are principally composed of foraminifera 

 with an admixture of calcareous algae and fragments of other organisms, but with 

 only a few corals or perhaps none ; above and below this layer the rock cores are 

 largely, if not entirely, of casts of corals, but usually some foraminifera, Lithothamnion, 

 * I have not noticed lines of stratification in any part of the cores, 



2 c 



