258 



L. HILLIS- COLIN VAUX 



Fig. 84. Scheme showing influences of accretion processes on the final composition of 

 atoll mass. 



consolidation. In particular, it is worth noting that most of the Fora- 

 minifera contributing to reef structures have calcite skeletons which 

 may well survive diagenetic processes better than the aragonite of 

 Halimeda or corals. 



Table XXVI describes some of the results from 3 of the 42 drill 

 cores from the Enewetak Atoll recently raised by Couch et al. (1975). 

 The core from Cactus Crater was chosen from this suite because it was 

 near the outer edge of the reef, taken under 10 m of water in the crater 

 left by an atom bomb exploded on the outer reef flat. The second core 

 from the same island (Runit) was chosen as being the longest core from 

 the middle of the island. The general sites of both these cores are shown 

 in Figs 85 and 97. The core from Engebi was chosen merely on the basis 

 of length. No examination of the matrices of the 42 cores was made in 

 choosing these three data sets. 



In Table XXVI the Enewetak core log data are abstracted at 

 arbitrary intervals of 5 m. The data are estimates by eye of the per- 

 centage composition of the various constituents of the core sections by 

 volume. Names are given, therefore, only to what is well and clearly 

 preserved. Both Halimeda and coral fragments are common, and 

 fluctuate up and down the cores. Foraminifera occasionally predomi- 

 nate, but are usually of less importance than both Halimeda segments 

 and coral fragments. As would be expected from the method of analysis, 



