130 FUNAFUTI: A SEQUEL 



2. True reef-rock was passed through in the boring 

 from the surface down to 185 fathoms. 



3. No rock, other than reef-rock, was encountered, and 

 in particular no Tertiary limestone. 



4. The structures met with were such as to exclude 

 the notion that the reef had grown upwards on talus of 

 its own debris. 



From these inferences, but one conclusion appears 

 possible, and we must admit that this atoll at least has 

 been formed during a subsidence of the foundation on 

 which it rests, a subsidence which must amount at least 

 to 877 feet. 



An unexpected confirmation of this result has lately 

 been afforded by the investigations of Dr. Skeats into the 

 process of dolomitisation of coral limestones. It has 

 already been pointed out that from a little more than 100 

 fathoms down to the bottom of the bore-hole the core 

 contains as much as 40 per cent, of magnesium carbonate. 

 When first formed the limestone was comparatively free 

 from this constituent, which has been subsequently intro- 

 duced, and Dr. Skeats has shown that the replacement 

 is most readily accomplished at depths of from 1 to 25 

 fathoms ; it would, therefore, seem to follow that the 

 magnesian limestone at the bottom of the bore-hole or 

 now at a depth of over 185 fathoms, originally stood 

 within the 25-fathom level, i.e., the limit of coral growth, 

 at the time dolomitisation took place. 



Now that we have completed our discussion of the 

 most important results, we may pass to others, which, 

 though subsidiary, are still of great interest. 



We have already alluded to the boring made from the 

 bows of H.M.S. Porpoise, by Commander F. C. D. 

 Sturdee, E.N., and Mr. G. H. Halligan.* This was sunk 

 through 110 feet of water and 245 feet of deposits, in all 



* P. 120. 



