NORTH AND SOUTH NILANDU. 



405 



The above facts appear to me to be 

 mation of lagoons in general, treated of 

 more particularly in my Chapter (vi.) on 

 North Mahlosmadulu bank. It seems to 

 me to be nearly impossible to believe that 

 there is any error on my side, or on that 

 of the original cartographers, by which the 

 above changes can be explained. The charts 

 were in the first place so carefully made, 

 and pools of deep water, wherever present 

 in the lagoon reefs, so carefully charted on 

 other banks that North and South Nilandu 

 — and probably also Ari — give the strongest 

 support to the view that atolls can be and 

 are commonly formed by the spreading 

 outwards of surface reefs and the solution 

 of their central parts. I believe that owing 

 to the shallow depths of their foundation 

 flats, their protected situations and other 

 peculiar conditions the lagoon reefs of these 

 two Nilandu banks show, even in the odd 

 64 years since the charts were drawn, the 

 change from a flat reef to a perfect atoll. 

 In their entirety, too, these lagoon reefs 

 give a complete series from the smallest 

 reef, a single coral head — perhaps only a 

 single coral colony — to an atoll a mile or 

 two in diameter. 



A point, everywhere observed in the 

 Nilandu atolls, was the decreased breadth 

 of the lagoon reefs, which sepai'ate the 

 velu of the rim from the lagoons of the 

 atolls. All the rim velu had increased in 

 size, and, while much of this was un- 

 doubtedly due to growth in length, yet 

 more would seem to have been caused by 

 increase on their lagoon sides. The lagoon 

 reef of any velu in the rim of either atoll 

 is generally perfect, but it is only a thin 

 line, 40 — 60 yards across, covered over the 

 greater part of its breadth with living 

 corals. It differs among other points from 

 the reefs to seaward in never having a 

 boulder zone and in not being backed be- 

 hind — and so separated from the velu — 

 by a sand flat of a quarter or half a mile 

 in breadth, such flat, if present at all, being 



of considerable significance as bearing on the for- 



•9 ^Q/'arMrt 



®0 0' 







^3, ^ LoUig 'i^ 



o 





Go-l'/""- 



jjuJ" 



Fig. 105. North and South Nilandu Atolls (considerably 

 altered from the Admiralty Charts). 



52—2 



