212 RENNELL - AN OUT OF THE WAY CORAL ISLAND 



(Natural History) about sending out a few zoologists, but that the idea 

 had had to be dropped owing to lack of funds/ 



The Galathea left Honiara, the capital of the Solomons, on October 5, 

 1 95 1, after landing the four of us with our films and preservatives, guns, 

 nets, and other gear. A few days later we were sailed over to Rennell to 

 begin work. 



The great majority of the islands in the Solomon group are formed 

 from bed-rock (granite and gneiss) or lava. Rennell is unique in consist- 

 ing entirely of coral limestone. It was originally an atoll, a ring-shaped 

 coral reef enclosing a lagoon, which usually has a steep drop on the outer 

 side into water several thousand metres deep. Imagine an elongated ring- 

 reef raised some 100 metres above sea-level, part of the lagoon having 

 dried out owing to the upheaval, and you have Rennell, one of the 

 largest and finest examples of a raised atoll in the world. 



In shape, as seen from above, it resembles a long narrow dish, the 

 edge being the former fringe reef which surrounds the whole island like 

 a ridge. This ridge in places is only a few metres thick, forming a razor- 

 sharp and jagged wall. From the sea the island presents the appearance 

 of a continuous wall of coral limestone 80 — 100 metres high, overgrown 

 with vegetation except where it is quite perpendicular. Along the coast 

 runs a barrier reef formed after the upheaval, and the surf beats against 

 this reef day and night. 



There are indications at a few points that the upheaval must have taken 

 place in two stages. On our laborious climb over the wall towards the sea 

 we encountered, about half way up, a ridge, and inside this a narrow 

 shelflike depression, before the final ascent to the top. This ridge and 

 depression doubtless represent a former barrier reef and lagoon, formed 

 during a lull in the upheaval. 



As already mentioned, the original lagoon has been only partly dried 

 up. The degree of upheaval not being everywhere the same, some of the 

 lagoon has remained in the form of a lake at the eastern end of the island. 

 With a length of about 25 kilometres and a width of 8 — 10 kilometres, 

 this is the largest lake in the South Seas. Its surface is now believed to be 

 almost at sea-level, and as there is at least 60 metres of water at the 

 eastern end the bottom is a good deal below sea-level. Towards the western 

 end, the irregular bed of the original lagoon is visible in the form of a 

 steadily increasing number of islets which, further west still, merge into a 

 swamp and then give way to the undulating bottom of the central de- 



^ A British Museum expedition was carried out later, in 1953. 



