436 Mr Gardiner, The Coral Reefs of [Mar. 7, 



atoll are being washed away. I have already noticed the under- 

 mining of the pinnacles on the outer reef, and the action of the 

 sea on this reef generally. Some of the breaks, between the 

 different islands, seem to have been but recently formed, and the 

 cliff on Amatuku, before referred to, shows that the action is still 

 going on. Tengako is a part of the main island to the north 

 joined by a low, bare sand-bank about twenty yards broad, across 

 which in a big gale the waves would break. The natives state 

 that this area was once covered by coconut trees. Additional 

 evidence is furnished by Afualiku a small island west of the north 

 entrance; it has now only one living coconut tree, but shows the 

 remains of several others which have fallen over through the 

 approach of the waves. 



Reference has been made before to the character of the reef 

 just outside the rim. Masses of reef-rock with fissures and cross 

 channels extend out for several fathoms ; in places, down to 

 depths of 10 — 12 fathoms, the bottom is similarly formed. These 

 masses are 'covered with encrusting nullipores, which seem 

 gradually to be joining them on to the rim and extending the reef 

 further seawards. I could find no signs of their having been torn 

 up, or washed away, except in a few negroheads on the leeward 

 reefs of the atoll, and it necessarily follows, as they are completely 

 protected from solution by growing organisms, that they must be 

 stationary, or growing upwards and outwards. We have thus the 

 islands of the rim of this atoll being washed away, while the reef 

 round them is gradually extending itself further and further 

 seawards. 



Professor Sollas has given, from the soundings taken by the 

 officers of the Penguin, a section 1 of the external slope of the 

 atoll, but the fall between 15 and 40 fathoms is by no means 

 always so rapid. Off Falefatu, between the two southern en- 

 trances, the fall from 15 fathoms was fairly gradual down to 40 

 fathoms, and I was able to take a haul with the swabs without 

 going into a less depth than 35 fathoms. There was also off 

 Fuafatu a broad flat with a depth of about 8 fathoms, on which 

 the Penguin anchored on several successive nights. A considerable 

 number of species of coral Avere obtained on the outer slopes in 

 depths down to 35 fathoms, but it was impossible to use dredges 

 on this area without a greater force than the steam launches of 

 the Penguin possessed, and so no knowledge of encrusting or 

 massive species could be obtained. From 35 fathoms I obtained 

 one small piece of Heliopora, a discovery of great interest as, 

 while its corallum is exceedingly abundant in the mangrove 

 swamp, it was only obtained alive at Funafuti on this occasion ; 



1 loc. cit., p. 375. 



