48 BULLETIX: MUSEUM OF COMPARATIVE ZOOLOGY. 



ness, — 800 feet at Tuvutha, 1,000 feet at Vatu Vara. Therefore as 

 soon as the drill struck the limestones it might correspond to any 

 height in the beds exposed elsewhere, beds which at Mango, Kambara, 

 and Vanua Mbalavu we had observed to rest upon a volcanic substratum. 

 It was natural that immediately on my return to Suva after our first 

 trip round the Eastern Archipelago I should send to Wailangilala or- 

 ders to stop further boring, and to bring the crew and machinery back 

 to Suva. For it seemed a waste of both time and money to bore and 

 obtain a core from an indefinite datum plane, when the same evidence 

 could be obtained by the examination of any one of the bluffs of ele- 

 vated coralliferous limestones with which w^e had become familiar in our 

 first trip. But, unfortunately, we were not equipped to make a thorough 

 exploitation of such a section, not being provided with explosives or 

 drills, and had to content ourselves with somewhat fragmentary collec- 

 tions at the more accessible points. However, this is a subject which 

 I hope to attack again under more favorable conditions. 



The boring at "Wailangilala shows that the island is the fragment of 

 an ancient island of larger size, which once covered the whole area of the 

 lagoon. Being at the northern extremity of the atoll, it was less subject 

 to the destructive agency of the sea due to the prevailing southeasterly 

 winds, and thus there was left a wider reef flat, the last to be worn 

 away by the action of the sea. It also shows that at a depth of forty 

 feet we meet the underlying elevated limestone forming the substratum 

 of the northern reef flat of the lagoon. i\s will be noticed from the 

 Figure on page 46, the western reef flat is much naiTower than the 

 eastern and less exposed face of the lagoon. 



The boring at AVailangilala is from the remains of an upheaved coral 

 island, as has been suggested by Gardiner ; ^ but it is also the remnant 

 of an island which once occupied the whole of that part of the atoll. 

 Aiwa shows a stage antecedent to that of Wailangilala, the island on the 

 rim of the lagoon being still of considerable heiglit. Many of the reef 

 rocks (negro-heads), which Gardiner considers as having been thrown up 

 by hurricanes, are the remnants of the elevated reef rock outliers left 

 from the denudation of the flats on which they occur, and which once 

 rose to a greater height but have gradually been eroded and planed down 

 to their present elevation. 



But Gai'diner is wrong in assuming that the islands of the atolls are 

 converted into land. Such is by no means necessarily the case. The 

 islands on the rim of an atoll, as Ngele Levu, consist of elevated coral- 



1 Loc. cit., p. 445. 



