THE GEOLOGY OF FUNAFUTI. 69 



It will be noticed that in the sections of the north, east, and south poitions of 

 the atoll the Ilcliopora caridca reef is shown in all cases to be the foundation rock. 

 As regards its boundary lagoonwards it does not in all cases terminate at the low 

 clift' at the edge of the lagoon platform, but can be traced for some little depth 

 on the bottom of the lagoon below low tide. In the northern portions of the lagoon 

 the dead Hdiopora ccerulaa merges in places into the living lleliopora ccBrulca, which 

 in that part of the atoll covers large areas of the floor of the lagoon. As regards 

 the development of the old lleliopora ccBrulea reef on the ocean side, one of us 

 (Mr. G. Sweet) discovered that it extended under the Hurricane Bank in several 

 places below a thin crust of dead Lit/iothamnion, while its extension to considerably 

 beyond the outer edge of the Hurricane Bank was ascertained by blasting the intensely 

 hard surface of the ocean platform with gun-cotton.* It was also found in situ in the 

 corrosion zone of the reef platform (0.2. B.), as well as up to the edge of O.L.IO 

 between the channels, as was seen a little to the north of easternmost point of the 

 main island. 



The positions of these blasts are shown on Plate 9. In view of the fact that 

 scarcely any trace was found by us of living lleliopora ccerulea on the ocean side of 

 the reef, it is strange that there should be on this side such an immense development 

 of dead Heliopora ccerulea reef ^;^ siLu on the ocean side of the reef A great extent 

 of the same dead reef can also be seen a few fathoms below low water west of the 

 main island. The evidence supplied by Professor Sollas's Nos. 1 and 2 diamond- 

 drill bores and our main bore with the small tore to the west of it, shows 

 that the lleliopora ccerulea reef extends to a depth of at least 40 feet below high 

 water. Ilcliopora ccerulea still retaining traces of its blue colour was also found in 

 the core from the main bore down to depths of at least 100 feet. As regards its 

 horizontal distribution the table of areas of the rock types represented at Funafut 



Analysis of air-diied sample of soil from the Taro Plantation. This consists of decomposed Ileliofora 

 ccerulea, with an admixture of foraminiferal shells, chiefly Tinoporus and Orbitoliies. 



Hygroscopic moisture 1'81 



CaO 47-23 



MgO 1-07 



K2O -05 



Na20 44 



Fe.Os -28 



P2O5 6-00 



SO3 -44 



CI , -02 



CO2 33-65 



Organic matter 8-97 



Residue (insol. in HCl) -04 



100-00 



* This was kindly supplied by Captain E. Eason, E.N., of H.M.S. " Eoyalist. 



