Report on the Boring in the Atoll of Funafuti. 201 



is described as fairly compact coral rock, so tliat very probably reefs 

 m situ, though of no great thickness, were pierced at these depths. 

 The sand appears to be largely derived from coral, but foraminifera 

 occur, sometimes in abundance ; so too do nullipores, and here and 

 there spines of echinids. Towards 150 feet signs of change begin 

 to appear in the corals, and these become more conspicuous as the 

 boring approaches its greatest depth. In such case, if I understand 

 rightly, some of the branching corals crumble away and are repre- 

 sented only by casts, while others remain, the surrounding matrix 

 becoming solid, cemented apparently by calcite. Below 202 feet a 

 decided change takes place in the character of the deposit. All 

 above this seems to be largely composed of material derived from 

 corals, with occasional rather brief interludes of true reef, and this 

 mass, measuring, as said above, rather over 200 feet in thickness, 

 may be termed the first or uppermost formation. Below this, down to 

 about 373 feet, sandy material distinctly dominates, which sometimes is 

 almost a calcareous mud. Still even there coral fragments and rubble 

 occasionally appear, and now and then a few isolated corals. Other 

 organisms may be detected, including nullipores, foraminifera, and 

 mollusca ; but until this material has been examined microscopically, 

 it would be premature to attempt any precise statement. This mass, 

 in thickness about 170 feet, may be termed the second or middle 

 formation. It is not reef, though obviously produced in the vicinity 

 of a reef. Below 370 feet is the third or lowest zone ; in this beds 

 composed of broken coral become frequent, which are intercalated 

 with masses of dead coral, though sandy bands also occur. The 

 character of the material suggests that it has been formed in the 

 immediate vicinity of a reef, which has occasionally grown out 

 laterally, though only for a time, and has built up a layer of true 

 reef, from 2 to 3 feet in thickness, upon a mass of detrital coral. 

 In one place the rock is specially noted as " hard," and hereabouts 

 even the shells of gasteropods have perfshed, only their casts remain- 

 ing. From 526 to 555 feet the bore passed through fairly compact 

 and (in places) very dense and hard " coral limestone " and " cav- 

 ernous coral rock." in which dendroid forms were numerous. As 

 regards the part between 557 feet and 643 feet only brief infor- 

 mation is to hand, but Prof essor David states that it is reported to be 

 chiefly coral limestone, hard and dense, with occasional soft bands of 

 coral sand or coral rubble. Thus the third, or lowest zone, about 

 270 feet in thickness, corresponds apparently with the first, but it 

 seems to contain larger and more numerous masses of true reef. 



Professor David has also forwarded with his latest letters a section 

 of the boring and of the exterior form of the island, down to about 

 730 fathoms : the one drawn from his notebook, the other from 

 Captain Field's record of soundings. From this I gather the 



VOL. LXII. Q 



