XAKKATIYE OF THE EXPEDITION IX 1806. 27 



width, ruimiiig for some Irandiecl yards obliquely across the "whole vridth of the reef 

 Fissures indicate a stretching of the earth's crust." 



Neither in Funafuti, nor apj^arently in the Oulleay Atoll, do the fissures pass into 

 faults ; should they do so, and a downthrow occur on the seaward side, the curve of 

 stability which now characterises the ocean beach of the atolls would be destroyed, 

 and the sea would make inroads on the land, which would almost certainly lead to a 

 redistribution of all superficial deposits in the vicinity. The effects, however, would 

 be limited within a narrow area, and submarine slips cannot be appealed to as an 

 explanation of quite general characters, such as those presented by the breccia 

 beds and pinnacles. In this connection attention may be again directed to the very 

 steep slopes, sometimes amounting to 80°, already mentioned. These can scarcely 

 exist in loose material ; submarine cliffs 300 feet high, and nearly vertical, must surely 

 correspond vs'ith hard rock. The steepest cliff, that just mentioned, begins to descend 

 at a depth of 450 feet, but some fairly steep slopes commence at 800 feet, and 

 some 90 feet in height at GO feet; hence, since our first bore-hole exceeded 60 feet 

 in depth without passing through thick limestone, it would appear that the hard 

 rock suggested by these outer steep slopes is not to be correlated with depth ; it is 

 more probably a feature of the outer reef, which consequently may possess a very 

 difierent structure to that part which is accessible to bore-holes. By the nature of 

 the case a bore-hole sunk, however near to the sea-margin, must enter the ground at 

 some distance from the growing reef and become the more remote from this the 

 deeper it descends, while at the same time it will approach continually nearer the 

 supposed site of lagoon deposits. Thus too much stress must not be laid on the 

 unconsolidated character of the material met with in our bore -holes ; the exterior 

 of the atoll may be faced with solid limestone, which, like a retaining wall, may hold 

 up the looser deposits within. These, though preserved from giving way on a large 

 scale, may still be liable to a certain amount of subsidence, sufficient to account for 

 the cracks which have been observed in the ocean glacis. 



Our observations on the lagoon suggest that it is gradually filling up. The three 

 chief rock-formers — corals, foraminifera, and calcareous algpe — abound in its waters. 

 Its floor is rich in growing corals, which, as shown in the chart prepared by 

 Captain Field, frequently form reefs rising nearly, and sometimes quite, to the 

 level of low tides. On one of these, Te Akau Tuluaga, I landed, and found both dead 

 and living corals at its margin, whilst its surface was covered with sand and coral 

 fragments. This reef seems to have grown noticeably in recent times, for Mr. O'Erieist, 

 the Avhite trader on the island, informed me that when he first knew it its surface was 

 3 or 'i feet loelo^v low-tide level. But the reefs shown on the chart represent only a 

 fraction of the coral which flourishes on the floor. On the western side (within the 

 " nose '■' of the atoll) is a perfect garden of corals in luxuriant growth, and at various 

 places near the shore corals may be seen extending in broad fields from the water's 

 edge towards the depths. On the leeward side of tlie lagoon, opposite the site of tlie 



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