TIKEI. 73 



rock which had been deposited on the underlying old ledge between its 

 outcrops; but the greater part of the beach rock conglomerate had been 

 disintegrated and reduced to isolated fragments, which in their turn had 

 become worn and weathered to fine sand (PI. 42). 



In the central pool, as well as in the smaller pools of other sinks, we 

 found mullet, probably the same species as that living in the lagoon (or 

 greater sink) of Niau, the former being not more at any time than four 

 to five feet in depth, the latter at least 12 to 15. The Tikei sink com- 

 municates more freely with the sea than the Niau lagoon, separated as it 

 is from it by a wall of nearly half a mile in width and fully 25 feet high. 



The shore platform is full of pot-holes of all sizes, containing the 

 pebbles of harder corals which formed them. The edge of the reef plat- 

 form is deeply indented and scalloped by channels varying in width from 

 a few inches to several feet, and some of them large enough to be used 

 as boat passages for landing. The points between these channels rise con- 

 siderably above the general level of the reef flat. They, as well as the 

 reef platform, are covered with Nullipores and other calcareous Algae, 

 which appear to thrive best in the full force of the breakers. They rise 

 sometimes as knolls fully four feet higher than the general level of the shore 

 platform. The depth of the channels varies from a few inches to two or 

 three fathoms, frequently the projecting irregulai-ities of adjacent sides be- 

 come soldered together, forming bridges under which the surf is forced, 

 and is projected behind these connecting bars in columns of spray or water 

 varying in height according to the size of the opening left. These bridges 

 frequently form a continuous floor for a considerable distance. When the 

 force of the "surf is too great, they are broken off, as well as the higher 

 knolls or projections wliich have been built too far out into the breakers 

 and are thrown up on the reef flat as boulders, often of great size, at the 

 base of the sand or shingle beach, to be ground into sand. 



As seen looking down upon them from the ship, these indentations 

 look like so many huge fingers extending into the edge of the mass of 

 the reef platform ; and in certain lights they look like light or dark blue 

 passes or cuts, standing out in marked contrast to the orange-red masses 

 of Nullipores and Pocillipores into which they have eaten. 



