TAPETEUEA. 239 



fig. 2), judging from the color of the water, which is light green, like that 

 on the reef flat on the inside of the lagoon. The character of the east 

 face of Tapeteuea is well indicated on the sketch chart of the atoll made 

 by the United States Exploring Expedition under Wilkes^ (PI. 226, fig. 1). 



Soiith of the island of Utiroa, we came upon a low elevated vertical wall, 

 consisting of short reaches from ten to forty or fifty feet in length. It is 

 not more than three to five feet in height, is deeply undercut, and has 

 the appearance of being composed of the tertiary elevated coralliferous 

 limestone. Where the reef platform is wide, the vertical wall passes, little 

 by little, into lines of buttresses running more or less diagonally across 

 the face of the steep coral sand beach. On the beaches is found an 

 immense mass of driftwood and of logs of all kinds, mainly of Pandanus 

 and cocoanut trees, as well as some of the hardwood trees. This we had 

 not seen before ; it shows that the east face of the atoll is bathed by 

 a strong current coming from the eastward, bringing a mass of drift 

 material from islands to the eastward. Some of the gaps between the 

 islands illustrate well the characteristic mode of formation of the land rim 

 of an atoll. We could see how a short sand bar had been deposited at 

 right angles to the line of the outer reef flat, where fragments of beach 

 rock or conglomerate have formed a spur towards the inside of the lagoon, 

 and had gradually grown towards the interior of the lagoon, increasing 

 also in width, and finally almost closing up the spaces between it and the 

 adjoining sand bars or islands or islets, leaving, as can be seen, a more or 

 less shallow gap through which the lagoon has an intermittent communi- 

 cation with the sea. 



Many of the islands of the land rim are covered with a fine growth of 

 Pandanus and of cocoanut trees. The last island on the northern part of 

 Tapeteuea shows the old ledge cropping out here and there, and extending 

 either as outliers, or as diagonal buttresses across the steep beaches, the 

 intervening spaces being covered with coarse coral shingle. The outer reef 

 platform off the northern point is wide ; we also find there traces and out- 

 liers of the low old ledge wall existing to the southward. At the northern 

 extremity of Tapeteuea two secondary lagoons are formed. They are due 



1 H. O. Chart 120. 



