52 



"ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



at the distance at which the " Peacock " sailed, she might have seen only 

 the bare part of the southwestern part of the atoll. But as Dana's 

 description is not based upon his own observation, too much reliance should 

 not be placed upon what he states on the authority of others. 



Old Ledge Dam and Spur, Lagoon Side of West Coast of Rangiroa. 



Tikahau. 



Plates SO, figs. 2-4. ; 201, 302; 9M4, fig. 4- 



On approaching the west side of Tikahau, we found it much like the west 

 coast of Rangiroa, broken up into islands and islets (PI. 20, fig. 2) separated 

 by gaps, some of them of considerable width, with here and there reaches of 

 the old ledge cropping out in them, and in one place a part of the ledge was 

 standing in the gap as a honeycombed, pitted, and undercut mass of columns 

 of irregular shape, similar to the great sea wall ledge on the south shore of 

 Rangiroa. We could see several islets covered with trees in the interior of 

 the lagoon, as well as rocky ledges similar to the ancient wall ledge on the 

 outer land belt mentioned above (PI. 20, fig. 3). 



The entrance to Tikahau is in a gap on the western side, between low 

 islands covered with cocoanut trees. The entrance is, like that of the 

 passes into Rangiroa, flanked with ledges and islets. The structure of this 

 atoll is in every way identical to that of Rangiroa, the sea faces of the 

 island belt being high sand beaches alternating with exposed ledges. The 



