70 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



beacli of that island is a steep sand beach topped with small coral shingle 

 (PI. 38, figs. 1, 3). To the south of the island a wide gap forming a 

 shallow passage towards the sea is covered with fine coral sand silt, and 

 shut off from the sea by a wide sand bar. An islet and a couple of 

 sand banks flank the side of the flat, which opens out broadly into ledge 

 flats extending far into the lagoon. 



On the lagoon side the beach rock consists of a conglomerate of recent 

 beach rock and corals, as well as fragments of the old ledge and its 

 component corals. 



The old ledge crops out in the lagoon about three quarters of a mile from 

 the wharf in Pakaka Entrance (PI. 34, fig. 3), its disintegration supplying 

 the materials for the beach on the lagoon face, and for the low dunes three 

 to four feet high, blown up occasionally on the lagoon side of the land rim 

 (PI. 39, fig. 1). The lagoon is less well closed than that of Rangiroa, 

 where there are high white sand as well as gray shingle beaches on the 

 sea face of the islands and islets of the land rim. The reef flat on the 

 sea face is quite narrow, not more than 75 to 100 feet wide, and negro- 

 heads of old ledge are scattered along the platform at the foot of the 

 beach (PI. 37, figs. 1, 2). 



On the lagoon face of Apataki the sand beach is low, not more than one 

 to three feet in height. It is made up of fragments of recent corals and 

 of broken shells. The highest islands of the land rim near the pass are 

 not more than seven to eight feet. The beach on the sea face is steep 

 (PI. 39) ; old ledge corals as well as recent corals are thrown up to- 

 gether, and form, as at Rangiroa, a more or less coarse shingle. 



Dr. Moore collected on the Apataki reef flats Pocillipora, Millepora, Pori- 

 tes, and Madrepores. An islet on the flats to the north runs nearly across 

 the entrance of Pakaka ; it is about three feet above high-water mark, and 

 made up of disintegrated old ledge rocks. Inside of the lagoon here and 

 there a long narrow ledge of old reef rock crops out, similar in all respects 

 to that seen in Pakaka Pass (PI. 38, fig. 3). Similar ledges also occur on 

 the lagoon side of the low reef flats, with occasionally a large negro-head 

 (PI. 39, figs. 1, 2). The land rim is an alternation of islets and low sand 

 flats, with beach rock ledges on the narrow reef flats connecting the islets. 



