112 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



the length of the island. The two islands are somewhat more than twenty 

 mUes in length. The greatest width of Marokau across the northern face is 

 about eight miles, while Ravahere is nowhere more than three to four miles 

 wide. The lagoons of both these islands are closed, there are no ship passages 

 or boat passages, but the sea has the fullest access to the lagoons over certain 

 parts of the reef flats. 



At the northwest end of Marokau beach rock and recent conglomerate 

 cover the old ledge, which crops out here and there on the wide reef 

 flat (PI. 70, fig. 1) of the western face, extending towards the southern 

 point of the island. Boulders also are scattered all along the outer reef- flat 

 of the western face, numerous bars of shingle extend across it, with 

 sand bars on the lagoon face, and with gaps of green water forming the 

 communication between the sea face and the interior of the lagoon. The 

 reef flat is at least from 700 to 1000 feet in width, as far as the southern 

 point (PI. 70, fig. 1). The sea face beaches of the islands are high 

 shingle beaches with small boulders, principally of beach rock, scattered 

 along the outer edge of the reef flat (PI. 70, fig. 1). The southern part of 

 the lagoon is much the shallowest, the flat on the lagoon face being fringed 

 with a broad belt of light green water. The lagoon edge of the western side 

 is faced with sand bars, one of which is specially noteworthy for its length ; 

 it must be over a mile in length, and separated from the adjoining reef flat. 

 Two islets could be seen on the eastern face of the atoll which seemed to 

 extend well into the lagoon. In a narrow channel there are some very large 

 masses of beach rock and recent conglomerate on the reef flats similar to 

 those of other lagoons. 



At the southwest horn of Marokau there is a wide reef flat, the continua- 

 tion of the western reef flat (PI. 70, fig. 1), wider than any we have as yet 

 seen in the Paumotus, with a line of large boulders running about parallel to 

 the raised edge of colored Nullipores and Pocillipores. The large island at 

 the southern extremity of the atoll is flanked by a high shingle beach. 



The two atolls of Marokau and Ravahere appear like a single atoll as 

 seen coming from the north, the islands of the one and of the other sepa- 

 rated seemingly by a somewhat wider gap than is usual, or by a wide pas- 

 sage opening into a lagoon. Passing through the strait between the atolls, 



