10 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



The lagoon of Ahe ' is said to be quite shallow and much obstructed by 

 growing corals. 



A cut- is given of what must probably be elevated old limestone rocks. 

 Unfortunately no locality is named ; it may be (Kauehi) Vincennes Island. 



There is a good cut of Metia* (Makatea) reproduced in Dana's " Geology 

 of the Exploring Expedition " and in his " Coral Islands." The ascent of 

 the bluff on the western face of Metia* is described: on reaching an open 

 space on the top a clear view of the interior was obtained. The general 

 shape, as far as it could be seen, was pan-like, or in the form of a dry lagoon. 

 He also says: "The island' has unequivocal marks of having been uplifted 

 at different periods; the cliff at two different heights appears to have 

 suffered abrasion by the sea." He gives a figure" of a part of the great sea 

 wall on the southern face of Rangiroa. with islands to the rear, taken from 

 a drawing made by Mr. Agate while the " Peacock '" ran along the south 

 shore. 



Lieutenant Johnson ' was left on Aratika to make some borings ; the 

 greatest depth reached was 21 feet, the principal difficulties encountered 

 being '• the looseness of the .sand and the falling in of the coral stones." * 



Wilkes also gives ^ an account of the method used by the Expedition in 

 surveying the coral i.slands. The basis of the method rested upon the 

 measure of distances by sound. Guns being fired alternately from the differ- 

 ent vessels, any three of them being stationary, the distances and positions of 

 objects could be determined from them by direct angles, or by angles be- 

 tween them taken from the shore, or from boats. On page 431 a woodcut 

 is given showing the method of surveying one of the islands. The survey 

 of an island ^^ about seven miles in length was made in three hours and 

 thirty-five minutes. 



1 Loc. cit., p. 337. 3 Loc. cil., p. 338. * Loc. cil., p 341. 



- Loc. cil., p. 334. * Loc. cit., p. 340. * Loc. cit.. p. 342. 



■ Loc. cit., p. 267, Vol. IV. 



* .\t Bow Island Captain Belcher bored to a depth of 45 feet : near Blossom anchorage he passed 

 tlirouj^h a fine coralline sand. A second attempt made on the outer belt of the island failed, as the 

 borer got jammed at a depth of 9 feet. Narrative of a Voyage round the World in the ''Sulphur," by 

 Captain Sir Edward Belcher, R. N., 2 vols., 1843. Vol. I. p. 3G6. 



9 Loc. cit., p. 429, Vol. T. 



w Probably Puka-ruha. H. O. Chart 78. The woodeut differs greatly in details from the island as 

 represented in the Hydrograpliic Chart, which is a bad copy of the original. 



