290 "ALBATROSS" TROPICAL PACIFIC EXPEDITION. 



the amount of material they pile up and shape into beaches and dams 

 on the lagoon face of the western islands is quite marked as compared 

 Avith the material moved on the west face of the islands forming the 

 eastern land rim of the atolls. 



On the western side, hardwood trees, the " iron wood trees," grow in 

 considerable numbers. The western passage is long, narrow, and wind- 

 ing (PI. 226, fig. 6); it extends into the lagoon from the western side 

 between lines of reef flats, composed mainly of Millepores and Porites, 

 killed as £hey approach the surface, much as we found the Millepores and 

 Porites of the Taritari lagoon flats covered by Nullipores. The reef 

 flats formed, in this case, a marked yellow belt on each side of the pass, 

 in striking contrast to the dark blue ribbon of the channel through which 

 we steamed. The reef flats on the lagoon side of the passage form a 

 large spit, cut in two by a narrow passage, and flanked on both sides 

 with beach rock. The southwest passage i-uns between the islands of Ai 

 and Medjerrurik. The channels we passed through, as well as the wide 

 bands of blue water indicating moderate depth on the reef flat in that part 

 of the lagoon, once formed, I have no doubt, part of the intricate passages 

 and channels which connected the sea with the lagoon. Land was gradu- 

 ally formed on the reef flat by material thrown up from the outer beach, 

 and the corals growing on the flat were gradually overwhelmed by sand 

 coming in either from the sea face or from the lagoon flats. The beaches 

 on the lagoon side of the land vim were formed in part of beach rock, and 

 in part of fine coral sand separating short stretches of beach rock con- 

 glomerate. A strong current was flowing in against the steady trades, 

 through the passage and gaps of adjoining islands, and to a certain 

 extent the reef flats on the two sides of the passage were swept clean 

 during that stage of the tide. On the lagoon edges of the flats the current 

 meeting the waves formed by the trades, the reef flats were more or less 

 covered with sand bars built up by the material brought on the one side 

 from the sea face of the land rim, and on the other from the lagoon side 

 by the trades blowing across the whole width of the atoll. 



The full force of the trades blowing across the lagoon is felt on the 

 lagoon edge of the western reef platform, while the sea face of the western 



