JALUIT. 289 



gradually filling with material derived from the sea face, and islands and 

 islets, similar to those existing on the lagoon side of Imrodj, are eventually 

 formed. 



A marked characteristic of the part of the sea face of Jaluit atoll near 

 Imrodj is the number of deep pools which separate the islands and islets, 

 showing that the sea must once have been driven through passes between 

 these islands, when they formed channels across the outer reef flat. These 

 channels have gradually become closed and the sea shut out from the 

 lagoon by the mass of material forming dams thrown across the gaps. At 

 Jabor, where the reef flat is of moderate width, one can see that should 

 hurricanes occur the whole island would be swept by the sea ; even during 

 one of the very high tides we experienced at the time of ordinary trade- 

 winds, the moderate sized rollers, pounding upon the outer sea face of 

 Jaluit, washed over the top of the low shingle dam land rim and flooded to 

 a certain extent the interior of the island, filling with sea water the sinks 

 and pools upon which the natives depend for fresh water. 



The filling up of the gaps at some of the passes is often quite rapid ; 

 when the sand spits on opposite sides reach out well into the deeper water 

 of the lagoon, and sand comes from the two sides of the gap, the building 

 up of the dams is rapid and the spits soon become connected. 



On leaving Jaluit we steamed directly across the atoll towards the 

 southwestern passage. As the islands and islets of the west side came 

 into view we saw that they arose from a wide reef flat which, like the 

 flats on the flanks of other passages, extended far into the interior of 

 the lagoon. The lagoon face of the islands and islets was edged with 

 fine coral sand beaches, while on the sea face they were edged with 

 coral beach rock conglomerate. The islands and islets of the western 

 land rim are connected by flats covered with beach rock conglom- 

 erate. It is not astonishing that the material on the lagoon face of 

 the islands on the western side of the atoll showed greater mobility 

 than the material on the reef flat off the western face of the eastern 

 islands.^ The sweep of the trades across the lagoon is considerable, and 



1 The western reef platform is wide, much wider than on the east side. This is natural, as the 

 conditions are exactly reversed. 



