MILADUMADULU. 389 



I have found Lithothamnion to be abundant on the edges and slopes of the reefs, but it 

 does not incrust large areas, as on the true seaward slopes. Off the west of many of the 

 east rim islands no reef flat occurs, but this is easily explicable by the consideration of the 

 recent changes in the land, such absence of reefs being usually associated with an outgrowth 

 of the land by the piling up of sand, or in other words with much movement of fine 

 matter by the winds and waves. 



As a whole our bank is a table-land beneath the sea with a number of gradually, or 

 precipitously, sloping, low table-hills, all of the same height. Its interior is remarkably level, 

 and, while there is generally a little sand covering the surfiice of the bottom, our sounding 

 leads never drove into a thick deposit except close to some island. In dredging we procured 

 a number of corals, especially near reefs, but more often the dredges came up with polished 

 metals and quite empty. Between the islands of the east rim the bottom was rougher, and we 

 obtained specimens of most of the sedentary animals found elsewhere in 20 fathoms. Between 

 Mafaro and Manadu we found two coral patches of 7 and 10 fathoms, but within the bank 

 we met with no areas which seemed to be growing up to form surface reefs. 



How the islands within the bank were built up in the first place is not at all clear. 

 In any former condition of the bank there is no reason why shoals should not have grown 

 up on any part, provided the reef corals and other organisms once managed to obtain a firm 

 foothold. An island like Dureadu with raised coral rock outside could only have been formed 

 by a change of level. But the large majority of the inner islands are formed of sand, perhaps 

 indeed all those charted as without anj' reefs, this absence of foundation reefs being due to the 

 movement of the sand on their slopes preventing any growth of rock-forming organisms. Further, 

 all these sandy islands appear to have their shores washing away, and how they have continued 

 to exist so long it is difficult to explain. They would necessarily seem to have been created 

 in the first place by a change of level, but the original shoals must have been built up 

 of rock rather than sand. Not only are these islands themselves washing away, but, since 

 they have no enclosing reefs or protecting growth of organisms on their slopes, their foundations 

 are being removed down to the level of the floor of the bank. It accordingly appears probable 

 that the sandy islands were formerly protected by belts of elevated rock against the sea, which 

 have now been completely removed, but the evidence, from which their former condition might 

 be deduced, is very meagre. 



It is most extraordinary that all the banks of the east rim should have land. Round 

 their seaward sides the reef flats are in all cases very narrow, and the islands would appear 

 to have been at one time almost conterminous with their reefs. The seaward beach is in 

 every case of rock, and the reef flat off the same is studded with pinnacles and masses of 

 rock ; its surface and edge are bare and it shows no definite outgrowth in any place. Where 

 there is no land, as in the middle of the reef of Furnadu and to the north-east of Mafaro 

 the reef flat is broader, and the reef has the regular fissured edge characteristic of an outgrowing 

 one. Accordingly, the absence of outgrowth off the land must be ascribed to the mud and dirt 

 which is being continually swept out from it, preventing the growth of the building organisms. 

 To the west of the same rim reefs, wherever a definite flat exists, its edge has the usual 

 outgro^^dng appearance, but owing probably to the shallower water this is often more marked 

 than to seaward. As already mentioned, a true reef is, however, seldom found off the inner 

 ends of the islands of the east rim, owing to the currents forming eddies behind their reefs 

 and constantly shifting the sand. 



50—2 



