164 PROF. W. J. DAKIN : EXPEDITION TO THE 



high tide. It has been turned over pretty thoroughly by the guano workers, 

 so that there is little material left over the rock and one can examine the 

 latter quite easily at any point. It is a coral limestone which has been so 

 compacted that a very hard homogeneous mass has been produced. Professor 

 Woolnough, who kindly made sections of this material for me, states that it 

 is coral rock completely infiltrated with secondary carbonates and completely 

 solid. I consider that the coral limestone of the central islets is slightly 

 older than any rocks exposed as part of the outer reef islets. 



The surface of the island is covered with the usual bushes standing about 

 four feet high at most. Many introduced plants occur, the result of the 

 residence of guano workers and fishermen. Numerous holes due to 

 subaerial denudation exist, and two or three of these may be termed wells — 

 they probably contain fresh water throughout the year. It is neither 

 satisfactory, nor plentiful enough, for the few guano workers at present on 

 the islands, who have all their supplies brought in tanks from the mainland. 



Surrounding the whole of Rat Island is a reef-flat which is increasing in 

 width, for the island is being rapidly eroded to this level. Close to the edge 

 of the reef-flat, just before the deeper waters of the lagoon are reached, is a 

 small boat channel about four feet deep. The section (text-fig. 9) shown 

 illustrates this character. 



Text-figure 9. 



/ BetF I 



H.gh >;d. 



Vv Lagoon 



The rim islands of the Easter Group and the eastern area of the lagoon 

 have been very closely examined — more so than other parts of the Abrolhos. 

 There are upwards of a dozen islets of varying size, some of which can hardly 

 be said to be separated from one another, for at low tide one can cross with- 

 out wetting the feet, whilst at high tide it is quite easy to wade across. 

 Others are, however, separated by deeper channels. 



A channel, with 6-10 fathoms of water, exists where we entered the lagoon 

 of the Easter Group (see chart), called Easter passage by the fishermen. 

 Another one occurs just south of Wooded Island where the charts are marked 

 " Channel reported." Between these two passages there are no deep 

 channels, and one could pass more or less easily from islet to islet, a distance 

 of roughly 5 miles. All these islets agree, as might be expected, in character. 

 They are largely composed of heaped up blocks and fragments of coral. For 

 the greater part these still remain loose and uncemented, or but slightly so. 

 In places, however, a more solid limestone is exposed, as for example on 

 Wooded Island and on the southern end of the islet immediately to the north 

 of it. It is a conglomerate composed chiefly of weathered fragments of coral. 

 The island immediately south of the Easter passage is also largely composed 



