HOUTMAN ABROLHOS ISLANDS. 157 



north and south. They are all flat-topped, and possess vertical or over- 

 hanging cliffs about 8 feet in height (they are highest on Pigeon Island, 

 8-10 feet). Again, there is ample evidence that they have once been 

 continuous. Pigeon Island is gradually becoming smaller, the cliffs 

 overhanging in places for 20 feet or so forming caverns. Here and there 

 great masses have broken off and are gradually being removed. The 

 structure of the coral limestone of which they are composed is similar to 

 that of the Wallaby Islands. 



Whilst a glimpse of these islands with the lagoon waters presents certain 

 pleasing features, they make a very uninteresting photograph. No palms or 

 tall plants break the monotony, and the elevation of the islands is so small 

 that from a little distance they appear simply as streaks in a photograph. 



It may be taken for granted that all these islets have been cut awaj' from 

 one mass, and they are still being reduced in size by the action of the sea. 

 The reef-flat connecting them together is all that remains of the elevated 

 limestone of which they once formed part. 



We are now left with one or two islets much further away from the 

 Wallaby Islands on the outer reefs to the east, a narrow island known as 

 Long Island by the fishermen and several islets not marked on the chart, 

 some of which are only a few yards across. Many of these islands are 

 obviously the result of blocks of coral heaped up by the waves, and their 

 loose structure is quite different from the more compact limestone of the 

 central mass. We are in fact dealing with structures more like the islets of 

 the rim of a coral atoll. 



Let us glance at Long Island, it being the largest islet in this situation. 

 It is about one mile long and only a few hundred feet across. Its surface 

 consists of small and loose coral fragments, and in fact the whole island is 

 made up of such coral fragments. They prevail above all else, and one 

 cannot consider coral as playing any subordinate part here to calcareous 

 algse, molluscs, or other calcareous structures in the formation of this mass. 

 In places, the weathered fragments have been more or less cemented together 

 to form a more definite kind of conglomerate. I consider that a slight 

 elevation (not more than 6 feet) has played some part in the formation of 

 Long Island as well as the heaping up of the coral fragments by the waves. 

 The straight line taken by the reef on which the land stands is no doubt due 

 to the current, which scours the eastern side, and has produced the channel 

 referred to later. 



A small lake exists at the northern extremity of the island and there are 

 one or two other similar depressions at other places. We shall see that these 

 are quite common on the islets of the rim of the Abrolhos Groups. This is 

 rather an interesting point, and I have found it very advantageous and 

 informing to compare the descriptions given by Stanley Gardiner of the 

 "faros'' of the Maldives with these islands of the outer rim possessing lakes 



