HOUTMAN ABROLHOS ISLANDS. 173 



Square Island and the northern extremity of Pelsart Island), the lagoon is 

 broken up in the most extraordinary way by reefs. The best illustration of 

 their character, that I can think of, is to refer the reader to the well-known 

 "maze" constructed of hedges that one meets with in certain of our famous 

 English gardens. Our attempts to find a way through the lagoon at this 

 place, with the motor dinghy, were absolutely the same as those of an 

 unfortunate stranger in a " maze." The " hedges" of the maze are represented 

 by coral reefs rising vertically from the bottom of the lagoon and having 

 flat tops which stand a little above low-water mark. They are circular, semi- 

 circular, straight, and of all manner of shapes. The water between them is 

 often of considerable depth, 13 to 16 fathoms in fact, and one careers along 

 happily for a little distance only to find perhaps a blind end in front. This 

 means a return and another trial along some other channel. 



Rich coral growths are found in this north-eastern corner of the lagoon, 

 and, as a matter of fact, this is the only place in the Abrolhos Group where 

 we found fields of Madrepora so close to the surface that they were exposed 

 at very low tide. This observation fits in with Saville Kent's "chromo" 

 made twenty years ago, but Kent did not know that he had pictured about 

 the only spot in the Abrolhos Group where such a growth of coral prevailed. 



I am convinced that the greater part of these lagoon reefs in the north- 

 eastern area of the Pelsart Atoll are due directly to coral growth from the 

 bottom of the lagoon, and not to the erosion of an elevated area. Their 

 sides rise almost vertically from the bottom, but growths extend outwards 

 from the top, and frequently overhanging portions break off and fall to the 

 bottom to be overgrown by fresh coral. Wherever coral growth is not 

 taking place one finds erosion, deposition of sand, or a temporary state of 

 equilibrium. The atoll is the result of no single factor, but of a complex 

 interaction of vital, physical, and chemical components. 



The larger islets of the lagoon were unfortunately (owing to lack of time) 

 but cursorily examined, but some of the smaller ones on the north were 

 visited several times and Pelsart Island itself was examined more closely. 

 The smaller islets consist of coral rocks and debris heaped up by the waves. 

 Some of those in the north, however, seem to have suffered an elevation 

 of a few feet, and this also applies to Pelsart Island. The coral fragments 

 do not remain loose but are compacted together by secondary deposition. A 

 well near the southern end of Pelsart Island enables one to obtain a glimpse 

 of 10-12 feet of rock, all of which is coral conglomerate. Much of Pelsart 

 Island is composed of loose fragments still, and in some places there are 

 enormous quantities of gastoropod shells which have been thrown up. The 

 island is 6-8 feet above sea-level, and sand and guano deposits occur here 

 and there. Guano workers have, however, visited this island, and con- 

 sequently the surface deposits have been somewhat tampered with. 



