148 PROF. W. J. DAKIN : EXPEDITION TO THfi 



NORTH ISLAND. 



North Island was only visited on our first expedition to the Abrolhos, and 

 our observations have not been so detailed there as at the other places. This 

 island does not appear to have been visited so frequently as the others, being 

 due in all probability to its greater distance from the coast. 



North Island is almost a square mile in area. It is not surrounded by 

 smaller islets, and differs from the other groups we shall consider, in being 

 without any real lagoon region. In fact, the part above water at all states 

 of the tide rises from a coral flat which fringes it on all sides, but it is very 

 much wider on the west than on the east. On the Eastern shore, a fringing 

 reef lies quite close to the island, and a few breaks or channels occur where 

 fishing luggers can obtnin some shelter and anchorage in bad weather. The 

 channels, which are very irregular, are about 5-6 fathoms in depth, with 

 sandy bottoms on which large holothurians may be easily seen through the 

 clear water. On the West side of North Island the margin of the reef lies 

 just over a mile away from the shores of the island. No boat channel or 

 lagoon exists between it and the shore. A broad reef-flat extends from the 

 shore out to the reef-margin and is covered by a foot or two of water at high 

 tide. One can walk out for the whole distance, but care must be taken, for 

 the coral surface is rotten and full of holes, with larger hollows here and there. 

 There are no living corals growing upon the surface of this flat. The same 

 reef-flat extends north and south of the island for a greater distance and is 

 continued as a submerged reef for a considerable stretch towards the Wallaby 

 Islands. 



The surface of the flat is covered with living Vermetus, and, as a matter 

 of fact, this gasteropod is the common animal of all the reef-flats of this 

 region. The shells puncture neat but exceedingly painful holes if anyone 

 carelessly places an unbooted foot on such ground. The rock-pools swarm 

 with young fish which must pass through their larval stages with some 

 rapidity in such heated water (the temperature rises to remarkable points 

 whilst the sun is shining). A blue crab, Thalamita sp. (probably stimpsoni, 

 an Indian form), was very abundant in holes in this coral, and also the sea- 

 urchin EcMnometra mathce. We shall meet with this species elsewhere. 



North Island itself and the two large islands of the Wallaby Group are 

 the only ones to attain any height above 8-14 feet. The highest point on 

 North Island is 42 feet above sea-level. All this high ground of North 

 Island consists of blown sand, which rises in the form of dunes quite close to 

 the eastern shore margin. Other hills lie irregularly behind these, so that a 

 distinctly high region occurs close to the eastern side. The height of the 

 island falls off rapidly as the centre is approached. At the south-eastern 

 corner of the island the margin takes the form of a low coral-limestone cliff 

 instead of sand-hills, and the coral-reef flat, already referred to above, runs 

 into the foot of this. As a matter of fact, in many places it is undercut by 



