154 PROF. "W. J. DAKIN : EXPEDITION TO THE 



Let us return to the limestone. The best exposures illustrating its 

 structure are to be seen in Turtle Bay on the west side of Fish Point 

 (PI. 10). The cliff is collapsing here, but the surface is not weathered in 

 the same way as at some other places where its structure is hidden. The 

 limestone is a conglomerate of coral and mollusc shells (PI. 10). In parts it 

 has quite a stratified appearance due to the presence of great flat coral 

 colonies of a species common at present in the lagoons and allied to 

 Madrepora corymbosa, if not this species itself. Between the corals is a 

 hard mass of coral-mud, or secondary deposits of calcium carbonate, which 

 cement everything together, and in which lamellibranch and gasteropod 

 shells are imbedded. These shells show little or no signs of weathering or of 

 abrasion. (See photo, PI. 10.) The most common of the molluscs are 



Turbo pulcher, Reeve. 

 Conus magus, Linn. 

 Cytherea reticulata, Linn. 

 Septifer bilocularis, Linn. 



There is every evidence of elevation to bring this coral limestone into its 

 present position, and the corals appear for the most part to have grown in 

 situ. We shall refer to this elevation later after describing West Wallaby 

 Island. 



It has been said that plutonic rocks occur on the Wallaby Islands. We 

 have now made traverses across these islands in every direction, and we have 

 also closely examined the wells which occur in one or two places. Nothing 

 but limestoue is to be seen anywhere, and we are quite sure that this rock 

 only is present. There are no references to the actual discovery, or 

 examination, of plutonic rock in the literature on the islands. What 

 statements are made appear to be due to a casual remark which has 

 been handed on by people who have not investigated, and in some cases not 

 even visited, the islands. 



West Wallaby Island. 



There is no need to describe in any detail the structure of West Wallaby 

 Island, for it is clearly the same as East Wallaby Island and obviously part 

 of the same elevated limestone mass. West Wallaby Island is of irregular 

 shape and is the largest island of the Abrolhos. From north to south the 

 greatest length is just short of three miles. A few points of interest should 

 be noted. The highest part of West Wallaby Island does not occur on the 

 eastern side [cf. East Wallaby Isle), but on the southern mile of the western 

 coast, and this elevated region is remarkably like that already described as 

 occurring on the N.E. coast of East Wallaby Island. The highest point, for 

 example, is again quite close to the shore, and a steep cliff rises at once from the 



