176 PKOF. W. J. DAKIN : EXPEDITION TO THE 



chain. I was rather sceptical at first about these stories, but am quite certain 

 now that whales do resort to this small enclosed area for this purpose, for we 

 had visitors whilst I was there. As it is not easy to find the entrance, and 

 the area is but small, any other good reason for the frequency of whales in 

 this particular spot seems to me entirely wanting. The visitors whilst 

 we were there were specimens of the Humpback. 



A detailed report on the general faunistic characters of the Abrolhos 

 Islands will be written up after the various collections have been investigated 

 by specialists. 



CONCLUSION. 



The Coral Formations of the Abrolhos Islands. 



It will be convenient if our observations on the coral reefs of the Abrolhos 

 Archipelago are brought together in the form of a theory relating to the 

 origin of these islands. 



To this end it will be advisable in the first place to repeat in summarised 

 form certain observations that have been made. They are as follows : — 



1. The islands consist entirely of limestones for the greater part composed 

 of recent corals cemented together by secondary deposits of carbonates. In 

 places, as, for example, the lowest rock exposures on West Wallaby Island, 

 the limestone consists of foraminifera, echinoid spine fragments, and nulliporo 

 fragments, cemented together by secondary carbonates into a compact rock. 

 The corals and molluscs are all recent and shallow-water species. 



No signs of an}' plutonic rock, or other rock older than the limestone 

 mentioned above, are to be found. 



2. The more northerly islands, i. e., the large central islands of the 

 Wallaby Group, show signs of considerable elevation, cliffs of limestone 

 rising to heights of 30 feet. The islands of the southern groups are not 

 nearly so high. 



3. All the island groups show evidence of a more recent elevation of about 

 8 feet. This is marked by the terrace on the East and West Wallaby 

 Islands, and by the uniform flat worn surface of other islands which rise to 

 about the height of this terrace, i.e., Rat Island, some parts of Wooded 

 Island, Gun Island, Pelsart Island (part), and some of the Mangrove 

 Islands. 



4. The most southern group of the Abrolhos Islands, the Pelsart Group, 

 takes the form of an atoll. The lagoon depths are moderate, 17 fathoms 

 being the greatest recorded, and the depths on the outside of the encircling 

 reeE are not very great, averaging probably about 30 fathoms, but not less 

 on the west side where the depths are considerable a few miles away. This 

 absence of depth is due to the fact that the atoll rises from the continental 

 shelf, which is uniformly level over a considerable area. Had this sea- 

 bottom sloped more rapidly, there is no doubt that the outward growth of the 



