HOUTMAN ABROLHOS ISLANDS. 137 



North Island (see map, text-fig. 2) is the most northerly of the Abrolhos 

 Group. It is situated about nine miles north of the Wallaby (or Wallabi) 

 Isles, and is about one square mile in area. The Wallaby Group proper 

 (see map, text-fig. 2) consists of two large islands, the East and West 

 Wallaby Islands, and a number of small ones which are either unnamed or 

 bear local names given by the fishermen. The West Wallaby Isle is the 

 largest of the Abrolhos Group. 



About 14 miles south of the Wallaby Group is situated the Easter Group 

 (see map, text-fig. 1, p. 128). The largest of this collection of islands is Rat 

 Island, which, however, is much smaller than either the East or the West 

 Wallaby Islands. 



The Zeewyk Channel (about seven miles across) separates the most 

 southerly islands of the Easter Group and the northern reefs of the Pelsart 

 Group. The largest island of the latter group is Pelsart Island itself (called 

 Long Island by the fishermen), an islet of considerable length extending to 

 the extreme south of the Abrolhos archipelago. Although far exceeding all 

 the other islands in length, being roughly eight miles long, Pelsart Island is 

 in most places only a few hundred feet across, aud much of this consists of 

 heaped coral fragments. The Pelsart Group takes much more closely than 

 any of the other groups the form of an atoll, a somewhat triangular atoll, 

 with the apex directed towards the south. Pelsart Island forms part of 

 one side of this triangle. A distinct resemblance is to be traced in the 

 Easter Group to the atoll, but this question will be considered in detail when 

 describing the structure of the different islands. 



Saville Kent stated that all the islands of the Houtman's Abrolhos were 

 coral formations with the exception of certain of the Wallaby Group. In 

 this region plutonic rocks were said to occur corresponding to those of the 

 mainland and having an elevation of some 30 or 40 feet. It is difficult 

 to understand to what particular rocks Kent referred, but in any case his 

 remarks are incorrect. The Wallaby Islands were carefully examined and, 

 although they are much larger than the other islets and attain the greatest 

 elevation, there is no trace of any rock other than recent limestone. All 

 the Abrolhos islets are coral formations. 



The nearest rock of Kent's plutonic type on the mainland is granite. 

 This has been met with in Geraldton at a depth of 420 feet and it 

 also occurs down the coast. It may be pointed out here that Michaelsen 

 and Hartmeyer in their introductory section to the ' Fauna Sudwest- 

 Australiens ' speak of the coastal limestone near Fremantle as being 

 uplifted coral-reef. This is also quite incorrect, and it is curious that these 

 German workers failed to notice it. The limestone of the Fremantle coast 

 has been formed by the action of water on vast accumulations of drift sand 

 containing much calcium carbonate. The uplifted coral limestone of the 

 Abrolhos is quite different from this seolian limestone of the more 

 southern coast. 



