156 PROF. W. J. DAKIN : EXPEDITION TO THE 



fact that it is entirely composed of Foraminifera, Nullipore fragments, and 

 Echinoderm spines, with a considerahle amount of secondary deposition 

 of carbonates round the individual grains. It is in fact an indurated beach- 

 formation. No trace of land-derived sediment exists. It is this rock which 

 forms the lowest part of the cliff, a layer of coral rock infiltrated with 

 secondary carbonates appears at a higber level. 



A reef-flat extends round the base of the West Wallaby Island. On the 

 eastern side it extends out for some distance and smaller islets rise from it. 

 This area will be dealt with again below. To the south the flat is narrow, 

 and lies close up against the outer reef at this point. On the south-western 

 side, at the foot of the high cliffs already described, the reef-flat is wide 

 again, and here one meets with plenty of evidence showing that the flat has 

 been formed by erosion. Pinnacles of rock are left standing, overhanging 

 on every side (PI. 14. fig. 7), and great pot-holes occur on the flat itself. 



The Reef and Smaller Islets of the Wallaby Group. 



It is convenient after discussing the character of the chief land masses of 

 the Wallaby Group to consider as a whole the remaining small islets and the 

 coral reefs surrounding them. The " tout ensemble " is much more irregular 

 than in the southern groups to be presently considered. A glance at the 

 chart (text-fig. 2, p. 136) will show that a mass of coral reef exists several miles 

 to the west of West Wallaby Island and protects a lagoon with 3-4 fathoms as 

 an average depth in the northern portion. Towards the south-western point of 

 West Wallaby Island this reef swings in, until it joins the reef-flat which 

 fringes both the Wallaby Islands and forms the inner shore of the lagoon. 

 Towards the same point, the broad lagoon becomes more and more shallow until 

 only one or two feet in depth. The outer reef, against which the ocean swell 

 beats, remains close to the coast of West Wallaby Island on the south as a 

 fringing reef, and then leaves the S.E. point of the island in the form 

 of another broad sweep whicb extends eastwards, but in a more irregular 

 manner, and can be traced past Noon Reef and Morning Reef, where it turns 

 northerh r (text-fig. 2, p. 136). Inside the large expanse sheltered by the 

 reef there are numerous coral growths and remains of islands, the whole 

 thing being the result of solution, denudation, and active coral growth. 



The two Wallaby Islands are connected, as we. have already pointed out, 

 by a broad and shallow reef-flat. This reef-flat extends over the shaded 

 area in text-fig. 2, and several small islands rise from it, three of wbich (the 

 more northerly ones) are shown on the map of East Wallaby Island 

 (text-tig. 5, p. 151) . The most northerly of these is called Pigeon Island by the 

 fishermen, who like to enter Recruit Bay as far as they can and anchor with 

 perfect shelter between Pigeon Island and East Wallaby. We camped on it 

 several times. All the islands on this reef-flat agree in type. They are 

 usually much longer than broad and with the long axis running nearly 



