RANGIROA. 3 1 



lagoon fiice of the reef platform on the weather and lee sides ot" the lagoon 

 and on the slopes of the islets found in the lagoon. 



On the lagoon side of the lee land the steep beach in places is made 

 up of fragments of coral more or less weathered, and forming what I 

 may call coral shingle (Pis. 6, fig. 2; 9, fig. 2). "When examined, the 

 shingle is found to be composed of fragments of recent species of corals, of 

 fragments of beach rock, of pieces of coral breccia or conglomerate mixed 

 with fragments of the old tertiary reef rock or corals disintegrated from 

 it. The breccia and conglomerate on the lagoon and sea face (Pis. 5, 8, 

 11) also are made up in part of modern material and in part of fragments 

 of the old reef rock torn by the waves from the edges and sea face of 

 the old platform and thrown up on the beach in benches. 



On crossing the island to the east of Avatoru Pass, we came upon the 

 different stages of its growth as first formed by the disintegration and 

 erosion of the old tertiary ledge, then of its fragments thrown up towards 

 the interior, mixed with those of recent corals growing at that point. Near 

 the gendarme's house we came upon a ledge of old reef rock (tertiary cor- 

 alliferoas limestone) in dtit about seven feet above high-water mark. In 

 the central part of the island, which varies in width from 800 to 1200 

 feet, are found large loose masses of recent beach rock, corals, and old reef 

 rock, together with finer and coarser blocks of coral. In the depressions 

 near the edge of Avatoru Pass and in some parts of the centre of the 

 island we come upon the ancient reef rock in situ. At a point near the 

 entrance to Avatoru Pass, on the east side, a projecting ledge consisted 

 in part of recent conglomerate and in part of ancient reef rock, which 

 had been eaten away to form the adjacent beach. On the sea face the 

 slope of the outer beach was covered with fragments of old reef corals 

 and coral rock which had been thrown up, mixed with the worn fragments 

 of recent reef corals, forming a gray shingle on the beach nearly 16 feet 

 high. In fact, the same conditions which exist on the lagoon face exist 

 on the sea face of the island. 



Isolated Astrajans are growing on the old reef rock plateau, which is 

 planed off" to a general level, and honeycombed and pitted and grooved and 

 covered with sharp points projecting from the surface of this flat ledge. 



