MAKATEA. 63 



of the lagoon platforms, the ledges and islets of the inner lagoon, the exist- 

 ence of beach rock ledges, of conglomerate ledges, — all these characteristics 

 of the modern atoll are nowhere to be traced in the sink of such an island 

 as Makatea. In fact, we can explain far more readily its existence through 

 atmospheric agencies and other factors which we know to act upon lime- 

 stones, after the island had been elevated, or during the course of its 

 elevation. 



Dana ' has well described the appearance of Makatea while crossing the 

 inland basin. He also states " that the rock of the elevated portion of the 

 island of Makatea " appears to correspond to the interior of the original 

 lagoon of the island, and exemplifies the kind of rock-making which is going 

 on in most of the coral island lagoons." This does not seem probable to 

 me. The material composing the pinnacles, spires, or ledges of the central 

 sink does not differ from that found on the fossiliferous cliff faces of any 

 of the elevated coralliferous limestone islands of the Paumotus and others 

 which have no lagoon, such as Guam, Nine, the Tonga Islands, and Fiji. 

 The material of the bottom of the lagoon generally contains comparatively 

 few corals and other invertebrates, and consists mainly of sand or ooze 

 made up of fragments of Nullipores and corallines. 



It seems to me as if Dana^ had laid too much stress upon the absence of 

 fossils in interior basins, as when he characterized these basins as eminently 

 the places for making non-fossiliferous limestones. While it is true that on 

 the lagoon beaches shells and other invertebrates are ground into fine 

 material, yet at a very moderate depth the calcareous mud of the bottom of 

 the lagoons is often filled with shells, Echini, Crustacea, and other inverte- 

 brates, and if fossilified would form anything but a limestone barren of fossils. 

 In many shallow lagoons which are in an eminently marshy condition 

 (as stated by Dana*), and have become so small and shallow that corals and 

 large shells have all disappeared, the bottom is covered by the finest kind of 

 calcareous mud. But this mud is not necessarily devoid of fossils; on the 

 contrary, we should infer very much the opposite, from the mass of small 

 marine shells found on the shores of the lagoon of Niau and of San 



• Loc. cit., p. 193. » Loc. cit., p. 389. 



2 Loc. cit., p. 386. * Ibid. 



