BevieiDs — Agassiz's Coral Beefs of the Pacific. 367 



Elevated islands of coralliferous limestone, like Fulanga, 

 Yangasa, Ongea, where the sea has eaten through the limestone 

 rim towards the inner sink, cutting the rim into islands, and has 

 formed a sound or lagoon dotted over with limestone outliers, 

 forming undercut and weathered islands and islets. The encircling 

 land-rim may disappear or be reduced to a few heads, as in Argo, 

 Ongea, or Yangasa. 



Elevated coralliferous limestone islands, cut down nearly to the 

 level of the sea by atmospheric agencies, like Niau in the Paumotus, 

 with a shallow sink (lagoon) connecting with the sea only through 

 the porous mass of the land-rim, or Rangiroa, and the majority of 

 the islands in the Paumotus, and some of the Gilbert Islands 

 (Apamama Tapeteuea), with a lagoon enclosed by a land - rim 

 composed of disconnected islands and islets forming passes and 

 gaps communicating with the sea ; islands all noted for the great 

 development of buttresses of modern reef rock and of Tertiary age 

 on the reef platforms, the remnants of a higher land mass now 

 denuded to the level of the sea. Similar outliers in the lagoon 

 form shoals, islands, and islets. 



Extensive elevated limestone masses, like those of the Tonga 

 Archipelago, with volcanic outbursts of limited extent that have 

 pushed through the limestone masses. 



Atolls with disconnected limestone and volcanic islands, the 

 remnants of islands partly volcanic and partly limestone, like Guam 

 and Eua, only on a smaller scale. In these the volcanic outbursts 

 as well as the limestone masses have been denuded and eroded, and 

 formed the groups of Vanua Mbalavu, Lakemba, Naitamba, Mothe, 

 and the like. 



Low atolls, like those of the Ellice, Marshall, and the Gilbert 

 Islands in part, where the land-rim is reduced to a minimum and 

 best developed on the weather side, and where the material com- 

 posing it is subject to constant transport, the material being derived 

 from the corals growing on the sea slope of the reef-flat platforms 

 and from the disintegration of the slightly elevated modern reef 

 rock conglomerate or breccia. Atolls all characterized by the great 

 changes taking place in the extent of the islands of the land-rim, 

 owing to the formation of sand bars, shoals, flats, bays, the closing 

 of gaps, the filling of lagoons by sand blown in from the sea face, 

 the throwing up of extensive dams on the lagoon flats to form 

 secondary lagoons, the existence of reef platform lagoons ; the 

 islands on the land-rims of these atolls being flanked with coral 

 sand, shingle, or boulder beaches on the sea face, with sand beaches 

 or beach rock flats on the lagoon faces. The islets, shoals, and 

 islands in the lagoons are either patches of elevated modern reef 

 rock or knolls of growing corals, many of them with deep passes, 

 usually most numerous on the lee side. The corals growing on the 

 sea slope of the reef platforms are often overwhelmed by sand dunes 

 blown over the land-rim from the lagoon flats. 



Atolls, like Tarawa, Tapeteuea, and Nonuti in the Gilbert 

 group, and Makemo, Fakarava, and others in the Paumotus, with 



