ANDREWS : LIMESTONES OF THE FIJI ISLANDS. 19 



On the northeast of the island there is a small lagoon (Plate 12) 

 having a longer diameter of 1000 yards (Plate 1) and a shorter one of 

 400 yards. A channel ten yards in width connects it with the sea 

 through a narrow limestone belt, 50 to 100 feet high. There is a 

 trace of an old reef on its margin. 



A fringing reef of modern date with enclosed lagoons conforms in a 

 general way to the shape of the land. These lagoons are deep holes, 

 true lakes at low tide, some of them are fully nine fathoms deep. The 

 floors are usually sandy, with scattered corals, while the steep walls of 

 the lagoon are often formed of growing reef. The reef itself is much 

 littered with huge blocks of coral debris, known locally as "nigger- 

 heads " and " horse-heads." Other larger blocks occur, some of them 

 40 feet in height. They result from cliff ruptures, and have undercut 

 bases (Plates 13, 14). In the deepest lagoon several small islands 

 occur, partly volcanic, and partly limestone agglomerates lying in a 

 cementing of andesite tuff. 



Along the shores of the island "beach rock" is well developed, and 

 at two or three spots along the shore streams of fresh water crop 

 up between low and high water marks from beneath this beach-rock 

 formation. 



A rapid glance at the centre of the island reveals a limestone ring 

 broken up by great volcanic outbursts of andesitic lava, dipping in most 

 cases towards a great central depression (Plates 15-17). The geometrical 

 shape of this hollow is lost, owing to the intrusion of a vast andesite 

 mass near its centre ; from the sides and from the slopes of the lava 

 streams forming the great amphitheatrical enclosure, vast alluvial masses 

 have spread over the ancient limestone floor of the hollow. The old 

 base or floor crops up now and again as a broken and weathered lime- 

 stone, or as huge isolated limestone masses projecting above the alluvium 

 or the lava slopes. At levels of 250 and 50 feet respectively above 

 high-water mark, remnants of old reefs are encountered along the inland 

 cliff exposures. The numerous caves of Mango are objects of in- 

 terest. One of these occurs in a large bluff 600 or 700 yards 

 inland. It is little more than a vertical hole 100 feet deep, with several 

 minor lateral ramifications. Other large caverns gape on the coastal 

 bluffs. They open out on the seaward faces of the cliffs in almost inac- 

 cessible positions. One or two penetrate the cliffs for distances exceed- 

 ing 60 yards. In all these large subterranean passages the examination 

 of the calcareous masses through which they have been formed is ob- 

 scured from various causes. In one or two places, however, the lime- 



