AGASSIZ: FIJI ISLANDS AXD CORAL REEFS. 



95 



slight angle with the west coast ridge, and is separated from it by a deep 

 valley. The three islets off the western part of the southern face of 

 Mango are all on the outer edge of the reef Hat (Plate 87). They con- 

 sist of volcanic rocks. The central 

 islet is the largest, and is com- 

 posed in part of stratified volcanic 

 mud miderlaid by harder rocks. 

 Between the islets, and extending 

 over the outer reef flats to the 

 north and to the east, stretch 

 numerous negro-beads of a vol- 



;«' 



!M 





WEST OF MANGO LANDING, VOLCANIC 

 SUBSTRATUM. 



canic natiTre. 



The island of Mango is of the 

 same type as Fulanga, except that 

 the erosion and denudation of the 

 lagoon has not been carried on to 

 so great an extent, Mango being 

 composed so largely of harder 

 volcanic X'ocks. The platform 

 forming the reef flat is dug out into a very narrow and shallow lagoon, 

 and both are studded with negro-heads, the remnants of the adjacent 

 shore slopes. The inner sound, which in the case of Fulanga has been 

 eroded and denuded to form a large inner basin, consists in Mango only 

 of a diminutive basin studded with elevated limestone heads and rocks, 

 and barely connecting with the exterior eastern lagoon ; the sea has not 

 found its way to any extent through the elevated limestone barrier lying 

 across the break of the rim of the island. 



Lakemba. 



Plates 19, 31. 



_ The island of Lakemba is elliptical, with a prominent spit extending 

 off" its southern face. Its greatest diameter is about five miles and a 

 half. The central mass of the island, which rises to a height of 720 

 feet, is volcanic ; on the flanks of this, on the northwestern and western 

 sides, are found nearly vertical steep shore bluffs of coralliferous lime- 

 stone elevated to a height of from 200 to 250 feet. The ridges extending 

 along the south shore, separated by a spur from the central mass, also 

 consist of elevated reef rock. Lakemba is surrounded by a fringing 

 reef, narrowest off" the northwestern point of the island ; it widens 



