60 FOYE. 



southward the passage-ways have been widened until mere remnants 

 of Hmestone tip the ends of the spur-ridges. 



Thus, the island, bearing a number of andesitic cones, underwent 

 mature erosion and subsided. The mature topography was not 

 entirely submerged, since 400 feet of the island still remained above 

 the sea. The sunken portion was overlain by 320 feet, or more, of 

 coralliferous limestone, and was later uplifted. 



The limestone remnants decrease in altitude along the coast towards 

 the east and do not occur throughout the eastern third of the island. 

 The disappearance may be explained in two ways. It may be due 

 to more rapid solution on the rainy side of the island or it may be due 

 to tilting during uplift. If erosion were the cause, it would seem that 

 the rainy side should show a more mature topography than the dry 

 side. It is, however, significant that the western side shows greater 

 erosion than the east. 



Again, the reef on the western side of Lakemba is narrow and fring- 

 ing, but on the northeast it sweeps far out and includes a lagoon 8 or 

 10 miles wide. The width of the eastern reef suggests that it has 

 either been long established or recently submerged. The western 

 reef on the contrary appears to have been established in sub-recent 

 times. Recent valleys cut in red clay at the southwestern side of the 

 island support this conception, whereas the drowned valleys of eastern 

 Lakemba indicate a tilting in that direction. 



In this connection it is important to note that the Lakemba lagoon 

 has a maximum depth of 14 fathoms; the Aiwa lagoon, 4 miles to the 

 southeast, 21 fathoms; and the lagoons of the Argo reefs, 15 miles 

 to the east, depths of 20 fathoms on their western side, of 35 fathoms 

 on their eastern side. These depths are greater than the a\'erage for 

 the Lau islands and may be attributed to the eastward tilting move- 

 ment described above, (see table II, p. 93). 



An outline of the geological history of Lakemba is as follows: — 



1. Period of volcanic acti\ity. 



2. Period of erosion, carving to maturity the volcanic peaks 

 formed in the first period. 



3. Period of subsidence, during which 4 to 5 feet of conglomerate, 

 15 to 20 feet of shell sandstone, and 300 to 325 feet of coralliferous 

 limestone were deposited unconformably on the andesitic surface. 



4. Period of uplift in the western part of the island accompanied 

 by tilting toward the east. 



5. Period of erosion. 



