II EVIDENCE OF RECENT EMERGENCE 19 



Admiralty plan of this bay which were described as sand-spits in 

 the time of Wilkes. The promontory of Lekumbi could scarcely 

 have been expected to show any extension during this time, since 

 there are depths of 10 to 16 fathoms close to its extremity ; and 

 there is in fact no difference of critical importance indicated in the 

 charts. 



Some of the principal points of this chapter may be thus 

 summed up : — 



(i) Upraised reef-limestones are of very limited occurrence. 

 They occur at and near the coast and do not extend higher than 

 300 feet. Their scarcity at the sea-border is to be attributed to the 

 denuding agencies. 



(2) Since foraminiferous muds and sedimentary tuffs with 

 marine organic remains occur at all elevations up to over 2000 

 feet, it is assumed that the absence of reef-limestones in the 

 elevated interior indicates the paucity or absence of reef-growths 

 in the early stages of the history of the island. The overlying 

 agglomerates have often preserved from destruction the soft 

 sedimentary deposits beneath ; but they seem to have never covered 

 over a coral reef 



(3) The relation between the mangrove-belt and the reef-flat 

 indicates a state of equilibrium which might have been established 

 long ago. If the movement of emergence is still in progress, it 

 must therefore be of a very gradual nature, since the normal 

 relation between the mangrove-belt and reef-flat now prevails. 



(4) From the circumstance that the submarine platform passes 

 with a uniform slope into the low-lying plains, covered with sub- 

 marine deposits, it may be inferred that a very gradual emergence 

 is now in operation. 



(5) A comparison of the charts of Wilkes and of the British 

 Admiralty shows that on the north coast of the island during the 

 last half century the destructive agencies of marine erosion have 

 not prevailed. 



(6) The results of the comparison of the charts, whilst they do 

 not directly imply a change of level, are quite consistent with the 

 conclusion that the movement of emergence, which has been 

 in operation probably since the later Tertiary period, is not sus- 

 pended. 



Note. — The extensive evidence of emergence presented by this 

 island is treated in Chapter XXVII. in connection with the whole 



C 2 



