﻿1851.] 



LOGAN — GEOLOGY OF SINGAPORE. 



.331 



from their extremities or exposed at their sides. When the sea has 

 worn down a portion of one of these islands below its level, the coral- 

 line polyps that incrust its outer margin, where it sinks into deep 

 water, begin to advance upon it towards the land and preserve it 

 from further abrasion. Were it not for the causes to be mentioned, 

 this curious organic shield would effectually defend the rocky foun- 

 dations of the islands from the attacks of the sea ; and in process of 

 time, when the Strait was denuded of all the hills that now rise above 

 its surface, each of them would be represented by a coral-reef of an 

 irregular annular shape * . But in many localities, after the corals have 

 flourished over a considerable horizontal space for some time, yielding 

 strata of sandstone come under the influence of the waves, which 

 grind them down and spread the sand over the coral-field. The speedy 

 consequence is that the polyps perish, and in their place a bed of 

 sand and dead coral is left, which sometimes cements into a hard 

 calcareous layer, but generally becomes a prey to the sea. Living 

 coral-fields are found in all parts of the Strait, but most abundantly 

 in the north-eastern portion of the most westerly basin in the shoals 

 around and between its numerous islets. Beaches from which corals 

 have perished occur frequently ; amongst the largest being those in 

 front of Blakang Mati village, the east coast of Sambo Besar, and 

 Bukum. On coasts of soft wasting sandstone they are seldom found ; 

 and in the proper mangrove localities, that is, in sheltered places where 

 mud accumulates, they are either wanting or are scattered in small 

 and weakly patches on spots where sand occurs. Their proper habi- 

 tat is a beach or shelf of indurated rock abraded to a level below that 

 of the ebb-tide, sinking at its outer margin into deep water, and with 

 a free exposure to the sea so as to be constantly scoured by the waves* 

 Such shelves seldom preserve all these conditions up to the land, so 

 that there is generally an inner space from which the waves retire at 

 ebb-tide. It is still moist, full of small pools, and dotted with pieces 

 of living coral, but the continuous coral-beds growing luxuriantly in 



* If the Strait were to remain perfectly undisturbed by subterranean forces, 

 neither undergoing subsidence nor elevation, it is obvious, from what we now see 

 to be going on, that these two antagonist powers, water and the coral-polyps, 

 would, in the course of time, leave the Strait without any vestige of land, save 

 some reefs and rings covered and shielded by the coral. These two simple and 

 ever-operating agencies, mechanical and organic, appear sufficient to explain the 

 fact, that patches of land are found over vast spaces of ocean at the same level. 

 Let the present condition of things last long enough, and an aggregation of moun- 

 tain-groups, like that of the Malay Peninsula, will be abraded, broken into islands 

 and coral-reefs, until island after island is worn down beneath the level of the sea, 

 those only remaining at that level in which the conditions for the continued ex- 

 istence and growth of coral are maintained throughout the process of degradation. 

 In endeavouring to follow out such a process from the facts presented by a coral- 

 line sea, like that of the Straits of Singapore, the shores where coral is absent are 

 as instructive as those where it is present ; for whatever successive changes the 

 configuration and disposition of the land may undergo in the progress of denuda- 

 tion, the same causes will continue to favour and oppose coralline growth so long 

 as wasting shores and streams of fresh water exist. The process would accelerate 

 as it advanced, and a condition of things approximating to that of the archi- 

 pelagoes in the open ocean be reached, in which both the mechanical and organic 

 powers are greater than in the Strait of Singapore. 



