II EVIDENCE OF RECENT EMERGENCE 13 



fragments of coral associated with concretions of chalcedony, bits 

 of flints and hornstones, jasper, impure siliceous nodules, &c. The 

 localities may be at the coast or a mile or two inland, and are not 

 usually more than 100 or 200 feet above the sea. This subject is 

 treated with some detail in Chapter XXV. Here I may say that 

 such localities are confined mostly to the open, low, undulating 

 districts on the north side of the island. Silicified corals are not 

 always present with the fragments of chalcedony and other siliceous 

 concretions that are found so frequently in these situations ; but 

 from their association in the plains of Kalikoso, where the silicifica- 

 tion of corals may almost be observed in operation, the previous 

 existence of corals may be more than suspected in localities where 

 only the other siliceous materials are observed. 



I pass on now to some general considerations regarding the 

 relations of the mangrove-belt to the sea-border and the character 

 of the slope of the land-surface as compared with that of the sub- 

 marine platform. An accurate conception respecting these matters 

 will help one to avoid some pitfalls in forming an estimate of the 

 character of the movement of emergence which this region has 

 experienced. 



Beginning with the mangrove-belt, some curious preliminary 

 reflections arise, when we endeavour to look back into the past 

 stages of the history of a mangrove tract in an area of emergence. 

 We might perhaps expect to find the remains of such a belt in the 

 upraised sea-borders ; or if no traces existed, we ought to find in 

 some places an extension inland of the reef-flat on which the 

 mangroves at one time flourished. If a rapid movement of emer- 

 gence is now in progress, the mangroves ought to cover the whole 

 or greater part of the reef-flat ; and in the mangrove tract of an 

 emerging area we might look for signs of central decay and mar- 

 ginal growth, the mangroves dying in the middle of the tract and 

 flourishing at the advancing margins. 



When, however, we look at the mangrove- belt, as it at present 

 exists around much of the coast of this island, we find that, except 

 in the vicinity of the mouths of rivers, there extends beyond it a 

 considerable extent of bare reef-flat, varying usually between 200 

 and 1,000 yards in width, and covered by the rising tide. There is 

 no evidence of recent emergence in this condition of things. This 

 relation between the mangrove-belt and the reef-flat indicates a 

 state of equilibrium which might have been established long ago. 

 It is the normal relation that exists between reef and mangrove 

 growth; and it excludes all but very gradual movements of 



