THE PRECIPITATION OF CALCIUM CARBONATE IN THE SEA. 500 



high, are found especially along the east coast. There is evidence to 

 show that formerly the level of the land was much higher than at 

 present, and signs of rapid erosion of the rock are everywhere obvious. 

 One of the most remarkable features is the absence of soil even in the 

 well-wooded parts of the island, the trees and bushes growing directly 

 out of crevices and holes in the rock, and giving rise to practically no 

 leaf mould. In the numerous " pot holes " which occur all over the 

 island, a small deposit of black leaf mould can be found, and these 

 " pot holes " are the favourite places for the cultivation of sugar-canes 

 and bananas. The erosive action of water on the rock is especially 

 noticeable where the slow drainage from an inland swamp can be 

 traced in its course to the sea : in such a locality the hard rock is 

 eroded, honeycombed, and undermined to a most remarkable degree, 

 even though the amount of drainage, except after the heaviest rains, 

 can scarcely be more than a slow trickle. Erosion of the rock along 

 the sea-coast, where it is exposed to the action of the sea-spray, is also 

 very marked. From the occurrence of this erosion it is obvious that 

 all the water draining from the land into the sea must contain a high 

 proportion of Calcium salts in solution. 



Towards the west of the island the land is remarkably flat, and near 

 the coast consists of while chalky mud, which has partially dried, and 

 in places has formed a harder crust on the surface. These half-dried 

 mud-flats slope almost imperceptibly into the sea, and are continuous 

 with the submarine flats which extend some sixty miles off the west 

 coast with an average depth of from two to three fathoms. The mud 

 forming these submerged flats is very soft, and near the coast it was 

 easily possible to push a twelve-foot sponge pole down to its full length 

 into it without touching any harder material : the surface layer of the 

 mud for a depth of about six inches is of a creamy white colour, but 

 below that it is of a greyish tinge and has a slight odour of sulphur- 

 etted hydrogen. Unfortunately there was no opportunity of obtaining 

 information as to the real thickness of this layer of mud, nor of 

 investigating more than the surface layers at any distance from the 

 coast. 



Microscopical examination showed that this mud was almost entirely 

 composed of minute unorganized particles of Calcium carbonate. 

 Near the shore a good deal of organic matter, chiefly in the form of 

 decaying mangrove roots, was present. Further out little organic 

 matter was noticeable, but it was not possible to examine the deeper 

 layers of the mud in these situations : the only organic matter that 

 was seen consisted of the rootlets of a species of Zostera, which was 

 found in occasional patches some miles off the coast. 



