On the Precipitation of Calcium Carbonate. 33 



but the amount of this drift was not determined, and moreover the drift 

 caused by the wind was an unknown factor. On May 8 the wind was SSE., 

 of force I at 8^30™ a.m. freshening to force 3 at 10^30™ a.m. A rough esti- 

 mate from the landfall on returning gave the drift of the boat as about 2 miles 

 south during the 4 hours occupied in working the station; the boat had a 

 large awning and exposed a considerable area to the wind and had drifted 

 this distance against the wind, so it would seem that on that occasion there 

 must have been a strong current setting south. 



Andros Island consists of a limestone formation, the exact nature of 

 which has been dealt with by Dr. T. Wayland Vaughan (17). The greater 

 part of the island is very flat and is elevated only a few feet above sea-level ; 

 a few irregular undulations, probably not more than 100 feet 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-mold. In the numerous "pot-holes" 

 which occur all over the island, a small deposit of black leaf-mold can be 

 found, and these "pot-holes" are the favorite places for the cultivation of 

 sugar cane and bananas. The erosive action of water on the rock is espe- 

 cially 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 white 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 60 miles off the west coast with an average depth 

 of 2 to 3 fathoms. The mud forming these submerged flats is very soft, 

 and near the coast it was easily possible to push a 12-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 6 inches is of a creamy white color, 

 but below that it is of a grayish tinge and has a slight odor of sulphureted 

 hydrogen. Unfortunately there was no opportunity of obtaining informa- 

 tion 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 



3 



