DEPARTMENT OF MARINE BIOLOGY. 137 



through the island to the west coast. The depth of the Tongue of the Ocean 

 varies from 1,200 fathoms at its mouth to about 740 fathoms at its southern 

 end. Off Golding Cay the depth varied between 800 and 850 fathoms in 

 different localities. The submarine slope off Andros is very abrupt and in 

 places must be nearly perpendicular a few yards from shore, but the slope on 

 the south and east margins of the Tongue is less steep. The tides are not 

 strong, the average rise and fall being from 2 to 3 feet ; currents are slight 

 and variable, and would appear to depend on the prevailing winds. The 

 surface-water of this region, except along the Andros shore, is everywhere 

 continuous with that overlying the thousands of square miles of shallows 

 forming the Great Bahama Bank and the flats and cays lying to the west of 

 the Exuma Islands, whereas the deeper water is only connected with the 

 outer ocean by the comparatively narrow entrance between New Providence 

 Island and the north of Andros. 



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

 which is dealt with by Dr. T. Wayland Vaughan in another part of this pub- 

 lication. The greater part of the island is very flat and is only elevated a 

 few feet above the sea-level; a few irregular undulations, never 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 "potholes" which occur all over the island a small deposit 

 of black leaf-mold can be found, and these "potholes" are the only suitable 

 places for cultivation. 



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 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 con- 

 tain a large proportion of calcium salts in solution. Towards the west coast 

 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 for 

 60 miles or more off the west coast at an average depth of not more than 2 

 fathoms. The mud forming the 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 information as to the 

 real thickness of this layer of mud, nor of investigating more than the sur- 

 face layers at any distance from the coast. 



The apparatus employed by previous workers for obtaining samples of 

 water for bacterial examination from the deep sea has either consisted of 

 some sort of water-bottle made of metal, or else of exhausted glass bulbs 

 with a neck drawn out into a capillary tube which could be broken off at the 



