DEPARTMENT OF MARINE BIOLOGY. 155 



partly to ascertain the nature of the declivity on the western side of the 

 trough of the Tongue of the Ocean. A heavy sea prevented accurate work, 

 but it was discovered that a depth exceeding lOO fathoms is attained at a 

 distance between one-quarter and one-third mile offshore (see map). The 

 descent from the shore platform is very abrupt, if not actually precipitous, 

 and the slope is hard and jagged. 



Bottom samples were collected at intervals across the Great Bahama Bank 

 from Gun Key to Northwest Passage into the Tongue of the Ocean, in Nas- 

 sau Harbor, and through South Bight, from the east to the west side of 

 Andros Island. Finely divided calcium-carbonate ooze or mud is of great 

 extent in South Bight, where in places its depth exceeds 12.5 feet, and off 

 the west side of Andros. This mud is precisely similar to that so abundant 

 in southern Florida.* On the west side of Andros mud of this nature over- 

 lies the oolite and rises a few feet above sea-level. 



The search to find oolite in process of formation by direct precipitation 

 and segregation of particles in the sea was continued, but as no instance of 

 such formation has so far been found, either in the Bahamas or in Florida, 

 it appears that the oolitization of the limy muds must be due to a secondary 

 process. (This subject is referred to in discussing the season's work in 

 Florida; see page 157.) 



The factors causing the disintegration and solution of coral skeletons (a 

 special study of boring organisms was made by Dr. Paul Bartsch) and the 

 effect of sand-feeding organisms on silt production were studied. 



The barrier reef off the eastern shore of Andros was examined in the 

 vicinity of the mouth of South Bight, from Long Bay Cays to Middle High 

 Cay. South of Sharp Rock Point to Long Bay Cays the barrier reef is not 

 continuous but patchy. These patches usually occur on the seaward margin 

 of a short platform at a distance of three-quarters to a mile offshore. The 

 depth of water on the platform ranges from i to 2 fathoms, while many of 

 the reefs are awash at low tide. There is, on the seaward face of the reefs, 

 a rapid drop to depths between 4 and 10 fathoms, and a depth of 50 fathoms 

 is usually attained within a mile of the shore. North of South Bight, until 

 near Middle High Cay, the same general relations of a shallow shore plat- 

 form with reefs on its seaward margin obtain, but the reefs along this line 

 are more nearly continuous, while within the outer reefs are some rather rich 

 inner patches. Reefs also occur in the mouth of South Bight at both ends 

 of Golding Cay and off Lisbon Point, and there is a shore reef between the 

 tip of Sharp Rock Point and the lighthouse (see map). 



On sheltered flats within the mouth of South Bight, as on the inner side of 

 Forsyth Point, are corals, usually representing species difTerent from those 

 flourishing on the more exposed reefs. The field study gave an accurate 

 idea of this part of the Andros Reef and of its general relations, and of the 

 conditions under which the different species of corals live in the vicinity of 

 South Bight. A considerable collection of corals, procured with particular 

 reference to habitat, was made, and most of the species were listed in the 

 field. The distribution of species according to habitat conforms to the prin- 

 ciples found to govern their distribution in Florida. The outer reefs are 

 characterized by such corals as Orhicella annularis, Mcuandra strigosa, M. 

 labyrinthifonnis, Sidcrastrea siderea, Agaricia agaricites, A. crassa, Acro- 

 pora pahnata. Pontes astrcoidcs, and P. clavaria (form with short, stumpy 

 branches). Dendrogyra cylindrus is also typically a reef coral. All these 



* The mode of precipitation of this material is discussed by G. Harold Drew, pp. 

 143, 144 of this Year Book. 



