AGASSIZ: BAHAMAS. 167 



of the shore sand Kept in more or less constant motion, the grains of 

 aeoliau sand become mixed with fragments of corallines, or of Inverte- 

 brates which have lived upon its surface, and where corallines occur in 

 great abundance the flat fragments of their stems often constitute the 

 greater mass of the bottom samples. In the vicinity of coral heads the 

 bottom is composed of aeolian sand of different degrees of coarseness, 

 more or less mixed with comminuted fragments of Gorgonians, of Mille- 

 pores, and of other corals. On such parts of the banks there also occur 

 a very considerable number of Orbitolites and other Foraminifera.. Of 

 course, in the proximity of the edging i-eefs and along their faces frag- 

 ments of corals, of corallines, of Nullipores, of alga^, and of Invertebrates 

 are an important component of the bottom, the pieces of coral and of 

 corallines often constituting by far the greater mass of the sand. 



The beaches are, according to their locality, composed either of very 

 fine coral sand, or of coarser coral sand mixed with corallines and aeolian 

 sand, or of large pieces of corals and of other Invertebrates which become 

 cemented together to form a breccia or a conglomerate, so that we may 

 have bottoms composed of particles varying from an impalpable powder 

 to coarse fragments, the components of which can readily be recognized. 

 When a considerable amount of vegetable matter has become mixed with 

 the seolian or coralline sand, the bottom becomes more or less sticky and 

 marl-like, and assumes a grayish color. This is the character of a great 

 part of the bottom on the interior of the Little Bahama Bank ; while on 

 the eastern shank of tlie Great Bahama Bank, and on the smaller banks 

 extending to the eastward of it, the bottom varies greatly according to 

 the local conditions ; on the western shank of the Great Bahama Bank a 

 large area off the west coast of Andros is covered with the " white marl" 

 already described. 



The principal coralline algse are species of Penicillus, Acetabularia, 

 Halimeda, and Udotea, fragments of which can readily be recognized as 

 components of the bottom specimens wherever they grow in numbers. 

 The decaying of other algae which compose the flora of the bottom merely 

 adds more or less vegetable matter to its calcareous components ; the 

 most abundant of these algae are species of Thalassia, of Padina, Cau- 



the Gulf of Mexico and the Caribbean Sea, and which also extends over the bottom 

 of the wider passages between the Bahamas. The so called coral ooze is in reality a 

 calcareous mud formed of decomposed corals and corallines, consisting sometimes of 

 very fine particles, which often accumulate along the shore line in sheltered localities, 

 or are carried to considerable distance when held in suspension in the water along 

 the line of currents. 



