BTGELOW. — SHOAL WATER DEPOSITS OF THE BERMUDA BANKS. 579 



George's Island, in one to three fathoms, the bottom is again shell sand. 

 Thus, just off St. Catherine's Point (Stations 438, 439, 440, and 441), 

 in from one to two fathoms, the bottom is very clean, the sand being 

 very coarse, white with a faint yellowish tinge, and with less than 1 per 

 cent of ooze. Foraminifera form less than 10 per cent, and the great 

 bulk, probably 50 per cent, of the sample consists of coralline and mille- 

 pore fragments of large size, the remainder being mollusk shells, cchi- 

 Doid plates, Polyzoa, corals, and limestone fragments. The fragments 

 are all much water-worn and honeycombed, and there are very few living 

 organisms in the bottom. In this neighborhood there are many de- 

 tached ledges, and in the shoal water along shore, where the scouring 

 action of the waves is considerable, the bottom consists almost -wholly of 

 the coarse detritus from them, and from the shore cliffs. 



In all other parts of the submerged lagoons, except those already 

 described, the bottom deposits consist of shell sands and marl, occurring 

 together in varying proportions. But in such of the lagoons as are 

 broken by great numbers of small reefs, the proportions in which these t\vo~ 

 materials occur often differ widely in closely adj'icent localities. In such 

 basins the depths over the floor are usually very uniform, and the shoals 

 and ledges rise very abruptly to near the surface. Their walls are often 

 nearly perpendicular, very much honeycombed, and often undercut by 

 the action of the water. Examples are the Brackish Pond Flats, the 

 flats north of Ireland Island, and the Cow Ground Flats, two miles west 

 of that island. The Brackish Pond Flats occupy the centre of the Ber- 

 muda Plateau, and consist of a perfect maze of shoals, deep channels, 

 and basins. At different stations the bottom deposits are very different. 

 Thus at Station No. 359, three miles northeast of the dockyard, in five 

 fathoms of water, it is chiefly shell sand, composed of large living For- 

 aminifera in great abundance, particularly Orbiculina, Orbitolites, and 

 Pulvinulinae, molluscan fragments, living lamellibranchs and gasteropods, 

 millepore fragments, a few coral fragments, worm tubes, corallines, and 

 calcareous spicules, with about 25 per cent of very fine calcareous silt. 

 At another station (No. 383?), in a small basin one mile directly north 

 of the last, in seven fathoms of water, the bottom consists almost entirely 

 of white marl, but contains also a considerable amount of broken shells 

 and calcareous spicules, although very few living organisms. On the 

 Cow Ground Flats the topographic conditions are very similar. At a 

 station one mile directly west of the dockyards, in a cut between the 

 ledges eight fathoms deep the bottom was white and coherent, with 

 80 per cent fine ooze or marl, the remainder being chiefly corallines and 



