BIG1:L0\V. — SHO.VL-WATRR DEPOSITS OF THE BERMUDA BANKS. 569 



bits of coral, echinoid plates and spines, starfish pedecillariae, liolothurian 

 plates, sponge spicules, and a few diatoms. The fine floccnlent dust or 

 ooze, mentioned above as forming 20 per cent of the sample and giving it 

 a sticky consistency, is composed of exceedingly minute amorphous cal- 

 careous particles. It is identical with the ooze, which, in larger deposits, 

 has already been described by Agassiz ('94, p. o2, and '95, p. 2')o) as 

 •' marl," and is undoubtedly produced by the slow triturating action of 

 the sea on aeolian rock. The fine dust thus formed is held so easily in 

 suspension in tiie water that it is carried and deposited, often at a great 

 distance from its point of origin, in all localities where absence of wave 

 action or currents allows. It is present, in greater or less degree, in 

 every bottom sample from the Bermuda Bank. 



As a whole, this bottom contains a great number of living organisms, 

 and the empty shells and shell fragments are fresh and but little water- 

 worn — good evidence that they are of very recent deposition. But at 

 Station 1412, at about the centre of Castle Harbor, in four fathoms of 

 water, the propoi'tion of fine cah-areous silt is very much greater, living 

 organisms are less numerous, and the whole sample has a much more 

 water-worn appearance ; while the honeycombed condition of most of 

 the dead shells shows that solution by the sea water is here of some im- 

 portance. This sample was taken from a small basin nearly surrounded 

 by shoals and ledges, where so much of the fine detritus formed by the 

 mechanical action of the water on these aeolian rocks, together with the 

 various organic remains, is being constantly deposited on the floor of 

 the basin that it effectually chokes most of the living organisms. In 

 such regions as Castle Harbor, and, in fact, over most of the Bermuda 

 Plateau, where the sea water always holds a vast amount of calcareous 

 silt in suspension, fixed and sand-dwelling organisms, such as raollusks, 

 tube-buililing worms, bryozoans, and hydroids, reach an extensive de- 

 velopment only on such bottoms as have an active circulation of water 

 that prevents the rapid deposit of silt. 



Castle Roads is a good example of the deeper channels connecting 

 Castle Harbor with the open sea on the south. This passage is about 

 four hundred yards wide, with a greatest depth of about six fathoms, 

 and during both incoming and outgoino; tides a strong but not violent 

 current runs through it. 



The bottom at Stations 409 and 1413, in five fathoms, is a rather 

 coarse shell saud, containing many large fragments ; most of the organ- 

 isms are macroscopic. It is white, spotted with pink ; very clean, with 

 less than 1 per cent of fine ooze. Foraminifera of the same species as 



