936 T. AV. VAUGHAN CHEMICAL DEPOSITS OF THE SEA 



agents, bacteria appear to be the most important. As the result of the 

 investigations of Drew and of Kellerman on dentrifying bacteria are now 

 generally known, it is here only necessary to say that these organisms 

 evolve ammonia which may take up CO2 from bicarbonates or may react 

 with calcium sulphate, producing an excess of CaCOg, which consequently 

 is precipitated. Any other ammonifying bacteria will produce the same 

 result, and green plants by robbing the water of CO2 may bring about 

 precipitation. 



An evaluation of the work done by inorganic and organic agencies has 

 not yet been made, and it is exceedingly difficult, if not actually impos- 

 sible, to make it. For instance, off the west side of Andros Island, Ba- 

 hamas, opposite South Bight, where the deposit is largely a chemical pre- 

 cipitate, the salinity of a spot sample of water was 38.86 parts per thou- 

 sand, while that of the tongue of the ocean east of Andros Island was 

 about 36.50 parts per thousand, and that of the water at Fowey Eocks, 

 Florida, is about 36 parts per thousand. The increased concentration 

 would necessarily cause precipitation. At the same locality there is sur- 

 face agitation of the water; and as there is an enormous submarine flat, 

 having a width east and west of 60 sea miles and a maximum depth of 

 only about 18 feet below mean low- tide level, the temperature during the 

 hotter months of the year would naturally be higher than in the open 

 ocean. Therefore all three inorganic agencies are operative. At the same 

 locality Drew found "160,000,000 dentrifying bacteria per 1 cubic centi- 

 meter," ^ and thought the actual number probably greater. The problem 

 is complex and needs further investigation. 



Although the criteria for recognizing chemical precipitates in bottom 

 samples have not yet been worked out in the desired detail, some of them 

 may be mentioned. Among them are spherulites, separate aragonite 

 needles, and aggregates of aragonite needles into the globular, ovoid, or 

 ellipsoidal bodies known as oolite grains. Illustrations of these are given 

 on plate 47, figures 1 to 7, and plate 48, figures 1 to 3 (see page 944). 



For purposes of comparison, besides mounts of such objects as are 

 shown on plates 47 and 48, those of us engaged in these studies have many 

 preparations of artificial and natural precipitates. The paper by Messrs. 

 Johnston, Mer^dn, and Williamson, entitled "The several forms of cal- 

 cium carbonate," ^ is of great value in this connection. 



With reference to the chemical composition of deposits of the kind 



•under consideration, it will be said that they are almost pure calcium 



carbonate. Excluding silica, the elevated oolites of Florida and the Ba- 



s Carnegie Inst. Washington Pub. No. 182, 1914, pp. 41-43. 

 8 Am. Jour. Sci., vol. 41, 1916, pp. 473-512, 



