218 ANNUAL REPORT SMITHSONIAN INSTITUTION, 191*7. 



carbonate of lime. There are several kinds of bacteria that cause 

 the formation of ammonia in the ocean. One of these kinds is known 

 as denitrifying bacteria, because they break up nitrate salts in the 

 sea, converting nitrates into nitrites and these into ammonia, and 

 they are to a considerable degree responsible for the limited develop- 

 ment of green plants in tropical seas, as they rob such plants of 

 an important part of their food. G. H. Drew found as many as 

 160,000,000 of these bacteria in 1 cubic centimeter of mud off the 

 west side of Andros Island. Bahamas, opposite the mouth of South 

 Bight. A figure (reproduced from one by Kellerman) is here given 

 of this very minute organism, which is known as Pseudomonas 

 calcis (Drew) Kellerman. Any other bacteria that will evolve am- 

 monia and green plants by taking C0 2 from the water will also 

 cause the precipitation of calcium carbonate. In such areas as the 

 shoal waters on the lee sides of the islands and in the lagoons in the 

 Bahamas, where all of the agencies mentioned are cooperating to bring 

 /-v about the precipitation of cal- 



^>f} cium carbonate, it is not at 



present possible to estimate 

 how much of the effect is at- 

 tributable to each. 



The material when first pre- 

 \J ( cipitated is very finely divided, 



and may form very minute 



Fig. 5.— Pseudomonas calcis (Drew) Kel- needles Or Small balls of the 

 leiiman. Greatly enlarged. After . 



kellerman. mineral known as aragonite. 



On plate 32, figure 3 illustrates some of the aragonite needles, 

 magnified 840 times, and figure 2 illustrates some balls taken from 

 the mud, both out of the same sample, from the west side of Andros 

 Island, Bahamas. 



Oolite grains of calcium carbonate may be produced artificially, 

 either by means of cultures of bacteria that evolve ammonia or by 

 adding ammonia to sea water. An illustration of a thin section of an 

 oolite grain from Great Salt Lake is given on plate 32, figure 4; the 

 figures on plate 33 illustrate artificially formed grains. As the very 

 fine concentric banding of the Bahamian oolite grains has not yet 

 been reproduced in the laboratory, there are still some features of 

 these grains that need more investigation. 



Some investigators of the origin of oolite grains have contended 

 that thej'' are formed by filamentous algae, because borings appar- 

 ently made by such organisms were found in the grains. Algae of 

 this kind bore into nearly all carbonate of lime structures exposed to 

 their attacks; they even bore into coral skeletons up to the limits of 

 the soft animal tissues. On plate 34, figure 1 illustrates some of 



