SEDIMENTCARPET 49 



matter through bacterial action, sink to the bottom and 

 build up sediments rich in lime or sihca. The lime com- 

 ponent dominates in the lower latitudes, while siliceous 

 organisms, like diatoms, are largely cold-water algae 

 and form layers of diatom ooze in the far North and 

 South, especially around the icebound Antarctic Con- 

 tinent. Enormous areas of the ocean floor are carpeted 

 with calcareous ooze, the dominant forms being tests 



Fig. 18. Diatom ooze 



or shells from Foraminifera, with the species Globi- 

 gerina the most typical component. Nearly 50 million 

 square miles of the deep-sea bottom are estimated to be 

 covered by calcareous ooze, whereas diatom ooze lags 

 far behind with only 12 million square miles. 



In great depths, however, there is a pronounced re- 

 duction in the lime content, generally setting in at 

 15,000 feet and progressing downward, so that below 

 18,000 feet carbonate of Hme is comparatively rare. In 

 these great depths, therefore, the whitish calcareous ooze 



