76 



COLLEGE ZOOLOGY 



from Spitzbergen, Greenland, England, 

 Japan, Australia, St. Helena, Barbados, 

 Mauritius, Africa, and the Argentine. Most 

 species of Testacea favor soils with a high 

 moisture content. A large amount of organic 

 matter, combined with small soil particles, 

 favors a rich protozoan fauna, as well as a 

 high bacterial content. There appears to be 

 a definite relation between the number of 

 Protozoa and the number of bacteria present 

 since the latter serve as food for the Proto- 

 zoa. This relationship may have an impor- 

 tant bearing on soil fertility. 



PROTOZOA AND GEOLOGY 



Though most protozoans leave no sub- 

 stantial remains after the death of the cell, 

 at least two large groups of Sarcodina de- 

 velop skeletal structures capable of being 

 preserved as fossils. These are the Radiolaria 

 (Fig. 40) and the Foraminifera, sometimes 

 shortened to forams. Because species of this 

 type have existed since very early times, a 

 great number of distinct rock strata of the 

 earth bear evidence of protozoan life. The 



Skeleton of radiolarion 



Imng radTolarlan 



Figure 40. Radiolarians are marine animals, usually with a skeleton of silicon which sinks to 

 the ocean floor when they die, forming a layer called radiolarian ooze. Left, helmet-shaped skeleton 

 of Podocyrtis. Right, Acanthometron. Highly magnified. 



forams, especially, are of great importance 

 to oil geologists in analyzing the results of 

 drilling operations. 



Under present conditions, as in the past, 

 the skeletons of ocean-dwelling forms are 

 continually sinking to the bottom to form 

 ever growing layers of ooze. The greater por- 

 tion of the bottom of the Atlantic Ocean, an 



area of perhaps 20 million square miles, is 

 covered with an ooze formed of skeletons of 

 the genus Globigerina. Eventual compac- 

 tion of such ooze results in the production 

 of limestone in the form of chalk. An impor- 

 tant chalk deposit in Alabama and Missis- 

 sippi, undoubtedly created in this way, is 

 approximately 1000 feet thick in certain 



