414 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1963 



as a coccolithophore. Coccolithophores are an interesting group of 

 organisms that possess some of the characters of both plants and ani- 

 mals and thus are intermediate between the two great biological 

 kingdoms. They are able to carry out photosynthesis, although the 

 color of the chloroplasts in the cells is golden yellow to amber rather 

 than green. They possess two whiplike flagellae which are used to 

 propel the organism through the water on an erratic course. The 

 coccolithophores secrete coccoliths and arrange them within the cell 

 to form a hollow sphere, known as a coccosphere (pi. 4, fig. 1). Upon 

 death or proper stimulation, the coccoliths are released from the en- 

 closing protoplasm, and begin to drift down to the ocean floor. Coc- 

 colithophores live suspended in the water as plankton and may be 

 found in shallow inshore waters as well as in the open sea. Usually 

 those forms inhabiting shallow waters have smaller, more delicate 

 coccoliths than those found in the open oceans. For tliis reason, they 

 are less likely to be preserved as fossils. In oceanic deposits, rela- 

 tively little material derived from land is present, and over broad 

 areas the sediments consist largely of the remains of planktonic orga- 

 nisms inhabiting the upper layers of water. In tropical and tem- 

 perate regions where the water is less than 20,000 feet deep, large 

 areas of the ocean floor are covered by a deposit called Glohigerina 

 ooze. Glohigerirm is a planktonic foraminifer and the shells of this 

 organism are the most conspicuous organic remains seen with low 

 power microscopic examination. However, more detailed inspection 

 of samples of Glohigerina ooze reveals that the deposit is composed 

 largely of coccoliths, so that large areas of the ocean floor are essen- 

 tially covered by coccoliths. 



It is interesting to consider the path by wliich the coccoliths have 

 come to rest on the ocean floor. The coccolithophores which produce 

 them live near the surface, and so the coccoliths must drift down 

 through nearly the whole water column before coming to rest. The 

 rate at which coccoliths settle in quiet standing water has been deter- 

 mined experimentally to range from 15 minutes to 2 hours per inch 

 in fresh water. In salt water they sink more slowly. This means that 

 in an oceanic area with depths of 20,000 feet, large coccoliths would 

 require 10 years, small coccoliths 50 years to reach the bottom, pro- 

 vided there were no ascending currents to retard their descent. But 

 because the waters of the oceans are always in motion, the coccoliths 

 will be carried great distances, often many thousands of miles from 

 the point where they were released, until they come to rest. The 

 coccoliths are caught up in the oceanic circulation of the planet and 

 distributed over vast areas. Herein lies their great importance to 

 modern stratigraphy. 



Most of the strata studied by geologists on land represent shallow- 

 water deposits. Deep-water deposits are relatively rare on the present 



