CHAP. 33] THE PKESERVED RECORD: PALEONTOLOGY OF PELAGIC SEDIMENTS 879 



1959). Bramlette {in litt.) has examined coccolithophorids and related forms 

 from portions of the European Tertiary sequence and their equivalents in 

 other widely separated parts of the world, and has found these microfossils 

 to be useful for rather detailed correlation. The ease with which coccolitho- 

 phorids can be prepared for preliminary microscoi3ic examination is a factor 

 which favors their routine use. A few milligrams of highly calcareous pelagic 

 sediment need only be puddled on a glass slide with a few drops of water, 

 dried and covered with Canada balsam: in the preparation of less calcareous 

 sediment samples the coccolithophorids may be concentrated by utilizing the 

 different settling velocities of the components of the dispersed sediment. 

 Discoasters appear to have been common in at least the warm waters of the 

 open ocean throughout Tertiary time, and to have become extinct (or virtually 

 so) at about the end of the Tertiary; thus the occurrence of numerous dis- 

 coasters in a pelagic sediment may be interpreted as indicating a Tertiary age 

 for the sample, or an admixture of reworked Tertiary material. 



B. Diatoms 



As with several other groups of pelagic microfossils, the paucity of described 

 assemblages of well established ages is the principal obstacle to the use of dia- 

 toms as indicators of age. Rheinhold (1937) was one of the first to attempt to 

 correlate Tertiary diatom assemblages, but he was hampered by erroneous 

 age assignments of some of the reference localities which formed the basis of 

 his comparative studies. Both Hanna (1932) and Lohman (1960) have pointed 

 out the striking similarity of Miocene diatom assemblages from the east and 

 west coasts of the United States and have expressed the belief that future 

 investigations will increase the applicability of these microfossils to problems 

 of stratigraphic correlation. Other investigators currently laying the ground- 

 work for future application of diatoms to problems of stratigraphic correlation 

 include Kanaya (1957, 1959), Jouse (1948, 1959), and Sheshukova-Poretskaja 

 (1959). 



C. Silicoflagellates 



In most pelagic sediments, both species and individuals of this group are too 

 few to permit extensive application as indicators of age. They do, however, 

 offer useful supplementary information on ages. Interpretation of the age- 

 significance of silicoflagellates is aided by several recent articles reviewing these 

 microfossils (Frenguelli, 1940; Deflandre, 1950; Tynan, 1957). 



D. Foraminifera 



Of all the groups of pelagic microfossils, it is the Foraminifera which have 

 been most extensively applied to stratigraphic problems. For several decades, 

 benthonic representatives of this grouj) received most of the attention of 



