fossils as well as animal microfossils, the barren sample is fast disappearing. 

 Microfossils are found in practically all types of sediments including salt and 

 continental red beds. Much useful information can be obtained by a careful 

 study of the composite fossil assemblage. 



Much advancement in oil-field paleontology has been made since Udden 

 (1914) pioneered the study on some micropaleontological features of well cut- 

 tings from Illinois. Only a few paleontologists at present are qualified to work 

 with all the various groups of microfossils mentioned here. A working knowl- 

 edge of spores, pollen, hystrichospherids, and foraminifera is most desirable. 

 Among the various groups of microfossils, those which are acid-insoluble, seem 

 to be the most promising for future oil-exploration studies. 



In conclusion, the factors that make microfossils useful in subsurface work 

 may be summarized as follows: 



1. They are found in practically all types of sedimentary rocks ranging 

 from pre-Cambrian to Recent, and because of this, are extremely valuable for 

 determining the age of sediments. Experience has shown that in many instances 

 the age of the rocks can be established within epoch level on a world-wide basis. 



2. Because of their small size, they escape destruction by drilling abrasion. 



3. Only a small amount of sample is required for examination. In addi- 

 tion, extraction or washing techniques require little time and no elaborate equip- 

 ment. 



4. Microfossils are generally good environmental indicators and thus can 

 be used to separate the favorable areas from the unfavorable areas for oil ex- 

 ploration. 



5. As paleontological studies progress, more and more types of microfossils 

 should prove their usefulness to the economic paleontologist. 



BIBLIOGRAPHY 



Arnold, C. A., 1947, An introduction to paleobotany: New York, McGraw-Hill Book Co., 



433 p. 

 Bronnimann, 0., 1955, Microfossils incertae sedis from the Upper Jurassic and Lower 



Cretaceous of Cuba: Micropaleontology, v. 1, p. 28-49. 

 Campbell, A. S., 1954, Radiolaria, treatise on invertebrate paleontology: pt. D, Protista 3, 



Univ. Kansas Press, p. D11-D163. 

 Clark, B. L., and Campbell, A. S., 1942, Eocene radiolarian fanuas from the Mt. Diablo 



area, California: Geol. Soc. America Special Paper 39, p. 1-112. 

 Cole, W. S., 1952, Eocene and Oligocene larger foraminifera from the Panama Canal 



Zone and vicinity: U. S. Geol. Survey Prof. Paper 244, 41 p. 

 , 1954, Larger foraminifera and smaller diagnostic foraminifera from Bikini 



drill holes: U.S. Geol. Survey Prof. Paper 260-0, p. 569-608. 

 Cooper, C. L., 1942, North American chitinozoa: Geol. Soc. America Bull. 53. 

 Croneis, Carey, 1941, Micropaleontology — past and future: Am. Assoc. Petroleum Geologists 



Bull., v. 25, no. 7, p. 1208-1255. 



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