variation in the section." After proper integration of such maps, much may be 

 learned of the tectonic and sedimentational history of the region. These maps 

 could not have been prepared until fundamental stratigraphic units had been 

 denned and correlated. 



DIFFICULTIES OF Some of the more common difficulties en- 



CORRELATION countered in correlation work are: (1) dis- 



continuity of stratigraphic units; (2) struc- 

 tural complexity; (3) lateral variations in thickness, lithology, and paleon- 

 tology; (4) poor development or absence of marker beds; (5) presence of 

 unrecognized unconformities; (6) limited number of control sections; (7) 

 multiplicity of lithogenetic and time-stratigraphic nomenclature; (8) erroneously 

 compiled data; and (9) lack of experienced personnel assigned the problem. 



BIBLIOGRAPHY 



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Petroleum Geologists Bull., v. 39, no. 9, p. 1703-1752. 

 Ashley, G. H., and others, 1933, Classification and nomenclature of rock units: Geol. Soc. 



America Bull., v. 44, p. 423-459. 

 Baillie, A. D., 1955, Devonian system of Williston Basin: Am. Assoc. Petroleum Geologists 



Bull., v. 39, no. 5, p. 575-629. 

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sedimentary section in West Texas and New Mexico: Am. Assoc. Petroleum Geologists 



Bull., v. 36, no. 4, p. 658-676. 

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group: Am. Assoc. Petroleum Geologists Bull., v. 39, no. 4, p. 444-467. 

 , Krumbein, W. C., and Sloss, L. L., 1948, Tectonic control of lithologic 



associations: Am. Assoc. Petroleum Geologists Bull., v. 32, no. 10, p. 1924-1947. 

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Geologists Bull., v. 39, no. 11, p. 2306-2320. 

 Forgotson, J. M., Jr., 1954, Regional stratigraphic analysis of Cotton Valley group of upper 



Gulf Coastal Plain: Am. Assoc. Petroleum Geologists Bull., v. 38, no. 12, p. 2476-2499. 

 Greenman, N. N., and LeBlanc, R. J., 1956, Recent marine sediments and environments of 



northwest Gulf of Mexico: Am. Assoc. Petroleum Geologists Bull., v. 40, no. 5, p. 813-847. 

 Hedberg, H. D., 1948, Time-stratigraphic classification of sedimentary rocks: Geol. Soc. 



America Bull., v. 59, p. 447-462. 

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Am. Assoc. Petroleum Geologists Bull., v. 32, no. 10, p. 1909-1923. 

 , 1952, Principles of facies map interpretation: Jour. Sedimentary Petrology, 



v. 22, p. 200-211. 

 , and Nagel, F. C, 1953, Regional stratigraphic analysis of "Upper 



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in Michigan Basin: Am. Assoc. Petroleum Geologists Bull., v. 38, no. 11, p. 2324-2356. 

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451 



