NO. 10 MISSISSIPPI EMBAYMENT SHORE LINES — COOKE 3 



the estimate of the volume to 1,200 cubic miles. Fisk (1944, p. 17) 

 assigns all of this alluvium to the Recent Epoch. It seems incredible 

 that this great mass of sediments could have accumulated in the short 

 interval since late Wisconsin time. 



Plate 32 and 33 of Fisk's (1944) report place the base of his 

 "Recent Alluvium" in Terrebonne Parish, La., nearly 400 feet below- 

 sea level and extend "Quaternary deposits" to approximately —3,500 

 feet. More recently Druid Wilson (oral communication, 1964) has 

 found well-preserved diagnostic late Miocene marine mollusks in 

 three cuttings from Terrebonne and St. Mary parishes at depths 

 around 2,500 feet. This proves that at least 1,000 feet of Fisk's 

 supposed Pleistocene is really Miocene. The remainder may be Plio- 

 cene. His "Recent Alluvium" probably includes the Pleistocene. 



Fisk apparently did not include in his estimate of the volume of 

 sediments the terrace deposits bordering the central alluvial plain. 

 He regarded these terrace deposits as fluvial and named them, in 

 ascending order, the Prairie Formation, the Montgomery Formation, 

 the Bentley Formation, and the Williana Formation (Fisk, 1938a, 

 pp. 51, 56, 59, 62). He correlated the four formations with four 

 interglaciations and attributed their present heights above sea level 

 to separate elevations of the land, each of which he conveniently 

 made coincident with a rise of sea level caused by glacial control 

 (Fisk, 1944, p. 69). He supposed that the terraces had been tilted, 

 and he assumed that terraces standing at different heights on the east 

 and west sides of the central plain were of the same age. 



Fisk's interpretation of the origin of the terraces in the Mississippi 

 Embayment differs fundamentally from the current interpretation of 

 terraces along the Atlantic seaboard, which explains the terraces as 

 the result of changes of sea level on a stable land. 



If the Atlantic Ocean stood higher in past ages, the Gulf of Mexico 

 must have stood at the same height at the same time, and the 

 abandoned shore lines should stand at the same levels in the two 

 regions unless the land has been tilted. If there is a similar sequence 

 of level emerged shore lines in both areas, the assumption is justified 

 that neither has been warped and that there has been no differential 

 change of level between the two areas. 



In the present paper an attempt is made to decipher the geologic 

 history of the Mississippi Embayment during the Quaternary Epoch 

 by using the evidence that can be interpreted from topographic maps 

 and to compare it with the results of similar studies along the Atlantic 

 seaboard. Large-scale maps of much of the embayment have been 



