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A certain amount of confusion in the nomenclature and in the correlation of certain formations encountered in deep wells in the Gulf Coastal areas which are now being exploited by oil development has necessarily occurred, perhaps primarily due to the fact that the more detailed stratigraphic and paleontological features of a number of the standard Tertiary sections of Mississippi and Alabama have not been known in greater comparative detail.

The exact demarcation of the upper and lower limits of the Oligocene is still a subject of controversy among paleontologists and geologists, particularly within the Gulf Coastal areas of Louisiana and Texas which are now undergoing exploitation by oil-field developments. It is particularly interesting that we may go to Mississippi for what appears to be the proper elucidation of the relationships of the standard Oligocene section of the Gulf Coastal Plains and the lowermost Miocene of Mississippi.

A marine formation lying between the Catahoula and the Byram marl of the Upper Vicksburg will be described. The evidence for the age of this formation and its position with respect to the Heterostegina zone will be discussed.

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