The middle Tertiary sedimentary regimen of the Gulf Coast is related directly to Rocky Mountain events, and most of the terrigenous sediments came from the Rocky Mountains. Correlation between the surface and subsurface is based on equation with transgressive and regressive phases. Criteria are given for identifying these phases. Gulf coastal stages are delimited by regressive maximums. The outer-shelf shale tongues, which are usually identified by distinctive foraminiferal assemblages, are regarded as regressive maximums. The Textularia warreni tongue of the subsurface Vicksburg and the Anhuac tongue represent transgressive peaks.

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