Careful study of micro-organisms which are abundant in many well samples from the Texas Gulf Coast has yielded information of importance concerning the seaward character of Tertiary formations which appear at the surface farther inland and has shown the presence of fossiliferous marine beds in parts of the section where no corresponding marine strata occur at the outcrop.

The Pleistocene and Recent deposits, and to a degree the Pliocene, have received scant study in well-sample investigations, for the oil of the Gulf Coast is mainly associated with Miocene and older rocks. Pliocene foraminiferal faunas resemble the Recent.

In the Miocene three distinct micro-faunas, distinguished by certain diagnostic genera, are recognized in many wells.

The Oligocene of Texas is represented in surface exposures only by unfossiliferous, non-marine sands and clays, but well sections show the presence of fossiliferous marine beds of Middle Oligocene age. Abundant Foraminifera are found in these strata, and it is readily possible to distinguish three zones. The Oligocene rests unconformably upon the Jackson, from which it differs both lithologically and in its fossils.

The upper part of the Eocene, including the Jackson and upper Claiborne beds, is encountered in many wells. The exposed parts of these formations are less fossiliferous and less complete than seaward sections revealed by well borings. The Jackson of Texas has been divided into three faunal zones. The Upper Claiborne has uniform and distinctive faunal characters where encountered in wells.

Detailed notes on the stratified rocks encountered in the salt domes of Texas are presented.