Lithofacies maps of the Nodosaria blanpiedi sand in the middle part of the Frio formation (Oligocene) in the eastern counties of the Upper Texas Gulf Coast were prepared from principally electric well-log correlations. These show a belt of maximum sand concentration extending from central Galveston County northeastward to northern Orange County, approximately paralleling the present coast line. This is interpreted to be a barrier island by comparison with present-day sand distribution along the Texas coast. Downdip from the belt of maximum sand concentration a marked increase in percentage of shale in the Nodosaria zone and in thickness of post-Nodosaria beds suggests the presence of a flexure or "hinge line."

Although the Nodosaria sand was deposited principally during a regression of the sea, local areas of thick sand occurring updip from the inferred barrier island indicate deposition in stream channels early in the subsequent transgression.

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