Based on need for convenient, small-scale cartographic units, the basal Cretaceous rocks in Texas from Red River to Burnet County and on the Callahan Divide are herein divided into three distinctive lithologic sequences.

This report treats the sedimentary petrology and history of the Haymond Formation, a monotonous sequence of interbedded sandstone and shale that has a maximum preserved thickness of 4,300 feet.

Limestone is one of the most important nonfuel mineral resources in Texas. Annual production exceeds $30 million; value added in the manufacture of such products as cement and lime amounts to about $100 million annually.

The wedge-shaped Black Gap area in southern Brewsier County, Texas, occupies approximately 4,50 square miles east of the Big Bend National Park.