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extending arm of the Western Cross Timbers, continues irregularly southward from its junction with the main belt of the Western Cross Timbers in Wise County, to the Leon. Hence in that portion of their extent where they are overlain by the Paluxy sands, the outcrops of the Glen Rose formation constitute prairie spots within the general area of the Western Cross Timbers, as seen between Weatherford and Millsap, on the Texas Pacific road, and in the slopes below the escarpment of Comanche Peak in Hood, Erath, and Somervell counties. South of the Cowhouse, where the Paluxy sands terminate, the outcrops of the Glen Rose beds are prairie lands continuous with those of the Walnut clays.

The inlying valley outcrops increase in area southward through Parker, Hood, Erath, Comanche, Lampasas, and Coryell counties. These rocks are well exposed along the valley of Lampasas River through Lampasas and Burnet counties, as well as along every creek valley tributary to this river. The confluents to these tributary creeks have also cut wide valleys into the rocks of the Glen Rose beds below the general level of the remnantal Edwards divides between Lampasas and Leon rivers along the east line of Lampasas County and between Lampasas and San Gabriel rivers.

The North Fork of San Gabriel River, with its main tributaries, Russell Fork and Bear Creek, runs in similar valleys for a great portion of its course in Burnet County. These valleys are narrow and contract continually as they pass southeast into Williamson County. In the counties of southwestern Texas between the Pecos and the Colorado and south of the Burnet-Llano Paleozoic region these rocks form the basement of the Edwards Plateau. The canyons of Guadalupe, Comal, Nueces, Frio, Medina, and Devils rivers cut down into them.

Typical sections of the formation, about 220 miles apart, near the northern and southern limits of the field of occurrence in the Grand Prairie region, illustrate the details of the formation. The more northern of these typical sections of the Glen Rose formation is seen in the lower part of the general Comanche Peak section (see fig. 12), in the slopes of the Paluxy Valley of Somervell County near Glen Rose, between the Paluxy sands above and the Bluffdale sands (the northern equivalent of the Hensell sands of the Colorado section) below.