32 RAYMOND C. MOORE AND FREDERICK B. PLUMMER 



beds and to which he applied stratigraphic names. The outcrops 

 of these beds extend from south to north across the Strawn area, 

 the dip being more or less steeply to the west. The sandstones 

 form escarpments, but because of variations in the deposits these 

 are very irregular and are not readily traceable or easily differ- 

 entiated, as are the limestone escarpments higher in the section. 

 The thickness of the Strawn in the Colorado River Valley as deter- 

 mined from measurements at the outcrop is more than 3,800 feet, 

 but the drill shows that the greatest thickness south of Brownwood 

 is not more than 1,200 feet. Wells 5 miles west of Brownwood 

 show a thickness of the Strawn amounting to 700 feet, and 9 miles 

 north of Coleman only 500 feet. Near Brady the Strawn is appar- 

 ently not represented, and higher divisions of the Pennsylvanian 

 rest directly upon the Bend. 



In the Brazos River Valley two main divisions of the Strawn 

 have been identified, the Millsap formation below and the Mineral 

 Wells formation above. Only the upper portion of the Millsap 

 formation is exposed at the surface, outcrops being found in the 

 eastern part of the Strawn area near Millsap and along Brazos 

 River in southwestern Parker County. The limestones which 

 appear in this part of the section are quite unlike any beds observed 

 in the Mineral Wells formation. Cummins^ defined the Millsap 

 division in 1890 to include all the beds in the Brazos River Valley 

 below "coal seam No. i " (Thurber coal) and the top of the black 

 Smithwick shale. Thus the lower portion of the Millsap formation 

 is known only from drill records. As a whole, the formation con- 

 sists mostly of dark blue and clayey shale, limestone, and several 

 thin, light-colored, friable sandstones. Locally it contains oil and 

 gas in commercial quantities. Well records show its thickness in 

 the Strawn area to range from 1,800 to 3,000 feet, and as in the case 

 of the Strawn of the Colorado River Valley the thickness diminishes 

 to the west: 2,200 feet at Brad in Palo Pinto County; 1,600 feet 

 at Caddo in Stephens County; and 800 feet at Breckenridge, 

 Stephens County. 



The Mineral Wells formation includes the sandstones and 

 shales of the upper part of the Strawn in the Brazos River Valley 



' W. F. Cummins, Texas Geol. Surv., Second Ann. Rept. (1890), p. 372. 



