420 abstracts: geology 



southwestern part of Cotton County, and is drained by Red River. The 

 interstream areas are a smooth, shghtly undulating, treeless prairie, 

 into which the smaller streams have cut very slightly except near their 

 mouths. The notable features of the topography are (1) the broad, 

 smooth surfaces, (2) a few low, round, isolated hills adjacent to the di- 

 vides, preserved by a capping of more resistant rocks, and (3) the many 

 large "breaks" or washes similar in character to the well-known bad- 

 lands of other portions of the West. 



The lowest outcropping rocks in the Grandfield district are "Red Beds" 

 of Permian age. There are relatively few data about the underlying 

 rocks in this district, and these come from several deep oil and gas well 

 records. The facts indicate that the upper portion of unexposed beds 

 is of Permian age and that this series is underlain by older Carboniferous 

 beds of the Pennsylvanian series. 



In most of the Grandfield district the hard rocks are hidden beneath 

 a surficial mantle of loose, unconsolidated material consisting of: (1) 

 Dune sand, spread over a broad belt adjacent to Red River; (2) a dark 

 or reddish sandy to clay soil, largely wind-blown, covering most of the 

 smooth slopes of the interstream areas; and (3) a red clay-silt alluvium 

 found in the broad, flat valleys of Deep Red Run and its tributaries. 

 Beneath this thin veneer of Quaternary beds, exposed in many places 

 in breaks and along the valley sides, lies a thin bed of coarse, hard quartz- 

 lime conglomerate (here named the Grandfield congloiiierate) , very 

 persistent and rarely exceeding five feet in thickness, which has been 

 variously classified as of Quaternary or of late Tertiary age. It is under- 

 lain unconformably by "Red Beds" of Permian age which are correlated 

 with the Wichita formation of northern Texas. 



The most important structural feature recognized in the district is a 

 low anticline that crosses it in a sinuous line trending generally east- 

 southeast and west-northwest. Along the axis of this anticline lie a 

 number of small elongated domes that are separated by low structural 

 saddles. The rocks over the entire district generally dip eastward, and 

 the dip is shown in the height of this anticline. The axis of this fold 

 dips from an elevation of about 1,160 feet at the western side of the dis- 

 trict to about 1,040 feet at its eastern edge, a distance of about 24 miles. 



Another important structural feature of this district is a broad flat 

 syncline or structural trough which lies north of and roughly parallel 

 to the anticline. The axis of this fold pitches slightly toward the east, 

 but is somewhat modified by one or two shallow basins. 



