The Markley Formation is the the basal formation of the Bowie Group (new).   It consists of sandstones and conglomerates.

https://mrdata.usgs.gov/geology/
"Overlies Canyon Group. Basal formation of Bowie Group (new), Hentz (1988). Continental and minor paralic strata on Bend arch and Ft Worth syncline (Young, Jack, Clay, Montague Cos., TX) Sandstone, mudstone, conglomerate, coal, scarce thin limestone. Easternmost outcrop, fluvial and minor fluvial-deltaic sandstone and chert-pebbly conglomerates form marker beds. Markley contains 15 sandstone members which occur as mappable stacked bodies and horizontally contiguous belts, separated by thin mudstone zones. Mudstone contains sandstone and siltstone lentils and discontinuous seams of subbituminous coal and carbonaceous shale (Newcastle Coal and others). In lower part are thin beds of weathered and fissile subbituminous coal. Ranges in thickness 320-600 ft."