Geology of the Ferris Quadrangle, Dallas and Ellis counties, Texas

The Ferris Quadrangle in southern Dallas and northern Ellis counties, Texas, is underlain by the Austin Chalk and Taylor Marl, both of Upper Cretaceous age. Two members of the Austin, the middle marl and the upper chalk, along with the lower blue-gray unit of the Taylor Marl, crop out within the area. The Austin-Taylor contact, within the area in Dallas County, is transitional and consists of chalk and marl sequences intermediate in lithology between the two formations. The contact in Ellis County is marked by a reddish-brown clay zone containing phosphate nodules, indicating an unconformity. Approximately one-half of the area is covered by two Quaternary terraces and recent alluvium. A large, northeast-trending, normal fault with a minimum displacement of 150 feet is exposed on Bear Creek in the southwest corner of the quadrangle. Taylor Marl has been downfaulted on the northwest against Austin Chalk on the southeast. It is probably a part of the Balcones Fault System