Gray to black chert is common.
Nodular chert is common.
It consists of flaggy limestone beds, and a 1-meter thick rudist bed overlain by dolomitic limestone. Its top is a calcarenitic limestone with sparse gluaconite grains. Boundaries - Both boundaries of the Edwards Limestone in the Austin area are gradational, the Lower Edwards gradually grades into Walnut beds to the north, and the uppermost Edwards Limestone grading into Georgetown beds to the north. In addition, many of the limestones thus deposited were altered to dolomite by the invasion meteoric waters shortly after deposition. In the Austin area, along the Balcones fault zone, some dolomitization occurred later, following the invasions of waters high in magnesium sulfate.