Diabase dikes of uncertain Triassic age intrude rocks in central South Carolina. The dikes range from 2 to 300 feet wide and up to 7 miles long, striking NW and dipping steeply NE. The dike rocks have an ophitic to intergranular texture and are composed of 40-60% plagioclase, 13-36% augite, 10-30% olivine, and accessory minerals. Plagioclase content increases from the edges to the centers of dikes while olivine and pyroxene decrease, though their amounts vary randomly within individual dikes. No systematic chemical changes were observed across the dikes.