15 January 1988
Vol 239, Issue 4837

About The Cover

Photomicrograph taken under cathodoluminescent illumination of 30-micrometer-thick slice of limestone from Jurassic Smackover formation, east Texas at 3.2-kilometer depth. Calcite cements (bright yellow and dull orange) fill the pore spaces between round sand-sized ooids. Grain in center is about 0.5 millimeter in diameter. See page 261. [Photo courtesy of Stuart C. Williams, Exxon Production Research Co., Houston, TX 77001]