The role of the subsurface stratigrapher increases in importance as the number of unexplored structural traps decreases, but little detailed information regarding the descriptions and interpretations of sample cuttings has been made available in one publication. Rocks may be described in sample cuttings as to rock type, color, grain or crystal size, cement or matrix, impurities, porosity, stain, luster, fossils, associated material, and subordinate features. Clast rocks are divided into non-carbonate clastics, which include sandstone, siltstone, and clay, or shale, and carbonate clastics which include most types of limestone and dolomite. Non-clastic carbonate rocks (reefs and bioherms) can be composed to a great extent of clastic material, but they originate from and are retained by non-clastic organisms. Evaporites compose a third major rock type. Sedimentary rocks may have interstitial and fracture porosity, and in addition, carbonate rocks may have solution porosity. Insoluble residues and paleontology are supplemental aids in establishing time surfaces and in indicating environments. Several simple tests for determining mineralogy and oil shows can be made by a stratigrapher. He can also identify in sample cuttings several criteria for the recognition of unconformities.