U.S. Geological Survey

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. 1987 CLAY A sedimentologic term for a rock or mineral fragment or a detrital particle of any composition smaller than a very fine silt grain, having a diameter less than 1/256 mm (4 microns, or 0.00026 in., or 8 phi units). COBBLE A sedimentologic term for a rock fragment or detrital particle larger than a pebble and smaller than a boulder, having a diameter in the range of 64 to 256 mm (2.5 to 10 in., or-6 to-8 phi units). CONSOLIDATION Gradual or slow reduction in volume and increase in density of a material mass in response to increased loads or compressive stress; e.g., the adjustment of a saturated material involving the squeezing of water from pore spaces. COMPACTION Any process by which a material mass loses pore space and achieves a higher density, thereby increasing the bearing capacity, reducing the tendency to settle or deform under load, and increasing the general stability of the material mass (soil). CRATER A typically bowl-shaped or saucer-shaped pit or depression, generally of considerable size and with steep inner slopes, formed on a terrestrial or planetary surface or in the ground by the explosive release of chemical or kinetic energy; e.g., an impact crater or an explosion crater. CRATER DIAMETER Distance measured from the crater rim, through ground zero, to the opposite crater rim. CRATER RADIAL A transect at any given azimuth extending from ground zero outward; in this volume, the radials extend beyond the current edge of the crater (i.e., beyond the crater rim crest). CRATER RIM CREST Current highest point on the crater rim (sensu Roddy, 1977, fig. 1). CRATER WALL Escarpment at the current edge of the crater, extending from the (true) crater floor upward to the rim crest (sensu Roddy, 1977, fig