54 DECEMBER 2021 WorldWide Drilling Resource ® RENEW - SUBSCRIBE NOW! Frequently-Used Geological Terms Part 93 Glossary Adapted from the Dictionary of Geological Terms S Shale - A fine-grained detrital sedimentary rock formed by the compaction of clay, silt, or mud. It has a finely laminated struc- ture giving it a fissility along which the rock splits readily, especially on weathered surfaces. Shale Oil - A crude oil obtained from oil shale by submitting it to destructive dis- tillation. Shallower-Pool Test - A well located within the known limits of a gas or oil pool and drilled with the object of searching for new producing zones above the pro- ducing zone of the pool. Shallow-Focus Earthquake - An earthquake with a focus at an approximate depth of less than 43 miles. Most earthquakes are this type. Shaly - Pertaining to or having the character of shale, especially its tendency to split readily along closely spaced bedding surfaces. Sharpstone - Any rock fragment larger than a sand grain having angular edges and corners. Shell - 1. The hard, rigid outer covering of an animal, commonly calcareous but sometimes chitinous or siliceous, e.g. the hard parts of an ammonoid. 2. The crust of the earth; also, any of the concentric zones composing the earth’s interior. 3. A drilling term for a thin, hard layer of rock encountered when drilling a well. Shield Volcano - A broad, gently sloping volcanic cone of flat domical shape, usually several tens or hundreds of square miles in extent, built chiefly of overlapping and interfingering basaltic lava flows. Typical examples are the volcanoes Mauna Loa and Kilauea on the island of Hawaii. Shock Wave - A compressional wave formed whenever the speed of a body relative to a medium exceeds that at which the medium can transmit sound, having an amplitude exceeding the elastic limit of the medium in which it travels, and characterized by a dis- turbed region of small but finite thickness within which abrupt changes occur in the pressure, temperature, density, and velocity of the medium. In rock, it travels at super- sonic velocities and is capable of vaporizing, melting, mineralogically transforming, or strongly deforming rock materials. Shock Zone - A volume of rock sur- rounding an explosion or impact crater in which the effects of shock metamor- phism are present. Shot Break - In seismic prospecting, a record of the instant of generation of seismic waves, as by an explosion. Shot Depth - In seismic work, the vertical distance from the surface to an explo- sive charge. Shot Elevation - In seismic prospecting, the elevation of the dynamite charge in the shot hole. Shothole - In seismic prospecting, a borehole in which an explosive is placed for generating seismic waves. Shot Point - The point at which a charge of dynamite is exploded for the genera- tion of seismic energy. In field practice, the shot point i n c l u d e s the hole and its immedi- ately sur- r o u n d i n g area. Look for more terms next month! EXB Mauna Loa eruption fountains in 1975.