WorldWide Drilling Resource

34 AUGUST 2014 WorldWide Drilling Resource ® Frequently-Used Geological Terms Part 32 Glossary Adapted from the Dictionary of Geological Terms I - Continued Internal Drainage - Surface drainage in which the water does not meet the ocean. Interpretive Log - A sample log based on rotary wel l cuttings in which the geologist attempts to show only the rock encountered by the bit at each sampled depth. Interpretive Map - A map prepared for the general public classifying a land’s suitability for a particular use on the basis of geologic characteristics. Uses include general construction, sand and gravel development, land burial of waste, and groundwater development. Interrupted Water Table - A water table sloping steeply over a groundwa- ter barrier with pronounced difference in elevation above and below it. Involution - 1) A highly irregular, aim- lessly contorted sedimentary structure developed by the formation, growth, and melting of ground ice in the active layer overlying permafrost. Iron Formation - A chemical sedimen- tary rock, typically thin-bedded, and/or finely laminated, containing at least 15% iron of sedimentary origin and commonly containing layers of chert. Iron Ore - Rock containing one or more minerals from which metallic iron may be profitably extracted. Iron Range - Iron formation located in the Great Lakes region of the U.S. and Canada. Ironstone - Rock containing a substantial portion of iron. This term is typically used for hard, coarsely banded or nonbanded sedimentary rock. Isinglass - Muscovite in thin transparent sheets. Iso - A prefix meaning equal. Isobaric Surface - Asurface where every point has the same barometric pressure. Photo of hematite, the most common sedimentary iron ore mineral, courtesy of famindia.com Isobath - A line on a map or chart which connects points of equal water depth. Also refers to an imaginary line on a land sur- face in which all points are the same ver- tical distance above the upper or lower surface of an aquifer or water table. Isochore - A line drawn on a map through points of equal drilled thickness of a spec- ified subsurface. Isocline - A fold whose limbs are parallel. Isofacial - Rocks belonging to the same metamorphic facies. Isogeotherm - A line or surface within the earth connecting points of equal tem- perature. Isohyetal Line - A line on a map connect- ing points which receive the same amount of precipitation. More terms next month!