WorldWide Drilling Resource

12 MARCH 2015 WorldWide Drilling Resource ® Frequently-Used Geological Terms Part 37 Glossary Adapted from the Dictionary of Geological Terms L - Continued Lens - A body of ore or rock which is thick in the middle and thin at the edges, like a double convex lens. Lensing - Thinning out of a stratum in one or more directions; its lateral dis- appearance. Lenticular - 1. Resembling the cross section of a lens in shape, especially a double-convex lens. 2. Pertaining to a stratigraphic lens or lentil. Lentil - 1. A lens-shaped rock body. 2. A minor rock stratigraphic unit; a subdi- vision of a formation similar in rank to a member, having relatively small geo- graphic extent, and thinning out in all directions. Leonardian - Upper series of the Lower Permian of North America. Lepidolite - A mineral of the mica group commonly occuring in rose or lilac-col- ored masses made of small scales, as in pegmatites. Lepidomelane - A black variety of biotite with a high content of ferric iron. Leptothermal - Describes a hydrother- mal mineral deposit formed at temper- ature and depth conditions intermediate between mesothermal and epithermal; also describes a type of environment. Leucite - White or gray mineral of a feldspathoid group; an important rock- forming mineral in alkalic rock, especially lavas; usually occurs in trapezohedral crystals with a glassy fracture. Leucocratic - Light-colored; applied to igneous rocks containing less than 30% mafic minerals. Aerial photo of the levee built to protect New Orleans from future natural disasters. Courtesy of the U.S. Army Corps of Engineers. Levee - A natural or artificial embank- ment along a watercourse or arm of the sea which protects land from flooding. Leveling - Determining the compara- tive altitude of different points on the earth’s surface, usual ly by sighting through a leveling instrument at one point, to a level rod at another point; also the finding of a horizontal line or establishing of grades by means of a level. Leveling Instrument - An instrument for establishing a horizontal line of sight, usually with a spirit level or pendulum device; used with a level rod to deter- mine differences in elevation between two separated points on the earth’s surface. Level of Zero Amplitude - Maximum depth below the earth’s surface reached by seasonal temperature changes. More terms to come next month! Win a prize! Send your completed puzzle to: WWDR PO Box 660 Bonifay, FL 32425 or fax to: 850-547-0329 Congratulations to: Ed I ls ley Ed Thetford Ctr . , VT Winner for February Time for a Little Fun! February Puzzle Solution: INNOVATION IS IMPORTANT D E A L H N S N A G C I G N A M E A N E A D M D N U E Q I U T R A Y O R E D S E P S Unscramble the editorial focus words and place them in the spaces provided. Once complete, the circled letters will reveal another word. Do you know what happened on March 1, 1921? See page 43 to find out!