WorldWide Drilling Resource

39 WorldWide Drilling Resource ® FEBRUARY 2015 Frequently-Used Geological Terms Part 36 Glossary Adapted from the Dictionary of Geological Terms L - Continued Law - In science, a formal statement of the regular manner in which natural phe- nomena occurs under given conditions. Law of Crosscutting Relationships - A stratigraphic principle which states the relative age of rocks can be established; a rock (especially an igneous rock) is younger than any other rock across which it cuts. Law of Original Continuity - A general law of geology. A water-laid stratum, at the time it was formed, must continue laterally in all directions until it thins out as a result of nondeposition or until it abuts against the edge of the original basin. Law of Original Horizontality - A gener- al law of geology. Water-laid sediments are deposited in strata which are horizon- tal or nearly horizontal, and parallel or nearly parallel to the earth’s surface. Layer - A bed or stratum of rock. Layering - A tabular succession of differ- ent components in igneous or metamor- phic rocks, or the formation of layers in a particular rock. Layering is preferable to banding as it implies three dimensions rather than two. Lazulite - A glassy, azure-blue to violet- blue mineral. An uncommon mineral which occurs disseminated in quartzite, schist, quartz veins, granite pegmatites, and as an alluvial and colluvial mineral. Lazurite - An intense blue or violet-blue feldspathoid mineral which is formed as a result of contact metamorphism of lime- stones. Unlike lazulite, it has a dull luster. Leaching - The dissolution of soluble constituents from a rock or orebody by the natural action of percolating water. Also refers to the removal in solution of mineral salts or organic matter from an upper to a lower soil horizon by the action of percolating water, either naturally (rain- water) or artificially (irrigation). Lead - A soft, heavy malleable isometric mineral. Lead rarely occurs in the native form, it is found mostly in combinations such as galena. Lean Clay - A clay of relatively low plas- ticity. Ledge - A narrow shelf or projection of rock, longer than wide, formed on a rock wall or cliff face; also refers to a quarry exposure or natural outcrop of a mineral deposit. Lee - The side of a hill, dune, or other prominent object which is sheltered, or turned away from the wind; also said of a side or slope of a hill or knob facing away Lazulite and lazurite may look alike, but they are very different. Photos courtesy of dakotamatrix.com from an advancing glacier or ice sheet; it is relatively protected from abrasive action. More terms to come next month! " ; # 511-,(2 0) 20'5&43 %9 4+(3( ,/( $/5)$&452(23 ; 08 029'0/ # ! : : $8 $,- 3$-(3 *,6(/3,/4(2/$4,0/$- &0. "(% ,4( 777 *,6(/3,/4(2/$4,0/$- &0.