WorldWide Drilling Resource

55 WorldWide Drilling Resource ® SEPTEMBER 2015 )0&"%1 "6)&4 ,, ,, 2)&0 -%3120*"+ )0&"%1 "-% 312., )0&"%1 "-3'"$230&0 .' -&02*" !&+%&% 0*++ */& 3"+ !"++ 0*++ */& !*0&+*-& 0*++ .% "1*-( .,/.1*2& !*0&+*-& 0*++ .%1 .-*$ 0*++ */& "1*-( *21 &0$311*.- "1*-( *21 0*++ .++"01 *1)*-( ..+1 3#1 2"02&0 .%1 "-% 2"#*+*7&01 0*++ */& -$ )*0% 2 8 !*-12&% ).-& 8 8 "5 2., %0*++/*/&*-$ $., 8 444 %0*++/*/&*-$ $., Frequently-Used Geological Terms Part 42 Glossary Adapted from the Dictionary of Geological Terms L - Continued Longitudinal Profile - The profile of a stream or valley drawn along its length from source to mouth. It is the straightened-out upper edge of a vertical section which follows the winding of the stream or valley. Longitudinal Section - A diagram drawn on a vertical or inclined plane and parallel to the longer axis of a given feature such as a section drawn parallel to the strike of a vein. Longitudinal Stream - A stream which follows the strike (direction) of the underlying rocks. Longitudinal Valley - The valley of a subsequent stream, developed parallel to the general strike of the underlying strata. Longshore Bar - A low sand ridge built chiefly by wave action, occurring at some distance from, and generally parallel with, the shoreline, being submerged at least by high tides and typically separated from the beach by an intervening trough. Loop - A pattern of field observations that begin and end at the same point with a num- ber of intervening observations. This pattern is useful in correcting for drift in gravity meter observations, for diurnal variation in magnetometer surveys, and for faults or other cause of misclosure in seismic dip shooting. Longwall - Amethod of underground mining used primarily in coal mining. Parallel en- tries are driven into a seam to the limit of the block to be mined. From the end of these entries, workings are driven at right angles in both direc- tions. A longwall face is produced as the workings are widened back toward the point of entry. Working space is provided by timbers or other supports. The roof is al- lowed to cave in behind the workers as mining pro- gresses. Lorac - A hyperbolic radio location system where two or more fixed transmitters emit continuous waves and the position of a mobile receiver in the resulting standing wave pattern is determined by measuring the phase differ- ence of the waves emanating from two of the trans- mitters. With longwall mining, over 80% of the face can be removed. More terms to come next month!