DRIFT (from "drive ")  , a verb or noun used in various connexions with the sense of propelled motion, especially (but not necessarily) of an aimless sort, undirected . Thus it is possible to speak of a snow-drift, an accumlation driven by the wind; of a ship drifting out of its course; of the drift of a speech, i.e. its general tendency . The word is also used in some technical senses, more immediately resulting from the action of driving something in . But the most important technical use of the word is in geology, as introduced by C . Lyell in 1840 in place of " Diluvium." The earlier geologists had been in the habit of dividing the Quaternary deposits into an older Diluvium and a younger Alluvium; the latter is still employed in England, but the former has dropped out of use, though it is still retained by some continental writers . The Alluvium was distinguished from Diluvium by the fact that its mammalian fossils were representatives of still living forms, but it is a matter of great difficulty to separate these two divisions in practice . " The term drift is now applied generally to the Quaternary deposits, which consist for the most part of gravel, sand, loam or brickearth and clay; it naturally refers to strata laid down at some distance from the rocks to whose destruction they are largely due; but, although applied to river deposits, the word drift is more appropriately used in reference to the accumulations of the Glacial period . " The occurrence of stones and boulders far removed from their parent source early attracted the attention of geologists, but for a long period the phenomena, now known as of glacial origin, were unexplained, and the drifts were looked upon as little more than ` extraneous rubbish,' the product of geological agents, quite distinct from those which helped to form the more solid ' rocks that underlie them." (See H . B . Woodward, The Geology of England and Wales, 2nd ed., 1887.) The conception of an -underlying " solid " geological structure covered by a superficial mantle of " drift " is still retained for certain practical purposes; thus, the Geological Survey of Great Britain issues many of the maps in two forms, the " Solid Edition," showing the " solid geology," which embraces all igneous rocks and the stratified rocks older than Pleistocene, and the "Drift Edition," which shows only such older strata as are unobscured by drift . In writing and in conversation the geological expression " drift " is now usually understood to mean Glacial drift, including boulder clay and all the varieties of sand, gravel and clay deposits formed by the agency of ice sheets, glaciers and icebergs . But in the " Drift " maps many other types of deposit are indicated, such, for instance, as the ordinary modern alluvium - of rivers, and the older river terraces (River-drift of various ages), including gravels, brickearth and loam; old raised sea beaches and blown-sand (Aeolian-drift); the " Head " of Cornwall and Devon, an angular detritus consisting of stones with clay or loam; clay-with-flints, rainwash (landwash), scree and talus; the " Warp," a marine and estuarine silt and clay of the Humber; and also beds of peat and diatomite .

See GLACIAL PERIOD; PLEISTOCENE; BOULDER CLAY . U . A .