Quicksand (quick—i.e. 'living' or 'moving,' and sand), in its usual significance, a tract of sand which, without differing much in appearance from the shore of which it forms part, remains permanently saturated with water to such an extent that it cannot support any weight. Quicksands are most often found near the mouths of large rivers. They appear only to be formed on flat shores, the substratum of which is an irregular expanse of stiff clay or other impervious formation. Pools of water are retained in the hollows, and become partially filled with sand or mud, which remains like the soft sediment in a cup of cocoa on account of the absence of drainage. The sand on a uniform shelving shore consolidates at low tide because the water which permeates it drains back freely to the sea. In narrow channels through which the configuration of the adjoining shore causes strong tidal currents to run the sand may be kept so constantly stirred up by the moving water that a quicksand results. Thus, while the summit of a sandbank rising from a gentle slope is usually firm, the hollow margin of the bank where it meets the shore is frequently a quicksand. Quicksands are not commonly of great extent, and their danger has prob- ably been exaggerated in the popular mind by sensational descriptions in works of fiction—e.g. in the Bride of Lammermoor and Wilkie Collins's Moonstone. Persons sink in a quicksand exactly as in water, only more slowly; and it is probable that if the victim did not struggle he would not sink over the head, as experiments show that water containing a quantity of solid matter in suspension has its floating power increased. It is a common belief amongst sailors that if a vessel is stranded on a quicksand it is inevitably sucked down. This cannot be the case unless the vessel springs a leak, or heels over sufficiently to let the semi-liquid sand enter. The idea may have taken rise from the popular association of quicksands with whirlpools, or from the fate of small vessels stranded at low tide on a stiff bank of clay which held them fast and allowed the rising tide to submerge them.
The name quicksand is sometimes applied, especially by old writers, to the drifting sands which are carried by wind over cultivated land bordering the seashore or a desert. See DOWNS, DRIFT, DUNES.