GRAVEL or PEBBLE-BEDS, the name given to deposits of rounded or sub-angular, waterworn stones, mingled with finer material such as sand or clay. The word "gravel" is adapted from the O.Fr. gravele, mod. gravelle, dim. of grave, coarse sand, sea shore, Mod. Fr. grave. In petrology, the word is used in a techni cal sense for material cif diameter greater than 2mm., material of smaller diameter being termed sand. The deposits of gravel are produced by the attrition of rock-fragments by moving water —the tides, waves of the sea and lakes, and the flow of rivers. Extensive beds of gravel (shingle-beaches) are formed at the present day on coasts where suitable rocks are exposed to the attack of the atmosphere and of waves. In consequence of the continuous movement by shore-currents, intensified during storms, the coasts are often protected and the gravel caused to accumu late by the building of groynes, sea-walls and piers. Where the pebbles are swept along to a projecting cape or into a quieter area, they may form nazes (e.g., Orfordness, Dungeness) or long spits (Chesil Bank), or submarine banks.
In many parts of Britain, Scandinavia and North America, there are marine gravels in every respect resembling those of the sea-shore, at levels considerably above high-tide. These gravel terraces (or "raised-beaches") often extend for great distances and are indication that the sea at one time stood higher than it does at present.
River-gravels occur most commonly in the middle and upper parts of streams where the currents are active in times of flood. Ancient terraces of gravel are often found at levels considerably above those of the present rivers. They mark the greater activity of the streams or are evidence of uplift of the country, whereby the rivers have been able to cut their beds to a lower level.
The pebbles of gravels resemble those of conglomerates (q.v.), which are pebble-beds cemented by calcareous, siliceous or other material. (P. G. H. B.)