What is gravel?

   Gravel is, a deposit of rounded, water-worn stones. Gravels are produced by the action of moving water, usually of streams or of the sea. In course of time gravels may become consolidated by cementing agents and by pressure and then form "conglomerate." The pebbles in a gravel may consist of any kind of rock, but most commonly they are of quartz. In addition to marine and fluviatile gravels, a third group is often recognized—the glacial gravels. These are partly due to the action of running waters emerging from the melting ice sheets and glaciers, which wash out the finer materials from the glacial debris. Such gravels deposited during the Glacial period often form terraces, which may be hundreds of feet above the present rivers. Gravel is extensively used for making concrete and mortar, and as road material.