Retreating glaciers leave behind silt, clay, sand, gravel, and boulders called drift. The quaternary sediments consist of clay, silt, and several grades of sand and gravel. They occupy a range of seafloors consisting of mud, sand, gravel, or rocks. Sand, natural gravel, and crushed stone are used mainly for this purpose. Drying beds are typically composed of four layers consisting of gravel and sand. Its content may vary from clays to mixtures of clay, sand, gravel, and boulders. Extraction includes filling materials, gravel, and sand. A crescent of sand and gravel deserts lies to the east. Geonets are synthetic drainage materials that are often used in lieu of sand and gravel. There are about fifteen streams that have watersheds with accumulation of sand and gravel. They often swallow grit such as fine gravel or sand to assist with digestion. He toughens his fists by plunging them into buckets of sand, gravel, and rock. Roads-mostly gravel and dirt trails-were in need of extensive repair. Bowfin eggs are adhesive, and will attach to aquatic vegetation, roots, gravel, and sand. This method works reasonably well for particles in the sand and gravel size range.