The forces of erosion eventually act upon even the most deeply buried igneous rocks. When this occurs, the rock will crumble and decompose under the influence of chemical and mechanical weathering, and particles will be dissolved in water or washed away by streams, blown by winds, or carried away by glaciers. Water is the most active factor in transporting sediment, as this weathered material is called, for rivers and streams continually shape the landscape and carry the sediment either as particles or in solution. Such material may settle out of the water because of its weight, or it may be precipitated chemically from a dissolved state. When this sediment becomes lithified into solid rock< it is termed sedimentary rock. When sand particles solidify. For instance, they become sandstone ; gravel becomes conglomerate ; clay or mud becomes shale. Rock salt and beds of borax are also sedimentary rocks.