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In stratigraphy, bedrock is consolidated rock underlying the surface of a terrestrial planet, usually the Earth. Above the bedrock is usually an area of broken and weathered unconsolidated rock in the basal subsoil. The surface of the bedrock beneath soil cover is known as rockhead in engineering geology〔Price, David George, ''Engineering Geology: Principles and Practice,'' Springer, 2009, p. 16 ISBN 978-3540292494〕 and identifying this, via excavations, drilling or geophysical methods, is an important task in most civil engineering projects. Superficial deposits (also known as drift) can be extremely thick, such that the bedrock lies hundreds of meters below the surface. Bedrock may also experience subsurface weathering at its upper boundary, forming saprolite. A solid geologic map of an area will usually show the distribution of differing bedrock types, i.e., rock that would be exposed at the surface if all soil or other superficial deposits were removed. Soil scientists use the capital letters O, A, B, C, and E to identify the master soil horizons, and lowercase letters for distinctions of these horizons. Most soils have three major horizons—the surface horizon (A), the subsoil (B), and the substratum (C). Some soils have an organic horizon (O) on the surface, but such a horizon can also be buried. The master horizon, E, is used for subsurface horizons that have a significant loss of minerals (eluviation). Hard bedrock, which is not soil, uses the letter R. ==See also== * Outcrop 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bedrock」の詳細全文を読む スポンサード リンク
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