Outcrop

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Outcrop is a geological term referring to the appearance of bedrock or superficial deposits exposed at the surface of the Earth. In most places the bedrock or superficial deposits are covered by a mantle of soil and vegetation and cannot be seen or examined closely. However in places where the overlying cover is removed through erosion, the rock may be exposed, or crop out. Such exposure will happen most frequently in areas where erosion is rapid and exceeds the weathering rate such as on steep hillsides, river banks, or tectonically active areas. Bedrock and superficial deposits may also be exposed at the earth's surface due to human excavations such as quarrying and building of transport routes.

Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps. In situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding earth history. Some of the types of information that can only be obtained from bedrock outcrops, or through precise drilling and coring operations, are; structural geology features orientations (e.g. bedding planes, fold (geology) axes, foliation), depositional features orientations (e.g. paleo-current directions, grading, facies changes), paleomagnetic orientations. Outcrops are also critically important for understanding fossil assemblages, paleo-environment, and evolution as they provide a record of relative changes within geologic strata.

Accurate description, mapping, and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as: law of superposition, principle of original horizontality, principle of lateral continuity, and principle of faunal succession. Outcrops can therefore be considered the fundamental element of geologic science