Geology Concepts

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Uniformitarianism

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The principle that most geologic events of the past are similar to processes observed in the present.

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Law of Superposition

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The principle that the lowest layers in rock strata are deposited before the layers above, unless turned upside down. The oldest rocks are generally at the bottom of an outcrop.

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Outcrop

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Bedrock exposed at the surface because it is not covered by soil.

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Orogeny

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The process of mountain building.

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Extrusion

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Molten, liquid rock (lava) flowing out onto the Earth's surface. A fine-grained igneous rock formed by the rapid crystallization of lava at or near the Earth's surface.

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Intrusion

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Molten, liquid rock (magma) is pushed into cracks within the Earth. It forms a body of coarse-grained igneous rock through slow cooling inside the Earth.

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Lava

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Molten rock at the surface of the Earth.

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Folded Strata

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Layers of rock that have been bent by forces within the Earth.

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Fault

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A break in the rock of the Earth’s crust along which there has been displacement (movement).

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Uplift

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The rising of the Earth's crust from forces within the Earth, generally related to motions of the tectonic plates.