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Geology Dictionary
Geological Terms Beginning With "U"
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Ultrabasic Rock:
An igneous rock with a very low silica content and rich in minerals such as hypersthene, augite and olivine. These rocks are also known as ultramafic rocks.
Ultramafic Rock:
See Ultrabasic Rock.
Unconformity:
A contact between two rock units of significantly different
ages. An unconformity is a gap in the time record for that location.
Unconsolidated:
A term used when referring to sediment that has not been lithified into a rock. Uncemented.
Uniformitarianism:
A basic geologic principle. Processes that act upon the Earth today are the same processes that have acted upon it in the past. The present is the key to the past.
Unit Cell:
The smallest sample of a substance that has a complete representation of its atomic structure. A crystal structure is formed by repetition of the unit cell in three dimensions.
Uplift:
A structurally high area in Earth's crust. Formed by movements that bend the crust into a structure such as a dome or an arch.
Upwelling:
Movement of cold water from the floor of a lake or ocean up into a shallow area.
U-shaped Valley:
A deep valley with a flat floor and very steep walls. Shaped in cross-section like the letter "U". Valleys with this geometry are frequently cut by a glacier.
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