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Comment: 18:59 - 20:12 (01:13)
Source: Annenberg/CPB Resources - Earth Revealed - 14. Intrusive Igneous Rocks
Keywords: "igneous rock", intrusion, dike, sill, laccolith, stock, pluton, batholith
Our transcription: Once formed, igneous intrusions are classified according to their geometric shapes and overall size.
Small common intrusions possessing sheet-like shapes that cut across the bedding or fabric of preexisting rocks are called dikes.
Sills are related to dikes; but instead of cutting across strata as dikes do, sills intrude between layers forming sheets parallel to the strata.
A laccolith is a shallow sill-like structure that bulges upward in its central portion also causing a hump or gentle rise in the overlying crust.
The largest intrusions, typically having the shape of spheroidal globs, are the plutons.
These range from masses called stocks which crop out over areas tens of square kilometers to gigantic intrusions exposed over hundreds of square kilometers.
Geologists call these huge plutons batholiths.
Plutons often rise in groups; so a batholith can, in fact, be composed of many plutons merged together.
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