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What is a sill in geology?
Quick Answer
A sill is a sheet of igneous rock that intrudes between older rock layers and cools parallel to them.
The Full Story
Unlike a dike, a sill spreads sideways along bedding planes or other weaknesses in the crust. It usually forms when magma forces its way between sedimentary layers and freezes into a flat or gently tilted body. Sills can be very large and may feed later volcanic activity or form hard resistant ridges after erosion. Famous examples include the Palisades Sill along the Hudson River in the United States.
Key Facts
1.Sills intrude parallel to existing layers
2.They are younger than the rocks around them
3.The Palisades Sill is a well-known example
YouTube Angle
Suggested video title for this topic:
"Flat lava sheets hidden inside the Earth"
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