Text File | 1994-05-02 | 658 b | 3 lines | [TEXT/MSWD]
Gneiss Rock: This coarse grained metamorphic rock is some of the Park's oldest, going back to 1 to 2 billion years ago. (The earth was created 4.6 billion years ago.) It is formed by re-crystallization of older granite, sandstone, or sandstone-shale layers.
Gneiss is often intricately banded with schist (a crystalline metamorphic rock which splits along parallel planes, formed from fine-grained sedimentary rock) and is formed at depths of between 5 and 10 miles under the earth's crust at temperatures as high as 1000°F. Rock flows here without breaking up, like a warm tar. Folded patterns appear as a result of this flowing action. #
