Ancient Mud
Shale is sedimentary rock formed when clay or mud deposits are compacted
under pressure.
Shales are fine-grained, smooth and relatively soft. Shale tends to crumble much easier than
harder sedimentary rocks such as
limestone or sandstone.
Shale appears in the Grand Canyon in the Hermit Shale and Bright Angel Shale
layers.
Shale, when subjected to heat and extreme pressure, forms slate
which is much more durable. Slate is used for blackboards, roofing and in the manufacture of billiard tables.
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