underclay

British  

/ ˈʌndəˌkleɪ /

noun

1. a grey or whitish clay rock containing fossilized plant roots and occurring beneath coal seams. When used as a refractory, it is known as fireclay

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Example Sentences

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underclay

The stigmariae on the other hand, abounded in the underclay, as it is called, and were not in any way compressed but retained what appeared to be their natural shape and position.

From The Story of a Piece of Coal What It Is, Whence It Comes, and Whither It Goes by Martin, Edward A.

I wish Ehrenberg would undertake a microscopical hunt for infusoria in the underclay and shales; it might reveal something.

From More Letters of Charles Darwin — Volume 2 by Darwin, Francis, Sir

Week 23 Another famous tree which grew in the coal-forests was the one whose roots we found in the floor or underclay of the coal.

From The Fairy-Land of Science by Buckley, Arabella B.

These roots were Stigmaria, and the stuff into which they penetrated was an underclay.

From Scientific American Supplement, No. 447, July 26, 1884 by Various

This lower bed is an underclay seven feet thick, with stigmarian rootlets, and the small land-shells occurring in it are in all stages of growth.

From The Student's Elements of Geology by Lyell, Charles, Sir