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

There is a class of deposit found among the coal-beds, which is known as the "underclay," and this is the most regular of all as to the position in which it is found.

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

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

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.

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

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.