from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A stratum of clay lying beneath a coal bed.
from the GNU version of the Collaborative International Dictionary of English
- n. A stratum of clay lying beneath a coal bed, often containing the roots of coal plants, especially the Stigmaria.
from The Century Dictionary and Cyclopedia
- n. Beds of clay frequently found immediately underlying beds of coal.
Whole masses of these root-stems, with ribbon-like roots lying scattered near them, are found buried in the layer of clay called the underclay which makes the floor of the coal, and they prove to us that this underclay must have been once the ground in which the roots of the coal-plants grew.
The group with which we have to deal is called the carboniferous or coal bearing system, and it includes four classes of rocks, viz.: 1, sandstone; 2, shale or bind; 3, limestone; 4, coal and underclay.
This theory was for some time but poorly received; but after the discovery of Sir William Logan, that every bed of coal had a bed of underclay beneath, and the discovery of Mr. Binney, that these underclays were true soils on which plants had undoubtedly grown, there was no doubt whatever that this was the real and true explanation of the matter.
These roots were Stigmaria, and the stuff into which they penetrated was an underclay.
Another famous tree which grew in the coal-forests was the one whose roots we found in the floor or underclay of the coal.
You will feel still more sure of this when you find that there is not only one straight gallery of coal, but that galleries branch out right and left, and that everywhere you find the coal lying like a sandwich between the floor and the roof, showing that quite a large piece of country must be covered by these remains of plants all rooted in the underclay.
I wish Ehrenberg would undertake a microscopical hunt for infusoria in the underclay and shales; it might reveal something.
From his examination, Tabor determined there was a lower and older layer of coal and underclay that was a poorly drained, swampy landscape dissected by well-drained Oxisol-forming uplands.