underclay


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Related to underclay: seat earth

underclay

[′ən·dər‚klā]
(geology)
A layer of clay or other fine-grained detrital material underlying a coal bed or comprising the floor of a coal seam. Also known as coal clay; root clay; seat clay; seat earth; thill; underearth; warrant.
References in periodicals archive ?
The coal underclay can be punctured due to coal mining operations, resulting in mixing of ground waters from different saturated zones after reclamation.
Core Depth in feet Lithology Type of analysis WM-8 246 Shale Palynology WM-8 321 Limestone Palynology WM-8 422 Shale Palynology WM-8 523 Underclay Palynology WM-10 175 Limestone Palynology WM-10 258 Limestone Thin section WM-10 330 Shale Palynology WM-10 450 Limestone Palynology WM-10 452 Limestone Thin section WM-10 537 Siltstone Palynology WM-10 627 Shale Palynology WM-10 683 Sandstone Thin section WM-10 704 Siltstone with interbeds Thin section of very fine sandstone Descriptions of dispersed organic matter in the samples.
This study also examined the possible influences of sea level fluctuations on the sedimentary rocks, and it appears that coal beds, underclays, and shales are correlative with sea level falls.
Sandstones, siltstones, shales, and underclays constitute approximately 40% of the core thickness in WM-8, and 45% in WM-10.
Coal seams formed from the accumulation of plant debris, and the underclays represent the swampy environment behind the coal swamps (Figure 6).
Our interpretation fits well with this revised model because we are interpreting coals and underclays as representing periods of sea level lowstand marked by the onset of transgression.