roofstone
nounUK /ˈɹuːfˌstəʊ̯n/ · CA, US /ˈɹufˌstoʊ̯n/
Etymology From roof + stone.
1
Business, Geography, Geology, Mining, Natural sciences The stone or rock layer immediately above a coal seam.
- The intention of the props is for the security of the workmen to keep up the roofstone; they have no effect in resisting the crush of the super-incumbent strata.1830, The Edinburgh Encyclopædia, volume 14, page 352:
2
Archaeology, History, Human sciences, Sciences A large, usually flat stone slab placed atop the side-stones (orthostats) of a megalithic burial chamber—such as in portal tombs, wedge tombs, or gallery graves—to form a roof covering the interior space.