Oil rich Mississippian!
shale
shale is
== Shale is a sedimentary rock, comprised of lithified mud and clay minerals.
Shamrock ;) Just kidding, obviously. I would say Shale.
Shale is the type of sedimentary rock that is impermeable.
sedimentary
Shale
shale
Shale is a type of rock. A piece of shale is normally flat and thin like a small chalkboard.
the type of rock made mostly from clay is the shale rock
Shale
Shale is a sedimentary rock, not a metamorphic rock.
Shale
shale is
Shale & Limestone !
Shale is the usual rock type to look for.
== Shale is a sedimentary rock, comprised of lithified mud and clay minerals.