This Ordovician rock is composed of laminated mudstone and siltstone with greywacke sandstone. Other rocks include sandstone, mudstone, and siltstone. Internal layers of mudstone, conglomerate and siltstone interrupt the limestone horizontally. The grey coloring is mudstone, siltstone, and shale. Elsewhere clasts of quartzite, limestone, sandstone, mudstone, jasper and basalt can be found. It is typically interbedded with bioturbated mudstone. Most fossils found are grey or yellow silty mudstone. The term "mudrock" allows for further subdivisions of siltstone, claystone, mudstone, and shale. This area is dominated by steep sandstone, greywacke and mudstone hills and winding valleys. The Haynesville Formation consists of marine and coastal plain limestone, shale, mudstone, and sandstone. Schist (pronounced ) is a medium-grade metamorphic rock formed from mudstone or shale. Mud rocks such as mudstone and shale account for some 65% of all sedimentary rocks. The layer commence with poorly cemented sandstone, mudstone, carbonaceous mudstone and coal (Cygnet Coal Measures). Siltstone, mudstone, and claystone implies lithified, or hardened, detritus without fissility. The underlying geology is sand overlaying clay overlaying mudstone.