An area with coal and shale in the ground would likely be a sedimentary basin. Sedimentary basins are formed when sediment accumulates in a depression in the Earth's crust. Over time, the sediment is buried and compacted, forming sedimentary rocks. Coal and shale are both sedimentary rocks. Coal is formed from the remains of plants that lived millions of years ago. Shale is formed from fine-grained sediment, such as clay and silt. Sedimentary basins are often found near mountain ranges or other areas where there is a lot of erosion.