Stratified rock consists of layers, or strata. Strata are also called beds. Each individual layer is known as a stratum. Shale, sandstone, conglomerate, limestone, and most other sedimentary rocks are stratified. Sedimentary rocks are stratified on land because rivers and wind spread them in layers. They are stratified on lake and ocean bottoms by currents of the water. Originally, all strata were more or less horizontal as they formed over broad areas of Earth’s surface. Deformation and buckling of Earth’s crust in many places disrupted these layers, breaking them along faults or causing them to tilt or fold. The amount of tilt in deformed layers, called the dip, may range from 0 to 90 degrees. See also Rock .
