Superposition is a concept in geology that states that the layers at the bottom of a rock column are older than the layers at the top of a rock column. This is especially true for layers of sedimentary rock that remain in their original horizontal position. These individual layers are known as beds.
|Sedimentary rock formations at Pictured Rocks National Lakeshore - layers at the the top of the formation are older than layers at the bottom|
|Pictured Rocks National Lakeshore - Sandstone deposited in distinct layers with the oldest layers at the bottom of the formation.|
If you think of a rock column as a layer cake this concept makes perfect sense. When a baker makes a layer cake, they add each new layer to the top of the cake. In nature, when sediment is deposited at the bottom of a lake or at the base of a hill new layers form over the top of older layers.
|Bedding in a dune a Sleeping Bear Dunes National Lakeshore - the upper beds are younger than the lower beds.|