Answer: Bottom layer of rock
Step-by-step explanation:
The bottom layer is the layer of the deposition of the sediments in which sedimentation and cementation occurs to form the rocks. These rocks are formed at the lowest horizon of the soil profile. These rocks are also called bedrocks. The layer present above the rock are younger and the layer at the top is the youngest layer. The older layer at the bottom and the younger layer at the top. This phenomena is called law of superimposition.