Bedrock.

Bedrock is the solid rock that underlies the layers of looser, weathered materials that are deposited on the earth’s surface, such as soil, subsoil, or alluvium. Because these unconsolidated layers can be very thick, the bedrock is often located hundreds of meters below the surface. In some places, however, weathering and erosion have removed surface deposits and exposed the underlying bedrock, or "outcrops." Bedrock is harder and more compact than the surface layers. It need not be homogenous and can consist of many different rocks compressed into a consolidated layer.