The soil layer also called subsoil is the B horizon.

Here's why:

* A horizon: This is the topsoil, rich in organic matter and where most plant roots grow.

* B horizon: This is the subsoil, characterized by accumulation of minerals and less organic matter compared to the A horizon. It's often denser and less porous than the topsoil.

* C horizon: This layer is mostly composed of weathered parent material, from which the soil above it formed.

So, the B horizon is the layer often referred to as the subsoil.