The B horizon, also known as the subsoil, is characterized by accumulated materials from above. This means it's a layer where:

* Clay, iron oxides, and other minerals have leached down from the A horizon (topsoil). This process is called illuviation.

* Organic matter content is lower than the A horizon.

* The soil is often denser and more compact than the A horizon. This is due to the accumulation of minerals.

* Color can vary depending on the specific minerals present. For example, red or yellow coloration can indicate high iron content.

So, in a cross-section of soil, the B horizon is the layer below the topsoil where minerals and other materials have accumulated.