Here's why:
* A horizon (topsoil): This layer is where organic matter decomposes and mixes with minerals. It's the most fertile layer and loses nutrients through leaching.
* B horizon (subsoil): This layer receives the leached materials from the A horizon. It's often denser and richer in clay, iron oxides, and other minerals that have been transported downwards.
* C horizon (parent material): This layer consists of partially weathered rock fragments from which the soil formed.
* O horizon (organic layer): This is the topmost layer, composed of freshly fallen leaves and other organic debris.
Therefore, the B horizon acts as a sort of "sink" for minerals that have been leached from the layers above.
