It's important to note that there are not exactly 4 layers of soil formation, but rather horizons that develop in a specific order. These horizons are layers of soil with distinct characteristics due to the processes of soil formation.

Here's a breakdown of the common soil horizons and their characteristics:

1. O Horizon (Organic Layer): This is the uppermost layer, composed of partially decomposed organic matter like leaves, twigs, and other plant and animal residues. It's often found in forests and is rich in nutrients.

2. A Horizon (Topsoil): This layer is made up of a mixture of mineral particles and decomposed organic matter. It's typically dark in color due to the presence of humus, a stable form of decomposed organic matter. It's also where most plant roots grow.

3. E Horizon (Eluviated Horizon): This layer is often found in older soils and is characterized by the loss of minerals and organic matter due to leaching. It's typically light in color and sandy in texture.

4. B Horizon (Subsoil): This layer is richer in minerals than the A horizon and is often compacted due to the accumulation of clay and other materials. It's also where you often find parent material, the rock from which the soil was formed.

5. C Horizon (Parent Material): This is the layer of partially weathered bedrock. It's the source of the mineral particles that make up the other horizons.

6. R Horizon (Bedrock): This is the unweathered bedrock that lies beneath the C horizon.

Not all soils have all of these horizons. The presence and development of each horizon depends on factors like climate, vegetation, parent material, time, and topography.

Remember: This is a simplified explanation. Soil formation is a complex process with many variations.