There are horizons in a soil profile, which are layers that develop over time due to various factors like weathering, organic matter decomposition, and biological activity.

The most common horizons found in a mature soil are:

* O Horizon: This is the uppermost layer, composed primarily of organic matter like leaves, twigs, and decaying organisms. It's often referred to as the "humus layer."

* A Horizon: Also called the "topsoil," it's a mix of mineral particles and organic matter. This layer is rich in nutrients and supports plant growth.

* E Horizon: This layer is often found under the A horizon and is characterized by leaching of minerals and organic matter. It's often pale in color.

* B Horizon: Known as the "subsoil," this layer is usually rich in minerals and clay. It has less organic matter compared to the A horizon.

* C Horizon: This layer is made up of partially weathered bedrock or parent material from which the soil developed.

* R Horizon: This is the bedrock layer, the unweathered parent material from which the soil originated.

Not all soils will have all of these horizons. Some soils might have more horizons, while others might have fewer or even lack certain horizons depending on the soil type, climate, and other factors.

Therefore, there's no fixed "three layers" for a complete soil. It's the complex interplay of horizons that defines a complete soil profile.