What does the grey layer(clay) do in
the soil profile?

In deeper horizons such as the B-horizon, a brown colour usually means that the soil has good natural drainage. A black or dark grey colour usually comes from an accumulation of organic matter. In areas of high rainfall, this may again mean poor drainage.

answer : haversian

[explanation: -(compact bone is organized as parallel columns, known as haversian systems, which run lengthwise down the axis of long bones. these columns are composed of lamellae, concentric rings of bone, surrounding a central channel, or haversian canal, that contains the nerves, blood vessels, and lymphatic system of the bone)]