Where would you find humus in this photograph

On the top of the dark band

Humus is a dark organic matter in the soil produced by the decomposition of the dead plants, animals and their traces.The humus develops mainly by the plant litter, when the plants drop their leaves, twigs and other materials piles up and degraded and decomposed by the soil microbes. Humus can be produced naturally or by the process of composting. The humus makes the soil fertile, it is a rich source of nutrients hence, supports growth and development in plants.

In the given picture the dark layer on the top of the soil horizon represents humus.