The given blank can be filled with loess.
The clay and the windblown silt deposited in the form of a layer over a big region are known as loess. The loess deposits produce desert or downwind of glacial outwash, where the fine particles are obtainable.
The loess deposits produce very fertile soils in various parts of the world. Approximately 10 percent of the land region on the Earth is enveloped by loess or similar deposits.