If one says to his fellow, "I am selling you a beit kor of earth, that is, land suitable for cultivation, and there were clefts 10 hand-breadths deep or more, or rock 10 hand-breadths high, they are is not included while measuring the area of the sold land. Instead, the seller must provide land of level ground, to the full measure of beit kor. Clefts smaller than 10 hand-breadths, however, do contribute to the total area.
If the seller said, "I am selling you about a beit kor," then even clefts larger than 10 hand-breadths count as part of the area because "about" means in whatever condition it is.
Art: Alfalfa Fields, Saint-Denis by Georges Seurat