Book 24, Question 140
Why do ghostly lines show up in dry grass or crops?
Buried stone walls or roads make the soil shallow above them, so plants dry out faster and turn yellow. Buried ditches hold more water, so plants above them grow greener and taller. From the air, these differences make faint lines called crop marks that reveal outlines of old buildings and forts. Archaeologists use the clues to decide where to dig.