Book 24, Question 14
Why does water sink through sand but sit on top of clay?
Sand grains are large, so the gaps between them are wide and water drains quickly. Clay grains are tiny and flat, packed so tightly that the gaps are very small, and water passes through very slowly. That is why puddles last longer on clay soils and why gardeners add compost to improve drainage. Layers of clay can also hold underground water in place.