Silt particles are too small to see with the naked eye. Silt is often found in places that have flooded and dried out again. Clay is made up of very tiny particles. The particles fit together so closely that it is difficult for water to flow through. The best kind of soil for plants allows water to move through slowly enough so that some of it stays in the soil for the plants to use.
Water moves too quickly through sand.
It moves very slowly through clay, but clay holds the water so tightly that plants can't get to it. Humus acts like a sponge to help the soil capture water. Humus is formed when plants and animals die. When organic matter is used up, soil packs together in clods. A cloddy soil has fewer air spaces.