(b) The next layer, middle layer called B-horizon has a lesser amount of humus but more of minerals. This layer is generally harder and more compact.
(c) The third layer is the C-horizon which is made up of small lumps of rocks with cracks and crevices.
(d) Below this layer is the bedrock, which is hard and difficult to dig with a spade. Water can be held in the tiny gaps.
(a) Sand particles are quite large and having large spaces between them. These spaces are filled with air. Water can drain quickly through these spaces. So, sandy soils tend to be light, well aerated and rather dry.
(b) Clay particles, being much smaller, pack tightly together, leaving little space for air. So, clay soils have little air. But they are heavy as they hold more water than the sandy soils.