Why coal is usually found in layers???

Coal if formed when dead animals and plants got buried inside the layer of Earth. The layers increase form time to time and more dead plants and animals get buried in the layers. Therefore, coal is found in layers. For example, let us consider the layers of sandwich, on the first bread we apply the toppings and cover it another slice. Then some more topping is added to second slice and is covered by third slide. Similarly, dead animals get buried in layers, leading to formation of coal in layers.