Laterite soil is a type of soil found in wet and hot tropical areas, such as Costa Rica. Laterite soil is often used to make bricks, and can be both malleable enough to carve into blocks or rigid enough to hold its own. In rain forests, laterite soil is the layer that is directly below the horizon and the topsoil. Laterite is the product of rocks in tropical areas wearing down and eroding; this process is expedited by increased rainfall and elevated temperatures, both of which are abundant in tropical rain forests.
http://bharatdiscovery.org/w/images/thumb/3/3a/Laterite-Soil.jpg/450px-Laterite-Soil.jpg