Question

what are permeable layers of material called

Answer 1

An aquifer is a permeable layer, saturated formation that will yield useful amounts of water when pumped. The most productive aquifers, such as sands and gravels, are typically thick and large in area and are replenished or recharged by infiltrating rainwater. Other formations, called aquitards (or confining layers), are made up of materials with low permeability, such as layers of clay and shale, which prevent any significant movement of water