The thickness is measured bank-right , i.e. perpendicular to the layer surfaces , regardless of the spatial orientation of a layer . The term originally comes from the miner's language , where it was mainly used to assess the mining potential of seams . Thickness is now an established term in geosciences , for example in geology for the thickness of rock layers , in hydrogeology for the vertical extent of the groundwater - i.e. the distance from the groundwater bed to the groundwater surface - or in soil science for the vertical extent of Soil horizons .