Similarly , the micro-porous ( Upper Cretaceous ) Chalk of south east England , although having a reasonably high porosity , has a low grain-to-grain permeability , with its good water-yielding characteristics mostly due to micro-fracturing and fissuring .
The ( Upper Cretaceous ) Chalk of south east England has a reasonably high porosity , but low grain-to-grain permeability . Much of its good water-yielding characteristics being due to micro-fracturing and fissuring .