 Traditional building stone in the Severn Vale is scarce, necessitating brick or half-timbered construction in the main, although along the scarp mentioned above harder limestone bands in the Lower Lias (known as 'Blue Lias') have been used in vernacular building.Towards the east side of the Severn Vale the Lias clays are overlain by the sands and limestones of the Middle Lias - well displayed on the slopes of Robinswood Hill, a Jurassic outlier overlooking the city of Gloucester.Further east, forming a rather unstable base to the Cotswold escarpment, are the sands and clays of the Upper Lias.