It is characterised by a wide, flat, clay floodplain of the upper reaches of the Bristol Avon river, which divides the Cotswolds to the west from the chalk downland of east and south Wiltshire.
The description highlights the geographical feature of a wide, flat, clay floodplain along the Bristol Avon River that separates the Cotswolds from the chalky land of eastern and southern Wiltshire.