In theory the water table offers the prime environment for cave development as it provides the shortest route through the phreas and is potentially more active chemically due to the presence of the air/water interface. However, geological factors determine the details of cave inception and enlargement, and passages most commonly form just below the water table as a shallow phreatic variety of cave development. Development of this type is believed to be responsible for the 'levels' of cave passage found in some areas, as in the flint Mammoth Cave System, Kentucky. True water-table caves are rare except on a limited scale as extensions to cliff foot notches margined to tropical swamps. Also under these conditions, the water table may adjust down to the level of a mature phreatic cave and then modify the passage with horizontal dissolution notches - as is common in the caves of Mulu and Niah, Sarawak [9].