...ry through which a river flows invisible for a considerable distance, and then emerges to the surface, as is the case with the Orontes in Syria, which sinks into the chasm (called Charybdis) between Apameia and Antiocheia and rises again forty stadia away. Similar, too, are the cases both of the Tigris in Mesopotamia and of the Nile in Libya, only a short distance from their sources. And the water in...