Tethys Sea

Over 40 million years ago the so-called Tethys Sea reached far south of the existing Mediterranean. This sea gradually retreated north depositing thick sediments of sandstone, limestone and shale, visible in three named rock formations which are visible in Wadi Al-Hitan. The oldest rocks are the Eocene Gehannam Formation, about 40-41 million years old, consisting of white marly limestone and gypseous clay and yielding many skeletons of whales, sirenians (sea-cows), shark teeth, turtles, and crocodilians. A middle layer, the Birket Qarun formation, of sandstone, clays and hard limestone, also yields whale skeletons. The youngest formation is the Qasr El-Sagha formation of late Eocene age, about 39 million years old. It is rich in marine invertebrate fauna, indicating a shallow marine environment. These formations were uplifted from the southwest, creating drainage systems, now buried beneath the sand, which emptied into the sea through mangrove-fringed estuaries and coastal lagoons when the coast was near what is now the Faiyum oasis, c. 37 million years ago. . . .

Three different species of Eocene whales have been identified with certainty at Wadi Al-Hitan. All are basilosaurids, the latest surviving group of archaeocete whales, and the group which are thought to have given rise to modern cetaceans.

http://whc.unesco.org/archive/advisory_body_evaluation/1186.pdf