MEDITERRANEAN SEA. The Mediterranean is all that remains of a great ocean which at an early geological epoch en circled half the globe along a line of latitude. This ocean, already diminished in area, retreated after Oligocene times from the Iranian plateau, Turkistan, Asia Minor and the region of the north-west Alps. Next the plains of eastern Europe were lost, then the Aralo-Caspian region, southern Russia and finally the valley of the Danube. The "Mediterranean region" as a geo graphical unit includes all this area ; the Black sea and the Sea of Marmora are within its submerged portion, and the climate of the whole is controlled by the oceanic influences of the Mediterranean sea. E. Suess, to whom the above description is due, finds that the Mediterranean forms no exception to the rule in affording no evidence of elevation or depression within historic times; but it is noteworthy that its present basin is remarkable in Europe for its volcanic and seismic activity. Submarine earthquakes are in some parts sufficiently frequent and violent as seriously to interfere with the working of telegraph cables. We divide, with E. Suess, the Mediterranean basin into four physical regions: (I) The western Mediterranean, from Gibraltar to Malta and Sicily, enclosed by the Apennines, the mountains of northern Africa, and of southern and south-eastern Spain (Cordillere betique). (2) The Adriatic, occupying the space between the Apennines and the Dinaric group. (3) A part surrounded by the fragments of the Dinaro Taurus arch, especially by Crete and Cyprus. This includes the Aegean and the Black sea. These three parts belong strictly to Eurasia. (4) The part of the coastal region of Indo-Africa, ter raced downwards in successive horizontal planes from the Shot, reaching the sea in the Little Syrte and continuing to the southern depressions of Syria, bounds the north of this area as the Sicily Roman basin with the Levant basin in (2) and (3) above. Malta and Gozo are the only islands of the Mediterranean which can be associated with this section. Murray estimated (1888) the total surface of the Mediterranean drainage area, with which must be included the Black sea, at 7,600,300 sq.km., of which 48% are
Eurasian and 52% are African. The principal rivers entering the Mediterranean directly are the Nile from Africa, and the Po, Rhone and Ebro from Europe.
The physical divisions of the Mediterranean given above hold good in describing the form of the sea-bed. The western Mediter ranean, opened in the west by the Strait of Gibraltar (14 km. wide and 400 metres deep), is cut off in the east by a bank cross ing the narrow strait between Sicily and Cape Bon, usually known as the Adventure Bank, on which the depth is nowhere 400 metres.
Between the Balearic islands and Corsica and Sardinia, the Mediterranean has an even floor of from 2,700-3,000 metres in depth. The greatest depth in this area is found off the south-west corner of Sardinia, with 3,151 metres. The Tyrrhenian sea is level in the north, but in the south, and between Sicily and Naples, has deep holes (3,731 metres). The Adriatic is the shallowest part of the Mediterranean, being, for the most part, less than 200 metres in depth, only reaching a depth of 1,200-1,300 metres in its southern part, west of Cattaro. The waters between Sicily and the Peloponnesus are the deepest of all the Mediterranean, having a depth of more than 4,000 metres. This area was sounded in 1891 by the Austrian Expedition boat "Pola" in 45' N., 21° 46' E., 7o km. S.W. from Cape Matapan, and a depth of 4,400 metres was found. The slope of the ocean bed is steep here, but it is steeper still off the island of Sapienza, near Navarino ; in this place, 13 km. from land, a depth of 3,15o metres was found. The depth of the Ionian sea is divided from that of the Levant basin by an undersea bank stretching north-easterly from Barka in North Africa to Crete, and for the most part the depth is less than 2,000 metres. Cyprus is tied to the Asiatic continent by the depth-line of i,000 metres, although in the east and south-east from Rhodes, the sea is from 3,000-3,500 metres deep. In the Aegean sea, only north of Crete and south-east of the Chalcidian peninsula is the sea more than i,000 metres deep.