264 THE MEDITERRANEAN, PHYSICAL AND HISTORICAL. 



have beeu found, as well as the Elephas antiquus, and two species of 

 hippopotamus, while nearly all these aud many other animals of African 

 type have beeu found in the Pliocene deposits aud caverns of the 

 Atlantic region. 



The rapidity with which such a transformation might have occurred 

 can be judged by the well-known instance of Graham's Shoal, between 

 Sicily and the island of Pantellaria; this, owing to volcanic agency, 

 actually rose above the water in 1832, and for a few weeks had an area 

 of 3,240 feet in circumference and a height of 107 feet. 



The submersion of this isthmus no doubt occurred when the waters 

 of the Atlantic were introduced through the Straits of Gibraltar. The 

 rainfall over the entire area of the Mediterranean is certainly not more 

 than 30 inches, while the evaporation is at least twice as great; there- 

 fore, were the straits to be once more closed and were there no other 

 agency for making good this deficiency, the level of the Mediterranean 

 would sink again till its basin became restricted to an area no larger 

 than might be necessary to equalize the amount of evaporation and 

 precipitation. Thus not only would the strait between Sicily and Africa 

 be again laid dry, but the Adriatic and ^geau Seas also, and a great 

 part of the Eastern Basin. 



The entire area of the Mediterranean and Black Seas has been esti- 

 mated at upwards of a million square miles, aud the volume of the 

 rivers which are discharged into them at 226 cubic miles. All this and 

 much more is evaporated annually. There are two constant currents 

 passing through the Straits of Gibraltar, super-imposed on each other; 

 the upper and most copious one flows in from the Atlantic at a rate of 

 nearly 3 miles an hour, or 140,000 cubic metres per second, and supplies 

 the difference between the rainfall and evaporation, while the under 

 current of warmer water, which has undergone concentration by evapora- 

 tion, is continually flowing out at about half the above rate of mov^e- 

 ment, getting rid of the excess of salinity; even thus, however, leaving 

 the Mediterranean Salter than any other i)art of the ocean except the 

 Eed Sea. 



A similar phenomenon occurs at the eastern end, where the fresher 

 water of the Black Sea flows as a surface current through the Darda- 

 nelles, aud the Salter water of the Mediterranean pours in below it. 



The general temperature of the Mediterranean from a depth of 50 

 fathoms down to the bottom is almost constantly 50° F., whatever may 

 be its surface rise of temperature. This is a great contrast to that of 

 the Atlantic, which at a similar depth is at least 3° colder, and which 

 at 1,000 fathoms sinks to 40° F. 



This fact was of the greatest utility to Dr. Carpenter in connection 

 with his investigations regarding currents through the straits, enabling 

 him to distinguish with precision between Atlantic and Mediterranean 

 water. 



For all practical purposes the Mediterranean may be accepted as being, 



