284 



CONCLUSION. 



Black Sea (the Dnjestr and the Don), as they 

 before did into the Aralo-Caspian. 



Physical changes have brought the marine fauna 

 of the Mediterranean in superposition on that of 

 the older Aralo-Caspian basin, and the relative ages 

 of the two are distinctly marked. Should changes 

 again happen — should the amount of evaporation 

 be diminished over this area, or should the escape 

 of the surplus water be arrested by some physical 

 disturbance, which should close the Bosphorus — 

 the fresh waters would again accumulate in the 

 great Aralo-Caspian basin ; the fauna of the Black 

 Sea would be gradually extinguished, and the rem- 

 nant of the older fauna, from the Danube, the 

 Dnjestr, and the Don, would again repeople this 

 great inland sea. 



The Black Sea depression has been produced 

 since a large portion of country to the north of it 

 was in the condition of the Aralo-Caspian sea-bed ; 

 and the Black Sea must have received its Testacea 

 after the North Atlantic fauna had extended itself 

 into the Mediterranean (Pliocene period of geo- 

 logists). The Aralo-Caspian fauna is the oldest 

 with which we are acquainted in connection with 

 the European area. 



It will have been seen that the several " Pro- 

 vinces " of our European seas do not admit of 

 limitation by definite lines ; a system of colours 



