XIV PRIMITIVE NEOLITHIC CIVILIZATIONS About 10,000 B.C. the geography of the world was very similar in its general outline to that of the world to-day. It is probable that by that time the great barrier across the Straits of Gibraltar that had hitherto banked back the ocean waters from the Mediterranean valley had been eaten through, and that the Mediterranean was a sea following much the same coastlines as it does now. The Caspian Sea was probably still far more extensive than it is at present, and it may have been continuous with the Black Sea to the north of