If, then, our judgment of this is right, the Ionians are in error concerning Egypt ; but if their opinion is right, then it is plain that they and the rest of the Greeks cannot reckon truly, when they divide the whole earth into three parts, Europe , Asia , and Libya ; they must add to these a fourth part, the Delta of Egypt , if it belongs neither to Asia nor to Libya ; for by their showing the Nile is not the river that separates Asia and Libya ; the Nile divides at the apex of this Delta, so that this land must be between Asia and Libya .