While Europe and probably North America were occupied by a warm temperate flora, tropical types had been driven southward, while the adaptation of others to arctic conditions had become accentuated.
The Mediterranean, however, has apparently been a barrier to the southward passage of the arcto-alpine flora which is totally wanting on the Atlas.
Before the 14th century B.C. the warrior kings of Egypt had carried the power of their arms southward from the delta of the Nile wellnigh to its source, and eastward to the confines of Assyria.
Herodotus (himself a notable traveller in the 5th century B.C.) relates that the Egyptian king Necho of the XXVIth Dynasty (c. 600 B.C.) built a fleet on the Red Sea, and confided it to Phoenician sailors with the orders to sail southward and return to Egypt by the Pillars of Hercules and the Mediterranean sea.
The rivers of the state include a number of small plateau streams flowing southward to the Sao Francisco River, and several large streams in the eastern part flowing eastward to the Atlantic. The former are the Moxoto, Ema, Pajehu, Terra Nova, Brigida, Boa Vista and Pontai, and are dry channels the greater part of the year.