It is necessary to regard northern Europe and northern Asia as forming one geographic province.

Asia Minor, together with the Euphrates valley and with Arabia in a lesser degree, belongs to the Mediterranean area.

India and China, with the south-eastern corner of Asia that lies between them, form another system that will be considered separately later on.
The Eurasian northland consists naturally, that is to say, where cultivation has not introduced changes, of four belts.

First, to the southward, come the mountain ranges passing eastwards into high plateau.

Then, north of this line, from the Lower Danube, as far as China, stretches a belt of grassland or steppe-country at a lower level, a belt which during the milder periods of the ice-age and immediately after it must have reached as far as the Atlantic.