From the Caspian to Karachi it is possible to pass without encountering any orographic obstacle greater than the divide which separates the valley of the Hari Rud from the Helmund hamun basin, which may be represented by an altitude of about 4000 ft.
The supreme orographic importance of this great Central Asian mountain system was recognized in a fashion even by the geographers of ancient Greece.
The orographic features of the Pacific Mountain system trend parallel to the coast-line of the Gulf of Alaska, changing with this at the great bend beyond the N., and of the Panhandle from S.E.
The Abyssinian highlands are thus a clearly marked orographic division.
On its northern side the valley of Borotala is skirted by the important orographic system of the Dzungarian Ala-tau, the northernmost member of the Tian-shan.