With increasing altitude vegetation becomes more varied and abundant, until the tree limit is reached; then follows a forest belt, which in the highest mountains is limited above by cold as it is below by aridity.
But during the summer, temperatures are affected as much by altitude as by latitude, and the coast is cooled at night by breezes from the Gulf.
Of Lake Aral; altitude 260 ft.
The ordinary altitude of the higher hills hardly exceeds 4000 ft.; the general level of the table-land lies between 3000 ft.
In altitude; along the foot of this range are the principal cultivated districts of central Asia, and here too are situated the few towns which have sprung up in this barren and thinly peopled region.