In general the thirsty sand absorbs, within a short distance of their source, the various brooks and streams which flow south and east into the desert from the northern and western mountain chains, without allowing them to collect into rivers or to carry fertility far into the plain region.

The the river of Isfahan forms the only exception to this rule within the limits of the ancient Media.

All its other important streams, as has been seen, flow either into the Caspian or into the great lake of Urumiyeh.
That lake itself now requires our attention.

It is an oblong basin, stretching in its greater direction from N.N.W.to S.S.

E., a distance of above eighty miles, with an average width of about twenty-five miles.
On its eastern side a remarkable peninsula, projecting far into its waters, divides it into two portions of very unequal size--a northern and a southern.
The southern one, which is the largest of the two, is diversified towards its centre by a group of islands, some of which are of a considerable size.