The Greater Zab is the most important of all the tributaries of the
Tigris. It rises near Konia, in the district of Karasu, about lat. 32°
20', long. 44° 30', a little west of the watershed which divides the
basins of Lakes Van and Urymiyeh. Its general course for the first 150
miles is S.S.W., after which for 25 or 30 miles it runs almost due south
through the country of the Tiyari. Near Amadiyeh it makes a sudden turn,
and flows S.E. or S.S.E. to its junction with the Rowandiz branch
whence, finally, it resumes its old direction, and runs south-west past
the Nimrud ruins into the Tigris. Its entire course, exclusive of small
windings, is above 350 miles, and of these nearly 100 are across the
plain country, which it enters soon after receiving the Rowandiz stream.
Like the Khabour, it is fordable at certain places and during the summer
season; but even then the water reaches above the bellies of horses. It
is 20 yards wide a little above its junction with the main steam. On
account of its strength and rapidity the Arabs sometimes call it the
"Mad River."

The Lesser Zab has its principal source near Legwin, about twenty miles
south of Lake Urumiyeh, in lat. 36° 40', long. 46° 25'. The source is to
the east of the great Zagros chain; and it might have been supposed that
the waters would necessarily flow northward or eastward, towards Lake
Urumiyeh, or towards the Caspian. But the Legwin river, called even at
its source the Zei or Zab, flows from the first westward, as if
determined to pierce the mountain barrier. Failing, however, to find an
opening where it meets the range, the Little Zab turns south and even
south-east along its base, till about 25 or 30 miles from its source it
suddenly resumes its original direction, enters the mountains in lat.
36° 20', and forces its way through the numerous parallel ranges,
flowing generally to the S.S.W., till it debouches upon the plain near