'IRAQ AND THE PERSIAN GULF' [‎51r] (106/862)

DESCRIPTION OF THE LAND 59
times white marbles and blue-grey limestones occur in strips, each
adding their tint.
(/) The Pattern of the Mountain Rivers
Draining the mountain borderland into the Tigris are four main
rivers: the Khabur, the Great Zab, the Little Zab, and the Diyala.
All rise beyond the boundary in south-east Turkey or in Persia and
are already large rivers when they enter Iraq. Within the Kurdish
mountains they collect the drainage of each long trough between the
folds and force a passage across the strike of the ranges wherever gaps
or structural weaknesses permit. Thus the river pattern is well
defined—valleys parallel to the strike alternating with narrow cuts or
gorges through the ranges at right angles to the strike. These gorges
are carved deeper than the general level of their tributaries, which
thus maintain great activity near their mouths, and are now cutting
gorges in their lower courses almost as deep as those of the main river.
This pattern is best exemplified by the course of the Great Zab
within the Iraq boundary (fig. 27), particularly near the point where
the Rubar-i-Ruwandiz meets the Great Zab head on, before their
combined waters cut through the Berat Dagh to the plains of Erbi .
Only a small part of the Khabur basin is in Iraq; its own lower
course and that of its principal tributary, the Hazil Su, form the
boundary with Turkey. The Great Zab also drains a large area in
the very difficult Hakari country beyond the Turkish border before
it enters Iraq territory 13 miles north of Amadia; but near this town,
from which it receives a small tributary, it turns south-east along
the strike, picking up the waters of two tributary gorges, the Rubar-
i-Shin and the Rukuchuk or Barasgird, before encountering the
Rubar-i-Ruwandiz. The principal head-streams of the Little Zab
are in Persia, where they drain a considerable area south-eastwards
beyond the boundary formed by the Kandil Dagh, before breaking
into Iraqi Kurdistan and doubling back north-west towards Qala
Dizeh and Rania. Between these places the river finds a comparative y
easy passage, but it meets some trouble from the Sulaimaniya group
of ranges. The Diyala head-waters are also in Persia; this river
receives no large right-bank tributaries south of the Qara Dagh, and
thence flows south-west almost parallel to the Persian border and
only from 10 to 20 miles distant from it, almost as far as Shahraban,
where it enters the Tigris plain. Thus its left-bank drainage which
is considerable and follows the general pattern described above, is
almost entirely outside Iraq.