'IRAQ AND THE PERSIAN GULF' [‎24v] (53/862)

20 GEOLOGY AND DESCRIPTION OF THE LAND
The levels of the Tigris from Baghdad southwards, and of the
Euphrates below Ramadi, are higher than the land beyond their banks
in time of high flood, and both rivers have to be enclosed by strong
earthen embankments. When these are breached the rivers sub
merge wide areas on either side, and are liable to change their courses.
Both rivers have indeed in prehistoric and in historical times changed
their lower courses several times; and in historical times the separate
mouths of the Tigris and Euphrates have been lost, their waters now
reaching the Persian Gulf The historical term used to describe the body of water between the Arabian Peninsula and Iran. through a single youthful channel, the
Shatt al Arab. (For a note on the recession of the head of the Persian
Gulf in historical times, see p. 54 and fig. 14.)
DESCRIPTION OF THE LAND
As mentioned above (p. 13), the kingdom of Iraq falls into three
broad structural divisions: the Arabian desert edge, the folded moun
tain belt, and the Mesopotamian plain. Geologically they came into
being in that order; historically their importance is exactly the reverse,
for it is the Mesopotamian plain that has nursed the great civiliza
tions of the past and its two great rivers that have nourished them.
Next in importance is the mountain borderland, peopled by a different
race, hardy and warlike, and living an entirely different life from that
of the Arabs settled on the rivers of the plain, or wandering with their
flocks and herds in the desert.
This description therefore begins with a general survey of the
Mesopotamian plain, an account of the regime of the Euphrates and
the Tigris, and a detailed survey of the courses of the two rivers.
Next is described the broad pattern of the mountains and of the
mountain rivers. This is followed by a regional description of the
three divisions—the plains, the mountain belt, and the desert. The
plains are divided into Lower and Upper Mesopotamia, the latter
including the Jazira between the two rivers above their deltas—only
a small part of which is in Iraq—and the gently folded, partly buried,
undulating lands of ancient Assyria east and west of the Tigris,
together with the plains south of Kirkuk and north of the Jabal Hamrin,
which though structurally part of the mountain belt are transitional
between the plains and the mountains, and the meeting-ground of
Arab and Kurd.
The Kurdish mountains are most conveniently subdivided into
their chief river basins. Lastly there is a short description of the
western and southern deserts. This layout is summarized as follows: