'IRAQ AND THE PERSIAN GULF' [‎49r] (102/862)

D
description of the land 55
'ates waters
)or t> Ma^
toia standi
Finland
a( l territory
: an almost
to the river
idal creeks,
^ a serious
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at different
ig. 14 have
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erian cities,
■ e been dis-
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Excepting
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ir channels;
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1 also illus-
aral causes,
picked out
he head of
rached the
ers of the
d between
evidence,
ailing into
the plains by the sea, makes lakes and marshes and fens’; 1 and in
rejecting Eratosthenes’ theory (c. 250 b.c.) that the marshes drain by
percolation to Coele-Syria because of the mountains, he adds: ‘but
these marshes are near the Persian Sea, and the isthmus which
separates them is not wide or rocky . 2
(e) The Pattern of the Mountains
An outline of the geological history of Iraq (p. 13) shows that all
the country south-west of the Euphrates and possibly part of the
south-western Jazira is controlled by the Arabian basement. Beyond
this basement, both north and north-east of the delta lands, the
sedimentary strata thicken until they reach a depth more than ten
times greater than in the south-west. These beds have been bent into
folds resembling petrified ocean swell. The outermost folds rise from
the plains as gentle and regular features. Many of them north-west
of the Diyala are similar, but some are higher and steeper than others.
Towards the Persian frontier in Kurdistan the regular folds are
replaced by numerous wrinkles which in turn give way to slabs of
disturbed strata packed like tiles on the roof of a house, each slab
dipping north-eastwards and with its south-western edge resting
on its neighbour. Their present position is the result of more
complex processes, the rock sheets having been forced in from out
side Iraq. Their line of overlap upon the simpler folds— the nappe
front’—is shown on fig. 15. j
Of the simpler folds nearer the plains, many can be traced north
westwards of the Diyala for long distances, for beyond the Great Zab,
also, folding is generally of simple type. West of the Tigris north and
south of Mosul, some can be traced far into the Jazira as low ranges
separated by many miles of plain. One such fold, the Jabal Sinjar of
Iraq, enters the Syrian Jazira as the Jebel Jeribeh, and is distantly
related to the Jebel Bishri beyond the Euphrates towards Palmyra.
All these structures, particularly those along the Persian border, are
important factors in rendering some regions inaccessible, whist
economically they are sought for, since oil has often been found to
accumulate in such crests. . .
The outer folds may be arranged in chains trending approximately
from south-east to north-west, until north of Mosul they begin to
swing from east to west (fig. 15)- ... r •
The first chain on the edge of the Tigris plains runs from just
1 l6t j. 9 . 2 16. 1. 12.