"العراق والخليج الفارسي" [ظ‎‎١‎٣‎٢] (٨٦٢/٢٦٩)

' irB 1 -- '-
182 CLIMATE, VEGETATION, AND FAUNA
mountains, decreases rapidly southwards towards the Persian Gulf.
In the deserts to the west and south, rainfall is low and sporadic.
Temperatures tend to be high with long, hot, dry summers; the
winters are short, more or less wet, with frequent low temperatures
at night.
Soils. Little information about soils is available, though some
studies have been made on those of lower Iraq. The alluvial soils of
this area are chiefly calcareous loams, with occasional sandy patches.
Their richness in lime is caused by the light calcareous silt brought
down from the northern highlands. Here and there are saline tracts,
found chiefly in depressions as a result of bad drainage and rapid
evaporation of successive river floods, or on sites of abandoned culti
vation where constant irrigation and inadequate drainage have pro
duced the same effect. Such areas, when excessively saline, are quite
incapable of supporting plant life; but with these exceptions, the soils
of the whole alluvial plain of lower Iraq are comparatively uniform,
differing slightly in texture and fertility, but always conforming to the
same general type—a silty calcareous loam. When watered they are
usually remarkably fertile since they abound in mineral salts, although
the nitrogen content is sometimes dangerously low.
Soils rich in gypsum are found over wide areas in Iraq, e.g. in the
Ghurfa desert north of Diltawa and in many parts of the Jazira desert.
In other parts of the Jazira the soil is composed of gravel or marl with
broad sandy stretches.
In the foothills and Assyrian plains in the north some very heavy
soils are encountered, such as the stiff red soil of the Erbil plain.
This soil contains relatively little gypsum and is much more fertile
than some of the Kirkuk soils which are similar in other respects.
In the Bakhtiari foothills the predominant soil is gravel, while heavy
marls are often found in the valleys of Kurdistan.
In the mountains of Kurdistan the soils are heavily calcareous,
some of them being little more than impure disintegrated limestone.
They vary in colour from cream through brown to red, are deficient
in soluble salts, and contain varying amounts of organic debris.
The soils of the Syrian desert for the most part consist of the
detritus resulting from the weathering, through countless ages, of the
underlying rocks, which are mostly limestone. This process has re
sulted in the production of two main types of soil, though various
intermediates and modifications exist: [a) greyish steppe soil, ashen
grey in colour, with a high content of lime and almost entirely lacking
in humus; it often possesses a high percentage of clay or fine sand