II. DESERT SOILS
79
Barren, exposed rock mountains, the Ahaggar and Tibesti, free of soils,
extend through the middle section of the Sahara (Durand, 1953) with
stony and gravelly residual debris concentrated mostly in the south. These
rough surfaces are referred to as regs. They are relics of an earlier,
humid climate, now exposed by wind action. Rocky plateaus, called
hamadas, are distributed throughout the Sahara. When the gravelly and
rocky plain surfaces occupy alluvial fan and floodplain positions, sometimes they are referred to as transported regs. Such surfaces occupy the
talus positions along breaks of mountains.
Ergs (high, connected sand dunes) cover much of Southern Algeria and
Tunisia, Northern Mali, Mauritania, and the Libyan Desert. Associated
with the ergs are pebbly deserts and a few clay pans.
Compact calcium carbonate and indurated gypsum layers formed under
another climate, are often exposed by erosion of wind. Some have been
eroded by water at an earlier time. Limy accumulations are so
compact and of such high quality in some places, they are mined for building
material and ground for liming agricultural soils. They appear as exposed
desert surfaces most conspicuously in Morocco, Northern Algeria, and
Tunisia.
Prominent in Mauritania, Mali, Niger, Chad, and Sudan are the clay
plains. These are broad, smooth plains of fine-textured lacustrine deposits
which are so poorly weathered, soil development is very weak. Sand deposits and dunes cover a minor part of the clay plains and isolated saline
depressions occur where water collects in depressions and penetration rate
is slow. On the coastal plain, both north and south of Port Sudan, as well
as the inland plains, Gray Desert soils are found. (Dixey and Aubert,
1962).
According to the map of d'Hoore (1964), soils are developed in Southern Tunisia and Mauritania where precipitation is higher. Oases soils show
some soil development. In general, these Sierozems appear to be less well
developed than the same type described in Central Asia.
The vegetation of the Sahara is described (McGinnies, 1967) as being
very sparse with herbs and small shrubs except in limited areas where
moisture is more abundant, larger shrubs and trees appear. Ephemerals
grow widely scattered over the desert, but most abundantly in the north.
Succulents are conspicuously absent and the large central desert is barren
of vegetation.
C. SOMALI-CHALBI
The area designated as Somali-Chalbi Desert lies along the East African
Coast extending both north and south of the equator, with almost all of
it actually north of the equator. The countries of Somalia and Kenya are
most involved. Soils maps with detail descriptions of the soils of this area
79
Barren, exposed rock mountains, the Ahaggar and Tibesti, free of soils,
extend through the middle section of the Sahara (Durand, 1953) with
stony and gravelly residual debris concentrated mostly in the south. These
rough surfaces are referred to as regs. They are relics of an earlier,
humid climate, now exposed by wind action. Rocky plateaus, called
hamadas, are distributed throughout the Sahara. When the gravelly and
rocky plain surfaces occupy alluvial fan and floodplain positions, sometimes they are referred to as transported regs. Such surfaces occupy the
talus positions along breaks of mountains.
Ergs (high, connected sand dunes) cover much of Southern Algeria and
Tunisia, Northern Mali, Mauritania, and the Libyan Desert. Associated
with the ergs are pebbly deserts and a few clay pans.
Compact calcium carbonate and indurated gypsum layers formed under
another climate, are often exposed by erosion of wind. Some have been
eroded by water at an earlier time. Limy accumulations are so
compact and of such high quality in some places, they are mined for building
material and ground for liming agricultural soils. They appear as exposed
desert surfaces most conspicuously in Morocco, Northern Algeria, and
Tunisia.
Prominent in Mauritania, Mali, Niger, Chad, and Sudan are the clay
plains. These are broad, smooth plains of fine-textured lacustrine deposits
which are so poorly weathered, soil development is very weak. Sand deposits and dunes cover a minor part of the clay plains and isolated saline
depressions occur where water collects in depressions and penetration rate
is slow. On the coastal plain, both north and south of Port Sudan, as well
as the inland plains, Gray Desert soils are found. (Dixey and Aubert,
1962).
According to the map of d'Hoore (1964), soils are developed in Southern Tunisia and Mauritania where precipitation is higher. Oases soils show
some soil development. In general, these Sierozems appear to be less well
developed than the same type described in Central Asia.
The vegetation of the Sahara is described (McGinnies, 1967) as being
very sparse with herbs and small shrubs except in limited areas where
moisture is more abundant, larger shrubs and trees appear. Ephemerals
grow widely scattered over the desert, but most abundantly in the north.
Succulents are conspicuously absent and the large central desert is barren
of vegetation.
C. SOMALI-CHALBI
The area designated as Somali-Chalbi Desert lies along the East African
Coast extending both north and south of the equator, with almost all of
it actually north of the equator. The countries of Somalia and Kenya are
most involved. Soils maps with detail descriptions of the soils of this area