46
WALLACE H. FULLER
Fig. 7. Creeping sand dunes in Canyon de Chelly, Arizona, U.S.A. Manley Photo.
tion. If they have vegetation, even though only an ephemeral covering,
they are classed as Psamments (G. D. Smith, 1965). Sand dunes and drifts
are discussed by H. T. U. Smith (1968) in Volume I of this series. Therefore no attempt will be made to cover dune characteristics, but rather to
supplement Smith's discussion by pointing out how sands form into soils
and relate to agriculture.
Alluvial desert valleys may be stratified with layers of sand, silt and
clay as well as gravel and stones as shown in Fig. 7. Sand as well as clay
in horizontal layers and lenses play an important part in water-holding
capacity, infiltration rate and root penetration. Surface sand can cause serious denuding of desert vegetation if it is blown across more stabilized soil
surfaces. Economic damage to cultivated crops can occur by covering over
of plants and shearing off young seedlings when it is blown through cultivated areas. Creeping sand dunes may bury well-developed soils and highly
valuable cropland. Buried soil profiles are commonly found under deep
sand overburdens. Wind control to reduce detrimental erosion of sand is
a continuing subject of world study ( Academia Sinica, Sand Control Team,
1962; Clements et ai, 1957; Food and Agriculture Organization, 1960;
H. T. U. Smith, 1955; 1965; Yakubov, 1959; Kao Shang-tun, 1963).
2. Composition
Shifting sand can have a marked effect on soils even though it may only
blow over the land and settle in a thin layer in a transitory fashion. Salts
WALLACE H. FULLER
Fig. 7. Creeping sand dunes in Canyon de Chelly, Arizona, U.S.A. Manley Photo.
tion. If they have vegetation, even though only an ephemeral covering,
they are classed as Psamments (G. D. Smith, 1965). Sand dunes and drifts
are discussed by H. T. U. Smith (1968) in Volume I of this series. Therefore no attempt will be made to cover dune characteristics, but rather to
supplement Smith's discussion by pointing out how sands form into soils
and relate to agriculture.
Alluvial desert valleys may be stratified with layers of sand, silt and
clay as well as gravel and stones as shown in Fig. 7. Sand as well as clay
in horizontal layers and lenses play an important part in water-holding
capacity, infiltration rate and root penetration. Surface sand can cause serious denuding of desert vegetation if it is blown across more stabilized soil
surfaces. Economic damage to cultivated crops can occur by covering over
of plants and shearing off young seedlings when it is blown through cultivated areas. Creeping sand dunes may bury well-developed soils and highly
valuable cropland. Buried soil profiles are commonly found under deep
sand overburdens. Wind control to reduce detrimental erosion of sand is
a continuing subject of world study ( Academia Sinica, Sand Control Team,
1962; Clements et ai, 1957; Food and Agriculture Organization, 1960;
H. T. U. Smith, 1955; 1965; Yakubov, 1959; Kao Shang-tun, 1963).
2. Composition
Shifting sand can have a marked effect on soils even though it may only
blow over the land and settle in a thin layer in a transitory fashion. Salts