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III. The Environment of Laterite
conflicting views may be the result of two confounding factors: (1) the
occurrence of laterite under climates that are unlike those under which
the laterite formed, and ( 2 ) differential effectiveness of climatic wetness
or dryness in combination with differences of topography, parent material, and time.
Laterite is found where temperatures are warm or are believed to
have been warm at the time of formation. This does not preclude the
possibility, however, that time, not temperature, is the controlling
factor. If the principal effect of high temperature is to accelerate rates of
reactions, the time interval necessary for laterite formation in temperate
regions may exceed the period of time that appropriate landscapes have
been stable. Similarly, observations of Oldham ( 1893), Joachim and Kandiah (1935), and Prescott and Pendleton (1952) that laterite has not
formed under the cool temperatures of highlands in the tropics may be
due less to cool temperature than to landscape instability. Nevertheless,
field observation generally agree with the hypothesis that warm temperatures favor the formation of laterite.
B . VEGETATION
A forest vegetation was considered necessary for laterite formation by
Glinka (1927, pp. 33-34). More detailed observations have shown that,
while laterite occurs in regions with a rain-forest vegetation, welldeveloped laterite is most commonly found under a low forest and that
hard surficial laterite is a very common feature of the open savannah
adjacent to the forest. Maignien (1958, p. 16) concluded that laterite is
most extensive and strongly expressed at the boundary of forest and
savannah. DHoore (1954,1957, p. 55) found iron mobilized to a greater
degree and to greater depth under tropical grasses than under forest.
Buchanan’s type of soft laterite is found in Ceylon in the forested areas
of the southwestern lowland.
Humbert (1948) suggested that laterite forms in a climate that has a
wet and a dry season, and his descriptions and illustrations indicate that
the laterite he observed was in an open savannah that was gradually
replacing forest, a common condition where a dry season is prominent.
The change from soft laterite to the hard form within a few years after
man has cleared the forests has been reported by Alexander and Cady
( 1962) in French Guinea and other parts of West Africa. Blackie’s (1949)
description of soils of Fiji and Aubert’s (1950) description of Dahomey
also confirm the hardening of laterite following a change from forest to
savannah caused by man’s activities. It would appear from the literature
that laterite is most extensive in areas of savannah but that laterite forms
under forest though its hardening is favored by lack of forest cover.
S. SIVARAJASLNGHAM ET AL.
Nodular forms are very common in forested areas, though they also
appear to be most widespread in the savannah.
Rosevear ( 1942) has reported a case where reforestation softened
hard laterite significantly in as little as 16 years. The possible explanations
of the effect of vegetation on hardening and softening will be considered
Laterite is found overlying a variety of kinds of rock. It is common
over basic igneous rocks such as basalt, norite, and diabase as well as
over acid rocks such as granite, granulites, gneisses, and sericitic schists.
Laterite has also been observed on shale, sandstone, and other sedimentary rocks including limestone (Jones, 1943; Stephens, 1946, p. 11).
Marbut (1932, p. 76) has described laterite outcropping on the banks of
the Amazon, presumably in alluvium, in association with a ground water
table. Maignien (1958) has shown that fermginous laterites may develop
on a variety of materials providing there i s a source of iron either in
the parent rock or in adjacent higher-lying areas from which water may
introduce ferruginous material.
The laterite layers may be in material unrelated to the underlying
bedrock. In some places, laterite clearly has formed in residuum of
rocks that have weathered in place, as evidenced by features such as a
constant proportion of iron oxides to alumina with depth or by a
continuation of quartz veins from the rock into the laterite. It is also
found in colluvial deposits; examples are described by Maignien ( 1958).
Often laterite is associated with material that has been transported
locally; recently recognition of stone lines in surhial mantles of this
character has directed attention to the frequency of such conditions
(Ruhe, 1959). Though such surficial deposits may not be directly
related to the underlying bedrock, they may not be very different from
residuum of the major rocks in the locality, since transport is often of a
local nature as in cases cited by Nye (1955a) and by Ollier ( 1959). The
parent material in which laterite forms may also be derived from material
of different and highly contrasting strata than the underlying rock
currently present. Whatever the source of material in which laterite
forms, an adequate supply of iron appears to be essential. Alexander and
Cady (1962) have noted that the thickness of laterite crusts is sometimes
related to the iron-richness of associated rocks.
Laterite has been generally associated with a level or gently sloping
surface. This characteristic was emphasized by Oldham (1893) in his
review of numerous laterite locations in India and has been subsequently
confirmed by many workers from other parts of the tropics. Campbell
( 1917), from his many observations, reported that laterite currently
being formed covers the flatter ground and stops where the slopes are
steep. Holmes (1914) observed that in Mozambique laterite occurs only
on gently undulating plateaus and never on steep slopes. Humbert
(1948), from his study of laterite in Australian New Guinea, concluded
that the best examples of laterite occur almost exclusively on areas of
low relief and gentle slopes. Prescott and Pendleton (1952, pp. 25-26)
also emphasized the nearly level nature of the terrain where laterite
The horizontal disposition of laterite deposits is very striking in many
relatively arid regions. Newbold (1846) observed that in the interior of
South India laterite occurs in almost horizontal beds as cappings on the
tops of mountains. Woolnough (1918) emphasized the significance of
relic laterite deposits in western Australia on slightly elevated plateaus.
Similarly in southwestern Australia, laterite is found in many localities as
massive or concretionary deposits forming protective cappings on flattopped residuals (Mulcahy, 1960, 1962). Laterite is also present in
extensive bodies on dissected tablelands (Stephens, 1946).
Laterite is found along river banks and on terraces adjacent to higher
ground. These masses of “gallery laterite” are believed by DHoore (1957,
p. 97) to be formed by enrichment with iron during flood stage followed
by its immobilization when the flood subsides. In the flat humid areas,
where it is believed that laterite is forming currently, a high but
fluctuating water table is common. The drainage is more or less imperfect,
and the ground water at and below the water table is thought to be
somewhat sluggish. This has led to a common opinion that topography
conducive to a high water table may be essential.
Soft laterite is found at a shallow depth on low hillocks in southwestern Ceylon, generally not much more than 100 to 200 feet above sea
level (Prescott and Pendleton, 1952, p. 9 ) . The slopes are undulating and
are certainly not level, Though Oldham (1893) dismissed these occurrences as “a more or less ferruginous subsoil which never passes into
laterite,” the descriptions of Joachin and Kandiah (1935) indicate that
these materials, locally called “cabook,” conform to Buchanan’s concept
in every way. It should be noted, however, that the underlying rock in
this region is charnockite, a quartzo-feldspathic gneiss or granulite with
hypersthene, and that the rainfall is over 100 inches per annum but with
dry intervals. High rainfall and high iron content of the parent rock
may favor the formation of laterite even where the surface is not level
but is stable owing to the nature of the weathered material and forest
cover. Mulcahy (1960, p. 222, 1962) emphasized that peneplain condi-
S . SIVARAJASINCHAM ET AL.
tions of low relief are not essential, though low available relief conducive
to stable land surfaces for long periods is most favorable.
Laterite on areas of low relief, nevertheless, is the most common.
Blanford (1879) classified the Indian laterites into high-level and lowlevel varieties, depending on the mode of occurrence. This distinction
was at first intended only to signify two contrasting positions, high-level
laterite capping the summits of hills and plateaus on the highlands of
central and western India and low-level laterite covering large tracts in
the coastal regions (Holland, 1903).
Subsequent workers observed that low-level laterite is generally
the more fenvginous and commonly does not exceed 30 feet in thickness.
It also commonly contains inclusions of sand and pebbles, which indicate
a multicycle or detrital origin (Oldham, 1893). Low-level laterite, however, does not everywhere contain such foreign inclusions. Since it was
once thought that laterite can form only at or near the water table, the
low-level laterite on areas with a high water table was called “live”
laterite. The laterite on ground above the reach of the water table was
thought to have been a product of an earlier period when the groundwater fluctuation reached the laterite zone. Hence, this was called “dead
laterite ( Campbell, 1917).
The high-level laterite is generally more homogeneous and may be
relatively thick, as much as 100 to 200 feet according to Oldham (1893),
though it is probable that such thickness is a feature of plateau margins.
Though it was considered “dead” by Campbell ( 1917), Harrison (1933,
p. 16) believed that laterite can form on high-level positions, as on the
plateau of the Eagle Mountain range in British Guiana, under conditions
of heavy rainfall though the water table is low. As it is presumably being
formed currently, this would be called “live” laterite. Laterite in highlevel position may include pebbles from even higher surfaces, indicating
detrital origin (Ruhe, 1954, p. 18).
The laterite found on distinct slopes adjacent to higher ground may
be called foot-slope laterite to indicate its topography. It is often detrital,
being formed by the consolidation of fragments of the laterite of the
higher level that have moved down the slope as erosion has advanced
(Oldham, 1893). The second member of Greene’s ( 1945) “ironstone
catena” would be this class. “Terrace” laterite occurs on terraces adjacent
to high ground or along the banks of streams. It is thought to be formed
by the deposition of dissolved material where ground water moving
laterally and down the adjacent slope encounters the oxidizing conditions
of the surface horizons (Campbell, 1917). Maignien (1958, 1959) emphasized the occurrence of laterite crusts at the borders of natural
drainage areas, such as piedmonts, river banks, dissection forms, and
other abrupt breaks in slopes where the profile of a saturated zone
approaches the surface. Another type recognized by Fermor (1911) is
“lake” laterite formed in marshy areas by water flowing from the
surrounding higher land, either along the surface or by seepage.
Lake (1890) used the accompanying tabulation to classify the laterites
in Malabar, India, according to topographic position, character, and origin:
Nature of the laterite
More elaborate schemes of classification, based on other factors, have
been published by DHoore (1955),Maignien (1958), and du Preez
Four physiographically distinct landscapes with which laterite is
commonly identified in the literature are: (1) high-level peneplain
remnants, (2) colluvial footslopes subject to water seepage, ( 3 ) lowlevel plains having high water tables or receiving water from higher
land, (4) residual uplands other than peneplain remnants. The first
three are illustrated diagramatically in Fig. 1.
wlth Loterite Cap
FIG. 1. Relationships among physiographically distinct landscapes with which
laterite is commonly associated.
Laterite on high-level peneplain remnants may be in residuum of
rocks weathered in place or may be in transported material deposited
prior to peneplain dissection. Its present position is a consequence of
landscape inversion such as that described by Bonnault (1938); it once
occupied a low-level position comparable to that illustrated in Fig. 1.
With uplift or with lowering of base level, areas protected by laterite
have remained as erosion lowered the surrounding areas. Such areas
now occupy the highest positions and are being reduced slowly by
lateral retreat of slopes, as on the two Tertiary surfaces described by
Ruhe (1954, p. 18-25).
At the base of peneplain remnants, detritus from above, including
fragments of the crust, accumulates and is recemented to form younger
laterite on the colluvial footslope (Maignien, 1958, 1959; D’Hoore, 1954,
1957). On low-level plains soft laterite is commonly currently forming
above a water table; and on undulating upland surfaces, laterite may be
forming locally in clayey iron-rich residuum whose impervious nature
periodically causes saturation with water.
Many existing laterites are clearly relics of geologic antiquity. Those
of Queensland, Australia, are reported to be products of two humid
periods of the Pliocene (Whitehouse, 1940). In Ceylon, of the crusts
described most are thought to be products of the Pleistocene and some,
of Pliocene or earlier periods (Fernando, 1948). Laterites of Nioka
(Ituri), Congo have been related to mid- and late-tertiary surfaces by
Ruhe (1954). Though laterite may be forming currently on some ancient
peneplain remnants, many high-level crusts are considered to be “dead
products of the age of peneplain development. Their existence may
commonly be considered a factor in the preservation of the land forms
on which they occur, and the period since the lowering of base level is
a measure of the time required for landscape inversion under given
Nevertheless, many examples of laterite believed to be forming
currently have been reported ( Fermor, 1911; Simpson, 1912; Campbell,
1917; Marbut, 1932; Harrison, 1933; Joachim and Kandiah, 1941; Pendleton and Sharasuvana, 1942; Kellogg and Davol, 1949). Though it is
commonly assumed that formation of laterite requires a very long time,
some laterites of “absolute accumulation” ( D’Hoore, 1957, pp. 94-98)
apparently may form rapidly. Obviously, formation of laterite from solid
unweathered rock can be no more rapid than the time required to attain
a high degree of weathering. In unconsolidated weathered material
subject to enrichment in iron from outside sources, however, rate of
development may be relatively rapid. Hardening of the soft preconditioned material may take place in a few years upon exposure
(Alexander and Cady, 1962).
IV. Profiles Containing Laterite
Though either nodular or vesicular laterite may lie within, and may
be genetically related to, the solum of the modem soil, as defined by
the Soil Survey Staff of U.S.D.A. (1951), many laterites appear to be
unrelated genetically to present soil horizons. Consequently, the Soil
Survey Staff (1960) has defined “plinthite” independently of soil horizon
definitions, though they use the presence of soft “plinthite” within the
solum as a criterion of soil classification. This discussion is concerned
with horizons or layers in the entire weathered section, which commonly
is much thicker than the part that would be considered “solum.”
At sites where laterite is thought to be forming, it is generally found
as a shallow but not surficial layer. Prescott and Pendleton (1952)
reported laterite in Ceylon at various depths, averaging about 2 feet, and
in Thailand from a fraction of a foot to 6 feet. Humbert (1948) described
“red to yellow loam” 2 to 6 feet thick over laterite in Queensland. Some
Iaterite layers have been described by Alexander and Cady (1!362) at a
depth as great as 13 feet in Sierra Leone but others were found near or
at the surface. Similar observations are very numerous in the literature
and indicate that soil material over laterite is mainly less than 10 feet
thick. Laterite crusts at the surface are very widespread ( Oldham, 1893;
Maclaren, 1906; Simpson, 1912; Walther, 1915; Prescott and Pendleton,
1952, among many authors), but such exposure is generally attributed to
erosion. Though hardening of laterite is thought to be a phenomenon
favored by surface position, the literature implies that the initial
development of material that will harden most commonly occurs at
some depth below the surface. Hardened laterite crusts as thick as 200
feet (Oldham, 1893) suggest that development can proceed to this
depth, but such an extreme may be only at the edge of peneplain remnants where the material is affected by vertical exposure. A crust 30 feet
thick has been reported by Alexander and Cady (1962); Campbell
(1917) observed that laterite seldom exceeds 30 feet in thickness.
Mohr (1944) considered laterite to be essentially a soil horizon of
sesquioxide accumulation to which the overlying soil material is related
genetically. This concept has been elaborated by Mohr and van Baren
(1954, pp. 300304) and was accepted by Pendleton (1936, p. 106).
Marbut ( 1932) postulated a comparable genetic relationship between
laterite and soil material above it. In all these cases, the authors have
dealt with restricted conditions, comparable in many respects to the
original laterite of Buchanan. The work of Maignien (1958, 1959),
Mulcahy (1960), and D’Hoore (1954, 1957) and observations by the
authors (Alexander and Cady, 1962) show clearly that the presence of
a suficial mantle of soil over laterite is no assurance that the soil is
related to the underlying laterite genetically, or that if genetic relationships are involved, they may be quite unlike those postulated.
S . SIVAEWJASINGHAM
The overlying soil material may be from sources different than the
material in which the laterite has formed. Stone lines marking erosion
surfaces (Ruhe, 19.59) are very common in the tropics and may mark
major discontinuities of material vertically. Ollier ( 1959), however, has
reported extensive areas in Uganda where the stone lines appear to be
the result of sorting by termites, leaving coarse fragments below and
moving fine earth to the surface. Nye (1954) also emphasized the
activities of termites but reported substantial sorting and downslope
creep of the sorted material. Berry and Ruxton (1959) also have
emphasized an upper zone of migration. Resistant minerals, such as
quartz, in soil over laterite from quartz-free rock are common and
indicate at least contamination of the upper layers of material from
In some cases surface material can be demonstrated to be residual
from the same rock as that from which underlying laterite has formed
and either predates or is contemporaneous with the laterite. There are
also cases known to the authors in which a surficial soil mantle has
developed by disintegration of the upper part of a laterite crust. Such
soils are commonly thin over the laterite and contain pieces of the
Thus, a great variety of soils may overlie laterite. Where such soil
horizons are residual, they are composed of highly weathered material
high in sesquioxides with or without kaolin and with some component of
whatever highly resistant minerals may have been present in the parent
rock. They may be uniform in character with depth, like Latosols, or
may have genetic A-B horizon sequences not unlike Red-Yellow Podzolic
Soils. Commonly, the first laterite encountered with depth is in the form
of individual nodules within the soil horizons. These may reach a
maximum with depth below which they decrease without being joined
into masses as in examples given by Nye (1954, 1955a) and Radwanski
and Ollier (1959), or they may pass into masses of nodular or vesicular
laterite, as in profiles described by Joachim and Kandiah (1941) and
Many soils of the tropics have laterite within genetic horizons. These
may be detrital nodules or fragments from adjacent higher-lying landscapes containing laterite ( Greene, 1945; Ruhe, 1954), relics of disintegrating laterite crusts in which soils are forming (Mulcahy, 1960, 1962),
or units developing concurrently with the modem soil (Ollier, 1959).
The “murram” used for surfacing roads in India (Prescott and Pendleton,
1952) is mainly nodular laterite and may be in horizons of the modern
soil. The authors have observed profiles comparable to both Red-Yellow
Podzolic Soils and Latosols, both containing nodular laterite in various
horizons, in widely separated areas of East and West Africa and in the
Philippines. The Tifton series, a Red-Yellow Podzolic Soil of southeastern United States, contains laterite nodules in both Az and B horizons.
The nodules in the B horizon of Tifton are intact and either forming or
stable, whereas those in the A2 are apparently dissolving, leaving quartz
grains protruding from the iron-rich matrix. Similar conditions in soils
Horizontal Scole, Feet
.z 3 6 -
Dork. Sendy Loom
h r k . Sandy Loom
with M Nodule.
I and Brownish
FIG.2. Laterite nodules in soils of a catenary association of Southern Nigeria.
containing iron nodules have been observed in Southern Rhodesia and
parts of Australia by the authors.
Though laterite nodules are common in soils that have no obvious
high water table ( Raychaudhuri, 1941) , such nodules commonly increase
progressively downslope on a given land form. Figure 2 shows this
relationship at a site near Ibadan, Xigeria where proximity of a zone of
saturation to the surface appears to be a controlling factor. It is believed
that these are developing concurrently with the modem soil and are
analogous to the forms described by Nye (1954, 1955a) in Ghana.
In the “Ground-Water Laterite” soil described by Kellogg and Davol
S. SWARAJASISGHASL ET AL.
(1949), the laterite is considered to be a genetic horizon of the modern
soil. In this profile, laterite nodules are present at a depth of 8 inches,
increase in numbers with depth, and occupy a major part of a weakly
cemented horizon from 23 to 45 inches, which rests on soft massive
laterite that hardens upon exposure to air. Mohr (1944) and Mohr and
van Baren ( 1954) have postulated progressive soil development involving
( I ) laterite-free profiles in which an impervious substratum forms, ( 2 )
stages having horizons containing nodular laterite, and ( 3 ) a final stage
involving massive laterite.
Obviously, detrital laterite fragments and nodules come to rest
capriciously on whatever material may be present on footslopes of
dissection forms, and in such areas of landscape inversion (Bonnault,
1938) the detrital laterite and the underlying material may be unrelated.
The laterite detritus, however, commonly contributes iron to enrichment
of adjacent layers (Maignien, 1958, 1959). A great variety of unrelated
layers may be found under laterite zones in such positions.
Where the laterite zone is apparently residual, however, the literature
reveals some measure of consistency of kinds of underlying layers.
Though Holland (1903) reported that laterite may rest on unaltered
bedrock, most descriptions show highly weathered, commonly thick,
earthy layers between the laterite zone and bedrock. In dry areas or
where conditions contribute to good aeration, as on some high-level
positions, the underlying material may be high in chroma (bright
colored) though commonly variegated in color ( Kellogg and Davol,
1949, p. 52). More commonly, especially on low-level positions, the
laterite zone is underlain by either a mottled zone, a light-colored layer,
or both, suggestive of poor aeration, reduction of iron, and possible
lateral leaching of sesquioxides.
U‘alther ( 1915) introduced the terms “mottled zone” and “pallid zone”
for comparable parts of profiles of western Australia, which contained
the following layers: (1) ironstone crust, ( 2 ) mottled zone, ( 3 ) pallid
zone, and (4)parent rock.
Simpson (1912) described similar sequences on both granite and
greenstone schist in the same region. Though Maclaren (1906) used
different terms in describing a lSfoot section in India, his sequence,
hard laterite-soft laterite-reddish buff sandy clay-white
grit-decomposed biotite and quartz schist, is very similar. Marbut’s (1932, p. 74)
idealized description of typical “Ground-Water Laterite” of the Amazon
Valley and Cuba reveals the same layers: (1) soil, ( 2 ) iron-oxide layer,
porous, slaglike, (3) mottled layer, ( 4 ) gray layer, and (5) unconsolidated clay and sand. He reported that the gray layer (pallid zone) may
be absent. Kellogg and Davol (1949) did not specify distinct mottled
and pallid zones in a “Ground-Water Laterite” of the Congo, but their
description shows mottling intermingled with high color values ( light
colors) in the lower part of the profile. Mohr and van Baren ( 1954,
p. 302) described similar layers in idealized profiles on volcanic ash
in which laterite is formidg in Indonesia:
B3- Layer of mottled
clay differentiable into an upper layer
of Fe203(incipient laterite) and a lower gibbsitic layer
Spotted white clay (pallid zone)
Layer with siliceous cement
Unaltered ash of the basic suite
The numbering of “ B horizons by superscripts upward indicates the
hypothesis of development upward above the slowly permeable silicacemented B1 layer, which supports a perched water table.
Mulcahy (1960, 1962) described thick pallid zones in Australia under
ancient laterite in high-level positions where mean annual rainfall is
now less than 20 inches per year, their thickness decreasing from 60 or
80 feet under 20 inches of rain to about 10 feet under 13 inches. Jessop
(1960) described pallid zones from 60 to 200 feet thick in the southeastern part of the Australian arid zone under a silicified cap on plateau
remnants and concluded that the pallid zone is a relic of an ancient
profile from which the ferruginous material has been stripped. From
observations in Africa and Australia, Alexander has concluded that some
pallid zones are consequences of exclusion of air by overlying laterite;
they appear to be actively forming even on high-level positions in
relatively dry climates when they lie beneath a crust dense enough to
permit little access of air and where the zone is saturated for some period
during a rainy season. A profile by Kellogg and Davol (1949, p. 52) in
the Congo suggests that on relatively dry sites a thick (4-foot) layer of
unmottled soil, comparable to laterite-free soils of the locality, may
lie between a relic laterite crust and a mottled zone.
Commonly immediately above unweathered rock is a soft layer that
has undergone major chemical change while retaining the structural
character of the rock from which it was formed. This was called “zersatz”
by Harrassowitz (1926, 1930). This may lie beneath a mottled or pallid
zone, as in the “Ground-Water Laterite” of Kellogg and Davol (1949).