Hawaiian Ferruginous Laterite Crusts — SHERMAN 
crusted surface horizons are the lateral move- 
ment of water through the friable layer and 
the alternating wet and dry season. The wa- 
ter moving laterally through the friable layer 
would contain dissolved ions from the weath- 
ering of the soils under a heavy rainfall con- 
dition where the soil solum is continuously 
moist. Sherman (1949) has shown that in 
these soils iron oxides are being reduced and 
are being leached away in the percolating 
water. He also pointed out that titanium 
content of these wet soils is low as compared 
to other Hawaiian soils. Thus it is possible 
for the percolating waters of these soils to 
contain iron in a reduced form and titanium 
as a hydrated titanium oxide or in an acid 
form. The former has been identified by 
Doelter (1913) in laterite soils, and the lat- 
ter is possibly due to the very acid condition 
of the soils of the very wet locations. The 
waters would also contain a small amount of 
dissolved silica. The greater portion of the 
silica is removed during the earlier stages of 
soil weathering and when the internal drain- 
age of the soil profile was good. As the soil 
matured, the internal drainage became poor 
due to the development of impervious clay 
layers. With the development of the poor 
internal drainage more of the percolating 
water will move down the slope laterally and 
less will percolate through the soil and its 
weathered parent material. When the lateral 
movement of percolating water reaches areas 
having an alternating wet and dry season, 
conditions become favorable for the capillary 
rise of the percolating waters during the dry 
season. The capillary rise of the percolating 
waters to the surface is greatly enhanced by 
the benches or level areas of the slopes. A 
similar case of enrichment of soils of lower 
elevations by lateral movement of percolat- 
ing waters has been proposed by Green 
(1947). 
The dissolved iron and titanium are 
brought to the surface in the capillary water. 
The iron is stabilized by its oxidation to the 
319 
ferric form. During the dry season the iron 
oxide, which probably exists as goethite, and 
the hydrated titanium oxides are dehydrated 
to form the minerals hematite and anatase, 
respectively. The dissolved silica in the per- 
colating waters would probably rise to the 
very surface before dehydration. The data in 
Table 1 would support this hypothesis. The 
lack of an appreciable amount of titanium 
oxide in the friable layer would suggest that 
the titanium must move as a colloidal hy- 
drated titanium oxide. Fujimoto et al. (1949) 
have reported the titanium oxide content of 
45 per cent in the colloidal fraction of the 
transitional zone between the friable layer 
and the laterite crust horizon. The low con- 
tent of volatile matter, which would include 
water of hydration, suggests that both tita- 
nium and iron oxides are stabilized by dehy- 
dration. This would account for the presence 
of the two secondary minerals hematite and 
anatase in the surface soil. The ilmenite con- 
tent of these soil horizons is extremely low 
and would rule out the possibility of resid- 
ual concentration. Furthermore, if ilmenite 
did not decompose under tropical soil weath- 
ering, titanium should be concentrated in 
greater quantities in the surface horizon of 
the soils developed in the regions of heavy 
rainfall as well as where it is found in the 
area having the hard surface crusts. The 
chemical analyses of these soils do not reveal 
a concentration of titanium. In Figures 1 and 
2 are given the graphical representation of 
the manner in which the ferruginous laterite 
crusts have become the zone of accumulation 
of iron and titanium oxides. 
The ferruginous laterite crust is considered 
to be the senile stage of tropical soil weather- 
ing under a climate having alternating wet 
and dry seasons. Thus as the crust area be- 
comes denuded of vegetation it will remain 
a stabilized land form until removed by ero- 
sion or degraded into another condition by 
general advancement of age of the general 
land area. The laterite crusts are very suscep- 
