Laterite Soils in Hawaii — SHERMAN 
313 
damental in any interpretation of the soil asso- 
ciations which occur in tropical regions. In this 
presentation every effort has been made to avoid 
the complexities in the soil associations due to 
transition zones, degradation due to shifting 
climatic conditions or to lowering of the gen- 
eral elevation of volcanic areas, and differences 
in the composition of the weathered geological 
materials. 
The initial weathering of parent materials 
is the breakdown of the primary minerals with 
the formation of secondary clay minerals of the 
kaolinite type. The rate of decomposition of the 
kaolinite minerals appears to be closely related 
to the amount of rainfall under which the soil 
is formed. Under extremely heavy rainfall the 
formation of the secondary clay mineral and its 
subsequent decomposition may be so rapid and 
transitory as to leave the outline of the original 
minerals and stratification of the parent ma- 
terials. The hydrol humic latosols often show 
the stratification of the original parent material. 
The distribution of rainfall plays an impor- 
tant role in the nature of the ultimate end- 
product of laterization in tropical soils. The 
stabilization of the iron oxide in soil has re- 
sulted from an alternating wet and dry season 
climate. Under a continuously wet soil profile 
environment, alumina becomes the stabilized 
free oxide. The amount of iron remaining in 
these soils depends on the amount of rainfall 
and aeration. This would explain to some degree 
the occurrence of aluminum oxide laterites and 
iron oxide laterites. The effect of the alternating 
wet and dry season can be destroyed by the de- 
velopment of a poor internal drainage in the 
soil solum. If this condition promotes lateral 
movement of water, as it will on slopes, it will 
facilitate the development of the iron oxide 
"laterite crust.” If the impervious condition pro- 
duces a stagnation of the water in the profile, a 
certain amount of resilication will take place 
with the removal of the easily reducible iron in 
the slow leaching of the impervious layer. The 
result of this condition will be the development 
of the profile of a very wet soil. 
CONCLUSION 
The data presented in this paper have em- 
phasized several important fundamental reac- 
tions which occur in tropical soil. In the devel- 
opment of tropical soils two weathering actions 
are taking place: (a) the formation of clay 
minerals of kaolinite type from the primary 
minerals, and (b) the decomposition of the 
clay minerals with the accumulation of free 
oxides of iron, aluminum, and titanium. 
The distribution of the rainfall and propor- 
tion of months receiving less than 2 Ys inches of 
rain ( the dry months ) and the months receiving 
more than 4 inches (the wet months), play an 
important role in the nature of the free oxides 
which will become stabilized and will accumu- 
late in the soil solum. In evaluating the quantity 
of rainfall it was found necessary to introduce 
the number of very wet months (more than 8 
inches of rain ) in order to differentiate between 
the humic latosol and hydrol humic latosol 
which are developed under very wet conditions. 
The low humic latosol and the ferruginous 
humic latosol have developed in a climate hav- 
ing a definite dry season alternating with a wet 
season of varying length and intensity. The soils 
developed under this type of season would ex- 
hibit the following chemical properties with in- 
creased weathering due either to the intensity 
of the alternating wet or dry conditions or to 
time of exposure of this type of weathering con- 
dition: (a) in the early stages both the kaolinite 
and alumina content increase and both decrease 
with further weathering; (b) silica content of 
the soil decreases with the age of weathering of 
the soil; (c) the content of iron and titanium 
oxides in the soil increases with the weathering 
age of the soil; and (d) the final end-product 
of weathering under these conditions is a 
"laterite crust” having a high content of iron 
and titanium minerals. 
The humic latosol and hydrol humic latosol 
are developed under climates which have no 
definite dry season. Soils developed under these 
conditions have the following chemical proper- 
ties: (a) the rapid decomposition of the clay 
