312 
PACIFIC SCIENCE, Vol. Ill, October, 1949 
CHEMICAL COMPOSITION OF THE SOILS 
DEVELOPED IN AN ABSENCE OF 
A DEFINITE DRY PERIOD 
The soils belonging to the humic latosol and 
the hydrol humic latosol have been developed 
under conditions in which the soil solum rarely 
dries out. These soils in the Hawaiian Islands 
are covered with dense cover of ohia, tree ferns, 
and staghorn fern. The latter two produce an 
extremely acid forest floor (Sherman, 1947). 
These soils have been separated in the field on 
the basis of their clay properties. The clay of the 
humic latosol can be pressed into a ribbon be- 
tween one’s fingers while that of the hydrol 
humic latosol will smear. A series of soil profiles 
representing a sequence of these clays developed 
under increasing rainfall was selected for analy- 
sis. These soils range from a soil profile belong- 
ing to an intrazonal group (brown forest) de- 
veloped under 70 inches of rain per annum to a 
hydrol humic latosol profile developed under 
273 inches of rain per annum; all have devel- 
oped on parent materials made up of volcanic 
ash. The data obtained from these analyses are 
given graphically in Figure 4. 
The data presented in Figure 4 show an in- 
crease in the alumina content with an increase 
in rainfall. The silica and iron oxide content 
appears to decrease with an increase in rainfall. 
This would suggest that under continuously wet' 
conditions the alumina will become stabilized 
and iron oxide will become unstable and leach 
away. Tanada (1944) has identified bauxite 
and limonite as the minerals representing 
alumina and iron oxide In these soils. It is 
likely that as this soil continues to weather, the 
bauxite will continue to accumulate as a result 
of the destruction of the kaolinite day minerals 
and the removal of silica and iron oxide by 
leaching. Thus, the end-product of weathering 
in the very wet tropics will probably be a 
"bauxite laterite.” 
The author has presented two sequences of 
soil weathering which are considered to be fun- 
BROWN HUMIC HYDROL HUMIC HYDROL HUMIC 
FOREST LATOSOL LATOSOL CA> LATOSOL CB; 
Fig. 4. The influence of an increase in annual rainfall on the chemical composition of soils developed in 
a continuously wet region. 
