Laterite Soils in Hawaii — SHERMAN 
311 
BROWN HUMIC HUMIC HUMIC CRUST 
LATOSOLCA) LATOSOL(B) LATOSOL 
Fig. 3. The influence of the lengthening of the 
wet season on the chemical composition of the B hori- 
zons of the soils shown in Figure 2. (A) and (B) 
profiles represent two low humic latosols. 
soil weathering progresses and in the "laterite 
crust" they constitute almost 80 per cent of the 
soil. These oxides are present as two secondary 
minerals-— hematite and anatase. 
The data presented graphically in Figure 3 
were obtained from the chemical analysis of soil 
samples representing the B horizons of the soils 
shown in Figure 2. The silica, alumina, and iron 
oxide show exactly the same trends as were 
found for the soils representing the A horizon. 
Titanium oxide content of the B horizons fails 
to increase with weathering. Since these soils 
are very acid, it is probable that the titanium 
was converted to metatitanic acid and moved 
upward to the A horizon where it was de- 
hydrated during the dry seasons ultimately to 
form anatase. The iron oxide of the B horizon 
of the "laterite crust" exists as hematite and 
goethite. 
The data presented in Figures 2 and 3 repre- 
sent, in general, a sequence of conditions em- 
phasizing a range in the proportion of dry 
months to wet months. The range spans from 
12 dry months to approximately 3 dry, 3 wet, 
and 6 intermediate months per year in the 
ferruginous humic latosol. It is obvious that 
the effectiveness of an alternating wet and dry 
season on the rate of soil weathering is gov- 
erned by the following factors: (a) amount of 
rainfall during the wet season and (b) the in- 
tensity and duration of the dry season. How- 
ever, the question arises as to the effect of time. 
Will the soils belonging to the low humic latosol 
continue to weather until they take on the 
characteristics of the ferruginous humic latosol? 
It is reasonable to assume that they will con- 
tinue to weather toward the end-product, the 
"laterite crust." The following evidence would 
support this contention: (a) the increase in 
area of soils belonging to the ferruginous humic 
latosol with the geological age of the parent 
materials and a simultaneous decrease in area 
of the soils belonging to the low humic latosols. 
The island of Kauai, geologically the oldest of 
the major Hawaiian islands, has the greatest 
area of ferruginous humic latosols, and the low 
humic latosols show greater advancement in 
weathering than the same type of soil on 
younger islands; (b) the decrease in kaolinite 
content and the increase in iron oxide content 
in low humic latosols on the older geological 
parent materials; (c) the occurrence of the 
"laterite crust" on relatively dry slopes receiving 
a rainfall comparable to that of the drier low 
humic latosols on the island of Kauai; and 
(d) the increase in compaction of the subsoils 
of the low humic latosols with age, which may 
favor formation of an impervious subsoil which 
will in turn develop conditions favorable for 
the lateral movement of water through those 
soils occurring on slopes. In the drier regions 
of the low humic latosols the rainfall will 
probably never be sufficient in quantity to pro- 
duce this transformation but in those which 
have a definite wet season, time will certainly 
produce ferruginous humic latosol. 
