318 
PACIFIC SCIENCE, Vol. IV, October, 1950 
TABLE 2 
The Chemical Composition of Typical Hawaiian Ferruginous Laterites 
and Siam Ferruginous Laterites* 
LOCATION OF 
FERRUGINOUS LATERITE 
Si0 2 
ai 2 o 3 
Fe 2 0 3 
Ti0 2 
TOTAL 
Kauai — Waimea Canyon 
per cent 
3.9 
per cent 
5.8 
per cent 
60.8 
per cent 
26.0 
per cent 
96.5 
Molokai — Just below forest line 
7.8 
3.6 
60.4 
24.0 
95.8 
Maui — From eroded trachyte cliffs 
5.8 
12.0 
64.8 
11.2 
93.8 
Siam — Ferruginous concretion 
11.8 
30.0 
46.2 
1.8 
89.8 
Siam — Ferruginous lens 
15.4 
24.8 
51.2 
2.4 
93.8 
* Samples of Siam ferruginous laterites were given to the author by Dr. R. L. Pendleton. The 
sample analyzed was from a portion of the specimen showing the greatest evidence of iron deposition. 
formation. The impervious layer, whether an 
unconformity or impervious clay layer, is al- 
ways found below the friable horizon. If one 
examines the lower portion of the friable 
layer, indications of the lateral movement of 
water will be observed. This has been sub- 
stantiated by the very wet condition found in 
this layer at a period of several days after 
heavy rainfalls at the higher elevations. The 
lateral movement of water through the fri- 
able layer has been demonstrated by the seep- 
age of water into wells dug in this type of 
a soil. The hard crust surfaces are formed in 
areas of the slope which are either a bench 
or the more level areas of the slope. The last 
condition, a very important one, is that the 
crusts are formed in a climatic region which 
has a very dry season alternating with a wet 
season. The greatest development occurs in 
the regions where the wet and dry seasons are 
of about the same duration. A typical case 
would be 4 months with less than 2Ys inches 
of rainfall and 3 months having more than 
4 inches of rainfall. Some of the dry months 
may have less than an inch of rainfall; thus, 
the vegetation of the area will be the type 
which falls between the shrub vegetation of 
the drier areas and the tropical canopy forest 
of the wetter areas. 
The two factors which appear to be most 
responsible for the development of the 
These soils have developed from the tra- 
chyte rock on which they are found. Even 
though these are residual soils, there is a 
sharp boundary between the unweathered 
trachyte rock and the soil solum. 
The chemical composition of the ferru- 
ginous laterite crust from West Maui is given 
in Table 2, along with the analysis of ferru- 
ginous laterite horizons from Kauai and 
Molokai. Also included in Table 2 are sam- 
ples of Siam laterites. The difference in the 
analyses indicates that Siam is not as old as 
the areas on Molokai and Kauai, or that the 
difference may be due to the nature of the 
more acidic parent material. Some of the 
crusts which occur at inaccessible higher ele- 
vations appear to have progressed further in 
their development than those at the acces- 
sible lower elevations. 
SOIL WEATHERING CYCLE INVOLVED IN 
FERRUGINOUS LATERITE CRUST FORMATION 
The ferruginous laterite crusts have devel- 
oped in Hawaii under certain definite weath- 
ering conditions. It has been pointed out 
that the ferruginous laterite crusts have 
formed on long slopes which have a heavy 
annual rainfall region at the higher eleva- 
tions and a low annual rainfall at the lower 
elevations. Certain other characteristics al- 
ways appear to be necessary for the crust 
