316 
(1949). These soils have a surface horizon 
which is a compacted or vesicular slaglike 
mass having a very high apparent specific 
gravity. Some of these areas are covered with 
a sparse dwarfed vegetation while others are 
practically barren areas in which the surface 
soil has a glazed surface with the hardness of 
a pavement. The high apparent specific 
gravity is due to presence of large quantities 
of iron and titanium oxides which make up 
more than 75 per cent of the soil. The hard 
sterile ferruginous laterite crusts have been 
found on the southern and western slopes of 
the island of Kauai; on the western slope of 
the main mountain range of Molokai; and 
on the white trachyte cliffs of West Maui. In 
every case the areas are found on long slopes 
in which heavy rainfall is received at the 
higher elevations while the lower elevations 
remain very dry. The areas of hard crusts are 
found just below the lower boundary of the 
canopy forest. 
MORPHOLOGICAL DESCRIPTIONS OF 
HAWAIIAN LATERITE CRUSTS 
Island of Kauai 
The hard sterile laterite crusts are found 
on the southern and western slopes of lee- 
ward Kauai. These areas are found on the 
benches or on broad and more level areas of 
the long ridges which run from the top of 
the mountains toward the ocean. The hard 
surface crusts are found in the transition zone 
between the shrub vegetation on the lower 
elevations of the slope and the dense canopy 
forest cover on the wet higher elevations of 
the slope. The surface horizon of the crusted 
areas is a very hard compacted purple silt 
loam having a very high apparent specific 
gravity. The volume weight of this layer ap- 
proaches 3.0 in some cases. This horizon is 
very hard and it is necessary to use a heavy 
sharp tool to break the layer. The chipped- 
off fragments crush readily in one’s hand to 
a very fine graphite-like powder. This pow- 
PACIFIC SCIENCE, Vol. IV, October, 1950 
dery material contains small pellets of mag- 
netite. About 30 per cent of the particles are 
of clay size, but even so this material does 
not exhibit any evidence of stickiness when 
wet. The thickness of the crust may vary from 
4 to 14 inches. 
The hard surface layer is underlain by a 
yellowish-brown to reddish-brown friable silt 
loam. There is very little evidence of heavy 
minerals which were responsible for the high 
apparent specific gravity of the surface hori- 
zon. While this soil has the physical proper- 
ties of a silt loam, mechanical analysis of the 
soil showed that more than 60 per cent of 
the soil particles are of clay size. The thick- 
ness of the friable layer ranges from 12 to 
36 inches. 
The friable layer lies over an impervious 
surface of an unconformity or an impervious 
soil horizon. In the former case the material 
is of different geological formation than the 
material from which the soil was formed. In 
the latter case it has not been established 
whether the impervious soil horizon is related 
to the soil solum or is the surface of a buried 
soil. Whether or not this plastic subsoil is 
related to the soil, it has provided an imper- 
vious layer which, apparently, is necessary for 
the formation of ferruginous laterite crust. 
The chemical analysis of a typical Kauai 
ferruginous laterite crust is given in Table 1. 
The high content of iron and titanium oxides 
in the hard crusted surface horizon is charac- 
teristic of these soils. The iron oxide exists 
as hematite, and titanium oxide as anatase. 8 
Another characteristic of the analysis of this 
horizon is the low content of volatile matter. 
The B horizon has an iron oxide content rang- 
ing from 70 to 80 per cent. The iron oxide 
of this horizon exists as goethite and hema- 
tite. The titanium oxide content of this layer 
is markedly lower than is that of the hard 
surface horizon. The chemical composition 
3 Cooperative studies with Dr. M. L. Jackson, 
University of Wisconsin. 
