288 
PACIFIC SCIENCE, Vol. XII, October, 1958 
C2 
C; 
c 4 
under pressure into moder- 
ate fine and medium sub- 
angular blocks; slightly 
hard, friable; brown fine 
concretions common; few 
fine roots; extremely acid. 
18-28" Variegated red (2.5YR 
4/8), weak red (10R 4/3), 
and reddish-yellow (5YR 
6/8) silty clay loam; mas- 
sive; slightly hard, friable; 
few light-gray fine concre- 
tions, few fine roots; ex- 
tremely acid. 
28-32" Variegated weak red (10R 
4/3), reddish-yellow (5YR 
6/8), and strong brown 
(7.5YR 5/6) silty clay 
loam; massive; slightly 
hard, friable; few brownish 
coarse and very coarse con- 
cretions; few speckles of 
gray (N 5/); extremely 
acid. 
32-76" Variegated weak red (10R 
4/3) and strong brown 
(7.5YR 5/6) gritty silty 
clay loam, appearing mot- 
tled because of light-gray 
(10YR 7/1) fine to coarse 
concretions; yellowish-red 
very coarse concretions 
common; extremely acid. 
76-96" Variegated weak red, 
strong brown, and black 
silty clay loam; weak coarse 
platy structure apparently 
retained from parent vol- 
canic breccia; very strongly 
acid. 
(c) Additional Notes . The concretions in the 
A horizon are large and tend 0 be roughly 
platy, with long axes ranging from 5 to 100 
mm. and short axes from 3 to 30 mm. All 
seem to be vesicular, and some have shiny 
surfaces. Concretions are most abundant in 
the surface layer and in the C horizon. 
The nature and distribution of concretions 
in the profiles of dominant Latosols in this 
association tend to follow certain patterns. 
For the most part, brown, reddish-brown, and 
yellowish-red concretions occur in the surface 
layer, though they are found at depth in some 
profiles. Gray and light gray concretions oc- 
cur in the C horizon, especially in the upper 
part. Colors suggest that concretions in the 
deeper profile are more often low in iron 
oxides than those near the surface. Most con- 
cretions in the upper horizons are somewhat 
flattened and platy, with a few being roughly 
spherical. In the deeper horizons, the concre- 
tions may be platy, spherical, or assume 
branching cylindrical forms much like reef 
coral. The spherical and platy forms are most 
common. Total numbers of concretions are 
greatest in the A and C horizons, and seem 
to be lowest in the B horizon. Numbers of 
concretions decrease with increasing depth in 
and below the C horizon, as a rule. 
Sequences and thicknesses of horizons and 
the degree of horizonation are not uniform 
among the bauxitic Latosols and related soils 
dominant in this association. As already indi- 
cated, these soils comprise about half of the 
total area of the association. Perhaps 25 per 
cent of the soils in this half have the horizon 
sequence and thicknesses as described for the 
one profile. Other soils either have been 
eroded or have failed to reach the same degree 
of horizon differentiation. Most of the soils 
have thinner A horizons than the described 
profile, some lack an A horizon, and others 
seem to have lost both A and B horizons. 
Some of these last-named soils have thin A 
horizons which seem to be in process of for- 
mation from former C horizons. Thus, about 
three-fourths of the bauxitic Latosols and re- 
lated soils in the association have profiles 
somewhat like but not identical with the one 
described near Ngardmau. Regardless of the 
character of the profile, the Regolith is con- 
sistently deep, commonly exceeding 30 feet 
and often reaching 50 feet. 
Second in extent in the association are 
