Soils of Palau — VESSEL AND SIMONSON 
of rubble, commonly small in size. The princi- 
pal volcanic rocks range from olivine-augite 
basalts to silicic hornblende dacites (Corwin, 
1951) identified as andesitic agglomerates by 
Japanese geologists (Tayama, 1953) and also 
known as basaltic and andesitic volcanic brec- 
cias. Associated with the flow rocks and ag- 
glomerates on Babelthuap are some basic vol- 
canic tuffs. Interbedded sedimentary clays 
and lignite comprise the surface formations in 
a few places in western and southeastern 
Babelthuap. 
The distribution of rocks on the Palau 
Islands is strongly reflected in the distribution 
of soils (Fig. 2). Rocks of volcanic origin are 
parent materials for most of the Latosols. 
Some latosolic soils have also been formed 
from interbedded sedimentary clays. Deep 
soils with distinct horizons have not been 
formed from limestones, most of which have 
rubble surfaces. Where the volcanic rocks are 
exposed on steep or moderately steep slopes, 
shallow rocky Lithosols have been formed. 
Deep unconsolidated materials of recent ori- 
gin have given rise to Regosols, Alluvial Soils, 
and Organic Soils. 
Climate 
Typical of the humid tropics, the islands 
have heavy annual rainfall and high mean 
temperatures with small seasonal differences 
(U. S. Dept, of Commerce, 1953). The islands 
also have rather steady winds, lying as they 
do in the trade-wind belt. The mean annual 
precipitation is 148 inches, with a maximum 
of about 19 inches in July and a minimum of 
nearly 8 inches in March. On the average, at 
least 15 days of each month have 0.04 inch 
or more of rain, whereas 7 days in July have 1 
inch or more. The average relative humidity 
is 82 per cent, with a low of 79 per cent in 
March and a high of 83 per cent in July, No- 
vember, and December. The mean annual 
temperature is 81° F. The maximum and mini- 
mum mean monthly temperatures are but one 
degree higher and lower, whereas the diurnal 
283 
variation is about ten degrees. Prevailing 
winds are from the northeast and east from 
November to June and from the south and 
southwest for the remainder of the year. 
Vegetation 
The native vegetation (Fosberg, 1946) in 
the Palau Islands was rain forest, which re- 
mains in only a few places on Babelthuap. 
The rain forest consists of large trees, includ- 
ing Parinarium , Campnosperma , Couth ovia, 
Cynometra , Dysoxylum, Ficus, Semecarpus, Ran- 
dia , Fagraea, Pittosporum , Schefflera, Horsfieldia, 
and many others. Growing also in the rain 
forest are such palms as Pseudopinanga and 
Exorrhiza; an occasional slender Pandanus; 
such climbers as Freycinetia , Canavalia, Piper , 
aroids, and Ipomoea; also ferns, orchids, and 
other epiphytes. On both the low and high 
limestone islands, vegetative cover consists 
mainly of small to medium-sized trees and 
shrubs because moisture conditions are un- 
favorable for plant growth. 
The most extensive vegetative type today 
is anthropic savanna consisting of coarse 
grasses, weeds, and occasional shrubs. Com- 
mon genera in the savanna are Ischaemum , 
P asp alum, Digitaria, Miscanthus, Lycopodium, 
Nepenthes, and Pandanus (Fosberg, 1946). 
Soils of extremely low fertility support almost 
pure stands of a fern, Gleichenia linearis. 
SOILS 
The general character and distribution of 
soils were determined through a reconnais- 
sance survey, according to procedures already 
described (Simonson, 1953; Soil Survey Staff, 
1951). This reconnaissance survey was part 
of a program of soil and geologic investiga- 
tions in the western Pacific Ocean (Simonson, 
1953). How the soils were being used was 
observed during the field mapping from 
March through August, 1948. 
Distribution of the soils and land types of 
the islands is shown in Figure 2. The map 
units are either soil associations or miscel- 
