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PACIFIC SCIENCE, VoL VII, July, 1953 
in the subsoil, indicating less favorable oxida- 
tion and aeration. 
The areas of volcanic rock outcrops are 
highly dissected and are at maximum relief. 
Ridges are generally sharp and narrow; ra- 
vines are deep. Many of these areas are under- 
going accelerated erosion with prominent 
gullies and erosion scars. As a result, very 
little soil material (i.e., horizons of organic 
accumulation and modified parent material) 
is present, and the weathered volcanic rocks 
(the "saprolite” or ^zersatz” of some authors) 
are exposed at the surface. Such areas are 
classified with the land type of rough broken 
land. Shallow soils, such as the Teo soils, are 
found where erosion is less severe. Deep soils 
underlaid by volcanics have developed only 
on broad ridge tops and the less strongly 
sloping areas. 
OTHER 2% 
TOTAL AREA -48 SQUARE MILES 
Fig. 2. Percentages of Saipan soil groups and land 
types. 
Climate 
Saipan at 15° north latitute is within the 
zone of tropical climates with year-round high 
temperatures (Reed, 1941). 
Mean monthly temperatures range from 82 
to 86°F. Absolute minima and maxima are 
within 10 to 15 degrees of the mean tem- 
peratures (Fig. 3). 
A weak dry season (according to criteria 
of Mohr, 1944) occurs in March and April. 
Fig. 3. Mean monthly temperatures of Saipan Island, 
Average yearly rainfall is 82.5 inches (Fig. 4). 
(The foregoing climatic data are from Japan- 
ese sources for the years 1928-1937, inclu- 
sive.) 
Time 
Geomorphic and stratigraphic evidence in- 
dicates that weathering and soil formation in 
the uplands have been proceeding without 
interruption since at least the latter part of the 
Pleistocene period. Presence of marine sedi- 
ments in the Tagpochau limestone indicates 
encroachment of the sea upon the land mass 
during the Miocene period. However, since 
probably late Pleistocene time and the uplift 
of the Mariana limestone, no interruptions 
in weathering and soil-forming processes on 
the uplands of the island have taken place. 
It may then be concluded that soil develop- 
ment in the upland areas has been continuous 
for more than 25,000 years. 
Vegetation 
The original vegetation of Saipan, inferred 
to have consisted of fairly dense forests and 
some savanna-like areas of minor extent, was 
greatly decimated by extensive clearing for 
sugar cane culture during the period of Jap- 
anese control. 
Fig. 4. Mean monthly rainfall of Saipan Island. 
