268 
PACIFIC SCIENCE, Vol. VII, July, 1953 
cene age are the oldest outcropping rocks on 
Saipan. They underlie less than one third of 
the soils. 
Dacitic (silica-rich) rocks of the Sankaku- 
yama formation are the oldest volcanic rocks. 
The dacites are exposed in two small areas 
totaling about square mile (included in the 
land type of rough stonyland on dacite (Fig. 
1). They contain about 80 per cent Si02 (Fig. 
5). 
Next younger are rocks of the Hagman and 
Densinyana formations. The Hagman rocks 
are andesitic breccias, conglomerates, tuffs, 
and flow rocks. Chemical composition of one 
of the andesites is shown in Fig. 5. The Den- 
sinyana formation is composed entirely of 
reworked, water-deposited conglomerates, 
sandstones, and breccias derived from vol- 
canic rocks. These two formations underlie 
about 8 to 10 square miles. 
Limestones underlie about two thirds of 
the soils of the island. The Tagpochau lime- 
stone of Miocene age and the Mariana lime- 
stone of Pliocene or Pleistocene age are the 
most extensive and important in relation to 
soils. 
The Tagpochau limestone makes up the 
central backbone of the island and is the most 
extensive geological unit. The Chinen soil 
and the land type of rough stonyland on 
limestone are extensive on this limestone. 
Deeper pocket-like areas are the sites of the 
Chacha and Saipan soil series. Sandstones and 
conglomerates of material derived from vol- 
canic rocks are found in the same timeplanes 
as this Miocene limestone. Soils developed 
from this material have been classified with 
the Teo series (a minor soil unit) or with the 
Akina or Dago series, according to their 
morphology. 
The Mariana limestone is found chiefly in 
rather level plains in southern and eastern 
Saipan. This limestone contains little volcanic 
contamination but does include an argilla- 
ceous (clayey) facies. The Dandan and Chinen 
soil series are developed from Mariana lime- 
stone, and some areas of Chacha and Saipan 
soils are also underlain by this material. 
Relief 
The most striking landforms of Saipan are 
the highlands of predominantly Miocene 
limestone which make a "backbone” along 
the center of the island, and bench levels in 
Miocene and younger limestone which flank 
this ridge (Fig. 1). The central ridge and the 
benches are broken in several localities by 
exposures of volcanic rocks. The central lime- 
stone ridge, most of which has a maximum 
elevation of 800-1,000 feet, rises to a point 
of 1,550 feet above sea level.This peak, known 
as Tagpochau, is the island's highest point. 
The wave-cut limestone benches are especi- 
ally well developed in the northern and eastern 
parts of the island. These bench levels are 
generally nearly level or gently sloping and 
vary from a few hundred to a few thousand 
feet in width. They are ordinarily separated 
by steep cliffs which give a giant stair-step 
aspect to regions where they are well devel- 
oped. Broad, nearly level limestone plains in 
the southern portion vary from about V 2 to 
1 mile in width. Presence of a few small sink- 
holes and caverns indicates some solution of 
the limestone in these areas. 
Soil depth and development in areas un- 
derlaid by limestone is closely related to slope. 
Shallow stony soils with little profile devel- 
opment (the Chinen series) and rough stony- 
land with little soil material are found on 
steeper slopes where geologic erosion ap- 
proximately keeps pace with soil develop- 
ment. Deeper soils with some horizon differ- 
entiation have developed on the bench levels 
and plains where geologic erosion is less 
rapid and soil material is received from ad- 
jacent steeper areas by colluviation. The deep 
soils on undulating and rolling topography 
(Saipan series) show subsoil colors of dom- 
inantly reddish hues, whereas deep soils of 
the nearly level areas (Chacha series) are of 
dominantly yellowish hue with some mottles 
