Soils of Saipan- — McCracken 
273 
Shallow and Moderately Deep Soils 
over Limestone 
Chinen stony clay loam, the most wide- 
spread (Fig, 2) of Saipan soil series, is a stony, 
dark brown, alkaline clay loam (to light clay) 
12 to 18 inches deep over limestone (Fig. 1). 
It can be fitted into the American scheme of 
classification as a lithosol (Baldwin et aL, 
1938). 
Dandan clay loam is a friable, brown, 
slightly alkaline soil 18 to 42 inches deep over 
the younger limestone (Fig. 2). Bodies of 
this soil are located on the lower limestone 
bench levels, chiefly at southern and northern 
ends of the island. On the basis of the above- 
described properties, this soil can be classified 
as a brown forest soil (Baldwin et aL, 1938). 
By inference from observations of tropical 
soils elsewhere, this soil can be expected to 
become more acid and redder with time, ow- 
ing to increasing loss of bases and to ses- 
quioxide concentration under the continuous- 
ly high temperature and moderately high 
annual rainfall prevailing. 
Shallow and Moderately Deep Soils over 
Volcanks and Volcanically Derived Rocks 
T eo soils are firm, reddish brown or brown, 
acid, of medium to heavy textures, and aver- 
age 12 to 18 inches deep over weathered 
volcanic tuffs, sediments from volcanic rocks, 
and highly impure limestones (Fig. 1). They 
are of limited extent (Fig. 2). In the central 
hilly uplands where these soils are found, 
parent materials are highly variable within 
short distances laterally, therefore these soils 
have been mapped as a "complex” rather than 
homogeneous soil series. Because of the un- 
consolidated nature of the parent materials 
and the shallowness of the solum (A and B 
horizons), these soils may be classified as re- 
gosols (Thorp and Smith, 1949). 
Deep Soils over Limestone 
Two principal soil series were recognized 
in the deeper soils underlaid by limestone. 
These two are of essentially similar texture, 
consistence, and reaction but differ chiefly in 
subsoil color. 
Saipan clay has a dark-brown granular clay 
surface soil about 6 inches thick which is 
neutral in reaction; the subsoil is yellowish 
red to red (the former dominant), firm, plas-* 
tic, and very slightly add. Depth to limestone 
ranges from a little less than 4 to 6 feet (pro- 
file diagram, Fig. 1). This soil is found chiefly 
on colluvial slopes and in pockets in rolling 
and hilly areas of the central uplands (Fig. 6). 
This soil series is the most extensive of the 
deeper soils of the island (Fig. 2). Tables 1, 
2, and 3 show chemical analyses of soil sam- 
ples from sites apparently within areas of Sai- 
pan clay reported by Kawamura et al. (1940). 
They are of uncertain value for our use, owing 
to uncertainty of correlation of the sampling 
sites described in this paper, uncertainty as 
to laboratory procedures used due to trans- 
lation difficulties, and lack of complete hori- 
zon-by-horizon determinations for a particular 
profile. Flowever, the results do give some 
idea of developmental trends and bulk chem- 
ical composition. A silica content (whole soil) 
of about 25 per cent, a cation exchange capa- 
city near 7 milliequivalents per 100 grams of 
dry soil, and a derived silica-sesquioxide ratio 
of slightly less than unity in the subsoil are 
indicated. (The significance of these data lies 
in their use as rough approximations, within 
limits, to the degree of tropical weathering 
which has taken place and for comparison to 
soils elsewhere.) 
Chacha clay has a dark-brown granular 
surface, which is about neutral in reaction and 
averages 6 inches in thickness; the subsoil is 
of strong, brown to yellowish-brown, firm 
plastic clay, slightly acid in reaction. Average 
depth to limestone is 4 to 6 feet (profile 
diagram, Fig. 1). Subsoil colors yellower than 
in the Saipan series appear to be correlated 
to the less well-drained position of this soil 
on the level limestone plains of the eastern 
peninsula and south-central part of the island. 
However, numerous manganiferous concre- 
