8 
the disintegration has been so complete that scarcely a trace of 
unaltered lava can be detected in the soil. 
The soils range from 6 inches to many feet in depth. After a few 
years of cultivation but little demarcation between the soil and the 
subsoil is left, except in locations of heavy rainfall. The humus con- 
tent in passing downward decreases slowly, but the fertility in the 
drier sections is not greatly different for many feet below the surface. 
Where the drainage and aeration conditions are suitable, plant roots 
penetrate to great depths, and there is every indication that the plant 
food is as available several feet below as on the surface. No inju- 
rious effects, such as commonly follow the turning up of inert subsoil, 
are produced in the drier sections by plowing to the depth of 30 inches. 
PHYSICAL PROPERTIES. 
It is recognized that the physical properties of Hawaiian soils 
demand far more attention than usual; and it seems that purely 
physical factors within the control of the farmer are probably more 
important than the chemistry involved. The difficulties met with 
in the maintenance of suitable tilth, the rapidity with which the soil 
becomes closely compacted following rains, the lack of drainage and 
aeration, and the striking effects of green manuring and soil burning 
are all probably explainable in large part on physical grounds. 
MECHANICAL CLASSIFICATION. 
No attempt will be made to classify completely the soils of every 
section; in general, however, they may be divided into clay, silt, 
sandy, and humus soils. The clay type is the most abundant and 
in some instances contains unusually large amounts of clay, ranging 
as high as 50 per cent. The upland soils of Oahu, with the exception 
of the manganiferous and titaniferous areas, belong to the heavy 
clay type. The subsoils usually contain still more clay. In these 
sections practically no sand or gravel occurs, and the humus content 
is comparatively low. The soils of windward Oahu contain some- 
what less clay than the above and more silt and gravel, and are con- 
sequently less difficult to till, but the subsoils contain higher per- 
centages of clay and much less organic matter than the surface soils. 
The manganiferous and titaniferous soils, above referred to, are 
silty in character, while small areas of arable land in some localities 
around the coast on the leeward side of Oahu resemble adobe. 
The Haiku district of Maui is composed largely of clay and clay 
loam soils with somewhat more humus than on Oahu. The Kula 
district is characterized by a light silty soil of high humus content 
which is several feet deep in some places. The Nahiku soils are 
high in humus and contain much stone and gravel. The soils of 
