There are also some very unusual types of soil in the islands. On 
Oahu highly manganiferous and titaniferous soils occur, the former 
sometimes containing almost 10 per cent manganese oxid and the 
latter as high as 35 per cent titanium dioxid (Ti0 2 ). No such soils 
are known to occur in any other country of the world. 
ORIGIN AND FORMATION. 
The soils of the Hawaiian Islands, with the exception of small 
areas near the sea, have been formed from the disintegration prod- 
ucts of basaltic lava. The lava is composed mainly of pyroxenes, 
amphiboles, and soda-lime feldspars, with small amounts of mag- 
netic oxid of iron. They are, therefore, highly ferruginous and basic. 
At the time of flow, and possibly to some extent afterwards, the 
vapors of burning sulphur act on the lava with the consequent forma- 
tion of sulphates. The frequent occurrence of gypsum is traceable 
to this cause. The most important disintegrating agent is weather- 
ing. One of the first changes which takes place in the lava is that of 
oxidation. The iron in the original lava occurs mainly in the ferrous 
state, but upon exposure to the air the normal gray color quickly 
changes to red or yellow, due to the oxidation and subsequent hydra- 
tion of the iron. Coincident with oxidation leaching takes place. 
The lime, magnesia, and soda to a large extent, and potash to lesser 
degree, are leached out by rain waters as silicates and carbonates, 
leaving behind a residue rich in iron and alumina, but much reduced 
in silica content. 
The normal lavas from the main craters seem to be quite uniform 
in composition, while the flows from the secondary craters vary in 
composition, due perhaps to mixing with weathered and partially 
decomposed material near the surface. As oxidation proceeds, the 
surface of the lava crumbles away, thus allowing rain waters free 
access to the interior, and consequently greatly increasing the rate 
of solution. Another potent agent in the formation of soils is the 
growth and subsequent decay of plant roots. Within an incredibly 
short time after a lava flow plant life gains a foothold, which, aided 
by the solvent and oxidative effects naturally going on, soon pushes 
its roots into cracks and crevices. The carbonic acid given off by 
the roots aids in the decomposition, and the excessive heat of the 
tropical sun considerably hastens the solutions and oxidations going 
on. In general, soil formation is extremely rapid in the islands. 
Much of the soil at the lower elevations has been formed by sedi- 
mentation and erosion from higher elevations. In fact there is much 
evidence that these processes account mainly for the location and 
formation of the sporadic types of manganiferous and titaniferous 
soils of Oahu. In many places, however, the soils are residual, with 
oidy slight transportation of soil material at most. In many sections 
