PHYSICAL PROPERTIES OF HAWAII SOILS 
cerning the origin, composition, and nature of the original parent 
material. It is sufficient here to mention that the original lava 
consists chiefly of aluminous amphiboles of the darker varieties, 
such as hornblende (silica, 40 to 51 per cent; magnesium, 10 to 23 
per cent ; calcium, 10 to 13 per cent ; aluminum, 6 to 14 per cent ; and 
iron, 12 to 20 per cent), aluminous pyroxenes such as augite and 
leucagite (silica, 49 to 52 per cent; magnesium, 13 to 18 per cent; 
calcium, 22 to 24 per cent; aluminum, 6 to 7 per cent; and iron, 
0.5 to 8 per cent), soda-lime feldspars (silica, 62 per cent; calcium, 
5 per cent; aluminum, 24 per cent; and sodium, 9 per cent), and 
small amounts of magnetite (ferric oxide, 69 per cent, and ferrous 
oxide, 31 per cent). The chemical composition of these minerals 
shows that they are highly ferruginous and contain considerable 
amounts of calcium and magnesium. The parent materials from 
different localities 
show marked simi- 
larity in chemical 
composition, and they 
differ little in this re- 
spect from volcanic 
basalts of the main- 
land. Cross (13, pp. 
62, 78) shows that the 
analogues of Hawaii 
magmas are widely 
distributed over the 
world and that "the 
analogues have been 
chosen on the basis of 
similarity in norms." 
In their physical and 
morphological char- 
acteristics they show 
conspicuous varia- 
tions giving rise, among others, to the well-known lava types of a-a 
and pahoehoe. (Figs. 1, 2, and 3.) 
While the chemical composition of the original parent lava is 
responsible to a certain extent for the composition of the resultant 
soil, weathering processes, often referred to as " laterization," play 
the principal role. Most of the known weathering agencies enter 
into soil formation to a greater or less degree, but the more impor- 
tant are temperature, rainfall, and humidity of the atmosphere. 
Under tropical temperatures decomposition and oxidation of the 
mineral constituents are rapid, and water which is present in very 
large amounts is constantly exerting its hydrolizing and solvent 
action. As a result, the basic elements, through action of the dis- 
solved carbonic dioxide in water, are leached out as carbonates and 
bicarbonates. The alkaline carbonates also react with the silica, 
forming soluble alkali silicates which are leached out. Conse- 
quently, of the remaining constituents, the sesquioxides of iron and 
alumina dominate the mineral part of the soil. The resulting soils 
are usually heavy in character, the clay fraction consisting of 
hydrated oxides of iron and alumina and double silicates of iron and 
alumina. 
Figure 3.- 
-Undecomposed lava (pahoehoe formation) show- 
ing scant vegetation 
