48 
Ihr Queensland Naturalist 
October, 1929 
conditions. Under these circumstances, owing to the very 
rapid bacterial decomposition of the organic matter very 
little humus will be present in the soil. The silicates which 
form a large part of the granite will be decomposed, and 
the potash, soda, and lime leached out in the form of 
carbonates or bicarbonates. These alkaline carbonates 
m their turn dissolve the silica, which is removed as silicic 
acid, so that all that is left of the original rock are the 
oxides of iron and aluminium. This explains why many 
of the aluminium and iron ore deposits of the world are 
superficial accumulations associated with laterites. 
An interesting point which is frequently not realised 
is that these tropical laterites are very poor soils from 
the agricultural point of view. In spite of the heavy 
cover of vegetation, the humus content i* slight. They 
are very low in lime and acid in reaction. They are de- 
ficient in potash and phosphates. Their only redeeming 
feature is their coarsely granular structure. In the third 
case where a granite yields as its soil a typical podzol, 
both the soi! processes and results are quite different. 
Podzols are soils developed under average moisture 
conditions, and occur in cold or temperate humid climates, 
They are grey ashy soils, and are found beneath the 
greater part of the coniferous forests or North America 
and Northern Europe and Asia. The climate is wet and 
cool with long winters and comparatively short summers. 
Like the laterites they are developed under a forest 
cover, but although the rainfall is less this is more than 
compensated by the smaller evaporation. Hence the soil 
conditions are actually moister. Thus aeration of the 
humus layer is poor, and decomposition relatively slow 
and of an anaerobic character, with the result that the 
humus is acid in reaction. Hence the descending waters 
we also acid, so that, unlike the case of the laterites, it 
L the iron and aluminium oxides that are removed while 
the silicic acid remains behind. There is thus formed 
the white or greyish ashy horizon which gives the podzols 
their name. Above lies a dark layer formed by the raw 
humus, and below the bleached horizon is a brownish 
layer where the iron and aluminium oxides, together with 
<’ good deal of humus is thrown out of solution either in 
the form of a continuous story layer or pan or as an 
aggregation of small concretionary bodies. The organic 
matter thus exists under the bleached zone, almost as 
though the soil profile had been turned upside down. 
Although so different in many respects, there are 
two features which the laterites and podzols have in 
