October, 1929 
The Queensland Naturalist 
47 
2. That the same rock under different climatic con- 
ditions will produce quite different soil types. 
As an example of the first rule, let us consider the 
famous Black Earth or Tschernozem which constitutes 
the great wheat-growing area of Russia and south- 
eastern Europe. In this belt the climatic conditions are 
well marked and the topographic conditions uniform. 
The soil is of wonderful uniformity over very large areas,, 
and is of a uniform thickness and texture notwithstand- 
ing the fact that the underlying rocks may be Loess, 
Cretaceous, Chalk, Jurassic Clays, or weathered granite. 
The second generalisation is well illustrated by 
granites. Under different climatic conditions similar 
granites give rise to ferruginous laterites in the wet 
tropics, to ashy podzols in the cold temperate region, and 
to black earths on the dry warm temperate plains. 
Let us consider briefly the processes at work in the 
transportation of a granite into (1) a Skeletal Soil, (2) 
a Laterite. and (3) a Podzol. 
In the first case the hard compact rock is disinte- 
grated largely as the result of purely physical actions 
such as the differential expansion of the constituent 
minerals as the result of heating of the rock surface by 
day and cooling by night. These physical processes may 
be and often are assisted by chemical processes which, 
whiie they did not bring about any important mineralo- 
gical changes in the rock, render it nevertheless more 
susceptible to the disintegrating physical processes. In 
the end a. soil is produced which is made up of the same 
minerals as the parent rock in much the same proportions. 
Such a soil is remarkably rich in plant foods, for all the 
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are still present in the soil. Hence there comes about the 
interesting fact that desert soils, which are often skeletal 
soils, on account of the great predominance of the pro- 
cesses of physical disintegration over those of chemical 
decomposition, are among the most fertile in the world. 
If water can be brought to such soils either by irrigation 
or other means, they are wonderfully prolific. * The world 
famous orchards of California illustrate these conditions. 
In the second case, conditions are very different. 
There is some difference of opinion as to the climatic 
conditions under which laterites are formed, but the 
majority verdict at the present time favours tropical con- 
ditions where the temperature is always high and where 
there is a heavy rainfall through much of the year, a state 
of affairs which Glinka describes as optimum moisture 
