2 
The Effect of Climate and Weathev \6n the Soil. 
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unknown and has yet to be written. But the main outlines 
have been discovered. The crust that formed when the earth 
first cooled sufficiently to have one, and the masses of molten 
material since extruded, soon began to break down under the 
action of the air, water, heat and cold. The particles chipped 
off did not necessarily remain where they were, but often got 
carried away by wind, water, or ice to remote places, and 
became further ground up or decomposed during the journey. 
Great quantities were washed out to sea and gradually deposited 
to form thick masses which ultimately consolidated ; when the 
sea-floor was uplifted to form dry land, these deposits appeared 
as new rocks and once again the breaking down and carrying 
away of the particles began. In some cases the newly formed 
particles remained where they were, elsewhere they were 
carried away to the sea, once more to go through the process of 
conversion into rock and subsequent re-conversion into new 
particles of a new soil. This process has not ended ; these 
changes are still going on, and every muddy stream carries 
away some of the particles of our soil to contribute to the 
formation of a new soil in untold years to come. 
There is no need to point out that these processes are 
profoundly affected by the climate ; indeed the very name 
“ weathering,” used to denote the breaking down of rock 
material under the influence of rain, air, and tempeiature, 
emphasises the vital part played by weather conditions. 
It is obvious, moreover, that the breaking down of one and 
the same rock may proceed in widely different fashion in 
places where the climatic conditions are very different, and in 
point of fact these differences have been observed. There are 
difficulties in the way of investigating this point thoroughly 
because it is not easy to find areas where the original rock is 
uniform and the climatic variations sharp. But cases have 
been observed where the differences in soil of two regions are 
greater than could be expected from the rocks alone, and these 
differences are therefore attributed to climate. In climatic con- 
ditions such as obtain in this country the rocks break up to yield 
enormous quantities of silica, the chief constituent of sand, and 
of various complex silicates, containing combinations of iron 
and aluminium, which occur largely in clay. The iron and 
aluminium compounds form only relatively small proportions 
of our soils. But in parts of the tropics, where the disintegra- 
tion processes have gone on under wholly different conditions, 
the rocks have broken down to yield soils containing only 
small amounts of silica and relatively large quantities of 
aluminium and iron oxides. These soils differ entirely from 
ours and have received a special name — laterite soils. In 
sub-tropical regions another type of disintegration has gone on, 
