3 
The Efeet of Climate and Weather on the Soil. 
giving rise to considerable areas of a distinct type of red soil, 
in which again there is only relatively little silica. The study 
of these changes is very incomplete, and it is not supposed that 
the original rocks were identical in all cases. But it is very 
significant that under these three sets of climatic conditions 
three distinct varieties of soil have arisen : in the temperate 
regions soils were formed characterised by great amounts of 
silica ; in tropical regions considerable areas of laterite soils 
have arisen characterised by the presence of much alumina and 
little silica ; while in sub-tropical regions there have been 
formed quantities of a third kind of soil which differs 
altogether from the other two. 
This is not the place to describe the laterite or the red soils ; 
it is sufficient to note that they are altogether different in 
character and require wholly different treatment from ours. 
The important point for our present purpose is that the soils to 
which we are accustomed and on which we have grown up owe 
part of their character to our past and present climate, for it 
was the climate that determined in part the way in which the 
rock broke down into the mineral particles of the soil. 
There is a second direction in which climate regulates the 
composition of the soil. As we have already seen, the particles 
formed from the rocks do not remain where they are formed 
but get carried away by various climatic agencies. Sometimes 
running water has been the transporting agent, sometimes ice, 
sometimes wind. Usually there was some selection and the 
particles got sorted out to some extent on the journey ; also 
they suffered change. Even where the sorting out processes 
did no more than grade the particles according to their size the 
effect was still very far-reaching. Many of the important 
agricultural properties of the soil are regulated by the size of 
the particles : large particles tend to make the soil light and 
easily worked, porous, non-retentive and early ; small particles 
tend to make it heavy, sticky, and late, retentive both of 
water and manure. Perhaps the best illustration of selection by 
the transportation medium is afforded by the famous loess soils 
of central and eastern Europe, the Mississippi valley and else- 
where. In this case wind was the transporting agent, but as 
the carrying capacity of wind is limited these soils are 
characterised by the relatively small variation in the size of 
their particles. In the northern parts of the Mississippi region 
large glaciers had brought down a great amount of drift. 
Some of this was carried for many miles by the wind and 
deposited to form new soils. The original drift material is 
very mixed containing particles ranging in size from large 
stones down to the finest clay. The loess soils, on the other 
hand, are much less mixed ; as found in Nebraska they are 
