7 
The Effect of Climate and Weather on the Soil. 
subsoil. This sometimes happens in our own country in hilly 
regions, and is not infrequent in lands of violent storms, 
especially where man has come in and removed the native 
vegetation that once afforded some measure of protection : 
thus arises the dongas of South Africa and some of the eroded 
lands of Australia. Fig. 1 is a photograph of a donga in 
Natal for which I am indebted to Dr. F. A. Hatch. Wherever 
some break in the surface of the veld allows the rain to start a 
little water course, the washing away goes on along that line. 
The break may be a natural depression, or it may result from 
clearing the veld for cultivation, or even from keeping cattle 
always to one track in passing to and from their drinking 
places. Torrential rains soon remove the soil and lead to the 
remarkable erosion shown in the illustration. 
Soil Belts and Climatic Zones. 
We have seen that right from the very commencement of 
its history the soil has been moulded by the climate, and it 
is not surprising, therefore, that parts of the earth with 
characteristic climates should also have correspondingly 
definite soils. Wherever there is a well-marked climatic 
zone we may look for a well marked soil type. Of course 
there are always subdivisions within the climatic zone arising 
out of the differences in the original rock and based therefore 
on geological grounds. But in any great classification of soils 
it is necessary to begin with the climatic zones and divide the 
soils into great groups according to these zones, then, and not 
till then, to subdivide the great groups according to the 
geological origin of the material. 
These zones can be recognised in any great continental 
area. In the great dry belt in the west of North America 
there is a scarcity of vegetation, consequently but little organic 
matter finds its way into the soil, and such as does get there 
possesses very characteristic properties. Further, the absence 
of rain leads to an accumulation of soluble substances derived 
from the breaking up of certain mineral particles, and some of 
these are directly harmful to the plant while others indirectly 
injure it by depriving it of such little soil moisture as is 
present — for plants can only take water from weak and not 
from strong solutions. Soils thus charged with salts are called 
alkali soils ; these occur sometimes in patches (often the result 
of seepage) and sometimes in great areas, but they are always 
dreaded alike by cultivators and travellers. For as they dry 
the wind blows them up into the eyes and mouth and nostrils 
till the membranes smart again : they carry no broad-leaved 
vegetation and they yield no drinking water. Patches in 
cultivated fields are marked by the failure of the plant. The 
