SOILS AND SUBSOILS 391 
fZolian Soils—The most notable zolian accumulations 
are the sazd dunes of maritime districts and certain inland 
areas. As the dominant ingredient of all dunes is quartz, 
they can hardly be said to yield a soil. Nevertheless, certain 
sand-loving plants find sustenance upon them, and succeed 
in binding the loose grains together, so that eventually some 
amount of humus is accumulated, and a thin soil is formed. 
But if zwolian sand accumulations yield very poor soils, such 
is not the case with certain other wind-blown formations. 
The fine dust swept by the wind from desiccated regions, and 
distributed over adjacent tracts, may not only add to the 
fertility of soils, but under certain conditions may accumulate 
to such an extent as to conceal all bed-rock and native soil- 
caps over extensive areas. There can be little doubt that 
desert-dust has added to the fertility of the Nile Valley, 
while, according to Baron Richthofen, the massive sheets of 
loess which cover enormous tracts in China are true dust- 
deposits, gradually accumulated by the winds flowing out- 
wards from the desiccated regions of Central Asia. In 
Europe, a similar deposit occurs in the Rhine Valley and in 
the low grounds traversed by the Danube, while the extensive 
sheets of “black-earth” forming the great plains of Southern 
Russia are alsoa variety of loess. The origin of the European 
loess has been much discussed, but it seems to be now the 
general opinion that the materials of the loess were, in the first 
place, of glacial and fluvio-glacial origin. The fine sand and 
clay that resulted from glacial grinding appear to have been 
introduced to the low grounds of Europe largely by the 
flooded rivers and inundations of the Ice Age. It is thought, 
however, that wind also played an important part in the 
transport of these fine-grained materials, Northern Europe 
covered with an ice-sheet must have formed an area of high- 
pressure, from which strong winds would flow southwards. 
During the severe winter season, all the streams and rivers 
would be reduced in volume, and wide areas, no longer 
inundated, would be exposed to the disintegrating action 
of frost. The fine fluvio-glacial deposits thus pulverised 
would be ready to be swept up by strong winds, and dis- 
tributed over wide areas in Central and South-eastern Europe. 
Similarly, the fluvio-glacial accumulations of the low grounds, 

