

376 STRUCTURAL AND FIELD GEOLOGY 
modified by the action of the wind. In Central France; 
for example, wind blowing from east or south-east is laden 
with fine dust, derived from the disintegration of the volcanic 
rocks of Mont Dore and Cantal. This dust; theremre 
contains many fertilising ingredients—notably potash and 
phosphoric acid. Brought down by rain and snow, it has 
appreciably increased the fertility of the soil of Limagne— 
each hectare of that region being estimated to receive 1000 
kilos of dust per annum. But if wind in some cases adds 
to the growth of soil and influences its character, it not 
infrequently operates adversely. The plateau of the Karst, 
between Carniola and Istria, for example, is practically devoid 
of soil—the strong winds constantly sweeping it away from 
all tracts which are not protected by forests, or sheltered 
by the configuration of the ground. In like manner, the 
mountains of Provence are denuded of soil by the mistral. 
Having recognised that all soils consist of disintegrated 
rock materials—derived either from immediately subjacent 
solid rocks or from more or less incoherent accumulations, 
under which the latter are often concealed, writers on agri- 
culture have classified soils as Sedentary and Travelled, or 
Transported. The terms are not strictly appropriate, but 
they may serve their purpose so long as we understand 
them to have reference to the nature and source of the 
materials from which the soils have been derived. It might 
obviate confusion, however, if we substituted the term Jded- 
rock sotl for sedentary soil, and adopted the term dvzft sozl 
employed by our Geological Survey in place of travelled or 
transported soil. We should thus have two tolerably well- 
defined classes of soil—one including soils derived directly 
from the bed-rock, and the other embracing every soil 
formed upon the surface of unconsolidated “superficial 
formations” of all kinds—whether glacial, alluvial, or zolian. 
1; ‘BED-ROCK SOILS 
Under ordinary conditions the soil-cap covering the bed- 
rock shows the following succession :— 
(a) Vegetable Soil or Sotl Proper.—A layer of variable thick- 
ness, but seldom thinner than two or three inches, or thicker 

