Progressive Descent of Weathering Fronts, other Pedogenetic Mechanisms and Spatial Organization of Soils - Major Soil Groups of the World - page 103

in total mass. In detail, dissolution at first affects mainly the particles
of clay size, especially the fine clays, leading to an evolution towards
the base of the triangle along a straight line passing through the clay
corner (see argilluviation above). Then the silts are attacked in their turn,
whereby an inflection is seen in the trajectory towards the sand corner.
It is actually observed in nature that ancient soils have an evolution of
the skeleton grains similar to what is simulated (Fig. 3.18, right).
If we start from a collection of already sandy particles (point Y),
there is no trajectory observable by simulation. The point representing
the collection remains almost in place in the triangle. In other words,
it is impossible to create a clayey or even silty material starting from a
sand composed of particles of size 2000 µ m. When the diameter will be
reduced to 1000 µ m, this sand will continue to be counted in the coarse
sands (particle-size class 2000 µ m-200 µ m). Its size class will not have
changed in our system of measurement. However it would have lost 87.5
per cent of its mass! The chemical reduction of sands does not change
the particle-size class! The sea beats its waves on the sandy shores whose
particles are subjected to intense dissolution, which does not, however,
prevent them from remaining sandy. On firm land we may find very
mature soils (e.g. Podzols) subject to processes of intense solubilization,
but which have a stable sandy texture from one horizon to another.

Simulation Observation

B

X

C

E

Albic
Luvisol

Y

A

Sand Silt Sand Silt

Fig. 3.18 Result of a simulated dissolution; comparison with the granulodynamic path of an
actual soil of the Albeluvisol type (see Chap. 8).
Also, by disappearing first, clays raise the relative value of all the
other categories of particles when the textural class is calculated for a
sample of 100 g of the remaining material. Thus silts increase before
being caught in their turn by dissolution, which reduces their content.
Consequently, ancient soils that were subject to intense weathering
have particle-size fractions confirming, from the B horizons up to
the A horizons, passing through the E horizons, what we call the law