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of
staggered maxima
. This is another view of the same phenomenon.
The observation made for the first time in the Bourbonnais region
(Loudyi 1969) found the explanation that we gave later with the help
of simulation trials (Legros 1982). Let us give an example of a soil that,
among so many others, confirms the same law (Table 3.5). It pertains
to profile no. 108 extracted from a pedological study we had done.
Table 3.5
Staggering of the maxima in an old Albeluvisol on Mio-Pliocene
deposits of the Bourbonnais region, France (Legros and Boyer 1969).
Horizons (cm)
Clay%
FSi%
CSi%
FS%
CS%
0-8
6.8
19.1
13.6
19.2
41.2
8-20
7.2
19.8
14.9
20.5
37.4
20-35
7.9
24.2
17.4
20.0
30.3
35-55
16.9
23.6
14.8
16.3
28.1
55-80
29.0
21.6
13.6
13.6
22.1
Thus there is a favourable conformity between simulations and field
observations.
Dissolution, such as what is simulated, returns to the assumption
that the particles are attacked according to their specific surface area or,
if preferred, in accordance with the factor 1/
r
2
, where
r
is their radius
(great reduction in susceptibility to dissolution when
r
increases).
3.4.4 Washing
Argilluviation being comparable to an inverse cube law of the radius,
and dissolution to an inverse square law of the radius, it seems logical
to test a law based on 1/
r
. This will be washing (lateral). In this case
the particles will be the more easily eliminated the smaller their radius.
We have done the corresponding simulations. But we did not find real
soils whose particle-size distribution could illustrate what was obtained
through simulation. This is why we do not believe a pedogenetic
evolution of this kind takes place, even in Planosols (Chap. 8). Of course,
erosion does exist. When it takes place, it appears to equally affect clays
and silts, and even sands at the same time.
3.4.5 Summary
Dissolution preserves sandy textures whereas fragmentation rapidly
modifies them.
One of the difficulties is that it is possible to confuse argilluviation
and dissolution since, in their first stages, the textural consequences are
