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BOOK II
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25
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while
the earthy varieties are smooth or intermediate. Marls differ in form.
Some form crusts, usually earthy and rarely stony. Tufaceous varieties
are porous, sometimes with openings like pipes that extend through the
entire body. The purer the marl the better it is for fertilizing and
the harder it is the longer its action. Some of the hard varieties are
richer than others. Soils can be made fertile for many years by either
applying a large amount at one time or small amounts over a period of
time. Softer varieties are best for dry soils, harder varieties,
arenaceous, tufaceous, or stony, for moist soils. In Greater Germany
only the farmers in Saxony use it. Some of the fields in Thuringia and
Bohemia are too fertile. When manure is abundant the farmers prefer to
use it.
Marl
does not occur in some of our mountainous districts. It is quarried in
many places in Saxony, namely, between Mundar and Cassel, a town in
Hesse, where it has a variety of colors; an iridescent variety in
western Hildesheim near the Indersta river at the foot of a hill; white
tufaceous marl on the south side of Mt. Alfeld; red and iridescent
varieties at localities in Desterus. A pale greenish blue variety is
also found at the foot of Mt. Desterus. Two varieties are found at
Goslar, one gray, the other whiter, the latter being used to make metal
molds. Solid masses of these two varieties are split into thin sheets
by the action of frost during the winter months. Two varieties are
found between Gandersheim and Sesena, a town about five miles from the
Harz forest. One is red, the other white, both being stony, tufaceous,
and arenaceous. French and British farmers have used marl within our
times. With either a rich, porous, or intermediate soil any farmer
would profit greatly by using it since it would increase the fertility
of his soil. The Ubii,1 according to Pliny, covered their
fields with a foot of marl and then dug them up to a depth of three
feet. This same method is used today by the inhabitants of Juliers and
their neighbors. The material they use is rich although not as dense
and hard as true marl. Pliny states that a poor soil can be improved by
spreading a rich soil over it. Many believe this although it is foolish
for the poor soil is not improved as has been proven in France and
Britain. Only marl can improve the fertility of compact soil. Columella
approved the practice of his uncle in using chalk on sandy soils when
manure was not available.
I
shall now consider the earths used by potters and sculptors. They, like
the farmer, use unctuous earths but the farmer prefers porous earths
while they prefer those which are dense and semi-soft, never as hard as
marl. Both Theophrastus and Dioscorides write that some of the earths
from Samos were suitable for their needs. If dense earths are not
available the intermediate varieties are superior to the porous.
Intermediate or semi-hard clays are the best, the soft, next. Porous
clays are rarely used and those which are incoherent are valueless.
When porous varieties are
1 An ancient German people who dwelt on the east bank of the Rhine near Cologne.
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