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BOOK II
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They
distinguish one earth from another on the basis of utility and the
different uses it offers to artisans. One is useful to farmers for
nourishing and supporting plant life. Another is used by physicians,
for example, Lemnian, Samian, and Armenian earths. Sculptors and
potters use another such as the clay which is called creta by
the potters. From this each fashions and shapes his works. Some are
used by carpenters, for example red ocher which, for that reason, is
called fabrilis. Painters have used Paraetonian, Melian, and other earths. Fullers use others such as Cimolian. Silversmiths use creta argentaria and
many other earths are used by other artisans. This classification does
not consider the true nature of earths and fails to distinguish
sufficiently one earth from another. For example, Egyptian earth is
both cultivated and used as a medicament. Red ocher (rubrica) is
used by physicians, artisans, and painters. Cimolian earth is
indispensable to fullers and physicians. Therefore, if we classify
earths as medical, potter's, artisan's, etc., we have to place the same
earth in several species and genera. Since a substance cannot be
transferred from its own genus to another genus, medical earth,
potter's earth artisan's earth, etc., cannot be species. While the mass
of common people may distinguish one earth from another in this way,
the expert in natural history who must treat his subject correctly
cannot use this classification. Some earths are classified as distinct
species under genera according to the place or region where they are
found and from which they take their names, such as Samian, Eretrian,
Chian, and Selinusian. Although people sometimes add to the name
certain characteristics in which one earth is known to differ from
others, nevertheless the true character cannot be satisfactorily
described in this manner.
First
we must enumerate the principal differences of earths, next make clear
to which class each earth belongs and the district from which the name
is derived. It will be seen that I accept the common practice of giving
locality names to earths because of the lack of another name and I
believe that earths from one locality may be worthless while similar
ones from another are valuable.
An
earth, like other mineral substances, is either simple or composite. I
do not say that simple earth is free from the other elements for
scarcely any earth is found that does not contain a certain amount of
water, fire, or air but it contains no other mineral or liquid juice. A
composite earth, on the contrary, contains either one or several
minerals or may have absorbed a liquid juice. For example, ochra is
usually simple even though it has been subjected to fire and has a
certain acrid quality, as is usually the case, while Melian earth is
composite because it contains alum. Simple
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