25

two soils, which in their general character as well as in their pro-
ductiveness, materially differ, can show exactly the same element-
ary composition; the difference between them is only a necessary
consequence of the different mode in which the various constitu-
ents in them are united to each other. Even if we look at the
composition of "Grauwacke," a rock, which is composed of quartz
and mica, we can hardly find out a difference between its element-
ary composition and that of a fertile soil.* A body of this kind
would be very similar in composition to a loamy soil, which is
capable of producing the fairest crops; while the grauwacke, even
if we would crush it into the finest powder, would not be able to
support the life of our cultivated plants in a prosperous manner,
until it became decomposed.

ON THE PHYSICAL PROPERTIES OF THE SOIL.

We perceive by the different analyses of soil, that the most con-
siderable mass of the soil, is formed of only four substances, viz :
Silica, Oxyd of Iron, Clay and Humus, and that all others, in
comparison to the quantity of these, are present only as traces.
This is true of all soils with the only exception of those which are
characterized by a notable quantity of Carbonate of Lime and
Magnesia which they contain, (calcareous soils.) The physical
properties of soils consequently depend on the relative quantities
of those four fundamental ingredients of which they are consti-
tuted, and are, therefore, as different as the numerous proportions
may differ, in which these substances can be mixed; or by the
same relative proportion of them, as different as the various modes
of combination may differ, in which these substances are united
to each other. All these circumstances are at once considered by
the farmer's practical eye and judgment whenever he gets a soil
under examination, and they give him indeed a true and sure

* The composition of the Grauwacke is the following:
Sand and Silica - - - -          72.2

Oxyd of Aluminum, (Clay,) - - 11.7
" Iron -                                  10.4

" Calcium, (Lime,) - - 1.0
" Magnesium, (Magnesia,)-            2.3

" Potassium, (Potash,) - " } 1.0
" Sodium, (Soda,) - - }
Phosphoric acid                                      0.4

Traces of Chlorides " " " }
" " Sulphates         - -           } 1.0

' " Organic Matter and Water - }