Sacramento daily record-union., 1882-04-29

to the agriculturist, as it is very seldom
that soils need to be arti6cially
supplied with magnesia. Dolomite is
double carbonate of lime and
magnesia. The basic proportions OF
this mineral differ widely, from pre-
ponderance Of lime, with little magnesia
to large quantities of magnesia, and only
traces of lime. Except as a sometimes
available source of lime, dolomite is not of
much practical Importance to the farmer.
Gypsum is hydrous sulphate OF lime.
Like limestone, it is of great value as
fertilizer and in the arts. 1t is found IN
considerable quantities in many parts OF
the civilized world. Plaster of Paris Is
simply pure unhydrous gypsum. The ag-
ricultural value of gypsum is very great,
as both of its ingredient elements-tme
and sulphuric acid-are largely needed by
soils. Probably its principal value, espe-
cially in California, is owing to the power
which it has of neutralizing alkalis. When
applied to alkali soils, in the presence OF
water, the caustic alkalis are reduced to
neutral and comparatively harmless
sulphates of the alkaline bases. More
will be said of this interesting sub
ject when we come to the con-
sideration of alkali soils. Pyrites is e
yellowish shining mineral, often found IN
perfect cubical or octahedral crystals. 1t
has been frequently mistaken for gold, and
is otter termed "fool's gold" Chemically
it is bisulphide Of iron. 1t is one of the
sources of iron in the soil, and some forms
of it are oxidized by the air with the
formation OF sulphate OF iron (green
vitrioll. Apatite or phosphorite, as it is
often termed, is mineral phosphate OF
lime, and usually containing more or less
chrorine, hourine and other substances.
1t is very generally distributed over the
earth, but is not generally found in large
masses Where such deposits are found
they are of great value as fertilizers, since,
as we all know, both of its principal con-
stituent elements, and especially phosphoric
acid, are essential ingredients of all soils.
ROCKS.
The solid mass or unbroken part of the
earth's crust is formed of rocks. These
may some times consist OF immense masses
of almost pure mineral matter, but are
most generally composed of different min.
erals. There are three distinct kinds of
rock formations-igneous, sedimentary
and metamorphic. The first are products
of fusion, and were formed by the cooling
of melted masses of earthly and mineral
matter. Such is the lava from volcanic
eruptions. The sedimentary rocks were
formed by the action of water. Mud, sand
and gravel were deposited in loose layers,
and afterwards cemented into solid rock.
1t was on account of their aqueous origin
that they were termed sedimentary rocks
Under certain conditions Of heat the sedi.
mentary rocks are changed at a tempera-
ture below the point of fusion into other
forms or notifications which are termed
metamorphic rocks. These rocks, then,
were formed by the united action of water
and heat. Rocks are again divided into
crystalline and fragmental. The first class
is subdivided into silicious and calcerous-
those in which the characteristic in
gredient is respectively silica and lime.
These are again subdivided accord.
ing to their characteristic Ingredients.
The calcerous rocks consist essentially of
limestones and dolomites. Fragmental
rocks are divided into conglomerates,
which are solid aggregations of coarse frag-
ments of many kinds OF rock sandstones,
which differ from the above in being COM
posed of small particles with a character
istic amount of silica or sand present
We also have calcerous, clayey and other
kinds of fragmental rocks, the names Of
which will themselves readily suggest their
proximate composition. We have pointed
out a few of the mineral and rock in
predients of soils simply to indicate the
line of study one would have to pursue in
order to make himself familiar with the
inorganic constituents of the soil. 1t is not
our province, even if we were able, to pre-
sent in detail the meteorological relations Of
the rock and minerals of the soil, nor is it a
subject upon which much may be learned
by simple reading. Its study, to be success
full, must be backed by fair knowledge of
geology and chemistry as well as the rudi.
ments of mineralogy.