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400 SCIENCE OE GARDENING.
constantly floating in the atmosphere, and which have made it their resting-place, begin
to vegetate ; their death, decomposition, and decay, afford a certain quantity of organisable
matter, whicli mixes with the earthy materials of the rock ; in this improved soil
more perfect plauts are capable of subsisting ; these in thcir turn absorb nourishment
from water and the atmosphere ; aud, after perishing, afford new materials to those
already provided : the decomposition of the rock still continues ; and at length, by such
slow and gradual processes, a soil is foi-med in which even forest trees can fix their roots,
and which is fitted to reward the labours of the cultivator.
1143. Soils may generally be distinguished from mere masses o f earth by their friable
texture and dark colour, and by the presence of some vegetable fibre or carbonaceous
matter. In uncultivated grounds, soils occupy only a few inches in depth on the surface,
unless in crevices, where they have been washed in by rains ; and in cultivated soils
thcir depth is generally the same as that to wliich the implements used in cultivation
have penetrated.
Sect. II. On the Nature and Nomenclature o f Soils.
1144. A ll lands capable o f cultivation is eaAQdi a surface soil resting upon
the rock or subsoil ; and this surface soil is generally composed partly of a portion of
the rock beneath, which has been decomposed by tho action of the weather, and partly
of decayed animal and vegetable substances, wliich have become accidentally mixed
witb the decomposed rock.
1145. Surface soils generaUy take their names fi-om the rocks on which they rest, and
the débris from which forms their principal component part ; soils of this nature being
generaUy easUy recognised by their colour. “ Thus,” as Morton observes, “ we find
argiUaceous soil resting on the various clay formations— calcareous soU over the chalk,
and oolitic rocks ; and siliceous soils over the various sandstones. On the chalk, the
soU is white ; on the red sandstone, it is red ; and on the sands and clays, the surface
has nearly the same shade of colour as the sub-soU.”
1146. The nomenclature o f soils o f this description is very simple, and is naturally
taken from the earth which predominates in the soU. Thus, soil in which argillaceous
matter abounds is caUed clayey soil ; that which is formed from chalk or any kind of
limestone is called calcareous ; and the sUiceous soUs are caUed sandy. I t is, however,
neeessai-y to use precision in applying those terms. Thus, as Sir H. Davy has observed,
the term sandy soU should never be applied to any soU that does not contain at least
seven-eighths of sand ; sandy soils which effervesce with acids should be distinguished
by the name of calcareous sandy soUs, to distinguish them from those that are siliceous.
The term clayey soU should not be apphcd to any land which contains less than one
sixth of impalpable earthy matter, not considerably effervescing with acids ; the word
loam should he limited to soils containing at least one third of impalpable earthy matter
copiously effervescing with acids. A soü, to be considered as peaty, ought to contain
a t least one half of vegetable matter.
1147. In cases where the earthy part o fa s o il evidently consists o fth e decomposed matter
o f one particular rock, a name derived from the rock may with propriety be applied to
it. Thus, if a fine red eaitli be found immediately above decomposing basalt, it rnay be
denominated basaltic soü. I f fragments of quartz and mica be found abundant _ in the
materials of the soil, which is often the case, it may be denominated granitic soil ; and
the same principles may be applied to other Uke instances. In general, the soüs, the
materials of which are the most various and heterogeneous, are those called alluvial, or
which have been formed fr-om the depositions of rivers ; and tbese deposits may be
designated as süiceous, calcareous, or argOJaceous ; and in some cases the term saline
may be added as a spécifie distinction, applicable, for example, at the mouths of rivers,
where their alluvial remains are overfloivn by the sea.
1148. Earths o f transportation is by Morton to those surface soils
wluch are of a ditferent nature to the rocks on which they rest. In some cases earths
ai-e washed down fr-om mountains into valleys, and even on level land in great floods,
earths may be taken up, and held in suspension by the water of a river which afterwai-ds
passes over a considerable extent of country carrying them with it, and thus they may
become deposited on rocks quite different to those from which they were originally
derived. Surface soils are also occasionally altered intentionally by the addition of other
SÜÜS which contain qualities in which they are deficient ; and it is in making these
additions judiciously that tho great a rt of culture consists.
1149. A//«ü/aZ so//which has been deposited by rivers is considered the most fertile,
as it generally consists of minute particles of soil of various kinds mixed with salts and
other minerals, and containing animal and vegetable matters in a state of complete
decay. I t is now well known that those soils are most fertile which contain the greatest
number of different ingredients ; and as alluvial soü must have been gathered by the
rivers wliich deposit it from many different lands, and as its particles must have been
m a state of minute subdivision to be held in solution by tbe water, they must of course
have been intimately mixed, and this is probably the cause of the great fertility of soils
of this description. I t raust be observed, however, that it is only sluggish rivers whieh
deposit rich alluvial soil, and that rapid currents are exceedingly injurious to tlie lands
g S o T ' produced naturally by rivers is sometimes imitated by frri-
1150. Diluvial soib. This is a tci-m generally applied to accumulations of sand and
gi-avel wluch are found in various parts of the kingdom, and which appear to have been
deposited by water, but which, have never hardened into the consistency of rocks Tliounb
there is generally some connexion between the diluvial soils and the rocks on which they
rest, this is not always the ca se ; for, as Morton observes, “ wc find in that which rerts
on the new red sandstone, not only roUcd fragments of that stratum, but also of m o s t^ f
the pnnutive rocks. These ai-e principally in the shape of boulder stones or large o-ravel
and the sand and earthy parts are mostly from the red sandstone. Tiiis accSmulation
111 the neighbourhood of Nottingham and Mansfield is, in many places, upwards of one
hundred feet m depth.” (Morton on Soib, 4th edition, p. 10.) Diluvial soils are generaily
speaking, remarkable for their poverty, but under proper management most of them
may be made productive. Thus, the tenacious clayey gravel wliich is found in Bed-
fordsMre and other places may be improved by the addition of clialk, or chalk and sand
Ih e diluvium which rests on a clayey subsoil may be improved by drainage and deen
ploughing ; and the siliceous sands of Norfolk and Suffolk may be improved by mixing
them with chalk marl. In some cases where a siliceous sand is found on a subsoil of
chalk, chalk marl, or plastic clay, the surface soil, Morton obsciwes, may be pei-manently
improved by digging up a portion of the subsoil, and spreading it over the surface
soil, though in most other cases it injures the surface soil to mix it with the subsoil.
1151. Feat soil. When successive generations of vegetables have grown and been
suffered to decay on the same soil, the vegetable matter increases so rapidly as to prevent
any mineral substance from becoming mixed with it. I f this mass of vegetable
matter accumulates in a situation where the water with which it is saturated cannot
escape, the tannin contained in the mosses included in the mass of vegetation imparts
its antiseptic properties to the water and prevents the further decay of the veo-etables
and the mass becomes what is called a peat bog. ’
Sect. III. On the Uses o f the Soil to Vegetables.
1152. Soib afford to plants a fixed abode, and also are essential to thcir nourishment
; and thus the soils in which vegetables are to be grown, must necessarily contain
cither naturally or artificially, the elements which plants require as their food, aud in
proportion as they abound in or are deficient in these elements, they ai-e fertile or the
reverse.
1153. To ascertain the fertility o f soib, it is, therefore, evident that the first step to be
taken is to discover what elements plants require as their food, ancl then to examine the
clilterent kinds of soil to sec whether they contain these elements.
1154. The food o f plants is, however, only partly derived from the soils in which they
grow, a very considerable portion of it being derived from the air.
U55. Humus, or decayed woody fibre, with the addition of water, was formerly
supposed to be all that was required for the, nourishment of plants ; and it was thouglit
that the soil acted only in retaining the water necessary for dissohing the humus, mid
the decayed animal matter, ou wliich the plants were to feed. Liebig, however, has
proved that most plants contain considerably more carbon than could be supplied to
them by the humus in the soil, and that tliey obtain this additional carbon from the
atmosphere. He also asserts, “ that humus in the foi-m in which it exists in the soil does
not yield the smallest nourishment to plants.” (Liebig's Chemistry, ^c., 4th edit., p. 7.)
The reason of this is, that humus is insoluble in water, and, therefore, cannot be taken up
by the roots of plants, unless it is first combined with potash, soda, or some other alkali
so as to change it into humic acid. ’
1156. A s a p roof that humus is not sufficient alone fo r the nourishment o f plants, it is
well known that peat or bog soil, wliich consists almost entfrely of humus, is one o fth e
most barren of all soils, and that the few plants which it produces are members of the
nish and sedge families, and consequently are plants of scai-cely any use to man. On
tlie contrai-y, the quantity of humus in fertile soils, ivhich produce the cereal grasses and
other plants used for food, has never been known to exceed ten per cent., and occasionally
it has been found as low as one per cent., or even less. Thus hiunus or vegetable mould
only becomes a fertile soil when mixed with sand, lime, or some other eai-thy substance,
which not only siipplies the plants grown in it ivith the necessary salts, but also keeps the
particles of mould open, so as to expose them to the atmospheric an-, from wliich they
extract the cai-bonic acid gas. Tliis is the reason that peat soil becomes fertile by mixing
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