AN ENCYCLOPADIA 
OF HORTICULTURE. 451 
Soil—continued. 
pushing its way down from the Norwegian mountains 
into the ocean. Probably, the present German Ocean was 
then blocked with ice; and ice from Scotland extended 
over the Isle of Man, the North of Ireland, and the 
Hebrides, and a considerable distance into the Atlantic 
Ocean. As the ice pressed down from the hills, its enor- 
mous weight ground down the looser and more promi- 
nent rocks, and pushed the Soil, loose rocks, and 
stones, before it in the direction in which it travelled, 
until they were deposited in hollows, protected behind 
hills or ridges. As the climate became warmer, the ice 
diminished, till it did not reach the sea; then it gradu- 
ally receded in the lowlands, till it became restricted 
‘to the mountain valleys; and, finally, it disappeared 
completely, even from our mountains, leaving its traces 
only in markings on rocks over which it had passed, 
and in the mounds of stones and earth (moraines) left 
behind as the glaciers receded. The Soils formed before 
the Ice Age were pushed by the ice from the situations 
in which they had originated, over rocks of a different 
kind, and were so mixed together as to frequently render 
it very difficult to trace their sources; but, by this 
mixing, the Soils have often been much improved—clays, 
sands, and limestones being mingled, so as to combine 
their valuable properties. 
Vegetable Earths, or Humus, are formed in great part 
of the remains of plants, and, to a slight extent, of 
animals; and along with these is a varying amount of 
Soils of purely mineral origin (as described above). 
Cultivated Soil usually contains a good deal of Humus, 
which gives a darker hue the greater the amount of 
it in the Soil. When the organisms decay in compara- 
tively dry. earth, the resulting Soil is known as Mould; 
and any Soil containing more than 6 per cent. of organic 
remains, is called a Vegetable Mould; but the propor- 
tion of organic matter is often much higher. These 
Moulds are known as sandy, clayey, or loamy, accord- 
ing to the nature of the mineral Soil mixed with them. 
Peat is the name given to Vegetable Earths formed in 
the temperate zones, under water, or in swamps saturated 
with water. It is frequently from 5ft. to 6ft. deep, and 
in some Irish Peat-bogs it even reaches 40ft. in depth. 
It is formed by the decay of aquatic and marsh plants. 
Peat-bogs seem frequently to have originated in forests, 
where fallen trees obstructed the drainage of the surface- 
water. The ground became saturated with water, but 
the surface of the swamps then, as now, bore a luxuriant 
vegetation of marsh-plants and Bog-mosses (Sphagna), 
which decayed below, and formed new Peat, while they 
continued to grow upwards. The Peat-mosses, so plenti- 
ful in many districts, have been formed chiefly, if not almost 
wholly, since the Ice Age; they seem to be now wasting 
away from natural causes, apart from human agency, 
more rapidly than they are renewed. Newly-formed Peat 
yields in general only 1 or 2 per cent. of mineral sub- 
stances derived from the plants, and is brown, light, 
porous, and fibrous. Deeper down, the Peat becomes 
much darker and denser, and gradually loses all traces 
of its vegetable origin: the ash may reach as much as 
from 10 to 30 per cent. of its weight. Peat-bogs are 
not adapted for cultivation in their natural condition, 
although they are the favourite habitat of certain 
plants, such as many of the Heaths, Rhododendrons, and 
allied plants, and although Peat is a most useful material 
in gardening operations, being employed in the Soils 
prepared for the cultivation of many plants from the 
Cape of Good Hope and Australia, and many Mono- 
cotyledons. Peat is also an excellent material for steep- 
ing in liquid farmyard manure, either in tanks, or as 
| 
litter, to prevent the manure running to waste, the Peat | 
being afterwards used as manure, alone or in composts. | 
To render Peat-bogs fertile, the excess of water must 
be drained off, and lime, sand, and clay added. The effect 
, | 
_ there being no crevices for it to pass down. 
Soil—continued. 
of this treatment is that the Soil is warmed, and the 
hurtful organic acids are destroyed by the lime; while 
the lime, sand, and clay, together, render the Soil more 
open and pervious to gases, and prevent stagnation of 
water in it. By such treatment, Peat-bogs may, in time, 
be converted into fields or gardens, capable of yielding 
_a good return; but the labour and expense incurred in 
improvements of this kind are usually considerable. 
CLAssIFICATION. The chief kinds of Soils have been 
incidentally mentioned above, but it will be well to 
recount their more important differences. They may be 
classed according to their composition as follows: 
Sandy Soils, with not less than 80 per cent. of pure 
quartz sand; such as may be met with among the dunes 
or sandhills, along our coasts. These contain little 
nourishment for plants, are very liable to suffer from 
drought, have little cohesion, and are blown about by 
the winds; they produce light, but early, crops. Sandy 
Soils can be improved by the addition of clay, and lime 
-in the form of marl or of chalk. Turnips often do well 
in the better class of Sandy Soils; and, in wet years, 
these Soils yield a very fair produce. 
Clay Soils, chiefly composed of clay (Aluminum 
Silicate), result from the breaking down of felspars in 
granites and in rocks of similar composition, They are 
heavy, dense, and very coherent, and are very retentive 
of water; but the water is apt to stagnate in them, 
and to render them late and cold by the amount of 
evaporation from the surface, near which it remains, 
In droughts, 
plants on Clay Soils are apt to suffer, as roots cannot 
penetrate into stiff clays, or obtain water from the Sub- 
soil. These Soils contain abundance of mineral food for 
plants; but it is rendered unavailable by their stiff 
texture. When this is corrected, by the addition of 
sand, lime, ashes, or suitable manures, and when the 
stagnant water is removed, by drainage, clays become 
very fertile. 
Caleareous Soils contain above 20 per cent. of Car- 
bonate of Lime, in the form of chalk, or mixed with 
clay to form marls. These may be dry and friable, or 
(e.g., marl) may approach the clays in texture. In pro- 
ductiveness they vary greatly. They are less frequent 
than the two soils already described. 
Peaty Soils have been discussed above at sufficient 
length ; as have been also the methods of improving them. 
Vegetable Moulds (Humus) vary much in percentages 
of organic matter contained in them. They belong to the 
more fertile kinds of Soils, and are retentive of water. 
Gravelly Soils may belong to any one of the first three 
classes, seldom to the fourth. The term applies only to 
the presence of gravel or stones in Soils, without refer- 
ence to their composition. 
Loamy Soils are intimate mixtures of all the first four, 
in which the clay is under 50 per cent., and the lime 
under 5 per cent. Loams are productive and excellent 
Soils, being easily cultivated and fertile. 
SOJA. Included under Glycine (which see). 
SOLANACEZ. A rather large natural order of 
herbs, erect or climbing shrubs, or rarely trees, mostly 
inhabiting the warmer regions of the globe. Flowers 
hermaphrodite, regular or slightly irregular; calyx five 
(rarely four, six, or seven) parted, toothed, or lobed, 
gamosepalous ; corolla gamopetalous, tubular, funnel, 
salver, or bell-shaped, or rotate; limb five (rarely four, 
six, or seven) parted or lobed, the lobes equal or 
obscurely bilabiate ; stamens alternating with the corolla — 
segments, affixed to the tube; inflorescence usually 
cymose. Fruit capsular or baccate. Leaves alternate, 
the upper ones usually twin, in one instance whorled, 
entire, toothed, lobed or dissected. Of all the plants 
comprised in this order, the most useful to man is the 
