AN ENCYCLOPAEDIA 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 e'nor- 

 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 forme'd 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 



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 b 

 classed according to their composition as follows: 



Sandy Soil*, 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 yearn, 

 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, 

 there being no crevices for it to pass down. In droughts, 

 plants on day Soils are apt to suffer, as roots cannot 

 penetrate into stiff clays, or obtain water from the Snb- 

 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. 



Calcareous Soils contain above 20 per cent, of Car- 

 bonate of Lime, in the form of challc, 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). 



SOLANACE.E. 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, 

 gamosepaloufl ; corolla gamopetalons, 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 



