Thus we shall expect great differences in the moisture of various soils. In some districts there is much more rain than in others, and therefore the soils get a larger supply of water. Sandy soils allow water to run through while a loam holds it like a sponge, in a loam also the water readily moves from wet to dry places. Further, water runs down hills and collects in low-lying hollows or valleys; here, therefore, the soil is moister than it is somewhat higher up. What will be the effect of these moisture differences on plants?

You must find out in two ways. Visit a soil that you know is dry—a sandy, gravelly or chalky soil in a high situation—and look carefully at the plants there, then go to some moister, lower ground and see what the plants show. You cannot be quite certain, however, that anything you see is simply due to water supply, because there may be other differences in the soil as well. So you must try the second method, and that is to find out by experiments what is the effect of varying {69} quantities of water on the plant growth. Both methods must be used, but it may be more convenient to start the experiments first, and while they are going on to collect observations in your rambles.



Fill four glazed pots with dry soil: keep one dry; one only just moist; the third is to be very moist and should be watered more frequently than the second; and the fourth is to be kept flooded with water, any way out being stopped up. Sow wheat or mustard in all four and keep out of the rain. The result of one experiment with mustard is shown in Fig. 32. Where no water was supplied there was no growth and the seeds remained unaltered. Where only little water was supplied (Pot 16) the plants made some growth, but not very much: the leaves were small and showed no great vigour; {70} where sufficient water was given (Pot 3) the plants grew very well and had thick stems and large leaves; where too much water was given (Pot 15) the plants were very sickly and small.

The weights were:—

Green weight After drying

Plants with too much water 3.9 0.5

" " too little water 5.3 0.9

" " a nice quantity of water 17.7 2.6

Fig. 33 shows two pots of wheat, one kept only just sufficiently moist for growth, the other kept very moist but not too wet. You can see what a difference there is; in the drier pot the leaves are rather narrow and the plants are small, in the moister pot the leaves are wide and the plants big. But there was also another difference that the photograph does not bring out very well—the plants in the rather dry soil were, as you can see, in full ear, ripe and yellow, while those in the very moist soil were still green and growing. We see then

(1) that on moist soils there is greater growth than on dry soils, but the plants do not ripen so quickly;

(2) in very wet soils mustard—and many other plants also—will not grow.

Water is not itself harmful. It is easy to grow many plants in water containing the proper food, but air must be blown through the water at frequent intervals. In the water-logged soil of Pot 15 the trouble arose not from too much water but from too little air. Air is wanted because plants are living and {71} breathing in every part, in the roots as well as in the leaves.



Now turn to what you have seen in your walks. You would probably notice that on the drier, sandy or gravel ground there was nothing like as great a growth of grass or of other plants as on the moister soil. This is so much like what we found in the pot experiments that we shall not be wrong in supposing that the difference in water supply largely accounted for the difference in growth. But you may also have noticed something else. Plants in the drier soil have generally {72} narrow leaves and the grasses are rolled up and fine, whilst those on the damp soil, including the grasses, have usually broad leaves. Thus in the dry sandy soil you may find broom, spurrey, sheep's fescue, pine trees, all with narrow leaves; whilst on the moister soil you may find burdock, primroses, cocksfoot and other broad-leaved plants. Figs. 34 a and b show some plants we found on a dry, gravelly patch on Harpenden common, and on a moist loam in the river valley below.



{73}

Before we can account for this observation, we must ascertain a little more closely what becomes of the water the plant takes up. It certainly does not all stay in the plant, and the only way out seems to be through the leaves. Put a test tube on the leaf of a growing plant and fix a split cork round the stem: leave in sunlight for a few hours and notice that water begins to collect in the test tube (Fig. 35). The experiment shows that water passes out of the plant through the leaves.



This experiment was first made by Stephen Hales, and described by him thus in 1727: "Having by many {74} evident proofs in the foregoing experiments seen the great quantities of liquor that were imbibed and perspired by trees, I was desirous to try if I could get any of this perspiring matter; and in order to do it, I took several glass chymical retorts, b a p [Fig. 36] and put the boughs of several sorts of trees, as they were growing with their leaves on, into the retorts, stopping up the mouth p of the retorts with bladder. By this means I got several ounces of the perspiring matter of vines, figtrees"—and other trees, which "matter" Hales found to be almost pure water. The test tube experiment should now be made with a narrow-leaved grass like sheep's fescue and with a wide-leaved grass like cocksfoot. You will find that wide-leaved plants pass out more water than those with narrow leaves, and hence wide-leaved plants occur in damp situations or on damp soils like loams and clays, while narrow-leaved plants can grow on dry, sandy soils.



Another thing you will notice is that fields lying at the side of a river and liable to be flooded, and fields {75} high up in wet hill districts, are covered with grass. In a clay country there is also a great deal of grass land and not much ploughed land; if you live where there is much clay you can easily discover the reason. Clay becomes very wet and sticky when rain falls, and very hard in dry weather: it is, therefore, difficult to cultivate. Farmers cannot afford to spend too much money on cultivation, and so they prefer grass, because once it is established it goes on indefinitely and does not want ploughing up and re-sowing. And besides, farmers have learned by experience that grass can tolerate more water and less warmth than most other English crops. There is much more grass land in those parts of England where the rainfall is high and the temperature rather {76} low—e.g. the northern parts of England—than in the eastern counties where the rainfall is low.



The difference in water supply, therefore, leads us to expect the following differences between sandy soils and clays or loams:—

On sandy soils (the water content being small) the wild plants and trees usually have small leaves. Cultivated plants do not give very heavy crops, but they ripen early.

On clay soils (the water content being good) wild plants and trees usually have larger leaves. Cultivated plants give good crops, but they ripen rather late. If the water content is too good or the clay is too sticky the land is generally put into grass.



Plants require to be sufficiently warm. Some like tropical heat and can only be grown in hot houses; others can withstand a certain amount of cold and will grow up on the mountains. Our common cultivated crops come in between and will not grow in too cold or exposed a situation; thus you find very little cultivated land 800 ft. above sea level, and not usually much above 500 ft. At this height it is left as grass land, and higher up as woodland, moor, or waste land. Grass requires less warmth and can therefore grow at greater heights than many other crops. If you start at the top of a hill in Derbyshire, and walk down, you will see that the top is moorland, lower down comes grass land, still lower you may find arable land, and if the valley is damp you will find more grass at the bottom. Figs. 37 and 38 show typical views of the hill slopes further south: they are taken near Harpenden. The top of the hill in each case is over 400 ft. above sea level, and has never been thought worth cultivating, but has always been left as {78} wood because it is too exposed for farm crops. On the lower slopes the arable fields are seen, while at the bottom bordering the river is rough grass land, shown in Fig. 39. The top is too cold and windy, and the bottom too wet, to be worth cultivating.



As the plant root is alive it wants air. The effect of keeping air out can be seen by sowing some barley or onion seeds in the ground and then pouring a lot of water on and plastering the soil down with a spade. Sow another row in nicely crumbled soil, not too wet, press the seeds well in, but do not plaster the soil. This second lot will generally do much better than the first. If the ground round a plant is frequently trodden so that it becomes very hard the plant makes much less growth than if the soil were kept nice and loose. A good gardener takes very great pains in preparing his ground before he sows his seeds, and he is careful that no one should walk on his beds lest his plants should suffer.

SUMMARY. We may now collect together the various things we have learnt in this chapter. Plants require water, air, warmth, food, and light, and they will not grow if harmful substances are present. The rain-water that falls remains for some time in the soil, and does not at once run away or dry off: water can also move from wet to dry places in the soil. Therefore the plant does not need rain every day, but can draw on the stock in the soil during dry weather. A sandy soil is usually drier than a loam or a clay, especially if it lies rather high: plants growing on a sandy soil make less growth and have narrower and smaller leaves than those on a moister soil.

Situations more than five or six hundred feet above sea level are, in England, as a rule, too bleak and {80} exposed for the ordinary cultivated crops. Such land is, therefore, either grass land, moorland, downland or woodland.

The roots of plants are living and require air. The soil must not be trodden too hard round them or air cannot get in, nor can it if too much water is present.

Grass can put up with more water and less warmth than most cultivated crops.



Instances of these facts may be found in going down any hill 500 ft. or more in height: the top is usually wood or waste, being too cold for crops, below this may come grass land, lower still arable land. It is both warmer and moister in the valley (since water runs down hill), and so we can account for the proverbial fertility of valleys. But just near the river, if there is one, the ground may be too wet for crops, and therefore grass is grown. Clay land that is rather too wet to plough is usually left in grass.



{82}

CHAPTER IX

CULTIVATION AND TILLAGE

Apparatus required.

Plot experiments, hoeing and mulching. Thermometer. Soil sampler (Fig. 42, p. 88). This tool consists of a steel tube 2 in. in diameter and 9 in. long, with a slit cut along its length and all the edges sharpened. The tube is fixed on to a vertical steel rod, bent at the end to a ring 2 in. in diameter, through which a stout wooden handle passes. It is readily made by a blacksmith.

Farmers and gardeners throughout the spring, summer and autumn, are busy ploughing or digging, hoeing or in other ways cultivating the soil. Unless all this is well done the soil fails to produce much; the sluggard's garden has always been a by-word and a reproach. In trying to understand why they do it we must remember that plant roots need water, warmth and air; if the soil is too compact or if there is too much water the plant suffers, as we have seen.



One great object of cultivation is, therefore, to prevent the soil being too compact and too wet. After the harvest the farmer breaks up his ground with a plough and then leaves it alone till seed time (Fig. 40). A gardener does the same thing with a fork in his kitchen garden—he cannot very well elsewhere, or the plant roots might {83} become too cold. If there is frost during the winter both farmer and gardener are pleased because they say the frost "mellows" the ground; you can see what they mean if you walk on a frosty morning over a ploughed field. The large clods of earth are no longer sticky, they already show signs of breaking up, and if they are not frozen too hard can easily be shattered by a kick. The change has been brought about in exactly the same way as the bursting of water-pipes by frost. When water freezes it expands with enormous force and bursts open anything that confines it; water freezing in the pores of the soil forces the little fragments apart. This action is so important that further illustrations should be looked for. A piece of wet chalk left out on a frosty night often crumbles to pieces. It is dangerous {84} to climb cliffs in the early spring because pieces of rock that have been split off during the winter frosts by the expanding water may easily give way. Frost plays havoc with walls built of flints and with old bricks that are beginning to wear. If there are several frosts, with falls of rain or snow and thaws coining in between, the soil is moved about a good deal by the freezing and melting water. Bulbs and cuttings are sometimes forced out of the ground, whilst grass and young wheat may be so loosened that they have to be rolled in again as soon as the weather permits. When the ground has been dug in autumn and left in a very rough state all this loosening work of the frost is very much helped, because so much of the soil may become frozen. If in spring you dig a piece of land that has already been dug in autumn, and then try digging a piece that has not, you will find the first much easier work than the second in all but very sandy soils.

A little before the seeds are sown, the soil has to be dug or cultivated again so that it may become more level and broken into smaller pieces. The farmer then harrows and the gardener rakes it, and it becomes still finer. Very great care is bestowed on the preparation of the seed bed, and it will take you longer to learn this than any other part of outdoor gardening. The soil has to be made fine and dry, and no pains must be spared in getting it so.

When at last the soil is fine enough the seed is put in. But it is not enough simply to let the seed tumble into the ground. It has to be pressed in gently with a spade or a roller, not too hard or the soil becomes too sticky. Fig. 41 shows this operation being carried out on the farm. Then the soil should be left alone.



{86} If you watch an allotment holder who grows onions really well working away at his seed-bed you will see what a beautifully fine tilth he gets. If you try to do the same you will probably fail; his seeds will be up before yours and will grow into healthier plants. Only after long practice will you succeed, and then you will have mastered one of the great mysteries of gardening.

As soon as the plants are up they have to be hoed, and the more often this is done the better. Hoeing has several useful effects on the soil; during summer time some experiments may be made to find out what these are. A piece of ground is wanted that has got no crop on it. Set out three strips each six feet wide and six feet long, leave one entirely alone, hoe the second once a week, and the third three times a week; put labels on so that no mistake can arise. The surface of the untouched plot becomes very compact and glazed in appearance; the other soils look nice and crumbly. Take the temperature of the soils by placing a thermometer into it at various depths—half inch, three inches, and six inches—also take the temperature of the air; enter up the results as in the table, which shows what happened at Harpenden.

Air Date temperature Soil temperature

Hoed Hoed Untouched once three times weekly weekly

1910 June 20th 30 1/2 inch 35 31.5 31.5 3 inches 30.5 29.8 28.8 6 inches 27 26.5 24

June 27th 18 1/2 inch 17.5 17 17 3 inches 16.7 16.3 16.2 6 inches 15.8 15.5 15.6

{87}

The thermometer readings are in degrees centigrade.

Remarks. June 20th: Hot sunny day, there had been no rain since June 11th.

June 27th: Cold, cloudy day, several cold, wet days during the past week.

On the cold day there was very little difference between the plots, but on the hot day the hoed plots were cooler than the others. Now only the top inch is touched by the hoe, and so it appears that the layer thus loosened shields the rest of the soil from the sun's heat. If this is the case we ought to find that any other loose material would act in just the same way. We must, therefore, set out a fourth plot alongside the others, cover it with straw or cut grass (a cover like this is called a mulch), and take the temperature there. Some of the results were as follows:—

Air Date temperature Soil temperature

Hoed plot Mulched plot

1910 Sept. 24th 15 1/2 inch 17.5 12.25 3 inches 12.5 11.75 6 inches 12.25 11.5

Oct. 5th 17 1/2 inch 17 15.5 3 inches 16.7 15 6 inches 15.5 14.5

Remarks. Sept. 24th: Warm day after a rather cold spell. Oct. 5th: After a long spell of dry, warm weather.

The untouched plot had become smothered in weeds and could no longer be used for this experiment. The mulched soil is, however, cooler even than the hoed soil, and our expectation that mulching would keep the soil cool has turned out to be correct.

{88}



It may be expected that the hotter soil—the unhoed plot—will also be drier than the others, and this can be found out by a simple experiment. Take a sample by making a hole six indies deep with straight and not with sloping sides: this is best done by driving a tube two inches wide into the soil (Fig. 42): if you have not got such a tool you may use a trowel, but you will have to be very quick and very careful. Weigh the soil—or a part of it if you have got a great deal—then set it to dry in a warm place for three or four days. Weigh again when it is dry: the difference gives the loss of water: find what it would be in a hundred parts. Our results were:—

{89}

Date Percentage of water in the

Untouched soil Soil hoed once Soil hoed three weekly times weekly

1910 June 4th 21.1 19.5 17.9

June 20th 14.7 16.0 16.0

June 27th 19.3 18.4 20.5

Remarks. June 4th; The weather is still cold and the summer has not yet begun.

June 20th: Hot day following on some hot, dry weather.

June 27th: Rain had recently fallen.

When hoeing is done in the early part of the summer it dries the soil, and the more frequent the hoeing the drier the soil (see June 4th results). But later on, when the hot weather begins, the hoed soil loses much less moisture than the untouched plot; the latter lost 6.4 per cent. in 16 days in the top six inches, whilst the soil hoed once weekly lost 3.1 per cent., and the one hoed three times weekly lost only 1.4; the two hoed soils are now equal, and are both moister than the untouched soil. When more rain comes they get just as wet as the others: hoeing does not prevent water from sinking in, but it does prevent water from getting lost.

Our experiment has, therefore, shown us that hoeing makes a loose layer of soil which shields the rest of the soil from the sun's heat, and prevents it getting too hot or too dry. A hoed soil is cooler and moister, and therefore better suited for the growth of plant roots than an unhoed soil.

{90}

The mulch of straw or dried grass was found to have the same effect in conserving the water as the loose layer of soil obtained by hoeing. Some results were:—

Percentage of moisture in

Date Hoed soil Mulched soil

1910 Sept. 24th 19.6 20.7



These results are so important that some indoor experiments should be made to furnish more proof. Fix up three inverted bell jars with corks and bent tubes as shown in Fig. 43, fill all with dry soil well pressed down, then add water carefully till it appears in the glass tubes. Next day mark with stamp paper the level of liquid in each tube and then leave one jar {91} untouched, carefully cultivate with a penknife every two or three days the top quarter of an inch of the second, and cover the third with a layer of grass. After a week notice again the levels of the liquid and mark with paper; you find that the water has fallen most in the untouched jar, showing that more has been lost from this than from the jars covered with a mulch either of soil or of dry grass.

A slate or flat stone acts like a mulch; if you leave one on the soil for a few days in hot weather and then lift it up on a hot day you will see that the soil underneath is quite moist; you may also find several slugs or other animals that have gone there for the sake of the coolness and the moisture. Plants and trees also keep off the sun's heat and so make the soil cold and moist. Grass land is in summer and autumn, and even in early winter, cooler near the surface than bare land. At Harpenden we found:—

Soil temperature Date Grass land Bare land

1910 Sept. 24th 1/2 inch 13 17.5 3 inches 12.5 12.5 6 inches 12.5 12.25

Oct. 5th 1/2 inch 17.5 17 3 inches 15 16.7 6 inches 14.5 15.5

Even if the ground is not covered a certain amount of protection is still possible. Trees are often planted round ponds to prevent evaporation of the water. The wind helps to dry the soil very much, and a hedge {92} that shields from the wind not only protects the crop but also keeps the soil moist: a road with high hedges at each side remains wet for a long time after more exposed parts have dried. The effect on the temperature can be well seen on a day when a N.E. wind is blowing. Fix up on a piece of the experimental ground a little hedge made of small pea-stakes or brushwood, and take the soil temperature at one inch depth, both on the windward and on the leeward side. Two results were:—

Temperature at 1 inch depth—sheltered side 15.5 " " " " windward side 14

We have already seen that on the hot day, June 20th, the top half-inch of soil was hotter than the air: the mercury in the thermometer rose directly it was put into the soil. There is nothing very unusual about this; if you touch a piece of iron lying on the soil you find it hotter than the air. Lower down the soil had the same temperature as the air, and still lower it was cooler[1]. The sun's heat travels so slowly into the soil in summer that months pass before it gets far down, but then, as it takes so long to get in, it also takes a long time to get out, and it takes still longer to get either in or out if there is a mulch or if grass is growing.

During the early winter you may notice that the first fall of snow soon melts on the arable land but remains longer on the grass; towards the end of the winter, however, the reverse happens and the snow melts first on the grass. There is no difficulty in explaining this. The arable land is, as we have seen, warmer in autumn and early winter than grass land, {93} and so it melts the snow more rapidly. But during winter the grass land loses its heat more slowly, and therefore it is warmer at the end of the winter than the arable land, hence the snow melts more quickly.

In Chap. V. it was pointed out that dark coloured soils rich in humus are greatly favoured by gardeners and farmers. The value of humus can easily be shown: take a sample of soil from a garden that has for a long time been well manured and another from a field close by—next to it if you can—and find the amounts of moisture present. Two soils at Rothamsted gave the following results:—

Date April 6th May 6th July 6th Oct. 28th

Moisture in dark soil rich in humus 20.0 18.0 20.7 23.3

Moisture in lighter soil poor in humus 13.1 11.9 12.0 17.5

Humus, therefore, keeps the water in the soil and saves it from being lost.

Another beneficial effect of hoeing is to keep down weeds. Weeds overcrowd the plant, shut out light, take food and water, and occupy space. Few plants can compete against weeds, some fail very badly in the struggle. Sow two rows of maize two yards apart; keep one well hoed for a yard on each side and leave the other alone to struggle with the weeds that will grow. Fig. 44 shows the result of this experiment at St George's School. At Rothamsted a piece of wheat was left unharvested in 1882, and the plot has not been touched since; the wheat was allowed to shed its seed {94} and to grow up without any attention. Weeds flourished, but the wheat did not; the next year there was but little wheat, and by 1886 only a few plants could be seen, so stunted that one would hardly recognise them. The ground still remains untouched, and is now the dense thicket seen in Fig. 45. Most of our land would become like this if it were neglected for a few years.



{95}

Farmers occasionally leave their ground without a crop for a whole year and cultivate it as often as they can to kill the weeds. This practice is called "fallowing," and is very ancient; it is much less common now that crops like mangolds and swedes are grown, which can, if necessary, be hoed all the summer.



We have already seen (p. 69) that ordinary cultivated plants will not live in a water-logged soil. {96} Wherever there is an excess of water it must be removed before satisfactory results can be obtained. Fig. 46 shows a field of wheat in May where the crop is all but killed and only certain weeds survive on a patch of undrained land that lay wet all the winter. Draining land is difficult and somewhat expensive; trenches are first cut to a proper depth, and drain pipes are laid on the bottom, taking care that there is a gentle slope all the way to the ditch. The rain soaks into the soil and gets into the pipes, for they are not joined together like gas or water pipes, but left with little spaces in between; it then runs out into the ditch. Usually only clay soils need drainage, but occasionally sandy soils do also (see pp. 30, 106). A great deal of drainage was carried out in England between 1840 and 1860, and it led to a marked improvement in agriculture and in country life generally. There is, however, a great deal that wants doing now.



The addition of chalk or lime to soil was found in Chap. III. to improve it very much by making it less sticky and less impervious to air and water. Chalk or lime does more than this. It puts out of action certain injurious substances or acids that may be formed, and thus makes the conditions more favourable for plants and for the useful micro-organisms; farmers and gardeners express this by saying that it "sweetens the soil." A United States proverb runs: "A lime country is a rich country." Very many soils in England are improved by adding lime or chalk. There are considerable areas in the south-eastern and eastern counties where the soil is very chalky; here you find a wonderfully rich assortment of flowers and shrubs. Where there is too much chalk the soil is not fertile, because it lets water {98} through too easily, as was shown on p. 26: but for this very reason it is admirable for residential purposes.

There are some exceptions to the rule that plants need lime. Some plants will not tolerate it at all; such are rhododendrons, azaleas, foxgloves, spurrey, and broom; wherever you see these growing you may be sure that lime is absent.

Lime really differs from chalk, but changes into it so quickly in the soil that the action of both is almost, though not quite, the same.



SUMMARY. The various things we have learnt in this Chapter are:—

Autumn and winter cultivation are needed to loosen the soil so that rain can soak in and not lie about in pools, and also to facilitate working in spring.

The soil has to be broken down very finely and made rather dry for a seed bed. The seed has to be rolled in and then left entirely alone.

As soon as the little plants are up the soil must be hoed, and the more often this is done the better. Hoeing keeps the soil cool and moist in hot weather, the loose layer acting like a mulch of straw. Anything else that shields the soil from the sun or the wind has the same action but is not so effective as the mulch. Further, hoeing keeps down weeds, which successfully compete against almost any cultivated plants. Humus also prevents the loss of moisture from soils.

Drainage may be necessary to remove excess of water.

Liming or chalking the soil is beneficial, not only because of the improvements mentioned in Chap. III., but also because certain injurious substances are thereby removed. There are, however, some plants that will not tolerate lime.



[1] At great depths below the surface the temperature rises again from quite another cause.



{100}

CHAPTER X

THE SOIL AND THE COUNTRYSIDE

In this chapter we want to put together much of what we have learned about the different kinds of soil, so that as we go about the country we may know what to look for on a clay soil, a sandy soil, and so on.

We have seen that clay holds water and is very wet and sticky in winter, while in summer it becomes hard and dry, and is liable to crack badly. "It greets a' winter and girns a' summer," as one of Dr John Brown's characters said of his soil. Clay soils are therefore hard to dig and expensive to cultivate: the farmer calls them heavy and usually prefers to put them into grass because once the grass is up it lasts as long as it is wanted and never needs to be resown. But in the days when we grew our own wheat, before we imported it from the United States and other countries, this clay land was widely cultivated for wheat and beans. So long as wheat was 60/- to 100/- a quarter it was a very profitable crop, but, when some forty years ago it fell to 40/- and then lower still, the land either went out of cultivation like the "derelict" farms of Essex, or it was changed to grass land and used for cattle grazing. Great was the distress that followed; some districts indeed were years in recovering. But new methods came in: the land near London was used for dairy {101} farming, and elsewhere it was improved for grazing, and the clay districts, although completely changed, are now more prosperous again. Many of the fields still show the ridges or "lands" in which, when they grew wheat, they were laid up to let the water run away, and many of them keep their old names, but these are the only relics of the old days. The land is not, and never was, very valuable. The roads are wide, and on either side have wide waste strips cut up roughly by horse tracks, cart ruts and ant hills. Bracken, gorse, rushes, thistles and brambles grow there, and you may find many fine blackberries in September. The coarse Aira grass is found with its leaves as rough as files. The villages are often built round greens which serve as the village playground, where the boys and young men now play cricket and football, and their forefathers practised archery, played quoits and other games. On a few village greens the Maypole can still be seen, whilst the stocks in which offenders were placed are also left in some places.

The hedges are often high and straggling, and there are numerous woods and plantations containing much oak. Some of the woods are very ancient and probably form part of the primeval forests that once largely covered England. Epping Forest in Essex, the Forest of Blean and the King's Wood in Kent, have probably never been cultivated land. In the days when ships were made of oak these woods and hedges were very valuable, but now they are of little use as sources of timber. Instead they are valued for quite another reason: they afford shelter for foxes and for game birds. The clay districts are and always have been famous for fox hunting; the Pytchley, Quorn, Belvoir, {102} and other celebrated packs have their homes in the broad, clay, grassy vales of the Midlands. The vale of Blackmoor and other clay regions are equally famous. The plantations and hedgerows are fine places for primroses and foxgloves, while in the pastures, and especially the poor pastures, are found the ox-eyed daisy and quaking grass, that make such fine nosegays, as well as that sure sign of poverty, the yellow rattle. But many of these poor pastures have been improved by draining, liming, and the use of suitable manures. Although the roads are better than they were (see p. 30) they are still often bad and lie wet for weeks together in winter, especially where the hedges are high. Numerous brick and tile yards may be found and iron ore is not uncommon; in some places it is worked now, in others it is no longer worked and nothing remains of the lost industry save only a few names of fields, of ponds, or of cottages.



A sandy soil is in so many ways the opposite of a clay soil that we shall expect to find corresponding differences in the look of the country. A sandy soil does not hold water: it may get water up from the subsoil to supply the plant (see p. 66), or, if it happens to lie in a basin of clay, it may even be very wet: otherwise it is likely to be too dry for ordinary plants. We may therefore look out for two sorts of sand country, the one cultivated because there is enough water for the crops, and the other not cultivated because the water is lacking. These can readily be found.

We will study the cultivated sands first. As sand is not good plant food (p. 43) these soils want a lot of manure, and so are not good for ordinary farmers. But they are very easy to cultivate—for which reason they {104} are called light soils—and can be dug at any time; seeds can be sown early, and early crops can be got. Consequently these soils are very useful for men doing special work like fattening winter and spring sheep, or producing special crops like fruit or potatoes, and for market gardeners who grow all sorts of vegetables, carrots, parsnips, potatoes, peas, and so on. Fig. 47 is a view of a highly cultivated sandy region in Kent showing gooseberries in the foreground, vegetables behind, and a hop garden behind that again.



The uncultivated sands are sometimes not really so very different, and some of them, perhaps many of them, might be improved or reclaimed and made to grow these special crops if it were worth while. But they always require special treatment and therefore they have been left alone. In days of old our ancestors disliked them very much; "villanous, rascally heaths" Cobbett always called them. There were practically no villages and few cottages, because the land was too barren to produce enough food; the few dwellers on the heath, or the "heathen," were so ignorant and benighted that the name came to stand generally for all such people and has remained in our language long after its original meaning was lost. As there were so few inhabitants the heaths used to be great places for robbers, highwaymen, and evil-doers generally; Gad's Hill on the Watling St. between Rochester and Gravesend, Finchley Common, Hounslow Heath and others equally dreaded by travellers of the seventeenth and eighteenth centuries, were barren sandy tracts. But in our time we no longer need to dread them; we can enjoy the infinite charm of the breezy, open country with its brown vegetation, the pink blossom of the bell-shaped heath and the lilac blossom of the {106} heather, the splashes of yellow from the ragwort or the gorse and the dark pine and larch plantations. In the spring the young shoots of bracken lend a beautiful light green colour to the scene, while in the autumn the faded growth covers it all with a rich brown. People now like to live amid such surroundings, and so these heaths, that have been untouched for so long and are part of the original primeval England as it was in the days of the Britons, are becoming dotted with red bricked and red tiled villas, and are fast losing their ancient character. The heaths are not everywhere dry; there are numerous clay basins where the sand lies wet, where peat forms (see p. 37), and where marsh plants like the bog asphodel, sundew, or cotton grass can be found. In walking over a heath you soon learn to find these wet places by the colour of the grass and the absence of heather. In some places there is a good deal of wood, especially pines, larches, and silver birches: all these are very common on the Surrey sands, willows also grow in the damp places. Fig. 48 shows a Surrey heath—Blackheath—with heather, gorse and bracken; with pine-woods in the distance and everywhere some bare patches of sand. Much of the New Forest is on the sand, as also is Bournemouth, famous for its fine pine woods. Fig. 49 is a view of such woods on Wimbledon common. But elsewhere there is no wood: the peasants burn the turf, and so you find their cottages have huge fireplaces: instead of fences round their gardens or round the plantations there are walls made of turf. Such are the Dorchester heaths so finely described by Hardy in The Return of the Native and other novels. Other sands, however, are covered with grass and not with heather, and many of these have a special value {108} for golf links, especially some of the dry, invigorating sands by the seaside. The famous links at St Andrews, and at Littlestone, are examples.



In between the fertile and the barren sands come a number that are cultivated without being very good. They are much like the others, carrying a vegetation that is usually of the narrow leaved type (p. 72), and not very dense. On the road sides you see broom, heather, heath, harebells, along with gorse and bracken with milkwort nestling underneath: crested dog's tail and sheep's fescue are common grasses, while spurrey, knotwood, corn marigold, are a few of the numerous weeds in the arable fields. Gardens are easily dug, but it is best to put into them only those plants that, like the native vegetation, can withstand drought: vegetable gardens must be well manured and well limed. Fig. 50 shows some of this kind of country in Surrey, the barley field is surrounded by wood and very poor grass on the higher slopes.



It is easy to travel in a sand country because the roads dry very quickly after rain, although they may be dusty in summer. Sometimes the lanes are sunk rather deeply in the soft sand, forming very pretty banks on either side.

Loams, as we have seen (p. 2), lie in between sands and clays: they are neither very wet nor very dry: not too heavy nor yet too light: they are very well suited to our ordinary farm crops, and they form by far the best soils for general farming; wheat, oats, barley, sheep, cattle, milk, fruit and vegetables can all be produced: indeed the farmer on a good loam is in the fortunate position of being able to produce almost anything he finds most profitable. In a loam district that does not {110} lie too high the land is generally all taken up, even the roads are narrow and there are few commons. The hedges are straight and cut short, the farm houses and buildings are well kept, and there is a general air of prosperity all round. Good elms grow and almost any tree that is planted will succeed. Loams shade off on one side into sand; the very fertile sands already described might quite truly be called sandy loams. On the other side they shade off into clays; the heavy loams used to be splendid wheat soils, but are now, like clays, often of little value. But they form pleasant, undulating country, nicely wooded, and dotted over with thatched cottages; the fields are less wet and the roads are rather better than on the clays. When properly managed they make excellent grass land.

Chalky soils stand out quite sharply from all others: their white colour, their lime kilns now often disused, their noble beech trees, and, above all, the great variety of flowering plants enable the traveller at once to know that he is on the chalk. Many plants like chalk and these may be found in abundance, but some, such as foxgloves, heather, broom or rhododendrons cannot tolerate it at all, and so they will not grow.

Chalk, like sand, is dry, and the roads can be traversed very soon after rain. They are not very good, however; often they are only mended with flints, which occur in the chalk and are therefore easily obtainable, and the sharp fragments play sad havoc with bicycle tyres. The bye roads and lanes are often narrow, winding, and worn deep especially at the foot of the hills, so that the banks get a fair amount of moisture and carry a dense vegetation. Among the profusion of flowers you can find scabious, the bedstraws, vetches, ragwort, {111} figwort, and many a plant rare in other places, like the wild orchids; while the cornfields are often yellow with charlock. In the hedgerows are hazels, guelder roses, maples, dogwood, all intwined with long trails of bryony and traveller's joy. In the autumn the traveller's joy produces the long, hairy tufts that have earned for it the name of old man's beard, while the guelder roses bear clusters of red berries. The great variety of flowers attracts a corresponding variety of butterflies, moths and other insects; there are also numbers of birds and rabbits—indeed a chalk country teems with life in spite of the bare look of the Downs. The roads running at the foot of the chalk Downs and connecting the villages, and farmhouses built there for the good water supply, are particularly rich in plants because they sometimes cut into the chalk and sometimes into the neighbouring clay, sand or rock. Now and then a spring bursts out and a little stream takes its rise: if you follow it you will generally find watercress cultivated somewhere.

Besides the beech trees you also find ash, sycamore, maples, and, in the church yards, some venerable yews. Usually the chalk districts were inhabited very early: they are dry and healthy, the land can be cultivated and the heights command extensive views over the country, so that approaching enemies could easily be seen. On the chalk downs and plains are found many remains of tribes that lived there in the remote ages of the past, whose very names are now lost. Strange weapons and ornaments are sometimes dug up in the camps where they lived and worked; the barrows can be seen in which they were buried, and the temples in which they worshipped; Stonehenge itself, the best known of all these, lies on the chalk. {112} Several of the camps still keep the name the ancient Britons gave them—the Mai-dun, the encampment on the hill, changed in the course of years to Maiden, as in Maiden Hill, near Dorchester, in Dorset, Maiden Bower, near Dunstable, and so on. Some of their roads are still in use to this day, the Icknield Way (the way of the Iceni, a Belgic tribe), the Pilgrim's Way of the southern counties and others.

Even the present villages go back to very ancient times, and the churches are often seven or eight hundred years old.

In places the land is too steep or too elevated to be cultivated, and so it is left as pasture for the sheep or "sheep walk"; where cultivation is possible the fields are large and without hedges, like those shown in Fig. 51; during autumn, winter and spring there are many sheep about, penned or "folded" on the arable land, eating the crops of swedes, turnips, rape, vetches or mustard grown for them, or grazing on the aftermath of sainfoin or grass and clover. So important are sheep in chalk districts that the whole scheme of farming is often based on their requirements, but corn is also a valuable crop, and, especially in dry districts, barley, so that chalk soils are often spoken of as "sheep and barley" soils. Although the pastures are very healthy there is not generally much food or "keep" for the animals during the summer because of the dryness.



The black soil of the fen districts and elsewhere is widely different from any of the preceding. It contains, as its colour shows, a large quantity of combustible material (Chap. V.), which has a great power of holding water. These fens are therefore very wet; until they were drained they were desolate wastes: you may {114} read in Kingsley's Hereward the Wake what they used to be like in old days, and even as late as 1662 Dugdale writes that here "no element is good. The air cloudy, gross and full of rotten harrs[1]; water putrid and muddy, yea, full of loathsome vermin; the earth spongy and boggy; and the fire noisome by the stink of smoking hassocks[2]." But during the Stuart period wide ditches or drains were dug, into which the water could flow and be pumped into rivers. This reclamation has been continued to the present time, and the black soils as well as the others in the Fen districts can be made very productive.

We have seen that a change in the soil produces a change in the plants that grow on it. The flora (i.e. the collection of plants) of a clay soil is quite different from that of a sandy soil, and both are different from that of a chalk or of a fen soil. In like manner draining a meadow or manuring it alters its flora: some of the plants disappear and new ones come in. Even an operation like mowing a lawn, if carried on sufficiently regularly, causes a change. In all these cases the plants favoured by the new conditions are enabled to grow rather better than those that are less favoured; thus in the regularly mown lawn the short growing grasses have an advantage over those like brome that grow taller, and so crowd them out. When land is drained those plants that like a great quantity of water no longer do quite so well as before, while those that cannot put up with much water now have a better chance. In the natural state there is a great deal of competition among {115} plants, and only those survive that are adapted to their surroundings. You should remember this on your rambles and when you see a plant growing wild you should think of it as one that has succeeded in the competition and try to find out why it has been enabled to do so.



[1] Harr is an old word meaning sea-fog.

[2] Hassock is the name given to coarse grass which forms part of the turf burnt in the cottages.



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CHAPTER XI

HOW SOIL HAS BEEN MADE

Apparatus required.

The apparatus in Fig. 54. The under surface, of the lips of the beakers should be vaselined to prevent the water trickling down the sides.

It is not uncommon to find cliffs or crags in inland places, but they usually show one very striking difference from seaside cliffs. The seaside cliffs may be nearly vertical, but the inland cliffs are not, excepting for a little way at the top; lower down a heap of stones and soil lies piled against the face of the cliff and makes a slope up which you can climb. If you look at the cliff you can find loose fragments of it split off either by the action of freezing water (p. 83) or by other causes ready to roll down if sufficiently disturbed. So long has this been going on that a pile has by now accumulated, and has been covered with plants growing on the soil of the heap. Our interest centres in this soil; no one has carried it there; it must have been made from the rock fragments. When you get an opportunity of studying such a heap, do so carefully; you can then see how, starting from a solid rock, soil has been formed. This breaking down of the rock is called weathering.



The same change has gone on at the top of the cliff. Fragments have split off and the rock has broken {118} down into soil which stops where it is unless the rain can wash it away. If there are no cliffs where you live you can see the same kind of action in the banks of the lanes, in a disused quarry, gravel pit or clay pit. Wherever a vertical cutting has been made this downward rolling begins and a heap quickly forms, making the vertical cut into a slope. Plants soon begin to grow, and before long it is clear that soil has been made out of the fragments that have rolled down. This process is known as soil formation, but there is another always going on that we must now study. The heap does not invariably lie at the foot of the cliff. If there is a stream, river, or sea at the foot the fragments may be carried away as fast as they roll down: the differences shown in Figs. 52 and 53 between a cliff at the seaside and a cliff inland arise simply in this way. In inland districts great valleys are in course of time carved out, and at the seaside large areas of land have been washed away.

What becomes of the fragments thus carried away by the water? The best way of answering the question would be to explore one of these mountain streams and follow it to the sea, but we can learn a good deal by a few experiments that can be made in the classroom. We want to make a model stream and see what happens to little fragments of soil that fall into it.



Fix up the apparatus shown in Fig. 54. The small beaker A is to represent the narrow mountain stream, the larger one B stands for the wide river, and the glass jar C for the mouth of the river or the sea. Run water through them; notice that it runs quickly through A, slowly through B, and still more slowly through C: we want it to do this, because the stream flows quickly and the river slowly.

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Now put some soil into A. At once the soil is stirred up, the water becomes muddy, and the muddy liquid flows into B. But very soon a change sets in, the liquid in A becomes clear, and only the grit and stones are left in the bottom: all the mud—the clay and the silt—is washed into B. There it stops for a long time, and some of it will never wash out. The liquid flowing into C is clearer than that flowing into B. If you keep on putting fresh portions of soil into A you can keep B always muddy, although A is usually clear. At the end of the experiment look at the sediment in each beaker: in A it is clear and gritty, in B it is muddy. If you can get hold of some sea water put some of the liquid from C into it: very soon this liquid clears and a deposit falls to the bottom, the sea water thus acting like the lime water on p. 20.



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The experiment shows us that the fine material washed away by a quickly flowing stream is partly deposited when the river becomes wider and the current slower, and a good deal more is deposited by the action of the salt water when the river flows into the sea. The rock that crumbles away inland is spread out on the bed of the river or at its mouth.



The river Stour at Wye showed all these things so clearly that I will describe it; you must then compare it with a river that you know, and see how far the same features occur. At the bridge the stream was shallow and flowed quickly: the bottom was gritty and pebbly, free from mud, and formed a safe place for paddling. Before the bridge was built there had been {122} a ford here. But further away, either up or down, the stream was deeper and wider, flowed more slowly, had a muddy bottom, and so was not good for paddling. At one place about a mile away some one had widened out the river to form a lake, but this made the stream flow so slowly (as it was now so much wider) that the silt and clay deposited and the lake became silted up, i.e. it became so shallow that it was little more than a lake of mud. The same facts were brought out at the bend of the river. On its convex side, Fig. 55, the water has rather further to go in getting round the bend than on its concave side B, it therefore flows more quickly, and carries away the soil of the bank and mud from the bottom. But on its concave aide where it flows more slowly it deposits material. There is at the bend a marked difference in depth at the two sides. On its convex side the stream is rapid and deep, and scours away the bank; on its concave side it is slower, shallower, and tends to become silted up. Thus the bend becomes more and more pronounced unless the bank round A is protected (the other bank of course needs no protection) and the whole river winds about just as you see in Fig. 56, and is perpetually changing its course, carrying away material from one place, mixing it up with material washed from somewhere else, and then deposits it at a bend or in a pool where it first becomes a mud flat and then dry land. Some, however, is carried out to sea. We need not follow the Stour to the sea; reference to an atlas will show what happens to other rivers. Some of the clay and silt they carry down is deposited at their mouths, and becomes a bar, gives rise to shoals and banks, or forms a delta. The rest is carried away and deposited on the floor of the sea. {124} Material washed away by the sea from the coast is either deposited on other parts of the coast, or is carried out and laid on the floor of the sea. Thus a thick deposit is accumulating, and if the sea were to become dry this deposit would be soil. This has actually happened in past ages. The land we live on, now dry land, has had a most wonderful history; it has more than once lain at the bottom of the sea and has been covered with a thick layer of sediment carried from other places. Then the sea became dry land and the sediment became pressed into rock, which formed new soil, but it at once began to get washed away by streams and rivers into new seas, and gave rise to new sediments on the floor of these seas. And so the rock particles have for untold ages been going this perpetual round: they become soil; they are carried away by the rivers, in time they reach the sea; they lie at the bottom of the sea while the sediment gradually piles up: then the sea becomes dry land and the sediments are pressed into rocks again. The eating away of the land by water is still going on: it is estimated that the whole of the Thames valley is being lowered at the rate of about one inch in eight hundred years. This seems very slow, but eight hundred years is only a short time in geology, the science that deals with these changes.



Water does more than merely push the rock particles along. It dissolves some of them, and in this way helps to break up the rock. Spring water always contains dissolved matter, derived from the rocks, some of which comes out as "fur" in the kettles when the water is boiled.

Rocks are also broken up by other agents. There is nearly always some lichen living on the rock, and if you {125} peel it off you can see that it has eaten away some of the rock. When the lichen dies it may change into food for other plants.

We have learnt these things about soil formation. First of all the rocks break up into fragments through the splitting action of freezing water, the dissolving action of liquid water, and other causes. This process goes on till the fragments are very small like soil particles. Then plants begin to grow, and as they die and decay they give rise to the black humus that we have seen is so valuable a part of the soil (p. 51). This is how very many of our soils have been made. But the action of water does not stop at breaking the rock up into soil; it goes further and carries the particles away to the lower parts of the river bed, or to the estuary, to form a delta, and mud flats that may be reclaimed, like Romney Marsh in England and many parts of Holland have been. Many of our present soils have been formed in this way. Finally the particles may be carried right away to sea and spread out on the bottom to lie there for many ages, but they may become dry land again and once more be soil.

One thing more we learnt from the river Stour. Why did it flow quickly at the bridge and slowly elsewhere? We knew that the soil round the bridge was gravelly, whilst up and down the stream it was clayey. The river had not been able to make so wide or so deep a bed through the gravel as it had through the clay, and it could therefore be forded here. We knew also that there was a gravel pit at the next village on the river, where also there was a bridge and had been a ford, and so we were able to make a rough map like Fig. 57, showing that fords had occurred at the gravel {126} patches, but not at the clay places. Now it was obvious that an inn, a blacksmith's forge, and a few shops and cottages would soon spring up round the ford, especially as the gravel patch was better to live on than the clay round about, and so we readily understood why our village had been built where it was and not a mile up or down the stream. Almost any river will show the same things: on the Lea near Harpenden we found the river flowed quickly at the ford (Fig. 58), where there was a hard, stony bottom and no mud: whilst above and below the ford the bottom was muddy and the stream flowed more slowly. At the ford there is as usual a small village. The Thames furnishes other examples: below Oxford there are numerous rocky or gravelly patches where fords were possible, and where villages therefore grew up. Above Oxford, however, the possibilities of fording were fewer, because the soil is clay and there is less rock; the roads and therefore the villages grew up away from the river.



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APPENDIX

The teacher is advised to procure, both for his own information and in order to read passages to the scholars:

Gilbert White, Natural History of Selborne. Charles Darwin, Earthworms and Vegetable Mould (Murray). A. D. Hall, The Soil (Murray).

Mr Hugh Richardson has supplied me with the following list of questions, through many of which his scholars at Bootham School, York, have worked. They are inserted here to afford hints to other teachers and to show how the lessons may be varied. They should also prove useful for revising and testing the scholars' knowledge.

1. Collect samples of the different soils in your neighbourhood—garden soil, soil from a ploughed field, from a mole-hill in a pasture field, leaf mould from a wood, etc. Collect also samples of the sub-soils, sand, gravel, clay, peat.

2. Supplement your collection by purchasing from a gardener's shop some mixed potting soil and also the separate ingredients used to form such a mixture—silver sand, leaf mould, peat.

3. How many different sorts of peat can you get samples of? Peat mould, peat moss litter, sphagnum moss, turf for burning, dry moor peat?

4. Find for what different purposes sand is in use, such as mortar making, iron founding, scouring, bird cages, and obtain samples of each kind.

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Analysis of Garden Soil. About a handful of soil will be required by each pupil.

5. Describe the appearance of the soil. Is it fine or in lumps? Does it seem damp or dry? Can you see the separate particles of mineral matter? How large are these? Is there any evidence of vegetable matter in the soil?

6. Put some of the soil in an evaporating basin and over this place a dry filtering funnel. Warm the basin gently. Is any moisture given off?

7. Dry some of the soil at a temperature not greater than that of boiling water, e.g. by spreading it out on a biscuit tin lid, and laying this on a radiator. How have the appearance and properties of the soil been changed by drying?

8. Crumble some of the dried soil as finely as you can with your fingers. Then sift it through a sheet of clean wire gauze. What fraction of the soil is fine enough to go through the gauze? Describe the portion which will not pass through the gauze. Count the number of wires per linear inch in the gauze.

9. Mix some of the soil with water in a flask. Let it stand. How long does it take before the water becomes quite clear again?

10. Mix some more soil with water. Let it settle for 30 seconds only. Pour off the muddy water into a tall glass cylinder. Add more water to the remaining soil, and pour off a second portion of muddy water, adding it to the first, and so on until all the fine mud is removed from the soil. Allow this muddy water ample time to settle.

11. When the fine mud has settled pour off the bulk of the water; stir up the mud with the rest of the water; transfer it to an evaporating basin, and evaporate to dryness.

12. Does this dried mud consist of very tiny grains of sand or of some material different from sand? Can you find out with a microscope?

13. If the mud consists of real clay and not of sand it should be possible to burn it into brick. Moisten the dried mud again. Roll it if you can into a round clay marble. Leave this to dry slowly for a day. Then bake it either in a chemical laboratory furnace or in an ordinary fire.

14. Return to the soil used in Question 10, from which only the fine mud has been washed away. Pour more water on to it, shake it {130} well, and pour off all the suspended matter without allowing it more than 5 seconds to settle. Repeat the process. Collect and dry the poured off material as before. What is the material this time, sand or clay?

15. Wash the remaining portion of the soil in Question 14 clean from all matter which does not settle promptly. Are there any pebbles left? If so, how large are they, and of what kind of stone?

16. Take a fresh sample of the soil. Mix it with distilled water in a flask. Boil the mixture. Allow it to settle. Filter. Divide the filtrate into two portions. Evaporate both, the larger portion in an evaporating basin over wire gauze, the smaller portion in a watch glass heated by steam. Is any residue left after heating to dryness?

17. Take a fresh sample of soil. Spread it on a clean sand bath and heat strongly with a Bunsen flame. Does any portion of the soil burn? Is there any change in its appearance after heating?

18. To a fresh sample of soil add some hydrochloric acid. Is there any effervescence? If so, what conclusions do you draw?

19. Make a solution of soil in distilled water, and filter as before. Is this solution acid, alkaline or neutral? Are you quite certain of your result? Did you test the distilled water with litmus paper? And are you sure that your litmus does not contain excess of free acid or free alkali?

Peat.

20. Examine different varieties of peat collected (see Question 2) and describe the appearance of each.

21. Burn a fragment of each kind of peat on wire gauze. What do you notice?

22. Boil some peat with distilled water and filter the solution. What colour is it? Can you tell whether it is acid, neutral or alkaline? Evaporate some of the solution to dryness.

Out-of-doors.

23. Describe the appearance of the soil in the flower beds (a) during hard frost, (b) in the thaw which follows a hard frost, (c) after an April shower, (d) in drought at the end of summer, (e) in damp October weather when the leaves are beginning to fall.

24. Is the soil equally friable at different times of the year?

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25. In what way do dead leaves get carried into the soil?

26. Can you find the worm holes in a garden lawn? in a garden path?

27. Take a flower bed or grass plot of small but known area (say 3 yards by 2 yards) and a watering can of known capacity (say 3 gallons). Find how much water must be added to the soil before some of the water will remain on the surface. What has been the capacity of the soil in gallons per square yard?

28. Take two thermometers. Lay one on the soil, the other with its bulb 3 inches deep in the soil. Compare their temperatures at morning, noon and night.

29. Find from the 25-inch Ordnance map the reference numbers of the fields near your school. Make a list of the fields, showing for what crop or purpose each field is being used.



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INDEX

Acid waters, 40 Air in soil, 16, 70, 95

Bars in estuaries, 122 Black soils, 36 Blowing sands, 22 Bricks, 10, 16-18

Chalk, 26, 96 Chalk soils, 110-112 Clay, 6, 9-21 Clay soils, 75, 100-102 Cliffs, 116-119

Darwin's experiments, 11, 56 Deltas, 122 Drainage, 19, 96 Dwellers in the soil, 53-63

Earthworms, 54-56 Error of experiment, 48

Fallow, 14, 95 Fens, 112 Flora, 114 Fords, 126 Frost, action of, on soil, 83

Grassland, 75 Grit, 6

Hales's experiment, 73 Heaths, 104 Heavy soils, 100 Hoeing, 86-93 Humus, 36, 51, 93, 125 Hypotheses, 36

Land slips, 12 Leaf mould, 33 Light soils, 104 Lime, action of, on clay and soil, 19-21, 96-98 Lime water, 19 Loams, 2, 65, 108

Marsh gas, 40 Micro-organisms, 56-62 Moorland, 80 Mulch, 87, 90

Peat, 37-40, 130 Peat bogs, overflow of, 38 Perspiration of plants, 74 Plant food, 41-52, 62 Plant requirements, 64 Ploughing, 82 Pot experiments, 41-52, 54, 69, 71

Roads, 30-32, 101-112 Rolling the soil, 84

Sand, 6, 22-32, 41 Sand dunes, 22 Sandy soils, 68-72, 102-108 Shrinkage of clay, 10 Silt, 7 Soil sampler, 82, 88 Sowing seed, 84 Springs, 24-31, 111 Subsoil, 2, 4, 42, 48-51 Swelling of clay, 11 Swelling of peat, 38

Temperature of soil, 86-93 Tilth, 86

Van Helmont's experiment, 46 Villages, situation of, 24, 30, 126

Wastes, 101, 104 Water content of soil, 88-93 Water, movement of in soils, 65-68 Water supply and plant growth, 69-74 Weathering, 116 Weeds, 94, 97 Woodland, 80, 101

THE END