Rethinking talent decisions a tale of complexity technology and subjectivity 1st edition wiblen comp
Rethinking Talent Decisions A Tale of Complexity Technology and Subjectivity 1st Edition Wiblen
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A comparison of the several numbers opposite to each other in these three columns, shews how unlike the quantities of the different substances are, which are contained in an equal weight of the ash of these three varieties of grain. The ash of wheat contains 19 lbs. of potash in the 100 lbs., while that of oats contains only 6 lbs. In wheat are 20½ per cent. of soda, in oats only 5 per cent. Wheat also contains more sulphuric acid than either of the other grains, while barley contains a still greater predominance of phosphoric acid.
It is thus evident that a crop of wheat will carry off from the soil—even suppose the whole quantity of ash left by each the same in weight—very different quantities of potash, soda, &c. from a crop of oats. It will take more of these, of sulphuric acid, and of certain other substances, from the soil. It will, therefore, exhaust the soil more of these substances —as barley and oats will of others—hence one reason why a piece of land may suit one of these crops and not suit the others. That which cannot grow wheat may yet grow oats. Hence, also, two successive crops of different kinds of grain may grow where it would greatly injure the soil to take two in succession of the same kind, especially of either wheat or barley; and hence we likewise deduce one natural reason for a rotation of crops. The surface soil may be so far exhausted of one inorganic substance, that it cannot afford it in sufficient quantity during the present season to bring a given crop to healthy maturity, and yet may, by natural processes, be so far supplied again, during the intermediate growth of certain other crops, as to be prepared in a future season fully to supply all the wants of the same crop, and to yield a plentiful harvest.
2. The kind of inorganic matter varies with the part of the plant. Thus the grain and the straw of the corn plants contain very unlike quantities of the several inorganic constituents, as will appear by comparing the following with the preceding table:— Wheat Straw. Barley Straw. Oat Straw.
Potash, ½ 3½ 15 Soda, ¾ 1 trace. Lime, 7 10½ 2¾ Magnesia, 1 1½ ½ Alumina, 2¾ 3 trace. Oxide of Iron, 0 ½ trace. Oxide of manganese, Silica, 81 73½ 80 Sulphuric acid, 1 2 1½ Phosphoric acid, 5 3 ¼ Chlorine, 1 1½ trace
100 100 100
Not only are the quantities of the several inorganic substances kinds of straw very unlike —especially the proportions of potash, lime, and phosphoric acid in each—but these quantities are also very different from those exhibited by the numbers in the preceding table as contained in the three varieties of grain. In this difference we see, further, one reason why the same soil which may be favourable to the growth of straw may not be equally
propitious to the growth of the ear Wheat straw contains little either of potash or of soda; the ash of the grain contains a large proportion; while the ash of the oat-straw, on the other hand, contains a much larger proportion of potash than that of its own ear does. It is clear, therefore, that the roots may, in certain plants and in certain soils, succeed in fully nourishing the straw while they cannot fully ripen the ear; or contrariwise, where they feed but a scanty straw, may yet be able to give ample sustenance to the filling ear.[8]
3. The quality of the ash varies also with the soil in which it grows. This will be understood from what is stated above. Where the soil is favourable, the roots can send up into the straw every thing which the healthy plant requires; when it is poorly supplied with some of those inorganic constituents which the plant desires, life may be prolonged, a stunted or unhealthy crop may be raised, in which the kind, and perhaps the quantity, of ash left in burning will necessarily be different from that left by the same species of plant grown under more favouring circumstances. Of this fact there can be no doubt, though the extent to which such variations may take place without absolutely killing the plant, has not yet been by any means made out.
4. It varies also with the period of a plant’s growth, or the season at which it is reaped. Thus, in the young leaf of the turnip and potato, a greater proportion of the inorganic matter they contain consists of potash than in the old leaf. The same is true of the stalk of wheat; and similar differences prevail in almost every kind of plant at different stages of its growth.
The enlightened agriculturist will perceive that all the facts above stated have a perceptible connection with the ordinary processes of practical agriculture, and tend to throw considerable light on some of the principles by which they ought to be regulated. One illustration of this is exhibited in the following section.
SECTION IV.—QUANTITY OF INORGANIC MATTER CONTAINED IN AN ORDINARY CROP OR SERIES OF CROPS.
The importance of the inorganic matter contained in living vegetables, or in vegetable substances when reaped and dry, will appear more distinctly if we consider the actual quantity carried off from the soil in a series of crops.
In a four-years’ course of cropping, in which the crops gathered amount per acre to—
1st year, Turnips, 25 tons of bulbs, and 7 tons of tops.
2d year, Barley, 38 bushels of 63 lbs. each, and 1 ton of straw
3d year, Clover and Rye Grass, 1 ton of each in hay.
4th year, Wheat, 25 bushels of 60 lbs., and 1¾ tons of straw
The quantity of inorganic matter carried off in the four crops, supposing none of them to be eaten on the land, amounts to—
or, in all, about 11 cwt.—of which gross weight the different substances form very unlike proportions.
A still clearer idea of these quantities will be obtained by a consideration of the fact, that if we carry off the entire produce, and return none of it again in the shape of manure, we must or ought in its stead, if the land is to be restored to its original condition, add to each acre every four years:—
Several observations suggest themselves from a consideration of the above statements: first, that if this inorganic matter be really necessary to the plant, the gradual and constant removal of it from the land ought by-and-by to impoverish the soil of this inorganic food; second, that the more of what grows upon the land we can again return to it in manure, the less will this deterioration be perceptible; third, that as many of these inorganic substances are readily soluble in water, the liquid manure of the farm-yard, so often allowed to run to waste, carries with it to the rivers much of the saline matter that ought to be returned to the land; and, lastly, that the utility and often indispensable necessity of certain artificial manures is owing, it may be, in some districts, to the natural poverty of the land in certain inorganic substances,—but more frequently to a want of acquaintance with the facts above stated, among practical men, and to the long continued neglect and waste which has been the natural consequence.
In certain districts, the soil and subsoil contain within themselves an almost unfailing supply of some of these inorganic substances, so that the waste is long in being felt; in others they become sooner exhausted, and hence call for more care, and, when exhausted, for a more expensive cultivation, in order to replace them.
One thing is of essential importance to be remembered by the practical farmer—that the deterioration of land is often an exceedingly slow process. In the hands of successive generations a field may so imperceptibly become less valuable, that a century even may elapse before the change prove such as to make a sensible diminution in the valued rental.
Such slow changes, however, have been seldom recorded; and hence the practical man is occasionally led to despise the clearest theoretical principles, because he has not happened to see them verified in his own limited experience, and to neglect therefore the suggestions and the wise precautions which these principles lay before him.
The agricultural history of tracts of land of different qualities, shewing how they had been cropped and tilled, and the average produce in grain, hay, straw, and other crops, every five years, during an entire century, would be invaluable materials both to theoretical and to practical agriculture.
CHAPTER V.
Of Soils their Organic and Inorganic Portions Saline Matter in Soils Examination and Classification of Soils Diversities of Soils and Subsoils.
Soils consist of two parts,—of an organic part, which can readily be burnt away when the soil is heated to redness; and of an inorganic part, which is fixed in the fire, and which consists entirely of earthy and saline substances.
SECTION I.—OF THE ORGANIC PART OF SOILS.
The organic part of soils is derived chiefly from the remains of vegetables and animals which have lived and died in or upon the soil, which have been spread over it by rivers and rains, or which have been added by the hand of man for the purpose of increasing its natural fertility.
This organic part varies very much in quantity in different soils. In some, as in peaty soils, it forms from 50 to 70 per cent. of their whole weight, and even in some rich long cultivated lands it has been found, in a few rare cases, to amount to as much as 25 per cent. In general, however, it is present in much smaller proportion, even in our best arable lands. Oats and rye will grow upon a soil containing only 1½ per cent., barley when 2 to 3 are present, while good wheat soils generally contain from 4 to 8 per cent. In stiff and very clayey soils 10 to 12 per cent. may occasionally be detected. In very old pasture lands and in gardens, vegetable matter occasionally accumulates, so as to overload the upper soil.
To this organic matter in the soil the name of humus has been given by some writers. It contains or yields to the plant the ulmic and humic acids described in a previous chapter. It supplies also, by its decay, in contact with the air which penetrates the soil, much
carbonic acid, which is supposed to enter the roots and minister to the growth of living vegetables. During the same decay ammonia is likewise produced,—and in larger quantity, if animal matter be present in considerable abundance,—which ammonia is found to promote vegetation in a remarkable manner. Other substances, more or less nutritious, are also formed from it in the soil. These enter by the roots, and contribute to nourish the growing plant, though the extent to which it is fed from this source is dependent, both upon the abundance with which these substances are supplied, and upon the nature of the plant itself, and of the climate in which it grows.
Another influence of this organic portion of the soil, whether naturally formed in it, or added to it as manure, is not to be neglected. It contains,—as we have seen that all vegetable substances do,—a considerable quantity of inorganic, that is, of saline and earthy matter, which is liberated as the organic part decays. Thus living plants derive from the remains of former races buried beneath the surface, a portion of that inorganic food which can only be obtained in the soil,—and which, if not thus directly supplied, must be sought for by the slow extension of their roots through a greater depth and breadth of the earth in which they grow. The addition of manure to the soil, therefore, places within the easy reach of the roots not only organic but inorganic food also.
SECTION II.—OF THE INORGANIC PART OF SOILS.
The inorganic part of soils,—that which remains behind, when every thing combustible is burned away by heating it to redness in the open air,—consists of two portions, one of which is soluble in water, the other insoluble. The soluble consists of saline substances, the insoluble of earthy substances.
1. The saline or soluble portion.—In this country the surface soil of our fields, in general, contains very little soluble matter. If a quantity of soil be dried in an oven, a pound weight of it taken, and a
pint and a half of pure boiling rain-water poured over it, the whole well stirred and allowed to settle,—the clear liquid, when poured off and boiled to dryness, may leave from 2 to 20 grains of saline matter. This saline matter will consist of common salt, gypsum, sulphate of soda (Glauber’s salts), sulphate of magnesia (Epsom salts), with traces of the chlorides of calcium, magnesium, and potassium, and of the nitrates of potash, soda, and lime.[9] It is from these soluble substances that the plants derive the greater portion of the saline ingredients contained in the ash they leave when burned.
Nor must the quantity thus obtained from a soil be considered too small to yield the whole supply which a crop requires. A single grain of saline matter in every pound of a soil a foot deep, is equal to 500 lbs. in an acre, which is more than is carried off from the soil in 10 rotations (40 years), where only the wheat and barley are sent to market, and the straw and green crops are regularly returned to the land in the manure.[10]
In some countries, indeed in some districts of our own country, the quantity of saline matter in the soil is so great, as in hot seasons to form a distinct incrustation on the surface. This may often be seen in the neighbourhood of Durham; and is more especially to be looked for in districts where the subsoil is sandy and porous, and more or less full of water. In hot weather the evaporation on the surface causes the water to ascend from the porous subsoil: and as this water always brings with it a quantity of saline matter,—which it leaves behind when it rises in vapour,—it is evident that the longer the dry weather and the consequent evaporation from the surface continue, the thicker the incrustations will be, or the greater the accumulation of saline matter on the surface. Hence, where such a moist and porous subsoil exists in countries rarely visited by rain, as in the plains of Peru, of Egypt, or of India, the country is whitened over in the dry season with an unbroken covering of the different saline substances above mentioned.
When rain falls, the saline matter is dissolved, and descends again to the subsoil,—in dry weather it reascends. Thus the surface soil of any field will contain a larger proportion of soluble inorganic
matter in the middle of a hot season than in one of even ordinary rain; and hence the fine dry weather which, in early summer, hastens the growth of corn, and later in the season favours its ripening, does so, among its other modes of action, by bringing up to the roots from beneath a more ready supply of those saline compounds which the crop requires for its healthful growth.
2. The earthy or insoluble portion.—The earthy or insoluble portion of soils rarely constitutes less than 95 lbs. in a hundred of their whole weight. It consists chiefly of silica in the form of sand, of alumina in the form of clay, and of lime in the form of carbonate of lime. It is rarely free, however, from one or two per cent. of oxide of iron; and where the soil is of a red colour, this oxide is present in a still larger quantity. A trace of magnesia also may be almost always detected, and a minute quantity of phosphate of lime. The principal ingredients, however, of the earthy part of all soils are sand, clay, and lime; and soils are named or classified according to the quantities of each of these three they may happen to contain.
If an ounce of soil be boiled in a pint of water till it is perfectly softened and diffused through it, and, after shaking, the heavy parts be allowed to settle for a few minutes, the sand will subside, while the clay—which is in finer particles, and is less heavy—will still remain floating. If the water and clay be now poured into another vessel, and be allowed to stand till the water has become clear, the sandy part of the soil will be on the bottom of the one vessel, the clayey part on that of the other, and they may be dried and weighed separately.
If 100 grains of dry soil leave no more than 10 of clay, it is called a sandy soil; if from 10 to 40, a sandy loam; if from 40 to 70, a loamy soil; if from 70 to 85, a clay loam; from 85 to 95, a strong clay soil; and when no sand is separated at all by this process, it is a pure agricultural clay.
The strong clay soils are such as are used for making tiles and bricks; the pure agricultural clay is such as is commonly employed for the manufacture of pipes (pipe-clay).
Soils consist of these three substances mixed together The pure clay is a chemical compound of silica and alumina, in the proportion of about 60 of the former to 40 of the latter. Pure clay soils rarely occur—it being well known to all practical men, that the strong clays (tile clays) which contain from 5 to 15 per cent. of sand, are brought into arable cultivation with the greatest possible difficulty. It will rarely happen, therefore, that arable land will contain more than 30 to 35 of alumina.
If a soil contain more than 5 per cent. of carbonate of lime, it is called a marl; if more than 20 per cent., it is a calcareous soil. Peaty soils, of course, are those in which the vegetable matter predominates very much.
To estimate the lime, a quantity of the soil should be burned in the air, and a weighed portion, 100 or 200 grains, diffused through half a pint of cold water mixed with half a wine glassful of spirit of salt (muriatic acid), and allowed to stand for a couple of hours, with occasional stirring. The water is then poured off, the soil dried, heated to redness as before, and weighed: the loss is nearly all lime. [11]
The quantity of vegetable or other organic matter is determined by drying the soil well upon paper in an oven, and then burning a weighed quantity in the air: the loss is nearly all organic matter. In stiff clays this loss will comprise a portion of water, which is not wholly driven off from such soils by drying upon paper in the way described.
SECTION III.—OF THE DIVERSITIES OF SOILS AND SUBSOILS.
Though the substances of which soils chiefly consist are so few in number, yet every practical man knows how very diversified they are in character—how very different in agricultural value. Thus, in some of our southern counties, we have a white soil, consisting apparently of nothing else but chalk; in the centre of England a wide plain of dark red land; in the border counties of Wales, and on many
of our coal-fields, tracts of country almost perfectly black; while yellow, white, and brown sands give the prevailing character to the soils of other districts. Such differences as these arise from the different proportions in which the sand, lime, clay, and the oxide of iron which colours the soils, have been mixed together.
But how have they been so mixed—differently in different parts of the country. By what natural agency?—for what end?
Again, the soil on the surface rests on what is usually denominated the subsoil. This, also, is very various in its character and quality Sometimes it is a porous sand or gravel, through which water readily ascends from beneath or sinks in from above; sometimes it is light and loamy like the soil that rests upon it; sometimes stiff and impervious to water.
The most ignorant farmer knows how much the value of a piece of land depends upon the characters of the surface soil,—the intelligent improver understands best the importance of a favourable subsoil. “When I came to look at this farm,” said an excellent agriculturist to me, “it was spring, and damp growing weather: the grass was beautifully green, the clover shooting up strong and healthy, and the whole farm had the appearance of being very good land. Had I come in June, when the heat had drunk up nearly all the moisture which the sandy subsoil had left in the surface, I should not have offered so much rent for it by ten shillings an acre.” He might have said also, “Had I taken a spade, and dug down 18 inches in various parts of the farm, I should have known what to expect in seasons of drought.”
But how come subsoils thus to differ—one from the other—and from the surface soil that rests upon them? Are there any principles by which such differences can be accounted for—by which they can be foreseen—by the aid of which we can tell what kind of soil may be expected in this or that district—even without visiting the spot—and on what kind of subsoil it is likely to rest?
Geology explains the cause of all such differences, and supplies us with principles by which we can predict the general quality of the
soil and subsoil in the several parts of entire kingdoms;—and where the soil is of inferior quality and yet susceptible of improvement, the same principles indicate whether the means of improving it are likely, in any given locality, to be attainable at a reasonable cost.
It will be proper shortly to illustrate these direct relations of geology to agriculture.
CHAPTER VI.
Direct relations of Geology to Agriculture Origin of Soils Causes of their Diversity Relation to the Rocks on which they rest Constancy in the relative Position and Character of the Stratified Rocks Relation of this fact to Practical Agriculture General Character of the Soils upon these Rocks
Geology is that branch of knowledge which embodies all ascertained facts in regard to the nature and internal structure, both physical and chemical, of the solid parts of our globe. This science has many close relations with practical agriculture, and especially throws much light on the nature and origin of soils,—on the cause of their diversity,—on the kind of materials by the admixture of which they may be permanently improved,—and on the sources from which these materials may be derived.
SECTION I.—OF THE ORIGIN OF SOILS.
If we dig down through the soil and subsoil to a sufficient depth, we always come sooner or later to the solid rock. In many places the rock actually reaches the surface, or rises in cliffs, hills, or ridges, far above it. The surface (or crust) of our globe, therefore, consists everywhere of a solid mass of rock, overlaid with a covering, generally thin, of loose materials. The upper or outer part of these loose materials forms the soil.
The geologist has travelled over great part of the earth’s surface, has examined the nature of the rocks, which everywhere repose beneath the soil, and has found them to be very unlike in character, in composition, and in hardness—in different countries and districts. In some places he has met with a sandstone, in other places a limestone, in others a slate or hardened rock of clay. But a careful
comparison of all the kinds of rock he has observed, has led him to the general conclusion, that they are all either sandstones, limestones, or clays of different degrees of hardness, or a mixture in different proportions of two or more of these kinds of matter.
When the loose covering of earth is removed from the surface of any of these rocks, and it is left exposed, summer and winter, to the action of the winds and rains and frosts, it may be seen gradually to crumble away. Such is the case even with many of those which, on account of their greater hardness, are employed as building-stones, and are kept generally dry; how much more with such as are less hard, and, beneath a covering of moist earth, are continually exposed to the action of water. The natural crumbling of a naked rock thus gradually covers it with loose materials, in which seeds fix themselves and vegetate, and which eventually forms a soil. The soil thus produced partakes necessarily of the character of the rock on which it rests, and to the crumbling of which it owes its origin. If the rock be a sandstone the soil is sandy; if a claystone, it is a more or less stiff clay; if a limestone, it is more or less calcareous; and if the rock consist of any peculiar mixture of those three substances, a similar mixture is observed in the earthy matter into which it has crumbled.
Led by this observation, the geologist, after comparing the rocks of different countries with one another, compared next the soils of various districts with the rocks on which they immediately rest. The general result of this comparison has been, that in almost every country the soils have as close a resemblance to the rocks beneath them—as the loose earth derived from the crumbling of a rock before our eyes, bears to the rock of which it lately formed a part. The conclusion therefore is irresistible, that soils, generally speaking, have been formed by the crumbling or decay of the solid rocks,—that there was a time when these rocks were uncovered by any loose materials,—and that the accumulation of soil has been the slow result of the natural degradation (wearing away) of the solid crust of the globe.
SECTION II.—CAUSE OF THE DIVERSITY OF SOILS.
The cause of the diversity of soils in different districts, therefore, is no longer obscure. If the subjacent rocks in two localities differ, the soils met with there must differ also, and in an equal degree.
But why, it may be asked, do we find the soil in some countries uniform, in mineral[12] character and general fertility, over hundreds or thousands of square miles, while in others it varies from field to field,—the same farm often presenting many well marked differences both in mineral character and in agricultural value? The cause of this is to be found in the mode in which the different rocks are observed to lie, one upon or by the side of the other.
Geologists distinguish rocks into two classes, the stratified and the unstratified. The former are found lying over each other in separate beds or strata, like the leaves of a book, when laid on its side, or like the layers of stones in the wall of a building; the latter form hills, mountains, or sometimes ridges of mountains, consisting of one more or less solid mass of the same material, in which no layers or strata are any where distinctly perceptible. Thus, in the following diagram, (No. 1), A and B represent unstratified masses, in connection with a series of stratified deposits, 1, 2, 3, lying over each other in a horizontal position. On A one kind of soil will be formed, on C another, on B a third, and on D a fourth,—the rocks being all different from each other.
N . 1.
If from A to D be a wide valley of many miles in extent, the undulating plain at the bottom of the valley, resting in great part on
the same rock (2), will be covered by a similar soil. On B the soil will be different for a short space; and again at C, and on the first ascent to A, where the rock (3) rises to the surface. In this case the stratified rocks lie horizontally; and it is the undulating nature of the country which, bringing different kinds of rock to the surface, causes a necessary diversity of soil.
But the degree of inclination, which the beds possess, is a more frequent cause of variation in the characters of the soil in the same district, and even at shorter distances. This is shewn in the annexed diagram (No. 2), where A, B, C, D, E, represent the mode in which the stratified rocks of a district of country not unfrequently occur in connection with each other.
N . 2.
Proceeding from E in the plain, the soil would change when we came upon the rock D, but would then continue uniform till we reached the layer C. Each of these layers may stretch over a comparatively level tract of perhaps hundreds of miles in extent. Again, on climbing the hill-side, another soil would present itself, which would not change till we arrived at B. Then, however, we begin to walk over the edges of the beds, and the soil may vary with every new stratum (or bed) we pass over, till we gain the ascent to A, where the beds are much thinner, and where, therefore, still more frequent variations may present themselves.
Everywhere over the British islands valleys are hollowed out, as in the former of these diagrams (No. 1), by which the rocks beneath are exposed, and differences of soil produced,—or the beds are more or less inclined, as in the latter diagram (No. 2), causing still more frequent variations of the land to appear. By a reference to
these facts, nearly all the great diversities which the soils of the country present may be satisfactorily accounted for.
SECTION III.—OF THE CONSTANCY IN THE CHARACTER
AND ORDER OF SUCCESSION OF THE STRATIFIED ROCKS.
Another fact alike important to agriculture and to geology, is the natural order or mode of arrangement in which the stratified rocks are observed to occur in the crust of the globe. Thus, if 1, 2, 3, in diagram No. 1 represent three different kinds of rock, a limestone, for example, a sandstone, and a hard clay rock (a shale or slate), lying over each other, in the order here represented; then, in whatever part of the country nay, in whatever part of the world, these same rocks are met with, they will always be found in the same relative position. The bed 2 or 3 will never be observed to lie over the bed 1.
This fact is important to geology, because it enables this science to arrange all the stratified rocks in a certain invariable order,—which order indicates their relative age or antiquity,—since that which is lowest, like the lowest layer of stones in the wall of a building, must generally have been the first deposited, or must be the oldest. It also enables the geologist, on observing the kind of rock which forms the surface in any country, to predict at once, whether certain other rocks are likely to be met with in that country or not. Thus at C (diagram, No. 1), where the rock (3) comes to the surface, he knows it would be in vain, either by sinking or otherwise, to seek for the rock (1), the natural place of which is far above it; while at D he knows that by sinking he is likely to find either 2 or 3, if it be worth his while to seek for them.
To the agriculturist this fact is important, among other reasons,—
1. Because it enables him to predict whether certain kinds of rock, which might be used with advantage in improving his soil, are likely to be met with within a reasonable distance or at an accessible
depth. Thus if the bed D (diagram No. 2) be a limestone, the instructed farmer at E knows that it is not to be found by sinking into his own land, and, therefore, brings it from D; while, to the farmer upon C, it may be less expensive to dig down to the bed D in one of his own fields, than to cart it from a distant spot where it occurs on the surface. Or if the farmer requires clay, or marl, or sand, to ameliorate his soil, this knowledge of the constant relative position of beds enables him to say where these materials are to be got, or where they are to be looked for, and whether the advantage to be derived is likely to repay the cost of procuring them.
2. It is observed, that when the soil on the surface of each of a series of rocks, such as C, or D, or E, in the same diagram, is uniformly bad, it is almost invariably of better quality at the point where the two rocks meet. Thus C may be dry, sandy, and barren; D may be cold, unproductive clay; and E a more or less unfruitful limestone soil: yet at either extremity of the tract D, where the soil is made up of an admixture of the decayed portions of the two adjacent rocks, the land may be of average fertility—the sand of C may adapt the adjacent clay to the growth of turnips, while the lime of E may cause it to yield large returns of wheat.[13] Thus, to the tenant in looking out for a farm, or to the capitalist in seeking an eligible investment, a knowledge of the mutual relations of geology and agriculture will often prove of the greatest assistance. Yet how little is such really useful knowledge diffused among either class of men— how little are either tenants or proprietors guided by it in their choice of the localities in which they desire to live!
And yet here and there the agricultural practice of more or less extended districts, if not really founded upon or directed by, is yet to be explained only by principles such as those I have above illustrated. I shall mention only one example. The chalk in Yorkshire, in Suffolk, and in other southern counties, consists of a vast number of beds, which, taken all together, form a deposit of very great thickness. Now, the upper beds of the chalk form poor, thin, dry soils, producing a scanty herbage, and only under the most skilful culture yielding profitable crops of corn. The lower beds, on the contrary, are marly; produce a more stiff, tenacious, and even fertile soil; and are
found in a remarkable degree to enrich the soils of the upper chalk, when laid on as a top-dressing in autumn, and allowed to crumble under the action of the winter’s frost. Hence in Yorkshire, Wiltshire, Hampshire, and Kent, where the lower chalk covers the surface, or is found at no great depth beneath it, it is dug out of the sides of the hills, or pits are sunk for it, and it is immediately laid upon the land with great benefit to the soil. But in parts of Suffolk, where the soil equally rests upon the upper chalk, there is no other chalk in the neighbourhood, or to be met with at any reasonable depth, which will materially improve the land. The farmers find it, from long experience, to be more economical to bring chalk by sea from Kent to lay on their lands in Suffolk, than to cover them with any portion of the same material from their own farms. The following imaginary section will fully explain the fact here mentioned:—
N . 3.
Suffolk. Mouth of the Thames. Kent.
In this diagram 1 represents the London clay; 2, the plastic clay which is below it; 3, the upper chalk with flints, rising to the surface in Suffolk; and 4, the lower chalk, without flints, which is too deep to be reached in Suffolk, but which rises to the surface in Kent,—where it is abundant, is easily accessible, and whence it is transmitted across the estuary of the Thames into Suffolk.
3. The further fact that the several stratified rocks are remarkably constant in their mineral character, renders this knowledge of the order of relative superposition still more valuable to the agriculturist. Thousands of different beds are known to geologists to occur on various parts of the earth’s surface—each occupying its own unvarying place in the series. Most of these beds also, when they
crumble or are worn down, produce soils possessed of some peculiarity by which their general agricultural capabilities are more or less affected,—and these peculiarities may generally be observed in soils formed from rocks of the same age—that is, occupying the same place in the series—in whatever part of the world we find them. Hence if the agricultural geologist be informed that his friend has bought, or is in treaty for a farm or an estate, and that it is situated upon such and such a rock, or geological formation, he can immediately give a very probable opinion in regard to the agricultural value of the soil, whether the property be in England, in Australia, or in New Zealand. If he knows the nature of the climate also, he will be able to estimate with tolerable correctness how far the soil is likely to repay the labours of the practical farmer,—nay, even whether it is likely to suit better for arable land or for pasture, and if for arable, what species of white crops it may be expected to produce most abundantly.
These facts are so very curious, and illustrate so beautifully the value of geological knowledge—if not to A and B, the holders or proprietors of this and that small farm, yet to enlightened agriculturists,—to scientific agriculture in general,—that I shall explain this part of the subject more fully in a separate section. To those who are now embarking in such numbers in quest of new homes in our numerous colonies, who hope to find, if not a more willing, at least a more attainable soil in new countries, no kind of agricultural knowledge can at the outset,—I may say, even through life,—be so valuable as that to which the rudiments of geology will lead them. Those who prepare themselves the best for becoming farmers or proprietors in Canada, in New Zealand, or in wide Australia, yet leave their native land in general without a particle of that preliminary practical knowledge, which would qualify them to say, when they reach the land of their adoption, “On this spot, rather than that,—in this district, rather than that,—will I purchase my allotment, because, though both appear equally inviting, yet I know from the geological structure of the country, that here I shall have the more permanently productive soil; here I am more within reach of the means of agricultural improvement; here, in addition to the riches of the surface, my descendants may hope to derive the means of
wealth from mineral riches beneath.” And this oversight has arisen chiefly from the value of such knowledge not being understood— often from the very nature of it being unknown, even to otherwise well instructed practical men. It is not to men well skilled merely in the details of local farming, and who are therefore deservedly considered as authorities and good teachers in regard to local or district practice, that we are to look for an exposition, often not even for a correct appreciation, of those general principles on which a universal system of agriculture must be based—without which principles, indeed, it must ever remain a mere collection of empirical rules, to be studied and laboriously mastered in every new district we go to—as the traveller in foreign lands must acquire a new language every successive frontier he passes. England, the mistress of so many wide and unpeopled lands, over which the dwellings of her adventurous sons are hereafter to be scattered, on which their toil is to be expended, and the glory of their motherland by their exertions to be perpetuated—England should especially encourage all such learning, and the sons of English farmers willingly avail themselves of every opportunity of acquiring it.
SECTION IV.—OF GEOLOGICAL FORMATIONS, AND
THE GENERAL CHARACTERS OF THE SOILS THAT REST UPON THEM.
The thousands of beds or strata of which I have spoken as lying one over the other in the crust of the globe, have, partly for convenience, and partly in consequence of certain remarkably distinctive characters observed among them, been separated by geologists into three great divisions—the primary, which are the lowest and the oldest; the secondary, which lie over them; and the tertiary, which are uppermost, and have been most recently formed. The strata, in these several divisions, have again been subdivided into groups, called formations. The following table exhibits the
