gaged, and in many countries, in searching for these nodules, wherever deposits like those of the crag or greensand rocks occur, and in inquiring whether other geological formations may not also contain them-so that it is impossible to assign a limit to the general gain to agriculture which may ultimately follow from this one investigation.

An examination of the beds of Marl, in which the greensand nodules are frequently found, has proved that they also contain phosphate of lime, sometimes in considerable abundance, distributed through their entire mass. Immediately on such discovery, these marls rose in estimation. People now found out the reason of their having been often dug up by the neighbouring farmers to lay upon their land. Where they had never been so used, their employment was recommended; and the peculiar and well-recognised fertility of certain soils, which either rested on, or were formed from, or adjoined these marl beds, was at length satisfactorily accounted for.

In many other districts marls occur, by which the adjoining lands have been long known to be improved. Such are the marls which underlie the sandy surface of northern Norfolk, and which gave Mr. Coke the chief means of redeeming from their poverty-stricken state the thousands of acres he lived himself to see enriched. Such also are the marls which, in the form of nests and irregular layers of chalk drift, underlie the immediate surface of a large portion of the counties of Huntingdon and Bedford. Are there any phosphates in these marls? Do those of Norfolk owe any of their fertilising virtue to the presence of mineral phosphate? These are questions which previous experience must now suggest to practical agriculturists: For science is a mistress who, in conferring one favour encourages her suitors to look for more, and shows them the way in which they are most likely to succeed.

But, in many other instances chemistry and geology cooperate for the benefit of agriculture. The former says: Springs which flow through the soil, or which naturally descend from higher ground, exercise the greatest influence upon vegetation. The substances which they hold in solution are sometimes the 'cause why particular applications, otherwise most useful, are in 'certain cases unnecessary, or even prejudicial.' It therefore analyses the waters. This is one of the duties which scientific Agriculture now requires from chemistry, as much as Boards of Health. Accordingly, the complacent science compares the nature of the minerals and rocks through which they have come; when it finds that waters which traverse aqueous rocks contain soluble silicates that mica slate springs contain silica and magnesia

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that the streams which so often gush from limestone rocks are charged with carbonate of lime, those from magnesian limestone or dolomites with sulphate of magnesia, from red sandstone formations with salt and gypsum, and from the Oxford clays with sulphate and carbonate of lime. Having performed its part of the appointed task, chemistry now hands over the practical agriculturist to descriptive geology: And she forthwith points out to him the places where these different varieties of rock occur; so that he may judge in what manner particular waters are likely to affect his soils, to influence his crops, or to modify the action of the mixtures he applies to aid their growth. But the reciprocating sciences do not stop here. Geology then takes the initiative: My greensand beds and my crag deposits are often rich in fossil phosphates. Will not the 'waters which pass through them be comparatively rich in phosphates also? and may not such waters materially influence 'the agricultural value of the adjoining lands?' Thus chemistry is again set to work, and arrives at new results; the pecuniary profit of which the unconscious farmer by-and-by steps in to reap, without ever dreaming that the labour of others, either manual or mental, had been concerned in placing them within his reach.

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Again: Some of my clays,' says Agriculture, are greatly improved by the use of lime, while on others no perceptible "good has followed from it.' Where are they respectively situ❝ated?' asks Geology. Informed on this point, Geology observes, that The London, the Plastic, and the Weald clays, which lime improves, are of a different geological age from the Oxford clay and its derivative soils, on which it is often applied ' without any sensible effect.' Both then turn to Chemistry to learn the cause of the difference in question? And her analysis speedily tells them, that the Oxford clay often contains one fourth of its weight of finely divided chalky matter, or carbonate of lime, and requires therefore no further addition of what is truly understood to be a necessary ingredient of every fertile soil. In conclusion, an intelligent interpretation of the experience of the past is full of instruction on the course most profitably to be followed for the future.

The Use of Lime in Agriculture is the subject to which one of the books we have placed at the head of this article is especially devoted: And from the many illustrations this work affords, we will select one of a large and general kind.

It may be laid down, as a universal principle, that in our climate a certain proportion of lime in the soil is necessary to bring out its full productive power. But as soils are generally

derived from the rocks on which they rest,-or from others at no great distance, geologically considered, the proportion of lime these rocks contain is a sufficient indication of the proportion which may be expected in the soils. That is to say, soils will not, in general, contain more lime than the rocks to which they belong if the one is poor in lime, the other is likely to be poor also. Hence the analysis of the rocks of a district becomes of importance to agriculture, as an index not only of the natural fertility of its soils, but also of the methods to be adopted in order to increase their productiveness. And, as rocks of the same kind often extend over very large areas, and are repeated at intervals more or less distant over the entire surface of the globe, it must frequently happen that the results deduced from a chemical examination of the rocks of one district will prove true of those of many other districts, the general composition of the natural soils will be the same, and the same practical conclusions will apply to them all.

Among other rocks, those commonly known by the names of whinstone and trap rocks, occur abundantly in Scotland; and the fertility of the soils formed from them is owing, in part, to the large per-centage of lime which they contain. Again, the absence of lime in granitic rocks is one reason for the general unproductiveness of soils formed from them. The inferences, of which we are speaking, must of course hold good of all other districts in which these several rocks occur, and which possess the same general composition.

But a more interesting case is that of the slate-rocks, (formerly called Grauwacke, and now distinguished as Silurian) which cross the island from the Mull of Galloway to St. Abb's Head. This is a tract of poor country, cold and inhospitable, and, as yet, little frequented by agricultural improvers. A suite of specimens from the rocks of this district has been analysed, with the following result: The proportion of lime in the different beds of this formation, in the south of Scotland, is small. In general, as a consequence, the soils formed from them will be deficient in lime. In this the reason appears why, in practice, it has been found that the addition of lime is an almost in'dispensable preliminary to any successful and permanent im'provement of the surface where these rocks prevail.'

Over this large breadth of country no available beds of limestone are at present known to exist; and from our own observations on its western shores, improvement appears to have begun along the borders of the sea, and in the neighbourhood of ports to which lime could be imported, as from Cumberland, from the Isle of Man, or from Ireland, and to have spread inland as far

and as fast as roads were made to allow of its being easily transported into the interior. It is surely a merit in chemical science to have shown why such a practice has succeeded; and to have assigned a reasonable ground for recommending its general extension as almost indispensable, in a region like this, to the successful development of its agricultural capabilities.

We have said that the practical benefit of such a deduction is not limited to the tract of country in which it has primarily been made. It extends to all countries similarly constituted, or in which the rocks have the same general mineral and chemical characters. This, with certain exceptions, is very much the case with rocks of the same geological age; and thus practical precepts like the above, when once recorded in our books, become part of the stock of chemico-agricultural truth, which is common to, and may be economically applied, in every country of the globe.

Take, for example, the memoir of Professor Dumont, of Liège, upon the Ardennes, a well-known tract of thinly-peopled and poorly-productive country, which stretches north-east from Mezieres, in France, to the Rhine, at Bonn, and, according to some geologists, far into Westphalia. In reading the description of his Terrain Ardennais, one could almost fancy he was treating of the zone of southern Scotland to which we have just been referring.

The greater part of the soil,' he says, is still barren.

Immense tracts are covered only with heath, fern, broom, and 'forests. The slaty parts present, in general, only deserts, dry 'or wet, covered with heath or with peat, according to their position. It is distinguished from the neighbouring countries by the almost total absence of lime. On its south

'eastern extremity the plateau of the Ardennes is covered with a layer of clay, overlying chalk marl, which ameliorates the 'soil, and changes its character.' The portion of the Ardennes to which the above description relates, is nearly of the same geological age as that of the southern slate country of Scotland; and the first steps towards agricultural improvement must be the same in both. The artificial application of lime has accordingly been found most advantageous in the one instance; while the natural admixture of marl in the other is seen to change and fertilise the soil. The researches of modern science, therefore, do not leave a doubt concerning the only prudent economical treatment of such a case.

But there is a host of lesser questions of a practical kind, in connexion with the use of lime, on which chemistry has thrown a useful light.

Every one at all conversant with the history of agriculture is aware of the immense sums which are annually expended in the purchase of this substance; of the numerous misapplications of it which are constantly made; and of the injury which has resulted from such misapplications in every country of Europe. Hence the different opinions entertained concerning the purposes which lime serves in the land; the quantity which ought to be administered; the frequency with which it should be repeated; the amount of compensation which ought to be given to a retiring tenant who has limed his farm; and the ridiculous stipulations, in regard to all these points, which have made their way into leases and farm agreements.

Some of the greatest practical mistakes in the use of lime appear to have arisen from supposing that it acts primarily as a manure, properly so called, and that it is capable, in good husbandry, of taking the place of a manure. In describing the treatment to which he means to subject his land, a farmer will say that he means to lime or manure' his land at such and such intervals; leases bind tenants to lime or manure' within certain fixed periods; and straw or hay is allowed to be sold off the farm, on condition that so much lime or manure be brought on to the farm in return. Chemistry has shown the erroneous nature of the opinions which gave rise to such practices and prescriptions; how evil must follow from them; of what special kind this evil must be; and yet that, with a use of lime as liberal as before, the recurrence of such evils may be prevented. This, of itself, is a sufficiently intelligible money gift conferred by science upon the rural community.

Again, limestones are of use to the farmer, only according to the kind and amount of action they exercise on certain soils and crops. Experience had long shown this. The ancient Greek and Roman writers were aware of it; and, in our home districts, wherever a choice of limes exists, the farmer prefers one variety to another, because of a difference, real or fancied, in their effects upon his land. It was something to ascertain the nature and cause of these diversities; to explain, by analysis, the chemical differences between the limes from which such different effects followed; and thus to connect observation and science. But when practical men are at issue among themselves, when they cannot agree on the unknown qualities of a new variety of lime,— when a prejudice exists against all the limes of a given district, in consequence of the mischief done by the lime of some particular lime-beds or lime-works,-chemistry has rendered the parties a still more obvious service. To the manifest advantage of both lime-burner and farmer, it is able rigidly to fix the absolute and relative values of each variety, and in every locality.