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 names and thicknesses of these formations, and the mineralogical characters of the rocks of which they severally consist.
I. TERTIARY STRATA.
1. The London and Plastic clays, 500 to 900 feet thick, consist of stiff, almost impervious, dark-coloured clays,—chiefly in pasture. The lower beds are mixed with sand, and produce an arable soil, but extensive heaths and wastes rest upon them in Berkshire, Hampshire, and Dorset.
II. SECONDARY STRATA.
2. The Chalk, about 600 feet in thickness, consists in the upper part ([see diagram, No. 3, p. 88]) of a purer chalk with layers of flint; in the lower, of a marly chalk without flints. The soil of the upper chalk is chiefly in sheep-walks, that of the lower chalk is very productive of corn.
3. The Green Sand, 500 feet thick, consists of 150 feet of clay, with about 100 feet of sand above, and 250 feet below it. The upper sand forms a very productive arable soil, and the clay impervious, wet and cold lands chiefly in pasture. The lower sand is generally unproductive.
It is an important agricultural remark, that where the clay (plastic clay) comes in contact with the top of the chalk, an improved soil is produced, and that where the chalk and the green sand mix, extremely fertile patches of country present themselves. ([See pages 86 and 87.])
4. The Wealden formation, nearly 1000 feet thick, consists of 400 feet of sand, covered by 300 of clay, and resting upon 250 of marls and limestones. The clay forms the poor wet pastures of Sussex and Kent. On the sands below the clay rest heaths and brushwood; but where the marls and limestones come to the surface, the land is of better quality, and is susceptible of profitable arable culture.