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.