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. [Illustration: NO. 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.