To this cause is due that discordance between the first indications of geology, as to the origin of soils from the rocks on which they rest, and the actually observed character of those soils in certain districts—of which discordance mention has been made as likely to awaken doubt and distrust in the mind of the less instructed student in regard to the predictions of agricultural geology. There are several circumstances, however, by which the careful observer is materially aided in endeavouring to understand what the nature of the soils is likely to be, and how they ought to be treated, even when the subjacent rocks are thus overlaid by masses of drifted materials. Thus— 1. It not unfrequently happens, that the materials brought from a distance are more or less mixed up with the fragments and decayed matter of the rocks which are native to the spot, so that though modified in quality, the soil, nevertheless, retains the general characters of that which is formed on other spots from the decay of these rocks alone. 2. Where the formation is extensive, or covers a large area, as the new red sandstones and coal measures do in this country,—the mountain limestones in Ireland, and the granites in the north of Scotland—the transported sand, gravel, or clay, strewed over one part of the formation, has not unfrequently been derived from the rocks of another part of the _same_ formation, so that, after all, the soils may be said to be produced from the rocks on which they rest, and may be judged of from the known constitution of these rocks. 3. Or if not from the rocks of the same formation, they have most frequently been derived from those of a neighbouring formation—from rocks which are to be found at _no great distance_, and generally on higher ground. Thus the ruins of the millstone grit rocks are often spread over the surface of the coal measures—of these, again, over the magnesian limestone,—of the latter, over the new red sandstone, and so on. The effect of this kind of transport upon the soils, is merely to overlap, as it were, the edges of one formation with the proper soils of the formations that adjoin it in the particular direction from which the drifted materials are known to have come. It appears, therefore, that the occurrence on certain spots, or tracts of country, of soils that have no apparent relation to the rocks on which they immediately rest, tends in no way to throw doubt upon, to discredit or to disprove, the conclusions drawn from the more general facts and principles of geology. It is still generally true that soils _are_ derived from the rocks on which they rest. The exceptions are local, and the difficulties which these local exceptions present, require only from the agricultural geologist a more careful study of the structure of each district, before he pronounces a decided opinion as to the degree of fertility it either naturally possesses, or by skilful cultivation may be made to attain.