At first sight, perhaps, it might be imagined that the order of time in which the various strata were deposited, can be easily learned from the relative position in which they lie. Since each stratum, when first produced, was spread out on the existing surface of the globe, it is clear that the one which lies uppermost in the series must be the newest, then that which lies next below, and so on till we reach the lowest of the pile, which must be the oldest of all. Nothing could be more satisfactory than this reasoning, if each stratum was spread out over the whole Earth, and if, after having been once deposited, it was never afterward removed. We might then regard each stratum as a volume in the Natural History of the Globe, which, when it was finished, was laid down upon that which contained the chronicles of the preceding age; and thus the position of every stratum would be in itself a sufficient evidence of the age to which it belonged. But such is not the case. Nowhere does the Crust of the Earth exhibit a complete series of the Stratified Rocks laid out one above another. In any given section we can find but a few only of the long series of groups that are familiar to Geologists. And if we follow them on, in a horizontal direction, we shall invariably find that some of the strata will _thin out_ and disappear, while new strata will gradually be developed between two groups that were before in immediate contact. Let it be observed, in passing, that this fact fits in most perfectly with the theory we have been all along defending. The Stratified Rocks were deposited under water; therefore, the strata of any given period were not _spread out over the whole Globe_, but at most over those parts only which, for the time, were submerged. With the next period came a change in the boundaries of land and water; and the formation of strata ceased in some localities and began in others: and so on from epoch to epoch. Thus the areas over which the process has been going on, have been, in every age, of limited extent, and have been ever shifting from place to place over the surface of the earth. Moreover, there is the opposite process of Denudation. Many of the strata deposited in the depths of the ocean must have been afterward swept away by the breakers, as they slowly emerged from the waters; or at a later time, reduced to their original elements, and carried back to the sea, by the action of rivers, rain, and frost. It should seem, therefore, as well from the _fact_, which is obvious to any one who will examine it, as from our _theory_, which harmonizes so completely with the fact, that the strata which we meet with in any given section of the Earth’s Crust present to us but a very broken and imperfect series of monuments. They are, as it were, but odd volumes of a long series, and though they lie in juxtaposition, they may belong, nevertheless, to Geological epochs widely removed from each other.