We shall be told, perhaps, that there are Six Days assigned to the work of creation in the Mosaic narrative, and that we have accounted but for three. Let it be remembered, however, that Geology does not profess to give a complete history of our Globe. It can set before us those events only which have left their impress indelibly stamped upon the rocks that compose the Crust of the Earth. These events Geologists have attempted to reduce to the order of a chronological system; and in prosecuting this task they have been guided almost exclusively by the evidence of Organic Remains. Hence it was not to be expected that, in Geological Chronology, we should find a Period specially set apart as the Period in which Light was made; or another as the Period in which the Firmament was spread out over the Earth; or a Third as the Period in which the sun and moon and stars shone forth in the expanse of Heaven. Such phenomena had, indeed, a very important influence on the physical condition of our globe. But they must occupy a very secondary place, if indeed they are distinctly chronicled at all in the records of Geology. It is the formation of rocks and the embedding therein of Fossil Remains that constitute the main study of the Geologist, and that guide him in the distribution of Geological time.
Furthermore, we would observe that the scheme of Chronology which Geologists put before us, affords abundant room for each and all of the Mosaic Days. Let it be assumed for a moment that the Carboniferous Period corresponds with the Third Day of the Sacred narrative. The earlier Periods of the Palæozoic Age will then fit in with the First and Second Days of Scripture; and the Permian, which intervenes between the Carboniferous Period and the Secondary Age, may be supposed to correspond with the Fourth Day of Scripture. This adjustment between the Mosaic Days and the Periods of Geology will probably be made more intelligible to the general reader by the Table that appears on the following page.
The reader must not think it amiss, in this distribution of the Mosaic Days, that four out of six are crowded together into one Geological Age, while each of the other two has an entire Age assigned to itself. If the Days of Creation were indefinite periods, there is no incongruity in supposing that one may have corresponded to a longer, another to a shorter interval in the history of our planet. But, in truth, our scheme of distribution does not of necessity imply that the Mosaic Days were periods of unequal length. Geologists do not pretend that there is even a remote approximation to equality between the several divisions of Geological time. The three great Epochs are distinguished from each other by reason of the very marked difference in the character of their Fossil Remains. And the multiplication of Periods in each Epoch seems to depend rather upon the degree of completeness with which the strata of that Age have been examined, than upon any conjecture as to the probable length of its duration. Thus, for example, Sir Charles Lyell thinks that, as far as the present condition of Science affords the means of forming an opinion, almost any one of the Periods in the Palæozoic Age was as long as all the Periods of the Tertiary Age taken together.[175]