Putting these facts together, we cannot doubt that the submergence at the close of the palanthropic age was very considerable, and that it was followed by a partial re-emergence. Further, there is no evidence of any serious fractures or folding of the crust taking place at the time, though it is possible that great lava ejections like some of those of Western America may belong to this period. It is therefore allowable to suppose that the cause of submergence may have been either depression of the land, or elevation of the bed of the ocean throwing its waters over the land, or possibly a combination of both. Movements of these kinds have recurred again and again in geological time. Their causes are mysterious, but their effects have been of the most stupendous character. Fortunately, they occur at rare intervals, and that to which we are now referring is the last of which we have any record, and differs from all others in having occurred at a time when man was widely spread over the world. The geological chronometers already referred to inform us that the land of the northern hemisphere rose from the great pleistocene submergence about eight thousand to ten thousand years ago, and the second continental period with its forests and its teeming and widely-extended animal and human life, may have been established within two thousand years of that time, or say six thousand to eight thousand years ago. How long the second continental or palanthropic period continued intact we do not know, but we can scarcely allow it less than two thousand years. Perhaps it was considerably longer. Now on historical evidence produced by Egypt, Chaldea, and other ancient countries in the Mediterranean region, we can trace the neanthropic age continuously back to, say, three thousand years B.C., or nearly five thousand years in all. Adding to this two thousand years for the palanthropic age, we are carried back to a time within one thousand years of the earliest we can assign on geological grounds to the termination of the great glacial period. Therefore, unless we suppose the last continental subsidence to have begun some time before the close of the palanthropic age, and to have continued to some degree into the beginning of the neanthropic, we cannot assign to it a very long time. That it could not have been sudden in the sense of being instantaneous is evident, because in that case terrestrial denudation of a stupendous character must have ensued, and no animal life except that of mountain tops and elevated table-lands could have escaped its destructive effects, but that it was by no means secular or long-continued is certain.