In the first place, I may remind the reader that the vertical movement of 250 feet, required to elevate the loess of Natchez to its present height, is exceeded by the upheaval which the marine stratum of Cagliari, containing pottery, has been ascertained by Count de la Marmora to have experienced. Such changes of level, therefore, have actually occurred in Europe in the human epoch, and may therefore have happened in America. In the second place, I may observe that if, since the Natchez mastodon was embedded in clay, the delta of the Mississippi has been formed, so, since the mammoth and rhinoceros of Abbeville and Amiens were enveloped in fluviatile mud and gravel, together with flint tools, a great thickness of peat has accumulated in the valley of the Somme; and antecedently to the first growth of peat, there had been time for the extinction of a great many mammalia, requiring, perhaps, a lapse of ages many times greater than that demanded for the formation of 30 feet of peat, for since the earliest growth of the latter there has been no change in the species of mammalia in Europe. Should future researches, therefore, confirm the opinion that the Natchez man co-existed with the mastodon, it would not enhance the value of the geological evidence in favour of Man's antiquity, but merely render the delta of the Mississippi available as a chronometer, by which the lapse of Pleistocene time could be measured somewhat less vaguely than by any means of measuring which have as yet been discovered or rendered available in Europe. CHAPTER 12. -- ANTIQUITY OF MAN RELATIVELY TO THE GLACIAL PERIOD AND TO THE EXISTING FAUNA AND FLORA. Chronological Relation of the Glacial Period, and the earliest known Signs of Man's Appearance in Europe. Series of Tertiary Deposits in Norfolk and Suffolk immediately antecedent to the Glacial Period. Gradual Refrigeration of Climate proved by the Marine Shells of successive Groups. Marine Newer Pliocene Shells of Northern Character near Woodbridge. Section of the Norfolk Cliffs. Norwich Crag. Forest Bed and Fluvio-marine Strata. Fossil Plants and Mammalia of the same. Overlying Boulder Clay and Contorted Drift. Newer freshwater Formation of Mundesley compared to that of Hoxne. Great Oscillations of Level implied by the Series of Strata in the Norfolk Cliffs. Earliest known Date of Man long subsequent to the existing Fauna and Flora. Frequent allusions have been made in the preceding pages to a period called the glacial, to which no reference is made in the Chronological Table of Formations given above (Chapter 1). It comprises a long series of ages, during which the power of cold, whether exerted by glaciers on the land, or by floating ice on the sea, was greater in the northern hemisphere, and extended to more southern latitudes than now. [19]