During the deposition of these secondary strata in the hollows of the surface, but little alteration of the relative situations of sea and land could have taken place, as the deposits for the most part lie conformably to the same hollows or "basins" (fig. 30 will illustrate this); but after the deposition of these strata, there appears to have been a very great disturbance, many chains of mountains were cast up (as the Apennines), carrying upwards with them these deposits; some of the strata were so displaced that they were left in a perpendicular position, as may be seen in several places at the south side of the Isle of Wight. These disturbances, however, did not amount to so general a convulsion as those before described, nor is it known whether all the effects produced on these strata took place at or near the same period of time; they nevertheless appear to have produced an almost total change in the situation of the land and sea, for the "downs" of chalk (on the southern coast of England, for example) were, before these changes, the beds of seas. This is the last of the great convulsions which the earth has undergone, for the tertiary strata which afterwards began to be deposited rest in the hollows or basins (chiefly in the chalk) then left; the alterations in and since these deposits appear to consist chiefly of the upheaval of certain localities, the depression of others, the evaporation of inland lakes, and the wear and tear of the land from these causes, which are still in continuous action (as from the washing down of cliffs by the sea, and the formation of mud deposits at the mouths of rivers), or the volcanic agencies which in some places (as in Ireland) have cast up basalt over the chalk. The tertiary strata contain remains of most of the classes of animals now in existence, but yet differing greatly in species, and as the strata approach the surface those species become more and more general; the plants also approach more nearly to those of the present time, but still most parts of Europe possessed a climate almost tropical. The tertiary strata consist chiefly of marine and fresh water deposits in the form of sands and clays, as the "London clay," which extends under London, resting upon a basin of chalk. The last deposits, forming the superficial layer of earth, and the formation last deposited before the creation of man, are called the Diluvium and Alluvium, and contain numerous remains of mammalia, birds, reptiles, and fishes. One of the most extraordinary animals of this period was the Dinotherium, a sort of walrus, which is supposed to have been the largest of quadrupeds, if indeed it was one (fig. 31). The quadrupeds of this, the "Pliocene" formation, are thus described by Professor Owen in his "History of British Fossil Mammals." [Illustration: FIG. 31.--SKULL OF THE DINOTHERIUM.] [Illustration: FIG. 32.--MAMMOTH, TELEOSAURUS, AND GLYPTODON.]