The Mastodon, that is, the mammillary-toothed elephant, was another of the extinct pachyderm class then inhabiting the island. Remains of this animal have been found in the Norwich Crag; there are several species, all of gigantic proportions, some of which have been detected in North America only, and others in Europe. The tigers of the period were larger than the largest of the Bengal race, as is proved by the fossil teeth and bones of the extremities that have been discovered, both at Kirkdale and other places. And so, generally, of all the extinct carnivora, in the qualities of strength and size, superior to all existing types, and cast in the mold of, as they had to contend with, the mammoths and monster theria among which their destiny was cast. And again, and again, will the questions recur to every curious reader of these details—when, and how, were these huge quadrupeds exterminated, or driven from this island, some of them now utterly extinct, and some of them only generically allied to existing tropical races? The epoch of their rule, according to the geological testimony, verges on the human age, if it does not actually run into it. Terror-stricken, shall we suppose, by the terrene and subaqueous movements which severed Great Britain from the continent—the rush of waters—the rending of the rocks—and the drying up of lakes, consequent on the change—they sought a refuge above the general wreck, where the weak were preyed upon by the strong, and a fierce carnival, for a season, was maintained? On the continent, while similar alterations were taking place over large superficial areas, and the tertiary deposits were being drifted up, many of the animals, and whole families, would escape into southern and warmer countries, and some of the species, in consequence, might long survive the destruction of others. But here, insulated and deprived of the means of performing their annual migrations, the races of every kind would all more speedily perish, preying more easily upon each other, and weakened by alteration of habits, and the great physical changes to which they were subjected. On the Ararat of Yorkshire, and other favored heights, they found a temporary resting-place! But, it was only temporary; for, as the island approximated to its present condition, it proved no longer a suitable dwelling to creatures of their mold—their course was run—and a new creation was to occupy their place. In closing these sketches of the geology of Great Britain, one may well marvel at the vast changes over the face of this island and of all its productions, as read in the varied and multiform disclosures which the interior structure, formation upon formation, makes known to us.