The degradation of a cliff, either suddenly or gradually, might throw a vast quantity of fragments into a rapid stream, and cause a deposit of gravel of considerable breadth and thickness in a comparatively short period of time,--say a century or two. Sir Charles Lyell has adduced examples of very rapid formation of certain stony deposits, which should make us cautious how we assert that such and such a thickness _must_ have required a vast number of years. In one of them there is a thickness of 200 or 300 feet of travertine of recent deposit, while in another, a solid mass _thirty feet thick was deposited in about twenty years_. There are countless places in Italy where the formation of limestone may be seen, as also in Auvergne and other volcanic districts.[23] From these and similar considerations it seems to me by no means unreasonable that the four thousand years which elapsed between the Creation and the commencement of Western European history should have been amply sufficient for many of those geological operations whose results are seen in what are known as the later Tertiary deposits,--the crag, the drift, the cavern-accumulations, and the like. And, as a corollary to this, that the great extinct Mammalia may have extended into this period, and thus have been contemporary with man, for a greater or less duration, according to the species; some, probably, having been extinguished at a very early period of the era, while others lived on to the time I have named, or even later. But have we nothing better for this conclusion than an assumption of the possibility, and a more or less probable conjecture? Yes; we have some facts of interest to warrant it, or I should not have ventured to introduce the subject in this work. There are facts,--besides the admixture of human workmanship with the animal remains in undisturbed deposits--direct evidence, not altogether shadowy, of the co-existence of the extinct animals with living men. And first, I would mention some circumstances bearing analogy to the exhumation of the fresh Pachyderms of Siberia. Some years ago, a portion of the leg of an Irish Elk, so-called, (_Megaceros hibernicus_,) with a part of the tendons, skin, and hair upon it, was dug up with other remains from a deposit on the estate of H. Grogan Morgan, Esq., of Johnstown Castle, Wexford, and is now in that gentleman's possession. This leg was exhibited, and formed the subject of a lecture at the time by Mr Peile, veterinary surgeon, Dublin.