rare accidents under which the bones in superficial deposits could have withstood the grinding of the ice-sheet, and the subsequent erosive action of the waves on the coast-line. It may therefore be concluded, that the pleistocene mammalia arrived in Europe before the temperature had reached its minimum in the glacial period. On the other hand, the occurrence of mammaliferous river strata, either in hollows of the boulder-clay as at Hoxne, or in valleys excavated after its deposition as at Bedford, prove that the characteristic animals occupied Britain after the retreat of the ice-sheet, and after the re-emergence of the land from beneath the glacial sea. _Mammalia lived in Britain during the Second Ice or Glacial Period._ The distribution of the animals in the river deposits gives us a clue to the physical geography during the second ice period. In an essay read before the Geological Society in 1869, and in a second printed in the “Popular Science Review” in 1872, I showed that there was a singular irregularity in the contents of the river strata, and that while the fossil mammalia were abundant throughout the area (marked with dots in the map, Fig. 126), there were certain districts in which they had not been met with. One of these barren areas comprises (plain in the map, Fig. 126), nearly the whole of Wales. A second includes a large portion of Lancashire, Yorkshire, Cumberland, Westmoreland, and the whole of Scotland (if the preglacial mammals in the low district between the Frith of Forth and Frith of Clyde in the map be omitted), and a third is represented by nearly the whole of Ireland. These areas are remarkable for the absence of the mammalia from the river deposits. They are also characterised by the freshness of the ice marks which they present. Nearly every valley has its own system of grooves and its own set of moraines; and the mounds of clay and marl left behind by the local glacier, as it slowly retreated to higher levels till it finally disappeared, are to be observed in great abundance. If we bring these facts into relation, the barrenness of the areas may be reasonably explained by the presence of glaciers, _while_ the pleistocene mammals were living in the south and east (see map, Fig. 126). A barrier of some kind may reasonably be inferred to have prevented their range over those districts, and its nature is indicated by the ice marks. It is very probable that these glaciers had not passed away before the close of the pleistocene age: for in that case the characteristic animals would be discovered in the river gravels, which are later than the deposits of local glaciers in those districts. _The Glacial Period does not separate one Life-era from another._