We have had a hint of this before, when we learned in _Life and her Children_ how infinitely minute the shells are of which chalk is made, and what enormous thicknesses remain of the chalk-beds. And now we find these facts strengthened by the great changes which then took place in the animal world, for even if (as is likely) older forms of these large milk-givers existed in earlier times, and we have not yet found them, yet there are such great differences between whales, bats, dogs, and lemurs, that our imagination stands appalled at the time required to account for them. Again, where are the traces of all the forms which must have existed between the little marsupials and this great army of four-footed beasts? At present no one can answer. Forty years ago we knew nothing even of those early marsupials, and people said there were no milk-giving animals until after the time when the chalk was formed. Now a few jaws have told us that milk-givers had been already in the world for ages; and it may be that before forty years more have passed, some child now reading these lines, and following in the footsteps of such patient explorers as Beckles and Gaudry, or the American naturalists Leidy, Cope, Marsh and others, who have such a grand field before them, may discover bones which will unravel the history of that crowd of mammalia which now seems to start up like Cadmus’ army from the ground. But for the present we can only begin with them as we find them immediately after the Chalk Period, and a strange motley group they appear. There, roaming among the palms, evergreens, screw-pines and tree-ferns, which flourished in Europe and North America in those warmer times, were beasts larger than oxen, with teeth partly like the tapir, partly like the bear, and feet like the elephant,[130] which may have been both animal and vegetable feeders. With them were true vegetarians, which could be called neither rhinoceroses, horses, nor tapirs, but had some likeness to each.[131] Others, half-pigs half-antelopes, were thick-skinned, but graceful and two-toed,[132] while a little fellow no bigger than a fox,[133] with five toes on his front feet and three behind, the ancestor of our horses, grazed in the open plains. There too, moles, hedgehogs, and dormice had already begun to make their underground homes, and squirrels and lemurs sprang about the trees of the forest, where bats roamed at night in search of insects. Nor was this life without its dangers, for beasts of prey, half-bears half-hyænas,[134] were there to feed upon their neighbours, and with them a creature half-dog half-civet,[135] with several other carnivorous animals with feeble brains and partly marsupial characters,[136] and lastly a large flat-footed dog-bear,[137] something between a dog, a cat, and a bear, with a very small brain but plenty of teeth, represented the most primitive flesh-eating animal known to us.