Some of them were peaceful vegetarians,[70] browsing on the tree-ferns and palms, and rearing their huge bodies to tear the leaves from the tall pine-trees. But others were fierce animal-feeders. Fancy a monster thirty feet high,[71] with a head four or five feet long, and a mouth armed with sabre-like teeth, standing upon its hind legs and attacking other creatures smaller than itself, or preying upon those other huge reptiles which were feeding peacefully among the trees. Surely a battle between a lion and an elephant now would count as nothing compared to the reptile-fights which must have taken place on those vast American lands of the west, or on the European pasture-grounds, where now the remains of these monsters are found. But where are they all gone? We know that they have lived, for we can put together the huge joints of their backbones, restore their gigantic limbs, and measure their formidable teeth, but they themselves have vanished like a dream. As time went on, other and more modern forms, the ancestors of our tortoises, lizards, crocodiles, and afterwards snakes, began to take the place of these gigantic types; while warm-blooded animals, birds and beasts, began to increase upon the earth. Whether it was that food became scarce for these enormous reptiles, or whether the birds and beasts drove them from their haunts, we are not yet able to find out. At any rate they disappeared, as the ancient enamelled fishes and large newts had disappeared before them, and soon after the beds of white chalk were formed, which now border the south of England and north of France, only the four divisions of tortoises, lizards, crocodiles, and snakes, survived as remnants of the great army of reptiles which once covered the earth. * * * * * Ah! if we could only have a whole book upon reptiles to show how strangely different these four remaining groups have become during the long ages that they have been using different means of defence; and how, even in a single group, they employ so many varied stratagems to survive in the battle of life! Look at the tortoises with their hard impregnable shells, the crocodiles with their sharp-pointed teeth and tough armour-plated skins, and the silently-gliding snakes with their poisonous fangs or powerful crushing coils. See how the tiny-scaled lizard darts out upon an insect and is gone in the twinkling of an eye, and then watch the solemn chamæleon trusting to his dusky colour for protection, and scarcely putting one foot before another in the space of a minute. Each of these has his own special device for escaping the dangers of life and attacking other animals, and yet we shall find, before we finish this chapter, that they are all formed on one plan, and that it is in adapting themselves to their different positions in life that they have become so unlike each other.