No animals perhaps are of more interest among the vanished forms than the ancestors of the _horse_. We first trace it several ages before man appeared, as a small creature not larger than a fox, with four toes on each foot, and the rudiments of a fifth toe; it had also two bones in the lower part of the leg. After this little creature came a horse-like animal as large as a sheep, with only three toes, the middle one being much longer and broader than the others, while the two bones of the lower leg began to unite. The next age shows us a horse as large as a Shetland pony; the two bones of the lower leg are merged into one; the big middle toe occupies nearly all of the foot. And finally, shortly before human beings came into the world, we find a true horse. The big middle toe had come to occupy almost the whole foot. Its nail had enlarged and strengthened to a hoof. Thus we see that the horse really stands on the tip of a single toe of each foot. Meanwhile, as the lower leg and the foot thus modified, the horse gained his present size, symmetry, beauty, and strength. FOOTNOTES: [22] For description of trilobite, see p. 119. [23] Pronounced _Ter-o-dak’-tils_. [24] Nature Reader, No. 2, Lesson 43. [25] Nature Reader, No. 1, Lesson 34. [26] Nature Reader, No. 1, Lesson 34. [27] Nature Reader, No. 3, page 238. LESSON XII. A MOUNTAIN OF FOSSILS. “The bleakest rock, upon the loneliest heath, Feels in its barrenness some touch of spring, And in the April dew, or beam of May, As moss and lichen freshen and revive.” --BEAUMONT. Each successive age of the world brought forth its children, nourished them to their prime, accompanied them in the stages of their decay, and laid them in the tomb. Each new age rocked its cradles above the cemeteries of the age that had preceded it. Some sea-bed swarming with corals and mollusks was slowly lifted; in the shallow waters, sand, chalk, or clay were deposited, and gradually formed thick beds above the “swarmers,” which had suffocated in the mud, or, having lived out their span, had failed to reproduce their like. So in successive strata the present surface of the world was built, and sometimes in throes of uplifting, some long-buried stratum was doubled upon itself, and having been thrust up through deposits lying above it, once more reached sunlight. But it spread out into the sunlight not living creatures, but their sepulchres.