The vulture has a habit of swallowing mice, little birds, and similar prey, with small ceremony of breaking or tearing; they go into the vulture’s maw feathers, fur, bones, and all. When fully gorged, the vulture sits in a meditative manner on a tree, and finally, in the process of digestion, the food parts of what it has eaten separates from the bone and feather refuse, and this latter is rolled into a ball and disgorged by the vulture. I have found such balls, probably a year or two old, bleached white and dry, and unrolling them have laid bare tiny skeletons, perfect, and white as ivory, of the feet and heads of mice. Now if mice had disappeared, it is evident that their skeletons, found in portions in such remains would be valuable, affording us a knowledge of an otherwise unknown creature. So the coprolites tell us their tale of the smaller fauna of the ancient lands and oceans. The term fossil is not limited to any especial method or state of preservation. In regard to preservation there are three principal varieties of fossils. First: All or nearly all the animal matter may have disappeared, and mineral matter may have taken its place; so that the organism is mineralized or petrified. This is the condition of the majority of fossils. Second: It may have happened that the entire organism has decayed, and as the animal matter when it perished was not rebuilt with mineral deposit, only a cast or natural lithograph of the former living thing remains in the rock. Third: The animal or plant may have been preserved unchanged for hundreds or thousands of years, so that the very creature, with its bones, flesh, hair, even the soft portions of the body, as the brain and eye-ball, may remain complete. This has happened in a few instances, as where ice or frozen mud has been the preserving agent, so that in Siberia certain animals, as the mammoth, have been disentombed after a burial of thousands of years. Of course as soon as these frozen fossils have been exposed to air and moisture, they begin to fall to pieces, and speedily only the hard parts, as the bones, are left. In most animal fossils only the bony or shelly portions, which consist largely of lime, have been petrified. Thus we find many fossil skeletons. Sometimes there has been a change on this wise: the action of water has carried off, grain by grain, the lime as well as the animal matter of the organism, and while it thus took the object to pieces, it rebuilt it in a similar way, adding grain by grain of flinty matter, or even of metal, so that in countries where silver abounds, fossil plants have been found cased in silver. I have seen some fossil bones of recent origin, as they were taken from an ancient burial-mound, and the marrow of the bones had been carried off by the action of water and replaced by delicate, shining crystals, so that the hollow or marrow portions of the bones shone as if filled with broken glass.